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::CItemKind, EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext,
  25 };
  26 use rustc_ast::attr::{self, HasAttrs};
  27 use rustc_ast::tokenstream::{TokenStream, TokenTree};
  28 use rustc_ast::visit::{FnCtxt, FnKind};
  29 use rustc_ast::{self as ast, *};
  30 use rustc_ast_pretty::pprust::{self, expr_to_string};
  31 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
  32 use rustc_data_structures::stack::ensure_sufficient_stack;
  33 use rustc_errors::{Applicability, DiagnosticBuilder, DiagnosticStyledString};
  34 use rustc_feature::{deprecated_attributes, AttributeGate, AttributeTemplate, AttributeType};
  35 use rustc_feature::{GateIssue, Stability};
  36 use rustc_hir as hir;
  37 use rustc_hir::def::{DefKind, Res};
  38 use rustc_hir::def_id::DefId;
  39 use rustc_hir::{ForeignItemKind, GenericParamKind, PatKind};
  40 use rustc_hir::{HirId, HirIdSet, Node};
  41 use rustc_index::vec::Idx;
  42 use rustc_middle::lint::LintDiagnosticBuilder;
  43 use rustc_middle::ty::subst::{GenericArgKind, Subst};
  44 use rustc_middle::ty::{self, layout::LayoutError, Ty, TyCtxt};
  45 use rustc_session::lint::FutureIncompatibleInfo;
  46 use rustc_session::Session;
  47 use rustc_span::edition::Edition;
  48 use rustc_span::source_map::Spanned;
  49 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  50 use rustc_span::{BytePos, Span};
  51 use rustc_target::abi::{LayoutOf, VariantIdx};
  52 use rustc_trait_selection::traits::misc::can_type_implement_copy;
  53
  54 use crate::nonstandard_style::{method_context, MethodLateContext};
  55
  56 use std::fmt::Write;
  57 use tracing::{debug, trace};
  58
  59 // hardwired lints from librustc_middle
  60 pub use rustc_session::lint::builtin::*;
  61
  62 declare_lint! {
  63     WHILE_TRUE,
  64     Warn,
  65     "suggest using `loop { }` instead of `while true { }`"
  66 }
  67
  68 declare_lint_pass!(WhileTrue => [WHILE_TRUE]);
  69
  70 /// Traverse through any amount of parenthesis and return the first non-parens expression.
  71 fn pierce_parens(mut expr: &ast::Expr) -> &ast::Expr {
  72     while let ast::ExprKind::Paren(sub) = &expr.kind {
  73         expr = sub;
  74     }
  75     expr
  76 }
  77
  78 impl EarlyLintPass for WhileTrue {
  79     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
  80         if let ast::ExprKind::While(cond, ..) = &e.kind {
  81             if let ast::ExprKind::Lit(ref lit) = pierce_parens(cond).kind {
  82                 if let ast::LitKind::Bool(true) = lit.kind {
  83                     if !lit.span.from_expansion() {
  84                         let msg = "denote infinite loops with `loop { ... }`";
  85                         let condition_span = cx.sess.source_map().guess_head_span(e.span);
  86                         cx.struct_span_lint(WHILE_TRUE, condition_span, |lint| {
  87                             lint.build(msg)
  88                                 .span_suggestion_short(
  89                                     condition_span,
  90                                     "use `loop`",
  91                                     "loop".to_owned(),
  92                                     Applicability::MachineApplicable,
  93                                 )
  94                                 .emit();
  95                         })
  96                     }
  97                 }
  98             }
  99         }
 100     }
 101 }
 102
 103 declare_lint! {
 104     BOX_POINTERS,
 105     Allow,
 106     "use of owned (Box type) heap memory"
 107 }
 108
 109 declare_lint_pass!(BoxPointers => [BOX_POINTERS]);
 110
 111 impl BoxPointers {
 112     fn check_heap_type(&self, cx: &LateContext<'_>, span: Span, ty: Ty<'_>) {
 113         for leaf in ty.walk() {
 114             if let GenericArgKind::Type(leaf_ty) = leaf.unpack() {
 115                 if leaf_ty.is_box() {
 116                     cx.struct_span_lint(BOX_POINTERS, span, |lint| {
 117                         lint.build(&format!("type uses owned (Box type) pointers: {}", ty)).emit()
 118                     });
 119                 }
 120             }
 121         }
 122     }
 123 }
 124
 125 impl<'tcx> LateLintPass<'tcx> for BoxPointers {
 126     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 127         match it.kind {
 128             hir::ItemKind::Fn(..)
 129             | hir::ItemKind::TyAlias(..)
 130             | hir::ItemKind::Enum(..)
 131             | hir::ItemKind::Struct(..)
 132             | hir::ItemKind::Union(..) => {
 133                 let def_id = cx.tcx.hir().local_def_id(it.hir_id);
 134                 self.check_heap_type(cx, it.span, cx.tcx.type_of(def_id))
 135             }
 136             _ => (),
 137         }
 138
 139         // If it's a struct, we also have to check the fields' types
 140         match it.kind {
 141             hir::ItemKind::Struct(ref struct_def, _) | hir::ItemKind::Union(ref struct_def, _) => {
 142                 for struct_field in struct_def.fields() {
 143                     let def_id = cx.tcx.hir().local_def_id(struct_field.hir_id);
 144                     self.check_heap_type(cx, struct_field.span, cx.tcx.type_of(def_id));
 145                 }
 146             }
 147             _ => (),
 148         }
 149     }
 150
 151     fn check_expr(&mut self, cx: &LateContext<'_>, e: &hir::Expr<'_>) {
 152         let ty = cx.typeck_results().node_type(e.hir_id);
 153         self.check_heap_type(cx, e.span, ty);
 154     }
 155 }
 156
 157 declare_lint! {
 158     NON_SHORTHAND_FIELD_PATTERNS,
 159     Warn,
 160     "using `Struct { x: x }` instead of `Struct { x }` in a pattern"
 161 }
 162
 163 declare_lint_pass!(NonShorthandFieldPatterns => [NON_SHORTHAND_FIELD_PATTERNS]);
 164
 165 impl<'tcx> LateLintPass<'tcx> for NonShorthandFieldPatterns {
 166     fn check_pat(&mut self, cx: &LateContext<'_>, pat: &hir::Pat<'_>) {
 167         if let PatKind::Struct(ref qpath, field_pats, _) = pat.kind {
 168             let variant = cx
 169                 .typeck_results()
 170                 .pat_ty(pat)
 171                 .ty_adt_def()
 172                 .expect("struct pattern type is not an ADT")
 173                 .variant_of_res(cx.qpath_res(qpath, pat.hir_id));
 174             for fieldpat in field_pats {
 175                 if fieldpat.is_shorthand {
 176                     continue;
 177                 }
 178                 if fieldpat.span.from_expansion() {
 179                     // Don't lint if this is a macro expansion: macro authors
 180                     // shouldn't have to worry about this kind of style issue
 181                     // (Issue #49588)
 182                     continue;
 183                 }
 184                 if let PatKind::Binding(binding_annot, _, ident, None) = fieldpat.pat.kind {
 185                     if cx.tcx.find_field_index(ident, &variant)
 186                         == Some(cx.tcx.field_index(fieldpat.hir_id, cx.typeck_results()))
 187                     {
 188                         cx.struct_span_lint(NON_SHORTHAND_FIELD_PATTERNS, fieldpat.span, |lint| {
 189                             let mut err = lint
 190                                 .build(&format!("the `{}:` in this pattern is redundant", ident));
 191                             let binding = match binding_annot {
 192                                 hir::BindingAnnotation::Unannotated => None,
 193                                 hir::BindingAnnotation::Mutable => Some("mut"),
 194                                 hir::BindingAnnotation::Ref => Some("ref"),
 195                                 hir::BindingAnnotation::RefMut => Some("ref mut"),
 196                             };
 197                             let ident = if let Some(binding) = binding {
 198                                 format!("{} {}", binding, ident)
 199                             } else {
 200                                 ident.to_string()
 201                             };
 202                             err.span_suggestion(
 203                                 fieldpat.span,
 204                                 "use shorthand field pattern",
 205                                 ident,
 206                                 Applicability::MachineApplicable,
 207                             );
 208                             err.emit();
 209                         });
 210                     }
 211                 }
 212             }
 213         }
 214     }
 215 }
 216
 217 declare_lint! {
 218     UNSAFE_CODE,
 219     Allow,
 220     "usage of `unsafe` code"
 221 }
 222
 223 declare_lint_pass!(UnsafeCode => [UNSAFE_CODE]);
 224
 225 impl UnsafeCode {
 226     fn report_unsafe(
 227         &self,
 228         cx: &EarlyContext<'_>,
 229         span: Span,
 230         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
 231     ) {
 232         // This comes from a macro that has `#[allow_internal_unsafe]`.
 233         if span.allows_unsafe() {
 234             return;
 235         }
 236
 237         cx.struct_span_lint(UNSAFE_CODE, span, decorate);
 238     }
 239 }
 240
 241 impl EarlyLintPass for UnsafeCode {
 242     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 243         if cx.sess().check_name(attr, sym::allow_internal_unsafe) {
 244             self.report_unsafe(cx, attr.span, |lint| {
 245                 lint.build(
 246                     "`allow_internal_unsafe` allows defining \
 247                                                macros using unsafe without triggering \
 248                                                the `unsafe_code` lint at their call site",
 249                 )
 250                 .emit()
 251             });
 252         }
 253     }
 254
 255     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
 256         if let ast::ExprKind::Block(ref blk, _) = e.kind {
 257             // Don't warn about generated blocks; that'll just pollute the output.
 258             if blk.rules == ast::BlockCheckMode::Unsafe(ast::UserProvided) {
 259                 self.report_unsafe(cx, blk.span, |lint| {
 260                     lint.build("usage of an `unsafe` block").emit()
 261                 });
 262             }
 263         }
 264     }
 265
 266     fn check_item(&mut self, cx: &EarlyContext<'_>, it: &ast::Item) {
 267         match it.kind {
 268             ast::ItemKind::Trait(_, ast::Unsafe::Yes(_), ..) => {
 269                 self.report_unsafe(cx, it.span, |lint| {
 270                     lint.build("declaration of an `unsafe` trait").emit()
 271                 })
 272             }
 273
 274             ast::ItemKind::Impl { unsafety: ast::Unsafe::Yes(_), .. } => {
 275                 self.report_unsafe(cx, it.span, |lint| {
 276                     lint.build("implementation of an `unsafe` trait").emit()
 277                 })
 278             }
 279
 280             _ => {}
 281         }
 282     }
 283
 284     fn check_fn(&mut self, cx: &EarlyContext<'_>, fk: FnKind<'_>, span: Span, _: ast::NodeId) {
 285         if let FnKind::Fn(
 286             ctxt,
 287             _,
 288             ast::FnSig { header: ast::FnHeader { unsafety: ast::Unsafe::Yes(_), .. }, .. },
 289             _,
 290             body,
 291         ) = fk
 292         {
 293             let msg = match ctxt {
 294                 FnCtxt::Foreign => return,
 295                 FnCtxt::Free => "declaration of an `unsafe` function",
 296                 FnCtxt::Assoc(_) if body.is_none() => "declaration of an `unsafe` method",
 297                 FnCtxt::Assoc(_) => "implementation of an `unsafe` method",
 298             };
 299             self.report_unsafe(cx, span, |lint| lint.build(msg).emit());
 300         }
 301     }
 302 }
 303
 304 declare_lint! {
 305     pub MISSING_DOCS,
 306     Allow,
 307     "detects missing documentation for public members",
 308     report_in_external_macro
 309 }
 310
 311 pub struct MissingDoc {
 312     /// Stack of whether `#[doc(hidden)]` is set at each level which has lint attributes.
