compiler/rustc_lint/src/builtin.rs

   1 //! Lints in the Rust compiler.
   2 //!
   3 //! This contains lints which can feasibly be implemented as their own
   4 //! AST visitor. Also see `rustc_session::lint::builtin`, which contains the
   5 //! definitions of lints that are emitted directly inside the main compiler.
   6 //!
   7 //! To add a new lint to rustc, declare it here using `declare_lint!()`.
   8 //! Then add code to emit the new lint in the appropriate circumstances.
   9 //! You can do that in an existing `LintPass` if it makes sense, or in a
  10 //! new `LintPass`, or using `Session::add_lint` elsewhere in the
  11 //! compiler. Only do the latter if the check can't be written cleanly as a
  12 //! `LintPass` (also, note that such lints will need to be defined in
  13 //! `rustc_session::lint::builtin`, not here).
  14 //!
  15 //! If you define a new `EarlyLintPass`, you will also need to add it to the
  16 //! `add_early_builtin!` or `add_early_builtin_with_new!` invocation in
  17 //! `lib.rs`. Use the former for unit-like structs and the latter for structs
  18 //! with a `pub fn new()`.
  19 //!
  20 //! If you define a new `LateLintPass`, you will also need to add it to the
  21 //! `late_lint_methods!` invocation in `lib.rs`.
  22
  23 use crate::{
  24     types::{transparent_newtype_field, CItemKind},
  25     EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext,
  26 };
  27 use rustc_ast::attr;
  28 use rustc_ast::tokenstream::{TokenStream, TokenTree};
  29 use rustc_ast::visit::{FnCtxt, FnKind};
  30 use rustc_ast::{self as ast, *};
  31 use rustc_ast_pretty::pprust::{self, expr_to_string};
  32 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
  33 use rustc_data_structures::stack::ensure_sufficient_stack;
  34 use rustc_errors::{Applicability, DiagnosticBuilder, DiagnosticStyledString};
  35 use rustc_feature::{deprecated_attributes, AttributeGate, BuiltinAttribute, GateIssue, Stability};
  36 use rustc_hir as hir;
  37 use rustc_hir::def::{DefKind, Res};
  38 use rustc_hir::def_id::{DefId, LocalDefId, LocalDefIdSet, CRATE_DEF_ID};
  39 use rustc_hir::{ForeignItemKind, GenericParamKind, PatKind};
  40 use rustc_hir::{HirId, Node};
  41 use rustc_index::vec::Idx;
  42 use rustc_middle::lint::LintDiagnosticBuilder;
  43 use rustc_middle::ty::layout::{LayoutError, LayoutOf};
  44 use rustc_middle::ty::print::with_no_trimmed_paths;
  45 use rustc_middle::ty::subst::{GenericArgKind, Subst};
  46 use rustc_middle::ty::Instance;
  47 use rustc_middle::ty::{self, Ty, TyCtxt};
  48 use rustc_session::lint::{BuiltinLintDiagnostics, FutureIncompatibilityReason};
  49 use rustc_span::edition::Edition;
  50 use rustc_span::source_map::Spanned;
  51 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  52 use rustc_span::{BytePos, InnerSpan, MultiSpan, Span};
  53 use rustc_target::abi::VariantIdx;
  54 use rustc_trait_selection::traits::misc::can_type_implement_copy;
  55
  56 use crate::nonstandard_style::{method_context, MethodLateContext};
  57
  58 use std::fmt::Write;
  59 use tracing::{debug, trace};
  60
  61 // hardwired lints from librustc_middle
  62 pub use rustc_session::lint::builtin::*;
  63
  64 declare_lint! {
  65     /// The `while_true` lint detects `while true { }`.
  66     ///
  67     /// ### Example
  68     ///
  69     /// ```rust,no_run
  70     /// while true {
  71     ///
  72     /// }
  73     /// ```
  74     ///
  75     /// {{produces}}
  76     ///
  77     /// ### Explanation
  78     ///
  79     /// `while true` should be replaced with `loop`. A `loop` expression is
  80     /// the preferred way to write an infinite loop because it more directly
  81     /// expresses the intent of the loop.
  82     WHILE_TRUE,
  83     Warn,
  84     "suggest using `loop { }` instead of `while true { }`"
  85 }
  86
  87 declare_lint_pass!(WhileTrue => [WHILE_TRUE]);
  88
  89 /// Traverse through any amount of parenthesis and return the first non-parens expression.
  90 fn pierce_parens(mut expr: &ast::Expr) -> &ast::Expr {
  91     while let ast::ExprKind::Paren(sub) = &expr.kind {
  92         expr = sub;
  93     }
  94     expr
  95 }
  96
  97 impl EarlyLintPass for WhileTrue {
  98     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
  99         if let ast::ExprKind::While(cond, _, label) = &e.kind {
 100             if let ast::ExprKind::Lit(ref lit) = pierce_parens(cond).kind {
 101                 if let ast::LitKind::Bool(true) = lit.kind {
 102                     if !lit.span.from_expansion() {
 103                         let msg = "denote infinite loops with `loop { ... }`";
 104                         let condition_span = e.span.with_hi(cond.span.hi());
 105                         cx.struct_span_lint(WHILE_TRUE, condition_span, |lint| {
 106                             lint.build(msg)
 107                                 .span_suggestion_short(
 108                                     condition_span,
 109                                     "use `loop`",
 110                                     format!(
 111                                         "{}loop",
 112                                         label.map_or_else(String::new, |label| format!(
 113                                             "{}: ",
 114                                             label.ident,
 115                                         ))
 116                                     ),
 117                                     Applicability::MachineApplicable,
 118                                 )
 119                                 .emit();
 120                         })
 121                     }
 122                 }
 123             }
 124         }
 125     }
 126 }
 127
 128 declare_lint! {
 129     /// The `box_pointers` lints use of the Box type.
 130     ///
 131     /// ### Example
 132     ///
 133     /// ```rust,compile_fail
 134     /// #![deny(box_pointers)]
 135     /// struct Foo {
 136     ///     x: Box<isize>,
 137     /// }
 138     /// ```
 139     ///
 140     /// {{produces}}
 141     ///
 142     /// ### Explanation
 143     ///
 144     /// This lint is mostly historical, and not particularly useful. `Box<T>`
 145     /// used to be built into the language, and the only way to do heap
 146     /// allocation. Today's Rust can call into other allocators, etc.
 147     BOX_POINTERS,
 148     Allow,
 149     "use of owned (Box type) heap memory"
 150 }
 151
 152 declare_lint_pass!(BoxPointers => [BOX_POINTERS]);
 153
 154 impl BoxPointers {
 155     fn check_heap_type<'tcx>(&self, cx: &LateContext<'tcx>, span: Span, ty: Ty<'tcx>) {
 156         for leaf in ty.walk(cx.tcx) {
 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 hir_id = cx.tcx.hir().local_def_id_to_hir_id(def_id);
 614                 let Some(Node::Item(item)) = cx.tcx.hir().find(hir_id) else { return };
 615                 if let hir::VisibilityKind::Inherited = item.vis.node {
 616                     for impl_item_ref in items {
 617                         self.private_traits.insert(impl_item_ref.id.hir_id());
 618                     }
 619                 }
 620                 return;
 621             }
 622
 623             hir::ItemKind::TyAlias(..)
 624             | hir::ItemKind::Fn(..)
 625             | hir::ItemKind::Macro(..)
 626             | hir::ItemKind::Mod(..)
 627             | hir::ItemKind::Enum(..)
 628             | hir::ItemKind::Struct(..)
 629             | hir::ItemKind::Union(..)
 630             | hir::ItemKind::Const(..)
 631             | hir::ItemKind::Static(..) => {}
 632
 633             _ => return,
 634         };
 635
 636         let (article, desc) = cx.tcx.article_and_description(it.def_id.to_def_id());
 637
 638         self.check_missing_docs_attrs(cx, it.def_id, it.span, article, desc);
 639     }
 640
 641     fn check_trait_item(&mut self, cx: &LateContext<'_>, trait_item: &hir::TraitItem<'_>) {
 642         if self.private_traits.contains(&trait_item.hir_id()) {
 643             return;
 644         }
 645
 646         let (article, desc) = cx.tcx.article_and_description(trait_item.def_id.to_def_id());
 647
 648         self.check_missing_docs_attrs(cx, trait_item.def_id, trait_item.span, article, desc);
 649     }
 650
 651     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
 652         // If the method is an impl for a trait, don't doc.
 653         if method_context(cx, impl_item.hir_id()) == MethodLateContext::TraitImpl {
 654             return;
 655         }
 656
 657         // If the method is an impl for an item with docs_hidden, don't doc.
 658         if method_context(cx, impl_item.hir_id()) == MethodLateContext::PlainImpl {
 659             let parent = cx.tcx.hir().get_parent_did(impl_item.hir_id());
 660             let impl_ty = cx.tcx.type_of(parent);
 661             let outerdef = match impl_ty.kind() {
 662                 ty::Adt(def, _) => Some(def.did),
 663                 ty::Foreign(def_id) => Some(*def_id),
 664                 _ => None,
 665             };
 666             let is_hidden = match outerdef {
 667                 Some(id) => cx.tcx.is_doc_hidden(id),
 668                 None => false,
 669             };
 670             if is_hidden {
 671                 return;
 672             }
 673         }
 674
 675         let (article, desc) = cx.tcx.article_and_description(impl_item.def_id.to_def_id());
 676         self.check_missing_docs_attrs(cx, impl_item.def_id, impl_item.span, article, desc);
 677     }
 678
 679     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'_>) {
 680         let (article, desc) = cx.tcx.article_and_description(foreign_item.def_id.to_def_id());
 681         self.check_missing_docs_attrs(cx, foreign_item.def_id, foreign_item.span, article, desc);
 682     }
 683
 684     fn check_field_def(&mut self, cx: &LateContext<'_>, sf: &hir::FieldDef<'_>) {
 685         if !sf.is_positional() {
 686             let def_id = cx.tcx.hir().local_def_id(sf.hir_id);
 687             self.check_missing_docs_attrs(cx, def_id, sf.span, "a", "struct field")
 688         }
 689     }
 690
 691     fn check_variant(&mut self, cx: &LateContext<'_>, v: &hir::Variant<'_>) {
 692         self.check_missing_docs_attrs(cx, cx.tcx.hir().local_def_id(v.id), v.span, "a", "variant");
 693     }
 694 }
 695
 696 declare_lint! {
 697     /// The `missing_copy_implementations` lint detects potentially-forgotten
 698     /// implementations of [`Copy`].
 699     ///
 700     /// [`Copy`]: https://doc.rust-lang.org/std/marker/trait.Copy.html
 701     ///
 702     /// ### Example
 703     ///
 704     /// ```rust,compile_fail
 705     /// #![deny(missing_copy_implementations)]
 706     /// pub struct Foo {
 707     ///     pub field: i32
 708     /// }
 709     /// # fn main() {}
 710     /// ```
 711     ///
 712     /// {{produces}}
 713     ///
 714     /// ### Explanation
 715     ///
 716     /// Historically (before 1.0), types were automatically marked as `Copy`
 717     /// if possible. This was changed so that it required an explicit opt-in
 718     /// by implementing the `Copy` trait. As part of this change, a lint was
 719     /// added to alert if a copyable type was not marked `Copy`.
 720     ///
 721     /// This lint is "allow" by default because this code isn't bad; it is
 722     /// common to write newtypes like this specifically so that a `Copy` type
 723     /// is no longer `Copy`. `Copy` types can result in unintended copies of
 724     /// large data which can impact performance.
 725     pub MISSING_COPY_IMPLEMENTATIONS,
 726     Allow,
 727     "detects potentially-forgotten implementations of `Copy`"
 728 }
 729
 730 declare_lint_pass!(MissingCopyImplementations => [MISSING_COPY_IMPLEMENTATIONS]);
 731
 732 impl<'tcx> LateLintPass<'tcx> for MissingCopyImplementations {
 733     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 734         if !cx.access_levels.is_reachable(item.def_id) {
 735             return;
 736         }
 737         let (def, ty) = match item.kind {
 738             hir::ItemKind::Struct(_, ref ast_generics) => {
 739                 if !ast_generics.params.is_empty() {
 740                     return;
 741                 }
 742                 let def = cx.tcx.adt_def(item.def_id);
 743                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 744             }
 745             hir::ItemKind::Union(_, ref ast_generics) => {
 746                 if !ast_generics.params.is_empty() {
 747                     return;
 748                 }
 749                 let def = cx.tcx.adt_def(item.def_id);
 750                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 751             }
 752             hir::ItemKind::Enum(_, ref ast_generics) => {
 753                 if !ast_generics.params.is_empty() {
 754                     return;
 755                 }
 756                 let def = cx.tcx.adt_def(item.def_id);
 757                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 758             }
 759             _ => return,
 760         };
 761         if def.has_dtor(cx.tcx) {
 762             return;
 763         }
 764         let param_env = ty::ParamEnv::empty();
 765         if ty.is_copy_modulo_regions(cx.tcx.at(item.span), param_env) {
 766             return;
 767         }
 768         if can_type_implement_copy(cx.tcx, param_env, ty).is_ok() {
 769             cx.struct_span_lint(MISSING_COPY_IMPLEMENTATIONS, item.span, |lint| {
 770                 lint.build(
 771                     "type could implement `Copy`; consider adding `impl \
 772                           Copy`",
 773                 )
 774                 .emit()
 775             })
 776         }
 777     }
 778 }
 779
 780 declare_lint! {
 781     /// The `missing_debug_implementations` lint detects missing
 782     /// implementations of [`fmt::Debug`].
