compiler/rustc_lint/src/builtin.rs

   1 // ignore-tidy-filelength
   2
   3 //! Lints in the Rust compiler.
   4 //!
   5 //! This contains lints which can feasibly be implemented as their own
   6 //! AST visitor. Also see `rustc_session::lint::builtin`, which contains the
   7 //! definitions of lints that are emitted directly inside the main compiler.
   8 //!
   9 //! To add a new lint to rustc, declare it here using `declare_lint!()`.
  10 //! Then add code to emit the new lint in the appropriate circumstances.
  11 //! You can do that in an existing `LintPass` if it makes sense, or in a
  12 //! new `LintPass`, or using `Session::add_lint` elsewhere in the
  13 //! compiler. Only do the latter if the check can't be written cleanly as a
  14 //! `LintPass` (also, note that such lints will need to be defined in
  15 //! `rustc_session::lint::builtin`, not here).
  16 //!
  17 //! If you define a new `EarlyLintPass`, you will also need to add it to the
  18 //! `add_early_builtin!` or `add_early_builtin_with_new!` invocation in
  19 //! `lib.rs`. Use the former for unit-like structs and the latter for structs
  20 //! with a `pub fn new()`.
  21 //!
  22 //! If you define a new `LateLintPass`, you will also need to add it to the
  23 //! `late_lint_methods!` invocation in `lib.rs`.
  24
  25 use crate::{
  26     types::{transparent_newtype_field, CItemKind},
  27     EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext,
  28 };
  29 use rustc_ast::attr;
  30 use rustc_ast::tokenstream::{TokenStream, TokenTree};
  31 use rustc_ast::visit::{FnCtxt, FnKind};
  32 use rustc_ast::{self as ast, *};
  33 use rustc_ast_pretty::pprust::{self, expr_to_string};
  34 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
  35 use rustc_data_structures::stack::ensure_sufficient_stack;
  36 use rustc_errors::{Applicability, DiagnosticBuilder, DiagnosticStyledString};
  37 use rustc_feature::{deprecated_attributes, AttributeGate, AttributeTemplate, AttributeType};
  38 use rustc_feature::{GateIssue, Stability};
  39 use rustc_hir as hir;
  40 use rustc_hir::def::{DefKind, Res};
  41 use rustc_hir::def_id::{DefId, LocalDefId, LocalDefIdSet};
  42 use rustc_hir::{ForeignItemKind, GenericParamKind, PatKind};
  43 use rustc_hir::{HirId, Node};
  44 use rustc_index::vec::Idx;
  45 use rustc_middle::lint::LintDiagnosticBuilder;
  46 use rustc_middle::ty::print::with_no_trimmed_paths;
  47 use rustc_middle::ty::subst::{GenericArgKind, Subst};
  48 use rustc_middle::ty::Instance;
  49 use rustc_middle::ty::{self, layout::LayoutError, Ty, TyCtxt};
  50 use rustc_session::lint::FutureIncompatibilityReason;
  51 use rustc_session::Session;
  52 use rustc_span::edition::Edition;
  53 use rustc_span::source_map::Spanned;
  54 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  55 use rustc_span::{BytePos, Span};
  56 use rustc_target::abi::{LayoutOf, VariantIdx};
  57 use rustc_trait_selection::traits::misc::can_type_implement_copy;
  58
  59 use crate::nonstandard_style::{method_context, MethodLateContext};
  60
  61 use std::fmt::Write;
  62 use tracing::{debug, trace};
  63
  64 // hardwired lints from librustc_middle
  65 pub use rustc_session::lint::builtin::*;
  66
  67 declare_lint! {
  68     /// The `while_true` lint detects `while true { }`.
  69     ///
  70     /// ### Example
  71     ///
  72     /// ```rust,no_run
  73     /// while true {
  74     ///
  75     /// }
  76     /// ```
  77     ///
  78     /// {{produces}}
  79     ///
  80     /// ### Explanation
  81     ///
  82     /// `while true` should be replaced with `loop`. A `loop` expression is
  83     /// the preferred way to write an infinite loop because it more directly
  84     /// expresses the intent of the loop.
  85     WHILE_TRUE,
  86     Warn,
  87     "suggest using `loop { }` instead of `while true { }`"
  88 }
  89
  90 declare_lint_pass!(WhileTrue => [WHILE_TRUE]);
  91
  92 /// Traverse through any amount of parenthesis and return the first non-parens expression.
  93 fn pierce_parens(mut expr: &ast::Expr) -> &ast::Expr {
  94     while let ast::ExprKind::Paren(sub) = &expr.kind {
  95         expr = sub;
  96     }
  97     expr
  98 }
  99
 100 impl EarlyLintPass for WhileTrue {
 101     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
 102         if let ast::ExprKind::While(cond, _, label) = &e.kind {
 103             if let ast::ExprKind::Lit(ref lit) = pierce_parens(cond).kind {
 104                 if let ast::LitKind::Bool(true) = lit.kind {
 105                     if !lit.span.from_expansion() {
 106                         let msg = "denote infinite loops with `loop { ... }`";
 107                         let condition_span = e.span.with_hi(cond.span.hi());
 108                         cx.struct_span_lint(WHILE_TRUE, condition_span, |lint| {
 109                             lint.build(msg)
 110                                 .span_suggestion_short(
 111                                     condition_span,
 112                                     "use `loop`",
 113                                     format!(
 114                                         "{}loop",
 115                                         label.map_or_else(String::new, |label| format!(
 116                                             "{}: ",
 117                                             label.ident,
 118                                         ))
 119                                     ),
 120                                     Applicability::MachineApplicable,
 121                                 )
 122                                 .emit();
 123                         })
 124                     }
 125                 }
 126             }
 127         }
 128     }
 129 }
 130
 131 declare_lint! {
 132     /// The `box_pointers` lints use of the Box type.
 133     ///
 134     /// ### Example
 135     ///
 136     /// ```rust,compile_fail
 137     /// #![deny(box_pointers)]
 138     /// struct Foo {
 139     ///     x: Box<isize>,
 140     /// }
 141     /// ```
 142     ///
 143     /// {{produces}}
 144     ///
 145     /// ### Explanation
 146     ///
 147     /// This lint is mostly historical, and not particularly useful. `Box<T>`
 148     /// used to be built into the language, and the only way to do heap
 149     /// allocation. Today's Rust can call into other allocators, etc.
 150     BOX_POINTERS,
 151     Allow,
 152     "use of owned (Box type) heap memory"
 153 }
 154
 155 declare_lint_pass!(BoxPointers => [BOX_POINTERS]);
 156
 157 impl BoxPointers {
 158     fn check_heap_type(&self, cx: &LateContext<'_>, span: Span, ty: Ty<'_>) {
 159         for leaf in ty.walk() {
 160             if let GenericArgKind::Type(leaf_ty) = leaf.unpack() {
 161                 if leaf_ty.is_box() {
 162                     cx.struct_span_lint(BOX_POINTERS, span, |lint| {
 163                         lint.build(&format!("type uses owned (Box type) pointers: {}", ty)).emit()
 164                     });
 165                 }
 166             }
 167         }
 168     }
 169 }
 170
 171 impl<'tcx> LateLintPass<'tcx> for BoxPointers {
 172     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 173         match it.kind {
 174             hir::ItemKind::Fn(..)
 175             | hir::ItemKind::TyAlias(..)
 176             | hir::ItemKind::Enum(..)
 177             | hir::ItemKind::Struct(..)
 178             | hir::ItemKind::Union(..) => {
 179                 self.check_heap_type(cx, it.span, cx.tcx.type_of(it.def_id))
 180             }
 181             _ => (),
 182         }
 183
 184         // If it's a struct, we also have to check the fields' types
 185         match it.kind {
 186             hir::ItemKind::Struct(ref struct_def, _) | hir::ItemKind::Union(ref struct_def, _) => {
 187                 for struct_field in struct_def.fields() {
 188                     let def_id = cx.tcx.hir().local_def_id(struct_field.hir_id);
 189                     self.check_heap_type(cx, struct_field.span, cx.tcx.type_of(def_id));
 190                 }
 191             }
 192             _ => (),
 193         }
 194     }
 195
 196     fn check_expr(&mut self, cx: &LateContext<'_>, e: &hir::Expr<'_>) {
 197         let ty = cx.typeck_results().node_type(e.hir_id);
 198         self.check_heap_type(cx, e.span, ty);
 199     }
 200 }
 201
 202 declare_lint! {
 203     /// The `non_shorthand_field_patterns` lint detects using `Struct { x: x }`
 204     /// instead of `Struct { x }` in a pattern.
 205     ///
 206     /// ### Example
 207     ///
 208     /// ```rust
 209     /// struct Point {
 210     ///     x: i32,
 211     ///     y: i32,
 212     /// }
 213     ///
 214     ///
 215     /// fn main() {
 216     ///     let p = Point {
 217     ///         x: 5,
 218     ///         y: 5,
 219     ///     };
 220     ///
 221     ///     match p {
 222     ///         Point { x: x, y: y } => (),
 223     ///     }
 224     /// }
 225     /// ```
 226     ///
 227     /// {{produces}}
 228     ///
 229     /// ### Explanation
 230     ///
 231     /// The preferred style is to avoid the repetition of specifying both the
 232     /// field name and the binding name if both identifiers are the same.
 233     NON_SHORTHAND_FIELD_PATTERNS,
 234     Warn,
 235     "using `Struct { x: x }` instead of `Struct { x }` in a pattern"
 236 }
 237
 238 declare_lint_pass!(NonShorthandFieldPatterns => [NON_SHORTHAND_FIELD_PATTERNS]);
 239
 240 impl<'tcx> LateLintPass<'tcx> for NonShorthandFieldPatterns {
 241     fn check_pat(&mut self, cx: &LateContext<'_>, pat: &hir::Pat<'_>) {
 242         if let PatKind::Struct(ref qpath, field_pats, _) = pat.kind {
 243             let variant = cx
 244                 .typeck_results()
 245                 .pat_ty(pat)
 246                 .ty_adt_def()
 247                 .expect("struct pattern type is not an ADT")
 248                 .variant_of_res(cx.qpath_res(qpath, pat.hir_id));
 249             for fieldpat in field_pats {
 250                 if fieldpat.is_shorthand {
 251                     continue;
 252                 }
 253                 if fieldpat.span.from_expansion() {
 254                     // Don't lint if this is a macro expansion: macro authors
 255                     // shouldn't have to worry about this kind of style issue
 256                     // (Issue #49588)
 257                     continue;
 258                 }
 259                 if let PatKind::Binding(binding_annot, _, ident, None) = fieldpat.pat.kind {
 260                     if cx.tcx.find_field_index(ident, &variant)
 261                         == Some(cx.tcx.field_index(fieldpat.hir_id, cx.typeck_results()))
 262                     {
 263                         cx.struct_span_lint(NON_SHORTHAND_FIELD_PATTERNS, fieldpat.span, |lint| {
 264                             let mut err = lint
 265                                 .build(&format!("the `{}:` in this pattern is redundant", ident));
 266                             let binding = match binding_annot {
 267                                 hir::BindingAnnotation::Unannotated => None,
 268                                 hir::BindingAnnotation::Mutable => Some("mut"),
 269                                 hir::BindingAnnotation::Ref => Some("ref"),
 270                                 hir::BindingAnnotation::RefMut => Some("ref mut"),
 271                             };
 272                             let ident = if let Some(binding) = binding {
 273                                 format!("{} {}", binding, ident)
 274                             } else {
 275                                 ident.to_string()
 276                             };
 277                             err.span_suggestion(
 278                                 fieldpat.span,
 279                                 "use shorthand field pattern",
 280                                 ident,
 281                                 Applicability::MachineApplicable,
 282                             );
 283                             err.emit();
 284                         });
 285                     }
 286                 }
 287             }
 288         }
 289     }
 290 }
 291
 292 declare_lint! {
 293     /// The `unsafe_code` lint catches usage of `unsafe` code.
 294     ///
 295     /// ### Example
 296     ///
 297     /// ```rust,compile_fail
 298     /// #![deny(unsafe_code)]
 299     /// fn main() {
 300     ///     unsafe {
 301     ///
 302     ///     }
 303     /// }
 304     /// ```
 305     ///
 306     /// {{produces}}
 307     ///
 308     /// ### Explanation
 309     ///
 310     /// This lint is intended to restrict the usage of `unsafe`, which can be
 311     /// difficult to use correctly.
 312     UNSAFE_CODE,
 313     Allow,
 314     "usage of `unsafe` code"
 315 }
 316
 317 declare_lint_pass!(UnsafeCode => [UNSAFE_CODE]);
 318
 319 impl UnsafeCode {
 320     fn report_unsafe(
 321         &self,
 322         cx: &EarlyContext<'_>,
 323         span: Span,
 324         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
 325     ) {
 326         // This comes from a macro that has `#[allow_internal_unsafe]`.
 327         if span.allows_unsafe() {
 328             return;
 329         }
 330
 331         cx.struct_span_lint(UNSAFE_CODE, span, decorate);
 332     }
 333
 334     fn report_overriden_symbol_name(&self, cx: &EarlyContext<'_>, span: Span, msg: &str) {
 335         self.report_unsafe(cx, span, |lint| {
 336             lint.build(msg)
 337                 .note(
 338                     "the linker's behavior with multiple libraries exporting duplicate symbol \
 339                     names is undefined and Rust cannot provide guarantees when you manually \
 340                     override them",
 341                 )
 342                 .emit();
 343         })
 344     }
 345 }
 346
 347 impl EarlyLintPass for UnsafeCode {
 348     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 349         if cx.sess().check_name(attr, sym::allow_internal_unsafe) {
 350             self.report_unsafe(cx, attr.span, |lint| {
 351                 lint.build(
 352                     "`allow_internal_unsafe` allows defining \
 353                                                macros using unsafe without triggering \
 354                                                the `unsafe_code` lint at their call site",
 355                 )
 356                 .emit()
 357             });
 358         }
 359     }
 360
 361     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
 362         if let ast::ExprKind::Block(ref blk, _) = e.kind {
 363             // Don't warn about generated blocks; that'll just pollute the output.