 313     doc_hidden_stack: Vec<bool>,
 314
 315     /// Private traits or trait items that leaked through. Don't check their methods.
 316     private_traits: FxHashSet<hir::HirId>,
 317 }
 318
 319 impl_lint_pass!(MissingDoc => [MISSING_DOCS]);
 320
 321 fn has_doc(sess: &Session, attr: &ast::Attribute) -> bool {
 322     if attr.is_doc_comment() {
 323         return true;
 324     }
 325
 326     if !sess.check_name(attr, sym::doc) {
 327         return false;
 328     }
 329
 330     if attr.is_value_str() {
 331         return true;
 332     }
 333
 334     if let Some(list) = attr.meta_item_list() {
 335         for meta in list {
 336             if meta.has_name(sym::include) || meta.has_name(sym::hidden) {
 337                 return true;
 338             }
 339         }
 340     }
 341
 342     false
 343 }
 344
 345 impl MissingDoc {
 346     pub fn new() -> MissingDoc {
 347         MissingDoc { doc_hidden_stack: vec![false], private_traits: FxHashSet::default() }
 348     }
 349
 350     fn doc_hidden(&self) -> bool {
 351         *self.doc_hidden_stack.last().expect("empty doc_hidden_stack")
 352     }
 353
 354     fn check_missing_docs_attrs(
 355         &self,
 356         cx: &LateContext<'_>,
 357         id: Option<hir::HirId>,
 358         attrs: &[ast::Attribute],
 359         sp: Span,
 360         article: &'static str,
 361         desc: &'static str,
 362     ) {
 363         // If we're building a test harness, then warning about
 364         // documentation is probably not really relevant right now.
 365         if cx.sess().opts.test {
 366             return;
 367         }
 368
 369         // `#[doc(hidden)]` disables missing_docs check.
 370         if self.doc_hidden() {
 371             return;
 372         }
 373
 374         // Only check publicly-visible items, using the result from the privacy pass.
 375         // It's an option so the crate root can also use this function (it doesn't
 376         // have a `NodeId`).
 377         if let Some(id) = id {
 378             if !cx.access_levels.is_exported(id) {
 379                 return;
 380             }
 381         }
 382
 383         let has_doc = attrs.iter().any(|a| has_doc(cx.sess(), a));
 384         if !has_doc {
 385             cx.struct_span_lint(
 386                 MISSING_DOCS,
 387                 cx.tcx.sess.source_map().guess_head_span(sp),
 388                 |lint| {
 389                     lint.build(&format!("missing documentation for {} {}", article, desc)).emit()
 390                 },
 391             );
 392         }
 393     }
 394 }
 395
 396 impl<'tcx> LateLintPass<'tcx> for MissingDoc {
 397     fn enter_lint_attrs(&mut self, cx: &LateContext<'_>, attrs: &[ast::Attribute]) {
 398         let doc_hidden = self.doc_hidden()
 399             || attrs.iter().any(|attr| {
 400                 cx.sess().check_name(attr, sym::doc)
 401                     && match attr.meta_item_list() {
 402                         None => false,
 403                         Some(l) => attr::list_contains_name(&l, sym::hidden),
 404                     }
 405             });
 406         self.doc_hidden_stack.push(doc_hidden);
 407     }
 408
 409     fn exit_lint_attrs(&mut self, _: &LateContext<'_>, _attrs: &[ast::Attribute]) {
 410         self.doc_hidden_stack.pop().expect("empty doc_hidden_stack");
 411     }
 412
 413     fn check_crate(&mut self, cx: &LateContext<'_>, krate: &hir::Crate<'_>) {
 414         self.check_missing_docs_attrs(cx, None, &krate.item.attrs, krate.item.span, "the", "crate");
 415
 416         for macro_def in krate.exported_macros {
 417             let has_doc = macro_def.attrs.iter().any(|a| has_doc(cx.sess(), a));
 418             if !has_doc {
 419                 cx.struct_span_lint(
 420                     MISSING_DOCS,
 421                     cx.tcx.sess.source_map().guess_head_span(macro_def.span),
 422                     |lint| lint.build("missing documentation for macro").emit(),
 423                 );
 424             }
 425         }
 426     }
 427
 428     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 429         match it.kind {
 430             hir::ItemKind::Trait(.., trait_item_refs) => {
 431                 // Issue #11592: traits are always considered exported, even when private.
 432                 if let hir::VisibilityKind::Inherited = it.vis.node {
 433                     self.private_traits.insert(it.hir_id);
 434                     for trait_item_ref in trait_item_refs {
 435                         self.private_traits.insert(trait_item_ref.id.hir_id);
 436                     }
 437                     return;
 438                 }
 439             }
 440             hir::ItemKind::Impl { of_trait: Some(ref trait_ref), items, .. } => {
 441                 // If the trait is private, add the impl items to `private_traits` so they don't get
 442                 // reported for missing docs.
 443                 let real_trait = trait_ref.path.res.def_id();
 444                 if let Some(def_id) = real_trait.as_local() {
 445                     let hir_id = cx.tcx.hir().local_def_id_to_hir_id(def_id);
 446                     if let Some(Node::Item(item)) = cx.tcx.hir().find(hir_id) {
 447                         if let hir::VisibilityKind::Inherited = item.vis.node {
 448                             for impl_item_ref in items {
 449                                 self.private_traits.insert(impl_item_ref.id.hir_id);
 450                             }
 451                         }
 452                     }
 453                 }
 454                 return;
 455             }
 456
 457             hir::ItemKind::TyAlias(..)
 458             | hir::ItemKind::Fn(..)
 459             | hir::ItemKind::Mod(..)
 460             | hir::ItemKind::Enum(..)
 461             | hir::ItemKind::Struct(..)
 462             | hir::ItemKind::Union(..)
 463             | hir::ItemKind::Const(..)
 464             | hir::ItemKind::Static(..) => {}
 465
 466             _ => return,
 467         };
 468
 469         let def_id = cx.tcx.hir().local_def_id(it.hir_id);
 470         let (article, desc) = cx.tcx.article_and_description(def_id.to_def_id());
 471
 472         self.check_missing_docs_attrs(cx, Some(it.hir_id), &it.attrs, it.span, article, desc);
 473     }
 474
 475     fn check_trait_item(&mut self, cx: &LateContext<'_>, trait_item: &hir::TraitItem<'_>) {
 476         if self.private_traits.contains(&trait_item.hir_id) {
 477             return;
 478         }
 479
 480         let def_id = cx.tcx.hir().local_def_id(trait_item.hir_id);
 481         let (article, desc) = cx.tcx.article_and_description(def_id.to_def_id());
 482
 483         self.check_missing_docs_attrs(
 484             cx,
 485             Some(trait_item.hir_id),
 486             &trait_item.attrs,
 487             trait_item.span,
 488             article,
 489             desc,
 490         );
 491     }
 492
 493     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
 494         // If the method is an impl for a trait, don't doc.
 495         if method_context(cx, impl_item.hir_id) == MethodLateContext::TraitImpl {
 496             return;
 497         }
 498
 499         let def_id = cx.tcx.hir().local_def_id(impl_item.hir_id);
 500         let (article, desc) = cx.tcx.article_and_description(def_id.to_def_id());
 501         self.check_missing_docs_attrs(
 502             cx,
 503             Some(impl_item.hir_id),
 504             &impl_item.attrs,
 505             impl_item.span,
 506             article,
 507             desc,
 508         );
 509     }
 510
 511     fn check_struct_field(&mut self, cx: &LateContext<'_>, sf: &hir::StructField<'_>) {
 512         if !sf.is_positional() {
 513             self.check_missing_docs_attrs(
 514                 cx,
 515                 Some(sf.hir_id),
 516                 &sf.attrs,
 517                 sf.span,
 518                 "a",
 519                 "struct field",
 520             )
 521         }
 522     }
 523
 524     fn check_variant(&mut self, cx: &LateContext<'_>, v: &hir::Variant<'_>) {
 525         self.check_missing_docs_attrs(cx, Some(v.id), &v.attrs, v.span, "a", "variant");
 526     }
 527 }
 528
 529 declare_lint! {
 530     pub MISSING_COPY_IMPLEMENTATIONS,
 531     Allow,
 532     "detects potentially-forgotten implementations of `Copy`"
 533 }
 534
 535 declare_lint_pass!(MissingCopyImplementations => [MISSING_COPY_IMPLEMENTATIONS]);
 536
 537 impl<'tcx> LateLintPass<'tcx> for MissingCopyImplementations {
 538     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 539         if !cx.access_levels.is_reachable(item.hir_id) {
 540             return;
 541         }
 542         let (def, ty) = match item.kind {
 543             hir::ItemKind::Struct(_, ref ast_generics) => {
 544                 if !ast_generics.params.is_empty() {
 545                     return;
 546                 }
 547                 let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
 548                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 549             }
 550             hir::ItemKind::Union(_, ref ast_generics) => {
 551                 if !ast_generics.params.is_empty() {
 552                     return;
 553                 }
 554                 let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
 555                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 556             }
 557             hir::ItemKind::Enum(_, ref ast_generics) => {
 558                 if !ast_generics.params.is_empty() {
 559                     return;
 560                 }
 561                 let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
 562                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 563             }
 564             _ => return,
 565         };
 566         if def.has_dtor(cx.tcx) {
 567             return;
 568         }
 569         let param_env = ty::ParamEnv::empty();
 570         if ty.is_copy_modulo_regions(cx.tcx.at(item.span), param_env) {
 571             return;
 572         }
 573         if can_type_implement_copy(cx.tcx, param_env, ty).is_ok() {
 574             cx.struct_span_lint(MISSING_COPY_IMPLEMENTATIONS, item.span, |lint| {
 575                 lint.build(
 576                     "type could implement `Copy`; consider adding `impl \
 577                           Copy`",
 578                 )
 579                 .emit()
 580             })
 581         }
 582     }
 583 }
 584
 585 declare_lint! {
 586     MISSING_DEBUG_IMPLEMENTATIONS,
 587     Allow,
 588     "detects missing implementations of Debug"
 589 }
 590
 591 #[derive(Default)]
 592 pub struct MissingDebugImplementations {
 593     impling_types: Option<HirIdSet>,
 594 }
 595
 596 impl_lint_pass!(MissingDebugImplementations => [MISSING_DEBUG_IMPLEMENTATIONS]);
 597
 598 impl<'tcx> LateLintPass<'tcx> for MissingDebugImplementations {
 599     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 600         if !cx.access_levels.is_reachable(item.hir_id) {
 601             return;
 602         }
 603
 604         match item.kind {
 605             hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) | hir::ItemKind::Enum(..) => {}
 606             _ => return,
 607         }
 608
 609         let debug = match cx.tcx.get_diagnostic_item(sym::debug_trait) {
 610             Some(debug) => debug,
 611             None => return,
 612         };
 613
 614         if self.impling_types.is_none() {
 615             let mut impls = HirIdSet::default();
 616             cx.tcx.for_each_impl(debug, |d| {
 617                 if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() {
 618                     if let Some(def_id) = ty_def.did.as_local() {
 619                         impls.insert(cx.tcx.hir().local_def_id_to_hir_id(def_id));
 620                     }
 621                 }
 622             });
 623
 624             self.impling_types = Some(impls);
 625             debug!("{:?}", self.impling_types);
 626         }
 627
 628         if !self.impling_types.as_ref().unwrap().contains(&item.hir_id) {
 629             cx.struct_span_lint(MISSING_DEBUG_IMPLEMENTATIONS, item.span, |lint| {
 630                 lint.build(&format!(
 631                     "type does not implement `{}`; consider adding `#[derive(Debug)]` \
 632                      or a manual implementation",
 633                     cx.tcx.def_path_str(debug)
 634                 ))
 635                 .emit()
 636             });
 637         }
 638     }
 639 }
 640
 641 declare_lint! {
 642     pub ANONYMOUS_PARAMETERS,
 643     Allow,
 644     "detects anonymous parameters",
 645     @future_incompatible = FutureIncompatibleInfo {
 646         reference: "issue #41686 <https://github.com/rust-lang/rust/issues/41686>",
 647         edition: Some(Edition::Edition2018),
 648     };
 649 }
 650
 651 declare_lint_pass!(
 652     /// Checks for use of anonymous parameters (RFC 1685).
