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::print::with_no_trimmed_paths;
  44 use rustc_middle::ty::subst::{GenericArgKind, Subst};
  45 use rustc_middle::ty::{self, layout::LayoutError, Ty, TyCtxt};
  46 use rustc_session::lint::FutureIncompatibleInfo;
  47 use rustc_session::Session;
  48 use rustc_span::edition::Edition;
  49 use rustc_span::source_map::Spanned;
  50 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  51 use rustc_span::{BytePos, Span};
  52 use rustc_target::abi::{LayoutOf, VariantIdx};
  53 use rustc_trait_selection::traits::misc::can_type_implement_copy;
  54
  55 use crate::nonstandard_style::{method_context, MethodLateContext};
  56
  57 use std::fmt::Write;
  58 use tracing::{debug, trace};
  59
  60 // hardwired lints from librustc_middle
  61 pub use rustc_session::lint::builtin::*;
  62
  63 declare_lint! {
  64     WHILE_TRUE,
  65     Warn,
  66     "suggest using `loop { }` instead of `while true { }`"
  67 }
  68
  69 declare_lint_pass!(WhileTrue => [WHILE_TRUE]);
  70
  71 /// Traverse through any amount of parenthesis and return the first non-parens expression.
  72 fn pierce_parens(mut expr: &ast::Expr) -> &ast::Expr {
  73     while let ast::ExprKind::Paren(sub) = &expr.kind {
  74         expr = sub;
  75     }
  76     expr
  77 }
  78
  79 impl EarlyLintPass for WhileTrue {
  80     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
  81         if let ast::ExprKind::While(cond, ..) = &e.kind {
  82             if let ast::ExprKind::Lit(ref lit) = pierce_parens(cond).kind {
  83                 if let ast::LitKind::Bool(true) = lit.kind {
  84                     if !lit.span.from_expansion() {
  85                         let msg = "denote infinite loops with `loop { ... }`";
  86                         let condition_span = cx.sess.source_map().guess_head_span(e.span);
  87                         cx.struct_span_lint(WHILE_TRUE, condition_span, |lint| {
  88                             lint.build(msg)
  89                                 .span_suggestion_short(
  90                                     condition_span,
  91                                     "use `loop`",
  92                                     "loop".to_owned(),
  93                                     Applicability::MachineApplicable,
  94                                 )
  95                                 .emit();
  96                         })
  97                     }
  98                 }
  99             }
 100         }
 101     }
 102 }
 103
 104 declare_lint! {
 105     BOX_POINTERS,
 106     Allow,
 107     "use of owned (Box type) heap memory"
 108 }
 109
 110 declare_lint_pass!(BoxPointers => [BOX_POINTERS]);
 111
 112 impl BoxPointers {
 113     fn check_heap_type(&self, cx: &LateContext<'_>, span: Span, ty: Ty<'_>) {
 114         for leaf in ty.walk() {
 115             if let GenericArgKind::Type(leaf_ty) = leaf.unpack() {
 116                 if leaf_ty.is_box() {
 117                     cx.struct_span_lint(BOX_POINTERS, span, |lint| {
 118                         lint.build(&format!("type uses owned (Box type) pointers: {}", ty)).emit()
 119                     });
 120                 }
 121             }
 122         }
 123     }
 124 }
 125
 126 impl<'tcx> LateLintPass<'tcx> for BoxPointers {
 127     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 128         match it.kind {
 129             hir::ItemKind::Fn(..)
 130             | hir::ItemKind::TyAlias(..)
 131             | hir::ItemKind::Enum(..)
 132             | hir::ItemKind::Struct(..)
 133             | hir::ItemKind::Union(..) => {
 134                 let def_id = cx.tcx.hir().local_def_id(it.hir_id);
 135                 self.check_heap_type(cx, it.span, cx.tcx.type_of(def_id))
 136             }
 137             _ => (),
 138         }
 139
 140         // If it's a struct, we also have to check the fields' types
 141         match it.kind {
 142             hir::ItemKind::Struct(ref struct_def, _) | hir::ItemKind::Union(ref struct_def, _) => {
 143                 for struct_field in struct_def.fields() {
 144                     let def_id = cx.tcx.hir().local_def_id(struct_field.hir_id);
 145                     self.check_heap_type(cx, struct_field.span, cx.tcx.type_of(def_id));
 146                 }
 147             }
 148             _ => (),
 149         }
 150     }
 151
 152     fn check_expr(&mut self, cx: &LateContext<'_>, e: &hir::Expr<'_>) {
 153         let ty = cx.typeck_results().node_type(e.hir_id);
 154         self.check_heap_type(cx, e.span, ty);
 155     }
 156 }
 157
 158 declare_lint! {
 159     NON_SHORTHAND_FIELD_PATTERNS,
 160     Warn,
 161     "using `Struct { x: x }` instead of `Struct { x }` in a pattern"
 162 }
 163
 164 declare_lint_pass!(NonShorthandFieldPatterns => [NON_SHORTHAND_FIELD_PATTERNS]);
 165
 166 impl<'tcx> LateLintPass<'tcx> for NonShorthandFieldPatterns {
 167     fn check_pat(&mut self, cx: &LateContext<'_>, pat: &hir::Pat<'_>) {
 168         if let PatKind::Struct(ref qpath, field_pats, _) = pat.kind {
 169             let variant = cx
 170                 .typeck_results()
 171                 .pat_ty(pat)
 172                 .ty_adt_def()
 173                 .expect("struct pattern type is not an ADT")
 174                 .variant_of_res(cx.qpath_res(qpath, pat.hir_id));
 175             for fieldpat in field_pats {
 176                 if fieldpat.is_shorthand {
 177                     continue;
 178                 }
 179                 if fieldpat.span.from_expansion() {
 180                     // Don't lint if this is a macro expansion: macro authors
 181                     // shouldn't have to worry about this kind of style issue
 182                     // (Issue #49588)
 183                     continue;
 184                 }
 185                 if let PatKind::Binding(binding_annot, _, ident, None) = fieldpat.pat.kind {
 186                     if cx.tcx.find_field_index(ident, &variant)
 187                         == Some(cx.tcx.field_index(fieldpat.hir_id, cx.typeck_results()))
 188                     {
 189                         cx.struct_span_lint(NON_SHORTHAND_FIELD_PATTERNS, fieldpat.span, |lint| {
 190                             let mut err = lint
 191                                 .build(&format!("the `{}:` in this pattern is redundant", ident));
 192                             let binding = match binding_annot {
 193                                 hir::BindingAnnotation::Unannotated => None,
 194                                 hir::BindingAnnotation::Mutable => Some("mut"),
 195                                 hir::BindingAnnotation::Ref => Some("ref"),
 196                                 hir::BindingAnnotation::RefMut => Some("ref mut"),
 197                             };
 198                             let ident = if let Some(binding) = binding {
 199                                 format!("{} {}", binding, ident)
 200                             } else {
 201                                 ident.to_string()
 202                             };
 203                             err.span_suggestion(
 204                                 fieldpat.span,
 205                                 "use shorthand field pattern",
 206                                 ident,
 207                                 Applicability::MachineApplicable,
 208                             );
 209                             err.emit();
 210                         });
 211                     }
 212                 }
 213             }
 214         }
 215     }
 216 }
 217
 218 declare_lint! {
 219     UNSAFE_CODE,
 220     Allow,
 221     "usage of `unsafe` code"
 222 }
 223
 224 declare_lint_pass!(UnsafeCode => [UNSAFE_CODE]);
 225
 226 impl UnsafeCode {
 227     fn report_unsafe(
 228         &self,
 229         cx: &EarlyContext<'_>,
 230         span: Span,
 231         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
 232     ) {
 233         // This comes from a macro that has `#[allow_internal_unsafe]`.
 234         if span.allows_unsafe() {
 235             return;
 236         }
 237
 238         cx.struct_span_lint(UNSAFE_CODE, span, decorate);
 239     }
 240 }
 241
 242 impl EarlyLintPass for UnsafeCode {
 243     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 244         if cx.sess().check_name(attr, sym::allow_internal_unsafe) {
 245             self.report_unsafe(cx, attr.span, |lint| {
 246                 lint.build(
 247                     "`allow_internal_unsafe` allows defining \
 248                                                macros using unsafe without triggering \
 249                                                the `unsafe_code` lint at their call site",
 250                 )
 251                 .emit()
 252             });
 253         }
 254     }
 255
 256     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
 257         if let ast::ExprKind::Block(ref blk, _) = e.kind {
 258             // Don't warn about generated blocks; that'll just pollute the output.
 259             if blk.rules == ast::BlockCheckMode::Unsafe(ast::UserProvided) {
 260                 self.report_unsafe(cx, blk.span, |lint| {
 261                     lint.build("usage of an `unsafe` block").emit()
 262                 });
 263             }
 264         }
 265     }
 266
 267     fn check_item(&mut self, cx: &EarlyContext<'_>, it: &ast::Item) {
 268         match it.kind {
 269             ast::ItemKind::Trait(_, ast::Unsafe::Yes(_), ..) => {
 270                 self.report_unsafe(cx, it.span, |lint| {
 271                     lint.build("declaration of an `unsafe` trait").emit()
 272                 })
 273             }
 274
 275             ast::ItemKind::Impl { unsafety: ast::Unsafe::Yes(_), .. } => {
 276                 self.report_unsafe(cx, it.span, |lint| {
 277                     lint.build("implementation of an `unsafe` trait").emit()
 278                 })
 279             }
 280
 281             _ => {}
 282         }
 283     }
 284
 285     fn check_fn(&mut self, cx: &EarlyContext<'_>, fk: FnKind<'_>, span: Span, _: ast::NodeId) {
 286         if let FnKind::Fn(
 287             ctxt,
 288             _,
 289             ast::FnSig { header: ast::FnHeader { unsafety: ast::Unsafe::Yes(_), .. }, .. },
 290             _,
 291             body,
 292         ) = fk
 293         {
 294             let msg = match ctxt {
 295                 FnCtxt::Foreign => return,
 296                 FnCtxt::Free => "declaration of an `unsafe` function",
 297                 FnCtxt::Assoc(_) if body.is_none() => "declaration of an `unsafe` method",
 298                 FnCtxt::Assoc(_) => "implementation of an `unsafe` method",
 299             };
 300             self.report_unsafe(cx, span, |lint| lint.build(msg).emit());
 301         }
 302     }
 303 }
 304
 305 declare_lint! {
 306     pub MISSING_DOCS,
 307     Allow,
 308     "detects missing documentation for public members",
 309     report_in_external_macro
 310 }
 311
 312 pub struct MissingDoc {
 313     /// Stack of whether `#[doc(hidden)]` is set at each level which has lint attributes.
 314     doc_hidden_stack: Vec<bool>,
 315
 316     /// Private traits or trait items that leaked through. Don't check their methods.
 317     private_traits: FxHashSet<hir::HirId>,
 318 }
 319
 320 impl_lint_pass!(MissingDoc => [MISSING_DOCS]);
 321
 322 fn has_doc(sess: &Session, attr: &ast::Attribute) -> bool {
 323     if attr.is_doc_comment() {
 324         return true;
 325     }
 326
 327     if !sess.check_name(attr, sym::doc) {
 328         return false;
 329     }
 330
 331     if attr.is_value_str() {
 332         return true;
 333     }
 334
 335     if let Some(list) = attr.meta_item_list() {
 336         for meta in list {
 337             if meta.has_name(sym::include) || meta.has_name(sym::hidden) {
 338                 return true;
 339             }
 340         }
 341     }
 342
 343     false
 344 }
 345
 346 impl MissingDoc {
 347     pub fn new() -> MissingDoc {
 348         MissingDoc { doc_hidden_stack: vec![false], private_traits: FxHashSet::default() }
 349     }
 350
 351     fn doc_hidden(&self) -> bool {
 352         *self.doc_hidden_stack.last().expect("empty doc_hidden_stack")
 353     }
 354
 355     fn check_missing_docs_attrs(
 356         &self,
 357         cx: &LateContext<'_>,
 358         id: Option<hir::HirId>,
 359         attrs: &[ast::Attribute],
 360         sp: Span,
 361         article: &'static str,
 362         desc: &'static str,
 363     ) {
 364         // If we're building a test harness, then warning about
 365         // documentation is probably not really relevant right now.
