compiler/rustc_lint/src/builtin.rs

   1 //! Lints in the Rust compiler.
   2 //!
   3 //! This contains lints which can feasibly be implemented as their own
   4 //! AST visitor. Also see `rustc_session::lint::builtin`, which contains the
   5 //! definitions of lints that are emitted directly inside the main compiler.
   6 //!
   7 //! To add a new lint to rustc, declare it here using `declare_lint!()`.
   8 //! Then add code to emit the new lint in the appropriate circumstances.
   9 //! You can do that in an existing `LintPass` if it makes sense, or in a
  10 //! new `LintPass`, or using `Session::add_lint` elsewhere in the
  11 //! compiler. Only do the latter if the check can't be written cleanly as a
  12 //! `LintPass` (also, note that such lints will need to be defined in
  13 //! `rustc_session::lint::builtin`, not here).
  14 //!
  15 //! If you define a new `EarlyLintPass`, you will also need to add it to the
  16 //! `add_early_builtin!` or `add_early_builtin_with_new!` invocation in
  17 //! `lib.rs`. Use the former for unit-like structs and the latter for structs
  18 //! with a `pub fn new()`.
  19 //!
  20 //! If you define a new `LateLintPass`, you will also need to add it to the
  21 //! `late_lint_methods!` invocation in `lib.rs`.
  22
  23 use crate::{
  24     errors::BuiltinEllpisisInclusiveRangePatterns,
  25     types::{transparent_newtype_field, CItemKind},
  26     EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext,
  27 };
  28 use rustc_ast::attr;
  29 use rustc_ast::tokenstream::{TokenStream, TokenTree};
  30 use rustc_ast::visit::{FnCtxt, FnKind};
  31 use rustc_ast::{self as ast, *};
  32 use rustc_ast_pretty::pprust::{self, expr_to_string};
  33 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
  34 use rustc_data_structures::stack::ensure_sufficient_stack;
  35 use rustc_errors::{
  36     fluent, Applicability, DelayDm, Diagnostic, DiagnosticBuilder, DiagnosticMessage,
  37     DiagnosticStyledString, MultiSpan,
  38 };
  39 use rustc_feature::{deprecated_attributes, AttributeGate, BuiltinAttribute, GateIssue, Stability};
  40 use rustc_hir as hir;
  41 use rustc_hir::def::{DefKind, Res};
  42 use rustc_hir::def_id::{DefId, LocalDefId, LocalDefIdSet, CRATE_DEF_ID};
  43 use rustc_hir::{ForeignItemKind, GenericParamKind, HirId, Node, PatKind, PredicateOrigin};
  44 use rustc_index::vec::Idx;
  45 use rustc_middle::lint::in_external_macro;
  46 use rustc_middle::ty::layout::{LayoutError, LayoutOf};
  47 use rustc_middle::ty::print::with_no_trimmed_paths;
  48 use rustc_middle::ty::subst::GenericArgKind;
  49 use rustc_middle::ty::{self, Instance, Ty, TyCtxt, VariantDef};
  50 use rustc_session::lint::{BuiltinLintDiagnostics, FutureIncompatibilityReason};
  51 use rustc_span::edition::Edition;
  52 use rustc_span::source_map::Spanned;
  53 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  54 use rustc_span::{BytePos, InnerSpan, Span};
  55 use rustc_target::abi::VariantIdx;
  56 use rustc_trait_selection::traits::{self, misc::can_type_implement_copy};
  57
  58 use crate::nonstandard_style::{method_context, MethodLateContext};
  59
  60 use std::fmt::Write;
  61
  62 // hardwired lints from librustc_middle
  63 pub use rustc_session::lint::builtin::*;
  64
  65 declare_lint! {
  66     /// The `while_true` lint detects `while true { }`.
  67     ///
  68     /// ### Example
  69     ///
  70     /// ```rust,no_run
  71     /// while true {
  72     ///
  73     /// }
  74     /// ```
  75     ///
  76     /// {{produces}}
  77     ///
  78     /// ### Explanation
  79     ///
  80     /// `while true` should be replaced with `loop`. A `loop` expression is
  81     /// the preferred way to write an infinite loop because it more directly
  82     /// expresses the intent of the loop.
  83     WHILE_TRUE,
  84     Warn,
  85     "suggest using `loop { }` instead of `while true { }`"
  86 }
  87
  88 declare_lint_pass!(WhileTrue => [WHILE_TRUE]);
  89
  90 /// Traverse through any amount of parenthesis and return the first non-parens expression.
  91 fn pierce_parens(mut expr: &ast::Expr) -> &ast::Expr {
  92     while let ast::ExprKind::Paren(sub) = &expr.kind {
  93         expr = sub;
  94     }
  95     expr
  96 }
  97
  98 impl EarlyLintPass for WhileTrue {
  99     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
 100         if let ast::ExprKind::While(cond, _, label) = &e.kind
 101             && let ast::ExprKind::Lit(ref lit) = pierce_parens(cond).kind
 102             && let ast::LitKind::Bool(true) = lit.kind
 103             && !lit.span.from_expansion()
 104         {
 105             let condition_span = e.span.with_hi(cond.span.hi());
 106             cx.struct_span_lint(
 107                             WHILE_TRUE,
 108                             condition_span,
 109                 fluent::lint_builtin_while_true,
 110                             |lint| {
 111                     lint.span_suggestion_short(
 112                         condition_span,
 113                         fluent::suggestion,
 114                         format!(
 115                             "{}loop",
 116                             label.map_or_else(String::new, |label| format!(
 117                                 "{}: ",
 118                                 label.ident,
 119                             ))
 120                         ),
 121                         Applicability::MachineApplicable,
 122                     )
 123                 },
 124             )
 125         }
 126     }
 127 }
 128
 129 declare_lint! {
 130     /// The `box_pointers` lints use of the Box type.
 131     ///
 132     /// ### Example
 133     ///
 134     /// ```rust,compile_fail
 135     /// #![deny(box_pointers)]
 136     /// struct Foo {
 137     ///     x: Box<isize>,
 138     /// }
 139     /// ```
 140     ///
 141     /// {{produces}}
 142     ///
 143     /// ### Explanation
 144     ///
 145     /// This lint is mostly historical, and not particularly useful. `Box<T>`
 146     /// used to be built into the language, and the only way to do heap
 147     /// allocation. Today's Rust can call into other allocators, etc.
 148     BOX_POINTERS,
 149     Allow,
 150     "use of owned (Box type) heap memory"
 151 }
 152
 153 declare_lint_pass!(BoxPointers => [BOX_POINTERS]);
 154
 155 impl BoxPointers {
 156     fn check_heap_type(&self, cx: &LateContext<'_>, span: Span, ty: Ty<'_>) {
 157         for leaf in ty.walk() {
 158             if let GenericArgKind::Type(leaf_ty) = leaf.unpack() {
 159                 if leaf_ty.is_box() {
 160                     cx.struct_span_lint(
 161                         BOX_POINTERS,
 162                         span,
 163                         fluent::lint_builtin_box_pointers,
 164                         |lint| lint.set_arg("ty", ty),
 165                     );
 166                 }
 167             }
 168         }
 169     }
 170 }
 171
 172 impl<'tcx> LateLintPass<'tcx> for BoxPointers {
 173     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 174         match it.kind {
 175             hir::ItemKind::Fn(..)
 176             | hir::ItemKind::TyAlias(..)
 177             | hir::ItemKind::Enum(..)
 178             | hir::ItemKind::Struct(..)
 179             | hir::ItemKind::Union(..) => {
 180                 self.check_heap_type(cx, it.span, cx.tcx.type_of(it.owner_id))
 181             }
 182             _ => (),
 183         }
 184
 185         // If it's a struct, we also have to check the fields' types
 186         match it.kind {
 187             hir::ItemKind::Struct(ref struct_def, _) | hir::ItemKind::Union(ref struct_def, _) => {
 188                 for struct_field in struct_def.fields() {
 189                     let def_id = cx.tcx.hir().local_def_id(struct_field.hir_id);
 190                     self.check_heap_type(cx, struct_field.span, cx.tcx.type_of(def_id));
 191                 }
 192             }
 193             _ => (),
 194         }
 195     }
 196
 197     fn check_expr(&mut self, cx: &LateContext<'_>, e: &hir::Expr<'_>) {
 198         let ty = cx.typeck_results().node_type(e.hir_id);
 199         self.check_heap_type(cx, e.span, ty);
 200     }
 201 }
 202
 203 declare_lint! {
 204     /// The `non_shorthand_field_patterns` lint detects using `Struct { x: x }`
 205     /// instead of `Struct { x }` in a pattern.
 206     ///
 207     /// ### Example
 208     ///
 209     /// ```rust
 210     /// struct Point {
 211     ///     x: i32,
 212     ///     y: i32,
 213     /// }
 214     ///
 215     ///
 216     /// fn main() {
 217     ///     let p = Point {
 218     ///         x: 5,
 219     ///         y: 5,
 220     ///     };
 221     ///
 222     ///     match p {
 223     ///         Point { x: x, y: y } => (),
 224     ///     }
 225     /// }
 226     /// ```
 227     ///
 228     /// {{produces}}
 229     ///
 230     /// ### Explanation
 231     ///
 232     /// The preferred style is to avoid the repetition of specifying both the
 233     /// field name and the binding name if both identifiers are the same.
 234     NON_SHORTHAND_FIELD_PATTERNS,
 235     Warn,
 236     "using `Struct { x: x }` instead of `Struct { x }` in a pattern"
 237 }
 238
 239 declare_lint_pass!(NonShorthandFieldPatterns => [NON_SHORTHAND_FIELD_PATTERNS]);
 240
 241 impl<'tcx> LateLintPass<'tcx> for NonShorthandFieldPatterns {
 242     fn check_pat(&mut self, cx: &LateContext<'_>, pat: &hir::Pat<'_>) {
 243         if let PatKind::Struct(ref qpath, field_pats, _) = pat.kind {
 244             let variant = cx
 245                 .typeck_results()
 246                 .pat_ty(pat)
 247                 .ty_adt_def()
 248                 .expect("struct pattern type is not an ADT")
 249                 .variant_of_res(cx.qpath_res(qpath, pat.hir_id));
 250             for fieldpat in field_pats {
 251                 if fieldpat.is_shorthand {
 252                     continue;
 253                 }
 254                 if fieldpat.span.from_expansion() {
 255                     // Don't lint if this is a macro expansion: macro authors
 256                     // shouldn't have to worry about this kind of style issue
 257                     // (Issue #49588)
 258                     continue;
 259                 }
 260                 if let PatKind::Binding(binding_annot, _, ident, None) = fieldpat.pat.kind {
 261                     if cx.tcx.find_field_index(ident, &variant)
 262                         == Some(cx.tcx.field_index(fieldpat.hir_id, cx.typeck_results()))
 263                     {
 264                         cx.struct_span_lint(
 265                             NON_SHORTHAND_FIELD_PATTERNS,
 266                             fieldpat.span,
 267                             fluent::lint_builtin_non_shorthand_field_patterns,
 268                             |lint| {
 269                                 let suggested_ident =
 270                                     format!("{}{}", binding_annot.prefix_str(), ident);
 271                                 lint.set_arg("ident", ident.clone()).span_suggestion(
 272                                     fieldpat.span,
 273                                     fluent::suggestion,
 274                                     suggested_ident,
 275                                     Applicability::MachineApplicable,
 276                                 )
 277                             },
 278                         );
 279                     }
 280                 }
 281             }
 282         }
 283     }
 284 }
 285
 286 declare_lint! {
 287     /// The `unsafe_code` lint catches usage of `unsafe` code.
 288     ///
 289     /// ### Example
 290     ///
 291     /// ```rust,compile_fail
 292     /// #![deny(unsafe_code)]
 293     /// fn main() {
 294     ///     unsafe {
 295     ///
 296     ///     }
 297     /// }
 298     /// ```
 299     ///
 300     /// {{produces}}
 301     ///
 302     /// ### Explanation
 303     ///
 304     /// This lint is intended to restrict the usage of `unsafe`, which can be
 305     /// difficult to use correctly.
 306     UNSAFE_CODE,
 307     Allow,
 308     "usage of `unsafe` code"
 309 }
 310
 311 declare_lint_pass!(UnsafeCode => [UNSAFE_CODE]);
 312
 313 impl UnsafeCode {
 314     fn report_unsafe(
 315         &self,
 316         cx: &EarlyContext<'_>,
 317         span: Span,
 318         msg: impl Into<DiagnosticMessage>,
 319         decorate: impl for<'a, 'b> FnOnce(
 320             &'b mut DiagnosticBuilder<'a, ()>,
 321         ) -> &'b mut DiagnosticBuilder<'a, ()>,
 322     ) {
 323         // This comes from a macro that has `#[allow_internal_unsafe]`.
 324         if span.allows_unsafe() {
 325             return;
 326         }
 327
 328         cx.struct_span_lint(UNSAFE_CODE, span, msg, decorate);
 329     }
 330
 331     fn report_overridden_symbol_name(
 332         &self,
 333         cx: &EarlyContext<'_>,
 334         span: Span,
 335         msg: DiagnosticMessage,
 336     ) {
 337         self.report_unsafe(cx, span, msg, |lint| {
 338             lint.note(fluent::lint_builtin_overridden_symbol_name)
 339         })
 340     }
 341
 342     fn report_overridden_symbol_section(
 343         &self,
 344         cx: &EarlyContext<'_>,
 345         span: Span,
 346         msg: DiagnosticMessage,
 347     ) {
 348         self.report_unsafe(cx, span, msg, |lint| {
 349             lint.note(fluent::lint_builtin_overridden_symbol_section)
 350         })
 351     }
 352 }
 353
 354 impl EarlyLintPass for UnsafeCode {
 355     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 356         if attr.has_name(sym::allow_internal_unsafe) {
 357             self.report_unsafe(cx, attr.span, fluent::lint_builtin_allow_internal_unsafe, |lint| {
 358                 lint
 359             });
 360         }
 361     }
 362
 363     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
 364         if let ast::ExprKind::Block(ref blk, _) = e.kind {
 365             // Don't warn about generated blocks; that'll just pollute the output.
 366             if blk.rules == ast::BlockCheckMode::Unsafe(ast::UserProvided) {
 367                 self.report_unsafe(cx, blk.span, fluent::lint_builtin_unsafe_block, |lint| lint);
 368             }
 369         }
 370     }
 371
 372     fn check_item(&mut self, cx: &EarlyContext<'_>, it: &ast::Item) {
 373         match it.kind {
 374             ast::ItemKind::Trait(box ast::Trait { unsafety: ast::Unsafe::Yes(_), .. }) => {
 375                 self.report_unsafe(cx, it.span, fluent::lint_builtin_unsafe_trait, |lint| lint)
 376             }
 377
 378             ast::ItemKind::Impl(box ast::Impl { unsafety: ast::Unsafe::Yes(_), .. }) => {
 379                 self.report_unsafe(cx, it.span, fluent::lint_builtin_unsafe_impl, |lint| lint)
 380             }
 381
 382             ast::ItemKind::Fn(..) => {
 383                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
 384                     self.report_overridden_symbol_name(
 385                         cx,
 386                         attr.span,
 387                         fluent::lint_builtin_no_mangle_fn,
 388                     );
 389                 }
 390
 391                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::export_name) {
 392                     self.report_overridden_symbol_name(
 393                         cx,
 394                         attr.span,
 395                         fluent::lint_builtin_export_name_fn,
 396                     );
 397                 }
 398
 399                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::link_section) {
 400                     self.report_overridden_symbol_section(
 401                         cx,
 402                         attr.span,
 403                         fluent::lint_builtin_link_section_fn,
 404                     );
 405                 }
 406             }
 407
 408             ast::ItemKind::Static(..) => {
 409                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
 410                     self.report_overridden_symbol_name(
 411                         cx,
 412                         attr.span,
 413                         fluent::lint_builtin_no_mangle_static,
 414                     );
 415                 }
 416
 417                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::export_name) {
 418                     self.report_overridden_symbol_name(
 419                         cx,
 420                         attr.span,
 421                         fluent::lint_builtin_export_name_static,
 422                     );
 423                 }
 424
 425                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::link_section) {
 426                     self.report_overridden_symbol_section(
 427                         cx,
 428                         attr.span,
 429                         fluent::lint_builtin_link_section_static,
 430                     );
 431                 }
 432             }
 433
 434             _ => {}
 435         }
 436     }
 437
 438     fn check_impl_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
 439         if let ast::AssocItemKind::Fn(..) = it.kind {
 440             if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
 441                 self.report_overridden_symbol_name(
 442                     cx,
 443                     attr.span,
 444                     fluent::lint_builtin_no_mangle_method,
 445                 );
 446             }
 447             if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::export_name) {
 448                 self.report_overridden_symbol_name(
 449                     cx,
 450                     attr.span,
 451                     fluent::lint_builtin_export_name_method,
 452                 );
 453             }
 454         }
 455     }
 456
 457     fn check_fn(&mut self, cx: &EarlyContext<'_>, fk: FnKind<'_>, span: Span, _: ast::NodeId) {
 458         if let FnKind::Fn(
 459             ctxt,
 460             _,
 461             ast::FnSig { header: ast::FnHeader { unsafety: ast::Unsafe::Yes(_), .. }, .. },
 462             _,
 463             _,
 464             body,
 465         ) = fk
 466         {
 467             let msg = match ctxt {
 468                 FnCtxt::Foreign => return,
 469                 FnCtxt::Free => fluent::lint_builtin_decl_unsafe_fn,
 470                 FnCtxt::Assoc(_) if body.is_none() => fluent::lint_builtin_decl_unsafe_method,
 471                 FnCtxt::Assoc(_) => fluent::lint_builtin_impl_unsafe_method,
 472             };
 473             self.report_unsafe(cx, span, msg, |lint| lint);
 474         }
 475     }
 476 }
 477
 478 declare_lint! {
 479     /// The `missing_docs` lint detects missing documentation for public items.