 653     AnonymousParameters => [ANONYMOUS_PARAMETERS]
 654 );
 655
 656 impl EarlyLintPass for AnonymousParameters {
 657     fn check_trait_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
 658         if let ast::AssocItemKind::Fn(_, ref sig, _, _) = it.kind {
 659             for arg in sig.decl.inputs.iter() {
 660                 if let ast::PatKind::Ident(_, ident, None) = arg.pat.kind {
 661                     if ident.name == kw::Invalid {
 662                         cx.struct_span_lint(ANONYMOUS_PARAMETERS, arg.pat.span, |lint| {
 663                             let ty_snip = cx.sess.source_map().span_to_snippet(arg.ty.span);
 664
 665                             let (ty_snip, appl) = if let Ok(ref snip) = ty_snip {
 666                                 (snip.as_str(), Applicability::MachineApplicable)
 667                             } else {
 668                                 ("<type>", Applicability::HasPlaceholders)
 669                             };
 670
 671                             lint.build(
 672                                 "anonymous parameters are deprecated and will be \
 673                                      removed in the next edition.",
 674                             )
 675                             .span_suggestion(
 676                                 arg.pat.span,
 677                                 "try naming the parameter or explicitly \
 678                                             ignoring it",
 679                                 format!("_: {}", ty_snip),
 680                                 appl,
 681                             )
 682                             .emit();
 683                         })
 684                     }
 685                 }
 686             }
 687         }
 688     }
 689 }
 690
 691 /// Check for use of attributes which have been deprecated.
 692 #[derive(Clone)]
 693 pub struct DeprecatedAttr {
 694     // This is not free to compute, so we want to keep it around, rather than
 695     // compute it for every attribute.
 696     depr_attrs: Vec<&'static (Symbol, AttributeType, AttributeTemplate, AttributeGate)>,
 697 }
 698
 699 impl_lint_pass!(DeprecatedAttr => []);
 700
 701 impl DeprecatedAttr {
 702     pub fn new() -> DeprecatedAttr {
 703         DeprecatedAttr { depr_attrs: deprecated_attributes() }
 704     }
 705 }
 706
 707 fn lint_deprecated_attr(
 708     cx: &EarlyContext<'_>,
 709     attr: &ast::Attribute,
 710     msg: &str,
 711     suggestion: Option<&str>,
 712 ) {
 713     cx.struct_span_lint(DEPRECATED, attr.span, |lint| {
 714         lint.build(msg)
 715             .span_suggestion_short(
 716                 attr.span,
 717                 suggestion.unwrap_or("remove this attribute"),
 718                 String::new(),
 719                 Applicability::MachineApplicable,
 720             )
 721             .emit();
 722     })
 723 }
 724
 725 impl EarlyLintPass for DeprecatedAttr {
 726     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 727         for &&(n, _, _, ref g) in &self.depr_attrs {
 728             if attr.ident().map(|ident| ident.name) == Some(n) {
 729                 if let &AttributeGate::Gated(
 730                     Stability::Deprecated(link, suggestion),
 731                     ref name,
 732                     ref reason,
 733                     _,
 734                 ) = g
 735                 {
 736                     let msg =
 737                         format!("use of deprecated attribute `{}`: {}. See {}", name, reason, link);
 738                     lint_deprecated_attr(cx, attr, &msg, suggestion);
 739                 }
 740                 return;
 741             }
 742         }
 743         if cx.sess().check_name(attr, sym::no_start) || cx.sess().check_name(attr, sym::crate_id) {
 744             let path_str = pprust::path_to_string(&attr.get_normal_item().path);
 745             let msg = format!("use of deprecated attribute `{}`: no longer used.", path_str);
 746             lint_deprecated_attr(cx, attr, &msg, None);
 747         }
 748     }
 749 }
 750
 751 fn warn_if_doc(cx: &EarlyContext<'_>, node_span: Span, node_kind: &str, attrs: &[ast::Attribute]) {
 752     let mut attrs = attrs.iter().peekable();
 753
 754     // Accumulate a single span for sugared doc comments.
 755     let mut sugared_span: Option<Span> = None;
 756
 757     while let Some(attr) = attrs.next() {
 758         if attr.is_doc_comment() {
 759             sugared_span =
 760                 Some(sugared_span.map_or_else(|| attr.span, |span| span.with_hi(attr.span.hi())));
 761         }
 762
 763         if attrs.peek().map(|next_attr| next_attr.is_doc_comment()).unwrap_or_default() {
 764             continue;
 765         }
 766
 767         let span = sugared_span.take().unwrap_or_else(|| attr.span);
 768
 769         if attr.is_doc_comment() || cx.sess().check_name(attr, sym::doc) {
 770             cx.struct_span_lint(UNUSED_DOC_COMMENTS, span, |lint| {
 771                 let mut err = lint.build("unused doc comment");
 772                 err.span_label(
 773                     node_span,
 774                     format!("rustdoc does not generate documentation for {}", node_kind),
 775                 );
 776                 err.emit();
 777             });
 778         }
 779     }
 780 }
 781
 782 impl EarlyLintPass for UnusedDocComment {
 783     fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &ast::Stmt) {
 784         let kind = match stmt.kind {
 785             ast::StmtKind::Local(..) => "statements",
 786             ast::StmtKind::Item(..) => "inner items",
 787             // expressions will be reported by `check_expr`.
 788             ast::StmtKind::Empty
 789             | ast::StmtKind::Semi(_)
 790             | ast::StmtKind::Expr(_)
 791             | ast::StmtKind::MacCall(_) => return,
 792         };
 793
 794         warn_if_doc(cx, stmt.span, kind, stmt.kind.attrs());
 795     }
 796
 797     fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) {
 798         let arm_span = arm.pat.span.with_hi(arm.body.span.hi());
 799         warn_if_doc(cx, arm_span, "match arms", &arm.attrs);
 800     }
 801
 802     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
 803         warn_if_doc(cx, expr.span, "expressions", &expr.attrs);
 804     }
 805 }
 806
 807 declare_lint! {
 808     NO_MANGLE_CONST_ITEMS,
 809     Deny,
 810     "const items will not have their symbols exported"
 811 }
 812
 813 declare_lint! {
 814     NO_MANGLE_GENERIC_ITEMS,
 815     Warn,
 816     "generic items must be mangled"
 817 }
 818
 819 declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS, NO_MANGLE_GENERIC_ITEMS]);
 820
 821 impl<'tcx> LateLintPass<'tcx> for InvalidNoMangleItems {
 822     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 823         match it.kind {
 824             hir::ItemKind::Fn(.., ref generics, _) => {
 825                 if let Some(no_mangle_attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
 826                     for param in generics.params {
 827                         match param.kind {
 828                             GenericParamKind::Lifetime { .. } => {}
 829                             GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
 830                                 cx.struct_span_lint(NO_MANGLE_GENERIC_ITEMS, it.span, |lint| {
 831                                     lint.build(
 832                                         "functions generic over types or consts must be mangled",
 833                                     )
 834                                     .span_suggestion_short(
 835                                         no_mangle_attr.span,
 836                                         "remove this attribute",
 837                                         String::new(),
 838                                         // Use of `#[no_mangle]` suggests FFI intent; correct
 839                                         // fix may be to monomorphize source by hand
 840                                         Applicability::MaybeIncorrect,
 841                                     )
 842                                     .emit();
 843                                 });
 844                                 break;
 845                             }
 846                         }
 847                     }
 848                 }
 849             }
 850             hir::ItemKind::Const(..) => {
 851                 if cx.sess().contains_name(&it.attrs, sym::no_mangle) {
 852                     // Const items do not refer to a particular location in memory, and therefore
 853                     // don't have anything to attach a symbol to
 854                     cx.struct_span_lint(NO_MANGLE_CONST_ITEMS, it.span, |lint| {
 855                         let msg = "const items should never be `#[no_mangle]`";
 856                         let mut err = lint.build(msg);
 857
 858                         // account for "pub const" (#45562)
 859                         let start = cx
 860                             .tcx
 861                             .sess
 862                             .source_map()
 863                             .span_to_snippet(it.span)
 864                             .map(|snippet| snippet.find("const").unwrap_or(0))
 865                             .unwrap_or(0) as u32;
 866                         // `const` is 5 chars
 867                         let const_span = it.span.with_hi(BytePos(it.span.lo().0 + start + 5));
 868                         err.span_suggestion(
 869                             const_span,
 870                             "try a static value",
 871                             "pub static".to_owned(),
 872                             Applicability::MachineApplicable,
 873                         );
 874                         err.emit();
 875                     });
 876                 }
 877             }
 878             _ => {}
 879         }
 880     }
 881 }
 882
 883 declare_lint! {
 884     MUTABLE_TRANSMUTES,
 885     Deny,
 886     "mutating transmuted &mut T from &T may cause undefined behavior"
 887 }
 888
 889 declare_lint_pass!(MutableTransmutes => [MUTABLE_TRANSMUTES]);
 890
 891 impl<'tcx> LateLintPass<'tcx> for MutableTransmutes {
 892     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &hir::Expr<'_>) {
 893         use rustc_target::spec::abi::Abi::RustIntrinsic;
 894         if let Some((&ty::Ref(_, _, from_mt), &ty::Ref(_, _, to_mt))) =
 895             get_transmute_from_to(cx, expr).map(|(ty1, ty2)| (&ty1.kind, &ty2.kind))
 896         {
 897             if to_mt == hir::Mutability::Mut && from_mt == hir::Mutability::Not {
 898                 let msg = "mutating transmuted &mut T from &T may cause undefined behavior, \
 899                                consider instead using an UnsafeCell";
 900                 cx.struct_span_lint(MUTABLE_TRANSMUTES, expr.span, |lint| lint.build(msg).emit());
 901             }
 902         }
 903
 904         fn get_transmute_from_to<'tcx>(
 905             cx: &LateContext<'tcx>,
 906             expr: &hir::Expr<'_>,
 907         ) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
 908             let def = if let hir::ExprKind::Path(ref qpath) = expr.kind {
 909                 cx.qpath_res(qpath, expr.hir_id)
 910             } else {
 911                 return None;
 912             };
 913             if let Res::Def(DefKind::Fn, did) = def {
 914                 if !def_id_is_transmute(cx, did) {
 915                     return None;
 916                 }
 917                 let sig = cx.typeck_results().node_type(expr.hir_id).fn_sig(cx.tcx);
 918                 let from = sig.inputs().skip_binder()[0];
 919                 let to = sig.output().skip_binder();
 920                 return Some((from, to));
 921             }
 922             None
 923         }
 924
 925         fn def_id_is_transmute(cx: &LateContext<'_>, def_id: DefId) -> bool {
 926             cx.tcx.fn_sig(def_id).abi() == RustIntrinsic
 927                 && cx.tcx.item_name(def_id) == sym::transmute
 928         }
 929     }
 930 }
 931
 932 declare_lint! {
 933     UNSTABLE_FEATURES,
 934     Allow,
 935     "enabling unstable features (deprecated. do not use)"
 936 }
 937
 938 declare_lint_pass!(
 939     /// Forbids using the `#[feature(...)]` attribute
 940     UnstableFeatures => [UNSTABLE_FEATURES]
 941 );
 942
 943 impl<'tcx> LateLintPass<'tcx> for UnstableFeatures {
 944     fn check_attribute(&mut self, cx: &LateContext<'_>, attr: &ast::Attribute) {
 945         if cx.sess().check_name(attr, sym::feature) {
 946             if let Some(items) = attr.meta_item_list() {
 947                 for item in items {
 948                     cx.struct_span_lint(UNSTABLE_FEATURES, item.span(), |lint| {
 949                         lint.build("unstable feature").emit()
 950                     });
 951                 }
 952             }
 953         }
 954     }
 955 }
 956
 957 declare_lint! {
 958     pub UNREACHABLE_PUB,
 959     Allow,
 960     "`pub` items not reachable from crate root"
 961 }
 962
 963 declare_lint_pass!(
 964     /// Lint for items marked `pub` that aren't reachable from other crates.
