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 crate::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext};
  25 use rustc::lint::LintDiagnosticBuilder;
  26 use rustc::ty::{self, layout::VariantIdx, Ty, TyCtxt};
  27 use rustc_ast::ast::{self, Expr};
  28 use rustc_ast::attr::{self, HasAttrs};
  29 use rustc_ast::tokenstream::{TokenStream, TokenTree};
  30 use rustc_ast::visit::{FnCtxt, FnKind};
  31 use rustc_ast_pretty::pprust::{self, expr_to_string};
  32 use rustc_data_structures::fx::FxHashSet;
  33 use rustc_errors::{Applicability, DiagnosticBuilder};
  34 use rustc_feature::Stability;
  35 use rustc_feature::{deprecated_attributes, AttributeGate, AttributeTemplate, AttributeType};
  36 use rustc_hir as hir;
  37 use rustc_hir::def::{DefKind, Res};
  38 use rustc_hir::def_id::DefId;
  39 use rustc_hir::{GenericParamKind, PatKind};
  40 use rustc_hir::{HirIdSet, Node};
  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, Symbol};
  45 use rustc_span::{BytePos, Span};
  46 use rustc_trait_selection::traits::misc::can_type_implement_copy;
  47
  48 use crate::nonstandard_style::{method_context, MethodLateContext};
  49
  50 use log::debug;
  51 use std::fmt::Write;
  52
  53 // hardwired lints from librustc
  54 pub use rustc_session::lint::builtin::*;
  55
  56 declare_lint! {
  57     WHILE_TRUE,
  58     Warn,
  59     "suggest using `loop { }` instead of `while true { }`"
  60 }
  61
  62 declare_lint_pass!(WhileTrue => [WHILE_TRUE]);
  63
  64 /// Traverse through any amount of parenthesis and return the first non-parens expression.
  65 fn pierce_parens(mut expr: &ast::Expr) -> &ast::Expr {
  66     while let ast::ExprKind::Paren(sub) = &expr.kind {
  67         expr = sub;
  68     }
  69     expr
  70 }
  71
  72 impl EarlyLintPass for WhileTrue {
  73     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
  74         if let ast::ExprKind::While(cond, ..) = &e.kind {
  75             if let ast::ExprKind::Lit(ref lit) = pierce_parens(cond).kind {
  76                 if let ast::LitKind::Bool(true) = lit.kind {
  77                     if !lit.span.from_expansion() {
  78                         let msg = "denote infinite loops with `loop { ... }`";
  79                         let condition_span = cx.sess.source_map().def_span(e.span);
  80                         cx.struct_span_lint(WHILE_TRUE, condition_span, |lint| {
  81                             lint.build(msg)
  82                                 .span_suggestion_short(
  83                                     condition_span,
  84                                     "use `loop`",
  85                                     "loop".to_owned(),
  86                                     Applicability::MachineApplicable,
  87                                 )
  88                                 .emit();
  89                         })
  90                     }
  91                 }
  92             }
  93         }
  94     }
  95 }
  96
  97 declare_lint! {
  98     BOX_POINTERS,
  99     Allow,
 100     "use of owned (Box type) heap memory"
 101 }
 102
 103 declare_lint_pass!(BoxPointers => [BOX_POINTERS]);
 104
 105 impl BoxPointers {
 106     fn check_heap_type(&self, cx: &LateContext<'_, '_>, span: Span, ty: Ty<'_>) {
 107         for leaf_ty in ty.walk() {
 108             if leaf_ty.is_box() {
 109                 cx.struct_span_lint(BOX_POINTERS, span, |lint| {
 110                     lint.build(&format!("type uses owned (Box type) pointers: {}", ty)).emit()
 111                 });
 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                         cx.struct_span_lint(NON_SHORTHAND_FIELD_PATTERNS, fieldpat.span, |lint| {
 181                             let mut err = lint
 182                                 .build(&format!("the `{}:` in this pattern is redundant", ident));
 183                             let binding = match binding_annot {
 184                                 hir::BindingAnnotation::Unannotated => None,
 185                                 hir::BindingAnnotation::Mutable => Some("mut"),
 186                                 hir::BindingAnnotation::Ref => Some("ref"),
 187                                 hir::BindingAnnotation::RefMut => Some("ref mut"),
 188                             };
 189                             let ident = if let Some(binding) = binding {
 190                                 format!("{} {}", binding, ident)
 191                             } else {
 192                                 ident.to_string()
 193                             };
 194                             err.span_suggestion(
 195                                 fieldpat.span,
 196                                 "use shorthand field pattern",
 197                                 ident,
 198                                 Applicability::MachineApplicable,
 199                             );
 200                             err.emit();
 201                         });
 202                     }
 203                 }
 204             }
 205         }
 206     }
 207 }
 208
 209 declare_lint! {
 210     UNSAFE_CODE,
 211     Allow,
 212     "usage of `unsafe` code"
 213 }
 214
 215 declare_lint_pass!(UnsafeCode => [UNSAFE_CODE]);
 216
 217 impl UnsafeCode {
 218     fn report_unsafe(
 219         &self,
 220         cx: &EarlyContext<'_>,
 221         span: Span,
 222         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
 223     ) {
 224         // This comes from a macro that has `#[allow_internal_unsafe]`.
 225         if span.allows_unsafe() {
 226             return;
 227         }
 228
 229         cx.struct_span_lint(UNSAFE_CODE, span, decorate);
 230     }
 231 }
 232
 233 impl EarlyLintPass for UnsafeCode {
 234     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 235         if attr.check_name(sym::allow_internal_unsafe) {
 236             self.report_unsafe(cx, attr.span, |lint| {
 237                 lint.build(
 238                     "`allow_internal_unsafe` allows defining \
 239                                                macros using unsafe without triggering \
 240                                                the `unsafe_code` lint at their call site",
 241                 )
 242                 .emit()
 243             });
 244         }
 245     }
 246
 247     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
 248         if let ast::ExprKind::Block(ref blk, _) = e.kind {
 249             // Don't warn about generated blocks; that'll just pollute the output.
 250             if blk.rules == ast::BlockCheckMode::Unsafe(ast::UserProvided) {
 251                 self.report_unsafe(cx, blk.span, |lint| {
 252                     lint.build("usage of an `unsafe` block").emit()
 253                 });
 254             }
 255         }
 256     }
 257
 258     fn check_item(&mut self, cx: &EarlyContext<'_>, it: &ast::Item) {
 259         match it.kind {
 260             ast::ItemKind::Trait(_, ast::Unsafe::Yes(_), ..) => {
 261                 self.report_unsafe(cx, it.span, |lint| {
 262                     lint.build("declaration of an `unsafe` trait").emit()
 263                 })
 264             }
 265
 266             ast::ItemKind::Impl { unsafety: ast::Unsafe::Yes(_), .. } => {
 267                 self.report_unsafe(cx, it.span, |lint| {
 268                     lint.build("implementation of an `unsafe` trait").emit()
 269                 })
 270             }
 271
 272             _ => {}
 273         }
 274     }
 275
 276     fn check_fn(&mut self, cx: &EarlyContext<'_>, fk: FnKind<'_>, span: Span, _: ast::NodeId) {
 277         if let FnKind::Fn(
 278             ctxt,
 279             _,
 280             ast::FnSig { header: ast::FnHeader { unsafety: ast::Unsafe::Yes(_), .. }, .. },
 281             _,
 282             body,
 283         ) = fk
 284         {
 285             let msg = match ctxt {
 286                 FnCtxt::Foreign => return,
 287                 FnCtxt::Free => "declaration of an `unsafe` function",
 288                 FnCtxt::Assoc(_) if body.is_none() => "declaration of an `unsafe` method",
 289                 FnCtxt::Assoc(_) => "implementation of an `unsafe` method",
 290             };
 291             self.report_unsafe(cx, span, |lint| lint.build(msg).emit());
 292         }
 293     }
 294 }
 295
 296 declare_lint! {
 297     pub MISSING_DOCS,
 298     Allow,
 299     "detects missing documentation for public members",
 300     report_in_external_macro
 301 }
 302
 303 pub struct MissingDoc {
 304     /// Stack of whether `#[doc(hidden)]` is set at each level which has lint attributes.
 305     doc_hidden_stack: Vec<bool>,
 306
 307     /// Private traits or trait items that leaked through. Don't check their methods.
