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