 965     UnreachablePub => [UNREACHABLE_PUB]
 966 );
 967
 968 impl UnreachablePub {
 969     fn perform_lint(
 970         &self,
 971         cx: &LateContext<'_>,
 972         what: &str,
 973         id: hir::HirId,
 974         vis: &hir::Visibility<'_>,
 975         span: Span,
 976         exportable: bool,
 977     ) {
 978         let mut applicability = Applicability::MachineApplicable;
 979         match vis.node {
 980             hir::VisibilityKind::Public if !cx.access_levels.is_reachable(id) => {
 981                 if span.from_expansion() {
 982                     applicability = Applicability::MaybeIncorrect;
 983                 }
 984                 let def_span = cx.tcx.sess.source_map().guess_head_span(span);
 985                 cx.struct_span_lint(UNREACHABLE_PUB, def_span, |lint| {
 986                     let mut err = lint.build(&format!("unreachable `pub` {}", what));
 987                     let replacement = if cx.tcx.features().crate_visibility_modifier {
 988                         "crate"
 989                     } else {
 990                         "pub(crate)"
 991                     }
 992                     .to_owned();
 993
 994                     err.span_suggestion(
 995                         vis.span,
 996                         "consider restricting its visibility",
 997                         replacement,
 998                         applicability,
 999                     );
1000                     if exportable {
1001                         err.help("or consider exporting it for use by other crates");
1002                     }
1003                     err.emit();
1004                 });
1005             }
1006             _ => {}
1007         }
1008     }
1009 }
1010
1011 impl<'tcx> LateLintPass<'tcx> for UnreachablePub {
1012     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1013         self.perform_lint(cx, "item", item.hir_id, &item.vis, item.span, true);
1014     }
1015
1016     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'tcx>) {
1017         self.perform_lint(
1018             cx,
1019             "item",
1020             foreign_item.hir_id,
1021             &foreign_item.vis,
1022             foreign_item.span,
1023             true,
1024         );
1025     }
1026
1027     fn check_struct_field(&mut self, cx: &LateContext<'_>, field: &hir::StructField<'_>) {
1028         self.perform_lint(cx, "field", field.hir_id, &field.vis, field.span, false);
1029     }
1030
1031     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
1032         self.perform_lint(cx, "item", impl_item.hir_id, &impl_item.vis, impl_item.span, false);
1033     }
1034 }
1035
1036 declare_lint! {
1037     TYPE_ALIAS_BOUNDS,
1038     Warn,
1039     "bounds in type aliases are not enforced"
1040 }
1041
1042 declare_lint_pass!(
1043     /// Lint for trait and lifetime bounds in type aliases being mostly ignored.
1044     /// They are relevant when using associated types, but otherwise neither checked
1045     /// at definition site nor enforced at use site.
1046     TypeAliasBounds => [TYPE_ALIAS_BOUNDS]
1047 );
1048
1049 impl TypeAliasBounds {
1050     fn is_type_variable_assoc(qpath: &hir::QPath<'_>) -> bool {
1051         match *qpath {
1052             hir::QPath::TypeRelative(ref ty, _) => {
1053                 // If this is a type variable, we found a `T::Assoc`.
1054                 match ty.kind {
1055                     hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => match path.res {
1056                         Res::Def(DefKind::TyParam, _) => true,
1057                         _ => false,
1058                     },
1059                     _ => false,
1060                 }
1061             }
1062             hir::QPath::Resolved(..) | hir::QPath::LangItem(..) => false,
1063         }
1064     }
1065
1066     fn suggest_changing_assoc_types(ty: &hir::Ty<'_>, err: &mut DiagnosticBuilder<'_>) {
1067         // Access to associates types should use `<T as Bound>::Assoc`, which does not need a
1068         // bound.  Let's see if this type does that.
1069
1070         // We use a HIR visitor to walk the type.
1071         use rustc_hir::intravisit::{self, Visitor};
1072         struct WalkAssocTypes<'a, 'db> {
1073             err: &'a mut DiagnosticBuilder<'db>,
1074         }
1075         impl<'a, 'db, 'v> Visitor<'v> for WalkAssocTypes<'a, 'db> {
1076             type Map = intravisit::ErasedMap<'v>;
1077
1078             fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1079                 intravisit::NestedVisitorMap::None
1080             }
1081
1082             fn visit_qpath(&mut self, qpath: &'v hir::QPath<'v>, id: hir::HirId, span: Span) {
1083                 if TypeAliasBounds::is_type_variable_assoc(qpath) {
1084                     self.err.span_help(
1085                         span,
1086                         "use fully disambiguated paths (i.e., `<T as Trait>::Assoc`) to refer to \
1087                          associated types in type aliases",
1088                     );
1089                 }
1090                 intravisit::walk_qpath(self, qpath, id, span)
1091             }
1092         }
1093
1094         // Let's go for a walk!
1095         let mut visitor = WalkAssocTypes { err };
1096         visitor.visit_ty(ty);
1097     }
1098 }
1099
1100 impl<'tcx> LateLintPass<'tcx> for TypeAliasBounds {
1101     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1102         let (ty, type_alias_generics) = match item.kind {
1103             hir::ItemKind::TyAlias(ref ty, ref generics) => (&*ty, generics),
1104             _ => return,
1105         };
1106         if let hir::TyKind::OpaqueDef(..) = ty.kind {
1107             // Bounds are respected for `type X = impl Trait`
1108             return;
1109         }
1110         let mut suggested_changing_assoc_types = false;
1111         // There must not be a where clause
1112         if !type_alias_generics.where_clause.predicates.is_empty() {
1113             cx.lint(
1114                 TYPE_ALIAS_BOUNDS,
1115                 |lint| {
1116                     let mut err = lint.build("where clauses are not enforced in type aliases");
1117                     let spans: Vec<_> = type_alias_generics
1118                         .where_clause
1119                         .predicates
1120                         .iter()
1121                         .map(|pred| pred.span())
1122                         .collect();
1123                     err.set_span(spans);
1124                     err.span_suggestion(
1125                         type_alias_generics.where_clause.span_for_predicates_or_empty_place(),
1126                         "the clause will not be checked when the type alias is used, and should be removed",
1127                         String::new(),
1128                         Applicability::MachineApplicable,
1129                     );
1130                     if !suggested_changing_assoc_types {
1131                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1132                         suggested_changing_assoc_types = true;
1133                     }
1134                     err.emit();
1135                 },
1136             );
1137         }
1138         // The parameters must not have bounds
1139         for param in type_alias_generics.params.iter() {
1140             let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
1141             let suggestion = spans
1142                 .iter()
1143                 .map(|sp| {
1144                     let start = param.span.between(*sp); // Include the `:` in `T: Bound`.
1145                     (start.to(*sp), String::new())
1146                 })
1147                 .collect();
1148             if !spans.is_empty() {
1149                 cx.struct_span_lint(TYPE_ALIAS_BOUNDS, spans, |lint| {
1150                     let mut err =
1151                         lint.build("bounds on generic parameters are not enforced in type aliases");
1152                     let msg = "the bound will not be checked when the type alias is used, \
1153                                    and should be removed";
1154                     err.multipart_suggestion(&msg, suggestion, Applicability::MachineApplicable);
1155                     if !suggested_changing_assoc_types {
1156                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1157                         suggested_changing_assoc_types = true;
1158                     }
1159                     err.emit();
1160                 });
1161             }
1162         }
1163     }
1164 }
1165
1166 declare_lint_pass!(
1167     /// Lint constants that are erroneous.
1168     /// Without this lint, we might not get any diagnostic if the constant is
1169     /// unused within this crate, even though downstream crates can't use it
1170     /// without producing an error.
1171     UnusedBrokenConst => []
1172 );
1173
1174 fn check_const(cx: &LateContext<'_>, body_id: hir::BodyId) {
1175     let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1176     // trigger the query once for all constants since that will already report the errors
1177     // FIXME: Use ensure here
1178     let _ = cx.tcx.const_eval_poly(def_id);
1179 }
1180
1181 impl<'tcx> LateLintPass<'tcx> for UnusedBrokenConst {
1182     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1183         match it.kind {
1184             hir::ItemKind::Const(_, body_id) => {
1185                 check_const(cx, body_id);
1186             }
1187             hir::ItemKind::Static(_, _, body_id) => {
1188                 check_const(cx, body_id);
1189             }
1190             _ => {}
1191         }
1192     }
1193 }
1194
1195 declare_lint! {
1196     TRIVIAL_BOUNDS,
1197     Warn,
1198     "these bounds don't depend on an type parameters"
1199 }
1200
1201 declare_lint_pass!(
1202     /// Lint for trait and lifetime bounds that don't depend on type parameters
1203     /// which either do nothing, or stop the item from being used.
1204     TrivialConstraints => [TRIVIAL_BOUNDS]
1205 );
1206
1207 impl<'tcx> LateLintPass<'tcx> for TrivialConstraints {
1208     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
1209         use rustc_middle::ty::fold::TypeFoldable;
1210         use rustc_middle::ty::PredicateAtom::*;
1211
1212         if cx.tcx.features().trivial_bounds {
1213             let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1214             let predicates = cx.tcx.predicates_of(def_id);
1215             for &(predicate, span) in predicates.predicates {
1216                 let predicate_kind_name = match predicate.skip_binders() {
1217                     Trait(..) => "Trait",
1218                     TypeOutlives(..) |
1219                     RegionOutlives(..) => "Lifetime",
1220
1221                     // Ignore projections, as they can only be global
1222                     // if the trait bound is global
1223                     Projection(..) |
1224                     // Ignore bounds that a user can't type
1225                     WellFormed(..) |
1226                     ObjectSafe(..) |
1227                     ClosureKind(..) |
1228                     Subtype(..) |
1229                     ConstEvaluatable(..) |
1230                     ConstEquate(..) => continue,
1231                 };
1232                 if predicate.is_global() {
1233                     cx.struct_span_lint(TRIVIAL_BOUNDS, span, |lint| {
1234                         lint.build(&format!(
1235                             "{} bound {} does not depend on any type \
1236                                 or lifetime parameters",
1237                             predicate_kind_name, predicate
1238                         ))
1239                         .emit()
1240                     });
1241                 }
1242             }
1243         }
1244     }
1245 }
1246
1247 declare_lint_pass!(
1248     /// Does nothing as a lint pass, but registers some `Lint`s
1249     /// which are used by other parts of the compiler.