 783     ///
 784     /// [`fmt::Debug`]: https://doc.rust-lang.org/std/fmt/trait.Debug.html
 785     ///
 786     /// ### Example
 787     ///
 788     /// ```rust,compile_fail
 789     /// #![deny(missing_debug_implementations)]
 790     /// pub struct Foo;
 791     /// # fn main() {}
 792     /// ```
 793     ///
 794     /// {{produces}}
 795     ///
 796     /// ### Explanation
 797     ///
 798     /// Having a `Debug` implementation on all types can assist with
 799     /// debugging, as it provides a convenient way to format and display a
 800     /// value. Using the `#[derive(Debug)]` attribute will automatically
 801     /// generate a typical implementation, or a custom implementation can be
 802     /// added by manually implementing the `Debug` trait.
 803     ///
 804     /// This lint is "allow" by default because adding `Debug` to all types can
 805     /// have a negative impact on compile time and code size. It also requires
 806     /// boilerplate to be added to every type, which can be an impediment.
 807     MISSING_DEBUG_IMPLEMENTATIONS,
 808     Allow,
 809     "detects missing implementations of Debug"
 810 }
 811
 812 #[derive(Default)]
 813 pub struct MissingDebugImplementations {
 814     impling_types: Option<LocalDefIdSet>,
 815 }
 816
 817 impl_lint_pass!(MissingDebugImplementations => [MISSING_DEBUG_IMPLEMENTATIONS]);
 818
 819 impl<'tcx> LateLintPass<'tcx> for MissingDebugImplementations {
 820     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 821         if !cx.access_levels.is_reachable(item.def_id) {
 822             return;
 823         }
 824
 825         match item.kind {
 826             hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) | hir::ItemKind::Enum(..) => {}
 827             _ => return,
 828         }
 829
 830         let Some(debug) = cx.tcx.get_diagnostic_item(sym::Debug) else {
 831             return
 832         };
 833
 834         if self.impling_types.is_none() {
 835             let mut impls = LocalDefIdSet::default();
 836             cx.tcx.for_each_impl(debug, |d| {
 837                 if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() {
 838                     if let Some(def_id) = ty_def.did.as_local() {
 839                         impls.insert(def_id);
 840                     }
 841                 }
 842             });
 843
 844             self.impling_types = Some(impls);
 845             debug!("{:?}", self.impling_types);
 846         }
 847
 848         if !self.impling_types.as_ref().unwrap().contains(&item.def_id) {
 849             cx.struct_span_lint(MISSING_DEBUG_IMPLEMENTATIONS, item.span, |lint| {
 850                 lint.build(&format!(
 851                     "type does not implement `{}`; consider adding `#[derive(Debug)]` \
 852                      or a manual implementation",
 853                     cx.tcx.def_path_str(debug)
 854                 ))
 855                 .emit()
 856             });
 857         }
 858     }
 859 }
 860
 861 declare_lint! {
 862     /// The `anonymous_parameters` lint detects anonymous parameters in trait
 863     /// definitions.
 864     ///
 865     /// ### Example
 866     ///
 867     /// ```rust,edition2015,compile_fail
 868     /// #![deny(anonymous_parameters)]
 869     /// // edition 2015
 870     /// pub trait Foo {
 871     ///     fn foo(usize);
 872     /// }
 873     /// fn main() {}
 874     /// ```
 875     ///
 876     /// {{produces}}
 877     ///
 878     /// ### Explanation
 879     ///
 880     /// This syntax is mostly a historical accident, and can be worked around
 881     /// quite easily by adding an `_` pattern or a descriptive identifier:
 882     ///
 883     /// ```rust
 884     /// trait Foo {
 885     ///     fn foo(_: usize);
 886     /// }
 887     /// ```
 888     ///
 889     /// This syntax is now a hard error in the 2018 edition. In the 2015
 890     /// edition, this lint is "warn" by default. This lint
 891     /// enables the [`cargo fix`] tool with the `--edition` flag to
 892     /// automatically transition old code from the 2015 edition to 2018. The
 893     /// tool will run this lint and automatically apply the
 894     /// suggested fix from the compiler (which is to add `_` to each
 895     /// parameter). This provides a completely automated way to update old
 896     /// code for a new edition. See [issue #41686] for more details.
 897     ///
 898     /// [issue #41686]: https://github.com/rust-lang/rust/issues/41686
 899     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
 900     pub ANONYMOUS_PARAMETERS,
 901     Warn,
 902     "detects anonymous parameters",
 903     @future_incompatible = FutureIncompatibleInfo {
 904         reference: "issue #41686 <https://github.com/rust-lang/rust/issues/41686>",
 905         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
 906     };
 907 }
 908
 909 declare_lint_pass!(
 910     /// Checks for use of anonymous parameters (RFC 1685).
 911     AnonymousParameters => [ANONYMOUS_PARAMETERS]
 912 );
 913
 914 impl EarlyLintPass for AnonymousParameters {
 915     fn check_trait_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
 916         if cx.sess.edition() != Edition::Edition2015 {
 917             // This is a hard error in future editions; avoid linting and erroring
 918             return;
 919         }
 920         if let ast::AssocItemKind::Fn(box Fn { ref sig, .. }) = it.kind {
 921             for arg in sig.decl.inputs.iter() {
 922                 if let ast::PatKind::Ident(_, ident, None) = arg.pat.kind {
 923                     if ident.name == kw::Empty {
 924                         cx.struct_span_lint(ANONYMOUS_PARAMETERS, arg.pat.span, |lint| {
 925                             let ty_snip = cx.sess.source_map().span_to_snippet(arg.ty.span);
 926
 927                             let (ty_snip, appl) = if let Ok(ref snip) = ty_snip {
 928                                 (snip.as_str(), Applicability::MachineApplicable)
 929                             } else {
 930                                 ("<type>", Applicability::HasPlaceholders)
 931                             };
 932
 933                             lint.build(
 934                                 "anonymous parameters are deprecated and will be \
 935                                      removed in the next edition",
 936                             )
 937                             .span_suggestion(
 938                                 arg.pat.span,
 939                                 "try naming the parameter or explicitly \
 940                                             ignoring it",
 941                                 format!("_: {}", ty_snip),
 942                                 appl,
 943                             )
 944                             .emit();
 945                         })
 946                     }
 947                 }
 948             }
 949         }
 950     }
 951 }
 952
 953 /// Check for use of attributes which have been deprecated.
 954 #[derive(Clone)]
 955 pub struct DeprecatedAttr {
 956     // This is not free to compute, so we want to keep it around, rather than
 957     // compute it for every attribute.
 958     depr_attrs: Vec<&'static BuiltinAttribute>,
 959 }
 960
 961 impl_lint_pass!(DeprecatedAttr => []);
 962
 963 impl DeprecatedAttr {
 964     pub fn new() -> DeprecatedAttr {
 965         DeprecatedAttr { depr_attrs: deprecated_attributes() }
 966     }
 967 }
 968
 969 fn lint_deprecated_attr(
 970     cx: &EarlyContext<'_>,
 971     attr: &ast::Attribute,
 972     msg: &str,
 973     suggestion: Option<&str>,
 974 ) {
 975     cx.struct_span_lint(DEPRECATED, attr.span, |lint| {
 976         lint.build(msg)
 977             .span_suggestion_short(
 978                 attr.span,
 979                 suggestion.unwrap_or("remove this attribute"),
 980                 String::new(),
 981                 Applicability::MachineApplicable,
 982             )
 983             .emit();
 984     })
 985 }
 986
 987 impl EarlyLintPass for DeprecatedAttr {
 988     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 989         for BuiltinAttribute { name, gate, .. } in &self.depr_attrs {
 990             if attr.ident().map(|ident| ident.name) == Some(*name) {
 991                 if let &AttributeGate::Gated(
 992                     Stability::Deprecated(link, suggestion),
 993                     name,
 994                     reason,
 995                     _,
 996                 ) = gate
 997                 {
 998                     let msg =
 999                         format!("use of deprecated attribute `{}`: {}. See {}", name, reason, link);
1000                     lint_deprecated_attr(cx, attr, &msg, suggestion);
1001                 }
1002                 return;
1003             }
1004         }
1005         if attr.has_name(sym::no_start) || attr.has_name(sym::crate_id) {
1006             let path_str = pprust::path_to_string(&attr.get_normal_item().path);
1007             let msg = format!("use of deprecated attribute `{}`: no longer used.", path_str);
1008             lint_deprecated_attr(cx, attr, &msg, None);
1009         }
1010     }
1011 }
1012
1013 fn warn_if_doc(cx: &EarlyContext<'_>, node_span: Span, node_kind: &str, attrs: &[ast::Attribute]) {
1014     use rustc_ast::token::CommentKind;
1015
1016     let mut attrs = attrs.iter().peekable();
1017
1018     // Accumulate a single span for sugared doc comments.
1019     let mut sugared_span: Option<Span> = None;
1020
1021     while let Some(attr) = attrs.next() {
1022         let is_doc_comment = attr.is_doc_comment();
1023         if is_doc_comment {
1024             sugared_span =
1025                 Some(sugared_span.map_or(attr.span, |span| span.with_hi(attr.span.hi())));
1026         }
1027
1028         if attrs.peek().map_or(false, |next_attr| next_attr.is_doc_comment()) {
1029             continue;
1030         }
1031
1032         let span = sugared_span.take().unwrap_or(attr.span);
1033
1034         if is_doc_comment || attr.has_name(sym::doc) {
1035             cx.struct_span_lint(UNUSED_DOC_COMMENTS, span, |lint| {
1036                 let mut err = lint.build("unused doc comment");
1037                 err.span_label(
1038                     node_span,
1039                     format!("rustdoc does not generate documentation for {}", node_kind),
1040                 );
1041                 match attr.kind {
1042                     AttrKind::DocComment(CommentKind::Line, _) | AttrKind::Normal(..) => {
1043                         err.help("use `//` for a plain comment");
1044                     }
1045                     AttrKind::DocComment(CommentKind::Block, _) => {
1046                         err.help("use `/* */` for a plain comment");
1047                     }
1048                 }
1049                 err.emit();
1050             });
1051         }
1052     }
1053 }
1054
1055 impl EarlyLintPass for UnusedDocComment {
1056     fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &ast::Stmt) {
1057         let kind = match stmt.kind {
1058             ast::StmtKind::Local(..) => "statements",
1059             // Disabled pending discussion in #78306
1060             ast::StmtKind::Item(..) => return,
1061             // expressions will be reported by `check_expr`.
1062             ast::StmtKind::Empty
1063             | ast::StmtKind::Semi(_)
1064             | ast::StmtKind::Expr(_)
1065             | ast::StmtKind::MacCall(_) => return,
1066         };
1067
1068         warn_if_doc(cx, stmt.span, kind, stmt.kind.attrs());
1069     }
1070
1071     fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) {
1072         let arm_span = arm.pat.span.with_hi(arm.body.span.hi());
1073         warn_if_doc(cx, arm_span, "match arms", &arm.attrs);
1074     }
1075
1076     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
1077         warn_if_doc(cx, expr.span, "expressions", &expr.attrs);
1078     }
1079
1080     fn check_generic_param(&mut self, cx: &EarlyContext<'_>, param: &ast::GenericParam) {
1081         warn_if_doc(cx, param.ident.span, "generic parameters", &param.attrs);
1082     }
1083 }
1084
1085 declare_lint! {
1086     /// The `no_mangle_const_items` lint detects any `const` items with the
1087     /// [`no_mangle` attribute].
1088     ///
1089     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1090     ///
1091     /// ### Example
1092     ///
1093     /// ```rust,compile_fail
1094     /// #[no_mangle]
1095     /// const FOO: i32 = 5;
1096     /// ```
1097     ///
1098     /// {{produces}}
1099     ///
1100     /// ### Explanation
1101     ///
1102     /// Constants do not have their symbols exported, and therefore, this
1103     /// probably means you meant to use a [`static`], not a [`const`].
1104     ///
1105     /// [`static`]: https://doc.rust-lang.org/reference/items/static-items.html
1106     /// [`const`]: https://doc.rust-lang.org/reference/items/constant-items.html
1107     NO_MANGLE_CONST_ITEMS,
1108     Deny,
1109     "const items will not have their symbols exported"
1110 }
1111
1112 declare_lint! {
1113     /// The `no_mangle_generic_items` lint detects generic items that must be
1114     /// mangled.
1115     ///
1116     /// ### Example
1117     ///
1118     /// ```rust
1119     /// #[no_mangle]
1120     /// fn foo<T>(t: T) {
1121     ///
1122     /// }
1123     /// ```
1124     ///
1125     /// {{produces}}
1126     ///
1127     /// ### Explanation
1128     ///
1129     /// A function with generics must have its symbol mangled to accommodate
1130     /// the generic parameter. The [`no_mangle` attribute] has no effect in
1131     /// this situation, and should be removed.