 364             if blk.rules == ast::BlockCheckMode::Unsafe(ast::UserProvided) {
 365                 self.report_unsafe(cx, blk.span, |lint| {
 366                     lint.build("usage of an `unsafe` block").emit()
 367                 });
 368             }
 369         }
 370     }
 371
 372     fn check_item(&mut self, cx: &EarlyContext<'_>, it: &ast::Item) {
 373         match it.kind {
 374             ast::ItemKind::Trait(box ast::TraitKind(_, ast::Unsafe::Yes(_), ..)) => self
 375                 .report_unsafe(cx, it.span, |lint| {
 376                     lint.build("declaration of an `unsafe` trait").emit()
 377                 }),
 378
 379             ast::ItemKind::Impl(box ast::ImplKind { unsafety: ast::Unsafe::Yes(_), .. }) => self
 380                 .report_unsafe(cx, it.span, |lint| {
 381                     lint.build("implementation of an `unsafe` trait").emit()
 382                 }),
 383
 384             ast::ItemKind::Fn(..) => {
 385                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
 386                     self.report_overriden_symbol_name(
 387                         cx,
 388                         attr.span,
 389                         "declaration of a `no_mangle` function",
 390                     );
 391                 }
 392                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::export_name) {
 393                     self.report_overriden_symbol_name(
 394                         cx,
 395                         attr.span,
 396                         "declaration of a function with `export_name`",
 397                     );
 398                 }
 399             }
 400
 401             ast::ItemKind::Static(..) => {
 402                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
 403                     self.report_overriden_symbol_name(
 404                         cx,
 405                         attr.span,
 406                         "declaration of a `no_mangle` static",
 407                     );
 408                 }
 409                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::export_name) {
 410                     self.report_overriden_symbol_name(
 411                         cx,
 412                         attr.span,
 413                         "declaration of a static with `export_name`",
 414                     );
 415                 }
 416             }
 417
 418             _ => {}
 419         }
 420     }
 421
 422     fn check_fn(&mut self, cx: &EarlyContext<'_>, fk: FnKind<'_>, span: Span, _: ast::NodeId) {
 423         if let FnKind::Fn(
 424             ctxt,
 425             _,
 426             ast::FnSig { header: ast::FnHeader { unsafety: ast::Unsafe::Yes(_), .. }, .. },
 427             _,
 428             body,
 429         ) = fk
 430         {
 431             let msg = match ctxt {
 432                 FnCtxt::Foreign => return,
 433                 FnCtxt::Free => "declaration of an `unsafe` function",
 434                 FnCtxt::Assoc(_) if body.is_none() => "declaration of an `unsafe` method",
 435                 FnCtxt::Assoc(_) => "implementation of an `unsafe` method",
 436             };
 437             self.report_unsafe(cx, span, |lint| lint.build(msg).emit());
 438         }
 439     }
 440 }
 441
 442 declare_lint! {
 443     /// The `missing_docs` lint detects missing documentation for public items.
 444     ///
 445     /// ### Example
 446     ///
 447     /// ```rust,compile_fail
 448     /// #![deny(missing_docs)]
 449     /// pub fn foo() {}
 450     /// ```
 451     ///
 452     /// {{produces}}
 453     ///
 454     /// ### Explanation
 455     ///
 456     /// This lint is intended to ensure that a library is well-documented.
 457     /// Items without documentation can be difficult for users to understand
 458     /// how to use properly.
 459     ///
 460     /// This lint is "allow" by default because it can be noisy, and not all
 461     /// projects may want to enforce everything to be documented.
 462     pub MISSING_DOCS,
 463     Allow,
 464     "detects missing documentation for public members",
 465     report_in_external_macro
 466 }
 467
 468 pub struct MissingDoc {
 469     /// Stack of whether `#[doc(hidden)]` is set at each level which has lint attributes.
 470     doc_hidden_stack: Vec<bool>,
 471
 472     /// Private traits or trait items that leaked through. Don't check their methods.
 473     private_traits: FxHashSet<hir::HirId>,
 474 }
 475
 476 impl_lint_pass!(MissingDoc => [MISSING_DOCS]);
 477
 478 fn has_doc(sess: &Session, attr: &ast::Attribute) -> bool {
 479     if attr.is_doc_comment() {
 480         return true;
 481     }
 482
 483     if !sess.check_name(attr, sym::doc) {
 484         return false;
 485     }
 486
 487     if attr.value_str().is_some() {
 488         return true;
 489     }
 490
 491     if let Some(list) = attr.meta_item_list() {
 492         for meta in list {
 493             if meta.has_name(sym::hidden) {
 494                 return true;
 495             }
 496         }
 497     }
 498
 499     false
 500 }
 501
 502 impl MissingDoc {
 503     pub fn new() -> MissingDoc {
 504         MissingDoc { doc_hidden_stack: vec![false], private_traits: FxHashSet::default() }
 505     }
 506
 507     fn doc_hidden(&self) -> bool {
 508         *self.doc_hidden_stack.last().expect("empty doc_hidden_stack")
 509     }
 510
 511     fn check_missing_docs_attrs(
 512         &self,
 513         cx: &LateContext<'_>,
 514         id: hir::HirId,
 515         sp: Span,
 516         article: &'static str,
 517         desc: &'static str,
 518     ) {
 519         // If we're building a test harness, then warning about
 520         // documentation is probably not really relevant right now.
 521         if cx.sess().opts.test {
 522             return;
 523         }
 524
 525         // `#[doc(hidden)]` disables missing_docs check.
 526         if self.doc_hidden() {
 527             return;
 528         }
 529
 530         // Only check publicly-visible items, using the result from the privacy pass.
 531         // It's an option so the crate root can also use this function (it doesn't
 532         // have a `NodeId`).
 533         if id != hir::CRATE_HIR_ID {
 534             if !cx.access_levels.is_exported(id) {
 535                 return;
 536             }
 537         }
 538
 539         let attrs = cx.tcx.hir().attrs(id);
 540         let has_doc = attrs.iter().any(|a| has_doc(cx.sess(), a));
 541         if !has_doc {
 542             cx.struct_span_lint(
 543                 MISSING_DOCS,
 544                 cx.tcx.sess.source_map().guess_head_span(sp),
 545                 |lint| {
 546                     lint.build(&format!("missing documentation for {} {}", article, desc)).emit()
 547                 },
 548             );
 549         }
 550     }
 551 }
 552
 553 impl<'tcx> LateLintPass<'tcx> for MissingDoc {
 554     fn enter_lint_attrs(&mut self, cx: &LateContext<'_>, attrs: &[ast::Attribute]) {
 555         let doc_hidden = self.doc_hidden()
 556             || attrs.iter().any(|attr| {
 557                 cx.sess().check_name(attr, sym::doc)
 558                     && match attr.meta_item_list() {
 559                         None => false,
 560                         Some(l) => attr::list_contains_name(&l, sym::hidden),
 561                     }
 562             });
 563         self.doc_hidden_stack.push(doc_hidden);
 564     }
 565
 566     fn exit_lint_attrs(&mut self, _: &LateContext<'_>, _attrs: &[ast::Attribute]) {
 567         self.doc_hidden_stack.pop().expect("empty doc_hidden_stack");
 568     }
 569
 570     fn check_crate(&mut self, cx: &LateContext<'_>, krate: &hir::Crate<'_>) {
 571         self.check_missing_docs_attrs(cx, hir::CRATE_HIR_ID, krate.item.inner, "the", "crate");
 572
 573         for macro_def in krate.exported_macros {
 574             let attrs = cx.tcx.hir().attrs(macro_def.hir_id());
 575             let has_doc = attrs.iter().any(|a| has_doc(cx.sess(), a));
 576             if !has_doc {
 577                 cx.struct_span_lint(
 578                     MISSING_DOCS,
 579                     cx.tcx.sess.source_map().guess_head_span(macro_def.span),
 580                     |lint| lint.build("missing documentation for macro").emit(),
 581                 );
 582             }
 583         }
 584     }
 585
 586     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 587         match it.kind {
 588             hir::ItemKind::Trait(.., trait_item_refs) => {
 589                 // Issue #11592: traits are always considered exported, even when private.
 590                 if let hir::VisibilityKind::Inherited = it.vis.node {
 591                     self.private_traits.insert(it.hir_id());
 592                     for trait_item_ref in trait_item_refs {
 593                         self.private_traits.insert(trait_item_ref.id.hir_id());
 594                     }
 595                     return;
 596                 }
 597             }
 598             hir::ItemKind::Impl(hir::Impl { of_trait: Some(ref trait_ref), items, .. }) => {
 599                 // If the trait is private, add the impl items to `private_traits` so they don't get
 600                 // reported for missing docs.
 601                 let real_trait = trait_ref.path.res.def_id();
 602                 if let Some(def_id) = real_trait.as_local() {
 603                     let hir_id = cx.tcx.hir().local_def_id_to_hir_id(def_id);
 604                     if let Some(Node::Item(item)) = cx.tcx.hir().find(hir_id) {
 605                         if let hir::VisibilityKind::Inherited = item.vis.node {
 606                             for impl_item_ref in items {
 607                                 self.private_traits.insert(impl_item_ref.id.hir_id());
 608                             }
 609                         }
 610                     }
 611                 }
 612                 return;
 613             }
 614
 615             hir::ItemKind::TyAlias(..)
 616             | hir::ItemKind::Fn(..)
 617             | hir::ItemKind::Mod(..)
 618             | hir::ItemKind::Enum(..)
 619             | hir::ItemKind::Struct(..)
 620             | hir::ItemKind::Union(..)
 621             | hir::ItemKind::Const(..)
 622             | hir::ItemKind::Static(..) => {}
 623
 624             _ => return,
 625         };
 626
 627         let (article, desc) = cx.tcx.article_and_description(it.def_id.to_def_id());
 628
 629         self.check_missing_docs_attrs(cx, it.hir_id(), it.span, article, desc);
 630     }
 631
 632     fn check_trait_item(&mut self, cx: &LateContext<'_>, trait_item: &hir::TraitItem<'_>) {
 633         if self.private_traits.contains(&trait_item.hir_id()) {
 634             return;
 635         }
 636
 637         let (article, desc) = cx.tcx.article_and_description(trait_item.def_id.to_def_id());
 638
 639         self.check_missing_docs_attrs(cx, trait_item.hir_id(), trait_item.span, article, desc);
 640     }
 641
 642     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
 643         // If the method is an impl for a trait, don't doc.
 644         if method_context(cx, impl_item.hir_id()) == MethodLateContext::TraitImpl {
 645             return;
 646         }
 647
 648         let (article, desc) = cx.tcx.article_and_description(impl_item.def_id.to_def_id());
 649         self.check_missing_docs_attrs(cx, impl_item.hir_id(), impl_item.span, article, desc);
 650     }
 651
 652     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'_>) {
 653         let (article, desc) = cx.tcx.article_and_description(foreign_item.def_id.to_def_id());
 654         self.check_missing_docs_attrs(cx, foreign_item.hir_id(), foreign_item.span, article, desc);
 655     }
 656
 657     fn check_field_def(&mut self, cx: &LateContext<'_>, sf: &hir::FieldDef<'_>) {
 658         if !sf.is_positional() {
 659             self.check_missing_docs_attrs(cx, sf.hir_id, sf.span, "a", "struct field")
 660         }
 661     }
 662
 663     fn check_variant(&mut self, cx: &LateContext<'_>, v: &hir::Variant<'_>) {
 664         self.check_missing_docs_attrs(cx, v.id, v.span, "a", "variant");
 665     }
 666 }
 667
 668 declare_lint! {
 669     /// The `missing_copy_implementations` lint detects potentially-forgotten
 670     /// implementations of [`Copy`].
 671     ///
 672     /// [`Copy`]: https://doc.rust-lang.org/std/marker/trait.Copy.html
 673     ///
 674     /// ### Example
 675     ///
 676     /// ```rust,compile_fail
 677     /// #![deny(missing_copy_implementations)]
 678     /// pub struct Foo {
 679     ///     pub field: i32
 680     /// }
 681     /// # fn main() {}
 682     /// ```
 683     ///
 684     /// {{produces}}
 685     ///
 686     /// ### Explanation
 687     ///
 688     /// Historically (before 1.0), types were automatically marked as `Copy`
 689     /// if possible. This was changed so that it required an explicit opt-in
 690     /// by implementing the `Copy` trait. As part of this change, a lint was
 691     /// added to alert if a copyable type was not marked `Copy`.
 692     ///
 693     /// This lint is "allow" by default because this code isn't bad; it is
 694     /// common to write newtypes like this specifically so that a `Copy` type
 695     /// is no longer `Copy`. `Copy` types can result in unintended copies of
 696     /// large data which can impact performance.
 697     pub MISSING_COPY_IMPLEMENTATIONS,
 698     Allow,
 699     "detects potentially-forgotten implementations of `Copy`"
 700 }
 701
 702 declare_lint_pass!(MissingCopyImplementations => [MISSING_COPY_IMPLEMENTATIONS]);
 703
 704 impl<'tcx> LateLintPass<'tcx> for MissingCopyImplementations {
 705     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 706         if !cx.access_levels.is_reachable(item.hir_id()) {
 707             return;
 708         }
 709         let (def, ty) = match item.kind {
 710             hir::ItemKind::Struct(_, ref ast_generics) => {
 711                 if !ast_generics.params.is_empty() {
 712                     return;
 713                 }
 714                 let def = cx.tcx.adt_def(item.def_id);
 715                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 716             }
 717             hir::ItemKind::Union(_, ref ast_generics) => {
 718                 if !ast_generics.params.is_empty() {
 719                     return;
 720                 }
 721                 let def = cx.tcx.adt_def(item.def_id);
 722                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 723             }
 724             hir::ItemKind::Enum(_, ref ast_generics) => {
 725                 if !ast_generics.params.is_empty() {
 726                     return;
 727                 }
 728                 let def = cx.tcx.adt_def(item.def_id);
 729                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 730             }
 731             _ => return,
 732         };
 733         if def.has_dtor(cx.tcx) {
 734             return;
 735         }
 736         let param_env = ty::ParamEnv::empty();
 737         if ty.is_copy_modulo_regions(cx.tcx.at(item.span), param_env) {
 738             return;
 739         }
 740         if can_type_implement_copy(cx.tcx, param_env, ty).is_ok() {
 741             cx.struct_span_lint(MISSING_COPY_IMPLEMENTATIONS, item.span, |lint| {
 742                 lint.build(
 743                     "type could implement `Copy`; consider adding `impl \
 744                           Copy`",
 745                 )
 746                 .emit()
 747             })
 748         }
 749     }
 750 }
 751
 752 declare_lint! {
 753     /// The `missing_debug_implementations` lint detects missing
 754     /// implementations of [`fmt::Debug`].
 755     ///
 756     /// [`fmt::Debug`]: https://doc.rust-lang.org/std/fmt/trait.Debug.html
 757     ///
 758     /// ### Example
 759     ///
 760     /// ```rust,compile_fail
 761     /// #![deny(missing_debug_implementations)]
 762     /// pub struct Foo;
 763     /// # fn main() {}
 764     /// ```
 765     ///
 766     /// {{produces}}
 767     ///
 768     /// ### Explanation
 769     ///
 770     /// Having a `Debug` implementation on all types can assist with
 771     /// debugging, as it provides a convenient way to format and display a
 772     /// value. Using the `#[derive(Debug)]` attribute will automatically
 773     /// generate a typical implementation, or a custom implementation can be
 774     /// added by manually implementing the `Debug` trait.
 775     ///
 776     /// This lint is "allow" by default because adding `Debug` to all types can
 777     /// have a negative impact on compile time and code size. It also requires
 778     /// boilerplate to be added to every type, which can be an impediment.