 480     ///
 481     /// ### Example
 482     ///
 483     /// ```rust,compile_fail
 484     /// #![deny(missing_docs)]
 485     /// pub fn foo() {}
 486     /// ```
 487     ///
 488     /// {{produces}}
 489     ///
 490     /// ### Explanation
 491     ///
 492     /// This lint is intended to ensure that a library is well-documented.
 493     /// Items without documentation can be difficult for users to understand
 494     /// how to use properly.
 495     ///
 496     /// This lint is "allow" by default because it can be noisy, and not all
 497     /// projects may want to enforce everything to be documented.
 498     pub MISSING_DOCS,
 499     Allow,
 500     "detects missing documentation for public members",
 501     report_in_external_macro
 502 }
 503
 504 pub struct MissingDoc {
 505     /// Stack of whether `#[doc(hidden)]` is set at each level which has lint attributes.
 506     doc_hidden_stack: Vec<bool>,
 507 }
 508
 509 impl_lint_pass!(MissingDoc => [MISSING_DOCS]);
 510
 511 fn has_doc(attr: &ast::Attribute) -> bool {
 512     if attr.is_doc_comment() {
 513         return true;
 514     }
 515
 516     if !attr.has_name(sym::doc) {
 517         return false;
 518     }
 519
 520     if attr.value_str().is_some() {
 521         return true;
 522     }
 523
 524     if let Some(list) = attr.meta_item_list() {
 525         for meta in list {
 526             if meta.has_name(sym::hidden) {
 527                 return true;
 528             }
 529         }
 530     }
 531
 532     false
 533 }
 534
 535 impl MissingDoc {
 536     pub fn new() -> MissingDoc {
 537         MissingDoc { doc_hidden_stack: vec![false] }
 538     }
 539
 540     fn doc_hidden(&self) -> bool {
 541         *self.doc_hidden_stack.last().expect("empty doc_hidden_stack")
 542     }
 543
 544     fn check_missing_docs_attrs(
 545         &self,
 546         cx: &LateContext<'_>,
 547         def_id: LocalDefId,
 548         article: &'static str,
 549         desc: &'static str,
 550     ) {
 551         // If we're building a test harness, then warning about
 552         // documentation is probably not really relevant right now.
 553         if cx.sess().opts.test {
 554             return;
 555         }
 556
 557         // `#[doc(hidden)]` disables missing_docs check.
 558         if self.doc_hidden() {
 559             return;
 560         }
 561
 562         // Only check publicly-visible items, using the result from the privacy pass.
 563         // It's an option so the crate root can also use this function (it doesn't
 564         // have a `NodeId`).
 565         if def_id != CRATE_DEF_ID {
 566             if !cx.effective_visibilities.is_exported(def_id) {
 567                 return;
 568             }
 569         }
 570
 571         let attrs = cx.tcx.hir().attrs(cx.tcx.hir().local_def_id_to_hir_id(def_id));
 572         let has_doc = attrs.iter().any(has_doc);
 573         if !has_doc {
 574             cx.struct_span_lint(
 575                 MISSING_DOCS,
 576                 cx.tcx.def_span(def_id),
 577                 fluent::lint_builtin_missing_doc,
 578                 |lint| lint.set_arg("article", article).set_arg("desc", desc),
 579             );
 580         }
 581     }
 582 }
 583
 584 impl<'tcx> LateLintPass<'tcx> for MissingDoc {
 585     fn enter_lint_attrs(&mut self, _cx: &LateContext<'_>, attrs: &[ast::Attribute]) {
 586         let doc_hidden = self.doc_hidden()
 587             || attrs.iter().any(|attr| {
 588                 attr.has_name(sym::doc)
 589                     && match attr.meta_item_list() {
 590                         None => false,
 591                         Some(l) => attr::list_contains_name(&l, sym::hidden),
 592                     }
 593             });
 594         self.doc_hidden_stack.push(doc_hidden);
 595     }
 596
 597     fn exit_lint_attrs(&mut self, _: &LateContext<'_>, _attrs: &[ast::Attribute]) {
 598         self.doc_hidden_stack.pop().expect("empty doc_hidden_stack");
 599     }
 600
 601     fn check_crate(&mut self, cx: &LateContext<'_>) {
 602         self.check_missing_docs_attrs(cx, CRATE_DEF_ID, "the", "crate");
 603     }
 604
 605     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 606         match it.kind {
 607             hir::ItemKind::Trait(..) => {
 608                 // Issue #11592: traits are always considered exported, even when private.
 609                 if cx.tcx.visibility(it.owner_id)
 610                     == ty::Visibility::Restricted(
 611                         cx.tcx.parent_module_from_def_id(it.owner_id.def_id).to_def_id(),
 612                     )
 613                 {
 614                     return;
 615                 }
 616             }
 617             hir::ItemKind::TyAlias(..)
 618             | hir::ItemKind::Fn(..)
 619             | hir::ItemKind::Macro(..)
 620             | hir::ItemKind::Mod(..)
 621             | hir::ItemKind::Enum(..)
 622             | hir::ItemKind::Struct(..)
 623             | hir::ItemKind::Union(..)
 624             | hir::ItemKind::Const(..)
 625             | hir::ItemKind::Static(..) => {}
 626
 627             _ => return,
 628         };
 629
 630         let (article, desc) = cx.tcx.article_and_description(it.owner_id.to_def_id());
 631
 632         self.check_missing_docs_attrs(cx, it.owner_id.def_id, article, desc);
 633     }
 634
 635     fn check_trait_item(&mut self, cx: &LateContext<'_>, trait_item: &hir::TraitItem<'_>) {
 636         let (article, desc) = cx.tcx.article_and_description(trait_item.owner_id.to_def_id());
 637
 638         self.check_missing_docs_attrs(cx, trait_item.owner_id.def_id, article, desc);
 639     }
 640
 641     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
 642         // If the method is an impl for a trait, don't doc.
 643         if method_context(cx, impl_item.hir_id()) == MethodLateContext::TraitImpl {
 644             return;
 645         }
 646
 647         // If the method is an impl for an item with docs_hidden, don't doc.
 648         if method_context(cx, impl_item.hir_id()) == MethodLateContext::PlainImpl {
 649             let parent = cx.tcx.hir().get_parent_item(impl_item.hir_id());
 650             let impl_ty = cx.tcx.type_of(parent);
 651             let outerdef = match impl_ty.kind() {
 652                 ty::Adt(def, _) => Some(def.did()),
 653                 ty::Foreign(def_id) => Some(*def_id),
 654                 _ => None,
 655             };
 656             let is_hidden = match outerdef {
 657                 Some(id) => cx.tcx.is_doc_hidden(id),
 658                 None => false,
 659             };
 660             if is_hidden {
 661                 return;
 662             }
 663         }
 664
 665         let (article, desc) = cx.tcx.article_and_description(impl_item.owner_id.to_def_id());
 666         self.check_missing_docs_attrs(cx, impl_item.owner_id.def_id, article, desc);
 667     }
 668
 669     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'_>) {
 670         let (article, desc) = cx.tcx.article_and_description(foreign_item.owner_id.to_def_id());
 671         self.check_missing_docs_attrs(cx, foreign_item.owner_id.def_id, article, desc);
 672     }
 673
 674     fn check_field_def(&mut self, cx: &LateContext<'_>, sf: &hir::FieldDef<'_>) {
 675         if !sf.is_positional() {
 676             let def_id = cx.tcx.hir().local_def_id(sf.hir_id);
 677             self.check_missing_docs_attrs(cx, def_id, "a", "struct field")
 678         }
 679     }
 680
 681     fn check_variant(&mut self, cx: &LateContext<'_>, v: &hir::Variant<'_>) {
 682         self.check_missing_docs_attrs(cx, cx.tcx.hir().local_def_id(v.id), "a", "variant");
 683     }
 684 }
 685
 686 declare_lint! {
 687     /// The `missing_copy_implementations` lint detects potentially-forgotten
 688     /// implementations of [`Copy`].
 689     ///
 690     /// [`Copy`]: https://doc.rust-lang.org/std/marker/trait.Copy.html
 691     ///
 692     /// ### Example
 693     ///
 694     /// ```rust,compile_fail
 695     /// #![deny(missing_copy_implementations)]
 696     /// pub struct Foo {
 697     ///     pub field: i32
 698     /// }
 699     /// # fn main() {}
 700     /// ```
 701     ///
 702     /// {{produces}}
 703     ///
 704     /// ### Explanation
 705     ///
 706     /// Historically (before 1.0), types were automatically marked as `Copy`
 707     /// if possible. This was changed so that it required an explicit opt-in
 708     /// by implementing the `Copy` trait. As part of this change, a lint was
 709     /// added to alert if a copyable type was not marked `Copy`.
 710     ///
 711     /// This lint is "allow" by default because this code isn't bad; it is
 712     /// common to write newtypes like this specifically so that a `Copy` type
 713     /// is no longer `Copy`. `Copy` types can result in unintended copies of
 714     /// large data which can impact performance.
 715     pub MISSING_COPY_IMPLEMENTATIONS,
 716     Allow,
 717     "detects potentially-forgotten implementations of `Copy`"
 718 }
 719
 720 declare_lint_pass!(MissingCopyImplementations => [MISSING_COPY_IMPLEMENTATIONS]);
 721
 722 impl<'tcx> LateLintPass<'tcx> for MissingCopyImplementations {
 723     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 724         if !cx.effective_visibilities.is_reachable(item.owner_id.def_id) {
 725             return;
 726         }
 727         let (def, ty) = match item.kind {
 728             hir::ItemKind::Struct(_, ref ast_generics) => {
 729                 if !ast_generics.params.is_empty() {
 730                     return;
 731                 }
 732                 let def = cx.tcx.adt_def(item.owner_id);
 733                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 734             }
 735             hir::ItemKind::Union(_, ref ast_generics) => {
 736                 if !ast_generics.params.is_empty() {
 737                     return;
 738                 }
 739                 let def = cx.tcx.adt_def(item.owner_id);
 740                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 741             }
 742             hir::ItemKind::Enum(_, ref ast_generics) => {
 743                 if !ast_generics.params.is_empty() {
 744                     return;
 745                 }
 746                 let def = cx.tcx.adt_def(item.owner_id);
 747                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 748             }
 749             _ => return,
 750         };
 751         if def.has_dtor(cx.tcx) {
 752             return;
 753         }
 754         let param_env = ty::ParamEnv::empty();
 755         if ty.is_copy_modulo_regions(cx.tcx, param_env) {
 756             return;
 757         }
 758         if can_type_implement_copy(
 759             cx.tcx,
 760             param_env,
 761             ty,
 762             traits::ObligationCause::misc(item.span, item.hir_id()),
 763         )
 764         .is_ok()
 765         {
 766             cx.struct_span_lint(
 767                 MISSING_COPY_IMPLEMENTATIONS,
 768                 item.span,
 769                 fluent::lint_builtin_missing_copy_impl,
 770                 |lint| lint,
 771             )
 772         }
 773     }
 774 }
 775
 776 declare_lint! {
 777     /// The `missing_debug_implementations` lint detects missing
 778     /// implementations of [`fmt::Debug`].
 779     ///
 780     /// [`fmt::Debug`]: https://doc.rust-lang.org/std/fmt/trait.Debug.html
 781     ///
 782     /// ### Example
 783     ///
 784     /// ```rust,compile_fail
 785     /// #![deny(missing_debug_implementations)]
 786     /// pub struct Foo;
 787     /// # fn main() {}
 788     /// ```
 789     ///
 790     /// {{produces}}
 791     ///
 792     /// ### Explanation
 793     ///
 794     /// Having a `Debug` implementation on all types can assist with
 795     /// debugging, as it provides a convenient way to format and display a
 796     /// value. Using the `#[derive(Debug)]` attribute will automatically
 797     /// generate a typical implementation, or a custom implementation can be
 798     /// added by manually implementing the `Debug` trait.
 799     ///
 800     /// This lint is "allow" by default because adding `Debug` to all types can
 801     /// have a negative impact on compile time and code size. It also requires
 802     /// boilerplate to be added to every type, which can be an impediment.
 803     MISSING_DEBUG_IMPLEMENTATIONS,
 804     Allow,
 805     "detects missing implementations of Debug"
 806 }
 807
 808 #[derive(Default)]
 809 pub struct MissingDebugImplementations {
 810     impling_types: Option<LocalDefIdSet>,
 811 }
 812
 813 impl_lint_pass!(MissingDebugImplementations => [MISSING_DEBUG_IMPLEMENTATIONS]);
 814
 815 impl<'tcx> LateLintPass<'tcx> for MissingDebugImplementations {
 816     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 817         if !cx.effective_visibilities.is_reachable(item.owner_id.def_id) {
 818             return;
 819         }
 820
 821         match item.kind {
 822             hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) | hir::ItemKind::Enum(..) => {}
 823             _ => return,
 824         }
 825
 826         let Some(debug) = cx.tcx.get_diagnostic_item(sym::Debug) else {
 827             return
 828         };
 829
 830         if self.impling_types.is_none() {
 831             let mut impls = LocalDefIdSet::default();
 832             cx.tcx.for_each_impl(debug, |d| {
 833                 if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() {
 834                     if let Some(def_id) = ty_def.did().as_local() {
 835                         impls.insert(def_id);
 836                     }
 837                 }
 838             });
 839
 840             self.impling_types = Some(impls);
 841             debug!("{:?}", self.impling_types);
 842         }
 843
 844         if !self.impling_types.as_ref().unwrap().contains(&item.owner_id.def_id) {
 845             cx.struct_span_lint(
 846                 MISSING_DEBUG_IMPLEMENTATIONS,
 847                 item.span,
 848                 fluent::lint_builtin_missing_debug_impl,
 849                 |lint| lint.set_arg("debug", cx.tcx.def_path_str(debug)),
 850             );
 851         }
 852     }
 853 }
 854
 855 declare_lint! {
 856     /// The `anonymous_parameters` lint detects anonymous parameters in trait
 857     /// definitions.