 366         if cx.sess().opts.test {
 367             return;
 368         }
 369
 370         // `#[doc(hidden)]` disables missing_docs check.
 371         if self.doc_hidden() {
 372             return;
 373         }
 374
 375         // Only check publicly-visible items, using the result from the privacy pass.
 376         // It's an option so the crate root can also use this function (it doesn't
 377         // have a `NodeId`).
 378         if let Some(id) = id {
 379             if !cx.access_levels.is_exported(id) {
 380                 return;
 381             }
 382         }
 383
 384         let has_doc = attrs.iter().any(|a| has_doc(cx.sess(), a));
 385         if !has_doc {
 386             cx.struct_span_lint(
 387                 MISSING_DOCS,
 388                 cx.tcx.sess.source_map().guess_head_span(sp),
 389                 |lint| {
 390                     lint.build(&format!("missing documentation for {} {}", article, desc)).emit()
 391                 },
 392             );
 393         }
 394     }
 395 }
 396
 397 impl<'tcx> LateLintPass<'tcx> for MissingDoc {
 398     fn enter_lint_attrs(&mut self, cx: &LateContext<'_>, attrs: &[ast::Attribute]) {
 399         let doc_hidden = self.doc_hidden()
 400             || attrs.iter().any(|attr| {
 401                 cx.sess().check_name(attr, sym::doc)
 402                     && match attr.meta_item_list() {
 403                         None => false,
 404                         Some(l) => attr::list_contains_name(&l, sym::hidden),
 405                     }
 406             });
 407         self.doc_hidden_stack.push(doc_hidden);
 408     }
 409
 410     fn exit_lint_attrs(&mut self, _: &LateContext<'_>, _attrs: &[ast::Attribute]) {
 411         self.doc_hidden_stack.pop().expect("empty doc_hidden_stack");
 412     }
 413
 414     fn check_crate(&mut self, cx: &LateContext<'_>, krate: &hir::Crate<'_>) {
 415         self.check_missing_docs_attrs(cx, None, &krate.item.attrs, krate.item.span, "the", "crate");
 416
 417         for macro_def in krate.exported_macros {
 418             let has_doc = macro_def.attrs.iter().any(|a| has_doc(cx.sess(), a));
 419             if !has_doc {
 420                 cx.struct_span_lint(
 421                     MISSING_DOCS,
 422                     cx.tcx.sess.source_map().guess_head_span(macro_def.span),
 423                     |lint| lint.build("missing documentation for macro").emit(),
 424                 );
 425             }
 426         }
 427     }
 428
 429     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 430         match it.kind {
 431             hir::ItemKind::Trait(.., trait_item_refs) => {
 432                 // Issue #11592: traits are always considered exported, even when private.
 433                 if let hir::VisibilityKind::Inherited = it.vis.node {
 434                     self.private_traits.insert(it.hir_id);
 435                     for trait_item_ref in trait_item_refs {
 436                         self.private_traits.insert(trait_item_ref.id.hir_id);
 437                     }
 438                     return;
 439                 }
 440             }
 441             hir::ItemKind::Impl { of_trait: Some(ref trait_ref), items, .. } => {
 442                 // If the trait is private, add the impl items to `private_traits` so they don't get
 443                 // reported for missing docs.
 444                 let real_trait = trait_ref.path.res.def_id();
 445                 if let Some(def_id) = real_trait.as_local() {
 446                     let hir_id = cx.tcx.hir().local_def_id_to_hir_id(def_id);
 447                     if let Some(Node::Item(item)) = cx.tcx.hir().find(hir_id) {
 448                         if let hir::VisibilityKind::Inherited = item.vis.node {
 449                             for impl_item_ref in items {
 450                                 self.private_traits.insert(impl_item_ref.id.hir_id);
 451                             }
 452                         }
 453                     }
 454                 }
 455                 return;
 456             }
 457
 458             hir::ItemKind::TyAlias(..)
 459             | hir::ItemKind::Fn(..)
 460             | hir::ItemKind::Mod(..)
 461             | hir::ItemKind::Enum(..)
 462             | hir::ItemKind::Struct(..)
 463             | hir::ItemKind::Union(..)
 464             | hir::ItemKind::Const(..)
 465             | hir::ItemKind::Static(..) => {}
 466
 467             _ => return,
 468         };
 469
 470         let def_id = cx.tcx.hir().local_def_id(it.hir_id);
 471         let (article, desc) = cx.tcx.article_and_description(def_id.to_def_id());
 472
 473         self.check_missing_docs_attrs(cx, Some(it.hir_id), &it.attrs, it.span, article, desc);
 474     }
 475
 476     fn check_trait_item(&mut self, cx: &LateContext<'_>, trait_item: &hir::TraitItem<'_>) {
 477         if self.private_traits.contains(&trait_item.hir_id) {
 478             return;
 479         }
 480
 481         let def_id = cx.tcx.hir().local_def_id(trait_item.hir_id);
 482         let (article, desc) = cx.tcx.article_and_description(def_id.to_def_id());
 483
 484         self.check_missing_docs_attrs(
 485             cx,
 486             Some(trait_item.hir_id),
 487             &trait_item.attrs,
 488             trait_item.span,
 489             article,
 490             desc,
 491         );
 492     }
 493
 494     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
 495         // If the method is an impl for a trait, don't doc.
 496         if method_context(cx, impl_item.hir_id) == MethodLateContext::TraitImpl {
 497             return;
 498         }
 499
 500         let def_id = cx.tcx.hir().local_def_id(impl_item.hir_id);
 501         let (article, desc) = cx.tcx.article_and_description(def_id.to_def_id());
 502         self.check_missing_docs_attrs(
 503             cx,
 504             Some(impl_item.hir_id),
 505             &impl_item.attrs,
 506             impl_item.span,
 507             article,
 508             desc,
 509         );
 510     }
 511
 512     fn check_struct_field(&mut self, cx: &LateContext<'_>, sf: &hir::StructField<'_>) {
 513         if !sf.is_positional() {
 514             self.check_missing_docs_attrs(
 515                 cx,
 516                 Some(sf.hir_id),
 517                 &sf.attrs,
 518                 sf.span,
 519                 "a",
 520                 "struct field",
 521             )
 522         }
 523     }
 524
 525     fn check_variant(&mut self, cx: &LateContext<'_>, v: &hir::Variant<'_>) {
 526         self.check_missing_docs_attrs(cx, Some(v.id), &v.attrs, v.span, "a", "variant");
 527     }
 528 }
 529
 530 declare_lint! {
 531     pub MISSING_COPY_IMPLEMENTATIONS,
 532     Allow,
 533     "detects potentially-forgotten implementations of `Copy`"
 534 }
 535
 536 declare_lint_pass!(MissingCopyImplementations => [MISSING_COPY_IMPLEMENTATIONS]);
 537
 538 impl<'tcx> LateLintPass<'tcx> for MissingCopyImplementations {
 539     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 540         if !cx.access_levels.is_reachable(item.hir_id) {
 541             return;
 542         }
 543         let (def, ty) = match item.kind {
 544             hir::ItemKind::Struct(_, ref ast_generics) => {
 545                 if !ast_generics.params.is_empty() {
 546                     return;
 547                 }
 548                 let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
 549                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 550             }
 551             hir::ItemKind::Union(_, ref ast_generics) => {
 552                 if !ast_generics.params.is_empty() {
 553                     return;
 554                 }
 555                 let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
 556                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 557             }
 558             hir::ItemKind::Enum(_, ref ast_generics) => {
 559                 if !ast_generics.params.is_empty() {
 560                     return;
 561                 }
 562                 let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
 563                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 564             }
 565             _ => return,
 566         };
 567         if def.has_dtor(cx.tcx) {
 568             return;
 569         }
 570         let param_env = ty::ParamEnv::empty();
 571         if ty.is_copy_modulo_regions(cx.tcx.at(item.span), param_env) {
 572             return;
 573         }
 574         if can_type_implement_copy(cx.tcx, param_env, ty).is_ok() {
 575             cx.struct_span_lint(MISSING_COPY_IMPLEMENTATIONS, item.span, |lint| {
 576                 lint.build(
 577                     "type could implement `Copy`; consider adding `impl \
 578                           Copy`",
 579                 )
 580                 .emit()
 581             })
 582         }
 583     }
 584 }
 585
 586 declare_lint! {
 587     MISSING_DEBUG_IMPLEMENTATIONS,
 588     Allow,
 589     "detects missing implementations of Debug"
 590 }
 591
 592 #[derive(Default)]
 593 pub struct MissingDebugImplementations {
 594     impling_types: Option<HirIdSet>,
 595 }
 596
 597 impl_lint_pass!(MissingDebugImplementations => [MISSING_DEBUG_IMPLEMENTATIONS]);
 598
 599 impl<'tcx> LateLintPass<'tcx> for MissingDebugImplementations {
 600     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 601         if !cx.access_levels.is_reachable(item.hir_id) {
 602             return;
 603         }
 604
 605         match item.kind {
 606             hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) | hir::ItemKind::Enum(..) => {}
 607             _ => return,
 608         }
 609
 610         let debug = match cx.tcx.get_diagnostic_item(sym::debug_trait) {
 611             Some(debug) => debug,
 612             None => return,
 613         };
 614
 615         if self.impling_types.is_none() {
 616             let mut impls = HirIdSet::default();
 617             cx.tcx.for_each_impl(debug, |d| {
 618                 if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() {
 619                     if let Some(def_id) = ty_def.did.as_local() {
 620                         impls.insert(cx.tcx.hir().local_def_id_to_hir_id(def_id));
 621                     }
 622                 }
 623             });
 624
 625             self.impling_types = Some(impls);
 626             debug!("{:?}", self.impling_types);
 627         }
 628
 629         if !self.impling_types.as_ref().unwrap().contains(&item.hir_id) {
 630             cx.struct_span_lint(MISSING_DEBUG_IMPLEMENTATIONS, item.span, |lint| {
 631                 lint.build(&format!(
 632                     "type does not implement `{}`; consider adding `#[derive(Debug)]` \
 633                      or a manual implementation",
 634                     cx.tcx.def_path_str(debug)
 635                 ))
 636                 .emit()
 637             });
 638         }
 639     }
 640 }
 641
 642 declare_lint! {
 643     pub ANONYMOUS_PARAMETERS,
 644     Allow,
 645     "detects anonymous parameters",
 646     @future_incompatible = FutureIncompatibleInfo {
 647         reference: "issue #41686 <https://github.com/rust-lang/rust/issues/41686>",
 648         edition: Some(Edition::Edition2018),
 649     };
 650 }
 651
 652 declare_lint_pass!(
 653     /// Checks for use of anonymous parameters (RFC 1685).