1250     SoftLints => [
1251         WHILE_TRUE,
1252         BOX_POINTERS,
1253         NON_SHORTHAND_FIELD_PATTERNS,
1254         UNSAFE_CODE,
1255         MISSING_DOCS,
1256         MISSING_COPY_IMPLEMENTATIONS,
1257         MISSING_DEBUG_IMPLEMENTATIONS,
1258         ANONYMOUS_PARAMETERS,
1259         UNUSED_DOC_COMMENTS,
1260         NO_MANGLE_CONST_ITEMS,
1261         NO_MANGLE_GENERIC_ITEMS,
1262         MUTABLE_TRANSMUTES,
1263         UNSTABLE_FEATURES,
1264         UNREACHABLE_PUB,
1265         TYPE_ALIAS_BOUNDS,
1266         TRIVIAL_BOUNDS
1267     ]
1268 );
1269
1270 declare_lint! {
1271     pub ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
1272     Warn,
1273     "`...` range patterns are deprecated"
1274 }
1275
1276 #[derive(Default)]
1277 pub struct EllipsisInclusiveRangePatterns {
1278     /// If `Some(_)`, suppress all subsequent pattern
1279     /// warnings for better diagnostics.
1280     node_id: Option<ast::NodeId>,
1281 }
1282
1283 impl_lint_pass!(EllipsisInclusiveRangePatterns => [ELLIPSIS_INCLUSIVE_RANGE_PATTERNS]);
1284
1285 impl EarlyLintPass for EllipsisInclusiveRangePatterns {
1286     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &ast::Pat) {
1287         if self.node_id.is_some() {
1288             // Don't recursively warn about patterns inside range endpoints.
1289             return;
1290         }
1291
1292         use self::ast::{PatKind, RangeSyntax::DotDotDot};
1293
1294         /// If `pat` is a `...` pattern, return the start and end of the range, as well as the span
1295         /// corresponding to the ellipsis.
1296         fn matches_ellipsis_pat(pat: &ast::Pat) -> Option<(Option<&Expr>, &Expr, Span)> {
1297             match &pat.kind {
1298                 PatKind::Range(
1299                     a,
1300                     Some(b),
1301                     Spanned { span, node: RangeEnd::Included(DotDotDot) },
1302                 ) => Some((a.as_deref(), b, *span)),
1303                 _ => None,
1304             }
1305         }
1306
1307         let (parenthesise, endpoints) = match &pat.kind {
1308             PatKind::Ref(subpat, _) => (true, matches_ellipsis_pat(&subpat)),
1309             _ => (false, matches_ellipsis_pat(pat)),
1310         };
1311
1312         if let Some((start, end, join)) = endpoints {
1313             let msg = "`...` range patterns are deprecated";
1314             let suggestion = "use `..=` for an inclusive range";
1315             if parenthesise {
1316                 self.node_id = Some(pat.id);
1317                 cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, pat.span, |lint| {
1318                     let end = expr_to_string(&end);
1319                     let replace = match start {
1320                         Some(start) => format!("&({}..={})", expr_to_string(&start), end),
1321                         None => format!("&(..={})", end),
1322                     };
1323                     lint.build(msg)
1324                         .span_suggestion(
1325                             pat.span,
1326                             suggestion,
1327                             replace,
1328                             Applicability::MachineApplicable,
1329                         )
1330                         .emit();
1331                 });
1332             } else {
1333                 cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, join, |lint| {
1334                     lint.build(msg)
1335                         .span_suggestion_short(
1336                             join,
1337                             suggestion,
1338                             "..=".to_owned(),
1339                             Applicability::MachineApplicable,
1340                         )
1341                         .emit();
1342                 });
1343             };
1344         }
1345     }
1346
1347     fn check_pat_post(&mut self, _cx: &EarlyContext<'_>, pat: &ast::Pat) {
1348         if let Some(node_id) = self.node_id {
1349             if pat.id == node_id {
1350                 self.node_id = None
1351             }
1352         }
1353     }
1354 }
1355
1356 declare_lint! {
1357     UNNAMEABLE_TEST_ITEMS,
1358     Warn,
1359     "detects an item that cannot be named being marked as `#[test_case]`",
1360     report_in_external_macro
1361 }
1362
1363 pub struct UnnameableTestItems {
1364     boundary: Option<hir::HirId>, // HirId of the item under which things are not nameable
1365     items_nameable: bool,
1366 }
1367
1368 impl_lint_pass!(UnnameableTestItems => [UNNAMEABLE_TEST_ITEMS]);
1369
1370 impl UnnameableTestItems {
1371     pub fn new() -> Self {
1372         Self { boundary: None, items_nameable: true }
1373     }
1374 }
1375
1376 impl<'tcx> LateLintPass<'tcx> for UnnameableTestItems {
1377     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1378         if self.items_nameable {
1379             if let hir::ItemKind::Mod(..) = it.kind {
1380             } else {
1381                 self.items_nameable = false;
1382                 self.boundary = Some(it.hir_id);
1383             }
1384             return;
1385         }
1386
1387         if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::rustc_test_marker) {
1388             cx.struct_span_lint(UNNAMEABLE_TEST_ITEMS, attr.span, |lint| {
1389                 lint.build("cannot test inner items").emit()
1390             });
1391         }
1392     }
1393
1394     fn check_item_post(&mut self, _cx: &LateContext<'_>, it: &hir::Item<'_>) {
1395         if !self.items_nameable && self.boundary == Some(it.hir_id) {
1396             self.items_nameable = true;
1397         }
1398     }
1399 }
1400
1401 declare_lint! {
1402     pub KEYWORD_IDENTS,
1403     Allow,
1404     "detects edition keywords being used as an identifier",
1405     @future_incompatible = FutureIncompatibleInfo {
1406         reference: "issue #49716 <https://github.com/rust-lang/rust/issues/49716>",
1407         edition: Some(Edition::Edition2018),
1408     };
1409 }
1410
1411 declare_lint_pass!(
1412     /// Check for uses of edition keywords used as an identifier.
1413     KeywordIdents => [KEYWORD_IDENTS]
1414 );
1415
1416 struct UnderMacro(bool);
1417
1418 impl KeywordIdents {
1419     fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: TokenStream) {
1420         for tt in tokens.into_trees() {
1421             match tt {
1422                 // Only report non-raw idents.
1423                 TokenTree::Token(token) => {
1424                     if let Some((ident, false)) = token.ident() {
1425                         self.check_ident_token(cx, UnderMacro(true), ident);
1426                     }
1427                 }
1428                 TokenTree::Delimited(_, _, tts) => self.check_tokens(cx, tts),
1429             }
1430         }
1431     }
1432
1433     fn check_ident_token(
1434         &mut self,
1435         cx: &EarlyContext<'_>,
1436         UnderMacro(under_macro): UnderMacro,
1437         ident: Ident,
1438     ) {
1439         let next_edition = match cx.sess.edition() {
1440             Edition::Edition2015 => {
1441                 match ident.name {
1442                     kw::Async | kw::Await | kw::Try => Edition::Edition2018,
1443
1444                     // rust-lang/rust#56327: Conservatively do not
1445                     // attempt to report occurrences of `dyn` within
1446                     // macro definitions or invocations, because `dyn`
1447                     // can legitimately occur as a contextual keyword
1448                     // in 2015 code denoting its 2018 meaning, and we
1449                     // do not want rustfix to inject bugs into working
1450                     // code by rewriting such occurrences.
1451                     //
1452                     // But if we see `dyn` outside of a macro, we know
1453                     // its precise role in the parsed AST and thus are
1454                     // assured this is truly an attempt to use it as
1455                     // an identifier.
1456                     kw::Dyn if !under_macro => Edition::Edition2018,
1457
1458                     _ => return,
1459                 }
1460             }
1461
1462             // There are no new keywords yet for the 2018 edition and beyond.
1463             _ => return,
1464         };
1465
1466         // Don't lint `r#foo`.
1467         if cx.sess.parse_sess.raw_identifier_spans.borrow().contains(&ident.span) {
1468             return;
1469         }
1470
1471         cx.struct_span_lint(KEYWORD_IDENTS, ident.span, |lint| {
1472             lint.build(&format!("`{}` is a keyword in the {} edition", ident, next_edition))
1473                 .span_suggestion(
1474                     ident.span,
1475                     "you can use a raw identifier to stay compatible",
1476                     format!("r#{}", ident),
1477                     Applicability::MachineApplicable,
1478                 )
1479                 .emit()
1480         });
1481     }
1482 }
1483
1484 impl EarlyLintPass for KeywordIdents {
1485     fn check_mac_def(&mut self, cx: &EarlyContext<'_>, mac_def: &ast::MacroDef, _id: ast::NodeId) {
1486         self.check_tokens(cx, mac_def.body.inner_tokens());
1487     }
1488     fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::MacCall) {
1489         self.check_tokens(cx, mac.args.inner_tokens());
1490     }
1491     fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: Ident) {
1492         self.check_ident_token(cx, UnderMacro(false), ident);
1493     }
1494 }
1495
1496 declare_lint_pass!(ExplicitOutlivesRequirements => [EXPLICIT_OUTLIVES_REQUIREMENTS]);
1497
1498 impl ExplicitOutlivesRequirements {
1499     fn lifetimes_outliving_lifetime<'tcx>(
1500         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
1501         index: u32,
1502     ) -> Vec<ty::Region<'tcx>> {
1503         inferred_outlives
1504             .iter()
1505             .filter_map(|(pred, _)| match pred.skip_binders() {
1506                 ty::PredicateAtom::RegionOutlives(ty::OutlivesPredicate(a, b)) => match a {
1507                     ty::ReEarlyBound(ebr) if ebr.index == index => Some(b),
1508                     _ => None,
1509                 },
1510                 _ => None,
1511             })
1512             .collect()
1513     }
1514
1515     fn lifetimes_outliving_type<'tcx>(
1516         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
1517         index: u32,
1518     ) -> Vec<ty::Region<'tcx>> {
1519         inferred_outlives
1520             .iter()
1521             .filter_map(|(pred, _)| match pred.skip_binders() {
1522                 ty::PredicateAtom::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
1523                     a.is_param(index).then_some(b)
1524                 }
1525                 _ => None,
1526             })
1527             .collect()
1528     }
1529
1530     fn collect_outlived_lifetimes<'tcx>(
1531         &self,
1532         param: &'tcx hir::GenericParam<'tcx>,
1533         tcx: TyCtxt<'tcx>,
1534         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
1535         ty_generics: &'tcx ty::Generics,
1536     ) -> Vec<ty::Region<'tcx>> {
1537         let index =
1538             ty_generics.param_def_id_to_index[&tcx.hir().local_def_id(param.hir_id).to_def_id()];
1539
1540         match param.kind {
1541             hir::GenericParamKind::Lifetime { .. } => {
1542                 Self::lifetimes_outliving_lifetime(inferred_outlives, index)
1543             }
1544             hir::GenericParamKind::Type { .. } => {
1545                 Self::lifetimes_outliving_type(inferred_outlives, index)
1546             }
1547             hir::GenericParamKind::Const { .. } => Vec::new(),
1548         }
1549     }
1550
1551     fn collect_outlives_bound_spans<'tcx>(
1552         &self,
1553         tcx: TyCtxt<'tcx>,
1554         bounds: &hir::GenericBounds<'_>,
1555         inferred_outlives: &[ty::Region<'tcx>],
1556         infer_static: bool,
1557     ) -> Vec<(usize, Span)> {
1558         use rustc_middle::middle::resolve_lifetime::Region;
1559
1560         bounds
1561             .iter()
1562             .enumerate()
1563             .filter_map(|(i, bound)| {
1564                 if let hir::GenericBound::Outlives(lifetime) = bound {
1565                     let is_inferred = match tcx.named_region(lifetime.hir_id) {
1566                         Some(Region::Static) if infer_static => inferred_outlives
1567                             .iter()
1568                             .any(|r| if let ty::ReStatic = r { true } else { false }),
1569                         Some(Region::EarlyBound(index, ..)) => inferred_outlives.iter().any(|r| {
1570                             if let ty::ReEarlyBound(ebr) = r { ebr.index == index } else { false }
1571                         }),
1572                         _ => false,
1573                     };
1574                     is_inferred.then_some((i, bound.span()))
1575                 } else {
1576                     None
1577                 }
1578             })
1579             .collect()
1580     }
1581
1582     fn consolidate_outlives_bound_spans(
1583         &self,
1584         lo: Span,
1585         bounds: &hir::GenericBounds<'_>,
1586         bound_spans: Vec<(usize, Span)>,
1587     ) -> Vec<Span> {
1588         if bounds.is_empty() {
1589             return Vec::new();
1590         }
1591         if bound_spans.len() == bounds.len() {
1592             let (_, last_bound_span) = bound_spans[bound_spans.len() - 1];
1593             // If all bounds are inferable, we want to delete the colon, so
1594             // start from just after the parameter (span passed as argument)
1595             vec![lo.to(last_bound_span)]
1596         } else {
1597             let mut merged = Vec::new();
1598             let mut last_merged_i = None;
1599
1600             let mut from_start = true;
1601             for (i, bound_span) in bound_spans {
1602                 match last_merged_i {
1603                     // If the first bound is inferable, our span should also eat the leading `+`.