 308     private_traits: FxHashSet<hir::HirId>,
 309 }
 310
 311 impl_lint_pass!(MissingDoc => [MISSING_DOCS]);
 312
 313 fn has_doc(attr: &ast::Attribute) -> bool {
 314     if attr.is_doc_comment() {
 315         return true;
 316     }
 317
 318     if !attr.check_name(sym::doc) {
 319         return false;
 320     }
 321
 322     if attr.is_value_str() {
 323         return true;
 324     }
 325
 326     if let Some(list) = attr.meta_item_list() {
 327         for meta in list {
 328             if meta.check_name(sym::include) || meta.check_name(sym::hidden) {
 329                 return true;
 330             }
 331         }
 332     }
 333
 334     false
 335 }
 336
 337 impl MissingDoc {
 338     pub fn new() -> MissingDoc {
 339         MissingDoc { doc_hidden_stack: vec![false], private_traits: FxHashSet::default() }
 340     }
 341
 342     fn doc_hidden(&self) -> bool {
 343         *self.doc_hidden_stack.last().expect("empty doc_hidden_stack")
 344     }
 345
 346     fn check_missing_docs_attrs(
 347         &self,
 348         cx: &LateContext<'_, '_>,
 349         id: Option<hir::HirId>,
 350         attrs: &[ast::Attribute],
 351         sp: Span,
 352         desc: &str,
 353     ) {
 354         // If we're building a test harness, then warning about
 355         // documentation is probably not really relevant right now.
 356         if cx.sess().opts.test {
 357             return;
 358         }
 359
 360         // `#[doc(hidden)]` disables missing_docs check.
 361         if self.doc_hidden() {
 362             return;
 363         }
 364
 365         // Only check publicly-visible items, using the result from the privacy pass.
 366         // It's an option so the crate root can also use this function (it doesn't
 367         // have a `NodeId`).
 368         if let Some(id) = id {
 369             if !cx.access_levels.is_exported(id) {
 370                 return;
 371             }
 372         }
 373
 374         let has_doc = attrs.iter().any(|a| has_doc(a));
 375         if !has_doc {
 376             cx.struct_span_lint(MISSING_DOCS, cx.tcx.sess.source_map().def_span(sp), |lint| {
 377                 lint.build(&format!("missing documentation for {}", desc)).emit()
 378             });
 379         }
 380     }
 381 }
 382
 383 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MissingDoc {
 384     fn enter_lint_attrs(&mut self, _: &LateContext<'_, '_>, attrs: &[ast::Attribute]) {
 385         let doc_hidden = self.doc_hidden()
 386             || attrs.iter().any(|attr| {
 387                 attr.check_name(sym::doc)
 388                     && match attr.meta_item_list() {
 389                         None => false,
 390                         Some(l) => attr::list_contains_name(&l, sym::hidden),
 391                     }
 392             });
 393         self.doc_hidden_stack.push(doc_hidden);
 394     }
 395
 396     fn exit_lint_attrs(&mut self, _: &LateContext<'_, '_>, _attrs: &[ast::Attribute]) {
 397         self.doc_hidden_stack.pop().expect("empty doc_hidden_stack");
 398     }
 399
 400     fn check_crate(&mut self, cx: &LateContext<'_, '_>, krate: &hir::Crate<'_>) {
 401         self.check_missing_docs_attrs(cx, None, &krate.item.attrs, krate.item.span, "crate");
 402
 403         for macro_def in krate.exported_macros {
 404             let has_doc = macro_def.attrs.iter().any(|a| has_doc(a));
 405             if !has_doc {
 406                 cx.struct_span_lint(
 407                     MISSING_DOCS,
 408                     cx.tcx.sess.source_map().def_span(macro_def.span),
 409                     |lint| lint.build("missing documentation for macro").emit(),
 410                 );
 411             }
 412         }
 413     }
 414
 415     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item<'_>) {
 416         match it.kind {
 417             hir::ItemKind::Trait(.., trait_item_refs) => {
 418                 // Issue #11592: traits are always considered exported, even when private.
 419                 if let hir::VisibilityKind::Inherited = it.vis.node {
 420                     self.private_traits.insert(it.hir_id);
 421                     for trait_item_ref in trait_item_refs {
 422                         self.private_traits.insert(trait_item_ref.id.hir_id);
 423                     }
 424                     return;
 425                 }
 426             }
 427             hir::ItemKind::Impl { of_trait: Some(ref trait_ref), items, .. } => {
 428                 // If the trait is private, add the impl items to `private_traits` so they don't get
 429                 // reported for missing docs.
 430                 let real_trait = trait_ref.path.res.def_id();
 431                 if let Some(hir_id) = cx.tcx.hir().as_local_hir_id(real_trait) {
 432                     if let Some(Node::Item(item)) = cx.tcx.hir().find(hir_id) {
 433                         if let hir::VisibilityKind::Inherited = item.vis.node {
 434                             for impl_item_ref in items {
 435                                 self.private_traits.insert(impl_item_ref.id.hir_id);
 436                             }
 437                         }
 438                     }
 439                 }
 440                 return;
 441             }
 442
 443             hir::ItemKind::TyAlias(..)
 444             | hir::ItemKind::Fn(..)
 445             | hir::ItemKind::Mod(..)
 446             | hir::ItemKind::Enum(..)
 447             | hir::ItemKind::Struct(..)
 448             | hir::ItemKind::Union(..)
 449             | hir::ItemKind::Const(..)
 450             | hir::ItemKind::Static(..) => {}
 451
 452             _ => return,
 453         };
 454
 455         let def_id = cx.tcx.hir().local_def_id(it.hir_id);
 456         let (article, desc) = cx.tcx.article_and_description(def_id);
 457
 458         self.check_missing_docs_attrs(
 459             cx,
 460             Some(it.hir_id),
 461             &it.attrs,
 462             it.span,
 463             &format!("{} {}", article, desc),
 464         );
 465     }
 466
 467     fn check_trait_item(&mut self, cx: &LateContext<'_, '_>, trait_item: &hir::TraitItem<'_>) {
 468         if self.private_traits.contains(&trait_item.hir_id) {
 469             return;
 470         }
 471
 472         let def_id = cx.tcx.hir().local_def_id(trait_item.hir_id);
 473         let (article, desc) = cx.tcx.article_and_description(def_id);
 474
 475         self.check_missing_docs_attrs(
 476             cx,
 477             Some(trait_item.hir_id),
 478             &trait_item.attrs,
 479             trait_item.span,
 480             &format!("{} {}", article, desc),
 481         );
 482     }
 483
 484     fn check_impl_item(&mut self, cx: &LateContext<'_, '_>, impl_item: &hir::ImplItem<'_>) {
 485         // If the method is an impl for a trait, don't doc.
 486         if method_context(cx, impl_item.hir_id) == MethodLateContext::TraitImpl {
 487             return;
 488         }
 489
 490         let def_id = cx.tcx.hir().local_def_id(impl_item.hir_id);
 491         let (article, desc) = cx.tcx.article_and_description(def_id);
 492         self.check_missing_docs_attrs(
 493             cx,
 494             Some(impl_item.hir_id),
 495             &impl_item.attrs,
 496             impl_item.span,
 497             &format!("{} {}", article, desc),
 498         );
 499     }
 500
 501     fn check_struct_field(&mut self, cx: &LateContext<'_, '_>, sf: &hir::StructField<'_>) {
 502         if !sf.is_positional() {
 503             self.check_missing_docs_attrs(cx, Some(sf.hir_id), &sf.attrs, sf.span, "a struct field")
 504         }
 505     }
 506
 507     fn check_variant(&mut self, cx: &LateContext<'_, '_>, v: &hir::Variant<'_>) {
 508         self.check_missing_docs_attrs(cx, Some(v.id), &v.attrs, v.span, "a variant");
 509     }
 510 }
 511
 512 declare_lint! {
 513     pub MISSING_COPY_IMPLEMENTATIONS,
 514     Allow,
 515     "detects potentially-forgotten implementations of `Copy`"
 516 }
 517
 518 declare_lint_pass!(MissingCopyImplementations => [MISSING_COPY_IMPLEMENTATIONS]);
 519
 520 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MissingCopyImplementations {
 521     fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &hir::Item<'_>) {
 522         if !cx.access_levels.is_reachable(item.hir_id) {
 523             return;
 524         }
 525         let (def, ty) = match item.kind {
 526             hir::ItemKind::Struct(_, ref ast_generics) => {
 527                 if !ast_generics.params.is_empty() {
 528                     return;
 529                 }
 530                 let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
 531                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 532             }
 533             hir::ItemKind::Union(_, ref ast_generics) => {
 534                 if !ast_generics.params.is_empty() {
 535                     return;
 536                 }
 537                 let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
 538                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 539             }
 540             hir::ItemKind::Enum(_, ref ast_generics) => {
 541                 if !ast_generics.params.is_empty() {
 542                     return;
 543                 }
 544                 let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
 545                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 546             }
 547             _ => return,
 548         };
 549         if def.has_dtor(cx.tcx) {
 550             return;
 551         }
 552         let param_env = ty::ParamEnv::empty();
 553         if ty.is_copy_modulo_regions(cx.tcx, param_env, item.span) {
 554             return;
 555         }
 556         if can_type_implement_copy(cx.tcx, param_env, ty).is_ok() {
 557             cx.struct_span_lint(MISSING_COPY_IMPLEMENTATIONS, item.span, |lint| {
 558                 lint.build(
