compiler/rustc_lint/src/builtin.rs

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