compiler/rustc_lint/src/builtin.rs

   1 //! Lints in the Rust compiler.
   2 //!
   3 //! This contains lints which can feasibly be implemented as their own
   4 //! AST visitor. Also see `rustc_session::lint::builtin`, which contains the
   5 //! definitions of lints that are emitted directly inside the main compiler.
   6 //!
   7 //! To add a new lint to rustc, declare it here using `declare_lint!()`.
   8 //! Then add code to emit the new lint in the appropriate circumstances.
   9 //! You can do that in an existing `LintPass` if it makes sense, or in a
  10 //! new `LintPass`, or using `Session::add_lint` elsewhere in the
  11 //! compiler. Only do the latter if the check can't be written cleanly as a
  12 //! `LintPass` (also, note that such lints will need to be defined in
  13 //! `rustc_session::lint::builtin`, not here).
  14 //!
  15 //! If you define a new `EarlyLintPass`, you will also need to add it to the
  16 //! `add_early_builtin!` or `add_early_builtin_with_new!` invocation in
  17 //! `lib.rs`. Use the former for unit-like structs and the latter for structs
  18 //! with a `pub fn new()`.
  19 //!
  20 //! If you define a new `LateLintPass`, you will also need to add it to the
  21 //! `late_lint_methods!` invocation in `lib.rs`.
  22
  23 use crate::{
  24     types::{transparent_newtype_field, CItemKind},
  25     EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext,
  26 };
  27 use rustc_ast::attr::{self, HasAttrs};
  28 use rustc_ast::tokenstream::{TokenStream, TokenTree};
  29 use rustc_ast::visit::{FnCtxt, FnKind};
  30 use rustc_ast::{self as ast, *};
  31 use rustc_ast_pretty::pprust::{self, expr_to_string};
  32 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
  33 use rustc_data_structures::stack::ensure_sufficient_stack;
  34 use rustc_errors::{Applicability, DiagnosticBuilder, DiagnosticStyledString};
  35 use rustc_feature::{deprecated_attributes, AttributeGate, AttributeTemplate, AttributeType};
  36 use rustc_feature::{GateIssue, Stability};
  37 use rustc_hir as hir;
  38 use rustc_hir::def::{DefKind, Res};
  39 use rustc_hir::def_id::DefId;
  40 use rustc_hir::{ForeignItemKind, GenericParamKind, PatKind};
  41 use rustc_hir::{HirId, HirIdSet, Node};
  42 use rustc_index::vec::Idx;
  43 use rustc_middle::lint::LintDiagnosticBuilder;
  44 use rustc_middle::ty::print::with_no_trimmed_paths;
  45 use rustc_middle::ty::subst::{GenericArgKind, Subst};
  46 use rustc_middle::ty::Instance;
  47 use rustc_middle::ty::{self, layout::LayoutError, Ty, TyCtxt};
  48 use rustc_session::Session;
  49 use rustc_span::edition::Edition;
  50 use rustc_span::source_map::Spanned;
  51 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  52 use rustc_span::{BytePos, Span};
  53 use rustc_target::abi::{LayoutOf, VariantIdx};
  54 use rustc_trait_selection::traits::misc::can_type_implement_copy;
  55
  56 use crate::nonstandard_style::{method_context, MethodLateContext};
  57
  58 use std::fmt::Write;
  59 use tracing::{debug, trace};
  60
  61 // hardwired lints from librustc_middle
  62 pub use rustc_session::lint::builtin::*;
  63
  64 declare_lint! {
  65     /// The `while_true` lint detects `while true { }`.
  66     ///
  67     /// ### Example
  68     ///
  69     /// ```rust,no_run
  70     /// while true {
  71     ///
  72     /// }
  73     /// ```
  74     ///
  75     /// {{produces}}
  76     ///
  77     /// ### Explanation
  78     ///
  79     /// `while true` should be replaced with `loop`. A `loop` expression is
  80     /// the preferred way to write an infinite loop because it more directly
  81     /// expresses the intent of the loop.
  82     WHILE_TRUE,
  83     Warn,
  84     "suggest using `loop { }` instead of `while true { }`"
  85 }
  86
  87 declare_lint_pass!(WhileTrue => [WHILE_TRUE]);
  88
  89 /// Traverse through any amount of parenthesis and return the first non-parens expression.
  90 fn pierce_parens(mut expr: &ast::Expr) -> &ast::Expr {
  91     while let ast::ExprKind::Paren(sub) = &expr.kind {
  92         expr = sub;
  93     }
  94     expr
  95 }
  96
  97 impl EarlyLintPass for WhileTrue {
  98     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
  99         if let ast::ExprKind::While(cond, _, label) = &e.kind {
 100             if let ast::ExprKind::Lit(ref lit) = pierce_parens(cond).kind {
 101                 if let ast::LitKind::Bool(true) = lit.kind {
 102                     if !lit.span.from_expansion() {
 103                         let msg = "denote infinite loops with `loop { ... }`";
 104                         let condition_span = e.span.with_hi(cond.span.hi());
 105                         cx.struct_span_lint(WHILE_TRUE, condition_span, |lint| {
 106                             lint.build(msg)
 107                                 .span_suggestion_short(
 108                                     condition_span,
 109                                     "use `loop`",
 110                                     format!(
 111                                         "{}loop",
 112                                         label.map_or_else(String::new, |label| format!(
 113                                             "{}: ",
 114                                             label.ident,
 115                                         ))
 116                                     ),
 117                                     Applicability::MachineApplicable,
 118                                 )
 119                                 .emit();
 120                         })
 121                     }
 122                 }
 123             }
 124         }
 125     }
 126 }
 127
 128 declare_lint! {
 129     /// The `box_pointers` lints use of the Box type.
 130     ///
 131     /// ### Example
 132     ///
 133     /// ```rust,compile_fail
 134     /// #![deny(box_pointers)]
 135     /// struct Foo {
 136     ///     x: Box<isize>,
 137     /// }
 138     /// ```
 139     ///
 140     /// {{produces}}
 141     ///
 142     /// ### Explanation
 143     ///
 144     /// This lint is mostly historical, and not particularly useful. `Box<T>`
 145     /// used to be built into the language, and the only way to do heap
 146     /// allocation. Today's Rust can call into other allocators, etc.
 147     BOX_POINTERS,
 148     Allow,
 149     "use of owned (Box type) heap memory"
 150 }
 151
 152 declare_lint_pass!(BoxPointers => [BOX_POINTERS]);
 153
 154 impl BoxPointers {
 155     fn check_heap_type(&self, cx: &LateContext<'_>, span: Span, ty: Ty<'_>) {
 156         for leaf in ty.walk() {
 157             if let GenericArgKind::Type(leaf_ty) = leaf.unpack() {
 158                 if leaf_ty.is_box() {
 159                     cx.struct_span_lint(BOX_POINTERS, span, |lint| {
 160                         lint.build(&format!("type uses owned (Box type) pointers: {}", ty)).emit()
 161                     });
 162                 }
 163             }
 164         }
 165     }
 166 }
 167
 168 impl<'tcx> LateLintPass<'tcx> for BoxPointers {
 169     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 170         match it.kind {
 171             hir::ItemKind::Fn(..)
 172             | hir::ItemKind::TyAlias(..)
 173             | hir::ItemKind::Enum(..)
 174             | hir::ItemKind::Struct(..)
 175             | hir::ItemKind::Union(..) => {
 176                 let def_id = cx.tcx.hir().local_def_id(it.hir_id);
 177                 self.check_heap_type(cx, it.span, cx.tcx.type_of(def_id))
 178             }
 179             _ => (),
 180         }
 181
 182         // If it's a struct, we also have to check the fields' types
 183         match it.kind {
 184             hir::ItemKind::Struct(ref struct_def, _) | hir::ItemKind::Union(ref struct_def, _) => {
 185                 for struct_field in struct_def.fields() {
 186                     let def_id = cx.tcx.hir().local_def_id(struct_field.hir_id);
 187                     self.check_heap_type(cx, struct_field.span, cx.tcx.type_of(def_id));
 188                 }
 189             }
 190             _ => (),
 191         }
 192     }
 193
 194     fn check_expr(&mut self, cx: &LateContext<'_>, e: &hir::Expr<'_>) {
 195         let ty = cx.typeck_results().node_type(e.hir_id);
 196         self.check_heap_type(cx, e.span, ty);
 197     }
 198 }
 199
 200 declare_lint! {
 201     /// The `non_shorthand_field_patterns` lint detects using `Struct { x: x }`
 202     /// instead of `Struct { x }` in a pattern.
 203     ///
 204     /// ### Example
 205     ///
 206     /// ```rust
 207     /// struct Point {
 208     ///     x: i32,
 209     ///     y: i32,
 210     /// }
 211     ///
 212     ///
 213     /// fn main() {
 214     ///     let p = Point {
 215     ///         x: 5,
 216     ///         y: 5,
 217     ///     };
 218     ///
 219     ///     match p {
 220     ///         Point { x: x, y: y } => (),
 221     ///     }
 222     /// }
 223     /// ```
 224     ///
 225     /// {{produces}}
 226     ///
 227     /// ### Explanation
 228     ///
 229     /// The preferred style is to avoid the repetition of specifying both the
 230     /// field name and the binding name if both identifiers are the same.
 231     NON_SHORTHAND_FIELD_PATTERNS,
 232     Warn,
 233     "using `Struct { x: x }` instead of `Struct { x }` in a pattern"
 234 }
 235
 236 declare_lint_pass!(NonShorthandFieldPatterns => [NON_SHORTHAND_FIELD_PATTERNS]);
 237
 238 impl<'tcx> LateLintPass<'tcx> for NonShorthandFieldPatterns {
 239     fn check_pat(&mut self, cx: &LateContext<'_>, pat: &hir::Pat<'_>) {
 240         if let PatKind::Struct(ref qpath, field_pats, _) = pat.kind {
 241             let variant = cx
 242                 .typeck_results()
 243                 .pat_ty(pat)
 244                 .ty_adt_def()
 245                 .expect("struct pattern type is not an ADT")
 246                 .variant_of_res(cx.qpath_res(qpath, pat.hir_id));
 247             for fieldpat in field_pats {
 248                 if fieldpat.is_shorthand {
 249                     continue;
 250                 }
 251                 if fieldpat.span.from_expansion() {
 252                     // Don't lint if this is a macro expansion: macro authors
 253                     // shouldn't have to worry about this kind of style issue
 254                     // (Issue #49588)
 255                     continue;
 256                 }
 257                 if let PatKind::Binding(binding_annot, _, ident, None) = fieldpat.pat.kind {
 258                     if cx.tcx.find_field_index(ident, &variant)
 259                         == Some(cx.tcx.field_index(fieldpat.hir_id, cx.typeck_results()))
 260                     {
 261                         cx.struct_span_lint(NON_SHORTHAND_FIELD_PATTERNS, fieldpat.span, |lint| {
 262                             let mut err = lint
 263                                 .build(&format!("the `{}:` in this pattern is redundant", ident));
 264                             let binding = match binding_annot {
 265                                 hir::BindingAnnotation::Unannotated => None,
 266                                 hir::BindingAnnotation::Mutable => Some("mut"),
 267                                 hir::BindingAnnotation::Ref => Some("ref"),
 268                                 hir::BindingAnnotation::RefMut => Some("ref mut"),
 269                             };
 270                             let ident = if let Some(binding) = binding {
 271                                 format!("{} {}", binding, ident)
 272                             } else {
 273                                 ident.to_string()
 274                             };
 275                             err.span_suggestion(
 276                                 fieldpat.span,
 277                                 "use shorthand field pattern",
 278                                 ident,
 279                                 Applicability::MachineApplicable,
 280                             );
 281                             err.emit();
 282                         });
 283                     }
 284                 }
 285             }
 286         }
 287     }
 288 }
 289
 290 declare_lint! {
 291     /// The `unsafe_code` lint catches usage of `unsafe` code.
 292     ///
 293     /// ### Example
 294     ///
 295     /// ```rust,compile_fail
 296     /// #![deny(unsafe_code)]
 297     /// fn main() {
 298     ///     unsafe {
 299     ///
 300     ///     }
 301     /// }
 302     /// ```
 303     ///
 304     /// {{produces}}
 305     ///
 306     /// ### Explanation
 307     ///
 308     /// This lint is intended to restrict the usage of `unsafe`, which can be
 309     /// difficult to use correctly.
 310     UNSAFE_CODE,
 311     Allow,
 312     "usage of `unsafe` code"
 313 }
 314
 315 declare_lint_pass!(UnsafeCode => [UNSAFE_CODE]);
 316
 317 impl UnsafeCode {
 318     fn report_unsafe(
 319         &self,
 320         cx: &EarlyContext<'_>,
 321         span: Span,
 322         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
 323     ) {
 324         // This comes from a macro that has `#[allow_internal_unsafe]`.
 325         if span.allows_unsafe() {
 326             return;
 327         }
 328
 329         cx.struct_span_lint(UNSAFE_CODE, span, decorate);
 330     }
 331
 332     fn report_overriden_symbol_name(&self, cx: &EarlyContext<'_>, span: Span, msg: &str) {
 333         self.report_unsafe(cx, span, |lint| {
 334             lint.build(msg)
 335                 .note(
 336                     "the linker's behavior with multiple libraries exporting duplicate symbol \
 337                     names is undefined and Rust cannot provide guarantees when you manually \
 338                     override them",
 339                 )
 340                 .emit();
 341         })
 342     }
 343 }
 344
 345 impl EarlyLintPass for UnsafeCode {
 346     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 347         if cx.sess().check_name(attr, sym::allow_internal_unsafe) {
 348             self.report_unsafe(cx, attr.span, |lint| {
 349                 lint.build(
 350                     "`allow_internal_unsafe` allows defining \
 351                                                macros using unsafe without triggering \
 352                                                the `unsafe_code` lint at their call site",
 353                 )
 354                 .emit()
 355             });
 356         }
 357     }
 358
 359     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
 360         if let ast::ExprKind::Block(ref blk, _) = e.kind {
 361             // Don't warn about generated blocks; that'll just pollute the output.