 779     MISSING_DEBUG_IMPLEMENTATIONS,
 780     Allow,
 781     "detects missing implementations of Debug"
 782 }
 783
 784 #[derive(Default)]
 785 pub struct MissingDebugImplementations {
 786     impling_types: Option<LocalDefIdSet>,
 787 }
 788
 789 impl_lint_pass!(MissingDebugImplementations => [MISSING_DEBUG_IMPLEMENTATIONS]);
 790
 791 impl<'tcx> LateLintPass<'tcx> for MissingDebugImplementations {
 792     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 793         if !cx.access_levels.is_reachable(item.hir_id()) {
 794             return;
 795         }
 796
 797         match item.kind {
 798             hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) | hir::ItemKind::Enum(..) => {}
 799             _ => return,
 800         }
 801
 802         let debug = match cx.tcx.get_diagnostic_item(sym::debug_trait) {
 803             Some(debug) => debug,
 804             None => return,
 805         };
 806
 807         if self.impling_types.is_none() {
 808             let mut impls = LocalDefIdSet::default();
 809             cx.tcx.for_each_impl(debug, |d| {
 810                 if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() {
 811                     if let Some(def_id) = ty_def.did.as_local() {
 812                         impls.insert(def_id);
 813                     }
 814                 }
 815             });
 816
 817             self.impling_types = Some(impls);
 818             debug!("{:?}", self.impling_types);
 819         }
 820
 821         if !self.impling_types.as_ref().unwrap().contains(&item.def_id) {
 822             cx.struct_span_lint(MISSING_DEBUG_IMPLEMENTATIONS, item.span, |lint| {
 823                 lint.build(&format!(
 824                     "type does not implement `{}`; consider adding `#[derive(Debug)]` \
 825                      or a manual implementation",
 826                     cx.tcx.def_path_str(debug)
 827                 ))
 828                 .emit()
 829             });
 830         }
 831     }
 832 }
 833
 834 declare_lint! {
 835     /// The `anonymous_parameters` lint detects anonymous parameters in trait
 836     /// definitions.
 837     ///
 838     /// ### Example
 839     ///
 840     /// ```rust,edition2015,compile_fail
 841     /// #![deny(anonymous_parameters)]
 842     /// // edition 2015
 843     /// pub trait Foo {
 844     ///     fn foo(usize);
 845     /// }
 846     /// fn main() {}
 847     /// ```
 848     ///
 849     /// {{produces}}
 850     ///
 851     /// ### Explanation
 852     ///
 853     /// This syntax is mostly a historical accident, and can be worked around
 854     /// quite easily by adding an `_` pattern or a descriptive identifier:
 855     ///
 856     /// ```rust
 857     /// trait Foo {
 858     ///     fn foo(_: usize);
 859     /// }
 860     /// ```
 861     ///
 862     /// This syntax is now a hard error in the 2018 edition. In the 2015
 863     /// edition, this lint is "warn" by default. This lint
 864     /// enables the [`cargo fix`] tool with the `--edition` flag to
 865     /// automatically transition old code from the 2015 edition to 2018. The
 866     /// tool will run this lint and automatically apply the
 867     /// suggested fix from the compiler (which is to add `_` to each
 868     /// parameter). This provides a completely automated way to update old
 869     /// code for a new edition. See [issue #41686] for more details.
 870     ///
 871     /// [issue #41686]: https://github.com/rust-lang/rust/issues/41686
 872     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
 873     pub ANONYMOUS_PARAMETERS,
 874     Warn,
 875     "detects anonymous parameters",
 876     @future_incompatible = FutureIncompatibleInfo {
 877         reference: "issue #41686 <https://github.com/rust-lang/rust/issues/41686>",
 878         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
 879     };
 880 }
 881
 882 declare_lint_pass!(
 883     /// Checks for use of anonymous parameters (RFC 1685).
 884     AnonymousParameters => [ANONYMOUS_PARAMETERS]
 885 );
 886
 887 impl EarlyLintPass for AnonymousParameters {
 888     fn check_trait_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
 889         if cx.sess.edition() != Edition::Edition2015 {
 890             // This is a hard error in future editions; avoid linting and erroring
 891             return;
 892         }
 893         if let ast::AssocItemKind::Fn(box FnKind(_, ref sig, _, _)) = it.kind {
 894             for arg in sig.decl.inputs.iter() {
 895                 if let ast::PatKind::Ident(_, ident, None) = arg.pat.kind {
 896                     if ident.name == kw::Empty {
 897                         cx.struct_span_lint(ANONYMOUS_PARAMETERS, arg.pat.span, |lint| {
 898                             let ty_snip = cx.sess.source_map().span_to_snippet(arg.ty.span);
 899
 900                             let (ty_snip, appl) = if let Ok(ref snip) = ty_snip {
 901                                 (snip.as_str(), Applicability::MachineApplicable)
 902                             } else {
 903                                 ("<type>", Applicability::HasPlaceholders)
 904                             };
 905
 906                             lint.build(
 907                                 "anonymous parameters are deprecated and will be \
 908                                      removed in the next edition.",
 909                             )
 910                             .span_suggestion(
 911                                 arg.pat.span,
 912                                 "try naming the parameter or explicitly \
 913                                             ignoring it",
 914                                 format!("_: {}", ty_snip),
 915                                 appl,
 916                             )
 917                             .emit();
 918                         })
 919                     }
 920                 }
 921             }
 922         }
 923     }
 924 }
 925
 926 /// Check for use of attributes which have been deprecated.
 927 #[derive(Clone)]
 928 pub struct DeprecatedAttr {
 929     // This is not free to compute, so we want to keep it around, rather than
 930     // compute it for every attribute.
 931     depr_attrs: Vec<&'static (Symbol, AttributeType, AttributeTemplate, AttributeGate)>,
 932 }
 933
 934 impl_lint_pass!(DeprecatedAttr => []);
 935
 936 impl DeprecatedAttr {
 937     pub fn new() -> DeprecatedAttr {
 938         DeprecatedAttr { depr_attrs: deprecated_attributes() }
 939     }
 940 }
 941
 942 fn lint_deprecated_attr(
 943     cx: &EarlyContext<'_>,
 944     attr: &ast::Attribute,
 945     msg: &str,
 946     suggestion: Option<&str>,
 947 ) {
 948     cx.struct_span_lint(DEPRECATED, attr.span, |lint| {
 949         lint.build(msg)
 950             .span_suggestion_short(
 951                 attr.span,
 952                 suggestion.unwrap_or("remove this attribute"),
 953                 String::new(),
 954                 Applicability::MachineApplicable,
 955             )
 956             .emit();
 957     })
 958 }
 959
 960 impl EarlyLintPass for DeprecatedAttr {
 961     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 962         for &&(n, _, _, ref g) in &self.depr_attrs {
 963             if attr.ident().map(|ident| ident.name) == Some(n) {
 964                 if let &AttributeGate::Gated(
 965                     Stability::Deprecated(link, suggestion),
 966                     name,
 967                     reason,
 968                     _,
 969                 ) = g
 970                 {
 971                     let msg =
 972                         format!("use of deprecated attribute `{}`: {}. See {}", name, reason, link);
 973                     lint_deprecated_attr(cx, attr, &msg, suggestion);
 974                 }
 975                 return;
 976             }
 977         }
 978         if cx.sess().check_name(attr, sym::no_start) || cx.sess().check_name(attr, sym::crate_id) {
 979             let path_str = pprust::path_to_string(&attr.get_normal_item().path);
 980             let msg = format!("use of deprecated attribute `{}`: no longer used.", path_str);
 981             lint_deprecated_attr(cx, attr, &msg, None);
 982         }
 983     }
 984 }
 985
 986 fn warn_if_doc(cx: &EarlyContext<'_>, node_span: Span, node_kind: &str, attrs: &[ast::Attribute]) {
 987     use rustc_ast::token::CommentKind;
 988
 989     let mut attrs = attrs.iter().peekable();
 990
 991     // Accumulate a single span for sugared doc comments.
 992     let mut sugared_span: Option<Span> = None;
 993
 994     while let Some(attr) = attrs.next() {
 995         let is_doc_comment = attr.is_doc_comment();
 996         if is_doc_comment {
 997             sugared_span =
 998                 Some(sugared_span.map_or(attr.span, |span| span.with_hi(attr.span.hi())));
 999         }
1000
1001         if attrs.peek().map_or(false, |next_attr| next_attr.is_doc_comment()) {
1002             continue;
1003         }
1004
1005         let span = sugared_span.take().unwrap_or(attr.span);
1006
1007         if is_doc_comment || cx.sess().check_name(attr, sym::doc) {
1008             cx.struct_span_lint(UNUSED_DOC_COMMENTS, span, |lint| {
1009                 let mut err = lint.build("unused doc comment");
1010                 err.span_label(
1011                     node_span,
1012                     format!("rustdoc does not generate documentation for {}", node_kind),
1013                 );
1014                 match attr.kind {
1015                     AttrKind::DocComment(CommentKind::Line, _) | AttrKind::Normal(..) => {
1016                         err.help("use `//` for a plain comment");
1017                     }
1018                     AttrKind::DocComment(CommentKind::Block, _) => {
1019                         err.help("use `/* */` for a plain comment");
1020                     }
1021                 }
1022                 err.emit();
1023             });
1024         }
1025     }
1026 }
1027
1028 impl EarlyLintPass for UnusedDocComment {
1029     fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &ast::Stmt) {
1030         let kind = match stmt.kind {
1031             ast::StmtKind::Local(..) => "statements",
1032             // Disabled pending discussion in #78306
1033             ast::StmtKind::Item(..) => return,
1034             // expressions will be reported by `check_expr`.
1035             ast::StmtKind::Empty
1036             | ast::StmtKind::Semi(_)
1037             | ast::StmtKind::Expr(_)
1038             | ast::StmtKind::MacCall(_) => return,
1039         };
1040
1041         warn_if_doc(cx, stmt.span, kind, stmt.kind.attrs());
1042     }
1043
1044     fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) {
1045         let arm_span = arm.pat.span.with_hi(arm.body.span.hi());
1046         warn_if_doc(cx, arm_span, "match arms", &arm.attrs);
1047     }
1048
1049     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
1050         warn_if_doc(cx, expr.span, "expressions", &expr.attrs);
1051     }
1052 }
1053
1054 declare_lint! {
1055     /// The `no_mangle_const_items` lint detects any `const` items with the
1056     /// [`no_mangle` attribute].
1057     ///
1058     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1059     ///
1060     /// ### Example
1061     ///
1062     /// ```rust,compile_fail
1063     /// #[no_mangle]
1064     /// const FOO: i32 = 5;
1065     /// ```
1066     ///
1067     /// {{produces}}
1068     ///
1069     /// ### Explanation
1070     ///
1071     /// Constants do not have their symbols exported, and therefore, this
1072     /// probably means you meant to use a [`static`], not a [`const`].
1073     ///
1074     /// [`static`]: https://doc.rust-lang.org/reference/items/static-items.html
1075     /// [`const`]: https://doc.rust-lang.org/reference/items/constant-items.html
1076     NO_MANGLE_CONST_ITEMS,
1077     Deny,
1078     "const items will not have their symbols exported"
1079 }
1080
1081 declare_lint! {
1082     /// The `no_mangle_generic_items` lint detects generic items that must be
1083     /// mangled.
1084     ///
1085     /// ### Example
1086     ///
1087     /// ```rust
1088     /// #[no_mangle]
1089     /// fn foo<T>(t: T) {
1090     ///
1091     /// }
1092     /// ```
1093     ///
1094     /// {{produces}}
1095     ///
1096     /// ### Explanation
1097     ///
1098     /// A function with generics must have its symbol mangled to accommodate
1099     /// the generic parameter. The [`no_mangle` attribute] has no effect in
1100     /// this situation, and should be removed.
1101     ///
1102     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1103     NO_MANGLE_GENERIC_ITEMS,
1104     Warn,
1105     "generic items must be mangled"
1106 }
1107
1108 declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS, NO_MANGLE_GENERIC_ITEMS]);
1109
1110 impl<'tcx> LateLintPass<'tcx> for InvalidNoMangleItems {
1111     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1112         let attrs = cx.tcx.hir().attrs(it.hir_id());
1113         match it.kind {
1114             hir::ItemKind::Fn(.., ref generics, _) => {
1115                 if let Some(no_mangle_attr) = cx.sess().find_by_name(attrs, sym::no_mangle) {
1116                     for param in generics.params {
1117                         match param.kind {
1118                             GenericParamKind::Lifetime { .. } => {}
1119                             GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1120                                 cx.struct_span_lint(NO_MANGLE_GENERIC_ITEMS, it.span, |lint| {
1121                                     lint.build(
1122                                         "functions generic over types or consts must be mangled",
1123                                     )
1124                                     .span_suggestion_short(
1125                                         no_mangle_attr.span,
1126                                         "remove this attribute",
1127                                         String::new(),
1128                                         // Use of `#[no_mangle]` suggests FFI intent; correct
1129                                         // fix may be to monomorphize source by hand
1130                                         Applicability::MaybeIncorrect,
1131                                     )
1132                                     .emit();
1133                                 });
1134                                 break;
1135                             }
1136                         }
1137                     }
1138                 }
1139             }
1140             hir::ItemKind::Const(..) => {
1141                 if cx.sess().contains_name(attrs, sym::no_mangle) {
1142                     // Const items do not refer to a particular location in memory, and therefore
1143                     // don't have anything to attach a symbol to
1144                     cx.struct_span_lint(NO_MANGLE_CONST_ITEMS, it.span, |lint| {
1145                         let msg = "const items should never be `#[no_mangle]`";
1146                         let mut err = lint.build(msg);
1147
1148                         // account for "pub const" (#45562)
1149                         let start = cx
1150                             .tcx
1151                             .sess
1152                             .source_map()
1153                             .span_to_snippet(it.span)
1154                             .map(|snippet| snippet.find("const").unwrap_or(0))
1155                             .unwrap_or(0) as u32;
1156                         // `const` is 5 chars
1157                         let const_span = it.span.with_hi(BytePos(it.span.lo().0 + start + 5));
1158                         err.span_suggestion(
1159                             const_span,
1160                             "try a static value",
1161                             "pub static".to_owned(),
1162                             Applicability::MachineApplicable,
1163                         );
1164                         err.emit();
1165                     });
1166                 }
1167             }
1168             _ => {}
1169         }
1170     }
1171 }
1172
1173 declare_lint! {
1174     /// The `mutable_transmutes` lint catches transmuting from `&T` to `&mut
1175     /// T` because it is [undefined behavior].
1176     ///
1177     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1178     ///
1179     /// ### Example
1180     ///
1181     /// ```rust,compile_fail
1182     /// unsafe {
1183     ///     let y = std::mem::transmute::<&i32, &mut i32>(&5);
1184     /// }
1185     /// ```
1186     ///
1187     /// {{produces}}
1188     ///
1189     /// ### Explanation
1190     ///
1191     /// Certain assumptions are made about aliasing of data, and this transmute
1192     /// violates those assumptions. Consider using [`UnsafeCell`] instead.
