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, CRATE_DEF_ID};
  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::lint::FutureIncompatibilityReason;
  49 use rustc_session::Session;
  50 use rustc_span::edition::Edition;
  51 use rustc_span::source_map::Spanned;
  52 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  53 use rustc_span::{BytePos, Span};
  54 use rustc_target::abi::{LayoutOf, VariantIdx};
  55 use rustc_trait_selection::traits::misc::can_type_implement_copy;
  56
  57 use crate::nonstandard_style::{method_context, MethodLateContext};
  58
  59 use std::fmt::Write;
  60 use tracing::{debug, trace};
  61
  62 // hardwired lints from librustc_middle
  63 pub use rustc_session::lint::builtin::*;
  64
  65 declare_lint! {
  66     /// The `while_true` lint detects `while true { }`.
  67     ///
  68     /// ### Example
  69     ///
  70     /// ```rust,no_run
  71     /// while true {
  72     ///
  73     /// }
  74     /// ```
  75     ///
  76     /// {{produces}}
  77     ///
  78     /// ### Explanation
  79     ///
  80     /// `while true` should be replaced with `loop`. A `loop` expression is
  81     /// the preferred way to write an infinite loop because it more directly
  82     /// expresses the intent of the loop.
  83     WHILE_TRUE,
  84     Warn,
  85     "suggest using `loop { }` instead of `while true { }`"
  86 }
  87
  88 declare_lint_pass!(WhileTrue => [WHILE_TRUE]);
  89
  90 /// Traverse through any amount of parenthesis and return the first non-parens expression.
  91 fn pierce_parens(mut expr: &ast::Expr) -> &ast::Expr {
  92     while let ast::ExprKind::Paren(sub) = &expr.kind {
  93         expr = sub;
  94     }
  95     expr
  96 }
  97
  98 impl EarlyLintPass for WhileTrue {
  99     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
 100         if let ast::ExprKind::While(cond, _, label) = &e.kind {
 101             if let ast::ExprKind::Lit(ref lit) = pierce_parens(cond).kind {
 102                 if let ast::LitKind::Bool(true) = lit.kind {
 103                     if !lit.span.from_expansion() {
 104                         let msg = "denote infinite loops with `loop { ... }`";
 105                         let condition_span = e.span.with_hi(cond.span.hi());
 106                         cx.struct_span_lint(WHILE_TRUE, condition_span, |lint| {
 107                             lint.build(msg)
 108                                 .span_suggestion_short(
 109                                     condition_span,
 110                                     "use `loop`",
 111                                     format!(
 112                                         "{}loop",
 113                                         label.map_or_else(String::new, |label| format!(
 114                                             "{}: ",
 115                                             label.ident,
 116                                         ))
 117                                     ),
 118                                     Applicability::MachineApplicable,
 119                                 )
 120                                 .emit();
 121                         })
 122                     }
 123                 }
 124             }
 125         }
 126     }
 127 }
 128
 129 declare_lint! {
 130     /// The `box_pointers` lints use of the Box type.
 131     ///
 132     /// ### Example
 133     ///
 134     /// ```rust,compile_fail
 135     /// #![deny(box_pointers)]
 136     /// struct Foo {
 137     ///     x: Box<isize>,
 138     /// }
 139     /// ```
 140     ///
 141     /// {{produces}}
 142     ///
 143     /// ### Explanation
 144     ///
 145     /// This lint is mostly historical, and not particularly useful. `Box<T>`
 146     /// used to be built into the language, and the only way to do heap
 147     /// allocation. Today's Rust can call into other allocators, etc.
 148     BOX_POINTERS,
 149     Allow,
 150     "use of owned (Box type) heap memory"
 151 }
 152
 153 declare_lint_pass!(BoxPointers => [BOX_POINTERS]);
 154
 155 impl BoxPointers {
 156     fn check_heap_type(&self, cx: &LateContext<'_>, span: Span, ty: Ty<'_>) {
 157         for leaf in ty.walk() {
 158             if let GenericArgKind::Type(leaf_ty) = leaf.unpack() {
 159                 if leaf_ty.is_box() {
 160                     cx.struct_span_lint(BOX_POINTERS, span, |lint| {
 161                         lint.build(&format!("type uses owned (Box type) pointers: {}", ty)).emit()
 162                     });
 163                 }
 164             }
 165         }
 166     }
 167 }
 168
 169 impl<'tcx> LateLintPass<'tcx> for BoxPointers {
 170     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 171         match it.kind {
 172             hir::ItemKind::Fn(..)
 173             | hir::ItemKind::TyAlias(..)
 174             | hir::ItemKind::Enum(..)
 175             | hir::ItemKind::Struct(..)
 176             | hir::ItemKind::Union(..) => {
 177                 self.check_heap_type(cx, it.span, cx.tcx.type_of(it.def_id))
 178             }
 179             _ => (),
 180         }
 181
 182         // If it's a struct, we also have to check the fields' types
 183         match it.kind {
 184             hir::ItemKind::Struct(ref struct_def, _) | hir::ItemKind::Union(ref struct_def, _) => {
 185                 for struct_field in struct_def.fields() {
 186                     let def_id = cx.tcx.hir().local_def_id(struct_field.hir_id);
 187                     self.check_heap_type(cx, struct_field.span, cx.tcx.type_of(def_id));
 188                 }
 189             }
 190             _ => (),
 191         }
 192     }
 193
 194     fn check_expr(&mut self, cx: &LateContext<'_>, e: &hir::Expr<'_>) {
 195         let ty = cx.typeck_results().node_type(e.hir_id);
 196         self.check_heap_type(cx, e.span, ty);
 197     }
 198 }
 199
 200 declare_lint! {
 201     /// The `non_shorthand_field_patterns` lint detects using `Struct { x: x }`
 202     /// instead of `Struct { x }` in a pattern.
 203     ///
 204     /// ### Example
 205     ///
 206     /// ```rust
 207     /// struct Point {
 208     ///     x: i32,
 209     ///     y: i32,
 210     /// }
 211     ///
 212     ///
 213     /// fn main() {
 214     ///     let p = Point {
 215     ///         x: 5,
 216     ///         y: 5,
 217     ///     };
 218     ///
 219     ///     match p {
 220     ///         Point { x: x, y: y } => (),
 221     ///     }
 222     /// }
 223     /// ```
 224     ///
 225     /// {{produces}}
 226     ///
 227     /// ### Explanation
 228     ///
 229     /// The preferred style is to avoid the repetition of specifying both the
 230     /// field name and the binding name if both identifiers are the same.
 231     NON_SHORTHAND_FIELD_PATTERNS,
 232     Warn,
 233     "using `Struct { x: x }` instead of `Struct { x }` in a pattern"
 234 }
 235
 236 declare_lint_pass!(NonShorthandFieldPatterns => [NON_SHORTHAND_FIELD_PATTERNS]);
 237
 238 impl<'tcx> LateLintPass<'tcx> for NonShorthandFieldPatterns {
 239     fn check_pat(&mut self, cx: &LateContext<'_>, pat: &hir::Pat<'_>) {
 240         if let PatKind::Struct(ref qpath, field_pats, _) = pat.kind {
 241             let variant = cx
 242                 .typeck_results()
 243                 .pat_ty(pat)
 244                 .ty_adt_def()
 245                 .expect("struct pattern type is not an ADT")
 246                 .variant_of_res(cx.qpath_res(qpath, pat.hir_id));
 247             for fieldpat in field_pats {
 248                 if fieldpat.is_shorthand {
 249                     continue;
 250                 }
 251                 if fieldpat.span.from_expansion() {
 252                     // Don't lint if this is a macro expansion: macro authors
 253                     // shouldn't have to worry about this kind of style issue
 254                     // (Issue #49588)
 255                     continue;
 256                 }
 257                 if let PatKind::Binding(binding_annot, _, ident, None) = fieldpat.pat.kind {
 258                     if cx.tcx.find_field_index(ident, &variant)
 259                         == Some(cx.tcx.field_index(fieldpat.hir_id, cx.typeck_results()))
 260                     {
 261                         cx.struct_span_lint(NON_SHORTHAND_FIELD_PATTERNS, fieldpat.span, |lint| {
 262                             let mut err = lint
 263                                 .build(&format!("the `{}:` in this pattern is redundant", ident));
 264                             let binding = match binding_annot {
 265                                 hir::BindingAnnotation::Unannotated => None,
 266                                 hir::BindingAnnotation::Mutable => Some("mut"),
 267                                 hir::BindingAnnotation::Ref => Some("ref"),
 268                                 hir::BindingAnnotation::RefMut => Some("ref mut"),
 269                             };
 270                             let ident = if let Some(binding) = binding {
 271                                 format!("{} {}", binding, ident)
 272                             } else {
 273                                 ident.to_string()
 274                             };
 275                             err.span_suggestion(
 276                                 fieldpat.span,
 277                                 "use shorthand field pattern",
 278                                 ident,
 279                                 Applicability::MachineApplicable,
 280                             );
 281                             err.emit();
 282                         });
 283                     }
 284                 }
 285             }
 286         }
 287     }
 288 }
 289
 290 declare_lint! {
 291     /// The `unsafe_code` lint catches usage of `unsafe` code.
 292     ///
 293     /// ### Example
 294     ///
 295     /// ```rust,compile_fail
 296     /// #![deny(unsafe_code)]
 297     /// fn main() {
 298     ///     unsafe {
 299     ///
 300     ///     }
 301     /// }
 302     /// ```
 303     ///
 304     /// {{produces}}
 305     ///
 306     /// ### Explanation
 307     ///
 308     /// This lint is intended to restrict the usage of `unsafe`, which can be
 309     /// difficult to use correctly.
 310     UNSAFE_CODE,
 311     Allow,
 312     "usage of `unsafe` code"
 313 }
 314
 315 declare_lint_pass!(UnsafeCode => [UNSAFE_CODE]);
 316
 317 impl UnsafeCode {
 318     fn report_unsafe(
 319         &self,
 320         cx: &EarlyContext<'_>,
 321         span: Span,
 322         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
 323     ) {
 324         // This comes from a macro that has `#[allow_internal_unsafe]`.
 325         if span.allows_unsafe() {
 326             return;
 327         }
 328
 329         cx.struct_span_lint(UNSAFE_CODE, span, decorate);
 330     }
 331
 332     fn report_overriden_symbol_name(&self, cx: &EarlyContext<'_>, span: Span, msg: &str) {
 333         self.report_unsafe(cx, span, |lint| {
 334             lint.build(msg)
 335                 .note(
 336                     "the linker's behavior with multiple libraries exporting duplicate symbol \
 337                     names is undefined and Rust cannot provide guarantees when you manually \
 338                     override them",
 339                 )
 340                 .emit();
 341         })
 342     }
 343 }
 344
 345 impl EarlyLintPass for UnsafeCode {
 346     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 347         if cx.sess().check_name(attr, sym::allow_internal_unsafe) {
 348             self.report_unsafe(cx, attr.span, |lint| {
 349                 lint.build(
 350                     "`allow_internal_unsafe` allows defining \
 351                                                macros using unsafe without triggering \
 352                                                the `unsafe_code` lint at their call site",
 353                 )
 354                 .emit()
 355             });
 356         }
 357     }
 358
 359     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
 360         if let ast::ExprKind::Block(ref blk, _) = e.kind {
 361             // Don't warn about generated blocks; that'll just pollute the output.
 362             if blk.rules == ast::BlockCheckMode::Unsafe(ast::UserProvided) {
 363                 self.report_unsafe(cx, blk.span, |lint| {
 364                     lint.build("usage of an `unsafe` block").emit()
 365                 });
 366             }
 367         }
 368     }
 369
 370     fn check_item(&mut self, cx: &EarlyContext<'_>, it: &ast::Item) {
 371         match it.kind {
 372             ast::ItemKind::Trait(box ast::TraitKind(_, ast::Unsafe::Yes(_), ..)) => self
 373                 .report_unsafe(cx, it.span, |lint| {
 374                     lint.build("declaration of an `unsafe` trait").emit()
 375                 }),
 376
 377             ast::ItemKind::Impl(box ast::ImplKind { unsafety: ast::Unsafe::Yes(_), .. }) => self
 378                 .report_unsafe(cx, it.span, |lint| {
 379                     lint.build("implementation of an `unsafe` trait").emit()
 380                 }),
 381
 382             ast::ItemKind::Fn(..) => {
 383                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
 384                     self.report_overriden_symbol_name(
 385                         cx,
 386                         attr.span,
 387                         "declaration of a `no_mangle` function",
 388                     );
 389                 }
 390                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::export_name) {
 391                     self.report_overriden_symbol_name(
 392                         cx,
 393                         attr.span,
 394                         "declaration of a function with `export_name`",
 395                     );
 396                 }
 397             }
 398
 399             ast::ItemKind::Static(..) => {
 400                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
 401                     self.report_overriden_symbol_name(
 402                         cx,
 403                         attr.span,
 404                         "declaration of a `no_mangle` static",
 405                     );
 406                 }
 407                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::export_name) {
 408                     self.report_overriden_symbol_name(
 409                         cx,
 410                         attr.span,
 411                         "declaration of a static with `export_name`",
 412                     );
 413                 }
 414             }
 415
 416             _ => {}
 417         }
 418     }
 419
 420     fn check_impl_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
 421         if let ast::AssocItemKind::Fn(..) = it.kind {
 422             if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
 423                 self.report_overriden_symbol_name(
 424                     cx,
 425                     attr.span,
 426                     "declaration of a `no_mangle` method",
 427                 );
 428             }
 429             if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::export_name) {
 430                 self.report_overriden_symbol_name(
 431                     cx,
 432                     attr.span,
 433                     "declaration of a method with `export_name`",
 434                 );
 435             }
 436         }
 437     }
 438
 439     fn check_fn(&mut self, cx: &EarlyContext<'_>, fk: FnKind<'_>, span: Span, _: ast::NodeId) {
 440         if let FnKind::Fn(
 441             ctxt,
 442             _,
 443             ast::FnSig { header: ast::FnHeader { unsafety: ast::Unsafe::Yes(_), .. }, .. },
 444             _,
 445             body,
 446         ) = fk
 447         {
 448             let msg = match ctxt {
 449                 FnCtxt::Foreign => return,
 450                 FnCtxt::Free => "declaration of an `unsafe` function",
 451                 FnCtxt::Assoc(_) if body.is_none() => "declaration of an `unsafe` method",
 452                 FnCtxt::Assoc(_) => "implementation of an `unsafe` method",
 453             };
 454             self.report_unsafe(cx, span, |lint| lint.build(msg).emit());
 455         }
 456     }
 457 }
 458
 459 declare_lint! {
 460     /// The `missing_docs` lint detects missing documentation for public items.
 461     ///
 462     /// ### Example
 463     ///
 464     /// ```rust,compile_fail
 465     /// #![deny(missing_docs)]
 466     /// pub fn foo() {}
 467     /// ```
 468     ///
 469     /// {{produces}}
 470     ///
 471     /// ### Explanation
 472     ///
 473     /// This lint is intended to ensure that a library is well-documented.
