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::lint::builtin`, which contains the
   5 //! definitions of lints that are emitted directly inside the main
   6 //! compiler.
   7 //!
   8 //! To add a new lint to rustc, declare it here using `declare_lint!()`.
   9 //! Then add code to emit the new lint in the appropriate circumstances.
  10 //! You can do that in an existing `LintPass` if it makes sense, or in a
  11 //! new `LintPass`, or using `Session::add_lint` elsewhere in the
  12 //! compiler. Only do the latter if the check can't be written cleanly as a
  13 //! `LintPass` (also, note that such lints will need to be defined in
  14 //! `rustc::lint::builtin`, not here).
  15 //!
  16 //! If you define a new `EarlyLintPass`, you will also need to add it to the
  17 //! `add_early_builtin!` or `add_early_builtin_with_new!` invocation in
  18 //! `lib.rs`. Use the former for unit-like structs and the latter for structs
  19 //! with a `pub fn new()`.
  20 //!
  21 //! If you define a new `LateLintPass`, you will also need to add it to the
  22 //! `late_lint_methods!` invocation in `lib.rs`.
  23
  24 use std::fmt::Write;
  25
  26 use lint::{EarlyContext, EarlyLintPass, LateLintPass, LintPass};
  27 use lint::{LateContext, LintArray, LintContext};
  28 use rustc::lint;
  29 use rustc::lint::FutureIncompatibleInfo;
  30 use rustc::traits::misc::can_type_implement_copy;
  31 use rustc::ty::{self, layout::VariantIdx, Ty, TyCtxt};
  32 use rustc_data_structures::fx::FxHashSet;
  33 use rustc_feature::Stability;
  34 use rustc_feature::{deprecated_attributes, AttributeGate, AttributeTemplate, AttributeType};
  35 use rustc_hir as hir;
  36 use rustc_hir::def::{DefKind, Res};
  37 use rustc_hir::def_id::DefId;
  38 use rustc_hir::{GenericParamKind, PatKind};
  39 use rustc_hir::{HirIdSet, Node};
  40 use rustc_span::edition::Edition;
  41 use rustc_span::source_map::Spanned;
  42 use rustc_span::symbol::{kw, sym, Symbol};
  43 use rustc_span::{BytePos, Span};
  44 use syntax::ast::{self, Expr};
  45 use syntax::attr::{self, HasAttrs};
  46 use syntax::errors::{Applicability, DiagnosticBuilder};
  47 use syntax::print::pprust::{self, expr_to_string};
  48 use syntax::ptr::P;
  49 use syntax::tokenstream::{TokenStream, TokenTree};
  50 use syntax::visit::FnKind;
  51
  52 use crate::nonstandard_style::{method_context, MethodLateContext};
  53
  54 use log::debug;
  55
  56 // hardwired lints from librustc
  57 pub use lint::builtin::*;
  58
  59 declare_lint! {
  60     WHILE_TRUE,
  61     Warn,
  62     "suggest using `loop { }` instead of `while true { }`"
  63 }
  64
  65 declare_lint_pass!(WhileTrue => [WHILE_TRUE]);
  66
  67 /// Traverse through any amount of parenthesis and return the first non-parens expression.
  68 fn pierce_parens(mut expr: &ast::Expr) -> &ast::Expr {
  69     while let ast::ExprKind::Paren(sub) = &expr.kind {
  70         expr = sub;
  71     }
  72     expr
  73 }
  74
  75 impl EarlyLintPass for WhileTrue {
  76     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
  77         if let ast::ExprKind::While(cond, ..) = &e.kind {
  78             if let ast::ExprKind::Lit(ref lit) = pierce_parens(cond).kind {
  79                 if let ast::LitKind::Bool(true) = lit.kind {
  80                     if !lit.span.from_expansion() {
  81                         let msg = "denote infinite loops with `loop { ... }`";
  82                         let condition_span = cx.sess.source_map().def_span(e.span);
  83                         cx.struct_span_lint(WHILE_TRUE, condition_span, msg)
  84                             .span_suggestion_short(
  85                                 condition_span,
  86                                 "use `loop`",
  87                                 "loop".to_owned(),
  88                                 Applicability::MachineApplicable,
  89                             )
  90                             .emit();
  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_ty in ty.walk() {
 109             if leaf_ty.is_box() {
 110                 let m = format!("type uses owned (Box type) pointers: {}", ty);
 111                 cx.span_lint(BOX_POINTERS, span, &m);
 112             }
 113         }
 114     }
 115 }
 116
 117 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BoxPointers {
 118     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item<'_>) {
 119         match it.kind {
 120             hir::ItemKind::Fn(..)
 121             | hir::ItemKind::TyAlias(..)
 122             | hir::ItemKind::Enum(..)
 123             | hir::ItemKind::Struct(..)
 124             | hir::ItemKind::Union(..) => {
 125                 let def_id = cx.tcx.hir().local_def_id(it.hir_id);
 126                 self.check_heap_type(cx, it.span, cx.tcx.type_of(def_id))
 127             }
 128             _ => (),
 129         }
 130
 131         // If it's a struct, we also have to check the fields' types
 132         match it.kind {
 133             hir::ItemKind::Struct(ref struct_def, _) | hir::ItemKind::Union(ref struct_def, _) => {
 134                 for struct_field in struct_def.fields() {
 135                     let def_id = cx.tcx.hir().local_def_id(struct_field.hir_id);
 136                     self.check_heap_type(cx, struct_field.span, cx.tcx.type_of(def_id));
 137                 }
 138             }
 139             _ => (),
 140         }
 141     }
 142
 143     fn check_expr(&mut self, cx: &LateContext<'_, '_>, e: &hir::Expr<'_>) {
 144         let ty = cx.tables.node_type(e.hir_id);
 145         self.check_heap_type(cx, e.span, ty);
 146     }
 147 }
 148
 149 declare_lint! {
 150     NON_SHORTHAND_FIELD_PATTERNS,
 151     Warn,
 152     "using `Struct { x: x }` instead of `Struct { x }` in a pattern"
 153 }
 154
 155 declare_lint_pass!(NonShorthandFieldPatterns => [NON_SHORTHAND_FIELD_PATTERNS]);
 156
 157 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NonShorthandFieldPatterns {
 158     fn check_pat(&mut self, cx: &LateContext<'_, '_>, pat: &hir::Pat<'_>) {
 159         if let PatKind::Struct(ref qpath, field_pats, _) = pat.kind {
 160             let variant = cx
 161                 .tables
 162                 .pat_ty(pat)
 163                 .ty_adt_def()
 164                 .expect("struct pattern type is not an ADT")
 165                 .variant_of_res(cx.tables.qpath_res(qpath, pat.hir_id));
 166             for fieldpat in field_pats {
 167                 if fieldpat.is_shorthand {
 168                     continue;
 169                 }
 170                 if fieldpat.span.from_expansion() {
 171                     // Don't lint if this is a macro expansion: macro authors
 172                     // shouldn't have to worry about this kind of style issue
 173                     // (Issue #49588)
 174                     continue;
 175                 }
 176                 if let PatKind::Binding(binding_annot, _, ident, None) = fieldpat.pat.kind {
 177                     if cx.tcx.find_field_index(ident, &variant)
 178                         == Some(cx.tcx.field_index(fieldpat.hir_id, cx.tables))
 179                     {
 180                         let mut err = cx.struct_span_lint(
 181                             NON_SHORTHAND_FIELD_PATTERNS,
 182                             fieldpat.span,
 183                             &format!("the `{}:` in this pattern is redundant", ident),
 184                         );
 185                         let binding = match binding_annot {
 186                             hir::BindingAnnotation::Unannotated => None,
 187                             hir::BindingAnnotation::Mutable => Some("mut"),
 188                             hir::BindingAnnotation::Ref => Some("ref"),
 189                             hir::BindingAnnotation::RefMut => Some("ref mut"),
 190                         };
 191                         let ident = if let Some(binding) = binding {
 192                             format!("{} {}", binding, ident)
 193                         } else {
 194                             ident.to_string()
 195                         };
 196                         err.span_suggestion(
 197                             fieldpat.span,
 198                             "use shorthand field pattern",
 199                             ident,
 200                             Applicability::MachineApplicable,
 201                         );
 202                         err.emit();
 203                     }
 204                 }
 205             }
 206         }
 207     }
 208 }
 209
 210 declare_lint! {
 211     UNSAFE_CODE,
 212     Allow,
 213     "usage of `unsafe` code"
 214 }
 215
 216 declare_lint_pass!(UnsafeCode => [UNSAFE_CODE]);
 217
 218 impl UnsafeCode {
 219     fn report_unsafe(&self, cx: &EarlyContext<'_>, span: Span, desc: &'static str) {
 220         // This comes from a macro that has `#[allow_internal_unsafe]`.
 221         if span.allows_unsafe() {
 222             return;
 223         }
 224
 225         cx.span_lint(UNSAFE_CODE, span, desc);
 226     }
 227 }
 228
 229 impl EarlyLintPass for UnsafeCode {
 230     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 231         if attr.check_name(sym::allow_internal_unsafe) {
 232             self.report_unsafe(
 233                 cx,
 234                 attr.span,
 235                 "`allow_internal_unsafe` allows defining \
 236                                                macros using unsafe without triggering \
 237                                                the `unsafe_code` lint at their call site",
 238             );
 239         }
 240     }
 241
 242     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
 243         if let ast::ExprKind::Block(ref blk, _) = e.kind {
 244             // Don't warn about generated blocks; that'll just pollute the output.
