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, Diagnostic, 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::{self, 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(
 768             cx.tcx,
 769             param_env,
 770             ty,
 771             traits::ObligationCause::misc(item.span, item.hir_id()),
 772         )
 773         .is_ok()
 774         {
 775             cx.struct_span_lint(MISSING_COPY_IMPLEMENTATIONS, item.span, |lint| {
 776                 lint.build(
 777                     "type could implement `Copy`; consider adding `impl \
 778                           Copy`",
 779                 )
 780                 .emit()
 781             })
 782         }
 783     }
 784 }
 785
 786 declare_lint! {
 787     /// The `missing_debug_implementations` lint detects missing
 788     /// implementations of [`fmt::Debug`].
 789     ///
 790     /// [`fmt::Debug`]: https://doc.rust-lang.org/std/fmt/trait.Debug.html
 791     ///
 792     /// ### Example
 793     ///
 794     /// ```rust,compile_fail
 795     /// #![deny(missing_debug_implementations)]
 796     /// pub struct Foo;
 797     /// # fn main() {}
 798     /// ```
 799     ///
 800     /// {{produces}}
 801     ///
 802     /// ### Explanation
 803     ///
 804     /// Having a `Debug` implementation on all types can assist with
 805     /// debugging, as it provides a convenient way to format and display a
 806     /// value. Using the `#[derive(Debug)]` attribute will automatically
 807     /// generate a typical implementation, or a custom implementation can be
 808     /// added by manually implementing the `Debug` trait.
 809     ///
 810     /// This lint is "allow" by default because adding `Debug` to all types can
 811     /// have a negative impact on compile time and code size. It also requires
 812     /// boilerplate to be added to every type, which can be an impediment.
 813     MISSING_DEBUG_IMPLEMENTATIONS,
 814     Allow,
 815     "detects missing implementations of Debug"
 816 }
 817
 818 #[derive(Default)]
 819 pub struct MissingDebugImplementations {
 820     impling_types: Option<LocalDefIdSet>,
 821 }
 822
 823 impl_lint_pass!(MissingDebugImplementations => [MISSING_DEBUG_IMPLEMENTATIONS]);
 824
 825 impl<'tcx> LateLintPass<'tcx> for MissingDebugImplementations {
 826     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 827         if !cx.access_levels.is_reachable(item.def_id) {
 828             return;
 829         }
 830
 831         match item.kind {
 832             hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) | hir::ItemKind::Enum(..) => {}
 833             _ => return,
 834         }
 835
 836         let Some(debug) = cx.tcx.get_diagnostic_item(sym::Debug) else {
 837             return
 838         };
 839
 840         if self.impling_types.is_none() {
 841             let mut impls = LocalDefIdSet::default();
 842             cx.tcx.for_each_impl(debug, |d| {
 843                 if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() {
 844                     if let Some(def_id) = ty_def.did.as_local() {
 845                         impls.insert(def_id);
 846                     }
 847                 }
 848             });
 849
 850             self.impling_types = Some(impls);
 851             debug!("{:?}", self.impling_types);
 852         }
 853
 854         if !self.impling_types.as_ref().unwrap().contains(&item.def_id) {
 855             cx.struct_span_lint(MISSING_DEBUG_IMPLEMENTATIONS, item.span, |lint| {
 856                 lint.build(&format!(
 857                     "type does not implement `{}`; consider adding `#[derive(Debug)]` \
 858                      or a manual implementation",
 859                     cx.tcx.def_path_str(debug)
 860                 ))
 861                 .emit()
 862             });
 863         }
 864     }
 865 }
 866
 867 declare_lint! {
 868     /// The `anonymous_parameters` lint detects anonymous parameters in trait
 869     /// definitions.
 870     ///
 871     /// ### Example
 872     ///
 873     /// ```rust,edition2015,compile_fail
 874     /// #![deny(anonymous_parameters)]
 875     /// // edition 2015
 876     /// pub trait Foo {
 877     ///     fn foo(usize);
 878     /// }
 879     /// fn main() {}
 880     /// ```
 881     ///
 882     /// {{produces}}
 883     ///
 884     /// ### Explanation
 885     ///
 886     /// This syntax is mostly a historical accident, and can be worked around
 887     /// quite easily by adding an `_` pattern or a descriptive identifier:
 888     ///
 889     /// ```rust
 890     /// trait Foo {
 891     ///     fn foo(_: usize);
 892     /// }
 893     /// ```
 894     ///
 895     /// This syntax is now a hard error in the 2018 edition. In the 2015
 896     /// edition, this lint is "warn" by default. This lint
 897     /// enables the [`cargo fix`] tool with the `--edition` flag to
 898     /// automatically transition old code from the 2015 edition to 2018. The
 899     /// tool will run this lint and automatically apply the
 900     /// suggested fix from the compiler (which is to add `_` to each
 901     /// parameter). This provides a completely automated way to update old
 902     /// code for a new edition. See [issue #41686] for more details.
 903     ///
 904     /// [issue #41686]: https://github.com/rust-lang/rust/issues/41686
 905     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
 906     pub ANONYMOUS_PARAMETERS,
 907     Warn,
 908     "detects anonymous parameters",
 909     @future_incompatible = FutureIncompatibleInfo {
 910         reference: "issue #41686 <https://github.com/rust-lang/rust/issues/41686>",
 911         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
 912     };
 913 }
 914
 915 declare_lint_pass!(
 916     /// Checks for use of anonymous parameters (RFC 1685).
 917     AnonymousParameters => [ANONYMOUS_PARAMETERS]
 918 );
 919
 920 impl EarlyLintPass for AnonymousParameters {
 921     fn check_trait_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
 922         if cx.sess().edition() != Edition::Edition2015 {
 923             // This is a hard error in future editions; avoid linting and erroring
 924             return;
 925         }
 926         if let ast::AssocItemKind::Fn(box Fn { ref sig, .. }) = it.kind {
 927             for arg in sig.decl.inputs.iter() {
 928                 if let ast::PatKind::Ident(_, ident, None) = arg.pat.kind {
 929                     if ident.name == kw::Empty {
 930                         cx.struct_span_lint(ANONYMOUS_PARAMETERS, arg.pat.span, |lint| {
 931                             let ty_snip = cx.sess().source_map().span_to_snippet(arg.ty.span);
 932
 933                             let (ty_snip, appl) = if let Ok(ref snip) = ty_snip {
 934                                 (snip.as_str(), Applicability::MachineApplicable)
 935                             } else {
 936                                 ("<type>", Applicability::HasPlaceholders)
 937                             };
 938
 939                             lint.build(
 940                                 "anonymous parameters are deprecated and will be \
 941                                      removed in the next edition",
 942                             )
 943                             .span_suggestion(
 944                                 arg.pat.span,
 945                                 "try naming the parameter or explicitly \
 946                                             ignoring it",
 947                                 format!("_: {}", ty_snip),
 948                                 appl,
 949                             )
 950                             .emit();
 951                         })
 952                     }
 953                 }
 954             }
 955         }
 956     }
 957 }
 958
 959 /// Check for use of attributes which have been deprecated.
 960 #[derive(Clone)]
 961 pub struct DeprecatedAttr {
 962     // This is not free to compute, so we want to keep it around, rather than
 963     // compute it for every attribute.
 964     depr_attrs: Vec<&'static BuiltinAttribute>,
 965 }
 966
 967 impl_lint_pass!(DeprecatedAttr => []);
 968
 969 impl DeprecatedAttr {
 970     pub fn new() -> DeprecatedAttr {
 971         DeprecatedAttr { depr_attrs: deprecated_attributes() }
 972     }
 973 }
 974
 975 fn lint_deprecated_attr(
 976     cx: &EarlyContext<'_>,
 977     attr: &ast::Attribute,
 978     msg: &str,
 979     suggestion: Option<&str>,
 980 ) {
 981     cx.struct_span_lint(DEPRECATED, attr.span, |lint| {
 982         lint.build(msg)
 983             .span_suggestion_short(
 984                 attr.span,
 985                 suggestion.unwrap_or("remove this attribute"),
 986                 String::new(),
 987                 Applicability::MachineApplicable,
 988             )
 989             .emit();
 990     })
 991 }
 992
 993 impl EarlyLintPass for DeprecatedAttr {
 994     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 995         for BuiltinAttribute { name, gate, .. } in &self.depr_attrs {
 996             if attr.ident().map(|ident| ident.name) == Some(*name) {
 997                 if let &AttributeGate::Gated(
 998                     Stability::Deprecated(link, suggestion),
 999                     name,
1000                     reason,
1001                     _,
1002                 ) = gate
1003                 {
1004                     let msg =
1005                         format!("use of deprecated attribute `{}`: {}. See {}", name, reason, link);
1006                     lint_deprecated_attr(cx, attr, &msg, suggestion);
1007                 }
1008                 return;
1009             }
1010         }
1011         if attr.has_name(sym::no_start) || attr.has_name(sym::crate_id) {
1012             let path_str = pprust::path_to_string(&attr.get_normal_item().path);
1013             let msg = format!("use of deprecated attribute `{}`: no longer used.", path_str);
1014             lint_deprecated_attr(cx, attr, &msg, None);
1015         }
1016     }
1017 }
1018
1019 fn warn_if_doc(cx: &EarlyContext<'_>, node_span: Span, node_kind: &str, attrs: &[ast::Attribute]) {
1020     use rustc_ast::token::CommentKind;
1021
1022     let mut attrs = attrs.iter().peekable();
1023
1024     // Accumulate a single span for sugared doc comments.
1025     let mut sugared_span: Option<Span> = None;
1026
1027     while let Some(attr) = attrs.next() {
1028         let is_doc_comment = attr.is_doc_comment();
1029         if is_doc_comment {
1030             sugared_span =
1031                 Some(sugared_span.map_or(attr.span, |span| span.with_hi(attr.span.hi())));
1032         }
1033
1034         if attrs.peek().map_or(false, |next_attr| next_attr.is_doc_comment()) {
1035             continue;
1036         }
1037
1038         let span = sugared_span.take().unwrap_or(attr.span);
1039
1040         if is_doc_comment || attr.has_name(sym::doc) {
1041             cx.struct_span_lint(UNUSED_DOC_COMMENTS, span, |lint| {
1042                 let mut err = lint.build("unused doc comment");
1043                 err.span_label(
1044                     node_span,
1045                     format!("rustdoc does not generate documentation for {}", node_kind),
1046                 );
1047                 match attr.kind {
1048                     AttrKind::DocComment(CommentKind::Line, _) | AttrKind::Normal(..) => {
1049                         err.help("use `//` for a plain comment");
1050                     }
1051                     AttrKind::DocComment(CommentKind::Block, _) => {
1052                         err.help("use `/* */` for a plain comment");
1053                     }
1054                 }
1055                 err.emit();
1056             });
1057         }
1058     }
1059 }
1060
1061 impl EarlyLintPass for UnusedDocComment {
1062     fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &ast::Stmt) {
1063         let kind = match stmt.kind {
1064             ast::StmtKind::Local(..) => "statements",
1065             // Disabled pending discussion in #78306
1066             ast::StmtKind::Item(..) => return,
1067             // expressions will be reported by `check_expr`.
1068             ast::StmtKind::Empty
1069             | ast::StmtKind::Semi(_)
1070             | ast::StmtKind::Expr(_)
1071             | ast::StmtKind::MacCall(_) => return,
1072         };
1073
1074         warn_if_doc(cx, stmt.span, kind, stmt.kind.attrs());
1075     }
1076
1077     fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) {
1078         let arm_span = arm.pat.span.with_hi(arm.body.span.hi());
1079         warn_if_doc(cx, arm_span, "match arms", &arm.attrs);
1080     }
1081
1082     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
1083         warn_if_doc(cx, expr.span, "expressions", &expr.attrs);
1084     }
1085
1086     fn check_generic_param(&mut self, cx: &EarlyContext<'_>, param: &ast::GenericParam) {
1087         warn_if_doc(cx, param.ident.span, "generic parameters", &param.attrs);
1088     }
1089
1090     fn check_block(&mut self, cx: &EarlyContext<'_>, block: &ast::Block) {
1091         warn_if_doc(cx, block.span, "block", &block.attrs());
1092     }
1093
1094     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) {
1095         if let ast::ItemKind::ForeignMod(_) = item.kind {
1096             warn_if_doc(cx, item.span, "extern block", &item.attrs);
1097         }
1098     }
1099 }
1100
1101 declare_lint! {
1102     /// The `no_mangle_const_items` lint detects any `const` items with the
1103     /// [`no_mangle` attribute].