 559                     "type could implement `Copy`; consider adding `impl \
 560                           Copy`",
 561                 )
 562                 .emit()
 563             })
 564         }
 565     }
 566 }
 567
 568 declare_lint! {
 569     MISSING_DEBUG_IMPLEMENTATIONS,
 570     Allow,
 571     "detects missing implementations of Debug"
 572 }
 573
 574 #[derive(Default)]
 575 pub struct MissingDebugImplementations {
 576     impling_types: Option<HirIdSet>,
 577 }
 578
 579 impl_lint_pass!(MissingDebugImplementations => [MISSING_DEBUG_IMPLEMENTATIONS]);
 580
 581 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MissingDebugImplementations {
 582     fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &hir::Item<'_>) {
 583         if !cx.access_levels.is_reachable(item.hir_id) {
 584             return;
 585         }
 586
 587         match item.kind {
 588             hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) | hir::ItemKind::Enum(..) => {}
 589             _ => return,
 590         }
 591
 592         let debug = match cx.tcx.get_diagnostic_item(sym::debug_trait) {
 593             Some(debug) => debug,
 594             None => return,
 595         };
 596
 597         if self.impling_types.is_none() {
 598             let mut impls = HirIdSet::default();
 599             cx.tcx.for_each_impl(debug, |d| {
 600                 if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() {
 601                     if let Some(hir_id) = cx.tcx.hir().as_local_hir_id(ty_def.did) {
 602                         impls.insert(hir_id);
 603                     }
 604                 }
 605             });
 606
 607             self.impling_types = Some(impls);
 608             debug!("{:?}", self.impling_types);
 609         }
 610
 611         if !self.impling_types.as_ref().unwrap().contains(&item.hir_id) {
 612             cx.struct_span_lint(MISSING_DEBUG_IMPLEMENTATIONS, item.span, |lint| {
 613                 lint.build(&format!(
 614                     "type does not implement `{}`; consider adding `#[derive(Debug)]` \
 615                      or a manual implementation",
 616                     cx.tcx.def_path_str(debug)
 617                 ))
 618                 .emit()
 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                                 cx.struct_span_lint(ANONYMOUS_PARAMETERS, arg.pat.span, |lint| {
 648                                     let ty_snip = cx.sess.source_map().span_to_snippet(arg.ty.span);
 649
 650                                     let (ty_snip, appl) = if let Ok(ref snip) = ty_snip {
 651                                         (snip.as_str(), Applicability::MachineApplicable)
 652                                     } else {
 653                                         ("<type>", Applicability::HasPlaceholders)
 654                                     };
 655
 656                                     lint.build(
 657                                         "anonymous parameters are deprecated and will be \
 658                                      removed in the next edition.",
 659                                     )
 660                                     .span_suggestion(
 661                                         arg.pat.span,
 662                                         "try naming the parameter or explicitly \
 663                                             ignoring it",
 664                                         format!("_: {}", ty_snip),
 665                                         appl,
 666                                     )
 667                                     .emit();
 668                                 })
 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, |lint| {
 703         lint.build(msg)
 704             .span_suggestion_short(
 705                 attr.span,
 706                 suggestion.unwrap_or("remove this attribute"),
 707                 String::new(),
 708                 Applicability::MachineApplicable,
 709             )
 710             .emit();
 711     })
 712 }
 713
 714 impl EarlyLintPass for DeprecatedAttr {
 715     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 716         for &&(n, _, _, ref g) in &self.depr_attrs {
 717             if attr.ident().map(|ident| ident.name) == Some(n) {
 718                 if let &AttributeGate::Gated(
 719                     Stability::Deprecated(link, suggestion),
 720                     ref name,
 721                     ref reason,
 722                     _,
 723                 ) = g
 724                 {
 725                     let msg =
 726                         format!("use of deprecated attribute `{}`: {}. See {}", name, reason, link);
 727                     lint_deprecated_attr(cx, attr, &msg, suggestion);
 728                 }
 729                 return;
 730             }
 731         }
 732         if attr.check_name(sym::no_start) || attr.check_name(sym::crate_id) {
 733             let path_str = pprust::path_to_string(&attr.get_normal_item().path);
 734             let msg = format!("use of deprecated attribute `{}`: no longer used.", path_str);
 735             lint_deprecated_attr(cx, attr, &msg, None);
 736         }
 737     }
 738 }
 739
 740 fn warn_if_doc(cx: &EarlyContext<'_>, node_span: Span, node_kind: &str, attrs: &[ast::Attribute]) {
 741     let mut attrs = attrs.iter().peekable();
 742
 743     // Accumulate a single span for sugared doc comments.
 744     let mut sugared_span: Option<Span> = None;
 745
 746     while let Some(attr) = attrs.next() {
 747         if attr.is_doc_comment() {
 748             sugared_span =
 749                 Some(sugared_span.map_or_else(|| attr.span, |span| span.with_hi(attr.span.hi())));
 750         }
 751
 752         if attrs.peek().map(|next_attr| next_attr.is_doc_comment()).unwrap_or_default() {
 753             continue;
 754         }
 755
 756         let span = sugared_span.take().unwrap_or_else(|| attr.span);
 757
 758         if attr.is_doc_comment() || attr.check_name(sym::doc) {
 759             cx.struct_span_lint(UNUSED_DOC_COMMENTS, span, |lint| {
 760                 let mut err = lint.build("unused doc comment");
 761                 err.span_label(
 762                     node_span,
 763                     format!("rustdoc does not generate documentation for {}", node_kind),
 764                 );
 765                 err.emit();
 766             });
 767         }
 768     }
 769 }
 770
 771 impl EarlyLintPass for UnusedDocComment {
 772     fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &ast::Stmt) {
 773         let kind = match stmt.kind {
 774             ast::StmtKind::Local(..) => "statements",
 775             ast::StmtKind::Item(..) => "inner items",
 776             // expressions will be reported by `check_expr`.
 777             ast::StmtKind::Empty
 778             | ast::StmtKind::Semi(_)
 779             | ast::StmtKind::Expr(_)
 780             | ast::StmtKind::MacCall(_) => return,
 781         };
 782
 783         warn_if_doc(cx, stmt.span, kind, stmt.kind.attrs());
 784     }
 785
 786     fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) {
 787         let arm_span = arm.pat.span.with_hi(arm.body.span.hi());
 788         warn_if_doc(cx, arm_span, "match arms", &arm.attrs);
 789     }
 790
 791     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
 792         warn_if_doc(cx, expr.span, "expressions", &expr.attrs);
 793     }
 794 }
 795
 796 declare_lint! {
 797     NO_MANGLE_CONST_ITEMS,
 798     Deny,
 799     "const items will not have their symbols exported"
 800 }
 801
 802 declare_lint! {
 803     NO_MANGLE_GENERIC_ITEMS,
 804     Warn,
 805     "generic items must be mangled"
 806 }
 807
 808 declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS, NO_MANGLE_GENERIC_ITEMS]);
 809
 810 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for InvalidNoMangleItems {
 811     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item<'_>) {
 812         match it.kind {
 813             hir::ItemKind::Fn(.., ref generics, _) => {
 814                 if let Some(no_mangle_attr) = attr::find_by_name(&it.attrs, sym::no_mangle) {
 815                     for param in generics.params {
 816                         match param.kind {
 817                             GenericParamKind::Lifetime { .. } => {}
 818                             GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
 819                                 cx.struct_span_lint(NO_MANGLE_GENERIC_ITEMS, it.span, |lint| {
 820                                     lint.build(
 821                                         "functions generic over types or consts must be mangled",
 822                                     )
 823                                     .span_suggestion_short(
 824                                         no_mangle_attr.span,
 825                                         "remove this attribute",
 826                                         String::new(),
 827                                         // Use of `#[no_mangle]` suggests FFI intent; correct
 828                                         // fix may be to monomorphize source by hand
 829                                         Applicability::MaybeIncorrect,
 830                                     )
 831                                     .emit();
 832                                 });
 833                                 break;
 834                             }
 835                         }
 836                     }
 837                 }
 838             }
 839             hir::ItemKind::Const(..) => {
 840                 if attr::contains_name(&it.attrs, sym::no_mangle) {
 841                     // Const items do not refer to a particular location in memory, and therefore
 842                     // don't have anything to attach a symbol to
 843                     cx.struct_span_lint(NO_MANGLE_CONST_ITEMS, it.span, |lint| {