 245             if blk.rules == ast::BlockCheckMode::Unsafe(ast::UserProvided) {
 246                 self.report_unsafe(cx, blk.span, "usage of an `unsafe` block");
 247             }
 248         }
 249     }
 250
 251     fn check_item(&mut self, cx: &EarlyContext<'_>, it: &ast::Item) {
 252         match it.kind {
 253             ast::ItemKind::Trait(_, ast::Unsafety::Unsafe, ..) => {
 254                 self.report_unsafe(cx, it.span, "declaration of an `unsafe` trait")
 255             }
 256
 257             ast::ItemKind::Impl(ast::Unsafety::Unsafe, ..) => {
 258                 self.report_unsafe(cx, it.span, "implementation of an `unsafe` trait")
 259             }
 260
 261             _ => return,
 262         }
 263     }
 264
 265     fn check_fn(
 266         &mut self,
 267         cx: &EarlyContext<'_>,
 268         fk: FnKind<'_>,
 269         _: &ast::FnDecl,
 270         span: Span,
 271         _: ast::NodeId,
 272     ) {
 273         match fk {
 274             FnKind::ItemFn(_, ast::FnHeader { unsafety: ast::Unsafety::Unsafe, .. }, ..) => {
 275                 self.report_unsafe(cx, span, "declaration of an `unsafe` function")
 276             }
 277
 278             FnKind::Method(_, sig, ..) => {
 279                 if sig.header.unsafety == ast::Unsafety::Unsafe {
 280                     self.report_unsafe(cx, span, "implementation of an `unsafe` method")
 281                 }
 282             }
 283
 284             _ => (),
 285         }
 286     }
 287
 288     fn check_trait_item(&mut self, cx: &EarlyContext<'_>, item: &ast::AssocItem) {
 289         if let ast::AssocItemKind::Fn(ref sig, None) = item.kind {
 290             if sig.header.unsafety == ast::Unsafety::Unsafe {
 291                 self.report_unsafe(cx, item.span, "declaration of an `unsafe` method")
 292             }
 293         }
 294     }
 295 }
 296
 297 declare_lint! {
 298     pub MISSING_DOCS,
 299     Allow,
 300     "detects missing documentation for public members",
 301     report_in_external_macro
 302 }
 303
 304 pub struct MissingDoc {
 305     /// Stack of whether `#[doc(hidden)]` is set at each level which has lint attributes.
 306     doc_hidden_stack: Vec<bool>,
 307
 308     /// Private traits or trait items that leaked through. Don't check their methods.
 309     private_traits: FxHashSet<hir::HirId>,
 310 }
 311
 312 impl_lint_pass!(MissingDoc => [MISSING_DOCS]);
 313
 314 fn has_doc(attr: &ast::Attribute) -> bool {
 315     if attr.is_doc_comment() {
 316         return true;
 317     }
 318
 319     if !attr.check_name(sym::doc) {
 320         return false;
 321     }
 322
 323     if attr.is_value_str() {
 324         return true;
 325     }
 326
 327     if let Some(list) = attr.meta_item_list() {
 328         for meta in list {
 329             if meta.check_name(sym::include) || meta.check_name(sym::hidden) {
 330                 return true;
 331             }
 332         }
 333     }
 334
 335     false
 336 }
 337
 338 impl MissingDoc {
 339     pub fn new() -> MissingDoc {
 340         MissingDoc { doc_hidden_stack: vec![false], private_traits: FxHashSet::default() }
 341     }
 342
 343     fn doc_hidden(&self) -> bool {
 344         *self.doc_hidden_stack.last().expect("empty doc_hidden_stack")
 345     }
 346
 347     fn check_missing_docs_attrs(
 348         &self,
 349         cx: &LateContext<'_, '_>,
 350         id: Option<hir::HirId>,
 351         attrs: &[ast::Attribute],
 352         sp: Span,
 353         desc: &'static str,
 354     ) {
 355         // If we're building a test harness, then warning about
 356         // documentation is probably not really relevant right now.
 357         if cx.sess().opts.test {
 358             return;
 359         }
 360
 361         // `#[doc(hidden)]` disables missing_docs check.
 362         if self.doc_hidden() {
 363             return;
 364         }
 365
 366         // Only check publicly-visible items, using the result from the privacy pass.
 367         // It's an option so the crate root can also use this function (it doesn't
 368         // have a `NodeId`).
 369         if let Some(id) = id {
 370             if !cx.access_levels.is_exported(id) {
 371                 return;
 372             }
 373         }
 374
 375         let has_doc = attrs.iter().any(|a| has_doc(a));
 376         if !has_doc {
 377             cx.span_lint(
 378                 MISSING_DOCS,
 379                 cx.tcx.sess.source_map().def_span(sp),
 380                 &format!("missing documentation for {}", desc),
 381             );
 382         }
 383     }
 384 }
 385
 386 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MissingDoc {
 387     fn enter_lint_attrs(&mut self, _: &LateContext<'_, '_>, attrs: &[ast::Attribute]) {
 388         let doc_hidden = self.doc_hidden()
 389             || attrs.iter().any(|attr| {
 390                 attr.check_name(sym::doc)
 391                     && match attr.meta_item_list() {
 392                         None => false,
 393                         Some(l) => attr::list_contains_name(&l, sym::hidden),
 394                     }
 395             });
 396         self.doc_hidden_stack.push(doc_hidden);
 397     }
 398
 399     fn exit_lint_attrs(&mut self, _: &LateContext<'_, '_>, _attrs: &[ast::Attribute]) {
 400         self.doc_hidden_stack.pop().expect("empty doc_hidden_stack");
 401     }
 402
 403     fn check_crate(&mut self, cx: &LateContext<'_, '_>, krate: &hir::Crate<'_>) {
 404         self.check_missing_docs_attrs(cx, None, &krate.attrs, krate.span, "crate");
 405
 406         for macro_def in krate.exported_macros {
 407             let has_doc = macro_def.attrs.iter().any(|a| has_doc(a));
 408             if !has_doc {
 409                 cx.span_lint(
 410                     MISSING_DOCS,
 411                     cx.tcx.sess.source_map().def_span(macro_def.span),
 412                     "missing documentation for macro",
 413                 );
 414             }
 415         }
 416     }
 417
 418     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item<'_>) {
 419         let desc = match it.kind {
 420             hir::ItemKind::Fn(..) => "a function",
 421             hir::ItemKind::Mod(..) => "a module",
 422             hir::ItemKind::Enum(..) => "an enum",
 423             hir::ItemKind::Struct(..) => "a struct",
 424             hir::ItemKind::Union(..) => "a union",
 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                 "a trait"
 435             }
 436             hir::ItemKind::TyAlias(..) => "a type alias",
 437             hir::ItemKind::Impl(.., Some(ref trait_ref), _, impl_item_refs) => {
 438                 // If the trait is private, add the impl items to `private_traits` so they don't get
 439                 // reported for missing docs.
 440                 let real_trait = trait_ref.path.res.def_id();
 441                 if let Some(hir_id) = cx.tcx.hir().as_local_hir_id(real_trait) {
 442                     match cx.tcx.hir().find(hir_id) {
 443                         Some(Node::Item(item)) => {
 444                             if let hir::VisibilityKind::Inherited = item.vis.node {
 445                                 for impl_item_ref in impl_item_refs {
 446                                     self.private_traits.insert(impl_item_ref.id.hir_id);
 447                                 }
 448                             }
 449                         }
 450                         _ => {}
 451                     }
 452                 }
 453                 return;
 454             }
 455             hir::ItemKind::Const(..) => "a constant",
 456             hir::ItemKind::Static(..) => "a static",
 457             _ => return,
 458         };
 459
 460         self.check_missing_docs_attrs(cx, Some(it.hir_id), &it.attrs, it.span, desc);
 461     }
 462
 463     fn check_trait_item(&mut self, cx: &LateContext<'_, '_>, trait_item: &hir::TraitItem<'_>) {
 464         if self.private_traits.contains(&trait_item.hir_id) {
 465             return;
 466         }
 467
 468         let desc = match trait_item.kind {
 469             hir::TraitItemKind::Const(..) => "an associated constant",
 470             hir::TraitItemKind::Method(..) => "a trait method",
 471             hir::TraitItemKind::Type(..) => "an associated type",
 472         };
 473
 474         self.check_missing_docs_attrs(
 475             cx,
 476             Some(trait_item.hir_id),
 477             &trait_item.attrs,
 478             trait_item.span,
 479             desc,
 480         );
 481     }
 482
 483     fn check_impl_item(&mut self, cx: &LateContext<'_, '_>, impl_item: &hir::ImplItem<'_>) {
 484         // If the method is an impl for a trait, don't doc.