 362             if blk.rules == ast::BlockCheckMode::Unsafe(ast::UserProvided) {
 363                 self.report_unsafe(cx, blk.span, |lint| {
 364                     lint.build("usage of an `unsafe` block").emit()
 365                 });
 366             }
 367         }
 368     }
 369
 370     fn check_item(&mut self, cx: &EarlyContext<'_>, it: &ast::Item) {
 371         match it.kind {
 372             ast::ItemKind::Trait(box ast::TraitKind(_, ast::Unsafe::Yes(_), ..)) => self
 373                 .report_unsafe(cx, it.span, |lint| {
 374                     lint.build("declaration of an `unsafe` trait").emit()
 375                 }),
 376
 377             ast::ItemKind::Impl(box ast::ImplKind { unsafety: ast::Unsafe::Yes(_), .. }) => self
 378                 .report_unsafe(cx, it.span, |lint| {
 379                     lint.build("implementation of an `unsafe` trait").emit()
 380                 }),
 381
 382             ast::ItemKind::Fn(..) => {
 383                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
 384                     self.report_overriden_symbol_name(
 385                         cx,
 386                         attr.span,
 387                         "declaration of a `no_mangle` function",
 388                     );
 389                 }
 390                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::export_name) {
 391                     self.report_overriden_symbol_name(
 392                         cx,
 393                         attr.span,
 394                         "declaration of a function with `export_name`",
 395                     );
 396                 }
 397             }
 398
 399             ast::ItemKind::Static(..) => {
 400                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
 401                     self.report_overriden_symbol_name(
 402                         cx,
 403                         attr.span,
 404                         "declaration of a `no_mangle` static",
 405                     );
 406                 }
 407                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::export_name) {
 408                     self.report_overriden_symbol_name(
 409                         cx,
 410                         attr.span,
 411                         "declaration of a static with `export_name`",
 412                     );
 413                 }
 414             }
 415
 416             _ => {}
 417         }
 418     }
 419
 420     fn check_fn(&mut self, cx: &EarlyContext<'_>, fk: FnKind<'_>, span: Span, _: ast::NodeId) {
 421         if let FnKind::Fn(
 422             ctxt,
 423             _,
 424             ast::FnSig { header: ast::FnHeader { unsafety: ast::Unsafe::Yes(_), .. }, .. },
 425             _,
 426             body,
 427         ) = fk
 428         {
 429             let msg = match ctxt {
 430                 FnCtxt::Foreign => return,
 431                 FnCtxt::Free => "declaration of an `unsafe` function",
 432                 FnCtxt::Assoc(_) if body.is_none() => "declaration of an `unsafe` method",
 433                 FnCtxt::Assoc(_) => "implementation of an `unsafe` method",
 434             };
 435             self.report_unsafe(cx, span, |lint| lint.build(msg).emit());
 436         }
 437     }
 438 }
 439
 440 declare_lint! {
 441     /// The `missing_docs` lint detects missing documentation for public items.
 442     ///
 443     /// ### Example
 444     ///
 445     /// ```rust,compile_fail
 446     /// #![deny(missing_docs)]
 447     /// pub fn foo() {}
 448     /// ```
 449     ///
 450     /// {{produces}}
 451     ///
 452     /// ### Explanation
 453     ///
 454     /// This lint is intended to ensure that a library is well-documented.
 455     /// Items without documentation can be difficult for users to understand
 456     /// how to use properly.
 457     ///
 458     /// This lint is "allow" by default because it can be noisy, and not all
 459     /// projects may want to enforce everything to be documented.
 460     pub MISSING_DOCS,
 461     Allow,
 462     "detects missing documentation for public members",
 463     report_in_external_macro
 464 }
 465
 466 pub struct MissingDoc {
 467     /// Stack of whether `#[doc(hidden)]` is set at each level which has lint attributes.
 468     doc_hidden_stack: Vec<bool>,
 469
 470     /// Private traits or trait items that leaked through. Don't check their methods.
 471     private_traits: FxHashSet<hir::HirId>,
 472 }
 473
 474 impl_lint_pass!(MissingDoc => [MISSING_DOCS]);
 475
 476 fn has_doc(sess: &Session, attr: &ast::Attribute) -> bool {
 477     if attr.is_doc_comment() {
 478         return true;
 479     }
 480
 481     if !sess.check_name(attr, sym::doc) {
 482         return false;
 483     }
 484
 485     if attr.is_value_str() {
 486         return true;
 487     }
 488
 489     if let Some(list) = attr.meta_item_list() {
 490         for meta in list {
 491             if meta.has_name(sym::include) || meta.has_name(sym::hidden) {
 492                 return true;
 493             }
 494         }
 495     }
 496
 497     false
 498 }
 499
 500 impl MissingDoc {
 501     pub fn new() -> MissingDoc {
 502         MissingDoc { doc_hidden_stack: vec![false], private_traits: FxHashSet::default() }
 503     }
 504
 505     fn doc_hidden(&self) -> bool {
 506         *self.doc_hidden_stack.last().expect("empty doc_hidden_stack")
 507     }
 508
 509     fn check_missing_docs_attrs(
 510         &self,
 511         cx: &LateContext<'_>,
 512         id: Option<hir::HirId>,
 513         attrs: &[ast::Attribute],
 514         sp: Span,
 515         article: &'static str,
 516         desc: &'static str,
 517     ) {
 518         // If we're building a test harness, then warning about
 519         // documentation is probably not really relevant right now.
 520         if cx.sess().opts.test {
 521             return;
 522         }
 523
 524         // `#[doc(hidden)]` disables missing_docs check.
 525         if self.doc_hidden() {
 526             return;
 527         }
 528
 529         // Only check publicly-visible items, using the result from the privacy pass.
 530         // It's an option so the crate root can also use this function (it doesn't
 531         // have a `NodeId`).
 532         if let Some(id) = id {
 533             if !cx.access_levels.is_exported(id) {
 534                 return;
 535             }
 536         }
 537
 538         let has_doc = attrs.iter().any(|a| has_doc(cx.sess(), a));
 539         if !has_doc {
 540             cx.struct_span_lint(
 541                 MISSING_DOCS,
 542                 cx.tcx.sess.source_map().guess_head_span(sp),
 543                 |lint| {
 544                     lint.build(&format!("missing documentation for {} {}", article, desc)).emit()
 545                 },
 546             );
 547         }
 548     }
 549 }
 550
 551 impl<'tcx> LateLintPass<'tcx> for MissingDoc {
 552     fn enter_lint_attrs(&mut self, cx: &LateContext<'_>, attrs: &[ast::Attribute]) {
 553         let doc_hidden = self.doc_hidden()
 554             || attrs.iter().any(|attr| {
 555                 cx.sess().check_name(attr, sym::doc)
 556                     && match attr.meta_item_list() {
 557                         None => false,
 558                         Some(l) => attr::list_contains_name(&l, sym::hidden),
 559                     }
 560             });
 561         self.doc_hidden_stack.push(doc_hidden);
 562     }
 563
 564     fn exit_lint_attrs(&mut self, _: &LateContext<'_>, _attrs: &[ast::Attribute]) {
 565         self.doc_hidden_stack.pop().expect("empty doc_hidden_stack");
 566     }
 567
 568     fn check_crate(&mut self, cx: &LateContext<'_>, krate: &hir::Crate<'_>) {
 569         self.check_missing_docs_attrs(cx, None, &krate.item.attrs, krate.item.span, "the", "crate");
 570
 571         for macro_def in krate.exported_macros {
 572             let has_doc = macro_def.attrs.iter().any(|a| has_doc(cx.sess(), a));
 573             if !has_doc {
 574                 cx.struct_span_lint(
 575                     MISSING_DOCS,
 576                     cx.tcx.sess.source_map().guess_head_span(macro_def.span),
 577                     |lint| lint.build("missing documentation for macro").emit(),
 578                 );
 579             }
 580         }
 581     }
 582
 583     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 584         match it.kind {
 585             hir::ItemKind::Trait(.., trait_item_refs) => {
 586                 // Issue #11592: traits are always considered exported, even when private.
 587                 if let hir::VisibilityKind::Inherited = it.vis.node {
 588                     self.private_traits.insert(it.hir_id);
 589                     for trait_item_ref in trait_item_refs {
 590                         self.private_traits.insert(trait_item_ref.id.hir_id);
 591                     }
 592                     return;
 593                 }
 594             }
 595             hir::ItemKind::Impl(hir::Impl { of_trait: Some(ref trait_ref), items, .. }) => {
 596                 // If the trait is private, add the impl items to `private_traits` so they don't get
 597                 // reported for missing docs.
 598                 let real_trait = trait_ref.path.res.def_id();
 599                 if let Some(def_id) = real_trait.as_local() {
 600                     let hir_id = cx.tcx.hir().local_def_id_to_hir_id(def_id);
 601                     if let Some(Node::Item(item)) = cx.tcx.hir().find(hir_id) {
 602                         if let hir::VisibilityKind::Inherited = item.vis.node {
 603                             for impl_item_ref in items {
 604                                 self.private_traits.insert(impl_item_ref.id.hir_id);
 605                             }
 606                         }
 607                     }
 608                 }
 609                 return;
 610             }
 611
 612             hir::ItemKind::TyAlias(..)
 613             | hir::ItemKind::Fn(..)
 614             | hir::ItemKind::Mod(..)
 615             | hir::ItemKind::Enum(..)
 616             | hir::ItemKind::Struct(..)
 617             | hir::ItemKind::Union(..)
 618             | hir::ItemKind::Const(..)
 619             | hir::ItemKind::Static(..) => {}
 620
 621             _ => return,
 622         };
 623
 624         let def_id = cx.tcx.hir().local_def_id(it.hir_id);
 625         let (article, desc) = cx.tcx.article_and_description(def_id.to_def_id());
 626
 627         self.check_missing_docs_attrs(cx, Some(it.hir_id), &it.attrs, it.span, article, desc);
 628     }
 629
 630     fn check_trait_item(&mut self, cx: &LateContext<'_>, trait_item: &hir::TraitItem<'_>) {
 631         if self.private_traits.contains(&trait_item.hir_id) {
 632             return;
 633         }
 634
 635         let def_id = cx.tcx.hir().local_def_id(trait_item.hir_id);
 636         let (article, desc) = cx.tcx.article_and_description(def_id.to_def_id());
 637
 638         self.check_missing_docs_attrs(
 639             cx,
 640             Some(trait_item.hir_id),
 641             &trait_item.attrs,
 642             trait_item.span,
 643             article,
 644             desc,
 645         );
 646     }
 647
 648     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
 649         // If the method is an impl for a trait, don't doc.
 650         if method_context(cx, impl_item.hir_id) == MethodLateContext::TraitImpl {
 651             return;
 652         }
 653
 654         let def_id = cx.tcx.hir().local_def_id(impl_item.hir_id);
 655         let (article, desc) = cx.tcx.article_and_description(def_id.to_def_id());
 656         self.check_missing_docs_attrs(
 657             cx,
 658             Some(impl_item.hir_id),
 659             &impl_item.attrs,
 660             impl_item.span,
 661             article,
 662             desc,
 663         );
 664     }
 665
 666     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'_>) {
 667         let def_id = cx.tcx.hir().local_def_id(foreign_item.hir_id);
 668         let (article, desc) = cx.tcx.article_and_description(def_id.to_def_id());
 669         self.check_missing_docs_attrs(
 670             cx,
 671             Some(foreign_item.hir_id),
 672             &foreign_item.attrs,
 673             foreign_item.span,
 674             article,
 675             desc,
 676         );
 677     }
 678
 679     fn check_struct_field(&mut self, cx: &LateContext<'_>, sf: &hir::StructField<'_>) {
 680         if !sf.is_positional() {
 681             self.check_missing_docs_attrs(
 682                 cx,
 683                 Some(sf.hir_id),
 684                 &sf.attrs,
 685                 sf.span,
 686                 "a",
 687                 "struct field",
 688             )
 689         }
 690     }
 691
 692     fn check_variant(&mut self, cx: &LateContext<'_>, v: &hir::Variant<'_>) {
 693         self.check_missing_docs_attrs(cx, Some(v.id), &v.attrs, v.span, "a", "variant");
 694     }
 695 }
 696
 697 declare_lint! {
 698     /// The `missing_copy_implementations` lint detects potentially-forgotten
 699     /// implementations of [`Copy`].
 700     ///
 701     /// [`Copy`]: https://doc.rust-lang.org/std/marker/trait.Copy.html
 702     ///
 703     /// ### Example
 704     ///
 705     /// ```rust,compile_fail
 706     /// #![deny(missing_copy_implementations)]
 707     /// pub struct Foo {
 708     ///     pub field: i32
 709     /// }
 710     /// # fn main() {}
 711     /// ```
 712     ///
 713     /// {{produces}}
 714     ///
 715     /// ### Explanation
 716     ///
 717     /// Historically (before 1.0), types were automatically marked as `Copy`
 718     /// if possible. This was changed so that it required an explicit opt-in
 719     /// by implementing the `Copy` trait. As part of this change, a lint was
 720     /// added to alert if a copyable type was not marked `Copy`.
 721     ///
 722     /// This lint is "allow" by default because this code isn't bad; it is
 723     /// common to write newtypes like this specifically so that a `Copy` type
 724     /// is no longer `Copy`. `Copy` types can result in unintended copies of
 725     /// large data which can impact performance.
 726     pub MISSING_COPY_IMPLEMENTATIONS,
 727     Allow,
 728     "detects potentially-forgotten implementations of `Copy`"
 729 }
 730
 731 declare_lint_pass!(MissingCopyImplementations => [MISSING_COPY_IMPLEMENTATIONS]);
 732
 733 impl<'tcx> LateLintPass<'tcx> for MissingCopyImplementations {
 734     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 735         if !cx.access_levels.is_reachable(item.hir_id) {
 736             return;
 737         }
 738         let (def, ty) = match item.kind {
 739             hir::ItemKind::Struct(_, ref ast_generics) => {
 740                 if !ast_generics.params.is_empty() {
 741                     return;
 742                 }
 743                 let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
 744                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 745             }
 746             hir::ItemKind::Union(_, ref ast_generics) => {
 747                 if !ast_generics.params.is_empty() {
 748                     return;
 749                 }
 750                 let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
 751                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 752             }
 753             hir::ItemKind::Enum(_, ref ast_generics) => {
 754                 if !ast_generics.params.is_empty() {
 755                     return;
 756                 }
 757                 let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
 758                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 759             }
 760             _ => return,
 761         };
 762         if def.has_dtor(cx.tcx) {
 763             return;
 764         }
 765         let param_env = ty::ParamEnv::empty();
 766         if ty.is_copy_modulo_regions(cx.tcx.at(item.span), param_env) {
 767             return;
 768         }
 769         if can_type_implement_copy(cx.tcx, param_env, ty).is_ok() {
 770             cx.struct_span_lint(MISSING_COPY_IMPLEMENTATIONS, item.span, |lint| {
 771                 lint.build(
 772                     "type could implement `Copy`; consider adding `impl \
 773                           Copy`",
 774                 )
 775                 .emit()
 776             })
 777         }
 778     }
 779 }
 780
 781 declare_lint! {
 782     /// The `missing_debug_implementations` lint detects missing
 783     /// implementations of [`fmt::Debug`].
