src/librustc_lint/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::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext};
  24 use rustc_ast::ast::{self, Expr};
  25 use rustc_ast::attr::{self, HasAttrs};
  26 use rustc_ast::tokenstream::{TokenStream, TokenTree};
  27 use rustc_ast::visit::{FnCtxt, FnKind};
  28 use rustc_ast_pretty::pprust::{self, expr_to_string};
  29 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
  30 use rustc_errors::{Applicability, DiagnosticBuilder, DiagnosticStyledString};
  31 use rustc_feature::{deprecated_attributes, AttributeGate, AttributeTemplate, AttributeType};
  32 use rustc_feature::{GateIssue, Stability};
  33 use rustc_hir as hir;
  34 use rustc_hir::def::{DefKind, Res};
  35 use rustc_hir::def_id::DefId;
  36 use rustc_hir::{ForeignItemKind, GenericParamKind, PatKind};
  37 use rustc_hir::{HirId, HirIdSet, Node};
  38 use rustc_middle::lint::LintDiagnosticBuilder;
  39 use rustc_middle::ty::subst::GenericArgKind;
  40 use rustc_middle::ty::{self, Ty, TyCtxt};
  41 use rustc_session::lint::FutureIncompatibleInfo;
  42 use rustc_span::edition::Edition;
  43 use rustc_span::source_map::Spanned;
  44 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  45 use rustc_span::{BytePos, Span};
  46 use rustc_target::abi::VariantIdx;
  47 use rustc_trait_selection::traits::misc::can_type_implement_copy;
  48
  49 use crate::nonstandard_style::{method_context, MethodLateContext};
  50
  51 use log::{debug, trace};
  52 use std::fmt::Write;
  53
  54 // hardwired lints from librustc_middle
  55 pub use rustc_session::lint::builtin::*;
  56
  57 declare_lint! {
  58     WHILE_TRUE,
  59     Warn,
  60     "suggest using `loop { }` instead of `while true { }`"
  61 }
  62
  63 declare_lint_pass!(WhileTrue => [WHILE_TRUE]);
  64
  65 /// Traverse through any amount of parenthesis and return the first non-parens expression.
  66 fn pierce_parens(mut expr: &ast::Expr) -> &ast::Expr {
  67     while let ast::ExprKind::Paren(sub) = &expr.kind {
  68         expr = sub;
  69     }
  70     expr
  71 }
  72
  73 impl EarlyLintPass for WhileTrue {
  74     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
  75         if let ast::ExprKind::While(cond, ..) = &e.kind {
  76             if let ast::ExprKind::Lit(ref lit) = pierce_parens(cond).kind {
  77                 if let ast::LitKind::Bool(true) = lit.kind {
  78                     if !lit.span.from_expansion() {
  79                         let msg = "denote infinite loops with `loop { ... }`";
  80                         let condition_span = cx.sess.source_map().guess_head_span(e.span);
  81                         cx.struct_span_lint(WHILE_TRUE, condition_span, |lint| {
  82                             lint.build(msg)
  83                                 .span_suggestion_short(
  84                                     condition_span,
  85                                     "use `loop`",
  86                                     "loop".to_owned(),
  87                                     Applicability::MachineApplicable,
  88                                 )
  89                                 .emit();
  90                         })
  91                     }
  92                 }
  93             }
  94         }
  95     }
  96 }
  97
  98 declare_lint! {
  99     BOX_POINTERS,
 100     Allow,
 101     "use of owned (Box type) heap memory"
 102 }
 103
 104 declare_lint_pass!(BoxPointers => [BOX_POINTERS]);
 105
 106 impl BoxPointers {
 107     fn check_heap_type(&self, cx: &LateContext<'_>, span: Span, ty: Ty<'_>) {
 108         for leaf in ty.walk() {
 109             if let GenericArgKind::Type(leaf_ty) = leaf.unpack() {
 110                 if leaf_ty.is_box() {
 111                     cx.struct_span_lint(BOX_POINTERS, span, |lint| {
 112                         lint.build(&format!("type uses owned (Box type) pointers: {}", ty)).emit()
 113                     });
 114                 }
 115             }
 116         }
 117     }
 118 }
 119
 120 impl<'tcx> LateLintPass<'tcx> for BoxPointers {
 121     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 122         match it.kind {
 123             hir::ItemKind::Fn(..)
 124             | hir::ItemKind::TyAlias(..)
 125             | hir::ItemKind::Enum(..)
 126             | hir::ItemKind::Struct(..)
 127             | hir::ItemKind::Union(..) => {
 128                 let def_id = cx.tcx.hir().local_def_id(it.hir_id);
 129                 self.check_heap_type(cx, it.span, cx.tcx.type_of(def_id))
 130             }
 131             _ => (),
 132         }
 133
 134         // If it's a struct, we also have to check the fields' types
 135         match it.kind {
 136             hir::ItemKind::Struct(ref struct_def, _) | hir::ItemKind::Union(ref struct_def, _) => {
 137                 for struct_field in struct_def.fields() {
 138                     let def_id = cx.tcx.hir().local_def_id(struct_field.hir_id);
 139                     self.check_heap_type(cx, struct_field.span, cx.tcx.type_of(def_id));
 140                 }
 141             }
 142             _ => (),
 143         }
 144     }
 145
 146     fn check_expr(&mut self, cx: &LateContext<'_>, e: &hir::Expr<'_>) {
 147         let ty = cx.typeck_results().node_type(e.hir_id);
 148         self.check_heap_type(cx, e.span, ty);
 149     }
 150 }
 151
 152 declare_lint! {
 153     NON_SHORTHAND_FIELD_PATTERNS,
 154     Warn,
 155     "using `Struct { x: x }` instead of `Struct { x }` in a pattern"
 156 }
 157
 158 declare_lint_pass!(NonShorthandFieldPatterns => [NON_SHORTHAND_FIELD_PATTERNS]);
 159
 160 impl<'tcx> LateLintPass<'tcx> for NonShorthandFieldPatterns {
 161     fn check_pat(&mut self, cx: &LateContext<'_>, pat: &hir::Pat<'_>) {
 162         if let PatKind::Struct(ref qpath, field_pats, _) = pat.kind {
 163             let variant = cx
 164                 .typeck_results()
 165                 .pat_ty(pat)
 166                 .ty_adt_def()
 167                 .expect("struct pattern type is not an ADT")
 168                 .variant_of_res(cx.qpath_res(qpath, pat.hir_id));
 169             for fieldpat in field_pats {
 170                 if fieldpat.is_shorthand {
 171                     continue;
 172                 }
 173                 if fieldpat.span.from_expansion() {
 174                     // Don't lint if this is a macro expansion: macro authors
 175                     // shouldn't have to worry about this kind of style issue
 176                     // (Issue #49588)
 177                     continue;
 178                 }
 179                 if let PatKind::Binding(binding_annot, _, ident, None) = fieldpat.pat.kind {
 180                     if cx.tcx.find_field_index(ident, &variant)
 181                         == Some(cx.tcx.field_index(fieldpat.hir_id, cx.typeck_results()))
 182                     {
 183                         cx.struct_span_lint(NON_SHORTHAND_FIELD_PATTERNS, fieldpat.span, |lint| {
 184                             let mut err = lint
 185                                 .build(&format!("the `{}:` in this pattern is redundant", ident));
 186                             let binding = match binding_annot {
 187                                 hir::BindingAnnotation::Unannotated => None,
 188                                 hir::BindingAnnotation::Mutable => Some("mut"),
 189                                 hir::BindingAnnotation::Ref => Some("ref"),
 190                                 hir::BindingAnnotation::RefMut => Some("ref mut"),
 191                             };
 192                             let ident = if let Some(binding) = binding {
 193                                 format!("{} {}", binding, ident)
 194                             } else {
 195                                 ident.to_string()
 196                             };
 197                             err.span_suggestion(
 198                                 fieldpat.span,
 199                                 "use shorthand field pattern",
 200                                 ident,
 201                                 Applicability::MachineApplicable,
 202                             );
 203                             err.emit();
 204                         });
 205                     }
 206                 }
 207             }
 208         }
 209     }
 210 }
 211
 212 declare_lint! {
 213     UNSAFE_CODE,
 214     Allow,
 215     "usage of `unsafe` code"
 216 }
 217
 218 declare_lint_pass!(UnsafeCode => [UNSAFE_CODE]);
 219
 220 impl UnsafeCode {
 221     fn report_unsafe(
 222         &self,
 223         cx: &EarlyContext<'_>,
 224         span: Span,
 225         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
 226     ) {
 227         // This comes from a macro that has `#[allow_internal_unsafe]`.