 485         if method_context(cx, impl_item.hir_id) == MethodLateContext::TraitImpl {
 486             return;
 487         }
 488
 489         let desc = match impl_item.kind {
 490             hir::ImplItemKind::Const(..) => "an associated constant",
 491             hir::ImplItemKind::Method(..) => "a method",
 492             hir::ImplItemKind::TyAlias(_) => "an associated type",
 493             hir::ImplItemKind::OpaqueTy(_) => "an associated `impl Trait` type",
 494         };
 495         self.check_missing_docs_attrs(
 496             cx,
 497             Some(impl_item.hir_id),
 498             &impl_item.attrs,
 499             impl_item.span,
 500             desc,
 501         );
 502     }
 503
 504     fn check_struct_field(&mut self, cx: &LateContext<'_, '_>, sf: &hir::StructField<'_>) {
 505         if !sf.is_positional() {
 506             self.check_missing_docs_attrs(cx, Some(sf.hir_id), &sf.attrs, sf.span, "a struct field")
 507         }
 508     }
 509
 510     fn check_variant(&mut self, cx: &LateContext<'_, '_>, v: &hir::Variant<'_>) {
 511         self.check_missing_docs_attrs(cx, Some(v.id), &v.attrs, v.span, "a variant");
 512     }
 513 }
 514
 515 declare_lint! {
 516     pub MISSING_COPY_IMPLEMENTATIONS,
 517     Allow,
 518     "detects potentially-forgotten implementations of `Copy`"
 519 }
 520
 521 declare_lint_pass!(MissingCopyImplementations => [MISSING_COPY_IMPLEMENTATIONS]);
 522
 523 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MissingCopyImplementations {
 524     fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &hir::Item<'_>) {
 525         if !cx.access_levels.is_reachable(item.hir_id) {
 526             return;
 527         }
 528         let (def, ty) = match item.kind {
 529             hir::ItemKind::Struct(_, ref ast_generics) => {
 530                 if !ast_generics.params.is_empty() {
 531                     return;
 532                 }
 533                 let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
 534                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 535             }
 536             hir::ItemKind::Union(_, ref ast_generics) => {
 537                 if !ast_generics.params.is_empty() {
 538                     return;
 539                 }
 540                 let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
 541                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 542             }
 543             hir::ItemKind::Enum(_, ref ast_generics) => {
 544                 if !ast_generics.params.is_empty() {
 545                     return;
 546                 }
 547                 let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
 548                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 549             }
 550             _ => return,
 551         };
 552         if def.has_dtor(cx.tcx) {
 553             return;
 554         }
 555         let param_env = ty::ParamEnv::empty();
 556         if ty.is_copy_modulo_regions(cx.tcx, param_env, item.span) {
 557             return;
 558         }
 559         if can_type_implement_copy(cx.tcx, param_env, ty).is_ok() {
 560             cx.span_lint(
 561                 MISSING_COPY_IMPLEMENTATIONS,
 562                 item.span,
 563                 "type could implement `Copy`; consider adding `impl \
 564                           Copy`",
 565             )
 566         }
 567     }
 568 }
 569
 570 declare_lint! {
 571     MISSING_DEBUG_IMPLEMENTATIONS,
 572     Allow,
 573     "detects missing implementations of fmt::Debug"
 574 }
 575
 576 #[derive(Default)]
 577 pub struct MissingDebugImplementations {
 578     impling_types: Option<HirIdSet>,
 579 }
 580
 581 impl_lint_pass!(MissingDebugImplementations => [MISSING_DEBUG_IMPLEMENTATIONS]);
 582
 583 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MissingDebugImplementations {
 584     fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &hir::Item<'_>) {
 585         if !cx.access_levels.is_reachable(item.hir_id) {
 586             return;
 587         }
 588
 589         match item.kind {
 590             hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) | hir::ItemKind::Enum(..) => {}
 591             _ => return,
 592         }
 593
 594         let debug = match cx.tcx.get_diagnostic_item(sym::debug_trait) {
 595             Some(debug) => debug,
 596             None => return,
 597         };
 598
 599         if self.impling_types.is_none() {
 600             let mut impls = HirIdSet::default();
 601             cx.tcx.for_each_impl(debug, |d| {
 602                 if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() {
 603                     if let Some(hir_id) = cx.tcx.hir().as_local_hir_id(ty_def.did) {
 604                         impls.insert(hir_id);
 605                     }
 606                 }
 607             });
 608
 609             self.impling_types = Some(impls);
 610             debug!("{:?}", self.impling_types);
 611         }
 612
 613         if !self.impling_types.as_ref().unwrap().contains(&item.hir_id) {
 614             cx.span_lint(
 615                 MISSING_DEBUG_IMPLEMENTATIONS,
 616                 item.span,
 617                 "type does not implement `fmt::Debug`; consider adding `#[derive(Debug)]` \
 618                           or a manual implementation",
 619             )
 620         }
 621     }
 622 }
 623
 624 declare_lint! {
 625     pub ANONYMOUS_PARAMETERS,
 626     Allow,
 627     "detects anonymous parameters",
 628     @future_incompatible = FutureIncompatibleInfo {
 629         reference: "issue #41686 <https://github.com/rust-lang/rust/issues/41686>",
 630         edition: Some(Edition::Edition2018),
 631     };
 632 }
 633
 634 declare_lint_pass!(
 635     /// Checks for use of anonymous parameters (RFC 1685).
 636     AnonymousParameters => [ANONYMOUS_PARAMETERS]
 637 );
 638
 639 impl EarlyLintPass for AnonymousParameters {
 640     fn check_trait_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
 641         match it.kind {
 642             ast::AssocItemKind::Fn(ref sig, _) => {
 643                 for arg in sig.decl.inputs.iter() {
 644                     match arg.pat.kind {
 645                         ast::PatKind::Ident(_, ident, None) => {
 646                             if ident.name == kw::Invalid {
 647                                 let ty_snip = cx.sess.source_map().span_to_snippet(arg.ty.span);
 648
 649                                 let (ty_snip, appl) = if let Ok(snip) = ty_snip {
 650                                     (snip, Applicability::MachineApplicable)
 651                                 } else {
 652                                     ("<type>".to_owned(), Applicability::HasPlaceholders)
 653                                 };
 654
 655                                 cx.struct_span_lint(
 656                                     ANONYMOUS_PARAMETERS,
 657                                     arg.pat.span,
 658                                     "anonymous parameters are deprecated and will be \
 659                                      removed in the next edition.",
 660                                 )
 661                                 .span_suggestion(
 662                                     arg.pat.span,
 663                                     "Try naming the parameter or explicitly \
 664                                     ignoring it",
 665                                     format!("_: {}", ty_snip),
 666                                     appl,
 667                                 )
 668                                 .emit();
 669                             }
 670                         }
 671                         _ => (),
 672                     }
 673                 }
 674             }
 675             _ => (),
 676         }
 677     }
 678 }
 679
 680 /// Check for use of attributes which have been deprecated.
 681 #[derive(Clone)]
 682 pub struct DeprecatedAttr {
 683     // This is not free to compute, so we want to keep it around, rather than
 684     // compute it for every attribute.
 685     depr_attrs: Vec<&'static (Symbol, AttributeType, AttributeTemplate, AttributeGate)>,
 686 }
 687
 688 impl_lint_pass!(DeprecatedAttr => []);
 689
 690 impl DeprecatedAttr {
 691     pub fn new() -> DeprecatedAttr {
 692         DeprecatedAttr { depr_attrs: deprecated_attributes() }
 693     }
 694 }
 695
 696 fn lint_deprecated_attr(
 697     cx: &EarlyContext<'_>,
 698     attr: &ast::Attribute,
 699     msg: &str,
 700     suggestion: Option<&str>,
 701 ) {
 702     cx.struct_span_lint(DEPRECATED, attr.span, &msg)
 703         .span_suggestion_short(
 704             attr.span,
 705             suggestion.unwrap_or("remove this attribute"),
 706             String::new(),
 707             Applicability::MachineApplicable,
 708         )
 709         .emit();
 710 }
 711
 712 impl EarlyLintPass for DeprecatedAttr {
 713     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 714         for &&(n, _, _, ref g) in &self.depr_attrs {
 715             if attr.ident().map(|ident| ident.name) == Some(n) {
 716                 if let &AttributeGate::Gated(
 717                     Stability::Deprecated(link, suggestion),
 718                     ref name,
 719                     ref reason,
 720                     _,
 721                 ) = g
 722                 {
 723                     let msg =
 724                         format!("use of deprecated attribute `{}`: {}. See {}", name, reason, link);
 725                     lint_deprecated_attr(cx, attr, &msg, suggestion);
 726                 }
 727                 return;
 728             }
 729         }
 730         if attr.check_name(sym::no_start) || attr.check_name(sym::crate_id) {
 731             let path_str = pprust::path_to_string(&attr.get_normal_item().path);
 732             let msg = format!("use of deprecated attribute `{}`: no longer used.", path_str);
 733             lint_deprecated_attr(cx, attr, &msg, None);
 734         }
 735     }
 736 }
 737
 738 declare_lint! {
 739     pub UNUSED_DOC_COMMENTS,
 740     Warn,
 741     "detects doc comments that aren't used by rustdoc"
 742 }
 743
 744 declare_lint_pass!(UnusedDocComment => [UNUSED_DOC_COMMENTS]);
 745
 746 impl UnusedDocComment {
 747     fn warn_if_doc(
 748         &self,
 749         cx: &EarlyContext<'_>,
 750         node_span: Span,
 751         node_kind: &str,
 752         is_macro_expansion: bool,
 753         attrs: &[ast::Attribute],
 754     ) {
 755         let mut attrs = attrs.into_iter().peekable();
 756
 757         // Accumulate a single span for sugared doc comments.
 758         let mut sugared_span: Option<Span> = None;
 759
 760         while let Some(attr) = attrs.next() {
 761             if attr.is_doc_comment() {
 762                 sugared_span = Some(
 763                     sugared_span.map_or_else(|| attr.span, |span| span.with_hi(attr.span.hi())),
 764                 );
 765             }
 766
 767             if attrs.peek().map(|next_attr| next_attr.is_doc_comment()).unwrap_or_default() {
 768                 continue;
 769             }
 770
 771             let span = sugared_span.take().unwrap_or_else(|| attr.span);
 772
 773             if attr.is_doc_comment() || attr.check_name(sym::doc) {
 774                 let mut err = cx.struct_span_lint(UNUSED_DOC_COMMENTS, span, "unused doc comment");
 775
 776                 err.span_label(
 777                     node_span,
 778                     format!("rustdoc does not generate documentation for {}", node_kind),
 779                 );
 780
 781                 if is_macro_expansion {
 782                     err.help(
 783                         "to document an item produced by a macro, \
 784                               the macro must produce the documentation as part of its expansion",
 785                     );
 786                 }
 787
 788                 err.emit();
 789             }
 790         }
 791     }
 792 }
 793
 794 impl EarlyLintPass for UnusedDocComment {
 795     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) {
 796         if let ast::ItemKind::Mac(..) = item.kind {
 797             self.warn_if_doc(cx, item.span, "macro expansions", true, &item.attrs);
 798         }
 799     }
 800
 801     fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &ast::Stmt) {
 802         let (kind, is_macro_expansion) = match stmt.kind {
 803             ast::StmtKind::Local(..) => ("statements", false),
 804             ast::StmtKind::Item(..) => ("inner items", false),
 805             ast::StmtKind::Mac(..) => ("macro expansions", true),
 806             // expressions will be reported by `check_expr`.