 474     /// Items without documentation can be difficult for users to understand
 475     /// how to use properly.
 476     ///
 477     /// This lint is "allow" by default because it can be noisy, and not all
 478     /// projects may want to enforce everything to be documented.
 479     pub MISSING_DOCS,
 480     Allow,
 481     "detects missing documentation for public members",
 482     report_in_external_macro
 483 }
 484
 485 pub struct MissingDoc {
 486     /// Stack of whether `#[doc(hidden)]` is set at each level which has lint attributes.
 487     doc_hidden_stack: Vec<bool>,
 488
 489     /// Private traits or trait items that leaked through. Don't check their methods.
 490     private_traits: FxHashSet<hir::HirId>,
 491 }
 492
 493 impl_lint_pass!(MissingDoc => [MISSING_DOCS]);
 494
 495 fn has_doc(sess: &Session, attr: &ast::Attribute) -> bool {
 496     if attr.is_doc_comment() {
 497         return true;
 498     }
 499
 500     if !sess.check_name(attr, sym::doc) {
 501         return false;
 502     }
 503
 504     if attr.value_str().is_some() {
 505         return true;
 506     }
 507
 508     if let Some(list) = attr.meta_item_list() {
 509         for meta in list {
 510             if meta.has_name(sym::hidden) {
 511                 return true;
 512             }
 513         }
 514     }
 515
 516     false
 517 }
 518
 519 impl MissingDoc {
 520     pub fn new() -> MissingDoc {
 521         MissingDoc { doc_hidden_stack: vec![false], private_traits: FxHashSet::default() }
 522     }
 523
 524     fn doc_hidden(&self) -> bool {
 525         *self.doc_hidden_stack.last().expect("empty doc_hidden_stack")
 526     }
 527
 528     fn check_missing_docs_attrs(
 529         &self,
 530         cx: &LateContext<'_>,
 531         def_id: LocalDefId,
 532         sp: Span,
 533         article: &'static str,
 534         desc: &'static str,
 535     ) {
 536         // If we're building a test harness, then warning about
 537         // documentation is probably not really relevant right now.
 538         if cx.sess().opts.test {
 539             return;
 540         }
 541
 542         // `#[doc(hidden)]` disables missing_docs check.
 543         if self.doc_hidden() {
 544             return;
 545         }
 546
 547         // Only check publicly-visible items, using the result from the privacy pass.
 548         // It's an option so the crate root can also use this function (it doesn't
 549         // have a `NodeId`).
 550         if def_id != CRATE_DEF_ID {
 551             if !cx.access_levels.is_exported(def_id) {
 552                 return;
 553             }
 554         }
 555
 556         let attrs = cx.tcx.get_attrs(def_id.to_def_id());
 557         let has_doc = attrs.iter().any(|a| has_doc(cx.sess(), a));
 558         if !has_doc {
 559             cx.struct_span_lint(
 560                 MISSING_DOCS,
 561                 cx.tcx.sess.source_map().guess_head_span(sp),
 562                 |lint| {
 563                     lint.build(&format!("missing documentation for {} {}", article, desc)).emit()
 564                 },
 565             );
 566         }
 567     }
 568 }
 569
 570 impl<'tcx> LateLintPass<'tcx> for MissingDoc {
 571     fn enter_lint_attrs(&mut self, cx: &LateContext<'_>, attrs: &[ast::Attribute]) {
 572         let doc_hidden = self.doc_hidden()
 573             || attrs.iter().any(|attr| {
 574                 cx.sess().check_name(attr, sym::doc)
 575                     && match attr.meta_item_list() {
 576                         None => false,
 577                         Some(l) => attr::list_contains_name(&l, sym::hidden),
 578                     }
 579             });
 580         self.doc_hidden_stack.push(doc_hidden);
 581     }
 582
 583     fn exit_lint_attrs(&mut self, _: &LateContext<'_>, _attrs: &[ast::Attribute]) {
 584         self.doc_hidden_stack.pop().expect("empty doc_hidden_stack");
 585     }
 586
 587     fn check_crate(&mut self, cx: &LateContext<'_>, krate: &hir::Crate<'_>) {
 588         self.check_missing_docs_attrs(cx, CRATE_DEF_ID, krate.module().inner, "the", "crate");
 589
 590         for macro_def in krate.exported_macros() {
 591             // Non exported macros should be skipped, since `missing_docs` only
 592             // applies to externally visible items.
 593             if !cx.access_levels.is_exported(macro_def.def_id) {
 594                 continue;
 595             }
 596
 597             let attrs = cx.tcx.hir().attrs(macro_def.hir_id());
 598             let has_doc = attrs.iter().any(|a| has_doc(cx.sess(), a));
 599             if !has_doc {
 600                 cx.struct_span_lint(
 601                     MISSING_DOCS,
 602                     cx.tcx.sess.source_map().guess_head_span(macro_def.span),
 603                     |lint| lint.build("missing documentation for macro").emit(),
 604                 );
 605             }
 606         }
 607     }
 608
 609     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 610         match it.kind {
 611             hir::ItemKind::Trait(.., trait_item_refs) => {
 612                 // Issue #11592: traits are always considered exported, even when private.
 613                 if let hir::VisibilityKind::Inherited = it.vis.node {
 614                     self.private_traits.insert(it.hir_id());
 615                     for trait_item_ref in trait_item_refs {
 616                         self.private_traits.insert(trait_item_ref.id.hir_id());
 617                     }
 618                     return;
 619                 }
 620             }
 621             hir::ItemKind::Impl(hir::Impl { of_trait: Some(ref trait_ref), items, .. }) => {
 622                 // If the trait is private, add the impl items to `private_traits` so they don't get
 623                 // reported for missing docs.
 624                 let real_trait = trait_ref.path.res.def_id();
 625                 if let Some(def_id) = real_trait.as_local() {
 626                     let hir_id = cx.tcx.hir().local_def_id_to_hir_id(def_id);
 627                     if let Some(Node::Item(item)) = cx.tcx.hir().find(hir_id) {
 628                         if let hir::VisibilityKind::Inherited = item.vis.node {
 629                             for impl_item_ref in items {
 630                                 self.private_traits.insert(impl_item_ref.id.hir_id());
 631                             }
 632                         }
 633                     }
 634                 }
 635                 return;
 636             }
 637
 638             hir::ItemKind::TyAlias(..)
 639             | hir::ItemKind::Fn(..)
 640             | hir::ItemKind::Mod(..)
 641             | hir::ItemKind::Enum(..)
 642             | hir::ItemKind::Struct(..)
 643             | hir::ItemKind::Union(..)
 644             | hir::ItemKind::Const(..)
 645             | hir::ItemKind::Static(..) => {}
 646
 647             _ => return,
 648         };
 649
 650         let (article, desc) = cx.tcx.article_and_description(it.def_id.to_def_id());
 651
 652         self.check_missing_docs_attrs(cx, it.def_id, it.span, article, desc);
 653     }
 654
 655     fn check_trait_item(&mut self, cx: &LateContext<'_>, trait_item: &hir::TraitItem<'_>) {
 656         if self.private_traits.contains(&trait_item.hir_id()) {
 657             return;
 658         }
 659
 660         let (article, desc) = cx.tcx.article_and_description(trait_item.def_id.to_def_id());
 661
 662         self.check_missing_docs_attrs(cx, trait_item.def_id, trait_item.span, article, desc);
 663     }
 664
 665     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
 666         // If the method is an impl for a trait, don't doc.
 667         if method_context(cx, impl_item.hir_id()) == MethodLateContext::TraitImpl {
 668             return;
 669         }
 670
 671         let (article, desc) = cx.tcx.article_and_description(impl_item.def_id.to_def_id());
 672         self.check_missing_docs_attrs(cx, impl_item.def_id, impl_item.span, article, desc);
 673     }
 674
 675     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'_>) {
 676         let (article, desc) = cx.tcx.article_and_description(foreign_item.def_id.to_def_id());
 677         self.check_missing_docs_attrs(cx, foreign_item.def_id, foreign_item.span, article, desc);
 678     }
 679
 680     fn check_field_def(&mut self, cx: &LateContext<'_>, sf: &hir::FieldDef<'_>) {
 681         if !sf.is_positional() {
 682             let def_id = cx.tcx.hir().local_def_id(sf.hir_id);
 683             self.check_missing_docs_attrs(cx, def_id, sf.span, "a", "struct field")
 684         }
 685     }
 686
 687     fn check_variant(&mut self, cx: &LateContext<'_>, v: &hir::Variant<'_>) {
 688         self.check_missing_docs_attrs(cx, cx.tcx.hir().local_def_id(v.id), v.span, "a", "variant");
 689     }
 690 }
 691
 692 declare_lint! {
 693     /// The `missing_copy_implementations` lint detects potentially-forgotten
 694     /// implementations of [`Copy`].
 695     ///
 696     /// [`Copy`]: https://doc.rust-lang.org/std/marker/trait.Copy.html
 697     ///
 698     /// ### Example
 699     ///
 700     /// ```rust,compile_fail
 701     /// #![deny(missing_copy_implementations)]
 702     /// pub struct Foo {
 703     ///     pub field: i32
 704     /// }
 705     /// # fn main() {}
 706     /// ```
 707     ///
 708     /// {{produces}}
 709     ///
 710     /// ### Explanation
 711     ///
 712     /// Historically (before 1.0), types were automatically marked as `Copy`
 713     /// if possible. This was changed so that it required an explicit opt-in
 714     /// by implementing the `Copy` trait. As part of this change, a lint was
 715     /// added to alert if a copyable type was not marked `Copy`.
 716     ///
 717     /// This lint is "allow" by default because this code isn't bad; it is
 718     /// common to write newtypes like this specifically so that a `Copy` type
 719     /// is no longer `Copy`. `Copy` types can result in unintended copies of
 720     /// large data which can impact performance.
 721     pub MISSING_COPY_IMPLEMENTATIONS,
 722     Allow,
 723     "detects potentially-forgotten implementations of `Copy`"
 724 }
 725
 726 declare_lint_pass!(MissingCopyImplementations => [MISSING_COPY_IMPLEMENTATIONS]);
 727
 728 impl<'tcx> LateLintPass<'tcx> for MissingCopyImplementations {
 729     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 730         if !cx.access_levels.is_reachable(item.def_id) {
 731             return;
 732         }
 733         let (def, ty) = match item.kind {
 734             hir::ItemKind::Struct(_, ref ast_generics) => {
 735                 if !ast_generics.params.is_empty() {
 736                     return;
 737                 }
 738                 let def = cx.tcx.adt_def(item.def_id);
 739                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 740             }
 741             hir::ItemKind::Union(_, ref ast_generics) => {
 742                 if !ast_generics.params.is_empty() {
 743                     return;
 744                 }
 745                 let def = cx.tcx.adt_def(item.def_id);
 746                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 747             }
 748             hir::ItemKind::Enum(_, ref ast_generics) => {
 749                 if !ast_generics.params.is_empty() {
 750                     return;
 751                 }
 752                 let def = cx.tcx.adt_def(item.def_id);
 753                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 754             }
 755             _ => return,
 756         };
 757         if def.has_dtor(cx.tcx) {
 758             return;
 759         }
 760         let param_env = ty::ParamEnv::empty();
 761         if ty.is_copy_modulo_regions(cx.tcx.at(item.span), param_env) {
 762             return;
 763         }
 764         if can_type_implement_copy(cx.tcx, param_env, ty).is_ok() {
 765             cx.struct_span_lint(MISSING_COPY_IMPLEMENTATIONS, item.span, |lint| {
 766                 lint.build(
 767                     "type could implement `Copy`; consider adding `impl \
 768                           Copy`",
 769                 )
 770                 .emit()
 771             })
 772         }
 773     }
 774 }
 775
 776 declare_lint! {
 777     /// The `missing_debug_implementations` lint detects missing
 778     /// implementations of [`fmt::Debug`].
 779     ///
 780     /// [`fmt::Debug`]: https://doc.rust-lang.org/std/fmt/trait.Debug.html
 781     ///
 782     /// ### Example
 783     ///
 784     /// ```rust,compile_fail
 785     /// #![deny(missing_debug_implementations)]
 786     /// pub struct Foo;
 787     /// # fn main() {}
 788     /// ```
 789     ///
 790     /// {{produces}}
 791     ///
 792     /// ### Explanation
 793     ///
 794     /// Having a `Debug` implementation on all types can assist with
 795     /// debugging, as it provides a convenient way to format and display a
 796     /// value. Using the `#[derive(Debug)]` attribute will automatically
 797     /// generate a typical implementation, or a custom implementation can be
 798     /// added by manually implementing the `Debug` trait.
 799     ///
 800     /// This lint is "allow" by default because adding `Debug` to all types can
 801     /// have a negative impact on compile time and code size. It also requires
 802     /// boilerplate to be added to every type, which can be an impediment.
 803     MISSING_DEBUG_IMPLEMENTATIONS,
 804     Allow,
 805     "detects missing implementations of Debug"
 806 }
 807
 808 #[derive(Default)]
 809 pub struct MissingDebugImplementations {
 810     impling_types: Option<LocalDefIdSet>,
 811 }
 812
 813 impl_lint_pass!(MissingDebugImplementations => [MISSING_DEBUG_IMPLEMENTATIONS]);
 814
 815 impl<'tcx> LateLintPass<'tcx> for MissingDebugImplementations {
 816     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 817         if !cx.access_levels.is_reachable(item.def_id) {
 818             return;
 819         }
 820
 821         match item.kind {
 822             hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) | hir::ItemKind::Enum(..) => {}
 823             _ => return,
 824         }
 825
 826         let debug = match cx.tcx.get_diagnostic_item(sym::debug_trait) {
 827             Some(debug) => debug,
 828             None => return,
 829         };
 830
 831         if self.impling_types.is_none() {
 832             let mut impls = LocalDefIdSet::default();
 833             cx.tcx.for_each_impl(debug, |d| {
 834                 if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() {
 835                     if let Some(def_id) = ty_def.did.as_local() {
 836                         impls.insert(def_id);
 837                     }
 838                 }
 839             });
 840
 841             self.impling_types = Some(impls);
 842             debug!("{:?}", self.impling_types);
 843         }
 844
 845         if !self.impling_types.as_ref().unwrap().contains(&item.def_id) {
 846             cx.struct_span_lint(MISSING_DEBUG_IMPLEMENTATIONS, item.span, |lint| {
 847                 lint.build(&format!(
 848                     "type does not implement `{}`; consider adding `#[derive(Debug)]` \
 849                      or a manual implementation",
 850                     cx.tcx.def_path_str(debug)
 851                 ))
 852                 .emit()
 853             });
 854         }
 855     }
 856 }
 857
 858 declare_lint! {
 859     /// The `anonymous_parameters` lint detects anonymous parameters in trait
 860     /// definitions.
