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     types::{transparent_newtype_field, CItemKind},
  25     EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext,
  26 };
  27 use rustc_ast::attr;
  28 use rustc_ast::tokenstream::{TokenStream, TokenTree};
  29 use rustc_ast::visit::{FnCtxt, FnKind};
  30 use rustc_ast::{self as ast, *};
  31 use rustc_ast_pretty::pprust::{self, expr_to_string};
  32 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
  33 use rustc_data_structures::stack::ensure_sufficient_stack;
  34 use rustc_errors::{Applicability, DiagnosticBuilder, DiagnosticStyledString};
  35 use rustc_feature::{deprecated_attributes, AttributeGate, BuiltinAttribute, GateIssue, Stability};
  36 use rustc_hir as hir;
  37 use rustc_hir::def::{DefKind, Res};
  38 use rustc_hir::def_id::{DefId, LocalDefId, LocalDefIdSet, CRATE_DEF_ID};
  39 use rustc_hir::{ForeignItemKind, GenericParamKind, PatKind};
  40 use rustc_hir::{HirId, Node};
  41 use rustc_index::vec::Idx;
  42 use rustc_middle::lint::LintDiagnosticBuilder;
  43 use rustc_middle::ty::layout::{LayoutError, LayoutOf};
  44 use rustc_middle::ty::print::with_no_trimmed_paths;
  45 use rustc_middle::ty::subst::{GenericArgKind, Subst};
  46 use rustc_middle::ty::Instance;
  47 use rustc_middle::ty::{self, Ty, TyCtxt};
  48 use rustc_session::lint::{BuiltinLintDiagnostics, FutureIncompatibilityReason};
  49 use rustc_span::edition::Edition;
  50 use rustc_span::source_map::Spanned;
  51 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  52 use rustc_span::{BytePos, InnerSpan, MultiSpan, Span};
  53 use rustc_target::abi::VariantIdx;
  54 use rustc_trait_selection::traits::misc::can_type_implement_copy;
  55
  56 use crate::nonstandard_style::{method_context, MethodLateContext};
  57
  58 use std::fmt::Write;
  59 use tracing::{debug, trace};
  60
  61 // hardwired lints from librustc_middle
  62 pub use rustc_session::lint::builtin::*;
  63
  64 declare_lint! {
  65     /// The `while_true` lint detects `while true { }`.
  66     ///
  67     /// ### Example
  68     ///
  69     /// ```rust,no_run
  70     /// while true {
  71     ///
  72     /// }
  73     /// ```
  74     ///
  75     /// {{produces}}
  76     ///
  77     /// ### Explanation
  78     ///
  79     /// `while true` should be replaced with `loop`. A `loop` expression is
  80     /// the preferred way to write an infinite loop because it more directly
  81     /// expresses the intent of the loop.
  82     WHILE_TRUE,
  83     Warn,
  84     "suggest using `loop { }` instead of `while true { }`"
  85 }
  86
  87 declare_lint_pass!(WhileTrue => [WHILE_TRUE]);
  88
  89 /// Traverse through any amount of parenthesis and return the first non-parens expression.
  90 fn pierce_parens(mut expr: &ast::Expr) -> &ast::Expr {
  91     while let ast::ExprKind::Paren(sub) = &expr.kind {
  92         expr = sub;
  93     }
  94     expr
  95 }
  96
  97 impl EarlyLintPass for WhileTrue {
  98     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
  99         if let ast::ExprKind::While(cond, _, label) = &e.kind {
 100             if let ast::ExprKind::Lit(ref lit) = pierce_parens(cond).kind {
 101                 if let ast::LitKind::Bool(true) = lit.kind {
 102                     if !lit.span.from_expansion() {
 103                         let msg = "denote infinite loops with `loop { ... }`";
 104                         let condition_span = e.span.with_hi(cond.span.hi());
 105                         cx.struct_span_lint(WHILE_TRUE, condition_span, |lint| {
 106                             lint.build(msg)
 107                                 .span_suggestion_short(
 108                                     condition_span,
 109                                     "use `loop`",
 110                                     format!(
 111                                         "{}loop",
 112                                         label.map_or_else(String::new, |label| format!(
 113                                             "{}: ",
 114                                             label.ident,
 115                                         ))
 116                                     ),
 117                                     Applicability::MachineApplicable,
 118                                 )
 119                                 .emit();
 120                         })
 121                     }
 122                 }
 123             }
 124         }
 125     }
 126 }
 127
 128 declare_lint! {
 129     /// The `box_pointers` lints use of the Box type.
 130     ///
 131     /// ### Example
 132     ///
 133     /// ```rust,compile_fail
 134     /// #![deny(box_pointers)]
 135     /// struct Foo {
 136     ///     x: Box<isize>,
 137     /// }
 138     /// ```
 139     ///
 140     /// {{produces}}
 141     ///
 142     /// ### Explanation
 143     ///
 144     /// This lint is mostly historical, and not particularly useful. `Box<T>`
 145     /// used to be built into the language, and the only way to do heap
 146     /// allocation. Today's Rust can call into other allocators, etc.
 147     BOX_POINTERS,
 148     Allow,
 149     "use of owned (Box type) heap memory"
 150 }
 151
 152 declare_lint_pass!(BoxPointers => [BOX_POINTERS]);
 153
 154 impl BoxPointers {
 155     fn check_heap_type(&self, cx: &LateContext<'_>, span: Span, ty: Ty<'_>) {
 156         for leaf in ty.walk() {
 157             if let GenericArgKind::Type(leaf_ty) = leaf.unpack() {
 158                 if leaf_ty.is_box() {
 159                     cx.struct_span_lint(BOX_POINTERS, span, |lint| {
 160                         lint.build(&format!("type uses owned (Box type) pointers: {}", ty)).emit()
 161                     });
 162                 }
 163             }
 164         }
 165     }
 166 }
 167
 168 impl<'tcx> LateLintPass<'tcx> for BoxPointers {
 169     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 170         match it.kind {
 171             hir::ItemKind::Fn(..)
 172             | hir::ItemKind::TyAlias(..)
 173             | hir::ItemKind::Enum(..)
 174             | hir::ItemKind::Struct(..)
 175             | hir::ItemKind::Union(..) => {
 176                 self.check_heap_type(cx, it.span, cx.tcx.type_of(it.def_id))
 177             }
 178             _ => (),
 179         }
 180
 181         // If it's a struct, we also have to check the fields' types
 182         match it.kind {
 183             hir::ItemKind::Struct(ref struct_def, _) | hir::ItemKind::Union(ref struct_def, _) => {
 184                 for struct_field in struct_def.fields() {
 185                     let def_id = cx.tcx.hir().local_def_id(struct_field.hir_id);
 186                     self.check_heap_type(cx, struct_field.span, cx.tcx.type_of(def_id));
 187                 }
 188             }
 189             _ => (),
 190         }
 191     }
 192
 193     fn check_expr(&mut self, cx: &LateContext<'_>, e: &hir::Expr<'_>) {
 194         let ty = cx.typeck_results().node_type(e.hir_id);
 195         self.check_heap_type(cx, e.span, ty);
 196     }
 197 }
 198
 199 declare_lint! {
 200     /// The `non_shorthand_field_patterns` lint detects using `Struct { x: x }`
 201     /// instead of `Struct { x }` in a pattern.
 202     ///
 203     /// ### Example
 204     ///
 205     /// ```rust
 206     /// struct Point {
 207     ///     x: i32,
 208     ///     y: i32,
 209     /// }
 210     ///
 211     ///
 212     /// fn main() {
 213     ///     let p = Point {
 214     ///         x: 5,
 215     ///         y: 5,
 216     ///     };
 217     ///
 218     ///     match p {
 219     ///         Point { x: x, y: y } => (),
 220     ///     }
 221     /// }
 222     /// ```
 223     ///
 224     /// {{produces}}
 225     ///
 226     /// ### Explanation
 227     ///
 228     /// The preferred style is to avoid the repetition of specifying both the
 229     /// field name and the binding name if both identifiers are the same.
 230     NON_SHORTHAND_FIELD_PATTERNS,
 231     Warn,
 232     "using `Struct { x: x }` instead of `Struct { x }` in a pattern"
 233 }
 234
 235 declare_lint_pass!(NonShorthandFieldPatterns => [NON_SHORTHAND_FIELD_PATTERNS]);
 236
 237 impl<'tcx> LateLintPass<'tcx> for NonShorthandFieldPatterns {
 238     fn check_pat(&mut self, cx: &LateContext<'_>, pat: &hir::Pat<'_>) {
 239         if let PatKind::Struct(ref qpath, field_pats, _) = pat.kind {
 240             let variant = cx
 241                 .typeck_results()
 242                 .pat_ty(pat)
 243                 .ty_adt_def()
 244                 .expect("struct pattern type is not an ADT")
 245                 .variant_of_res(cx.qpath_res(qpath, pat.hir_id));
 246             for fieldpat in field_pats {
 247                 if fieldpat.is_shorthand {
 248                     continue;
 249                 }
 250                 if fieldpat.span.from_expansion() {
 251                     // Don't lint if this is a macro expansion: macro authors
 252                     // shouldn't have to worry about this kind of style issue
 253                     // (Issue #49588)
 254                     continue;
 255                 }
 256                 if let PatKind::Binding(binding_annot, _, ident, None) = fieldpat.pat.kind {
 257                     if cx.tcx.find_field_index(ident, &variant)
 258                         == Some(cx.tcx.field_index(fieldpat.hir_id, cx.typeck_results()))
 259                     {
 260                         cx.struct_span_lint(NON_SHORTHAND_FIELD_PATTERNS, fieldpat.span, |lint| {
 261                             let mut err = lint
 262                                 .build(&format!("the `{}:` in this pattern is redundant", ident));
 263                             let binding = match binding_annot {
 264                                 hir::BindingAnnotation::Unannotated => None,
 265                                 hir::BindingAnnotation::Mutable => Some("mut"),
 266                                 hir::BindingAnnotation::Ref => Some("ref"),
 267                                 hir::BindingAnnotation::RefMut => Some("ref mut"),
 268                             };
 269                             let ident = if let Some(binding) = binding {
 270                                 format!("{} {}", binding, ident)
 271                             } else {
 272                                 ident.to_string()
 273                             };
 274                             err.span_suggestion(
 275                                 fieldpat.span,
 276                                 "use shorthand field pattern",
 277                                 ident,
 278                                 Applicability::MachineApplicable,
 279                             );
 280                             err.emit();
 281                         });
 282                     }
 283                 }
 284             }
 285         }
 286     }
 287 }
 288
 289 declare_lint! {
 290     /// The `unsafe_code` lint catches usage of `unsafe` code.
 291     ///
 292     /// ### Example
 293     ///
 294     /// ```rust,compile_fail
 295     /// #![deny(unsafe_code)]
 296     /// fn main() {
 297     ///     unsafe {
 298     ///
 299     ///     }
 300     /// }
 301     /// ```
 302     ///
 303     /// {{produces}}
 304     ///
 305     /// ### Explanation
 306     ///
 307     /// This lint is intended to restrict the usage of `unsafe`, which can be
 308     /// difficult to use correctly.
 309     UNSAFE_CODE,
 310     Allow,
 311     "usage of `unsafe` code"
 312 }
 313
 314 declare_lint_pass!(UnsafeCode => [UNSAFE_CODE]);
 315
 316 impl UnsafeCode {
 317     fn report_unsafe(
 318         &self,
 319         cx: &EarlyContext<'_>,
 320         span: Span,
 321         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'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, decorate);
 329     }
 330
 331     fn report_overriden_symbol_name(&self, cx: &EarlyContext<'_>, span: Span, msg: &str) {
 332         self.report_unsafe(cx, span, |lint| {
 333             lint.build(msg)
 334                 .note(
 335                     "the linker's behavior with multiple libraries exporting duplicate symbol \
 336                     names is undefined and Rust cannot provide guarantees when you manually \
 337                     override them",
 338                 )
 339                 .emit();
 340         })
 341     }
 342 }
 343
 344 impl EarlyLintPass for UnsafeCode {
 345     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 346         if attr.has_name(sym::allow_internal_unsafe) {
 347             self.report_unsafe(cx, attr.span, |lint| {
 348                 lint.build(
 349                     "`allow_internal_unsafe` allows defining \
 350                                                macros using unsafe without triggering \
 351                                                the `unsafe_code` lint at their call site",
 352                 )
 353                 .emit()
 354             });
 355         }
 356     }
 357
 358     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
 359         if let ast::ExprKind::Block(ref blk, _) = e.kind {
 360             // Don't warn about generated blocks; that'll just pollute the output.
 361             if blk.rules == ast::BlockCheckMode::Unsafe(ast::UserProvided) {
 362                 self.report_unsafe(cx, blk.span, |lint| {
 363                     lint.build("usage of an `unsafe` block").emit()
 364                 });
 365             }
 366         }
 367     }
 368
 369     fn check_item(&mut self, cx: &EarlyContext<'_>, it: &ast::Item) {
 370         match it.kind {
 371             ast::ItemKind::Trait(box ast::Trait { unsafety: ast::Unsafe::Yes(_), .. }) => self
 372                 .report_unsafe(cx, it.span, |lint| {
 373                     lint.build("declaration of an `unsafe` trait").emit()
 374                 }),
 375
 376             ast::ItemKind::Impl(box ast::Impl { unsafety: ast::Unsafe::Yes(_), .. }) => self
 377                 .report_unsafe(cx, it.span, |lint| {
 378                     lint.build("implementation of an `unsafe` trait").emit()
 379                 }),
 380
 381             ast::ItemKind::Fn(..) => {
 382                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
 383                     self.report_overriden_symbol_name(
 384                         cx,
 385                         attr.span,
 386                         "declaration of a `no_mangle` function",
 387                     );
 388                 }
 389                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::export_name) {
 390                     self.report_overriden_symbol_name(
 391                         cx,
 392                         attr.span,
 393                         "declaration of a function with `export_name`",
 394                     );
 395                 }
 396             }
 397
 398             ast::ItemKind::Static(..) => {
 399                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
 400                     self.report_overriden_symbol_name(
 401                         cx,
 402                         attr.span,
 403                         "declaration of a `no_mangle` static",
 404                     );
 405                 }
 406                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::export_name) {
 407                     self.report_overriden_symbol_name(
 408                         cx,
 409                         attr.span,
 410                         "declaration of a static with `export_name`",
 411                     );
 412                 }
 413             }
 414
 415             _ => {}
 416         }
 417     }
 418
 419     fn check_impl_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
 420         if let ast::AssocItemKind::Fn(..) = it.kind {
 421             if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
 422                 self.report_overriden_symbol_name(
 423                     cx,
 424                     attr.span,
 425                     "declaration of a `no_mangle` method",
 426                 );
 427             }
 428             if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::export_name) {
 429                 self.report_overriden_symbol_name(
 430                     cx,
 431                     attr.span,
 432                     "declaration of a method with `export_name`",
 433                 );
 434             }
 435         }
 436     }
 437
 438     fn check_fn(&mut self, cx: &EarlyContext<'_>, fk: FnKind<'_>, span: Span, _: ast::NodeId) {
 439         if let FnKind::Fn(
 440             ctxt,
 441             _,
 442             ast::FnSig { header: ast::FnHeader { unsafety: ast::Unsafe::Yes(_), .. }, .. },
 443             _,
 444             body,
 445         ) = fk
 446         {
 447             let msg = match ctxt {
 448                 FnCtxt::Foreign => return,
 449                 FnCtxt::Free => "declaration of an `unsafe` function",
 450                 FnCtxt::Assoc(_) if body.is_none() => "declaration of an `unsafe` method",
 451                 FnCtxt::Assoc(_) => "implementation of an `unsafe` method",
 452             };
 453             self.report_unsafe(cx, span, |lint| lint.build(msg).emit());
 454         }
 455     }
 456 }
 457
 458 declare_lint! {
 459     /// The `missing_docs` lint detects missing documentation for public items.