 807             ast::StmtKind::Semi(..) | ast::StmtKind::Expr(..) => return,
 808         };
 809
 810         self.warn_if_doc(cx, stmt.span, kind, is_macro_expansion, stmt.kind.attrs());
 811     }
 812
 813     fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) {
 814         let arm_span = arm.pat.span.with_hi(arm.body.span.hi());
 815         self.warn_if_doc(cx, arm_span, "match arms", false, &arm.attrs);
 816     }
 817
 818     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
 819         self.warn_if_doc(cx, expr.span, "expressions", false, &expr.attrs);
 820     }
 821 }
 822
 823 declare_lint! {
 824     NO_MANGLE_CONST_ITEMS,
 825     Deny,
 826     "const items will not have their symbols exported"
 827 }
 828
 829 declare_lint! {
 830     NO_MANGLE_GENERIC_ITEMS,
 831     Warn,
 832     "generic items must be mangled"
 833 }
 834
 835 declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS, NO_MANGLE_GENERIC_ITEMS]);
 836
 837 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for InvalidNoMangleItems {
 838     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item<'_>) {
 839         match it.kind {
 840             hir::ItemKind::Fn(.., ref generics, _) => {
 841                 if let Some(no_mangle_attr) = attr::find_by_name(&it.attrs, sym::no_mangle) {
 842                     for param in generics.params {
 843                         match param.kind {
 844                             GenericParamKind::Lifetime { .. } => {}
 845                             GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
 846                                 let mut err = cx.struct_span_lint(
 847                                     NO_MANGLE_GENERIC_ITEMS,
 848                                     it.span,
 849                                     "functions generic over types or consts must be mangled",
 850                                 );
 851                                 err.span_suggestion_short(
 852                                     no_mangle_attr.span,
 853                                     "remove this attribute",
 854                                     String::new(),
 855                                     // Use of `#[no_mangle]` suggests FFI intent; correct
 856                                     // fix may be to monomorphize source by hand
 857                                     Applicability::MaybeIncorrect,
 858                                 );
 859                                 err.emit();
 860                                 break;
 861                             }
 862                         }
 863                     }
 864                 }
 865             }
 866             hir::ItemKind::Const(..) => {
 867                 if attr::contains_name(&it.attrs, sym::no_mangle) {
 868                     // Const items do not refer to a particular location in memory, and therefore
 869                     // don't have anything to attach a symbol to
 870                     let msg = "const items should never be `#[no_mangle]`";
 871                     let mut err = cx.struct_span_lint(NO_MANGLE_CONST_ITEMS, it.span, msg);
 872
 873                     // account for "pub const" (#45562)
 874                     let start = cx
 875                         .tcx
 876                         .sess
 877                         .source_map()
 878                         .span_to_snippet(it.span)
 879                         .map(|snippet| snippet.find("const").unwrap_or(0))
 880                         .unwrap_or(0) as u32;
 881                     // `const` is 5 chars
 882                     let const_span = it.span.with_hi(BytePos(it.span.lo().0 + start + 5));
 883                     err.span_suggestion(
 884                         const_span,
 885                         "try a static value",
 886                         "pub static".to_owned(),
 887                         Applicability::MachineApplicable,
 888                     );
 889                     err.emit();
 890                 }
 891             }
 892             _ => {}
 893         }
 894     }
 895 }
 896
 897 declare_lint! {
 898     MUTABLE_TRANSMUTES,
 899     Deny,
 900     "mutating transmuted &mut T from &T may cause undefined behavior"
 901 }
 902
 903 declare_lint_pass!(MutableTransmutes => [MUTABLE_TRANSMUTES]);
 904
 905 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MutableTransmutes {
 906     fn check_expr(&mut self, cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>) {
 907         use rustc_target::spec::abi::Abi::RustIntrinsic;
 908
 909         let msg = "mutating transmuted &mut T from &T may cause undefined behavior, \
 910                    consider instead using an UnsafeCell";
 911         match get_transmute_from_to(cx, expr).map(|(ty1, ty2)| (&ty1.kind, &ty2.kind)) {
 912             Some((&ty::Ref(_, _, from_mt), &ty::Ref(_, _, to_mt))) => {
 913                 if to_mt == hir::Mutability::Mut && from_mt == hir::Mutability::Not {
 914                     cx.span_lint(MUTABLE_TRANSMUTES, expr.span, msg);
 915                 }
 916             }
 917             _ => (),
 918         }
 919
 920         fn get_transmute_from_to<'a, 'tcx>(
 921             cx: &LateContext<'a, 'tcx>,
 922             expr: &hir::Expr<'_>,
 923         ) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
 924             let def = if let hir::ExprKind::Path(ref qpath) = expr.kind {
 925                 cx.tables.qpath_res(qpath, expr.hir_id)
 926             } else {
 927                 return None;
 928             };
 929             if let Res::Def(DefKind::Fn, did) = def {
 930                 if !def_id_is_transmute(cx, did) {
 931                     return None;
 932                 }
 933                 let sig = cx.tables.node_type(expr.hir_id).fn_sig(cx.tcx);
 934                 let from = sig.inputs().skip_binder()[0];
 935                 let to = *sig.output().skip_binder();
 936                 return Some((from, to));
 937             }
 938             None
 939         }
 940
 941         fn def_id_is_transmute(cx: &LateContext<'_, '_>, def_id: DefId) -> bool {
 942             cx.tcx.fn_sig(def_id).abi() == RustIntrinsic
 943                 && cx.tcx.item_name(def_id) == sym::transmute
 944         }
 945     }
 946 }
 947
 948 declare_lint! {
 949     UNSTABLE_FEATURES,
 950     Allow,
 951     "enabling unstable features (deprecated. do not use)"
 952 }
 953
 954 declare_lint_pass!(
 955     /// Forbids using the `#[feature(...)]` attribute
 956     UnstableFeatures => [UNSTABLE_FEATURES]
 957 );
 958
 959 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnstableFeatures {
 960     fn check_attribute(&mut self, ctx: &LateContext<'_, '_>, attr: &ast::Attribute) {
 961         if attr.check_name(sym::feature) {
 962             if let Some(items) = attr.meta_item_list() {
 963                 for item in items {
 964                     ctx.span_lint(UNSTABLE_FEATURES, item.span(), "unstable feature");
 965                 }
 966             }
 967         }
 968     }
 969 }
 970
 971 declare_lint! {
 972     pub UNREACHABLE_PUB,
 973     Allow,
 974     "`pub` items not reachable from crate root"
 975 }
 976
 977 declare_lint_pass!(
 978     /// Lint for items marked `pub` that aren't reachable from other crates.
 979     UnreachablePub => [UNREACHABLE_PUB]
 980 );
 981
 982 impl UnreachablePub {
 983     fn perform_lint(
 984         &self,
 985         cx: &LateContext<'_, '_>,
 986         what: &str,
 987         id: hir::HirId,
 988         vis: &hir::Visibility<'_>,
 989         span: Span,
 990         exportable: bool,
 991     ) {
 992         let mut applicability = Applicability::MachineApplicable;
 993         match vis.node {
 994             hir::VisibilityKind::Public if !cx.access_levels.is_reachable(id) => {
 995                 if span.from_expansion() {
 996                     applicability = Applicability::MaybeIncorrect;
 997                 }
 998                 let def_span = cx.tcx.sess.source_map().def_span(span);
 999                 let mut err = cx.struct_span_lint(
1000                     UNREACHABLE_PUB,
1001                     def_span,
1002                     &format!("unreachable `pub` {}", what),
1003                 );
1004                 let replacement = if cx.tcx.features().crate_visibility_modifier {
1005                     "crate"
1006                 } else {
1007                     "pub(crate)"
1008                 }
1009                 .to_owned();
1010
1011                 err.span_suggestion(
1012                     vis.span,
1013                     "consider restricting its visibility",
1014                     replacement,
1015                     applicability,
1016                 );
1017                 if exportable {
1018                     err.help("or consider exporting it for use by other crates");
1019                 }
1020                 err.emit();
1021             }
1022             _ => {}
1023         }
1024     }
1025 }
1026
1027 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnreachablePub {
1028     fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &hir::Item<'_>) {
1029         self.perform_lint(cx, "item", item.hir_id, &item.vis, item.span, true);
1030     }
1031
1032     fn check_foreign_item(
1033         &mut self,
1034         cx: &LateContext<'_, '_>,
1035         foreign_item: &hir::ForeignItem<'tcx>,
1036     ) {
1037         self.perform_lint(
1038             cx,
1039             "item",
1040             foreign_item.hir_id,
1041             &foreign_item.vis,
1042             foreign_item.span,
1043             true,
1044         );
1045     }
1046
1047     fn check_struct_field(&mut self, cx: &LateContext<'_, '_>, field: &hir::StructField<'_>) {
1048         self.perform_lint(cx, "field", field.hir_id, &field.vis, field.span, false);
1049     }
1050
1051     fn check_impl_item(&mut self, cx: &LateContext<'_, '_>, impl_item: &hir::ImplItem<'_>) {
1052         self.perform_lint(cx, "item", impl_item.hir_id, &impl_item.vis, impl_item.span, false);
1053     }
1054 }
1055
1056 declare_lint! {
1057     TYPE_ALIAS_BOUNDS,
1058     Warn,
1059     "bounds in type aliases are not enforced"
1060 }
1061
1062 declare_lint_pass!(
1063     /// Lint for trait and lifetime bounds in type aliases being mostly ignored.