 861     ///
 862     /// ### Example
 863     ///
 864     /// ```rust,edition2015,compile_fail
 865     /// #![deny(anonymous_parameters)]
 866     /// // edition 2015
 867     /// pub trait Foo {
 868     ///     fn foo(usize);
 869     /// }
 870     /// fn main() {}
 871     /// ```
 872     ///
 873     /// {{produces}}
 874     ///
 875     /// ### Explanation
 876     ///
 877     /// This syntax is mostly a historical accident, and can be worked around
 878     /// quite easily by adding an `_` pattern or a descriptive identifier:
 879     ///
 880     /// ```rust
 881     /// trait Foo {
 882     ///     fn foo(_: usize);
 883     /// }
 884     /// ```
 885     ///
 886     /// This syntax is now a hard error in the 2018 edition. In the 2015
 887     /// edition, this lint is "warn" by default. This lint
 888     /// enables the [`cargo fix`] tool with the `--edition` flag to
 889     /// automatically transition old code from the 2015 edition to 2018. The
 890     /// tool will run this lint and automatically apply the
 891     /// suggested fix from the compiler (which is to add `_` to each
 892     /// parameter). This provides a completely automated way to update old
 893     /// code for a new edition. See [issue #41686] for more details.
 894     ///
 895     /// [issue #41686]: https://github.com/rust-lang/rust/issues/41686
 896     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
 897     pub ANONYMOUS_PARAMETERS,
 898     Warn,
 899     "detects anonymous parameters",
 900     @future_incompatible = FutureIncompatibleInfo {
 901         reference: "issue #41686 <https://github.com/rust-lang/rust/issues/41686>",
 902         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
 903     };
 904 }
 905
 906 declare_lint_pass!(
 907     /// Checks for use of anonymous parameters (RFC 1685).
 908     AnonymousParameters => [ANONYMOUS_PARAMETERS]
 909 );
 910
 911 impl EarlyLintPass for AnonymousParameters {
 912     fn check_trait_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
 913         if cx.sess.edition() != Edition::Edition2015 {
 914             // This is a hard error in future editions; avoid linting and erroring
 915             return;
 916         }
 917         if let ast::AssocItemKind::Fn(box FnKind(_, ref sig, _, _)) = it.kind {
 918             for arg in sig.decl.inputs.iter() {
 919                 if let ast::PatKind::Ident(_, ident, None) = arg.pat.kind {
 920                     if ident.name == kw::Empty {
 921                         cx.struct_span_lint(ANONYMOUS_PARAMETERS, arg.pat.span, |lint| {
 922                             let ty_snip = cx.sess.source_map().span_to_snippet(arg.ty.span);
 923
 924                             let (ty_snip, appl) = if let Ok(ref snip) = ty_snip {
 925                                 (snip.as_str(), Applicability::MachineApplicable)
 926                             } else {
 927                                 ("<type>", Applicability::HasPlaceholders)
 928                             };
 929
 930                             lint.build(
 931                                 "anonymous parameters are deprecated and will be \
 932                                      removed in the next edition.",
 933                             )
 934                             .span_suggestion(
 935                                 arg.pat.span,
 936                                 "try naming the parameter or explicitly \
 937                                             ignoring it",
 938                                 format!("_: {}", ty_snip),
 939                                 appl,
 940                             )
 941                             .emit();
 942                         })
 943                     }
 944                 }
 945             }
 946         }
 947     }
 948 }
 949
 950 /// Check for use of attributes which have been deprecated.
 951 #[derive(Clone)]
 952 pub struct DeprecatedAttr {
 953     // This is not free to compute, so we want to keep it around, rather than
 954     // compute it for every attribute.
 955     depr_attrs: Vec<&'static (Symbol, AttributeType, AttributeTemplate, AttributeGate)>,
 956 }
 957
 958 impl_lint_pass!(DeprecatedAttr => []);
 959
 960 impl DeprecatedAttr {
 961     pub fn new() -> DeprecatedAttr {
 962         DeprecatedAttr { depr_attrs: deprecated_attributes() }
 963     }
 964 }
 965
 966 fn lint_deprecated_attr(
 967     cx: &EarlyContext<'_>,
 968     attr: &ast::Attribute,
 969     msg: &str,
 970     suggestion: Option<&str>,
 971 ) {
 972     cx.struct_span_lint(DEPRECATED, attr.span, |lint| {
 973         lint.build(msg)
 974             .span_suggestion_short(
 975                 attr.span,
 976                 suggestion.unwrap_or("remove this attribute"),
 977                 String::new(),
 978                 Applicability::MachineApplicable,
 979             )
 980             .emit();
 981     })
 982 }
 983
 984 impl EarlyLintPass for DeprecatedAttr {
 985     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 986         for &&(n, _, _, ref g) in &self.depr_attrs {
 987             if attr.ident().map(|ident| ident.name) == Some(n) {
 988                 if let &AttributeGate::Gated(
 989                     Stability::Deprecated(link, suggestion),
 990                     name,
 991                     reason,
 992                     _,
 993                 ) = g
 994                 {
 995                     let msg =
 996                         format!("use of deprecated attribute `{}`: {}. See {}", name, reason, link);
 997                     lint_deprecated_attr(cx, attr, &msg, suggestion);
 998                 }
 999                 return;
1000             }
1001         }
1002         if cx.sess().check_name(attr, sym::no_start) || cx.sess().check_name(attr, sym::crate_id) {
1003             let path_str = pprust::path_to_string(&attr.get_normal_item().path);
1004             let msg = format!("use of deprecated attribute `{}`: no longer used.", path_str);
1005             lint_deprecated_attr(cx, attr, &msg, None);
1006         }
1007     }
1008 }
1009
1010 fn warn_if_doc(cx: &EarlyContext<'_>, node_span: Span, node_kind: &str, attrs: &[ast::Attribute]) {
1011     use rustc_ast::token::CommentKind;
1012
1013     let mut attrs = attrs.iter().peekable();
1014
1015     // Accumulate a single span for sugared doc comments.
1016     let mut sugared_span: Option<Span> = None;
1017
1018     while let Some(attr) = attrs.next() {
1019         let is_doc_comment = attr.is_doc_comment();
1020         if is_doc_comment {
1021             sugared_span =
1022                 Some(sugared_span.map_or(attr.span, |span| span.with_hi(attr.span.hi())));
1023         }
1024
1025         if attrs.peek().map_or(false, |next_attr| next_attr.is_doc_comment()) {
1026             continue;
1027         }
1028
1029         let span = sugared_span.take().unwrap_or(attr.span);
1030
1031         if is_doc_comment || cx.sess().check_name(attr, sym::doc) {
1032             cx.struct_span_lint(UNUSED_DOC_COMMENTS, span, |lint| {
1033                 let mut err = lint.build("unused doc comment");
1034                 err.span_label(
1035                     node_span,
1036                     format!("rustdoc does not generate documentation for {}", node_kind),
1037                 );
1038                 match attr.kind {
1039                     AttrKind::DocComment(CommentKind::Line, _) | AttrKind::Normal(..) => {
1040                         err.help("use `//` for a plain comment");
1041                     }
1042                     AttrKind::DocComment(CommentKind::Block, _) => {
1043                         err.help("use `/* */` for a plain comment");
1044                     }
1045                 }
1046                 err.emit();
1047             });
1048         }
1049     }
1050 }
1051
1052 impl EarlyLintPass for UnusedDocComment {
1053     fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &ast::Stmt) {
1054         let kind = match stmt.kind {
1055             ast::StmtKind::Local(..) => "statements",
1056             // Disabled pending discussion in #78306
1057             ast::StmtKind::Item(..) => return,
1058             // expressions will be reported by `check_expr`.
1059             ast::StmtKind::Empty
1060             | ast::StmtKind::Semi(_)
1061             | ast::StmtKind::Expr(_)
1062             | ast::StmtKind::MacCall(_) => return,
1063         };
1064
1065         warn_if_doc(cx, stmt.span, kind, stmt.kind.attrs());
1066     }
1067
1068     fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) {
1069         let arm_span = arm.pat.span.with_hi(arm.body.span.hi());
1070         warn_if_doc(cx, arm_span, "match arms", &arm.attrs);
1071     }
1072
1073     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
1074         warn_if_doc(cx, expr.span, "expressions", &expr.attrs);
1075     }
1076 }
1077
1078 declare_lint! {
1079     /// The `no_mangle_const_items` lint detects any `const` items with the
1080     /// [`no_mangle` attribute].
1081     ///
1082     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1083     ///
1084     /// ### Example
1085     ///
1086     /// ```rust,compile_fail
1087     /// #[no_mangle]
1088     /// const FOO: i32 = 5;
1089     /// ```
1090     ///
1091     /// {{produces}}
1092     ///
1093     /// ### Explanation
1094     ///
1095     /// Constants do not have their symbols exported, and therefore, this
1096     /// probably means you meant to use a [`static`], not a [`const`].
1097     ///
1098     /// [`static`]: https://doc.rust-lang.org/reference/items/static-items.html
1099     /// [`const`]: https://doc.rust-lang.org/reference/items/constant-items.html
1100     NO_MANGLE_CONST_ITEMS,
1101     Deny,
1102     "const items will not have their symbols exported"
1103 }
1104
1105 declare_lint! {
1106     /// The `no_mangle_generic_items` lint detects generic items that must be
1107     /// mangled.
1108     ///
1109     /// ### Example
1110     ///
1111     /// ```rust
1112     /// #[no_mangle]
1113     /// fn foo<T>(t: T) {
1114     ///
1115     /// }
1116     /// ```
1117     ///
1118     /// {{produces}}
1119     ///
1120     /// ### Explanation
1121     ///
1122     /// A function with generics must have its symbol mangled to accommodate
1123     /// the generic parameter. The [`no_mangle` attribute] has no effect in
1124     /// this situation, and should be removed.
1125     ///
1126     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1127     NO_MANGLE_GENERIC_ITEMS,
1128     Warn,
1129     "generic items must be mangled"
1130 }
1131
1132 declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS, NO_MANGLE_GENERIC_ITEMS]);
1133
1134 impl<'tcx> LateLintPass<'tcx> for InvalidNoMangleItems {
1135     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1136         let attrs = cx.tcx.hir().attrs(it.hir_id());
1137         let check_no_mangle_on_generic_fn = |no_mangle_attr: &ast::Attribute,
1138                                              impl_generics: Option<&hir::Generics<'_>>,
1139                                              generics: &hir::Generics<'_>,
1140                                              span| {
1141             for param in
1142                 generics.params.iter().chain(impl_generics.map(|g| g.params).into_iter().flatten())
1143             {
1144                 match param.kind {
1145                     GenericParamKind::Lifetime { .. } => {}
1146                     GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1147                         cx.struct_span_lint(NO_MANGLE_GENERIC_ITEMS, span, |lint| {
1148                             lint.build("functions generic over types or consts must be mangled")
1149                                 .span_suggestion_short(
1150                                     no_mangle_attr.span,
1151                                     "remove this attribute",
1152                                     String::new(),
1153                                     // Use of `#[no_mangle]` suggests FFI intent; correct
1154                                     // fix may be to monomorphize source by hand
1155                                     Applicability::MaybeIncorrect,
1156                                 )
1157                                 .emit();
1158                         });
1159                         break;
1160                     }
1161                 }
1162             }
1163         };
1164         match it.kind {
1165             hir::ItemKind::Fn(.., ref generics, _) => {
1166                 if let Some(no_mangle_attr) = cx.sess().find_by_name(attrs, sym::no_mangle) {
1167                     check_no_mangle_on_generic_fn(no_mangle_attr, None, generics, it.span);
1168                 }
1169             }
1170             hir::ItemKind::Const(..) => {
1171                 if cx.sess().contains_name(attrs, sym::no_mangle) {
1172                     // Const items do not refer to a particular location in memory, and therefore
1173                     // don't have anything to attach a symbol to
1174                     cx.struct_span_lint(NO_MANGLE_CONST_ITEMS, it.span, |lint| {
1175                         let msg = "const items should never be `#[no_mangle]`";
1176                         let mut err = lint.build(msg);
1177
1178                         // account for "pub const" (#45562)
1179                         let start = cx
1180                             .tcx
1181                             .sess
1182                             .source_map()
1183                             .span_to_snippet(it.span)
1184                             .map(|snippet| snippet.find("const").unwrap_or(0))
1185                             .unwrap_or(0) as u32;
1186                         // `const` is 5 chars
1187                         let const_span = it.span.with_hi(BytePos(it.span.lo().0 + start + 5));
1188                         err.span_suggestion(
1189                             const_span,
1190                             "try a static value",
1191                             "pub static".to_owned(),
1192                             Applicability::MachineApplicable,
1193                         );
1194                         err.emit();
1195                     });
1196                 }
1197             }
1198             hir::ItemKind::Impl(hir::Impl { ref generics, items, .. }) => {
1199                 for it in items {
1200                     if let hir::AssocItemKind::Fn { .. } = it.kind {
1201                         if let Some(no_mangle_attr) = cx
1202                             .sess()
1203                             .find_by_name(cx.tcx.hir().attrs(it.id.hir_id()), sym::no_mangle)
1204                         {
1205                             check_no_mangle_on_generic_fn(
1206                                 no_mangle_attr,
1207                                 Some(generics),
1208                                 cx.tcx.hir().get_generics(it.id.def_id.to_def_id()).unwrap(),
1209                                 it.span,
1210                             );
1211                         }
1212                     }
1213                 }
1214             }
1215             _ => {}
1216         }
1217     }
1218 }
1219
1220 declare_lint! {
1221     /// The `mutable_transmutes` lint catches transmuting from `&T` to `&mut
1222     /// T` because it is [undefined behavior].
1223     ///
1224     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1225     ///
1226     /// ### Example
1227     ///
1228     /// ```rust,compile_fail
1229     /// unsafe {
1230     ///     let y = std::mem::transmute::<&i32, &mut i32>(&5);
1231     /// }
1232     /// ```
1233     ///
1234     /// {{produces}}
1235     ///
1236     /// ### Explanation
1237     ///
1238     /// Certain assumptions are made about aliasing of data, and this transmute
1239     /// violates those assumptions. Consider using [`UnsafeCell`] instead.