 228         if span.allows_unsafe() {
 229             return;
 230         }
 231
 232         cx.struct_span_lint(UNSAFE_CODE, span, decorate);
 233     }
 234 }
 235
 236 impl EarlyLintPass for UnsafeCode {
 237     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 238         if attr.check_name(sym::allow_internal_unsafe) {
 239             self.report_unsafe(cx, attr.span, |lint| {
 240                 lint.build(
 241                     "`allow_internal_unsafe` allows defining \
 242                                                macros using unsafe without triggering \
 243                                                the `unsafe_code` lint at their call site",
 244                 )
 245                 .emit()
 246             });
 247         }
 248     }
 249
 250     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
 251         if let ast::ExprKind::Block(ref blk, _) = e.kind {
 252             // Don't warn about generated blocks; that'll just pollute the output.
 253             if blk.rules == ast::BlockCheckMode::Unsafe(ast::UserProvided) {
 254                 self.report_unsafe(cx, blk.span, |lint| {
 255                     lint.build("usage of an `unsafe` block").emit()
 256                 });
 257             }
 258         }
 259     }
 260
 261     fn check_item(&mut self, cx: &EarlyContext<'_>, it: &ast::Item) {
 262         match it.kind {
 263             ast::ItemKind::Trait(_, ast::Unsafe::Yes(_), ..) => {
 264                 self.report_unsafe(cx, it.span, |lint| {
 265                     lint.build("declaration of an `unsafe` trait").emit()
 266                 })
 267             }
 268
 269             ast::ItemKind::Impl { unsafety: ast::Unsafe::Yes(_), .. } => {
 270                 self.report_unsafe(cx, it.span, |lint| {
 271                     lint.build("implementation of an `unsafe` trait").emit()
 272                 })
 273             }
 274
 275             _ => {}
 276         }
 277     }
 278
 279     fn check_fn(&mut self, cx: &EarlyContext<'_>, fk: FnKind<'_>, span: Span, _: ast::NodeId) {
 280         if let FnKind::Fn(
 281             ctxt,
 282             _,
 283             ast::FnSig { header: ast::FnHeader { unsafety: ast::Unsafe::Yes(_), .. }, .. },
 284             _,
 285             body,
 286         ) = fk
 287         {
 288             let msg = match ctxt {
 289                 FnCtxt::Foreign => return,
 290                 FnCtxt::Free => "declaration of an `unsafe` function",
 291                 FnCtxt::Assoc(_) if body.is_none() => "declaration of an `unsafe` method",
 292                 FnCtxt::Assoc(_) => "implementation of an `unsafe` method",
 293             };
 294             self.report_unsafe(cx, span, |lint| lint.build(msg).emit());
 295         }
 296     }
 297 }
 298
 299 declare_lint! {
 300     pub MISSING_DOCS,
 301     Allow,
 302     "detects missing documentation for public members",
 303     report_in_external_macro
 304 }
 305
 306 pub struct MissingDoc {
 307     /// Stack of whether `#[doc(hidden)]` is set at each level which has lint attributes.
 308     doc_hidden_stack: Vec<bool>,
 309
 310     /// Private traits or trait items that leaked through. Don't check their methods.
 311     private_traits: FxHashSet<hir::HirId>,
 312 }
 313
 314 impl_lint_pass!(MissingDoc => [MISSING_DOCS]);
 315
 316 fn has_doc(attr: &ast::Attribute) -> bool {
 317     if attr.is_doc_comment() {
 318         return true;
 319     }
 320
 321     if !attr.check_name(sym::doc) {
 322         return false;
 323     }
 324
 325     if attr.is_value_str() {
 326         return true;
 327     }
 328
 329     if let Some(list) = attr.meta_item_list() {
 330         for meta in list {
 331             if meta.check_name(sym::include) || meta.check_name(sym::hidden) {
 332                 return true;
 333             }
 334         }
 335     }
 336
 337     false
 338 }
 339
 340 impl MissingDoc {
 341     pub fn new() -> MissingDoc {
 342         MissingDoc { doc_hidden_stack: vec![false], private_traits: FxHashSet::default() }
 343     }
 344
 345     fn doc_hidden(&self) -> bool {
 346         *self.doc_hidden_stack.last().expect("empty doc_hidden_stack")
 347     }
 348
 349     fn check_missing_docs_attrs(
 350         &self,
 351         cx: &LateContext<'_>,
 352         id: Option<hir::HirId>,
 353         attrs: &[ast::Attribute],
 354         sp: Span,
 355         article: &'static str,
 356         desc: &'static str,
 357     ) {
 358         // If we're building a test harness, then warning about
 359         // documentation is probably not really relevant right now.
 360         if cx.sess().opts.test {
 361             return;
 362         }
 363
 364         // `#[doc(hidden)]` disables missing_docs check.
 365         if self.doc_hidden() {
 366             return;
 367         }
 368
 369         // Only check publicly-visible items, using the result from the privacy pass.
 370         // It's an option so the crate root can also use this function (it doesn't
 371         // have a `NodeId`).
 372         if let Some(id) = id {
 373             if !cx.access_levels.is_exported(id) {
 374                 return;
 375             }
 376         }
 377
 378         let has_doc = attrs.iter().any(|a| has_doc(a));
 379         if !has_doc {
 380             cx.struct_span_lint(
 381                 MISSING_DOCS,
 382                 cx.tcx.sess.source_map().guess_head_span(sp),
 383                 |lint| {
 384                     lint.build(&format!("missing documentation for {} {}", article, desc)).emit()
 385                 },
 386             );
 387         }
 388     }
 389 }
 390
 391 impl<'tcx> LateLintPass<'tcx> for MissingDoc {
 392     fn enter_lint_attrs(&mut self, _: &LateContext<'_>, attrs: &[ast::Attribute]) {
 393         let doc_hidden = self.doc_hidden()
 394             || attrs.iter().any(|attr| {
 395                 attr.check_name(sym::doc)
 396                     && match attr.meta_item_list() {
 397                         None => false,
 398                         Some(l) => attr::list_contains_name(&l, sym::hidden),
 399                     }
 400             });
 401         self.doc_hidden_stack.push(doc_hidden);
 402     }
 403
 404     fn exit_lint_attrs(&mut self, _: &LateContext<'_>, _attrs: &[ast::Attribute]) {
 405         self.doc_hidden_stack.pop().expect("empty doc_hidden_stack");
 406     }
 407
 408     fn check_crate(&mut self, cx: &LateContext<'_>, krate: &hir::Crate<'_>) {
 409         self.check_missing_docs_attrs(cx, None, &krate.item.attrs, krate.item.span, "the", "crate");
 410
 411         for macro_def in krate.exported_macros {
 412             let has_doc = macro_def.attrs.iter().any(|a| has_doc(a));
 413             if !has_doc {
 414                 cx.struct_span_lint(
 415                     MISSING_DOCS,
 416                     cx.tcx.sess.source_map().guess_head_span(macro_def.span),
 417                     |lint| lint.build("missing documentation for macro").emit(),
 418                 );
 419             }
 420         }
 421     }
 422
 423     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 424         match it.kind {
 425             hir::ItemKind::Trait(.., trait_item_refs) => {
 426                 // Issue #11592: traits are always considered exported, even when private.
 427                 if let hir::VisibilityKind::Inherited = it.vis.node {
 428                     self.private_traits.insert(it.hir_id);
 429                     for trait_item_ref in trait_item_refs {
 430                         self.private_traits.insert(trait_item_ref.id.hir_id);
 431                     }
 432                     return;
 433                 }
 434             }
 435             hir::ItemKind::Impl { of_trait: Some(ref trait_ref), items, .. } => {
 436                 // If the trait is private, add the impl items to `private_traits` so they don't get
 437                 // reported for missing docs.
 438                 let real_trait = trait_ref.path.res.def_id();
 439                 if let Some(def_id) = real_trait.as_local() {
 440                     let hir_id = cx.tcx.hir().as_local_hir_id(def_id);
 441                     if let Some(Node::Item(item)) = cx.tcx.hir().find(hir_id) {
 442                         if let hir::VisibilityKind::Inherited = item.vis.node {
 443                             for impl_item_ref in items {
 444                                 self.private_traits.insert(impl_item_ref.id.hir_id);
 445                             }
 446                         }
 447                     }
 448                 }
 449                 return;
 450             }
 451
 452             hir::ItemKind::TyAlias(..)
 453             | hir::ItemKind::Fn(..)
 454             | hir::ItemKind::Mod(..)