 784     ///
 785     /// [`fmt::Debug`]: https://doc.rust-lang.org/std/fmt/trait.Debug.html
 786     ///
 787     /// ### Example
 788     ///
 789     /// ```rust,compile_fail
 790     /// #![deny(missing_debug_implementations)]
 791     /// pub struct Foo;
 792     /// # fn main() {}
 793     /// ```
 794     ///
 795     /// {{produces}}
 796     ///
 797     /// ### Explanation
 798     ///
 799     /// Having a `Debug` implementation on all types can assist with
 800     /// debugging, as it provides a convenient way to format and display a
 801     /// value. Using the `#[derive(Debug)]` attribute will automatically
 802     /// generate a typical implementation, or a custom implementation can be
 803     /// added by manually implementing the `Debug` trait.
 804     ///
 805     /// This lint is "allow" by default because adding `Debug` to all types can
 806     /// have a negative impact on compile time and code size. It also requires
 807     /// boilerplate to be added to every type, which can be an impediment.
 808     MISSING_DEBUG_IMPLEMENTATIONS,
 809     Allow,
 810     "detects missing implementations of Debug"
 811 }
 812
 813 #[derive(Default)]
 814 pub struct MissingDebugImplementations {
 815     impling_types: Option<HirIdSet>,
 816 }
 817
 818 impl_lint_pass!(MissingDebugImplementations => [MISSING_DEBUG_IMPLEMENTATIONS]);
 819
 820 impl<'tcx> LateLintPass<'tcx> for MissingDebugImplementations {
 821     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 822         if !cx.access_levels.is_reachable(item.hir_id) {
 823             return;
 824         }
 825
 826         match item.kind {
 827             hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) | hir::ItemKind::Enum(..) => {}
 828             _ => return,
 829         }
 830
 831         let debug = match cx.tcx.get_diagnostic_item(sym::debug_trait) {
 832             Some(debug) => debug,
 833             None => return,
 834         };
 835
 836         if self.impling_types.is_none() {
 837             let mut impls = HirIdSet::default();
 838             cx.tcx.for_each_impl(debug, |d| {
 839                 if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() {
 840                     if let Some(def_id) = ty_def.did.as_local() {
 841                         impls.insert(cx.tcx.hir().local_def_id_to_hir_id(def_id));
 842                     }
 843                 }
 844             });
 845
 846             self.impling_types = Some(impls);
 847             debug!("{:?}", self.impling_types);
 848         }
 849
 850         if !self.impling_types.as_ref().unwrap().contains(&item.hir_id) {
 851             cx.struct_span_lint(MISSING_DEBUG_IMPLEMENTATIONS, item.span, |lint| {
 852                 lint.build(&format!(
 853                     "type does not implement `{}`; consider adding `#[derive(Debug)]` \
 854                      or a manual implementation",
 855                     cx.tcx.def_path_str(debug)
 856                 ))
 857                 .emit()
 858             });
 859         }
 860     }
 861 }
 862
 863 declare_lint! {
 864     /// The `anonymous_parameters` lint detects anonymous parameters in trait
 865     /// definitions.
 866     ///
 867     /// ### Example
 868     ///
 869     /// ```rust,edition2015,compile_fail
 870     /// #![deny(anonymous_parameters)]
 871     /// // edition 2015
 872     /// pub trait Foo {
 873     ///     fn foo(usize);
 874     /// }
 875     /// fn main() {}
 876     /// ```
 877     ///
 878     /// {{produces}}
 879     ///
 880     /// ### Explanation
 881     ///
 882     /// This syntax is mostly a historical accident, and can be worked around
 883     /// quite easily by adding an `_` pattern or a descriptive identifier:
 884     ///
 885     /// ```rust
 886     /// trait Foo {
 887     ///     fn foo(_: usize);
 888     /// }
 889     /// ```
 890     ///
 891     /// This syntax is now a hard error in the 2018 edition. In the 2015
 892     /// edition, this lint is "allow" by default, because the old code is
 893     /// still valid, and warning for all old code can be noisy. This lint
 894     /// enables the [`cargo fix`] tool with the `--edition` flag to
 895     /// automatically transition old code from the 2015 edition to 2018. The
 896     /// tool will switch this lint to "warn" and will automatically apply the
 897     /// suggested fix from the compiler (which is to add `_` to each
 898     /// parameter). This provides a completely automated way to update old
 899     /// code for a new edition. See [issue #41686] for more details.
 900     ///
 901     /// [issue #41686]: https://github.com/rust-lang/rust/issues/41686
 902     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
 903     pub ANONYMOUS_PARAMETERS,
 904     Allow,
 905     "detects anonymous parameters",
 906     @future_incompatible = FutureIncompatibleInfo {
 907         reference: "issue #41686 <https://github.com/rust-lang/rust/issues/41686>",
 908         edition: Some(Edition::Edition2018),
 909     };
 910 }
 911
 912 declare_lint_pass!(
 913     /// Checks for use of anonymous parameters (RFC 1685).
 914     AnonymousParameters => [ANONYMOUS_PARAMETERS]
 915 );
 916
 917 impl EarlyLintPass for AnonymousParameters {
 918     fn check_trait_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
 919         if let ast::AssocItemKind::Fn(box FnKind(_, ref sig, _, _)) = it.kind {
 920             for arg in sig.decl.inputs.iter() {
 921                 if let ast::PatKind::Ident(_, ident, None) = arg.pat.kind {
 922                     if ident.name == kw::Empty {
 923                         cx.struct_span_lint(ANONYMOUS_PARAMETERS, arg.pat.span, |lint| {
 924                             let ty_snip = cx.sess.source_map().span_to_snippet(arg.ty.span);
 925
 926                             let (ty_snip, appl) = if let Ok(ref snip) = ty_snip {
 927                                 (snip.as_str(), Applicability::MachineApplicable)
 928                             } else {
 929                                 ("<type>", Applicability::HasPlaceholders)
 930                             };
 931
 932                             lint.build(
 933                                 "anonymous parameters are deprecated and will be \
 934                                      removed in the next edition.",
 935                             )
 936                             .span_suggestion(
 937                                 arg.pat.span,
 938                                 "try naming the parameter or explicitly \
 939                                             ignoring it",
 940                                 format!("_: {}", ty_snip),
 941                                 appl,
 942                             )
 943                             .emit();
 944                         })
 945                     }
 946                 }
 947             }
 948         }
 949     }
 950 }
 951
 952 /// Check for use of attributes which have been deprecated.
 953 #[derive(Clone)]
 954 pub struct DeprecatedAttr {
 955     // This is not free to compute, so we want to keep it around, rather than
 956     // compute it for every attribute.
 957     depr_attrs: Vec<&'static (Symbol, AttributeType, AttributeTemplate, AttributeGate)>,
 958 }
 959
 960 impl_lint_pass!(DeprecatedAttr => []);
 961
 962 impl DeprecatedAttr {
 963     pub fn new() -> DeprecatedAttr {
 964         DeprecatedAttr { depr_attrs: deprecated_attributes() }
 965     }
 966 }
 967
 968 fn lint_deprecated_attr(
 969     cx: &EarlyContext<'_>,
 970     attr: &ast::Attribute,
 971     msg: &str,
 972     suggestion: Option<&str>,
 973 ) {
 974     cx.struct_span_lint(DEPRECATED, attr.span, |lint| {
 975         lint.build(msg)
 976             .span_suggestion_short(
 977                 attr.span,
 978                 suggestion.unwrap_or("remove this attribute"),
 979                 String::new(),
 980                 Applicability::MachineApplicable,
 981             )
 982             .emit();
 983     })
 984 }
 985
 986 impl EarlyLintPass for DeprecatedAttr {
 987     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 988         for &&(n, _, _, ref g) in &self.depr_attrs {
 989             if attr.ident().map(|ident| ident.name) == Some(n) {
 990                 if let &AttributeGate::Gated(
 991                     Stability::Deprecated(link, suggestion),
 992                     name,
 993                     reason,
 994                     _,
 995                 ) = g
 996                 {
 997                     let msg =
 998                         format!("use of deprecated attribute `{}`: {}. See {}", name, reason, link);
 999                     lint_deprecated_attr(cx, attr, &msg, suggestion);
1000                 }
1001                 return;
1002             }
1003         }
1004         if cx.sess().check_name(attr, sym::no_start) || cx.sess().check_name(attr, sym::crate_id) {
1005             let path_str = pprust::path_to_string(&attr.get_normal_item().path);
1006             let msg = format!("use of deprecated attribute `{}`: no longer used.", path_str);
1007             lint_deprecated_attr(cx, attr, &msg, None);
1008         }
1009     }
1010 }
1011
1012 fn warn_if_doc(cx: &EarlyContext<'_>, node_span: Span, node_kind: &str, attrs: &[ast::Attribute]) {
1013     let mut attrs = attrs.iter().peekable();
1014
1015     // Accumulate a single span for sugared doc comments.
1016     let mut sugared_span: Option<Span> = None;
1017
1018     while let Some(attr) = attrs.next() {
1019         if attr.is_doc_comment() {
1020             sugared_span =
1021                 Some(sugared_span.map_or(attr.span, |span| span.with_hi(attr.span.hi())));
1022         }
1023
1024         if attrs.peek().map(|next_attr| next_attr.is_doc_comment()).unwrap_or_default() {
1025             continue;
1026         }
1027
1028         let span = sugared_span.take().unwrap_or(attr.span);
1029
1030         if attr.is_doc_comment() || cx.sess().check_name(attr, sym::doc) {
1031             cx.struct_span_lint(UNUSED_DOC_COMMENTS, span, |lint| {
1032                 let mut err = lint.build("unused doc comment");
1033                 err.span_label(
1034                     node_span,
1035                     format!("rustdoc does not generate documentation for {}", node_kind),
1036                 );
1037                 err.emit();
1038             });
1039         }
1040     }
1041 }
1042
1043 impl EarlyLintPass for UnusedDocComment {
1044     fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &ast::Stmt) {
1045         let kind = match stmt.kind {
1046             ast::StmtKind::Local(..) => "statements",
1047             // Disabled pending discussion in #78306
1048             ast::StmtKind::Item(..) => return,
1049             // expressions will be reported by `check_expr`.
1050             ast::StmtKind::Empty
1051             | ast::StmtKind::Semi(_)
1052             | ast::StmtKind::Expr(_)
1053             | ast::StmtKind::MacCall(_) => return,
1054         };
1055
1056         warn_if_doc(cx, stmt.span, kind, stmt.kind.attrs());
1057     }
1058
1059     fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) {
1060         let arm_span = arm.pat.span.with_hi(arm.body.span.hi());
1061         warn_if_doc(cx, arm_span, "match arms", &arm.attrs);
1062     }
1063
1064     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
1065         warn_if_doc(cx, expr.span, "expressions", &expr.attrs);
1066     }
1067 }
1068
1069 declare_lint! {
1070     /// The `no_mangle_const_items` lint detects any `const` items with the
1071     /// [`no_mangle` attribute].
1072     ///
1073     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1074     ///
1075     /// ### Example
1076     ///
1077     /// ```rust,compile_fail
1078     /// #[no_mangle]
1079     /// const FOO: i32 = 5;
1080     /// ```
1081     ///
1082     /// {{produces}}
1083     ///
1084     /// ### Explanation
1085     ///
1086     /// Constants do not have their symbols exported, and therefore, this
1087     /// probably means you meant to use a [`static`], not a [`const`].
1088     ///
1089     /// [`static`]: https://doc.rust-lang.org/reference/items/static-items.html
1090     /// [`const`]: https://doc.rust-lang.org/reference/items/constant-items.html
1091     NO_MANGLE_CONST_ITEMS,
1092     Deny,
1093     "const items will not have their symbols exported"
1094 }
1095
1096 declare_lint! {
1097     /// The `no_mangle_generic_items` lint detects generic items that must be
1098     /// mangled.
1099     ///
1100     /// ### Example
1101     ///
1102     /// ```rust
1103     /// #[no_mangle]
1104     /// fn foo<T>(t: T) {
1105     ///
1106     /// }
1107     /// ```
1108     ///
1109     /// {{produces}}
1110     ///
1111     /// ### Explanation
1112     ///
1113     /// An function with generics must have its symbol mangled to accommodate
1114     /// the generic parameter. The [`no_mangle` attribute] has no effect in
1115     /// this situation, and should be removed.
1116     ///
1117     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1118     NO_MANGLE_GENERIC_ITEMS,
1119     Warn,
1120     "generic items must be mangled"
1121 }
1122
1123 declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS, NO_MANGLE_GENERIC_ITEMS]);
1124
1125 impl<'tcx> LateLintPass<'tcx> for InvalidNoMangleItems {
1126     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1127         match it.kind {
1128             hir::ItemKind::Fn(.., ref generics, _) => {
1129                 if let Some(no_mangle_attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
1130                     for param in generics.params {
1131                         match param.kind {
1132                             GenericParamKind::Lifetime { .. } => {}
1133                             GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1134                                 cx.struct_span_lint(NO_MANGLE_GENERIC_ITEMS, it.span, |lint| {
1135                                     lint.build(
1136                                         "functions generic over types or consts must be mangled",
1137                                     )
1138                                     .span_suggestion_short(
1139                                         no_mangle_attr.span,
1140                                         "remove this attribute",
1141                                         String::new(),
1142                                         // Use of `#[no_mangle]` suggests FFI intent; correct
1143                                         // fix may be to monomorphize source by hand
1144                                         Applicability::MaybeIncorrect,
1145                                     )
1146                                     .emit();
1147                                 });
1148                                 break;
1149                             }
1150                         }
1151                     }
1152                 }
1153             }
1154             hir::ItemKind::Const(..) => {
1155                 if cx.sess().contains_name(&it.attrs, sym::no_mangle) {
1156                     // Const items do not refer to a particular location in memory, and therefore
1157                     // don't have anything to attach a symbol to
1158                     cx.struct_span_lint(NO_MANGLE_CONST_ITEMS, it.span, |lint| {
1159                         let msg = "const items should never be `#[no_mangle]`";
1160                         let mut err = lint.build(msg);
1161
1162                         // account for "pub const" (#45562)
1163                         let start = cx
1164                             .tcx
1165                             .sess
1166                             .source_map()
1167                             .span_to_snippet(it.span)
1168                             .map(|snippet| snippet.find("const").unwrap_or(0))
1169                             .unwrap_or(0) as u32;
1170                         // `const` is 5 chars
1171                         let const_span = it.span.with_hi(BytePos(it.span.lo().0 + start + 5));
1172                         err.span_suggestion(
1173                             const_span,
1174                             "try a static value",
1175                             "pub static".to_owned(),
1176                             Applicability::MachineApplicable,
1177                         );
1178                         err.emit();
1179                     });
1180                 }
1181             }
1182             _ => {}
1183         }
1184     }
1185 }
1186
1187 declare_lint! {
1188     /// The `mutable_transmutes` lint catches transmuting from `&T` to `&mut
1189     /// T` because it is [undefined behavior].