 460     ///
 461     /// ### Example
 462     ///
 463     /// ```rust,compile_fail
 464     /// #![deny(missing_docs)]
 465     /// pub fn foo() {}
 466     /// ```
 467     ///
 468     /// {{produces}}
 469     ///
 470     /// ### Explanation
 471     ///
 472     /// This lint is intended to ensure that a library is well-documented.
 473     /// Items without documentation can be difficult for users to understand
 474     /// how to use properly.
 475     ///
 476     /// This lint is "allow" by default because it can be noisy, and not all
 477     /// projects may want to enforce everything to be documented.
 478     pub MISSING_DOCS,
 479     Allow,
 480     "detects missing documentation for public members",
 481     report_in_external_macro
 482 }
 483
 484 pub struct MissingDoc {
 485     /// Stack of whether `#[doc(hidden)]` is set at each level which has lint attributes.
 486     doc_hidden_stack: Vec<bool>,
 487
 488     /// Private traits or trait items that leaked through. Don't check their methods.
 489     private_traits: FxHashSet<hir::HirId>,
 490 }
 491
 492 impl_lint_pass!(MissingDoc => [MISSING_DOCS]);
 493
 494 fn has_doc(attr: &ast::Attribute) -> bool {
 495     if attr.is_doc_comment() {
 496         return true;
 497     }
 498
 499     if !attr.has_name(sym::doc) {
 500         return false;
 501     }
 502
 503     if attr.value_str().is_some() {
 504         return true;
 505     }
 506
 507     if let Some(list) = attr.meta_item_list() {
 508         for meta in list {
 509             if meta.has_name(sym::hidden) {
 510                 return true;
 511             }
 512         }
 513     }
 514
 515     false
 516 }
 517
 518 impl MissingDoc {
 519     pub fn new() -> MissingDoc {
 520         MissingDoc { doc_hidden_stack: vec![false], private_traits: FxHashSet::default() }
 521     }
 522
 523     fn doc_hidden(&self) -> bool {
 524         *self.doc_hidden_stack.last().expect("empty doc_hidden_stack")
 525     }
 526
 527     fn check_missing_docs_attrs(
 528         &self,
 529         cx: &LateContext<'_>,
 530         def_id: LocalDefId,
 531         sp: Span,
 532         article: &'static str,
 533         desc: &'static str,
 534     ) {
 535         // If we're building a test harness, then warning about
 536         // documentation is probably not really relevant right now.
 537         if cx.sess().opts.test {
 538             return;
 539         }
 540
 541         // `#[doc(hidden)]` disables missing_docs check.
 542         if self.doc_hidden() {
 543             return;
 544         }
 545
 546         // Only check publicly-visible items, using the result from the privacy pass.
 547         // It's an option so the crate root can also use this function (it doesn't
 548         // have a `NodeId`).
 549         if def_id != CRATE_DEF_ID {
 550             if !cx.access_levels.is_exported(def_id) {
 551                 return;
 552             }
 553         }
 554
 555         let attrs = cx.tcx.get_attrs(def_id.to_def_id());
 556         let has_doc = attrs.iter().any(has_doc);
 557         if !has_doc {
 558             cx.struct_span_lint(
 559                 MISSING_DOCS,
 560                 cx.tcx.sess.source_map().guess_head_span(sp),
 561                 |lint| {
 562                     lint.build(&format!("missing documentation for {} {}", article, desc)).emit()
 563                 },
 564             );
 565         }
 566     }
 567 }
 568
 569 impl<'tcx> LateLintPass<'tcx> for MissingDoc {
 570     fn enter_lint_attrs(&mut self, _cx: &LateContext<'_>, attrs: &[ast::Attribute]) {
 571         let doc_hidden = self.doc_hidden()
 572             || attrs.iter().any(|attr| {
 573                 attr.has_name(sym::doc)
 574                     && match attr.meta_item_list() {
 575                         None => false,
 576                         Some(l) => attr::list_contains_name(&l, sym::hidden),
 577                     }
 578             });
 579         self.doc_hidden_stack.push(doc_hidden);
 580     }
 581
 582     fn exit_lint_attrs(&mut self, _: &LateContext<'_>, _attrs: &[ast::Attribute]) {
 583         self.doc_hidden_stack.pop().expect("empty doc_hidden_stack");
 584     }
 585
 586     fn check_crate(&mut self, cx: &LateContext<'_>) {
 587         self.check_missing_docs_attrs(
 588             cx,
 589             CRATE_DEF_ID,
 590             cx.tcx.def_span(CRATE_DEF_ID),
 591             "the",
 592             "crate",
 593         );
 594     }
 595
 596     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 597         match it.kind {
 598             hir::ItemKind::Trait(.., trait_item_refs) => {
 599                 // Issue #11592: traits are always considered exported, even when private.
 600                 if let hir::VisibilityKind::Inherited = it.vis.node {
 601                     self.private_traits.insert(it.hir_id());
 602                     for trait_item_ref in trait_item_refs {
 603                         self.private_traits.insert(trait_item_ref.id.hir_id());
 604                     }
 605                     return;
 606                 }
 607             }
 608             hir::ItemKind::Impl(hir::Impl { of_trait: Some(ref trait_ref), items, .. }) => {
 609                 // If the trait is private, add the impl items to `private_traits` so they don't get
 610                 // reported for missing docs.
 611                 let real_trait = trait_ref.path.res.def_id();
 612                 let Some(def_id) = real_trait.as_local() else { return };
 613                 let Some(Node::Item(item)) = cx.tcx.hir().find_by_def_id(def_id) else { return };
 614                 if let hir::VisibilityKind::Inherited = item.vis.node {
 615                     for impl_item_ref in items {
 616                         self.private_traits.insert(impl_item_ref.id.hir_id());
 617                     }
 618                 }
 619                 return;
 620             }
 621
 622             hir::ItemKind::TyAlias(..)
 623             | hir::ItemKind::Fn(..)
 624             | hir::ItemKind::Macro(..)
 625             | hir::ItemKind::Mod(..)
 626             | hir::ItemKind::Enum(..)
 627             | hir::ItemKind::Struct(..)
 628             | hir::ItemKind::Union(..)
 629             | hir::ItemKind::Const(..)
 630             | hir::ItemKind::Static(..) => {}
 631
 632             _ => return,
 633         };
 634
 635         let (article, desc) = cx.tcx.article_and_description(it.def_id.to_def_id());
 636
 637         self.check_missing_docs_attrs(cx, it.def_id, it.span, article, desc);
 638     }
 639
 640     fn check_trait_item(&mut self, cx: &LateContext<'_>, trait_item: &hir::TraitItem<'_>) {
 641         if self.private_traits.contains(&trait_item.hir_id()) {
 642             return;
 643         }
 644
 645         let (article, desc) = cx.tcx.article_and_description(trait_item.def_id.to_def_id());
 646
 647         self.check_missing_docs_attrs(cx, trait_item.def_id, trait_item.span, article, desc);
 648     }
 649
 650     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
 651         // If the method is an impl for a trait, don't doc.
 652         if method_context(cx, impl_item.hir_id()) == MethodLateContext::TraitImpl {
 653             return;
 654         }
 655
 656         // If the method is an impl for an item with docs_hidden, don't doc.
 657         if method_context(cx, impl_item.hir_id()) == MethodLateContext::PlainImpl {
 658             let parent = cx.tcx.hir().get_parent_item(impl_item.hir_id());
 659             let impl_ty = cx.tcx.type_of(parent);
 660             let outerdef = match impl_ty.kind() {
 661                 ty::Adt(def, _) => Some(def.did),
 662                 ty::Foreign(def_id) => Some(*def_id),
 663                 _ => None,
 664             };
 665             let is_hidden = match outerdef {
 666                 Some(id) => cx.tcx.is_doc_hidden(id),
 667                 None => false,
 668             };
 669             if is_hidden {
 670                 return;
 671             }
 672         }
 673
 674         let (article, desc) = cx.tcx.article_and_description(impl_item.def_id.to_def_id());
 675         self.check_missing_docs_attrs(cx, impl_item.def_id, impl_item.span, article, desc);
 676     }
 677
 678     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'_>) {
 679         let (article, desc) = cx.tcx.article_and_description(foreign_item.def_id.to_def_id());
 680         self.check_missing_docs_attrs(cx, foreign_item.def_id, foreign_item.span, article, desc);
 681     }
 682
 683     fn check_field_def(&mut self, cx: &LateContext<'_>, sf: &hir::FieldDef<'_>) {
 684         if !sf.is_positional() {
 685             let def_id = cx.tcx.hir().local_def_id(sf.hir_id);
 686             self.check_missing_docs_attrs(cx, def_id, sf.span, "a", "struct field")
 687         }
 688     }
 689
 690     fn check_variant(&mut self, cx: &LateContext<'_>, v: &hir::Variant<'_>) {
 691         self.check_missing_docs_attrs(cx, cx.tcx.hir().local_def_id(v.id), v.span, "a", "variant");
 692     }
 693 }
 694
 695 declare_lint! {
 696     /// The `missing_copy_implementations` lint detects potentially-forgotten
 697     /// implementations of [`Copy`].
 698     ///
 699     /// [`Copy`]: https://doc.rust-lang.org/std/marker/trait.Copy.html
 700     ///
 701     /// ### Example
 702     ///
 703     /// ```rust,compile_fail
 704     /// #![deny(missing_copy_implementations)]
 705     /// pub struct Foo {
 706     ///     pub field: i32
 707     /// }
 708     /// # fn main() {}
 709     /// ```
 710     ///
 711     /// {{produces}}
 712     ///
 713     /// ### Explanation
 714     ///
 715     /// Historically (before 1.0), types were automatically marked as `Copy`
 716     /// if possible. This was changed so that it required an explicit opt-in
 717     /// by implementing the `Copy` trait. As part of this change, a lint was
 718     /// added to alert if a copyable type was not marked `Copy`.
 719     ///
 720     /// This lint is "allow" by default because this code isn't bad; it is
 721     /// common to write newtypes like this specifically so that a `Copy` type
 722     /// is no longer `Copy`. `Copy` types can result in unintended copies of
 723     /// large data which can impact performance.
 724     pub MISSING_COPY_IMPLEMENTATIONS,
 725     Allow,
 726     "detects potentially-forgotten implementations of `Copy`"
 727 }
 728
 729 declare_lint_pass!(MissingCopyImplementations => [MISSING_COPY_IMPLEMENTATIONS]);
 730
 731 impl<'tcx> LateLintPass<'tcx> for MissingCopyImplementations {
 732     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 733         if !cx.access_levels.is_reachable(item.def_id) {
 734             return;
 735         }
 736         let (def, ty) = match item.kind {
 737             hir::ItemKind::Struct(_, ref ast_generics) => {
 738                 if !ast_generics.params.is_empty() {
 739                     return;
 740                 }
 741                 let def = cx.tcx.adt_def(item.def_id);
 742                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 743             }
 744             hir::ItemKind::Union(_, ref ast_generics) => {
 745                 if !ast_generics.params.is_empty() {
 746                     return;
 747                 }
 748                 let def = cx.tcx.adt_def(item.def_id);
 749                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 750             }
 751             hir::ItemKind::Enum(_, ref ast_generics) => {
 752                 if !ast_generics.params.is_empty() {
 753                     return;
 754                 }
 755                 let def = cx.tcx.adt_def(item.def_id);
 756                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 757             }
 758             _ => return,
 759         };
 760         if def.has_dtor(cx.tcx) {
 761             return;
 762         }
 763         let param_env = ty::ParamEnv::empty();
 764         if ty.is_copy_modulo_regions(cx.tcx.at(item.span), param_env) {
 765             return;
 766         }
 767         if can_type_implement_copy(cx.tcx, param_env, ty).is_ok() {
 768             cx.struct_span_lint(MISSING_COPY_IMPLEMENTATIONS, item.span, |lint| {
 769                 lint.build(
 770                     "type could implement `Copy`; consider adding `impl \
 771                           Copy`",
 772                 )
 773                 .emit()
 774             })
 775         }
 776     }
 777 }
 778
 779 declare_lint! {
 780     /// The `missing_debug_implementations` lint detects missing
 781     /// implementations of [`fmt::Debug`].
 782     ///
 783     /// [`fmt::Debug`]: https://doc.rust-lang.org/std/fmt/trait.Debug.html
 784     ///
 785     /// ### Example
 786     ///
 787     /// ```rust,compile_fail
 788     /// #![deny(missing_debug_implementations)]
 789     /// pub struct Foo;
 790     /// # fn main() {}
 791     /// ```
 792     ///
 793     /// {{produces}}
 794     ///
 795     /// ### Explanation
 796     ///
 797     /// Having a `Debug` implementation on all types can assist with
 798     /// debugging, as it provides a convenient way to format and display a
 799     /// value. Using the `#[derive(Debug)]` attribute will automatically
 800     /// generate a typical implementation, or a custom implementation can be
 801     /// added by manually implementing the `Debug` trait.
 802     ///
 803     /// This lint is "allow" by default because adding `Debug` to all types can
 804     /// have a negative impact on compile time and code size. It also requires
 805     /// boilerplate to be added to every type, which can be an impediment.
 806     MISSING_DEBUG_IMPLEMENTATIONS,
 807     Allow,
 808     "detects missing implementations of Debug"
 809 }
 810
 811 #[derive(Default)]
 812 pub struct MissingDebugImplementations {
 813     impling_types: Option<LocalDefIdSet>,
 814 }
 815
 816 impl_lint_pass!(MissingDebugImplementations => [MISSING_DEBUG_IMPLEMENTATIONS]);
 817
 818 impl<'tcx> LateLintPass<'tcx> for MissingDebugImplementations {
 819     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 820         if !cx.access_levels.is_reachable(item.def_id) {
 821             return;
 822         }
 823
 824         match item.kind {
 825             hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) | hir::ItemKind::Enum(..) => {}
 826             _ => return,
 827         }
 828
 829         let Some(debug) = cx.tcx.get_diagnostic_item(sym::Debug) else {
 830             return
 831         };
 832
 833         if self.impling_types.is_none() {
 834             let mut impls = LocalDefIdSet::default();
 835             cx.tcx.for_each_impl(debug, |d| {
 836                 if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() {
 837                     if let Some(def_id) = ty_def.did.as_local() {
 838                         impls.insert(def_id);
 839                     }
 840                 }
 841             });
 842
 843             self.impling_types = Some(impls);
 844             debug!("{:?}", self.impling_types);
 845         }
 846
 847         if !self.impling_types.as_ref().unwrap().contains(&item.def_id) {
 848             cx.struct_span_lint(MISSING_DEBUG_IMPLEMENTATIONS, item.span, |lint| {
 849                 lint.build(&format!(
 850                     "type does not implement `{}`; consider adding `#[derive(Debug)]` \
 851                      or a manual implementation",
 852                     cx.tcx.def_path_str(debug)
 853                 ))
 854                 .emit()
 855             });
 856         }
 857     }
 858 }
 859
 860 declare_lint! {
 861     /// The `anonymous_parameters` lint detects anonymous parameters in trait
 862     /// definitions.
