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