 858     ///
 859     /// ### Example
 860     ///
 861     /// ```rust,edition2015,compile_fail
 862     /// #![deny(anonymous_parameters)]
 863     /// // edition 2015
 864     /// pub trait Foo {
 865     ///     fn foo(usize);
 866     /// }
 867     /// fn main() {}
 868     /// ```
 869     ///
 870     /// {{produces}}
 871     ///
 872     /// ### Explanation
 873     ///
 874     /// This syntax is mostly a historical accident, and can be worked around
 875     /// quite easily by adding an `_` pattern or a descriptive identifier:
 876     ///
 877     /// ```rust
 878     /// trait Foo {
 879     ///     fn foo(_: usize);
 880     /// }
 881     /// ```
 882     ///
 883     /// This syntax is now a hard error in the 2018 edition. In the 2015
 884     /// edition, this lint is "warn" by default. This lint
 885     /// enables the [`cargo fix`] tool with the `--edition` flag to
 886     /// automatically transition old code from the 2015 edition to 2018. The
 887     /// tool will run this lint and automatically apply the
 888     /// suggested fix from the compiler (which is to add `_` to each
 889     /// parameter). This provides a completely automated way to update old
 890     /// code for a new edition. See [issue #41686] for more details.
 891     ///
 892     /// [issue #41686]: https://github.com/rust-lang/rust/issues/41686
 893     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
 894     pub ANONYMOUS_PARAMETERS,
 895     Warn,
 896     "detects anonymous parameters",
 897     @future_incompatible = FutureIncompatibleInfo {
 898         reference: "issue #41686 <https://github.com/rust-lang/rust/issues/41686>",
 899         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
 900     };
 901 }
 902
 903 declare_lint_pass!(
 904     /// Checks for use of anonymous parameters (RFC 1685).
 905     AnonymousParameters => [ANONYMOUS_PARAMETERS]
 906 );
 907
 908 impl EarlyLintPass for AnonymousParameters {
 909     fn check_trait_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
 910         if cx.sess().edition() != Edition::Edition2015 {
 911             // This is a hard error in future editions; avoid linting and erroring
 912             return;
 913         }
 914         if let ast::AssocItemKind::Fn(box Fn { ref sig, .. }) = it.kind {
 915             for arg in sig.decl.inputs.iter() {
 916                 if let ast::PatKind::Ident(_, ident, None) = arg.pat.kind {
 917                     if ident.name == kw::Empty {
 918                         let ty_snip = cx.sess().source_map().span_to_snippet(arg.ty.span);
 919
 920                         let (ty_snip, appl) = if let Ok(ref snip) = ty_snip {
 921                             (snip.as_str(), Applicability::MachineApplicable)
 922                         } else {
 923                             ("<type>", Applicability::HasPlaceholders)
 924                         };
 925                         cx.struct_span_lint(
 926                             ANONYMOUS_PARAMETERS,
 927                             arg.pat.span,
 928                             fluent::lint_builtin_anonymous_params,
 929                             |lint| {
 930                                 lint.span_suggestion(
 931                                     arg.pat.span,
 932                                     fluent::suggestion,
 933                                     format!("_: {}", ty_snip),
 934                                     appl,
 935                                 )
 936                             },
 937                         )
 938                     }
 939                 }
 940             }
 941         }
 942     }
 943 }
 944
 945 /// Check for use of attributes which have been deprecated.
 946 #[derive(Clone)]
 947 pub struct DeprecatedAttr {
 948     // This is not free to compute, so we want to keep it around, rather than
 949     // compute it for every attribute.
 950     depr_attrs: Vec<&'static BuiltinAttribute>,
 951 }
 952
 953 impl_lint_pass!(DeprecatedAttr => []);
 954
 955 impl DeprecatedAttr {
 956     pub fn new() -> DeprecatedAttr {
 957         DeprecatedAttr { depr_attrs: deprecated_attributes() }
 958     }
 959 }
 960
 961 impl EarlyLintPass for DeprecatedAttr {
 962     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 963         for BuiltinAttribute { name, gate, .. } in &self.depr_attrs {
 964             if attr.ident().map(|ident| ident.name) == Some(*name) {
 965                 if let &AttributeGate::Gated(
 966                     Stability::Deprecated(link, suggestion),
 967                     name,
 968                     reason,
 969                     _,
 970                 ) = gate
 971                 {
 972                     // FIXME(davidtwco) translatable deprecated attr
 973                     cx.struct_span_lint(
 974                         DEPRECATED,
 975                         attr.span,
 976                         fluent::lint_builtin_deprecated_attr_link,
 977                         |lint| {
 978                             lint.set_arg("name", name)
 979                                 .set_arg("reason", reason)
 980                                 .set_arg("link", link)
 981                                 .span_suggestion_short(
 982                                     attr.span,
 983                                     suggestion.map(|s| s.into()).unwrap_or(
 984                                         fluent::lint_builtin_deprecated_attr_default_suggestion,
 985                                     ),
 986                                     "",
 987                                     Applicability::MachineApplicable,
 988                                 )
 989                         },
 990                     );
 991                 }
 992                 return;
 993             }
 994         }
 995         if attr.has_name(sym::no_start) || attr.has_name(sym::crate_id) {
 996             cx.struct_span_lint(
 997                 DEPRECATED,
 998                 attr.span,
 999                 fluent::lint_builtin_deprecated_attr_used,
1000                 |lint| {
1001                     lint.set_arg("name", pprust::path_to_string(&attr.get_normal_item().path))
1002                         .span_suggestion_short(
1003                             attr.span,
1004                             fluent::lint_builtin_deprecated_attr_default_suggestion,
1005                             "",
1006                             Applicability::MachineApplicable,
1007                         )
1008                 },
1009             );
1010         }
1011     }
1012 }
1013
1014 fn warn_if_doc(cx: &EarlyContext<'_>, node_span: Span, node_kind: &str, attrs: &[ast::Attribute]) {
1015     use rustc_ast::token::CommentKind;
1016
1017     let mut attrs = attrs.iter().peekable();
1018
1019     // Accumulate a single span for sugared doc comments.
1020     let mut sugared_span: Option<Span> = None;
1021
1022     while let Some(attr) = attrs.next() {
1023         let is_doc_comment = attr.is_doc_comment();
1024         if is_doc_comment {
1025             sugared_span =
1026                 Some(sugared_span.map_or(attr.span, |span| span.with_hi(attr.span.hi())));
1027         }
1028
1029         if attrs.peek().map_or(false, |next_attr| next_attr.is_doc_comment()) {
1030             continue;
1031         }
1032
1033         let span = sugared_span.take().unwrap_or(attr.span);
1034
1035         if is_doc_comment || attr.has_name(sym::doc) {
1036             cx.struct_span_lint(
1037                 UNUSED_DOC_COMMENTS,
1038                 span,
1039                 fluent::lint_builtin_unused_doc_comment,
1040                 |lint| {
1041                     lint.set_arg("kind", node_kind).span_label(node_span, fluent::label).help(
1042                         match attr.kind {
1043                             AttrKind::DocComment(CommentKind::Line, _) | AttrKind::Normal(..) => {
1044                                 fluent::plain_help
1045                             }
1046                             AttrKind::DocComment(CommentKind::Block, _) => fluent::block_help,
1047                         },
1048                     )
1049                 },
1050             );
1051         }
1052     }
1053 }
1054
1055 impl EarlyLintPass for UnusedDocComment {
1056     fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &ast::Stmt) {
1057         let kind = match stmt.kind {
1058             ast::StmtKind::Local(..) => "statements",
1059             // Disabled pending discussion in #78306
1060             ast::StmtKind::Item(..) => return,
1061             // expressions will be reported by `check_expr`.
1062             ast::StmtKind::Empty
1063             | ast::StmtKind::Semi(_)
1064             | ast::StmtKind::Expr(_)
1065             | ast::StmtKind::MacCall(_) => return,
1066         };
1067
1068         warn_if_doc(cx, stmt.span, kind, stmt.kind.attrs());
1069     }
1070
1071     fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) {
1072         let arm_span = arm.pat.span.with_hi(arm.body.span.hi());
1073         warn_if_doc(cx, arm_span, "match arms", &arm.attrs);
1074     }
1075
1076     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
1077         warn_if_doc(cx, expr.span, "expressions", &expr.attrs);
1078     }
1079
1080     fn check_generic_param(&mut self, cx: &EarlyContext<'_>, param: &ast::GenericParam) {
1081         warn_if_doc(cx, param.ident.span, "generic parameters", &param.attrs);
1082     }
1083
1084     fn check_block(&mut self, cx: &EarlyContext<'_>, block: &ast::Block) {
1085         warn_if_doc(cx, block.span, "blocks", &block.attrs());
1086     }
1087
1088     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) {
1089         if let ast::ItemKind::ForeignMod(_) = item.kind {
1090             warn_if_doc(cx, item.span, "extern blocks", &item.attrs);
1091         }
1092     }
1093 }
1094
1095 declare_lint! {
1096     /// The `no_mangle_const_items` lint detects any `const` items with the
1097     /// [`no_mangle` attribute].
1098     ///
1099     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1100     ///
1101     /// ### Example
1102     ///
1103     /// ```rust,compile_fail
1104     /// #[no_mangle]
1105     /// const FOO: i32 = 5;
1106     /// ```
1107     ///
1108     /// {{produces}}
1109     ///
1110     /// ### Explanation
1111     ///
1112     /// Constants do not have their symbols exported, and therefore, this
1113     /// probably means you meant to use a [`static`], not a [`const`].
1114     ///
1115     /// [`static`]: https://doc.rust-lang.org/reference/items/static-items.html
1116     /// [`const`]: https://doc.rust-lang.org/reference/items/constant-items.html
1117     NO_MANGLE_CONST_ITEMS,
1118     Deny,
1119     "const items will not have their symbols exported"
1120 }
1121
1122 declare_lint! {
1123     /// The `no_mangle_generic_items` lint detects generic items that must be
1124     /// mangled.
1125     ///
1126     /// ### Example
1127     ///
1128     /// ```rust
1129     /// #[no_mangle]
1130     /// fn foo<T>(t: T) {
1131     ///
1132     /// }
1133     /// ```
1134     ///
1135     /// {{produces}}
1136     ///
1137     /// ### Explanation
1138     ///
1139     /// A function with generics must have its symbol mangled to accommodate
1140     /// the generic parameter. The [`no_mangle` attribute] has no effect in
1141     /// this situation, and should be removed.
1142     ///
1143     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1144     NO_MANGLE_GENERIC_ITEMS,
1145     Warn,
1146     "generic items must be mangled"
1147 }
1148
1149 declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS, NO_MANGLE_GENERIC_ITEMS]);
1150
1151 impl<'tcx> LateLintPass<'tcx> for InvalidNoMangleItems {
1152     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1153         let attrs = cx.tcx.hir().attrs(it.hir_id());
1154         let check_no_mangle_on_generic_fn = |no_mangle_attr: &ast::Attribute,
1155                                              impl_generics: Option<&hir::Generics<'_>>,
1156                                              generics: &hir::Generics<'_>,
1157                                              span| {
1158             for param in
1159                 generics.params.iter().chain(impl_generics.map(|g| g.params).into_iter().flatten())
1160             {
1161                 match param.kind {
1162                     GenericParamKind::Lifetime { .. } => {}
1163                     GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1164                         cx.struct_span_lint(
1165                             NO_MANGLE_GENERIC_ITEMS,
1166                             span,
1167                             fluent::lint_builtin_no_mangle_generic,
1168                             |lint| {
1169                                 lint.span_suggestion_short(
1170                                     no_mangle_attr.span,
1171                                     fluent::suggestion,
1172                                     "",
1173                                     // Use of `#[no_mangle]` suggests FFI intent; correct
1174                                     // fix may be to monomorphize source by hand
1175                                     Applicability::MaybeIncorrect,
1176                                 )
1177                             },
1178                         );
1179                         break;
1180                     }
1181                 }
1182             }
1183         };
1184         match it.kind {
1185             hir::ItemKind::Fn(.., ref generics, _) => {
1186                 if let Some(no_mangle_attr) = cx.sess().find_by_name(attrs, sym::no_mangle) {
1187                     check_no_mangle_on_generic_fn(no_mangle_attr, None, generics, it.span);
1188                 }
1189             }
1190             hir::ItemKind::Const(..) => {
1191                 if cx.sess().contains_name(attrs, sym::no_mangle) {
1192                     // Const items do not refer to a particular location in memory, and therefore
1193                     // don't have anything to attach a symbol to
1194                     cx.struct_span_lint(
1195                         NO_MANGLE_CONST_ITEMS,
1196                         it.span,
1197                         fluent::lint_builtin_const_no_mangle,
1198                         |lint| {
1199                             // account for "pub const" (#45562)
1200                             let start = cx
1201                                 .tcx
1202                                 .sess
1203                                 .source_map()
1204                                 .span_to_snippet(it.span)
1205                                 .map(|snippet| snippet.find("const").unwrap_or(0))
1206                                 .unwrap_or(0) as u32;
1207                             // `const` is 5 chars
1208                             let const_span = it.span.with_hi(BytePos(it.span.lo().0 + start + 5));
1209                             lint.span_suggestion(
1210                                 const_span,
1211                                 fluent::suggestion,
1212                                 "pub static",
1213                                 Applicability::MachineApplicable,
1214                             )
1215                         },
1216                     );
1217                 }
1218             }
1219             hir::ItemKind::Impl(hir::Impl { generics, items, .. }) => {
1220                 for it in *items {
1221                     if let hir::AssocItemKind::Fn { .. } = it.kind {
1222                         if let Some(no_mangle_attr) = cx
1223                             .sess()
1224                             .find_by_name(cx.tcx.hir().attrs(it.id.hir_id()), sym::no_mangle)
1225                         {
1226                             check_no_mangle_on_generic_fn(
1227                                 no_mangle_attr,
1228                                 Some(generics),
1229                                 cx.tcx.hir().get_generics(it.id.owner_id.def_id).unwrap(),
1230                                 it.span,
1231                             );
1232                         }
1233                     }
1234                 }
1235             }
1236             _ => {}
1237         }
1238     }
1239 }
1240
1241 declare_lint! {
1242     /// The `mutable_transmutes` lint catches transmuting from `&T` to `&mut
1243     /// T` because it is [undefined behavior].
1244     ///
1245     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1246     ///
1247     /// ### Example
1248     ///
1249     /// ```rust,compile_fail
1250     /// unsafe {
1251     ///     let y = std::mem::transmute::<&i32, &mut i32>(&5);
1252     /// }
1253     /// ```
1254     ///
1255     /// {{produces}}
1256     ///
1257     /// ### Explanation
1258     ///
1259     /// Certain assumptions are made about aliasing of data, and this transmute
1260     /// violates those assumptions. Consider using [`UnsafeCell`] instead.
1261     ///
1262     /// [`UnsafeCell`]: https://doc.rust-lang.org/std/cell/struct.UnsafeCell.html
1263     MUTABLE_TRANSMUTES,
1264     Deny,
1265     "transmuting &T to &mut T is undefined behavior, even if the reference is unused"
1266 }
1267
1268 declare_lint_pass!(MutableTransmutes => [MUTABLE_TRANSMUTES]);
1269
1270 impl<'tcx> LateLintPass<'tcx> for MutableTransmutes {
1271     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &hir::Expr<'_>) {
1272         if let Some((&ty::Ref(_, _, from_mt), &ty::Ref(_, _, to_mt))) =
1273             get_transmute_from_to(cx, expr).map(|(ty1, ty2)| (ty1.kind(), ty2.kind()))
1274         {
1275             if to_mt == hir::Mutability::Mut && from_mt == hir::Mutability::Not {
1276                 cx.struct_span_lint(
1277                     MUTABLE_TRANSMUTES,
1278                     expr.span,
1279                     fluent::lint_builtin_mutable_transmutes,
1280                     |lint| lint,
1281                 );
1282             }
1283         }
1284
1285         fn get_transmute_from_to<'tcx>(
1286             cx: &LateContext<'tcx>,
1287             expr: &hir::Expr<'_>,
1288         ) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
1289             let def = if let hir::ExprKind::Path(ref qpath) = expr.kind {
1290                 cx.qpath_res(qpath, expr.hir_id)
1291             } else {
1292                 return None;
1293             };
1294             if let Res::Def(DefKind::Fn, did) = def {
1295                 if !def_id_is_transmute(cx, did) {
1296                     return None;
1297                 }
1298                 let sig = cx.typeck_results().node_type(expr.hir_id).fn_sig(cx.tcx);
1299                 let from = sig.inputs().skip_binder()[0];
1300                 let to = sig.output().skip_binder();
1301                 return Some((from, to));
1302             }
1303             None
1304         }
1305
1306         fn def_id_is_transmute(cx: &LateContext<'_>, def_id: DefId) -> bool {
1307             cx.tcx.is_intrinsic(def_id) && cx.tcx.item_name(def_id) == sym::transmute
1308         }
1309     }
1310 }
1311
1312 declare_lint! {
1313     /// The `unstable_features` is deprecated and should no longer be used.