 844                         let msg = "const items should never be `#[no_mangle]`";
 845                         let mut err = lint.build(msg);
 846
 847                         // account for "pub const" (#45562)
 848                         let start = cx
 849                             .tcx
 850                             .sess
 851                             .source_map()
 852                             .span_to_snippet(it.span)
 853                             .map(|snippet| snippet.find("const").unwrap_or(0))
 854                             .unwrap_or(0) as u32;
 855                         // `const` is 5 chars
 856                         let const_span = it.span.with_hi(BytePos(it.span.lo().0 + start + 5));
 857                         err.span_suggestion(
 858                             const_span,
 859                             "try a static value",
 860                             "pub static".to_owned(),
 861                             Applicability::MachineApplicable,
 862                         );
 863                         err.emit();
 864                     });
 865                 }
 866             }
 867             _ => {}
 868         }
 869     }
 870 }
 871
 872 declare_lint! {
 873     MUTABLE_TRANSMUTES,
 874     Deny,
 875     "mutating transmuted &mut T from &T may cause undefined behavior"
 876 }
 877
 878 declare_lint_pass!(MutableTransmutes => [MUTABLE_TRANSMUTES]);
 879
 880 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MutableTransmutes {
 881     fn check_expr(&mut self, cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>) {
 882         use rustc_target::spec::abi::Abi::RustIntrinsic;
 883
 884         match get_transmute_from_to(cx, expr).map(|(ty1, ty2)| (&ty1.kind, &ty2.kind)) {
 885             Some((&ty::Ref(_, _, from_mt), &ty::Ref(_, _, to_mt))) => {
 886                 if to_mt == hir::Mutability::Mut && from_mt == hir::Mutability::Not {
 887                     let msg = "mutating transmuted &mut T from &T may cause undefined behavior, \
 888                                consider instead using an UnsafeCell";
 889                     cx.struct_span_lint(MUTABLE_TRANSMUTES, expr.span, |lint| {
 890                         lint.build(msg).emit()
 891                     });
 892                 }
 893             }
 894             _ => (),
 895         }
 896
 897         fn get_transmute_from_to<'a, 'tcx>(
 898             cx: &LateContext<'a, 'tcx>,
 899             expr: &hir::Expr<'_>,
 900         ) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
 901             let def = if let hir::ExprKind::Path(ref qpath) = expr.kind {
 902                 cx.tables.qpath_res(qpath, expr.hir_id)
 903             } else {
 904                 return None;
 905             };
 906             if let Res::Def(DefKind::Fn, did) = def {
 907                 if !def_id_is_transmute(cx, did) {
 908                     return None;
 909                 }
 910                 let sig = cx.tables.node_type(expr.hir_id).fn_sig(cx.tcx);
 911                 let from = sig.inputs().skip_binder()[0];
 912                 let to = *sig.output().skip_binder();
 913                 return Some((from, to));
 914             }
 915             None
 916         }
 917
 918         fn def_id_is_transmute(cx: &LateContext<'_, '_>, def_id: DefId) -> bool {
 919             cx.tcx.fn_sig(def_id).abi() == RustIntrinsic
 920                 && cx.tcx.item_name(def_id) == sym::transmute
 921         }
 922     }
 923 }
 924
 925 declare_lint! {
 926     UNSTABLE_FEATURES,
 927     Allow,
 928     "enabling unstable features (deprecated. do not use)"
 929 }
 930
 931 declare_lint_pass!(
 932     /// Forbids using the `#[feature(...)]` attribute
 933     UnstableFeatures => [UNSTABLE_FEATURES]
 934 );
 935
 936 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnstableFeatures {
 937     fn check_attribute(&mut self, ctx: &LateContext<'_, '_>, attr: &ast::Attribute) {
 938         if attr.check_name(sym::feature) {
 939             if let Some(items) = attr.meta_item_list() {
 940                 for item in items {
 941                     ctx.struct_span_lint(UNSTABLE_FEATURES, item.span(), |lint| {
 942                         lint.build("unstable feature").emit()
 943                     });
 944                 }
 945             }
 946         }
 947     }
 948 }
 949
 950 declare_lint! {
 951     pub UNREACHABLE_PUB,
 952     Allow,
 953     "`pub` items not reachable from crate root"
 954 }
 955
 956 declare_lint_pass!(
 957     /// Lint for items marked `pub` that aren't reachable from other crates.
 958     UnreachablePub => [UNREACHABLE_PUB]
 959 );
 960
 961 impl UnreachablePub {
 962     fn perform_lint(
 963         &self,
 964         cx: &LateContext<'_, '_>,
 965         what: &str,
 966         id: hir::HirId,
 967         vis: &hir::Visibility<'_>,
 968         span: Span,
 969         exportable: bool,
 970     ) {
 971         let mut applicability = Applicability::MachineApplicable;
 972         match vis.node {
 973             hir::VisibilityKind::Public if !cx.access_levels.is_reachable(id) => {
 974                 if span.from_expansion() {
 975                     applicability = Applicability::MaybeIncorrect;
 976                 }
 977                 let def_span = cx.tcx.sess.source_map().def_span(span);
 978                 cx.struct_span_lint(UNREACHABLE_PUB, def_span, |lint| {
 979                     let mut err = lint.build(&format!("unreachable `pub` {}", what));
 980                     let replacement = if cx.tcx.features().crate_visibility_modifier {
 981                         "crate"
 982                     } else {
 983                         "pub(crate)"
 984                     }
 985                     .to_owned();
 986
 987                     err.span_suggestion(
 988                         vis.span,
 989                         "consider restricting its visibility",
 990                         replacement,
 991                         applicability,
 992                     );
 993                     if exportable {
 994                         err.help("or consider exporting it for use by other crates");
 995                     }
 996                     err.emit();
 997                 });
 998             }
 999             _ => {}
1000         }
1001     }
1002 }
1003
1004 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnreachablePub {
1005     fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &hir::Item<'_>) {
1006         self.perform_lint(cx, "item", item.hir_id, &item.vis, item.span, true);
1007     }
1008
1009     fn check_foreign_item(
1010         &mut self,
1011         cx: &LateContext<'_, '_>,
1012         foreign_item: &hir::ForeignItem<'tcx>,
1013     ) {
1014         self.perform_lint(
1015             cx,
1016             "item",
1017             foreign_item.hir_id,
1018             &foreign_item.vis,
1019             foreign_item.span,
1020             true,
1021         );
1022     }
1023
1024     fn check_struct_field(&mut self, cx: &LateContext<'_, '_>, field: &hir::StructField<'_>) {
1025         self.perform_lint(cx, "field", field.hir_id, &field.vis, field.span, false);
1026     }
1027
1028     fn check_impl_item(&mut self, cx: &LateContext<'_, '_>, impl_item: &hir::ImplItem<'_>) {
1029         self.perform_lint(cx, "item", impl_item.hir_id, &impl_item.vis, impl_item.span, false);
1030     }
1031 }
1032
1033 declare_lint! {
1034     TYPE_ALIAS_BOUNDS,
1035     Warn,
1036     "bounds in type aliases are not enforced"
1037 }
1038
1039 declare_lint_pass!(
1040     /// Lint for trait and lifetime bounds in type aliases being mostly ignored.
1041     /// They are relevant when using associated types, but otherwise neither checked
1042     /// at definition site nor enforced at use site.
1043     TypeAliasBounds => [TYPE_ALIAS_BOUNDS]
1044 );
1045
1046 impl TypeAliasBounds {
1047     fn is_type_variable_assoc(qpath: &hir::QPath<'_>) -> bool {
1048         match *qpath {
1049             hir::QPath::TypeRelative(ref ty, _) => {
1050                 // If this is a type variable, we found a `T::Assoc`.
1051                 match ty.kind {
1052                     hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => match path.res {
1053                         Res::Def(DefKind::TyParam, _) => true,
1054                         _ => false,
1055                     },
1056                     _ => false,
1057                 }
1058             }
1059             hir::QPath::Resolved(..) => false,
1060         }
1061     }
1062
1063     fn suggest_changing_assoc_types(ty: &hir::Ty<'_>, err: &mut DiagnosticBuilder<'_>) {
1064         // Access to associates types should use `<T as Bound>::Assoc`, which does not need a
1065         // bound.  Let's see if this type does that.
1066
1067         // We use a HIR visitor to walk the type.
1068         use rustc_hir::intravisit::{self, Visitor};
1069         struct WalkAssocTypes<'a, 'db> {
1070             err: &'a mut DiagnosticBuilder<'db>,
1071         }
1072         impl<'a, 'db, 'v> Visitor<'v> for WalkAssocTypes<'a, 'db> {
1073             type Map = intravisit::ErasedMap<'v>;
1074
1075             fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1076                 intravisit::NestedVisitorMap::None
1077             }
1078
1079             fn visit_qpath(&mut self, qpath: &'v hir::QPath<'v>, id: hir::HirId, span: Span) {
1080                 if TypeAliasBounds::is_type_variable_assoc(qpath) {
1081                     self.err.span_help(
1082                         span,
1083                         "use fully disambiguated paths (i.e., `<T as Trait>::Assoc`) to refer to \
1084                          associated types in type aliases",
1085                     );
1086                 }
1087                 intravisit::walk_qpath(self, qpath, id, span)
1088             }
1089         }
1090
1091         // Let's go for a walk!