1240     ///
1241     /// [`UnsafeCell`]: https://doc.rust-lang.org/std/cell/struct.UnsafeCell.html
1242     MUTABLE_TRANSMUTES,
1243     Deny,
1244     "mutating transmuted &mut T from &T may cause undefined behavior"
1245 }
1246
1247 declare_lint_pass!(MutableTransmutes => [MUTABLE_TRANSMUTES]);
1248
1249 impl<'tcx> LateLintPass<'tcx> for MutableTransmutes {
1250     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &hir::Expr<'_>) {
1251         use rustc_target::spec::abi::Abi::RustIntrinsic;
1252         if let Some((&ty::Ref(_, _, from_mt), &ty::Ref(_, _, to_mt))) =
1253             get_transmute_from_to(cx, expr).map(|(ty1, ty2)| (ty1.kind(), ty2.kind()))
1254         {
1255             if to_mt == hir::Mutability::Mut && from_mt == hir::Mutability::Not {
1256                 let msg = "mutating transmuted &mut T from &T may cause undefined behavior, \
1257                                consider instead using an UnsafeCell";
1258                 cx.struct_span_lint(MUTABLE_TRANSMUTES, expr.span, |lint| lint.build(msg).emit());
1259             }
1260         }
1261
1262         fn get_transmute_from_to<'tcx>(
1263             cx: &LateContext<'tcx>,
1264             expr: &hir::Expr<'_>,
1265         ) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
1266             let def = if let hir::ExprKind::Path(ref qpath) = expr.kind {
1267                 cx.qpath_res(qpath, expr.hir_id)
1268             } else {
1269                 return None;
1270             };
1271             if let Res::Def(DefKind::Fn, did) = def {
1272                 if !def_id_is_transmute(cx, did) {
1273                     return None;
1274                 }
1275                 let sig = cx.typeck_results().node_type(expr.hir_id).fn_sig(cx.tcx);
1276                 let from = sig.inputs().skip_binder()[0];
1277                 let to = sig.output().skip_binder();
1278                 return Some((from, to));
1279             }
1280             None
1281         }
1282
1283         fn def_id_is_transmute(cx: &LateContext<'_>, def_id: DefId) -> bool {
1284             cx.tcx.fn_sig(def_id).abi() == RustIntrinsic
1285                 && cx.tcx.item_name(def_id) == sym::transmute
1286         }
1287     }
1288 }
1289
1290 declare_lint! {
1291     /// The `unstable_features` is deprecated and should no longer be used.
1292     UNSTABLE_FEATURES,
1293     Allow,
1294     "enabling unstable features (deprecated. do not use)"
1295 }
1296
1297 declare_lint_pass!(
1298     /// Forbids using the `#[feature(...)]` attribute
1299     UnstableFeatures => [UNSTABLE_FEATURES]
1300 );
1301
1302 impl<'tcx> LateLintPass<'tcx> for UnstableFeatures {
1303     fn check_attribute(&mut self, cx: &LateContext<'_>, attr: &ast::Attribute) {
1304         if cx.sess().check_name(attr, sym::feature) {
1305             if let Some(items) = attr.meta_item_list() {
1306                 for item in items {
1307                     cx.struct_span_lint(UNSTABLE_FEATURES, item.span(), |lint| {
1308                         lint.build("unstable feature").emit()
1309                     });
1310                 }
1311             }
1312         }
1313     }
1314 }
1315
1316 declare_lint! {
1317     /// The `unreachable_pub` lint triggers for `pub` items not reachable from
1318     /// the crate root.
1319     ///
1320     /// ### Example
1321     ///
1322     /// ```rust,compile_fail
1323     /// #![deny(unreachable_pub)]
1324     /// mod foo {
1325     ///     pub mod bar {
1326     ///
1327     ///     }
1328     /// }
1329     /// ```
1330     ///
1331     /// {{produces}}
1332     ///
1333     /// ### Explanation
1334     ///
1335     /// A bare `pub` visibility may be misleading if the item is not actually
1336     /// publicly exported from the crate. The `pub(crate)` visibility is
1337     /// recommended to be used instead, which more clearly expresses the intent
1338     /// that the item is only visible within its own crate.
1339     ///
1340     /// This lint is "allow" by default because it will trigger for a large
1341     /// amount existing Rust code, and has some false-positives. Eventually it
1342     /// is desired for this to become warn-by-default.
1343     pub UNREACHABLE_PUB,
1344     Allow,
1345     "`pub` items not reachable from crate root"
1346 }
1347
1348 declare_lint_pass!(
1349     /// Lint for items marked `pub` that aren't reachable from other crates.
1350     UnreachablePub => [UNREACHABLE_PUB]
1351 );
1352
1353 impl UnreachablePub {
1354     fn perform_lint(
1355         &self,
1356         cx: &LateContext<'_>,
1357         what: &str,
1358         def_id: LocalDefId,
1359         vis: &hir::Visibility<'_>,
1360         span: Span,
1361         exportable: bool,
1362     ) {
1363         let mut applicability = Applicability::MachineApplicable;
1364         match vis.node {
1365             hir::VisibilityKind::Public if !cx.access_levels.is_reachable(def_id) => {
1366                 if span.from_expansion() {
1367                     applicability = Applicability::MaybeIncorrect;
1368                 }
1369                 let def_span = cx.tcx.sess.source_map().guess_head_span(span);
1370                 cx.struct_span_lint(UNREACHABLE_PUB, def_span, |lint| {
1371                     let mut err = lint.build(&format!("unreachable `pub` {}", what));
1372                     let replacement = if cx.tcx.features().crate_visibility_modifier {
1373                         "crate"
1374                     } else {
1375                         "pub(crate)"
1376                     }
1377                     .to_owned();
1378
1379                     err.span_suggestion(
1380                         vis.span,
1381                         "consider restricting its visibility",
1382                         replacement,
1383                         applicability,
1384                     );
1385                     if exportable {
1386                         err.help("or consider exporting it for use by other crates");
1387                     }
1388                     err.emit();
1389                 });
1390             }
1391             _ => {}
1392         }
1393     }
1394 }
1395
1396 impl<'tcx> LateLintPass<'tcx> for UnreachablePub {
1397     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1398         self.perform_lint(cx, "item", item.def_id, &item.vis, item.span, true);
1399     }
1400
1401     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'tcx>) {
1402         self.perform_lint(
1403             cx,
1404             "item",
1405             foreign_item.def_id,
1406             &foreign_item.vis,
1407             foreign_item.span,
1408             true,
1409         );
1410     }
1411
1412     fn check_field_def(&mut self, cx: &LateContext<'_>, field: &hir::FieldDef<'_>) {
1413         let def_id = cx.tcx.hir().local_def_id(field.hir_id);
1414         self.perform_lint(cx, "field", def_id, &field.vis, field.span, false);
1415     }
1416
1417     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
1418         self.perform_lint(cx, "item", impl_item.def_id, &impl_item.vis, impl_item.span, false);
1419     }
1420 }
1421
1422 declare_lint! {
1423     /// The `type_alias_bounds` lint detects bounds in type aliases.
1424     ///
1425     /// ### Example
1426     ///
1427     /// ```rust
1428     /// type SendVec<T: Send> = Vec<T>;
1429     /// ```
1430     ///
1431     /// {{produces}}
1432     ///
1433     /// ### Explanation
1434     ///
1435     /// The trait bounds in a type alias are currently ignored, and should not
1436     /// be included to avoid confusion. This was previously allowed
1437     /// unintentionally; this may become a hard error in the future.
1438     TYPE_ALIAS_BOUNDS,
1439     Warn,
1440     "bounds in type aliases are not enforced"
1441 }
1442
1443 declare_lint_pass!(
1444     /// Lint for trait and lifetime bounds in type aliases being mostly ignored.
1445     /// They are relevant when using associated types, but otherwise neither checked
1446     /// at definition site nor enforced at use site.
1447     TypeAliasBounds => [TYPE_ALIAS_BOUNDS]
1448 );
1449
1450 impl TypeAliasBounds {
1451     fn is_type_variable_assoc(qpath: &hir::QPath<'_>) -> bool {
1452         match *qpath {
1453             hir::QPath::TypeRelative(ref ty, _) => {
1454                 // If this is a type variable, we found a `T::Assoc`.
1455                 match ty.kind {
1456                     hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
1457                         matches!(path.res, Res::Def(DefKind::TyParam, _))
1458                     }
1459                     _ => false,
1460                 }
1461             }
1462             hir::QPath::Resolved(..) | hir::QPath::LangItem(..) => false,
1463         }
1464     }
1465
1466     fn suggest_changing_assoc_types(ty: &hir::Ty<'_>, err: &mut DiagnosticBuilder<'_>) {
1467         // Access to associates types should use `<T as Bound>::Assoc`, which does not need a
1468         // bound.  Let's see if this type does that.
1469
1470         // We use a HIR visitor to walk the type.
1471         use rustc_hir::intravisit::{self, Visitor};
1472         struct WalkAssocTypes<'a, 'db> {
1473             err: &'a mut DiagnosticBuilder<'db>,
1474         }
1475         impl<'a, 'db, 'v> Visitor<'v> for WalkAssocTypes<'a, 'db> {
1476             type Map = intravisit::ErasedMap<'v>;
1477
1478             fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1479                 intravisit::NestedVisitorMap::None
1480             }
1481
1482             fn visit_qpath(&mut self, qpath: &'v hir::QPath<'v>, id: hir::HirId, span: Span) {
1483                 if TypeAliasBounds::is_type_variable_assoc(qpath) {
1484                     self.err.span_help(
1485                         span,
1486                         "use fully disambiguated paths (i.e., `<T as Trait>::Assoc`) to refer to \
1487                          associated types in type aliases",
1488                     );
1489                 }
1490                 intravisit::walk_qpath(self, qpath, id, span)
1491             }
1492         }
1493
1494         // Let's go for a walk!
1495         let mut visitor = WalkAssocTypes { err };
1496         visitor.visit_ty(ty);
1497     }
1498 }
1499
1500 impl<'tcx> LateLintPass<'tcx> for TypeAliasBounds {
1501     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1502         let (ty, type_alias_generics) = match item.kind {
1503             hir::ItemKind::TyAlias(ref ty, ref generics) => (&*ty, generics),
1504             _ => return,
1505         };
1506         if let hir::TyKind::OpaqueDef(..) = ty.kind {
1507             // Bounds are respected for `type X = impl Trait`
1508             return;
1509         }
1510         let mut suggested_changing_assoc_types = false;
1511         // There must not be a where clause
1512         if !type_alias_generics.where_clause.predicates.is_empty() {
1513             cx.lint(
1514                 TYPE_ALIAS_BOUNDS,
1515                 |lint| {
1516                     let mut err = lint.build("where clauses are not enforced in type aliases");
1517                     let spans: Vec<_> = type_alias_generics
1518                         .where_clause
1519                         .predicates
1520                         .iter()
1521                         .map(|pred| pred.span())
1522                         .collect();
1523                     err.set_span(spans);
1524                     err.span_suggestion(
1525                         type_alias_generics.where_clause.span_for_predicates_or_empty_place(),
1526                         "the clause will not be checked when the type alias is used, and should be removed",
1527                         String::new(),
1528                         Applicability::MachineApplicable,
1529                     );
1530                     if !suggested_changing_assoc_types {
1531                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1532                         suggested_changing_assoc_types = true;
1533                     }
1534                     err.emit();
1535                 },
1536             );
1537         }
1538         // The parameters must not have bounds
1539         for param in type_alias_generics.params.iter() {
1540             let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
1541             let suggestion = spans
1542                 .iter()
1543                 .map(|sp| {
1544                     let start = param.span.between(*sp); // Include the `:` in `T: Bound`.
1545                     (start.to(*sp), String::new())
1546                 })
1547                 .collect();
1548             if !spans.is_empty() {
1549                 cx.struct_span_lint(TYPE_ALIAS_BOUNDS, spans, |lint| {
1550                     let mut err =
1551                         lint.build("bounds on generic parameters are not enforced in type aliases");
1552                     let msg = "the bound will not be checked when the type alias is used, \
1553                                    and should be removed";
1554                     err.multipart_suggestion(&msg, suggestion, Applicability::MachineApplicable);
1555                     if !suggested_changing_assoc_types {
1556                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1557                         suggested_changing_assoc_types = true;
1558                     }
1559                     err.emit();
1560                 });
1561             }
1562         }
1563     }
1564 }
1565
1566 declare_lint_pass!(
1567     /// Lint constants that are erroneous.
1568     /// Without this lint, we might not get any diagnostic if the constant is
1569     /// unused within this crate, even though downstream crates can't use it
1570     /// without producing an error.
1571     UnusedBrokenConst => []
1572 );
1573
1574 impl<'tcx> LateLintPass<'tcx> for UnusedBrokenConst {
1575     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1576         match it.kind {
1577             hir::ItemKind::Const(_, body_id) => {
1578                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1579                 // trigger the query once for all constants since that will already report the errors
1580                 // FIXME: Use ensure here
1581                 let _ = cx.tcx.const_eval_poly(def_id);
1582             }
1583             hir::ItemKind::Static(_, _, body_id) => {
1584                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1585                 // FIXME: Use ensure here
1586                 let _ = cx.tcx.eval_static_initializer(def_id);
1587             }
1588             _ => {}
1589         }
1590     }
1591 }
1592
1593 declare_lint! {
1594     /// The `trivial_bounds` lint detects trait bounds that don't depend on
1595     /// any type parameters.
1596     ///
1597     /// ### Example
1598     ///
1599     /// ```rust
1600     /// #![feature(trivial_bounds)]
1601     /// pub struct A where i32: Copy;
1602     /// ```
1603     ///
1604     /// {{produces}}
1605     ///
1606     /// ### Explanation
1607     ///
1608     /// Usually you would not write a trait bound that you know is always
1609     /// true, or never true. However, when using macros, the macro may not
1610     /// know whether or not the constraint would hold or not at the time when
1611     /// generating the code. Currently, the compiler does not alert you if the
1612     /// constraint is always true, and generates an error if it is never true.
1613     /// The `trivial_bounds` feature changes this to be a warning in both
1614     /// cases, giving macros more freedom and flexibility to generate code,
1615     /// while still providing a signal when writing non-macro code that
1616     /// something is amiss.
1617     ///
1618     /// See [RFC 2056] for more details. This feature is currently only
1619     /// available on the nightly channel, see [tracking issue #48214].
1620     ///
1621     /// [RFC 2056]: https://github.com/rust-lang/rfcs/blob/master/text/2056-allow-trivial-where-clause-constraints.md
1622     /// [tracking issue #48214]: https://github.com/rust-lang/rust/issues/48214
1623     TRIVIAL_BOUNDS,
1624     Warn,
1625     "these bounds don't depend on an type parameters"
1626 }
1627
1628 declare_lint_pass!(
1629     /// Lint for trait and lifetime bounds that don't depend on type parameters
1630     /// which either do nothing, or stop the item from being used.