1314     UNSTABLE_FEATURES,
1315     Allow,
1316     "enabling unstable features (deprecated. do not use)"
1317 }
1318
1319 declare_lint_pass!(
1320     /// Forbids using the `#[feature(...)]` attribute
1321     UnstableFeatures => [UNSTABLE_FEATURES]
1322 );
1323
1324 impl<'tcx> LateLintPass<'tcx> for UnstableFeatures {
1325     fn check_attribute(&mut self, cx: &LateContext<'_>, attr: &ast::Attribute) {
1326         if attr.has_name(sym::feature) {
1327             if let Some(items) = attr.meta_item_list() {
1328                 for item in items {
1329                     cx.struct_span_lint(
1330                         UNSTABLE_FEATURES,
1331                         item.span(),
1332                         fluent::lint_builtin_unstable_features,
1333                         |lint| lint,
1334                     );
1335                 }
1336             }
1337         }
1338     }
1339 }
1340
1341 declare_lint! {
1342     /// The `unreachable_pub` lint triggers for `pub` items not reachable from
1343     /// the crate root.
1344     ///
1345     /// ### Example
1346     ///
1347     /// ```rust,compile_fail
1348     /// #![deny(unreachable_pub)]
1349     /// mod foo {
1350     ///     pub mod bar {
1351     ///
1352     ///     }
1353     /// }
1354     /// ```
1355     ///
1356     /// {{produces}}
1357     ///
1358     /// ### Explanation
1359     ///
1360     /// A bare `pub` visibility may be misleading if the item is not actually
1361     /// publicly exported from the crate. The `pub(crate)` visibility is
1362     /// recommended to be used instead, which more clearly expresses the intent
1363     /// that the item is only visible within its own crate.
1364     ///
1365     /// This lint is "allow" by default because it will trigger for a large
1366     /// amount existing Rust code, and has some false-positives. Eventually it
1367     /// is desired for this to become warn-by-default.
1368     pub UNREACHABLE_PUB,
1369     Allow,
1370     "`pub` items not reachable from crate root"
1371 }
1372
1373 declare_lint_pass!(
1374     /// Lint for items marked `pub` that aren't reachable from other crates.
1375     UnreachablePub => [UNREACHABLE_PUB]
1376 );
1377
1378 impl UnreachablePub {
1379     fn perform_lint(
1380         &self,
1381         cx: &LateContext<'_>,
1382         what: &str,
1383         def_id: LocalDefId,
1384         vis_span: Span,
1385         exportable: bool,
1386     ) {
1387         let mut applicability = Applicability::MachineApplicable;
1388         if cx.tcx.visibility(def_id).is_public() && !cx.effective_visibilities.is_reachable(def_id)
1389         {
1390             if vis_span.from_expansion() {
1391                 applicability = Applicability::MaybeIncorrect;
1392             }
1393             let def_span = cx.tcx.def_span(def_id);
1394             cx.struct_span_lint(
1395                 UNREACHABLE_PUB,
1396                 def_span,
1397                 fluent::lint_builtin_unreachable_pub,
1398                 |lint| {
1399                     lint.set_arg("what", what);
1400
1401                     lint.span_suggestion(vis_span, fluent::suggestion, "pub(crate)", applicability);
1402                     if exportable {
1403                         lint.help(fluent::help);
1404                     }
1405                     lint
1406                 },
1407             );
1408         }
1409     }
1410 }
1411
1412 impl<'tcx> LateLintPass<'tcx> for UnreachablePub {
1413     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1414         // Do not warn for fake `use` statements.
1415         if let hir::ItemKind::Use(_, hir::UseKind::ListStem) = &item.kind {
1416             return;
1417         }
1418         self.perform_lint(cx, "item", item.owner_id.def_id, item.vis_span, true);
1419     }
1420
1421     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'tcx>) {
1422         self.perform_lint(cx, "item", foreign_item.owner_id.def_id, foreign_item.vis_span, true);
1423     }
1424
1425     fn check_field_def(&mut self, cx: &LateContext<'_>, field: &hir::FieldDef<'_>) {
1426         let map = cx.tcx.hir();
1427         let def_id = map.local_def_id(field.hir_id);
1428         if matches!(map.get(map.get_parent_node(field.hir_id)), Node::Variant(_)) {
1429             return;
1430         }
1431         self.perform_lint(cx, "field", def_id, field.vis_span, false);
1432     }
1433
1434     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
1435         // Only lint inherent impl items.
1436         if cx.tcx.associated_item(impl_item.owner_id).trait_item_def_id.is_none() {
1437             self.perform_lint(cx, "item", impl_item.owner_id.def_id, impl_item.vis_span, false);
1438         }
1439     }
1440 }
1441
1442 declare_lint! {
1443     /// The `type_alias_bounds` lint detects bounds in type aliases.
1444     ///
1445     /// ### Example
1446     ///
1447     /// ```rust
1448     /// type SendVec<T: Send> = Vec<T>;
1449     /// ```
1450     ///
1451     /// {{produces}}
1452     ///
1453     /// ### Explanation
1454     ///
1455     /// The trait bounds in a type alias are currently ignored, and should not
1456     /// be included to avoid confusion. This was previously allowed
1457     /// unintentionally; this may become a hard error in the future.
1458     TYPE_ALIAS_BOUNDS,
1459     Warn,
1460     "bounds in type aliases are not enforced"
1461 }
1462
1463 declare_lint_pass!(
1464     /// Lint for trait and lifetime bounds in type aliases being mostly ignored.
1465     /// They are relevant when using associated types, but otherwise neither checked
1466     /// at definition site nor enforced at use site.
1467     TypeAliasBounds => [TYPE_ALIAS_BOUNDS]
1468 );
1469
1470 impl TypeAliasBounds {
1471     fn is_type_variable_assoc(qpath: &hir::QPath<'_>) -> bool {
1472         match *qpath {
1473             hir::QPath::TypeRelative(ref ty, _) => {
1474                 // If this is a type variable, we found a `T::Assoc`.
1475                 match ty.kind {
1476                     hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
1477                         matches!(path.res, Res::Def(DefKind::TyParam, _))
1478                     }
1479                     _ => false,
1480                 }
1481             }
1482             hir::QPath::Resolved(..) | hir::QPath::LangItem(..) => false,
1483         }
1484     }
1485
1486     fn suggest_changing_assoc_types(ty: &hir::Ty<'_>, err: &mut Diagnostic) {
1487         // Access to associates types should use `<T as Bound>::Assoc`, which does not need a
1488         // bound.  Let's see if this type does that.
1489
1490         // We use a HIR visitor to walk the type.
1491         use rustc_hir::intravisit::{self, Visitor};
1492         struct WalkAssocTypes<'a> {
1493             err: &'a mut Diagnostic,
1494         }
1495         impl Visitor<'_> for WalkAssocTypes<'_> {
1496             fn visit_qpath(&mut self, qpath: &hir::QPath<'_>, id: hir::HirId, span: Span) {
1497                 if TypeAliasBounds::is_type_variable_assoc(qpath) {
1498                     self.err.span_help(span, fluent::lint_builtin_type_alias_bounds_help);
1499                 }
1500                 intravisit::walk_qpath(self, qpath, id)
1501             }
1502         }
1503
1504         // Let's go for a walk!
1505         let mut visitor = WalkAssocTypes { err };
1506         visitor.visit_ty(ty);
1507     }
1508 }
1509
1510 impl<'tcx> LateLintPass<'tcx> for TypeAliasBounds {
1511     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1512         let hir::ItemKind::TyAlias(ty, type_alias_generics) = &item.kind else {
1513             return
1514         };
1515         if let hir::TyKind::OpaqueDef(..) = ty.kind {
1516             // Bounds are respected for `type X = impl Trait`
1517             return;
1518         }
1519         // There must not be a where clause
1520         if type_alias_generics.predicates.is_empty() {
1521             return;
1522         }
1523
1524         let mut where_spans = Vec::new();
1525         let mut inline_spans = Vec::new();
1526         let mut inline_sugg = Vec::new();
1527         for p in type_alias_generics.predicates {
1528             let span = p.span();
1529             if p.in_where_clause() {
1530                 where_spans.push(span);
1531             } else {
1532                 for b in p.bounds() {
1533                     inline_spans.push(b.span());
1534                 }
1535                 inline_sugg.push((span, String::new()));
1536             }
1537         }
1538
1539         let mut suggested_changing_assoc_types = false;
1540         if !where_spans.is_empty() {
1541             cx.lint(TYPE_ALIAS_BOUNDS, fluent::lint_builtin_type_alias_where_clause, |lint| {
1542                 lint.set_span(where_spans);
1543                 lint.span_suggestion(
1544                     type_alias_generics.where_clause_span,
1545                     fluent::suggestion,
1546                     "",
1547                     Applicability::MachineApplicable,
1548                 );
1549                 if !suggested_changing_assoc_types {
1550                     TypeAliasBounds::suggest_changing_assoc_types(ty, lint);
1551                     suggested_changing_assoc_types = true;
1552                 }
1553                 lint
1554             });
1555         }
1556
1557         if !inline_spans.is_empty() {
1558             cx.lint(TYPE_ALIAS_BOUNDS, fluent::lint_builtin_type_alias_generic_bounds, |lint| {
1559                 lint.set_span(inline_spans);
1560                 lint.multipart_suggestion(
1561                     fluent::suggestion,
1562                     inline_sugg,
1563                     Applicability::MachineApplicable,
1564                 );
1565                 if !suggested_changing_assoc_types {
1566                     TypeAliasBounds::suggest_changing_assoc_types(ty, lint);
1567                 }
1568                 lint
1569             });
1570         }
1571     }
1572 }
1573
1574 declare_lint_pass!(
1575     /// Lint constants that are erroneous.
1576     /// Without this lint, we might not get any diagnostic if the constant is
1577     /// unused within this crate, even though downstream crates can't use it
1578     /// without producing an error.
1579     UnusedBrokenConst => []
1580 );
1581
1582 impl<'tcx> LateLintPass<'tcx> for UnusedBrokenConst {
1583     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1584         match it.kind {
1585             hir::ItemKind::Const(_, body_id) => {
1586                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1587                 // trigger the query once for all constants since that will already report the errors
1588                 cx.tcx.ensure().const_eval_poly(def_id);
1589             }
1590             hir::ItemKind::Static(_, _, body_id) => {
1591                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1592                 cx.tcx.ensure().eval_static_initializer(def_id);
1593             }
1594             _ => {}
1595         }
1596     }
1597 }
1598
1599 declare_lint! {
1600     /// The `trivial_bounds` lint detects trait bounds that don't depend on
1601     /// any type parameters.
1602     ///
1603     /// ### Example
1604     ///
1605     /// ```rust
1606     /// #![feature(trivial_bounds)]
1607     /// pub struct A where i32: Copy;
1608     /// ```
1609     ///
1610     /// {{produces}}
1611     ///
1612     /// ### Explanation
1613     ///
1614     /// Usually you would not write a trait bound that you know is always
1615     /// true, or never true. However, when using macros, the macro may not
1616     /// know whether or not the constraint would hold or not at the time when
1617     /// generating the code. Currently, the compiler does not alert you if the
1618     /// constraint is always true, and generates an error if it is never true.
1619     /// The `trivial_bounds` feature changes this to be a warning in both
1620     /// cases, giving macros more freedom and flexibility to generate code,
1621     /// while still providing a signal when writing non-macro code that
1622     /// something is amiss.
1623     ///
1624     /// See [RFC 2056] for more details. This feature is currently only
1625     /// available on the nightly channel, see [tracking issue #48214].
1626     ///
1627     /// [RFC 2056]: https://github.com/rust-lang/rfcs/blob/master/text/2056-allow-trivial-where-clause-constraints.md
1628     /// [tracking issue #48214]: https://github.com/rust-lang/rust/issues/48214
1629     TRIVIAL_BOUNDS,
1630     Warn,
1631     "these bounds don't depend on an type parameters"
1632 }
1633
1634 declare_lint_pass!(
1635     /// Lint for trait and lifetime bounds that don't depend on type parameters
1636     /// which either do nothing, or stop the item from being used.
1637     TrivialConstraints => [TRIVIAL_BOUNDS]
1638 );
1639
1640 impl<'tcx> LateLintPass<'tcx> for TrivialConstraints {
1641     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
1642         use rustc_middle::ty::visit::TypeVisitable;
1643         use rustc_middle::ty::PredicateKind::*;
1644
1645         if cx.tcx.features().trivial_bounds {
1646             let predicates = cx.tcx.predicates_of(item.owner_id);
1647             for &(predicate, span) in predicates.predicates {
1648                 let predicate_kind_name = match predicate.kind().skip_binder() {
1649                     Trait(..) => "trait",
1650                     TypeOutlives(..) |
1651                     RegionOutlives(..) => "lifetime",
1652
1653                     // Ignore projections, as they can only be global
1654                     // if the trait bound is global
1655                     Projection(..) |
1656                     // Ignore bounds that a user can't type
1657                     WellFormed(..) |
1658                     ObjectSafe(..) |
1659                     ClosureKind(..) |
1660                     Subtype(..) |
1661                     Coerce(..) |
1662                     ConstEvaluatable(..) |
1663                     ConstEquate(..) |
1664                     TypeWellFormedFromEnv(..) => continue,
1665                 };
1666                 if predicate.is_global() {
1667                     cx.struct_span_lint(
1668                         TRIVIAL_BOUNDS,
1669                         span,
1670                         fluent::lint_builtin_trivial_bounds,
1671                         |lint| {
1672                             lint.set_arg("predicate_kind_name", predicate_kind_name)
1673                                 .set_arg("predicate", predicate)
1674                         },
1675                     );
1676                 }
1677             }
1678         }
1679     }
1680 }
1681
1682 declare_lint_pass!(
1683     /// Does nothing as a lint pass, but registers some `Lint`s
1684     /// which are used by other parts of the compiler.
1685     SoftLints => [
1686         WHILE_TRUE,
1687         BOX_POINTERS,
1688         NON_SHORTHAND_FIELD_PATTERNS,
1689         UNSAFE_CODE,
1690         MISSING_DOCS,
1691         MISSING_COPY_IMPLEMENTATIONS,
1692         MISSING_DEBUG_IMPLEMENTATIONS,
1693         ANONYMOUS_PARAMETERS,
1694         UNUSED_DOC_COMMENTS,
1695         NO_MANGLE_CONST_ITEMS,
1696         NO_MANGLE_GENERIC_ITEMS,
1697         MUTABLE_TRANSMUTES,
1698         UNSTABLE_FEATURES,
1699         UNREACHABLE_PUB,
1700         TYPE_ALIAS_BOUNDS,
1701         TRIVIAL_BOUNDS
1702     ]
1703 );
1704
1705 declare_lint! {
1706     /// The `ellipsis_inclusive_range_patterns` lint detects the [`...` range
1707     /// pattern], which is deprecated.
1708     ///
1709     /// [`...` range pattern]: https://doc.rust-lang.org/reference/patterns.html#range-patterns
1710     ///
1711     /// ### Example
1712     ///
1713     /// ```rust,edition2018
1714     /// let x = 123;
1715     /// match x {
1716     ///     0...100 => {}
1717     ///     _ => {}
1718     /// }
1719     /// ```
1720     ///
1721     /// {{produces}}
1722     ///
1723     /// ### Explanation
1724     ///
1725     /// The `...` range pattern syntax was changed to `..=` to avoid potential
1726     /// confusion with the [`..` range expression]. Use the new form instead.
1727     ///
1728     /// [`..` range expression]: https://doc.rust-lang.org/reference/expressions/range-expr.html
1729     pub ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
1730     Warn,
1731     "`...` range patterns are deprecated",
1732     @future_incompatible = FutureIncompatibleInfo {
1733         reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>",
1734         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
1735     };
1736 }
1737
1738 #[derive(Default)]
1739 pub struct EllipsisInclusiveRangePatterns {
1740     /// If `Some(_)`, suppress all subsequent pattern
1741     /// warnings for better diagnostics.