 455             | hir::ItemKind::Enum(..)
 456             | hir::ItemKind::Struct(..)
 457             | hir::ItemKind::Union(..)
 458             | hir::ItemKind::Const(..)
 459             | hir::ItemKind::Static(..) => {}
 460
 461             _ => return,
 462         };
 463
 464         let def_id = cx.tcx.hir().local_def_id(it.hir_id);
 465         let (article, desc) = cx.tcx.article_and_description(def_id.to_def_id());
 466
 467         self.check_missing_docs_attrs(cx, Some(it.hir_id), &it.attrs, it.span, article, desc);
 468     }
 469
 470     fn check_trait_item(&mut self, cx: &LateContext<'_>, trait_item: &hir::TraitItem<'_>) {
 471         if self.private_traits.contains(&trait_item.hir_id) {
 472             return;
 473         }
 474
 475         let def_id = cx.tcx.hir().local_def_id(trait_item.hir_id);
 476         let (article, desc) = cx.tcx.article_and_description(def_id.to_def_id());
 477
 478         self.check_missing_docs_attrs(
 479             cx,
 480             Some(trait_item.hir_id),
 481             &trait_item.attrs,
 482             trait_item.span,
 483             article,
 484             desc,
 485         );
 486     }
 487
 488     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
 489         // If the method is an impl for a trait, don't doc.
 490         if method_context(cx, impl_item.hir_id) == MethodLateContext::TraitImpl {
 491             return;
 492         }
 493
 494         let def_id = cx.tcx.hir().local_def_id(impl_item.hir_id);
 495         let (article, desc) = cx.tcx.article_and_description(def_id.to_def_id());
 496         self.check_missing_docs_attrs(
 497             cx,
 498             Some(impl_item.hir_id),
 499             &impl_item.attrs,
 500             impl_item.span,
 501             article,
 502             desc,
 503         );
 504     }
 505
 506     fn check_struct_field(&mut self, cx: &LateContext<'_>, sf: &hir::StructField<'_>) {
 507         if !sf.is_positional() {
 508             self.check_missing_docs_attrs(
 509                 cx,
 510                 Some(sf.hir_id),
 511                 &sf.attrs,
 512                 sf.span,
 513                 "a",
 514                 "struct field",
 515             )
 516         }
 517     }
 518
 519     fn check_variant(&mut self, cx: &LateContext<'_>, v: &hir::Variant<'_>) {
 520         self.check_missing_docs_attrs(cx, Some(v.id), &v.attrs, v.span, "a", "variant");
 521     }
 522 }
 523
 524 declare_lint! {
 525     pub MISSING_COPY_IMPLEMENTATIONS,
 526     Allow,
 527     "detects potentially-forgotten implementations of `Copy`"
 528 }
 529
 530 declare_lint_pass!(MissingCopyImplementations => [MISSING_COPY_IMPLEMENTATIONS]);
 531
 532 impl<'tcx> LateLintPass<'tcx> for MissingCopyImplementations {
 533     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 534         if !cx.access_levels.is_reachable(item.hir_id) {
 535             return;
 536         }
 537         let (def, ty) = match item.kind {
 538             hir::ItemKind::Struct(_, ref ast_generics) => {
 539                 if !ast_generics.params.is_empty() {
 540                     return;
 541                 }
 542                 let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
 543                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 544             }
 545             hir::ItemKind::Union(_, ref ast_generics) => {
 546                 if !ast_generics.params.is_empty() {
 547                     return;
 548                 }
 549                 let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
 550                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 551             }
 552             hir::ItemKind::Enum(_, ref ast_generics) => {
 553                 if !ast_generics.params.is_empty() {
 554                     return;
 555                 }
 556                 let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
 557                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 558             }
 559             _ => return,
 560         };
 561         if def.has_dtor(cx.tcx) {
 562             return;
 563         }
 564         let param_env = ty::ParamEnv::empty();
 565         if ty.is_copy_modulo_regions(cx.tcx.at(item.span), param_env) {
 566             return;
 567         }
 568         if can_type_implement_copy(cx.tcx, param_env, ty).is_ok() {
 569             cx.struct_span_lint(MISSING_COPY_IMPLEMENTATIONS, item.span, |lint| {
 570                 lint.build(
 571                     "type could implement `Copy`; consider adding `impl \
 572                           Copy`",
 573                 )
 574                 .emit()
 575             })
 576         }
 577     }
 578 }
 579
 580 declare_lint! {
 581     MISSING_DEBUG_IMPLEMENTATIONS,
 582     Allow,
 583     "detects missing implementations of Debug"
 584 }
 585
 586 #[derive(Default)]
 587 pub struct MissingDebugImplementations {
 588     impling_types: Option<HirIdSet>,
 589 }
 590
 591 impl_lint_pass!(MissingDebugImplementations => [MISSING_DEBUG_IMPLEMENTATIONS]);
 592
 593 impl<'tcx> LateLintPass<'tcx> for MissingDebugImplementations {
 594     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 595         if !cx.access_levels.is_reachable(item.hir_id) {
 596             return;
 597         }
 598
 599         match item.kind {
 600             hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) | hir::ItemKind::Enum(..) => {}
 601             _ => return,
 602         }
 603
 604         let debug = match cx.tcx.get_diagnostic_item(sym::debug_trait) {
 605             Some(debug) => debug,
 606             None => return,
 607         };
 608
 609         if self.impling_types.is_none() {
 610             let mut impls = HirIdSet::default();
 611             cx.tcx.for_each_impl(debug, |d| {
 612                 if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() {
 613                     if let Some(def_id) = ty_def.did.as_local() {
 614                         impls.insert(cx.tcx.hir().as_local_hir_id(def_id));
 615                     }
 616                 }
 617             });
 618
 619             self.impling_types = Some(impls);
 620             debug!("{:?}", self.impling_types);
 621         }
 622
 623         if !self.impling_types.as_ref().unwrap().contains(&item.hir_id) {
 624             cx.struct_span_lint(MISSING_DEBUG_IMPLEMENTATIONS, item.span, |lint| {
 625                 lint.build(&format!(
 626                     "type does not implement `{}`; consider adding `#[derive(Debug)]` \
 627                      or a manual implementation",
 628                     cx.tcx.def_path_str(debug)
 629                 ))
 630                 .emit()
 631             });
 632         }
 633     }
 634 }
 635
 636 declare_lint! {
 637     pub ANONYMOUS_PARAMETERS,
 638     Allow,
 639     "detects anonymous parameters",
 640     @future_incompatible = FutureIncompatibleInfo {
 641         reference: "issue #41686 <https://github.com/rust-lang/rust/issues/41686>",
 642         edition: Some(Edition::Edition2018),
 643     };
 644 }
 645
 646 declare_lint_pass!(
 647     /// Checks for use of anonymous parameters (RFC 1685).
 648     AnonymousParameters => [ANONYMOUS_PARAMETERS]
 649 );
 650
 651 impl EarlyLintPass for AnonymousParameters {
 652     fn check_trait_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
 653         if let ast::AssocItemKind::Fn(_, ref sig, _, _) = it.kind {
 654             for arg in sig.decl.inputs.iter() {
 655                 if let ast::PatKind::Ident(_, ident, None) = arg.pat.kind {
 656                     if ident.name == kw::Invalid {
 657                         cx.struct_span_lint(ANONYMOUS_PARAMETERS, arg.pat.span, |lint| {
 658                             let ty_snip = cx.sess.source_map().span_to_snippet(arg.ty.span);
 659
 660                             let (ty_snip, appl) = if let Ok(ref snip) = ty_snip {
 661                                 (snip.as_str(), Applicability::MachineApplicable)
 662                             } else {
 663                                 ("<type>", Applicability::HasPlaceholders)
 664                             };
 665
 666                             lint.build(
 667                                 "anonymous parameters are deprecated and will be \
 668                                      removed in the next edition.",
 669                             )
 670                             .span_suggestion(
 671                                 arg.pat.span,
 672                                 "try naming the parameter or explicitly \
 673                                             ignoring it",
 674                                 format!("_: {}", ty_snip),
 675                                 appl,
 676                             )
 677                             .emit();
 678                         })
 679                     }
 680                 }
 681             }
 682         }
 683     }
 684 }
 685
 686 /// Check for use of attributes which have been deprecated.
 687 #[derive(Clone)]
 688 pub struct DeprecatedAttr {
 689     // This is not free to compute, so we want to keep it around, rather than
 690     // compute it for every attribute.