1190     ///
1191     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1192     ///
1193     /// ### Example
1194     ///
1195     /// ```rust,compile_fail
1196     /// unsafe {
1197     ///     let y = std::mem::transmute::<&i32, &mut i32>(&5);
1198     /// }
1199     /// ```
1200     ///
1201     /// {{produces}}
1202     ///
1203     /// ### Explanation
1204     ///
1205     /// Certain assumptions are made about aliasing of data, and this transmute
1206     /// violates those assumptions. Consider using [`UnsafeCell`] instead.
1207     ///
1208     /// [`UnsafeCell`]: https://doc.rust-lang.org/std/cell/struct.UnsafeCell.html
1209     MUTABLE_TRANSMUTES,
1210     Deny,
1211     "mutating transmuted &mut T from &T may cause undefined behavior"
1212 }
1213
1214 declare_lint_pass!(MutableTransmutes => [MUTABLE_TRANSMUTES]);
1215
1216 impl<'tcx> LateLintPass<'tcx> for MutableTransmutes {
1217     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &hir::Expr<'_>) {
1218         use rustc_target::spec::abi::Abi::RustIntrinsic;
1219         if let Some((&ty::Ref(_, _, from_mt), &ty::Ref(_, _, to_mt))) =
1220             get_transmute_from_to(cx, expr).map(|(ty1, ty2)| (ty1.kind(), ty2.kind()))
1221         {
1222             if to_mt == hir::Mutability::Mut && from_mt == hir::Mutability::Not {
1223                 let msg = "mutating transmuted &mut T from &T may cause undefined behavior, \
1224                                consider instead using an UnsafeCell";
1225                 cx.struct_span_lint(MUTABLE_TRANSMUTES, expr.span, |lint| lint.build(msg).emit());
1226             }
1227         }
1228
1229         fn get_transmute_from_to<'tcx>(
1230             cx: &LateContext<'tcx>,
1231             expr: &hir::Expr<'_>,
1232         ) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
1233             let def = if let hir::ExprKind::Path(ref qpath) = expr.kind {
1234                 cx.qpath_res(qpath, expr.hir_id)
1235             } else {
1236                 return None;
1237             };
1238             if let Res::Def(DefKind::Fn, did) = def {
1239                 if !def_id_is_transmute(cx, did) {
1240                     return None;
1241                 }
1242                 let sig = cx.typeck_results().node_type(expr.hir_id).fn_sig(cx.tcx);
1243                 let from = sig.inputs().skip_binder()[0];
1244                 let to = sig.output().skip_binder();
1245                 return Some((from, to));
1246             }
1247             None
1248         }
1249
1250         fn def_id_is_transmute(cx: &LateContext<'_>, def_id: DefId) -> bool {
1251             cx.tcx.fn_sig(def_id).abi() == RustIntrinsic
1252                 && cx.tcx.item_name(def_id) == sym::transmute
1253         }
1254     }
1255 }
1256
1257 declare_lint! {
1258     /// The `unstable_features` is deprecated and should no longer be used.
1259     UNSTABLE_FEATURES,
1260     Allow,
1261     "enabling unstable features (deprecated. do not use)"
1262 }
1263
1264 declare_lint_pass!(
1265     /// Forbids using the `#[feature(...)]` attribute
1266     UnstableFeatures => [UNSTABLE_FEATURES]
1267 );
1268
1269 impl<'tcx> LateLintPass<'tcx> for UnstableFeatures {
1270     fn check_attribute(&mut self, cx: &LateContext<'_>, attr: &ast::Attribute) {
1271         if cx.sess().check_name(attr, sym::feature) {
1272             if let Some(items) = attr.meta_item_list() {
1273                 for item in items {
1274                     cx.struct_span_lint(UNSTABLE_FEATURES, item.span(), |lint| {
1275                         lint.build("unstable feature").emit()
1276                     });
1277                 }
1278             }
1279         }
1280     }
1281 }
1282
1283 declare_lint! {
1284     /// The `unreachable_pub` lint triggers for `pub` items not reachable from
1285     /// the crate root.
1286     ///
1287     /// ### Example
1288     ///
1289     /// ```rust,compile_fail
1290     /// #![deny(unreachable_pub)]
1291     /// mod foo {
1292     ///     pub mod bar {
1293     ///
1294     ///     }
1295     /// }
1296     /// ```
1297     ///
1298     /// {{produces}}
1299     ///
1300     /// ### Explanation
1301     ///
1302     /// A bare `pub` visibility may be misleading if the item is not actually
1303     /// publicly exported from the crate. The `pub(crate)` visibility is
1304     /// recommended to be used instead, which more clearly expresses the intent
1305     /// that the item is only visible within its own crate.
1306     ///
1307     /// This lint is "allow" by default because it will trigger for a large
1308     /// amount existing Rust code, and has some false-positives. Eventually it
1309     /// is desired for this to become warn-by-default.
1310     pub UNREACHABLE_PUB,
1311     Allow,
1312     "`pub` items not reachable from crate root"
1313 }
1314
1315 declare_lint_pass!(
1316     /// Lint for items marked `pub` that aren't reachable from other crates.
1317     UnreachablePub => [UNREACHABLE_PUB]
1318 );
1319
1320 impl UnreachablePub {
1321     fn perform_lint(
1322         &self,
1323         cx: &LateContext<'_>,
1324         what: &str,
1325         id: hir::HirId,
1326         vis: &hir::Visibility<'_>,
1327         span: Span,
1328         exportable: bool,
1329     ) {
1330         let mut applicability = Applicability::MachineApplicable;
1331         match vis.node {
1332             hir::VisibilityKind::Public if !cx.access_levels.is_reachable(id) => {
1333                 if span.from_expansion() {
1334                     applicability = Applicability::MaybeIncorrect;
1335                 }
1336                 let def_span = cx.tcx.sess.source_map().guess_head_span(span);
1337                 cx.struct_span_lint(UNREACHABLE_PUB, def_span, |lint| {
1338                     let mut err = lint.build(&format!("unreachable `pub` {}", what));
1339                     let replacement = if cx.tcx.features().crate_visibility_modifier {
1340                         "crate"
1341                     } else {
1342                         "pub(crate)"
1343                     }
1344                     .to_owned();
1345
1346                     err.span_suggestion(
1347                         vis.span,
1348                         "consider restricting its visibility",
1349                         replacement,
1350                         applicability,
1351                     );
1352                     if exportable {
1353                         err.help("or consider exporting it for use by other crates");
1354                     }
1355                     err.emit();
1356                 });
1357             }
1358             _ => {}
1359         }
1360     }
1361 }
1362
1363 impl<'tcx> LateLintPass<'tcx> for UnreachablePub {
1364     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1365         self.perform_lint(cx, "item", item.hir_id, &item.vis, item.span, true);
1366     }
1367
1368     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'tcx>) {
1369         self.perform_lint(
1370             cx,
1371             "item",
1372             foreign_item.hir_id,
1373             &foreign_item.vis,
1374             foreign_item.span,
1375             true,
1376         );
1377     }
1378
1379     fn check_struct_field(&mut self, cx: &LateContext<'_>, field: &hir::StructField<'_>) {
1380         self.perform_lint(cx, "field", field.hir_id, &field.vis, field.span, false);
1381     }
1382
1383     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
1384         self.perform_lint(cx, "item", impl_item.hir_id, &impl_item.vis, impl_item.span, false);
1385     }
1386 }
1387
1388 declare_lint! {
1389     /// The `type_alias_bounds` lint detects bounds in type aliases.
1390     ///
1391     /// ### Example
1392     ///
1393     /// ```rust
1394     /// type SendVec<T: Send> = Vec<T>;
1395     /// ```
1396     ///
1397     /// {{produces}}
1398     ///
1399     /// ### Explanation
1400     ///
1401     /// The trait bounds in a type alias are currently ignored, and should not
1402     /// be included to avoid confusion. This was previously allowed
1403     /// unintentionally; this may become a hard error in the future.
1404     TYPE_ALIAS_BOUNDS,
1405     Warn,
1406     "bounds in type aliases are not enforced"
1407 }
1408
1409 declare_lint_pass!(
1410     /// Lint for trait and lifetime bounds in type aliases being mostly ignored.
1411     /// They are relevant when using associated types, but otherwise neither checked
1412     /// at definition site nor enforced at use site.
1413     TypeAliasBounds => [TYPE_ALIAS_BOUNDS]
1414 );
1415
1416 impl TypeAliasBounds {
1417     fn is_type_variable_assoc(qpath: &hir::QPath<'_>) -> bool {
1418         match *qpath {
1419             hir::QPath::TypeRelative(ref ty, _) => {
1420                 // If this is a type variable, we found a `T::Assoc`.
1421                 match ty.kind {
1422                     hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
1423                         matches!(path.res, Res::Def(DefKind::TyParam, _))
1424                     }
1425                     _ => false,
1426                 }
1427             }
1428             hir::QPath::Resolved(..) | hir::QPath::LangItem(..) => false,
1429         }
1430     }
1431
1432     fn suggest_changing_assoc_types(ty: &hir::Ty<'_>, err: &mut DiagnosticBuilder<'_>) {
1433         // Access to associates types should use `<T as Bound>::Assoc`, which does not need a
1434         // bound.  Let's see if this type does that.
1435
1436         // We use a HIR visitor to walk the type.
1437         use rustc_hir::intravisit::{self, Visitor};
1438         struct WalkAssocTypes<'a, 'db> {
1439             err: &'a mut DiagnosticBuilder<'db>,
1440         }
1441         impl<'a, 'db, 'v> Visitor<'v> for WalkAssocTypes<'a, 'db> {
1442             type Map = intravisit::ErasedMap<'v>;
1443
1444             fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1445                 intravisit::NestedVisitorMap::None
1446             }
1447
1448             fn visit_qpath(&mut self, qpath: &'v hir::QPath<'v>, id: hir::HirId, span: Span) {
1449                 if TypeAliasBounds::is_type_variable_assoc(qpath) {
1450                     self.err.span_help(
1451                         span,
1452                         "use fully disambiguated paths (i.e., `<T as Trait>::Assoc`) to refer to \
1453                          associated types in type aliases",
1454                     );
1455                 }
1456                 intravisit::walk_qpath(self, qpath, id, span)
1457             }
1458         }
1459
1460         // Let's go for a walk!
1461         let mut visitor = WalkAssocTypes { err };
1462         visitor.visit_ty(ty);
1463     }
1464 }
1465
1466 impl<'tcx> LateLintPass<'tcx> for TypeAliasBounds {
1467     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1468         let (ty, type_alias_generics) = match item.kind {
1469             hir::ItemKind::TyAlias(ref ty, ref generics) => (&*ty, generics),
1470             _ => return,
1471         };
1472         if let hir::TyKind::OpaqueDef(..) = ty.kind {
1473             // Bounds are respected for `type X = impl Trait`
1474             return;
1475         }
1476         let mut suggested_changing_assoc_types = false;
1477         // There must not be a where clause
1478         if !type_alias_generics.where_clause.predicates.is_empty() {
1479             cx.lint(
1480                 TYPE_ALIAS_BOUNDS,
1481                 |lint| {
1482                     let mut err = lint.build("where clauses are not enforced in type aliases");
1483                     let spans: Vec<_> = type_alias_generics
1484                         .where_clause
1485                         .predicates
1486                         .iter()
1487                         .map(|pred| pred.span())
1488                         .collect();
1489                     err.set_span(spans);
1490                     err.span_suggestion(
1491                         type_alias_generics.where_clause.span_for_predicates_or_empty_place(),
1492                         "the clause will not be checked when the type alias is used, and should be removed",
1493                         String::new(),
1494                         Applicability::MachineApplicable,
1495                     );
1496                     if !suggested_changing_assoc_types {
1497                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1498                         suggested_changing_assoc_types = true;
1499                     }
1500                     err.emit();
1501                 },
1502             );
1503         }
1504         // The parameters must not have bounds
1505         for param in type_alias_generics.params.iter() {
1506             let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
1507             let suggestion = spans
1508                 .iter()
1509                 .map(|sp| {
1510                     let start = param.span.between(*sp); // Include the `:` in `T: Bound`.
1511                     (start.to(*sp), String::new())
1512                 })
1513                 .collect();
1514             if !spans.is_empty() {
1515                 cx.struct_span_lint(TYPE_ALIAS_BOUNDS, spans, |lint| {
1516                     let mut err =
1517                         lint.build("bounds on generic parameters are not enforced in type aliases");
1518                     let msg = "the bound will not be checked when the type alias is used, \
1519                                    and should be removed";
1520                     err.multipart_suggestion(&msg, suggestion, Applicability::MachineApplicable);
1521                     if !suggested_changing_assoc_types {
1522                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1523                         suggested_changing_assoc_types = true;
1524                     }
1525                     err.emit();
1526                 });
1527             }
1528         }
1529     }
1530 }
1531
1532 declare_lint_pass!(
1533     /// Lint constants that are erroneous.
1534     /// Without this lint, we might not get any diagnostic if the constant is
1535     /// unused within this crate, even though downstream crates can't use it
1536     /// without producing an error.
1537     UnusedBrokenConst => []
1538 );
1539
1540 impl<'tcx> LateLintPass<'tcx> for UnusedBrokenConst {
1541     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1542         match it.kind {
1543             hir::ItemKind::Const(_, body_id) => {
1544                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1545                 // trigger the query once for all constants since that will already report the errors
1546                 // FIXME: Use ensure here
1547                 let _ = cx.tcx.const_eval_poly(def_id);
1548             }
1549             hir::ItemKind::Static(_, _, body_id) => {
1550                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1551                 // FIXME: Use ensure here
1552                 let _ = cx.tcx.eval_static_initializer(def_id);
1553             }
1554             _ => {}
1555         }
1556     }
1557 }
1558
1559 declare_lint! {
1560     /// The `trivial_bounds` lint detects trait bounds that don't depend on
1561     /// any type parameters.