 654     AnonymousParameters => [ANONYMOUS_PARAMETERS]
 655 );
 656
 657 impl EarlyLintPass for AnonymousParameters {
 658     fn check_trait_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
 659         if let ast::AssocItemKind::Fn(_, ref sig, _, _) = it.kind {
 660             for arg in sig.decl.inputs.iter() {
 661                 if let ast::PatKind::Ident(_, ident, None) = arg.pat.kind {
 662                     if ident.name == kw::Invalid {
 663                         cx.struct_span_lint(ANONYMOUS_PARAMETERS, arg.pat.span, |lint| {
 664                             let ty_snip = cx.sess.source_map().span_to_snippet(arg.ty.span);
 665
 666                             let (ty_snip, appl) = if let Ok(ref snip) = ty_snip {
 667                                 (snip.as_str(), Applicability::MachineApplicable)
 668                             } else {
 669                                 ("<type>", Applicability::HasPlaceholders)
 670                             };
 671
 672                             lint.build(
 673                                 "anonymous parameters are deprecated and will be \
 674                                      removed in the next edition.",
 675                             )
 676                             .span_suggestion(
 677                                 arg.pat.span,
 678                                 "try naming the parameter or explicitly \
 679                                             ignoring it",
 680                                 format!("_: {}", ty_snip),
 681                                 appl,
 682                             )
 683                             .emit();
 684                         })
 685                     }
 686                 }
 687             }
 688         }
 689     }
 690 }
 691
 692 /// Check for use of attributes which have been deprecated.
 693 #[derive(Clone)]
 694 pub struct DeprecatedAttr {
 695     // This is not free to compute, so we want to keep it around, rather than
 696     // compute it for every attribute.
 697     depr_attrs: Vec<&'static (Symbol, AttributeType, AttributeTemplate, AttributeGate)>,
 698 }
 699
 700 impl_lint_pass!(DeprecatedAttr => []);
 701
 702 impl DeprecatedAttr {
 703     pub fn new() -> DeprecatedAttr {
 704         DeprecatedAttr { depr_attrs: deprecated_attributes() }
 705     }
 706 }
 707
 708 fn lint_deprecated_attr(
 709     cx: &EarlyContext<'_>,
 710     attr: &ast::Attribute,
 711     msg: &str,
 712     suggestion: Option<&str>,
 713 ) {
 714     cx.struct_span_lint(DEPRECATED, attr.span, |lint| {
 715         lint.build(msg)
 716             .span_suggestion_short(
 717                 attr.span,
 718                 suggestion.unwrap_or("remove this attribute"),
 719                 String::new(),
 720                 Applicability::MachineApplicable,
 721             )
 722             .emit();
 723     })
 724 }
 725
 726 impl EarlyLintPass for DeprecatedAttr {
 727     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 728         for &&(n, _, _, ref g) in &self.depr_attrs {
 729             if attr.ident().map(|ident| ident.name) == Some(n) {
 730                 if let &AttributeGate::Gated(
 731                     Stability::Deprecated(link, suggestion),
 732                     ref name,
 733                     ref reason,
 734                     _,
 735                 ) = g
 736                 {
 737                     let msg =
 738                         format!("use of deprecated attribute `{}`: {}. See {}", name, reason, link);
 739                     lint_deprecated_attr(cx, attr, &msg, suggestion);
 740                 }
 741                 return;
 742             }
 743         }
 744         if cx.sess().check_name(attr, sym::no_start) || cx.sess().check_name(attr, sym::crate_id) {
 745             let path_str = pprust::path_to_string(&attr.get_normal_item().path);
 746             let msg = format!("use of deprecated attribute `{}`: no longer used.", path_str);
 747             lint_deprecated_attr(cx, attr, &msg, None);
 748         }
 749     }
 750 }
 751
 752 fn warn_if_doc(cx: &EarlyContext<'_>, node_span: Span, node_kind: &str, attrs: &[ast::Attribute]) {
 753     let mut attrs = attrs.iter().peekable();
 754
 755     // Accumulate a single span for sugared doc comments.
 756     let mut sugared_span: Option<Span> = None;
 757
 758     while let Some(attr) = attrs.next() {
 759         if attr.is_doc_comment() {
 760             sugared_span =
 761                 Some(sugared_span.map_or_else(|| attr.span, |span| span.with_hi(attr.span.hi())));
 762         }
 763
 764         if attrs.peek().map(|next_attr| next_attr.is_doc_comment()).unwrap_or_default() {
 765             continue;
 766         }
 767
 768         let span = sugared_span.take().unwrap_or_else(|| attr.span);
 769
 770         if attr.is_doc_comment() || cx.sess().check_name(attr, sym::doc) {
 771             cx.struct_span_lint(UNUSED_DOC_COMMENTS, span, |lint| {
 772                 let mut err = lint.build("unused doc comment");
 773                 err.span_label(
 774                     node_span,
 775                     format!("rustdoc does not generate documentation for {}", node_kind),
 776                 );
 777                 err.emit();
 778             });
 779         }
 780     }
 781 }
 782
 783 impl EarlyLintPass for UnusedDocComment {
 784     fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &ast::Stmt) {
 785         let kind = match stmt.kind {
 786             ast::StmtKind::Local(..) => "statements",
 787             ast::StmtKind::Item(..) => "inner items",
 788             // expressions will be reported by `check_expr`.
 789             ast::StmtKind::Empty
 790             | ast::StmtKind::Semi(_)
 791             | ast::StmtKind::Expr(_)
 792             | ast::StmtKind::MacCall(_) => return,
 793         };
 794
 795         warn_if_doc(cx, stmt.span, kind, stmt.kind.attrs());
 796     }
 797
 798     fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) {
 799         let arm_span = arm.pat.span.with_hi(arm.body.span.hi());
 800         warn_if_doc(cx, arm_span, "match arms", &arm.attrs);
 801     }
 802
 803     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
 804         warn_if_doc(cx, expr.span, "expressions", &expr.attrs);
 805     }
 806 }
 807
 808 declare_lint! {
 809     NO_MANGLE_CONST_ITEMS,
 810     Deny,
 811     "const items will not have their symbols exported"
 812 }
 813
 814 declare_lint! {
 815     NO_MANGLE_GENERIC_ITEMS,
 816     Warn,
 817     "generic items must be mangled"
 818 }
 819
 820 declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS, NO_MANGLE_GENERIC_ITEMS]);
 821
 822 impl<'tcx> LateLintPass<'tcx> for InvalidNoMangleItems {
 823     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 824         match it.kind {
 825             hir::ItemKind::Fn(.., ref generics, _) => {
 826                 if let Some(no_mangle_attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
 827                     for param in generics.params {
 828                         match param.kind {
 829                             GenericParamKind::Lifetime { .. } => {}
 830                             GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
 831                                 cx.struct_span_lint(NO_MANGLE_GENERIC_ITEMS, it.span, |lint| {
 832                                     lint.build(
 833                                         "functions generic over types or consts must be mangled",
 834                                     )
 835                                     .span_suggestion_short(
 836                                         no_mangle_attr.span,
 837                                         "remove this attribute",
 838                                         String::new(),
 839                                         // Use of `#[no_mangle]` suggests FFI intent; correct
 840                                         // fix may be to monomorphize source by hand
 841                                         Applicability::MaybeIncorrect,
 842                                     )
 843                                     .emit();
 844                                 });
 845                                 break;
 846                             }
 847                         }
 848                     }
 849                 }
 850             }
 851             hir::ItemKind::Const(..) => {
 852                 if cx.sess().contains_name(&it.attrs, sym::no_mangle) {
 853                     // Const items do not refer to a particular location in memory, and therefore
 854                     // don't have anything to attach a symbol to
 855                     cx.struct_span_lint(NO_MANGLE_CONST_ITEMS, it.span, |lint| {
 856                         let msg = "const items should never be `#[no_mangle]`";
 857                         let mut err = lint.build(msg);
 858
 859                         // account for "pub const" (#45562)
 860                         let start = cx
 861                             .tcx
 862                             .sess
 863                             .source_map()
 864                             .span_to_snippet(it.span)
 865                             .map(|snippet| snippet.find("const").unwrap_or(0))
 866                             .unwrap_or(0) as u32;
 867                         // `const` is 5 chars
 868                         let const_span = it.span.with_hi(BytePos(it.span.lo().0 + start + 5));
 869                         err.span_suggestion(
 870                             const_span,
 871                             "try a static value",
 872                             "pub static".to_owned(),
 873                             Applicability::MachineApplicable,
 874                         );
 875                         err.emit();
 876                     });
 877                 }
 878             }
 879             _ => {}
 880         }
 881     }
 882 }
 883
 884 declare_lint! {
 885     MUTABLE_TRANSMUTES,
 886     Deny,
 887     "mutating transmuted &mut T from &T may cause undefined behavior"
 888 }
 889
 890 declare_lint_pass!(MutableTransmutes => [MUTABLE_TRANSMUTES]);
 891
 892 impl<'tcx> LateLintPass<'tcx> for MutableTransmutes {
 893     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &hir::Expr<'_>) {
 894         use rustc_target::spec::abi::Abi::RustIntrinsic;
 895         if let Some((&ty::Ref(_, _, from_mt), &ty::Ref(_, _, to_mt))) =
 896             get_transmute_from_to(cx, expr).map(|(ty1, ty2)| (ty1.kind(), ty2.kind()))
 897         {
 898             if to_mt == hir::Mutability::Mut && from_mt == hir::Mutability::Not {
 899                 let msg = "mutating transmuted &mut T from &T may cause undefined behavior, \
 900                                consider instead using an UnsafeCell";
 901                 cx.struct_span_lint(MUTABLE_TRANSMUTES, expr.span, |lint| lint.build(msg).emit());
 902             }
 903         }
 904
 905         fn get_transmute_from_to<'tcx>(
 906             cx: &LateContext<'tcx>,
 907             expr: &hir::Expr<'_>,
 908         ) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
 909             let def = if let hir::ExprKind::Path(ref qpath) = expr.kind {
 910                 cx.qpath_res(qpath, expr.hir_id)
 911             } else {
 912                 return None;
 913             };
 914             if let Res::Def(DefKind::Fn, did) = def {
 915                 if !def_id_is_transmute(cx, did) {
 916                     return None;
 917                 }
 918                 let sig = cx.typeck_results().node_type(expr.hir_id).fn_sig(cx.tcx);
 919                 let from = sig.inputs().skip_binder()[0];
 920                 let to = sig.output().skip_binder();
 921                 return Some((from, to));
 922             }
 923             None
 924         }
 925
 926         fn def_id_is_transmute(cx: &LateContext<'_>, def_id: DefId) -> bool {
 927             cx.tcx.fn_sig(def_id).abi() == RustIntrinsic
 928                 && cx.tcx.item_name(def_id) == sym::transmute
 929         }
 930     }
 931 }
 932
 933 declare_lint! {
 934     UNSTABLE_FEATURES,
 935     Allow,
 936     "enabling unstable features (deprecated. do not use)"
 937 }
 938
 939 declare_lint_pass!(
 940     /// Forbids using the `#[feature(...)]` attribute
 941     UnstableFeatures => [UNSTABLE_FEATURES]
 942 );
 943
 944 impl<'tcx> LateLintPass<'tcx> for UnstableFeatures {
 945     fn check_attribute(&mut self, cx: &LateContext<'_>, attr: &ast::Attribute) {
 946         if cx.sess().check_name(attr, sym::feature) {
 947             if let Some(items) = attr.meta_item_list() {
 948                 for item in items {
 949                     cx.struct_span_lint(UNSTABLE_FEATURES, item.span(), |lint| {
 950                         lint.build("unstable feature").emit()
 951                     });
 952                 }
 953             }
 954         }
 955     }
 956 }
 957
 958 declare_lint! {
 959     pub UNREACHABLE_PUB,
 960     Allow,
 961     "`pub` items not reachable from crate root"
 962 }
 963
 964 declare_lint_pass!(
 965     /// Lint for items marked `pub` that aren't reachable from other crates.