1104     ///
1105     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1106     ///
1107     /// ### Example
1108     ///
1109     /// ```rust,compile_fail
1110     /// #[no_mangle]
1111     /// const FOO: i32 = 5;
1112     /// ```
1113     ///
1114     /// {{produces}}
1115     ///
1116     /// ### Explanation
1117     ///
1118     /// Constants do not have their symbols exported, and therefore, this
1119     /// probably means you meant to use a [`static`], not a [`const`].
1120     ///
1121     /// [`static`]: https://doc.rust-lang.org/reference/items/static-items.html
1122     /// [`const`]: https://doc.rust-lang.org/reference/items/constant-items.html
1123     NO_MANGLE_CONST_ITEMS,
1124     Deny,
1125     "const items will not have their symbols exported"
1126 }
1127
1128 declare_lint! {
1129     /// The `no_mangle_generic_items` lint detects generic items that must be
1130     /// mangled.
1131     ///
1132     /// ### Example
1133     ///
1134     /// ```rust
1135     /// #[no_mangle]
1136     /// fn foo<T>(t: T) {
1137     ///
1138     /// }
1139     /// ```
1140     ///
1141     /// {{produces}}
1142     ///
1143     /// ### Explanation
1144     ///
1145     /// A function with generics must have its symbol mangled to accommodate
1146     /// the generic parameter. The [`no_mangle` attribute] has no effect in
1147     /// this situation, and should be removed.
1148     ///
1149     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1150     NO_MANGLE_GENERIC_ITEMS,
1151     Warn,
1152     "generic items must be mangled"
1153 }
1154
1155 declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS, NO_MANGLE_GENERIC_ITEMS]);
1156
1157 impl<'tcx> LateLintPass<'tcx> for InvalidNoMangleItems {
1158     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1159         let attrs = cx.tcx.hir().attrs(it.hir_id());
1160         let check_no_mangle_on_generic_fn = |no_mangle_attr: &ast::Attribute,
1161                                              impl_generics: Option<&hir::Generics<'_>>,
1162                                              generics: &hir::Generics<'_>,
1163                                              span| {
1164             for param in
1165                 generics.params.iter().chain(impl_generics.map(|g| g.params).into_iter().flatten())
1166             {
1167                 match param.kind {
1168                     GenericParamKind::Lifetime { .. } => {}
1169                     GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1170                         cx.struct_span_lint(NO_MANGLE_GENERIC_ITEMS, span, |lint| {
1171                             lint.build("functions generic over types or consts must be mangled")
1172                                 .span_suggestion_short(
1173                                     no_mangle_attr.span,
1174                                     "remove this attribute",
1175                                     String::new(),
1176                                     // Use of `#[no_mangle]` suggests FFI intent; correct
1177                                     // fix may be to monomorphize source by hand
1178                                     Applicability::MaybeIncorrect,
1179                                 )
1180                                 .emit();
1181                         });
1182                         break;
1183                     }
1184                 }
1185             }
1186         };
1187         match it.kind {
1188             hir::ItemKind::Fn(.., ref generics, _) => {
1189                 if let Some(no_mangle_attr) = cx.sess().find_by_name(attrs, sym::no_mangle) {
1190                     check_no_mangle_on_generic_fn(no_mangle_attr, None, generics, it.span);
1191                 }
1192             }
1193             hir::ItemKind::Const(..) => {
1194                 if cx.sess().contains_name(attrs, sym::no_mangle) {
1195                     // Const items do not refer to a particular location in memory, and therefore
1196                     // don't have anything to attach a symbol to
1197                     cx.struct_span_lint(NO_MANGLE_CONST_ITEMS, it.span, |lint| {
1198                         let msg = "const items should never be `#[no_mangle]`";
1199                         let mut err = lint.build(msg);
1200
1201                         // account for "pub const" (#45562)
1202                         let start = cx
1203                             .tcx
1204                             .sess
1205                             .source_map()
1206                             .span_to_snippet(it.span)
1207                             .map(|snippet| snippet.find("const").unwrap_or(0))
1208                             .unwrap_or(0) as u32;
1209                         // `const` is 5 chars
1210                         let const_span = it.span.with_hi(BytePos(it.span.lo().0 + start + 5));
1211                         err.span_suggestion(
1212                             const_span,
1213                             "try a static value",
1214                             "pub static".to_owned(),
1215                             Applicability::MachineApplicable,
1216                         );
1217                         err.emit();
1218                     });
1219                 }
1220             }
1221             hir::ItemKind::Impl(hir::Impl { ref generics, items, .. }) => {
1222                 for it in items {
1223                     if let hir::AssocItemKind::Fn { .. } = it.kind {
1224                         if let Some(no_mangle_attr) = cx
1225                             .sess()
1226                             .find_by_name(cx.tcx.hir().attrs(it.id.hir_id()), sym::no_mangle)
1227                         {
1228                             check_no_mangle_on_generic_fn(
1229                                 no_mangle_attr,
1230                                 Some(generics),
1231                                 cx.tcx.hir().get_generics(it.id.def_id).unwrap(),
1232                                 it.span,
1233                             );
1234                         }
1235                     }
1236                 }
1237             }
1238             _ => {}
1239         }
1240     }
1241 }
1242
1243 declare_lint! {
1244     /// The `mutable_transmutes` lint catches transmuting from `&T` to `&mut
1245     /// T` because it is [undefined behavior].
1246     ///
1247     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1248     ///
1249     /// ### Example
1250     ///
1251     /// ```rust,compile_fail
1252     /// unsafe {
1253     ///     let y = std::mem::transmute::<&i32, &mut i32>(&5);
1254     /// }
1255     /// ```
1256     ///
1257     /// {{produces}}
1258     ///
1259     /// ### Explanation
1260     ///
1261     /// Certain assumptions are made about aliasing of data, and this transmute
1262     /// violates those assumptions. Consider using [`UnsafeCell`] instead.
1263     ///
1264     /// [`UnsafeCell`]: https://doc.rust-lang.org/std/cell/struct.UnsafeCell.html
1265     MUTABLE_TRANSMUTES,
1266     Deny,
1267     "transmuting &T to &mut T is undefined behavior, even if the reference is unused"
1268 }
1269
1270 declare_lint_pass!(MutableTransmutes => [MUTABLE_TRANSMUTES]);
1271
1272 impl<'tcx> LateLintPass<'tcx> for MutableTransmutes {
1273     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &hir::Expr<'_>) {
1274         use rustc_target::spec::abi::Abi::RustIntrinsic;
1275         if let Some((&ty::Ref(_, _, from_mt), &ty::Ref(_, _, to_mt))) =
1276             get_transmute_from_to(cx, expr).map(|(ty1, ty2)| (ty1.kind(), ty2.kind()))
1277         {
1278             if to_mt == hir::Mutability::Mut && from_mt == hir::Mutability::Not {
1279                 let msg = "transmuting &T to &mut T is undefined behavior, \
1280                     even if the reference is unused, consider instead using an UnsafeCell";
1281                 cx.struct_span_lint(MUTABLE_TRANSMUTES, expr.span, |lint| lint.build(msg).emit());
1282             }
1283         }
1284
1285         fn get_transmute_from_to<'tcx>(
1286             cx: &LateContext<'tcx>,
1287             expr: &hir::Expr<'_>,
1288         ) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
1289             let def = if let hir::ExprKind::Path(ref qpath) = expr.kind {
1290                 cx.qpath_res(qpath, expr.hir_id)
1291             } else {
1292                 return None;
1293             };
1294             if let Res::Def(DefKind::Fn, did) = def {
1295                 if !def_id_is_transmute(cx, did) {
1296                     return None;
1297                 }
1298                 let sig = cx.typeck_results().node_type(expr.hir_id).fn_sig(cx.tcx);
1299                 let from = sig.inputs().skip_binder()[0];
1300                 let to = sig.output().skip_binder();
1301                 return Some((from, to));
1302             }
1303             None
1304         }
1305
1306         fn def_id_is_transmute(cx: &LateContext<'_>, def_id: DefId) -> bool {
1307             cx.tcx.fn_sig(def_id).abi() == RustIntrinsic
1308                 && cx.tcx.item_name(def_id) == sym::transmute
1309         }
1310     }
1311 }
1312
1313 declare_lint! {
1314     /// The `unstable_features` is deprecated and should no longer be used.
1315     UNSTABLE_FEATURES,
1316     Allow,
1317     "enabling unstable features (deprecated. do not use)"
1318 }
1319
1320 declare_lint_pass!(
1321     /// Forbids using the `#[feature(...)]` attribute
1322     UnstableFeatures => [UNSTABLE_FEATURES]
1323 );
1324
1325 impl<'tcx> LateLintPass<'tcx> for UnstableFeatures {
1326     fn check_attribute(&mut self, cx: &LateContext<'_>, attr: &ast::Attribute) {
1327         if attr.has_name(sym::feature) {
1328             if let Some(items) = attr.meta_item_list() {
1329                 for item in items {
1330                     cx.struct_span_lint(UNSTABLE_FEATURES, item.span(), |lint| {
1331                         lint.build("unstable feature").emit()
1332                     });
1333                 }
1334             }
1335         }
1336     }
1337 }
1338
1339 declare_lint! {
1340     /// The `unreachable_pub` lint triggers for `pub` items not reachable from
1341     /// the crate root.
1342     ///
1343     /// ### Example
1344     ///
1345     /// ```rust,compile_fail
1346     /// #![deny(unreachable_pub)]
1347     /// mod foo {
1348     ///     pub mod bar {
1349     ///
1350     ///     }
1351     /// }
1352     /// ```
1353     ///
1354     /// {{produces}}
1355     ///
1356     /// ### Explanation
1357     ///
1358     /// A bare `pub` visibility may be misleading if the item is not actually
1359     /// publicly exported from the crate. The `pub(crate)` visibility is
1360     /// recommended to be used instead, which more clearly expresses the intent
1361     /// that the item is only visible within its own crate.
1362     ///
1363     /// This lint is "allow" by default because it will trigger for a large
1364     /// amount existing Rust code, and has some false-positives. Eventually it
1365     /// is desired for this to become warn-by-default.
1366     pub UNREACHABLE_PUB,
1367     Allow,
1368     "`pub` items not reachable from crate root"
1369 }
1370
1371 declare_lint_pass!(
1372     /// Lint for items marked `pub` that aren't reachable from other crates.
1373     UnreachablePub => [UNREACHABLE_PUB]
1374 );
1375
1376 impl UnreachablePub {
1377     fn perform_lint(
1378         &self,
1379         cx: &LateContext<'_>,
1380         what: &str,
1381         def_id: LocalDefId,
1382         vis: &hir::Visibility<'_>,
1383         span: Span,
1384         exportable: bool,
1385     ) {
1386         let mut applicability = Applicability::MachineApplicable;
1387         match vis.node {
1388             hir::VisibilityKind::Public if !cx.access_levels.is_reachable(def_id) => {
1389                 if span.from_expansion() {
1390                     applicability = Applicability::MaybeIncorrect;
1391                 }
1392                 let def_span = cx.tcx.sess.source_map().guess_head_span(span);
1393                 cx.struct_span_lint(UNREACHABLE_PUB, def_span, |lint| {
1394                     let mut err = lint.build(&format!("unreachable `pub` {}", what));
1395                     let replacement = if cx.tcx.features().crate_visibility_modifier {
1396                         "crate"
1397                     } else {
1398                         "pub(crate)"
1399                     }
1400                     .to_owned();
1401
1402                     err.span_suggestion(
1403                         vis.span,
1404                         "consider restricting its visibility",
1405                         replacement,
1406                         applicability,
1407                     );
1408                     if exportable {
1409                         err.help("or consider exporting it for use by other crates");
1410                     }
1411                     err.emit();
1412                 });
1413             }
1414             _ => {}
1415         }
1416     }
1417 }
1418
1419 impl<'tcx> LateLintPass<'tcx> for UnreachablePub {
1420     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1421         self.perform_lint(cx, "item", item.def_id, &item.vis, item.span, true);
1422     }
1423
1424     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'tcx>) {
1425         self.perform_lint(
1426             cx,
1427             "item",
1428             foreign_item.def_id,
1429             &foreign_item.vis,
1430             foreign_item.span,
1431             true,
1432         );
1433     }
1434
1435     fn check_field_def(&mut self, cx: &LateContext<'_>, field: &hir::FieldDef<'_>) {
1436         let def_id = cx.tcx.hir().local_def_id(field.hir_id);
1437         self.perform_lint(cx, "field", def_id, &field.vis, field.span, false);
1438     }
1439
1440     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
1441         self.perform_lint(cx, "item", impl_item.def_id, &impl_item.vis, impl_item.span, false);
1442     }
1443 }
1444
1445 declare_lint! {
1446     /// The `type_alias_bounds` lint detects bounds in type aliases.