1631     TrivialConstraints => [TRIVIAL_BOUNDS]
1632 );
1633
1634 impl<'tcx> LateLintPass<'tcx> for TrivialConstraints {
1635     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
1636         use rustc_middle::ty::fold::TypeFoldable;
1637         use rustc_middle::ty::PredicateKind::*;
1638
1639         if cx.tcx.features().trivial_bounds {
1640             let predicates = cx.tcx.predicates_of(item.def_id);
1641             for &(predicate, span) in predicates.predicates {
1642                 let predicate_kind_name = match predicate.kind().skip_binder() {
1643                     Trait(..) => "Trait",
1644                     TypeOutlives(..) |
1645                     RegionOutlives(..) => "Lifetime",
1646
1647                     // Ignore projections, as they can only be global
1648                     // if the trait bound is global
1649                     Projection(..) |
1650                     // Ignore bounds that a user can't type
1651                     WellFormed(..) |
1652                     ObjectSafe(..) |
1653                     ClosureKind(..) |
1654                     Subtype(..) |
1655                     ConstEvaluatable(..) |
1656                     ConstEquate(..) |
1657                     TypeWellFormedFromEnv(..) => continue,
1658                 };
1659                 if predicate.is_global() {
1660                     cx.struct_span_lint(TRIVIAL_BOUNDS, span, |lint| {
1661                         lint.build(&format!(
1662                             "{} bound {} does not depend on any type \
1663                                 or lifetime parameters",
1664                             predicate_kind_name, predicate
1665                         ))
1666                         .emit()
1667                     });
1668                 }
1669             }
1670         }
1671     }
1672 }
1673
1674 declare_lint_pass!(
1675     /// Does nothing as a lint pass, but registers some `Lint`s
1676     /// which are used by other parts of the compiler.
1677     SoftLints => [
1678         WHILE_TRUE,
1679         BOX_POINTERS,
1680         NON_SHORTHAND_FIELD_PATTERNS,
1681         UNSAFE_CODE,
1682         MISSING_DOCS,
1683         MISSING_COPY_IMPLEMENTATIONS,
1684         MISSING_DEBUG_IMPLEMENTATIONS,
1685         ANONYMOUS_PARAMETERS,
1686         UNUSED_DOC_COMMENTS,
1687         NO_MANGLE_CONST_ITEMS,
1688         NO_MANGLE_GENERIC_ITEMS,
1689         MUTABLE_TRANSMUTES,
1690         UNSTABLE_FEATURES,
1691         UNREACHABLE_PUB,
1692         TYPE_ALIAS_BOUNDS,
1693         TRIVIAL_BOUNDS
1694     ]
1695 );
1696
1697 declare_lint! {
1698     /// The `ellipsis_inclusive_range_patterns` lint detects the [`...` range
1699     /// pattern], which is deprecated.
1700     ///
1701     /// [`...` range pattern]: https://doc.rust-lang.org/reference/patterns.html#range-patterns
1702     ///
1703     /// ### Example
1704     ///
1705     /// ```rust
1706     /// let x = 123;
1707     /// match x {
1708     ///     0...100 => {}
1709     ///     _ => {}
1710     /// }
1711     /// ```
1712     ///
1713     /// {{produces}}
1714     ///
1715     /// ### Explanation
1716     ///
1717     /// The `...` range pattern syntax was changed to `..=` to avoid potential
1718     /// confusion with the [`..` range expression]. Use the new form instead.
1719     ///
1720     /// [`..` range expression]: https://doc.rust-lang.org/reference/expressions/range-expr.html
1721     pub ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
1722     Warn,
1723     "`...` range patterns are deprecated",
1724     @future_incompatible = FutureIncompatibleInfo {
1725         reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>",
1726         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
1727     };
1728 }
1729
1730 #[derive(Default)]
1731 pub struct EllipsisInclusiveRangePatterns {
1732     /// If `Some(_)`, suppress all subsequent pattern
1733     /// warnings for better diagnostics.
1734     node_id: Option<ast::NodeId>,
1735 }
1736
1737 impl_lint_pass!(EllipsisInclusiveRangePatterns => [ELLIPSIS_INCLUSIVE_RANGE_PATTERNS]);
1738
1739 impl EarlyLintPass for EllipsisInclusiveRangePatterns {
1740     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &ast::Pat) {
1741         if self.node_id.is_some() {
1742             // Don't recursively warn about patterns inside range endpoints.
1743             return;
1744         }
1745
1746         use self::ast::{PatKind, RangeSyntax::DotDotDot};
1747
1748         /// If `pat` is a `...` pattern, return the start and end of the range, as well as the span
1749         /// corresponding to the ellipsis.
1750         fn matches_ellipsis_pat(pat: &ast::Pat) -> Option<(Option<&Expr>, &Expr, Span)> {
1751             match &pat.kind {
1752                 PatKind::Range(
1753                     a,
1754                     Some(b),
1755                     Spanned { span, node: RangeEnd::Included(DotDotDot) },
1756                 ) => Some((a.as_deref(), b, *span)),
1757                 _ => None,
1758             }
1759         }
1760
1761         let (parenthesise, endpoints) = match &pat.kind {
1762             PatKind::Ref(subpat, _) => (true, matches_ellipsis_pat(&subpat)),
1763             _ => (false, matches_ellipsis_pat(pat)),
1764         };
1765
1766         if let Some((start, end, join)) = endpoints {
1767             let msg = "`...` range patterns are deprecated";
1768             let suggestion = "use `..=` for an inclusive range";
1769             if parenthesise {
1770                 self.node_id = Some(pat.id);
1771                 let end = expr_to_string(&end);
1772                 let replace = match start {
1773                     Some(start) => format!("&({}..={})", expr_to_string(&start), end),
1774                     None => format!("&(..={})", end),
1775                 };
1776                 if join.edition() >= Edition::Edition2021 {
1777                     let mut err =
1778                         rustc_errors::struct_span_err!(cx.sess, pat.span, E0783, "{}", msg,);
1779                     err.span_suggestion(
1780                         pat.span,
1781                         suggestion,
1782                         replace,
1783                         Applicability::MachineApplicable,
1784                     )
1785                     .emit();
1786                 } else {
1787                     cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, pat.span, |lint| {
1788                         lint.build(msg)
1789                             .span_suggestion(
1790                                 pat.span,
1791                                 suggestion,
1792                                 replace,
1793                                 Applicability::MachineApplicable,
1794                             )
1795                             .emit();
1796                     });
1797                 }
1798             } else {
1799                 let replace = "..=".to_owned();
1800                 if join.edition() >= Edition::Edition2021 {
1801                     let mut err =
1802                         rustc_errors::struct_span_err!(cx.sess, pat.span, E0783, "{}", msg,);
1803                     err.span_suggestion_short(
1804                         join,
1805                         suggestion,
1806                         replace,
1807                         Applicability::MachineApplicable,
1808                     )
1809                     .emit();
1810                 } else {
1811                     cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, join, |lint| {
1812                         lint.build(msg)
1813                             .span_suggestion_short(
1814                                 join,
1815                                 suggestion,
1816                                 replace,
1817                                 Applicability::MachineApplicable,
1818                             )
1819                             .emit();
1820                     });
1821                 }
1822             };
1823         }
1824     }
1825
1826     fn check_pat_post(&mut self, _cx: &EarlyContext<'_>, pat: &ast::Pat) {
1827         if let Some(node_id) = self.node_id {
1828             if pat.id == node_id {
1829                 self.node_id = None
1830             }
1831         }
1832     }
1833 }
1834
1835 declare_lint! {
1836     /// The `unnameable_test_items` lint detects [`#[test]`][test] functions
1837     /// that are not able to be run by the test harness because they are in a
1838     /// position where they are not nameable.
1839     ///
1840     /// [test]: https://doc.rust-lang.org/reference/attributes/testing.html#the-test-attribute
1841     ///
1842     /// ### Example
1843     ///
1844     /// ```rust,test
1845     /// fn main() {
1846     ///     #[test]
1847     ///     fn foo() {
1848     ///         // This test will not fail because it does not run.
1849     ///         assert_eq!(1, 2);
1850     ///     }
1851     /// }
1852     /// ```
1853     ///
1854     /// {{produces}}
1855     ///
1856     /// ### Explanation
1857     ///
1858     /// In order for the test harness to run a test, the test function must be
1859     /// located in a position where it can be accessed from the crate root.
1860     /// This generally means it must be defined in a module, and not anywhere
1861     /// else such as inside another function. The compiler previously allowed
1862     /// this without an error, so a lint was added as an alert that a test is
1863     /// not being used. Whether or not this should be allowed has not yet been
1864     /// decided, see [RFC 2471] and [issue #36629].
1865     ///
1866     /// [RFC 2471]: https://github.com/rust-lang/rfcs/pull/2471#issuecomment-397414443
1867     /// [issue #36629]: https://github.com/rust-lang/rust/issues/36629
1868     UNNAMEABLE_TEST_ITEMS,
1869     Warn,
1870     "detects an item that cannot be named being marked as `#[test_case]`",
1871     report_in_external_macro
1872 }
1873
1874 pub struct UnnameableTestItems {
1875     boundary: Option<LocalDefId>, // Id of the item under which things are not nameable
1876     items_nameable: bool,
1877 }
1878
1879 impl_lint_pass!(UnnameableTestItems => [UNNAMEABLE_TEST_ITEMS]);
1880
1881 impl UnnameableTestItems {
1882     pub fn new() -> Self {
1883         Self { boundary: None, items_nameable: true }
1884     }
1885 }
1886
1887 impl<'tcx> LateLintPass<'tcx> for UnnameableTestItems {
1888     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1889         if self.items_nameable {
1890             if let hir::ItemKind::Mod(..) = it.kind {
1891             } else {
1892                 self.items_nameable = false;
1893                 self.boundary = Some(it.def_id);
1894             }
1895             return;
1896         }
1897
1898         let attrs = cx.tcx.hir().attrs(it.hir_id());
1899         if let Some(attr) = cx.sess().find_by_name(attrs, sym::rustc_test_marker) {
1900             cx.struct_span_lint(UNNAMEABLE_TEST_ITEMS, attr.span, |lint| {
1901                 lint.build("cannot test inner items").emit()
1902             });
1903         }
1904     }
1905
1906     fn check_item_post(&mut self, _cx: &LateContext<'_>, it: &hir::Item<'_>) {
1907         if !self.items_nameable && self.boundary == Some(it.def_id) {
1908             self.items_nameable = true;
1909         }
1910     }
1911 }
1912
1913 declare_lint! {
1914     /// The `keyword_idents` lint detects edition keywords being used as an
1915     /// identifier.
1916     ///
1917     /// ### Example
1918     ///
1919     /// ```rust,edition2015,compile_fail
1920     /// #![deny(keyword_idents)]
1921     /// // edition 2015
1922     /// fn dyn() {}
1923     /// ```
1924     ///
1925     /// {{produces}}
1926     ///
1927     /// ### Explanation
1928     ///
1929     /// Rust [editions] allow the language to evolve without breaking
1930     /// backwards compatibility. This lint catches code that uses new keywords
1931     /// that are added to the language that are used as identifiers (such as a
1932     /// variable name, function name, etc.). If you switch the compiler to a
1933     /// new edition without updating the code, then it will fail to compile if
1934     /// you are using a new keyword as an identifier.
1935     ///
1936     /// You can manually change the identifiers to a non-keyword, or use a
1937     /// [raw identifier], for example `r#dyn`, to transition to a new edition.
1938     ///
1939     /// This lint solves the problem automatically. It is "allow" by default
1940     /// because the code is perfectly valid in older editions. The [`cargo
1941     /// fix`] tool with the `--edition` flag will switch this lint to "warn"
1942     /// and automatically apply the suggested fix from the compiler (which is
1943     /// to use a raw identifier). This provides a completely automated way to
1944     /// update old code for a new edition.
1945     ///
1946     /// [editions]: https://doc.rust-lang.org/edition-guide/
1947     /// [raw identifier]: https://doc.rust-lang.org/reference/identifiers.html
1948     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
1949     pub KEYWORD_IDENTS,
1950     Allow,
1951     "detects edition keywords being used as an identifier",
1952     @future_incompatible = FutureIncompatibleInfo {
1953         reference: "issue #49716 <https://github.com/rust-lang/rust/issues/49716>",
1954         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
1955     };
1956 }
1957
1958 declare_lint_pass!(
1959     /// Check for uses of edition keywords used as an identifier.
1960     KeywordIdents => [KEYWORD_IDENTS]
1961 );
1962
1963 struct UnderMacro(bool);
1964
1965 impl KeywordIdents {
1966     fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: TokenStream) {
1967         for tt in tokens.into_trees() {
1968             match tt {
1969                 // Only report non-raw idents.
1970                 TokenTree::Token(token) => {
1971                     if let Some((ident, false)) = token.ident() {
1972                         self.check_ident_token(cx, UnderMacro(true), ident);
1973                     }
1974                 }
1975                 TokenTree::Delimited(_, _, tts) => self.check_tokens(cx, tts),
1976             }
1977         }
1978     }
1979
1980     fn check_ident_token(
1981         &mut self,
1982         cx: &EarlyContext<'_>,
1983         UnderMacro(under_macro): UnderMacro,
1984         ident: Ident,
1985     ) {
1986         let next_edition = match cx.sess.edition() {
1987             Edition::Edition2015 => {
1988                 match ident.name {
1989                     kw::Async | kw::Await | kw::Try => Edition::Edition2018,
1990
1991                     // rust-lang/rust#56327: Conservatively do not
1992                     // attempt to report occurrences of `dyn` within
1993                     // macro definitions or invocations, because `dyn`
1994                     // can legitimately occur as a contextual keyword
1995                     // in 2015 code denoting its 2018 meaning, and we
1996                     // do not want rustfix to inject bugs into working
1997                     // code by rewriting such occurrences.
1998                     //
1999                     // But if we see `dyn` outside of a macro, we know
2000                     // its precise role in the parsed AST and thus are
2001                     // assured this is truly an attempt to use it as
2002                     // an identifier.
2003                     kw::Dyn if !under_macro => Edition::Edition2018,
2004
2005                     _ => return,
2006                 }
2007             }
2008
2009             // There are no new keywords yet for the 2018 edition and beyond.
2010             _ => return,
2011         };
2012
2013         // Don't lint `r#foo`.