 966     UnreachablePub => [UNREACHABLE_PUB]
 967 );
 968
 969 impl UnreachablePub {
 970     fn perform_lint(
 971         &self,
 972         cx: &LateContext<'_>,
 973         what: &str,
 974         id: hir::HirId,
 975         vis: &hir::Visibility<'_>,
 976         span: Span,
 977         exportable: bool,
 978     ) {
 979         let mut applicability = Applicability::MachineApplicable;
 980         match vis.node {
 981             hir::VisibilityKind::Public if !cx.access_levels.is_reachable(id) => {
 982                 if span.from_expansion() {
 983                     applicability = Applicability::MaybeIncorrect;
 984                 }
 985                 let def_span = cx.tcx.sess.source_map().guess_head_span(span);
 986                 cx.struct_span_lint(UNREACHABLE_PUB, def_span, |lint| {
 987                     let mut err = lint.build(&format!("unreachable `pub` {}", what));
 988                     let replacement = if cx.tcx.features().crate_visibility_modifier {
 989                         "crate"
 990                     } else {
 991                         "pub(crate)"
 992                     }
 993                     .to_owned();
 994
 995                     err.span_suggestion(
 996                         vis.span,
 997                         "consider restricting its visibility",
 998                         replacement,
 999                         applicability,
1000                     );
1001                     if exportable {
1002                         err.help("or consider exporting it for use by other crates");
1003                     }
1004                     err.emit();
1005                 });
1006             }
1007             _ => {}
1008         }
1009     }
1010 }
1011
1012 impl<'tcx> LateLintPass<'tcx> for UnreachablePub {
1013     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1014         self.perform_lint(cx, "item", item.hir_id, &item.vis, item.span, true);
1015     }
1016
1017     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'tcx>) {
1018         self.perform_lint(
1019             cx,
1020             "item",
1021             foreign_item.hir_id,
1022             &foreign_item.vis,
1023             foreign_item.span,
1024             true,
1025         );
1026     }
1027
1028     fn check_struct_field(&mut self, cx: &LateContext<'_>, field: &hir::StructField<'_>) {
1029         self.perform_lint(cx, "field", field.hir_id, &field.vis, field.span, false);
1030     }
1031
1032     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
1033         self.perform_lint(cx, "item", impl_item.hir_id, &impl_item.vis, impl_item.span, false);
1034     }
1035 }
1036
1037 declare_lint! {
1038     TYPE_ALIAS_BOUNDS,
1039     Warn,
1040     "bounds in type aliases are not enforced"
1041 }
1042
1043 declare_lint_pass!(
1044     /// Lint for trait and lifetime bounds in type aliases being mostly ignored.
1045     /// They are relevant when using associated types, but otherwise neither checked
1046     /// at definition site nor enforced at use site.
1047     TypeAliasBounds => [TYPE_ALIAS_BOUNDS]
1048 );
1049
1050 impl TypeAliasBounds {
1051     fn is_type_variable_assoc(qpath: &hir::QPath<'_>) -> bool {
1052         match *qpath {
1053             hir::QPath::TypeRelative(ref ty, _) => {
1054                 // If this is a type variable, we found a `T::Assoc`.
1055                 match ty.kind {
1056                     hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => match path.res {
1057                         Res::Def(DefKind::TyParam, _) => true,
1058                         _ => false,
1059                     },
1060                     _ => false,
1061                 }
1062             }
1063             hir::QPath::Resolved(..) | hir::QPath::LangItem(..) => false,
1064         }
1065     }
1066
1067     fn suggest_changing_assoc_types(ty: &hir::Ty<'_>, err: &mut DiagnosticBuilder<'_>) {
1068         // Access to associates types should use `<T as Bound>::Assoc`, which does not need a
1069         // bound.  Let's see if this type does that.
1070
1071         // We use a HIR visitor to walk the type.
1072         use rustc_hir::intravisit::{self, Visitor};
1073         struct WalkAssocTypes<'a, 'db> {
1074             err: &'a mut DiagnosticBuilder<'db>,
1075         }
1076         impl<'a, 'db, 'v> Visitor<'v> for WalkAssocTypes<'a, 'db> {
1077             type Map = intravisit::ErasedMap<'v>;
1078
1079             fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1080                 intravisit::NestedVisitorMap::None
1081             }
1082
1083             fn visit_qpath(&mut self, qpath: &'v hir::QPath<'v>, id: hir::HirId, span: Span) {
1084                 if TypeAliasBounds::is_type_variable_assoc(qpath) {
1085                     self.err.span_help(
1086                         span,
1087                         "use fully disambiguated paths (i.e., `<T as Trait>::Assoc`) to refer to \
1088                          associated types in type aliases",
1089                     );
1090                 }
1091                 intravisit::walk_qpath(self, qpath, id, span)
1092             }
1093         }
1094
1095         // Let's go for a walk!
1096         let mut visitor = WalkAssocTypes { err };
1097         visitor.visit_ty(ty);
1098     }
1099 }
1100
1101 impl<'tcx> LateLintPass<'tcx> for TypeAliasBounds {
1102     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1103         let (ty, type_alias_generics) = match item.kind {
1104             hir::ItemKind::TyAlias(ref ty, ref generics) => (&*ty, generics),
1105             _ => return,
1106         };
1107         if let hir::TyKind::OpaqueDef(..) = ty.kind {
1108             // Bounds are respected for `type X = impl Trait`
1109             return;
1110         }
1111         let mut suggested_changing_assoc_types = false;
1112         // There must not be a where clause
1113         if !type_alias_generics.where_clause.predicates.is_empty() {
1114             cx.lint(
1115                 TYPE_ALIAS_BOUNDS,
1116                 |lint| {
1117                     let mut err = lint.build("where clauses are not enforced in type aliases");
1118                     let spans: Vec<_> = type_alias_generics
1119                         .where_clause
1120                         .predicates
1121                         .iter()
1122                         .map(|pred| pred.span())
1123                         .collect();
1124                     err.set_span(spans);
1125                     err.span_suggestion(
1126                         type_alias_generics.where_clause.span_for_predicates_or_empty_place(),
1127                         "the clause will not be checked when the type alias is used, and should be removed",
1128                         String::new(),
1129                         Applicability::MachineApplicable,
1130                     );
1131                     if !suggested_changing_assoc_types {
1132                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1133                         suggested_changing_assoc_types = true;
1134                     }
1135                     err.emit();
1136                 },
1137             );
1138         }
1139         // The parameters must not have bounds
1140         for param in type_alias_generics.params.iter() {
1141             let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
1142             let suggestion = spans
1143                 .iter()
1144                 .map(|sp| {
1145                     let start = param.span.between(*sp); // Include the `:` in `T: Bound`.
1146                     (start.to(*sp), String::new())
1147                 })
1148                 .collect();
1149             if !spans.is_empty() {
1150                 cx.struct_span_lint(TYPE_ALIAS_BOUNDS, spans, |lint| {
1151                     let mut err =
1152                         lint.build("bounds on generic parameters are not enforced in type aliases");
1153                     let msg = "the bound will not be checked when the type alias is used, \
1154                                    and should be removed";
1155                     err.multipart_suggestion(&msg, suggestion, Applicability::MachineApplicable);
1156                     if !suggested_changing_assoc_types {
1157                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1158                         suggested_changing_assoc_types = true;
1159                     }
1160                     err.emit();
1161                 });
1162             }
1163         }
1164     }
1165 }
1166
1167 declare_lint_pass!(
1168     /// Lint constants that are erroneous.
1169     /// Without this lint, we might not get any diagnostic if the constant is
1170     /// unused within this crate, even though downstream crates can't use it
1171     /// without producing an error.
1172     UnusedBrokenConst => []
1173 );
1174
1175 fn check_const(cx: &LateContext<'_>, body_id: hir::BodyId) {
1176     let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1177     // trigger the query once for all constants since that will already report the errors
1178     // FIXME: Use ensure here
1179     let _ = cx.tcx.const_eval_poly(def_id);
1180 }
1181
1182 impl<'tcx> LateLintPass<'tcx> for UnusedBrokenConst {
1183     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1184         match it.kind {
1185             hir::ItemKind::Const(_, body_id) => {
1186                 check_const(cx, body_id);
1187             }
1188             hir::ItemKind::Static(_, _, body_id) => {
1189                 check_const(cx, body_id);
1190             }
1191             _ => {}
1192         }
1193     }
1194 }
1195
1196 declare_lint! {
1197     TRIVIAL_BOUNDS,
1198     Warn,
1199     "these bounds don't depend on an type parameters"
1200 }
1201
1202 declare_lint_pass!(
1203     /// Lint for trait and lifetime bounds that don't depend on type parameters
1204     /// which either do nothing, or stop the item from being used.
1205     TrivialConstraints => [TRIVIAL_BOUNDS]
1206 );
1207
1208 impl<'tcx> LateLintPass<'tcx> for TrivialConstraints {
1209     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
1210         use rustc_middle::ty::fold::TypeFoldable;
1211         use rustc_middle::ty::PredicateAtom::*;
1212
1213         if cx.tcx.features().trivial_bounds {
1214             let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1215             let predicates = cx.tcx.predicates_of(def_id);
1216             for &(predicate, span) in predicates.predicates {
1217                 let predicate_kind_name = match predicate.skip_binders() {
1218                     Trait(..) => "Trait",
1219                     TypeOutlives(..) |
1220                     RegionOutlives(..) => "Lifetime",
1221
1222                     // Ignore projections, as they can only be global
1223                     // if the trait bound is global
1224                     Projection(..) |
1225                     // Ignore bounds that a user can't type
1226                     WellFormed(..) |
1227                     ObjectSafe(..) |
1228                     ClosureKind(..) |
1229                     Subtype(..) |
1230                     ConstEvaluatable(..) |
1231                     ConstEquate(..) |
1232                     TypeWellFormedFromEnv(..) => continue,
1233                 };
1234                 if predicate.is_global() {
1235                     cx.struct_span_lint(TRIVIAL_BOUNDS, span, |lint| {
1236                         lint.build(&format!(
1237                             "{} bound {} does not depend on any type \
1238                                 or lifetime parameters",
1239                             predicate_kind_name, predicate
1240                         ))
1241                         .emit()
1242                     });
1243                 }
1244             }
1245         }
1246     }
1247 }
1248
1249 declare_lint_pass!(
1250     /// Does nothing as a lint pass, but registers some `Lint`s
1251     /// which are used by other parts of the compiler.
1252     SoftLints => [
1253         WHILE_TRUE,
1254         BOX_POINTERS,
1255         NON_SHORTHAND_FIELD_PATTERNS,
1256         UNSAFE_CODE,
1257         MISSING_DOCS,
1258         MISSING_COPY_IMPLEMENTATIONS,
1259         MISSING_DEBUG_IMPLEMENTATIONS,
1260         ANONYMOUS_PARAMETERS,
1261         UNUSED_DOC_COMMENTS,
1262         NO_MANGLE_CONST_ITEMS,
1263         NO_MANGLE_GENERIC_ITEMS,
1264         MUTABLE_TRANSMUTES,
1265         UNSTABLE_FEATURES,
1266         UNREACHABLE_PUB,
1267         TYPE_ALIAS_BOUNDS,
1268         TRIVIAL_BOUNDS
1269     ]
1270 );
1271
1272 declare_lint! {
1273     pub ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
1274     Warn,
1275     "`...` range patterns are deprecated"
1276 }
1277
1278 #[derive(Default)]
1279 pub struct EllipsisInclusiveRangePatterns {
1280     /// If `Some(_)`, suppress all subsequent pattern
1281     /// warnings for better diagnostics.