1447     ///
1448     /// ### Example
1449     ///
1450     /// ```rust
1451     /// type SendVec<T: Send> = Vec<T>;
1452     /// ```
1453     ///
1454     /// {{produces}}
1455     ///
1456     /// ### Explanation
1457     ///
1458     /// The trait bounds in a type alias are currently ignored, and should not
1459     /// be included to avoid confusion. This was previously allowed
1460     /// unintentionally; this may become a hard error in the future.
1461     TYPE_ALIAS_BOUNDS,
1462     Warn,
1463     "bounds in type aliases are not enforced"
1464 }
1465
1466 declare_lint_pass!(
1467     /// Lint for trait and lifetime bounds in type aliases being mostly ignored.
1468     /// They are relevant when using associated types, but otherwise neither checked
1469     /// at definition site nor enforced at use site.
1470     TypeAliasBounds => [TYPE_ALIAS_BOUNDS]
1471 );
1472
1473 impl TypeAliasBounds {
1474     fn is_type_variable_assoc(qpath: &hir::QPath<'_>) -> bool {
1475         match *qpath {
1476             hir::QPath::TypeRelative(ref ty, _) => {
1477                 // If this is a type variable, we found a `T::Assoc`.
1478                 match ty.kind {
1479                     hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
1480                         matches!(path.res, Res::Def(DefKind::TyParam, _))
1481                     }
1482                     _ => false,
1483                 }
1484             }
1485             hir::QPath::Resolved(..) | hir::QPath::LangItem(..) => false,
1486         }
1487     }
1488
1489     fn suggest_changing_assoc_types(ty: &hir::Ty<'_>, err: &mut Diagnostic) {
1490         // Access to associates types should use `<T as Bound>::Assoc`, which does not need a
1491         // bound.  Let's see if this type does that.
1492
1493         // We use a HIR visitor to walk the type.
1494         use rustc_hir::intravisit::{self, Visitor};
1495         struct WalkAssocTypes<'a> {
1496             err: &'a mut Diagnostic,
1497         }
1498         impl Visitor<'_> for WalkAssocTypes<'_> {
1499             fn visit_qpath(&mut self, qpath: &hir::QPath<'_>, id: hir::HirId, span: Span) {
1500                 if TypeAliasBounds::is_type_variable_assoc(qpath) {
1501                     self.err.span_help(
1502                         span,
1503                         "use fully disambiguated paths (i.e., `<T as Trait>::Assoc`) to refer to \
1504                          associated types in type aliases",
1505                     );
1506                 }
1507                 intravisit::walk_qpath(self, qpath, id, span)
1508             }
1509         }
1510
1511         // Let's go for a walk!
1512         let mut visitor = WalkAssocTypes { err };
1513         visitor.visit_ty(ty);
1514     }
1515 }
1516
1517 impl<'tcx> LateLintPass<'tcx> for TypeAliasBounds {
1518     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1519         let hir::ItemKind::TyAlias(ty, type_alias_generics) = &item.kind else {
1520             return
1521         };
1522         if let hir::TyKind::OpaqueDef(..) = ty.kind {
1523             // Bounds are respected for `type X = impl Trait`
1524             return;
1525         }
1526         let mut suggested_changing_assoc_types = false;
1527         // There must not be a where clause
1528         if !type_alias_generics.where_clause.predicates.is_empty() {
1529             cx.lint(
1530                 TYPE_ALIAS_BOUNDS,
1531                 |lint| {
1532                     let mut err = lint.build("where clauses are not enforced in type aliases");
1533                     let spans: Vec<_> = type_alias_generics
1534                         .where_clause
1535                         .predicates
1536                         .iter()
1537                         .map(|pred| pred.span())
1538                         .collect();
1539                     err.set_span(spans);
1540                     err.span_suggestion(
1541                         type_alias_generics.where_clause.span_for_predicates_or_empty_place(),
1542                         "the clause will not be checked when the type alias is used, and should be removed",
1543                         String::new(),
1544                         Applicability::MachineApplicable,
1545                     );
1546                     if !suggested_changing_assoc_types {
1547                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1548                         suggested_changing_assoc_types = true;
1549                     }
1550                     err.emit();
1551                 },
1552             );
1553         }
1554         // The parameters must not have bounds
1555         for param in type_alias_generics.params.iter() {
1556             let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
1557             let suggestion = spans
1558                 .iter()
1559                 .map(|sp| {
1560                     let start = param.span.between(*sp); // Include the `:` in `T: Bound`.
1561                     (start.to(*sp), String::new())
1562                 })
1563                 .collect();
1564             if !spans.is_empty() {
1565                 cx.struct_span_lint(TYPE_ALIAS_BOUNDS, spans, |lint| {
1566                     let mut err =
1567                         lint.build("bounds on generic parameters are not enforced in type aliases");
1568                     let msg = "the bound will not be checked when the type alias is used, \
1569                                    and should be removed";
1570                     err.multipart_suggestion(&msg, suggestion, Applicability::MachineApplicable);
1571                     if !suggested_changing_assoc_types {
1572                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1573                         suggested_changing_assoc_types = true;
1574                     }
1575                     err.emit();
1576                 });
1577             }
1578         }
1579     }
1580 }
1581
1582 declare_lint_pass!(
1583     /// Lint constants that are erroneous.
1584     /// Without this lint, we might not get any diagnostic if the constant is
1585     /// unused within this crate, even though downstream crates can't use it
1586     /// without producing an error.
1587     UnusedBrokenConst => []
1588 );
1589
1590 impl<'tcx> LateLintPass<'tcx> for UnusedBrokenConst {
1591     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1592         match it.kind {
1593             hir::ItemKind::Const(_, body_id) => {
1594                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1595                 // trigger the query once for all constants since that will already report the errors
1596                 // FIXME: Use ensure here
1597                 let _ = cx.tcx.const_eval_poly(def_id);
1598             }
1599             hir::ItemKind::Static(_, _, body_id) => {
1600                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1601                 // FIXME: Use ensure here
1602                 let _ = cx.tcx.eval_static_initializer(def_id);
1603             }
1604             _ => {}
1605         }
1606     }
1607 }
1608
1609 declare_lint! {
1610     /// The `trivial_bounds` lint detects trait bounds that don't depend on
1611     /// any type parameters.
1612     ///
1613     /// ### Example
1614     ///
1615     /// ```rust
1616     /// #![feature(trivial_bounds)]
1617     /// pub struct A where i32: Copy;
1618     /// ```
1619     ///
1620     /// {{produces}}
1621     ///
1622     /// ### Explanation
1623     ///
1624     /// Usually you would not write a trait bound that you know is always
1625     /// true, or never true. However, when using macros, the macro may not
1626     /// know whether or not the constraint would hold or not at the time when
1627     /// generating the code. Currently, the compiler does not alert you if the
1628     /// constraint is always true, and generates an error if it is never true.
1629     /// The `trivial_bounds` feature changes this to be a warning in both
1630     /// cases, giving macros more freedom and flexibility to generate code,
1631     /// while still providing a signal when writing non-macro code that
1632     /// something is amiss.
1633     ///
1634     /// See [RFC 2056] for more details. This feature is currently only
1635     /// available on the nightly channel, see [tracking issue #48214].
1636     ///
1637     /// [RFC 2056]: https://github.com/rust-lang/rfcs/blob/master/text/2056-allow-trivial-where-clause-constraints.md
1638     /// [tracking issue #48214]: https://github.com/rust-lang/rust/issues/48214
1639     TRIVIAL_BOUNDS,
1640     Warn,
1641     "these bounds don't depend on an type parameters"
1642 }
1643
1644 declare_lint_pass!(
1645     /// Lint for trait and lifetime bounds that don't depend on type parameters
1646     /// which either do nothing, or stop the item from being used.
1647     TrivialConstraints => [TRIVIAL_BOUNDS]
1648 );
1649
1650 impl<'tcx> LateLintPass<'tcx> for TrivialConstraints {
1651     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
1652         use rustc_middle::ty::fold::TypeFoldable;
1653         use rustc_middle::ty::PredicateKind::*;
1654
1655         if cx.tcx.features().trivial_bounds {
1656             let predicates = cx.tcx.predicates_of(item.def_id);
1657             for &(predicate, span) in predicates.predicates {
1658                 let predicate_kind_name = match predicate.kind().skip_binder() {
1659                     Trait(..) => "trait",
1660                     TypeOutlives(..) |
1661                     RegionOutlives(..) => "lifetime",
1662
1663                     // Ignore projections, as they can only be global
1664                     // if the trait bound is global
1665                     Projection(..) |
1666                     // Ignore bounds that a user can't type
1667                     WellFormed(..) |
1668                     ObjectSafe(..) |
1669                     ClosureKind(..) |
1670                     Subtype(..) |
1671                     Coerce(..) |
1672                     ConstEvaluatable(..) |
1673                     ConstEquate(..) |
1674                     TypeWellFormedFromEnv(..) => continue,
1675                 };
1676                 if predicate.is_global() {
1677                     cx.struct_span_lint(TRIVIAL_BOUNDS, span, |lint| {
1678                         lint.build(&format!(
1679                             "{} bound {} does not depend on any type \
1680                                 or lifetime parameters",
1681                             predicate_kind_name, predicate
1682                         ))
1683                         .emit()
1684                     });
1685                 }
1686             }
1687         }
1688     }
1689 }
1690
1691 declare_lint_pass!(
1692     /// Does nothing as a lint pass, but registers some `Lint`s
1693     /// which are used by other parts of the compiler.
1694     SoftLints => [
1695         WHILE_TRUE,
1696         BOX_POINTERS,
1697         NON_SHORTHAND_FIELD_PATTERNS,
1698         UNSAFE_CODE,
1699         MISSING_DOCS,
1700         MISSING_COPY_IMPLEMENTATIONS,
1701         MISSING_DEBUG_IMPLEMENTATIONS,
1702         ANONYMOUS_PARAMETERS,
1703         UNUSED_DOC_COMMENTS,
1704         NO_MANGLE_CONST_ITEMS,
1705         NO_MANGLE_GENERIC_ITEMS,
1706         MUTABLE_TRANSMUTES,
1707         UNSTABLE_FEATURES,
1708         UNREACHABLE_PUB,
1709         TYPE_ALIAS_BOUNDS,
1710         TRIVIAL_BOUNDS
1711     ]
1712 );
1713
1714 declare_lint! {
1715     /// The `ellipsis_inclusive_range_patterns` lint detects the [`...` range
1716     /// pattern], which is deprecated.
1717     ///
1718     /// [`...` range pattern]: https://doc.rust-lang.org/reference/patterns.html#range-patterns
1719     ///
1720     /// ### Example
1721     ///
1722     /// ```rust,edition2018
1723     /// let x = 123;
1724     /// match x {
1725     ///     0...100 => {}
1726     ///     _ => {}
1727     /// }
1728     /// ```
1729     ///
1730     /// {{produces}}
1731     ///
1732     /// ### Explanation
1733     ///
1734     /// The `...` range pattern syntax was changed to `..=` to avoid potential
1735     /// confusion with the [`..` range expression]. Use the new form instead.
1736     ///
1737     /// [`..` range expression]: https://doc.rust-lang.org/reference/expressions/range-expr.html
1738     pub ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
1739     Warn,
1740     "`...` range patterns are deprecated",
1741     @future_incompatible = FutureIncompatibleInfo {
1742         reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>",
1743         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
1744     };
1745 }
1746
1747 #[derive(Default)]
1748 pub struct EllipsisInclusiveRangePatterns {
1749     /// If `Some(_)`, suppress all subsequent pattern
1750     /// warnings for better diagnostics.