1742     node_id: Option<ast::NodeId>,
1743 }
1744
1745 impl_lint_pass!(EllipsisInclusiveRangePatterns => [ELLIPSIS_INCLUSIVE_RANGE_PATTERNS]);
1746
1747 impl EarlyLintPass for EllipsisInclusiveRangePatterns {
1748     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &ast::Pat) {
1749         if self.node_id.is_some() {
1750             // Don't recursively warn about patterns inside range endpoints.
1751             return;
1752         }
1753
1754         use self::ast::{PatKind, RangeSyntax::DotDotDot};
1755
1756         /// If `pat` is a `...` pattern, return the start and end of the range, as well as the span
1757         /// corresponding to the ellipsis.
1758         fn matches_ellipsis_pat(pat: &ast::Pat) -> Option<(Option<&Expr>, &Expr, Span)> {
1759             match &pat.kind {
1760                 PatKind::Range(
1761                     a,
1762                     Some(b),
1763                     Spanned { span, node: RangeEnd::Included(DotDotDot) },
1764                 ) => Some((a.as_deref(), b, *span)),
1765                 _ => None,
1766             }
1767         }
1768
1769         let (parenthesise, endpoints) = match &pat.kind {
1770             PatKind::Ref(subpat, _) => (true, matches_ellipsis_pat(&subpat)),
1771             _ => (false, matches_ellipsis_pat(pat)),
1772         };
1773
1774         if let Some((start, end, join)) = endpoints {
1775             let msg = fluent::lint_builtin_ellipsis_inclusive_range_patterns;
1776             let suggestion = fluent::suggestion;
1777             if parenthesise {
1778                 self.node_id = Some(pat.id);
1779                 let end = expr_to_string(&end);
1780                 let replace = match start {
1781                     Some(start) => format!("&({}..={})", expr_to_string(&start), end),
1782                     None => format!("&(..={})", end),
1783                 };
1784                 if join.edition() >= Edition::Edition2021 {
1785                     cx.sess().emit_err(BuiltinEllpisisInclusiveRangePatterns {
1786                         span: pat.span,
1787                         suggestion: pat.span,
1788                         replace,
1789                     });
1790                 } else {
1791                     cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, pat.span, msg, |lint| {
1792                         lint.span_suggestion(
1793                             pat.span,
1794                             suggestion,
1795                             replace,
1796                             Applicability::MachineApplicable,
1797                         )
1798                     });
1799                 }
1800             } else {
1801                 let replace = "..=";
1802                 if join.edition() >= Edition::Edition2021 {
1803                     cx.sess().emit_err(BuiltinEllpisisInclusiveRangePatterns {
1804                         span: pat.span,
1805                         suggestion: join,
1806                         replace: replace.to_string(),
1807                     });
1808                 } else {
1809                     cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, join, msg, |lint| {
1810                         lint.span_suggestion_short(
1811                             join,
1812                             suggestion,
1813                             replace,
1814                             Applicability::MachineApplicable,
1815                         )
1816                     });
1817                 }
1818             };
1819         }
1820     }
1821
1822     fn check_pat_post(&mut self, _cx: &EarlyContext<'_>, pat: &ast::Pat) {
1823         if let Some(node_id) = self.node_id {
1824             if pat.id == node_id {
1825                 self.node_id = None
1826             }
1827         }
1828     }
1829 }
1830
1831 declare_lint! {
1832     /// The `unnameable_test_items` lint detects [`#[test]`][test] functions
1833     /// that are not able to be run by the test harness because they are in a
1834     /// position where they are not nameable.
1835     ///
1836     /// [test]: https://doc.rust-lang.org/reference/attributes/testing.html#the-test-attribute
1837     ///
1838     /// ### Example
1839     ///
1840     /// ```rust,test
1841     /// fn main() {
1842     ///     #[test]
1843     ///     fn foo() {
1844     ///         // This test will not fail because it does not run.
1845     ///         assert_eq!(1, 2);
1846     ///     }
1847     /// }
1848     /// ```
1849     ///
1850     /// {{produces}}
1851     ///
1852     /// ### Explanation
1853     ///
1854     /// In order for the test harness to run a test, the test function must be
1855     /// located in a position where it can be accessed from the crate root.
1856     /// This generally means it must be defined in a module, and not anywhere
1857     /// else such as inside another function. The compiler previously allowed
1858     /// this without an error, so a lint was added as an alert that a test is
1859     /// not being used. Whether or not this should be allowed has not yet been
1860     /// decided, see [RFC 2471] and [issue #36629].
1861     ///
1862     /// [RFC 2471]: https://github.com/rust-lang/rfcs/pull/2471#issuecomment-397414443
1863     /// [issue #36629]: https://github.com/rust-lang/rust/issues/36629
1864     UNNAMEABLE_TEST_ITEMS,
1865     Warn,
1866     "detects an item that cannot be named being marked as `#[test_case]`",
1867     report_in_external_macro
1868 }
1869
1870 pub struct UnnameableTestItems {
1871     boundary: Option<hir::OwnerId>, // Id of the item under which things are not nameable
1872     items_nameable: bool,
1873 }
1874
1875 impl_lint_pass!(UnnameableTestItems => [UNNAMEABLE_TEST_ITEMS]);
1876
1877 impl UnnameableTestItems {
1878     pub fn new() -> Self {
1879         Self { boundary: None, items_nameable: true }
1880     }
1881 }
1882
1883 impl<'tcx> LateLintPass<'tcx> for UnnameableTestItems {
1884     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1885         if self.items_nameable {
1886             if let hir::ItemKind::Mod(..) = it.kind {
1887             } else {
1888                 self.items_nameable = false;
1889                 self.boundary = Some(it.owner_id);
1890             }
1891             return;
1892         }
1893
1894         let attrs = cx.tcx.hir().attrs(it.hir_id());
1895         if let Some(attr) = cx.sess().find_by_name(attrs, sym::rustc_test_marker) {
1896             cx.struct_span_lint(
1897                 UNNAMEABLE_TEST_ITEMS,
1898                 attr.span,
1899                 fluent::lint_builtin_unnameable_test_items,
1900                 |lint| lint,
1901             );
1902         }
1903     }
1904
1905     fn check_item_post(&mut self, _cx: &LateContext<'_>, it: &hir::Item<'_>) {
1906         if !self.items_nameable && self.boundary == Some(it.owner_id) {
1907             self.items_nameable = true;
1908         }
1909     }
1910 }
1911
1912 declare_lint! {
1913     /// The `keyword_idents` lint detects edition keywords being used as an
1914     /// identifier.
1915     ///
1916     /// ### Example
1917     ///
1918     /// ```rust,edition2015,compile_fail
1919     /// #![deny(keyword_idents)]
1920     /// // edition 2015
1921     /// fn dyn() {}
1922     /// ```
1923     ///
1924     /// {{produces}}
1925     ///
1926     /// ### Explanation
1927     ///
1928     /// Rust [editions] allow the language to evolve without breaking
1929     /// backwards compatibility. This lint catches code that uses new keywords
1930     /// that are added to the language that are used as identifiers (such as a
1931     /// variable name, function name, etc.). If you switch the compiler to a
1932     /// new edition without updating the code, then it will fail to compile if
1933     /// you are using a new keyword as an identifier.
1934     ///
1935     /// You can manually change the identifiers to a non-keyword, or use a
1936     /// [raw identifier], for example `r#dyn`, to transition to a new edition.
1937     ///
1938     /// This lint solves the problem automatically. It is "allow" by default
1939     /// because the code is perfectly valid in older editions. The [`cargo
1940     /// fix`] tool with the `--edition` flag will switch this lint to "warn"
1941     /// and automatically apply the suggested fix from the compiler (which is
1942     /// to use a raw identifier). This provides a completely automated way to
1943     /// update old code for a new edition.
1944     ///
1945     /// [editions]: https://doc.rust-lang.org/edition-guide/
1946     /// [raw identifier]: https://doc.rust-lang.org/reference/identifiers.html
1947     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
1948     pub KEYWORD_IDENTS,
1949     Allow,
1950     "detects edition keywords being used as an identifier",
1951     @future_incompatible = FutureIncompatibleInfo {
1952         reference: "issue #49716 <https://github.com/rust-lang/rust/issues/49716>",
1953         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
1954     };
1955 }
1956
1957 declare_lint_pass!(
1958     /// Check for uses of edition keywords used as an identifier.
1959     KeywordIdents => [KEYWORD_IDENTS]
1960 );
1961
1962 struct UnderMacro(bool);
1963
1964 impl KeywordIdents {
1965     fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: TokenStream) {
1966         for tt in tokens.into_trees() {
1967             match tt {
1968                 // Only report non-raw idents.
1969                 TokenTree::Token(token, _) => {
1970                     if let Some((ident, false)) = token.ident() {
1971                         self.check_ident_token(cx, UnderMacro(true), ident);
1972                     }
1973                 }
1974                 TokenTree::Delimited(_, _, tts) => self.check_tokens(cx, tts),
1975             }
1976         }
1977     }
1978
1979     fn check_ident_token(
1980         &mut self,
1981         cx: &EarlyContext<'_>,
1982         UnderMacro(under_macro): UnderMacro,
1983         ident: Ident,
1984     ) {
1985         let next_edition = match cx.sess().edition() {
1986             Edition::Edition2015 => {
1987                 match ident.name {
1988                     kw::Async | kw::Await | kw::Try => Edition::Edition2018,
1989
1990                     // rust-lang/rust#56327: Conservatively do not
1991                     // attempt to report occurrences of `dyn` within
1992                     // macro definitions or invocations, because `dyn`
1993                     // can legitimately occur as a contextual keyword
1994                     // in 2015 code denoting its 2018 meaning, and we
1995                     // do not want rustfix to inject bugs into working
1996                     // code by rewriting such occurrences.
1997                     //
1998                     // But if we see `dyn` outside of a macro, we know
1999                     // its precise role in the parsed AST and thus are
2000                     // assured this is truly an attempt to use it as
2001                     // an identifier.
2002                     kw::Dyn if !under_macro => Edition::Edition2018,
2003
2004                     _ => return,
2005                 }
2006             }
2007
2008             // There are no new keywords yet for the 2018 edition and beyond.
2009             _ => return,
2010         };
2011
2012         // Don't lint `r#foo`.
2013         if cx.sess().parse_sess.raw_identifier_spans.borrow().contains(&ident.span) {
2014             return;
2015         }
2016
2017         cx.struct_span_lint(
2018             KEYWORD_IDENTS,
2019             ident.span,
2020             fluent::lint_builtin_keyword_idents,
2021             |lint| {
2022                 lint.set_arg("kw", ident.clone()).set_arg("next", next_edition).span_suggestion(
2023                     ident.span,
2024                     fluent::suggestion,
2025                     format!("r#{}", ident),
2026                     Applicability::MachineApplicable,
2027                 )
2028             },
2029         );
2030     }
2031 }
2032
2033 impl EarlyLintPass for KeywordIdents {
2034     fn check_mac_def(&mut self, cx: &EarlyContext<'_>, mac_def: &ast::MacroDef) {
2035         self.check_tokens(cx, mac_def.body.inner_tokens());
2036     }
2037     fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::MacCall) {
2038         self.check_tokens(cx, mac.args.inner_tokens());
2039     }
2040     fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: Ident) {
2041         self.check_ident_token(cx, UnderMacro(false), ident);
2042     }
2043 }
2044
2045 declare_lint_pass!(ExplicitOutlivesRequirements => [EXPLICIT_OUTLIVES_REQUIREMENTS]);
2046
2047 impl ExplicitOutlivesRequirements {
2048     fn lifetimes_outliving_lifetime<'tcx>(
2049         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2050         def_id: DefId,
2051     ) -> Vec<ty::Region<'tcx>> {
2052         inferred_outlives
2053             .iter()
2054             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
2055                 ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => match *a {
2056                     ty::ReEarlyBound(ebr) if ebr.def_id == def_id => Some(b),
2057                     _ => None,
2058                 },
2059                 _ => None,
2060             })
2061             .collect()
2062     }
2063
2064     fn lifetimes_outliving_type<'tcx>(
2065         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2066         index: u32,
2067     ) -> Vec<ty::Region<'tcx>> {
2068         inferred_outlives
2069             .iter()
2070             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
2071                 ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
2072                     a.is_param(index).then_some(b)
2073                 }
2074                 _ => None,
2075             })
2076             .collect()
2077     }
2078
2079     fn collect_outlives_bound_spans<'tcx>(
2080         &self,
2081         tcx: TyCtxt<'tcx>,
2082         bounds: &hir::GenericBounds<'_>,
2083         inferred_outlives: &[ty::Region<'tcx>],
2084     ) -> Vec<(usize, Span)> {
2085         use rustc_middle::middle::resolve_lifetime::Region;
2086
2087         bounds
2088             .iter()
2089             .enumerate()
2090             .filter_map(|(i, bound)| {
2091                 if let hir::GenericBound::Outlives(lifetime) = bound {
2092                     let is_inferred = match tcx.named_region(lifetime.hir_id) {
2093                         Some(Region::EarlyBound(def_id)) => inferred_outlives.iter().any(|r| {
2094                             if let ty::ReEarlyBound(ebr) = **r {
2095                                 ebr.def_id == def_id
2096                             } else {
2097                                 false
2098                             }
2099                         }),
2100                         _ => false,
2101                     };
2102                     is_inferred.then_some((i, bound.span()))
2103                 } else {
2104                     None
2105                 }
2106             })
2107             .filter(|(_, span)| !in_external_macro(tcx.sess, *span))
2108             .collect()
2109     }
2110
2111     fn consolidate_outlives_bound_spans(
2112         &self,
2113         lo: Span,
2114         bounds: &hir::GenericBounds<'_>,
2115         bound_spans: Vec<(usize, Span)>,
2116     ) -> Vec<Span> {
2117         if bounds.is_empty() {
2118             return Vec::new();
2119         }
2120         if bound_spans.len() == bounds.len() {
2121             let (_, last_bound_span) = bound_spans[bound_spans.len() - 1];
2122             // If all bounds are inferable, we want to delete the colon, so
2123             // start from just after the parameter (span passed as argument)
2124             vec![lo.to(last_bound_span)]
2125         } else {
2126             let mut merged = Vec::new();
2127             let mut last_merged_i = None;
2128
2129             let mut from_start = true;
2130             for (i, bound_span) in bound_spans {
2131                 match last_merged_i {
2132                     // If the first bound is inferable, our span should also eat the leading `+`.
2133                     None if i == 0 => {
2134                         merged.push(bound_span.to(bounds[1].span().shrink_to_lo()));
2135                         last_merged_i = Some(0);
2136                     }
2137                     // If consecutive bounds are inferable, merge their spans
2138                     Some(h) if i == h + 1 => {
2139                         if let Some(tail) = merged.last_mut() {
2140                             // Also eat the trailing `+` if the first
2141                             // more-than-one bound is inferable
2142                             let to_span = if from_start && i < bounds.len() {
2143                                 bounds[i + 1].span().shrink_to_lo()
2144                             } else {
2145                                 bound_span
2146                             };
2147                             *tail = tail.to(to_span);
2148                             last_merged_i = Some(i);
2149                         } else {
2150                             bug!("another bound-span visited earlier");
2151                         }
2152                     }
2153                     _ => {
2154                         // When we find a non-inferable bound, subsequent inferable bounds
2155                         // won't be consecutive from the start (and we'll eat the leading
2156                         // `+` rather than the trailing one)
2157                         from_start = false;
2158                         merged.push(bounds[i - 1].span().shrink_to_hi().to(bound_span));
2159                         last_merged_i = Some(i);
2160                     }
2161                 }
2162             }
2163             merged
2164         }
2165     }
2166 }
2167
2168 impl<'tcx> LateLintPass<'tcx> for ExplicitOutlivesRequirements {
2169     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
2170         use rustc_middle::middle::resolve_lifetime::Region;
2171
2172         let def_id = item.owner_id.def_id;
2173         if let hir::ItemKind::Struct(_, ref hir_generics)
2174         | hir::ItemKind::Enum(_, ref hir_generics)
2175         | hir::ItemKind::Union(_, ref hir_generics) = item.kind
2176         {
2177             let inferred_outlives = cx.tcx.inferred_outlives_of(def_id);
2178             if inferred_outlives.is_empty() {
2179                 return;
2180             }
2181
2182             let ty_generics = cx.tcx.generics_of(def_id);
2183
2184             let mut bound_count = 0;
2185             let mut lint_spans = Vec::new();
2186             let mut where_lint_spans = Vec::new();
2187             let mut dropped_predicate_count = 0;
2188             let num_predicates = hir_generics.predicates.len();
2189             for (i, where_predicate) in hir_generics.predicates.iter().enumerate() {
2190                 let (relevant_lifetimes, bounds, span, in_where_clause) = match where_predicate {
2191                     hir::WherePredicate::RegionPredicate(predicate) => {
2192                         if let Some(Region::EarlyBound(region_def_id)) =
2193                             cx.tcx.named_region(predicate.lifetime.hir_id)
2194                         {
2195                             (
2196                                 Self::lifetimes_outliving_lifetime(
2197                                     inferred_outlives,
2198                                     region_def_id,
2199                                 ),
2200                                 &predicate.bounds,
2201                                 predicate.span,
2202                                 predicate.in_where_clause,
2203                             )
2204                         } else {
2205                             continue;
2206                         }
2207                     }
2208                     hir::WherePredicate::BoundPredicate(predicate) => {
2209                         // FIXME we can also infer bounds on associated types,
2210                         // and should check for them here.