 691     depr_attrs: Vec<&'static (Symbol, AttributeType, AttributeTemplate, AttributeGate)>,
 692 }
 693
 694 impl_lint_pass!(DeprecatedAttr => []);
 695
 696 impl DeprecatedAttr {
 697     pub fn new() -> DeprecatedAttr {
 698         DeprecatedAttr { depr_attrs: deprecated_attributes() }
 699     }
 700 }
 701
 702 fn lint_deprecated_attr(
 703     cx: &EarlyContext<'_>,
 704     attr: &ast::Attribute,
 705     msg: &str,
 706     suggestion: Option<&str>,
 707 ) {
 708     cx.struct_span_lint(DEPRECATED, attr.span, |lint| {
 709         lint.build(msg)
 710             .span_suggestion_short(
 711                 attr.span,
 712                 suggestion.unwrap_or("remove this attribute"),
 713                 String::new(),
 714                 Applicability::MachineApplicable,
 715             )
 716             .emit();
 717     })
 718 }
 719
 720 impl EarlyLintPass for DeprecatedAttr {
 721     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 722         for &&(n, _, _, ref g) in &self.depr_attrs {
 723             if attr.ident().map(|ident| ident.name) == Some(n) {
 724                 if let &AttributeGate::Gated(
 725                     Stability::Deprecated(link, suggestion),
 726                     ref name,
 727                     ref reason,
 728                     _,
 729                 ) = g
 730                 {
 731                     let msg =
 732                         format!("use of deprecated attribute `{}`: {}. See {}", name, reason, link);
 733                     lint_deprecated_attr(cx, attr, &msg, suggestion);
 734                 }
 735                 return;
 736             }
 737         }
 738         if attr.check_name(sym::no_start) || attr.check_name(sym::crate_id) {
 739             let path_str = pprust::path_to_string(&attr.get_normal_item().path);
 740             let msg = format!("use of deprecated attribute `{}`: no longer used.", path_str);
 741             lint_deprecated_attr(cx, attr, &msg, None);
 742         }
 743     }
 744 }
 745
 746 fn warn_if_doc(cx: &EarlyContext<'_>, node_span: Span, node_kind: &str, attrs: &[ast::Attribute]) {
 747     let mut attrs = attrs.iter().peekable();
 748
 749     // Accumulate a single span for sugared doc comments.
 750     let mut sugared_span: Option<Span> = None;
 751
 752     while let Some(attr) = attrs.next() {
 753         if attr.is_doc_comment() {
 754             sugared_span =
 755                 Some(sugared_span.map_or_else(|| attr.span, |span| span.with_hi(attr.span.hi())));
 756         }
 757
 758         if attrs.peek().map(|next_attr| next_attr.is_doc_comment()).unwrap_or_default() {
 759             continue;
 760         }
 761
 762         let span = sugared_span.take().unwrap_or_else(|| attr.span);
 763
 764         if attr.is_doc_comment() || attr.check_name(sym::doc) {
 765             cx.struct_span_lint(UNUSED_DOC_COMMENTS, span, |lint| {
 766                 let mut err = lint.build("unused doc comment");
 767                 err.span_label(
 768                     node_span,
 769                     format!("rustdoc does not generate documentation for {}", node_kind),
 770                 );
 771                 err.emit();
 772             });
 773         }
 774     }
 775 }
 776
 777 impl EarlyLintPass for UnusedDocComment {
 778     fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &ast::Stmt) {
 779         let kind = match stmt.kind {
 780             ast::StmtKind::Local(..) => "statements",
 781             ast::StmtKind::Item(..) => "inner items",
 782             // expressions will be reported by `check_expr`.
 783             ast::StmtKind::Empty
 784             | ast::StmtKind::Semi(_)
 785             | ast::StmtKind::Expr(_)
 786             | ast::StmtKind::MacCall(_) => return,
 787         };
 788
 789         warn_if_doc(cx, stmt.span, kind, stmt.kind.attrs());
 790     }
 791
 792     fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) {
 793         let arm_span = arm.pat.span.with_hi(arm.body.span.hi());
 794         warn_if_doc(cx, arm_span, "match arms", &arm.attrs);
 795     }
 796
 797     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
 798         warn_if_doc(cx, expr.span, "expressions", &expr.attrs);
 799     }
 800 }
 801
 802 declare_lint! {
 803     NO_MANGLE_CONST_ITEMS,
 804     Deny,
 805     "const items will not have their symbols exported"
 806 }
 807
 808 declare_lint! {
 809     NO_MANGLE_GENERIC_ITEMS,
 810     Warn,
 811     "generic items must be mangled"
 812 }
 813
 814 declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS, NO_MANGLE_GENERIC_ITEMS]);
 815
 816 impl<'tcx> LateLintPass<'tcx> for InvalidNoMangleItems {
 817     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 818         match it.kind {
 819             hir::ItemKind::Fn(.., ref generics, _) => {
 820                 if let Some(no_mangle_attr) = attr::find_by_name(&it.attrs, sym::no_mangle) {
 821                     for param in generics.params {
 822                         match param.kind {
 823                             GenericParamKind::Lifetime { .. } => {}
 824                             GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
 825                                 cx.struct_span_lint(NO_MANGLE_GENERIC_ITEMS, it.span, |lint| {
 826                                     lint.build(
 827                                         "functions generic over types or consts must be mangled",
 828                                     )
 829                                     .span_suggestion_short(
 830                                         no_mangle_attr.span,
 831                                         "remove this attribute",
 832                                         String::new(),
 833                                         // Use of `#[no_mangle]` suggests FFI intent; correct
 834                                         // fix may be to monomorphize source by hand
 835                                         Applicability::MaybeIncorrect,
 836                                     )
 837                                     .emit();
 838                                 });
 839                                 break;
 840                             }
 841                         }
 842                     }
 843                 }
 844             }
 845             hir::ItemKind::Const(..) => {
 846                 if attr::contains_name(&it.attrs, sym::no_mangle) {
 847                     // Const items do not refer to a particular location in memory, and therefore
 848                     // don't have anything to attach a symbol to
 849                     cx.struct_span_lint(NO_MANGLE_CONST_ITEMS, it.span, |lint| {
 850                         let msg = "const items should never be `#[no_mangle]`";
 851                         let mut err = lint.build(msg);
 852
 853                         // account for "pub const" (#45562)
 854                         let start = cx
 855                             .tcx
 856                             .sess
 857                             .source_map()
 858                             .span_to_snippet(it.span)
 859                             .map(|snippet| snippet.find("const").unwrap_or(0))
 860                             .unwrap_or(0) as u32;
 861                         // `const` is 5 chars
 862                         let const_span = it.span.with_hi(BytePos(it.span.lo().0 + start + 5));
 863                         err.span_suggestion(
 864                             const_span,
 865                             "try a static value",
 866                             "pub static".to_owned(),
 867                             Applicability::MachineApplicable,
 868                         );
 869                         err.emit();
 870                     });
 871                 }
 872             }
 873             _ => {}
 874         }
 875     }
 876 }
 877
 878 declare_lint! {
 879     MUTABLE_TRANSMUTES,
 880     Deny,
 881     "mutating transmuted &mut T from &T may cause undefined behavior"
 882 }
 883
 884 declare_lint_pass!(MutableTransmutes => [MUTABLE_TRANSMUTES]);
 885
 886 impl<'tcx> LateLintPass<'tcx> for MutableTransmutes {
 887     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &hir::Expr<'_>) {
 888         use rustc_target::spec::abi::Abi::RustIntrinsic;
 889         if let Some((&ty::Ref(_, _, from_mt), &ty::Ref(_, _, to_mt))) =
 890             get_transmute_from_to(cx, expr).map(|(ty1, ty2)| (&ty1.kind, &ty2.kind))
 891         {
 892             if to_mt == hir::Mutability::Mut && from_mt == hir::Mutability::Not {
 893                 let msg = "mutating transmuted &mut T from &T may cause undefined behavior, \
 894                                consider instead using an UnsafeCell";
 895                 cx.struct_span_lint(MUTABLE_TRANSMUTES, expr.span, |lint| lint.build(msg).emit());
 896             }
 897         }
 898
 899         fn get_transmute_from_to<'tcx>(
 900             cx: &LateContext<'tcx>,
 901             expr: &hir::Expr<'_>,
 902         ) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
 903             let def = if let hir::ExprKind::Path(ref qpath) = expr.kind {
 904                 cx.qpath_res(qpath, expr.hir_id)
 905             } else {
 906                 return None;
 907             };
 908             if let Res::Def(DefKind::Fn, did) = def {
 909                 if !def_id_is_transmute(cx, did) {
 910                     return None;
 911                 }
 912                 let sig = cx.typeck_results().node_type(expr.hir_id).fn_sig(cx.tcx);
 913                 let from = sig.inputs().skip_binder()[0];
 914                 let to = sig.output().skip_binder();
 915                 return Some((from, to));
 916             }
 917             None
 918         }
 919
 920         fn def_id_is_transmute(cx: &LateContext<'_>, def_id: DefId) -> bool {
 921             cx.tcx.fn_sig(def_id).abi() == RustIntrinsic
 922                 && cx.tcx.item_name(def_id) == sym::transmute
 923         }
 924     }
 925 }
 926
 927 declare_lint! {
 928     UNSTABLE_FEATURES,
 929     Allow,
 930     "enabling unstable features (deprecated. do not use)"
 931 }
 932
 933 declare_lint_pass!(
 934     /// Forbids using the `#[feature(...)]` attribute
 935     UnstableFeatures => [UNSTABLE_FEATURES]
 936 );
 937
 938 impl<'tcx> LateLintPass<'tcx> for UnstableFeatures {
 939     fn check_attribute(&mut self, ctx: &LateContext<'_>, attr: &ast::Attribute) {
 940         if attr.check_name(sym::feature) {
 941             if let Some(items) = attr.meta_item_list() {
 942                 for item in items {
 943                     ctx.struct_span_lint(UNSTABLE_FEATURES, item.span(), |lint| {
 944                         lint.build("unstable feature").emit()
 945                     });
 946                 }
 947             }
 948         }
 949     }
 950 }
 951
 952 declare_lint! {
 953     pub UNREACHABLE_PUB,
 954     Allow,
 955     "`pub` items not reachable from crate root"
 956 }
 957
 958 declare_lint_pass!(
 959     /// Lint for items marked `pub` that aren't reachable from other crates.