1751     node_id: Option<ast::NodeId>,
1752 }
1753
1754 impl_lint_pass!(EllipsisInclusiveRangePatterns => [ELLIPSIS_INCLUSIVE_RANGE_PATTERNS]);
1755
1756 impl EarlyLintPass for EllipsisInclusiveRangePatterns {
1757     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &ast::Pat) {
1758         if self.node_id.is_some() {
1759             // Don't recursively warn about patterns inside range endpoints.
1760             return;
1761         }
1762
1763         use self::ast::{PatKind, RangeSyntax::DotDotDot};
1764
1765         /// If `pat` is a `...` pattern, return the start and end of the range, as well as the span
1766         /// corresponding to the ellipsis.
1767         fn matches_ellipsis_pat(pat: &ast::Pat) -> Option<(Option<&Expr>, &Expr, Span)> {
1768             match &pat.kind {
1769                 PatKind::Range(
1770                     a,
1771                     Some(b),
1772                     Spanned { span, node: RangeEnd::Included(DotDotDot) },
1773                 ) => Some((a.as_deref(), b, *span)),
1774                 _ => None,
1775             }
1776         }
1777
1778         let (parenthesise, endpoints) = match &pat.kind {
1779             PatKind::Ref(subpat, _) => (true, matches_ellipsis_pat(&subpat)),
1780             _ => (false, matches_ellipsis_pat(pat)),
1781         };
1782
1783         if let Some((start, end, join)) = endpoints {
1784             let msg = "`...` range patterns are deprecated";
1785             let suggestion = "use `..=` for an inclusive range";
1786             if parenthesise {
1787                 self.node_id = Some(pat.id);
1788                 let end = expr_to_string(&end);
1789                 let replace = match start {
1790                     Some(start) => format!("&({}..={})", expr_to_string(&start), end),
1791                     None => format!("&(..={})", end),
1792                 };
1793                 if join.edition() >= Edition::Edition2021 {
1794                     let mut err =
1795                         rustc_errors::struct_span_err!(cx.sess(), pat.span, E0783, "{}", msg,);
1796                     err.span_suggestion(
1797                         pat.span,
1798                         suggestion,
1799                         replace,
1800                         Applicability::MachineApplicable,
1801                     )
1802                     .emit();
1803                 } else {
1804                     cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, pat.span, |lint| {
1805                         lint.build(msg)
1806                             .span_suggestion(
1807                                 pat.span,
1808                                 suggestion,
1809                                 replace,
1810                                 Applicability::MachineApplicable,
1811                             )
1812                             .emit();
1813                     });
1814                 }
1815             } else {
1816                 let replace = "..=".to_owned();
1817                 if join.edition() >= Edition::Edition2021 {
1818                     let mut err =
1819                         rustc_errors::struct_span_err!(cx.sess(), pat.span, E0783, "{}", msg,);
1820                     err.span_suggestion_short(
1821                         join,
1822                         suggestion,
1823                         replace,
1824                         Applicability::MachineApplicable,
1825                     )
1826                     .emit();
1827                 } else {
1828                     cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, join, |lint| {
1829                         lint.build(msg)
1830                             .span_suggestion_short(
1831                                 join,
1832                                 suggestion,
1833                                 replace,
1834                                 Applicability::MachineApplicable,
1835                             )
1836                             .emit();
1837                     });
1838                 }
1839             };
1840         }
1841     }
1842
1843     fn check_pat_post(&mut self, _cx: &EarlyContext<'_>, pat: &ast::Pat) {
1844         if let Some(node_id) = self.node_id {
1845             if pat.id == node_id {
1846                 self.node_id = None
1847             }
1848         }
1849     }
1850 }
1851
1852 declare_lint! {
1853     /// The `unnameable_test_items` lint detects [`#[test]`][test] functions
1854     /// that are not able to be run by the test harness because they are in a
1855     /// position where they are not nameable.
1856     ///
1857     /// [test]: https://doc.rust-lang.org/reference/attributes/testing.html#the-test-attribute
1858     ///
1859     /// ### Example
1860     ///
1861     /// ```rust,test
1862     /// fn main() {
1863     ///     #[test]
1864     ///     fn foo() {
1865     ///         // This test will not fail because it does not run.
1866     ///         assert_eq!(1, 2);
1867     ///     }
1868     /// }
1869     /// ```
1870     ///
1871     /// {{produces}}
1872     ///
1873     /// ### Explanation
1874     ///
1875     /// In order for the test harness to run a test, the test function must be
1876     /// located in a position where it can be accessed from the crate root.
1877     /// This generally means it must be defined in a module, and not anywhere
1878     /// else such as inside another function. The compiler previously allowed
1879     /// this without an error, so a lint was added as an alert that a test is
1880     /// not being used. Whether or not this should be allowed has not yet been
1881     /// decided, see [RFC 2471] and [issue #36629].
1882     ///
1883     /// [RFC 2471]: https://github.com/rust-lang/rfcs/pull/2471#issuecomment-397414443
1884     /// [issue #36629]: https://github.com/rust-lang/rust/issues/36629
1885     UNNAMEABLE_TEST_ITEMS,
1886     Warn,
1887     "detects an item that cannot be named being marked as `#[test_case]`",
1888     report_in_external_macro
1889 }
1890
1891 pub struct UnnameableTestItems {
1892     boundary: Option<LocalDefId>, // Id of the item under which things are not nameable
1893     items_nameable: bool,
1894 }
1895
1896 impl_lint_pass!(UnnameableTestItems => [UNNAMEABLE_TEST_ITEMS]);
1897
1898 impl UnnameableTestItems {
1899     pub fn new() -> Self {
1900         Self { boundary: None, items_nameable: true }
1901     }
1902 }
1903
1904 impl<'tcx> LateLintPass<'tcx> for UnnameableTestItems {
1905     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1906         if self.items_nameable {
1907             if let hir::ItemKind::Mod(..) = it.kind {
1908             } else {
1909                 self.items_nameable = false;
1910                 self.boundary = Some(it.def_id);
1911             }
1912             return;
1913         }
1914
1915         let attrs = cx.tcx.hir().attrs(it.hir_id());
1916         if let Some(attr) = cx.sess().find_by_name(attrs, sym::rustc_test_marker) {
1917             cx.struct_span_lint(UNNAMEABLE_TEST_ITEMS, attr.span, |lint| {
1918                 lint.build("cannot test inner items").emit()
1919             });
1920         }
1921     }
1922
1923     fn check_item_post(&mut self, _cx: &LateContext<'_>, it: &hir::Item<'_>) {
1924         if !self.items_nameable && self.boundary == Some(it.def_id) {
1925             self.items_nameable = true;
1926         }
1927     }
1928 }
1929
1930 declare_lint! {
1931     /// The `keyword_idents` lint detects edition keywords being used as an
1932     /// identifier.
1933     ///
1934     /// ### Example
1935     ///
1936     /// ```rust,edition2015,compile_fail
1937     /// #![deny(keyword_idents)]
1938     /// // edition 2015
1939     /// fn dyn() {}
1940     /// ```
1941     ///
1942     /// {{produces}}
1943     ///
1944     /// ### Explanation
1945     ///
1946     /// Rust [editions] allow the language to evolve without breaking
1947     /// backwards compatibility. This lint catches code that uses new keywords
1948     /// that are added to the language that are used as identifiers (such as a
1949     /// variable name, function name, etc.). If you switch the compiler to a
1950     /// new edition without updating the code, then it will fail to compile if
1951     /// you are using a new keyword as an identifier.
1952     ///
1953     /// You can manually change the identifiers to a non-keyword, or use a
1954     /// [raw identifier], for example `r#dyn`, to transition to a new edition.
1955     ///
1956     /// This lint solves the problem automatically. It is "allow" by default
1957     /// because the code is perfectly valid in older editions. The [`cargo
1958     /// fix`] tool with the `--edition` flag will switch this lint to "warn"
1959     /// and automatically apply the suggested fix from the compiler (which is
1960     /// to use a raw identifier). This provides a completely automated way to
1961     /// update old code for a new edition.
1962     ///
1963     /// [editions]: https://doc.rust-lang.org/edition-guide/
1964     /// [raw identifier]: https://doc.rust-lang.org/reference/identifiers.html
1965     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
1966     pub KEYWORD_IDENTS,
1967     Allow,
1968     "detects edition keywords being used as an identifier",
1969     @future_incompatible = FutureIncompatibleInfo {
1970         reference: "issue #49716 <https://github.com/rust-lang/rust/issues/49716>",
1971         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
1972     };
1973 }
1974
1975 declare_lint_pass!(
1976     /// Check for uses of edition keywords used as an identifier.
1977     KeywordIdents => [KEYWORD_IDENTS]
1978 );
1979
1980 struct UnderMacro(bool);
1981
1982 impl KeywordIdents {
1983     fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: TokenStream) {
1984         for tt in tokens.into_trees() {
1985             match tt {
1986                 // Only report non-raw idents.
1987                 TokenTree::Token(token) => {
1988                     if let Some((ident, false)) = token.ident() {
1989                         self.check_ident_token(cx, UnderMacro(true), ident);
1990                     }
1991                 }
1992                 TokenTree::Delimited(_, _, tts) => self.check_tokens(cx, tts),
1993             }
1994         }
1995     }
1996
1997     fn check_ident_token(
1998         &mut self,
1999         cx: &EarlyContext<'_>,
2000         UnderMacro(under_macro): UnderMacro,
2001         ident: Ident,
2002     ) {
2003         let next_edition = match cx.sess().edition() {
2004             Edition::Edition2015 => {
2005                 match ident.name {
2006                     kw::Async | kw::Await | kw::Try => Edition::Edition2018,
2007
2008                     // rust-lang/rust#56327: Conservatively do not
2009                     // attempt to report occurrences of `dyn` within
2010                     // macro definitions or invocations, because `dyn`
2011                     // can legitimately occur as a contextual keyword
2012                     // in 2015 code denoting its 2018 meaning, and we
2013                     // do not want rustfix to inject bugs into working
2014                     // code by rewriting such occurrences.
2015                     //
2016                     // But if we see `dyn` outside of a macro, we know
2017                     // its precise role in the parsed AST and thus are
2018                     // assured this is truly an attempt to use it as
2019                     // an identifier.
2020                     kw::Dyn if !under_macro => Edition::Edition2018,
2021
2022                     _ => return,
2023                 }
2024             }
2025
2026             // There are no new keywords yet for the 2018 edition and beyond.
2027             _ => return,
2028         };
2029
2030         // Don't lint `r#foo`.