2014         if cx.sess.parse_sess.raw_identifier_spans.borrow().contains(&ident.span) {
2015             return;
2016         }
2017
2018         cx.struct_span_lint(KEYWORD_IDENTS, ident.span, |lint| {
2019             lint.build(&format!("`{}` is a keyword in the {} edition", ident, next_edition))
2020                 .span_suggestion(
2021                     ident.span,
2022                     "you can use a raw identifier to stay compatible",
2023                     format!("r#{}", ident),
2024                     Applicability::MachineApplicable,
2025                 )
2026                 .emit()
2027         });
2028     }
2029 }
2030
2031 impl EarlyLintPass for KeywordIdents {
2032     fn check_mac_def(&mut self, cx: &EarlyContext<'_>, mac_def: &ast::MacroDef, _id: ast::NodeId) {
2033         self.check_tokens(cx, mac_def.body.inner_tokens());
2034     }
2035     fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::MacCall) {
2036         self.check_tokens(cx, mac.args.inner_tokens());
2037     }
2038     fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: Ident) {
2039         self.check_ident_token(cx, UnderMacro(false), ident);
2040     }
2041 }
2042
2043 declare_lint_pass!(ExplicitOutlivesRequirements => [EXPLICIT_OUTLIVES_REQUIREMENTS]);
2044
2045 impl ExplicitOutlivesRequirements {
2046     fn lifetimes_outliving_lifetime<'tcx>(
2047         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2048         index: u32,
2049     ) -> Vec<ty::Region<'tcx>> {
2050         inferred_outlives
2051             .iter()
2052             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
2053                 ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => match a {
2054                     ty::ReEarlyBound(ebr) if ebr.index == index => Some(b),
2055                     _ => None,
2056                 },
2057                 _ => None,
2058             })
2059             .collect()
2060     }
2061
2062     fn lifetimes_outliving_type<'tcx>(
2063         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2064         index: u32,
2065     ) -> Vec<ty::Region<'tcx>> {
2066         inferred_outlives
2067             .iter()
2068             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
2069                 ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
2070                     a.is_param(index).then_some(b)
2071                 }
2072                 _ => None,
2073             })
2074             .collect()
2075     }
2076
2077     fn collect_outlived_lifetimes<'tcx>(
2078         &self,
2079         param: &'tcx hir::GenericParam<'tcx>,
2080         tcx: TyCtxt<'tcx>,
2081         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2082         ty_generics: &'tcx ty::Generics,
2083     ) -> Vec<ty::Region<'tcx>> {
2084         let index =
2085             ty_generics.param_def_id_to_index[&tcx.hir().local_def_id(param.hir_id).to_def_id()];
2086
2087         match param.kind {
2088             hir::GenericParamKind::Lifetime { .. } => {
2089                 Self::lifetimes_outliving_lifetime(inferred_outlives, index)
2090             }
2091             hir::GenericParamKind::Type { .. } => {
2092                 Self::lifetimes_outliving_type(inferred_outlives, index)
2093             }
2094             hir::GenericParamKind::Const { .. } => Vec::new(),
2095         }
2096     }
2097
2098     fn collect_outlives_bound_spans<'tcx>(
2099         &self,
2100         tcx: TyCtxt<'tcx>,
2101         bounds: &hir::GenericBounds<'_>,
2102         inferred_outlives: &[ty::Region<'tcx>],
2103         infer_static: bool,
2104     ) -> Vec<(usize, Span)> {
2105         use rustc_middle::middle::resolve_lifetime::Region;
2106
2107         bounds
2108             .iter()
2109             .enumerate()
2110             .filter_map(|(i, bound)| {
2111                 if let hir::GenericBound::Outlives(lifetime) = bound {
2112                     let is_inferred = match tcx.named_region(lifetime.hir_id) {
2113                         Some(Region::Static) if infer_static => {
2114                             inferred_outlives.iter().any(|r| matches!(r, ty::ReStatic))
2115                         }
2116                         Some(Region::EarlyBound(index, ..)) => inferred_outlives.iter().any(|r| {
2117                             if let ty::ReEarlyBound(ebr) = r { ebr.index == index } else { false }
2118                         }),
2119                         _ => false,
2120                     };
2121                     is_inferred.then_some((i, bound.span()))
2122                 } else {
2123                     None
2124                 }
2125             })
2126             .collect()
2127     }
2128
2129     fn consolidate_outlives_bound_spans(
2130         &self,
2131         lo: Span,
2132         bounds: &hir::GenericBounds<'_>,
2133         bound_spans: Vec<(usize, Span)>,
2134     ) -> Vec<Span> {
2135         if bounds.is_empty() {
2136             return Vec::new();
2137         }
2138         if bound_spans.len() == bounds.len() {
2139             let (_, last_bound_span) = bound_spans[bound_spans.len() - 1];
2140             // If all bounds are inferable, we want to delete the colon, so
2141             // start from just after the parameter (span passed as argument)
2142             vec![lo.to(last_bound_span)]
2143         } else {
2144             let mut merged = Vec::new();
2145             let mut last_merged_i = None;
2146
2147             let mut from_start = true;
2148             for (i, bound_span) in bound_spans {
2149                 match last_merged_i {
2150                     // If the first bound is inferable, our span should also eat the leading `+`.
2151                     None if i == 0 => {
2152                         merged.push(bound_span.to(bounds[1].span().shrink_to_lo()));
2153                         last_merged_i = Some(0);
2154                     }
2155                     // If consecutive bounds are inferable, merge their spans
2156                     Some(h) if i == h + 1 => {
2157                         if let Some(tail) = merged.last_mut() {
2158                             // Also eat the trailing `+` if the first
2159                             // more-than-one bound is inferable
2160                             let to_span = if from_start && i < bounds.len() {
2161                                 bounds[i + 1].span().shrink_to_lo()
2162                             } else {
2163                                 bound_span
2164                             };
2165                             *tail = tail.to(to_span);
2166                             last_merged_i = Some(i);
2167                         } else {
2168                             bug!("another bound-span visited earlier");
2169                         }
2170                     }
2171                     _ => {
2172                         // When we find a non-inferable bound, subsequent inferable bounds
2173                         // won't be consecutive from the start (and we'll eat the leading
2174                         // `+` rather than the trailing one)
2175                         from_start = false;
2176                         merged.push(bounds[i - 1].span().shrink_to_hi().to(bound_span));
2177                         last_merged_i = Some(i);
2178                     }
2179                 }
2180             }
2181             merged
2182         }
2183     }
2184 }
2185
2186 impl<'tcx> LateLintPass<'tcx> for ExplicitOutlivesRequirements {
2187     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
2188         use rustc_middle::middle::resolve_lifetime::Region;
2189
2190         let infer_static = cx.tcx.features().infer_static_outlives_requirements;
2191         let def_id = item.def_id;
2192         if let hir::ItemKind::Struct(_, ref hir_generics)
2193         | hir::ItemKind::Enum(_, ref hir_generics)
2194         | hir::ItemKind::Union(_, ref hir_generics) = item.kind
2195         {
2196             let inferred_outlives = cx.tcx.inferred_outlives_of(def_id);
2197             if inferred_outlives.is_empty() {
2198                 return;
2199             }
2200
2201             let ty_generics = cx.tcx.generics_of(def_id);
2202
2203             let mut bound_count = 0;
2204             let mut lint_spans = Vec::new();
2205
2206             for param in hir_generics.params {
2207                 let has_lifetime_bounds = param
2208                     .bounds
2209                     .iter()
2210                     .any(|bound| matches!(bound, hir::GenericBound::Outlives(_)));
2211                 if !has_lifetime_bounds {
2212                     continue;
2213                 }
2214
2215                 let relevant_lifetimes =
2216                     self.collect_outlived_lifetimes(param, cx.tcx, inferred_outlives, ty_generics);
2217                 if relevant_lifetimes.is_empty() {
2218                     continue;
2219                 }
2220
2221                 let bound_spans = self.collect_outlives_bound_spans(
2222                     cx.tcx,
2223                     &param.bounds,
2224                     &relevant_lifetimes,
2225                     infer_static,
2226                 );
2227                 bound_count += bound_spans.len();
2228                 lint_spans.extend(self.consolidate_outlives_bound_spans(
2229                     param.span.shrink_to_hi(),
2230                     &param.bounds,
2231                     bound_spans,
2232                 ));
2233             }
2234
2235             let mut where_lint_spans = Vec::new();
2236             let mut dropped_predicate_count = 0;
2237             let num_predicates = hir_generics.where_clause.predicates.len();
2238             for (i, where_predicate) in hir_generics.where_clause.predicates.iter().enumerate() {
2239                 let (relevant_lifetimes, bounds, span) = match where_predicate {
2240                     hir::WherePredicate::RegionPredicate(predicate) => {
2241                         if let Some(Region::EarlyBound(index, ..)) =
2242                             cx.tcx.named_region(predicate.lifetime.hir_id)
2243                         {
2244                             (
2245                                 Self::lifetimes_outliving_lifetime(inferred_outlives, index),
2246                                 &predicate.bounds,
2247                                 predicate.span,
2248                             )
2249                         } else {
2250                             continue;
2251                         }
2252                     }
2253                     hir::WherePredicate::BoundPredicate(predicate) => {
2254                         // FIXME we can also infer bounds on associated types,
2255                         // and should check for them here.
2256                         match predicate.bounded_ty.kind {
2257                             hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
2258                                 if let Res::Def(DefKind::TyParam, def_id) = path.res {
2259                                     let index = ty_generics.param_def_id_to_index[&def_id];
2260                                     (
2261                                         Self::lifetimes_outliving_type(inferred_outlives, index),
2262                                         &predicate.bounds,
2263                                         predicate.span,
2264                                     )
2265                                 } else {
2266                                     continue;
2267                                 }
2268                             }
2269                             _ => {
2270                                 continue;
2271                             }
2272                         }
2273                     }
2274                     _ => continue,
2275                 };
2276                 if relevant_lifetimes.is_empty() {
2277                     continue;
2278                 }
2279
2280                 let bound_spans = self.collect_outlives_bound_spans(
2281                     cx.tcx,
2282                     bounds,
2283                     &relevant_lifetimes,
2284                     infer_static,
2285                 );
2286                 bound_count += bound_spans.len();
2287
2288                 let drop_predicate = bound_spans.len() == bounds.len();
2289                 if drop_predicate {
2290                     dropped_predicate_count += 1;
2291                 }
2292
2293                 // If all the bounds on a predicate were inferable and there are
2294                 // further predicates, we want to eat the trailing comma.
2295                 if drop_predicate && i + 1 < num_predicates {
2296                     let next_predicate_span = hir_generics.where_clause.predicates[i + 1].span();
2297                     where_lint_spans.push(span.to(next_predicate_span.shrink_to_lo()));
2298                 } else {
2299                     where_lint_spans.extend(self.consolidate_outlives_bound_spans(
2300                         span.shrink_to_lo(),
2301                         bounds,
2302                         bound_spans,
2303                     ));
2304                 }
2305             }
2306
2307             // If all predicates are inferable, drop the entire clause
2308             // (including the `where`)
2309             if num_predicates > 0 && dropped_predicate_count == num_predicates {
2310                 let where_span = hir_generics
2311                     .where_clause
2312                     .span()
2313                     .expect("span of (nonempty) where clause should exist");
2314                 // Extend the where clause back to the closing `>` of the
2315                 // generics, except for tuple struct, which have the `where`
2316                 // after the fields of the struct.
2317                 let full_where_span =
2318                     if let hir::ItemKind::Struct(hir::VariantData::Tuple(..), _) = item.kind {
2319                         where_span
2320                     } else {
2321                         hir_generics.span.shrink_to_hi().to(where_span)
2322                     };
2323                 lint_spans.push(full_where_span);
2324             } else {
2325                 lint_spans.extend(where_lint_spans);
2326             }
2327
2328             if !lint_spans.is_empty() {
2329                 cx.struct_span_lint(EXPLICIT_OUTLIVES_REQUIREMENTS, lint_spans.clone(), |lint| {
2330                     lint.build("outlives requirements can be inferred")
2331                         .multipart_suggestion(
2332                             if bound_count == 1 {
2333                                 "remove this bound"
2334                             } else {
2335                                 "remove these bounds"
2336                             },
2337                             lint_spans
2338                                 .into_iter()
2339                                 .map(|span| (span, "".to_owned()))
2340                                 .collect::<Vec<_>>(),
2341                             Applicability::MachineApplicable,
2342                         )
2343                         .emit();
2344                 });
2345             }
2346         }
2347     }
2348 }
2349
2350 declare_lint! {
2351     /// The `incomplete_features` lint detects unstable features enabled with
2352     /// the [`feature` attribute] that may function improperly in some or all
2353     /// cases.
2354     ///
2355     /// [`feature` attribute]: https://doc.rust-lang.org/nightly/unstable-book/
2356     ///
2357     /// ### Example
2358     ///
2359     /// ```rust
2360     /// #![feature(const_generics)]
2361     /// ```
2362     ///
2363     /// {{produces}}
2364     ///
2365     /// ### Explanation
2366     ///
2367     /// Although it is encouraged for people to experiment with unstable
2368     /// features, some of them are known to be incomplete or faulty. This lint
2369     /// is a signal that the feature has not yet been finished, and you may
2370     /// experience problems with it.
2371     pub INCOMPLETE_FEATURES,
2372     Warn,
2373     "incomplete features that may function improperly in some or all cases"
2374 }
2375
2376 declare_lint_pass!(
2377     /// Check for used feature gates in `INCOMPLETE_FEATURES` in `rustc_feature/src/active.rs`.
2378     IncompleteFeatures => [INCOMPLETE_FEATURES]
2379 );
2380
2381 impl EarlyLintPass for IncompleteFeatures {
2382     fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
2383         let features = cx.sess.features_untracked();
2384         features
2385             .declared_lang_features
2386             .iter()
2387             .map(|(name, span, _)| (name, span))
2388             .chain(features.declared_lib_features.iter().map(|(name, span)| (name, span)))
2389             .filter(|(&name, _)| features.incomplete(name))
2390             .for_each(|(&name, &span)| {
2391                 cx.struct_span_lint(INCOMPLETE_FEATURES, span, |lint| {
2392                     let mut builder = lint.build(&format!(
2393                         "the feature `{}` is incomplete and may not be safe to use \
2394                          and/or cause compiler crashes",
2395                         name,
2396                     ));
2397                     if let Some(n) = rustc_feature::find_feature_issue(name, GateIssue::Language) {
2398                         builder.note(&format!(
2399                             "see issue #{} <https://github.com/rust-lang/rust/issues/{}> \
2400                              for more information",
2401                             n, n,
2402                         ));
2403                     }
2404                     if HAS_MIN_FEATURES.contains(&name) {
2405                         builder.help(&format!(
2406                             "consider using `min_{}` instead, which is more stable and complete",
2407                             name,
2408                         ));
2409                     }
2410                     builder.emit();
2411                 })
2412             });
2413     }
2414 }
2415
2416 const HAS_MIN_FEATURES: &[Symbol] = &[sym::specialization];
2417
2418 declare_lint! {
2419     /// The `invalid_value` lint detects creating a value that is not valid,
2420     /// such as a null reference.
2421     ///
2422     /// ### Example
2423     ///
2424     /// ```rust,no_run
2425     /// # #![allow(unused)]
2426     /// unsafe {
2427     ///     let x: &'static i32 = std::mem::zeroed();
2428     /// }
2429     /// ```
2430     ///
2431     /// {{produces}}
2432     ///
2433     /// ### Explanation
2434     ///
2435     /// In some situations the compiler can detect that the code is creating
2436     /// an invalid value, which should be avoided.
2437     ///
2438     /// In particular, this lint will check for improper use of
2439     /// [`mem::zeroed`], [`mem::uninitialized`], [`mem::transmute`], and
2440     /// [`MaybeUninit::assume_init`] that can cause [undefined behavior]. The
2441     /// lint should provide extra information to indicate what the problem is
2442     /// and a possible solution.