 960     UnreachablePub => [UNREACHABLE_PUB]
 961 );
 962
 963 impl UnreachablePub {
 964     fn perform_lint(
 965         &self,
 966         cx: &LateContext<'_>,
 967         what: &str,
 968         id: hir::HirId,
 969         vis: &hir::Visibility<'_>,
 970         span: Span,
 971         exportable: bool,
 972     ) {
 973         let mut applicability = Applicability::MachineApplicable;
 974         match vis.node {
 975             hir::VisibilityKind::Public if !cx.access_levels.is_reachable(id) => {
 976                 if span.from_expansion() {
 977                     applicability = Applicability::MaybeIncorrect;
 978                 }
 979                 let def_span = cx.tcx.sess.source_map().guess_head_span(span);
 980                 cx.struct_span_lint(UNREACHABLE_PUB, def_span, |lint| {
 981                     let mut err = lint.build(&format!("unreachable `pub` {}", what));
 982                     let replacement = if cx.tcx.features().crate_visibility_modifier {
 983                         "crate"
 984                     } else {
 985                         "pub(crate)"
 986                     }
 987                     .to_owned();
 988
 989                     err.span_suggestion(
 990                         vis.span,
 991                         "consider restricting its visibility",
 992                         replacement,
 993                         applicability,
 994                     );
 995                     if exportable {
 996                         err.help("or consider exporting it for use by other crates");
 997                     }
 998                     err.emit();
 999                 });
1000             }
1001             _ => {}
1002         }
1003     }
1004 }
1005
1006 impl<'tcx> LateLintPass<'tcx> for UnreachablePub {
1007     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1008         self.perform_lint(cx, "item", item.hir_id, &item.vis, item.span, true);
1009     }
1010
1011     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'tcx>) {
1012         self.perform_lint(
1013             cx,
1014             "item",
1015             foreign_item.hir_id,
1016             &foreign_item.vis,
1017             foreign_item.span,
1018             true,
1019         );
1020     }
1021
1022     fn check_struct_field(&mut self, cx: &LateContext<'_>, field: &hir::StructField<'_>) {
1023         self.perform_lint(cx, "field", field.hir_id, &field.vis, field.span, false);
1024     }
1025
1026     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
1027         self.perform_lint(cx, "item", impl_item.hir_id, &impl_item.vis, impl_item.span, false);
1028     }
1029 }
1030
1031 declare_lint! {
1032     TYPE_ALIAS_BOUNDS,
1033     Warn,
1034     "bounds in type aliases are not enforced"
1035 }
1036
1037 declare_lint_pass!(
1038     /// Lint for trait and lifetime bounds in type aliases being mostly ignored.
1039     /// They are relevant when using associated types, but otherwise neither checked
1040     /// at definition site nor enforced at use site.
1041     TypeAliasBounds => [TYPE_ALIAS_BOUNDS]
1042 );
1043
1044 impl TypeAliasBounds {
1045     fn is_type_variable_assoc(qpath: &hir::QPath<'_>) -> bool {
1046         match *qpath {
1047             hir::QPath::TypeRelative(ref ty, _) => {
1048                 // If this is a type variable, we found a `T::Assoc`.
1049                 match ty.kind {
1050                     hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => match path.res {
1051                         Res::Def(DefKind::TyParam, _) => true,
1052                         _ => false,
1053                     },
1054                     _ => false,
1055                 }
1056             }
1057             hir::QPath::Resolved(..) => false,
1058         }
1059     }
1060
1061     fn suggest_changing_assoc_types(ty: &hir::Ty<'_>, err: &mut DiagnosticBuilder<'_>) {
1062         // Access to associates types should use `<T as Bound>::Assoc`, which does not need a
1063         // bound.  Let's see if this type does that.
1064
1065         // We use a HIR visitor to walk the type.
1066         use rustc_hir::intravisit::{self, Visitor};
1067         struct WalkAssocTypes<'a, 'db> {
1068             err: &'a mut DiagnosticBuilder<'db>,
1069         }
1070         impl<'a, 'db, 'v> Visitor<'v> for WalkAssocTypes<'a, 'db> {
1071             type Map = intravisit::ErasedMap<'v>;
1072
1073             fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1074                 intravisit::NestedVisitorMap::None
1075             }
1076
1077             fn visit_qpath(&mut self, qpath: &'v hir::QPath<'v>, id: hir::HirId, span: Span) {
1078                 if TypeAliasBounds::is_type_variable_assoc(qpath) {
1079                     self.err.span_help(
1080                         span,
1081                         "use fully disambiguated paths (i.e., `<T as Trait>::Assoc`) to refer to \
1082                          associated types in type aliases",
1083                     );
1084                 }
1085                 intravisit::walk_qpath(self, qpath, id, span)
1086             }
1087         }
1088
1089         // Let's go for a walk!
1090         let mut visitor = WalkAssocTypes { err };
1091         visitor.visit_ty(ty);
1092     }
1093 }
1094
1095 impl<'tcx> LateLintPass<'tcx> for TypeAliasBounds {
1096     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1097         let (ty, type_alias_generics) = match item.kind {
1098             hir::ItemKind::TyAlias(ref ty, ref generics) => (&*ty, generics),
1099             _ => return,
1100         };
1101         if let hir::TyKind::OpaqueDef(..) = ty.kind {
1102             // Bounds are respected for `type X = impl Trait`
1103             return;
1104         }
1105         let mut suggested_changing_assoc_types = false;
1106         // There must not be a where clause
1107         if !type_alias_generics.where_clause.predicates.is_empty() {
1108             cx.lint(
1109                 TYPE_ALIAS_BOUNDS,
1110                 |lint| {
1111                     let mut err = lint.build("where clauses are not enforced in type aliases");
1112                     let spans: Vec<_> = type_alias_generics
1113                         .where_clause
1114                         .predicates
1115                         .iter()
1116                         .map(|pred| pred.span())
1117                         .collect();
1118                     err.set_span(spans);
1119                     err.span_suggestion(
1120                         type_alias_generics.where_clause.span_for_predicates_or_empty_place(),
1121                         "the clause will not be checked when the type alias is used, and should be removed",
1122                         String::new(),
1123                         Applicability::MachineApplicable,
1124                     );
1125                     if !suggested_changing_assoc_types {
1126                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1127                         suggested_changing_assoc_types = true;
1128                     }
1129                     err.emit();
1130                 },
1131             );
1132         }
1133         // The parameters must not have bounds
1134         for param in type_alias_generics.params.iter() {
1135             let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
1136             let suggestion = spans
1137                 .iter()
1138                 .map(|sp| {
1139                     let start = param.span.between(*sp); // Include the `:` in `T: Bound`.