2211                         match predicate.bounded_ty.kind {
2212                             hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
2213                                 let Res::Def(DefKind::TyParam, def_id) = path.res else {
2214                                     continue
2215                                 };
2216                                 let index = ty_generics.param_def_id_to_index[&def_id];
2217                                 (
2218                                     Self::lifetimes_outliving_type(inferred_outlives, index),
2219                                     &predicate.bounds,
2220                                     predicate.span,
2221                                     predicate.origin == PredicateOrigin::WhereClause,
2222                                 )
2223                             }
2224                             _ => {
2225                                 continue;
2226                             }
2227                         }
2228                     }
2229                     _ => continue,
2230                 };
2231                 if relevant_lifetimes.is_empty() {
2232                     continue;
2233                 }
2234
2235                 let bound_spans =
2236                     self.collect_outlives_bound_spans(cx.tcx, bounds, &relevant_lifetimes);
2237                 bound_count += bound_spans.len();
2238
2239                 let drop_predicate = bound_spans.len() == bounds.len();
2240                 if drop_predicate {
2241                     dropped_predicate_count += 1;
2242                 }
2243
2244                 if drop_predicate && !in_where_clause {
2245                     lint_spans.push(span);
2246                 } else if drop_predicate && i + 1 < num_predicates {
2247                     // If all the bounds on a predicate were inferable and there are
2248                     // further predicates, we want to eat the trailing comma.
2249                     let next_predicate_span = hir_generics.predicates[i + 1].span();
2250                     where_lint_spans.push(span.to(next_predicate_span.shrink_to_lo()));
2251                 } else {
2252                     where_lint_spans.extend(self.consolidate_outlives_bound_spans(
2253                         span.shrink_to_lo(),
2254                         bounds,
2255                         bound_spans,
2256                     ));
2257                 }
2258             }
2259
2260             // If all predicates are inferable, drop the entire clause
2261             // (including the `where`)
2262             if hir_generics.has_where_clause_predicates && dropped_predicate_count == num_predicates
2263             {
2264                 let where_span = hir_generics.where_clause_span;
2265                 // Extend the where clause back to the closing `>` of the
2266                 // generics, except for tuple struct, which have the `where`
2267                 // after the fields of the struct.
2268                 let full_where_span =
2269                     if let hir::ItemKind::Struct(hir::VariantData::Tuple(..), _) = item.kind {
2270                         where_span
2271                     } else {
2272                         hir_generics.span.shrink_to_hi().to(where_span)
2273                     };
2274                 lint_spans.push(full_where_span);
2275             } else {
2276                 lint_spans.extend(where_lint_spans);
2277             }
2278
2279             if !lint_spans.is_empty() {
2280                 cx.struct_span_lint(
2281                     EXPLICIT_OUTLIVES_REQUIREMENTS,
2282                     lint_spans.clone(),
2283                     fluent::lint_builtin_explicit_outlives,
2284                     |lint| {
2285                         lint.set_arg("count", bound_count).multipart_suggestion(
2286                             fluent::suggestion,
2287                             lint_spans
2288                                 .into_iter()
2289                                 .map(|span| (span, String::new()))
2290                                 .collect::<Vec<_>>(),
2291                             Applicability::MachineApplicable,
2292                         )
2293                     },
2294                 );
2295             }
2296         }
2297     }
2298 }
2299
2300 declare_lint! {
2301     /// The `incomplete_features` lint detects unstable features enabled with
2302     /// the [`feature` attribute] that may function improperly in some or all
2303     /// cases.
2304     ///
2305     /// [`feature` attribute]: https://doc.rust-lang.org/nightly/unstable-book/
2306     ///
2307     /// ### Example
2308     ///
2309     /// ```rust
2310     /// #![feature(generic_const_exprs)]
2311     /// ```
2312     ///
2313     /// {{produces}}
2314     ///
2315     /// ### Explanation
2316     ///
2317     /// Although it is encouraged for people to experiment with unstable
2318     /// features, some of them are known to be incomplete or faulty. This lint
2319     /// is a signal that the feature has not yet been finished, and you may
2320     /// experience problems with it.
2321     pub INCOMPLETE_FEATURES,
2322     Warn,
2323     "incomplete features that may function improperly in some or all cases"
2324 }
2325
2326 declare_lint_pass!(
2327     /// Check for used feature gates in `INCOMPLETE_FEATURES` in `rustc_feature/src/active.rs`.
2328     IncompleteFeatures => [INCOMPLETE_FEATURES]
2329 );
2330
2331 impl EarlyLintPass for IncompleteFeatures {
2332     fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
2333         let features = cx.sess().features_untracked();
2334         features
2335             .declared_lang_features
2336             .iter()
2337             .map(|(name, span, _)| (name, span))
2338             .chain(features.declared_lib_features.iter().map(|(name, span)| (name, span)))
2339             .filter(|(&name, _)| features.incomplete(name))
2340             .for_each(|(&name, &span)| {
2341                 cx.struct_span_lint(
2342                     INCOMPLETE_FEATURES,
2343                     span,
2344                     fluent::lint_builtin_incomplete_features,
2345                     |lint| {
2346                         lint.set_arg("name", name);
2347                         if let Some(n) =
2348                             rustc_feature::find_feature_issue(name, GateIssue::Language)
2349                         {
2350                             lint.set_arg("n", n);
2351                             lint.note(fluent::note);
2352                         }
2353                         if HAS_MIN_FEATURES.contains(&name) {
2354                             lint.help(fluent::help);
2355                         }
2356                         lint
2357                     },
2358                 )
2359             });
2360     }
2361 }
2362
2363 const HAS_MIN_FEATURES: &[Symbol] = &[sym::specialization];
2364
2365 declare_lint! {
2366     /// The `invalid_value` lint detects creating a value that is not valid,
2367     /// such as a null reference.
2368     ///
2369     /// ### Example
2370     ///
2371     /// ```rust,no_run
2372     /// # #![allow(unused)]
2373     /// unsafe {
2374     ///     let x: &'static i32 = std::mem::zeroed();
2375     /// }
2376     /// ```
2377     ///
2378     /// {{produces}}
2379     ///
2380     /// ### Explanation
2381     ///
2382     /// In some situations the compiler can detect that the code is creating
2383     /// an invalid value, which should be avoided.
2384     ///
2385     /// In particular, this lint will check for improper use of
2386     /// [`mem::zeroed`], [`mem::uninitialized`], [`mem::transmute`], and
2387     /// [`MaybeUninit::assume_init`] that can cause [undefined behavior]. The
2388     /// lint should provide extra information to indicate what the problem is
2389     /// and a possible solution.
2390     ///
2391     /// [`mem::zeroed`]: https://doc.rust-lang.org/std/mem/fn.zeroed.html
2392     /// [`mem::uninitialized`]: https://doc.rust-lang.org/std/mem/fn.uninitialized.html
2393     /// [`mem::transmute`]: https://doc.rust-lang.org/std/mem/fn.transmute.html
2394     /// [`MaybeUninit::assume_init`]: https://doc.rust-lang.org/std/mem/union.MaybeUninit.html#method.assume_init
2395     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
2396     pub INVALID_VALUE,
2397     Warn,
2398     "an invalid value is being created (such as a null reference)"
2399 }
2400
2401 declare_lint_pass!(InvalidValue => [INVALID_VALUE]);
2402
2403 impl<'tcx> LateLintPass<'tcx> for InvalidValue {
2404     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
2405         #[derive(Debug, Copy, Clone, PartialEq)]
2406         enum InitKind {
2407             Zeroed,
2408             Uninit,
2409         }
2410
2411         /// Information about why a type cannot be initialized this way.
2412         /// Contains an error message and optionally a span to point at.
2413         type InitError = (String, Option<Span>);
2414
2415         /// Test if this constant is all-0.
2416         fn is_zero(expr: &hir::Expr<'_>) -> bool {
2417             use hir::ExprKind::*;
2418             use rustc_ast::LitKind::*;
2419             match &expr.kind {
2420                 Lit(lit) => {
2421                     if let Int(i, _) = lit.node {
2422                         i == 0
2423                     } else {
2424                         false
2425                     }
2426                 }
2427                 Tup(tup) => tup.iter().all(is_zero),
2428                 _ => false,
2429             }
2430         }
2431
2432         /// Determine if this expression is a "dangerous initialization".
2433         fn is_dangerous_init(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> Option<InitKind> {
2434             if let hir::ExprKind::Call(ref path_expr, ref args) = expr.kind {
2435                 // Find calls to `mem::{uninitialized,zeroed}` methods.
2436                 if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2437                     let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2438                     match cx.tcx.get_diagnostic_name(def_id) {
2439                         Some(sym::mem_zeroed) => return Some(InitKind::Zeroed),
2440                         Some(sym::mem_uninitialized) => return Some(InitKind::Uninit),
2441                         Some(sym::transmute) if is_zero(&args[0]) => return Some(InitKind::Zeroed),
2442                         _ => {}
2443                     }
2444                 }
2445             } else if let hir::ExprKind::MethodCall(_, receiver, ..) = expr.kind {
2446                 // Find problematic calls to `MaybeUninit::assume_init`.
2447                 let def_id = cx.typeck_results().type_dependent_def_id(expr.hir_id)?;
2448                 if cx.tcx.is_diagnostic_item(sym::assume_init, def_id) {
2449                     // This is a call to *some* method named `assume_init`.
2450                     // See if the `self` parameter is one of the dangerous constructors.
2451                     if let hir::ExprKind::Call(ref path_expr, _) = receiver.kind {
2452                         if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2453                             let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2454                             match cx.tcx.get_diagnostic_name(def_id) {
2455                                 Some(sym::maybe_uninit_zeroed) => return Some(InitKind::Zeroed),
2456                                 Some(sym::maybe_uninit_uninit) => return Some(InitKind::Uninit),
2457                                 _ => {}
2458                             }
2459                         }
2460                     }
2461                 }
2462             }
2463
2464             None
2465         }
2466
2467         fn variant_find_init_error<'tcx>(
2468             cx: &LateContext<'tcx>,
2469             variant: &VariantDef,
2470             substs: ty::SubstsRef<'tcx>,
2471             descr: &str,
2472             init: InitKind,
2473         ) -> Option<InitError> {
2474             variant.fields.iter().find_map(|field| {
2475                 ty_find_init_error(cx, field.ty(cx.tcx, substs), init).map(|(mut msg, span)| {
2476                     if span.is_none() {
2477                         // Point to this field, should be helpful for figuring
2478                         // out where the source of the error is.
2479                         let span = cx.tcx.def_span(field.did);
2480                         write!(&mut msg, " (in this {descr})").unwrap();
2481                         (msg, Some(span))
2482                     } else {
2483                         // Just forward.
2484                         (msg, span)
2485                     }
2486                 })
2487             })
2488         }
2489
2490         /// Return `Some` only if we are sure this type does *not*
2491         /// allow zero initialization.
2492         fn ty_find_init_error<'tcx>(
2493             cx: &LateContext<'tcx>,
2494             ty: Ty<'tcx>,
2495             init: InitKind,
2496         ) -> Option<InitError> {
2497             use rustc_type_ir::sty::TyKind::*;
2498             match ty.kind() {
2499                 // Primitive types that don't like 0 as a value.
2500                 Ref(..) => Some(("references must be non-null".to_string(), None)),
2501                 Adt(..) if ty.is_box() => Some(("`Box` must be non-null".to_string(), None)),
2502                 FnPtr(..) => Some(("function pointers must be non-null".to_string(), None)),
2503                 Never => Some(("the `!` type has no valid value".to_string(), None)),
2504                 RawPtr(tm) if matches!(tm.ty.kind(), Dynamic(..)) =>
2505                 // raw ptr to dyn Trait
2506                 {
2507                     Some(("the vtable of a wide raw pointer must be non-null".to_string(), None))
2508                 }
2509                 // Primitive types with other constraints.
2510                 Bool if init == InitKind::Uninit => {
2511                     Some(("booleans must be either `true` or `false`".to_string(), None))
2512                 }
2513                 Char if init == InitKind::Uninit => {
2514                     Some(("characters must be a valid Unicode codepoint".to_string(), None))
2515                 }
2516                 Int(_) | Uint(_) if init == InitKind::Uninit => {
2517                     Some(("integers must not be uninitialized".to_string(), None))
2518                 }
2519                 Float(_) if init == InitKind::Uninit => {
2520                     Some(("floats must not be uninitialized".to_string(), None))
2521                 }
2522                 RawPtr(_) if init == InitKind::Uninit => {
2523                     Some(("raw pointers must not be uninitialized".to_string(), None))
2524                 }
2525                 // Recurse and checks for some compound types. (but not unions)
2526                 Adt(adt_def, substs) if !adt_def.is_union() => {
2527                     // First check if this ADT has a layout attribute (like `NonNull` and friends).
2528                     use std::ops::Bound;
2529                     match cx.tcx.layout_scalar_valid_range(adt_def.did()) {
2530                         // We exploit here that `layout_scalar_valid_range` will never
2531                         // return `Bound::Excluded`.  (And we have tests checking that we
2532                         // handle the attribute correctly.)
2533                         // We don't add a span since users cannot declare such types anyway.
2534                         (Bound::Included(lo), Bound::Included(hi)) if 0 < lo && lo < hi => {
2535                             return Some((format!("`{}` must be non-null", ty), None));
2536                         }
2537                         (Bound::Included(lo), Bound::Unbounded) if 0 < lo => {
2538                             return Some((format!("`{}` must be non-null", ty), None));
2539                         }
2540                         (Bound::Included(_), _) | (_, Bound::Included(_))
2541                             if init == InitKind::Uninit =>
2542                         {
2543                             return Some((
2544                                 format!(
2545                                     "`{}` must be initialized inside its custom valid range",
2546                                     ty,
2547                                 ),
2548                                 None,
2549                             ));
2550                         }
2551                         _ => {}
2552                     }
2553                     // Handle structs.
2554                     if adt_def.is_struct() {
2555                         return variant_find_init_error(
2556                             cx,
2557                             adt_def.non_enum_variant(),
2558                             substs,
2559                             "struct field",
2560                             init,
2561                         );
2562                     }
2563                     // And now, enums.
2564                     let span = cx.tcx.def_span(adt_def.did());
2565                     let mut potential_variants = adt_def.variants().iter().filter_map(|variant| {
2566                         let definitely_inhabited = match variant
2567                             .inhabited_predicate(cx.tcx, *adt_def)
2568                             .subst(cx.tcx, substs)
2569                             .apply_any_module(cx.tcx, cx.param_env)
2570                         {
2571                             // Entirely skip uninhbaited variants.
2572                             Some(false) => return None,
2573                             // Forward the others, but remember which ones are definitely inhabited.