1604                     None if i == 0 => {
1605                         merged.push(bound_span.to(bounds[1].span().shrink_to_lo()));
1606                         last_merged_i = Some(0);
1607                     }
1608                     // If consecutive bounds are inferable, merge their spans
1609                     Some(h) if i == h + 1 => {
1610                         if let Some(tail) = merged.last_mut() {
1611                             // Also eat the trailing `+` if the first
1612                             // more-than-one bound is inferable
1613                             let to_span = if from_start && i < bounds.len() {
1614                                 bounds[i + 1].span().shrink_to_lo()
1615                             } else {
1616                                 bound_span
1617                             };
1618                             *tail = tail.to(to_span);
1619                             last_merged_i = Some(i);
1620                         } else {
1621                             bug!("another bound-span visited earlier");
1622                         }
1623                     }
1624                     _ => {
1625                         // When we find a non-inferable bound, subsequent inferable bounds
1626                         // won't be consecutive from the start (and we'll eat the leading
1627                         // `+` rather than the trailing one)
1628                         from_start = false;
1629                         merged.push(bounds[i - 1].span().shrink_to_hi().to(bound_span));
1630                         last_merged_i = Some(i);
1631                     }
1632                 }
1633             }
1634             merged
1635         }
1636     }
1637 }
1638
1639 impl<'tcx> LateLintPass<'tcx> for ExplicitOutlivesRequirements {
1640     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
1641         use rustc_middle::middle::resolve_lifetime::Region;
1642
1643         let infer_static = cx.tcx.features().infer_static_outlives_requirements;
1644         let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1645         if let hir::ItemKind::Struct(_, ref hir_generics)
1646         | hir::ItemKind::Enum(_, ref hir_generics)
1647         | hir::ItemKind::Union(_, ref hir_generics) = item.kind
1648         {
1649             let inferred_outlives = cx.tcx.inferred_outlives_of(def_id);
1650             if inferred_outlives.is_empty() {
1651                 return;
1652             }
1653
1654             let ty_generics = cx.tcx.generics_of(def_id);
1655
1656             let mut bound_count = 0;
1657             let mut lint_spans = Vec::new();
1658
1659             for param in hir_generics.params {
1660                 let has_lifetime_bounds = param.bounds.iter().any(|bound| {
1661                     if let hir::GenericBound::Outlives(_) = bound { true } else { false }
1662                 });
1663                 if !has_lifetime_bounds {
1664                     continue;
1665                 }
1666
1667                 let relevant_lifetimes =
1668                     self.collect_outlived_lifetimes(param, cx.tcx, inferred_outlives, ty_generics);
1669                 if relevant_lifetimes.is_empty() {
1670                     continue;
1671                 }
1672
1673                 let bound_spans = self.collect_outlives_bound_spans(
1674                     cx.tcx,
1675                     &param.bounds,
1676                     &relevant_lifetimes,
1677                     infer_static,
1678                 );
1679                 bound_count += bound_spans.len();
1680                 lint_spans.extend(self.consolidate_outlives_bound_spans(
1681                     param.span.shrink_to_hi(),
1682                     &param.bounds,
1683                     bound_spans,
1684                 ));
1685             }
1686
1687             let mut where_lint_spans = Vec::new();
1688             let mut dropped_predicate_count = 0;
1689             let num_predicates = hir_generics.where_clause.predicates.len();
1690             for (i, where_predicate) in hir_generics.where_clause.predicates.iter().enumerate() {
1691                 let (relevant_lifetimes, bounds, span) = match where_predicate {
1692                     hir::WherePredicate::RegionPredicate(predicate) => {
1693                         if let Some(Region::EarlyBound(index, ..)) =
1694                             cx.tcx.named_region(predicate.lifetime.hir_id)
1695                         {
1696                             (
1697                                 Self::lifetimes_outliving_lifetime(inferred_outlives, index),
1698                                 &predicate.bounds,
1699                                 predicate.span,
1700                             )
1701                         } else {
1702                             continue;
1703                         }
1704                     }
1705                     hir::WherePredicate::BoundPredicate(predicate) => {
1706                         // FIXME we can also infer bounds on associated types,
1707                         // and should check for them here.
1708                         match predicate.bounded_ty.kind {
1709                             hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
1710                                 if let Res::Def(DefKind::TyParam, def_id) = path.res {
1711                                     let index = ty_generics.param_def_id_to_index[&def_id];
1712                                     (
1713                                         Self::lifetimes_outliving_type(inferred_outlives, index),
1714                                         &predicate.bounds,
1715                                         predicate.span,
1716                                     )
1717                                 } else {
1718                                     continue;
1719                                 }
1720                             }
1721                             _ => {
1722                                 continue;
1723                             }
1724                         }
1725                     }
1726                     _ => continue,
1727                 };
1728                 if relevant_lifetimes.is_empty() {
1729                     continue;
1730                 }
1731
1732                 let bound_spans = self.collect_outlives_bound_spans(
1733                     cx.tcx,
1734                     bounds,
1735                     &relevant_lifetimes,
1736                     infer_static,
1737                 );
1738                 bound_count += bound_spans.len();
1739
1740                 let drop_predicate = bound_spans.len() == bounds.len();
1741                 if drop_predicate {
1742                     dropped_predicate_count += 1;
1743                 }
1744
1745                 // If all the bounds on a predicate were inferable and there are
1746                 // further predicates, we want to eat the trailing comma.
1747                 if drop_predicate && i + 1 < num_predicates {
1748                     let next_predicate_span = hir_generics.where_clause.predicates[i + 1].span();
1749                     where_lint_spans.push(span.to(next_predicate_span.shrink_to_lo()));
1750                 } else {
1751                     where_lint_spans.extend(self.consolidate_outlives_bound_spans(
1752                         span.shrink_to_lo(),
1753                         bounds,
1754                         bound_spans,
1755                     ));
1756                 }
1757             }
1758
1759             // If all predicates are inferable, drop the entire clause
1760             // (including the `where`)
1761             if num_predicates > 0 && dropped_predicate_count == num_predicates {
1762                 let where_span = hir_generics
1763                     .where_clause
1764                     .span()
1765                     .expect("span of (nonempty) where clause should exist");
1766                 // Extend the where clause back to the closing `>` of the
1767                 // generics, except for tuple struct, which have the `where`
1768                 // after the fields of the struct.
1769                 let full_where_span =
1770                     if let hir::ItemKind::Struct(hir::VariantData::Tuple(..), _) = item.kind {
1771                         where_span
1772                     } else {
1773                         hir_generics.span.shrink_to_hi().to(where_span)
1774                     };
1775                 lint_spans.push(full_where_span);
1776             } else {
1777                 lint_spans.extend(where_lint_spans);
1778             }
1779
1780             if !lint_spans.is_empty() {
1781                 cx.struct_span_lint(EXPLICIT_OUTLIVES_REQUIREMENTS, lint_spans.clone(), |lint| {
1782                     lint.build("outlives requirements can be inferred")
1783                         .multipart_suggestion(
1784                             if bound_count == 1 {
1785                                 "remove this bound"
1786                             } else {
1787                                 "remove these bounds"
1788                             },
1789                             lint_spans
1790                                 .into_iter()
1791                                 .map(|span| (span, "".to_owned()))
1792                                 .collect::<Vec<_>>(),
1793                             Applicability::MachineApplicable,
1794                         )
1795                         .emit();
1796                 });
1797             }
1798         }
1799     }
1800 }
1801
1802 declare_lint! {
1803     pub INCOMPLETE_FEATURES,
1804     Warn,
1805     "incomplete features that may function improperly in some or all cases"
1806 }
1807
1808 declare_lint_pass!(
1809     /// Check for used feature gates in `INCOMPLETE_FEATURES` in `librustc_feature/active.rs`.
1810     IncompleteFeatures => [INCOMPLETE_FEATURES]
1811 );
1812
1813 impl EarlyLintPass for IncompleteFeatures {
1814     fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
1815         let features = cx.sess.features_untracked();
1816         features
1817             .declared_lang_features
1818             .iter()
1819             .map(|(name, span, _)| (name, span))
1820             .chain(features.declared_lib_features.iter().map(|(name, span)| (name, span)))
1821             .filter(|(name, _)| rustc_feature::INCOMPLETE_FEATURES.iter().any(|f| name == &f))
1822             .for_each(|(&name, &span)| {
1823                 cx.struct_span_lint(INCOMPLETE_FEATURES, span, |lint| {
1824                     let mut builder = lint.build(&format!(
1825                         "the feature `{}` is incomplete and may not be safe to use \
1826                          and/or cause compiler crashes",
1827                         name,
1828                     ));
1829                     if let Some(n) = rustc_feature::find_feature_issue(name, GateIssue::Language) {
1830                         builder.note(&format!(
1831                             "see issue #{} <https://github.com/rust-lang/rust/issues/{}> \
1832                              for more information",
1833                             n, n,
1834                         ));
1835                     }
1836                     builder.emit();
1837                 })
1838             });
1839     }
1840 }
1841
1842 declare_lint! {
1843     pub INVALID_VALUE,
1844     Warn,
1845     "an invalid value is being created (such as a NULL reference)"
1846 }
1847
1848 declare_lint_pass!(InvalidValue => [INVALID_VALUE]);
1849
1850 impl<'tcx> LateLintPass<'tcx> for InvalidValue {
1851     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
1852         #[derive(Debug, Copy, Clone, PartialEq)]
1853         enum InitKind {
1854             Zeroed,
1855             Uninit,
1856         };
1857
1858         /// Information about why a type cannot be initialized this way.
1859         /// Contains an error message and optionally a span to point at.
1860         type InitError = (String, Option<Span>);
1861
1862         /// Test if this constant is all-0.
1863         fn is_zero(expr: &hir::Expr<'_>) -> bool {
1864             use hir::ExprKind::*;
1865             use rustc_ast::LitKind::*;
1866             match &expr.kind {
1867                 Lit(lit) => {
1868                     if let Int(i, _) = lit.node {
1869                         i == 0
1870                     } else {
1871                         false
1872                     }
1873                 }
1874                 Tup(tup) => tup.iter().all(is_zero),
1875                 _ => false,
1876             }
1877         }
1878
1879         /// Determine if this expression is a "dangerous initialization".
1880         fn is_dangerous_init(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> Option<InitKind> {
1881             // `transmute` is inside an anonymous module (the `extern` block?);
1882             // `Invalid` represents the empty string and matches that.
1883             // FIXME(#66075): use diagnostic items.  Somehow, that does not seem to work
1884             // on intrinsics right now.