1092         let mut visitor = WalkAssocTypes { err };
1093         visitor.visit_ty(ty);
1094     }
1095 }
1096
1097 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeAliasBounds {
1098     fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &hir::Item<'_>) {
1099         let (ty, type_alias_generics) = match item.kind {
1100             hir::ItemKind::TyAlias(ref ty, ref generics) => (&*ty, generics),
1101             _ => return,
1102         };
1103         let mut suggested_changing_assoc_types = false;
1104         // There must not be a where clause
1105         if !type_alias_generics.where_clause.predicates.is_empty() {
1106             cx.lint(
1107                 TYPE_ALIAS_BOUNDS,
1108                 |lint| {
1109                     let mut err = lint.build("where clauses are not enforced in type aliases");
1110                     let spans: Vec<_> = type_alias_generics
1111                         .where_clause
1112                         .predicates
1113                         .iter()
1114                         .map(|pred| pred.span())
1115                         .collect();
1116                     err.set_span(spans);
1117                     err.span_suggestion(
1118                         type_alias_generics.where_clause.span_for_predicates_or_empty_place(),
1119                         "the clause will not be checked when the type alias is used, and should be removed",
1120                         String::new(),
1121                         Applicability::MachineApplicable,
1122                     );
1123                     if !suggested_changing_assoc_types {
1124                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1125                         suggested_changing_assoc_types = true;
1126                     }
1127                     err.emit();
1128                 },
1129             );
1130         }
1131         // The parameters must not have bounds
1132         for param in type_alias_generics.params.iter() {
1133             let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
1134             let suggestion = spans
1135                 .iter()
1136                 .map(|sp| {
1137                     let start = param.span.between(*sp); // Include the `:` in `T: Bound`.
1138                     (start.to(*sp), String::new())
1139                 })
1140                 .collect();
1141             if !spans.is_empty() {
1142                 cx.struct_span_lint(TYPE_ALIAS_BOUNDS, spans, |lint| {
1143                     let mut err =
1144                         lint.build("bounds on generic parameters are not enforced in type aliases");
1145                     let msg = "the bound will not be checked when the type alias is used, \
1146                                    and should be removed";
1147                     err.multipart_suggestion(&msg, suggestion, Applicability::MachineApplicable);
1148                     if !suggested_changing_assoc_types {
1149                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1150                         suggested_changing_assoc_types = true;
1151                     }
1152                     err.emit();
1153                 });
1154             }
1155         }
1156     }
1157 }
1158
1159 declare_lint_pass!(
1160     /// Lint constants that are erroneous.
1161     /// Without this lint, we might not get any diagnostic if the constant is
1162     /// unused within this crate, even though downstream crates can't use it
1163     /// without producing an error.
1164     UnusedBrokenConst => []
1165 );
1166
1167 fn check_const(cx: &LateContext<'_, '_>, body_id: hir::BodyId) {
1168     let def_id = cx.tcx.hir().body_owner_def_id(body_id);
1169     // trigger the query once for all constants since that will already report the errors
1170     // FIXME: Use ensure here
1171     let _ = cx.tcx.const_eval_poly(def_id);
1172 }
1173
1174 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedBrokenConst {
1175     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item<'_>) {
1176         match it.kind {
1177             hir::ItemKind::Const(_, body_id) => {
1178                 check_const(cx, body_id);
1179             }
1180             hir::ItemKind::Static(_, _, body_id) => {
1181                 check_const(cx, body_id);
1182             }
1183             _ => {}
1184         }
1185     }
1186 }
1187
1188 declare_lint! {
1189     TRIVIAL_BOUNDS,
1190     Warn,
1191     "these bounds don't depend on an type parameters"
1192 }
1193
1194 declare_lint_pass!(
1195     /// Lint for trait and lifetime bounds that don't depend on type parameters
1196     /// which either do nothing, or stop the item from being used.
1197     TrivialConstraints => [TRIVIAL_BOUNDS]
1198 );
1199
1200 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TrivialConstraints {
1201     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item<'tcx>) {
1202         use rustc::ty::fold::TypeFoldable;
1203         use rustc::ty::Predicate::*;
1204
1205         if cx.tcx.features().trivial_bounds {
1206             let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1207             let predicates = cx.tcx.predicates_of(def_id);
1208             for &(predicate, span) in predicates.predicates {
1209                 let predicate_kind_name = match predicate {
1210                     Trait(..) => "Trait",
1211                     TypeOutlives(..) |
1212                     RegionOutlives(..) => "Lifetime",
1213
1214                     // Ignore projections, as they can only be global
1215                     // if the trait bound is global
1216                     Projection(..) |
1217                     // Ignore bounds that a user can't type
1218                     WellFormed(..) |
1219                     ObjectSafe(..) |
1220                     ClosureKind(..) |
1221                     Subtype(..) |
1222                     ConstEvaluatable(..) => continue,
1223                 };
1224                 if predicate.is_global() {
1225                     cx.struct_span_lint(TRIVIAL_BOUNDS, span, |lint| {
1226                         lint.build(&format!(
1227                             "{} bound {} does not depend on any type \
1228                                 or lifetime parameters",
1229                             predicate_kind_name, predicate
1230                         ))
1231                         .emit()
1232                     });
1233                 }
1234             }
1235         }
1236     }
1237 }
1238
1239 declare_lint_pass!(
1240     /// Does nothing as a lint pass, but registers some `Lint`s
1241     /// which are used by other parts of the compiler.
1242     SoftLints => [
1243         WHILE_TRUE,
1244         BOX_POINTERS,
1245         NON_SHORTHAND_FIELD_PATTERNS,
1246         UNSAFE_CODE,
1247         MISSING_DOCS,
1248         MISSING_COPY_IMPLEMENTATIONS,
1249         MISSING_DEBUG_IMPLEMENTATIONS,
1250         ANONYMOUS_PARAMETERS,
1251         UNUSED_DOC_COMMENTS,
1252         NO_MANGLE_CONST_ITEMS,
1253         NO_MANGLE_GENERIC_ITEMS,
1254         MUTABLE_TRANSMUTES,
1255         UNSTABLE_FEATURES,
1256         UNREACHABLE_PUB,
1257         TYPE_ALIAS_BOUNDS,
1258         TRIVIAL_BOUNDS
1259     ]
1260 );
1261
1262 declare_lint! {
1263     pub ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
1264     Warn,
1265     "`...` range patterns are deprecated"
1266 }
1267
1268 #[derive(Default)]
1269 pub struct EllipsisInclusiveRangePatterns {
1270     /// If `Some(_)`, suppress all subsequent pattern
1271     /// warnings for better diagnostics.
1272     node_id: Option<ast::NodeId>,
1273 }
1274
1275 impl_lint_pass!(EllipsisInclusiveRangePatterns => [ELLIPSIS_INCLUSIVE_RANGE_PATTERNS]);
1276
1277 impl EarlyLintPass for EllipsisInclusiveRangePatterns {
1278     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &ast::Pat) {
1279         if self.node_id.is_some() {
1280             // Don't recursively warn about patterns inside range endpoints.
1281             return;
1282         }
1283
1284         use self::ast::{PatKind, RangeEnd, RangeSyntax::DotDotDot};
1285
1286         /// If `pat` is a `...` pattern, return the start and end of the range, as well as the span
1287         /// corresponding to the ellipsis.
1288         fn matches_ellipsis_pat(pat: &ast::Pat) -> Option<(Option<&Expr>, &Expr, Span)> {
1289             match &pat.kind {
1290                 PatKind::Range(
1291                     a,
1292                     Some(b),
1293                     Spanned { span, node: RangeEnd::Included(DotDotDot) },
1294                 ) => Some((a.as_deref(), b, *span)),
1295                 _ => None,
1296             }
1297         }
1298
1299         let (parenthesise, endpoints) = match &pat.kind {
1300             PatKind::Ref(subpat, _) => (true, matches_ellipsis_pat(&subpat)),
1301             _ => (false, matches_ellipsis_pat(pat)),
1302         };
1303
1304         if let Some((start, end, join)) = endpoints {
1305             let msg = "`...` range patterns are deprecated";
1306             let suggestion = "use `..=` for an inclusive range";
1307             if parenthesise {
1308                 self.node_id = Some(pat.id);
1309                 cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, pat.span, |lint| {
1310                     let end = expr_to_string(&end);
1311                     let replace = match start {
1312                         Some(start) => format!("&({}..={})", expr_to_string(&start), end),
1313                         None => format!("&(..={})", end),
1314                     };
1315                     lint.build(msg)
1316                         .span_suggestion(
1317                             pat.span,
1318                             suggestion,
1319                             replace,
1320                             Applicability::MachineApplicable,
1321                         )
1322                         .emit();
1323                 });
1324             } else {
1325                 cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, join, |lint| {
1326                     lint.build(msg)
1327                         .span_suggestion_short(
1328                             join,
1329                             suggestion,
1330                             "..=".to_owned(),
1331                             Applicability::MachineApplicable,
1332                         )
1333                         .emit();
1334                 });
1335             };
1336         }
1337     }
1338
1339     fn check_pat_post(&mut self, _cx: &EarlyContext<'_>, pat: &ast::Pat) {
1340         if let Some(node_id) = self.node_id {
1341             if pat.id == node_id {
1342                 self.node_id = None
1343             }
1344         }
1345     }
1346 }
1347
1348 declare_lint! {
1349     UNNAMEABLE_TEST_ITEMS,
1350     Warn,
1351     "detects an item that cannot be named being marked as `#[test_case]`",
1352     report_in_external_macro
1353 }
1354
1355 pub struct UnnameableTestItems {
1356     boundary: hir::HirId, // HirId of the item under which things are not nameable
1357     items_nameable: bool,
1358 }
1359
1360 impl_lint_pass!(UnnameableTestItems => [UNNAMEABLE_TEST_ITEMS]);
1361
1362 impl UnnameableTestItems {
1363     pub fn new() -> Self {
1364         Self { boundary: hir::DUMMY_HIR_ID, items_nameable: true }
1365     }
1366 }
1367
1368 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnnameableTestItems {
1369     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item<'_>) {
1370         if self.items_nameable {
1371             if let hir::ItemKind::Mod(..) = it.kind {
1372             } else {
1373                 self.items_nameable = false;
1374                 self.boundary = it.hir_id;
1375             }
1376             return;
1377         }
1378
1379         if let Some(attr) = attr::find_by_name(&it.attrs, sym::rustc_test_marker) {
1380             cx.struct_span_lint(UNNAMEABLE_TEST_ITEMS, attr.span, |lint| {
1381                 lint.build("cannot test inner items").emit()
1382             });
1383         }
1384     }
1385
1386     fn check_item_post(&mut self, _cx: &LateContext<'_, '_>, it: &hir::Item<'_>) {
1387         if !self.items_nameable && self.boundary == it.hir_id {
1388             self.items_nameable = true;
1389         }
1390     }
1391 }
1392
1393 declare_lint! {
1394     pub KEYWORD_IDENTS,
1395     Allow,
1396     "detects edition keywords being used as an identifier",
1397     @future_incompatible = FutureIncompatibleInfo {
1398         reference: "issue #49716 <https://github.com/rust-lang/rust/issues/49716>",
1399         edition: Some(Edition::Edition2018),
1400     };
1401 }
1402
1403 declare_lint_pass!(
1404     /// Check for uses of edition keywords used as an identifier.