2574                             Some(true) => true,
2575                             None => false,
2576                         };
2577                         Some((variant, definitely_inhabited))
2578                     });
2579                     let Some(first_variant) = potential_variants.next() else {
2580                         return Some(("enums with no inhabited variants have no valid value".to_string(), Some(span)));
2581                     };
2582                     // So we have at least one potentially inhabited variant. Might we have two?
2583                     let Some(second_variant) = potential_variants.next() else {
2584                         // There is only one potentially inhabited variant. So we can recursively check that variant!
2585                         return variant_find_init_error(
2586                             cx,
2587                             &first_variant.0,
2588                             substs,
2589                             "field of the only potentially inhabited enum variant",
2590                             init,
2591                         );
2592                     };
2593                     // So we have at least two potentially inhabited variants.
2594                     // If we can prove that we have at least two *definitely* inhabited variants,
2595                     // then we have a tag and hence leaving this uninit is definitely disallowed.
2596                     // (Leaving it zeroed could be okay, depending on which variant is encoded as zero tag.)
2597                     if init == InitKind::Uninit {
2598                         let definitely_inhabited = (first_variant.1 as usize)
2599                             + (second_variant.1 as usize)
2600                             + potential_variants
2601                                 .filter(|(_variant, definitely_inhabited)| *definitely_inhabited)
2602                                 .count();
2603                         if definitely_inhabited > 1 {
2604                             return Some((
2605                                 "enums with multiple inhabited variants have to be initialized to a variant".to_string(),
2606                                 Some(span),
2607                             ));
2608                         }
2609                     }
2610                     // We couldn't find anything wrong here.
2611                     None
2612                 }
2613                 Tuple(..) => {
2614                     // Proceed recursively, check all fields.
2615                     ty.tuple_fields().iter().find_map(|field| ty_find_init_error(cx, field, init))
2616                 }
2617                 Array(ty, len) => {
2618                     if matches!(len.try_eval_usize(cx.tcx, cx.param_env), Some(v) if v > 0) {
2619                         // Array length known at array non-empty -- recurse.
2620                         ty_find_init_error(cx, *ty, init)
2621                     } else {
2622                         // Empty array or size unknown.
2623                         None
2624                     }
2625                 }
2626                 // Conservative fallback.
2627                 _ => None,
2628             }
2629         }
2630
2631         if let Some(init) = is_dangerous_init(cx, expr) {
2632             // This conjures an instance of a type out of nothing,
2633             // using zeroed or uninitialized memory.
2634             // We are extremely conservative with what we warn about.
2635             let conjured_ty = cx.typeck_results().expr_ty(expr);
2636             if let Some((msg, span)) =
2637                 with_no_trimmed_paths!(ty_find_init_error(cx, conjured_ty, init))
2638             {
2639                 // FIXME(davidtwco): make translatable
2640                 cx.struct_span_lint(
2641                     INVALID_VALUE,
2642                     expr.span,
2643                     DelayDm(|| {
2644                         format!(
2645                             "the type `{}` does not permit {}",
2646                             conjured_ty,
2647                             match init {
2648                                 InitKind::Zeroed => "zero-initialization",
2649                                 InitKind::Uninit => "being left uninitialized",
2650                             },
2651                         )
2652                     }),
2653                     |lint| {
2654                         lint.span_label(
2655                             expr.span,
2656                             "this code causes undefined behavior when executed",
2657                         );
2658                         lint.span_label(
2659                             expr.span,
2660                             "help: use `MaybeUninit<T>` instead, \
2661                             and only call `assume_init` after initialization is done",
2662                         );
2663                         if let Some(span) = span {
2664                             lint.span_note(span, &msg);
2665                         } else {
2666                             lint.note(&msg);
2667                         }
2668                         lint
2669                     },
2670                 );
2671             }
2672         }
2673     }
2674 }
2675
2676 declare_lint! {
2677     /// The `clashing_extern_declarations` lint detects when an `extern fn`
2678     /// has been declared with the same name but different types.
2679     ///
2680     /// ### Example
2681     ///
2682     /// ```rust
2683     /// mod m {
2684     ///     extern "C" {
2685     ///         fn foo();
2686     ///     }
2687     /// }
2688     ///
2689     /// extern "C" {
2690     ///     fn foo(_: u32);
2691     /// }
2692     /// ```
2693     ///
2694     /// {{produces}}
2695     ///
2696     /// ### Explanation
2697     ///
2698     /// Because two symbols of the same name cannot be resolved to two
2699     /// different functions at link time, and one function cannot possibly
2700     /// have two types, a clashing extern declaration is almost certainly a
2701     /// mistake. Check to make sure that the `extern` definitions are correct
2702     /// and equivalent, and possibly consider unifying them in one location.
2703     ///
2704     /// This lint does not run between crates because a project may have
2705     /// dependencies which both rely on the same extern function, but declare
2706     /// it in a different (but valid) way. For example, they may both declare
2707     /// an opaque type for one or more of the arguments (which would end up
2708     /// distinct types), or use types that are valid conversions in the
2709     /// language the `extern fn` is defined in. In these cases, the compiler
2710     /// can't say that the clashing declaration is incorrect.
2711     pub CLASHING_EXTERN_DECLARATIONS,
2712     Warn,
2713     "detects when an extern fn has been declared with the same name but different types"
2714 }
2715
2716 pub struct ClashingExternDeclarations {
2717     /// Map of function symbol name to the first-seen hir id for that symbol name.. If seen_decls
2718     /// contains an entry for key K, it means a symbol with name K has been seen by this lint and
2719     /// the symbol should be reported as a clashing declaration.
2720     // FIXME: Technically, we could just store a &'tcx str here without issue; however, the
2721     // `impl_lint_pass` macro doesn't currently support lints parametric over a lifetime.
2722     seen_decls: FxHashMap<Symbol, HirId>,
2723 }
2724
2725 /// Differentiate between whether the name for an extern decl came from the link_name attribute or
2726 /// just from declaration itself. This is important because we don't want to report clashes on
2727 /// symbol name if they don't actually clash because one or the other links against a symbol with a
2728 /// different name.
2729 enum SymbolName {
2730     /// The name of the symbol + the span of the annotation which introduced the link name.
2731     Link(Symbol, Span),
2732     /// No link name, so just the name of the symbol.
2733     Normal(Symbol),
2734 }
2735
2736 impl SymbolName {
2737     fn get_name(&self) -> Symbol {
2738         match self {
2739             SymbolName::Link(s, _) | SymbolName::Normal(s) => *s,
2740         }
2741     }
2742 }
2743
2744 impl ClashingExternDeclarations {
2745     pub(crate) fn new() -> Self {
2746         ClashingExternDeclarations { seen_decls: FxHashMap::default() }
2747     }
2748     /// Insert a new foreign item into the seen set. If a symbol with the same name already exists
2749     /// for the item, return its HirId without updating the set.
2750     fn insert(&mut self, tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> Option<HirId> {
2751         let did = fi.owner_id.to_def_id();
2752         let instance = Instance::new(did, ty::List::identity_for_item(tcx, did));
2753         let name = Symbol::intern(tcx.symbol_name(instance).name);
2754         if let Some(&hir_id) = self.seen_decls.get(&name) {
2755             // Avoid updating the map with the new entry when we do find a collision. We want to
2756             // make sure we're always pointing to the first definition as the previous declaration.
2757             // This lets us avoid emitting "knock-on" diagnostics.
2758             Some(hir_id)
2759         } else {
2760             self.seen_decls.insert(name, fi.hir_id())
2761         }
2762     }
2763
2764     /// Get the name of the symbol that's linked against for a given extern declaration. That is,
2765     /// the name specified in a #[link_name = ...] attribute if one was specified, else, just the
2766     /// symbol's name.
2767     fn name_of_extern_decl(tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> SymbolName {
2768         if let Some((overridden_link_name, overridden_link_name_span)) =
2769             tcx.codegen_fn_attrs(fi.owner_id).link_name.map(|overridden_link_name| {
2770                 // FIXME: Instead of searching through the attributes again to get span
2771                 // information, we could have codegen_fn_attrs also give span information back for
2772                 // where the attribute was defined. However, until this is found to be a
2773                 // bottleneck, this does just fine.
2774                 (
2775                     overridden_link_name,
2776                     tcx.get_attr(fi.owner_id.to_def_id(), sym::link_name).unwrap().span,
2777                 )
2778             })
2779         {
2780             SymbolName::Link(overridden_link_name, overridden_link_name_span)
2781         } else {
2782             SymbolName::Normal(fi.ident.name)
2783         }
2784     }
2785
2786     /// Checks whether two types are structurally the same enough that the declarations shouldn't
2787     /// clash. We need this so we don't emit a lint when two modules both declare an extern struct,
2788     /// with the same members (as the declarations shouldn't clash).
2789     fn structurally_same_type<'tcx>(
2790         cx: &LateContext<'tcx>,
2791         a: Ty<'tcx>,
2792         b: Ty<'tcx>,
2793         ckind: CItemKind,
2794     ) -> bool {
2795         fn structurally_same_type_impl<'tcx>(
2796             seen_types: &mut FxHashSet<(Ty<'tcx>, Ty<'tcx>)>,
2797             cx: &LateContext<'tcx>,
2798             a: Ty<'tcx>,
2799             b: Ty<'tcx>,
2800             ckind: CItemKind,
2801         ) -> bool {
2802             debug!("structurally_same_type_impl(cx, a = {:?}, b = {:?})", a, b);
2803             let tcx = cx.tcx;
2804
2805             // Given a transparent newtype, reach through and grab the inner
2806             // type unless the newtype makes the type non-null.
2807             let non_transparent_ty = |ty: Ty<'tcx>| -> Ty<'tcx> {
2808                 let mut ty = ty;
2809                 loop {
2810                     if let ty::Adt(def, substs) = *ty.kind() {
2811                         let is_transparent = def.repr().transparent();
2812                         let is_non_null = crate::types::nonnull_optimization_guaranteed(tcx, def);
2813                         debug!(
2814                             "non_transparent_ty({:?}) -- type is transparent? {}, type is non-null? {}",
2815                             ty, is_transparent, is_non_null
2816                         );
2817                         if is_transparent && !is_non_null {
2818                             debug_assert!(def.variants().len() == 1);
2819                             let v = &def.variant(VariantIdx::new(0));
2820                             ty = transparent_newtype_field(tcx, v)
2821                                 .expect(
2822                                     "single-variant transparent structure with zero-sized field",
2823                                 )
2824                                 .ty(tcx, substs);
2825                             continue;
2826                         }
2827                     }
2828                     debug!("non_transparent_ty -> {:?}", ty);
2829                     return ty;
2830                 }
2831             };
2832
2833             let a = non_transparent_ty(a);
2834             let b = non_transparent_ty(b);
2835
2836             if !seen_types.insert((a, b)) {
2837                 // We've encountered a cycle. There's no point going any further -- the types are
2838                 // structurally the same.
2839                 return true;
2840             }
2841             let tcx = cx.tcx;
2842             if a == b {
2843                 // All nominally-same types are structurally same, too.
2844                 true
2845             } else {
2846                 // Do a full, depth-first comparison between the two.
2847                 use rustc_type_ir::sty::TyKind::*;
2848                 let a_kind = a.kind();
2849                 let b_kind = b.kind();
2850
2851                 let compare_layouts = |a, b| -> Result<bool, LayoutError<'tcx>> {
2852                     debug!("compare_layouts({:?}, {:?})", a, b);
2853                     let a_layout = &cx.layout_of(a)?.layout.abi();
2854                     let b_layout = &cx.layout_of(b)?.layout.abi();
2855                     debug!(
2856                         "comparing layouts: {:?} == {:?} = {}",
2857                         a_layout,
2858                         b_layout,
2859                         a_layout == b_layout
2860                     );
2861                     Ok(a_layout == b_layout)
2862                 };
2863
2864                 #[allow(rustc::usage_of_ty_tykind)]
2865                 let is_primitive_or_pointer = |kind: &ty::TyKind<'_>| {
2866                     kind.is_primitive() || matches!(kind, RawPtr(..) | Ref(..))
2867                 };
2868
2869                 ensure_sufficient_stack(|| {
2870                     match (a_kind, b_kind) {
2871                         (Adt(a_def, _), Adt(b_def, _)) => {
2872                             // We can immediately rule out these types as structurally same if
2873                             // their layouts differ.
2874                             match compare_layouts(a, b) {
2875                                 Ok(false) => return false,
2876                                 _ => (), // otherwise, continue onto the full, fields comparison
2877                             }
2878
2879                             // Grab a flattened representation of all fields.
2880                             let a_fields = a_def.variants().iter().flat_map(|v| v.fields.iter());
2881                             let b_fields = b_def.variants().iter().flat_map(|v| v.fields.iter());
2882
2883                             // Perform a structural comparison for each field.
2884                             a_fields.eq_by(
2885                                 b_fields,
2886                                 |&ty::FieldDef { did: a_did, .. },
2887                                  &ty::FieldDef { did: b_did, .. }| {
2888                                     structurally_same_type_impl(
2889                                         seen_types,
2890                                         cx,
2891                                         tcx.type_of(a_did),
2892                                         tcx.type_of(b_did),
2893                                         ckind,
2894                                     )
2895                                 },
2896                             )
2897                         }
2898                         (Array(a_ty, a_const), Array(b_ty, b_const)) => {
2899                             // For arrays, we also check the constness of the type.
2900                             a_const.kind() == b_const.kind()
2901                                 && structurally_same_type_impl(seen_types, cx, *a_ty, *b_ty, ckind)
2902                         }
2903                         (Slice(a_ty), Slice(b_ty)) => {
2904                             structurally_same_type_impl(seen_types, cx, *a_ty, *b_ty, ckind)
2905                         }
2906                         (RawPtr(a_tymut), RawPtr(b_tymut)) => {
2907                             a_tymut.mutbl == b_tymut.mutbl
2908                                 && structurally_same_type_impl(
2909                                     seen_types, cx, a_tymut.ty, b_tymut.ty, ckind,
2910                                 )
2911                         }
2912                         (Ref(_a_region, a_ty, a_mut), Ref(_b_region, b_ty, b_mut)) => {
2913                             // For structural sameness, we don't need the region to be same.
2914                             a_mut == b_mut
2915                                 && structurally_same_type_impl(seen_types, cx, *a_ty, *b_ty, ckind)
2916                         }
2917                         (FnDef(..), FnDef(..)) => {
2918                             let a_poly_sig = a.fn_sig(tcx);
2919                             let b_poly_sig = b.fn_sig(tcx);
2920
2921                             // We don't compare regions, but leaving bound regions around ICEs, so
2922                             // we erase them.
2923                             let a_sig = tcx.erase_late_bound_regions(a_poly_sig);
2924                             let b_sig = tcx.erase_late_bound_regions(b_poly_sig);
2925
2926                             (a_sig.abi, a_sig.unsafety, a_sig.c_variadic)
2927                                 == (b_sig.abi, b_sig.unsafety, b_sig.c_variadic)
2928                                 && a_sig.inputs().iter().eq_by(b_sig.inputs().iter(), |a, b| {
2929                                     structurally_same_type_impl(seen_types, cx, *a, *b, ckind)
2930                                 })
2931                                 && structurally_same_type_impl(
2932                                     seen_types,
2933                                     cx,
2934                                     a_sig.output(),
2935                                     b_sig.output(),
2936                                     ckind,
2937                                 )
2938                         }
2939                         (Tuple(a_substs), Tuple(b_substs)) => {
2940                             a_substs.iter().eq_by(b_substs.iter(), |a_ty, b_ty| {
2941                                 structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2942                             })
2943                         }
2944                         // For these, it's not quite as easy to define structural-sameness quite so easily.
2945                         // For the purposes of this lint, take the conservative approach and mark them as
2946                         // not structurally same.
2947                         (Dynamic(..), Dynamic(..))
2948                         | (Error(..), Error(..))
2949                         | (Closure(..), Closure(..))
2950                         | (Generator(..), Generator(..))
2951                         | (GeneratorWitness(..), GeneratorWitness(..))
2952                         | (Projection(..), Projection(..))
2953                         | (Opaque(..), Opaque(..)) => false,
2954
2955                         // These definitely should have been caught above.