1282     node_id: Option<ast::NodeId>,
1283 }
1284
1285 impl_lint_pass!(EllipsisInclusiveRangePatterns => [ELLIPSIS_INCLUSIVE_RANGE_PATTERNS]);
1286
1287 impl EarlyLintPass for EllipsisInclusiveRangePatterns {
1288     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &ast::Pat) {
1289         if self.node_id.is_some() {
1290             // Don't recursively warn about patterns inside range endpoints.
1291             return;
1292         }
1293
1294         use self::ast::{PatKind, RangeSyntax::DotDotDot};
1295
1296         /// If `pat` is a `...` pattern, return the start and end of the range, as well as the span
1297         /// corresponding to the ellipsis.
1298         fn matches_ellipsis_pat(pat: &ast::Pat) -> Option<(Option<&Expr>, &Expr, Span)> {
1299             match &pat.kind {
1300                 PatKind::Range(
1301                     a,
1302                     Some(b),
1303                     Spanned { span, node: RangeEnd::Included(DotDotDot) },
1304                 ) => Some((a.as_deref(), b, *span)),
1305                 _ => None,
1306             }
1307         }
1308
1309         let (parenthesise, endpoints) = match &pat.kind {
1310             PatKind::Ref(subpat, _) => (true, matches_ellipsis_pat(&subpat)),
1311             _ => (false, matches_ellipsis_pat(pat)),
1312         };
1313
1314         if let Some((start, end, join)) = endpoints {
1315             let msg = "`...` range patterns are deprecated";
1316             let suggestion = "use `..=` for an inclusive range";
1317             if parenthesise {
1318                 self.node_id = Some(pat.id);
1319                 cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, pat.span, |lint| {
1320                     let end = expr_to_string(&end);
1321                     let replace = match start {
1322                         Some(start) => format!("&({}..={})", expr_to_string(&start), end),
1323                         None => format!("&(..={})", end),
1324                     };
1325                     lint.build(msg)
1326                         .span_suggestion(
1327                             pat.span,
1328                             suggestion,
1329                             replace,
1330                             Applicability::MachineApplicable,
1331                         )
1332                         .emit();
1333                 });
1334             } else {
1335                 cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, join, |lint| {
1336                     lint.build(msg)
1337                         .span_suggestion_short(
1338                             join,
1339                             suggestion,
1340                             "..=".to_owned(),
1341                             Applicability::MachineApplicable,
1342                         )
1343                         .emit();
1344                 });
1345             };
1346         }
1347     }
1348
1349     fn check_pat_post(&mut self, _cx: &EarlyContext<'_>, pat: &ast::Pat) {
1350         if let Some(node_id) = self.node_id {
1351             if pat.id == node_id {
1352                 self.node_id = None
1353             }
1354         }
1355     }
1356 }
1357
1358 declare_lint! {
1359     UNNAMEABLE_TEST_ITEMS,
1360     Warn,
1361     "detects an item that cannot be named being marked as `#[test_case]`",
1362     report_in_external_macro
1363 }
1364
1365 pub struct UnnameableTestItems {
1366     boundary: Option<hir::HirId>, // HirId of the item under which things are not nameable
1367     items_nameable: bool,
1368 }
1369
1370 impl_lint_pass!(UnnameableTestItems => [UNNAMEABLE_TEST_ITEMS]);
1371
1372 impl UnnameableTestItems {
1373     pub fn new() -> Self {
1374         Self { boundary: None, items_nameable: true }
1375     }
1376 }
1377
1378 impl<'tcx> LateLintPass<'tcx> for UnnameableTestItems {
1379     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1380         if self.items_nameable {
1381             if let hir::ItemKind::Mod(..) = it.kind {
1382             } else {
1383                 self.items_nameable = false;
1384                 self.boundary = Some(it.hir_id);
1385             }
1386             return;
1387         }
1388
1389         if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::rustc_test_marker) {
1390             cx.struct_span_lint(UNNAMEABLE_TEST_ITEMS, attr.span, |lint| {
1391                 lint.build("cannot test inner items").emit()
1392             });
1393         }
1394     }
1395
1396     fn check_item_post(&mut self, _cx: &LateContext<'_>, it: &hir::Item<'_>) {
1397         if !self.items_nameable && self.boundary == Some(it.hir_id) {
1398             self.items_nameable = true;
1399         }
1400     }
1401 }
1402
1403 declare_lint! {
1404     pub KEYWORD_IDENTS,
1405     Allow,
1406     "detects edition keywords being used as an identifier",
1407     @future_incompatible = FutureIncompatibleInfo {
1408         reference: "issue #49716 <https://github.com/rust-lang/rust/issues/49716>",
1409         edition: Some(Edition::Edition2018),
1410     };
1411 }
1412
1413 declare_lint_pass!(
1414     /// Check for uses of edition keywords used as an identifier.
1415     KeywordIdents => [KEYWORD_IDENTS]
1416 );
1417
1418 struct UnderMacro(bool);
1419
1420 impl KeywordIdents {
1421     fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: TokenStream) {
1422         for tt in tokens.into_trees() {
1423             match tt {
1424                 // Only report non-raw idents.
1425                 TokenTree::Token(token) => {
1426                     if let Some((ident, false)) = token.ident() {
1427                         self.check_ident_token(cx, UnderMacro(true), ident);
1428                     }
1429                 }
1430                 TokenTree::Delimited(_, _, tts) => self.check_tokens(cx, tts),
1431             }
1432         }
1433     }
1434
1435     fn check_ident_token(
1436         &mut self,
1437         cx: &EarlyContext<'_>,
1438         UnderMacro(under_macro): UnderMacro,
1439         ident: Ident,
1440     ) {
1441         let next_edition = match cx.sess.edition() {
1442             Edition::Edition2015 => {
1443                 match ident.name {
1444                     kw::Async | kw::Await | kw::Try => Edition::Edition2018,
1445
1446                     // rust-lang/rust#56327: Conservatively do not
1447                     // attempt to report occurrences of `dyn` within
1448                     // macro definitions or invocations, because `dyn`
1449                     // can legitimately occur as a contextual keyword
1450                     // in 2015 code denoting its 2018 meaning, and we
1451                     // do not want rustfix to inject bugs into working
1452                     // code by rewriting such occurrences.
1453                     //
1454                     // But if we see `dyn` outside of a macro, we know
1455                     // its precise role in the parsed AST and thus are
1456                     // assured this is truly an attempt to use it as
1457                     // an identifier.
1458                     kw::Dyn if !under_macro => Edition::Edition2018,
1459
1460                     _ => return,
1461                 }
1462             }
1463
1464             // There are no new keywords yet for the 2018 edition and beyond.
1465             _ => return,
1466         };
1467
1468         // Don't lint `r#foo`.
1469         if cx.sess.parse_sess.raw_identifier_spans.borrow().contains(&ident.span) {
1470             return;
1471         }
1472
1473         cx.struct_span_lint(KEYWORD_IDENTS, ident.span, |lint| {
1474             lint.build(&format!("`{}` is a keyword in the {} edition", ident, next_edition))
1475                 .span_suggestion(
1476                     ident.span,
1477                     "you can use a raw identifier to stay compatible",
1478                     format!("r#{}", ident),
1479                     Applicability::MachineApplicable,
1480                 )
1481                 .emit()
1482         });
1483     }
1484 }
1485
1486 impl EarlyLintPass for KeywordIdents {
1487     fn check_mac_def(&mut self, cx: &EarlyContext<'_>, mac_def: &ast::MacroDef, _id: ast::NodeId) {
1488         self.check_tokens(cx, mac_def.body.inner_tokens());
1489     }
1490     fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::MacCall) {
1491         self.check_tokens(cx, mac.args.inner_tokens());
1492     }
1493     fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: Ident) {
1494         self.check_ident_token(cx, UnderMacro(false), ident);
1495     }
1496 }
1497
1498 declare_lint_pass!(ExplicitOutlivesRequirements => [EXPLICIT_OUTLIVES_REQUIREMENTS]);
1499
1500 impl ExplicitOutlivesRequirements {
1501     fn lifetimes_outliving_lifetime<'tcx>(
1502         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
1503         index: u32,
1504     ) -> Vec<ty::Region<'tcx>> {
1505         inferred_outlives
1506             .iter()
1507             .filter_map(|(pred, _)| match pred.skip_binders() {
1508                 ty::PredicateAtom::RegionOutlives(ty::OutlivesPredicate(a, b)) => match a {
1509                     ty::ReEarlyBound(ebr) if ebr.index == index => Some(b),
1510                     _ => None,
1511                 },
1512                 _ => None,
1513             })
1514             .collect()
1515     }
1516
1517     fn lifetimes_outliving_type<'tcx>(
1518         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
1519         index: u32,
1520     ) -> Vec<ty::Region<'tcx>> {
1521         inferred_outlives
1522             .iter()
1523             .filter_map(|(pred, _)| match pred.skip_binders() {
1524                 ty::PredicateAtom::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
1525                     a.is_param(index).then_some(b)
1526                 }
1527                 _ => None,
1528             })
1529             .collect()
1530     }
1531
1532     fn collect_outlived_lifetimes<'tcx>(
1533         &self,
1534         param: &'tcx hir::GenericParam<'tcx>,
1535         tcx: TyCtxt<'tcx>,
1536         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
1537         ty_generics: &'tcx ty::Generics,
1538     ) -> Vec<ty::Region<'tcx>> {
1539         let index =
1540             ty_generics.param_def_id_to_index[&tcx.hir().local_def_id(param.hir_id).to_def_id()];
1541
1542         match param.kind {
1543             hir::GenericParamKind::Lifetime { .. } => {
1544                 Self::lifetimes_outliving_lifetime(inferred_outlives, index)
1545             }
1546             hir::GenericParamKind::Type { .. } => {
1547                 Self::lifetimes_outliving_type(inferred_outlives, index)
1548             }
1549             hir::GenericParamKind::Const { .. } => Vec::new(),
1550         }
1551     }
1552
1553     fn collect_outlives_bound_spans<'tcx>(
1554         &self,
1555         tcx: TyCtxt<'tcx>,
1556         bounds: &hir::GenericBounds<'_>,
1557         inferred_outlives: &[ty::Region<'tcx>],
1558         infer_static: bool,
1559     ) -> Vec<(usize, Span)> {
1560         use rustc_middle::middle::resolve_lifetime::Region;
1561
1562         bounds
1563             .iter()
1564             .enumerate()
1565             .filter_map(|(i, bound)| {
1566                 if let hir::GenericBound::Outlives(lifetime) = bound {
1567                     let is_inferred = match tcx.named_region(lifetime.hir_id) {
1568                         Some(Region::Static) if infer_static => inferred_outlives
1569                             .iter()
1570                             .any(|r| if let ty::ReStatic = r { true } else { false }),
1571                         Some(Region::EarlyBound(index, ..)) => inferred_outlives.iter().any(|r| {
1572                             if let ty::ReEarlyBound(ebr) = r { ebr.index == index } else { false }
1573                         }),
1574                         _ => false,
1575                     };
1576                     is_inferred.then_some((i, bound.span()))
1577                 } else {
1578                     None
1579                 }
1580             })
1581             .collect()
1582     }
1583
1584     fn consolidate_outlives_bound_spans(
1585         &self,
1586         lo: Span,
1587         bounds: &hir::GenericBounds<'_>,
1588         bound_spans: Vec<(usize, Span)>,
1589     ) -> Vec<Span> {
1590         if bounds.is_empty() {
1591             return Vec::new();
1592         }
1593         if bound_spans.len() == bounds.len() {
1594             let (_, last_bound_span) = bound_spans[bound_spans.len() - 1];
1595             // If all bounds are inferable, we want to delete the colon, so
1596             // start from just after the parameter (span passed as argument)
1597             vec![lo.to(last_bound_span)]
1598         } else {
1599             let mut merged = Vec::new();
1600             let mut last_merged_i = None;
1601
1602             let mut from_start = true;
1603             for (i, bound_span) in bound_spans {
1604                 match last_merged_i {
1605                     // If the first bound is inferable, our span should also eat the leading `+`.