1405     KeywordIdents => [KEYWORD_IDENTS]
1406 );
1407
1408 struct UnderMacro(bool);
1409
1410 impl KeywordIdents {
1411     fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: TokenStream) {
1412         for tt in tokens.into_trees() {
1413             match tt {
1414                 // Only report non-raw idents.
1415                 TokenTree::Token(token) => {
1416                     if let Some((ident, false)) = token.ident() {
1417                         self.check_ident_token(cx, UnderMacro(true), ident);
1418                     }
1419                 }
1420                 TokenTree::Delimited(_, _, tts) => self.check_tokens(cx, tts),
1421             }
1422         }
1423     }
1424
1425     fn check_ident_token(
1426         &mut self,
1427         cx: &EarlyContext<'_>,
1428         UnderMacro(under_macro): UnderMacro,
1429         ident: ast::Ident,
1430     ) {
1431         let next_edition = match cx.sess.edition() {
1432             Edition::Edition2015 => {
1433                 match ident.name {
1434                     kw::Async | kw::Await | kw::Try => Edition::Edition2018,
1435
1436                     // rust-lang/rust#56327: Conservatively do not
1437                     // attempt to report occurrences of `dyn` within
1438                     // macro definitions or invocations, because `dyn`
1439                     // can legitimately occur as a contextual keyword
1440                     // in 2015 code denoting its 2018 meaning, and we
1441                     // do not want rustfix to inject bugs into working
1442                     // code by rewriting such occurrences.
1443                     //
1444                     // But if we see `dyn` outside of a macro, we know
1445                     // its precise role in the parsed AST and thus are
1446                     // assured this is truly an attempt to use it as
1447                     // an identifier.
1448                     kw::Dyn if !under_macro => Edition::Edition2018,
1449
1450                     _ => return,
1451                 }
1452             }
1453
1454             // There are no new keywords yet for the 2018 edition and beyond.
1455             _ => return,
1456         };
1457
1458         // Don't lint `r#foo`.
1459         if cx.sess.parse_sess.raw_identifier_spans.borrow().contains(&ident.span) {
1460             return;
1461         }
1462
1463         cx.struct_span_lint(KEYWORD_IDENTS, ident.span, |lint| {
1464             lint.build(&format!("`{}` is a keyword in the {} edition", ident, next_edition))
1465                 .span_suggestion(
1466                     ident.span,
1467                     "you can use a raw identifier to stay compatible",
1468                     format!("r#{}", ident),
1469                     Applicability::MachineApplicable,
1470                 )
1471                 .emit()
1472         });
1473     }
1474 }
1475
1476 impl EarlyLintPass for KeywordIdents {
1477     fn check_mac_def(&mut self, cx: &EarlyContext<'_>, mac_def: &ast::MacroDef, _id: ast::NodeId) {
1478         self.check_tokens(cx, mac_def.body.inner_tokens());
1479     }
1480     fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::MacCall) {
1481         self.check_tokens(cx, mac.args.inner_tokens());
1482     }
1483     fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: ast::Ident) {
1484         self.check_ident_token(cx, UnderMacro(false), ident);
1485     }
1486 }
1487
1488 declare_lint_pass!(ExplicitOutlivesRequirements => [EXPLICIT_OUTLIVES_REQUIREMENTS]);
1489
1490 impl ExplicitOutlivesRequirements {
1491     fn lifetimes_outliving_lifetime<'tcx>(
1492         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
1493         index: u32,
1494     ) -> Vec<ty::Region<'tcx>> {
1495         inferred_outlives
1496             .iter()
1497             .filter_map(|(pred, _)| match pred {
1498                 ty::Predicate::RegionOutlives(outlives) => {
1499                     let outlives = outlives.skip_binder();
1500                     match outlives.0 {
1501                         ty::ReEarlyBound(ebr) if ebr.index == index => Some(outlives.1),
1502                         _ => None,
1503                     }
1504                 }
1505                 _ => None,
1506             })
1507             .collect()
1508     }
1509
1510     fn lifetimes_outliving_type<'tcx>(
1511         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
1512         index: u32,
1513     ) -> Vec<ty::Region<'tcx>> {
1514         inferred_outlives
1515             .iter()
1516             .filter_map(|(pred, _)| match pred {
1517                 ty::Predicate::TypeOutlives(outlives) => {
1518                     let outlives = outlives.skip_binder();
1519                     outlives.0.is_param(index).then_some(outlives.1)
1520                 }
1521                 _ => None,
1522             })
1523             .collect()
1524     }
1525
1526     fn collect_outlived_lifetimes<'tcx>(
1527         &self,
1528         param: &'tcx hir::GenericParam<'tcx>,
1529         tcx: TyCtxt<'tcx>,
1530         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
1531         ty_generics: &'tcx ty::Generics,
1532     ) -> Vec<ty::Region<'tcx>> {
1533         let index = ty_generics.param_def_id_to_index[&tcx.hir().local_def_id(param.hir_id)];
1534
1535         match param.kind {
1536             hir::GenericParamKind::Lifetime { .. } => {
1537                 Self::lifetimes_outliving_lifetime(inferred_outlives, index)
1538             }
1539             hir::GenericParamKind::Type { .. } => {
1540                 Self::lifetimes_outliving_type(inferred_outlives, index)
1541             }
1542             hir::GenericParamKind::Const { .. } => Vec::new(),
1543         }
1544     }
1545
1546     fn collect_outlives_bound_spans<'tcx>(
1547         &self,
1548         tcx: TyCtxt<'tcx>,
1549         bounds: &hir::GenericBounds<'_>,
1550         inferred_outlives: &[ty::Region<'tcx>],
1551         infer_static: bool,
1552     ) -> Vec<(usize, Span)> {
1553         use rustc::middle::resolve_lifetime::Region;
1554
1555         bounds
1556             .iter()
1557             .enumerate()
1558             .filter_map(|(i, bound)| {
1559                 if let hir::GenericBound::Outlives(lifetime) = bound {
1560                     let is_inferred = match tcx.named_region(lifetime.hir_id) {
1561                         Some(Region::Static) if infer_static => inferred_outlives
1562                             .iter()
1563                             .any(|r| if let ty::ReStatic = r { true } else { false }),
1564                         Some(Region::EarlyBound(index, ..)) => inferred_outlives.iter().any(|r| {
1565                             if let ty::ReEarlyBound(ebr) = r { ebr.index == index } else { false }
1566                         }),
1567                         _ => false,
1568                     };
1569                     is_inferred.then_some((i, bound.span()))
1570                 } else {
1571                     None
1572                 }
1573             })
1574             .collect()
1575     }
1576
1577     fn consolidate_outlives_bound_spans(
1578         &self,
1579         lo: Span,
1580         bounds: &hir::GenericBounds<'_>,
1581         bound_spans: Vec<(usize, Span)>,
1582     ) -> Vec<Span> {
1583         if bounds.is_empty() {
1584             return Vec::new();
1585         }
1586         if bound_spans.len() == bounds.len() {
1587             let (_, last_bound_span) = bound_spans[bound_spans.len() - 1];
1588             // If all bounds are inferable, we want to delete the colon, so
1589             // start from just after the parameter (span passed as argument)
1590             vec![lo.to(last_bound_span)]
1591         } else {
1592             let mut merged = Vec::new();
1593             let mut last_merged_i = None;
1594
1595             let mut from_start = true;
1596             for (i, bound_span) in bound_spans {
1597                 match last_merged_i {
1598                     // If the first bound is inferable, our span should also eat the leading `+`.