 863     ///
 864     /// ### Example
 865     ///
 866     /// ```rust,edition2015,compile_fail
 867     /// #![deny(anonymous_parameters)]
 868     /// // edition 2015
 869     /// pub trait Foo {
 870     ///     fn foo(usize);
 871     /// }
 872     /// fn main() {}
 873     /// ```
 874     ///
 875     /// {{produces}}
 876     ///
 877     /// ### Explanation
 878     ///
 879     /// This syntax is mostly a historical accident, and can be worked around
 880     /// quite easily by adding an `_` pattern or a descriptive identifier:
 881     ///
 882     /// ```rust
 883     /// trait Foo {
 884     ///     fn foo(_: usize);
 885     /// }
 886     /// ```
 887     ///
 888     /// This syntax is now a hard error in the 2018 edition. In the 2015
 889     /// edition, this lint is "warn" by default. This lint
 890     /// enables the [`cargo fix`] tool with the `--edition` flag to
 891     /// automatically transition old code from the 2015 edition to 2018. The
 892     /// tool will run this lint and automatically apply the
 893     /// suggested fix from the compiler (which is to add `_` to each
 894     /// parameter). This provides a completely automated way to update old
 895     /// code for a new edition. See [issue #41686] for more details.
 896     ///
 897     /// [issue #41686]: https://github.com/rust-lang/rust/issues/41686
 898     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
 899     pub ANONYMOUS_PARAMETERS,
 900     Warn,
 901     "detects anonymous parameters",
 902     @future_incompatible = FutureIncompatibleInfo {
 903         reference: "issue #41686 <https://github.com/rust-lang/rust/issues/41686>",
 904         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
 905     };
 906 }
 907
 908 declare_lint_pass!(
 909     /// Checks for use of anonymous parameters (RFC 1685).
 910     AnonymousParameters => [ANONYMOUS_PARAMETERS]
 911 );
 912
 913 impl EarlyLintPass for AnonymousParameters {
 914     fn check_trait_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
 915         if cx.sess().edition() != Edition::Edition2015 {
 916             // This is a hard error in future editions; avoid linting and erroring
 917             return;
 918         }
 919         if let ast::AssocItemKind::Fn(box Fn { ref sig, .. }) = it.kind {
 920             for arg in sig.decl.inputs.iter() {
 921                 if let ast::PatKind::Ident(_, ident, None) = arg.pat.kind {
 922                     if ident.name == kw::Empty {
 923                         cx.struct_span_lint(ANONYMOUS_PARAMETERS, arg.pat.span, |lint| {
 924                             let ty_snip = cx.sess().source_map().span_to_snippet(arg.ty.span);
 925
 926                             let (ty_snip, appl) = if let Ok(ref snip) = ty_snip {
 927                                 (snip.as_str(), Applicability::MachineApplicable)
 928                             } else {
 929                                 ("<type>", Applicability::HasPlaceholders)
 930                             };
 931
 932                             lint.build(
 933                                 "anonymous parameters are deprecated and will be \
 934                                      removed in the next edition",
 935                             )
 936                             .span_suggestion(
 937                                 arg.pat.span,
 938                                 "try naming the parameter or explicitly \
 939                                             ignoring it",
 940                                 format!("_: {}", ty_snip),
 941                                 appl,
 942                             )
 943                             .emit();
 944                         })
 945                     }
 946                 }
 947             }
 948         }
 949     }
 950 }
 951
 952 /// Check for use of attributes which have been deprecated.
 953 #[derive(Clone)]
 954 pub struct DeprecatedAttr {
 955     // This is not free to compute, so we want to keep it around, rather than
 956     // compute it for every attribute.
 957     depr_attrs: Vec<&'static BuiltinAttribute>,
 958 }
 959
 960 impl_lint_pass!(DeprecatedAttr => []);
 961
 962 impl DeprecatedAttr {
 963     pub fn new() -> DeprecatedAttr {
 964         DeprecatedAttr { depr_attrs: deprecated_attributes() }
 965     }
 966 }
 967
 968 fn lint_deprecated_attr(
 969     cx: &EarlyContext<'_>,
 970     attr: &ast::Attribute,
 971     msg: &str,
 972     suggestion: Option<&str>,
 973 ) {
 974     cx.struct_span_lint(DEPRECATED, attr.span, |lint| {
 975         lint.build(msg)
 976             .span_suggestion_short(
 977                 attr.span,
 978                 suggestion.unwrap_or("remove this attribute"),
 979                 String::new(),
 980                 Applicability::MachineApplicable,
 981             )
 982             .emit();
 983     })
 984 }
 985
 986 impl EarlyLintPass for DeprecatedAttr {
 987     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 988         for BuiltinAttribute { name, gate, .. } in &self.depr_attrs {
 989             if attr.ident().map(|ident| ident.name) == Some(*name) {
 990                 if let &AttributeGate::Gated(
 991                     Stability::Deprecated(link, suggestion),
 992                     name,
 993                     reason,
 994                     _,
 995                 ) = gate
 996                 {
 997                     let msg =
 998                         format!("use of deprecated attribute `{}`: {}. See {}", name, reason, link);
 999                     lint_deprecated_attr(cx, attr, &msg, suggestion);
1000                 }
1001                 return;
1002             }
1003         }
1004         if attr.has_name(sym::no_start) || attr.has_name(sym::crate_id) {
1005             let path_str = pprust::path_to_string(&attr.get_normal_item().path);
1006             let msg = format!("use of deprecated attribute `{}`: no longer used.", path_str);
1007             lint_deprecated_attr(cx, attr, &msg, None);
1008         }
1009     }
1010 }
1011
1012 fn warn_if_doc(cx: &EarlyContext<'_>, node_span: Span, node_kind: &str, attrs: &[ast::Attribute]) {
1013     use rustc_ast::token::CommentKind;
1014
1015     let mut attrs = attrs.iter().peekable();
1016
1017     // Accumulate a single span for sugared doc comments.
1018     let mut sugared_span: Option<Span> = None;
1019
1020     while let Some(attr) = attrs.next() {
1021         let is_doc_comment = attr.is_doc_comment();
1022         if is_doc_comment {
1023             sugared_span =
1024                 Some(sugared_span.map_or(attr.span, |span| span.with_hi(attr.span.hi())));
1025         }
1026
1027         if attrs.peek().map_or(false, |next_attr| next_attr.is_doc_comment()) {
1028             continue;
1029         }
1030
1031         let span = sugared_span.take().unwrap_or(attr.span);
1032
1033         if is_doc_comment || attr.has_name(sym::doc) {
1034             cx.struct_span_lint(UNUSED_DOC_COMMENTS, span, |lint| {
1035                 let mut err = lint.build("unused doc comment");
1036                 err.span_label(
1037                     node_span,
1038                     format!("rustdoc does not generate documentation for {}", node_kind),
1039                 );
1040                 match attr.kind {
1041                     AttrKind::DocComment(CommentKind::Line, _) | AttrKind::Normal(..) => {
1042                         err.help("use `//` for a plain comment");
1043                     }
1044                     AttrKind::DocComment(CommentKind::Block, _) => {
1045                         err.help("use `/* */` for a plain comment");
1046                     }
1047                 }
1048                 err.emit();
1049             });
1050         }
1051     }
1052 }
1053
1054 impl EarlyLintPass for UnusedDocComment {
1055     fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &ast::Stmt) {
1056         let kind = match stmt.kind {
1057             ast::StmtKind::Local(..) => "statements",
1058             // Disabled pending discussion in #78306
1059             ast::StmtKind::Item(..) => return,
1060             // expressions will be reported by `check_expr`.
1061             ast::StmtKind::Empty
1062             | ast::StmtKind::Semi(_)
1063             | ast::StmtKind::Expr(_)
1064             | ast::StmtKind::MacCall(_) => return,
1065         };
1066
1067         warn_if_doc(cx, stmt.span, kind, stmt.kind.attrs());
1068     }
1069
1070     fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) {
1071         let arm_span = arm.pat.span.with_hi(arm.body.span.hi());
1072         warn_if_doc(cx, arm_span, "match arms", &arm.attrs);
1073     }
1074
1075     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
1076         warn_if_doc(cx, expr.span, "expressions", &expr.attrs);
1077     }
1078
1079     fn check_generic_param(&mut self, cx: &EarlyContext<'_>, param: &ast::GenericParam) {
1080         warn_if_doc(cx, param.ident.span, "generic parameters", &param.attrs);
1081     }
1082 }
1083
1084 declare_lint! {
1085     /// The `no_mangle_const_items` lint detects any `const` items with the
1086     /// [`no_mangle` attribute].
1087     ///
1088     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1089     ///
1090     /// ### Example
1091     ///
1092     /// ```rust,compile_fail
1093     /// #[no_mangle]
1094     /// const FOO: i32 = 5;
1095     /// ```
1096     ///
1097     /// {{produces}}
1098     ///
1099     /// ### Explanation
1100     ///
1101     /// Constants do not have their symbols exported, and therefore, this
1102     /// probably means you meant to use a [`static`], not a [`const`].
1103     ///
1104     /// [`static`]: https://doc.rust-lang.org/reference/items/static-items.html
1105     /// [`const`]: https://doc.rust-lang.org/reference/items/constant-items.html
1106     NO_MANGLE_CONST_ITEMS,
1107     Deny,
1108     "const items will not have their symbols exported"
1109 }
1110
1111 declare_lint! {
1112     /// The `no_mangle_generic_items` lint detects generic items that must be
1113     /// mangled.
1114     ///
1115     /// ### Example
1116     ///
1117     /// ```rust
1118     /// #[no_mangle]
1119     /// fn foo<T>(t: T) {
1120     ///
1121     /// }
1122     /// ```
1123     ///
1124     /// {{produces}}
1125     ///
1126     /// ### Explanation
1127     ///
1128     /// A function with generics must have its symbol mangled to accommodate
1129     /// the generic parameter. The [`no_mangle` attribute] has no effect in
1130     /// this situation, and should be removed.
1131     ///
1132     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1133     NO_MANGLE_GENERIC_ITEMS,
1134     Warn,
1135     "generic items must be mangled"
1136 }
1137
1138 declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS, NO_MANGLE_GENERIC_ITEMS]);
1139
1140 impl<'tcx> LateLintPass<'tcx> for InvalidNoMangleItems {
1141     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1142         let attrs = cx.tcx.hir().attrs(it.hir_id());
1143         let check_no_mangle_on_generic_fn = |no_mangle_attr: &ast::Attribute,
1144                                              impl_generics: Option<&hir::Generics<'_>>,
1145                                              generics: &hir::Generics<'_>,
1146                                              span| {
1147             for param in
1148                 generics.params.iter().chain(impl_generics.map(|g| g.params).into_iter().flatten())
1149             {
1150                 match param.kind {
1151                     GenericParamKind::Lifetime { .. } => {}
1152                     GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1153                         cx.struct_span_lint(NO_MANGLE_GENERIC_ITEMS, span, |lint| {
1154                             lint.build("functions generic over types or consts must be mangled")
1155                                 .span_suggestion_short(
1156                                     no_mangle_attr.span,
1157                                     "remove this attribute",
1158                                     String::new(),
1159                                     // Use of `#[no_mangle]` suggests FFI intent; correct
1160                                     // fix may be to monomorphize source by hand
1161                                     Applicability::MaybeIncorrect,
1162                                 )
1163                                 .emit();
1164                         });
1165                         break;
1166                     }
1167                 }
1168             }
1169         };
1170         match it.kind {
1171             hir::ItemKind::Fn(.., ref generics, _) => {
1172                 if let Some(no_mangle_attr) = cx.sess().find_by_name(attrs, sym::no_mangle) {
1173                     check_no_mangle_on_generic_fn(no_mangle_attr, None, generics, it.span);
1174                 }
1175             }
1176             hir::ItemKind::Const(..) => {
1177                 if cx.sess().contains_name(attrs, sym::no_mangle) {
1178                     // Const items do not refer to a particular location in memory, and therefore
1179                     // don't have anything to attach a symbol to
1180                     cx.struct_span_lint(NO_MANGLE_CONST_ITEMS, it.span, |lint| {
1181                         let msg = "const items should never be `#[no_mangle]`";
1182                         let mut err = lint.build(msg);
1183
1184                         // account for "pub const" (#45562)
1185                         let start = cx
1186                             .tcx
1187                             .sess
1188                             .source_map()
1189                             .span_to_snippet(it.span)
1190                             .map(|snippet| snippet.find("const").unwrap_or(0))
1191                             .unwrap_or(0) as u32;
1192                         // `const` is 5 chars
1193                         let const_span = it.span.with_hi(BytePos(it.span.lo().0 + start + 5));
1194                         err.span_suggestion(
1195                             const_span,
1196                             "try a static value",
1197                             "pub static".to_owned(),
1198                             Applicability::MachineApplicable,
1199                         );
1200                         err.emit();
1201                     });
1202                 }
1203             }
1204             hir::ItemKind::Impl(hir::Impl { ref generics, items, .. }) => {
1205                 for it in items {
1206                     if let hir::AssocItemKind::Fn { .. } = it.kind {
1207                         if let Some(no_mangle_attr) = cx
1208                             .sess()
1209                             .find_by_name(cx.tcx.hir().attrs(it.id.hir_id()), sym::no_mangle)
1210                         {
1211                             check_no_mangle_on_generic_fn(
1212                                 no_mangle_attr,
1213                                 Some(generics),
1214                                 cx.tcx.hir().get_generics(it.id.def_id).unwrap(),
1215                                 it.span,
1216                             );
1217                         }
1218                     }
1219                 }
1220             }
1221             _ => {}
1222         }
1223     }
1224 }
1225
1226 declare_lint! {
1227     /// The `mutable_transmutes` lint catches transmuting from `&T` to `&mut
1228     /// T` because it is [undefined behavior].
1229     ///
1230     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1231     ///
1232     /// ### Example
1233     ///
1234     /// ```rust,compile_fail
1235     /// unsafe {
1236     ///     let y = std::mem::transmute::<&i32, &mut i32>(&5);
1237     /// }
1238     /// ```
1239     ///
1240     /// {{produces}}
1241     ///
1242     /// ### Explanation
1243     ///
1244     /// Certain assumptions are made about aliasing of data, and this transmute
1245     /// violates those assumptions. Consider using [`UnsafeCell`] instead.
1246     ///
1247     /// [`UnsafeCell`]: https://doc.rust-lang.org/std/cell/struct.UnsafeCell.html
1248     MUTABLE_TRANSMUTES,
1249     Deny,
1250     "transmuting &T to &mut T is undefined behavior, even if the reference is unused"
1251 }
1252
1253 declare_lint_pass!(MutableTransmutes => [MUTABLE_TRANSMUTES]);
1254
1255 impl<'tcx> LateLintPass<'tcx> for MutableTransmutes {
1256     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &hir::Expr<'_>) {
1257         use rustc_target::spec::abi::Abi::RustIntrinsic;
1258         if let Some((&ty::Ref(_, _, from_mt), &ty::Ref(_, _, to_mt))) =
1259             get_transmute_from_to(cx, expr).map(|(ty1, ty2)| (ty1.kind(), ty2.kind()))
1260         {
1261             if to_mt == hir::Mutability::Mut && from_mt == hir::Mutability::Not {
1262                 let msg = "transmuting &T to &mut T is undefined behavior, \
1263                     even if the reference is unused, consider instead using an UnsafeCell";
1264                 cx.struct_span_lint(MUTABLE_TRANSMUTES, expr.span, |lint| lint.build(msg).emit());
1265             }
1266         }
1267
1268         fn get_transmute_from_to<'tcx>(
1269             cx: &LateContext<'tcx>,
1270             expr: &hir::Expr<'_>,
1271         ) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
1272             let def = if let hir::ExprKind::Path(ref qpath) = expr.kind {
1273                 cx.qpath_res(qpath, expr.hir_id)
1274             } else {
1275                 return None;
1276             };
1277             if let Res::Def(DefKind::Fn, did) = def {
1278                 if !def_id_is_transmute(cx, did) {
1279                     return None;
1280                 }
1281                 let sig = cx.typeck_results().node_type(expr.hir_id).fn_sig(cx.tcx);
1282                 let from = sig.inputs().skip_binder()[0];
1283                 let to = sig.output().skip_binder();
1284                 return Some((from, to));
1285             }
1286             None
1287         }
1288
1289         fn def_id_is_transmute(cx: &LateContext<'_>, def_id: DefId) -> bool {
1290             cx.tcx.fn_sig(def_id).abi() == RustIntrinsic
1291                 && cx.tcx.item_name(def_id) == sym::transmute
1292         }
1293     }
1294 }
1295
1296 declare_lint! {
1297     /// The `unstable_features` is deprecated and should no longer be used.