1193     ///
1194     /// [`UnsafeCell`]: https://doc.rust-lang.org/std/cell/struct.UnsafeCell.html
1195     MUTABLE_TRANSMUTES,
1196     Deny,
1197     "mutating transmuted &mut T from &T may cause undefined behavior"
1198 }
1199
1200 declare_lint_pass!(MutableTransmutes => [MUTABLE_TRANSMUTES]);
1201
1202 impl<'tcx> LateLintPass<'tcx> for MutableTransmutes {
1203     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &hir::Expr<'_>) {
1204         use rustc_target::spec::abi::Abi::RustIntrinsic;
1205         if let Some((&ty::Ref(_, _, from_mt), &ty::Ref(_, _, to_mt))) =
1206             get_transmute_from_to(cx, expr).map(|(ty1, ty2)| (ty1.kind(), ty2.kind()))
1207         {
1208             if to_mt == hir::Mutability::Mut && from_mt == hir::Mutability::Not {
1209                 let msg = "mutating transmuted &mut T from &T may cause undefined behavior, \
1210                                consider instead using an UnsafeCell";
1211                 cx.struct_span_lint(MUTABLE_TRANSMUTES, expr.span, |lint| lint.build(msg).emit());
1212             }
1213         }
1214
1215         fn get_transmute_from_to<'tcx>(
1216             cx: &LateContext<'tcx>,
1217             expr: &hir::Expr<'_>,
1218         ) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
1219             let def = if let hir::ExprKind::Path(ref qpath) = expr.kind {
1220                 cx.qpath_res(qpath, expr.hir_id)
1221             } else {
1222                 return None;
1223             };
1224             if let Res::Def(DefKind::Fn, did) = def {
1225                 if !def_id_is_transmute(cx, did) {
1226                     return None;
1227                 }
1228                 let sig = cx.typeck_results().node_type(expr.hir_id).fn_sig(cx.tcx);
1229                 let from = sig.inputs().skip_binder()[0];
1230                 let to = sig.output().skip_binder();
1231                 return Some((from, to));
1232             }
1233             None
1234         }
1235
1236         fn def_id_is_transmute(cx: &LateContext<'_>, def_id: DefId) -> bool {
1237             cx.tcx.fn_sig(def_id).abi() == RustIntrinsic
1238                 && cx.tcx.item_name(def_id) == sym::transmute
1239         }
1240     }
1241 }
1242
1243 declare_lint! {
1244     /// The `unstable_features` is deprecated and should no longer be used.
1245     UNSTABLE_FEATURES,
1246     Allow,
1247     "enabling unstable features (deprecated. do not use)"
1248 }
1249
1250 declare_lint_pass!(
1251     /// Forbids using the `#[feature(...)]` attribute
1252     UnstableFeatures => [UNSTABLE_FEATURES]
1253 );
1254
1255 impl<'tcx> LateLintPass<'tcx> for UnstableFeatures {
1256     fn check_attribute(&mut self, cx: &LateContext<'_>, attr: &ast::Attribute) {
1257         if cx.sess().check_name(attr, sym::feature) {
1258             if let Some(items) = attr.meta_item_list() {
1259                 for item in items {
1260                     cx.struct_span_lint(UNSTABLE_FEATURES, item.span(), |lint| {
1261                         lint.build("unstable feature").emit()
1262                     });
1263                 }
1264             }
1265         }
1266     }
1267 }
1268
1269 declare_lint! {
1270     /// The `unreachable_pub` lint triggers for `pub` items not reachable from
1271     /// the crate root.
1272     ///
1273     /// ### Example
1274     ///
1275     /// ```rust,compile_fail
1276     /// #![deny(unreachable_pub)]
1277     /// mod foo {
1278     ///     pub mod bar {
1279     ///
1280     ///     }
1281     /// }
1282     /// ```
1283     ///
1284     /// {{produces}}
1285     ///
1286     /// ### Explanation
1287     ///
1288     /// A bare `pub` visibility may be misleading if the item is not actually
1289     /// publicly exported from the crate. The `pub(crate)` visibility is
1290     /// recommended to be used instead, which more clearly expresses the intent
1291     /// that the item is only visible within its own crate.
1292     ///
1293     /// This lint is "allow" by default because it will trigger for a large
1294     /// amount existing Rust code, and has some false-positives. Eventually it
1295     /// is desired for this to become warn-by-default.
1296     pub UNREACHABLE_PUB,
1297     Allow,
1298     "`pub` items not reachable from crate root"
1299 }
1300
1301 declare_lint_pass!(
1302     /// Lint for items marked `pub` that aren't reachable from other crates.
1303     UnreachablePub => [UNREACHABLE_PUB]
1304 );
1305
1306 impl UnreachablePub {
1307     fn perform_lint(
1308         &self,
1309         cx: &LateContext<'_>,
1310         what: &str,
1311         id: hir::HirId,
1312         vis: &hir::Visibility<'_>,
1313         span: Span,
1314         exportable: bool,
1315     ) {
1316         let mut applicability = Applicability::MachineApplicable;
1317         match vis.node {
1318             hir::VisibilityKind::Public if !cx.access_levels.is_reachable(id) => {
1319                 if span.from_expansion() {
1320                     applicability = Applicability::MaybeIncorrect;
1321                 }
1322                 let def_span = cx.tcx.sess.source_map().guess_head_span(span);
1323                 cx.struct_span_lint(UNREACHABLE_PUB, def_span, |lint| {
1324                     let mut err = lint.build(&format!("unreachable `pub` {}", what));
1325                     let replacement = if cx.tcx.features().crate_visibility_modifier {
1326                         "crate"
1327                     } else {
1328                         "pub(crate)"
1329                     }
1330                     .to_owned();
1331
1332                     err.span_suggestion(
1333                         vis.span,
1334                         "consider restricting its visibility",
1335                         replacement,
1336                         applicability,
1337                     );
1338                     if exportable {
1339                         err.help("or consider exporting it for use by other crates");
1340                     }
1341                     err.emit();
1342                 });
1343             }
1344             _ => {}
1345         }
1346     }
1347 }
1348
1349 impl<'tcx> LateLintPass<'tcx> for UnreachablePub {
1350     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1351         self.perform_lint(cx, "item", item.hir_id(), &item.vis, item.span, true);
1352     }
1353
1354     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'tcx>) {
1355         self.perform_lint(
1356             cx,
1357             "item",
1358             foreign_item.hir_id(),
1359             &foreign_item.vis,
1360             foreign_item.span,
1361             true,
1362         );
1363     }
1364
1365     fn check_field_def(&mut self, cx: &LateContext<'_>, field: &hir::FieldDef<'_>) {
1366         self.perform_lint(cx, "field", field.hir_id, &field.vis, field.span, false);
1367     }
1368
1369     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
1370         self.perform_lint(cx, "item", impl_item.hir_id(), &impl_item.vis, impl_item.span, false);
1371     }
1372 }
1373
1374 declare_lint! {
1375     /// The `type_alias_bounds` lint detects bounds in type aliases.
1376     ///
1377     /// ### Example
1378     ///
1379     /// ```rust
1380     /// type SendVec<T: Send> = Vec<T>;
1381     /// ```
1382     ///
1383     /// {{produces}}
1384     ///
1385     /// ### Explanation
1386     ///
1387     /// The trait bounds in a type alias are currently ignored, and should not
1388     /// be included to avoid confusion. This was previously allowed
1389     /// unintentionally; this may become a hard error in the future.
1390     TYPE_ALIAS_BOUNDS,
1391     Warn,
1392     "bounds in type aliases are not enforced"
1393 }
1394
1395 declare_lint_pass!(
1396     /// Lint for trait and lifetime bounds in type aliases being mostly ignored.
1397     /// They are relevant when using associated types, but otherwise neither checked
1398     /// at definition site nor enforced at use site.
1399     TypeAliasBounds => [TYPE_ALIAS_BOUNDS]
1400 );
1401
1402 impl TypeAliasBounds {
1403     fn is_type_variable_assoc(qpath: &hir::QPath<'_>) -> bool {
1404         match *qpath {
1405             hir::QPath::TypeRelative(ref ty, _) => {
1406                 // If this is a type variable, we found a `T::Assoc`.
1407                 match ty.kind {
1408                     hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
1409                         matches!(path.res, Res::Def(DefKind::TyParam, _))
1410                     }
1411                     _ => false,
1412                 }
1413             }
1414             hir::QPath::Resolved(..) | hir::QPath::LangItem(..) => false,
1415         }
1416     }
1417
1418     fn suggest_changing_assoc_types(ty: &hir::Ty<'_>, err: &mut DiagnosticBuilder<'_>) {
1419         // Access to associates types should use `<T as Bound>::Assoc`, which does not need a
1420         // bound.  Let's see if this type does that.
1421
1422         // We use a HIR visitor to walk the type.
1423         use rustc_hir::intravisit::{self, Visitor};
1424         struct WalkAssocTypes<'a, 'db> {
1425             err: &'a mut DiagnosticBuilder<'db>,
1426         }
1427         impl<'a, 'db, 'v> Visitor<'v> for WalkAssocTypes<'a, 'db> {
1428             type Map = intravisit::ErasedMap<'v>;
1429
1430             fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1431                 intravisit::NestedVisitorMap::None
1432             }
1433
1434             fn visit_qpath(&mut self, qpath: &'v hir::QPath<'v>, id: hir::HirId, span: Span) {
1435                 if TypeAliasBounds::is_type_variable_assoc(qpath) {
1436                     self.err.span_help(
1437                         span,
1438                         "use fully disambiguated paths (i.e., `<T as Trait>::Assoc`) to refer to \
1439                          associated types in type aliases",
1440                     );
1441                 }
1442                 intravisit::walk_qpath(self, qpath, id, span)
1443             }
1444         }
1445
1446         // Let's go for a walk!
1447         let mut visitor = WalkAssocTypes { err };
1448         visitor.visit_ty(ty);
1449     }
1450 }
1451
1452 impl<'tcx> LateLintPass<'tcx> for TypeAliasBounds {
1453     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1454         let (ty, type_alias_generics) = match item.kind {
1455             hir::ItemKind::TyAlias(ref ty, ref generics) => (&*ty, generics),
1456             _ => return,
1457         };
1458         if let hir::TyKind::OpaqueDef(..) = ty.kind {
1459             // Bounds are respected for `type X = impl Trait`
1460             return;
1461         }
1462         let mut suggested_changing_assoc_types = false;
1463         // There must not be a where clause
1464         if !type_alias_generics.where_clause.predicates.is_empty() {
1465             cx.lint(
1466                 TYPE_ALIAS_BOUNDS,
1467                 |lint| {
1468                     let mut err = lint.build("where clauses are not enforced in type aliases");
1469                     let spans: Vec<_> = type_alias_generics
1470                         .where_clause
1471                         .predicates
1472                         .iter()
1473                         .map(|pred| pred.span())
1474                         .collect();
1475                     err.set_span(spans);
1476                     err.span_suggestion(
1477                         type_alias_generics.where_clause.span_for_predicates_or_empty_place(),
1478                         "the clause will not be checked when the type alias is used, and should be removed",
1479                         String::new(),
1480                         Applicability::MachineApplicable,
1481                     );
1482                     if !suggested_changing_assoc_types {
1483                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1484                         suggested_changing_assoc_types = true;
1485                     }
1486                     err.emit();
1487                 },
1488             );
1489         }
1490         // The parameters must not have bounds
1491         for param in type_alias_generics.params.iter() {
1492             let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
1493             let suggestion = spans
1494                 .iter()
1495                 .map(|sp| {
1496                     let start = param.span.between(*sp); // Include the `:` in `T: Bound`.
1497                     (start.to(*sp), String::new())
1498                 })
1499                 .collect();
1500             if !spans.is_empty() {
1501                 cx.struct_span_lint(TYPE_ALIAS_BOUNDS, spans, |lint| {
1502                     let mut err =
1503                         lint.build("bounds on generic parameters are not enforced in type aliases");
1504                     let msg = "the bound will not be checked when the type alias is used, \
1505                                    and should be removed";
1506                     err.multipart_suggestion(&msg, suggestion, Applicability::MachineApplicable);
1507                     if !suggested_changing_assoc_types {
1508                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1509                         suggested_changing_assoc_types = true;
1510                     }
1511                     err.emit();
1512                 });
1513             }
1514         }
1515     }
1516 }
1517
1518 declare_lint_pass!(
1519     /// Lint constants that are erroneous.
1520     /// Without this lint, we might not get any diagnostic if the constant is
1521     /// unused within this crate, even though downstream crates can't use it
1522     /// without producing an error.
1523     UnusedBrokenConst => []
1524 );
1525
1526 impl<'tcx> LateLintPass<'tcx> for UnusedBrokenConst {
1527     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1528         match it.kind {
1529             hir::ItemKind::Const(_, body_id) => {
1530                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1531                 // trigger the query once for all constants since that will already report the errors
1532                 // FIXME: Use ensure here
1533                 let _ = cx.tcx.const_eval_poly(def_id);
1534             }
1535             hir::ItemKind::Static(_, _, body_id) => {
1536                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1537                 // FIXME: Use ensure here
1538                 let _ = cx.tcx.eval_static_initializer(def_id);
1539             }
1540             _ => {}
1541         }
1542     }
1543 }
1544
1545 declare_lint! {
1546     /// The `trivial_bounds` lint detects trait bounds that don't depend on
1547     /// any type parameters.
1548     ///
1549     /// ### Example
1550     ///
1551     /// ```rust
1552     /// #![feature(trivial_bounds)]
1553     /// pub struct A where i32: Copy;
1554     /// ```
1555     ///
1556     /// {{produces}}
1557     ///
1558     /// ### Explanation
1559     ///
1560     /// Usually you would not write a trait bound that you know is always
1561     /// true, or never true. However, when using macros, the macro may not
1562     /// know whether or not the constraint would hold or not at the time when
1563     /// generating the code. Currently, the compiler does not alert you if the
1564     /// constraint is always true, and generates an error if it is never true.
1565     /// The `trivial_bounds` feature changes this to be a warning in both
1566     /// cases, giving macros more freedom and flexibility to generate code,
1567     /// while still providing a signal when writing non-macro code that
1568     /// something is amiss.
1569     ///
1570     /// See [RFC 2056] for more details. This feature is currently only
1571     /// available on the nightly channel, see [tracking issue #48214].
1572     ///
1573     /// [RFC 2056]: https://github.com/rust-lang/rfcs/blob/master/text/2056-allow-trivial-where-clause-constraints.md
1574     /// [tracking issue #48214]: https://github.com/rust-lang/rust/issues/48214
1575     TRIVIAL_BOUNDS,
1576     Warn,
1577     "these bounds don't depend on an type parameters"
1578 }
1579
1580 declare_lint_pass!(
1581     /// Lint for trait and lifetime bounds that don't depend on type parameters
1582     /// which either do nothing, or stop the item from being used.