1885             const TRANSMUTE_PATH: &[Symbol] =
1886                 &[sym::core, sym::intrinsics, kw::Invalid, sym::transmute];
1887
1888             if let hir::ExprKind::Call(ref path_expr, ref args) = expr.kind {
1889                 // Find calls to `mem::{uninitialized,zeroed}` methods.
1890                 if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
1891                     let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
1892
1893                     if cx.tcx.is_diagnostic_item(sym::mem_zeroed, def_id) {
1894                         return Some(InitKind::Zeroed);
1895                     } else if cx.tcx.is_diagnostic_item(sym::mem_uninitialized, def_id) {
1896                         return Some(InitKind::Uninit);
1897                     } else if cx.match_def_path(def_id, TRANSMUTE_PATH) {
1898                         if is_zero(&args[0]) {
1899                             return Some(InitKind::Zeroed);
1900                         }
1901                     }
1902                 }
1903             } else if let hir::ExprKind::MethodCall(_, _, ref args, _) = expr.kind {
1904                 // Find problematic calls to `MaybeUninit::assume_init`.
1905                 let def_id = cx.typeck_results().type_dependent_def_id(expr.hir_id)?;
1906                 if cx.tcx.is_diagnostic_item(sym::assume_init, def_id) {
1907                     // This is a call to *some* method named `assume_init`.
1908                     // See if the `self` parameter is one of the dangerous constructors.
1909                     if let hir::ExprKind::Call(ref path_expr, _) = args[0].kind {
1910                         if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
1911                             let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
1912
1913                             if cx.tcx.is_diagnostic_item(sym::maybe_uninit_zeroed, def_id) {
1914                                 return Some(InitKind::Zeroed);
1915                             } else if cx.tcx.is_diagnostic_item(sym::maybe_uninit_uninit, def_id) {
1916                                 return Some(InitKind::Uninit);
1917                             }
1918                         }
1919                     }
1920                 }
1921             }
1922
1923             None
1924         }
1925
1926         /// Test if this enum has several actually "existing" variants.
1927         /// Zero-sized uninhabited variants do not always have a tag assigned and thus do not "exist".
1928         fn is_multi_variant(adt: &ty::AdtDef) -> bool {
1929             // As an approximation, we only count dataless variants. Those are definitely inhabited.
1930             let existing_variants = adt.variants.iter().filter(|v| v.fields.is_empty()).count();
1931             existing_variants > 1
1932         }
1933
1934         /// Return `Some` only if we are sure this type does *not*
1935         /// allow zero initialization.
1936         fn ty_find_init_error<'tcx>(
1937             tcx: TyCtxt<'tcx>,
1938             ty: Ty<'tcx>,
1939             init: InitKind,
1940         ) -> Option<InitError> {
1941             use rustc_middle::ty::TyKind::*;
1942             match ty.kind {
1943                 // Primitive types that don't like 0 as a value.
1944                 Ref(..) => Some(("references must be non-null".to_string(), None)),
1945                 Adt(..) if ty.is_box() => Some(("`Box` must be non-null".to_string(), None)),
1946                 FnPtr(..) => Some(("function pointers must be non-null".to_string(), None)),
1947                 Never => Some(("the `!` type has no valid value".to_string(), None)),
1948                 RawPtr(tm) if matches!(tm.ty.kind, Dynamic(..)) =>
1949                 // raw ptr to dyn Trait
1950                 {
1951                     Some(("the vtable of a wide raw pointer must be non-null".to_string(), None))
1952                 }
1953                 // Primitive types with other constraints.
1954                 Bool if init == InitKind::Uninit => {
1955                     Some(("booleans must be either `true` or `false`".to_string(), None))
1956                 }
1957                 Char if init == InitKind::Uninit => {
1958                     Some(("characters must be a valid Unicode codepoint".to_string(), None))
1959                 }
1960                 // Recurse and checks for some compound types.
1961                 Adt(adt_def, substs) if !adt_def.is_union() => {
1962                     // First check if this ADT has a layout attribute (like `NonNull` and friends).
1963                     use std::ops::Bound;
1964                     match tcx.layout_scalar_valid_range(adt_def.did) {
1965                         // We exploit here that `layout_scalar_valid_range` will never
1966                         // return `Bound::Excluded`.  (And we have tests checking that we
1967                         // handle the attribute correctly.)
1968                         (Bound::Included(lo), _) if lo > 0 => {
1969                             return Some((format!("`{}` must be non-null", ty), None));
1970                         }
1971                         (Bound::Included(_), _) | (_, Bound::Included(_))
1972                             if init == InitKind::Uninit =>
1973                         {
1974                             return Some((
1975                                 format!(
1976                                     "`{}` must be initialized inside its custom valid range",
1977                                     ty,
1978                                 ),
1979                                 None,
1980                             ));
1981                         }
1982                         _ => {}
1983                     }
1984                     // Now, recurse.
1985                     match adt_def.variants.len() {
1986                         0 => Some(("enums with no variants have no valid value".to_string(), None)),
1987                         1 => {
1988                             // Struct, or enum with exactly one variant.
1989                             // Proceed recursively, check all fields.
1990                             let variant = &adt_def.variants[VariantIdx::from_u32(0)];
1991                             variant.fields.iter().find_map(|field| {
1992                                 ty_find_init_error(tcx, field.ty(tcx, substs), init).map(
1993                                     |(mut msg, span)| {
1994                                         if span.is_none() {
1995                                             // Point to this field, should be helpful for figuring
1996                                             // out where the source of the error is.
1997                                             let span = tcx.def_span(field.did);
1998                                             write!(
1999                                                 &mut msg,
2000                                                 " (in this {} field)",
2001                                                 adt_def.descr()
2002                                             )
2003                                             .unwrap();
2004                                             (msg, Some(span))
2005                                         } else {
2006                                             // Just forward.
2007                                             (msg, span)
2008                                         }
2009                                     },
2010                                 )
2011                             })
2012                         }
2013                         // Multi-variant enum.
2014                         _ => {
2015                             if init == InitKind::Uninit && is_multi_variant(adt_def) {
2016                                 let span = tcx.def_span(adt_def.did);
2017                                 Some((
2018                                     "enums have to be initialized to a variant".to_string(),
2019                                     Some(span),
2020                                 ))
2021                             } else {
2022                                 // In principle, for zero-initialization we could figure out which variant corresponds
2023                                 // to tag 0, and check that... but for now we just accept all zero-initializations.
2024                                 None
2025                             }
2026                         }
2027                     }
2028                 }
2029                 Tuple(..) => {
2030                     // Proceed recursively, check all fields.
2031                     ty.tuple_fields().find_map(|field| ty_find_init_error(tcx, field, init))
2032                 }
2033                 // Conservative fallback.
2034                 _ => None,
2035             }
2036         }
2037
2038         if let Some(init) = is_dangerous_init(cx, expr) {
2039             // This conjures an instance of a type out of nothing,
2040             // using zeroed or uninitialized memory.
2041             // We are extremely conservative with what we warn about.
2042             let conjured_ty = cx.typeck_results().expr_ty(expr);
2043             if let Some((msg, span)) = ty_find_init_error(cx.tcx, conjured_ty, init) {
2044                 cx.struct_span_lint(INVALID_VALUE, expr.span, |lint| {
2045                     let mut err = lint.build(&format!(
2046                         "the type `{}` does not permit {}",
2047                         conjured_ty,
2048                         match init {
2049                             InitKind::Zeroed => "zero-initialization",
2050                             InitKind::Uninit => "being left uninitialized",
2051                         },
2052                     ));
2053                     err.span_label(expr.span, "this code causes undefined behavior when executed");
2054                     err.span_label(
2055                         expr.span,
2056                         "help: use `MaybeUninit<T>` instead, \
2057                             and only call `assume_init` after initialization is done",
2058                     );
2059                     if let Some(span) = span {
2060                         err.span_note(span, &msg);
2061                     } else {
2062                         err.note(&msg);
2063                     }
2064                     err.emit();
2065                 });
2066             }
2067         }
2068     }
2069 }
2070
2071 declare_lint! {
2072     pub CLASHING_EXTERN_DECLARATIONS,
2073     Warn,
2074     "detects when an extern fn has been declared with the same name but different types"
2075 }
2076
2077 pub struct ClashingExternDeclarations {
2078     seen_decls: FxHashMap<Symbol, HirId>,
2079 }
2080
2081 /// Differentiate between whether the name for an extern decl came from the link_name attribute or
2082 /// just from declaration itself. This is important because we don't want to report clashes on
2083 /// symbol name if they don't actually clash because one or the other links against a symbol with a
2084 /// different name.
2085 enum SymbolName {
2086     /// The name of the symbol + the span of the annotation which introduced the link name.
2087     Link(Symbol, Span),
2088     /// No link name, so just the name of the symbol.
2089     Normal(Symbol),
2090 }
2091
2092 impl SymbolName {
2093     fn get_name(&self) -> Symbol {
2094         match self {
2095             SymbolName::Link(s, _) | SymbolName::Normal(s) => *s,
2096         }
2097     }
2098 }
2099
2100 impl ClashingExternDeclarations {
2101     crate fn new() -> Self {
2102         ClashingExternDeclarations { seen_decls: FxHashMap::default() }
2103     }
2104     /// Insert a new foreign item into the seen set. If a symbol with the same name already exists
2105     /// for the item, return its HirId without updating the set.
2106     fn insert(&mut self, tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> Option<HirId> {
2107         let hid = fi.hir_id;
2108
2109         let name =
2110             &tcx.codegen_fn_attrs(tcx.hir().local_def_id(hid)).link_name.unwrap_or(fi.ident.name);
2111
2112         if self.seen_decls.contains_key(name) {
2113             // Avoid updating the map with the new entry when we do find a collision. We want to
2114             // make sure we're always pointing to the first definition as the previous declaration.
2115             // This lets us avoid emitting "knock-on" diagnostics.
2116             Some(*self.seen_decls.get(name).unwrap())
2117         } else {
2118             self.seen_decls.insert(*name, hid)
2119         }
2120     }
2121
2122     /// Get the name of the symbol that's linked against for a given extern declaration. That is,
2123     /// the name specified in a #[link_name = ...] attribute if one was specified, else, just the
2124     /// symbol's name.
2125     fn name_of_extern_decl(tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> SymbolName {
2126         let did = tcx.hir().local_def_id(fi.hir_id);
2127         if let Some((overridden_link_name, overridden_link_name_span)) =
2128             tcx.codegen_fn_attrs(did).link_name.map(|overridden_link_name| {
2129                 // FIXME: Instead of searching through the attributes again to get span
2130                 // information, we could have codegen_fn_attrs also give span information back for
2131                 // where the attribute was defined. However, until this is found to be a
2132                 // bottleneck, this does just fine.
2133                 (
2134                     overridden_link_name,
2135                     tcx.get_attrs(did.to_def_id())
2136                         .iter()
2137                         .find(|at| tcx.sess.check_name(at, sym::link_name))
2138                         .unwrap()
2139                         .span,
2140                 )
2141             })
2142         {
2143             SymbolName::Link(overridden_link_name, overridden_link_name_span)
2144         } else {
2145             SymbolName::Normal(fi.ident.name)
2146         }
2147     }
2148
2149     /// Checks whether two types are structurally the same enough that the declarations shouldn't
2150     /// clash. We need this so we don't emit a lint when two modules both declare an extern struct,
2151     /// with the same members (as the declarations shouldn't clash).