1298     UNSTABLE_FEATURES,
1299     Allow,
1300     "enabling unstable features (deprecated. do not use)"
1301 }
1302
1303 declare_lint_pass!(
1304     /// Forbids using the `#[feature(...)]` attribute
1305     UnstableFeatures => [UNSTABLE_FEATURES]
1306 );
1307
1308 impl<'tcx> LateLintPass<'tcx> for UnstableFeatures {
1309     fn check_attribute(&mut self, cx: &LateContext<'_>, attr: &ast::Attribute) {
1310         if attr.has_name(sym::feature) {
1311             if let Some(items) = attr.meta_item_list() {
1312                 for item in items {
1313                     cx.struct_span_lint(UNSTABLE_FEATURES, item.span(), |lint| {
1314                         lint.build("unstable feature").emit()
1315                     });
1316                 }
1317             }
1318         }
1319     }
1320 }
1321
1322 declare_lint! {
1323     /// The `unreachable_pub` lint triggers for `pub` items not reachable from
1324     /// the crate root.
1325     ///
1326     /// ### Example
1327     ///
1328     /// ```rust,compile_fail
1329     /// #![deny(unreachable_pub)]
1330     /// mod foo {
1331     ///     pub mod bar {
1332     ///
1333     ///     }
1334     /// }
1335     /// ```
1336     ///
1337     /// {{produces}}
1338     ///
1339     /// ### Explanation
1340     ///
1341     /// A bare `pub` visibility may be misleading if the item is not actually
1342     /// publicly exported from the crate. The `pub(crate)` visibility is
1343     /// recommended to be used instead, which more clearly expresses the intent
1344     /// that the item is only visible within its own crate.
1345     ///
1346     /// This lint is "allow" by default because it will trigger for a large
1347     /// amount existing Rust code, and has some false-positives. Eventually it
1348     /// is desired for this to become warn-by-default.
1349     pub UNREACHABLE_PUB,
1350     Allow,
1351     "`pub` items not reachable from crate root"
1352 }
1353
1354 declare_lint_pass!(
1355     /// Lint for items marked `pub` that aren't reachable from other crates.
1356     UnreachablePub => [UNREACHABLE_PUB]
1357 );
1358
1359 impl UnreachablePub {
1360     fn perform_lint(
1361         &self,
1362         cx: &LateContext<'_>,
1363         what: &str,
1364         def_id: LocalDefId,
1365         vis: &hir::Visibility<'_>,
1366         span: Span,
1367         exportable: bool,
1368     ) {
1369         let mut applicability = Applicability::MachineApplicable;
1370         match vis.node {
1371             hir::VisibilityKind::Public if !cx.access_levels.is_reachable(def_id) => {
1372                 if span.from_expansion() {
1373                     applicability = Applicability::MaybeIncorrect;
1374                 }
1375                 let def_span = cx.tcx.sess.source_map().guess_head_span(span);
1376                 cx.struct_span_lint(UNREACHABLE_PUB, def_span, |lint| {
1377                     let mut err = lint.build(&format!("unreachable `pub` {}", what));
1378                     let replacement = if cx.tcx.features().crate_visibility_modifier {
1379                         "crate"
1380                     } else {
1381                         "pub(crate)"
1382                     }
1383                     .to_owned();
1384
1385                     err.span_suggestion(
1386                         vis.span,
1387                         "consider restricting its visibility",
1388                         replacement,
1389                         applicability,
1390                     );
1391                     if exportable {
1392                         err.help("or consider exporting it for use by other crates");
1393                     }
1394                     err.emit();
1395                 });
1396             }
1397             _ => {}
1398         }
1399     }
1400 }
1401
1402 impl<'tcx> LateLintPass<'tcx> for UnreachablePub {
1403     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1404         self.perform_lint(cx, "item", item.def_id, &item.vis, item.span, true);
1405     }
1406
1407     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'tcx>) {
1408         self.perform_lint(
1409             cx,
1410             "item",
1411             foreign_item.def_id,
1412             &foreign_item.vis,
1413             foreign_item.span,
1414             true,
1415         );
1416     }
1417
1418     fn check_field_def(&mut self, cx: &LateContext<'_>, field: &hir::FieldDef<'_>) {
1419         let def_id = cx.tcx.hir().local_def_id(field.hir_id);
1420         self.perform_lint(cx, "field", def_id, &field.vis, field.span, false);
1421     }
1422
1423     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
1424         self.perform_lint(cx, "item", impl_item.def_id, &impl_item.vis, impl_item.span, false);
1425     }
1426 }
1427
1428 declare_lint! {
1429     /// The `type_alias_bounds` lint detects bounds in type aliases.
1430     ///
1431     /// ### Example
1432     ///
1433     /// ```rust
1434     /// type SendVec<T: Send> = Vec<T>;
1435     /// ```
1436     ///
1437     /// {{produces}}
1438     ///
1439     /// ### Explanation
1440     ///
1441     /// The trait bounds in a type alias are currently ignored, and should not
1442     /// be included to avoid confusion. This was previously allowed
1443     /// unintentionally; this may become a hard error in the future.
1444     TYPE_ALIAS_BOUNDS,
1445     Warn,
1446     "bounds in type aliases are not enforced"
1447 }
1448
1449 declare_lint_pass!(
1450     /// Lint for trait and lifetime bounds in type aliases being mostly ignored.
1451     /// They are relevant when using associated types, but otherwise neither checked
1452     /// at definition site nor enforced at use site.
1453     TypeAliasBounds => [TYPE_ALIAS_BOUNDS]
1454 );
1455
1456 impl TypeAliasBounds {
1457     fn is_type_variable_assoc(qpath: &hir::QPath<'_>) -> bool {
1458         match *qpath {
1459             hir::QPath::TypeRelative(ref ty, _) => {
1460                 // If this is a type variable, we found a `T::Assoc`.
1461                 match ty.kind {
1462                     hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
1463                         matches!(path.res, Res::Def(DefKind::TyParam, _))
1464                     }
1465                     _ => false,
1466                 }
1467             }
1468             hir::QPath::Resolved(..) | hir::QPath::LangItem(..) => false,
1469         }
1470     }
1471
1472     fn suggest_changing_assoc_types(ty: &hir::Ty<'_>, err: &mut DiagnosticBuilder<'_>) {
1473         // Access to associates types should use `<T as Bound>::Assoc`, which does not need a
1474         // bound.  Let's see if this type does that.
1475
1476         // We use a HIR visitor to walk the type.
1477         use rustc_hir::intravisit::{self, Visitor};
1478         struct WalkAssocTypes<'a, 'db> {
1479             err: &'a mut DiagnosticBuilder<'db>,
1480         }
1481         impl<'a, 'db, 'v> Visitor<'v> for WalkAssocTypes<'a, 'db> {
1482             fn visit_qpath(&mut self, qpath: &'v hir::QPath<'v>, id: hir::HirId, span: Span) {
1483                 if TypeAliasBounds::is_type_variable_assoc(qpath) {
1484                     self.err.span_help(
1485                         span,
1486                         "use fully disambiguated paths (i.e., `<T as Trait>::Assoc`) to refer to \
1487                          associated types in type aliases",
1488                     );
1489                 }
1490                 intravisit::walk_qpath(self, qpath, id, span)
1491             }
1492         }
1493
1494         // Let's go for a walk!
1495         let mut visitor = WalkAssocTypes { err };
1496         visitor.visit_ty(ty);
1497     }
1498 }
1499
1500 impl<'tcx> LateLintPass<'tcx> for TypeAliasBounds {
1501     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1502         let hir::ItemKind::TyAlias(ty, type_alias_generics) = &item.kind else {
1503             return
1504         };
1505         if let hir::TyKind::OpaqueDef(..) = ty.kind {
1506             // Bounds are respected for `type X = impl Trait`
1507             return;
1508         }
1509         let mut suggested_changing_assoc_types = false;
1510         // There must not be a where clause
1511         if !type_alias_generics.where_clause.predicates.is_empty() {
1512             cx.lint(
1513                 TYPE_ALIAS_BOUNDS,
1514                 |lint| {
1515                     let mut err = lint.build("where clauses are not enforced in type aliases");
1516                     let spans: Vec<_> = type_alias_generics
1517                         .where_clause
1518                         .predicates
1519                         .iter()
1520                         .map(|pred| pred.span())
1521                         .collect();
1522                     err.set_span(spans);
1523                     err.span_suggestion(
1524                         type_alias_generics.where_clause.span_for_predicates_or_empty_place(),
1525                         "the clause will not be checked when the type alias is used, and should be removed",
1526                         String::new(),
1527                         Applicability::MachineApplicable,
1528                     );
1529                     if !suggested_changing_assoc_types {
1530                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1531                         suggested_changing_assoc_types = true;
1532                     }
1533                     err.emit();
1534                 },
1535             );
1536         }
1537         // The parameters must not have bounds
1538         for param in type_alias_generics.params.iter() {
1539             let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
1540             let suggestion = spans
1541                 .iter()
1542                 .map(|sp| {
1543                     let start = param.span.between(*sp); // Include the `:` in `T: Bound`.
1544                     (start.to(*sp), String::new())
1545                 })
1546                 .collect();
1547             if !spans.is_empty() {
1548                 cx.struct_span_lint(TYPE_ALIAS_BOUNDS, spans, |lint| {
1549                     let mut err =
1550                         lint.build("bounds on generic parameters are not enforced in type aliases");
1551                     let msg = "the bound will not be checked when the type alias is used, \
1552                                    and should be removed";
1553                     err.multipart_suggestion(&msg, suggestion, Applicability::MachineApplicable);
1554                     if !suggested_changing_assoc_types {
1555                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1556                         suggested_changing_assoc_types = true;
1557                     }
1558                     err.emit();
1559                 });
1560             }
1561         }
1562     }
1563 }
1564
1565 declare_lint_pass!(
1566     /// Lint constants that are erroneous.
1567     /// Without this lint, we might not get any diagnostic if the constant is
1568     /// unused within this crate, even though downstream crates can't use it
1569     /// without producing an error.
1570     UnusedBrokenConst => []
1571 );
1572
1573 impl<'tcx> LateLintPass<'tcx> for UnusedBrokenConst {
1574     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1575         match it.kind {
1576             hir::ItemKind::Const(_, body_id) => {
1577                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1578                 // trigger the query once for all constants since that will already report the errors
1579                 // FIXME: Use ensure here
1580                 let _ = cx.tcx.const_eval_poly(def_id);
1581             }
1582             hir::ItemKind::Static(_, _, body_id) => {
1583                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1584                 // FIXME: Use ensure here
1585                 let _ = cx.tcx.eval_static_initializer(def_id);
1586             }
1587             _ => {}
1588         }
1589     }
1590 }
1591
1592 declare_lint! {
1593     /// The `trivial_bounds` lint detects trait bounds that don't depend on
1594     /// any type parameters.
1595     ///
1596     /// ### Example
1597     ///
1598     /// ```rust
1599     /// #![feature(trivial_bounds)]
1600     /// pub struct A where i32: Copy;
1601     /// ```
1602     ///
1603     /// {{produces}}
1604     ///
1605     /// ### Explanation
1606     ///
1607     /// Usually you would not write a trait bound that you know is always
1608     /// true, or never true. However, when using macros, the macro may not
1609     /// know whether or not the constraint would hold or not at the time when
1610     /// generating the code. Currently, the compiler does not alert you if the
1611     /// constraint is always true, and generates an error if it is never true.
1612     /// The `trivial_bounds` feature changes this to be a warning in both
1613     /// cases, giving macros more freedom and flexibility to generate code,
1614     /// while still providing a signal when writing non-macro code that
1615     /// something is amiss.
1616     ///
1617     /// See [RFC 2056] for more details. This feature is currently only
1618     /// available on the nightly channel, see [tracking issue #48214].
1619     ///
1620     /// [RFC 2056]: https://github.com/rust-lang/rfcs/blob/master/text/2056-allow-trivial-where-clause-constraints.md
1621     /// [tracking issue #48214]: https://github.com/rust-lang/rust/issues/48214
1622     TRIVIAL_BOUNDS,
1623     Warn,
1624     "these bounds don't depend on an type parameters"
1625 }
1626
1627 declare_lint_pass!(
1628     /// Lint for trait and lifetime bounds that don't depend on type parameters
1629     /// which either do nothing, or stop the item from being used.
1630     TrivialConstraints => [TRIVIAL_BOUNDS]
1631 );
1632
1633 impl<'tcx> LateLintPass<'tcx> for TrivialConstraints {
1634     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
1635         use rustc_middle::ty::fold::TypeFoldable;
1636         use rustc_middle::ty::PredicateKind::*;
1637
1638         if cx.tcx.features().trivial_bounds {
1639             let predicates = cx.tcx.predicates_of(item.def_id);
1640             for &(predicate, span) in predicates.predicates {
1641                 let predicate_kind_name = match predicate.kind().skip_binder() {
1642                     Trait(..) => "trait",
1643                     TypeOutlives(..) |
1644                     RegionOutlives(..) => "lifetime",
1645
1646                     // Ignore projections, as they can only be global
1647                     // if the trait bound is global
1648                     Projection(..) |
1649                     // Ignore bounds that a user can't type
1650                     WellFormed(..) |
1651                     ObjectSafe(..) |
1652                     ClosureKind(..) |
1653                     Subtype(..) |
1654                     Coerce(..) |
1655                     ConstEvaluatable(..) |
1656                     ConstEquate(..) |
1657                     TypeWellFormedFromEnv(..) => continue,
1658                 };
1659                 if predicate.is_global() {
1660                     cx.struct_span_lint(TRIVIAL_BOUNDS, span, |lint| {
1661                         lint.build(&format!(
1662                             "{} bound {} does not depend on any type \
1663                                 or lifetime parameters",
1664                             predicate_kind_name, predicate
1665                         ))
1666                         .emit()
1667                     });
1668                 }
1669             }
1670         }
1671     }
1672 }
1673
1674 declare_lint_pass!(
1675     /// Does nothing as a lint pass, but registers some `Lint`s
1676     /// which are used by other parts of the compiler.