1064     /// They are relevant when using associated types, but otherwise neither checked
1065     /// at definition site nor enforced at use site.
1066     TypeAliasBounds => [TYPE_ALIAS_BOUNDS]
1067 );
1068
1069 impl TypeAliasBounds {
1070     fn is_type_variable_assoc(qpath: &hir::QPath<'_>) -> bool {
1071         match *qpath {
1072             hir::QPath::TypeRelative(ref ty, _) => {
1073                 // If this is a type variable, we found a `T::Assoc`.
1074                 match ty.kind {
1075                     hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => match path.res {
1076                         Res::Def(DefKind::TyParam, _) => true,
1077                         _ => false,
1078                     },
1079                     _ => false,
1080                 }
1081             }
1082             hir::QPath::Resolved(..) => false,
1083         }
1084     }
1085
1086     fn suggest_changing_assoc_types(ty: &hir::Ty<'_>, err: &mut DiagnosticBuilder<'_>) {
1087         // Access to associates types should use `<T as Bound>::Assoc`, which does not need a
1088         // bound.  Let's see if this type does that.
1089
1090         // We use a HIR visitor to walk the type.
1091         use rustc::hir::intravisit::{self, Visitor};
1092         struct WalkAssocTypes<'a, 'db> {
1093             err: &'a mut DiagnosticBuilder<'db>,
1094         }
1095         impl<'a, 'db, 'v> Visitor<'v> for WalkAssocTypes<'a, 'db> {
1096             fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'v> {
1097                 intravisit::NestedVisitorMap::None
1098             }
1099
1100             fn visit_qpath(&mut self, qpath: &'v hir::QPath<'v>, id: hir::HirId, span: Span) {
1101                 if TypeAliasBounds::is_type_variable_assoc(qpath) {
1102                     self.err.span_help(
1103                         span,
1104                         "use fully disambiguated paths (i.e., `<T as Trait>::Assoc`) to refer to \
1105                          associated types in type aliases",
1106                     );
1107                 }
1108                 intravisit::walk_qpath(self, qpath, id, span)
1109             }
1110         }
1111
1112         // Let's go for a walk!
1113         let mut visitor = WalkAssocTypes { err };
1114         visitor.visit_ty(ty);
1115     }
1116 }
1117
1118 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeAliasBounds {
1119     fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &hir::Item<'_>) {
1120         let (ty, type_alias_generics) = match item.kind {
1121             hir::ItemKind::TyAlias(ref ty, ref generics) => (&*ty, generics),
1122             _ => return,
1123         };
1124         let mut suggested_changing_assoc_types = false;
1125         // There must not be a where clause
1126         if !type_alias_generics.where_clause.predicates.is_empty() {
1127             let spans: Vec<_> = type_alias_generics
1128                 .where_clause
1129                 .predicates
1130                 .iter()
1131                 .map(|pred| pred.span())
1132                 .collect();
1133             let mut err = cx.struct_span_lint(
1134                 TYPE_ALIAS_BOUNDS,
1135                 spans,
1136                 "where clauses are not enforced in type aliases",
1137             );
1138             err.span_suggestion(
1139                 type_alias_generics.where_clause.span_for_predicates_or_empty_place(),
1140                 "the clause will not be checked when the type alias is used, and should be removed",
1141                 String::new(),
1142                 Applicability::MachineApplicable,
1143             );
1144             if !suggested_changing_assoc_types {
1145                 TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1146                 suggested_changing_assoc_types = true;
1147             }
1148             err.emit();
1149         }
1150         // The parameters must not have bounds
1151         for param in type_alias_generics.params.iter() {
1152             let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
1153             let suggestion = spans
1154                 .iter()
1155                 .map(|sp| {
1156                     let start = param.span.between(*sp); // Include the `:` in `T: Bound`.
1157                     (start.to(*sp), String::new())
1158                 })
1159                 .collect();
1160             if !spans.is_empty() {
1161                 let mut err = cx.struct_span_lint(
1162                     TYPE_ALIAS_BOUNDS,
1163                     spans,
1164                     "bounds on generic parameters are not enforced in type aliases",
1165                 );
1166                 let msg = "the bound will not be checked when the type alias is used, \
1167                            and should be removed";
1168                 err.multipart_suggestion(&msg, suggestion, Applicability::MachineApplicable);
1169                 if !suggested_changing_assoc_types {
1170                     TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1171                     suggested_changing_assoc_types = true;
1172                 }
1173                 err.emit();
1174             }
1175         }
1176     }
1177 }
1178
1179 declare_lint_pass!(
1180     /// Lint constants that are erroneous.
1181     /// Without this lint, we might not get any diagnostic if the constant is
1182     /// unused within this crate, even though downstream crates can't use it
1183     /// without producing an error.
1184     UnusedBrokenConst => []
1185 );
1186
1187 fn check_const(cx: &LateContext<'_, '_>, body_id: hir::BodyId) {
1188     let def_id = cx.tcx.hir().body_owner_def_id(body_id);
1189     // trigger the query once for all constants since that will already report the errors
1190     // FIXME: Use ensure here
1191     let _ = cx.tcx.const_eval_poly(def_id);
1192 }
1193
1194 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedBrokenConst {
1195     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item<'_>) {
1196         match it.kind {
1197             hir::ItemKind::Const(_, body_id) => {
1198                 check_const(cx, body_id);
1199             }
1200             hir::ItemKind::Static(_, _, body_id) => {
1201                 check_const(cx, body_id);
1202             }
1203             _ => {}
1204         }
1205     }
1206 }
1207
1208 declare_lint! {
1209     TRIVIAL_BOUNDS,
1210     Warn,
1211     "these bounds don't depend on an type parameters"
1212 }
1213
1214 declare_lint_pass!(
1215     /// Lint for trait and lifetime bounds that don't depend on type parameters
1216     /// which either do nothing, or stop the item from being used.
1217     TrivialConstraints => [TRIVIAL_BOUNDS]
1218 );
1219
1220 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TrivialConstraints {
1221     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item<'tcx>) {
1222         use rustc::ty::fold::TypeFoldable;
1223         use rustc::ty::Predicate::*;
1224
1225         if cx.tcx.features().trivial_bounds {
1226             let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1227             let predicates = cx.tcx.predicates_of(def_id);
1228             for &(predicate, span) in predicates.predicates {
1229                 let predicate_kind_name = match predicate {
1230                     Trait(..) => "Trait",
1231                     TypeOutlives(..) |
1232                     RegionOutlives(..) => "Lifetime",
1233
1234                     // Ignore projections, as they can only be global
1235                     // if the trait bound is global
1236                     Projection(..) |
1237                     // Ignore bounds that a user can't type
1238                     WellFormed(..) |
1239                     ObjectSafe(..) |
1240                     ClosureKind(..) |
1241                     Subtype(..) |
1242                     ConstEvaluatable(..) => continue,
1243                 };
1244                 if predicate.is_global() {
1245                     cx.span_lint(
1246                         TRIVIAL_BOUNDS,
1247                         span,
1248                         &format!(
1249                             "{} bound {} does not depend on any type \
1250                                 or lifetime parameters",
1251                             predicate_kind_name, predicate
1252                         ),
1253                     );
1254                 }
1255             }
1256         }
1257     }
1258 }
1259
1260 declare_lint_pass!(
1261     /// Does nothing as a lint pass, but registers some `Lint`s
1262     /// which are used by other parts of the compiler.
1263     SoftLints => [
1264         WHILE_TRUE,
1265         BOX_POINTERS,
1266         NON_SHORTHAND_FIELD_PATTERNS,
1267         UNSAFE_CODE,
1268         MISSING_DOCS,
1269         MISSING_COPY_IMPLEMENTATIONS,
1270         MISSING_DEBUG_IMPLEMENTATIONS,
1271         ANONYMOUS_PARAMETERS,
1272         UNUSED_DOC_COMMENTS,
1273         NO_MANGLE_CONST_ITEMS,
1274         NO_MANGLE_GENERIC_ITEMS,
1275         MUTABLE_TRANSMUTES,
1276         UNSTABLE_FEATURES,
1277         UNREACHABLE_PUB,
1278         TYPE_ALIAS_BOUNDS,
1279         TRIVIAL_BOUNDS
1280     ]
1281 );
1282
1283 declare_lint! {
1284     pub ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
1285     Warn,
1286     "`...` range patterns are deprecated"
1287 }
1288
1289 #[derive(Default)]
1290 pub struct EllipsisInclusiveRangePatterns {
1291     /// If `Some(_)`, suppress all subsequent pattern
1292     /// warnings for better diagnostics.
1293     node_id: Option<ast::NodeId>,
1294 }
1295
1296 impl_lint_pass!(EllipsisInclusiveRangePatterns => [ELLIPSIS_INCLUSIVE_RANGE_PATTERNS]);
1297
1298 impl EarlyLintPass for EllipsisInclusiveRangePatterns {
1299     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &ast::Pat) {
1300         if self.node_id.is_some() {
1301             // Don't recursively warn about patterns inside range endpoints.