1132     ///
1133     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1134     NO_MANGLE_GENERIC_ITEMS,
1135     Warn,
1136     "generic items must be mangled"
1137 }
1138
1139 declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS, NO_MANGLE_GENERIC_ITEMS]);
1140
1141 impl<'tcx> LateLintPass<'tcx> for InvalidNoMangleItems {
1142     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1143         let attrs = cx.tcx.hir().attrs(it.hir_id());
1144         let check_no_mangle_on_generic_fn = |no_mangle_attr: &ast::Attribute,
1145                                              impl_generics: Option<&hir::Generics<'_>>,
1146                                              generics: &hir::Generics<'_>,
1147                                              span| {
1148             for param in
1149                 generics.params.iter().chain(impl_generics.map(|g| g.params).into_iter().flatten())
1150             {
1151                 match param.kind {
1152                     GenericParamKind::Lifetime { .. } => {}
1153                     GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1154                         cx.struct_span_lint(NO_MANGLE_GENERIC_ITEMS, span, |lint| {
1155                             lint.build("functions generic over types or consts must be mangled")
1156                                 .span_suggestion_short(
1157                                     no_mangle_attr.span,
1158                                     "remove this attribute",
1159                                     String::new(),
1160                                     // Use of `#[no_mangle]` suggests FFI intent; correct
1161                                     // fix may be to monomorphize source by hand
1162                                     Applicability::MaybeIncorrect,
1163                                 )
1164                                 .emit();
1165                         });
1166                         break;
1167                     }
1168                 }
1169             }
1170         };
1171         match it.kind {
1172             hir::ItemKind::Fn(.., ref generics, _) => {
1173                 if let Some(no_mangle_attr) = cx.sess().find_by_name(attrs, sym::no_mangle) {
1174                     check_no_mangle_on_generic_fn(no_mangle_attr, None, generics, it.span);
1175                 }
1176             }
1177             hir::ItemKind::Const(..) => {
1178                 if cx.sess().contains_name(attrs, sym::no_mangle) {
1179                     // Const items do not refer to a particular location in memory, and therefore
1180                     // don't have anything to attach a symbol to
1181                     cx.struct_span_lint(NO_MANGLE_CONST_ITEMS, it.span, |lint| {
1182                         let msg = "const items should never be `#[no_mangle]`";
1183                         let mut err = lint.build(msg);
1184
1185                         // account for "pub const" (#45562)
1186                         let start = cx
1187                             .tcx
1188                             .sess
1189                             .source_map()
1190                             .span_to_snippet(it.span)
1191                             .map(|snippet| snippet.find("const").unwrap_or(0))
1192                             .unwrap_or(0) as u32;
1193                         // `const` is 5 chars
1194                         let const_span = it.span.with_hi(BytePos(it.span.lo().0 + start + 5));
1195                         err.span_suggestion(
1196                             const_span,
1197                             "try a static value",
1198                             "pub static".to_owned(),
1199                             Applicability::MachineApplicable,
1200                         );
1201                         err.emit();
1202                     });
1203                 }
1204             }
1205             hir::ItemKind::Impl(hir::Impl { ref generics, items, .. }) => {
1206                 for it in items {
1207                     if let hir::AssocItemKind::Fn { .. } = it.kind {
1208                         if let Some(no_mangle_attr) = cx
1209                             .sess()
1210                             .find_by_name(cx.tcx.hir().attrs(it.id.hir_id()), sym::no_mangle)
1211                         {
1212                             check_no_mangle_on_generic_fn(
1213                                 no_mangle_attr,
1214                                 Some(generics),
1215                                 cx.tcx.hir().get_generics(it.id.def_id.to_def_id()).unwrap(),
1216                                 it.span,
1217                             );
1218                         }
1219                     }
1220                 }
1221             }
1222             _ => {}
1223         }
1224     }
1225 }
1226
1227 declare_lint! {
1228     /// The `mutable_transmutes` lint catches transmuting from `&T` to `&mut
1229     /// T` because it is [undefined behavior].
1230     ///
1231     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1232     ///
1233     /// ### Example
1234     ///
1235     /// ```rust,compile_fail
1236     /// unsafe {
1237     ///     let y = std::mem::transmute::<&i32, &mut i32>(&5);
1238     /// }
1239     /// ```
1240     ///
1241     /// {{produces}}
1242     ///
1243     /// ### Explanation
1244     ///
1245     /// Certain assumptions are made about aliasing of data, and this transmute
1246     /// violates those assumptions. Consider using [`UnsafeCell`] instead.
1247     ///
1248     /// [`UnsafeCell`]: https://doc.rust-lang.org/std/cell/struct.UnsafeCell.html
1249     MUTABLE_TRANSMUTES,
1250     Deny,
1251     "mutating transmuted &mut T from &T may cause undefined behavior"
1252 }
1253
1254 declare_lint_pass!(MutableTransmutes => [MUTABLE_TRANSMUTES]);
1255
1256 impl<'tcx> LateLintPass<'tcx> for MutableTransmutes {
1257     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &hir::Expr<'_>) {
1258         use rustc_target::spec::abi::Abi::RustIntrinsic;
1259         if let Some((&ty::Ref(_, _, from_mt), &ty::Ref(_, _, to_mt))) =
1260             get_transmute_from_to(cx, expr).map(|(ty1, ty2)| (ty1.kind(), ty2.kind()))
1261         {
1262             if to_mt == hir::Mutability::Mut && from_mt == hir::Mutability::Not {
1263                 let msg = "mutating transmuted &mut T from &T may cause undefined behavior, \
1264                                consider instead using an UnsafeCell";
1265                 cx.struct_span_lint(MUTABLE_TRANSMUTES, expr.span, |lint| lint.build(msg).emit());
1266             }
1267         }
1268
1269         fn get_transmute_from_to<'tcx>(
1270             cx: &LateContext<'tcx>,
1271             expr: &hir::Expr<'_>,
1272         ) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
1273             let def = if let hir::ExprKind::Path(ref qpath) = expr.kind {
1274                 cx.qpath_res(qpath, expr.hir_id)
1275             } else {
1276                 return None;
1277             };
1278             if let Res::Def(DefKind::Fn, did) = def {
1279                 if !def_id_is_transmute(cx, did) {
1280                     return None;
1281                 }
1282                 let sig = cx.typeck_results().node_type(expr.hir_id).fn_sig(cx.tcx);
1283                 let from = sig.inputs().skip_binder()[0];
1284                 let to = sig.output().skip_binder();
1285                 return Some((from, to));
1286             }
1287             None
1288         }
1289
1290         fn def_id_is_transmute(cx: &LateContext<'_>, def_id: DefId) -> bool {
1291             cx.tcx.fn_sig(def_id).abi() == RustIntrinsic
1292                 && cx.tcx.item_name(def_id) == sym::transmute
1293         }
1294     }
1295 }
1296
1297 declare_lint! {
1298     /// The `unstable_features` is deprecated and should no longer be used.
1299     UNSTABLE_FEATURES,
1300     Allow,
1301     "enabling unstable features (deprecated. do not use)"
1302 }
1303
1304 declare_lint_pass!(
1305     /// Forbids using the `#[feature(...)]` attribute
1306     UnstableFeatures => [UNSTABLE_FEATURES]
1307 );
1308
1309 impl<'tcx> LateLintPass<'tcx> for UnstableFeatures {
1310     fn check_attribute(&mut self, cx: &LateContext<'_>, attr: &ast::Attribute) {
1311         if attr.has_name(sym::feature) {
1312             if let Some(items) = attr.meta_item_list() {
1313                 for item in items {
1314                     cx.struct_span_lint(UNSTABLE_FEATURES, item.span(), |lint| {
1315                         lint.build("unstable feature").emit()
1316                     });
1317                 }
1318             }
1319         }
1320     }
1321 }
1322
1323 declare_lint! {
1324     /// The `unreachable_pub` lint triggers for `pub` items not reachable from
1325     /// the crate root.
1326     ///
1327     /// ### Example
1328     ///
1329     /// ```rust,compile_fail
1330     /// #![deny(unreachable_pub)]
1331     /// mod foo {
1332     ///     pub mod bar {
1333     ///
1334     ///     }
1335     /// }
1336     /// ```
1337     ///
1338     /// {{produces}}
1339     ///
1340     /// ### Explanation
1341     ///
1342     /// A bare `pub` visibility may be misleading if the item is not actually
1343     /// publicly exported from the crate. The `pub(crate)` visibility is
1344     /// recommended to be used instead, which more clearly expresses the intent
1345     /// that the item is only visible within its own crate.
1346     ///
1347     /// This lint is "allow" by default because it will trigger for a large
1348     /// amount existing Rust code, and has some false-positives. Eventually it
1349     /// is desired for this to become warn-by-default.
1350     pub UNREACHABLE_PUB,
1351     Allow,
1352     "`pub` items not reachable from crate root"
1353 }
1354
1355 declare_lint_pass!(
1356     /// Lint for items marked `pub` that aren't reachable from other crates.
1357     UnreachablePub => [UNREACHABLE_PUB]
1358 );
1359
1360 impl UnreachablePub {
1361     fn perform_lint(
1362         &self,
1363         cx: &LateContext<'_>,
1364         what: &str,
1365         def_id: LocalDefId,
1366         vis: &hir::Visibility<'_>,
1367         span: Span,
1368         exportable: bool,
1369     ) {
1370         let mut applicability = Applicability::MachineApplicable;
1371         match vis.node {
1372             hir::VisibilityKind::Public if !cx.access_levels.is_reachable(def_id) => {
1373                 if span.from_expansion() {
1374                     applicability = Applicability::MaybeIncorrect;
1375                 }
1376                 let def_span = cx.tcx.sess.source_map().guess_head_span(span);
1377                 cx.struct_span_lint(UNREACHABLE_PUB, def_span, |lint| {
1378                     let mut err = lint.build(&format!("unreachable `pub` {}", what));
1379                     let replacement = if cx.tcx.features().crate_visibility_modifier {
1380                         "crate"
1381                     } else {
1382                         "pub(crate)"
1383                     }
1384                     .to_owned();
1385
1386                     err.span_suggestion(
1387                         vis.span,
1388                         "consider restricting its visibility",
1389                         replacement,
1390                         applicability,
1391                     );
1392                     if exportable {
1393                         err.help("or consider exporting it for use by other crates");
1394                     }
1395                     err.emit();
1396                 });
1397             }
1398             _ => {}
1399         }
1400     }
1401 }
1402
1403 impl<'tcx> LateLintPass<'tcx> for UnreachablePub {
1404     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1405         self.perform_lint(cx, "item", item.def_id, &item.vis, item.span, true);
1406     }
1407
1408     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'tcx>) {
1409         self.perform_lint(
1410             cx,
1411             "item",
1412             foreign_item.def_id,
1413             &foreign_item.vis,
1414             foreign_item.span,
1415             true,
1416         );
1417     }
1418
1419     fn check_field_def(&mut self, cx: &LateContext<'_>, field: &hir::FieldDef<'_>) {
1420         let def_id = cx.tcx.hir().local_def_id(field.hir_id);
1421         self.perform_lint(cx, "field", def_id, &field.vis, field.span, false);
1422     }
1423
1424     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
1425         self.perform_lint(cx, "item", impl_item.def_id, &impl_item.vis, impl_item.span, false);
1426     }
1427 }
1428
1429 declare_lint! {
1430     /// The `type_alias_bounds` lint detects bounds in type aliases.
1431     ///
1432     /// ### Example
1433     ///
1434     /// ```rust
1435     /// type SendVec<T: Send> = Vec<T>;
1436     /// ```
1437     ///
1438     /// {{produces}}
1439     ///
1440     /// ### Explanation
1441     ///
1442     /// The trait bounds in a type alias are currently ignored, and should not
1443     /// be included to avoid confusion. This was previously allowed
1444     /// unintentionally; this may become a hard error in the future.
1445     TYPE_ALIAS_BOUNDS,
1446     Warn,
1447     "bounds in type aliases are not enforced"
1448 }
1449
1450 declare_lint_pass!(
1451     /// Lint for trait and lifetime bounds in type aliases being mostly ignored.
1452     /// They are relevant when using associated types, but otherwise neither checked
1453     /// at definition site nor enforced at use site.
1454     TypeAliasBounds => [TYPE_ALIAS_BOUNDS]
1455 );
1456
1457 impl TypeAliasBounds {
1458     fn is_type_variable_assoc(qpath: &hir::QPath<'_>) -> bool {
1459         match *qpath {
1460             hir::QPath::TypeRelative(ref ty, _) => {
1461                 // If this is a type variable, we found a `T::Assoc`.
1462                 match ty.kind {
1463                     hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
1464                         matches!(path.res, Res::Def(DefKind::TyParam, _))
1465                     }
1466                     _ => false,
1467                 }
1468             }
1469             hir::QPath::Resolved(..) | hir::QPath::LangItem(..) => false,
1470         }
1471     }
1472
1473     fn suggest_changing_assoc_types(ty: &hir::Ty<'_>, err: &mut DiagnosticBuilder<'_>) {
1474         // Access to associates types should use `<T as Bound>::Assoc`, which does not need a
1475         // bound.  Let's see if this type does that.
1476
1477         // We use a HIR visitor to walk the type.
1478         use rustc_hir::intravisit::{self, Visitor};
1479         struct WalkAssocTypes<'a, 'db> {
1480             err: &'a mut DiagnosticBuilder<'db>,
1481         }
1482         impl<'a, 'db, 'v> Visitor<'v> for WalkAssocTypes<'a, 'db> {
1483             type Map = intravisit::ErasedMap<'v>;
1484
1485             fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1486                 intravisit::NestedVisitorMap::None
1487             }
1488
1489             fn visit_qpath(&mut self, qpath: &'v hir::QPath<'v>, id: hir::HirId, span: Span) {
1490                 if TypeAliasBounds::is_type_variable_assoc(qpath) {
1491                     self.err.span_help(
1492                         span,
1493                         "use fully disambiguated paths (i.e., `<T as Trait>::Assoc`) to refer to \
1494                          associated types in type aliases",
1495                     );
1496                 }
1497                 intravisit::walk_qpath(self, qpath, id, span)
1498             }
1499         }
1500
1501         // Let's go for a walk!