1140                     (start.to(*sp), String::new())
1141                 })
1142                 .collect();
1143             if !spans.is_empty() {
1144                 cx.struct_span_lint(TYPE_ALIAS_BOUNDS, spans, |lint| {
1145                     let mut err =
1146                         lint.build("bounds on generic parameters are not enforced in type aliases");
1147                     let msg = "the bound will not be checked when the type alias is used, \
1148                                    and should be removed";
1149                     err.multipart_suggestion(&msg, suggestion, Applicability::MachineApplicable);
1150                     if !suggested_changing_assoc_types {
1151                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1152                         suggested_changing_assoc_types = true;
1153                     }
1154                     err.emit();
1155                 });
1156             }
1157         }
1158     }
1159 }
1160
1161 declare_lint_pass!(
1162     /// Lint constants that are erroneous.
1163     /// Without this lint, we might not get any diagnostic if the constant is
1164     /// unused within this crate, even though downstream crates can't use it
1165     /// without producing an error.
1166     UnusedBrokenConst => []
1167 );
1168
1169 fn check_const(cx: &LateContext<'_>, body_id: hir::BodyId) {
1170     let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1171     // trigger the query once for all constants since that will already report the errors
1172     // FIXME: Use ensure here
1173     let _ = cx.tcx.const_eval_poly(def_id);
1174 }
1175
1176 impl<'tcx> LateLintPass<'tcx> for UnusedBrokenConst {
1177     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1178         match it.kind {
1179             hir::ItemKind::Const(_, body_id) => {
1180                 check_const(cx, body_id);
1181             }
1182             hir::ItemKind::Static(_, _, body_id) => {
1183                 check_const(cx, body_id);
1184             }
1185             _ => {}
1186         }
1187     }
1188 }
1189
1190 declare_lint! {
1191     TRIVIAL_BOUNDS,
1192     Warn,
1193     "these bounds don't depend on an type parameters"
1194 }
1195
1196 declare_lint_pass!(
1197     /// Lint for trait and lifetime bounds that don't depend on type parameters
1198     /// which either do nothing, or stop the item from being used.
1199     TrivialConstraints => [TRIVIAL_BOUNDS]
1200 );
1201
1202 impl<'tcx> LateLintPass<'tcx> for TrivialConstraints {
1203     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
1204         use rustc_middle::ty::fold::TypeFoldable;
1205         use rustc_middle::ty::PredicateKint::*;
1206
1207         if cx.tcx.features().trivial_bounds {
1208             let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1209             let predicates = cx.tcx.predicates_of(def_id);
1210             for &(predicate, span) in predicates.predicates {
1211                 // We don't actually look inside of the predicate,
1212                 // so it is safe to skip this binder here.
1213                 let predicate_kind_name = match predicate.kint(cx.tcx).ignore_qualifiers().skip_binder() {
1214                     Trait(..) => "Trait",
1215                     TypeOutlives(..) |
1216                     RegionOutlives(..) => "Lifetime",
1217
1218                     // Ignore projections, as they can only be global
1219                     // if the trait bound is global
1220                     Projection(..) |
1221                     // Ignore bounds that a user can't type
1222                     WellFormed(..) |
1223                     ObjectSafe(..) |
1224                     ClosureKind(..) |
1225                     Subtype(..) |
1226                     ConstEvaluatable(..) |
1227                     ConstEquate(..) => continue,
1228                     ForAll(_) => bug!("unexpected predicate: {:?}", predicate)
1229                 };
1230                 if predicate.is_global() {
1231                     cx.struct_span_lint(TRIVIAL_BOUNDS, span, |lint| {
1232                         lint.build(&format!(
1233                             "{} bound {} does not depend on any type \
1234                                 or lifetime parameters",
1235                             predicate_kind_name, predicate
1236                         ))
1237                         .emit()
1238                     });
1239                 }
1240             }
1241         }
1242     }
1243 }
1244
1245 declare_lint_pass!(
1246     /// Does nothing as a lint pass, but registers some `Lint`s
1247     /// which are used by other parts of the compiler.
1248     SoftLints => [
1249         WHILE_TRUE,
1250         BOX_POINTERS,
1251         NON_SHORTHAND_FIELD_PATTERNS,
1252         UNSAFE_CODE,
1253         MISSING_DOCS,
1254         MISSING_COPY_IMPLEMENTATIONS,
1255         MISSING_DEBUG_IMPLEMENTATIONS,
1256         ANONYMOUS_PARAMETERS,
1257         UNUSED_DOC_COMMENTS,
1258         NO_MANGLE_CONST_ITEMS,
1259         NO_MANGLE_GENERIC_ITEMS,
1260         MUTABLE_TRANSMUTES,
1261         UNSTABLE_FEATURES,
1262         UNREACHABLE_PUB,
1263         TYPE_ALIAS_BOUNDS,
1264         TRIVIAL_BOUNDS
1265     ]
1266 );
1267
1268 declare_lint! {
1269     pub ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
1270     Warn,
1271     "`...` range patterns are deprecated"
1272 }
1273
1274 #[derive(Default)]
1275 pub struct EllipsisInclusiveRangePatterns {
1276     /// If `Some(_)`, suppress all subsequent pattern
1277     /// warnings for better diagnostics.
1278     node_id: Option<ast::NodeId>,
1279 }
1280
1281 impl_lint_pass!(EllipsisInclusiveRangePatterns => [ELLIPSIS_INCLUSIVE_RANGE_PATTERNS]);
1282
1283 impl EarlyLintPass for EllipsisInclusiveRangePatterns {
1284     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &ast::Pat) {
1285         if self.node_id.is_some() {
1286             // Don't recursively warn about patterns inside range endpoints.
1287             return;
1288         }
1289
1290         use self::ast::{PatKind, RangeEnd, RangeSyntax::DotDotDot};
1291
1292         /// If `pat` is a `...` pattern, return the start and end of the range, as well as the span
1293         /// corresponding to the ellipsis.
1294         fn matches_ellipsis_pat(pat: &ast::Pat) -> Option<(Option<&Expr>, &Expr, Span)> {
1295             match &pat.kind {
1296                 PatKind::Range(
1297                     a,
1298                     Some(b),
1299                     Spanned { span, node: RangeEnd::Included(DotDotDot) },
1300                 ) => Some((a.as_deref(), b, *span)),
1301                 _ => None,
1302             }
1303         }
1304
1305         let (parenthesise, endpoints) = match &pat.kind {
1306             PatKind::Ref(subpat, _) => (true, matches_ellipsis_pat(&subpat)),
1307             _ => (false, matches_ellipsis_pat(pat)),
1308         };
1309
1310         if let Some((start, end, join)) = endpoints {
1311             let msg = "`...` range patterns are deprecated";
1312             let suggestion = "use `..=` for an inclusive range";
1313             if parenthesise {
1314                 self.node_id = Some(pat.id);
1315                 cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, pat.span, |lint| {
1316                     let end = expr_to_string(&end);
1317                     let replace = match start {
1318                         Some(start) => format!("&({}..={})", expr_to_string(&start), end),
1319                         None => format!("&(..={})", end),
1320                     };
1321                     lint.build(msg)
1322                         .span_suggestion(
1323                             pat.span,
1324                             suggestion,
1325                             replace,
1326                             Applicability::MachineApplicable,
1327                         )
1328                         .emit();
1329                 });
1330             } else {
1331                 cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, join, |lint| {
1332                     lint.build(msg)
1333                         .span_suggestion_short(
1334                             join,
1335                             suggestion,
1336                             "..=".to_owned(),
1337                             Applicability::MachineApplicable,
1338                         )
1339                         .emit();
1340                 });
1341             };
1342         }
1343     }
1344
1345     fn check_pat_post(&mut self, _cx: &EarlyContext<'_>, pat: &ast::Pat) {
1346         if let Some(node_id) = self.node_id {
1347             if pat.id == node_id {
1348                 self.node_id = None
1349             }
1350         }
1351     }
1352 }
1353
1354 declare_lint! {
1355     UNNAMEABLE_TEST_ITEMS,
1356     Warn,
1357     "detects an item that cannot be named being marked as `#[test_case]`",
1358     report_in_external_macro
1359 }
1360
1361 pub struct UnnameableTestItems {
1362     boundary: Option<hir::HirId>, // HirId of the item under which things are not nameable
1363     items_nameable: bool,
1364 }
1365
1366 impl_lint_pass!(UnnameableTestItems => [UNNAMEABLE_TEST_ITEMS]);
1367
1368 impl UnnameableTestItems {
1369     pub fn new() -> Self {
1370         Self { boundary: None, items_nameable: true }
1371     }
1372 }
1373
1374 impl<'tcx> LateLintPass<'tcx> for UnnameableTestItems {
1375     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1376         if self.items_nameable {
1377             if let hir::ItemKind::Mod(..) = it.kind {
1378             } else {
1379                 self.items_nameable = false;
1380                 self.boundary = Some(it.hir_id);
1381             }
1382             return;
1383         }
1384
1385         if let Some(attr) = attr::find_by_name(&it.attrs, sym::rustc_test_marker) {
1386             cx.struct_span_lint(UNNAMEABLE_TEST_ITEMS, attr.span, |lint| {
1387                 lint.build("cannot test inner items").emit()
1388             });
1389         }
1390     }
1391
1392     fn check_item_post(&mut self, _cx: &LateContext<'_>, it: &hir::Item<'_>) {
1393         if !self.items_nameable && self.boundary == Some(it.hir_id) {
1394             self.items_nameable = true;
1395         }
1396     }
1397 }
1398
1399 declare_lint! {
1400     pub KEYWORD_IDENTS,
1401     Allow,
1402     "detects edition keywords being used as an identifier",
1403     @future_incompatible = FutureIncompatibleInfo {
1404         reference: "issue #49716 <https://github.com/rust-lang/rust/issues/49716>",
1405         edition: Some(Edition::Edition2018),
1406     };
1407 }
1408
1409 declare_lint_pass!(
1410     /// Check for uses of edition keywords used as an identifier.