1583     TrivialConstraints => [TRIVIAL_BOUNDS]
1584 );
1585
1586 impl<'tcx> LateLintPass<'tcx> for TrivialConstraints {
1587     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
1588         use rustc_middle::ty::fold::TypeFoldable;
1589         use rustc_middle::ty::PredicateKind::*;
1590
1591         if cx.tcx.features().trivial_bounds {
1592             let predicates = cx.tcx.predicates_of(item.def_id);
1593             for &(predicate, span) in predicates.predicates {
1594                 let predicate_kind_name = match predicate.kind().skip_binder() {
1595                     Trait(..) => "Trait",
1596                     TypeOutlives(..) |
1597                     RegionOutlives(..) => "Lifetime",
1598
1599                     // Ignore projections, as they can only be global
1600                     // if the trait bound is global
1601                     Projection(..) |
1602                     // Ignore bounds that a user can't type
1603                     WellFormed(..) |
1604                     ObjectSafe(..) |
1605                     ClosureKind(..) |
1606                     Subtype(..) |
1607                     ConstEvaluatable(..) |
1608                     ConstEquate(..) |
1609                     TypeWellFormedFromEnv(..) => continue,
1610                 };
1611                 if predicate.is_global() {
1612                     cx.struct_span_lint(TRIVIAL_BOUNDS, span, |lint| {
1613                         lint.build(&format!(
1614                             "{} bound {} does not depend on any type \
1615                                 or lifetime parameters",
1616                             predicate_kind_name, predicate
1617                         ))
1618                         .emit()
1619                     });
1620                 }
1621             }
1622         }
1623     }
1624 }
1625
1626 declare_lint_pass!(
1627     /// Does nothing as a lint pass, but registers some `Lint`s
1628     /// which are used by other parts of the compiler.
1629     SoftLints => [
1630         WHILE_TRUE,
1631         BOX_POINTERS,
1632         NON_SHORTHAND_FIELD_PATTERNS,
1633         UNSAFE_CODE,
1634         MISSING_DOCS,
1635         MISSING_COPY_IMPLEMENTATIONS,
1636         MISSING_DEBUG_IMPLEMENTATIONS,
1637         ANONYMOUS_PARAMETERS,
1638         UNUSED_DOC_COMMENTS,
1639         NO_MANGLE_CONST_ITEMS,
1640         NO_MANGLE_GENERIC_ITEMS,
1641         MUTABLE_TRANSMUTES,
1642         UNSTABLE_FEATURES,
1643         UNREACHABLE_PUB,
1644         TYPE_ALIAS_BOUNDS,
1645         TRIVIAL_BOUNDS
1646     ]
1647 );
1648
1649 declare_lint! {
1650     /// The `ellipsis_inclusive_range_patterns` lint detects the [`...` range
1651     /// pattern], which is deprecated.
1652     ///
1653     /// [`...` range pattern]: https://doc.rust-lang.org/reference/patterns.html#range-patterns
1654     ///
1655     /// ### Example
1656     ///
1657     /// ```rust
1658     /// let x = 123;
1659     /// match x {
1660     ///     0...100 => {}
1661     ///     _ => {}
1662     /// }
1663     /// ```
1664     ///
1665     /// {{produces}}
1666     ///
1667     /// ### Explanation
1668     ///
1669     /// The `...` range pattern syntax was changed to `..=` to avoid potential
1670     /// confusion with the [`..` range expression]. Use the new form instead.
1671     ///
1672     /// [`..` range expression]: https://doc.rust-lang.org/reference/expressions/range-expr.html
1673     pub ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
1674     Warn,
1675     "`...` range patterns are deprecated",
1676     @future_incompatible = FutureIncompatibleInfo {
1677         reference: "issue #80165 <https://github.com/rust-lang/rust/issues/80165>",
1678         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
1679     };
1680 }
1681
1682 #[derive(Default)]
1683 pub struct EllipsisInclusiveRangePatterns {
1684     /// If `Some(_)`, suppress all subsequent pattern
1685     /// warnings for better diagnostics.
1686     node_id: Option<ast::NodeId>,
1687 }
1688
1689 impl_lint_pass!(EllipsisInclusiveRangePatterns => [ELLIPSIS_INCLUSIVE_RANGE_PATTERNS]);
1690
1691 impl EarlyLintPass for EllipsisInclusiveRangePatterns {
1692     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &ast::Pat) {
1693         if self.node_id.is_some() {
1694             // Don't recursively warn about patterns inside range endpoints.
1695             return;
1696         }
1697
1698         use self::ast::{PatKind, RangeSyntax::DotDotDot};
1699
1700         /// If `pat` is a `...` pattern, return the start and end of the range, as well as the span
1701         /// corresponding to the ellipsis.
1702         fn matches_ellipsis_pat(pat: &ast::Pat) -> Option<(Option<&Expr>, &Expr, Span)> {
1703             match &pat.kind {
1704                 PatKind::Range(
1705                     a,
1706                     Some(b),
1707                     Spanned { span, node: RangeEnd::Included(DotDotDot) },
1708                 ) => Some((a.as_deref(), b, *span)),
1709                 _ => None,
1710             }
1711         }
1712
1713         let (parenthesise, endpoints) = match &pat.kind {
1714             PatKind::Ref(subpat, _) => (true, matches_ellipsis_pat(&subpat)),
1715             _ => (false, matches_ellipsis_pat(pat)),
1716         };
1717
1718         if let Some((start, end, join)) = endpoints {
1719             let msg = "`...` range patterns are deprecated";
1720             let suggestion = "use `..=` for an inclusive range";
1721             if parenthesise {
1722                 self.node_id = Some(pat.id);
1723                 let end = expr_to_string(&end);
1724                 let replace = match start {
1725                     Some(start) => format!("&({}..={})", expr_to_string(&start), end),
1726                     None => format!("&(..={})", end),
1727                 };
1728                 if join.edition() >= Edition::Edition2021 {
1729                     let mut err =
1730                         rustc_errors::struct_span_err!(cx.sess, pat.span, E0783, "{}", msg,);
1731                     err.span_suggestion(
1732                         pat.span,
1733                         suggestion,
1734                         replace,
1735                         Applicability::MachineApplicable,
1736                     )
1737                     .emit();
1738                 } else {
1739                     cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, pat.span, |lint| {
1740                         lint.build(msg)
1741                             .span_suggestion(
1742                                 pat.span,
1743                                 suggestion,
1744                                 replace,
1745                                 Applicability::MachineApplicable,
1746                             )
1747                             .emit();
1748                     });
1749                 }
1750             } else {
1751                 let replace = "..=".to_owned();
1752                 if join.edition() >= Edition::Edition2021 {
1753                     let mut err =
1754                         rustc_errors::struct_span_err!(cx.sess, pat.span, E0783, "{}", msg,);
1755                     err.span_suggestion_short(
1756                         join,
1757                         suggestion,
1758                         replace,
1759                         Applicability::MachineApplicable,
1760                     )
1761                     .emit();
1762                 } else {
1763                     cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, join, |lint| {
1764                         lint.build(msg)
1765                             .span_suggestion_short(
1766                                 join,
1767                                 suggestion,
1768                                 replace,
1769                                 Applicability::MachineApplicable,
1770                             )
1771                             .emit();
1772                     });
1773                 }
1774             };
1775         }
1776     }
1777
1778     fn check_pat_post(&mut self, _cx: &EarlyContext<'_>, pat: &ast::Pat) {
1779         if let Some(node_id) = self.node_id {
1780             if pat.id == node_id {
1781                 self.node_id = None
1782             }
1783         }
1784     }
1785 }
1786
1787 declare_lint! {
1788     /// The `unnameable_test_items` lint detects [`#[test]`][test] functions
1789     /// that are not able to be run by the test harness because they are in a
1790     /// position where they are not nameable.
1791     ///
1792     /// [test]: https://doc.rust-lang.org/reference/attributes/testing.html#the-test-attribute
1793     ///
1794     /// ### Example
1795     ///
1796     /// ```rust,test
1797     /// fn main() {
1798     ///     #[test]
1799     ///     fn foo() {
1800     ///         // This test will not fail because it does not run.
1801     ///         assert_eq!(1, 2);
1802     ///     }
1803     /// }
1804     /// ```
1805     ///
1806     /// {{produces}}
1807     ///
1808     /// ### Explanation
1809     ///
1810     /// In order for the test harness to run a test, the test function must be
1811     /// located in a position where it can be accessed from the crate root.
1812     /// This generally means it must be defined in a module, and not anywhere
1813     /// else such as inside another function. The compiler previously allowed
1814     /// this without an error, so a lint was added as an alert that a test is
1815     /// not being used. Whether or not this should be allowed has not yet been
1816     /// decided, see [RFC 2471] and [issue #36629].
1817     ///
1818     /// [RFC 2471]: https://github.com/rust-lang/rfcs/pull/2471#issuecomment-397414443
1819     /// [issue #36629]: https://github.com/rust-lang/rust/issues/36629
1820     UNNAMEABLE_TEST_ITEMS,
1821     Warn,
1822     "detects an item that cannot be named being marked as `#[test_case]`",
1823     report_in_external_macro
1824 }
1825
1826 pub struct UnnameableTestItems {
1827     boundary: Option<LocalDefId>, // Id of the item under which things are not nameable
1828     items_nameable: bool,
1829 }
1830
1831 impl_lint_pass!(UnnameableTestItems => [UNNAMEABLE_TEST_ITEMS]);
1832
1833 impl UnnameableTestItems {
1834     pub fn new() -> Self {
1835         Self { boundary: None, items_nameable: true }
1836     }
1837 }
1838
1839 impl<'tcx> LateLintPass<'tcx> for UnnameableTestItems {
1840     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1841         if self.items_nameable {
1842             if let hir::ItemKind::Mod(..) = it.kind {
1843             } else {
1844                 self.items_nameable = false;
1845                 self.boundary = Some(it.def_id);
1846             }
1847             return;
1848         }
1849
1850         let attrs = cx.tcx.hir().attrs(it.hir_id());
1851         if let Some(attr) = cx.sess().find_by_name(attrs, sym::rustc_test_marker) {
1852             cx.struct_span_lint(UNNAMEABLE_TEST_ITEMS, attr.span, |lint| {
1853                 lint.build("cannot test inner items").emit()
1854             });
1855         }
1856     }
1857
1858     fn check_item_post(&mut self, _cx: &LateContext<'_>, it: &hir::Item<'_>) {
1859         if !self.items_nameable && self.boundary == Some(it.def_id) {
1860             self.items_nameable = true;
1861         }
1862     }
1863 }
1864
1865 declare_lint! {
1866     /// The `keyword_idents` lint detects edition keywords being used as an
1867     /// identifier.
1868     ///
1869     /// ### Example
1870     ///
1871     /// ```rust,edition2015,compile_fail
1872     /// #![deny(keyword_idents)]
1873     /// // edition 2015
1874     /// fn dyn() {}
1875     /// ```
1876     ///
1877     /// {{produces}}
1878     ///
1879     /// ### Explanation
1880     ///
1881     /// Rust [editions] allow the language to evolve without breaking
1882     /// backwards compatibility. This lint catches code that uses new keywords
1883     /// that are added to the language that are used as identifiers (such as a
1884     /// variable name, function name, etc.). If you switch the compiler to a
1885     /// new edition without updating the code, then it will fail to compile if
1886     /// you are using a new keyword as an identifier.
1887     ///
1888     /// You can manually change the identifiers to a non-keyword, or use a
1889     /// [raw identifier], for example `r#dyn`, to transition to a new edition.
1890     ///
1891     /// This lint solves the problem automatically. It is "allow" by default
1892     /// because the code is perfectly valid in older editions. The [`cargo
1893     /// fix`] tool with the `--edition` flag will switch this lint to "warn"
1894     /// and automatically apply the suggested fix from the compiler (which is
1895     /// to use a raw identifier). This provides a completely automated way to
1896     /// update old code for a new edition.
1897     ///
1898     /// [editions]: https://doc.rust-lang.org/edition-guide/
1899     /// [raw identifier]: https://doc.rust-lang.org/reference/identifiers.html
1900     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
1901     pub KEYWORD_IDENTS,
1902     Allow,
1903     "detects edition keywords being used as an identifier",
1904     @future_incompatible = FutureIncompatibleInfo {
1905         reference: "issue #49716 <https://github.com/rust-lang/rust/issues/49716>",
1906         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
1907     };
1908 }
1909
1910 declare_lint_pass!(
1911     /// Check for uses of edition keywords used as an identifier.
1912     KeywordIdents => [KEYWORD_IDENTS]
1913 );
1914
1915 struct UnderMacro(bool);
1916
1917 impl KeywordIdents {
1918     fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: TokenStream) {
1919         for tt in tokens.into_trees() {
1920             match tt {
1921                 // Only report non-raw idents.
1922                 TokenTree::Token(token) => {
1923                     if let Some((ident, false)) = token.ident() {
1924                         self.check_ident_token(cx, UnderMacro(true), ident);
1925                     }
1926                 }
1927                 TokenTree::Delimited(_, _, tts) => self.check_tokens(cx, tts),
1928             }
1929         }
1930     }
1931
1932     fn check_ident_token(
1933         &mut self,
1934         cx: &EarlyContext<'_>,
1935         UnderMacro(under_macro): UnderMacro,
1936         ident: Ident,
1937     ) {
1938         let next_edition = match cx.sess.edition() {
1939             Edition::Edition2015 => {
1940                 match ident.name {
1941                     kw::Async | kw::Await | kw::Try => Edition::Edition2018,
1942
1943                     // rust-lang/rust#56327: Conservatively do not
1944                     // attempt to report occurrences of `dyn` within
1945                     // macro definitions or invocations, because `dyn`
1946                     // can legitimately occur as a contextual keyword
1947                     // in 2015 code denoting its 2018 meaning, and we
1948                     // do not want rustfix to inject bugs into working
1949                     // code by rewriting such occurrences.
1950                     //
1951                     // But if we see `dyn` outside of a macro, we know
1952                     // its precise role in the parsed AST and thus are
1953                     // assured this is truly an attempt to use it as
1954                     // an identifier.
1955                     kw::Dyn if !under_macro => Edition::Edition2018,
1956
1957                     _ => return,
1958                 }
1959             }
1960
1961             // There are no new keywords yet for the 2018 edition and beyond.
1962             _ => return,
1963         };
1964
1965         // Don't lint `r#foo`.