1599                     None if i == 0 => {
1600                         merged.push(bound_span.to(bounds[1].span().shrink_to_lo()));
1601                         last_merged_i = Some(0);
1602                     }
1603                     // If consecutive bounds are inferable, merge their spans
1604                     Some(h) if i == h + 1 => {
1605                         if let Some(tail) = merged.last_mut() {
1606                             // Also eat the trailing `+` if the first
1607                             // more-than-one bound is inferable
1608                             let to_span = if from_start && i < bounds.len() {
1609                                 bounds[i + 1].span().shrink_to_lo()
1610                             } else {
1611                                 bound_span
1612                             };
1613                             *tail = tail.to(to_span);
1614                             last_merged_i = Some(i);
1615                         } else {
1616                             bug!("another bound-span visited earlier");
1617                         }
1618                     }
1619                     _ => {
1620                         // When we find a non-inferable bound, subsequent inferable bounds
1621                         // won't be consecutive from the start (and we'll eat the leading
1622                         // `+` rather than the trailing one)
1623                         from_start = false;
1624                         merged.push(bounds[i - 1].span().shrink_to_hi().to(bound_span));
1625                         last_merged_i = Some(i);
1626                     }
1627                 }
1628             }
1629             merged
1630         }
1631     }
1632 }
1633
1634 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ExplicitOutlivesRequirements {
1635     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item<'_>) {
1636         use rustc::middle::resolve_lifetime::Region;
1637
1638         let infer_static = cx.tcx.features().infer_static_outlives_requirements;
1639         let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1640         if let hir::ItemKind::Struct(_, ref hir_generics)
1641         | hir::ItemKind::Enum(_, ref hir_generics)
1642         | hir::ItemKind::Union(_, ref hir_generics) = item.kind
1643         {
1644             let inferred_outlives = cx.tcx.inferred_outlives_of(def_id);
1645             if inferred_outlives.is_empty() {
1646                 return;
1647             }
1648
1649             let ty_generics = cx.tcx.generics_of(def_id);
1650
1651             let mut bound_count = 0;
1652             let mut lint_spans = Vec::new();
1653
1654             for param in hir_generics.params {
1655                 let has_lifetime_bounds = param.bounds.iter().any(|bound| {
1656                     if let hir::GenericBound::Outlives(_) = bound { true } else { false }
1657                 });
1658                 if !has_lifetime_bounds {
1659                     continue;
1660                 }
1661
1662                 let relevant_lifetimes =
1663                     self.collect_outlived_lifetimes(param, cx.tcx, inferred_outlives, ty_generics);
1664                 if relevant_lifetimes.is_empty() {
1665                     continue;
1666                 }
1667
1668                 let bound_spans = self.collect_outlives_bound_spans(
1669                     cx.tcx,
1670                     &param.bounds,
1671                     &relevant_lifetimes,
1672                     infer_static,
1673                 );
1674                 bound_count += bound_spans.len();
1675                 lint_spans.extend(self.consolidate_outlives_bound_spans(
1676                     param.span.shrink_to_hi(),
1677                     &param.bounds,
1678                     bound_spans,
1679                 ));
1680             }
1681
1682             let mut where_lint_spans = Vec::new();
1683             let mut dropped_predicate_count = 0;
1684             let num_predicates = hir_generics.where_clause.predicates.len();
1685             for (i, where_predicate) in hir_generics.where_clause.predicates.iter().enumerate() {
1686                 let (relevant_lifetimes, bounds, span) = match where_predicate {
1687                     hir::WherePredicate::RegionPredicate(predicate) => {
1688                         if let Some(Region::EarlyBound(index, ..)) =
1689                             cx.tcx.named_region(predicate.lifetime.hir_id)
1690                         {
1691                             (
1692                                 Self::lifetimes_outliving_lifetime(inferred_outlives, index),
1693                                 &predicate.bounds,
1694                                 predicate.span,
1695                             )
1696                         } else {
1697                             continue;
1698                         }
1699                     }
1700                     hir::WherePredicate::BoundPredicate(predicate) => {
1701                         // FIXME we can also infer bounds on associated types,
1702                         // and should check for them here.
1703                         match predicate.bounded_ty.kind {
1704                             hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
1705                                 if let Res::Def(DefKind::TyParam, def_id) = path.res {
1706                                     let index = ty_generics.param_def_id_to_index[&def_id];
1707                                     (
1708                                         Self::lifetimes_outliving_type(inferred_outlives, index),
1709                                         &predicate.bounds,
1710                                         predicate.span,
1711                                     )
1712                                 } else {
1713                                     continue;
1714                                 }
1715                             }
1716                             _ => {
1717                                 continue;
1718                             }
1719                         }
1720                     }
1721                     _ => continue,
1722                 };
1723                 if relevant_lifetimes.is_empty() {
1724                     continue;
1725                 }
1726
1727                 let bound_spans = self.collect_outlives_bound_spans(
1728                     cx.tcx,
1729                     bounds,
1730                     &relevant_lifetimes,
1731                     infer_static,
1732                 );
1733                 bound_count += bound_spans.len();
1734
1735                 let drop_predicate = bound_spans.len() == bounds.len();
1736                 if drop_predicate {
1737                     dropped_predicate_count += 1;
1738                 }
1739
1740                 // If all the bounds on a predicate were inferable and there are
1741                 // further predicates, we want to eat the trailing comma.
1742                 if drop_predicate && i + 1 < num_predicates {
1743                     let next_predicate_span = hir_generics.where_clause.predicates[i + 1].span();
1744                     where_lint_spans.push(span.to(next_predicate_span.shrink_to_lo()));
1745                 } else {
1746                     where_lint_spans.extend(self.consolidate_outlives_bound_spans(
1747                         span.shrink_to_lo(),
1748                         bounds,
1749                         bound_spans,
1750                     ));
1751                 }
1752             }
1753
1754             // If all predicates are inferable, drop the entire clause
1755             // (including the `where`)
1756             if num_predicates > 0 && dropped_predicate_count == num_predicates {
1757                 let where_span = hir_generics
1758                     .where_clause
1759                     .span()
1760                     .expect("span of (nonempty) where clause should exist");
1761                 // Extend the where clause back to the closing `>` of the
1762                 // generics, except for tuple struct, which have the `where`
1763                 // after the fields of the struct.
1764                 let full_where_span =
1765                     if let hir::ItemKind::Struct(hir::VariantData::Tuple(..), _) = item.kind {
1766                         where_span
1767                     } else {
1768                         hir_generics.span.shrink_to_hi().to(where_span)
1769                     };
1770                 lint_spans.push(full_where_span);
1771             } else {
1772                 lint_spans.extend(where_lint_spans);
1773             }
1774
1775             if !lint_spans.is_empty() {
1776                 cx.struct_span_lint(EXPLICIT_OUTLIVES_REQUIREMENTS, lint_spans.clone(), |lint| {
1777                     lint.build("outlives requirements can be inferred")
1778                         .multipart_suggestion(
1779                             if bound_count == 1 {
1780                                 "remove this bound"
1781                             } else {
1782                                 "remove these bounds"
1783                             },
1784                             lint_spans
1785                                 .into_iter()
1786                                 .map(|span| (span, "".to_owned()))
1787                                 .collect::<Vec<_>>(),
1788                             Applicability::MachineApplicable,
1789                         )
1790                         .emit();
1791                 });
1792             }
1793         }
1794     }
1795 }
1796
1797 declare_lint! {
1798     pub INCOMPLETE_FEATURES,
1799     Warn,
1800     "incomplete features that may function improperly in some or all cases"
1801 }
1802
1803 declare_lint_pass!(
1804     /// Check for used feature gates in `INCOMPLETE_FEATURES` in `librustc_feature/active.rs`.
1805     IncompleteFeatures => [INCOMPLETE_FEATURES]
1806 );
1807
1808 impl EarlyLintPass for IncompleteFeatures {
1809     fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
1810         let features = cx.sess.features_untracked();
1811         features
1812             .declared_lang_features
1813             .iter()
1814             .map(|(name, span, _)| (name, span))
1815             .chain(features.declared_lib_features.iter().map(|(name, span)| (name, span)))
1816             .filter(|(name, _)| rustc_feature::INCOMPLETE_FEATURES.iter().any(|f| name == &f))
1817             .for_each(|(name, &span)| {
1818                 cx.struct_span_lint(INCOMPLETE_FEATURES, span, |lint| {
1819                     lint.build(&format!(
1820                         "the feature `{}` is incomplete and may cause the compiler to crash",
1821                         name,
1822                     ))
1823                     .emit()
1824                 })
1825             });
1826     }
1827 }
1828
1829 declare_lint! {
1830     pub INVALID_VALUE,
1831     Warn,
1832     "an invalid value is being created (such as a NULL reference)"
1833 }
1834
1835 declare_lint_pass!(InvalidValue => [INVALID_VALUE]);
1836
1837 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for InvalidValue {
1838     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &hir::Expr<'_>) {
1839         #[derive(Debug, Copy, Clone, PartialEq)]
1840         enum InitKind {
1841             Zeroed,
1842             Uninit,
1843         };
1844
1845         /// Information about why a type cannot be initialized this way.