1677     SoftLints => [
1678         WHILE_TRUE,
1679         BOX_POINTERS,
1680         NON_SHORTHAND_FIELD_PATTERNS,
1681         UNSAFE_CODE,
1682         MISSING_DOCS,
1683         MISSING_COPY_IMPLEMENTATIONS,
1684         MISSING_DEBUG_IMPLEMENTATIONS,
1685         ANONYMOUS_PARAMETERS,
1686         UNUSED_DOC_COMMENTS,
1687         NO_MANGLE_CONST_ITEMS,
1688         NO_MANGLE_GENERIC_ITEMS,
1689         MUTABLE_TRANSMUTES,
1690         UNSTABLE_FEATURES,
1691         UNREACHABLE_PUB,
1692         TYPE_ALIAS_BOUNDS,
1693         TRIVIAL_BOUNDS
1694     ]
1695 );
1696
1697 declare_lint! {
1698     /// The `ellipsis_inclusive_range_patterns` lint detects the [`...` range
1699     /// pattern], which is deprecated.
1700     ///
1701     /// [`...` range pattern]: https://doc.rust-lang.org/reference/patterns.html#range-patterns
1702     ///
1703     /// ### Example
1704     ///
1705     /// ```rust,edition2018
1706     /// let x = 123;
1707     /// match x {
1708     ///     0...100 => {}
1709     ///     _ => {}
1710     /// }
1711     /// ```
1712     ///
1713     /// {{produces}}
1714     ///
1715     /// ### Explanation
1716     ///
1717     /// The `...` range pattern syntax was changed to `..=` to avoid potential
1718     /// confusion with the [`..` range expression]. Use the new form instead.
1719     ///
1720     /// [`..` range expression]: https://doc.rust-lang.org/reference/expressions/range-expr.html
1721     pub ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
1722     Warn,
1723     "`...` range patterns are deprecated",
1724     @future_incompatible = FutureIncompatibleInfo {
1725         reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>",
1726         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
1727     };
1728 }
1729
1730 #[derive(Default)]
1731 pub struct EllipsisInclusiveRangePatterns {
1732     /// If `Some(_)`, suppress all subsequent pattern
1733     /// warnings for better diagnostics.
1734     node_id: Option<ast::NodeId>,
1735 }
1736
1737 impl_lint_pass!(EllipsisInclusiveRangePatterns => [ELLIPSIS_INCLUSIVE_RANGE_PATTERNS]);
1738
1739 impl EarlyLintPass for EllipsisInclusiveRangePatterns {
1740     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &ast::Pat) {
1741         if self.node_id.is_some() {
1742             // Don't recursively warn about patterns inside range endpoints.
1743             return;
1744         }
1745
1746         use self::ast::{PatKind, RangeSyntax::DotDotDot};
1747
1748         /// If `pat` is a `...` pattern, return the start and end of the range, as well as the span
1749         /// corresponding to the ellipsis.
1750         fn matches_ellipsis_pat(pat: &ast::Pat) -> Option<(Option<&Expr>, &Expr, Span)> {
1751             match &pat.kind {
1752                 PatKind::Range(
1753                     a,
1754                     Some(b),
1755                     Spanned { span, node: RangeEnd::Included(DotDotDot) },
1756                 ) => Some((a.as_deref(), b, *span)),
1757                 _ => None,
1758             }
1759         }
1760
1761         let (parenthesise, endpoints) = match &pat.kind {
1762             PatKind::Ref(subpat, _) => (true, matches_ellipsis_pat(&subpat)),
1763             _ => (false, matches_ellipsis_pat(pat)),
1764         };
1765
1766         if let Some((start, end, join)) = endpoints {
1767             let msg = "`...` range patterns are deprecated";
1768             let suggestion = "use `..=` for an inclusive range";
1769             if parenthesise {
1770                 self.node_id = Some(pat.id);
1771                 let end = expr_to_string(&end);
1772                 let replace = match start {
1773                     Some(start) => format!("&({}..={})", expr_to_string(&start), end),
1774                     None => format!("&(..={})", end),
1775                 };
1776                 if join.edition() >= Edition::Edition2021 {
1777                     let mut err =
1778                         rustc_errors::struct_span_err!(cx.sess(), pat.span, E0783, "{}", msg,);
1779                     err.span_suggestion(
1780                         pat.span,
1781                         suggestion,
1782                         replace,
1783                         Applicability::MachineApplicable,
1784                     )
1785                     .emit();
1786                 } else {
1787                     cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, pat.span, |lint| {
1788                         lint.build(msg)
1789                             .span_suggestion(
1790                                 pat.span,
1791                                 suggestion,
1792                                 replace,
1793                                 Applicability::MachineApplicable,
1794                             )
1795                             .emit();
1796                     });
1797                 }
1798             } else {
1799                 let replace = "..=".to_owned();
1800                 if join.edition() >= Edition::Edition2021 {
1801                     let mut err =
1802                         rustc_errors::struct_span_err!(cx.sess(), pat.span, E0783, "{}", msg,);
1803                     err.span_suggestion_short(
1804                         join,
1805                         suggestion,
1806                         replace,
1807                         Applicability::MachineApplicable,
1808                     )
1809                     .emit();
1810                 } else {
1811                     cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, join, |lint| {
1812                         lint.build(msg)
1813                             .span_suggestion_short(
1814                                 join,
1815                                 suggestion,
1816                                 replace,
1817                                 Applicability::MachineApplicable,
1818                             )
1819                             .emit();
1820                     });
1821                 }
1822             };
1823         }
1824     }
1825
1826     fn check_pat_post(&mut self, _cx: &EarlyContext<'_>, pat: &ast::Pat) {
1827         if let Some(node_id) = self.node_id {
1828             if pat.id == node_id {
1829                 self.node_id = None
1830             }
1831         }
1832     }
1833 }
1834
1835 declare_lint! {
1836     /// The `unnameable_test_items` lint detects [`#[test]`][test] functions
1837     /// that are not able to be run by the test harness because they are in a
1838     /// position where they are not nameable.
1839     ///
1840     /// [test]: https://doc.rust-lang.org/reference/attributes/testing.html#the-test-attribute
1841     ///
1842     /// ### Example
1843     ///
1844     /// ```rust,test
1845     /// fn main() {
1846     ///     #[test]
1847     ///     fn foo() {
1848     ///         // This test will not fail because it does not run.
1849     ///         assert_eq!(1, 2);
1850     ///     }
1851     /// }
1852     /// ```
1853     ///
1854     /// {{produces}}
1855     ///
1856     /// ### Explanation
1857     ///
1858     /// In order for the test harness to run a test, the test function must be
1859     /// located in a position where it can be accessed from the crate root.
1860     /// This generally means it must be defined in a module, and not anywhere
1861     /// else such as inside another function. The compiler previously allowed
1862     /// this without an error, so a lint was added as an alert that a test is
1863     /// not being used. Whether or not this should be allowed has not yet been
1864     /// decided, see [RFC 2471] and [issue #36629].
1865     ///
1866     /// [RFC 2471]: https://github.com/rust-lang/rfcs/pull/2471#issuecomment-397414443
1867     /// [issue #36629]: https://github.com/rust-lang/rust/issues/36629
1868     UNNAMEABLE_TEST_ITEMS,
1869     Warn,
1870     "detects an item that cannot be named being marked as `#[test_case]`",
1871     report_in_external_macro
1872 }
1873
1874 pub struct UnnameableTestItems {
1875     boundary: Option<LocalDefId>, // Id of the item under which things are not nameable
1876     items_nameable: bool,
1877 }
1878
1879 impl_lint_pass!(UnnameableTestItems => [UNNAMEABLE_TEST_ITEMS]);
1880
1881 impl UnnameableTestItems {
1882     pub fn new() -> Self {
1883         Self { boundary: None, items_nameable: true }
1884     }
1885 }
1886
1887 impl<'tcx> LateLintPass<'tcx> for UnnameableTestItems {
1888     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1889         if self.items_nameable {
1890             if let hir::ItemKind::Mod(..) = it.kind {
1891             } else {
1892                 self.items_nameable = false;
1893                 self.boundary = Some(it.def_id);
1894             }
1895             return;
1896         }
1897
1898         let attrs = cx.tcx.hir().attrs(it.hir_id());
1899         if let Some(attr) = cx.sess().find_by_name(attrs, sym::rustc_test_marker) {
1900             cx.struct_span_lint(UNNAMEABLE_TEST_ITEMS, attr.span, |lint| {
1901                 lint.build("cannot test inner items").emit()
1902             });
1903         }
1904     }
1905
1906     fn check_item_post(&mut self, _cx: &LateContext<'_>, it: &hir::Item<'_>) {
1907         if !self.items_nameable && self.boundary == Some(it.def_id) {
1908             self.items_nameable = true;
1909         }
1910     }
1911 }
1912
1913 declare_lint! {
1914     /// The `keyword_idents` lint detects edition keywords being used as an
1915     /// identifier.
1916     ///
1917     /// ### Example
1918     ///
1919     /// ```rust,edition2015,compile_fail
1920     /// #![deny(keyword_idents)]
1921     /// // edition 2015
1922     /// fn dyn() {}
1923     /// ```
1924     ///
1925     /// {{produces}}
1926     ///
1927     /// ### Explanation
1928     ///
1929     /// Rust [editions] allow the language to evolve without breaking
1930     /// backwards compatibility. This lint catches code that uses new keywords
1931     /// that are added to the language that are used as identifiers (such as a
1932     /// variable name, function name, etc.). If you switch the compiler to a
1933     /// new edition without updating the code, then it will fail to compile if
1934     /// you are using a new keyword as an identifier.
1935     ///
1936     /// You can manually change the identifiers to a non-keyword, or use a
1937     /// [raw identifier], for example `r#dyn`, to transition to a new edition.
1938     ///
1939     /// This lint solves the problem automatically. It is "allow" by default
1940     /// because the code is perfectly valid in older editions. The [`cargo
1941     /// fix`] tool with the `--edition` flag will switch this lint to "warn"
1942     /// and automatically apply the suggested fix from the compiler (which is
1943     /// to use a raw identifier). This provides a completely automated way to
1944     /// update old code for a new edition.
1945     ///
1946     /// [editions]: https://doc.rust-lang.org/edition-guide/
1947     /// [raw identifier]: https://doc.rust-lang.org/reference/identifiers.html
1948     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
1949     pub KEYWORD_IDENTS,
1950     Allow,
1951     "detects edition keywords being used as an identifier",
1952     @future_incompatible = FutureIncompatibleInfo {
1953         reference: "issue #49716 <https://github.com/rust-lang/rust/issues/49716>",
1954         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
1955     };
1956 }
1957
1958 declare_lint_pass!(
1959     /// Check for uses of edition keywords used as an identifier.
1960     KeywordIdents => [KEYWORD_IDENTS]
1961 );
1962
1963 struct UnderMacro(bool);
1964
1965 impl KeywordIdents {
1966     fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: TokenStream) {
1967         for tt in tokens.into_trees() {
1968             match tt {
1969                 // Only report non-raw idents.
1970                 TokenTree::Token(token) => {
1971                     if let Some((ident, false)) = token.ident() {
1972                         self.check_ident_token(cx, UnderMacro(true), ident);
1973                     }
1974                 }
1975                 TokenTree::Delimited(_, _, tts) => self.check_tokens(cx, tts),
1976             }
1977         }
1978     }
1979
1980     fn check_ident_token(
1981         &mut self,
1982         cx: &EarlyContext<'_>,
1983         UnderMacro(under_macro): UnderMacro,
1984         ident: Ident,
1985     ) {
1986         let next_edition = match cx.sess().edition() {
1987             Edition::Edition2015 => {
1988                 match ident.name {
1989                     kw::Async | kw::Await | kw::Try => Edition::Edition2018,
1990
1991                     // rust-lang/rust#56327: Conservatively do not
1992                     // attempt to report occurrences of `dyn` within
1993                     // macro definitions or invocations, because `dyn`
1994                     // can legitimately occur as a contextual keyword
1995                     // in 2015 code denoting its 2018 meaning, and we
1996                     // do not want rustfix to inject bugs into working
1997                     // code by rewriting such occurrences.
1998                     //
1999                     // But if we see `dyn` outside of a macro, we know
2000                     // its precise role in the parsed AST and thus are
2001                     // assured this is truly an attempt to use it as
2002                     // an identifier.
2003                     kw::Dyn if !under_macro => Edition::Edition2018,
2004
2005                     _ => return,
2006                 }
2007             }
2008
2009             // There are no new keywords yet for the 2018 edition and beyond.
2010             _ => return,
2011         };
2012
2013         // Don't lint `r#foo`.
2014         if cx.sess().parse_sess.raw_identifier_spans.borrow().contains(&ident.span) {
2015             return;
2016         }
2017
2018         cx.struct_span_lint(KEYWORD_IDENTS, ident.span, |lint| {
2019             lint.build(&format!("`{}` is a keyword in the {} edition", ident, next_edition))
2020                 .span_suggestion(
2021                     ident.span,
2022                     "you can use a raw identifier to stay compatible",
2023                     format!("r#{}", ident),
2024                     Applicability::MachineApplicable,
2025                 )
2026                 .emit()
2027         });
2028     }
2029 }
2030
2031 impl EarlyLintPass for KeywordIdents {
2032     fn check_mac_def(&mut self, cx: &EarlyContext<'_>, mac_def: &ast::MacroDef, _id: ast::NodeId) {
2033         self.check_tokens(cx, mac_def.body.inner_tokens());
2034     }
2035     fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::MacCall) {
2036         self.check_tokens(cx, mac.args.inner_tokens());
2037     }
2038     fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: Ident) {
2039         self.check_ident_token(cx, UnderMacro(false), ident);
2040     }
2041 }
2042
2043 declare_lint_pass!(ExplicitOutlivesRequirements => [EXPLICIT_OUTLIVES_REQUIREMENTS]);
2044
2045 impl ExplicitOutlivesRequirements {
2046     fn lifetimes_outliving_lifetime<'tcx>(
2047         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2048         index: u32,
2049     ) -> Vec<ty::Region<'tcx>> {
2050         inferred_outlives
2051             .iter()
2052             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
2053                 ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => match a {
2054                     ty::ReEarlyBound(ebr) if ebr.index == index => Some(b),
2055                     _ => None,
2056                 },
2057                 _ => None,
2058             })
2059             .collect()
2060     }
2061
2062     fn lifetimes_outliving_type<'tcx>(
2063         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2064         index: u32,
2065     ) -> Vec<ty::Region<'tcx>> {
2066         inferred_outlives
2067             .iter()
2068             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
2069                 ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
2070                     a.is_param(index).then_some(b)
2071                 }
2072                 _ => None,
2073             })
2074             .collect()
2075     }
2076
2077     fn collect_outlived_lifetimes<'tcx>(
2078         &self,
2079         param: &'tcx hir::GenericParam<'tcx>,
2080         tcx: TyCtxt<'tcx>,
2081         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2082         ty_generics: &'tcx ty::Generics,
2083     ) -> Vec<ty::Region<'tcx>> {
2084         let index =
2085             ty_generics.param_def_id_to_index[&tcx.hir().local_def_id(param.hir_id).to_def_id()];
2086
2087         match param.kind {
2088             hir::GenericParamKind::Lifetime { .. } => {
2089                 Self::lifetimes_outliving_lifetime(inferred_outlives, index)
2090             }
2091             hir::GenericParamKind::Type { .. } => {
2092                 Self::lifetimes_outliving_type(inferred_outlives, index)
2093             }
2094             hir::GenericParamKind::Const { .. } => Vec::new(),
2095         }
2096     }
2097
2098     fn collect_outlives_bound_spans<'tcx>(
2099         &self,
2100         tcx: TyCtxt<'tcx>,
2101         bounds: &hir::GenericBounds<'_>,
2102         inferred_outlives: &[ty::Region<'tcx>],
2103         infer_static: bool,
2104     ) -> Vec<(usize, Span)> {
2105         use rustc_middle::middle::resolve_lifetime::Region;
2106
2107         bounds
2108             .iter()
2109             .enumerate()
2110             .filter_map(|(i, bound)| {
2111                 if let hir::GenericBound::Outlives(lifetime) = bound {
2112                     let is_inferred = match tcx.named_region(lifetime.hir_id) {
2113                         Some(Region::Static) if infer_static => {
2114                             inferred_outlives.iter().any(|r| matches!(r, ty::ReStatic))
2115                         }
2116                         Some(Region::EarlyBound(index, ..)) => inferred_outlives.iter().any(|r| {
2117                             if let ty::ReEarlyBound(ebr) = r { ebr.index == index } else { false }
2118                         }),
2119                         _ => false,
2120                     };
2121                     is_inferred.then_some((i, bound.span()))
2122                 } else {
2123                     None
2124                 }
2125             })
2126             .collect()
2127     }
2128
2129     fn consolidate_outlives_bound_spans(
2130         &self,
2131         lo: Span,
2132         bounds: &hir::GenericBounds<'_>,
2133         bound_spans: Vec<(usize, Span)>,
2134     ) -> Vec<Span> {
2135         if bounds.is_empty() {
2136             return Vec::new();
2137         }
2138         if bound_spans.len() == bounds.len() {
2139             let (_, last_bound_span) = bound_spans[bound_spans.len() - 1];
2140             // If all bounds are inferable, we want to delete the colon, so
2141             // start from just after the parameter (span passed as argument)
2142             vec![lo.to(last_bound_span)]
2143         } else {
2144             let mut merged = Vec::new();
2145             let mut last_merged_i = None;
2146
2147             let mut from_start = true;
2148             for (i, bound_span) in bound_spans {
2149                 match last_merged_i {
2150                     // If the first bound is inferable, our span should also eat the leading `+`.