2152     fn structurally_same_type<'tcx>(
2153         cx: &LateContext<'tcx>,
2154         a: Ty<'tcx>,
2155         b: Ty<'tcx>,
2156         ckind: CItemKind,
2157     ) -> bool {
2158         fn structurally_same_type_impl<'tcx>(
2159             seen_types: &mut FxHashSet<(Ty<'tcx>, Ty<'tcx>)>,
2160             cx: &LateContext<'tcx>,
2161             a: Ty<'tcx>,
2162             b: Ty<'tcx>,
2163             ckind: CItemKind,
2164         ) -> bool {
2165             debug!("structurally_same_type_impl(cx, a = {:?}, b = {:?})", a, b);
2166             let tcx = cx.tcx;
2167
2168             // Given a transparent newtype, reach through and grab the inner
2169             // type unless the newtype makes the type non-null.
2170             let non_transparent_ty = |ty: Ty<'tcx>| -> Ty<'tcx> {
2171                 let mut ty = ty;
2172                 loop {
2173                     if let ty::Adt(def, substs) = ty.kind {
2174                         let is_transparent = def.subst(tcx, substs).repr.transparent();
2175                         let is_non_null = crate::types::nonnull_optimization_guaranteed(tcx, &def);
2176                         debug!(
2177                             "non_transparent_ty({:?}) -- type is transparent? {}, type is non-null? {}",
2178                             ty, is_transparent, is_non_null
2179                         );
2180                         if is_transparent && !is_non_null {
2181                             debug_assert!(def.variants.len() == 1);
2182                             let v = &def.variants[VariantIdx::new(0)];
2183                             ty = v
2184                                 .transparent_newtype_field(tcx)
2185                                 .expect(
2186                                     "single-variant transparent structure with zero-sized field",
2187                                 )
2188                                 .ty(tcx, substs);
2189                             continue;
2190                         }
2191                     }
2192                     debug!("non_transparent_ty -> {:?}", ty);
2193                     return ty;
2194                 }
2195             };
2196
2197             let a = non_transparent_ty(a);
2198             let b = non_transparent_ty(b);
2199
2200             if !seen_types.insert((a, b)) {
2201                 // We've encountered a cycle. There's no point going any further -- the types are
2202                 // structurally the same.
2203                 return true;
2204             }
2205             let tcx = cx.tcx;
2206             if a == b || rustc_middle::ty::TyS::same_type(a, b) {
2207                 // All nominally-same types are structurally same, too.
2208                 true
2209             } else {
2210                 // Do a full, depth-first comparison between the two.
2211                 use rustc_middle::ty::TyKind::*;
2212                 let a_kind = &a.kind;
2213                 let b_kind = &b.kind;
2214
2215                 let compare_layouts = |a, b| -> Result<bool, LayoutError<'tcx>> {
2216                     debug!("compare_layouts({:?}, {:?})", a, b);
2217                     let a_layout = &cx.layout_of(a)?.layout.abi;
2218                     let b_layout = &cx.layout_of(b)?.layout.abi;
2219                     debug!(
2220                         "comparing layouts: {:?} == {:?} = {}",
2221                         a_layout,
2222                         b_layout,
2223                         a_layout == b_layout
2224                     );
2225                     Ok(a_layout == b_layout)
2226                 };
2227
2228                 #[allow(rustc::usage_of_ty_tykind)]
2229                 let is_primitive_or_pointer = |kind: &ty::TyKind<'_>| {
2230                     kind.is_primitive() || matches!(kind, RawPtr(..) | Ref(..))
2231                 };
2232
2233                 ensure_sufficient_stack(|| {
2234                     match (a_kind, b_kind) {
2235                         (Adt(a_def, a_substs), Adt(b_def, b_substs)) => {
2236                             let a = a.subst(cx.tcx, a_substs);
2237                             let b = b.subst(cx.tcx, b_substs);
2238                             debug!("Comparing {:?} and {:?}", a, b);
2239
2240                             // We can immediately rule out these types as structurally same if
2241                             // their layouts differ.
2242                             match compare_layouts(a, b) {
2243                                 Ok(false) => return false,
2244                                 _ => (), // otherwise, continue onto the full, fields comparison
2245                             }
2246
2247                             // Grab a flattened representation of all fields.
2248                             let a_fields = a_def.variants.iter().flat_map(|v| v.fields.iter());
2249                             let b_fields = b_def.variants.iter().flat_map(|v| v.fields.iter());
2250
2251                             // Perform a structural comparison for each field.
2252                             a_fields.eq_by(
2253                                 b_fields,
2254                                 |&ty::FieldDef { did: a_did, .. },
2255                                  &ty::FieldDef { did: b_did, .. }| {
2256                                     structurally_same_type_impl(
2257                                         seen_types,
2258                                         cx,
2259                                         tcx.type_of(a_did),
2260                                         tcx.type_of(b_did),
2261                                         ckind,
2262                                     )
2263                                 },
2264                             )
2265                         }
2266                         (Array(a_ty, a_const), Array(b_ty, b_const)) => {
2267                             // For arrays, we also check the constness of the type.
2268                             a_const.val == b_const.val
2269                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2270                         }
2271                         (Slice(a_ty), Slice(b_ty)) => {
2272                             structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2273                         }
2274                         (RawPtr(a_tymut), RawPtr(b_tymut)) => {
2275                             a_tymut.mutbl == b_tymut.mutbl
2276                                 && structurally_same_type_impl(
2277                                     seen_types,
2278                                     cx,
2279                                     &a_tymut.ty,
2280                                     &b_tymut.ty,
2281                                     ckind,
2282                                 )
2283                         }
2284                         (Ref(_a_region, a_ty, a_mut), Ref(_b_region, b_ty, b_mut)) => {
2285                             // For structural sameness, we don't need the region to be same.
2286                             a_mut == b_mut
2287                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2288                         }
2289                         (FnDef(..), FnDef(..)) => {
2290                             let a_poly_sig = a.fn_sig(tcx);
2291                             let b_poly_sig = b.fn_sig(tcx);
2292
2293                             // As we don't compare regions, skip_binder is fine.
2294                             let a_sig = a_poly_sig.skip_binder();
2295                             let b_sig = b_poly_sig.skip_binder();
2296
2297                             (a_sig.abi, a_sig.unsafety, a_sig.c_variadic)
2298                                 == (b_sig.abi, b_sig.unsafety, b_sig.c_variadic)
2299                                 && a_sig.inputs().iter().eq_by(b_sig.inputs().iter(), |a, b| {
2300                                     structurally_same_type_impl(seen_types, cx, a, b, ckind)
2301                                 })
2302                                 && structurally_same_type_impl(
2303                                     seen_types,
2304                                     cx,
2305                                     a_sig.output(),
2306                                     b_sig.output(),
2307                                     ckind,
2308                                 )
2309                         }
2310                         (Tuple(a_substs), Tuple(b_substs)) => {
2311                             a_substs.types().eq_by(b_substs.types(), |a_ty, b_ty| {
2312                                 structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2313                             })
2314                         }
2315                         // For these, it's not quite as easy to define structural-sameness quite so easily.
2316                         // For the purposes of this lint, take the conservative approach and mark them as
2317                         // not structurally same.
2318                         (Dynamic(..), Dynamic(..))
2319                         | (Error(..), Error(..))
2320                         | (Closure(..), Closure(..))
2321                         | (Generator(..), Generator(..))
2322                         | (GeneratorWitness(..), GeneratorWitness(..))
2323                         | (Projection(..), Projection(..))
2324                         | (Opaque(..), Opaque(..)) => false,
2325
2326                         // These definitely should have been caught above.
2327                         (Bool, Bool) | (Char, Char) | (Never, Never) | (Str, Str) => unreachable!(),
2328
2329                         // An Adt and a primitive or pointer type. This can be FFI-safe if non-null
2330                         // enum layout optimisation is being applied.
2331                         (Adt(..), other_kind) | (other_kind, Adt(..))
2332                             if is_primitive_or_pointer(other_kind) =>
2333                         {
2334                             let (primitive, adt) =
2335                                 if is_primitive_or_pointer(&a.kind) { (a, b) } else { (b, a) };
2336                             if let Some(ty) = crate::types::repr_nullable_ptr(cx, adt, ckind) {
2337                                 ty == primitive
2338                             } else {
2339                                 compare_layouts(a, b).unwrap_or(false)
2340                             }
2341                         }
2342                         // Otherwise, just compare the layouts. This may fail to lint for some
2343                         // incompatible types, but at the very least, will stop reads into
2344                         // uninitialised memory.
2345                         _ => compare_layouts(a, b).unwrap_or(false),
2346                     }
2347                 })
2348             }
2349         }
2350         let mut seen_types = FxHashSet::default();
2351         structurally_same_type_impl(&mut seen_types, cx, a, b, ckind)
2352     }
2353 }
2354
2355 impl_lint_pass!(ClashingExternDeclarations => [CLASHING_EXTERN_DECLARATIONS]);
2356
2357 impl<'tcx> LateLintPass<'tcx> for ClashingExternDeclarations {
2358     fn check_foreign_item(&mut self, cx: &LateContext<'tcx>, this_fi: &hir::ForeignItem<'_>) {
2359         trace!("ClashingExternDeclarations: check_foreign_item: {:?}", this_fi);
2360         if let ForeignItemKind::Fn(..) = this_fi.kind {
2361             let tcx = *&cx.tcx;
2362             if let Some(existing_hid) = self.insert(tcx, this_fi) {
2363                 let existing_decl_ty = tcx.type_of(tcx.hir().local_def_id(existing_hid));
2364                 let this_decl_ty = tcx.type_of(tcx.hir().local_def_id(this_fi.hir_id));
2365                 debug!(
2366                     "ClashingExternDeclarations: Comparing existing {:?}: {:?} to this {:?}: {:?}",
2367                     existing_hid, existing_decl_ty, this_fi.hir_id, this_decl_ty
2368                 );
2369                 // Check that the declarations match.
2370                 if !Self::structurally_same_type(
2371                     cx,
2372                     existing_decl_ty,
2373                     this_decl_ty,
2374                     CItemKind::Declaration,
2375                 ) {
2376                     let orig_fi = tcx.hir().expect_foreign_item(existing_hid);
2377                     let orig = Self::name_of_extern_decl(tcx, orig_fi);
2378
2379                     // We want to ensure that we use spans for both decls that include where the
2380                     // name was defined, whether that was from the link_name attribute or not.
2381                     let get_relevant_span =
2382                         |fi: &hir::ForeignItem<'_>| match Self::name_of_extern_decl(tcx, fi) {
2383                             SymbolName::Normal(_) => fi.span,
2384                             SymbolName::Link(_, annot_span) => fi.span.to(annot_span),
2385                         };
2386                     // Finally, emit the diagnostic.
2387                     tcx.struct_span_lint_hir(
2388                         CLASHING_EXTERN_DECLARATIONS,
2389                         this_fi.hir_id,
2390                         get_relevant_span(this_fi),
2391                         |lint| {
2392                             let mut expected_str = DiagnosticStyledString::new();
2393                             expected_str.push(existing_decl_ty.fn_sig(tcx).to_string(), false);
2394                             let mut found_str = DiagnosticStyledString::new();
2395                             found_str.push(this_decl_ty.fn_sig(tcx).to_string(), true);
2396
2397                             lint.build(&format!(
2398                                 "`{}` redeclare{} with a different signature",
2399                                 this_fi.ident.name,
2400                                 if orig.get_name() == this_fi.ident.name {
2401                                     "d".to_string()
2402                                 } else {
2403                                     format!("s `{}`", orig.get_name())
2404                                 }
2405                             ))
2406                             .span_label(
2407                                 get_relevant_span(orig_fi),
2408                                 &format!("`{}` previously declared here", orig.get_name()),
2409                             )
2410                             .span_label(
2411                                 get_relevant_span(this_fi),
2412                                 "this signature doesn't match the previous declaration",
2413                             )
2414                             .note_expected_found(&"", expected_str, &"", found_str)
2415                             .emit()
2416                         },
2417                     );
2418                 }
2419             }
2420         }
2421     }
2422 }