2443     ///
2444     /// [`mem::zeroed`]: https://doc.rust-lang.org/std/mem/fn.zeroed.html
2445     /// [`mem::uninitialized`]: https://doc.rust-lang.org/std/mem/fn.uninitialized.html
2446     /// [`mem::transmute`]: https://doc.rust-lang.org/std/mem/fn.transmute.html
2447     /// [`MaybeUninit::assume_init`]: https://doc.rust-lang.org/std/mem/union.MaybeUninit.html#method.assume_init
2448     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
2449     pub INVALID_VALUE,
2450     Warn,
2451     "an invalid value is being created (such as a null reference)"
2452 }
2453
2454 declare_lint_pass!(InvalidValue => [INVALID_VALUE]);
2455
2456 impl<'tcx> LateLintPass<'tcx> for InvalidValue {
2457     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
2458         #[derive(Debug, Copy, Clone, PartialEq)]
2459         enum InitKind {
2460             Zeroed,
2461             Uninit,
2462         }
2463
2464         /// Information about why a type cannot be initialized this way.
2465         /// Contains an error message and optionally a span to point at.
2466         type InitError = (String, Option<Span>);
2467
2468         /// Test if this constant is all-0.
2469         fn is_zero(expr: &hir::Expr<'_>) -> bool {
2470             use hir::ExprKind::*;
2471             use rustc_ast::LitKind::*;
2472             match &expr.kind {
2473                 Lit(lit) => {
2474                     if let Int(i, _) = lit.node {
2475                         i == 0
2476                     } else {
2477                         false
2478                     }
2479                 }
2480                 Tup(tup) => tup.iter().all(is_zero),
2481                 _ => false,
2482             }
2483         }
2484
2485         /// Determine if this expression is a "dangerous initialization".
2486         fn is_dangerous_init(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> Option<InitKind> {
2487             if let hir::ExprKind::Call(ref path_expr, ref args) = expr.kind {
2488                 // Find calls to `mem::{uninitialized,zeroed}` methods.
2489                 if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2490                     let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2491
2492                     if cx.tcx.is_diagnostic_item(sym::mem_zeroed, def_id) {
2493                         return Some(InitKind::Zeroed);
2494                     } else if cx.tcx.is_diagnostic_item(sym::mem_uninitialized, def_id) {
2495                         return Some(InitKind::Uninit);
2496                     } else if cx.tcx.is_diagnostic_item(sym::transmute, def_id) && is_zero(&args[0])
2497                     {
2498                         return Some(InitKind::Zeroed);
2499                     }
2500                 }
2501             } else if let hir::ExprKind::MethodCall(_, _, ref args, _) = expr.kind {
2502                 // Find problematic calls to `MaybeUninit::assume_init`.
2503                 let def_id = cx.typeck_results().type_dependent_def_id(expr.hir_id)?;
2504                 if cx.tcx.is_diagnostic_item(sym::assume_init, def_id) {
2505                     // This is a call to *some* method named `assume_init`.
2506                     // See if the `self` parameter is one of the dangerous constructors.
2507                     if let hir::ExprKind::Call(ref path_expr, _) = args[0].kind {
2508                         if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2509                             let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2510
2511                             if cx.tcx.is_diagnostic_item(sym::maybe_uninit_zeroed, def_id) {
2512                                 return Some(InitKind::Zeroed);
2513                             } else if cx.tcx.is_diagnostic_item(sym::maybe_uninit_uninit, def_id) {
2514                                 return Some(InitKind::Uninit);
2515                             }
2516                         }
2517                     }
2518                 }
2519             }
2520
2521             None
2522         }
2523
2524         /// Test if this enum has several actually "existing" variants.
2525         /// Zero-sized uninhabited variants do not always have a tag assigned and thus do not "exist".
2526         fn is_multi_variant(adt: &ty::AdtDef) -> bool {
2527             // As an approximation, we only count dataless variants. Those are definitely inhabited.
2528             let existing_variants = adt.variants.iter().filter(|v| v.fields.is_empty()).count();
2529             existing_variants > 1
2530         }
2531
2532         /// Return `Some` only if we are sure this type does *not*
2533         /// allow zero initialization.
2534         fn ty_find_init_error<'tcx>(
2535             tcx: TyCtxt<'tcx>,
2536             ty: Ty<'tcx>,
2537             init: InitKind,
2538         ) -> Option<InitError> {
2539             use rustc_middle::ty::TyKind::*;
2540             match ty.kind() {
2541                 // Primitive types that don't like 0 as a value.
2542                 Ref(..) => Some(("references must be non-null".to_string(), None)),
2543                 Adt(..) if ty.is_box() => Some(("`Box` must be non-null".to_string(), None)),
2544                 FnPtr(..) => Some(("function pointers must be non-null".to_string(), None)),
2545                 Never => Some(("the `!` type has no valid value".to_string(), None)),
2546                 RawPtr(tm) if matches!(tm.ty.kind(), Dynamic(..)) =>
2547                 // raw ptr to dyn Trait
2548                 {
2549                     Some(("the vtable of a wide raw pointer must be non-null".to_string(), None))
2550                 }
2551                 // Primitive types with other constraints.
2552                 Bool if init == InitKind::Uninit => {
2553                     Some(("booleans must be either `true` or `false`".to_string(), None))
2554                 }
2555                 Char if init == InitKind::Uninit => {
2556                     Some(("characters must be a valid Unicode codepoint".to_string(), None))
2557                 }
2558                 // Recurse and checks for some compound types.
2559                 Adt(adt_def, substs) if !adt_def.is_union() => {
2560                     // First check if this ADT has a layout attribute (like `NonNull` and friends).
2561                     use std::ops::Bound;
2562                     match tcx.layout_scalar_valid_range(adt_def.did) {
2563                         // We exploit here that `layout_scalar_valid_range` will never
2564                         // return `Bound::Excluded`.  (And we have tests checking that we
2565                         // handle the attribute correctly.)
2566                         (Bound::Included(lo), _) if lo > 0 => {
2567                             return Some((format!("`{}` must be non-null", ty), None));
2568                         }
2569                         (Bound::Included(_), _) | (_, Bound::Included(_))
2570                             if init == InitKind::Uninit =>
2571                         {
2572                             return Some((
2573                                 format!(
2574                                     "`{}` must be initialized inside its custom valid range",
2575                                     ty,
2576                                 ),
2577                                 None,
2578                             ));
2579                         }
2580                         _ => {}
2581                     }
2582                     // Now, recurse.
2583                     match adt_def.variants.len() {
2584                         0 => Some(("enums with no variants have no valid value".to_string(), None)),
2585                         1 => {
2586                             // Struct, or enum with exactly one variant.
2587                             // Proceed recursively, check all fields.
2588                             let variant = &adt_def.variants[VariantIdx::from_u32(0)];
2589                             variant.fields.iter().find_map(|field| {
2590                                 ty_find_init_error(tcx, field.ty(tcx, substs), init).map(
2591                                     |(mut msg, span)| {
2592                                         if span.is_none() {
2593                                             // Point to this field, should be helpful for figuring
2594                                             // out where the source of the error is.
2595                                             let span = tcx.def_span(field.did);
2596                                             write!(
2597                                                 &mut msg,
2598                                                 " (in this {} field)",
2599                                                 adt_def.descr()
2600                                             )
2601                                             .unwrap();
2602                                             (msg, Some(span))
2603                                         } else {
2604                                             // Just forward.
2605                                             (msg, span)
2606                                         }
2607                                     },
2608                                 )
2609                             })
2610                         }
2611                         // Multi-variant enum.
2612                         _ => {
2613                             if init == InitKind::Uninit && is_multi_variant(adt_def) {
2614                                 let span = tcx.def_span(adt_def.did);
2615                                 Some((
2616                                     "enums have to be initialized to a variant".to_string(),
2617                                     Some(span),
2618                                 ))
2619                             } else {
2620                                 // In principle, for zero-initialization we could figure out which variant corresponds
2621                                 // to tag 0, and check that... but for now we just accept all zero-initializations.
2622                                 None
2623                             }
2624                         }
2625                     }
2626                 }
2627                 Tuple(..) => {
2628                     // Proceed recursively, check all fields.
2629                     ty.tuple_fields().find_map(|field| ty_find_init_error(tcx, field, init))
2630                 }
2631                 // Conservative fallback.
2632                 _ => None,
2633             }
2634         }
2635
2636         if let Some(init) = is_dangerous_init(cx, expr) {
2637             // This conjures an instance of a type out of nothing,
2638             // using zeroed or uninitialized memory.
2639             // We are extremely conservative with what we warn about.
2640             let conjured_ty = cx.typeck_results().expr_ty(expr);
2641             if let Some((msg, span)) =
2642                 with_no_trimmed_paths(|| ty_find_init_error(cx.tcx, conjured_ty, init))
2643             {
2644                 cx.struct_span_lint(INVALID_VALUE, expr.span, |lint| {
2645                     let mut err = lint.build(&format!(
2646                         "the type `{}` does not permit {}",
2647                         conjured_ty,
2648                         match init {
2649                             InitKind::Zeroed => "zero-initialization",
2650                             InitKind::Uninit => "being left uninitialized",
2651                         },
2652                     ));
2653                     err.span_label(expr.span, "this code causes undefined behavior when executed");
2654                     err.span_label(
2655                         expr.span,
2656                         "help: use `MaybeUninit<T>` instead, \
2657                             and only call `assume_init` after initialization is done",
2658                     );
2659                     if let Some(span) = span {
2660                         err.span_note(span, &msg);
2661                     } else {
2662                         err.note(&msg);
2663                     }
2664                     err.emit();
2665                 });
2666             }
2667         }
2668     }
2669 }
2670
2671 declare_lint! {
2672     /// The `clashing_extern_declarations` lint detects when an `extern fn`
2673     /// has been declared with the same name but different types.
2674     ///
2675     /// ### Example
2676     ///
2677     /// ```rust
2678     /// mod m {
2679     ///     extern "C" {
2680     ///         fn foo();
2681     ///     }
2682     /// }
2683     ///
2684     /// extern "C" {
2685     ///     fn foo(_: u32);
2686     /// }
2687     /// ```
2688     ///
2689     /// {{produces}}
2690     ///
2691     /// ### Explanation
2692     ///
2693     /// Because two symbols of the same name cannot be resolved to two
2694     /// different functions at link time, and one function cannot possibly
2695     /// have two types, a clashing extern declaration is almost certainly a
2696     /// mistake. Check to make sure that the `extern` definitions are correct
2697     /// and equivalent, and possibly consider unifying them in one location.
2698     ///
2699     /// This lint does not run between crates because a project may have
2700     /// dependencies which both rely on the same extern function, but declare
2701     /// it in a different (but valid) way. For example, they may both declare
2702     /// an opaque type for one or more of the arguments (which would end up
2703     /// distinct types), or use types that are valid conversions in the
2704     /// language the `extern fn` is defined in. In these cases, the compiler
2705     /// can't say that the clashing declaration is incorrect.
2706     pub CLASHING_EXTERN_DECLARATIONS,
2707     Warn,
2708     "detects when an extern fn has been declared with the same name but different types"
2709 }
2710
2711 pub struct ClashingExternDeclarations {
2712     /// Map of function symbol name to the first-seen hir id for that symbol name.. If seen_decls
2713     /// contains an entry for key K, it means a symbol with name K has been seen by this lint and
2714     /// the symbol should be reported as a clashing declaration.
2715     // FIXME: Technically, we could just store a &'tcx str here without issue; however, the
2716     // `impl_lint_pass` macro doesn't currently support lints parametric over a lifetime.
2717     seen_decls: FxHashMap<Symbol, HirId>,
2718 }
2719
2720 /// Differentiate between whether the name for an extern decl came from the link_name attribute or
2721 /// just from declaration itself. This is important because we don't want to report clashes on
2722 /// symbol name if they don't actually clash because one or the other links against a symbol with a
2723 /// different name.
2724 enum SymbolName {
2725     /// The name of the symbol + the span of the annotation which introduced the link name.
2726     Link(Symbol, Span),
2727     /// No link name, so just the name of the symbol.
2728     Normal(Symbol),
2729 }
2730
2731 impl SymbolName {
2732     fn get_name(&self) -> Symbol {
2733         match self {
2734             SymbolName::Link(s, _) | SymbolName::Normal(s) => *s,
2735         }
2736     }
2737 }
2738
2739 impl ClashingExternDeclarations {
2740     crate fn new() -> Self {
2741         ClashingExternDeclarations { seen_decls: FxHashMap::default() }
2742     }
2743     /// Insert a new foreign item into the seen set. If a symbol with the same name already exists
2744     /// for the item, return its HirId without updating the set.
2745     fn insert(&mut self, tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> Option<HirId> {
2746         let did = fi.def_id.to_def_id();
2747         let instance = Instance::new(did, ty::List::identity_for_item(tcx, did));
2748         let name = Symbol::intern(tcx.symbol_name(instance).name);
2749         if let Some(&hir_id) = self.seen_decls.get(&name) {
2750             // Avoid updating the map with the new entry when we do find a collision. We want to
2751             // make sure we're always pointing to the first definition as the previous declaration.
2752             // This lets us avoid emitting "knock-on" diagnostics.
2753             Some(hir_id)
2754         } else {
2755             self.seen_decls.insert(name, fi.hir_id())
2756         }
2757     }
2758
2759     /// Get the name of the symbol that's linked against for a given extern declaration. That is,
2760     /// the name specified in a #[link_name = ...] attribute if one was specified, else, just the
2761     /// symbol's name.
2762     fn name_of_extern_decl(tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> SymbolName {
2763         if let Some((overridden_link_name, overridden_link_name_span)) =
2764             tcx.codegen_fn_attrs(fi.def_id).link_name.map(|overridden_link_name| {
2765                 // FIXME: Instead of searching through the attributes again to get span
2766                 // information, we could have codegen_fn_attrs also give span information back for
2767                 // where the attribute was defined. However, until this is found to be a
2768                 // bottleneck, this does just fine.
2769                 (
2770                     overridden_link_name,
2771                     tcx.get_attrs(fi.def_id.to_def_id())
2772                         .iter()
2773                         .find(|at| tcx.sess.check_name(at, sym::link_name))
2774                         .unwrap()
2775                         .span,
2776                 )
2777             })
2778         {
2779             SymbolName::Link(overridden_link_name, overridden_link_name_span)
2780         } else {
2781             SymbolName::Normal(fi.ident.name)
2782         }
2783     }
2784
2785     /// Checks whether two types are structurally the same enough that the declarations shouldn't
2786     /// clash. We need this so we don't emit a lint when two modules both declare an extern struct,
2787     /// with the same members (as the declarations shouldn't clash).