1502         let mut visitor = WalkAssocTypes { err };
1503         visitor.visit_ty(ty);
1504     }
1505 }
1506
1507 impl<'tcx> LateLintPass<'tcx> for TypeAliasBounds {
1508     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1509         let hir::ItemKind::TyAlias(ty, type_alias_generics) = &item.kind else {
1510             return
1511         };
1512         if let hir::TyKind::OpaqueDef(..) = ty.kind {
1513             // Bounds are respected for `type X = impl Trait`
1514             return;
1515         }
1516         let mut suggested_changing_assoc_types = false;
1517         // There must not be a where clause
1518         if !type_alias_generics.where_clause.predicates.is_empty() {
1519             cx.lint(
1520                 TYPE_ALIAS_BOUNDS,
1521                 |lint| {
1522                     let mut err = lint.build("where clauses are not enforced in type aliases");
1523                     let spans: Vec<_> = type_alias_generics
1524                         .where_clause
1525                         .predicates
1526                         .iter()
1527                         .map(|pred| pred.span())
1528                         .collect();
1529                     err.set_span(spans);
1530                     err.span_suggestion(
1531                         type_alias_generics.where_clause.span_for_predicates_or_empty_place(),
1532                         "the clause will not be checked when the type alias is used, and should be removed",
1533                         String::new(),
1534                         Applicability::MachineApplicable,
1535                     );
1536                     if !suggested_changing_assoc_types {
1537                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1538                         suggested_changing_assoc_types = true;
1539                     }
1540                     err.emit();
1541                 },
1542             );
1543         }
1544         // The parameters must not have bounds
1545         for param in type_alias_generics.params.iter() {
1546             let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
1547             let suggestion = spans
1548                 .iter()
1549                 .map(|sp| {
1550                     let start = param.span.between(*sp); // Include the `:` in `T: Bound`.
1551                     (start.to(*sp), String::new())
1552                 })
1553                 .collect();
1554             if !spans.is_empty() {
1555                 cx.struct_span_lint(TYPE_ALIAS_BOUNDS, spans, |lint| {
1556                     let mut err =
1557                         lint.build("bounds on generic parameters are not enforced in type aliases");
1558                     let msg = "the bound will not be checked when the type alias is used, \
1559                                    and should be removed";
1560                     err.multipart_suggestion(&msg, suggestion, Applicability::MachineApplicable);
1561                     if !suggested_changing_assoc_types {
1562                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1563                         suggested_changing_assoc_types = true;
1564                     }
1565                     err.emit();
1566                 });
1567             }
1568         }
1569     }
1570 }
1571
1572 declare_lint_pass!(
1573     /// Lint constants that are erroneous.
1574     /// Without this lint, we might not get any diagnostic if the constant is
1575     /// unused within this crate, even though downstream crates can't use it
1576     /// without producing an error.
1577     UnusedBrokenConst => []
1578 );
1579
1580 impl<'tcx> LateLintPass<'tcx> for UnusedBrokenConst {
1581     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1582         match it.kind {
1583             hir::ItemKind::Const(_, body_id) => {
1584                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1585                 // trigger the query once for all constants since that will already report the errors
1586                 // FIXME: Use ensure here
1587                 let _ = cx.tcx.const_eval_poly(def_id);
1588             }
1589             hir::ItemKind::Static(_, _, body_id) => {
1590                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1591                 // FIXME: Use ensure here
1592                 let _ = cx.tcx.eval_static_initializer(def_id);
1593             }
1594             _ => {}
1595         }
1596     }
1597 }
1598
1599 declare_lint! {
1600     /// The `trivial_bounds` lint detects trait bounds that don't depend on
1601     /// any type parameters.
1602     ///
1603     /// ### Example
1604     ///
1605     /// ```rust
1606     /// #![feature(trivial_bounds)]
1607     /// pub struct A where i32: Copy;
1608     /// ```
1609     ///
1610     /// {{produces}}
1611     ///
1612     /// ### Explanation
1613     ///
1614     /// Usually you would not write a trait bound that you know is always
1615     /// true, or never true. However, when using macros, the macro may not
1616     /// know whether or not the constraint would hold or not at the time when
1617     /// generating the code. Currently, the compiler does not alert you if the
1618     /// constraint is always true, and generates an error if it is never true.
1619     /// The `trivial_bounds` feature changes this to be a warning in both
1620     /// cases, giving macros more freedom and flexibility to generate code,
1621     /// while still providing a signal when writing non-macro code that
1622     /// something is amiss.
1623     ///
1624     /// See [RFC 2056] for more details. This feature is currently only
1625     /// available on the nightly channel, see [tracking issue #48214].
1626     ///
1627     /// [RFC 2056]: https://github.com/rust-lang/rfcs/blob/master/text/2056-allow-trivial-where-clause-constraints.md
1628     /// [tracking issue #48214]: https://github.com/rust-lang/rust/issues/48214
1629     TRIVIAL_BOUNDS,
1630     Warn,
1631     "these bounds don't depend on an type parameters"
1632 }
1633
1634 declare_lint_pass!(
1635     /// Lint for trait and lifetime bounds that don't depend on type parameters
1636     /// which either do nothing, or stop the item from being used.
1637     TrivialConstraints => [TRIVIAL_BOUNDS]
1638 );
1639
1640 impl<'tcx> LateLintPass<'tcx> for TrivialConstraints {
1641     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
1642         use rustc_middle::ty::fold::TypeFoldable;
1643         use rustc_middle::ty::PredicateKind::*;
1644
1645         if cx.tcx.features().trivial_bounds {
1646             let predicates = cx.tcx.predicates_of(item.def_id);
1647             for &(predicate, span) in predicates.predicates {
1648                 let predicate_kind_name = match predicate.kind().skip_binder() {
1649                     Trait(..) => "trait",
1650                     TypeOutlives(..) |
1651                     RegionOutlives(..) => "lifetime",
1652
1653                     // Ignore projections, as they can only be global
1654                     // if the trait bound is global
1655                     Projection(..) |
1656                     // Ignore bounds that a user can't type
1657                     WellFormed(..) |
1658                     ObjectSafe(..) |
1659                     ClosureKind(..) |
1660                     Subtype(..) |
1661                     Coerce(..) |
1662                     ConstEvaluatable(..) |
1663                     ConstEquate(..) |
1664                     TypeWellFormedFromEnv(..) => continue,
1665                 };
1666                 if predicate.is_global(cx.tcx) {
1667                     cx.struct_span_lint(TRIVIAL_BOUNDS, span, |lint| {
1668                         lint.build(&format!(
1669                             "{} bound {} does not depend on any type \
1670                                 or lifetime parameters",
1671                             predicate_kind_name, predicate
1672                         ))
1673                         .emit()
1674                     });
1675                 }
1676             }
1677         }
1678     }
1679 }
1680
1681 declare_lint_pass!(
1682     /// Does nothing as a lint pass, but registers some `Lint`s
1683     /// which are used by other parts of the compiler.
1684     SoftLints => [
1685         WHILE_TRUE,
1686         BOX_POINTERS,
1687         NON_SHORTHAND_FIELD_PATTERNS,
1688         UNSAFE_CODE,
1689         MISSING_DOCS,
1690         MISSING_COPY_IMPLEMENTATIONS,
1691         MISSING_DEBUG_IMPLEMENTATIONS,
1692         ANONYMOUS_PARAMETERS,
1693         UNUSED_DOC_COMMENTS,
1694         NO_MANGLE_CONST_ITEMS,
1695         NO_MANGLE_GENERIC_ITEMS,
1696         MUTABLE_TRANSMUTES,
1697         UNSTABLE_FEATURES,
1698         UNREACHABLE_PUB,
1699         TYPE_ALIAS_BOUNDS,
1700         TRIVIAL_BOUNDS
1701     ]
1702 );
1703
1704 declare_lint! {
1705     /// The `ellipsis_inclusive_range_patterns` lint detects the [`...` range
1706     /// pattern], which is deprecated.
1707     ///
1708     /// [`...` range pattern]: https://doc.rust-lang.org/reference/patterns.html#range-patterns
1709     ///
1710     /// ### Example
1711     ///
1712     /// ```rust,edition2018
1713     /// let x = 123;
1714     /// match x {
1715     ///     0...100 => {}
1716     ///     _ => {}
1717     /// }
1718     /// ```
1719     ///
1720     /// {{produces}}
1721     ///
1722     /// ### Explanation
1723     ///
1724     /// The `...` range pattern syntax was changed to `..=` to avoid potential
1725     /// confusion with the [`..` range expression]. Use the new form instead.
1726     ///
1727     /// [`..` range expression]: https://doc.rust-lang.org/reference/expressions/range-expr.html
1728     pub ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
1729     Warn,
1730     "`...` range patterns are deprecated",
1731     @future_incompatible = FutureIncompatibleInfo {
1732         reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>",
1733         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
1734     };
1735 }
1736
1737 #[derive(Default)]
1738 pub struct EllipsisInclusiveRangePatterns {
1739     /// If `Some(_)`, suppress all subsequent pattern
1740     /// warnings for better diagnostics.
1741     node_id: Option<ast::NodeId>,
1742 }
1743
1744 impl_lint_pass!(EllipsisInclusiveRangePatterns => [ELLIPSIS_INCLUSIVE_RANGE_PATTERNS]);
1745
1746 impl EarlyLintPass for EllipsisInclusiveRangePatterns {
1747     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &ast::Pat) {
1748         if self.node_id.is_some() {
1749             // Don't recursively warn about patterns inside range endpoints.
1750             return;
1751         }
1752
1753         use self::ast::{PatKind, RangeSyntax::DotDotDot};
1754
1755         /// If `pat` is a `...` pattern, return the start and end of the range, as well as the span
1756         /// corresponding to the ellipsis.
1757         fn matches_ellipsis_pat(pat: &ast::Pat) -> Option<(Option<&Expr>, &Expr, Span)> {
1758             match &pat.kind {
1759                 PatKind::Range(
1760                     a,
1761                     Some(b),
1762                     Spanned { span, node: RangeEnd::Included(DotDotDot) },
1763                 ) => Some((a.as_deref(), b, *span)),
1764                 _ => None,
1765             }
1766         }
1767
1768         let (parenthesise, endpoints) = match &pat.kind {
1769             PatKind::Ref(subpat, _) => (true, matches_ellipsis_pat(&subpat)),
1770             _ => (false, matches_ellipsis_pat(pat)),
1771         };
1772
1773         if let Some((start, end, join)) = endpoints {
1774             let msg = "`...` range patterns are deprecated";
1775             let suggestion = "use `..=` for an inclusive range";
1776             if parenthesise {
1777                 self.node_id = Some(pat.id);
1778                 let end = expr_to_string(&end);
1779                 let replace = match start {
1780                     Some(start) => format!("&({}..={})", expr_to_string(&start), end),
1781                     None => format!("&(..={})", end),
1782                 };
1783                 if join.edition() >= Edition::Edition2021 {
1784                     let mut err =
1785                         rustc_errors::struct_span_err!(cx.sess, pat.span, E0783, "{}", msg,);
1786                     err.span_suggestion(
1787                         pat.span,
1788                         suggestion,
1789                         replace,
1790                         Applicability::MachineApplicable,
1791                     )
1792                     .emit();
1793                 } else {
1794                     cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, pat.span, |lint| {
1795                         lint.build(msg)
1796                             .span_suggestion(
1797                                 pat.span,
1798                                 suggestion,
1799                                 replace,
1800                                 Applicability::MachineApplicable,
1801                             )
1802                             .emit();
1803                     });
1804                 }
1805             } else {
1806                 let replace = "..=".to_owned();
1807                 if join.edition() >= Edition::Edition2021 {
1808                     let mut err =
1809                         rustc_errors::struct_span_err!(cx.sess, pat.span, E0783, "{}", msg,);
1810                     err.span_suggestion_short(
1811                         join,
1812                         suggestion,
1813                         replace,
1814                         Applicability::MachineApplicable,
1815                     )
1816                     .emit();
1817                 } else {
1818                     cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, join, |lint| {
1819                         lint.build(msg)
1820                             .span_suggestion_short(
1821                                 join,
1822                                 suggestion,
1823                                 replace,
1824                                 Applicability::MachineApplicable,
1825                             )
1826                             .emit();
1827                     });
1828                 }
1829             };
1830         }
1831     }
1832
1833     fn check_pat_post(&mut self, _cx: &EarlyContext<'_>, pat: &ast::Pat) {
1834         if let Some(node_id) = self.node_id {
1835             if pat.id == node_id {
1836                 self.node_id = None
1837             }
1838         }
1839     }
1840 }
1841
1842 declare_lint! {
1843     /// The `unnameable_test_items` lint detects [`#[test]`][test] functions
1844     /// that are not able to be run by the test harness because they are in a
1845     /// position where they are not nameable.
1846     ///
1847     /// [test]: https://doc.rust-lang.org/reference/attributes/testing.html#the-test-attribute
1848     ///
1849     /// ### Example
1850     ///
1851     /// ```rust,test
1852     /// fn main() {
1853     ///     #[test]
1854     ///     fn foo() {
1855     ///         // This test will not fail because it does not run.
1856     ///         assert_eq!(1, 2);
1857     ///     }
1858     /// }
1859     /// ```
1860     ///
1861     /// {{produces}}
1862     ///
1863     /// ### Explanation
1864     ///
1865     /// In order for the test harness to run a test, the test function must be
1866     /// located in a position where it can be accessed from the crate root.
1867     /// This generally means it must be defined in a module, and not anywhere
1868     /// else such as inside another function. The compiler previously allowed
1869     /// this without an error, so a lint was added as an alert that a test is
1870     /// not being used. Whether or not this should be allowed has not yet been
1871     /// decided, see [RFC 2471] and [issue #36629].
