compiler/rustc_lint/src/builtin.rs

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