1302             return;
1303         }
1304
1305         use self::ast::{PatKind, RangeEnd, RangeSyntax::DotDotDot};
1306
1307         /// If `pat` is a `...` pattern, return the start and end of the range, as well as the span
1308         /// corresponding to the ellipsis.
1309         fn matches_ellipsis_pat(pat: &ast::Pat) -> Option<(&P<Expr>, &P<Expr>, Span)> {
1310             match &pat.kind {
1311                 PatKind::Range(a, b, Spanned { span, node: RangeEnd::Included(DotDotDot), .. }) => {
1312                     Some((a, b, *span))
1313                 }
1314                 _ => None,
1315             }
1316         }
1317
1318         let (parenthesise, endpoints) = match &pat.kind {
1319             PatKind::Ref(subpat, _) => (true, matches_ellipsis_pat(&subpat)),
1320             _ => (false, matches_ellipsis_pat(pat)),
1321         };
1322
1323         if let Some((start, end, join)) = endpoints {
1324             let msg = "`...` range patterns are deprecated";
1325             let suggestion = "use `..=` for an inclusive range";
1326             if parenthesise {
1327                 self.node_id = Some(pat.id);
1328                 let mut err = cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, pat.span, msg);
1329                 err.span_suggestion(
1330                     pat.span,
1331                     suggestion,
1332                     format!("&({}..={})", expr_to_string(&start), expr_to_string(&end)),
1333                     Applicability::MachineApplicable,
1334                 );
1335                 err.emit();
1336             } else {
1337                 let mut err = cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, join, msg);
1338                 err.span_suggestion_short(
1339                     join,
1340                     suggestion,
1341                     "..=".to_owned(),
1342                     Applicability::MachineApplicable,
1343                 );
1344                 err.emit();
1345             };
1346         }
1347     }
1348
1349     fn check_pat_post(&mut self, _cx: &EarlyContext<'_>, pat: &ast::Pat) {
1350         if let Some(node_id) = self.node_id {
1351             if pat.id == node_id {
1352                 self.node_id = None
1353             }
1354         }
1355     }
1356 }
1357
1358 declare_lint! {
1359     UNNAMEABLE_TEST_ITEMS,
1360     Warn,
1361     "detects an item that cannot be named being marked as `#[test_case]`",
1362     report_in_external_macro
1363 }
1364
1365 pub struct UnnameableTestItems {
1366     boundary: hir::HirId, // HirId of the item under which things are not nameable
1367     items_nameable: bool,
1368 }
1369
1370 impl_lint_pass!(UnnameableTestItems => [UNNAMEABLE_TEST_ITEMS]);
1371
1372 impl UnnameableTestItems {
1373     pub fn new() -> Self {
1374         Self { boundary: hir::DUMMY_HIR_ID, items_nameable: true }
1375     }
1376 }
1377
1378 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnnameableTestItems {
1379     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item<'_>) {
1380         if self.items_nameable {
1381             if let hir::ItemKind::Mod(..) = it.kind {
1382             } else {
1383                 self.items_nameable = false;
1384                 self.boundary = it.hir_id;
1385             }
1386             return;
1387         }
1388
1389         if let Some(attr) = attr::find_by_name(&it.attrs, sym::rustc_test_marker) {
1390             cx.struct_span_lint(UNNAMEABLE_TEST_ITEMS, attr.span, "cannot test inner items").emit();
1391         }
1392     }
1393
1394     fn check_item_post(&mut self, _cx: &LateContext<'_, '_>, it: &hir::Item<'_>) {
1395         if !self.items_nameable && self.boundary == it.hir_id {
1396             self.items_nameable = true;
1397         }
1398     }
1399 }
1400
1401 declare_lint! {
1402     pub KEYWORD_IDENTS,
1403     Allow,
1404     "detects edition keywords being used as an identifier",
1405     @future_incompatible = FutureIncompatibleInfo {
1406         reference: "issue #49716 <https://github.com/rust-lang/rust/issues/49716>",
1407         edition: Some(Edition::Edition2018),
1408     };
1409 }
1410
1411 declare_lint_pass!(
1412     /// Check for uses of edition keywords used as an identifier.
1413     KeywordIdents => [KEYWORD_IDENTS]
1414 );
1415
1416 struct UnderMacro(bool);
1417
1418 impl KeywordIdents {
1419     fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: TokenStream) {
1420         for tt in tokens.into_trees() {
1421             match tt {
1422                 // Only report non-raw idents.
1423                 TokenTree::Token(token) => {
1424                     if let Some((ident, false)) = token.ident() {
1425                         self.check_ident_token(cx, UnderMacro(true), ident);
1426                     }
1427                 }
1428                 TokenTree::Delimited(_, _, tts) => self.check_tokens(cx, tts),
1429             }
1430         }
1431     }
1432
1433     fn check_ident_token(
1434         &mut self,
1435         cx: &EarlyContext<'_>,
1436         UnderMacro(under_macro): UnderMacro,
1437         ident: ast::Ident,
1438     ) {
1439         let next_edition = match cx.sess.edition() {
1440             Edition::Edition2015 => {
1441                 match ident.name {
1442                     kw::Async | kw::Await | kw::Try => Edition::Edition2018,
1443
1444                     // rust-lang/rust#56327: Conservatively do not
1445                     // attempt to report occurrences of `dyn` within
1446                     // macro definitions or invocations, because `dyn`
1447                     // can legitimately occur as a contextual keyword
1448                     // in 2015 code denoting its 2018 meaning, and we
1449                     // do not want rustfix to inject bugs into working
1450                     // code by rewriting such occurrences.
1451                     //
1452                     // But if we see `dyn` outside of a macro, we know
1453                     // its precise role in the parsed AST and thus are
1454                     // assured this is truly an attempt to use it as
1455                     // an identifier.
1456                     kw::Dyn if !under_macro => Edition::Edition2018,
1457
1458                     _ => return,
1459                 }
1460             }
1461
1462             // There are no new keywords yet for the 2018 edition and beyond.
1463             _ => return,
1464         };
1465
1466         // Don't lint `r#foo`.
1467         if cx.sess.parse_sess.raw_identifier_spans.borrow().contains(&ident.span) {
1468             return;
1469         }
1470
1471         let mut lint = cx.struct_span_lint(
1472             KEYWORD_IDENTS,
1473             ident.span,
1474             &format!("`{}` is a keyword in the {} edition", ident, next_edition),
1475         );
1476         lint.span_suggestion(
1477             ident.span,
1478             "you can use a raw identifier to stay compatible",
1479             format!("r#{}", ident),
1480             Applicability::MachineApplicable,
1481         );
1482         lint.emit()
1483     }
1484 }
1485
1486 impl EarlyLintPass for KeywordIdents {
1487     fn check_mac_def(&mut self, cx: &EarlyContext<'_>, mac_def: &ast::MacroDef, _id: ast::NodeId) {
1488         self.check_tokens(cx, mac_def.body.inner_tokens());
1489     }
1490     fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::Mac) {
1491         self.check_tokens(cx, mac.args.inner_tokens());
1492     }
1493     fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: ast::Ident) {
1494         self.check_ident_token(cx, UnderMacro(false), ident);
1495     }
1496 }
1497
1498 declare_lint_pass!(ExplicitOutlivesRequirements => [EXPLICIT_OUTLIVES_REQUIREMENTS]);
1499
1500 impl ExplicitOutlivesRequirements {
1501     fn lifetimes_outliving_lifetime<'tcx>(
1502         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
1503         index: u32,
1504     ) -> Vec<ty::Region<'tcx>> {
1505         inferred_outlives
1506             .iter()
1507             .filter_map(|(pred, _)| match pred {
1508                 ty::Predicate::RegionOutlives(outlives) => {
1509                     let outlives = outlives.skip_binder();
1510                     match outlives.0 {
1511                         ty::ReEarlyBound(ebr) if ebr.index == index => Some(outlives.1),
1512                         _ => None,
1513                     }
1514                 }
1515                 _ => None,
1516             })
1517             .collect()
1518     }
1519
1520     fn lifetimes_outliving_type<'tcx>(
1521         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
1522         index: u32,
1523     ) -> Vec<ty::Region<'tcx>> {
1524         inferred_outlives
1525             .iter()
1526             .filter_map(|(pred, _)| match pred {
1527                 ty::Predicate::TypeOutlives(outlives) => {
1528                     let outlives = outlives.skip_binder();
1529                     outlives.0.is_param(index).then_some(outlives.1)
1530                 }
1531                 _ => None,
1532             })
1533             .collect()
1534     }
1535
1536     fn collect_outlived_lifetimes<'tcx>(
1537         &self,
1538         param: &'tcx hir::GenericParam<'tcx>,
1539         tcx: TyCtxt<'tcx>,
1540         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
1541         ty_generics: &'tcx ty::Generics,
1542     ) -> Vec<ty::Region<'tcx>> {
1543         let index = ty_generics.param_def_id_to_index[&tcx.hir().local_def_id(param.hir_id)];
1544
1545         match param.kind {
1546             hir::GenericParamKind::Lifetime { .. } => {
1547                 Self::lifetimes_outliving_lifetime(inferred_outlives, index)
1548             }
1549             hir::GenericParamKind::Type { .. } => {
1550                 Self::lifetimes_outliving_type(inferred_outlives, index)
1551             }
1552             hir::GenericParamKind::Const { .. } => Vec::new(),
1553         }
1554     }
1555
1556     fn collect_outlives_bound_spans<'tcx>(
1557         &self,
1558         tcx: TyCtxt<'tcx>,
1559         bounds: &hir::GenericBounds<'_>,
1560         inferred_outlives: &[ty::Region<'tcx>],
1561         infer_static: bool,
1562     ) -> Vec<(usize, Span)> {
1563         use rustc::middle::resolve_lifetime::Region;
1564
1565         bounds
1566             .iter()
1567             .enumerate()
1568             .filter_map(|(i, bound)| {
1569                 if let hir::GenericBound::Outlives(lifetime) = bound {
1570                     let is_inferred = match tcx.named_region(lifetime.hir_id) {
1571                         Some(Region::Static) if infer_static => inferred_outlives
1572                             .iter()
1573                             .any(|r| if let ty::ReStatic = r { true } else { false }),
1574                         Some(Region::EarlyBound(index, ..)) => inferred_outlives.iter().any(|r| {
1575                             if let ty::ReEarlyBound(ebr) = r { ebr.index == index } else { false }
1576                         }),
1577                         _ => false,
1578                     };
1579                     is_inferred.then_some((i, bound.span()))
1580                 } else {
1581                     None
1582                 }
1583             })
1584             .collect()
1585     }
1586
1587     fn consolidate_outlives_bound_spans(
1588         &self,
1589         lo: Span,
1590         bounds: &hir::GenericBounds<'_>,
1591         bound_spans: Vec<(usize, Span)>,
1592     ) -> Vec<Span> {
1593         if bounds.is_empty() {
1594             return Vec::new();
1595         }
1596         if bound_spans.len() == bounds.len() {
1597             let (_, last_bound_span) = bound_spans[bound_spans.len() - 1];
1598             // If all bounds are inferable, we want to delete the colon, so
1599             // start from just after the parameter (span passed as argument)
1600             vec![lo.to(last_bound_span)]
1601         } else {
1602             let mut merged = Vec::new();
1603             let mut last_merged_i = None;
1604
1605             let mut from_start = true;
1606             for (i, bound_span) in bound_spans {
1607                 match last_merged_i {
1608                     // If the first bound is inferable, our span should also eat the leading `+`.