1562     ///
1563     /// ### Example
1564     ///
1565     /// ```rust
1566     /// #![feature(trivial_bounds)]
1567     /// pub struct A where i32: Copy;
1568     /// ```
1569     ///
1570     /// {{produces}}
1571     ///
1572     /// ### Explanation
1573     ///
1574     /// Usually you would not write a trait bound that you know is always
1575     /// true, or never true. However, when using macros, the macro may not
1576     /// know whether or not the constraint would hold or not at the time when
1577     /// generating the code. Currently, the compiler does not alert you if the
1578     /// constraint is always true, and generates an error if it is never true.
1579     /// The `trivial_bounds` feature changes this to be a warning in both
1580     /// cases, giving macros more freedom and flexibility to generate code,
1581     /// while still providing a signal when writing non-macro code that
1582     /// something is amiss.
1583     ///
1584     /// See [RFC 2056] for more details. This feature is currently only
1585     /// available on the nightly channel, see [tracking issue #48214].
1586     ///
1587     /// [RFC 2056]: https://github.com/rust-lang/rfcs/blob/master/text/2056-allow-trivial-where-clause-constraints.md
1588     /// [tracking issue #48214]: https://github.com/rust-lang/rust/issues/48214
1589     TRIVIAL_BOUNDS,
1590     Warn,
1591     "these bounds don't depend on an type parameters"
1592 }
1593
1594 declare_lint_pass!(
1595     /// Lint for trait and lifetime bounds that don't depend on type parameters
1596     /// which either do nothing, or stop the item from being used.
1597     TrivialConstraints => [TRIVIAL_BOUNDS]
1598 );
1599
1600 impl<'tcx> LateLintPass<'tcx> for TrivialConstraints {
1601     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
1602         use rustc_middle::ty::fold::TypeFoldable;
1603         use rustc_middle::ty::PredicateKind::*;
1604
1605         if cx.tcx.features().trivial_bounds {
1606             let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1607             let predicates = cx.tcx.predicates_of(def_id);
1608             for &(predicate, span) in predicates.predicates {
1609                 let predicate_kind_name = match predicate.kind().skip_binder() {
1610                     Trait(..) => "Trait",
1611                     TypeOutlives(..) |
1612                     RegionOutlives(..) => "Lifetime",
1613
1614                     // Ignore projections, as they can only be global
1615                     // if the trait bound is global
1616                     Projection(..) |
1617                     // Ignore bounds that a user can't type
1618                     WellFormed(..) |
1619                     ObjectSafe(..) |
1620                     ClosureKind(..) |
1621                     Subtype(..) |
1622                     ConstEvaluatable(..) |
1623                     ConstEquate(..) |
1624                     TypeWellFormedFromEnv(..) => continue,
1625                 };
1626                 if predicate.is_global() {
1627                     cx.struct_span_lint(TRIVIAL_BOUNDS, span, |lint| {
1628                         lint.build(&format!(
1629                             "{} bound {} does not depend on any type \
1630                                 or lifetime parameters",
1631                             predicate_kind_name, predicate
1632                         ))
1633                         .emit()
1634                     });
1635                 }
1636             }
1637         }
1638     }
1639 }
1640
1641 declare_lint_pass!(
1642     /// Does nothing as a lint pass, but registers some `Lint`s
1643     /// which are used by other parts of the compiler.
1644     SoftLints => [
1645         WHILE_TRUE,
1646         BOX_POINTERS,
1647         NON_SHORTHAND_FIELD_PATTERNS,
1648         UNSAFE_CODE,
1649         MISSING_DOCS,
1650         MISSING_COPY_IMPLEMENTATIONS,
1651         MISSING_DEBUG_IMPLEMENTATIONS,
1652         ANONYMOUS_PARAMETERS,
1653         UNUSED_DOC_COMMENTS,
1654         NO_MANGLE_CONST_ITEMS,
1655         NO_MANGLE_GENERIC_ITEMS,
1656         MUTABLE_TRANSMUTES,
1657         UNSTABLE_FEATURES,
1658         UNREACHABLE_PUB,
1659         TYPE_ALIAS_BOUNDS,
1660         TRIVIAL_BOUNDS
1661     ]
1662 );
1663
1664 declare_lint! {
1665     /// The `ellipsis_inclusive_range_patterns` lint detects the [`...` range
1666     /// pattern], which is deprecated.
1667     ///
1668     /// [`...` range pattern]: https://doc.rust-lang.org/reference/patterns.html#range-patterns
1669     ///
1670     /// ### Example
1671     ///
1672     /// ```rust
1673     /// let x = 123;
1674     /// match x {
1675     ///     0...100 => {}
1676     ///     _ => {}
1677     /// }
1678     /// ```
1679     ///
1680     /// {{produces}}
1681     ///
1682     /// ### Explanation
1683     ///
1684     /// The `...` range pattern syntax was changed to `..=` to avoid potential
1685     /// confusion with the [`..` range expression]. Use the new form instead.
1686     ///
1687     /// [`..` range expression]: https://doc.rust-lang.org/reference/expressions/range-expr.html
1688     pub ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
1689     Warn,
1690     "`...` range patterns are deprecated"
1691 }
1692
1693 #[derive(Default)]
1694 pub struct EllipsisInclusiveRangePatterns {
1695     /// If `Some(_)`, suppress all subsequent pattern
1696     /// warnings for better diagnostics.
1697     node_id: Option<ast::NodeId>,
1698 }
1699
1700 impl_lint_pass!(EllipsisInclusiveRangePatterns => [ELLIPSIS_INCLUSIVE_RANGE_PATTERNS]);
1701
1702 impl EarlyLintPass for EllipsisInclusiveRangePatterns {
1703     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &ast::Pat) {
1704         if self.node_id.is_some() {
1705             // Don't recursively warn about patterns inside range endpoints.
1706             return;
1707         }
1708
1709         use self::ast::{PatKind, RangeSyntax::DotDotDot};
1710
1711         /// If `pat` is a `...` pattern, return the start and end of the range, as well as the span
1712         /// corresponding to the ellipsis.
1713         fn matches_ellipsis_pat(pat: &ast::Pat) -> Option<(Option<&Expr>, &Expr, Span)> {
1714             match &pat.kind {
1715                 PatKind::Range(
1716                     a,
1717                     Some(b),
1718                     Spanned { span, node: RangeEnd::Included(DotDotDot) },
1719                 ) => Some((a.as_deref(), b, *span)),
1720                 _ => None,
1721             }
1722         }
1723
1724         let (parenthesise, endpoints) = match &pat.kind {
1725             PatKind::Ref(subpat, _) => (true, matches_ellipsis_pat(&subpat)),
1726             _ => (false, matches_ellipsis_pat(pat)),
1727         };
1728
1729         if let Some((start, end, join)) = endpoints {
1730             let msg = "`...` range patterns are deprecated";
1731             let suggestion = "use `..=` for an inclusive range";
1732             if parenthesise {
1733                 self.node_id = Some(pat.id);
1734                 cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, pat.span, |lint| {
1735                     let end = expr_to_string(&end);
1736                     let replace = match start {
1737                         Some(start) => format!("&({}..={})", expr_to_string(&start), end),
1738                         None => format!("&(..={})", end),
1739                     };
1740                     lint.build(msg)
1741                         .span_suggestion(
1742                             pat.span,
1743                             suggestion,
1744                             replace,
1745                             Applicability::MachineApplicable,
1746                         )
1747                         .emit();
1748                 });
1749             } else {
1750                 cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, join, |lint| {
1751                     lint.build(msg)
1752                         .span_suggestion_short(
1753                             join,
1754                             suggestion,
1755                             "..=".to_owned(),
1756                             Applicability::MachineApplicable,
1757                         )
1758                         .emit();
1759                 });
1760             };
1761         }
1762     }
1763
1764     fn check_pat_post(&mut self, _cx: &EarlyContext<'_>, pat: &ast::Pat) {
1765         if let Some(node_id) = self.node_id {
1766             if pat.id == node_id {
1767                 self.node_id = None
1768             }
1769         }
1770     }
1771 }
1772
1773 declare_lint! {
1774     /// The `unnameable_test_items` lint detects [`#[test]`][test] functions
1775     /// that are not able to be run by the test harness because they are in a
1776     /// position where they are not nameable.
1777     ///
1778     /// [test]: https://doc.rust-lang.org/reference/attributes/testing.html#the-test-attribute
1779     ///
1780     /// ### Example
1781     ///
1782     /// ```rust,test
1783     /// fn main() {
1784     ///     #[test]
1785     ///     fn foo() {
1786     ///         // This test will not fail because it does not run.
1787     ///         assert_eq!(1, 2);
1788     ///     }
1789     /// }
1790     /// ```
1791     ///
1792     /// {{produces}}
1793     ///
1794     /// ### Explanation
1795     ///
1796     /// In order for the test harness to run a test, the test function must be
1797     /// located in a position where it can be accessed from the crate root.
1798     /// This generally means it must be defined in a module, and not anywhere
1799     /// else such as inside another function. The compiler previously allowed
1800     /// this without an error, so a lint was added as an alert that a test is
1801     /// not being used. Whether or not this should be allowed has not yet been
1802     /// decided, see [RFC 2471] and [issue #36629].
1803     ///
1804     /// [RFC 2471]: https://github.com/rust-lang/rfcs/pull/2471#issuecomment-397414443
1805     /// [issue #36629]: https://github.com/rust-lang/rust/issues/36629
1806     UNNAMEABLE_TEST_ITEMS,
1807     Warn,
1808     "detects an item that cannot be named being marked as `#[test_case]`",
1809     report_in_external_macro
1810 }
1811
1812 pub struct UnnameableTestItems {
1813     boundary: Option<hir::HirId>, // HirId of the item under which things are not nameable
1814     items_nameable: bool,
1815 }
1816
1817 impl_lint_pass!(UnnameableTestItems => [UNNAMEABLE_TEST_ITEMS]);
1818
1819 impl UnnameableTestItems {
1820     pub fn new() -> Self {
1821         Self { boundary: None, items_nameable: true }
1822     }
1823 }
1824
1825 impl<'tcx> LateLintPass<'tcx> for UnnameableTestItems {
1826     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1827         if self.items_nameable {
1828             if let hir::ItemKind::Mod(..) = it.kind {
1829             } else {
1830                 self.items_nameable = false;
1831                 self.boundary = Some(it.hir_id);
1832             }
1833             return;
1834         }
1835
1836         if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::rustc_test_marker) {
1837             cx.struct_span_lint(UNNAMEABLE_TEST_ITEMS, attr.span, |lint| {
1838                 lint.build("cannot test inner items").emit()
1839             });
1840         }
1841     }
1842
1843     fn check_item_post(&mut self, _cx: &LateContext<'_>, it: &hir::Item<'_>) {
1844         if !self.items_nameable && self.boundary == Some(it.hir_id) {
1845             self.items_nameable = true;
1846         }
1847     }
1848 }
1849
1850 declare_lint! {
1851     /// The `keyword_idents` lint detects edition keywords being used as an
1852     /// identifier.
1853     ///
1854     /// ### Example
1855     ///
1856     /// ```rust,edition2015,compile_fail
1857     /// #![deny(keyword_idents)]
1858     /// // edition 2015
1859     /// fn dyn() {}
1860     /// ```
1861     ///
1862     /// {{produces}}
1863     ///
1864     /// ### Explanation
1865     ///
1866     /// Rust [editions] allow the language to evolve without breaking
1867     /// backwards compatibility. This lint catches code that uses new keywords
1868     /// that are added to the language that are used as identifiers (such as a
1869     /// variable name, function name, etc.). If you switch the compiler to a
1870     /// new edition without updating the code, then it will fail to compile if
1871     /// you are using a new keyword as an identifier.
1872     ///
1873     /// You can manually change the identifiers to a non-keyword, or use a
1874     /// [raw identifier], for example `r#dyn`, to transition to a new edition.
1875     ///
1876     /// This lint solves the problem automatically. It is "allow" by default
1877     /// because the code is perfectly valid in older editions. The [`cargo
1878     /// fix`] tool with the `--edition` flag will switch this lint to "warn"
1879     /// and automatically apply the suggested fix from the compiler (which is
1880     /// to use a raw identifier). This provides a completely automated way to
1881     /// update old code for a new edition.
1882     ///
1883     /// [editions]: https://doc.rust-lang.org/edition-guide/
1884     /// [raw identifier]: https://doc.rust-lang.org/reference/identifiers.html
1885     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
1886     pub KEYWORD_IDENTS,
1887     Allow,
1888     "detects edition keywords being used as an identifier",
1889     @future_incompatible = FutureIncompatibleInfo {
1890         reference: "issue #49716 <https://github.com/rust-lang/rust/issues/49716>",
1891         edition: Some(Edition::Edition2018),
1892     };
1893 }
1894
1895 declare_lint_pass!(
1896     /// Check for uses of edition keywords used as an identifier.
1897     KeywordIdents => [KEYWORD_IDENTS]
1898 );
1899
1900 struct UnderMacro(bool);
1901
1902 impl KeywordIdents {
1903     fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: TokenStream) {
1904         for tt in tokens.into_trees() {
1905             match tt {
1906                 // Only report non-raw idents.
1907                 TokenTree::Token(token) => {
1908                     if let Some((ident, false)) = token.ident() {
1909                         self.check_ident_token(cx, UnderMacro(true), ident);
1910                     }
1911                 }
1912                 TokenTree::Delimited(_, _, tts) => self.check_tokens(cx, tts),
1913             }
1914         }
1915     }
1916
1917     fn check_ident_token(
1918         &mut self,
1919         cx: &EarlyContext<'_>,
1920         UnderMacro(under_macro): UnderMacro,
1921         ident: Ident,
1922     ) {
1923         let next_edition = match cx.sess.edition() {
1924             Edition::Edition2015 => {
1925                 match ident.name {
1926                     kw::Async | kw::Await | kw::Try => Edition::Edition2018,
1927
1928                     // rust-lang/rust#56327: Conservatively do not
1929                     // attempt to report occurrences of `dyn` within
1930                     // macro definitions or invocations, because `dyn`
1931                     // can legitimately occur as a contextual keyword
1932                     // in 2015 code denoting its 2018 meaning, and we
1933                     // do not want rustfix to inject bugs into working
1934                     // code by rewriting such occurrences.