1606                     None if i == 0 => {
1607                         merged.push(bound_span.to(bounds[1].span().shrink_to_lo()));
1608                         last_merged_i = Some(0);
1609                     }
1610                     // If consecutive bounds are inferable, merge their spans
1611                     Some(h) if i == h + 1 => {
1612                         if let Some(tail) = merged.last_mut() {
1613                             // Also eat the trailing `+` if the first
1614                             // more-than-one bound is inferable
1615                             let to_span = if from_start && i < bounds.len() {
1616                                 bounds[i + 1].span().shrink_to_lo()
1617                             } else {
1618                                 bound_span
1619                             };
1620                             *tail = tail.to(to_span);
1621                             last_merged_i = Some(i);
1622                         } else {
1623                             bug!("another bound-span visited earlier");
1624                         }
1625                     }
1626                     _ => {
1627                         // When we find a non-inferable bound, subsequent inferable bounds
1628                         // won't be consecutive from the start (and we'll eat the leading
1629                         // `+` rather than the trailing one)
1630                         from_start = false;
1631                         merged.push(bounds[i - 1].span().shrink_to_hi().to(bound_span));
1632                         last_merged_i = Some(i);
1633                     }
1634                 }
1635             }
1636             merged
1637         }
1638     }
1639 }
1640
1641 impl<'tcx> LateLintPass<'tcx> for ExplicitOutlivesRequirements {
1642     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
1643         use rustc_middle::middle::resolve_lifetime::Region;
1644
1645         let infer_static = cx.tcx.features().infer_static_outlives_requirements;
1646         let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1647         if let hir::ItemKind::Struct(_, ref hir_generics)
1648         | hir::ItemKind::Enum(_, ref hir_generics)
1649         | hir::ItemKind::Union(_, ref hir_generics) = item.kind
1650         {
1651             let inferred_outlives = cx.tcx.inferred_outlives_of(def_id);
1652             if inferred_outlives.is_empty() {
1653                 return;
1654             }
1655
1656             let ty_generics = cx.tcx.generics_of(def_id);
1657
1658             let mut bound_count = 0;
1659             let mut lint_spans = Vec::new();
1660
1661             for param in hir_generics.params {
1662                 let has_lifetime_bounds = param.bounds.iter().any(|bound| {
1663                     if let hir::GenericBound::Outlives(_) = bound { true } else { false }
1664                 });
1665                 if !has_lifetime_bounds {
1666                     continue;
1667                 }
1668
1669                 let relevant_lifetimes =
1670                     self.collect_outlived_lifetimes(param, cx.tcx, inferred_outlives, ty_generics);
1671                 if relevant_lifetimes.is_empty() {
1672                     continue;
1673                 }
1674
1675                 let bound_spans = self.collect_outlives_bound_spans(
1676                     cx.tcx,
1677                     &param.bounds,
1678                     &relevant_lifetimes,
1679                     infer_static,
1680                 );
1681                 bound_count += bound_spans.len();
1682                 lint_spans.extend(self.consolidate_outlives_bound_spans(
1683                     param.span.shrink_to_hi(),
1684                     &param.bounds,
1685                     bound_spans,
1686                 ));
1687             }
1688
1689             let mut where_lint_spans = Vec::new();
1690             let mut dropped_predicate_count = 0;
1691             let num_predicates = hir_generics.where_clause.predicates.len();
1692             for (i, where_predicate) in hir_generics.where_clause.predicates.iter().enumerate() {
1693                 let (relevant_lifetimes, bounds, span) = match where_predicate {
1694                     hir::WherePredicate::RegionPredicate(predicate) => {
1695                         if let Some(Region::EarlyBound(index, ..)) =
1696                             cx.tcx.named_region(predicate.lifetime.hir_id)
1697                         {
1698                             (
1699                                 Self::lifetimes_outliving_lifetime(inferred_outlives, index),
1700                                 &predicate.bounds,
1701                                 predicate.span,
1702                             )
1703                         } else {
1704                             continue;
1705                         }
1706                     }
1707                     hir::WherePredicate::BoundPredicate(predicate) => {
1708                         // FIXME we can also infer bounds on associated types,
1709                         // and should check for them here.
1710                         match predicate.bounded_ty.kind {
1711                             hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
1712                                 if let Res::Def(DefKind::TyParam, def_id) = path.res {
1713                                     let index = ty_generics.param_def_id_to_index[&def_id];
1714                                     (
1715                                         Self::lifetimes_outliving_type(inferred_outlives, index),
1716                                         &predicate.bounds,
1717                                         predicate.span,
1718                                     )
1719                                 } else {
1720                                     continue;
1721                                 }
1722                             }
1723                             _ => {
1724                                 continue;
1725                             }
1726                         }
1727                     }
1728                     _ => continue,
1729                 };
1730                 if relevant_lifetimes.is_empty() {
1731                     continue;
1732                 }
1733
1734                 let bound_spans = self.collect_outlives_bound_spans(
1735                     cx.tcx,
1736                     bounds,
1737                     &relevant_lifetimes,
1738                     infer_static,
1739                 );
1740                 bound_count += bound_spans.len();
1741
1742                 let drop_predicate = bound_spans.len() == bounds.len();
1743                 if drop_predicate {
1744                     dropped_predicate_count += 1;
1745                 }
1746
1747                 // If all the bounds on a predicate were inferable and there are
1748                 // further predicates, we want to eat the trailing comma.
1749                 if drop_predicate && i + 1 < num_predicates {
1750                     let next_predicate_span = hir_generics.where_clause.predicates[i + 1].span();
1751                     where_lint_spans.push(span.to(next_predicate_span.shrink_to_lo()));
1752                 } else {
1753                     where_lint_spans.extend(self.consolidate_outlives_bound_spans(
1754                         span.shrink_to_lo(),
1755                         bounds,
1756                         bound_spans,
1757                     ));
1758                 }
1759             }
1760
1761             // If all predicates are inferable, drop the entire clause
1762             // (including the `where`)
1763             if num_predicates > 0 && dropped_predicate_count == num_predicates {
1764                 let where_span = hir_generics
1765                     .where_clause
1766                     .span()
1767                     .expect("span of (nonempty) where clause should exist");
1768                 // Extend the where clause back to the closing `>` of the
1769                 // generics, except for tuple struct, which have the `where`
1770                 // after the fields of the struct.
1771                 let full_where_span =
1772                     if let hir::ItemKind::Struct(hir::VariantData::Tuple(..), _) = item.kind {
1773                         where_span
1774                     } else {
1775                         hir_generics.span.shrink_to_hi().to(where_span)
1776                     };
1777                 lint_spans.push(full_where_span);
1778             } else {
1779                 lint_spans.extend(where_lint_spans);
1780             }
1781
1782             if !lint_spans.is_empty() {
1783                 cx.struct_span_lint(EXPLICIT_OUTLIVES_REQUIREMENTS, lint_spans.clone(), |lint| {
1784                     lint.build("outlives requirements can be inferred")
1785                         .multipart_suggestion(
1786                             if bound_count == 1 {
1787                                 "remove this bound"
1788                             } else {
1789                                 "remove these bounds"
1790                             },
1791                             lint_spans
1792                                 .into_iter()
1793                                 .map(|span| (span, "".to_owned()))
1794                                 .collect::<Vec<_>>(),
1795                             Applicability::MachineApplicable,
1796                         )
1797                         .emit();
1798                 });
1799             }
1800         }
1801     }
1802 }
1803
1804 declare_lint! {
1805     pub INCOMPLETE_FEATURES,
1806     Warn,
1807     "incomplete features that may function improperly in some or all cases"
1808 }
1809
1810 declare_lint_pass!(
1811     /// Check for used feature gates in `INCOMPLETE_FEATURES` in `librustc_feature/active.rs`.
1812     IncompleteFeatures => [INCOMPLETE_FEATURES]
1813 );
1814
1815 impl EarlyLintPass for IncompleteFeatures {
1816     fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
1817         let features = cx.sess.features_untracked();
1818         features
1819             .declared_lang_features
1820             .iter()
1821             .map(|(name, span, _)| (name, span))
1822             .chain(features.declared_lib_features.iter().map(|(name, span)| (name, span)))
1823             .filter(|(name, _)| rustc_feature::INCOMPLETE_FEATURES.iter().any(|f| name == &f))
1824             .for_each(|(&name, &span)| {
1825                 cx.struct_span_lint(INCOMPLETE_FEATURES, span, |lint| {
1826                     let mut builder = lint.build(&format!(
1827                         "the feature `{}` is incomplete and may not be safe to use \
1828                          and/or cause compiler crashes",
1829                         name,
1830                     ));
1831                     if let Some(n) = rustc_feature::find_feature_issue(name, GateIssue::Language) {
1832                         builder.note(&format!(
1833                             "see issue #{} <https://github.com/rust-lang/rust/issues/{}> \
1834                              for more information",
1835                             n, n,
1836                         ));
1837                     }
1838                     builder.emit();
1839                 })
1840             });
1841     }
1842 }
1843
1844 declare_lint! {
1845     pub INVALID_VALUE,
1846     Warn,
1847     "an invalid value is being created (such as a NULL reference)"
1848 }
1849
1850 declare_lint_pass!(InvalidValue => [INVALID_VALUE]);
1851
1852 impl<'tcx> LateLintPass<'tcx> for InvalidValue {
1853     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
1854         #[derive(Debug, Copy, Clone, PartialEq)]
1855         enum InitKind {
1856             Zeroed,
1857             Uninit,
1858         };
1859
1860         /// Information about why a type cannot be initialized this way.
1861         /// Contains an error message and optionally a span to point at.
1862         type InitError = (String, Option<Span>);
1863
1864         /// Test if this constant is all-0.
1865         fn is_zero(expr: &hir::Expr<'_>) -> bool {
1866             use hir::ExprKind::*;
1867             use rustc_ast::LitKind::*;
1868             match &expr.kind {
1869                 Lit(lit) => {
1870                     if let Int(i, _) = lit.node {
1871                         i == 0
1872                     } else {
1873                         false
1874                     }
1875                 }
1876                 Tup(tup) => tup.iter().all(is_zero),
1877                 _ => false,
1878             }
1879         }
1880
1881         /// Determine if this expression is a "dangerous initialization".
1882         fn is_dangerous_init(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> Option<InitKind> {
1883             // `transmute` is inside an anonymous module (the `extern` block?);
1884             // `Invalid` represents the empty string and matches that.
1885             // FIXME(#66075): use diagnostic items.  Somehow, that does not seem to work
1886             // on intrinsics right now.
1887             const TRANSMUTE_PATH: &[Symbol] =
1888                 &[sym::core, sym::intrinsics, kw::Invalid, sym::transmute];
1889
1890             if let hir::ExprKind::Call(ref path_expr, ref args) = expr.kind {
1891                 // Find calls to `mem::{uninitialized,zeroed}` methods.