2031         if cx.sess().parse_sess.raw_identifier_spans.borrow().contains(&ident.span) {
2032             return;
2033         }
2034
2035         cx.struct_span_lint(KEYWORD_IDENTS, ident.span, |lint| {
2036             lint.build(&format!("`{}` is a keyword in the {} edition", ident, next_edition))
2037                 .span_suggestion(
2038                     ident.span,
2039                     "you can use a raw identifier to stay compatible",
2040                     format!("r#{}", ident),
2041                     Applicability::MachineApplicable,
2042                 )
2043                 .emit()
2044         });
2045     }
2046 }
2047
2048 impl EarlyLintPass for KeywordIdents {
2049     fn check_mac_def(&mut self, cx: &EarlyContext<'_>, mac_def: &ast::MacroDef, _id: ast::NodeId) {
2050         self.check_tokens(cx, mac_def.body.inner_tokens());
2051     }
2052     fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::MacCall) {
2053         self.check_tokens(cx, mac.args.inner_tokens());
2054     }
2055     fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: Ident) {
2056         self.check_ident_token(cx, UnderMacro(false), ident);
2057     }
2058 }
2059
2060 declare_lint_pass!(ExplicitOutlivesRequirements => [EXPLICIT_OUTLIVES_REQUIREMENTS]);
2061
2062 impl ExplicitOutlivesRequirements {
2063     fn lifetimes_outliving_lifetime<'tcx>(
2064         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2065         index: u32,
2066     ) -> Vec<ty::Region<'tcx>> {
2067         inferred_outlives
2068             .iter()
2069             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
2070                 ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => match *a {
2071                     ty::ReEarlyBound(ebr) if ebr.index == index => Some(b),
2072                     _ => None,
2073                 },
2074                 _ => None,
2075             })
2076             .collect()
2077     }
2078
2079     fn lifetimes_outliving_type<'tcx>(
2080         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2081         index: u32,
2082     ) -> Vec<ty::Region<'tcx>> {
2083         inferred_outlives
2084             .iter()
2085             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
2086                 ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
2087                     a.is_param(index).then_some(b)
2088                 }
2089                 _ => None,
2090             })
2091             .collect()
2092     }
2093
2094     fn collect_outlived_lifetimes<'tcx>(
2095         &self,
2096         param: &'tcx hir::GenericParam<'tcx>,
2097         tcx: TyCtxt<'tcx>,
2098         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2099         ty_generics: &'tcx ty::Generics,
2100     ) -> Vec<ty::Region<'tcx>> {
2101         let index =
2102             ty_generics.param_def_id_to_index[&tcx.hir().local_def_id(param.hir_id).to_def_id()];
2103
2104         match param.kind {
2105             hir::GenericParamKind::Lifetime { .. } => {
2106                 Self::lifetimes_outliving_lifetime(inferred_outlives, index)
2107             }
2108             hir::GenericParamKind::Type { .. } => {
2109                 Self::lifetimes_outliving_type(inferred_outlives, index)
2110             }
2111             hir::GenericParamKind::Const { .. } => Vec::new(),
2112         }
2113     }
2114
2115     fn collect_outlives_bound_spans<'tcx>(
2116         &self,
2117         tcx: TyCtxt<'tcx>,
2118         bounds: &hir::GenericBounds<'_>,
2119         inferred_outlives: &[ty::Region<'tcx>],
2120         infer_static: bool,
2121     ) -> Vec<(usize, Span)> {
2122         use rustc_middle::middle::resolve_lifetime::Region;
2123
2124         bounds
2125             .iter()
2126             .enumerate()
2127             .filter_map(|(i, bound)| {
2128                 if let hir::GenericBound::Outlives(lifetime) = bound {
2129                     let is_inferred = match tcx.named_region(lifetime.hir_id) {
2130                         Some(Region::Static) if infer_static => {
2131                             inferred_outlives.iter().any(|r| matches!(**r, ty::ReStatic))
2132                         }
2133                         Some(Region::EarlyBound(index, ..)) => inferred_outlives.iter().any(|r| {
2134                             if let ty::ReEarlyBound(ebr) = **r { ebr.index == index } else { false }
2135                         }),
2136                         _ => false,
2137                     };
2138                     is_inferred.then_some((i, bound.span()))
2139                 } else {
2140                     None
2141                 }
2142             })
2143             .collect()
2144     }
2145
2146     fn consolidate_outlives_bound_spans(
2147         &self,
2148         lo: Span,
2149         bounds: &hir::GenericBounds<'_>,
2150         bound_spans: Vec<(usize, Span)>,
2151     ) -> Vec<Span> {
2152         if bounds.is_empty() {
2153             return Vec::new();
2154         }
2155         if bound_spans.len() == bounds.len() {
2156             let (_, last_bound_span) = bound_spans[bound_spans.len() - 1];
2157             // If all bounds are inferable, we want to delete the colon, so
2158             // start from just after the parameter (span passed as argument)
2159             vec![lo.to(last_bound_span)]
2160         } else {
2161             let mut merged = Vec::new();
2162             let mut last_merged_i = None;
2163
2164             let mut from_start = true;
2165             for (i, bound_span) in bound_spans {
2166                 match last_merged_i {
2167                     // If the first bound is inferable, our span should also eat the leading `+`.
2168                     None if i == 0 => {
2169                         merged.push(bound_span.to(bounds[1].span().shrink_to_lo()));
2170                         last_merged_i = Some(0);
2171                     }
2172                     // If consecutive bounds are inferable, merge their spans
2173                     Some(h) if i == h + 1 => {
2174                         if let Some(tail) = merged.last_mut() {
2175                             // Also eat the trailing `+` if the first
2176                             // more-than-one bound is inferable
2177                             let to_span = if from_start && i < bounds.len() {
2178                                 bounds[i + 1].span().shrink_to_lo()
2179                             } else {
2180                                 bound_span
2181                             };
2182                             *tail = tail.to(to_span);
2183                             last_merged_i = Some(i);
2184                         } else {
2185                             bug!("another bound-span visited earlier");
2186                         }
2187                     }
2188                     _ => {
2189                         // When we find a non-inferable bound, subsequent inferable bounds
2190                         // won't be consecutive from the start (and we'll eat the leading
2191                         // `+` rather than the trailing one)
2192                         from_start = false;
2193                         merged.push(bounds[i - 1].span().shrink_to_hi().to(bound_span));
2194                         last_merged_i = Some(i);
2195                     }
2196                 }
2197             }
2198             merged
2199         }
2200     }
2201 }
2202
2203 impl<'tcx> LateLintPass<'tcx> for ExplicitOutlivesRequirements {
2204     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
2205         use rustc_middle::middle::resolve_lifetime::Region;
2206
2207         let infer_static = cx.tcx.features().infer_static_outlives_requirements;
2208         let def_id = item.def_id;
2209         if let hir::ItemKind::Struct(_, ref hir_generics)
2210         | hir::ItemKind::Enum(_, ref hir_generics)
2211         | hir::ItemKind::Union(_, ref hir_generics) = item.kind
2212         {
2213             let inferred_outlives = cx.tcx.inferred_outlives_of(def_id);
2214             if inferred_outlives.is_empty() {
2215                 return;
2216             }
2217
2218             let ty_generics = cx.tcx.generics_of(def_id);
2219
2220             let mut bound_count = 0;
2221             let mut lint_spans = Vec::new();
2222
2223             for param in hir_generics.params {
2224                 let has_lifetime_bounds = param
2225                     .bounds
2226                     .iter()
2227                     .any(|bound| matches!(bound, hir::GenericBound::Outlives(_)));
2228                 if !has_lifetime_bounds {
2229                     continue;
2230                 }
2231
2232                 let relevant_lifetimes =
2233                     self.collect_outlived_lifetimes(param, cx.tcx, inferred_outlives, ty_generics);
2234                 if relevant_lifetimes.is_empty() {
2235                     continue;
2236                 }
2237
2238                 let bound_spans = self.collect_outlives_bound_spans(
2239                     cx.tcx,
2240                     &param.bounds,
2241                     &relevant_lifetimes,
2242                     infer_static,
2243                 );
2244                 bound_count += bound_spans.len();
2245                 lint_spans.extend(self.consolidate_outlives_bound_spans(
2246                     param.span.shrink_to_hi(),
2247                     &param.bounds,
2248                     bound_spans,
2249                 ));
2250             }
2251
2252             let mut where_lint_spans = Vec::new();
2253             let mut dropped_predicate_count = 0;
2254             let num_predicates = hir_generics.where_clause.predicates.len();
2255             for (i, where_predicate) in hir_generics.where_clause.predicates.iter().enumerate() {
2256                 let (relevant_lifetimes, bounds, span) = match where_predicate {
2257                     hir::WherePredicate::RegionPredicate(predicate) => {
2258                         if let Some(Region::EarlyBound(index, ..)) =
2259                             cx.tcx.named_region(predicate.lifetime.hir_id)
2260                         {
2261                             (
2262                                 Self::lifetimes_outliving_lifetime(inferred_outlives, index),
2263                                 &predicate.bounds,
2264                                 predicate.span,
2265                             )
2266                         } else {
2267                             continue;
2268                         }
2269                     }
2270                     hir::WherePredicate::BoundPredicate(predicate) => {
2271                         // FIXME we can also infer bounds on associated types,
2272                         // and should check for them here.
2273                         match predicate.bounded_ty.kind {
2274                             hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
2275                                 let Res::Def(DefKind::TyParam, def_id) = path.res else {
2276                                     continue
2277                                 };
2278                                 let index = ty_generics.param_def_id_to_index[&def_id];
2279                                 (
2280                                     Self::lifetimes_outliving_type(inferred_outlives, index),
2281                                     &predicate.bounds,
2282                                     predicate.span,
2283                                 )
2284                             }
2285                             _ => {
2286                                 continue;
2287                             }
2288                         }
2289                     }
2290                     _ => continue,
2291                 };
2292                 if relevant_lifetimes.is_empty() {
2293                     continue;
2294                 }
2295
2296                 let bound_spans = self.collect_outlives_bound_spans(
2297                     cx.tcx,
2298                     bounds,
2299                     &relevant_lifetimes,
2300                     infer_static,
2301                 );
2302                 bound_count += bound_spans.len();
2303
2304                 let drop_predicate = bound_spans.len() == bounds.len();
2305                 if drop_predicate {
2306                     dropped_predicate_count += 1;
2307                 }
2308
2309                 // If all the bounds on a predicate were inferable and there are
2310                 // further predicates, we want to eat the trailing comma.
2311                 if drop_predicate && i + 1 < num_predicates {
2312                     let next_predicate_span = hir_generics.where_clause.predicates[i + 1].span();
2313                     where_lint_spans.push(span.to(next_predicate_span.shrink_to_lo()));
2314                 } else {
2315                     where_lint_spans.extend(self.consolidate_outlives_bound_spans(
2316                         span.shrink_to_lo(),
2317                         bounds,
2318                         bound_spans,
2319                     ));
2320                 }
2321             }
2322
2323             // If all predicates are inferable, drop the entire clause
2324             // (including the `where`)
2325             if num_predicates > 0 && dropped_predicate_count == num_predicates {
2326                 let where_span = hir_generics
2327                     .where_clause
2328                     .span()
2329                     .expect("span of (nonempty) where clause should exist");
2330                 // Extend the where clause back to the closing `>` of the
2331                 // generics, except for tuple struct, which have the `where`
2332                 // after the fields of the struct.
2333                 let full_where_span =
2334                     if let hir::ItemKind::Struct(hir::VariantData::Tuple(..), _) = item.kind {
2335                         where_span
2336                     } else {
2337                         hir_generics.span.shrink_to_hi().to(where_span)
2338                     };
2339                 lint_spans.push(full_where_span);
2340             } else {
2341                 lint_spans.extend(where_lint_spans);
2342             }
2343
2344             if !lint_spans.is_empty() {
2345                 cx.struct_span_lint(EXPLICIT_OUTLIVES_REQUIREMENTS, lint_spans.clone(), |lint| {
2346                     lint.build("outlives requirements can be inferred")
2347                         .multipart_suggestion(
2348                             if bound_count == 1 {
2349                                 "remove this bound"
2350                             } else {
2351                                 "remove these bounds"
2352                             },
2353                             lint_spans
2354                                 .into_iter()
2355                                 .map(|span| (span, "".to_owned()))
2356                                 .collect::<Vec<_>>(),
2357                             Applicability::MachineApplicable,
2358                         )
2359                         .emit();
2360                 });
2361             }
2362         }
2363     }
2364 }
2365
2366 declare_lint! {
2367     /// The `incomplete_features` lint detects unstable features enabled with
2368     /// the [`feature` attribute] that may function improperly in some or all
2369     /// cases.
2370     ///
2371     /// [`feature` attribute]: https://doc.rust-lang.org/nightly/unstable-book/
2372     ///
2373     /// ### Example
2374     ///
2375     /// ```rust
2376     /// #![feature(generic_const_exprs)]
2377     /// ```
2378     ///
2379     /// {{produces}}
2380     ///
2381     /// ### Explanation
2382     ///
2383     /// Although it is encouraged for people to experiment with unstable
2384     /// features, some of them are known to be incomplete or faulty. This lint
2385     /// is a signal that the feature has not yet been finished, and you may
2386     /// experience problems with it.
2387     pub INCOMPLETE_FEATURES,
2388     Warn,
2389     "incomplete features that may function improperly in some or all cases"
2390 }
2391
2392 declare_lint_pass!(
2393     /// Check for used feature gates in `INCOMPLETE_FEATURES` in `rustc_feature/src/active.rs`.