1872     ///
1873     /// [RFC 2471]: https://github.com/rust-lang/rfcs/pull/2471#issuecomment-397414443
1874     /// [issue #36629]: https://github.com/rust-lang/rust/issues/36629
1875     UNNAMEABLE_TEST_ITEMS,
1876     Warn,
1877     "detects an item that cannot be named being marked as `#[test_case]`",
1878     report_in_external_macro
1879 }
1880
1881 pub struct UnnameableTestItems {
1882     boundary: Option<LocalDefId>, // Id of the item under which things are not nameable
1883     items_nameable: bool,
1884 }
1885
1886 impl_lint_pass!(UnnameableTestItems => [UNNAMEABLE_TEST_ITEMS]);
1887
1888 impl UnnameableTestItems {
1889     pub fn new() -> Self {
1890         Self { boundary: None, items_nameable: true }
1891     }
1892 }
1893
1894 impl<'tcx> LateLintPass<'tcx> for UnnameableTestItems {
1895     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1896         if self.items_nameable {
1897             if let hir::ItemKind::Mod(..) = it.kind {
1898             } else {
1899                 self.items_nameable = false;
1900                 self.boundary = Some(it.def_id);
1901             }
1902             return;
1903         }
1904
1905         let attrs = cx.tcx.hir().attrs(it.hir_id());
1906         if let Some(attr) = cx.sess().find_by_name(attrs, sym::rustc_test_marker) {
1907             cx.struct_span_lint(UNNAMEABLE_TEST_ITEMS, attr.span, |lint| {
1908                 lint.build("cannot test inner items").emit()
1909             });
1910         }
1911     }
1912
1913     fn check_item_post(&mut self, _cx: &LateContext<'_>, it: &hir::Item<'_>) {
1914         if !self.items_nameable && self.boundary == Some(it.def_id) {
1915             self.items_nameable = true;
1916         }
1917     }
1918 }
1919
1920 declare_lint! {
1921     /// The `keyword_idents` lint detects edition keywords being used as an
1922     /// identifier.
1923     ///
1924     /// ### Example
1925     ///
1926     /// ```rust,edition2015,compile_fail
1927     /// #![deny(keyword_idents)]
1928     /// // edition 2015
1929     /// fn dyn() {}
1930     /// ```
1931     ///
1932     /// {{produces}}
1933     ///
1934     /// ### Explanation
1935     ///
1936     /// Rust [editions] allow the language to evolve without breaking
1937     /// backwards compatibility. This lint catches code that uses new keywords
1938     /// that are added to the language that are used as identifiers (such as a
1939     /// variable name, function name, etc.). If you switch the compiler to a
1940     /// new edition without updating the code, then it will fail to compile if
1941     /// you are using a new keyword as an identifier.
1942     ///
1943     /// You can manually change the identifiers to a non-keyword, or use a
1944     /// [raw identifier], for example `r#dyn`, to transition to a new edition.
1945     ///
1946     /// This lint solves the problem automatically. It is "allow" by default
1947     /// because the code is perfectly valid in older editions. The [`cargo
1948     /// fix`] tool with the `--edition` flag will switch this lint to "warn"
1949     /// and automatically apply the suggested fix from the compiler (which is
1950     /// to use a raw identifier). This provides a completely automated way to
1951     /// update old code for a new edition.
1952     ///
1953     /// [editions]: https://doc.rust-lang.org/edition-guide/
1954     /// [raw identifier]: https://doc.rust-lang.org/reference/identifiers.html
1955     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
1956     pub KEYWORD_IDENTS,
1957     Allow,
1958     "detects edition keywords being used as an identifier",
1959     @future_incompatible = FutureIncompatibleInfo {
1960         reference: "issue #49716 <https://github.com/rust-lang/rust/issues/49716>",
1961         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
1962     };
1963 }
1964
1965 declare_lint_pass!(
1966     /// Check for uses of edition keywords used as an identifier.
1967     KeywordIdents => [KEYWORD_IDENTS]
1968 );
1969
1970 struct UnderMacro(bool);
1971
1972 impl KeywordIdents {
1973     fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: TokenStream) {
1974         for tt in tokens.into_trees() {
1975             match tt {
1976                 // Only report non-raw idents.
1977                 TokenTree::Token(token) => {
1978                     if let Some((ident, false)) = token.ident() {
1979                         self.check_ident_token(cx, UnderMacro(true), ident);
1980                     }
1981                 }
1982                 TokenTree::Delimited(_, _, tts) => self.check_tokens(cx, tts),
1983             }
1984         }
1985     }
1986
1987     fn check_ident_token(
1988         &mut self,
1989         cx: &EarlyContext<'_>,
1990         UnderMacro(under_macro): UnderMacro,
1991         ident: Ident,
1992     ) {
1993         let next_edition = match cx.sess.edition() {
1994             Edition::Edition2015 => {
1995                 match ident.name {
1996                     kw::Async | kw::Await | kw::Try => Edition::Edition2018,
1997
1998                     // rust-lang/rust#56327: Conservatively do not
1999                     // attempt to report occurrences of `dyn` within
2000                     // macro definitions or invocations, because `dyn`
2001                     // can legitimately occur as a contextual keyword
2002                     // in 2015 code denoting its 2018 meaning, and we
2003                     // do not want rustfix to inject bugs into working
2004                     // code by rewriting such occurrences.
2005                     //
2006                     // But if we see `dyn` outside of a macro, we know
2007                     // its precise role in the parsed AST and thus are
2008                     // assured this is truly an attempt to use it as
2009                     // an identifier.
2010                     kw::Dyn if !under_macro => Edition::Edition2018,
2011
2012                     _ => return,
2013                 }
2014             }
2015
2016             // There are no new keywords yet for the 2018 edition and beyond.
2017             _ => return,
2018         };
2019
2020         // Don't lint `r#foo`.
2021         if cx.sess.parse_sess.raw_identifier_spans.borrow().contains(&ident.span) {
2022             return;
2023         }
2024
2025         cx.struct_span_lint(KEYWORD_IDENTS, ident.span, |lint| {
2026             lint.build(&format!("`{}` is a keyword in the {} edition", ident, next_edition))
2027                 .span_suggestion(
2028                     ident.span,
2029                     "you can use a raw identifier to stay compatible",
2030                     format!("r#{}", ident),
2031                     Applicability::MachineApplicable,
2032                 )
2033                 .emit()
2034         });
2035     }
2036 }
2037
2038 impl EarlyLintPass for KeywordIdents {
2039     fn check_mac_def(&mut self, cx: &EarlyContext<'_>, mac_def: &ast::MacroDef, _id: ast::NodeId) {
2040         self.check_tokens(cx, mac_def.body.inner_tokens());
2041     }
2042     fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::MacCall) {
2043         self.check_tokens(cx, mac.args.inner_tokens());
2044     }
2045     fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: Ident) {
2046         self.check_ident_token(cx, UnderMacro(false), ident);
2047     }
2048 }
2049
2050 declare_lint_pass!(ExplicitOutlivesRequirements => [EXPLICIT_OUTLIVES_REQUIREMENTS]);
2051
2052 impl ExplicitOutlivesRequirements {
2053     fn lifetimes_outliving_lifetime<'tcx>(
2054         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2055         index: u32,
2056     ) -> Vec<ty::Region<'tcx>> {
2057         inferred_outlives
2058             .iter()
2059             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
2060                 ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => match a {
2061                     ty::ReEarlyBound(ebr) if ebr.index == index => Some(b),
2062                     _ => None,
2063                 },
2064                 _ => None,
2065             })
2066             .collect()
2067     }
2068
2069     fn lifetimes_outliving_type<'tcx>(
2070         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2071         index: u32,
2072     ) -> Vec<ty::Region<'tcx>> {
2073         inferred_outlives
2074             .iter()
2075             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
2076                 ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
2077                     a.is_param(index).then_some(b)
2078                 }
2079                 _ => None,
2080             })
2081             .collect()
2082     }
2083
2084     fn collect_outlived_lifetimes<'tcx>(
2085         &self,
2086         param: &'tcx hir::GenericParam<'tcx>,
2087         tcx: TyCtxt<'tcx>,
2088         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2089         ty_generics: &'tcx ty::Generics,
2090     ) -> Vec<ty::Region<'tcx>> {
2091         let index =
2092             ty_generics.param_def_id_to_index[&tcx.hir().local_def_id(param.hir_id).to_def_id()];
2093
2094         match param.kind {
2095             hir::GenericParamKind::Lifetime { .. } => {
2096                 Self::lifetimes_outliving_lifetime(inferred_outlives, index)
2097             }
2098             hir::GenericParamKind::Type { .. } => {
2099                 Self::lifetimes_outliving_type(inferred_outlives, index)
2100             }
2101             hir::GenericParamKind::Const { .. } => Vec::new(),
2102         }
2103     }
2104
2105     fn collect_outlives_bound_spans<'tcx>(
2106         &self,
2107         tcx: TyCtxt<'tcx>,
2108         bounds: &hir::GenericBounds<'_>,
2109         inferred_outlives: &[ty::Region<'tcx>],
2110         infer_static: bool,
2111     ) -> Vec<(usize, Span)> {
2112         use rustc_middle::middle::resolve_lifetime::Region;
2113
2114         bounds
2115             .iter()
2116             .enumerate()
2117             .filter_map(|(i, bound)| {
2118                 if let hir::GenericBound::Outlives(lifetime) = bound {
2119                     let is_inferred = match tcx.named_region(lifetime.hir_id) {
2120                         Some(Region::Static) if infer_static => {
2121                             inferred_outlives.iter().any(|r| matches!(r, ty::ReStatic))
2122                         }
2123                         Some(Region::EarlyBound(index, ..)) => inferred_outlives.iter().any(|r| {
2124                             if let ty::ReEarlyBound(ebr) = r { ebr.index == index } else { false }
2125                         }),
2126                         _ => false,
2127                     };
2128                     is_inferred.then_some((i, bound.span()))
2129                 } else {
2130                     None
2131                 }
2132             })
2133             .collect()
2134     }
2135
2136     fn consolidate_outlives_bound_spans(
2137         &self,
2138         lo: Span,
2139         bounds: &hir::GenericBounds<'_>,
2140         bound_spans: Vec<(usize, Span)>,
2141     ) -> Vec<Span> {
2142         if bounds.is_empty() {
2143             return Vec::new();
2144         }
2145         if bound_spans.len() == bounds.len() {
2146             let (_, last_bound_span) = bound_spans[bound_spans.len() - 1];
2147             // If all bounds are inferable, we want to delete the colon, so
2148             // start from just after the parameter (span passed as argument)
2149             vec![lo.to(last_bound_span)]
2150         } else {
2151             let mut merged = Vec::new();
2152             let mut last_merged_i = None;
2153
2154             let mut from_start = true;
2155             for (i, bound_span) in bound_spans {
2156                 match last_merged_i {
2157                     // If the first bound is inferable, our span should also eat the leading `+`.
2158                     None if i == 0 => {
2159                         merged.push(bound_span.to(bounds[1].span().shrink_to_lo()));
2160                         last_merged_i = Some(0);
2161                     }
2162                     // If consecutive bounds are inferable, merge their spans
2163                     Some(h) if i == h + 1 => {
2164                         if let Some(tail) = merged.last_mut() {
2165                             // Also eat the trailing `+` if the first
2166                             // more-than-one bound is inferable
2167                             let to_span = if from_start && i < bounds.len() {
2168                                 bounds[i + 1].span().shrink_to_lo()
2169                             } else {
2170                                 bound_span
2171                             };
2172                             *tail = tail.to(to_span);
2173                             last_merged_i = Some(i);
2174                         } else {
2175                             bug!("another bound-span visited earlier");
2176                         }
2177                     }
2178                     _ => {
2179                         // When we find a non-inferable bound, subsequent inferable bounds
2180                         // won't be consecutive from the start (and we'll eat the leading
2181                         // `+` rather than the trailing one)
2182                         from_start = false;
2183                         merged.push(bounds[i - 1].span().shrink_to_hi().to(bound_span));
2184                         last_merged_i = Some(i);
2185                     }
2186                 }
2187             }
2188             merged
2189         }
2190     }
2191 }
2192
2193 impl<'tcx> LateLintPass<'tcx> for ExplicitOutlivesRequirements {
2194     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
2195         use rustc_middle::middle::resolve_lifetime::Region;
2196
2197         let infer_static = cx.tcx.features().infer_static_outlives_requirements;
2198         let def_id = item.def_id;
2199         if let hir::ItemKind::Struct(_, ref hir_generics)
2200         | hir::ItemKind::Enum(_, ref hir_generics)
2201         | hir::ItemKind::Union(_, ref hir_generics) = item.kind
2202         {
2203             let inferred_outlives = cx.tcx.inferred_outlives_of(def_id);
2204             if inferred_outlives.is_empty() {
2205                 return;
2206             }
2207
2208             let ty_generics = cx.tcx.generics_of(def_id);
2209
2210             let mut bound_count = 0;
2211             let mut lint_spans = Vec::new();
2212
2213             for param in hir_generics.params {
2214                 let has_lifetime_bounds = param
2215                     .bounds
2216                     .iter()
2217                     .any(|bound| matches!(bound, hir::GenericBound::Outlives(_)));
2218                 if !has_lifetime_bounds {
2219                     continue;
2220                 }
2221
2222                 let relevant_lifetimes =
2223                     self.collect_outlived_lifetimes(param, cx.tcx, inferred_outlives, ty_generics);
2224                 if relevant_lifetimes.is_empty() {
2225                     continue;
2226                 }
2227
2228                 let bound_spans = self.collect_outlives_bound_spans(
2229                     cx.tcx,
2230                     &param.bounds,
2231                     &relevant_lifetimes,
2232                     infer_static,
2233                 );
2234                 bound_count += bound_spans.len();
2235                 lint_spans.extend(self.consolidate_outlives_bound_spans(
2236                     param.span.shrink_to_hi(),
2237                     &param.bounds,
2238                     bound_spans,
2239                 ));
2240             }
2241
2242             let mut where_lint_spans = Vec::new();
2243             let mut dropped_predicate_count = 0;
2244             let num_predicates = hir_generics.where_clause.predicates.len();
2245             for (i, where_predicate) in hir_generics.where_clause.predicates.iter().enumerate() {
2246                 let (relevant_lifetimes, bounds, span) = match where_predicate {
2247                     hir::WherePredicate::RegionPredicate(predicate) => {
2248                         if let Some(Region::EarlyBound(index, ..)) =
2249                             cx.tcx.named_region(predicate.lifetime.hir_id)
2250                         {
2251                             (
2252                                 Self::lifetimes_outliving_lifetime(inferred_outlives, index),
2253                                 &predicate.bounds,
2254                                 predicate.span,
2255                             )
2256                         } else {
2257                             continue;
2258                         }
2259                     }
2260                     hir::WherePredicate::BoundPredicate(predicate) => {
2261                         // FIXME we can also infer bounds on associated types,
2262                         // and should check for them here.