1411     KeywordIdents => [KEYWORD_IDENTS]
1412 );
1413
1414 struct UnderMacro(bool);
1415
1416 impl KeywordIdents {
1417     fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: TokenStream) {
1418         for tt in tokens.into_trees() {
1419             match tt {
1420                 // Only report non-raw idents.
1421                 TokenTree::Token(token) => {
1422                     if let Some((ident, false)) = token.ident() {
1423                         self.check_ident_token(cx, UnderMacro(true), ident);
1424                     }
1425                 }
1426                 TokenTree::Delimited(_, _, tts) => self.check_tokens(cx, tts),
1427             }
1428         }
1429     }
1430
1431     fn check_ident_token(
1432         &mut self,
1433         cx: &EarlyContext<'_>,
1434         UnderMacro(under_macro): UnderMacro,
1435         ident: Ident,
1436     ) {
1437         let next_edition = match cx.sess.edition() {
1438             Edition::Edition2015 => {
1439                 match ident.name {
1440                     kw::Async | kw::Await | kw::Try => Edition::Edition2018,
1441
1442                     // rust-lang/rust#56327: Conservatively do not
1443                     // attempt to report occurrences of `dyn` within
1444                     // macro definitions or invocations, because `dyn`
1445                     // can legitimately occur as a contextual keyword
1446                     // in 2015 code denoting its 2018 meaning, and we
1447                     // do not want rustfix to inject bugs into working
1448                     // code by rewriting such occurrences.
1449                     //
1450                     // But if we see `dyn` outside of a macro, we know
1451                     // its precise role in the parsed AST and thus are
1452                     // assured this is truly an attempt to use it as
1453                     // an identifier.
1454                     kw::Dyn if !under_macro => Edition::Edition2018,
1455
1456                     _ => return,
1457                 }
1458             }
1459
1460             // There are no new keywords yet for the 2018 edition and beyond.
1461             _ => return,
1462         };
1463
1464         // Don't lint `r#foo`.
1465         if cx.sess.parse_sess.raw_identifier_spans.borrow().contains(&ident.span) {
1466             return;
1467         }
1468
1469         cx.struct_span_lint(KEYWORD_IDENTS, ident.span, |lint| {
1470             lint.build(&format!("`{}` is a keyword in the {} edition", ident, next_edition))
1471                 .span_suggestion(
1472                     ident.span,
1473                     "you can use a raw identifier to stay compatible",
1474                     format!("r#{}", ident),
1475                     Applicability::MachineApplicable,
1476                 )
1477                 .emit()
1478         });
1479     }
1480 }
1481
1482 impl EarlyLintPass for KeywordIdents {
1483     fn check_mac_def(&mut self, cx: &EarlyContext<'_>, mac_def: &ast::MacroDef, _id: ast::NodeId) {
1484         self.check_tokens(cx, mac_def.body.inner_tokens());
1485     }
1486     fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::MacCall) {
1487         self.check_tokens(cx, mac.args.inner_tokens());
1488     }
1489     fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: Ident) {
1490         self.check_ident_token(cx, UnderMacro(false), ident);
1491     }
1492 }
1493
1494 declare_lint_pass!(ExplicitOutlivesRequirements => [EXPLICIT_OUTLIVES_REQUIREMENTS]);
1495
1496 impl ExplicitOutlivesRequirements {
1497     fn lifetimes_outliving_lifetime<'tcx>(
1498         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
1499         index: u32,
1500     ) -> Vec<ty::Region<'tcx>> {
1501         inferred_outlives
1502             .iter()
1503             .filter_map(|(pred, _)| match pred.kind() {
1504                 ty::PredicateKind::RegionOutlives(outlives) => {
1505                     let outlives = outlives.skip_binder();
1506                     match outlives.0 {
1507                         ty::ReEarlyBound(ebr) if ebr.index == index => Some(outlives.1),
1508                         _ => None,
1509                     }
1510                 }
1511                 _ => None,
1512             })
1513             .collect()
1514     }
1515
1516     fn lifetimes_outliving_type<'tcx>(
1517         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
1518         index: u32,
1519     ) -> Vec<ty::Region<'tcx>> {
1520         inferred_outlives
1521             .iter()
1522             .filter_map(|(pred, _)| match pred.kind() {
1523                 ty::PredicateKind::TypeOutlives(outlives) => {
1524                     let outlives = outlives.skip_binder();
1525                     outlives.0.is_param(index).then_some(outlives.1)
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::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)) = ty_find_init_error(cx.tcx, conjured_ty, init) {
2046                 cx.struct_span_lint(INVALID_VALUE, expr.span, |lint| {
2047                     let mut err = lint.build(&format!(
2048                         "the type `{}` does not permit {}",
2049                         conjured_ty,
2050                         match init {
2051                             InitKind::Zeroed => "zero-initialization",
2052                             InitKind::Uninit => "being left uninitialized",
2053                         },
2054                     ));
2055                     err.span_label(expr.span, "this code causes undefined behavior when executed");
2056                     err.span_label(
2057                         expr.span,
2058                         "help: use `MaybeUninit<T>` instead, \
2059                             and only call `assume_init` after initialization is done",
2060                     );
2061                     if let Some(span) = span {
2062                         err.span_note(span, &msg);
2063                     } else {
2064                         err.note(&msg);
2065                     }
2066                     err.emit();
2067                 });
2068             }
2069         }
2070     }
2071 }
2072
2073 declare_lint! {
2074     pub CLASHING_EXTERN_DECLARATIONS,
2075     Warn,
2076     "detects when an extern fn has been declared with the same name but different types"
2077 }
2078
2079 pub struct ClashingExternDeclarations {
2080     seen_decls: FxHashMap<Symbol, HirId>,
2081 }
2082
2083 /// Differentiate between whether the name for an extern decl came from the link_name attribute or
2084 /// just from declaration itself. This is important because we don't want to report clashes on
2085 /// symbol name if they don't actually clash because one or the other links against a symbol with a
2086 /// different name.
2087 enum SymbolName {
2088     /// The name of the symbol + the span of the annotation which introduced the link name.
2089     Link(Symbol, Span),
2090     /// No link name, so just the name of the symbol.
2091     Normal(Symbol),
2092 }
2093
2094 impl SymbolName {
2095     fn get_name(&self) -> Symbol {
2096         match self {
2097             SymbolName::Link(s, _) | SymbolName::Normal(s) => *s,
2098         }
2099     }
2100 }
2101
2102 impl ClashingExternDeclarations {
2103     crate fn new() -> Self {
2104         ClashingExternDeclarations { seen_decls: FxHashMap::default() }
2105     }
2106     /// Insert a new foreign item into the seen set. If a symbol with the same name already exists
2107     /// for the item, return its HirId without updating the set.
2108     fn insert(&mut self, tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> Option<HirId> {
2109         let hid = fi.hir_id;
2110
2111         let name =
2112             &tcx.codegen_fn_attrs(tcx.hir().local_def_id(hid)).link_name.unwrap_or(fi.ident.name);
2113
2114         if self.seen_decls.contains_key(name) {
2115             // Avoid updating the map with the new entry when we do find a collision. We want to
2116             // make sure we're always pointing to the first definition as the previous declaration.
2117             // This lets us avoid emitting "knock-on" diagnostics.