2788     fn structurally_same_type<'tcx>(
2789         cx: &LateContext<'tcx>,
2790         a: Ty<'tcx>,
2791         b: Ty<'tcx>,
2792         ckind: CItemKind,
2793     ) -> bool {
2794         fn structurally_same_type_impl<'tcx>(
2795             seen_types: &mut FxHashSet<(Ty<'tcx>, Ty<'tcx>)>,
2796             cx: &LateContext<'tcx>,
2797             a: Ty<'tcx>,
2798             b: Ty<'tcx>,
2799             ckind: CItemKind,
2800         ) -> bool {
2801             debug!("structurally_same_type_impl(cx, a = {:?}, b = {:?})", a, b);
2802             let tcx = cx.tcx;
2803
2804             // Given a transparent newtype, reach through and grab the inner
2805             // type unless the newtype makes the type non-null.
2806             let non_transparent_ty = |ty: Ty<'tcx>| -> Ty<'tcx> {
2807                 let mut ty = ty;
2808                 loop {
2809                     if let ty::Adt(def, substs) = *ty.kind() {
2810                         let is_transparent = def.subst(tcx, substs).repr.transparent();
2811                         let is_non_null = crate::types::nonnull_optimization_guaranteed(tcx, &def);
2812                         debug!(
2813                             "non_transparent_ty({:?}) -- type is transparent? {}, type is non-null? {}",
2814                             ty, is_transparent, is_non_null
2815                         );
2816                         if is_transparent && !is_non_null {
2817                             debug_assert!(def.variants.len() == 1);
2818                             let v = &def.variants[VariantIdx::new(0)];
2819                             ty = transparent_newtype_field(tcx, v)
2820                                 .expect(
2821                                     "single-variant transparent structure with zero-sized field",
2822                                 )
2823                                 .ty(tcx, substs);
2824                             continue;
2825                         }
2826                     }
2827                     debug!("non_transparent_ty -> {:?}", ty);
2828                     return ty;
2829                 }
2830             };
2831
2832             let a = non_transparent_ty(a);
2833             let b = non_transparent_ty(b);
2834
2835             if !seen_types.insert((a, b)) {
2836                 // We've encountered a cycle. There's no point going any further -- the types are
2837                 // structurally the same.
2838                 return true;
2839             }
2840             let tcx = cx.tcx;
2841             if a == b || rustc_middle::ty::TyS::same_type(a, b) {
2842                 // All nominally-same types are structurally same, too.
2843                 true
2844             } else {
2845                 // Do a full, depth-first comparison between the two.
2846                 use rustc_middle::ty::TyKind::*;
2847                 let a_kind = a.kind();
2848                 let b_kind = b.kind();
2849
2850                 let compare_layouts = |a, b| -> Result<bool, LayoutError<'tcx>> {
2851                     debug!("compare_layouts({:?}, {:?})", a, b);
2852                     let a_layout = &cx.layout_of(a)?.layout.abi;
2853                     let b_layout = &cx.layout_of(b)?.layout.abi;
2854                     debug!(
2855                         "comparing layouts: {:?} == {:?} = {}",
2856                         a_layout,
2857                         b_layout,
2858                         a_layout == b_layout
2859                     );
2860                     Ok(a_layout == b_layout)
2861                 };
2862
2863                 #[allow(rustc::usage_of_ty_tykind)]
2864                 let is_primitive_or_pointer = |kind: &ty::TyKind<'_>| {
2865                     kind.is_primitive() || matches!(kind, RawPtr(..) | Ref(..))
2866                 };
2867
2868                 ensure_sufficient_stack(|| {
2869                     match (a_kind, b_kind) {
2870                         (Adt(a_def, a_substs), Adt(b_def, b_substs)) => {
2871                             let a = a.subst(cx.tcx, a_substs);
2872                             let b = b.subst(cx.tcx, b_substs);
2873                             debug!("Comparing {:?} and {:?}", a, b);
2874
2875                             // We can immediately rule out these types as structurally same if
2876                             // their layouts differ.
2877                             match compare_layouts(a, b) {
2878                                 Ok(false) => return false,
2879                                 _ => (), // otherwise, continue onto the full, fields comparison
2880                             }
2881
2882                             // Grab a flattened representation of all fields.
2883                             let a_fields = a_def.variants.iter().flat_map(|v| v.fields.iter());
2884                             let b_fields = b_def.variants.iter().flat_map(|v| v.fields.iter());
2885
2886                             // Perform a structural comparison for each field.
2887                             a_fields.eq_by(
2888                                 b_fields,
2889                                 |&ty::FieldDef { did: a_did, .. },
2890                                  &ty::FieldDef { did: b_did, .. }| {
2891                                     structurally_same_type_impl(
2892                                         seen_types,
2893                                         cx,
2894                                         tcx.type_of(a_did),
2895                                         tcx.type_of(b_did),
2896                                         ckind,
2897                                     )
2898                                 },
2899                             )
2900                         }
2901                         (Array(a_ty, a_const), Array(b_ty, b_const)) => {
2902                             // For arrays, we also check the constness of the type.
2903                             a_const.val == b_const.val
2904                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2905                         }
2906                         (Slice(a_ty), Slice(b_ty)) => {
2907                             structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2908                         }
2909                         (RawPtr(a_tymut), RawPtr(b_tymut)) => {
2910                             a_tymut.mutbl == b_tymut.mutbl
2911                                 && structurally_same_type_impl(
2912                                     seen_types,
2913                                     cx,
2914                                     &a_tymut.ty,
2915                                     &b_tymut.ty,
2916                                     ckind,
2917                                 )
2918                         }
2919                         (Ref(_a_region, a_ty, a_mut), Ref(_b_region, b_ty, b_mut)) => {
2920                             // For structural sameness, we don't need the region to be same.
2921                             a_mut == b_mut
2922                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2923                         }
2924                         (FnDef(..), FnDef(..)) => {
2925                             let a_poly_sig = a.fn_sig(tcx);
2926                             let b_poly_sig = b.fn_sig(tcx);
2927
2928                             // As we don't compare regions, skip_binder is fine.
2929                             let a_sig = a_poly_sig.skip_binder();
2930                             let b_sig = b_poly_sig.skip_binder();
2931
2932                             (a_sig.abi, a_sig.unsafety, a_sig.c_variadic)
2933                                 == (b_sig.abi, b_sig.unsafety, b_sig.c_variadic)
2934                                 && a_sig.inputs().iter().eq_by(b_sig.inputs().iter(), |a, b| {
2935                                     structurally_same_type_impl(seen_types, cx, a, b, ckind)
2936                                 })
2937                                 && structurally_same_type_impl(
2938                                     seen_types,
2939                                     cx,
2940                                     a_sig.output(),
2941                                     b_sig.output(),
2942                                     ckind,
2943                                 )
2944                         }
2945                         (Tuple(a_substs), Tuple(b_substs)) => {
2946                             a_substs.types().eq_by(b_substs.types(), |a_ty, b_ty| {
2947                                 structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2948                             })
2949                         }
2950                         // For these, it's not quite as easy to define structural-sameness quite so easily.
2951                         // For the purposes of this lint, take the conservative approach and mark them as
2952                         // not structurally same.
2953                         (Dynamic(..), Dynamic(..))
2954                         | (Error(..), Error(..))
2955                         | (Closure(..), Closure(..))
2956                         | (Generator(..), Generator(..))
2957                         | (GeneratorWitness(..), GeneratorWitness(..))
2958                         | (Projection(..), Projection(..))
2959                         | (Opaque(..), Opaque(..)) => false,
2960
2961                         // These definitely should have been caught above.
2962                         (Bool, Bool) | (Char, Char) | (Never, Never) | (Str, Str) => unreachable!(),
2963
2964                         // An Adt and a primitive or pointer type. This can be FFI-safe if non-null
2965                         // enum layout optimisation is being applied.
2966                         (Adt(..), other_kind) | (other_kind, Adt(..))
2967                             if is_primitive_or_pointer(other_kind) =>
2968                         {
2969                             let (primitive, adt) =
2970                                 if is_primitive_or_pointer(a.kind()) { (a, b) } else { (b, a) };
2971                             if let Some(ty) = crate::types::repr_nullable_ptr(cx, adt, ckind) {
2972                                 ty == primitive
2973                             } else {
2974                                 compare_layouts(a, b).unwrap_or(false)
2975                             }
2976                         }
2977                         // Otherwise, just compare the layouts. This may fail to lint for some
2978                         // incompatible types, but at the very least, will stop reads into
2979                         // uninitialised memory.
2980                         _ => compare_layouts(a, b).unwrap_or(false),
2981                     }
2982                 })
2983             }
2984         }
2985         let mut seen_types = FxHashSet::default();
2986         structurally_same_type_impl(&mut seen_types, cx, a, b, ckind)
2987     }
2988 }
2989
2990 impl_lint_pass!(ClashingExternDeclarations => [CLASHING_EXTERN_DECLARATIONS]);
2991
2992 impl<'tcx> LateLintPass<'tcx> for ClashingExternDeclarations {
2993     fn check_foreign_item(&mut self, cx: &LateContext<'tcx>, this_fi: &hir::ForeignItem<'_>) {
2994         trace!("ClashingExternDeclarations: check_foreign_item: {:?}", this_fi);
2995         if let ForeignItemKind::Fn(..) = this_fi.kind {
2996             let tcx = cx.tcx;
2997             if let Some(existing_hid) = self.insert(tcx, this_fi) {
2998                 let existing_decl_ty = tcx.type_of(tcx.hir().local_def_id(existing_hid));
2999                 let this_decl_ty = tcx.type_of(this_fi.def_id);
3000                 debug!(
3001                     "ClashingExternDeclarations: Comparing existing {:?}: {:?} to this {:?}: {:?}",
3002                     existing_hid, existing_decl_ty, this_fi.def_id, this_decl_ty
3003                 );
3004                 // Check that the declarations match.
3005                 if !Self::structurally_same_type(
3006                     cx,
3007                     existing_decl_ty,
3008                     this_decl_ty,
3009                     CItemKind::Declaration,
3010                 ) {
3011                     let orig_fi = tcx.hir().expect_foreign_item(existing_hid);
3012                     let orig = Self::name_of_extern_decl(tcx, orig_fi);
3013
3014                     // We want to ensure that we use spans for both decls that include where the
3015                     // name was defined, whether that was from the link_name attribute or not.
3016                     let get_relevant_span =
3017                         |fi: &hir::ForeignItem<'_>| match Self::name_of_extern_decl(tcx, fi) {
3018                             SymbolName::Normal(_) => fi.span,
3019                             SymbolName::Link(_, annot_span) => fi.span.to(annot_span),
3020                         };
3021                     // Finally, emit the diagnostic.
3022                     tcx.struct_span_lint_hir(
3023                         CLASHING_EXTERN_DECLARATIONS,
3024                         this_fi.hir_id(),
3025                         get_relevant_span(this_fi),
3026                         |lint| {
3027                             let mut expected_str = DiagnosticStyledString::new();
3028                             expected_str.push(existing_decl_ty.fn_sig(tcx).to_string(), false);
3029                             let mut found_str = DiagnosticStyledString::new();
3030                             found_str.push(this_decl_ty.fn_sig(tcx).to_string(), true);
3031
3032                             lint.build(&format!(
3033                                 "`{}` redeclare{} with a different signature",
3034                                 this_fi.ident.name,
3035                                 if orig.get_name() == this_fi.ident.name {
3036                                     "d".to_string()
3037                                 } else {
3038                                     format!("s `{}`", orig.get_name())
3039                                 }
3040                             ))
3041                             .span_label(
3042                                 get_relevant_span(orig_fi),
3043                                 &format!("`{}` previously declared here", orig.get_name()),
3044                             )
3045                             .span_label(
3046                                 get_relevant_span(this_fi),
3047                                 "this signature doesn't match the previous declaration",
3048                             )
3049                             .note_expected_found(&"", expected_str, &"", found_str)
3050                             .emit()
3051                         },
3052                     );
3053                 }
3054             }
3055         }
3056     }
3057 }
3058
3059 declare_lint! {
3060     /// The `deref_nullptr` lint detects when an null pointer is dereferenced,
3061     /// which causes [undefined behavior].
3062     ///
3063     /// ### Example
3064     ///
3065     /// ```rust,no_run
3066     /// # #![allow(unused)]
3067     /// use std::ptr;
3068     /// unsafe {
3069     ///     let x = &*ptr::null::<i32>();
3070     ///     let x = ptr::addr_of!(*ptr::null::<i32>());
3071     ///     let x = *(0 as *const i32);
3072     /// }
3073     /// ```
3074     ///
3075     /// {{produces}}
3076     ///
3077     /// ### Explanation
3078     ///
3079     /// Dereferencing a null pointer causes [undefined behavior] even as a place expression,
3080     /// like `&*(0 as *const i32)` or `addr_of!(*(0 as *const i32))`.
3081     ///
3082     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
3083     pub DEREF_NULLPTR,
3084     Warn,
3085     "detects when an null pointer is dereferenced"
3086 }
3087
3088 declare_lint_pass!(DerefNullPtr => [DEREF_NULLPTR]);
3089
3090 impl<'tcx> LateLintPass<'tcx> for DerefNullPtr {
3091     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
3092         /// test if expression is a null ptr
3093         fn is_null_ptr(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> bool {
3094             match &expr.kind {
3095                 rustc_hir::ExprKind::Cast(ref expr, ref ty) => {
3096                     if let rustc_hir::TyKind::Ptr(_) = ty.kind {
3097                         return is_zero(expr) || is_null_ptr(cx, expr);
3098                     }
3099                 }
3100                 // check for call to `core::ptr::null` or `core::ptr::null_mut`
3101                 rustc_hir::ExprKind::Call(ref path, _) => {
3102                     if let rustc_hir::ExprKind::Path(ref qpath) = path.kind {
3103                         if let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id() {
3104                             return cx.tcx.is_diagnostic_item(sym::ptr_null, def_id)
3105                                 || cx.tcx.is_diagnostic_item(sym::ptr_null_mut, def_id);
3106                         }
3107                     }
3108                 }
3109                 _ => {}
3110             }
3111             false
3112         }
3113
3114         /// test if expression is the literal `0`
3115         fn is_zero(expr: &hir::Expr<'_>) -> bool {
3116             match &expr.kind {
3117                 rustc_hir::ExprKind::Lit(ref lit) => {
3118                     if let LitKind::Int(a, _) = lit.node {
3119                         return a == 0;
3120                     }
3121                 }
3122                 _ => {}
3123             }
3124             false
3125         }
3126
3127         if let rustc_hir::ExprKind::Unary(ref un_op, ref expr_deref) = expr.kind {
3128             if let rustc_hir::UnOp::Deref = un_op {
3129                 if is_null_ptr(cx, expr_deref) {
3130                     cx.struct_span_lint(DEREF_NULLPTR, expr.span, |lint| {
3131                         let mut err = lint.build("dereferencing a null pointer");
3132                         err.span_label(
3133                             expr.span,
3134                             "this code causes undefined behavior when executed",
3135                         );
3136                         err.emit();
3137                     });
3138                 }
3139             }
3140         }
3141     }
3142 }