1609                     None if i == 0 => {
1610                         merged.push(bound_span.to(bounds[1].span().shrink_to_lo()));
1611                         last_merged_i = Some(0);
1612                     }
1613                     // If consecutive bounds are inferable, merge their spans
1614                     Some(h) if i == h + 1 => {
1615                         if let Some(tail) = merged.last_mut() {
1616                             // Also eat the trailing `+` if the first
1617                             // more-than-one bound is inferable
1618                             let to_span = if from_start && i < bounds.len() {
1619                                 bounds[i + 1].span().shrink_to_lo()
1620                             } else {
1621                                 bound_span
1622                             };
1623                             *tail = tail.to(to_span);
1624                             last_merged_i = Some(i);
1625                         } else {
1626                             bug!("another bound-span visited earlier");
1627                         }
1628                     }
1629                     _ => {
1630                         // When we find a non-inferable bound, subsequent inferable bounds
1631                         // won't be consecutive from the start (and we'll eat the leading
1632                         // `+` rather than the trailing one)
1633                         from_start = false;
1634                         merged.push(bounds[i - 1].span().shrink_to_hi().to(bound_span));
1635                         last_merged_i = Some(i);
1636                     }
1637                 }
1638             }
1639             merged
1640         }
1641     }
1642 }
1643
1644 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ExplicitOutlivesRequirements {
1645     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item<'_>) {
1646         use rustc::middle::resolve_lifetime::Region;
1647
1648         let infer_static = cx.tcx.features().infer_static_outlives_requirements;
1649         let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1650         if let hir::ItemKind::Struct(_, ref hir_generics)
1651         | hir::ItemKind::Enum(_, ref hir_generics)
1652         | hir::ItemKind::Union(_, ref hir_generics) = item.kind
1653         {
1654             let inferred_outlives = cx.tcx.inferred_outlives_of(def_id);
1655             if inferred_outlives.is_empty() {
1656                 return;
1657             }
1658
1659             let ty_generics = cx.tcx.generics_of(def_id);
1660
1661             let mut bound_count = 0;
1662             let mut lint_spans = Vec::new();
1663
1664             for param in hir_generics.params {
1665                 let has_lifetime_bounds = param.bounds.iter().any(|bound| {
1666                     if let hir::GenericBound::Outlives(_) = bound { true } else { false }
1667                 });
1668                 if !has_lifetime_bounds {
1669                     continue;
1670                 }
1671
1672                 let relevant_lifetimes =
1673                     self.collect_outlived_lifetimes(param, cx.tcx, inferred_outlives, ty_generics);
1674                 if relevant_lifetimes.is_empty() {
1675                     continue;
1676                 }
1677
1678                 let bound_spans = self.collect_outlives_bound_spans(
1679                     cx.tcx,
1680                     &param.bounds,
1681                     &relevant_lifetimes,
1682                     infer_static,
1683                 );
1684                 bound_count += bound_spans.len();
1685                 lint_spans.extend(self.consolidate_outlives_bound_spans(
1686                     param.span.shrink_to_hi(),
1687                     &param.bounds,
1688                     bound_spans,
1689                 ));
1690             }
1691
1692             let mut where_lint_spans = Vec::new();
1693             let mut dropped_predicate_count = 0;
1694             let num_predicates = hir_generics.where_clause.predicates.len();
1695             for (i, where_predicate) in hir_generics.where_clause.predicates.iter().enumerate() {
1696                 let (relevant_lifetimes, bounds, span) = match where_predicate {
1697                     hir::WherePredicate::RegionPredicate(predicate) => {
1698                         if let Some(Region::EarlyBound(index, ..)) =
1699                             cx.tcx.named_region(predicate.lifetime.hir_id)
1700                         {
1701                             (
1702                                 Self::lifetimes_outliving_lifetime(inferred_outlives, index),
1703                                 &predicate.bounds,
1704                                 predicate.span,
1705                             )
1706                         } else {
1707                             continue;
1708                         }
1709                     }
1710                     hir::WherePredicate::BoundPredicate(predicate) => {
1711                         // FIXME we can also infer bounds on associated types,
1712                         // and should check for them here.
1713                         match predicate.bounded_ty.kind {
1714                             hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
1715                                 if let Res::Def(DefKind::TyParam, def_id) = path.res {
1716                                     let index = ty_generics.param_def_id_to_index[&def_id];
1717                                     (
1718                                         Self::lifetimes_outliving_type(inferred_outlives, index),
1719                                         &predicate.bounds,
1720                                         predicate.span,
1721                                     )
1722                                 } else {
1723                                     continue;
1724                                 }
1725                             }
1726                             _ => {
1727                                 continue;
1728                             }
1729                         }
1730                     }
1731                     _ => continue,
1732                 };
1733                 if relevant_lifetimes.is_empty() {
1734                     continue;
1735                 }
1736
1737                 let bound_spans = self.collect_outlives_bound_spans(
1738                     cx.tcx,
1739                     bounds,
1740                     &relevant_lifetimes,
1741                     infer_static,
1742                 );
1743                 bound_count += bound_spans.len();
1744
1745                 let drop_predicate = bound_spans.len() == bounds.len();
1746                 if drop_predicate {
1747                     dropped_predicate_count += 1;
1748                 }
1749
1750                 // If all the bounds on a predicate were inferable and there are
1751                 // further predicates, we want to eat the trailing comma.
1752                 if drop_predicate && i + 1 < num_predicates {
1753                     let next_predicate_span = hir_generics.where_clause.predicates[i + 1].span();
1754                     where_lint_spans.push(span.to(next_predicate_span.shrink_to_lo()));
1755                 } else {
1756                     where_lint_spans.extend(self.consolidate_outlives_bound_spans(
1757                         span.shrink_to_lo(),
1758                         bounds,
1759                         bound_spans,
1760                     ));
1761                 }
1762             }
1763
1764             // If all predicates are inferable, drop the entire clause
1765             // (including the `where`)
1766             if num_predicates > 0 && dropped_predicate_count == num_predicates {
1767                 let where_span = hir_generics
1768                     .where_clause
1769                     .span()
1770                     .expect("span of (nonempty) where clause should exist");
1771                 // Extend the where clause back to the closing `>` of the
1772                 // generics, except for tuple struct, which have the `where`
1773                 // after the fields of the struct.
1774                 let full_where_span =
1775                     if let hir::ItemKind::Struct(hir::VariantData::Tuple(..), _) = item.kind {
1776                         where_span
1777                     } else {
1778                         hir_generics.span.shrink_to_hi().to(where_span)
1779                     };
1780                 lint_spans.push(full_where_span);
1781             } else {
1782                 lint_spans.extend(where_lint_spans);
1783             }
1784
1785             if !lint_spans.is_empty() {
1786                 let mut err = cx.struct_span_lint(
1787                     EXPLICIT_OUTLIVES_REQUIREMENTS,
1788                     lint_spans.clone(),
1789                     "outlives requirements can be inferred",
1790                 );
1791                 err.multipart_suggestion(
1792                     if bound_count == 1 { "remove this bound" } else { "remove these bounds" },
1793                     lint_spans.into_iter().map(|span| (span, "".to_owned())).collect::<Vec<_>>(),
1794                     Applicability::MachineApplicable,
1795                 );
1796                 err.emit();
1797             }
1798         }
1799     }
1800 }
1801
1802 declare_lint! {
1803     pub INCOMPLETE_FEATURES,
1804     Warn,
1805     "incomplete features that may function improperly in some or all cases"
1806 }
1807
1808 declare_lint_pass!(
1809     /// Check for used feature gates in `INCOMPLETE_FEATURES` in `feature_gate.rs`.