1846         /// Contains an error message and optionally a span to point at.
1847         type InitError = (String, Option<Span>);
1848
1849         /// Test if this constant is all-0.
1850         fn is_zero(expr: &hir::Expr<'_>) -> bool {
1851             use hir::ExprKind::*;
1852             use rustc_ast::ast::LitKind::*;
1853             match &expr.kind {
1854                 Lit(lit) => {
1855                     if let Int(i, _) = lit.node {
1856                         i == 0
1857                     } else {
1858                         false
1859                     }
1860                 }
1861                 Tup(tup) => tup.iter().all(is_zero),
1862                 _ => false,
1863             }
1864         }
1865
1866         /// Determine if this expression is a "dangerous initialization".
1867         fn is_dangerous_init(cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>) -> Option<InitKind> {
1868             // `transmute` is inside an anonymous module (the `extern` block?);
1869             // `Invalid` represents the empty string and matches that.
1870             // FIXME(#66075): use diagnostic items.  Somehow, that does not seem to work
1871             // on intrinsics right now.
1872             const TRANSMUTE_PATH: &[Symbol] =
1873                 &[sym::core, sym::intrinsics, kw::Invalid, sym::transmute];
1874
1875             if let hir::ExprKind::Call(ref path_expr, ref args) = expr.kind {
1876                 // Find calls to `mem::{uninitialized,zeroed}` methods.
1877                 if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
1878                     let def_id = cx.tables.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
1879
1880                     if cx.tcx.is_diagnostic_item(sym::mem_zeroed, def_id) {
1881                         return Some(InitKind::Zeroed);
1882                     } else if cx.tcx.is_diagnostic_item(sym::mem_uninitialized, def_id) {
1883                         return Some(InitKind::Uninit);
1884                     } else if cx.match_def_path(def_id, TRANSMUTE_PATH) {
1885                         if is_zero(&args[0]) {
1886                             return Some(InitKind::Zeroed);
1887                         }
1888                     }
1889                 }
1890             } else if let hir::ExprKind::MethodCall(_, _, ref args) = expr.kind {
1891                 // Find problematic calls to `MaybeUninit::assume_init`.
1892                 let def_id = cx.tables.type_dependent_def_id(expr.hir_id)?;
1893                 if cx.tcx.is_diagnostic_item(sym::assume_init, def_id) {
1894                     // This is a call to *some* method named `assume_init`.
1895                     // See if the `self` parameter is one of the dangerous constructors.
1896                     if let hir::ExprKind::Call(ref path_expr, _) = args[0].kind {
1897                         if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
1898                             let def_id =
1899                                 cx.tables.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
1900
1901                             if cx.tcx.is_diagnostic_item(sym::maybe_uninit_zeroed, def_id) {
1902                                 return Some(InitKind::Zeroed);
1903                             } else if cx.tcx.is_diagnostic_item(sym::maybe_uninit_uninit, def_id) {
1904                                 return Some(InitKind::Uninit);
1905                             }
1906                         }
1907                     }
1908                 }
1909             }
1910
1911             None
1912         }
1913
1914         /// Return `Some` only if we are sure this type does *not*
1915         /// allow zero initialization.
1916         fn ty_find_init_error<'tcx>(
1917             tcx: TyCtxt<'tcx>,
1918             ty: Ty<'tcx>,
1919             init: InitKind,
1920         ) -> Option<InitError> {
1921             use rustc::ty::TyKind::*;
1922             match ty.kind {
1923                 // Primitive types that don't like 0 as a value.
1924                 Ref(..) => Some(("references must be non-null".to_string(), None)),
1925                 Adt(..) if ty.is_box() => Some(("`Box` must be non-null".to_string(), None)),
1926                 FnPtr(..) => Some(("function pointers must be non-null".to_string(), None)),
1927                 Never => Some(("the `!` type has no valid value".to_string(), None)),
1928                 RawPtr(tm) if matches!(tm.ty.kind, Dynamic(..)) =>
1929                 // raw ptr to dyn Trait
1930                 {
1931                     Some(("the vtable of a wide raw pointer must be non-null".to_string(), None))
1932                 }
1933                 // Primitive types with other constraints.
1934                 Bool if init == InitKind::Uninit => {
1935                     Some(("booleans must be either `true` or `false`".to_string(), None))
1936                 }
1937                 Char if init == InitKind::Uninit => {
1938                     Some(("characters must be a valid Unicode codepoint".to_string(), None))
1939                 }
1940                 // Recurse and checks for some compound types.
1941                 Adt(adt_def, substs) if !adt_def.is_union() => {
1942                     // First check f this ADT has a layout attribute (like `NonNull` and friends).
1943                     use std::ops::Bound;
1944                     match tcx.layout_scalar_valid_range(adt_def.did) {
1945                         // We exploit here that `layout_scalar_valid_range` will never
1946                         // return `Bound::Excluded`.  (And we have tests checking that we
1947                         // handle the attribute correctly.)
1948                         (Bound::Included(lo), _) if lo > 0 => {
1949                             return Some((format!("`{}` must be non-null", ty), None));
1950                         }
1951                         (Bound::Included(_), _) | (_, Bound::Included(_))
1952                             if init == InitKind::Uninit =>
1953                         {
1954                             return Some((
1955                                 format!(
1956                                     "`{}` must be initialized inside its custom valid range",
1957                                     ty,
1958                                 ),
1959                                 None,
1960                             ));
1961                         }
1962                         _ => {}
1963                     }
1964                     // Now, recurse.
1965                     match adt_def.variants.len() {
1966                         0 => Some(("enums with no variants have no valid value".to_string(), None)),
1967                         1 => {
1968                             // Struct, or enum with exactly one variant.
1969                             // Proceed recursively, check all fields.
1970                             let variant = &adt_def.variants[VariantIdx::from_u32(0)];
1971                             variant.fields.iter().find_map(|field| {
1972                                 ty_find_init_error(tcx, field.ty(tcx, substs), init).map(
1973                                     |(mut msg, span)| {
1974                                         if span.is_none() {
1975                                             // Point to this field, should be helpful for figuring
1976                                             // out where the source of the error is.
1977                                             let span = tcx.def_span(field.did);
1978                                             write!(
1979                                                 &mut msg,
1980                                                 " (in this {} field)",
1981                                                 adt_def.descr()
1982                                             )
1983                                             .unwrap();
1984                                             (msg, Some(span))
1985                                         } else {
1986                                             // Just forward.
1987                                             (msg, span)
1988                                         }
1989                                     },
1990                                 )
1991                             })
1992                         }
1993                         // Multi-variant enums are tricky: if all but one variant are
1994                         // uninhabited, we might actually do layout like for a single-variant
1995                         // enum, and then even leaving them uninitialized could be okay.
1996                         _ => None, // Conservative fallback for multi-variant enum.
1997                     }
1998                 }
1999                 Tuple(..) => {
2000                     // Proceed recursively, check all fields.
2001                     ty.tuple_fields().find_map(|field| ty_find_init_error(tcx, field, init))
2002                 }
2003                 // Conservative fallback.
2004                 _ => None,
2005             }
2006         }
2007
2008         if let Some(init) = is_dangerous_init(cx, expr) {
2009             // This conjures an instance of a type out of nothing,
2010             // using zeroed or uninitialized memory.
2011             // We are extremely conservative with what we warn about.
2012             let conjured_ty = cx.tables.expr_ty(expr);
2013             if let Some((msg, span)) = ty_find_init_error(cx.tcx, conjured_ty, init) {
2014                 cx.struct_span_lint(INVALID_VALUE, expr.span, |lint| {
2015                     let mut err = lint.build(&format!(
2016                         "the type `{}` does not permit {}",
2017                         conjured_ty,
2018                         match init {
2019                             InitKind::Zeroed => "zero-initialization",
2020                             InitKind::Uninit => "being left uninitialized",
2021                         },
2022                     ));
2023                     err.span_label(expr.span, "this code causes undefined behavior when executed");
2024                     err.span_label(
2025                         expr.span,
2026                         "help: use `MaybeUninit<T>` instead, \
2027                             and only call `assume_init` after initialization is done",
2028                     );
2029                     if let Some(span) = span {
2030                         err.span_note(span, &msg);
2031                     } else {
2032                         err.note(&msg);
2033                     }
2034                     err.emit();
2035                 });
2036             }
2037         }
2038     }
2039 }