1966         if cx.sess.parse_sess.raw_identifier_spans.borrow().contains(&ident.span) {
1967             return;
1968         }
1969
1970         cx.struct_span_lint(KEYWORD_IDENTS, ident.span, |lint| {
1971             lint.build(&format!("`{}` is a keyword in the {} edition", ident, next_edition))
1972                 .span_suggestion(
1973                     ident.span,
1974                     "you can use a raw identifier to stay compatible",
1975                     format!("r#{}", ident),
1976                     Applicability::MachineApplicable,
1977                 )
1978                 .emit()
1979         });
1980     }
1981 }
1982
1983 impl EarlyLintPass for KeywordIdents {
1984     fn check_mac_def(&mut self, cx: &EarlyContext<'_>, mac_def: &ast::MacroDef, _id: ast::NodeId) {
1985         self.check_tokens(cx, mac_def.body.inner_tokens());
1986     }
1987     fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::MacCall) {
1988         self.check_tokens(cx, mac.args.inner_tokens());
1989     }
1990     fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: Ident) {
1991         self.check_ident_token(cx, UnderMacro(false), ident);
1992     }
1993 }
1994
1995 declare_lint_pass!(ExplicitOutlivesRequirements => [EXPLICIT_OUTLIVES_REQUIREMENTS]);
1996
1997 impl ExplicitOutlivesRequirements {
1998     fn lifetimes_outliving_lifetime<'tcx>(
1999         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2000         index: u32,
2001     ) -> Vec<ty::Region<'tcx>> {
2002         inferred_outlives
2003             .iter()
2004             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
2005                 ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => match a {
2006                     ty::ReEarlyBound(ebr) if ebr.index == index => Some(b),
2007                     _ => None,
2008                 },
2009                 _ => None,
2010             })
2011             .collect()
2012     }
2013
2014     fn lifetimes_outliving_type<'tcx>(
2015         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2016         index: u32,
2017     ) -> Vec<ty::Region<'tcx>> {
2018         inferred_outlives
2019             .iter()
2020             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
2021                 ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
2022                     a.is_param(index).then_some(b)
2023                 }
2024                 _ => None,
2025             })
2026             .collect()
2027     }
2028
2029     fn collect_outlived_lifetimes<'tcx>(
2030         &self,
2031         param: &'tcx hir::GenericParam<'tcx>,
2032         tcx: TyCtxt<'tcx>,
2033         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2034         ty_generics: &'tcx ty::Generics,
2035     ) -> Vec<ty::Region<'tcx>> {
2036         let index =
2037             ty_generics.param_def_id_to_index[&tcx.hir().local_def_id(param.hir_id).to_def_id()];
2038
2039         match param.kind {
2040             hir::GenericParamKind::Lifetime { .. } => {
2041                 Self::lifetimes_outliving_lifetime(inferred_outlives, index)
2042             }
2043             hir::GenericParamKind::Type { .. } => {
2044                 Self::lifetimes_outliving_type(inferred_outlives, index)
2045             }
2046             hir::GenericParamKind::Const { .. } => Vec::new(),
2047         }
2048     }
2049
2050     fn collect_outlives_bound_spans<'tcx>(
2051         &self,
2052         tcx: TyCtxt<'tcx>,
2053         bounds: &hir::GenericBounds<'_>,
2054         inferred_outlives: &[ty::Region<'tcx>],
2055         infer_static: bool,
2056     ) -> Vec<(usize, Span)> {
2057         use rustc_middle::middle::resolve_lifetime::Region;
2058
2059         bounds
2060             .iter()
2061             .enumerate()
2062             .filter_map(|(i, bound)| {
2063                 if let hir::GenericBound::Outlives(lifetime) = bound {
2064                     let is_inferred = match tcx.named_region(lifetime.hir_id) {
2065                         Some(Region::Static) if infer_static => {
2066                             inferred_outlives.iter().any(|r| matches!(r, ty::ReStatic))
2067                         }
2068                         Some(Region::EarlyBound(index, ..)) => inferred_outlives.iter().any(|r| {
2069                             if let ty::ReEarlyBound(ebr) = r { ebr.index == index } else { false }
2070                         }),
2071                         _ => false,
2072                     };
2073                     is_inferred.then_some((i, bound.span()))
2074                 } else {
2075                     None
2076                 }
2077             })
2078             .collect()
2079     }
2080
2081     fn consolidate_outlives_bound_spans(
2082         &self,
2083         lo: Span,
2084         bounds: &hir::GenericBounds<'_>,
2085         bound_spans: Vec<(usize, Span)>,
2086     ) -> Vec<Span> {
2087         if bounds.is_empty() {
2088             return Vec::new();
2089         }
2090         if bound_spans.len() == bounds.len() {
2091             let (_, last_bound_span) = bound_spans[bound_spans.len() - 1];
2092             // If all bounds are inferable, we want to delete the colon, so
2093             // start from just after the parameter (span passed as argument)
2094             vec![lo.to(last_bound_span)]
2095         } else {
2096             let mut merged = Vec::new();
2097             let mut last_merged_i = None;
2098
2099             let mut from_start = true;
2100             for (i, bound_span) in bound_spans {
2101                 match last_merged_i {
2102                     // If the first bound is inferable, our span should also eat the leading `+`.
2103                     None if i == 0 => {
2104                         merged.push(bound_span.to(bounds[1].span().shrink_to_lo()));
2105                         last_merged_i = Some(0);
2106                     }
2107                     // If consecutive bounds are inferable, merge their spans
2108                     Some(h) if i == h + 1 => {
2109                         if let Some(tail) = merged.last_mut() {
2110                             // Also eat the trailing `+` if the first
2111                             // more-than-one bound is inferable
2112                             let to_span = if from_start && i < bounds.len() {
2113                                 bounds[i + 1].span().shrink_to_lo()
2114                             } else {
2115                                 bound_span
2116                             };
2117                             *tail = tail.to(to_span);
2118                             last_merged_i = Some(i);
2119                         } else {
2120                             bug!("another bound-span visited earlier");
2121                         }
2122                     }
2123                     _ => {
2124                         // When we find a non-inferable bound, subsequent inferable bounds
2125                         // won't be consecutive from the start (and we'll eat the leading
2126                         // `+` rather than the trailing one)
2127                         from_start = false;
2128                         merged.push(bounds[i - 1].span().shrink_to_hi().to(bound_span));
2129                         last_merged_i = Some(i);
2130                     }
2131                 }
2132             }
2133             merged
2134         }
2135     }
2136 }
2137
2138 impl<'tcx> LateLintPass<'tcx> for ExplicitOutlivesRequirements {
2139     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
2140         use rustc_middle::middle::resolve_lifetime::Region;
2141
2142         let infer_static = cx.tcx.features().infer_static_outlives_requirements;
2143         let def_id = item.def_id;
2144         if let hir::ItemKind::Struct(_, ref hir_generics)
2145         | hir::ItemKind::Enum(_, ref hir_generics)
2146         | hir::ItemKind::Union(_, ref hir_generics) = item.kind
2147         {
2148             let inferred_outlives = cx.tcx.inferred_outlives_of(def_id);
2149             if inferred_outlives.is_empty() {
2150                 return;
2151             }
2152
2153             let ty_generics = cx.tcx.generics_of(def_id);
2154
2155             let mut bound_count = 0;
2156             let mut lint_spans = Vec::new();
2157
2158             for param in hir_generics.params {
2159                 let has_lifetime_bounds = param
2160                     .bounds
2161                     .iter()
2162                     .any(|bound| matches!(bound, hir::GenericBound::Outlives(_)));
2163                 if !has_lifetime_bounds {
2164                     continue;
2165                 }
2166
2167                 let relevant_lifetimes =
2168                     self.collect_outlived_lifetimes(param, cx.tcx, inferred_outlives, ty_generics);
2169                 if relevant_lifetimes.is_empty() {
2170                     continue;
2171                 }
2172
2173                 let bound_spans = self.collect_outlives_bound_spans(
2174                     cx.tcx,
2175                     &param.bounds,
2176                     &relevant_lifetimes,
2177                     infer_static,
2178                 );
2179                 bound_count += bound_spans.len();
2180                 lint_spans.extend(self.consolidate_outlives_bound_spans(
2181                     param.span.shrink_to_hi(),
2182                     &param.bounds,
2183                     bound_spans,
2184                 ));
2185             }
2186
2187             let mut where_lint_spans = Vec::new();
2188             let mut dropped_predicate_count = 0;
2189             let num_predicates = hir_generics.where_clause.predicates.len();
2190             for (i, where_predicate) in hir_generics.where_clause.predicates.iter().enumerate() {
2191                 let (relevant_lifetimes, bounds, span) = match where_predicate {
2192                     hir::WherePredicate::RegionPredicate(predicate) => {
2193                         if let Some(Region::EarlyBound(index, ..)) =
2194                             cx.tcx.named_region(predicate.lifetime.hir_id)
2195                         {
2196                             (
2197                                 Self::lifetimes_outliving_lifetime(inferred_outlives, index),
2198                                 &predicate.bounds,
2199                                 predicate.span,
2200                             )
2201                         } else {
2202                             continue;
2203                         }
2204                     }
2205                     hir::WherePredicate::BoundPredicate(predicate) => {
2206                         // FIXME we can also infer bounds on associated types,
2207                         // and should check for them here.
2208                         match predicate.bounded_ty.kind {
2209                             hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
2210                                 if let Res::Def(DefKind::TyParam, def_id) = path.res {
2211                                     let index = ty_generics.param_def_id_to_index[&def_id];
2212                                     (
2213                                         Self::lifetimes_outliving_type(inferred_outlives, index),
2214                                         &predicate.bounds,
2215                                         predicate.span,
2216                                     )
2217                                 } else {
2218                                     continue;
2219                                 }
2220                             }
2221                             _ => {
2222                                 continue;
2223                             }
2224                         }
2225                     }
2226                     _ => continue,
2227                 };
2228                 if relevant_lifetimes.is_empty() {
2229                     continue;
2230                 }
2231
2232                 let bound_spans = self.collect_outlives_bound_spans(
2233                     cx.tcx,
2234                     bounds,
2235                     &relevant_lifetimes,
2236                     infer_static,
2237                 );
2238                 bound_count += bound_spans.len();
2239
2240                 let drop_predicate = bound_spans.len() == bounds.len();
2241                 if drop_predicate {
2242                     dropped_predicate_count += 1;
2243                 }
2244
2245                 // If all the bounds on a predicate were inferable and there are
2246                 // further predicates, we want to eat the trailing comma.
2247                 if drop_predicate && i + 1 < num_predicates {
2248                     let next_predicate_span = hir_generics.where_clause.predicates[i + 1].span();
2249                     where_lint_spans.push(span.to(next_predicate_span.shrink_to_lo()));
2250                 } else {
2251                     where_lint_spans.extend(self.consolidate_outlives_bound_spans(
2252                         span.shrink_to_lo(),
2253                         bounds,
2254                         bound_spans,
2255                     ));
2256                 }
2257             }
2258
2259             // If all predicates are inferable, drop the entire clause
2260             // (including the `where`)
2261             if num_predicates > 0 && dropped_predicate_count == num_predicates {
2262                 let where_span = hir_generics
2263                     .where_clause
2264                     .span()
2265                     .expect("span of (nonempty) where clause should exist");
2266                 // Extend the where clause back to the closing `>` of the
2267                 // generics, except for tuple struct, which have the `where`
2268                 // after the fields of the struct.
2269                 let full_where_span =
2270                     if let hir::ItemKind::Struct(hir::VariantData::Tuple(..), _) = item.kind {
2271                         where_span
2272                     } else {
2273                         hir_generics.span.shrink_to_hi().to(where_span)
2274                     };
2275                 lint_spans.push(full_where_span);
2276             } else {
2277                 lint_spans.extend(where_lint_spans);
2278             }
2279
2280             if !lint_spans.is_empty() {
2281                 cx.struct_span_lint(EXPLICIT_OUTLIVES_REQUIREMENTS, lint_spans.clone(), |lint| {
2282                     lint.build("outlives requirements can be inferred")
2283                         .multipart_suggestion(
2284                             if bound_count == 1 {
2285                                 "remove this bound"
2286                             } else {
2287                                 "remove these bounds"
2288                             },
2289                             lint_spans
2290                                 .into_iter()
2291                                 .map(|span| (span, "".to_owned()))
2292                                 .collect::<Vec<_>>(),
2293                             Applicability::MachineApplicable,
2294                         )
2295                         .emit();
2296                 });
2297             }
2298         }
2299     }
2300 }
2301
2302 declare_lint! {
2303     /// The `incomplete_features` lint detects unstable features enabled with
2304     /// the [`feature` attribute] that may function improperly in some or all
2305     /// cases.
2306     ///
2307     /// [`feature` attribute]: https://doc.rust-lang.org/nightly/unstable-book/
2308     ///
2309     /// ### Example
2310     ///
2311     /// ```rust
2312     /// #![feature(generic_associated_types)]
2313     /// ```
2314     ///
2315     /// {{produces}}
2316     ///
2317     /// ### Explanation
2318     ///
2319     /// Although it is encouraged for people to experiment with unstable
2320     /// features, some of them are known to be incomplete or faulty. This lint
2321     /// is a signal that the feature has not yet been finished, and you may
2322     /// experience problems with it.
2323     pub INCOMPLETE_FEATURES,
2324     Warn,
2325     "incomplete features that may function improperly in some or all cases"
2326 }
2327
2328 declare_lint_pass!(
2329     /// Check for used feature gates in `INCOMPLETE_FEATURES` in `rustc_feature/src/active.rs`.
2330     IncompleteFeatures => [INCOMPLETE_FEATURES]
2331 );
2332
2333 impl EarlyLintPass for IncompleteFeatures {
2334     fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
2335         let features = cx.sess.features_untracked();
2336         features
2337             .declared_lang_features
2338             .iter()
2339             .map(|(name, span, _)| (name, span))
2340             .chain(features.declared_lib_features.iter().map(|(name, span)| (name, span)))
2341             .filter(|(&name, _)| features.incomplete(name))
2342             .for_each(|(&name, &span)| {
2343                 cx.struct_span_lint(INCOMPLETE_FEATURES, span, |lint| {
2344                     let mut builder = lint.build(&format!(
2345                         "the feature `{}` is incomplete and may not be safe to use \
2346                          and/or cause compiler crashes",
2347                         name,
2348                     ));
2349                     if let Some(n) = rustc_feature::find_feature_issue(name, GateIssue::Language) {
2350                         builder.note(&format!(
2351                             "see issue #{} <https://github.com/rust-lang/rust/issues/{}> \
2352                              for more information",
2353                             n, n,
2354                         ));
2355                     }
2356                     if HAS_MIN_FEATURES.contains(&name) {
2357                         builder.help(&format!(
2358                             "consider using `min_{}` instead, which is more stable and complete",
2359                             name,
2360                         ));
2361                     }
2362                     builder.emit();
2363                 })
2364             });
2365     }
2366 }
2367
2368 const HAS_MIN_FEATURES: &[Symbol] = &[sym::specialization];
2369
2370 declare_lint! {
2371     /// The `invalid_value` lint detects creating a value that is not valid,
2372     /// such as a null reference.
2373     ///
2374     /// ### Example
2375     ///
2376     /// ```rust,no_run
2377     /// # #![allow(unused)]
2378     /// unsafe {
2379     ///     let x: &'static i32 = std::mem::zeroed();
2380     /// }
2381     /// ```
2382     ///
2383     /// {{produces}}
2384     ///
2385     /// ### Explanation
2386     ///
2387     /// In some situations the compiler can detect that the code is creating
2388     /// an invalid value, which should be avoided.