2263                         match predicate.bounded_ty.kind {
2264                             hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
2265                                 let Res::Def(DefKind::TyParam, def_id) = path.res else {
2266                                     continue
2267                                 };
2268                                 let index = ty_generics.param_def_id_to_index[&def_id];
2269                                 (
2270                                     Self::lifetimes_outliving_type(inferred_outlives, index),
2271                                     &predicate.bounds,
2272                                     predicate.span,
2273                                 )
2274                             }
2275                             _ => {
2276                                 continue;
2277                             }
2278                         }
2279                     }
2280                     _ => continue,
2281                 };
2282                 if relevant_lifetimes.is_empty() {
2283                     continue;
2284                 }
2285
2286                 let bound_spans = self.collect_outlives_bound_spans(
2287                     cx.tcx,
2288                     bounds,
2289                     &relevant_lifetimes,
2290                     infer_static,
2291                 );
2292                 bound_count += bound_spans.len();
2293
2294                 let drop_predicate = bound_spans.len() == bounds.len();
2295                 if drop_predicate {
2296                     dropped_predicate_count += 1;
2297                 }
2298
2299                 // If all the bounds on a predicate were inferable and there are
2300                 // further predicates, we want to eat the trailing comma.
2301                 if drop_predicate && i + 1 < num_predicates {
2302                     let next_predicate_span = hir_generics.where_clause.predicates[i + 1].span();
2303                     where_lint_spans.push(span.to(next_predicate_span.shrink_to_lo()));
2304                 } else {
2305                     where_lint_spans.extend(self.consolidate_outlives_bound_spans(
2306                         span.shrink_to_lo(),
2307                         bounds,
2308                         bound_spans,
2309                     ));
2310                 }
2311             }
2312
2313             // If all predicates are inferable, drop the entire clause
2314             // (including the `where`)
2315             if num_predicates > 0 && dropped_predicate_count == num_predicates {
2316                 let where_span = hir_generics
2317                     .where_clause
2318                     .span()
2319                     .expect("span of (nonempty) where clause should exist");
2320                 // Extend the where clause back to the closing `>` of the
2321                 // generics, except for tuple struct, which have the `where`
2322                 // after the fields of the struct.
2323                 let full_where_span =
2324                     if let hir::ItemKind::Struct(hir::VariantData::Tuple(..), _) = item.kind {
2325                         where_span
2326                     } else {
2327                         hir_generics.span.shrink_to_hi().to(where_span)
2328                     };
2329                 lint_spans.push(full_where_span);
2330             } else {
2331                 lint_spans.extend(where_lint_spans);
2332             }
2333
2334             if !lint_spans.is_empty() {
2335                 cx.struct_span_lint(EXPLICIT_OUTLIVES_REQUIREMENTS, lint_spans.clone(), |lint| {
2336                     lint.build("outlives requirements can be inferred")
2337                         .multipart_suggestion(
2338                             if bound_count == 1 {
2339                                 "remove this bound"
2340                             } else {
2341                                 "remove these bounds"
2342                             },
2343                             lint_spans
2344                                 .into_iter()
2345                                 .map(|span| (span, "".to_owned()))
2346                                 .collect::<Vec<_>>(),
2347                             Applicability::MachineApplicable,
2348                         )
2349                         .emit();
2350                 });
2351             }
2352         }
2353     }
2354 }
2355
2356 declare_lint! {
2357     /// The `incomplete_features` lint detects unstable features enabled with
2358     /// the [`feature` attribute] that may function improperly in some or all
2359     /// cases.
2360     ///
2361     /// [`feature` attribute]: https://doc.rust-lang.org/nightly/unstable-book/
2362     ///
2363     /// ### Example
2364     ///
2365     /// ```rust
2366     /// #![feature(generic_const_exprs)]
2367     /// ```
2368     ///
2369     /// {{produces}}
2370     ///
2371     /// ### Explanation
2372     ///
2373     /// Although it is encouraged for people to experiment with unstable
2374     /// features, some of them are known to be incomplete or faulty. This lint
2375     /// is a signal that the feature has not yet been finished, and you may
2376     /// experience problems with it.
2377     pub INCOMPLETE_FEATURES,
2378     Warn,
2379     "incomplete features that may function improperly in some or all cases"
2380 }
2381
2382 declare_lint_pass!(
2383     /// Check for used feature gates in `INCOMPLETE_FEATURES` in `rustc_feature/src/active.rs`.
2384     IncompleteFeatures => [INCOMPLETE_FEATURES]
2385 );
2386
2387 impl EarlyLintPass for IncompleteFeatures {
2388     fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
2389         let features = cx.sess.features_untracked();
2390         features
2391             .declared_lang_features
2392             .iter()
2393             .map(|(name, span, _)| (name, span))
2394             .chain(features.declared_lib_features.iter().map(|(name, span)| (name, span)))
2395             .filter(|(&name, _)| features.incomplete(name))
2396             .for_each(|(&name, &span)| {
2397                 cx.struct_span_lint(INCOMPLETE_FEATURES, span, |lint| {
2398                     let mut builder = lint.build(&format!(
2399                         "the feature `{}` is incomplete and may not be safe to use \
2400                          and/or cause compiler crashes",
2401                         name,
2402                     ));
2403                     if let Some(n) = rustc_feature::find_feature_issue(name, GateIssue::Language) {
2404                         builder.note(&format!(
2405                             "see issue #{} <https://github.com/rust-lang/rust/issues/{}> \
2406                              for more information",
2407                             n, n,
2408                         ));
2409                     }
2410                     if HAS_MIN_FEATURES.contains(&name) {
2411                         builder.help(&format!(
2412                             "consider using `min_{}` instead, which is more stable and complete",
2413                             name,
2414                         ));
2415                     }
2416                     builder.emit();
2417                 })
2418             });
2419     }
2420 }
2421
2422 const HAS_MIN_FEATURES: &[Symbol] = &[sym::specialization];
2423
2424 declare_lint! {
2425     /// The `invalid_value` lint detects creating a value that is not valid,
2426     /// such as a null reference.
2427     ///
2428     /// ### Example
2429     ///
2430     /// ```rust,no_run
2431     /// # #![allow(unused)]
2432     /// unsafe {
2433     ///     let x: &'static i32 = std::mem::zeroed();
2434     /// }
2435     /// ```
2436     ///
2437     /// {{produces}}
2438     ///
2439     /// ### Explanation
2440     ///
2441     /// In some situations the compiler can detect that the code is creating
2442     /// an invalid value, which should be avoided.
2443     ///
2444     /// In particular, this lint will check for improper use of
2445     /// [`mem::zeroed`], [`mem::uninitialized`], [`mem::transmute`], and
2446     /// [`MaybeUninit::assume_init`] that can cause [undefined behavior]. The
2447     /// lint should provide extra information to indicate what the problem is
2448     /// and a possible solution.
2449     ///
2450     /// [`mem::zeroed`]: https://doc.rust-lang.org/std/mem/fn.zeroed.html
2451     /// [`mem::uninitialized`]: https://doc.rust-lang.org/std/mem/fn.uninitialized.html
2452     /// [`mem::transmute`]: https://doc.rust-lang.org/std/mem/fn.transmute.html
2453     /// [`MaybeUninit::assume_init`]: https://doc.rust-lang.org/std/mem/union.MaybeUninit.html#method.assume_init
2454     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
2455     pub INVALID_VALUE,
2456     Warn,
2457     "an invalid value is being created (such as a null reference)"
2458 }
2459
2460 declare_lint_pass!(InvalidValue => [INVALID_VALUE]);
2461
2462 impl<'tcx> LateLintPass<'tcx> for InvalidValue {
2463     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
2464         #[derive(Debug, Copy, Clone, PartialEq)]
2465         enum InitKind {
2466             Zeroed,
2467             Uninit,
2468         }
2469
2470         /// Information about why a type cannot be initialized this way.
2471         /// Contains an error message and optionally a span to point at.
2472         type InitError = (String, Option<Span>);
2473
2474         /// Test if this constant is all-0.
2475         fn is_zero(expr: &hir::Expr<'_>) -> bool {
2476             use hir::ExprKind::*;
2477             use rustc_ast::LitKind::*;
2478             match &expr.kind {
2479                 Lit(lit) => {
2480                     if let Int(i, _) = lit.node {
2481                         i == 0
2482                     } else {
2483                         false
2484                     }
2485                 }
2486                 Tup(tup) => tup.iter().all(is_zero),
2487                 _ => false,
2488             }
2489         }
2490
2491         /// Determine if this expression is a "dangerous initialization".
2492         fn is_dangerous_init(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> Option<InitKind> {
2493             if let hir::ExprKind::Call(ref path_expr, ref args) = expr.kind {
2494                 // Find calls to `mem::{uninitialized,zeroed}` methods.
2495                 if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2496                     let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2497                     match cx.tcx.get_diagnostic_name(def_id) {
2498                         Some(sym::mem_zeroed) => return Some(InitKind::Zeroed),
2499                         Some(sym::mem_uninitialized) => return Some(InitKind::Uninit),
2500                         Some(sym::transmute) if is_zero(&args[0]) => return Some(InitKind::Zeroed),
2501                         _ => {}
2502                     }
2503                 }
2504             } else if let hir::ExprKind::MethodCall(_, _, ref args, _) = expr.kind {
2505                 // Find problematic calls to `MaybeUninit::assume_init`.
2506                 let def_id = cx.typeck_results().type_dependent_def_id(expr.hir_id)?;
2507                 if cx.tcx.is_diagnostic_item(sym::assume_init, def_id) {
2508                     // This is a call to *some* method named `assume_init`.
2509                     // See if the `self` parameter is one of the dangerous constructors.
2510                     if let hir::ExprKind::Call(ref path_expr, _) = args[0].kind {
2511                         if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2512                             let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2513                             match cx.tcx.get_diagnostic_name(def_id) {
2514                                 Some(sym::maybe_uninit_zeroed) => return Some(InitKind::Zeroed),
2515                                 Some(sym::maybe_uninit_uninit) => return Some(InitKind::Uninit),
2516                                 _ => {}
2517                             }
2518                         }
2519                     }
2520                 }
2521             }
2522
2523             None
2524         }
2525
2526         /// Test if this enum has several actually "existing" variants.
2527         /// Zero-sized uninhabited variants do not always have a tag assigned and thus do not "exist".
2528         fn is_multi_variant(adt: &ty::AdtDef) -> bool {
2529             // As an approximation, we only count dataless variants. Those are definitely inhabited.
2530             let existing_variants = adt.variants.iter().filter(|v| v.fields.is_empty()).count();
2531             existing_variants > 1
2532         }
2533
2534         /// Return `Some` only if we are sure this type does *not*
2535         /// allow zero initialization.
2536         fn ty_find_init_error<'tcx>(
2537             tcx: TyCtxt<'tcx>,
2538             ty: Ty<'tcx>,
2539             init: InitKind,
2540         ) -> Option<InitError> {
2541             use rustc_middle::ty::TyKind::*;
2542             match ty.kind() {
2543                 // Primitive types that don't like 0 as a value.
2544                 Ref(..) => Some(("references must be non-null".to_string(), None)),
2545                 Adt(..) if ty.is_box() => Some(("`Box` must be non-null".to_string(), None)),
2546                 FnPtr(..) => Some(("function pointers must be non-null".to_string(), None)),
2547                 Never => Some(("the `!` type has no valid value".to_string(), None)),
2548                 RawPtr(tm) if matches!(tm.ty.kind(), Dynamic(..)) =>
2549                 // raw ptr to dyn Trait
2550                 {
2551                     Some(("the vtable of a wide raw pointer must be non-null".to_string(), None))
2552                 }
2553                 // Primitive types with other constraints.
2554                 Bool if init == InitKind::Uninit => {
2555                     Some(("booleans must be either `true` or `false`".to_string(), None))
2556                 }
2557                 Char if init == InitKind::Uninit => {
2558                     Some(("characters must be a valid Unicode codepoint".to_string(), None))
2559                 }
2560                 // Recurse and checks for some compound types.
2561                 Adt(adt_def, substs) if !adt_def.is_union() => {
2562                     // First check if this ADT has a layout attribute (like `NonNull` and friends).
2563                     use std::ops::Bound;
2564                     match tcx.layout_scalar_valid_range(adt_def.did) {
2565                         // We exploit here that `layout_scalar_valid_range` will never
2566                         // return `Bound::Excluded`.  (And we have tests checking that we
2567                         // handle the attribute correctly.)
2568                         (Bound::Included(lo), _) if lo > 0 => {
2569                             return Some((format!("`{}` must be non-null", ty), None));
2570                         }
2571                         (Bound::Included(_), _) | (_, Bound::Included(_))
2572                             if init == InitKind::Uninit =>
2573                         {
2574                             return Some((
2575                                 format!(
2576                                     "`{}` must be initialized inside its custom valid range",
2577                                     ty,
2578                                 ),
2579                                 None,
2580                             ));
2581                         }
2582                         _ => {}
2583                     }
2584                     // Now, recurse.
2585                     match adt_def.variants.len() {
2586                         0 => Some(("enums with no variants have no valid value".to_string(), None)),
2587                         1 => {
2588                             // Struct, or enum with exactly one variant.
2589                             // Proceed recursively, check all fields.