1935                     //
1936                     // But if we see `dyn` outside of a macro, we know
1937                     // its precise role in the parsed AST and thus are
1938                     // assured this is truly an attempt to use it as
1939                     // an identifier.
1940                     kw::Dyn if !under_macro => Edition::Edition2018,
1941
1942                     _ => return,
1943                 }
1944             }
1945
1946             // There are no new keywords yet for the 2018 edition and beyond.
1947             _ => return,
1948         };
1949
1950         // Don't lint `r#foo`.
1951         if cx.sess.parse_sess.raw_identifier_spans.borrow().contains(&ident.span) {
1952             return;
1953         }
1954
1955         cx.struct_span_lint(KEYWORD_IDENTS, ident.span, |lint| {
1956             lint.build(&format!("`{}` is a keyword in the {} edition", ident, next_edition))
1957                 .span_suggestion(
1958                     ident.span,
1959                     "you can use a raw identifier to stay compatible",
1960                     format!("r#{}", ident),
1961                     Applicability::MachineApplicable,
1962                 )
1963                 .emit()
1964         });
1965     }
1966 }
1967
1968 impl EarlyLintPass for KeywordIdents {
1969     fn check_mac_def(&mut self, cx: &EarlyContext<'_>, mac_def: &ast::MacroDef, _id: ast::NodeId) {
1970         self.check_tokens(cx, mac_def.body.inner_tokens());
1971     }
1972     fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::MacCall) {
1973         self.check_tokens(cx, mac.args.inner_tokens());
1974     }
1975     fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: Ident) {
1976         self.check_ident_token(cx, UnderMacro(false), ident);
1977     }
1978 }
1979
1980 declare_lint_pass!(ExplicitOutlivesRequirements => [EXPLICIT_OUTLIVES_REQUIREMENTS]);
1981
1982 impl ExplicitOutlivesRequirements {
1983     fn lifetimes_outliving_lifetime<'tcx>(
1984         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
1985         index: u32,
1986     ) -> Vec<ty::Region<'tcx>> {
1987         inferred_outlives
1988             .iter()
1989             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
1990                 ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => match a {
1991                     ty::ReEarlyBound(ebr) if ebr.index == index => Some(b),
1992                     _ => None,
1993                 },
1994                 _ => None,
1995             })
1996             .collect()
1997     }
1998
1999     fn lifetimes_outliving_type<'tcx>(
2000         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2001         index: u32,
2002     ) -> Vec<ty::Region<'tcx>> {
2003         inferred_outlives
2004             .iter()
2005             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
2006                 ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
2007                     a.is_param(index).then_some(b)
2008                 }
2009                 _ => None,
2010             })
2011             .collect()
2012     }
2013
2014     fn collect_outlived_lifetimes<'tcx>(
2015         &self,
2016         param: &'tcx hir::GenericParam<'tcx>,
2017         tcx: TyCtxt<'tcx>,
2018         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2019         ty_generics: &'tcx ty::Generics,
2020     ) -> Vec<ty::Region<'tcx>> {
2021         let index =
2022             ty_generics.param_def_id_to_index[&tcx.hir().local_def_id(param.hir_id).to_def_id()];
2023
2024         match param.kind {
2025             hir::GenericParamKind::Lifetime { .. } => {
2026                 Self::lifetimes_outliving_lifetime(inferred_outlives, index)
2027             }
2028             hir::GenericParamKind::Type { .. } => {
2029                 Self::lifetimes_outliving_type(inferred_outlives, index)
2030             }
2031             hir::GenericParamKind::Const { .. } => Vec::new(),
2032         }
2033     }
2034
2035     fn collect_outlives_bound_spans<'tcx>(
2036         &self,
2037         tcx: TyCtxt<'tcx>,
2038         bounds: &hir::GenericBounds<'_>,
2039         inferred_outlives: &[ty::Region<'tcx>],
2040         infer_static: bool,
2041     ) -> Vec<(usize, Span)> {
2042         use rustc_middle::middle::resolve_lifetime::Region;
2043
2044         bounds
2045             .iter()
2046             .enumerate()
2047             .filter_map(|(i, bound)| {
2048                 if let hir::GenericBound::Outlives(lifetime) = bound {
2049                     let is_inferred = match tcx.named_region(lifetime.hir_id) {
2050                         Some(Region::Static) if infer_static => {
2051                             inferred_outlives.iter().any(|r| matches!(r, ty::ReStatic))
2052                         }
2053                         Some(Region::EarlyBound(index, ..)) => inferred_outlives.iter().any(|r| {
2054                             if let ty::ReEarlyBound(ebr) = r { ebr.index == index } else { false }
2055                         }),
2056                         _ => false,
2057                     };
2058                     is_inferred.then_some((i, bound.span()))
2059                 } else {
2060                     None
2061                 }
2062             })
2063             .collect()
2064     }
2065
2066     fn consolidate_outlives_bound_spans(
2067         &self,
2068         lo: Span,
2069         bounds: &hir::GenericBounds<'_>,
2070         bound_spans: Vec<(usize, Span)>,
2071     ) -> Vec<Span> {
2072         if bounds.is_empty() {
2073             return Vec::new();
2074         }
2075         if bound_spans.len() == bounds.len() {
2076             let (_, last_bound_span) = bound_spans[bound_spans.len() - 1];
2077             // If all bounds are inferable, we want to delete the colon, so
2078             // start from just after the parameter (span passed as argument)
2079             vec![lo.to(last_bound_span)]
2080         } else {
2081             let mut merged = Vec::new();
2082             let mut last_merged_i = None;
2083
2084             let mut from_start = true;
2085             for (i, bound_span) in bound_spans {
2086                 match last_merged_i {
2087                     // If the first bound is inferable, our span should also eat the leading `+`.
2088                     None if i == 0 => {
2089                         merged.push(bound_span.to(bounds[1].span().shrink_to_lo()));
2090                         last_merged_i = Some(0);
2091                     }
2092                     // If consecutive bounds are inferable, merge their spans
2093                     Some(h) if i == h + 1 => {
2094                         if let Some(tail) = merged.last_mut() {
2095                             // Also eat the trailing `+` if the first
2096                             // more-than-one bound is inferable
2097                             let to_span = if from_start && i < bounds.len() {
2098                                 bounds[i + 1].span().shrink_to_lo()
2099                             } else {
2100                                 bound_span
2101                             };
2102                             *tail = tail.to(to_span);
2103                             last_merged_i = Some(i);
2104                         } else {
2105                             bug!("another bound-span visited earlier");
2106                         }
2107                     }
2108                     _ => {
2109                         // When we find a non-inferable bound, subsequent inferable bounds
2110                         // won't be consecutive from the start (and we'll eat the leading
2111                         // `+` rather than the trailing one)
2112                         from_start = false;
2113                         merged.push(bounds[i - 1].span().shrink_to_hi().to(bound_span));
2114                         last_merged_i = Some(i);
2115                     }
2116                 }
2117             }
2118             merged
2119         }
2120     }
2121 }
2122
2123 impl<'tcx> LateLintPass<'tcx> for ExplicitOutlivesRequirements {
2124     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
2125         use rustc_middle::middle::resolve_lifetime::Region;
2126
2127         let infer_static = cx.tcx.features().infer_static_outlives_requirements;
2128         let def_id = cx.tcx.hir().local_def_id(item.hir_id);
2129         if let hir::ItemKind::Struct(_, ref hir_generics)
2130         | hir::ItemKind::Enum(_, ref hir_generics)
2131         | hir::ItemKind::Union(_, ref hir_generics) = item.kind
2132         {
2133             let inferred_outlives = cx.tcx.inferred_outlives_of(def_id);
2134             if inferred_outlives.is_empty() {
2135                 return;
2136             }
2137
2138             let ty_generics = cx.tcx.generics_of(def_id);
2139
2140             let mut bound_count = 0;
2141             let mut lint_spans = Vec::new();
2142
2143             for param in hir_generics.params {
2144                 let has_lifetime_bounds = param
2145                     .bounds
2146                     .iter()
2147                     .any(|bound| matches!(bound, hir::GenericBound::Outlives(_)));
2148                 if !has_lifetime_bounds {
2149                     continue;
2150                 }
2151
2152                 let relevant_lifetimes =
2153                     self.collect_outlived_lifetimes(param, cx.tcx, inferred_outlives, ty_generics);
2154                 if relevant_lifetimes.is_empty() {
2155                     continue;
2156                 }
2157
2158                 let bound_spans = self.collect_outlives_bound_spans(
2159                     cx.tcx,
2160                     &param.bounds,
2161                     &relevant_lifetimes,
2162                     infer_static,
2163                 );
2164                 bound_count += bound_spans.len();
2165                 lint_spans.extend(self.consolidate_outlives_bound_spans(
2166                     param.span.shrink_to_hi(),
2167                     &param.bounds,
2168                     bound_spans,
2169                 ));
2170             }
2171
2172             let mut where_lint_spans = Vec::new();
2173             let mut dropped_predicate_count = 0;
2174             let num_predicates = hir_generics.where_clause.predicates.len();
2175             for (i, where_predicate) in hir_generics.where_clause.predicates.iter().enumerate() {
2176                 let (relevant_lifetimes, bounds, span) = match where_predicate {
2177                     hir::WherePredicate::RegionPredicate(predicate) => {
2178                         if let Some(Region::EarlyBound(index, ..)) =
2179                             cx.tcx.named_region(predicate.lifetime.hir_id)
2180                         {
2181                             (
2182                                 Self::lifetimes_outliving_lifetime(inferred_outlives, index),
2183                                 &predicate.bounds,
2184                                 predicate.span,
2185                             )
2186                         } else {
2187                             continue;
2188                         }
2189                     }
2190                     hir::WherePredicate::BoundPredicate(predicate) => {
2191                         // FIXME we can also infer bounds on associated types,
2192                         // and should check for them here.
2193                         match predicate.bounded_ty.kind {
2194                             hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
2195                                 if let Res::Def(DefKind::TyParam, def_id) = path.res {
2196                                     let index = ty_generics.param_def_id_to_index[&def_id];
2197                                     (
2198                                         Self::lifetimes_outliving_type(inferred_outlives, index),
2199                                         &predicate.bounds,
2200                                         predicate.span,
2201                                     )
2202                                 } else {
2203                                     continue;
2204                                 }
2205                             }
2206                             _ => {
2207                                 continue;
2208                             }
2209                         }
2210                     }
2211                     _ => continue,
2212                 };
2213                 if relevant_lifetimes.is_empty() {
2214                     continue;
2215                 }
2216
2217                 let bound_spans = self.collect_outlives_bound_spans(
2218                     cx.tcx,
2219                     bounds,
2220                     &relevant_lifetimes,
2221                     infer_static,
2222                 );
2223                 bound_count += bound_spans.len();
2224
2225                 let drop_predicate = bound_spans.len() == bounds.len();
2226                 if drop_predicate {
2227                     dropped_predicate_count += 1;
2228                 }
2229
2230                 // If all the bounds on a predicate were inferable and there are
2231                 // further predicates, we want to eat the trailing comma.
2232                 if drop_predicate && i + 1 < num_predicates {
2233                     let next_predicate_span = hir_generics.where_clause.predicates[i + 1].span();
2234                     where_lint_spans.push(span.to(next_predicate_span.shrink_to_lo()));
2235                 } else {
2236                     where_lint_spans.extend(self.consolidate_outlives_bound_spans(
2237                         span.shrink_to_lo(),
2238                         bounds,
2239                         bound_spans,
2240                     ));
2241                 }
2242             }
2243
2244             // If all predicates are inferable, drop the entire clause
2245             // (including the `where`)
2246             if num_predicates > 0 && dropped_predicate_count == num_predicates {
2247                 let where_span = hir_generics
2248                     .where_clause
2249                     .span()
2250                     .expect("span of (nonempty) where clause should exist");
2251                 // Extend the where clause back to the closing `>` of the
2252                 // generics, except for tuple struct, which have the `where`
2253                 // after the fields of the struct.
2254                 let full_where_span =
2255                     if let hir::ItemKind::Struct(hir::VariantData::Tuple(..), _) = item.kind {
2256                         where_span
2257                     } else {
2258                         hir_generics.span.shrink_to_hi().to(where_span)
2259                     };
2260                 lint_spans.push(full_where_span);
2261             } else {
2262                 lint_spans.extend(where_lint_spans);
2263             }
2264
2265             if !lint_spans.is_empty() {
2266                 cx.struct_span_lint(EXPLICIT_OUTLIVES_REQUIREMENTS, lint_spans.clone(), |lint| {
2267                     lint.build("outlives requirements can be inferred")
2268                         .multipart_suggestion(
2269                             if bound_count == 1 {
2270                                 "remove this bound"
2271                             } else {
2272                                 "remove these bounds"
2273                             },
2274                             lint_spans
2275                                 .into_iter()
2276                                 .map(|span| (span, "".to_owned()))
2277                                 .collect::<Vec<_>>(),
2278                             Applicability::MachineApplicable,
2279                         )
2280                         .emit();
2281                 });
2282             }
2283         }
2284     }
2285 }
2286
2287 declare_lint! {
2288     /// The `incomplete_features` lint detects unstable features enabled with
2289     /// the [`feature` attribute] that may function improperly in some or all
2290     /// cases.
2291     ///
2292     /// [`feature` attribute]: https://doc.rust-lang.org/nightly/unstable-book/
2293     ///
2294     /// ### Example
2295     ///
2296     /// ```rust
2297     /// #![feature(generic_associated_types)]
2298     /// ```
2299     ///
2300     /// {{produces}}
2301     ///
2302     /// ### Explanation
2303     ///
2304     /// Although it is encouraged for people to experiment with unstable
2305     /// features, some of them are known to be incomplete or faulty. This lint
2306     /// is a signal that the feature has not yet been finished, and you may
2307     /// experience problems with it.
2308     pub INCOMPLETE_FEATURES,
2309     Warn,
2310     "incomplete features that may function improperly in some or all cases"
2311 }
2312
2313 declare_lint_pass!(
2314     /// Check for used feature gates in `INCOMPLETE_FEATURES` in `librustc_feature/active.rs`.