2389     ///
2390     /// In particular, this lint will check for improper use of
2391     /// [`mem::zeroed`], [`mem::uninitialized`], [`mem::transmute`], and
2392     /// [`MaybeUninit::assume_init`] that can cause [undefined behavior]. The
2393     /// lint should provide extra information to indicate what the problem is
2394     /// and a possible solution.
2395     ///
2396     /// [`mem::zeroed`]: https://doc.rust-lang.org/std/mem/fn.zeroed.html
2397     /// [`mem::uninitialized`]: https://doc.rust-lang.org/std/mem/fn.uninitialized.html
2398     /// [`mem::transmute`]: https://doc.rust-lang.org/std/mem/fn.transmute.html
2399     /// [`MaybeUninit::assume_init`]: https://doc.rust-lang.org/std/mem/union.MaybeUninit.html#method.assume_init
2400     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
2401     pub INVALID_VALUE,
2402     Warn,
2403     "an invalid value is being created (such as a null reference)"
2404 }
2405
2406 declare_lint_pass!(InvalidValue => [INVALID_VALUE]);
2407
2408 impl<'tcx> LateLintPass<'tcx> for InvalidValue {
2409     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
2410         #[derive(Debug, Copy, Clone, PartialEq)]
2411         enum InitKind {
2412             Zeroed,
2413             Uninit,
2414         }
2415
2416         /// Information about why a type cannot be initialized this way.
2417         /// Contains an error message and optionally a span to point at.
2418         type InitError = (String, Option<Span>);
2419
2420         /// Test if this constant is all-0.
2421         fn is_zero(expr: &hir::Expr<'_>) -> bool {
2422             use hir::ExprKind::*;
2423             use rustc_ast::LitKind::*;
2424             match &expr.kind {
2425                 Lit(lit) => {
2426                     if let Int(i, _) = lit.node {
2427                         i == 0
2428                     } else {
2429                         false
2430                     }
2431                 }
2432                 Tup(tup) => tup.iter().all(is_zero),
2433                 _ => false,
2434             }
2435         }
2436
2437         /// Determine if this expression is a "dangerous initialization".
2438         fn is_dangerous_init(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> Option<InitKind> {
2439             if let hir::ExprKind::Call(ref path_expr, ref args) = expr.kind {
2440                 // Find calls to `mem::{uninitialized,zeroed}` methods.
2441                 if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2442                     let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2443
2444                     if cx.tcx.is_diagnostic_item(sym::mem_zeroed, def_id) {
2445                         return Some(InitKind::Zeroed);
2446                     } else if cx.tcx.is_diagnostic_item(sym::mem_uninitialized, def_id) {
2447                         return Some(InitKind::Uninit);
2448                     } else if cx.tcx.is_diagnostic_item(sym::transmute, def_id) && is_zero(&args[0])
2449                     {
2450                         return Some(InitKind::Zeroed);
2451                     }
2452                 }
2453             } else if let hir::ExprKind::MethodCall(_, _, ref args, _) = expr.kind {
2454                 // Find problematic calls to `MaybeUninit::assume_init`.
2455                 let def_id = cx.typeck_results().type_dependent_def_id(expr.hir_id)?;
2456                 if cx.tcx.is_diagnostic_item(sym::assume_init, def_id) {
2457                     // This is a call to *some* method named `assume_init`.
2458                     // See if the `self` parameter is one of the dangerous constructors.
2459                     if let hir::ExprKind::Call(ref path_expr, _) = args[0].kind {
2460                         if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2461                             let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2462
2463                             if cx.tcx.is_diagnostic_item(sym::maybe_uninit_zeroed, def_id) {
2464                                 return Some(InitKind::Zeroed);
2465                             } else if cx.tcx.is_diagnostic_item(sym::maybe_uninit_uninit, def_id) {
2466                                 return Some(InitKind::Uninit);
2467                             }
2468                         }
2469                     }
2470                 }
2471             }
2472
2473             None
2474         }
2475
2476         /// Test if this enum has several actually "existing" variants.
2477         /// Zero-sized uninhabited variants do not always have a tag assigned and thus do not "exist".
2478         fn is_multi_variant(adt: &ty::AdtDef) -> bool {
2479             // As an approximation, we only count dataless variants. Those are definitely inhabited.
2480             let existing_variants = adt.variants.iter().filter(|v| v.fields.is_empty()).count();
2481             existing_variants > 1
2482         }
2483
2484         /// Return `Some` only if we are sure this type does *not*
2485         /// allow zero initialization.
2486         fn ty_find_init_error<'tcx>(
2487             tcx: TyCtxt<'tcx>,
2488             ty: Ty<'tcx>,
2489             init: InitKind,
2490         ) -> Option<InitError> {
2491             use rustc_middle::ty::TyKind::*;
2492             match ty.kind() {
2493                 // Primitive types that don't like 0 as a value.
2494                 Ref(..) => Some(("references must be non-null".to_string(), None)),
2495                 Adt(..) if ty.is_box() => Some(("`Box` must be non-null".to_string(), None)),
2496                 FnPtr(..) => Some(("function pointers must be non-null".to_string(), None)),
2497                 Never => Some(("the `!` type has no valid value".to_string(), None)),
2498                 RawPtr(tm) if matches!(tm.ty.kind(), Dynamic(..)) =>
2499                 // raw ptr to dyn Trait
2500                 {
2501                     Some(("the vtable of a wide raw pointer must be non-null".to_string(), None))
2502                 }
2503                 // Primitive types with other constraints.
2504                 Bool if init == InitKind::Uninit => {
2505                     Some(("booleans must be either `true` or `false`".to_string(), None))
2506                 }
2507                 Char if init == InitKind::Uninit => {
2508                     Some(("characters must be a valid Unicode codepoint".to_string(), None))
2509                 }
2510                 // Recurse and checks for some compound types.
2511                 Adt(adt_def, substs) if !adt_def.is_union() => {
2512                     // First check if this ADT has a layout attribute (like `NonNull` and friends).
2513                     use std::ops::Bound;
2514                     match tcx.layout_scalar_valid_range(adt_def.did) {
2515                         // We exploit here that `layout_scalar_valid_range` will never
2516                         // return `Bound::Excluded`.  (And we have tests checking that we
2517                         // handle the attribute correctly.)
2518                         (Bound::Included(lo), _) if lo > 0 => {
2519                             return Some((format!("`{}` must be non-null", ty), None));
2520                         }
2521                         (Bound::Included(_), _) | (_, Bound::Included(_))
2522                             if init == InitKind::Uninit =>
2523                         {
2524                             return Some((
2525                                 format!(
2526                                     "`{}` must be initialized inside its custom valid range",
2527                                     ty,
2528                                 ),
2529                                 None,
2530                             ));
2531                         }
2532                         _ => {}
2533                     }
2534                     // Now, recurse.
2535                     match adt_def.variants.len() {
2536                         0 => Some(("enums with no variants have no valid value".to_string(), None)),
2537                         1 => {
2538                             // Struct, or enum with exactly one variant.
2539                             // Proceed recursively, check all fields.
2540                             let variant = &adt_def.variants[VariantIdx::from_u32(0)];
2541                             variant.fields.iter().find_map(|field| {
2542                                 ty_find_init_error(tcx, field.ty(tcx, substs), init).map(
2543                                     |(mut msg, span)| {
2544                                         if span.is_none() {
2545                                             // Point to this field, should be helpful for figuring
2546                                             // out where the source of the error is.
2547                                             let span = tcx.def_span(field.did);
2548                                             write!(
2549                                                 &mut msg,
2550                                                 " (in this {} field)",
2551                                                 adt_def.descr()
2552                                             )
2553                                             .unwrap();
2554                                             (msg, Some(span))
2555                                         } else {
2556                                             // Just forward.
2557                                             (msg, span)
2558                                         }
2559                                     },
2560                                 )
2561                             })
2562                         }
2563                         // Multi-variant enum.
2564                         _ => {
2565                             if init == InitKind::Uninit && is_multi_variant(adt_def) {
2566                                 let span = tcx.def_span(adt_def.did);
2567                                 Some((
2568                                     "enums have to be initialized to a variant".to_string(),
2569                                     Some(span),
2570                                 ))
2571                             } else {
2572                                 // In principle, for zero-initialization we could figure out which variant corresponds
2573                                 // to tag 0, and check that... but for now we just accept all zero-initializations.
2574                                 None
2575                             }
2576                         }
2577                     }
2578                 }
2579                 Tuple(..) => {
2580                     // Proceed recursively, check all fields.
2581                     ty.tuple_fields().find_map(|field| ty_find_init_error(tcx, field, init))
2582                 }
2583                 // Conservative fallback.
2584                 _ => None,
2585             }
2586         }
2587
2588         if let Some(init) = is_dangerous_init(cx, expr) {
2589             // This conjures an instance of a type out of nothing,
2590             // using zeroed or uninitialized memory.
2591             // We are extremely conservative with what we warn about.
2592             let conjured_ty = cx.typeck_results().expr_ty(expr);
2593             if let Some((msg, span)) =
2594                 with_no_trimmed_paths(|| ty_find_init_error(cx.tcx, conjured_ty, init))
2595             {
2596                 cx.struct_span_lint(INVALID_VALUE, expr.span, |lint| {
2597                     let mut err = lint.build(&format!(
2598                         "the type `{}` does not permit {}",
2599                         conjured_ty,
2600                         match init {
2601                             InitKind::Zeroed => "zero-initialization",
2602                             InitKind::Uninit => "being left uninitialized",
2603                         },
2604                     ));
2605                     err.span_label(expr.span, "this code causes undefined behavior when executed");
2606                     err.span_label(
2607                         expr.span,
2608                         "help: use `MaybeUninit<T>` instead, \
2609                             and only call `assume_init` after initialization is done",
2610                     );
2611                     if let Some(span) = span {
2612                         err.span_note(span, &msg);
2613                     } else {
2614                         err.note(&msg);
2615                     }
2616                     err.emit();
2617                 });
2618             }
2619         }
2620     }
2621 }
2622
2623 declare_lint! {
2624     /// The `clashing_extern_declarations` lint detects when an `extern fn`
2625     /// has been declared with the same name but different types.
2626     ///
2627     /// ### Example
2628     ///
2629     /// ```rust
2630     /// mod m {
2631     ///     extern "C" {
2632     ///         fn foo();
2633     ///     }
2634     /// }
2635     ///
2636     /// extern "C" {
2637     ///     fn foo(_: u32);
2638     /// }
2639     /// ```
2640     ///
2641     /// {{produces}}
2642     ///
2643     /// ### Explanation
2644     ///
2645     /// Because two symbols of the same name cannot be resolved to two
2646     /// different functions at link time, and one function cannot possibly
2647     /// have two types, a clashing extern declaration is almost certainly a
2648     /// mistake. Check to make sure that the `extern` definitions are correct
2649     /// and equivalent, and possibly consider unifying them in one location.
2650     ///
2651     /// This lint does not run between crates because a project may have
2652     /// dependencies which both rely on the same extern function, but declare
2653     /// it in a different (but valid) way. For example, they may both declare
2654     /// an opaque type for one or more of the arguments (which would end up
2655     /// distinct types), or use types that are valid conversions in the
2656     /// language the `extern fn` is defined in. In these cases, the compiler
2657     /// can't say that the clashing declaration is incorrect.
2658     pub CLASHING_EXTERN_DECLARATIONS,
2659     Warn,
2660     "detects when an extern fn has been declared with the same name but different types"
2661 }
2662
2663 pub struct ClashingExternDeclarations {
2664     /// Map of function symbol name to the first-seen hir id for that symbol name.. If seen_decls
2665     /// contains an entry for key K, it means a symbol with name K has been seen by this lint and
2666     /// the symbol should be reported as a clashing declaration.
2667     // FIXME: Technically, we could just store a &'tcx str here without issue; however, the
2668     // `impl_lint_pass` macro doesn't currently support lints parametric over a lifetime.
2669     seen_decls: FxHashMap<Symbol, HirId>,
2670 }
2671
2672 /// Differentiate between whether the name for an extern decl came from the link_name attribute or
2673 /// just from declaration itself. This is important because we don't want to report clashes on
2674 /// symbol name if they don't actually clash because one or the other links against a symbol with a
2675 /// different name.
2676 enum SymbolName {
2677     /// The name of the symbol + the span of the annotation which introduced the link name.
2678     Link(Symbol, Span),
2679     /// No link name, so just the name of the symbol.
2680     Normal(Symbol),
2681 }
2682
2683 impl SymbolName {
2684     fn get_name(&self) -> Symbol {
2685         match self {
2686             SymbolName::Link(s, _) | SymbolName::Normal(s) => *s,
2687         }
2688     }
2689 }
2690
2691 impl ClashingExternDeclarations {
2692     crate fn new() -> Self {
2693         ClashingExternDeclarations { seen_decls: FxHashMap::default() }
2694     }
2695     /// Insert a new foreign item into the seen set. If a symbol with the same name already exists
2696     /// for the item, return its HirId without updating the set.
2697     fn insert(&mut self, tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> Option<HirId> {
2698         let did = fi.def_id.to_def_id();
2699         let instance = Instance::new(did, ty::List::identity_for_item(tcx, did));
2700         let name = Symbol::intern(tcx.symbol_name(instance).name);
2701         if let Some(&hir_id) = self.seen_decls.get(&name) {
2702             // Avoid updating the map with the new entry when we do find a collision. We want to
2703             // make sure we're always pointing to the first definition as the previous declaration.
2704             // This lets us avoid emitting "knock-on" diagnostics.
2705             Some(hir_id)
2706         } else {
2707             self.seen_decls.insert(name, fi.hir_id())
2708         }
2709     }
2710
2711     /// Get the name of the symbol that's linked against for a given extern declaration. That is,
2712     /// the name specified in a #[link_name = ...] attribute if one was specified, else, just the
2713     /// symbol's name.
2714     fn name_of_extern_decl(tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> SymbolName {
2715         if let Some((overridden_link_name, overridden_link_name_span)) =
2716             tcx.codegen_fn_attrs(fi.def_id).link_name.map(|overridden_link_name| {
2717                 // FIXME: Instead of searching through the attributes again to get span
2718                 // information, we could have codegen_fn_attrs also give span information back for
2719                 // where the attribute was defined. However, until this is found to be a
2720                 // bottleneck, this does just fine.
2721                 (
2722                     overridden_link_name,
2723                     tcx.get_attrs(fi.def_id.to_def_id())
2724                         .iter()
2725                         .find(|at| tcx.sess.check_name(at, sym::link_name))
2726                         .unwrap()
2727                         .span,
2728                 )
2729             })
2730         {
2731             SymbolName::Link(overridden_link_name, overridden_link_name_span)
2732         } else {
2733             SymbolName::Normal(fi.ident.name)
2734         }
2735     }
2736
2737     /// Checks whether two types are structurally the same enough that the declarations shouldn't
2738     /// clash. We need this so we don't emit a lint when two modules both declare an extern struct,
2739     /// with the same members (as the declarations shouldn't clash).