2590                             let variant = &adt_def.variants[VariantIdx::from_u32(0)];
2591                             variant.fields.iter().find_map(|field| {
2592                                 ty_find_init_error(tcx, field.ty(tcx, substs), init).map(
2593                                     |(mut msg, span)| {
2594                                         if span.is_none() {
2595                                             // Point to this field, should be helpful for figuring
2596                                             // out where the source of the error is.
2597                                             let span = tcx.def_span(field.did);
2598                                             write!(
2599                                                 &mut msg,
2600                                                 " (in this {} field)",
2601                                                 adt_def.descr()
2602                                             )
2603                                             .unwrap();
2604                                             (msg, Some(span))
2605                                         } else {
2606                                             // Just forward.
2607                                             (msg, span)
2608                                         }
2609                                     },
2610                                 )
2611                             })
2612                         }
2613                         // Multi-variant enum.
2614                         _ => {
2615                             if init == InitKind::Uninit && is_multi_variant(adt_def) {
2616                                 let span = tcx.def_span(adt_def.did);
2617                                 Some((
2618                                     "enums have to be initialized to a variant".to_string(),
2619                                     Some(span),
2620                                 ))
2621                             } else {
2622                                 // In principle, for zero-initialization we could figure out which variant corresponds
2623                                 // to tag 0, and check that... but for now we just accept all zero-initializations.
2624                                 None
2625                             }
2626                         }
2627                     }
2628                 }
2629                 Tuple(..) => {
2630                     // Proceed recursively, check all fields.
2631                     ty.tuple_fields().find_map(|field| ty_find_init_error(tcx, field, init))
2632                 }
2633                 // Conservative fallback.
2634                 _ => None,
2635             }
2636         }
2637
2638         if let Some(init) = is_dangerous_init(cx, expr) {
2639             // This conjures an instance of a type out of nothing,
2640             // using zeroed or uninitialized memory.
2641             // We are extremely conservative with what we warn about.
2642             let conjured_ty = cx.typeck_results().expr_ty(expr);
2643             if let Some((msg, span)) =
2644                 with_no_trimmed_paths(|| ty_find_init_error(cx.tcx, conjured_ty, init))
2645             {
2646                 cx.struct_span_lint(INVALID_VALUE, expr.span, |lint| {
2647                     let mut err = lint.build(&format!(
2648                         "the type `{}` does not permit {}",
2649                         conjured_ty,
2650                         match init {
2651                             InitKind::Zeroed => "zero-initialization",
2652                             InitKind::Uninit => "being left uninitialized",
2653                         },
2654                     ));
2655                     err.span_label(expr.span, "this code causes undefined behavior when executed");
2656                     err.span_label(
2657                         expr.span,
2658                         "help: use `MaybeUninit<T>` instead, \
2659                             and only call `assume_init` after initialization is done",
2660                     );
2661                     if let Some(span) = span {
2662                         err.span_note(span, &msg);
2663                     } else {
2664                         err.note(&msg);
2665                     }
2666                     err.emit();
2667                 });
2668             }
2669         }
2670     }
2671 }
2672
2673 declare_lint! {
2674     /// The `clashing_extern_declarations` lint detects when an `extern fn`
2675     /// has been declared with the same name but different types.
2676     ///
2677     /// ### Example
2678     ///
2679     /// ```rust
2680     /// mod m {
2681     ///     extern "C" {
2682     ///         fn foo();
2683     ///     }
2684     /// }
2685     ///
2686     /// extern "C" {
2687     ///     fn foo(_: u32);
2688     /// }
2689     /// ```
2690     ///
2691     /// {{produces}}
2692     ///
2693     /// ### Explanation
2694     ///
2695     /// Because two symbols of the same name cannot be resolved to two
2696     /// different functions at link time, and one function cannot possibly
2697     /// have two types, a clashing extern declaration is almost certainly a
2698     /// mistake. Check to make sure that the `extern` definitions are correct
2699     /// and equivalent, and possibly consider unifying them in one location.
2700     ///
2701     /// This lint does not run between crates because a project may have
2702     /// dependencies which both rely on the same extern function, but declare
2703     /// it in a different (but valid) way. For example, they may both declare
2704     /// an opaque type for one or more of the arguments (which would end up
2705     /// distinct types), or use types that are valid conversions in the
2706     /// language the `extern fn` is defined in. In these cases, the compiler
2707     /// can't say that the clashing declaration is incorrect.
2708     pub CLASHING_EXTERN_DECLARATIONS,
2709     Warn,
2710     "detects when an extern fn has been declared with the same name but different types"
2711 }
2712
2713 pub struct ClashingExternDeclarations {
2714     /// Map of function symbol name to the first-seen hir id for that symbol name.. If seen_decls
2715     /// contains an entry for key K, it means a symbol with name K has been seen by this lint and
2716     /// the symbol should be reported as a clashing declaration.
2717     // FIXME: Technically, we could just store a &'tcx str here without issue; however, the
2718     // `impl_lint_pass` macro doesn't currently support lints parametric over a lifetime.
2719     seen_decls: FxHashMap<Symbol, HirId>,
2720 }
2721
2722 /// Differentiate between whether the name for an extern decl came from the link_name attribute or
2723 /// just from declaration itself. This is important because we don't want to report clashes on
2724 /// symbol name if they don't actually clash because one or the other links against a symbol with a
2725 /// different name.
2726 enum SymbolName {
2727     /// The name of the symbol + the span of the annotation which introduced the link name.
2728     Link(Symbol, Span),
2729     /// No link name, so just the name of the symbol.
2730     Normal(Symbol),
2731 }
2732
2733 impl SymbolName {
2734     fn get_name(&self) -> Symbol {
2735         match self {
2736             SymbolName::Link(s, _) | SymbolName::Normal(s) => *s,
2737         }
2738     }
2739 }
2740
2741 impl ClashingExternDeclarations {
2742     crate fn new() -> Self {
2743         ClashingExternDeclarations { seen_decls: FxHashMap::default() }
2744     }
2745     /// Insert a new foreign item into the seen set. If a symbol with the same name already exists
2746     /// for the item, return its HirId without updating the set.
2747     fn insert(&mut self, tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> Option<HirId> {
2748         let did = fi.def_id.to_def_id();
2749         let instance = Instance::new(did, ty::List::identity_for_item(tcx, did));
2750         let name = Symbol::intern(tcx.symbol_name(instance).name);
2751         if let Some(&hir_id) = self.seen_decls.get(&name) {
2752             // Avoid updating the map with the new entry when we do find a collision. We want to
2753             // make sure we're always pointing to the first definition as the previous declaration.
2754             // This lets us avoid emitting "knock-on" diagnostics.
2755             Some(hir_id)
2756         } else {
2757             self.seen_decls.insert(name, fi.hir_id())
2758         }
2759     }
2760
2761     /// Get the name of the symbol that's linked against for a given extern declaration. That is,
2762     /// the name specified in a #[link_name = ...] attribute if one was specified, else, just the
2763     /// symbol's name.
2764     fn name_of_extern_decl(tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> SymbolName {
2765         if let Some((overridden_link_name, overridden_link_name_span)) =
2766             tcx.codegen_fn_attrs(fi.def_id).link_name.map(|overridden_link_name| {
2767                 // FIXME: Instead of searching through the attributes again to get span
2768                 // information, we could have codegen_fn_attrs also give span information back for
2769                 // where the attribute was defined. However, until this is found to be a
2770                 // bottleneck, this does just fine.
2771                 (
2772                     overridden_link_name,
2773                     tcx.get_attrs(fi.def_id.to_def_id())
2774                         .iter()
2775                         .find(|at| at.has_name(sym::link_name))
2776                         .unwrap()
2777                         .span,
2778                 )
2779             })
2780         {
2781             SymbolName::Link(overridden_link_name, overridden_link_name_span)
2782         } else {
2783             SymbolName::Normal(fi.ident.name)
2784         }
2785     }
2786
2787     /// Checks whether two types are structurally the same enough that the declarations shouldn't
2788     /// clash. We need this so we don't emit a lint when two modules both declare an extern struct,
2789     /// with the same members (as the declarations shouldn't clash).
2790     fn structurally_same_type<'tcx>(
2791         cx: &LateContext<'tcx>,
2792         a: Ty<'tcx>,
2793         b: Ty<'tcx>,
2794         ckind: CItemKind,
2795     ) -> bool {
2796         fn structurally_same_type_impl<'tcx>(
2797             seen_types: &mut FxHashSet<(Ty<'tcx>, Ty<'tcx>)>,
2798             cx: &LateContext<'tcx>,
2799             a: Ty<'tcx>,
2800             b: Ty<'tcx>,
2801             ckind: CItemKind,
2802         ) -> bool {
2803             debug!("structurally_same_type_impl(cx, a = {:?}, b = {:?})", a, b);
2804             let tcx = cx.tcx;
2805
2806             // Given a transparent newtype, reach through and grab the inner
2807             // type unless the newtype makes the type non-null.
2808             let non_transparent_ty = |ty: Ty<'tcx>| -> Ty<'tcx> {
2809                 let mut ty = ty;
2810                 loop {
2811                     if let ty::Adt(def, substs) = *ty.kind() {
2812                         let is_transparent = def.subst(tcx, substs).repr.transparent();
2813                         let is_non_null = crate::types::nonnull_optimization_guaranteed(tcx, &def);
2814                         debug!(
2815                             "non_transparent_ty({:?}) -- type is transparent? {}, type is non-null? {}",
2816                             ty, is_transparent, is_non_null
2817                         );
2818                         if is_transparent && !is_non_null {
2819                             debug_assert!(def.variants.len() == 1);
2820                             let v = &def.variants[VariantIdx::new(0)];
2821                             ty = transparent_newtype_field(tcx, v)
2822                                 .expect(
2823                                     "single-variant transparent structure with zero-sized field",
2824                                 )
2825                                 .ty(tcx, substs);
2826                             continue;
2827                         }
2828                     }
2829                     debug!("non_transparent_ty -> {:?}", ty);
2830                     return ty;
2831                 }
2832             };
2833
2834             let a = non_transparent_ty(a);
2835             let b = non_transparent_ty(b);
2836
2837             if !seen_types.insert((a, b)) {
2838                 // We've encountered a cycle. There's no point going any further -- the types are
2839                 // structurally the same.
2840                 return true;
2841             }
2842             let tcx = cx.tcx;
2843             if a == b || rustc_middle::ty::TyS::same_type(a, b) {
2844                 // All nominally-same types are structurally same, too.
2845                 true
2846             } else {
2847                 // Do a full, depth-first comparison between the two.
2848                 use rustc_middle::ty::TyKind::*;
2849                 let a_kind = a.kind();
2850                 let b_kind = b.kind();
2851
2852                 let compare_layouts = |a, b| -> Result<bool, LayoutError<'tcx>> {
2853                     debug!("compare_layouts({:?}, {:?})", a, b);
2854                     let a_layout = &cx.layout_of(a)?.layout.abi;
2855                     let b_layout = &cx.layout_of(b)?.layout.abi;
2856                     debug!(
2857                         "comparing layouts: {:?} == {:?} = {}",
2858                         a_layout,
2859                         b_layout,
2860                         a_layout == b_layout
2861                     );
2862                     Ok(a_layout == b_layout)
2863                 };
2864
2865                 #[allow(rustc::usage_of_ty_tykind)]
2866                 let is_primitive_or_pointer = |kind: &ty::TyKind<'_>| {
2867                     kind.is_primitive() || matches!(kind, RawPtr(..) | Ref(..))
2868                 };
2869
2870                 ensure_sufficient_stack(|| {
2871                     match (a_kind, b_kind) {
2872                         (Adt(a_def, a_substs), Adt(b_def, b_substs)) => {
2873                             let a = a.subst(cx.tcx, a_substs);
2874                             let b = b.subst(cx.tcx, b_substs);
2875                             debug!("Comparing {:?} and {:?}", a, b);
2876
2877                             // We can immediately rule out these types as structurally same if
2878                             // their layouts differ.
2879                             match compare_layouts(a, b) {
2880                                 Ok(false) => return false,
2881                                 _ => (), // otherwise, continue onto the full, fields comparison
2882                             }
2883
2884                             // Grab a flattened representation of all fields.
2885                             let a_fields = a_def.variants.iter().flat_map(|v| v.fields.iter());
2886                             let b_fields = b_def.variants.iter().flat_map(|v| v.fields.iter());
2887
2888                             // Perform a structural comparison for each field.
2889                             a_fields.eq_by(
2890                                 b_fields,
2891                                 |&ty::FieldDef { did: a_did, .. },
2892                                  &ty::FieldDef { did: b_did, .. }| {
2893                                     structurally_same_type_impl(
2894                                         seen_types,
2895                                         cx,
2896                                         tcx.type_of(a_did),
2897                                         tcx.type_of(b_did),
2898                                         ckind,
2899                                     )
2900                                 },
2901                             )
2902                         }
2903                         (Array(a_ty, a_const), Array(b_ty, b_const)) => {
2904                             // For arrays, we also check the constness of the type.
2905                             a_const.val == b_const.val
2906                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2907                         }
2908                         (Slice(a_ty), Slice(b_ty)) => {
2909                             structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2910                         }
2911                         (RawPtr(a_tymut), RawPtr(b_tymut)) => {
2912                             a_tymut.mutbl == b_tymut.mutbl
2913                                 && structurally_same_type_impl(
2914                                     seen_types,
2915                                     cx,
2916                                     &a_tymut.ty,
2917                                     &b_tymut.ty,
2918                                     ckind,
2919                                 )
2920                         }
2921                         (Ref(_a_region, a_ty, a_mut), Ref(_b_region, b_ty, b_mut)) => {
2922                             // For structural sameness, we don't need the region to be same.