2394     IncompleteFeatures => [INCOMPLETE_FEATURES]
2395 );
2396
2397 impl EarlyLintPass for IncompleteFeatures {
2398     fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
2399         let features = cx.sess().features_untracked();
2400         features
2401             .declared_lang_features
2402             .iter()
2403             .map(|(name, span, _)| (name, span))
2404             .chain(features.declared_lib_features.iter().map(|(name, span)| (name, span)))
2405             .filter(|(&name, _)| features.incomplete(name))
2406             .for_each(|(&name, &span)| {
2407                 cx.struct_span_lint(INCOMPLETE_FEATURES, span, |lint| {
2408                     let mut builder = lint.build(&format!(
2409                         "the feature `{}` is incomplete and may not be safe to use \
2410                          and/or cause compiler crashes",
2411                         name,
2412                     ));
2413                     if let Some(n) = rustc_feature::find_feature_issue(name, GateIssue::Language) {
2414                         builder.note(&format!(
2415                             "see issue #{} <https://github.com/rust-lang/rust/issues/{}> \
2416                              for more information",
2417                             n, n,
2418                         ));
2419                     }
2420                     if HAS_MIN_FEATURES.contains(&name) {
2421                         builder.help(&format!(
2422                             "consider using `min_{}` instead, which is more stable and complete",
2423                             name,
2424                         ));
2425                     }
2426                     builder.emit();
2427                 })
2428             });
2429     }
2430 }
2431
2432 const HAS_MIN_FEATURES: &[Symbol] = &[sym::specialization];
2433
2434 declare_lint! {
2435     /// The `invalid_value` lint detects creating a value that is not valid,
2436     /// such as a null reference.
2437     ///
2438     /// ### Example
2439     ///
2440     /// ```rust,no_run
2441     /// # #![allow(unused)]
2442     /// unsafe {
2443     ///     let x: &'static i32 = std::mem::zeroed();
2444     /// }
2445     /// ```
2446     ///
2447     /// {{produces}}
2448     ///
2449     /// ### Explanation
2450     ///
2451     /// In some situations the compiler can detect that the code is creating
2452     /// an invalid value, which should be avoided.
2453     ///
2454     /// In particular, this lint will check for improper use of
2455     /// [`mem::zeroed`], [`mem::uninitialized`], [`mem::transmute`], and
2456     /// [`MaybeUninit::assume_init`] that can cause [undefined behavior]. The
2457     /// lint should provide extra information to indicate what the problem is
2458     /// and a possible solution.
2459     ///
2460     /// [`mem::zeroed`]: https://doc.rust-lang.org/std/mem/fn.zeroed.html
2461     /// [`mem::uninitialized`]: https://doc.rust-lang.org/std/mem/fn.uninitialized.html
2462     /// [`mem::transmute`]: https://doc.rust-lang.org/std/mem/fn.transmute.html
2463     /// [`MaybeUninit::assume_init`]: https://doc.rust-lang.org/std/mem/union.MaybeUninit.html#method.assume_init
2464     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
2465     pub INVALID_VALUE,
2466     Warn,
2467     "an invalid value is being created (such as a null reference)"
2468 }
2469
2470 declare_lint_pass!(InvalidValue => [INVALID_VALUE]);
2471
2472 impl<'tcx> LateLintPass<'tcx> for InvalidValue {
2473     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
2474         #[derive(Debug, Copy, Clone, PartialEq)]
2475         enum InitKind {
2476             Zeroed,
2477             Uninit,
2478         }
2479
2480         /// Information about why a type cannot be initialized this way.
2481         /// Contains an error message and optionally a span to point at.
2482         type InitError = (String, Option<Span>);
2483
2484         /// Test if this constant is all-0.
2485         fn is_zero(expr: &hir::Expr<'_>) -> bool {
2486             use hir::ExprKind::*;
2487             use rustc_ast::LitKind::*;
2488             match &expr.kind {
2489                 Lit(lit) => {
2490                     if let Int(i, _) = lit.node {
2491                         i == 0
2492                     } else {
2493                         false
2494                     }
2495                 }
2496                 Tup(tup) => tup.iter().all(is_zero),
2497                 _ => false,
2498             }
2499         }
2500
2501         /// Determine if this expression is a "dangerous initialization".
2502         fn is_dangerous_init(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> Option<InitKind> {
2503             if let hir::ExprKind::Call(ref path_expr, ref args) = expr.kind {
2504                 // Find calls to `mem::{uninitialized,zeroed}` methods.
2505                 if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2506                     let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2507                     match cx.tcx.get_diagnostic_name(def_id) {
2508                         Some(sym::mem_zeroed) => return Some(InitKind::Zeroed),
2509                         Some(sym::mem_uninitialized) => return Some(InitKind::Uninit),
2510                         Some(sym::transmute) if is_zero(&args[0]) => return Some(InitKind::Zeroed),
2511                         _ => {}
2512                     }
2513                 }
2514             } else if let hir::ExprKind::MethodCall(_, ref args, _) = expr.kind {
2515                 // Find problematic calls to `MaybeUninit::assume_init`.
2516                 let def_id = cx.typeck_results().type_dependent_def_id(expr.hir_id)?;
2517                 if cx.tcx.is_diagnostic_item(sym::assume_init, def_id) {
2518                     // This is a call to *some* method named `assume_init`.
2519                     // See if the `self` parameter is one of the dangerous constructors.
2520                     if let hir::ExprKind::Call(ref path_expr, _) = args[0].kind {
2521                         if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2522                             let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2523                             match cx.tcx.get_diagnostic_name(def_id) {
2524                                 Some(sym::maybe_uninit_zeroed) => return Some(InitKind::Zeroed),
2525                                 Some(sym::maybe_uninit_uninit) => return Some(InitKind::Uninit),
2526                                 _ => {}
2527                             }
2528                         }
2529                     }
2530                 }
2531             }
2532
2533             None
2534         }
2535
2536         /// Test if this enum has several actually "existing" variants.
2537         /// Zero-sized uninhabited variants do not always have a tag assigned and thus do not "exist".
2538         fn is_multi_variant(adt: &ty::AdtDef) -> bool {
2539             // As an approximation, we only count dataless variants. Those are definitely inhabited.
2540             let existing_variants = adt.variants.iter().filter(|v| v.fields.is_empty()).count();
2541             existing_variants > 1
2542         }
2543
2544         /// Return `Some` only if we are sure this type does *not*
2545         /// allow zero initialization.
2546         fn ty_find_init_error<'tcx>(
2547             tcx: TyCtxt<'tcx>,
2548             ty: Ty<'tcx>,
2549             init: InitKind,
2550         ) -> Option<InitError> {
2551             use rustc_middle::ty::TyKind::*;
2552             match ty.kind() {
2553                 // Primitive types that don't like 0 as a value.
2554                 Ref(..) => Some(("references must be non-null".to_string(), None)),
2555                 Adt(..) if ty.is_box() => Some(("`Box` must be non-null".to_string(), None)),
2556                 FnPtr(..) => Some(("function pointers must be non-null".to_string(), None)),
2557                 Never => Some(("the `!` type has no valid value".to_string(), None)),
2558                 RawPtr(tm) if matches!(tm.ty.kind(), Dynamic(..)) =>
2559                 // raw ptr to dyn Trait
2560                 {
2561                     Some(("the vtable of a wide raw pointer must be non-null".to_string(), None))
2562                 }
2563                 // Primitive types with other constraints.
2564                 Bool if init == InitKind::Uninit => {
2565                     Some(("booleans must be either `true` or `false`".to_string(), None))
2566                 }
2567                 Char if init == InitKind::Uninit => {
2568                     Some(("characters must be a valid Unicode codepoint".to_string(), None))
2569                 }
2570                 // Recurse and checks for some compound types.
2571                 Adt(adt_def, substs) if !adt_def.is_union() => {
2572                     // First check if this ADT has a layout attribute (like `NonNull` and friends).
2573                     use std::ops::Bound;
2574                     match tcx.layout_scalar_valid_range(adt_def.did) {
2575                         // We exploit here that `layout_scalar_valid_range` will never
2576                         // return `Bound::Excluded`.  (And we have tests checking that we
2577                         // handle the attribute correctly.)
2578                         (Bound::Included(lo), _) if lo > 0 => {
2579                             return Some((format!("`{}` must be non-null", ty), None));
2580                         }
2581                         (Bound::Included(_), _) | (_, Bound::Included(_))
2582                             if init == InitKind::Uninit =>
2583                         {
2584                             return Some((
2585                                 format!(
2586                                     "`{}` must be initialized inside its custom valid range",
2587                                     ty,
2588                                 ),
2589                                 None,
2590                             ));
2591                         }
2592                         _ => {}
2593                     }
2594                     // Now, recurse.
2595                     match adt_def.variants.len() {
2596                         0 => Some(("enums with no variants have no valid value".to_string(), None)),
2597                         1 => {
2598                             // Struct, or enum with exactly one variant.
2599                             // Proceed recursively, check all fields.
2600                             let variant = &adt_def.variants[VariantIdx::from_u32(0)];
2601                             variant.fields.iter().find_map(|field| {
2602                                 ty_find_init_error(tcx, field.ty(tcx, substs), init).map(
2603                                     |(mut msg, span)| {
2604                                         if span.is_none() {
2605                                             // Point to this field, should be helpful for figuring
2606                                             // out where the source of the error is.
2607                                             let span = tcx.def_span(field.did);
2608                                             write!(
2609                                                 &mut msg,
2610                                                 " (in this {} field)",
2611                                                 adt_def.descr()
2612                                             )
2613                                             .unwrap();
2614                                             (msg, Some(span))
2615                                         } else {
2616                                             // Just forward.
2617                                             (msg, span)
2618                                         }
2619                                     },
2620                                 )
2621                             })
2622                         }
2623                         // Multi-variant enum.
2624                         _ => {
2625                             if init == InitKind::Uninit && is_multi_variant(adt_def) {
2626                                 let span = tcx.def_span(adt_def.did);
2627                                 Some((
2628                                     "enums have to be initialized to a variant".to_string(),
2629                                     Some(span),
2630                                 ))
2631                             } else {
2632                                 // In principle, for zero-initialization we could figure out which variant corresponds
2633                                 // to tag 0, and check that... but for now we just accept all zero-initializations.
2634                                 None
2635                             }
2636                         }
2637                     }
2638                 }
2639                 Tuple(..) => {
2640                     // Proceed recursively, check all fields.
2641                     ty.tuple_fields().iter().find_map(|field| ty_find_init_error(tcx, field, init))
2642                 }
2643                 // Conservative fallback.
2644                 _ => None,
2645             }
2646         }
2647
2648         if let Some(init) = is_dangerous_init(cx, expr) {
2649             // This conjures an instance of a type out of nothing,
2650             // using zeroed or uninitialized memory.
2651             // We are extremely conservative with what we warn about.
2652             let conjured_ty = cx.typeck_results().expr_ty(expr);
2653             if let Some((msg, span)) =
2654                 with_no_trimmed_paths!(ty_find_init_error(cx.tcx, conjured_ty, init))
2655             {
2656                 cx.struct_span_lint(INVALID_VALUE, expr.span, |lint| {
2657                     let mut err = lint.build(&format!(
2658                         "the type `{}` does not permit {}",
2659                         conjured_ty,
2660                         match init {
2661                             InitKind::Zeroed => "zero-initialization",
2662                             InitKind::Uninit => "being left uninitialized",
2663                         },
2664                     ));
2665                     err.span_label(expr.span, "this code causes undefined behavior when executed");
2666                     err.span_label(
2667                         expr.span,
2668                         "help: use `MaybeUninit<T>` instead, \
2669                             and only call `assume_init` after initialization is done",
2670                     );
2671                     if let Some(span) = span {
2672                         err.span_note(span, &msg);
2673                     } else {
2674                         err.note(&msg);
2675                     }
2676                     err.emit();
2677                 });
2678             }
2679         }
2680     }
2681 }
2682
2683 declare_lint! {
2684     /// The `clashing_extern_declarations` lint detects when an `extern fn`
2685     /// has been declared with the same name but different types.
2686     ///
2687     /// ### Example
2688     ///
2689     /// ```rust
2690     /// mod m {
2691     ///     extern "C" {
2692     ///         fn foo();
2693     ///     }
2694     /// }
2695     ///
2696     /// extern "C" {
2697     ///     fn foo(_: u32);
2698     /// }
2699     /// ```
2700     ///
2701     /// {{produces}}
2702     ///
2703     /// ### Explanation
2704     ///
2705     /// Because two symbols of the same name cannot be resolved to two
2706     /// different functions at link time, and one function cannot possibly
2707     /// have two types, a clashing extern declaration is almost certainly a
2708     /// mistake. Check to make sure that the `extern` definitions are correct
2709     /// and equivalent, and possibly consider unifying them in one location.