2118             Some(*self.seen_decls.get(name).unwrap())
2119         } else {
2120             self.seen_decls.insert(*name, hid)
2121         }
2122     }
2123
2124     /// Get the name of the symbol that's linked against for a given extern declaration. That is,
2125     /// the name specified in a #[link_name = ...] attribute if one was specified, else, just the
2126     /// symbol's name.
2127     fn name_of_extern_decl(tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> SymbolName {
2128         let did = tcx.hir().local_def_id(fi.hir_id);
2129         if let Some((overridden_link_name, overridden_link_name_span)) =
2130             tcx.codegen_fn_attrs(did).link_name.map(|overridden_link_name| {
2131                 // FIXME: Instead of searching through the attributes again to get span
2132                 // information, we could have codegen_fn_attrs also give span information back for
2133                 // where the attribute was defined. However, until this is found to be a
2134                 // bottleneck, this does just fine.
2135                 (
2136                     overridden_link_name,
2137                     tcx.get_attrs(did.to_def_id())
2138                         .iter()
2139                         .find(|at| at.check_name(sym::link_name))
2140                         .unwrap()
2141                         .span,
2142                 )
2143             })
2144         {
2145             SymbolName::Link(overridden_link_name, overridden_link_name_span)
2146         } else {
2147             SymbolName::Normal(fi.ident.name)
2148         }
2149     }
2150
2151     /// Checks whether two types are structurally the same enough that the declarations shouldn't
2152     /// clash. We need this so we don't emit a lint when two modules both declare an extern struct,
2153     /// with the same members (as the declarations shouldn't clash).
2154     fn structurally_same_type<'tcx>(cx: &LateContext<'tcx>, a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
2155         let tcx = cx.tcx;
2156         if a == b || rustc_middle::ty::TyS::same_type(a, b) {
2157             // All nominally-same types are structurally same, too.
2158             true
2159         } else {
2160             // Do a full, depth-first comparison between the two.
2161             use rustc_middle::ty::TyKind::*;
2162             let a_kind = &a.kind;
2163             let b_kind = &b.kind;
2164
2165             match (a_kind, b_kind) {
2166                 (Adt(..), Adt(..)) => {
2167                     // Adts are pretty straightforward: just compare the layouts.
2168                     use rustc_target::abi::LayoutOf;
2169                     let a_layout = cx.layout_of(a).unwrap().layout;
2170                     let b_layout = cx.layout_of(b).unwrap().layout;
2171                     a_layout == b_layout
2172                 }
2173                 (Array(a_ty, a_const), Array(b_ty, b_const)) => {
2174                     // For arrays, we also check the constness of the type.
2175                     a_const.val == b_const.val
2176                         && Self::structurally_same_type(cx, a_const.ty, b_const.ty)
2177                         && Self::structurally_same_type(cx, a_ty, b_ty)
2178                 }
2179                 (Slice(a_ty), Slice(b_ty)) => Self::structurally_same_type(cx, a_ty, b_ty),
2180                 (RawPtr(a_tymut), RawPtr(b_tymut)) => {
2181                     a_tymut.mutbl == a_tymut.mutbl
2182                         && Self::structurally_same_type(cx, &a_tymut.ty, &b_tymut.ty)
2183                 }
2184                 (Ref(_a_region, a_ty, a_mut), Ref(_b_region, b_ty, b_mut)) => {
2185                     // For structural sameness, we don't need the region to be same.
2186                     a_mut == b_mut && Self::structurally_same_type(cx, a_ty, b_ty)
2187                 }
2188                 (FnDef(..), FnDef(..)) => {
2189                     // As we don't compare regions, skip_binder is fine.
2190                     let a_poly_sig = a.fn_sig(tcx);
2191                     let b_poly_sig = b.fn_sig(tcx);
2192
2193                     let a_sig = a_poly_sig.skip_binder();
2194                     let b_sig = b_poly_sig.skip_binder();
2195
2196                     (a_sig.abi, a_sig.unsafety, a_sig.c_variadic)
2197                         == (b_sig.abi, b_sig.unsafety, b_sig.c_variadic)
2198                         && a_sig.inputs().iter().eq_by(b_sig.inputs().iter(), |a, b| {
2199                             Self::structurally_same_type(cx, a, b)
2200                         })
2201                         && Self::structurally_same_type(cx, a_sig.output(), b_sig.output())
2202                 }
2203                 (Tuple(a_substs), Tuple(b_substs)) => {
2204                     a_substs.types().eq_by(b_substs.types(), |a_ty, b_ty| {
2205                         Self::structurally_same_type(cx, a_ty, b_ty)
2206                     })
2207                 }
2208                 // For these, it's not quite as easy to define structural-sameness quite so easily.
2209                 // For the purposes of this lint, take the conservative approach and mark them as
2210                 // not structurally same.
2211                 (Dynamic(..), Dynamic(..))
2212                 | (Error(..), Error(..))
2213                 | (Closure(..), Closure(..))
2214                 | (Generator(..), Generator(..))
2215                 | (GeneratorWitness(..), GeneratorWitness(..))
2216                 | (Projection(..), Projection(..))
2217                 | (Opaque(..), Opaque(..)) => false,
2218                 // These definitely should have been caught above.
2219                 (Bool, Bool) | (Char, Char) | (Never, Never) | (Str, Str) => unreachable!(),
2220                 _ => false,
2221             }
2222         }
2223     }
2224 }
2225
2226 impl_lint_pass!(ClashingExternDeclarations => [CLASHING_EXTERN_DECLARATIONS]);
2227
2228 impl<'tcx> LateLintPass<'tcx> for ClashingExternDeclarations {
2229     fn check_foreign_item(&mut self, cx: &LateContext<'tcx>, this_fi: &hir::ForeignItem<'_>) {
2230         trace!("ClashingExternDeclarations: check_foreign_item: {:?}", this_fi);
2231         if let ForeignItemKind::Fn(..) = this_fi.kind {
2232             let tcx = *&cx.tcx;
2233             if let Some(existing_hid) = self.insert(tcx, this_fi) {
2234                 let existing_decl_ty = tcx.type_of(tcx.hir().local_def_id(existing_hid));
2235                 let this_decl_ty = tcx.type_of(tcx.hir().local_def_id(this_fi.hir_id));
2236                 debug!(
2237                     "ClashingExternDeclarations: Comparing existing {:?}: {:?} to this {:?}: {:?}",
2238                     existing_hid, existing_decl_ty, this_fi.hir_id, this_decl_ty
2239                 );
2240                 // Check that the declarations match.
2241                 if !Self::structurally_same_type(cx, existing_decl_ty, this_decl_ty) {
2242                     let orig_fi = tcx.hir().expect_foreign_item(existing_hid);
2243                     let orig = Self::name_of_extern_decl(tcx, orig_fi);
2244
2245                     // We want to ensure that we use spans for both decls that include where the
2246                     // name was defined, whether that was from the link_name attribute or not.
2247                     let get_relevant_span =
2248                         |fi: &hir::ForeignItem<'_>| match Self::name_of_extern_decl(tcx, fi) {
2249                             SymbolName::Normal(_) => fi.span,
2250                             SymbolName::Link(_, annot_span) => fi.span.to(annot_span),
2251                         };
2252                     // Finally, emit the diagnostic.
2253                     tcx.struct_span_lint_hir(
2254                         CLASHING_EXTERN_DECLARATIONS,
2255                         this_fi.hir_id,
2256                         get_relevant_span(this_fi),
2257                         |lint| {
2258                             let mut expected_str = DiagnosticStyledString::new();
2259                             expected_str.push(existing_decl_ty.fn_sig(tcx).to_string(), false);
2260                             let mut found_str = DiagnosticStyledString::new();
2261                             found_str.push(this_decl_ty.fn_sig(tcx).to_string(), true);
2262
2263                             lint.build(&format!(
2264                                 "`{}` redeclare{} with a different signature",
2265                                 this_fi.ident.name,
2266                                 if orig.get_name() == this_fi.ident.name {
2267                                     "d".to_string()
2268                                 } else {
2269                                     format!("s `{}`", orig.get_name())
2270                                 }
2271                             ))
2272                             .span_label(
2273                                 get_relevant_span(orig_fi),
2274                                 &format!("`{}` previously declared here", orig.get_name()),
2275                             )
2276                             .span_label(
2277                                 get_relevant_span(this_fi),
2278                                 "this signature doesn't match the previous declaration",
2279                             )
2280                             .note_expected_found(&"", expected_str, &"", found_str)
2281                             .emit()
2282                         },
2283                     );
2284                 }
2285             }
2286         }
2287     }
2288 }