compiler/rustc_lint/src/builtin.rs

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