2710     ///
2711     /// This lint does not run between crates because a project may have
2712     /// dependencies which both rely on the same extern function, but declare
2713     /// it in a different (but valid) way. For example, they may both declare
2714     /// an opaque type for one or more of the arguments (which would end up
2715     /// distinct types), or use types that are valid conversions in the
2716     /// language the `extern fn` is defined in. In these cases, the compiler
2717     /// can't say that the clashing declaration is incorrect.
2718     pub CLASHING_EXTERN_DECLARATIONS,
2719     Warn,
2720     "detects when an extern fn has been declared with the same name but different types"
2721 }
2722
2723 pub struct ClashingExternDeclarations {
2724     /// Map of function symbol name to the first-seen hir id for that symbol name.. If seen_decls
2725     /// contains an entry for key K, it means a symbol with name K has been seen by this lint and
2726     /// the symbol should be reported as a clashing declaration.
2727     // FIXME: Technically, we could just store a &'tcx str here without issue; however, the
2728     // `impl_lint_pass` macro doesn't currently support lints parametric over a lifetime.
2729     seen_decls: FxHashMap<Symbol, HirId>,
2730 }
2731
2732 /// Differentiate between whether the name for an extern decl came from the link_name attribute or
2733 /// just from declaration itself. This is important because we don't want to report clashes on
2734 /// symbol name if they don't actually clash because one or the other links against a symbol with a
2735 /// different name.
2736 enum SymbolName {
2737     /// The name of the symbol + the span of the annotation which introduced the link name.
2738     Link(Symbol, Span),
2739     /// No link name, so just the name of the symbol.
2740     Normal(Symbol),
2741 }
2742
2743 impl SymbolName {
2744     fn get_name(&self) -> Symbol {
2745         match self {
2746             SymbolName::Link(s, _) | SymbolName::Normal(s) => *s,
2747         }
2748     }
2749 }
2750
2751 impl ClashingExternDeclarations {
2752     crate fn new() -> Self {
2753         ClashingExternDeclarations { seen_decls: FxHashMap::default() }
2754     }
2755     /// Insert a new foreign item into the seen set. If a symbol with the same name already exists
2756     /// for the item, return its HirId without updating the set.
2757     fn insert(&mut self, tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> Option<HirId> {
2758         let did = fi.def_id.to_def_id();
2759         let instance = Instance::new(did, ty::List::identity_for_item(tcx, did));
2760         let name = Symbol::intern(tcx.symbol_name(instance).name);
2761         if let Some(&hir_id) = self.seen_decls.get(&name) {
2762             // Avoid updating the map with the new entry when we do find a collision. We want to
2763             // make sure we're always pointing to the first definition as the previous declaration.
2764             // This lets us avoid emitting "knock-on" diagnostics.
2765             Some(hir_id)
2766         } else {
2767             self.seen_decls.insert(name, fi.hir_id())
2768         }
2769     }
2770
2771     /// Get the name of the symbol that's linked against for a given extern declaration. That is,
2772     /// the name specified in a #[link_name = ...] attribute if one was specified, else, just the
2773     /// symbol's name.
2774     fn name_of_extern_decl(tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> SymbolName {
2775         if let Some((overridden_link_name, overridden_link_name_span)) =
2776             tcx.codegen_fn_attrs(fi.def_id).link_name.map(|overridden_link_name| {
2777                 // FIXME: Instead of searching through the attributes again to get span
2778                 // information, we could have codegen_fn_attrs also give span information back for
2779                 // where the attribute was defined. However, until this is found to be a
2780                 // bottleneck, this does just fine.
2781                 (
2782                     overridden_link_name,
2783                     tcx.get_attrs(fi.def_id.to_def_id())
2784                         .iter()
2785                         .find(|at| at.has_name(sym::link_name))
2786                         .unwrap()
2787                         .span,
2788                 )
2789             })
2790         {
2791             SymbolName::Link(overridden_link_name, overridden_link_name_span)
2792         } else {
2793             SymbolName::Normal(fi.ident.name)
2794         }
2795     }
2796
2797     /// Checks whether two types are structurally the same enough that the declarations shouldn't
2798     /// clash. We need this so we don't emit a lint when two modules both declare an extern struct,
2799     /// with the same members (as the declarations shouldn't clash).
2800     fn structurally_same_type<'tcx>(
2801         cx: &LateContext<'tcx>,
2802         a: Ty<'tcx>,
2803         b: Ty<'tcx>,
2804         ckind: CItemKind,
2805     ) -> bool {
2806         fn structurally_same_type_impl<'tcx>(
2807             seen_types: &mut FxHashSet<(Ty<'tcx>, Ty<'tcx>)>,
2808             cx: &LateContext<'tcx>,
2809             a: Ty<'tcx>,
2810             b: Ty<'tcx>,
2811             ckind: CItemKind,
2812         ) -> bool {
2813             debug!("structurally_same_type_impl(cx, a = {:?}, b = {:?})", a, b);
2814             let tcx = cx.tcx;
2815
2816             // Given a transparent newtype, reach through and grab the inner
2817             // type unless the newtype makes the type non-null.
2818             let non_transparent_ty = |ty: Ty<'tcx>| -> Ty<'tcx> {
2819                 let mut ty = ty;
2820                 loop {
2821                     if let ty::Adt(def, substs) = *ty.kind() {
2822                         let is_transparent = def.subst(tcx, substs).repr.transparent();
2823                         let is_non_null = crate::types::nonnull_optimization_guaranteed(tcx, &def);
2824                         debug!(
2825                             "non_transparent_ty({:?}) -- type is transparent? {}, type is non-null? {}",
2826                             ty, is_transparent, is_non_null
2827                         );
2828                         if is_transparent && !is_non_null {
2829                             debug_assert!(def.variants.len() == 1);
2830                             let v = &def.variants[VariantIdx::new(0)];
2831                             ty = transparent_newtype_field(tcx, v)
2832                                 .expect(
2833                                     "single-variant transparent structure with zero-sized field",
2834                                 )
2835                                 .ty(tcx, substs);
2836                             continue;
2837                         }
2838                     }
2839                     debug!("non_transparent_ty -> {:?}", ty);
2840                     return ty;
2841                 }
2842             };
2843
2844             let a = non_transparent_ty(a);
2845             let b = non_transparent_ty(b);
2846
2847             if !seen_types.insert((a, b)) {
2848                 // We've encountered a cycle. There's no point going any further -- the types are
2849                 // structurally the same.
2850                 return true;
2851             }
2852             let tcx = cx.tcx;
2853             if a == b {
2854                 // All nominally-same types are structurally same, too.
2855                 true
2856             } else {
2857                 // Do a full, depth-first comparison between the two.
2858                 use rustc_middle::ty::TyKind::*;
2859                 let a_kind = a.kind();
2860                 let b_kind = b.kind();
2861
2862                 let compare_layouts = |a, b| -> Result<bool, LayoutError<'tcx>> {
2863                     debug!("compare_layouts({:?}, {:?})", a, b);
2864                     let a_layout = &cx.layout_of(a)?.layout.abi;
2865                     let b_layout = &cx.layout_of(b)?.layout.abi;
2866                     debug!(
2867                         "comparing layouts: {:?} == {:?} = {}",
2868                         a_layout,
2869                         b_layout,
2870                         a_layout == b_layout
2871                     );
2872                     Ok(a_layout == b_layout)
2873                 };
2874
2875                 #[allow(rustc::usage_of_ty_tykind)]
2876                 let is_primitive_or_pointer = |kind: &ty::TyKind<'_>| {
2877                     kind.is_primitive() || matches!(kind, RawPtr(..) | Ref(..))
2878                 };
2879
2880                 ensure_sufficient_stack(|| {
2881                     match (a_kind, b_kind) {
2882                         (Adt(a_def, a_substs), Adt(b_def, b_substs)) => {
2883                             let a = a.subst(cx.tcx, a_substs);
2884                             let b = b.subst(cx.tcx, b_substs);
2885                             debug!("Comparing {:?} and {:?}", a, b);
2886
2887                             // We can immediately rule out these types as structurally same if
2888                             // their layouts differ.
2889                             match compare_layouts(a, b) {
2890                                 Ok(false) => return false,
2891                                 _ => (), // otherwise, continue onto the full, fields comparison
2892                             }
2893
2894                             // Grab a flattened representation of all fields.
2895                             let a_fields = a_def.variants.iter().flat_map(|v| v.fields.iter());
2896                             let b_fields = b_def.variants.iter().flat_map(|v| v.fields.iter());
2897
2898                             // Perform a structural comparison for each field.
2899                             a_fields.eq_by(
2900                                 b_fields,
2901                                 |&ty::FieldDef { did: a_did, .. },
2902                                  &ty::FieldDef { did: b_did, .. }| {
2903                                     structurally_same_type_impl(
2904                                         seen_types,
2905                                         cx,
2906                                         tcx.type_of(a_did),
2907                                         tcx.type_of(b_did),
2908                                         ckind,
2909                                     )
2910                                 },
2911                             )
2912                         }
2913                         (Array(a_ty, a_const), Array(b_ty, b_const)) => {
2914                             // For arrays, we also check the constness of the type.
2915                             a_const.val() == b_const.val()
2916                                 && structurally_same_type_impl(seen_types, cx, *a_ty, *b_ty, ckind)
2917                         }
2918                         (Slice(a_ty), Slice(b_ty)) => {
2919                             structurally_same_type_impl(seen_types, cx, *a_ty, *b_ty, ckind)
2920                         }
2921                         (RawPtr(a_tymut), RawPtr(b_tymut)) => {
2922                             a_tymut.mutbl == b_tymut.mutbl
2923                                 && structurally_same_type_impl(
2924                                     seen_types, cx, a_tymut.ty, b_tymut.ty, ckind,
2925                                 )
2926                         }
2927                         (Ref(_a_region, a_ty, a_mut), Ref(_b_region, b_ty, b_mut)) => {
2928                             // For structural sameness, we don't need the region to be same.
2929                             a_mut == b_mut
2930                                 && structurally_same_type_impl(seen_types, cx, *a_ty, *b_ty, ckind)
2931                         }
2932                         (FnDef(..), FnDef(..)) => {
2933                             let a_poly_sig = a.fn_sig(tcx);
2934                             let b_poly_sig = b.fn_sig(tcx);
2935
2936                             // As we don't compare regions, skip_binder is fine.
2937                             let a_sig = a_poly_sig.skip_binder();
2938                             let b_sig = b_poly_sig.skip_binder();
2939
2940                             (a_sig.abi, a_sig.unsafety, a_sig.c_variadic)
2941                                 == (b_sig.abi, b_sig.unsafety, b_sig.c_variadic)
2942                                 && a_sig.inputs().iter().eq_by(b_sig.inputs().iter(), |a, b| {
2943                                     structurally_same_type_impl(seen_types, cx, *a, *b, ckind)
2944                                 })
2945                                 && structurally_same_type_impl(
2946                                     seen_types,
2947                                     cx,
2948                                     a_sig.output(),
2949                                     b_sig.output(),
2950                                     ckind,
2951                                 )
2952                         }
2953                         (Tuple(a_substs), Tuple(b_substs)) => {
2954                             a_substs.iter().eq_by(b_substs.iter(), |a_ty, b_ty| {
2955                                 structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2956                             })
2957                         }
2958                         // For these, it's not quite as easy to define structural-sameness quite so easily.
2959                         // For the purposes of this lint, take the conservative approach and mark them as
2960                         // not structurally same.
2961                         (Dynamic(..), Dynamic(..))
2962                         | (Error(..), Error(..))
2963                         | (Closure(..), Closure(..))
2964                         | (Generator(..), Generator(..))
2965                         | (GeneratorWitness(..), GeneratorWitness(..))
2966                         | (Projection(..), Projection(..))
2967                         | (Opaque(..), Opaque(..)) => false,
2968
2969                         // These definitely should have been caught above.