2740     fn structurally_same_type<'tcx>(
2741         cx: &LateContext<'tcx>,
2742         a: Ty<'tcx>,
2743         b: Ty<'tcx>,
2744         ckind: CItemKind,
2745     ) -> bool {
2746         fn structurally_same_type_impl<'tcx>(
2747             seen_types: &mut FxHashSet<(Ty<'tcx>, Ty<'tcx>)>,
2748             cx: &LateContext<'tcx>,
2749             a: Ty<'tcx>,
2750             b: Ty<'tcx>,
2751             ckind: CItemKind,
2752         ) -> bool {
2753             debug!("structurally_same_type_impl(cx, a = {:?}, b = {:?})", a, b);
2754             let tcx = cx.tcx;
2755
2756             // Given a transparent newtype, reach through and grab the inner
2757             // type unless the newtype makes the type non-null.
2758             let non_transparent_ty = |ty: Ty<'tcx>| -> Ty<'tcx> {
2759                 let mut ty = ty;
2760                 loop {
2761                     if let ty::Adt(def, substs) = *ty.kind() {
2762                         let is_transparent = def.subst(tcx, substs).repr.transparent();
2763                         let is_non_null = crate::types::nonnull_optimization_guaranteed(tcx, &def);
2764                         debug!(
2765                             "non_transparent_ty({:?}) -- type is transparent? {}, type is non-null? {}",
2766                             ty, is_transparent, is_non_null
2767                         );
2768                         if is_transparent && !is_non_null {
2769                             debug_assert!(def.variants.len() == 1);
2770                             let v = &def.variants[VariantIdx::new(0)];
2771                             ty = transparent_newtype_field(tcx, v)
2772                                 .expect(
2773                                     "single-variant transparent structure with zero-sized field",
2774                                 )
2775                                 .ty(tcx, substs);
2776                             continue;
2777                         }
2778                     }
2779                     debug!("non_transparent_ty -> {:?}", ty);
2780                     return ty;
2781                 }
2782             };
2783
2784             let a = non_transparent_ty(a);
2785             let b = non_transparent_ty(b);
2786
2787             if !seen_types.insert((a, b)) {
2788                 // We've encountered a cycle. There's no point going any further -- the types are
2789                 // structurally the same.
2790                 return true;
2791             }
2792             let tcx = cx.tcx;
2793             if a == b || rustc_middle::ty::TyS::same_type(a, b) {
2794                 // All nominally-same types are structurally same, too.
2795                 true
2796             } else {
2797                 // Do a full, depth-first comparison between the two.
2798                 use rustc_middle::ty::TyKind::*;
2799                 let a_kind = a.kind();
2800                 let b_kind = b.kind();
2801
2802                 let compare_layouts = |a, b| -> Result<bool, LayoutError<'tcx>> {
2803                     debug!("compare_layouts({:?}, {:?})", a, b);
2804                     let a_layout = &cx.layout_of(a)?.layout.abi;
2805                     let b_layout = &cx.layout_of(b)?.layout.abi;
2806                     debug!(
2807                         "comparing layouts: {:?} == {:?} = {}",
2808                         a_layout,
2809                         b_layout,
2810                         a_layout == b_layout
2811                     );
2812                     Ok(a_layout == b_layout)
2813                 };
2814
2815                 #[allow(rustc::usage_of_ty_tykind)]
2816                 let is_primitive_or_pointer = |kind: &ty::TyKind<'_>| {
2817                     kind.is_primitive() || matches!(kind, RawPtr(..) | Ref(..))
2818                 };
2819
2820                 ensure_sufficient_stack(|| {
2821                     match (a_kind, b_kind) {
2822                         (Adt(a_def, a_substs), Adt(b_def, b_substs)) => {
2823                             let a = a.subst(cx.tcx, a_substs);
2824                             let b = b.subst(cx.tcx, b_substs);
2825                             debug!("Comparing {:?} and {:?}", a, b);
2826
2827                             // We can immediately rule out these types as structurally same if
2828                             // their layouts differ.
2829                             match compare_layouts(a, b) {
2830                                 Ok(false) => return false,
2831                                 _ => (), // otherwise, continue onto the full, fields comparison
2832                             }
2833
2834                             // Grab a flattened representation of all fields.
2835                             let a_fields = a_def.variants.iter().flat_map(|v| v.fields.iter());
2836                             let b_fields = b_def.variants.iter().flat_map(|v| v.fields.iter());
2837
2838                             // Perform a structural comparison for each field.
2839                             a_fields.eq_by(
2840                                 b_fields,
2841                                 |&ty::FieldDef { did: a_did, .. },
2842                                  &ty::FieldDef { did: b_did, .. }| {
2843                                     structurally_same_type_impl(
2844                                         seen_types,
2845                                         cx,
2846                                         tcx.type_of(a_did),
2847                                         tcx.type_of(b_did),
2848                                         ckind,
2849                                     )
2850                                 },
2851                             )
2852                         }
2853                         (Array(a_ty, a_const), Array(b_ty, b_const)) => {
2854                             // For arrays, we also check the constness of the type.
2855                             a_const.val == b_const.val
2856                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2857                         }
2858                         (Slice(a_ty), Slice(b_ty)) => {
2859                             structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2860                         }
2861                         (RawPtr(a_tymut), RawPtr(b_tymut)) => {
2862                             a_tymut.mutbl == b_tymut.mutbl
2863                                 && structurally_same_type_impl(
2864                                     seen_types,
2865                                     cx,
2866                                     &a_tymut.ty,
2867                                     &b_tymut.ty,
2868                                     ckind,
2869                                 )
2870                         }
2871                         (Ref(_a_region, a_ty, a_mut), Ref(_b_region, b_ty, b_mut)) => {
2872                             // For structural sameness, we don't need the region to be same.
2873                             a_mut == b_mut
2874                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2875                         }
2876                         (FnDef(..), FnDef(..)) => {
2877                             let a_poly_sig = a.fn_sig(tcx);
2878                             let b_poly_sig = b.fn_sig(tcx);
2879
2880                             // As we don't compare regions, skip_binder is fine.
2881                             let a_sig = a_poly_sig.skip_binder();
2882                             let b_sig = b_poly_sig.skip_binder();
2883
2884                             (a_sig.abi, a_sig.unsafety, a_sig.c_variadic)
2885                                 == (b_sig.abi, b_sig.unsafety, b_sig.c_variadic)
2886                                 && a_sig.inputs().iter().eq_by(b_sig.inputs().iter(), |a, b| {
2887                                     structurally_same_type_impl(seen_types, cx, a, b, ckind)
2888                                 })
2889                                 && structurally_same_type_impl(
2890                                     seen_types,
2891                                     cx,
2892                                     a_sig.output(),
2893                                     b_sig.output(),
2894                                     ckind,
2895                                 )
2896                         }
2897                         (Tuple(a_substs), Tuple(b_substs)) => {
2898                             a_substs.types().eq_by(b_substs.types(), |a_ty, b_ty| {
2899                                 structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2900                             })
2901                         }
2902                         // For these, it's not quite as easy to define structural-sameness quite so easily.
2903                         // For the purposes of this lint, take the conservative approach and mark them as
2904                         // not structurally same.
2905                         (Dynamic(..), Dynamic(..))
2906                         | (Error(..), Error(..))
2907                         | (Closure(..), Closure(..))
2908                         | (Generator(..), Generator(..))
2909                         | (GeneratorWitness(..), GeneratorWitness(..))
2910                         | (Projection(..), Projection(..))
2911                         | (Opaque(..), Opaque(..)) => false,
2912
2913                         // These definitely should have been caught above.
2914                         (Bool, Bool) | (Char, Char) | (Never, Never) | (Str, Str) => unreachable!(),
2915
2916                         // An Adt and a primitive or pointer type. This can be FFI-safe if non-null
2917                         // enum layout optimisation is being applied.
2918                         (Adt(..), other_kind) | (other_kind, Adt(..))
2919                             if is_primitive_or_pointer(other_kind) =>
2920                         {
2921                             let (primitive, adt) =
2922                                 if is_primitive_or_pointer(a.kind()) { (a, b) } else { (b, a) };
2923                             if let Some(ty) = crate::types::repr_nullable_ptr(cx, adt, ckind) {
2924                                 ty == primitive
2925                             } else {
2926                                 compare_layouts(a, b).unwrap_or(false)
2927                             }
2928                         }
2929                         // Otherwise, just compare the layouts. This may fail to lint for some
2930                         // incompatible types, but at the very least, will stop reads into
2931                         // uninitialised memory.
2932                         _ => compare_layouts(a, b).unwrap_or(false),
2933                     }
2934                 })
2935             }
2936         }
2937         let mut seen_types = FxHashSet::default();
2938         structurally_same_type_impl(&mut seen_types, cx, a, b, ckind)
2939     }
2940 }
2941
2942 impl_lint_pass!(ClashingExternDeclarations => [CLASHING_EXTERN_DECLARATIONS]);
2943
2944 impl<'tcx> LateLintPass<'tcx> for ClashingExternDeclarations {
2945     fn check_foreign_item(&mut self, cx: &LateContext<'tcx>, this_fi: &hir::ForeignItem<'_>) {
2946         trace!("ClashingExternDeclarations: check_foreign_item: {:?}", this_fi);
2947         if let ForeignItemKind::Fn(..) = this_fi.kind {
2948             let tcx = cx.tcx;
2949             if let Some(existing_hid) = self.insert(tcx, this_fi) {
2950                 let existing_decl_ty = tcx.type_of(tcx.hir().local_def_id(existing_hid));
2951                 let this_decl_ty = tcx.type_of(this_fi.def_id);
2952                 debug!(
2953                     "ClashingExternDeclarations: Comparing existing {:?}: {:?} to this {:?}: {:?}",
2954                     existing_hid, existing_decl_ty, this_fi.def_id, this_decl_ty
2955                 );
2956                 // Check that the declarations match.
2957                 if !Self::structurally_same_type(
2958                     cx,
2959                     existing_decl_ty,
2960                     this_decl_ty,
2961                     CItemKind::Declaration,
2962                 ) {
2963                     let orig_fi = tcx.hir().expect_foreign_item(existing_hid);
2964                     let orig = Self::name_of_extern_decl(tcx, orig_fi);
2965
2966                     // We want to ensure that we use spans for both decls that include where the
2967                     // name was defined, whether that was from the link_name attribute or not.
2968                     let get_relevant_span =
2969                         |fi: &hir::ForeignItem<'_>| match Self::name_of_extern_decl(tcx, fi) {
2970                             SymbolName::Normal(_) => fi.span,
2971                             SymbolName::Link(_, annot_span) => fi.span.to(annot_span),
2972                         };
2973                     // Finally, emit the diagnostic.
2974                     tcx.struct_span_lint_hir(
2975                         CLASHING_EXTERN_DECLARATIONS,
2976                         this_fi.hir_id(),
2977                         get_relevant_span(this_fi),
2978                         |lint| {
2979                             let mut expected_str = DiagnosticStyledString::new();
2980                             expected_str.push(existing_decl_ty.fn_sig(tcx).to_string(), false);
2981                             let mut found_str = DiagnosticStyledString::new();
2982                             found_str.push(this_decl_ty.fn_sig(tcx).to_string(), true);
2983
2984                             lint.build(&format!(
2985                                 "`{}` redeclare{} with a different signature",
2986                                 this_fi.ident.name,
2987                                 if orig.get_name() == this_fi.ident.name {
2988                                     "d".to_string()
2989                                 } else {
2990                                     format!("s `{}`", orig.get_name())
2991                                 }
2992                             ))
2993                             .span_label(
2994                                 get_relevant_span(orig_fi),
2995                                 &format!("`{}` previously declared here", orig.get_name()),
2996                             )
2997                             .span_label(
2998                                 get_relevant_span(this_fi),
2999                                 "this signature doesn't match the previous declaration",
3000                             )
3001                             .note_expected_found(&"", expected_str, &"", found_str)
3002                             .emit()
3003                         },
3004                     );
3005                 }
3006             }
3007         }
3008     }
3009 }
3010
3011 declare_lint! {
3012     /// The `deref_nullptr` lint detects when an null pointer is dereferenced,
3013     /// which causes [undefined behavior].
3014     ///
3015     /// ### Example
3016     ///
3017     /// ```rust,no_run
3018     /// # #![allow(unused)]
3019     /// use std::ptr;
3020     /// unsafe {
3021     ///     let x = &*ptr::null::<i32>();
3022     ///     let x = ptr::addr_of!(*ptr::null::<i32>());
3023     ///     let x = *(0 as *const i32);
3024     /// }
3025     /// ```
3026     ///
3027     /// {{produces}}
3028     ///
3029     /// ### Explanation
3030     ///
3031     /// Dereferencing a null pointer causes [undefined behavior] even as a place expression,
3032     /// like `&*(0 as *const i32)` or `addr_of!(*(0 as *const i32))`.
3033     ///
3034     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
3035     pub DEREF_NULLPTR,
3036     Warn,
3037     "detects when an null pointer is dereferenced"
3038 }
3039
3040 declare_lint_pass!(DerefNullPtr => [DEREF_NULLPTR]);
3041
3042 impl<'tcx> LateLintPass<'tcx> for DerefNullPtr {
3043     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
3044         /// test if expression is a null ptr
3045         fn is_null_ptr(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> bool {
3046             match &expr.kind {
3047                 rustc_hir::ExprKind::Cast(ref expr, ref ty) => {
3048                     if let rustc_hir::TyKind::Ptr(_) = ty.kind {
3049                         return is_zero(expr) || is_null_ptr(cx, expr);
3050                     }
3051                 }
3052                 // check for call to `core::ptr::null` or `core::ptr::null_mut`
3053                 rustc_hir::ExprKind::Call(ref path, _) => {
3054                     if let rustc_hir::ExprKind::Path(ref qpath) = path.kind {
3055                         if let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id() {
3056                             return cx.tcx.is_diagnostic_item(sym::ptr_null, def_id)
3057                                 || cx.tcx.is_diagnostic_item(sym::ptr_null_mut, def_id);
3058                         }
3059                     }
3060                 }
3061                 _ => {}
3062             }
3063             false
3064         }
3065
3066         /// test if expression is the literal `0`
3067         fn is_zero(expr: &hir::Expr<'_>) -> bool {
3068             match &expr.kind {
3069                 rustc_hir::ExprKind::Lit(ref lit) => {
3070                     if let LitKind::Int(a, _) = lit.node {
3071                         return a == 0;
3072                     }
3073                 }
3074                 _ => {}
3075             }
3076             false
3077         }
3078
3079         if let rustc_hir::ExprKind::Unary(ref un_op, ref expr_deref) = expr.kind {
3080             if let rustc_hir::UnOp::Deref = un_op {
3081                 if is_null_ptr(cx, expr_deref) {
3082                     cx.struct_span_lint(DEREF_NULLPTR, expr.span, |lint| {
3083                         let mut err = lint.build("dereferencing a null pointer");
3084                         err.span_label(
3085                             expr.span,
3086                             "this code causes undefined behavior when executed",
3087                         );
3088                         err.emit();
3089                     });
3090                 }
3091             }
3092         }
3093     }
3094 }