1810     IncompleteFeatures => [INCOMPLETE_FEATURES]
1811 );
1812
1813 impl EarlyLintPass for IncompleteFeatures {
1814     fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
1815         let features = cx.sess.features_untracked();
1816         features
1817             .declared_lang_features
1818             .iter()
1819             .map(|(name, span, _)| (name, span))
1820             .chain(features.declared_lib_features.iter().map(|(name, span)| (name, span)))
1821             .filter(|(name, _)| rustc_feature::INCOMPLETE_FEATURES.iter().any(|f| name == &f))
1822             .for_each(|(name, &span)| {
1823                 cx.struct_span_lint(
1824                     INCOMPLETE_FEATURES,
1825                     span,
1826                     &format!(
1827                         "the feature `{}` is incomplete and may cause the compiler to crash",
1828                         name,
1829                     ),
1830                 )
1831                 .emit();
1832             });
1833     }
1834 }
1835
1836 declare_lint! {
1837     pub INVALID_VALUE,
1838     Warn,
1839     "an invalid value is being created (such as a NULL reference)"
1840 }
1841
1842 declare_lint_pass!(InvalidValue => [INVALID_VALUE]);
1843
1844 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for InvalidValue {
1845     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &hir::Expr<'_>) {
1846         #[derive(Debug, Copy, Clone, PartialEq)]
1847         enum InitKind {
1848             Zeroed,
1849             Uninit,
1850         };
1851
1852         /// Information about why a type cannot be initialized this way.
1853         /// Contains an error message and optionally a span to point at.
1854         type InitError = (String, Option<Span>);
1855
1856         /// Test if this constant is all-0.
1857         fn is_zero(expr: &hir::Expr<'_>) -> bool {
1858             use hir::ExprKind::*;
1859             use syntax::ast::LitKind::*;
1860             match &expr.kind {
1861                 Lit(lit) => {
1862                     if let Int(i, _) = lit.node {
1863                         i == 0
1864                     } else {
1865                         false
1866                     }
1867                 }
1868                 Tup(tup) => tup.iter().all(is_zero),
1869                 _ => false,
1870             }
1871         }
1872
1873         /// Determine if this expression is a "dangerous initialization".
1874         fn is_dangerous_init(cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>) -> Option<InitKind> {
1875             // `transmute` is inside an anonymous module (the `extern` block?);
1876             // `Invalid` represents the empty string and matches that.
1877             // FIXME(#66075): use diagnostic items.  Somehow, that does not seem to work
1878             // on intrinsics right now.
1879             const TRANSMUTE_PATH: &[Symbol] =
1880                 &[sym::core, sym::intrinsics, kw::Invalid, sym::transmute];
1881
1882             if let hir::ExprKind::Call(ref path_expr, ref args) = expr.kind {
1883                 // Find calls to `mem::{uninitialized,zeroed}` methods.
1884                 if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
1885                     let def_id = cx.tables.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
1886
1887                     if cx.tcx.is_diagnostic_item(sym::mem_zeroed, def_id) {
1888                         return Some(InitKind::Zeroed);
1889                     } else if cx.tcx.is_diagnostic_item(sym::mem_uninitialized, def_id) {
1890                         return Some(InitKind::Uninit);
1891                     } else if cx.match_def_path(def_id, TRANSMUTE_PATH) {
1892                         if is_zero(&args[0]) {
1893                             return Some(InitKind::Zeroed);
1894                         }
1895                     }
1896                 }
1897             } else if let hir::ExprKind::MethodCall(_, _, ref args) = expr.kind {
1898                 // Find problematic calls to `MaybeUninit::assume_init`.
1899                 let def_id = cx.tables.type_dependent_def_id(expr.hir_id)?;
1900                 if cx.tcx.is_diagnostic_item(sym::assume_init, def_id) {
1901                     // This is a call to *some* method named `assume_init`.
1902                     // See if the `self` parameter is one of the dangerous constructors.
1903                     if let hir::ExprKind::Call(ref path_expr, _) = args[0].kind {
1904                         if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
1905                             let def_id =
1906                                 cx.tables.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
1907
1908                             if cx.tcx.is_diagnostic_item(sym::maybe_uninit_zeroed, def_id) {
1909                                 return Some(InitKind::Zeroed);
1910                             } else if cx.tcx.is_diagnostic_item(sym::maybe_uninit_uninit, def_id) {
1911                                 return Some(InitKind::Uninit);
1912                             }
1913                         }
1914                     }
1915                 }
1916             }
1917
1918             None
1919         }
1920
1921         /// Return `Some` only if we are sure this type does *not*
1922         /// allow zero initialization.
1923         fn ty_find_init_error<'tcx>(
1924             tcx: TyCtxt<'tcx>,
1925             ty: Ty<'tcx>,
1926             init: InitKind,
1927         ) -> Option<InitError> {
1928             use rustc::ty::TyKind::*;
1929             match ty.kind {
1930                 // Primitive types that don't like 0 as a value.
1931                 Ref(..) => Some((format!("References must be non-null"), None)),
1932                 Adt(..) if ty.is_box() => Some((format!("`Box` must be non-null"), None)),
1933                 FnPtr(..) => Some((format!("Function pointers must be non-null"), None)),
1934                 Never => Some((format!("The never type (`!`) has no valid value"), None)),
1935                 RawPtr(tm) if matches!(tm.ty.kind, Dynamic(..)) =>
1936                 // raw ptr to dyn Trait
1937                 {
1938                     Some((format!("The vtable of a wide raw pointer must be non-null"), None))
1939                 }
1940                 // Primitive types with other constraints.
1941                 Bool if init == InitKind::Uninit => {
1942                     Some((format!("Booleans must be `true` or `false`"), None))
1943                 }
1944                 Char if init == InitKind::Uninit => {
1945                     Some((format!("Characters must be a valid unicode codepoint"), None))
1946                 }
1947                 // Recurse and checks for some compound types.
1948                 Adt(adt_def, substs) if !adt_def.is_union() => {
1949                     // First check f this ADT has a layout attribute (like `NonNull` and friends).
1950                     use std::ops::Bound;
1951                     match tcx.layout_scalar_valid_range(adt_def.did) {
1952                         // We exploit here that `layout_scalar_valid_range` will never
1953                         // return `Bound::Excluded`.  (And we have tests checking that we
1954                         // handle the attribute correctly.)
1955                         (Bound::Included(lo), _) if lo > 0 => {
1956                             return Some((format!("{} must be non-null", ty), None));
1957                         }
1958                         (Bound::Included(_), _) | (_, Bound::Included(_))
1959                             if init == InitKind::Uninit =>
1960                         {
1961                             return Some((
1962                                 format!("{} must be initialized inside its custom valid range", ty),
1963                                 None,
1964                             ));
1965                         }
1966                         _ => {}
1967                     }
1968                     // Now, recurse.
1969                     match adt_def.variants.len() {
1970                         0 => Some((format!("0-variant enums have no valid value"), None)),
1971                         1 => {
1972                             // Struct, or enum with exactly one variant.
1973                             // Proceed recursively, check all fields.
1974                             let variant = &adt_def.variants[VariantIdx::from_u32(0)];
1975                             variant.fields.iter().find_map(|field| {
1976                                 ty_find_init_error(tcx, field.ty(tcx, substs), init).map(
1977                                     |(mut msg, span)| {
1978                                         if span.is_none() {
1979                                             // Point to this field, should be helpful for figuring
1980                                             // out where the source of the error is.
1981                                             let span = tcx.def_span(field.did);
1982                                             write!(
1983                                                 &mut msg,
1984                                                 " (in this {} field)",
1985                                                 adt_def.descr()
1986                                             )
1987                                             .unwrap();
1988                                             (msg, Some(span))
1989                                         } else {
1990                                             // Just forward.
1991                                             (msg, span)
1992                                         }
1993                                     },
1994                                 )
1995                             })
1996                         }
1997                         // Multi-variant enums are tricky: if all but one variant are
1998                         // uninhabited, we might actually do layout like for a single-variant
1999                         // enum, and then even leaving them uninitialized could be okay.
2000                         _ => None, // Conservative fallback for multi-variant enum.
2001                     }
2002                 }
2003                 Tuple(..) => {
2004                     // Proceed recursively, check all fields.
2005                     ty.tuple_fields().find_map(|field| ty_find_init_error(tcx, field, init))
2006                 }
2007                 // Conservative fallback.
2008                 _ => None,
2009             }
2010         }
2011
2012         if let Some(init) = is_dangerous_init(cx, expr) {
2013             // This conjures an instance of a type out of nothing,
2014             // using zeroed or uninitialized memory.
2015             // We are extremely conservative with what we warn about.
2016             let conjured_ty = cx.tables.expr_ty(expr);
2017             if let Some((msg, span)) = ty_find_init_error(cx.tcx, conjured_ty, init) {
2018                 let mut err = cx.struct_span_lint(
2019                     INVALID_VALUE,
2020                     expr.span,
2021                     &format!(
2022                         "the type `{}` does not permit {}",
2023                         conjured_ty,
2024                         match init {
2025                             InitKind::Zeroed => "zero-initialization",
2026                             InitKind::Uninit => "being left uninitialized",
2027                         },
2028                     ),
2029                 );
2030                 err.span_label(expr.span, "this code causes undefined behavior when executed");
2031                 err.span_label(
2032                     expr.span,
2033                     "help: use `MaybeUninit<T>` instead, \
2034                     and only call `assume_init` after initialization is done",
2035                 );
2036                 if let Some(span) = span {
2037                     err.span_note(span, &msg);
2038                 } else {
2039                     err.note(&msg);
2040                 }
2041                 err.emit();
2042             }
2043         }
2044     }
2045 }