2923                             a_mut == b_mut
2924                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2925                         }
2926                         (FnDef(..), FnDef(..)) => {
2927                             let a_poly_sig = a.fn_sig(tcx);
2928                             let b_poly_sig = b.fn_sig(tcx);
2929
2930                             // As we don't compare regions, skip_binder is fine.
2931                             let a_sig = a_poly_sig.skip_binder();
2932                             let b_sig = b_poly_sig.skip_binder();
2933
2934                             (a_sig.abi, a_sig.unsafety, a_sig.c_variadic)
2935                                 == (b_sig.abi, b_sig.unsafety, b_sig.c_variadic)
2936                                 && a_sig.inputs().iter().eq_by(b_sig.inputs().iter(), |a, b| {
2937                                     structurally_same_type_impl(seen_types, cx, a, b, ckind)
2938                                 })
2939                                 && structurally_same_type_impl(
2940                                     seen_types,
2941                                     cx,
2942                                     a_sig.output(),
2943                                     b_sig.output(),
2944                                     ckind,
2945                                 )
2946                         }
2947                         (Tuple(a_substs), Tuple(b_substs)) => {
2948                             a_substs.types().eq_by(b_substs.types(), |a_ty, b_ty| {
2949                                 structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2950                             })
2951                         }
2952                         // For these, it's not quite as easy to define structural-sameness quite so easily.
2953                         // For the purposes of this lint, take the conservative approach and mark them as
2954                         // not structurally same.
2955                         (Dynamic(..), Dynamic(..))
2956                         | (Error(..), Error(..))
2957                         | (Closure(..), Closure(..))
2958                         | (Generator(..), Generator(..))
2959                         | (GeneratorWitness(..), GeneratorWitness(..))
2960                         | (Projection(..), Projection(..))
2961                         | (Opaque(..), Opaque(..)) => false,
2962
2963                         // These definitely should have been caught above.
2964                         (Bool, Bool) | (Char, Char) | (Never, Never) | (Str, Str) => unreachable!(),
2965
2966                         // An Adt and a primitive or pointer type. This can be FFI-safe if non-null
2967                         // enum layout optimisation is being applied.
2968                         (Adt(..), other_kind) | (other_kind, Adt(..))
2969                             if is_primitive_or_pointer(other_kind) =>
2970                         {
2971                             let (primitive, adt) =
2972                                 if is_primitive_or_pointer(a.kind()) { (a, b) } else { (b, a) };
2973                             if let Some(ty) = crate::types::repr_nullable_ptr(cx, adt, ckind) {
2974                                 ty == primitive
2975                             } else {
2976                                 compare_layouts(a, b).unwrap_or(false)
2977                             }
2978                         }
2979                         // Otherwise, just compare the layouts. This may fail to lint for some
2980                         // incompatible types, but at the very least, will stop reads into
2981                         // uninitialised memory.
2982                         _ => compare_layouts(a, b).unwrap_or(false),
2983                     }
2984                 })
2985             }
2986         }
2987         let mut seen_types = FxHashSet::default();
2988         structurally_same_type_impl(&mut seen_types, cx, a, b, ckind)
2989     }
2990 }
2991
2992 impl_lint_pass!(ClashingExternDeclarations => [CLASHING_EXTERN_DECLARATIONS]);
2993
2994 impl<'tcx> LateLintPass<'tcx> for ClashingExternDeclarations {
2995     fn check_foreign_item(&mut self, cx: &LateContext<'tcx>, this_fi: &hir::ForeignItem<'_>) {
2996         trace!("ClashingExternDeclarations: check_foreign_item: {:?}", this_fi);
2997         if let ForeignItemKind::Fn(..) = this_fi.kind {
2998             let tcx = cx.tcx;
2999             if let Some(existing_hid) = self.insert(tcx, this_fi) {
3000                 let existing_decl_ty = tcx.type_of(tcx.hir().local_def_id(existing_hid));
3001                 let this_decl_ty = tcx.type_of(this_fi.def_id);
3002                 debug!(
3003                     "ClashingExternDeclarations: Comparing existing {:?}: {:?} to this {:?}: {:?}",
3004                     existing_hid, existing_decl_ty, this_fi.def_id, this_decl_ty
3005                 );
3006                 // Check that the declarations match.
3007                 if !Self::structurally_same_type(
3008                     cx,
3009                     existing_decl_ty,
3010                     this_decl_ty,
3011                     CItemKind::Declaration,
3012                 ) {
3013                     let orig_fi = tcx.hir().expect_foreign_item(existing_hid.expect_owner());
3014                     let orig = Self::name_of_extern_decl(tcx, orig_fi);
3015
3016                     // We want to ensure that we use spans for both decls that include where the
3017                     // name was defined, whether that was from the link_name attribute or not.
3018                     let get_relevant_span =
3019                         |fi: &hir::ForeignItem<'_>| match Self::name_of_extern_decl(tcx, fi) {
3020                             SymbolName::Normal(_) => fi.span,
3021                             SymbolName::Link(_, annot_span) => fi.span.to(annot_span),
3022                         };
3023                     // Finally, emit the diagnostic.
3024                     tcx.struct_span_lint_hir(
3025                         CLASHING_EXTERN_DECLARATIONS,
3026                         this_fi.hir_id(),
3027                         get_relevant_span(this_fi),
3028                         |lint| {
3029                             let mut expected_str = DiagnosticStyledString::new();
3030                             expected_str.push(existing_decl_ty.fn_sig(tcx).to_string(), false);
3031                             let mut found_str = DiagnosticStyledString::new();
3032                             found_str.push(this_decl_ty.fn_sig(tcx).to_string(), true);
3033
3034                             lint.build(&format!(
3035                                 "`{}` redeclare{} with a different signature",
3036                                 this_fi.ident.name,
3037                                 if orig.get_name() == this_fi.ident.name {
3038                                     "d".to_string()
3039                                 } else {
3040                                     format!("s `{}`", orig.get_name())
3041                                 }
3042                             ))
3043                             .span_label(
3044                                 get_relevant_span(orig_fi),
3045                                 &format!("`{}` previously declared here", orig.get_name()),
3046                             )
3047                             .span_label(
3048                                 get_relevant_span(this_fi),
3049                                 "this signature doesn't match the previous declaration",
3050                             )
3051                             .note_expected_found(&"", expected_str, &"", found_str)
3052                             .emit()
3053                         },
3054                     );
3055                 }
3056             }
3057         }
3058     }
3059 }
3060
3061 declare_lint! {
3062     /// The `deref_nullptr` lint detects when an null pointer is dereferenced,
3063     /// which causes [undefined behavior].
3064     ///
3065     /// ### Example
3066     ///
3067     /// ```rust,no_run
3068     /// # #![allow(unused)]
3069     /// use std::ptr;
3070     /// unsafe {
3071     ///     let x = &*ptr::null::<i32>();
3072     ///     let x = ptr::addr_of!(*ptr::null::<i32>());
3073     ///     let x = *(0 as *const i32);
3074     /// }
3075     /// ```
3076     ///
3077     /// {{produces}}
3078     ///
3079     /// ### Explanation
3080     ///
3081     /// Dereferencing a null pointer causes [undefined behavior] even as a place expression,
3082     /// like `&*(0 as *const i32)` or `addr_of!(*(0 as *const i32))`.
3083     ///
3084     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
3085     pub DEREF_NULLPTR,
3086     Warn,
3087     "detects when an null pointer is dereferenced"
3088 }
3089
3090 declare_lint_pass!(DerefNullPtr => [DEREF_NULLPTR]);
3091
3092 impl<'tcx> LateLintPass<'tcx> for DerefNullPtr {
3093     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
3094         /// test if expression is a null ptr
3095         fn is_null_ptr(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> bool {
3096             match &expr.kind {
3097                 rustc_hir::ExprKind::Cast(ref expr, ref ty) => {
3098                     if let rustc_hir::TyKind::Ptr(_) = ty.kind {
3099                         return is_zero(expr) || is_null_ptr(cx, expr);
3100                     }
3101                 }
3102                 // check for call to `core::ptr::null` or `core::ptr::null_mut`
3103                 rustc_hir::ExprKind::Call(ref path, _) => {
3104                     if let rustc_hir::ExprKind::Path(ref qpath) = path.kind {
3105                         if let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id() {
3106                             return matches!(
3107                                 cx.tcx.get_diagnostic_name(def_id),
3108                                 Some(sym::ptr_null | sym::ptr_null_mut)
3109                             );
3110                         }
3111                     }
3112                 }
3113                 _ => {}
3114             }
3115             false
3116         }
3117
3118         /// test if expression is the literal `0`
3119         fn is_zero(expr: &hir::Expr<'_>) -> bool {
3120             match &expr.kind {
3121                 rustc_hir::ExprKind::Lit(ref lit) => {
3122                     if let LitKind::Int(a, _) = lit.node {
3123                         return a == 0;
3124                     }
3125                 }
3126                 _ => {}
3127             }
3128             false
3129         }
3130
3131         if let rustc_hir::ExprKind::Unary(rustc_hir::UnOp::Deref, expr_deref) = expr.kind {
3132             if is_null_ptr(cx, expr_deref) {
3133                 cx.struct_span_lint(DEREF_NULLPTR, expr.span, |lint| {
3134                     let mut err = lint.build("dereferencing a null pointer");
3135                     err.span_label(expr.span, "this code causes undefined behavior when executed");
3136                     err.emit();
3137                 });
3138             }
3139         }
3140     }
3141 }
3142
3143 declare_lint! {
3144     /// The `named_asm_labels` lint detects the use of named labels in the
3145     /// inline `asm!` macro.
3146     ///
3147     /// ### Example
3148     ///
3149     /// ```rust,compile_fail
3150     /// use std::arch::asm;
3151     ///
3152     /// fn main() {
3153     ///     unsafe {
3154     ///         asm!("foo: bar");
3155     ///     }
3156     /// }
3157     /// ```
3158     ///
3159     /// {{produces}}
3160     ///
3161     /// ### Explanation
3162     ///
3163     /// LLVM is allowed to duplicate inline assembly blocks for any
3164     /// reason, for example when it is in a function that gets inlined. Because
3165     /// of this, GNU assembler [local labels] *must* be used instead of labels
3166     /// with a name. Using named labels might cause assembler or linker errors.
3167     ///
3168     /// [local labels]: https://sourceware.org/binutils/docs/as/Symbol-Names.html#Local-Labels
3169     pub NAMED_ASM_LABELS,
3170     Deny,
3171     "named labels in inline assembly",
3172 }
3173
3174 declare_lint_pass!(NamedAsmLabels => [NAMED_ASM_LABELS]);
3175
3176 impl<'tcx> LateLintPass<'tcx> for NamedAsmLabels {
3177     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
3178         if let hir::Expr {
3179             kind: hir::ExprKind::InlineAsm(hir::InlineAsm { template_strs, .. }),
3180             ..
3181         } = expr
3182         {
3183             for (template_sym, template_snippet, template_span) in template_strs.iter() {
3184                 let template_str = &template_sym.as_str();
3185                 let find_label_span = |needle: &str| -> Option<Span> {
3186                     if let Some(template_snippet) = template_snippet {
3187                         let snippet = template_snippet.as_str();
3188                         if let Some(pos) = snippet.find(needle) {
3189                             let end = pos
3190                                 + snippet[pos..]
3191                                     .find(|c| c == ':')
3192                                     .unwrap_or(snippet[pos..].len() - 1);
3193                             let inner = InnerSpan::new(pos, end);
3194                             return Some(template_span.from_inner(inner));
3195                         }
3196                     }
3197
3198                     None
3199                 };
3200
3201                 let mut found_labels = Vec::new();
3202
3203                 // A semicolon might not actually be specified as a separator for all targets, but it seems like LLVM accepts it always
3204                 let statements = template_str.split(|c| matches!(c, '\n' | ';'));
3205                 for statement in statements {
3206                     // If there's a comment, trim it from the statement
3207                     let statement = statement.find("//").map_or(statement, |idx| &statement[..idx]);
3208                     let mut start_idx = 0;
3209                     for (idx, _) in statement.match_indices(':') {
3210                         let possible_label = statement[start_idx..idx].trim();
3211                         let mut chars = possible_label.chars();
3212                         let Some(c) = chars.next() else {
3213                             // Empty string means a leading ':' in this section, which is not a label
3214                             break
3215                         };
3216                         // A label starts with an alphabetic character or . or _ and continues with alphanumeric characters, _, or $
3217                         if (c.is_alphabetic() || matches!(c, '.' | '_'))
3218                             && chars.all(|c| c.is_alphanumeric() || matches!(c, '_' | '$'))
3219                         {
3220                             found_labels.push(possible_label);
3221                         } else {
3222                             // If we encounter a non-label, there cannot be any further labels, so stop checking
3223                             break;
3224                         }
3225
3226                         start_idx = idx + 1;
3227                     }
3228                 }
3229
3230                 debug!("NamedAsmLabels::check_expr(): found_labels: {:#?}", &found_labels);
3231
3232                 if found_labels.len() > 0 {
3233                     let spans = found_labels
3234                         .into_iter()
3235                         .filter_map(|label| find_label_span(label))
3236                         .collect::<Vec<Span>>();
3237                     // If there were labels but we couldn't find a span, combine the warnings and use the template span
3238                     let target_spans: MultiSpan =
3239                         if spans.len() > 0 { spans.into() } else { (*template_span).into() };
3240
3241                     cx.lookup_with_diagnostics(
3242                             NAMED_ASM_LABELS,
3243                             Some(target_spans),
3244                             |diag| {
3245                                 let mut err =
3246                                     diag.build("avoid using named labels in inline assembly");
3247                                 err.emit();
3248                             },
3249                             BuiltinLintDiagnostics::NamedAsmLabel(
3250                                 "only local labels of the form `<number>:` should be used in inline asm"
3251                                     .to_string(),
3252                             ),
3253                         );
3254                 }
3255             }
3256         }
3257     }
3258 }