1892                 if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
1893                     let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
1894
1895                     if cx.tcx.is_diagnostic_item(sym::mem_zeroed, def_id) {
1896                         return Some(InitKind::Zeroed);
1897                     } else if cx.tcx.is_diagnostic_item(sym::mem_uninitialized, def_id) {
1898                         return Some(InitKind::Uninit);
1899                     } else if cx.match_def_path(def_id, TRANSMUTE_PATH) {
1900                         if is_zero(&args[0]) {
1901                             return Some(InitKind::Zeroed);
1902                         }
1903                     }
1904                 }
1905             } else if let hir::ExprKind::MethodCall(_, _, ref args, _) = expr.kind {
1906                 // Find problematic calls to `MaybeUninit::assume_init`.
1907                 let def_id = cx.typeck_results().type_dependent_def_id(expr.hir_id)?;
1908                 if cx.tcx.is_diagnostic_item(sym::assume_init, def_id) {
1909                     // This is a call to *some* method named `assume_init`.
1910                     // See if the `self` parameter is one of the dangerous constructors.
1911                     if let hir::ExprKind::Call(ref path_expr, _) = args[0].kind {
1912                         if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
1913                             let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
1914
1915                             if cx.tcx.is_diagnostic_item(sym::maybe_uninit_zeroed, def_id) {
1916                                 return Some(InitKind::Zeroed);
1917                             } else if cx.tcx.is_diagnostic_item(sym::maybe_uninit_uninit, def_id) {
1918                                 return Some(InitKind::Uninit);
1919                             }
1920                         }
1921                     }
1922                 }
1923             }
1924
1925             None
1926         }
1927
1928         /// Test if this enum has several actually "existing" variants.
1929         /// Zero-sized uninhabited variants do not always have a tag assigned and thus do not "exist".
1930         fn is_multi_variant(adt: &ty::AdtDef) -> bool {
1931             // As an approximation, we only count dataless variants. Those are definitely inhabited.
1932             let existing_variants = adt.variants.iter().filter(|v| v.fields.is_empty()).count();
1933             existing_variants > 1
1934         }
1935
1936         /// Return `Some` only if we are sure this type does *not*
1937         /// allow zero initialization.
1938         fn ty_find_init_error<'tcx>(
1939             tcx: TyCtxt<'tcx>,
1940             ty: Ty<'tcx>,
1941             init: InitKind,
1942         ) -> Option<InitError> {
1943             use rustc_middle::ty::TyKind::*;
1944             match ty.kind() {
1945                 // Primitive types that don't like 0 as a value.
1946                 Ref(..) => Some(("references must be non-null".to_string(), None)),
1947                 Adt(..) if ty.is_box() => Some(("`Box` must be non-null".to_string(), None)),
1948                 FnPtr(..) => Some(("function pointers must be non-null".to_string(), None)),
1949                 Never => Some(("the `!` type has no valid value".to_string(), None)),
1950                 RawPtr(tm) if matches!(tm.ty.kind(), Dynamic(..)) =>
1951                 // raw ptr to dyn Trait
1952                 {
1953                     Some(("the vtable of a wide raw pointer must be non-null".to_string(), None))
1954                 }
1955                 // Primitive types with other constraints.
1956                 Bool if init == InitKind::Uninit => {
1957                     Some(("booleans must be either `true` or `false`".to_string(), None))
1958                 }
1959                 Char if init == InitKind::Uninit => {
1960                     Some(("characters must be a valid Unicode codepoint".to_string(), None))
1961                 }
1962                 // Recurse and checks for some compound types.
1963                 Adt(adt_def, substs) if !adt_def.is_union() => {
1964                     // First check if this ADT has a layout attribute (like `NonNull` and friends).
1965                     use std::ops::Bound;
1966                     match tcx.layout_scalar_valid_range(adt_def.did) {
1967                         // We exploit here that `layout_scalar_valid_range` will never
1968                         // return `Bound::Excluded`.  (And we have tests checking that we
1969                         // handle the attribute correctly.)
1970                         (Bound::Included(lo), _) if lo > 0 => {
1971                             return Some((format!("`{}` must be non-null", ty), None));
1972                         }
1973                         (Bound::Included(_), _) | (_, Bound::Included(_))
1974                             if init == InitKind::Uninit =>
1975                         {
1976                             return Some((
1977                                 format!(
1978                                     "`{}` must be initialized inside its custom valid range",
1979                                     ty,
1980                                 ),
1981                                 None,
1982                             ));
1983                         }
1984                         _ => {}
1985                     }
1986                     // Now, recurse.
1987                     match adt_def.variants.len() {
1988                         0 => Some(("enums with no variants have no valid value".to_string(), None)),
1989                         1 => {
1990                             // Struct, or enum with exactly one variant.
1991                             // Proceed recursively, check all fields.
1992                             let variant = &adt_def.variants[VariantIdx::from_u32(0)];
1993                             variant.fields.iter().find_map(|field| {
1994                                 ty_find_init_error(tcx, field.ty(tcx, substs), init).map(
1995                                     |(mut msg, span)| {
1996                                         if span.is_none() {
1997                                             // Point to this field, should be helpful for figuring
1998                                             // out where the source of the error is.
1999                                             let span = tcx.def_span(field.did);
2000                                             write!(
2001                                                 &mut msg,
2002                                                 " (in this {} field)",
2003                                                 adt_def.descr()
2004                                             )
2005                                             .unwrap();
2006                                             (msg, Some(span))
2007                                         } else {
2008                                             // Just forward.
2009                                             (msg, span)
2010                                         }
2011                                     },
2012                                 )
2013                             })
2014                         }
2015                         // Multi-variant enum.
2016                         _ => {
2017                             if init == InitKind::Uninit && is_multi_variant(adt_def) {
2018                                 let span = tcx.def_span(adt_def.did);
2019                                 Some((
2020                                     "enums have to be initialized to a variant".to_string(),
2021                                     Some(span),
2022                                 ))
2023                             } else {
2024                                 // In principle, for zero-initialization we could figure out which variant corresponds
2025                                 // to tag 0, and check that... but for now we just accept all zero-initializations.
2026                                 None
2027                             }
2028                         }
2029                     }
2030                 }
2031                 Tuple(..) => {
2032                     // Proceed recursively, check all fields.
2033                     ty.tuple_fields().find_map(|field| ty_find_init_error(tcx, field, init))
2034                 }
2035                 // Conservative fallback.
2036                 _ => None,
2037             }
2038         }
2039
2040         if let Some(init) = is_dangerous_init(cx, expr) {
2041             // This conjures an instance of a type out of nothing,
2042             // using zeroed or uninitialized memory.
2043             // We are extremely conservative with what we warn about.
2044             let conjured_ty = cx.typeck_results().expr_ty(expr);
2045             if let Some((msg, span)) =
2046                 with_no_trimmed_paths(|| ty_find_init_error(cx.tcx, conjured_ty, init))
2047             {
2048                 cx.struct_span_lint(INVALID_VALUE, expr.span, |lint| {
2049                     let mut err = lint.build(&format!(
2050                         "the type `{}` does not permit {}",
2051                         conjured_ty,
2052                         match init {
2053                             InitKind::Zeroed => "zero-initialization",
2054                             InitKind::Uninit => "being left uninitialized",
2055                         },
2056                     ));
2057                     err.span_label(expr.span, "this code causes undefined behavior when executed");
2058                     err.span_label(
2059                         expr.span,
2060                         "help: use `MaybeUninit<T>` instead, \
2061                             and only call `assume_init` after initialization is done",
2062                     );
2063                     if let Some(span) = span {
2064                         err.span_note(span, &msg);
2065                     } else {
2066                         err.note(&msg);
2067                     }
2068                     err.emit();
2069                 });
2070             }
2071         }
2072     }
2073 }
2074
2075 declare_lint! {
2076     pub CLASHING_EXTERN_DECLARATIONS,
2077     Warn,
2078     "detects when an extern fn has been declared with the same name but different types"
2079 }
2080
2081 pub struct ClashingExternDeclarations {
2082     seen_decls: FxHashMap<Symbol, HirId>,
2083 }
2084
2085 /// Differentiate between whether the name for an extern decl came from the link_name attribute or
2086 /// just from declaration itself. This is important because we don't want to report clashes on
2087 /// symbol name if they don't actually clash because one or the other links against a symbol with a
2088 /// different name.
2089 enum SymbolName {
2090     /// The name of the symbol + the span of the annotation which introduced the link name.
2091     Link(Symbol, Span),
2092     /// No link name, so just the name of the symbol.
2093     Normal(Symbol),
2094 }
2095
2096 impl SymbolName {
2097     fn get_name(&self) -> Symbol {
2098         match self {
2099             SymbolName::Link(s, _) | SymbolName::Normal(s) => *s,
2100         }
2101     }
2102 }
2103
2104 impl ClashingExternDeclarations {
2105     crate fn new() -> Self {
2106         ClashingExternDeclarations { seen_decls: FxHashMap::default() }
2107     }
2108     /// Insert a new foreign item into the seen set. If a symbol with the same name already exists
2109     /// for the item, return its HirId without updating the set.
2110     fn insert(&mut self, tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> Option<HirId> {
2111         let hid = fi.hir_id;
2112
2113         let name =
2114             &tcx.codegen_fn_attrs(tcx.hir().local_def_id(hid)).link_name.unwrap_or(fi.ident.name);
2115
2116         if self.seen_decls.contains_key(name) {
2117             // Avoid updating the map with the new entry when we do find a collision. We want to
2118             // make sure we're always pointing to the first definition as the previous declaration.
2119             // This lets us avoid emitting "knock-on" diagnostics.
2120             Some(*self.seen_decls.get(name).unwrap())
2121         } else {
2122             self.seen_decls.insert(*name, hid)
2123         }
2124     }
2125
2126     /// Get the name of the symbol that's linked against for a given extern declaration. That is,
2127     /// the name specified in a #[link_name = ...] attribute if one was specified, else, just the
2128     /// symbol's name.
2129     fn name_of_extern_decl(tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> SymbolName {
2130         let did = tcx.hir().local_def_id(fi.hir_id);
2131         if let Some((overridden_link_name, overridden_link_name_span)) =
2132             tcx.codegen_fn_attrs(did).link_name.map(|overridden_link_name| {
2133                 // FIXME: Instead of searching through the attributes again to get span
2134                 // information, we could have codegen_fn_attrs also give span information back for
2135                 // where the attribute was defined. However, until this is found to be a
2136                 // bottleneck, this does just fine.
2137                 (
2138                     overridden_link_name,
2139                     tcx.get_attrs(did.to_def_id())
2140                         .iter()
2141                         .find(|at| tcx.sess.check_name(at, sym::link_name))
2142                         .unwrap()
2143                         .span,
2144                 )
2145             })
2146         {
2147             SymbolName::Link(overridden_link_name, overridden_link_name_span)
2148         } else {
2149             SymbolName::Normal(fi.ident.name)
2150         }
2151     }
2152
2153     /// Checks whether two types are structurally the same enough that the declarations shouldn't
2154     /// clash. We need this so we don't emit a lint when two modules both declare an extern struct,
2155     /// with the same members (as the declarations shouldn't clash).
2156     fn structurally_same_type<'tcx>(
2157         cx: &LateContext<'tcx>,
2158         a: Ty<'tcx>,
2159         b: Ty<'tcx>,
2160         ckind: CItemKind,
2161     ) -> bool {
2162         fn structurally_same_type_impl<'tcx>(
2163             seen_types: &mut FxHashSet<(Ty<'tcx>, Ty<'tcx>)>,
2164             cx: &LateContext<'tcx>,
2165             a: Ty<'tcx>,
2166             b: Ty<'tcx>,
2167             ckind: CItemKind,
2168         ) -> bool {
2169             debug!("structurally_same_type_impl(cx, a = {:?}, b = {:?})", a, b);
2170             let tcx = cx.tcx;
2171
2172             // Given a transparent newtype, reach through and grab the inner
2173             // type unless the newtype makes the type non-null.