2315     IncompleteFeatures => [INCOMPLETE_FEATURES]
2316 );
2317
2318 impl EarlyLintPass for IncompleteFeatures {
2319     fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
2320         let features = cx.sess.features_untracked();
2321         features
2322             .declared_lang_features
2323             .iter()
2324             .map(|(name, span, _)| (name, span))
2325             .chain(features.declared_lib_features.iter().map(|(name, span)| (name, span)))
2326             .filter(|(name, _)| rustc_feature::INCOMPLETE_FEATURES.iter().any(|f| name == &f))
2327             .for_each(|(&name, &span)| {
2328                 cx.struct_span_lint(INCOMPLETE_FEATURES, span, |lint| {
2329                     let mut builder = lint.build(&format!(
2330                         "the feature `{}` is incomplete and may not be safe to use \
2331                          and/or cause compiler crashes",
2332                         name,
2333                     ));
2334                     if let Some(n) = rustc_feature::find_feature_issue(name, GateIssue::Language) {
2335                         builder.note(&format!(
2336                             "see issue #{} <https://github.com/rust-lang/rust/issues/{}> \
2337                              for more information",
2338                             n, n,
2339                         ));
2340                     }
2341                     if HAS_MIN_FEATURES.contains(&name) {
2342                         builder.help(&format!(
2343                             "consider using `min_{}` instead, which is more stable and complete",
2344                             name,
2345                         ));
2346                     }
2347                     builder.emit();
2348                 })
2349             });
2350     }
2351 }
2352
2353 const HAS_MIN_FEATURES: &[Symbol] = &[sym::specialization];
2354
2355 declare_lint! {
2356     /// The `invalid_value` lint detects creating a value that is not valid,
2357     /// such as a NULL reference.
2358     ///
2359     /// ### Example
2360     ///
2361     /// ```rust,no_run
2362     /// # #![allow(unused)]
2363     /// unsafe {
2364     ///     let x: &'static i32 = std::mem::zeroed();
2365     /// }
2366     /// ```
2367     ///
2368     /// {{produces}}
2369     ///
2370     /// ### Explanation
2371     ///
2372     /// In some situations the compiler can detect that the code is creating
2373     /// an invalid value, which should be avoided.
2374     ///
2375     /// In particular, this lint will check for improper use of
2376     /// [`mem::zeroed`], [`mem::uninitialized`], [`mem::transmute`], and
2377     /// [`MaybeUninit::assume_init`] that can cause [undefined behavior]. The
2378     /// lint should provide extra information to indicate what the problem is
2379     /// and a possible solution.
2380     ///
2381     /// [`mem::zeroed`]: https://doc.rust-lang.org/std/mem/fn.zeroed.html
2382     /// [`mem::uninitialized`]: https://doc.rust-lang.org/std/mem/fn.uninitialized.html
2383     /// [`mem::transmute`]: https://doc.rust-lang.org/std/mem/fn.transmute.html
2384     /// [`MaybeUninit::assume_init`]: https://doc.rust-lang.org/std/mem/union.MaybeUninit.html#method.assume_init
2385     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
2386     pub INVALID_VALUE,
2387     Warn,
2388     "an invalid value is being created (such as a NULL reference)"
2389 }
2390
2391 declare_lint_pass!(InvalidValue => [INVALID_VALUE]);
2392
2393 impl<'tcx> LateLintPass<'tcx> for InvalidValue {
2394     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
2395         #[derive(Debug, Copy, Clone, PartialEq)]
2396         enum InitKind {
2397             Zeroed,
2398             Uninit,
2399         }
2400
2401         /// Information about why a type cannot be initialized this way.
2402         /// Contains an error message and optionally a span to point at.
2403         type InitError = (String, Option<Span>);
2404
2405         /// Test if this constant is all-0.
2406         fn is_zero(expr: &hir::Expr<'_>) -> bool {
2407             use hir::ExprKind::*;
2408             use rustc_ast::LitKind::*;
2409             match &expr.kind {
2410                 Lit(lit) => {
2411                     if let Int(i, _) = lit.node {
2412                         i == 0
2413                     } else {
2414                         false
2415                     }
2416                 }
2417                 Tup(tup) => tup.iter().all(is_zero),
2418                 _ => false,
2419             }
2420         }
2421
2422         /// Determine if this expression is a "dangerous initialization".
2423         fn is_dangerous_init(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> Option<InitKind> {
2424             if let hir::ExprKind::Call(ref path_expr, ref args) = expr.kind {
2425                 // Find calls to `mem::{uninitialized,zeroed}` methods.
2426                 if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2427                     let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2428
2429                     if cx.tcx.is_diagnostic_item(sym::mem_zeroed, def_id) {
2430                         return Some(InitKind::Zeroed);
2431                     } else if cx.tcx.is_diagnostic_item(sym::mem_uninitialized, def_id) {
2432                         return Some(InitKind::Uninit);
2433                     } else if cx.tcx.is_diagnostic_item(sym::transmute, def_id) && is_zero(&args[0])
2434                     {
2435                         return Some(InitKind::Zeroed);
2436                     }
2437                 }
2438             } else if let hir::ExprKind::MethodCall(_, _, ref args, _) = expr.kind {
2439                 // Find problematic calls to `MaybeUninit::assume_init`.
2440                 let def_id = cx.typeck_results().type_dependent_def_id(expr.hir_id)?;
2441                 if cx.tcx.is_diagnostic_item(sym::assume_init, def_id) {
2442                     // This is a call to *some* method named `assume_init`.
2443                     // See if the `self` parameter is one of the dangerous constructors.
2444                     if let hir::ExprKind::Call(ref path_expr, _) = args[0].kind {
2445                         if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2446                             let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2447
2448                             if cx.tcx.is_diagnostic_item(sym::maybe_uninit_zeroed, def_id) {
2449                                 return Some(InitKind::Zeroed);
2450                             } else if cx.tcx.is_diagnostic_item(sym::maybe_uninit_uninit, def_id) {
2451                                 return Some(InitKind::Uninit);
2452                             }
2453                         }
2454                     }
2455                 }
2456             }
2457
2458             None
2459         }
2460
2461         /// Test if this enum has several actually "existing" variants.
2462         /// Zero-sized uninhabited variants do not always have a tag assigned and thus do not "exist".
2463         fn is_multi_variant(adt: &ty::AdtDef) -> bool {
2464             // As an approximation, we only count dataless variants. Those are definitely inhabited.
2465             let existing_variants = adt.variants.iter().filter(|v| v.fields.is_empty()).count();
2466             existing_variants > 1
2467         }
2468
2469         /// Return `Some` only if we are sure this type does *not*
2470         /// allow zero initialization.
2471         fn ty_find_init_error<'tcx>(
2472             tcx: TyCtxt<'tcx>,
2473             ty: Ty<'tcx>,
2474             init: InitKind,
2475         ) -> Option<InitError> {
2476             use rustc_middle::ty::TyKind::*;
2477             match ty.kind() {
2478                 // Primitive types that don't like 0 as a value.
2479                 Ref(..) => Some(("references must be non-null".to_string(), None)),
2480                 Adt(..) if ty.is_box() => Some(("`Box` must be non-null".to_string(), None)),
2481                 FnPtr(..) => Some(("function pointers must be non-null".to_string(), None)),
2482                 Never => Some(("the `!` type has no valid value".to_string(), None)),
2483                 RawPtr(tm) if matches!(tm.ty.kind(), Dynamic(..)) =>
2484                 // raw ptr to dyn Trait
2485                 {
2486                     Some(("the vtable of a wide raw pointer must be non-null".to_string(), None))
2487                 }
2488                 // Primitive types with other constraints.
2489                 Bool if init == InitKind::Uninit => {
2490                     Some(("booleans must be either `true` or `false`".to_string(), None))
2491                 }
2492                 Char if init == InitKind::Uninit => {
2493                     Some(("characters must be a valid Unicode codepoint".to_string(), None))
2494                 }
2495                 // Recurse and checks for some compound types.
2496                 Adt(adt_def, substs) if !adt_def.is_union() => {
2497                     // First check if this ADT has a layout attribute (like `NonNull` and friends).
2498                     use std::ops::Bound;
2499                     match tcx.layout_scalar_valid_range(adt_def.did) {
2500                         // We exploit here that `layout_scalar_valid_range` will never
2501                         // return `Bound::Excluded`.  (And we have tests checking that we
2502                         // handle the attribute correctly.)
2503                         (Bound::Included(lo), _) if lo > 0 => {
2504                             return Some((format!("`{}` must be non-null", ty), None));
2505                         }
2506                         (Bound::Included(_), _) | (_, Bound::Included(_))
2507                             if init == InitKind::Uninit =>
2508                         {
2509                             return Some((
2510                                 format!(
2511                                     "`{}` must be initialized inside its custom valid range",
2512                                     ty,
2513                                 ),
2514                                 None,
2515                             ));
2516                         }
2517                         _ => {}
2518                     }
2519                     // Now, recurse.
2520                     match adt_def.variants.len() {
2521                         0 => Some(("enums with no variants have no valid value".to_string(), None)),
2522                         1 => {
2523                             // Struct, or enum with exactly one variant.
2524                             // Proceed recursively, check all fields.
2525                             let variant = &adt_def.variants[VariantIdx::from_u32(0)];
2526                             variant.fields.iter().find_map(|field| {
2527                                 ty_find_init_error(tcx, field.ty(tcx, substs), init).map(
2528                                     |(mut msg, span)| {
2529                                         if span.is_none() {
2530                                             // Point to this field, should be helpful for figuring
2531                                             // out where the source of the error is.
2532                                             let span = tcx.def_span(field.did);
2533                                             write!(
2534                                                 &mut msg,
2535                                                 " (in this {} field)",
2536                                                 adt_def.descr()
2537                                             )
2538                                             .unwrap();
2539                                             (msg, Some(span))
2540                                         } else {
2541                                             // Just forward.
2542                                             (msg, span)
2543                                         }
2544                                     },
2545                                 )
2546                             })
2547                         }
2548                         // Multi-variant enum.
2549                         _ => {
2550                             if init == InitKind::Uninit && is_multi_variant(adt_def) {
2551                                 let span = tcx.def_span(adt_def.did);
2552                                 Some((
2553                                     "enums have to be initialized to a variant".to_string(),
2554                                     Some(span),
2555                                 ))
2556                             } else {
2557                                 // In principle, for zero-initialization we could figure out which variant corresponds
2558                                 // to tag 0, and check that... but for now we just accept all zero-initializations.
2559                                 None
2560                             }
2561                         }
2562                     }
2563                 }
2564                 Tuple(..) => {
2565                     // Proceed recursively, check all fields.
2566                     ty.tuple_fields().find_map(|field| ty_find_init_error(tcx, field, init))
2567                 }
2568                 // Conservative fallback.
2569                 _ => None,
2570             }
2571         }
2572
2573         if let Some(init) = is_dangerous_init(cx, expr) {
2574             // This conjures an instance of a type out of nothing,
2575             // using zeroed or uninitialized memory.
2576             // We are extremely conservative with what we warn about.
2577             let conjured_ty = cx.typeck_results().expr_ty(expr);
2578             if let Some((msg, span)) =
2579                 with_no_trimmed_paths(|| ty_find_init_error(cx.tcx, conjured_ty, init))
2580             {
2581                 cx.struct_span_lint(INVALID_VALUE, expr.span, |lint| {
2582                     let mut err = lint.build(&format!(
2583                         "the type `{}` does not permit {}",
2584                         conjured_ty,
2585                         match init {
2586                             InitKind::Zeroed => "zero-initialization",
2587                             InitKind::Uninit => "being left uninitialized",
2588                         },
2589                     ));
2590                     err.span_label(expr.span, "this code causes undefined behavior when executed");
2591                     err.span_label(
2592                         expr.span,
2593                         "help: use `MaybeUninit<T>` instead, \
2594                             and only call `assume_init` after initialization is done",
2595                     );
2596                     if let Some(span) = span {
2597                         err.span_note(span, &msg);
2598                     } else {
2599                         err.note(&msg);
2600                     }
2601                     err.emit();
2602                 });
2603             }
2604         }
2605     }
2606 }
2607
2608 declare_lint! {
2609     /// The `clashing_extern_declarations` lint detects when an `extern fn`
2610     /// has been declared with the same name but different types.
2611     ///
2612     /// ### Example
2613     ///
2614     /// ```rust
2615     /// mod m {
2616     ///     extern "C" {
2617     ///         fn foo();
2618     ///     }
2619     /// }
2620     ///
2621     /// extern "C" {
2622     ///     fn foo(_: u32);
2623     /// }
2624     /// ```
2625     ///
2626     /// {{produces}}
2627     ///
2628     /// ### Explanation
2629     ///
2630     /// Because two symbols of the same name cannot be resolved to two
2631     /// different functions at link time, and one function cannot possibly
2632     /// have two types, a clashing extern declaration is almost certainly a
2633     /// mistake. Check to make sure that the `extern` definitions are correct
2634     /// and equivalent, and possibly consider unifying them in one location.
2635     ///
2636     /// This lint does not run between crates because a project may have
2637     /// dependencies which both rely on the same extern function, but declare
2638     /// it in a different (but valid) way. For example, they may both declare
2639     /// an opaque type for one or more of the arguments (which would end up
2640     /// distinct types), or use types that are valid conversions in the
2641     /// language the `extern fn` is defined in. In these cases, the compiler
2642     /// can't say that the clashing declaration is incorrect.
2643     pub CLASHING_EXTERN_DECLARATIONS,
2644     Warn,
2645     "detects when an extern fn has been declared with the same name but different types"
2646 }
2647
2648 pub struct ClashingExternDeclarations {
2649     /// Map of function symbol name to the first-seen hir id for that symbol name.. If seen_decls
2650     /// contains an entry for key K, it means a symbol with name K has been seen by this lint and
2651     /// the symbol should be reported as a clashing declaration.
2652     // FIXME: Technically, we could just store a &'tcx str here without issue; however, the
2653     // `impl_lint_pass` macro doesn't currently support lints parametric over a lifetime.
2654     seen_decls: FxHashMap<Symbol, HirId>,
2655 }
2656
2657 /// Differentiate between whether the name for an extern decl came from the link_name attribute or
2658 /// just from declaration itself. This is important because we don't want to report clashes on
2659 /// symbol name if they don't actually clash because one or the other links against a symbol with a
2660 /// different name.
2661 enum SymbolName {
2662     /// The name of the symbol + the span of the annotation which introduced the link name.
2663     Link(Symbol, Span),
2664     /// No link name, so just the name of the symbol.
2665     Normal(Symbol),
2666 }
2667
2668 impl SymbolName {
2669     fn get_name(&self) -> Symbol {
2670         match self {
2671             SymbolName::Link(s, _) | SymbolName::Normal(s) => *s,
2672         }
2673     }
2674 }
2675
2676 impl ClashingExternDeclarations {
2677     crate fn new() -> Self {
2678         ClashingExternDeclarations { seen_decls: FxHashMap::default() }
2679     }
2680     /// Insert a new foreign item into the seen set. If a symbol with the same name already exists
2681     /// for the item, return its HirId without updating the set.