2151                     None if i == 0 => {
2152                         merged.push(bound_span.to(bounds[1].span().shrink_to_lo()));
2153                         last_merged_i = Some(0);
2154                     }
2155                     // If consecutive bounds are inferable, merge their spans
2156                     Some(h) if i == h + 1 => {
2157                         if let Some(tail) = merged.last_mut() {
2158                             // Also eat the trailing `+` if the first
2159                             // more-than-one bound is inferable
2160                             let to_span = if from_start && i < bounds.len() {
2161                                 bounds[i + 1].span().shrink_to_lo()
2162                             } else {
2163                                 bound_span
2164                             };
2165                             *tail = tail.to(to_span);
2166                             last_merged_i = Some(i);
2167                         } else {
2168                             bug!("another bound-span visited earlier");
2169                         }
2170                     }
2171                     _ => {
2172                         // When we find a non-inferable bound, subsequent inferable bounds
2173                         // won't be consecutive from the start (and we'll eat the leading
2174                         // `+` rather than the trailing one)
2175                         from_start = false;
2176                         merged.push(bounds[i - 1].span().shrink_to_hi().to(bound_span));
2177                         last_merged_i = Some(i);
2178                     }
2179                 }
2180             }
2181             merged
2182         }
2183     }
2184 }
2185
2186 impl<'tcx> LateLintPass<'tcx> for ExplicitOutlivesRequirements {
2187     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
2188         use rustc_middle::middle::resolve_lifetime::Region;
2189
2190         let infer_static = cx.tcx.features().infer_static_outlives_requirements;
2191         let def_id = item.def_id;
2192         if let hir::ItemKind::Struct(_, ref hir_generics)
2193         | hir::ItemKind::Enum(_, ref hir_generics)
2194         | hir::ItemKind::Union(_, ref hir_generics) = item.kind
2195         {
2196             let inferred_outlives = cx.tcx.inferred_outlives_of(def_id);
2197             if inferred_outlives.is_empty() {
2198                 return;
2199             }
2200
2201             let ty_generics = cx.tcx.generics_of(def_id);
2202
2203             let mut bound_count = 0;
2204             let mut lint_spans = Vec::new();
2205
2206             for param in hir_generics.params {
2207                 let has_lifetime_bounds = param
2208                     .bounds
2209                     .iter()
2210                     .any(|bound| matches!(bound, hir::GenericBound::Outlives(_)));
2211                 if !has_lifetime_bounds {
2212                     continue;
2213                 }
2214
2215                 let relevant_lifetimes =
2216                     self.collect_outlived_lifetimes(param, cx.tcx, inferred_outlives, ty_generics);
2217                 if relevant_lifetimes.is_empty() {
2218                     continue;
2219                 }
2220
2221                 let bound_spans = self.collect_outlives_bound_spans(
2222                     cx.tcx,
2223                     &param.bounds,
2224                     &relevant_lifetimes,
2225                     infer_static,
2226                 );
2227                 bound_count += bound_spans.len();
2228                 lint_spans.extend(self.consolidate_outlives_bound_spans(
2229                     param.span.shrink_to_hi(),
2230                     &param.bounds,
2231                     bound_spans,
2232                 ));
2233             }
2234
2235             let mut where_lint_spans = Vec::new();
2236             let mut dropped_predicate_count = 0;
2237             let num_predicates = hir_generics.where_clause.predicates.len();
2238             for (i, where_predicate) in hir_generics.where_clause.predicates.iter().enumerate() {
2239                 let (relevant_lifetimes, bounds, span) = match where_predicate {
2240                     hir::WherePredicate::RegionPredicate(predicate) => {
2241                         if let Some(Region::EarlyBound(index, ..)) =
2242                             cx.tcx.named_region(predicate.lifetime.hir_id)
2243                         {
2244                             (
2245                                 Self::lifetimes_outliving_lifetime(inferred_outlives, index),
2246                                 &predicate.bounds,
2247                                 predicate.span,
2248                             )
2249                         } else {
2250                             continue;
2251                         }
2252                     }
2253                     hir::WherePredicate::BoundPredicate(predicate) => {
2254                         // FIXME we can also infer bounds on associated types,
2255                         // and should check for them here.
2256                         match predicate.bounded_ty.kind {
2257                             hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
2258                                 let Res::Def(DefKind::TyParam, def_id) = path.res else {
2259                                     continue
2260                                 };
2261                                 let index = ty_generics.param_def_id_to_index[&def_id];
2262                                 (
2263                                     Self::lifetimes_outliving_type(inferred_outlives, index),
2264                                     &predicate.bounds,
2265                                     predicate.span,
2266                                 )
2267                             }
2268                             _ => {
2269                                 continue;
2270                             }
2271                         }
2272                     }
2273                     _ => continue,
2274                 };
2275                 if relevant_lifetimes.is_empty() {
2276                     continue;
2277                 }
2278
2279                 let bound_spans = self.collect_outlives_bound_spans(
2280                     cx.tcx,
2281                     bounds,
2282                     &relevant_lifetimes,
2283                     infer_static,
2284                 );
2285                 bound_count += bound_spans.len();
2286
2287                 let drop_predicate = bound_spans.len() == bounds.len();
2288                 if drop_predicate {
2289                     dropped_predicate_count += 1;
2290                 }
2291
2292                 // If all the bounds on a predicate were inferable and there are
2293                 // further predicates, we want to eat the trailing comma.
2294                 if drop_predicate && i + 1 < num_predicates {
2295                     let next_predicate_span = hir_generics.where_clause.predicates[i + 1].span();
2296                     where_lint_spans.push(span.to(next_predicate_span.shrink_to_lo()));
2297                 } else {
2298                     where_lint_spans.extend(self.consolidate_outlives_bound_spans(
2299                         span.shrink_to_lo(),
2300                         bounds,
2301                         bound_spans,
2302                     ));
2303                 }
2304             }
2305
2306             // If all predicates are inferable, drop the entire clause
2307             // (including the `where`)
2308             if num_predicates > 0 && dropped_predicate_count == num_predicates {
2309                 let where_span = hir_generics
2310                     .where_clause
2311                     .span()
2312                     .expect("span of (nonempty) where clause should exist");
2313                 // Extend the where clause back to the closing `>` of the
2314                 // generics, except for tuple struct, which have the `where`
2315                 // after the fields of the struct.
2316                 let full_where_span =
2317                     if let hir::ItemKind::Struct(hir::VariantData::Tuple(..), _) = item.kind {
2318                         where_span
2319                     } else {
2320                         hir_generics.span.shrink_to_hi().to(where_span)
2321                     };
2322                 lint_spans.push(full_where_span);
2323             } else {
2324                 lint_spans.extend(where_lint_spans);
2325             }
2326
2327             if !lint_spans.is_empty() {
2328                 cx.struct_span_lint(EXPLICIT_OUTLIVES_REQUIREMENTS, lint_spans.clone(), |lint| {
2329                     lint.build("outlives requirements can be inferred")
2330                         .multipart_suggestion(
2331                             if bound_count == 1 {
2332                                 "remove this bound"
2333                             } else {
2334                                 "remove these bounds"
2335                             },
2336                             lint_spans
2337                                 .into_iter()
2338                                 .map(|span| (span, "".to_owned()))
2339                                 .collect::<Vec<_>>(),
2340                             Applicability::MachineApplicable,
2341                         )
2342                         .emit();
2343                 });
2344             }
2345         }
2346     }
2347 }
2348
2349 declare_lint! {
2350     /// The `incomplete_features` lint detects unstable features enabled with
2351     /// the [`feature` attribute] that may function improperly in some or all
2352     /// cases.
2353     ///
2354     /// [`feature` attribute]: https://doc.rust-lang.org/nightly/unstable-book/
2355     ///
2356     /// ### Example
2357     ///
2358     /// ```rust
2359     /// #![feature(generic_const_exprs)]
2360     /// ```
2361     ///
2362     /// {{produces}}
2363     ///
2364     /// ### Explanation
2365     ///
2366     /// Although it is encouraged for people to experiment with unstable
2367     /// features, some of them are known to be incomplete or faulty. This lint
2368     /// is a signal that the feature has not yet been finished, and you may
2369     /// experience problems with it.
2370     pub INCOMPLETE_FEATURES,
2371     Warn,
2372     "incomplete features that may function improperly in some or all cases"
2373 }
2374
2375 declare_lint_pass!(
2376     /// Check for used feature gates in `INCOMPLETE_FEATURES` in `rustc_feature/src/active.rs`.
2377     IncompleteFeatures => [INCOMPLETE_FEATURES]
2378 );
2379
2380 impl EarlyLintPass for IncompleteFeatures {
2381     fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
2382         let features = cx.sess().features_untracked();
2383         features
2384             .declared_lang_features
2385             .iter()
2386             .map(|(name, span, _)| (name, span))
2387             .chain(features.declared_lib_features.iter().map(|(name, span)| (name, span)))
2388             .filter(|(&name, _)| features.incomplete(name))
2389             .for_each(|(&name, &span)| {
2390                 cx.struct_span_lint(INCOMPLETE_FEATURES, span, |lint| {
2391                     let mut builder = lint.build(&format!(
2392                         "the feature `{}` is incomplete and may not be safe to use \
2393                          and/or cause compiler crashes",
2394                         name,
2395                     ));
2396                     if let Some(n) = rustc_feature::find_feature_issue(name, GateIssue::Language) {
2397                         builder.note(&format!(
2398                             "see issue #{} <https://github.com/rust-lang/rust/issues/{}> \
2399                              for more information",
2400                             n, n,
2401                         ));
2402                     }
2403                     if HAS_MIN_FEATURES.contains(&name) {
2404                         builder.help(&format!(
2405                             "consider using `min_{}` instead, which is more stable and complete",
2406                             name,
2407                         ));
2408                     }
2409                     builder.emit();
2410                 })
2411             });
2412     }
2413 }
2414
2415 const HAS_MIN_FEATURES: &[Symbol] = &[sym::specialization];
2416
2417 declare_lint! {
2418     /// The `invalid_value` lint detects creating a value that is not valid,
2419     /// such as a null reference.
2420     ///
2421     /// ### Example
2422     ///
2423     /// ```rust,no_run
2424     /// # #![allow(unused)]
2425     /// unsafe {
2426     ///     let x: &'static i32 = std::mem::zeroed();
2427     /// }
2428     /// ```
2429     ///
2430     /// {{produces}}
2431     ///
2432     /// ### Explanation
2433     ///
2434     /// In some situations the compiler can detect that the code is creating
2435     /// an invalid value, which should be avoided.
2436     ///
2437     /// In particular, this lint will check for improper use of
2438     /// [`mem::zeroed`], [`mem::uninitialized`], [`mem::transmute`], and
2439     /// [`MaybeUninit::assume_init`] that can cause [undefined behavior]. The
2440     /// lint should provide extra information to indicate what the problem is
2441     /// and a possible solution.
2442     ///
2443     /// [`mem::zeroed`]: https://doc.rust-lang.org/std/mem/fn.zeroed.html
2444     /// [`mem::uninitialized`]: https://doc.rust-lang.org/std/mem/fn.uninitialized.html
2445     /// [`mem::transmute`]: https://doc.rust-lang.org/std/mem/fn.transmute.html
2446     /// [`MaybeUninit::assume_init`]: https://doc.rust-lang.org/std/mem/union.MaybeUninit.html#method.assume_init
2447     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
2448     pub INVALID_VALUE,
2449     Warn,
2450     "an invalid value is being created (such as a null reference)"
2451 }
2452
2453 declare_lint_pass!(InvalidValue => [INVALID_VALUE]);
2454
2455 impl<'tcx> LateLintPass<'tcx> for InvalidValue {
2456     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
2457         #[derive(Debug, Copy, Clone, PartialEq)]
2458         enum InitKind {
2459             Zeroed,
2460             Uninit,
2461         }
2462
2463         /// Information about why a type cannot be initialized this way.
2464         /// Contains an error message and optionally a span to point at.
2465         type InitError = (String, Option<Span>);
2466
2467         /// Test if this constant is all-0.
2468         fn is_zero(expr: &hir::Expr<'_>) -> bool {
2469             use hir::ExprKind::*;
2470             use rustc_ast::LitKind::*;
2471             match &expr.kind {
2472                 Lit(lit) => {
2473                     if let Int(i, _) = lit.node {
2474                         i == 0
2475                     } else {
2476                         false
2477                     }
2478                 }
2479                 Tup(tup) => tup.iter().all(is_zero),
2480                 _ => false,
2481             }
2482         }
2483
2484         /// Determine if this expression is a "dangerous initialization".
2485         fn is_dangerous_init(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> Option<InitKind> {
2486             if let hir::ExprKind::Call(ref path_expr, ref args) = expr.kind {
2487                 // Find calls to `mem::{uninitialized,zeroed}` methods.
2488                 if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2489                     let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2490                     match cx.tcx.get_diagnostic_name(def_id) {
2491                         Some(sym::mem_zeroed) => return Some(InitKind::Zeroed),
2492                         Some(sym::mem_uninitialized) => return Some(InitKind::Uninit),
2493                         Some(sym::transmute) if is_zero(&args[0]) => return Some(InitKind::Zeroed),
2494                         _ => {}
2495                     }
2496                 }
2497             } else if let hir::ExprKind::MethodCall(_, ref args, _) = expr.kind {
2498                 // Find problematic calls to `MaybeUninit::assume_init`.
2499                 let def_id = cx.typeck_results().type_dependent_def_id(expr.hir_id)?;
2500                 if cx.tcx.is_diagnostic_item(sym::assume_init, def_id) {
2501                     // This is a call to *some* method named `assume_init`.