2970                         (Bool, Bool) | (Char, Char) | (Never, Never) | (Str, Str) => unreachable!(),
2971
2972                         // An Adt and a primitive or pointer type. This can be FFI-safe if non-null
2973                         // enum layout optimisation is being applied.
2974                         (Adt(..), other_kind) | (other_kind, Adt(..))
2975                             if is_primitive_or_pointer(other_kind) =>
2976                         {
2977                             let (primitive, adt) =
2978                                 if is_primitive_or_pointer(a.kind()) { (a, b) } else { (b, a) };
2979                             if let Some(ty) = crate::types::repr_nullable_ptr(cx, adt, ckind) {
2980                                 ty == primitive
2981                             } else {
2982                                 compare_layouts(a, b).unwrap_or(false)
2983                             }
2984                         }
2985                         // Otherwise, just compare the layouts. This may fail to lint for some
2986                         // incompatible types, but at the very least, will stop reads into
2987                         // uninitialised memory.
2988                         _ => compare_layouts(a, b).unwrap_or(false),
2989                     }
2990                 })
2991             }
2992         }
2993         let mut seen_types = FxHashSet::default();
2994         structurally_same_type_impl(&mut seen_types, cx, a, b, ckind)
2995     }
2996 }
2997
2998 impl_lint_pass!(ClashingExternDeclarations => [CLASHING_EXTERN_DECLARATIONS]);
2999
3000 impl<'tcx> LateLintPass<'tcx> for ClashingExternDeclarations {
3001     fn check_foreign_item(&mut self, cx: &LateContext<'tcx>, this_fi: &hir::ForeignItem<'_>) {
3002         trace!("ClashingExternDeclarations: check_foreign_item: {:?}", this_fi);
3003         if let ForeignItemKind::Fn(..) = this_fi.kind {
3004             let tcx = cx.tcx;
3005             if let Some(existing_hid) = self.insert(tcx, this_fi) {
3006                 let existing_decl_ty = tcx.type_of(tcx.hir().local_def_id(existing_hid));
3007                 let this_decl_ty = tcx.type_of(this_fi.def_id);
3008                 debug!(
3009                     "ClashingExternDeclarations: Comparing existing {:?}: {:?} to this {:?}: {:?}",
3010                     existing_hid, existing_decl_ty, this_fi.def_id, this_decl_ty
3011                 );
3012                 // Check that the declarations match.
3013                 if !Self::structurally_same_type(
3014                     cx,
3015                     existing_decl_ty,
3016                     this_decl_ty,
3017                     CItemKind::Declaration,
3018                 ) {
3019                     let orig_fi = tcx.hir().expect_foreign_item(existing_hid.expect_owner());
3020                     let orig = Self::name_of_extern_decl(tcx, orig_fi);
3021
3022                     // We want to ensure that we use spans for both decls that include where the
3023                     // name was defined, whether that was from the link_name attribute or not.
3024                     let get_relevant_span =
3025                         |fi: &hir::ForeignItem<'_>| match Self::name_of_extern_decl(tcx, fi) {
3026                             SymbolName::Normal(_) => fi.span,
3027                             SymbolName::Link(_, annot_span) => fi.span.to(annot_span),
3028                         };
3029                     // Finally, emit the diagnostic.
3030                     tcx.struct_span_lint_hir(
3031                         CLASHING_EXTERN_DECLARATIONS,
3032                         this_fi.hir_id(),
3033                         get_relevant_span(this_fi),
3034                         |lint| {
3035                             let mut expected_str = DiagnosticStyledString::new();
3036                             expected_str.push(existing_decl_ty.fn_sig(tcx).to_string(), false);
3037                             let mut found_str = DiagnosticStyledString::new();
3038                             found_str.push(this_decl_ty.fn_sig(tcx).to_string(), true);
3039
3040                             lint.build(&format!(
3041                                 "`{}` redeclare{} with a different signature",
3042                                 this_fi.ident.name,
3043                                 if orig.get_name() == this_fi.ident.name {
3044                                     "d".to_string()
3045                                 } else {
3046                                     format!("s `{}`", orig.get_name())
3047                                 }
3048                             ))
3049                             .span_label(
3050                                 get_relevant_span(orig_fi),
3051                                 &format!("`{}` previously declared here", orig.get_name()),
3052                             )
3053                             .span_label(
3054                                 get_relevant_span(this_fi),
3055                                 "this signature doesn't match the previous declaration",
3056                             )
3057                             .note_expected_found(&"", expected_str, &"", found_str)
3058                             .emit()
3059                         },
3060                     );
3061                 }
3062             }
3063         }
3064     }
3065 }
3066
3067 declare_lint! {
3068     /// The `deref_nullptr` lint detects when an null pointer is dereferenced,
3069     /// which causes [undefined behavior].
3070     ///
3071     /// ### Example
3072     ///
3073     /// ```rust,no_run
3074     /// # #![allow(unused)]
3075     /// use std::ptr;
3076     /// unsafe {
3077     ///     let x = &*ptr::null::<i32>();
3078     ///     let x = ptr::addr_of!(*ptr::null::<i32>());
3079     ///     let x = *(0 as *const i32);
3080     /// }
3081     /// ```
3082     ///
3083     /// {{produces}}
3084     ///
3085     /// ### Explanation
3086     ///
3087     /// Dereferencing a null pointer causes [undefined behavior] even as a place expression,
3088     /// like `&*(0 as *const i32)` or `addr_of!(*(0 as *const i32))`.
3089     ///
3090     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
3091     pub DEREF_NULLPTR,
3092     Warn,
3093     "detects when an null pointer is dereferenced"
3094 }
3095
3096 declare_lint_pass!(DerefNullPtr => [DEREF_NULLPTR]);
3097
3098 impl<'tcx> LateLintPass<'tcx> for DerefNullPtr {
3099     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
3100         /// test if expression is a null ptr
3101         fn is_null_ptr(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> bool {
3102             match &expr.kind {
3103                 rustc_hir::ExprKind::Cast(ref expr, ref ty) => {
3104                     if let rustc_hir::TyKind::Ptr(_) = ty.kind {
3105                         return is_zero(expr) || is_null_ptr(cx, expr);
3106                     }
3107                 }
3108                 // check for call to `core::ptr::null` or `core::ptr::null_mut`
3109                 rustc_hir::ExprKind::Call(ref path, _) => {
3110                     if let rustc_hir::ExprKind::Path(ref qpath) = path.kind {
3111                         if let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id() {
3112                             return matches!(
3113                                 cx.tcx.get_diagnostic_name(def_id),
3114                                 Some(sym::ptr_null | sym::ptr_null_mut)
3115                             );
3116                         }
3117                     }
3118                 }
3119                 _ => {}
3120             }
3121             false
3122         }
3123
3124         /// test if expression is the literal `0`
3125         fn is_zero(expr: &hir::Expr<'_>) -> bool {
3126             match &expr.kind {
3127                 rustc_hir::ExprKind::Lit(ref lit) => {
3128                     if let LitKind::Int(a, _) = lit.node {
3129                         return a == 0;
3130                     }
3131                 }
3132                 _ => {}
3133             }
3134             false
3135         }
3136
3137         if let rustc_hir::ExprKind::Unary(rustc_hir::UnOp::Deref, expr_deref) = expr.kind {
3138             if is_null_ptr(cx, expr_deref) {
3139                 cx.struct_span_lint(DEREF_NULLPTR, expr.span, |lint| {
3140                     let mut err = lint.build("dereferencing a null pointer");
3141                     err.span_label(expr.span, "this code causes undefined behavior when executed");
3142                     err.emit();
3143                 });
3144             }
3145         }
3146     }
3147 }
3148
3149 declare_lint! {
3150     /// The `named_asm_labels` lint detects the use of named labels in the
3151     /// inline `asm!` macro.
3152     ///
3153     /// ### Example
3154     ///
3155     /// ```rust,compile_fail
3156     /// use std::arch::asm;
3157     ///
3158     /// fn main() {
3159     ///     unsafe {
3160     ///         asm!("foo: bar");
3161     ///     }
3162     /// }
3163     /// ```
3164     ///
3165     /// {{produces}}
3166     ///
3167     /// ### Explanation
3168     ///
3169     /// LLVM is allowed to duplicate inline assembly blocks for any
3170     /// reason, for example when it is in a function that gets inlined. Because
3171     /// of this, GNU assembler [local labels] *must* be used instead of labels
3172     /// with a name. Using named labels might cause assembler or linker errors.
3173     ///
3174     /// See the explanation in [Rust By Example] for more details.
3175     ///
3176     /// [local labels]: https://sourceware.org/binutils/docs/as/Symbol-Names.html#Local-Labels
3177     /// [Rust By Example]: https://doc.rust-lang.org/nightly/rust-by-example/unsafe/asm.html#labels
3178     pub NAMED_ASM_LABELS,
3179     Deny,
3180     "named labels in inline assembly",
3181 }
3182
3183 declare_lint_pass!(NamedAsmLabels => [NAMED_ASM_LABELS]);
3184
3185 impl<'tcx> LateLintPass<'tcx> for NamedAsmLabels {
3186     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
3187         if let hir::Expr {
3188             kind: hir::ExprKind::InlineAsm(hir::InlineAsm { template_strs, .. }),
3189             ..
3190         } = expr
3191         {
3192             for (template_sym, template_snippet, template_span) in template_strs.iter() {
3193                 let template_str = template_sym.as_str();
3194                 let find_label_span = |needle: &str| -> Option<Span> {
3195                     if let Some(template_snippet) = template_snippet {
3196                         let snippet = template_snippet.as_str();
3197                         if let Some(pos) = snippet.find(needle) {
3198                             let end = pos
3199                                 + snippet[pos..]
3200                                     .find(|c| c == ':')
3201                                     .unwrap_or(snippet[pos..].len() - 1);
3202                             let inner = InnerSpan::new(pos, end);
3203                             return Some(template_span.from_inner(inner));
3204                         }
3205                     }
3206
3207                     None
3208                 };
3209
3210                 let mut found_labels = Vec::new();
3211
3212                 // A semicolon might not actually be specified as a separator for all targets, but it seems like LLVM accepts it always
3213                 let statements = template_str.split(|c| matches!(c, '\n' | ';'));
3214                 for statement in statements {
3215                     // If there's a comment, trim it from the statement
3216                     let statement = statement.find("//").map_or(statement, |idx| &statement[..idx]);
3217                     let mut start_idx = 0;
3218                     for (idx, _) in statement.match_indices(':') {
3219                         let possible_label = statement[start_idx..idx].trim();
3220                         let mut chars = possible_label.chars();
3221                         let Some(c) = chars.next() else {
3222                             // Empty string means a leading ':' in this section, which is not a label
3223                             break
3224                         };
3225                         // A label starts with an alphabetic character or . or _ and continues with alphanumeric characters, _, or $
3226                         if (c.is_alphabetic() || matches!(c, '.' | '_'))
3227                             && chars.all(|c| c.is_alphanumeric() || matches!(c, '_' | '$'))
3228                         {
3229                             found_labels.push(possible_label);
3230                         } else {
3231                             // If we encounter a non-label, there cannot be any further labels, so stop checking
3232                             break;
3233                         }
3234
3235                         start_idx = idx + 1;
3236                     }
3237                 }
3238
3239                 debug!("NamedAsmLabels::check_expr(): found_labels: {:#?}", &found_labels);
3240
3241                 if found_labels.len() > 0 {
3242                     let spans = found_labels
3243                         .into_iter()
3244                         .filter_map(|label| find_label_span(label))
3245                         .collect::<Vec<Span>>();
3246                     // If there were labels but we couldn't find a span, combine the warnings and use the template span
3247                     let target_spans: MultiSpan =
3248                         if spans.len() > 0 { spans.into() } else { (*template_span).into() };
3249
3250                     cx.lookup_with_diagnostics(
3251                             NAMED_ASM_LABELS,
3252                             Some(target_spans),
3253                             |diag| {
3254                                 let mut err =
3255                                     diag.build("avoid using named labels in inline assembly");
3256                                 err.emit();
3257                             },
3258                             BuiltinLintDiagnostics::NamedAsmLabel(
3259                                 "only local labels of the form `<number>:` should be used in inline asm"
3260                                     .to_string(),
3261                             ),
3262                         );
3263                 }
3264             }
3265         }
3266     }
3267 }