2682     fn insert(&mut self, tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> Option<HirId> {
2683         let hid = fi.hir_id;
2684
2685         let local_did = tcx.hir().local_def_id(fi.hir_id);
2686         let did = local_did.to_def_id();
2687         let instance = Instance::new(did, ty::List::identity_for_item(tcx, did));
2688         let name = Symbol::intern(tcx.symbol_name(instance).name);
2689         if let Some(&hir_id) = self.seen_decls.get(&name) {
2690             // Avoid updating the map with the new entry when we do find a collision. We want to
2691             // make sure we're always pointing to the first definition as the previous declaration.
2692             // This lets us avoid emitting "knock-on" diagnostics.
2693             Some(hir_id)
2694         } else {
2695             self.seen_decls.insert(name, hid)
2696         }
2697     }
2698
2699     /// Get the name of the symbol that's linked against for a given extern declaration. That is,
2700     /// the name specified in a #[link_name = ...] attribute if one was specified, else, just the
2701     /// symbol's name.
2702     fn name_of_extern_decl(tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> SymbolName {
2703         let did = tcx.hir().local_def_id(fi.hir_id);
2704         if let Some((overridden_link_name, overridden_link_name_span)) =
2705             tcx.codegen_fn_attrs(did).link_name.map(|overridden_link_name| {
2706                 // FIXME: Instead of searching through the attributes again to get span
2707                 // information, we could have codegen_fn_attrs also give span information back for
2708                 // where the attribute was defined. However, until this is found to be a
2709                 // bottleneck, this does just fine.
2710                 (
2711                     overridden_link_name,
2712                     tcx.get_attrs(did.to_def_id())
2713                         .iter()
2714                         .find(|at| tcx.sess.check_name(at, sym::link_name))
2715                         .unwrap()
2716                         .span,
2717                 )
2718             })
2719         {
2720             SymbolName::Link(overridden_link_name, overridden_link_name_span)
2721         } else {
2722             SymbolName::Normal(fi.ident.name)
2723         }
2724     }
2725
2726     /// Checks whether two types are structurally the same enough that the declarations shouldn't
2727     /// clash. We need this so we don't emit a lint when two modules both declare an extern struct,
2728     /// with the same members (as the declarations shouldn't clash).
2729     fn structurally_same_type<'tcx>(
2730         cx: &LateContext<'tcx>,
2731         a: Ty<'tcx>,
2732         b: Ty<'tcx>,
2733         ckind: CItemKind,
2734     ) -> bool {
2735         fn structurally_same_type_impl<'tcx>(
2736             seen_types: &mut FxHashSet<(Ty<'tcx>, Ty<'tcx>)>,
2737             cx: &LateContext<'tcx>,
2738             a: Ty<'tcx>,
2739             b: Ty<'tcx>,
2740             ckind: CItemKind,
2741         ) -> bool {
2742             debug!("structurally_same_type_impl(cx, a = {:?}, b = {:?})", a, b);
2743             let tcx = cx.tcx;
2744
2745             // Given a transparent newtype, reach through and grab the inner
2746             // type unless the newtype makes the type non-null.
2747             let non_transparent_ty = |ty: Ty<'tcx>| -> Ty<'tcx> {
2748                 let mut ty = ty;
2749                 loop {
2750                     if let ty::Adt(def, substs) = *ty.kind() {
2751                         let is_transparent = def.subst(tcx, substs).repr.transparent();
2752                         let is_non_null = crate::types::nonnull_optimization_guaranteed(tcx, &def);
2753                         debug!(
2754                             "non_transparent_ty({:?}) -- type is transparent? {}, type is non-null? {}",
2755                             ty, is_transparent, is_non_null
2756                         );
2757                         if is_transparent && !is_non_null {
2758                             debug_assert!(def.variants.len() == 1);
2759                             let v = &def.variants[VariantIdx::new(0)];
2760                             ty = transparent_newtype_field(tcx, v)
2761                                 .expect(
2762                                     "single-variant transparent structure with zero-sized field",
2763                                 )
2764                                 .ty(tcx, substs);
2765                             continue;
2766                         }
2767                     }
2768                     debug!("non_transparent_ty -> {:?}", ty);
2769                     return ty;
2770                 }
2771             };
2772
2773             let a = non_transparent_ty(a);
2774             let b = non_transparent_ty(b);
2775
2776             if !seen_types.insert((a, b)) {
2777                 // We've encountered a cycle. There's no point going any further -- the types are
2778                 // structurally the same.
2779                 return true;
2780             }
2781             let tcx = cx.tcx;
2782             if a == b || rustc_middle::ty::TyS::same_type(a, b) {
2783                 // All nominally-same types are structurally same, too.
2784                 true
2785             } else {
2786                 // Do a full, depth-first comparison between the two.
2787                 use rustc_middle::ty::TyKind::*;
2788                 let a_kind = a.kind();
2789                 let b_kind = b.kind();
2790
2791                 let compare_layouts = |a, b| -> Result<bool, LayoutError<'tcx>> {
2792                     debug!("compare_layouts({:?}, {:?})", a, b);
2793                     let a_layout = &cx.layout_of(a)?.layout.abi;
2794                     let b_layout = &cx.layout_of(b)?.layout.abi;
2795                     debug!(
2796                         "comparing layouts: {:?} == {:?} = {}",
2797                         a_layout,
2798                         b_layout,
2799                         a_layout == b_layout
2800                     );
2801                     Ok(a_layout == b_layout)
2802                 };
2803
2804                 #[allow(rustc::usage_of_ty_tykind)]
2805                 let is_primitive_or_pointer = |kind: &ty::TyKind<'_>| {
2806                     kind.is_primitive() || matches!(kind, RawPtr(..) | Ref(..))
2807                 };
2808
2809                 ensure_sufficient_stack(|| {
2810                     match (a_kind, b_kind) {
2811                         (Adt(a_def, a_substs), Adt(b_def, b_substs)) => {
2812                             let a = a.subst(cx.tcx, a_substs);
2813                             let b = b.subst(cx.tcx, b_substs);
2814                             debug!("Comparing {:?} and {:?}", a, b);
2815
2816                             // We can immediately rule out these types as structurally same if
2817                             // their layouts differ.
2818                             match compare_layouts(a, b) {
2819                                 Ok(false) => return false,
2820                                 _ => (), // otherwise, continue onto the full, fields comparison
2821                             }
2822
2823                             // Grab a flattened representation of all fields.
2824                             let a_fields = a_def.variants.iter().flat_map(|v| v.fields.iter());
2825                             let b_fields = b_def.variants.iter().flat_map(|v| v.fields.iter());
2826
2827                             // Perform a structural comparison for each field.
2828                             a_fields.eq_by(
2829                                 b_fields,
2830                                 |&ty::FieldDef { did: a_did, .. },
2831                                  &ty::FieldDef { did: b_did, .. }| {
2832                                     structurally_same_type_impl(
2833                                         seen_types,
2834                                         cx,
2835                                         tcx.type_of(a_did),
2836                                         tcx.type_of(b_did),
2837                                         ckind,
2838                                     )
2839                                 },
2840                             )
2841                         }
2842                         (Array(a_ty, a_const), Array(b_ty, b_const)) => {
2843                             // For arrays, we also check the constness of the type.
2844                             a_const.val == b_const.val
2845                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2846                         }
2847                         (Slice(a_ty), Slice(b_ty)) => {
2848                             structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2849                         }
2850                         (RawPtr(a_tymut), RawPtr(b_tymut)) => {
2851                             a_tymut.mutbl == b_tymut.mutbl
2852                                 && structurally_same_type_impl(
2853                                     seen_types,
2854                                     cx,
2855                                     &a_tymut.ty,
2856                                     &b_tymut.ty,
2857                                     ckind,
2858                                 )
2859                         }
2860                         (Ref(_a_region, a_ty, a_mut), Ref(_b_region, b_ty, b_mut)) => {
2861                             // For structural sameness, we don't need the region to be same.
2862                             a_mut == b_mut
2863                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2864                         }
2865                         (FnDef(..), FnDef(..)) => {
2866                             let a_poly_sig = a.fn_sig(tcx);
2867                             let b_poly_sig = b.fn_sig(tcx);
2868
2869                             // As we don't compare regions, skip_binder is fine.
2870                             let a_sig = a_poly_sig.skip_binder();
2871                             let b_sig = b_poly_sig.skip_binder();
2872
2873                             (a_sig.abi, a_sig.unsafety, a_sig.c_variadic)
2874                                 == (b_sig.abi, b_sig.unsafety, b_sig.c_variadic)
2875                                 && a_sig.inputs().iter().eq_by(b_sig.inputs().iter(), |a, b| {
2876                                     structurally_same_type_impl(seen_types, cx, a, b, ckind)
2877                                 })
2878                                 && structurally_same_type_impl(
2879                                     seen_types,
2880                                     cx,
2881                                     a_sig.output(),
2882                                     b_sig.output(),
2883                                     ckind,
2884                                 )
2885                         }
2886                         (Tuple(a_substs), Tuple(b_substs)) => {
2887                             a_substs.types().eq_by(b_substs.types(), |a_ty, b_ty| {
2888                                 structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2889                             })
2890                         }
2891                         // For these, it's not quite as easy to define structural-sameness quite so easily.
2892                         // For the purposes of this lint, take the conservative approach and mark them as
2893                         // not structurally same.
2894                         (Dynamic(..), Dynamic(..))
2895                         | (Error(..), Error(..))
2896                         | (Closure(..), Closure(..))
2897                         | (Generator(..), Generator(..))
2898                         | (GeneratorWitness(..), GeneratorWitness(..))
2899                         | (Projection(..), Projection(..))
2900                         | (Opaque(..), Opaque(..)) => false,
2901
2902                         // These definitely should have been caught above.
2903                         (Bool, Bool) | (Char, Char) | (Never, Never) | (Str, Str) => unreachable!(),
2904
2905                         // An Adt and a primitive or pointer type. This can be FFI-safe if non-null
2906                         // enum layout optimisation is being applied.
2907                         (Adt(..), other_kind) | (other_kind, Adt(..))
2908                             if is_primitive_or_pointer(other_kind) =>
2909                         {
2910                             let (primitive, adt) =
2911                                 if is_primitive_or_pointer(a.kind()) { (a, b) } else { (b, a) };
2912                             if let Some(ty) = crate::types::repr_nullable_ptr(cx, adt, ckind) {
2913                                 ty == primitive
2914                             } else {
2915                                 compare_layouts(a, b).unwrap_or(false)
2916                             }
2917                         }
2918                         // Otherwise, just compare the layouts. This may fail to lint for some
2919                         // incompatible types, but at the very least, will stop reads into
2920                         // uninitialised memory.
2921                         _ => compare_layouts(a, b).unwrap_or(false),
2922                     }
2923                 })
2924             }
2925         }
2926         let mut seen_types = FxHashSet::default();
2927         structurally_same_type_impl(&mut seen_types, cx, a, b, ckind)
2928     }
2929 }
2930
2931 impl_lint_pass!(ClashingExternDeclarations => [CLASHING_EXTERN_DECLARATIONS]);
2932
2933 impl<'tcx> LateLintPass<'tcx> for ClashingExternDeclarations {
2934     fn check_foreign_item(&mut self, cx: &LateContext<'tcx>, this_fi: &hir::ForeignItem<'_>) {
2935         trace!("ClashingExternDeclarations: check_foreign_item: {:?}", this_fi);
2936         if let ForeignItemKind::Fn(..) = this_fi.kind {
2937             let tcx = cx.tcx;
2938             if let Some(existing_hid) = self.insert(tcx, this_fi) {
2939                 let existing_decl_ty = tcx.type_of(tcx.hir().local_def_id(existing_hid));
2940                 let this_decl_ty = tcx.type_of(tcx.hir().local_def_id(this_fi.hir_id));
2941                 debug!(
2942                     "ClashingExternDeclarations: Comparing existing {:?}: {:?} to this {:?}: {:?}",
2943                     existing_hid, existing_decl_ty, this_fi.hir_id, this_decl_ty
2944                 );
2945                 // Check that the declarations match.
2946                 if !Self::structurally_same_type(
2947                     cx,
2948                     existing_decl_ty,
2949                     this_decl_ty,
2950                     CItemKind::Declaration,
2951                 ) {
2952                     let orig_fi = tcx.hir().expect_foreign_item(existing_hid);
2953                     let orig = Self::name_of_extern_decl(tcx, orig_fi);
2954
2955                     // We want to ensure that we use spans for both decls that include where the
2956                     // name was defined, whether that was from the link_name attribute or not.
2957                     let get_relevant_span =
2958                         |fi: &hir::ForeignItem<'_>| match Self::name_of_extern_decl(tcx, fi) {
2959                             SymbolName::Normal(_) => fi.span,
2960                             SymbolName::Link(_, annot_span) => fi.span.to(annot_span),
2961                         };
2962                     // Finally, emit the diagnostic.
2963                     tcx.struct_span_lint_hir(
2964                         CLASHING_EXTERN_DECLARATIONS,
2965                         this_fi.hir_id,
2966                         get_relevant_span(this_fi),
2967                         |lint| {
2968                             let mut expected_str = DiagnosticStyledString::new();
2969                             expected_str.push(existing_decl_ty.fn_sig(tcx).to_string(), false);
2970                             let mut found_str = DiagnosticStyledString::new();
2971                             found_str.push(this_decl_ty.fn_sig(tcx).to_string(), true);
2972
2973                             lint.build(&format!(
2974                                 "`{}` redeclare{} with a different signature",
2975                                 this_fi.ident.name,
2976                                 if orig.get_name() == this_fi.ident.name {
2977                                     "d".to_string()
2978                                 } else {
2979                                     format!("s `{}`", orig.get_name())
2980                                 }
2981                             ))
2982                             .span_label(
2983                                 get_relevant_span(orig_fi),
2984                                 &format!("`{}` previously declared here", orig.get_name()),
2985                             )
2986                             .span_label(
2987                                 get_relevant_span(this_fi),
2988                                 "this signature doesn't match the previous declaration",
2989                             )
2990                             .note_expected_found(&"", expected_str, &"", found_str)
2991                             .emit()
2992                         },
2993                     );
2994                 }
2995             }
2996         }
2997     }
2998 }