2502                     // See if the `self` parameter is one of the dangerous constructors.
2503                     if let hir::ExprKind::Call(ref path_expr, _) = args[0].kind {
2504                         if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2505                             let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2506                             match cx.tcx.get_diagnostic_name(def_id) {
2507                                 Some(sym::maybe_uninit_zeroed) => return Some(InitKind::Zeroed),
2508                                 Some(sym::maybe_uninit_uninit) => return Some(InitKind::Uninit),
2509                                 _ => {}
2510                             }
2511                         }
2512                     }
2513                 }
2514             }
2515
2516             None
2517         }
2518
2519         /// Test if this enum has several actually "existing" variants.
2520         /// Zero-sized uninhabited variants do not always have a tag assigned and thus do not "exist".
2521         fn is_multi_variant(adt: &ty::AdtDef) -> bool {
2522             // As an approximation, we only count dataless variants. Those are definitely inhabited.
2523             let existing_variants = adt.variants.iter().filter(|v| v.fields.is_empty()).count();
2524             existing_variants > 1
2525         }
2526
2527         /// Return `Some` only if we are sure this type does *not*
2528         /// allow zero initialization.
2529         fn ty_find_init_error<'tcx>(
2530             tcx: TyCtxt<'tcx>,
2531             ty: Ty<'tcx>,
2532             init: InitKind,
2533         ) -> Option<InitError> {
2534             use rustc_middle::ty::TyKind::*;
2535             match ty.kind() {
2536                 // Primitive types that don't like 0 as a value.
2537                 Ref(..) => Some(("references must be non-null".to_string(), None)),
2538                 Adt(..) if ty.is_box() => Some(("`Box` must be non-null".to_string(), None)),
2539                 FnPtr(..) => Some(("function pointers must be non-null".to_string(), None)),
2540                 Never => Some(("the `!` type has no valid value".to_string(), None)),
2541                 RawPtr(tm) if matches!(tm.ty.kind(), Dynamic(..)) =>
2542                 // raw ptr to dyn Trait
2543                 {
2544                     Some(("the vtable of a wide raw pointer must be non-null".to_string(), None))
2545                 }
2546                 // Primitive types with other constraints.
2547                 Bool if init == InitKind::Uninit => {
2548                     Some(("booleans must be either `true` or `false`".to_string(), None))
2549                 }
2550                 Char if init == InitKind::Uninit => {
2551                     Some(("characters must be a valid Unicode codepoint".to_string(), None))
2552                 }
2553                 // Recurse and checks for some compound types.
2554                 Adt(adt_def, substs) if !adt_def.is_union() => {
2555                     // First check if this ADT has a layout attribute (like `NonNull` and friends).
2556                     use std::ops::Bound;
2557                     match tcx.layout_scalar_valid_range(adt_def.did) {
2558                         // We exploit here that `layout_scalar_valid_range` will never
2559                         // return `Bound::Excluded`.  (And we have tests checking that we
2560                         // handle the attribute correctly.)
2561                         (Bound::Included(lo), _) if lo > 0 => {
2562                             return Some((format!("`{}` must be non-null", ty), None));
2563                         }
2564                         (Bound::Included(_), _) | (_, Bound::Included(_))
2565                             if init == InitKind::Uninit =>
2566                         {
2567                             return Some((
2568                                 format!(
2569                                     "`{}` must be initialized inside its custom valid range",
2570                                     ty,
2571                                 ),
2572                                 None,
2573                             ));
2574                         }
2575                         _ => {}
2576                     }
2577                     // Now, recurse.
2578                     match adt_def.variants.len() {
2579                         0 => Some(("enums with no variants have no valid value".to_string(), None)),
2580                         1 => {
2581                             // Struct, or enum with exactly one variant.
2582                             // Proceed recursively, check all fields.
2583                             let variant = &adt_def.variants[VariantIdx::from_u32(0)];
2584                             variant.fields.iter().find_map(|field| {
2585                                 ty_find_init_error(tcx, field.ty(tcx, substs), init).map(
2586                                     |(mut msg, span)| {
2587                                         if span.is_none() {
2588                                             // Point to this field, should be helpful for figuring
2589                                             // out where the source of the error is.
2590                                             let span = tcx.def_span(field.did);
2591                                             write!(
2592                                                 &mut msg,
2593                                                 " (in this {} field)",
2594                                                 adt_def.descr()
2595                                             )
2596                                             .unwrap();
2597                                             (msg, Some(span))
2598                                         } else {
2599                                             // Just forward.
2600                                             (msg, span)
2601                                         }
2602                                     },
2603                                 )
2604                             })
2605                         }
2606                         // Multi-variant enum.
2607                         _ => {
2608                             if init == InitKind::Uninit && is_multi_variant(adt_def) {
2609                                 let span = tcx.def_span(adt_def.did);
2610                                 Some((
2611                                     "enums have to be initialized to a variant".to_string(),
2612                                     Some(span),
2613                                 ))
2614                             } else {
2615                                 // In principle, for zero-initialization we could figure out which variant corresponds
2616                                 // to tag 0, and check that... but for now we just accept all zero-initializations.
2617                                 None
2618                             }
2619                         }
2620                     }
2621                 }
2622                 Tuple(..) => {
2623                     // Proceed recursively, check all fields.
2624                     ty.tuple_fields().find_map(|field| ty_find_init_error(tcx, field, init))
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.tcx, conjured_ty, init))
2638             {
2639                 cx.struct_span_lint(INVALID_VALUE, expr.span, |lint| {
2640                     let mut err = lint.build(&format!(
2641                         "the type `{}` does not permit {}",
2642                         conjured_ty,
2643                         match init {
2644                             InitKind::Zeroed => "zero-initialization",
2645                             InitKind::Uninit => "being left uninitialized",
2646                         },
2647                     ));
2648                     err.span_label(expr.span, "this code causes undefined behavior when executed");
2649                     err.span_label(
2650                         expr.span,
2651                         "help: use `MaybeUninit<T>` instead, \
2652                             and only call `assume_init` after initialization is done",
2653                     );
2654                     if let Some(span) = span {
2655                         err.span_note(span, &msg);
2656                     } else {
2657                         err.note(&msg);
2658                     }
2659                     err.emit();
2660                 });
2661             }
2662         }
2663     }
2664 }
2665
2666 declare_lint! {
2667     /// The `clashing_extern_declarations` lint detects when an `extern fn`
2668     /// has been declared with the same name but different types.
2669     ///
2670     /// ### Example
2671     ///
2672     /// ```rust
2673     /// mod m {
2674     ///     extern "C" {
2675     ///         fn foo();
2676     ///     }
2677     /// }
2678     ///
2679     /// extern "C" {
2680     ///     fn foo(_: u32);
2681     /// }
2682     /// ```
2683     ///
2684     /// {{produces}}
2685     ///
2686     /// ### Explanation
2687     ///
2688     /// Because two symbols of the same name cannot be resolved to two
2689     /// different functions at link time, and one function cannot possibly
2690     /// have two types, a clashing extern declaration is almost certainly a
2691     /// mistake. Check to make sure that the `extern` definitions are correct
2692     /// and equivalent, and possibly consider unifying them in one location.
2693     ///
2694     /// This lint does not run between crates because a project may have
2695     /// dependencies which both rely on the same extern function, but declare
2696     /// it in a different (but valid) way. For example, they may both declare
2697     /// an opaque type for one or more of the arguments (which would end up
2698     /// distinct types), or use types that are valid conversions in the
2699     /// language the `extern fn` is defined in. In these cases, the compiler
2700     /// can't say that the clashing declaration is incorrect.
2701     pub CLASHING_EXTERN_DECLARATIONS,
2702     Warn,
2703     "detects when an extern fn has been declared with the same name but different types"
2704 }
2705
2706 pub struct ClashingExternDeclarations {
2707     /// Map of function symbol name to the first-seen hir id for that symbol name.. If seen_decls
2708     /// contains an entry for key K, it means a symbol with name K has been seen by this lint and
2709     /// the symbol should be reported as a clashing declaration.
2710     // FIXME: Technically, we could just store a &'tcx str here without issue; however, the
2711     // `impl_lint_pass` macro doesn't currently support lints parametric over a lifetime.
2712     seen_decls: FxHashMap<Symbol, HirId>,
2713 }
2714
2715 /// Differentiate between whether the name for an extern decl came from the link_name attribute or
2716 /// just from declaration itself. This is important because we don't want to report clashes on
2717 /// symbol name if they don't actually clash because one or the other links against a symbol with a
2718 /// different name.
2719 enum SymbolName {
2720     /// The name of the symbol + the span of the annotation which introduced the link name.
2721     Link(Symbol, Span),
2722     /// No link name, so just the name of the symbol.
2723     Normal(Symbol),
2724 }
2725
2726 impl SymbolName {
2727     fn get_name(&self) -> Symbol {
2728         match self {
2729             SymbolName::Link(s, _) | SymbolName::Normal(s) => *s,
2730         }
2731     }
2732 }
2733
2734 impl ClashingExternDeclarations {
2735     crate fn new() -> Self {
2736         ClashingExternDeclarations { seen_decls: FxHashMap::default() }
2737     }
2738     /// Insert a new foreign item into the seen set. If a symbol with the same name already exists
2739     /// for the item, return its HirId without updating the set.
2740     fn insert(&mut self, tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> Option<HirId> {
2741         let did = fi.def_id.to_def_id();
2742         let instance = Instance::new(did, ty::List::identity_for_item(tcx, did));
2743         let name = Symbol::intern(tcx.symbol_name(instance).name);
2744         if let Some(&hir_id) = self.seen_decls.get(&name) {
2745             // Avoid updating the map with the new entry when we do find a collision. We want to
2746             // make sure we're always pointing to the first definition as the previous declaration.
2747             // This lets us avoid emitting "knock-on" diagnostics.
2748             Some(hir_id)
2749         } else {
2750             self.seen_decls.insert(name, fi.hir_id())
2751         }
2752     }
2753
2754     /// Get the name of the symbol that's linked against for a given extern declaration. That is,
2755     /// the name specified in a #[link_name = ...] attribute if one was specified, else, just the
2756     /// symbol's name.
2757     fn name_of_extern_decl(tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> SymbolName {
2758         if let Some((overridden_link_name, overridden_link_name_span)) =
2759             tcx.codegen_fn_attrs(fi.def_id).link_name.map(|overridden_link_name| {
2760                 // FIXME: Instead of searching through the attributes again to get span
2761                 // information, we could have codegen_fn_attrs also give span information back for
2762                 // where the attribute was defined. However, until this is found to be a
2763                 // bottleneck, this does just fine.
2764                 (
2765                     overridden_link_name,
2766                     tcx.get_attrs(fi.def_id.to_def_id())
2767                         .iter()
2768                         .find(|at| at.has_name(sym::link_name))
2769                         .unwrap()
2770                         .span,
2771                 )
2772             })
2773         {
2774             SymbolName::Link(overridden_link_name, overridden_link_name_span)
2775         } else {
2776             SymbolName::Normal(fi.ident.name)
2777         }
2778     }
2779
2780     /// Checks whether two types are structurally the same enough that the declarations shouldn't
2781     /// clash. We need this so we don't emit a lint when two modules both declare an extern struct,
2782     /// with the same members (as the declarations shouldn't clash).
2783     fn structurally_same_type<'tcx>(
2784         cx: &LateContext<'tcx>,
2785         a: Ty<'tcx>,
2786         b: Ty<'tcx>,
2787         ckind: CItemKind,
2788     ) -> bool {
2789         fn structurally_same_type_impl<'tcx>(
2790             seen_types: &mut FxHashSet<(Ty<'tcx>, Ty<'tcx>)>,
2791             cx: &LateContext<'tcx>,
2792             a: Ty<'tcx>,
2793             b: Ty<'tcx>,
2794             ckind: CItemKind,
2795         ) -> bool {
2796             debug!("structurally_same_type_impl(cx, a = {:?}, b = {:?})", a, b);
2797             let tcx = cx.tcx;
2798
2799             // Given a transparent newtype, reach through and grab the inner
2800             // type unless the newtype makes the type non-null.
2801             let non_transparent_ty = |ty: Ty<'tcx>| -> Ty<'tcx> {
2802                 let mut ty = ty;
2803                 loop {
2804                     if let ty::Adt(def, substs) = *ty.kind() {
2805                         let is_transparent = def.subst(tcx, substs).repr.transparent();
2806                         let is_non_null = crate::types::nonnull_optimization_guaranteed(tcx, &def);
2807                         debug!(
2808                             "non_transparent_ty({:?}) -- type is transparent? {}, type is non-null? {}",
2809                             ty, is_transparent, is_non_null
2810                         );
2811                         if is_transparent && !is_non_null {
2812                             debug_assert!(def.variants.len() == 1);
2813                             let v = &def.variants[VariantIdx::new(0)];
2814                             ty = transparent_newtype_field(tcx, v)
2815                                 .expect(
2816                                     "single-variant transparent structure with zero-sized field",
2817                                 )
2818                                 .ty(tcx, substs);
2819                             continue;
2820                         }
2821                     }
2822                     debug!("non_transparent_ty -> {:?}", ty);
2823                     return ty;
2824                 }
2825             };
2826
2827             let a = non_transparent_ty(a);
2828             let b = non_transparent_ty(b);
2829
2830             if !seen_types.insert((a, b)) {
2831                 // We've encountered a cycle. There's no point going any further -- the types are
2832                 // structurally the same.
2833                 return true;
2834             }
2835             let tcx = cx.tcx;
2836             if a == b {
2837                 // All nominally-same types are structurally same, too.
2838                 true
2839             } else {
2840                 // Do a full, depth-first comparison between the two.
2841                 use rustc_middle::ty::TyKind::*;
2842                 let a_kind = a.kind();
2843                 let b_kind = b.kind();
2844
2845                 let compare_layouts = |a, b| -> Result<bool, LayoutError<'tcx>> {
2846                     debug!("compare_layouts({:?}, {:?})", a, b);
2847                     let a_layout = &cx.layout_of(a)?.layout.abi;
2848                     let b_layout = &cx.layout_of(b)?.layout.abi;
2849                     debug!(
2850                         "comparing layouts: {:?} == {:?} = {}",
2851                         a_layout,
2852                         b_layout,
2853                         a_layout == b_layout
2854                     );
2855                     Ok(a_layout == b_layout)
2856                 };
2857
2858                 #[allow(rustc::usage_of_ty_tykind)]
2859                 let is_primitive_or_pointer = |kind: &ty::TyKind<'_>| {
2860                     kind.is_primitive() || matches!(kind, RawPtr(..) | Ref(..))
2861                 };
2862
2863                 ensure_sufficient_stack(|| {
2864                     match (a_kind, b_kind) {
2865                         (Adt(a_def, a_substs), Adt(b_def, b_substs)) => {
2866                             let a = a.subst(cx.tcx, a_substs);
2867                             let b = b.subst(cx.tcx, b_substs);
2868                             debug!("Comparing {:?} and {:?}", a, b);
2869
2870                             // We can immediately rule out these types as structurally same if
2871                             // their layouts differ.
2872                             match compare_layouts(a, b) {
2873                                 Ok(false) => return false,
2874                                 _ => (), // otherwise, continue onto the full, fields comparison
2875                             }
2876
2877                             // Grab a flattened representation of all fields.
2878                             let a_fields = a_def.variants.iter().flat_map(|v| v.fields.iter());
2879                             let b_fields = b_def.variants.iter().flat_map(|v| v.fields.iter());
2880
2881                             // Perform a structural comparison for each field.