2174             let non_transparent_ty = |ty: Ty<'tcx>| -> Ty<'tcx> {
2175                 let mut ty = ty;
2176                 loop {
2177                     if let ty::Adt(def, substs) = *ty.kind() {
2178                         let is_transparent = def.subst(tcx, substs).repr.transparent();
2179                         let is_non_null = crate::types::nonnull_optimization_guaranteed(tcx, &def);
2180                         debug!(
2181                             "non_transparent_ty({:?}) -- type is transparent? {}, type is non-null? {}",
2182                             ty, is_transparent, is_non_null
2183                         );
2184                         if is_transparent && !is_non_null {
2185                             debug_assert!(def.variants.len() == 1);
2186                             let v = &def.variants[VariantIdx::new(0)];
2187                             ty = v
2188                                 .transparent_newtype_field(tcx)
2189                                 .expect(
2190                                     "single-variant transparent structure with zero-sized field",
2191                                 )
2192                                 .ty(tcx, substs);
2193                             continue;
2194                         }
2195                     }
2196                     debug!("non_transparent_ty -> {:?}", ty);
2197                     return ty;
2198                 }
2199             };
2200
2201             let a = non_transparent_ty(a);
2202             let b = non_transparent_ty(b);
2203
2204             if !seen_types.insert((a, b)) {
2205                 // We've encountered a cycle. There's no point going any further -- the types are
2206                 // structurally the same.
2207                 return true;
2208             }
2209             let tcx = cx.tcx;
2210             if a == b || rustc_middle::ty::TyS::same_type(a, b) {
2211                 // All nominally-same types are structurally same, too.
2212                 true
2213             } else {
2214                 // Do a full, depth-first comparison between the two.
2215                 use rustc_middle::ty::TyKind::*;
2216                 let a_kind = a.kind();
2217                 let b_kind = b.kind();
2218
2219                 let compare_layouts = |a, b| -> Result<bool, LayoutError<'tcx>> {
2220                     debug!("compare_layouts({:?}, {:?})", a, b);
2221                     let a_layout = &cx.layout_of(a)?.layout.abi;
2222                     let b_layout = &cx.layout_of(b)?.layout.abi;
2223                     debug!(
2224                         "comparing layouts: {:?} == {:?} = {}",
2225                         a_layout,
2226                         b_layout,
2227                         a_layout == b_layout
2228                     );
2229                     Ok(a_layout == b_layout)
2230                 };
2231
2232                 #[allow(rustc::usage_of_ty_tykind)]
2233                 let is_primitive_or_pointer = |kind: &ty::TyKind<'_>| {
2234                     kind.is_primitive() || matches!(kind, RawPtr(..) | Ref(..))
2235                 };
2236
2237                 ensure_sufficient_stack(|| {
2238                     match (a_kind, b_kind) {
2239                         (Adt(a_def, a_substs), Adt(b_def, b_substs)) => {
2240                             let a = a.subst(cx.tcx, a_substs);
2241                             let b = b.subst(cx.tcx, b_substs);
2242                             debug!("Comparing {:?} and {:?}", a, b);
2243
2244                             // We can immediately rule out these types as structurally same if
2245                             // their layouts differ.
2246                             match compare_layouts(a, b) {
2247                                 Ok(false) => return false,
2248                                 _ => (), // otherwise, continue onto the full, fields comparison
2249                             }
2250
2251                             // Grab a flattened representation of all fields.
2252                             let a_fields = a_def.variants.iter().flat_map(|v| v.fields.iter());
2253                             let b_fields = b_def.variants.iter().flat_map(|v| v.fields.iter());
2254
2255                             // Perform a structural comparison for each field.
2256                             a_fields.eq_by(
2257                                 b_fields,
2258                                 |&ty::FieldDef { did: a_did, .. },
2259                                  &ty::FieldDef { did: b_did, .. }| {
2260                                     structurally_same_type_impl(
2261                                         seen_types,
2262                                         cx,
2263                                         tcx.type_of(a_did),
2264                                         tcx.type_of(b_did),
2265                                         ckind,
2266                                     )
2267                                 },
2268                             )
2269                         }
2270                         (Array(a_ty, a_const), Array(b_ty, b_const)) => {
2271                             // For arrays, we also check the constness of the type.
2272                             a_const.val == b_const.val
2273                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2274                         }
2275                         (Slice(a_ty), Slice(b_ty)) => {
2276                             structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2277                         }
2278                         (RawPtr(a_tymut), RawPtr(b_tymut)) => {
2279                             a_tymut.mutbl == b_tymut.mutbl
2280                                 && structurally_same_type_impl(
2281                                     seen_types,
2282                                     cx,
2283                                     &a_tymut.ty,
2284                                     &b_tymut.ty,
2285                                     ckind,
2286                                 )
2287                         }
2288                         (Ref(_a_region, a_ty, a_mut), Ref(_b_region, b_ty, b_mut)) => {
2289                             // For structural sameness, we don't need the region to be same.
2290                             a_mut == b_mut
2291                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2292                         }
2293                         (FnDef(..), FnDef(..)) => {
2294                             let a_poly_sig = a.fn_sig(tcx);
2295                             let b_poly_sig = b.fn_sig(tcx);
2296
2297                             // As we don't compare regions, skip_binder is fine.
2298                             let a_sig = a_poly_sig.skip_binder();
2299                             let b_sig = b_poly_sig.skip_binder();
2300
2301                             (a_sig.abi, a_sig.unsafety, a_sig.c_variadic)
2302                                 == (b_sig.abi, b_sig.unsafety, b_sig.c_variadic)
2303                                 && a_sig.inputs().iter().eq_by(b_sig.inputs().iter(), |a, b| {
2304                                     structurally_same_type_impl(seen_types, cx, a, b, ckind)
2305                                 })
2306                                 && structurally_same_type_impl(
2307                                     seen_types,
2308                                     cx,
2309                                     a_sig.output(),
2310                                     b_sig.output(),
2311                                     ckind,
2312                                 )
2313                         }
2314                         (Tuple(a_substs), Tuple(b_substs)) => {
2315                             a_substs.types().eq_by(b_substs.types(), |a_ty, b_ty| {
2316                                 structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2317                             })
2318                         }
2319                         // For these, it's not quite as easy to define structural-sameness quite so easily.
2320                         // For the purposes of this lint, take the conservative approach and mark them as
2321                         // not structurally same.
2322                         (Dynamic(..), Dynamic(..))
2323                         | (Error(..), Error(..))
2324                         | (Closure(..), Closure(..))
2325                         | (Generator(..), Generator(..))
2326                         | (GeneratorWitness(..), GeneratorWitness(..))
2327                         | (Projection(..), Projection(..))
2328                         | (Opaque(..), Opaque(..)) => false,
2329
2330                         // These definitely should have been caught above.
2331                         (Bool, Bool) | (Char, Char) | (Never, Never) | (Str, Str) => unreachable!(),
2332
2333                         // An Adt and a primitive or pointer type. This can be FFI-safe if non-null
2334                         // enum layout optimisation is being applied.
2335                         (Adt(..), other_kind) | (other_kind, Adt(..))
2336                             if is_primitive_or_pointer(other_kind) =>
2337                         {
2338                             let (primitive, adt) =
2339                                 if is_primitive_or_pointer(a.kind()) { (a, b) } else { (b, a) };
2340                             if let Some(ty) = crate::types::repr_nullable_ptr(cx, adt, ckind) {
2341                                 ty == primitive
2342                             } else {
2343                                 compare_layouts(a, b).unwrap_or(false)
2344                             }
2345                         }
2346                         // Otherwise, just compare the layouts. This may fail to lint for some
2347                         // incompatible types, but at the very least, will stop reads into
2348                         // uninitialised memory.
2349                         _ => compare_layouts(a, b).unwrap_or(false),
2350                     }
2351                 })
2352             }
2353         }
2354         let mut seen_types = FxHashSet::default();
2355         structurally_same_type_impl(&mut seen_types, cx, a, b, ckind)
2356     }
2357 }
2358
2359 impl_lint_pass!(ClashingExternDeclarations => [CLASHING_EXTERN_DECLARATIONS]);
2360
2361 impl<'tcx> LateLintPass<'tcx> for ClashingExternDeclarations {
2362     fn check_foreign_item(&mut self, cx: &LateContext<'tcx>, this_fi: &hir::ForeignItem<'_>) {
2363         trace!("ClashingExternDeclarations: check_foreign_item: {:?}", this_fi);
2364         if let ForeignItemKind::Fn(..) = this_fi.kind {
2365             let tcx = *&cx.tcx;
2366             if let Some(existing_hid) = self.insert(tcx, this_fi) {
2367                 let existing_decl_ty = tcx.type_of(tcx.hir().local_def_id(existing_hid));
2368                 let this_decl_ty = tcx.type_of(tcx.hir().local_def_id(this_fi.hir_id));
2369                 debug!(
2370                     "ClashingExternDeclarations: Comparing existing {:?}: {:?} to this {:?}: {:?}",
2371                     existing_hid, existing_decl_ty, this_fi.hir_id, this_decl_ty
2372                 );
2373                 // Check that the declarations match.
2374                 if !Self::structurally_same_type(
2375                     cx,
2376                     existing_decl_ty,
2377                     this_decl_ty,
2378                     CItemKind::Declaration,
2379                 ) {
2380                     let orig_fi = tcx.hir().expect_foreign_item(existing_hid);
2381                     let orig = Self::name_of_extern_decl(tcx, orig_fi);
2382
2383                     // We want to ensure that we use spans for both decls that include where the
2384                     // name was defined, whether that was from the link_name attribute or not.
2385                     let get_relevant_span =
2386                         |fi: &hir::ForeignItem<'_>| match Self::name_of_extern_decl(tcx, fi) {
2387                             SymbolName::Normal(_) => fi.span,
2388                             SymbolName::Link(_, annot_span) => fi.span.to(annot_span),
2389                         };
2390                     // Finally, emit the diagnostic.
2391                     tcx.struct_span_lint_hir(
2392                         CLASHING_EXTERN_DECLARATIONS,
2393                         this_fi.hir_id,
2394                         get_relevant_span(this_fi),
2395                         |lint| {
2396                             let mut expected_str = DiagnosticStyledString::new();
2397                             expected_str.push(existing_decl_ty.fn_sig(tcx).to_string(), false);
2398                             let mut found_str = DiagnosticStyledString::new();
2399                             found_str.push(this_decl_ty.fn_sig(tcx).to_string(), true);
2400
2401                             lint.build(&format!(
2402                                 "`{}` redeclare{} with a different signature",
2403                                 this_fi.ident.name,
2404                                 if orig.get_name() == this_fi.ident.name {
2405                                     "d".to_string()
2406                                 } else {
2407                                     format!("s `{}`", orig.get_name())
2408                                 }
2409                             ))
2410                             .span_label(
2411                                 get_relevant_span(orig_fi),
2412                                 &format!("`{}` previously declared here", orig.get_name()),
2413                             )
2414                             .span_label(
2415                                 get_relevant_span(this_fi),
2416                                 "this signature doesn't match the previous declaration",
2417                             )
2418                             .note_expected_found(&"", expected_str, &"", found_str)
2419                             .emit()
2420                         },
2421                     );
2422                 }
2423             }
2424         }
2425     }
2426 }