2956                         (Bool, Bool) | (Char, Char) | (Never, Never) | (Str, Str) => unreachable!(),
2957
2958                         // An Adt and a primitive or pointer type. This can be FFI-safe if non-null
2959                         // enum layout optimisation is being applied.
2960                         (Adt(..), other_kind) | (other_kind, Adt(..))
2961                             if is_primitive_or_pointer(other_kind) =>
2962                         {
2963                             let (primitive, adt) =
2964                                 if is_primitive_or_pointer(a.kind()) { (a, b) } else { (b, a) };
2965                             if let Some(ty) = crate::types::repr_nullable_ptr(cx, adt, ckind) {
2966                                 ty == primitive
2967                             } else {
2968                                 compare_layouts(a, b).unwrap_or(false)
2969                             }
2970                         }
2971                         // Otherwise, just compare the layouts. This may fail to lint for some
2972                         // incompatible types, but at the very least, will stop reads into
2973                         // uninitialised memory.
2974                         _ => compare_layouts(a, b).unwrap_or(false),
2975                     }
2976                 })
2977             }
2978         }
2979         let mut seen_types = FxHashSet::default();
2980         structurally_same_type_impl(&mut seen_types, cx, a, b, ckind)
2981     }
2982 }
2983
2984 impl_lint_pass!(ClashingExternDeclarations => [CLASHING_EXTERN_DECLARATIONS]);
2985
2986 impl<'tcx> LateLintPass<'tcx> for ClashingExternDeclarations {
2987     fn check_foreign_item(&mut self, cx: &LateContext<'tcx>, this_fi: &hir::ForeignItem<'_>) {
2988         trace!("ClashingExternDeclarations: check_foreign_item: {:?}", this_fi);
2989         if let ForeignItemKind::Fn(..) = this_fi.kind {
2990             let tcx = cx.tcx;
2991             if let Some(existing_hid) = self.insert(tcx, this_fi) {
2992                 let existing_decl_ty = tcx.type_of(tcx.hir().local_def_id(existing_hid));
2993                 let this_decl_ty = tcx.type_of(this_fi.owner_id);
2994                 debug!(
2995                     "ClashingExternDeclarations: Comparing existing {:?}: {:?} to this {:?}: {:?}",
2996                     existing_hid, existing_decl_ty, this_fi.owner_id, this_decl_ty
2997                 );
2998                 // Check that the declarations match.
2999                 if !Self::structurally_same_type(
3000                     cx,
3001                     existing_decl_ty,
3002                     this_decl_ty,
3003                     CItemKind::Declaration,
3004                 ) {
3005                     let orig_fi = tcx.hir().expect_foreign_item(existing_hid.expect_owner());
3006                     let orig = Self::name_of_extern_decl(tcx, orig_fi);
3007
3008                     // We want to ensure that we use spans for both decls that include where the
3009                     // name was defined, whether that was from the link_name attribute or not.
3010                     let get_relevant_span =
3011                         |fi: &hir::ForeignItem<'_>| match Self::name_of_extern_decl(tcx, fi) {
3012                             SymbolName::Normal(_) => fi.span,
3013                             SymbolName::Link(_, annot_span) => fi.span.to(annot_span),
3014                         };
3015                     // Finally, emit the diagnostic.
3016
3017                     let msg = if orig.get_name() == this_fi.ident.name {
3018                         fluent::lint_builtin_clashing_extern_same_name
3019                     } else {
3020                         fluent::lint_builtin_clashing_extern_diff_name
3021                     };
3022                     tcx.struct_span_lint_hir(
3023                         CLASHING_EXTERN_DECLARATIONS,
3024                         this_fi.hir_id(),
3025                         get_relevant_span(this_fi),
3026                         msg,
3027                         |lint| {
3028                             let mut expected_str = DiagnosticStyledString::new();
3029                             expected_str.push(existing_decl_ty.fn_sig(tcx).to_string(), false);
3030                             let mut found_str = DiagnosticStyledString::new();
3031                             found_str.push(this_decl_ty.fn_sig(tcx).to_string(), true);
3032
3033                             lint.set_arg("this_fi", this_fi.ident.name)
3034                                 .set_arg("orig", orig.get_name())
3035                                 .span_label(get_relevant_span(orig_fi), fluent::previous_decl_label)
3036                                 .span_label(get_relevant_span(this_fi), fluent::mismatch_label)
3037                                 // FIXME(davidtwco): translatable expected/found
3038                                 .note_expected_found(&"", expected_str, &"", found_str)
3039                         },
3040                     );
3041                 }
3042             }
3043         }
3044     }
3045 }
3046
3047 declare_lint! {
3048     /// The `deref_nullptr` lint detects when an null pointer is dereferenced,
3049     /// which causes [undefined behavior].
3050     ///
3051     /// ### Example
3052     ///
3053     /// ```rust,no_run
3054     /// # #![allow(unused)]
3055     /// use std::ptr;
3056     /// unsafe {
3057     ///     let x = &*ptr::null::<i32>();
3058     ///     let x = ptr::addr_of!(*ptr::null::<i32>());
3059     ///     let x = *(0 as *const i32);
3060     /// }
3061     /// ```
3062     ///
3063     /// {{produces}}
3064     ///
3065     /// ### Explanation
3066     ///
3067     /// Dereferencing a null pointer causes [undefined behavior] even as a place expression,
3068     /// like `&*(0 as *const i32)` or `addr_of!(*(0 as *const i32))`.
3069     ///
3070     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
3071     pub DEREF_NULLPTR,
3072     Warn,
3073     "detects when an null pointer is dereferenced"
3074 }
3075
3076 declare_lint_pass!(DerefNullPtr => [DEREF_NULLPTR]);
3077
3078 impl<'tcx> LateLintPass<'tcx> for DerefNullPtr {
3079     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
3080         /// test if expression is a null ptr
3081         fn is_null_ptr(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> bool {
3082             match &expr.kind {
3083                 rustc_hir::ExprKind::Cast(ref expr, ref ty) => {
3084                     if let rustc_hir::TyKind::Ptr(_) = ty.kind {
3085                         return is_zero(expr) || is_null_ptr(cx, expr);
3086                     }
3087                 }
3088                 // check for call to `core::ptr::null` or `core::ptr::null_mut`
3089                 rustc_hir::ExprKind::Call(ref path, _) => {
3090                     if let rustc_hir::ExprKind::Path(ref qpath) = path.kind {
3091                         if let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id() {
3092                             return matches!(
3093                                 cx.tcx.get_diagnostic_name(def_id),
3094                                 Some(sym::ptr_null | sym::ptr_null_mut)
3095                             );
3096                         }
3097                     }
3098                 }
3099                 _ => {}
3100             }
3101             false
3102         }
3103
3104         /// test if expression is the literal `0`
3105         fn is_zero(expr: &hir::Expr<'_>) -> bool {
3106             match &expr.kind {
3107                 rustc_hir::ExprKind::Lit(ref lit) => {
3108                     if let LitKind::Int(a, _) = lit.node {
3109                         return a == 0;
3110                     }
3111                 }
3112                 _ => {}
3113             }
3114             false
3115         }
3116
3117         if let rustc_hir::ExprKind::Unary(rustc_hir::UnOp::Deref, expr_deref) = expr.kind {
3118             if is_null_ptr(cx, expr_deref) {
3119                 cx.struct_span_lint(
3120                     DEREF_NULLPTR,
3121                     expr.span,
3122                     fluent::lint_builtin_deref_nullptr,
3123                     |lint| lint.span_label(expr.span, fluent::label),
3124                 );
3125             }
3126         }
3127     }
3128 }
3129
3130 declare_lint! {
3131     /// The `named_asm_labels` lint detects the use of named labels in the
3132     /// inline `asm!` macro.
3133     ///
3134     /// ### Example
3135     ///
3136     /// ```rust,compile_fail
3137     /// # #![feature(asm_experimental_arch)]
3138     /// use std::arch::asm;
3139     ///
3140     /// fn main() {
3141     ///     unsafe {
3142     ///         asm!("foo: bar");
3143     ///     }
3144     /// }
3145     /// ```
3146     ///
3147     /// {{produces}}
3148     ///
3149     /// ### Explanation
3150     ///
3151     /// LLVM is allowed to duplicate inline assembly blocks for any
3152     /// reason, for example when it is in a function that gets inlined. Because
3153     /// of this, GNU assembler [local labels] *must* be used instead of labels
3154     /// with a name. Using named labels might cause assembler or linker errors.
3155     ///
3156     /// See the explanation in [Rust By Example] for more details.
3157     ///
3158     /// [local labels]: https://sourceware.org/binutils/docs/as/Symbol-Names.html#Local-Labels
3159     /// [Rust By Example]: https://doc.rust-lang.org/nightly/rust-by-example/unsafe/asm.html#labels
3160     pub NAMED_ASM_LABELS,
3161     Deny,
3162     "named labels in inline assembly",
3163 }
3164
3165 declare_lint_pass!(NamedAsmLabels => [NAMED_ASM_LABELS]);
3166
3167 impl<'tcx> LateLintPass<'tcx> for NamedAsmLabels {
3168     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
3169         if let hir::Expr {
3170             kind: hir::ExprKind::InlineAsm(hir::InlineAsm { template_strs, .. }),
3171             ..
3172         } = expr
3173         {
3174             for (template_sym, template_snippet, template_span) in template_strs.iter() {
3175                 let template_str = template_sym.as_str();
3176                 let find_label_span = |needle: &str| -> Option<Span> {
3177                     if let Some(template_snippet) = template_snippet {
3178                         let snippet = template_snippet.as_str();
3179                         if let Some(pos) = snippet.find(needle) {
3180                             let end = pos
3181                                 + snippet[pos..]
3182                                     .find(|c| c == ':')
3183                                     .unwrap_or(snippet[pos..].len() - 1);
3184                             let inner = InnerSpan::new(pos, end);
3185                             return Some(template_span.from_inner(inner));
3186                         }
3187                     }
3188
3189                     None
3190                 };
3191
3192                 let mut found_labels = Vec::new();
3193
3194                 // A semicolon might not actually be specified as a separator for all targets, but it seems like LLVM accepts it always
3195                 let statements = template_str.split(|c| matches!(c, '\n' | ';'));
3196                 for statement in statements {
3197                     // If there's a comment, trim it from the statement
3198                     let statement = statement.find("//").map_or(statement, |idx| &statement[..idx]);
3199                     let mut start_idx = 0;
3200                     for (idx, _) in statement.match_indices(':') {
3201                         let possible_label = statement[start_idx..idx].trim();
3202                         let mut chars = possible_label.chars();
3203                         let Some(c) = chars.next() else {
3204                             // Empty string means a leading ':' in this section, which is not a label
3205                             break
3206                         };
3207                         // A label starts with an alphabetic character or . or _ and continues with alphanumeric characters, _, or $
3208                         if (c.is_alphabetic() || matches!(c, '.' | '_'))
3209                             && chars.all(|c| c.is_alphanumeric() || matches!(c, '_' | '$'))
3210                         {
3211                             found_labels.push(possible_label);
3212                         } else {
3213                             // If we encounter a non-label, there cannot be any further labels, so stop checking
3214                             break;
3215                         }
3216
3217                         start_idx = idx + 1;
3218                     }
3219                 }
3220
3221                 debug!("NamedAsmLabels::check_expr(): found_labels: {:#?}", &found_labels);
3222
3223                 if found_labels.len() > 0 {
3224                     let spans = found_labels
3225                         .into_iter()
3226                         .filter_map(|label| find_label_span(label))
3227                         .collect::<Vec<Span>>();
3228                     // If there were labels but we couldn't find a span, combine the warnings and use the template span
3229                     let target_spans: MultiSpan =
3230                         if spans.len() > 0 { spans.into() } else { (*template_span).into() };
3231
3232                     cx.lookup_with_diagnostics(
3233                             NAMED_ASM_LABELS,
3234                             Some(target_spans),
3235                             fluent::lint_builtin_asm_labels,
3236                             |lint| lint,
3237                             BuiltinLintDiagnostics::NamedAsmLabel(
3238                                 "only local labels of the form `<number>:` should be used in inline asm"
3239                                     .to_string(),
3240                             ),
3241                         );
3242                 }
3243             }
3244         }
3245     }
3246 }
3247
3248 declare_lint! {
3249     /// The `special_module_name` lint detects module
3250     /// declarations for files that have a special meaning.
3251     ///
3252     /// ### Example
3253     ///
3254     /// ```rust,compile_fail
3255     /// mod lib;
3256     ///
3257     /// fn main() {
3258     ///     lib::run();
3259     /// }
3260     /// ```
3261     ///
3262     /// {{produces}}
3263     ///
3264     /// ### Explanation
3265     ///
3266     /// Cargo recognizes `lib.rs` and `main.rs` as the root of a
3267     /// library or binary crate, so declaring them as modules
3268     /// will lead to miscompilation of the crate unless configured
3269     /// explicitly.
3270     ///
3271     /// To access a library from a binary target within the same crate,
3272     /// use `your_crate_name::` as the path instead of `lib::`:
3273     ///
3274     /// ```rust,compile_fail
3275     /// // bar/src/lib.rs
3276     /// fn run() {
3277     ///     // ...
3278     /// }
3279     ///
3280     /// // bar/src/main.rs
3281     /// fn main() {
3282     ///     bar::run();
3283     /// }
3284     /// ```
3285     ///
3286     /// Binary targets cannot be used as libraries and so declaring
3287     /// one as a module is not allowed.
3288     pub SPECIAL_MODULE_NAME,
3289     Warn,
3290     "module declarations for files with a special meaning",
3291 }
3292
3293 declare_lint_pass!(SpecialModuleName => [SPECIAL_MODULE_NAME]);
3294
3295 impl EarlyLintPass for SpecialModuleName {
3296     fn check_crate(&mut self, cx: &EarlyContext<'_>, krate: &ast::Crate) {
3297         for item in &krate.items {
3298             if let ast::ItemKind::Mod(
3299                 _,
3300                 ast::ModKind::Unloaded | ast::ModKind::Loaded(_, ast::Inline::No, _),
3301             ) = item.kind
3302             {
3303                 if item.attrs.iter().any(|a| a.has_name(sym::path)) {
3304                     continue;
3305                 }
3306
3307                 match item.ident.name.as_str() {
3308                     "lib" => cx.struct_span_lint(SPECIAL_MODULE_NAME, item.span, "found module declaration for lib.rs", |lint| {
3309                         lint
3310                             .note("lib.rs is the root of this crate's library target")
3311                             .help("to refer to it from other targets, use the library's name as the path")
3312                     }),
3313                     "main" => cx.struct_span_lint(SPECIAL_MODULE_NAME, item.span, "found module declaration for main.rs", |lint| {
3314                         lint
3315                             .note("a binary crate cannot be used as library")
3316                     }),
3317                     _ => continue
3318                 }
3319             }
3320         }
3321     }
3322 }
3323
3324 pub use rustc_session::lint::builtin::UNEXPECTED_CFGS;
3325
3326 declare_lint_pass!(UnexpectedCfgs => [UNEXPECTED_CFGS]);
3327
3328 impl EarlyLintPass for UnexpectedCfgs {
3329     fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
3330         let cfg = &cx.sess().parse_sess.config;
3331         let check_cfg = &cx.sess().parse_sess.check_config;
3332         for &(name, value) in cfg {
3333             if let Some(names_valid) = &check_cfg.names_valid {
3334                 if !names_valid.contains(&name) {
3335                     cx.lookup(
3336                         UNEXPECTED_CFGS,
3337                         None::<MultiSpan>,
3338                         fluent::lint_builtin_unexpected_cli_config_name,
3339                         |diag| diag.help(fluent::help).set_arg("name", name),
3340                     );
3341                 }
3342             }
3343             if let Some(value) = value {
3344                 if let Some(values) = &check_cfg.values_valid.get(&name) {
3345                     if !values.contains(&value) {
3346                         cx.lookup(
3347                             UNEXPECTED_CFGS,
3348                             None::<MultiSpan>,
3349                             fluent::lint_builtin_unexpected_cli_config_value,
3350                             |diag| {
3351                                 diag.help(fluent::help)
3352                                     .set_arg("name", name)
3353                                     .set_arg("value", value)
3354                             },
3355                         );
3356                     }
3357                 }
3358             }
3359         }
3360     }
3361 }