2882                             a_fields.eq_by(
2883                                 b_fields,
2884                                 |&ty::FieldDef { did: a_did, .. },
2885                                  &ty::FieldDef { did: b_did, .. }| {
2886                                     structurally_same_type_impl(
2887                                         seen_types,
2888                                         cx,
2889                                         tcx.type_of(a_did),
2890                                         tcx.type_of(b_did),
2891                                         ckind,
2892                                     )
2893                                 },
2894                             )
2895                         }
2896                         (Array(a_ty, a_const), Array(b_ty, b_const)) => {
2897                             // For arrays, we also check the constness of the type.
2898                             a_const.val == b_const.val
2899                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2900                         }
2901                         (Slice(a_ty), Slice(b_ty)) => {
2902                             structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2903                         }
2904                         (RawPtr(a_tymut), RawPtr(b_tymut)) => {
2905                             a_tymut.mutbl == b_tymut.mutbl
2906                                 && structurally_same_type_impl(
2907                                     seen_types,
2908                                     cx,
2909                                     &a_tymut.ty,
2910                                     &b_tymut.ty,
2911                                     ckind,
2912                                 )
2913                         }
2914                         (Ref(_a_region, a_ty, a_mut), Ref(_b_region, b_ty, b_mut)) => {
2915                             // For structural sameness, we don't need the region to be same.
2916                             a_mut == b_mut
2917                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2918                         }
2919                         (FnDef(..), FnDef(..)) => {
2920                             let a_poly_sig = a.fn_sig(tcx);
2921                             let b_poly_sig = b.fn_sig(tcx);
2922
2923                             // As we don't compare regions, skip_binder is fine.
2924                             let a_sig = a_poly_sig.skip_binder();
2925                             let b_sig = b_poly_sig.skip_binder();
2926
2927                             (a_sig.abi, a_sig.unsafety, a_sig.c_variadic)
2928                                 == (b_sig.abi, b_sig.unsafety, b_sig.c_variadic)
2929                                 && a_sig.inputs().iter().eq_by(b_sig.inputs().iter(), |a, b| {
2930                                     structurally_same_type_impl(seen_types, cx, a, b, ckind)
2931                                 })
2932                                 && structurally_same_type_impl(
2933                                     seen_types,
2934                                     cx,
2935                                     a_sig.output(),
2936                                     b_sig.output(),
2937                                     ckind,
2938                                 )
2939                         }
2940                         (Tuple(a_substs), Tuple(b_substs)) => {
2941                             a_substs.types().eq_by(b_substs.types(), |a_ty, b_ty| {
2942                                 structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2943                             })
2944                         }
2945                         // For these, it's not quite as easy to define structural-sameness quite so easily.
2946                         // For the purposes of this lint, take the conservative approach and mark them as
2947                         // not structurally same.
2948                         (Dynamic(..), Dynamic(..))
2949                         | (Error(..), Error(..))
2950                         | (Closure(..), Closure(..))
2951                         | (Generator(..), Generator(..))
2952                         | (GeneratorWitness(..), GeneratorWitness(..))
2953                         | (Projection(..), Projection(..))
2954                         | (Opaque(..), Opaque(..)) => false,
2955
2956                         // These definitely should have been caught above.
2957                         (Bool, Bool) | (Char, Char) | (Never, Never) | (Str, Str) => unreachable!(),
2958
2959                         // An Adt and a primitive or pointer type. This can be FFI-safe if non-null
2960                         // enum layout optimisation is being applied.
2961                         (Adt(..), other_kind) | (other_kind, Adt(..))
2962                             if is_primitive_or_pointer(other_kind) =>
2963                         {
2964                             let (primitive, adt) =
2965                                 if is_primitive_or_pointer(a.kind()) { (a, b) } else { (b, a) };
2966                             if let Some(ty) = crate::types::repr_nullable_ptr(cx, adt, ckind) {
2967                                 ty == primitive
2968                             } else {
2969                                 compare_layouts(a, b).unwrap_or(false)
2970                             }
2971                         }
2972                         // Otherwise, just compare the layouts. This may fail to lint for some
2973                         // incompatible types, but at the very least, will stop reads into
2974                         // uninitialised memory.
2975                         _ => compare_layouts(a, b).unwrap_or(false),
2976                     }
2977                 })
2978             }
2979         }
2980         let mut seen_types = FxHashSet::default();
2981         structurally_same_type_impl(&mut seen_types, cx, a, b, ckind)
2982     }
2983 }
2984
2985 impl_lint_pass!(ClashingExternDeclarations => [CLASHING_EXTERN_DECLARATIONS]);
2986
2987 impl<'tcx> LateLintPass<'tcx> for ClashingExternDeclarations {
2988     fn check_foreign_item(&mut self, cx: &LateContext<'tcx>, this_fi: &hir::ForeignItem<'_>) {
2989         trace!("ClashingExternDeclarations: check_foreign_item: {:?}", this_fi);
2990         if let ForeignItemKind::Fn(..) = this_fi.kind {
2991             let tcx = cx.tcx;
2992             if let Some(existing_hid) = self.insert(tcx, this_fi) {
2993                 let existing_decl_ty = tcx.type_of(tcx.hir().local_def_id(existing_hid));
2994                 let this_decl_ty = tcx.type_of(this_fi.def_id);
2995                 debug!(
2996                     "ClashingExternDeclarations: Comparing existing {:?}: {:?} to this {:?}: {:?}",
2997                     existing_hid, existing_decl_ty, this_fi.def_id, this_decl_ty
2998                 );
2999                 // Check that the declarations match.
3000                 if !Self::structurally_same_type(
3001                     cx,
3002                     existing_decl_ty,
3003                     this_decl_ty,
3004                     CItemKind::Declaration,
3005                 ) {
3006                     let orig_fi = tcx.hir().expect_foreign_item(existing_hid.expect_owner());
3007                     let orig = Self::name_of_extern_decl(tcx, orig_fi);
3008
3009                     // We want to ensure that we use spans for both decls that include where the
3010                     // name was defined, whether that was from the link_name attribute or not.
3011                     let get_relevant_span =
3012                         |fi: &hir::ForeignItem<'_>| match Self::name_of_extern_decl(tcx, fi) {
3013                             SymbolName::Normal(_) => fi.span,
3014                             SymbolName::Link(_, annot_span) => fi.span.to(annot_span),
3015                         };
3016                     // Finally, emit the diagnostic.
3017                     tcx.struct_span_lint_hir(
3018                         CLASHING_EXTERN_DECLARATIONS,
3019                         this_fi.hir_id(),
3020                         get_relevant_span(this_fi),
3021                         |lint| {
3022                             let mut expected_str = DiagnosticStyledString::new();
3023                             expected_str.push(existing_decl_ty.fn_sig(tcx).to_string(), false);
3024                             let mut found_str = DiagnosticStyledString::new();
3025                             found_str.push(this_decl_ty.fn_sig(tcx).to_string(), true);
3026
3027                             lint.build(&format!(
3028                                 "`{}` redeclare{} with a different signature",
3029                                 this_fi.ident.name,
3030                                 if orig.get_name() == this_fi.ident.name {
3031                                     "d".to_string()
3032                                 } else {
3033                                     format!("s `{}`", orig.get_name())
3034                                 }
3035                             ))
3036                             .span_label(
3037                                 get_relevant_span(orig_fi),
3038                                 &format!("`{}` previously declared here", orig.get_name()),
3039                             )
3040                             .span_label(
3041                                 get_relevant_span(this_fi),
3042                                 "this signature doesn't match the previous declaration",
3043                             )
3044                             .note_expected_found(&"", expected_str, &"", found_str)
3045                             .emit()
3046                         },
3047                     );
3048                 }
3049             }
3050         }
3051     }
3052 }
3053
3054 declare_lint! {
3055     /// The `deref_nullptr` lint detects when an null pointer is dereferenced,
3056     /// which causes [undefined behavior].
3057     ///
3058     /// ### Example
3059     ///
3060     /// ```rust,no_run
3061     /// # #![allow(unused)]
3062     /// use std::ptr;
3063     /// unsafe {
3064     ///     let x = &*ptr::null::<i32>();
3065     ///     let x = ptr::addr_of!(*ptr::null::<i32>());
3066     ///     let x = *(0 as *const i32);
3067     /// }
3068     /// ```
3069     ///
3070     /// {{produces}}
3071     ///
3072     /// ### Explanation
3073     ///
3074     /// Dereferencing a null pointer causes [undefined behavior] even as a place expression,
3075     /// like `&*(0 as *const i32)` or `addr_of!(*(0 as *const i32))`.
3076     ///
3077     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
3078     pub DEREF_NULLPTR,
3079     Warn,
3080     "detects when an null pointer is dereferenced"
3081 }
3082
3083 declare_lint_pass!(DerefNullPtr => [DEREF_NULLPTR]);
3084
3085 impl<'tcx> LateLintPass<'tcx> for DerefNullPtr {
3086     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
3087         /// test if expression is a null ptr
3088         fn is_null_ptr(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> bool {
3089             match &expr.kind {
3090                 rustc_hir::ExprKind::Cast(ref expr, ref ty) => {
3091                     if let rustc_hir::TyKind::Ptr(_) = ty.kind {
3092                         return is_zero(expr) || is_null_ptr(cx, expr);
3093                     }
3094                 }
3095                 // check for call to `core::ptr::null` or `core::ptr::null_mut`
3096                 rustc_hir::ExprKind::Call(ref path, _) => {
3097                     if let rustc_hir::ExprKind::Path(ref qpath) = path.kind {
3098                         if let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id() {
3099                             return matches!(
3100                                 cx.tcx.get_diagnostic_name(def_id),
3101                                 Some(sym::ptr_null | sym::ptr_null_mut)
3102                             );
3103                         }
3104                     }
3105                 }
3106                 _ => {}
3107             }
3108             false
3109         }
3110
3111         /// test if expression is the literal `0`
3112         fn is_zero(expr: &hir::Expr<'_>) -> bool {
3113             match &expr.kind {
3114                 rustc_hir::ExprKind::Lit(ref lit) => {
3115                     if let LitKind::Int(a, _) = lit.node {
3116                         return a == 0;
3117                     }
3118                 }
3119                 _ => {}
3120             }
3121             false
3122         }
3123
3124         if let rustc_hir::ExprKind::Unary(rustc_hir::UnOp::Deref, expr_deref) = expr.kind {
3125             if is_null_ptr(cx, expr_deref) {
3126                 cx.struct_span_lint(DEREF_NULLPTR, expr.span, |lint| {
3127                     let mut err = lint.build("dereferencing a null pointer");
3128                     err.span_label(expr.span, "this code causes undefined behavior when executed");
3129                     err.emit();
3130                 });
3131             }
3132         }
3133     }
3134 }
3135
3136 declare_lint! {
3137     /// The `named_asm_labels` lint detects the use of named labels in the
3138     /// inline `asm!` macro.
3139     ///
3140     /// ### Example
3141     ///
3142     /// ```rust,compile_fail
3143     /// use std::arch::asm;
3144     ///
3145     /// fn main() {
3146     ///     unsafe {
3147     ///         asm!("foo: bar");
3148     ///     }
3149     /// }
3150     /// ```
3151     ///
3152     /// {{produces}}
3153     ///
3154     /// ### Explanation
3155     ///
3156     /// LLVM is allowed to duplicate inline assembly blocks for any
3157     /// reason, for example when it is in a function that gets inlined. Because
3158     /// of this, GNU assembler [local labels] *must* be used instead of labels
3159     /// with a name. Using named labels might cause assembler or linker errors.
3160     ///
3161     /// See the explanation in [Rust By Example] for more details.
3162     ///
3163     /// [local labels]: https://sourceware.org/binutils/docs/as/Symbol-Names.html#Local-Labels
3164     /// [Rust By Example]: https://doc.rust-lang.org/nightly/rust-by-example/unsafe/asm.html#labels
3165     pub NAMED_ASM_LABELS,
3166     Deny,
3167     "named labels in inline assembly",
3168 }
3169
3170 declare_lint_pass!(NamedAsmLabels => [NAMED_ASM_LABELS]);
3171
3172 impl<'tcx> LateLintPass<'tcx> for NamedAsmLabels {
3173     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
3174         if let hir::Expr {
3175             kind: hir::ExprKind::InlineAsm(hir::InlineAsm { template_strs, .. }),
3176             ..
3177         } = expr
3178         {
3179             for (template_sym, template_snippet, template_span) in template_strs.iter() {
3180                 let template_str = template_sym.as_str();
3181                 let find_label_span = |needle: &str| -> Option<Span> {
3182                     if let Some(template_snippet) = template_snippet {
3183                         let snippet = template_snippet.as_str();
3184                         if let Some(pos) = snippet.find(needle) {
3185                             let end = pos
3186                                 + snippet[pos..]
3187                                     .find(|c| c == ':')
3188                                     .unwrap_or(snippet[pos..].len() - 1);
3189                             let inner = InnerSpan::new(pos, end);
3190                             return Some(template_span.from_inner(inner));
3191                         }
3192                     }
3193
3194                     None
3195                 };
3196
3197                 let mut found_labels = Vec::new();
3198
3199                 // A semicolon might not actually be specified as a separator for all targets, but it seems like LLVM accepts it always
3200                 let statements = template_str.split(|c| matches!(c, '\n' | ';'));
3201                 for statement in statements {
3202                     // If there's a comment, trim it from the statement
3203                     let statement = statement.find("//").map_or(statement, |idx| &statement[..idx]);
3204                     let mut start_idx = 0;
3205                     for (idx, _) in statement.match_indices(':') {
3206                         let possible_label = statement[start_idx..idx].trim();
3207                         let mut chars = possible_label.chars();
3208                         let Some(c) = chars.next() else {
3209                             // Empty string means a leading ':' in this section, which is not a label
3210                             break
3211                         };
3212                         // A label starts with an alphabetic character or . or _ and continues with alphanumeric characters, _, or $
3213                         if (c.is_alphabetic() || matches!(c, '.' | '_'))
3214                             && chars.all(|c| c.is_alphanumeric() || matches!(c, '_' | '$'))
3215                         {
3216                             found_labels.push(possible_label);
3217                         } else {
3218                             // If we encounter a non-label, there cannot be any further labels, so stop checking
3219                             break;
3220                         }
3221
3222                         start_idx = idx + 1;
3223                     }
3224                 }
3225
3226                 debug!("NamedAsmLabels::check_expr(): found_labels: {:#?}", &found_labels);
3227
3228                 if found_labels.len() > 0 {
3229                     let spans = found_labels
3230                         .into_iter()
3231                         .filter_map(|label| find_label_span(label))
3232                         .collect::<Vec<Span>>();
3233                     // If there were labels but we couldn't find a span, combine the warnings and use the template span
3234                     let target_spans: MultiSpan =
3235                         if spans.len() > 0 { spans.into() } else { (*template_span).into() };
3236
3237                     cx.lookup_with_diagnostics(
3238                             NAMED_ASM_LABELS,
3239                             Some(target_spans),
3240                             |diag| {
3241                                 let mut err =
3242                                     diag.build("avoid using named labels in inline assembly");
3243                                 err.emit();
3244                             },
3245                             BuiltinLintDiagnostics::NamedAsmLabel(
3246                                 "only local labels of the form `<number>:` should be used in inline asm"
3247                                     .to_string(),
3248                             ),
3249                         );
3250                 }
3251             }
3252         }
3253     }
3254 }