compiler/rustc_lint/src/builtin.rs

   1 //! Lints in the Rust compiler.
   2 //!
   3 //! This contains lints which can feasibly be implemented as their own
   4 //! AST visitor. Also see `rustc_session::lint::builtin`, which contains the
   5 //! definitions of lints that are emitted directly inside the main compiler.
   6 //!
   7 //! To add a new lint to rustc, declare it here using `declare_lint!()`.
   8 //! Then add code to emit the new lint in the appropriate circumstances.
   9 //! You can do that in an existing `LintPass` if it makes sense, or in a
  10 //! new `LintPass`, or using `Session::add_lint` elsewhere in the
  11 //! compiler. Only do the latter if the check can't be written cleanly as a
  12 //! `LintPass` (also, note that such lints will need to be defined in
  13 //! `rustc_session::lint::builtin`, not here).
  14 //!
  15 //! If you define a new `EarlyLintPass`, you will also need to add it to the
  16 //! `add_early_builtin!` or `add_early_builtin_with_new!` invocation in
  17 //! `lib.rs`. Use the former for unit-like structs and the latter for structs
  18 //! with a `pub fn new()`.
  19 //!
  20 //! If you define a new `LateLintPass`, you will also need to add it to the
  21 //! `late_lint_methods!` invocation in `lib.rs`.
  22
  23 use crate::{
  24     types::{transparent_newtype_field, CItemKind},
  25     EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext,
  26 };
  27 use rustc_ast::attr;
  28 use rustc_ast::tokenstream::{TokenStream, TokenTree};
  29 use rustc_ast::visit::{FnCtxt, FnKind};
  30 use rustc_ast::{self as ast, *};
  31 use rustc_ast_pretty::pprust::{self, expr_to_string};
  32 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
  33 use rustc_data_structures::stack::ensure_sufficient_stack;
  34 use rustc_errors::{Applicability, DiagnosticBuilder, DiagnosticStyledString};
  35 use rustc_feature::{deprecated_attributes, AttributeGate, AttributeTemplate, AttributeType};
  36 use rustc_feature::{GateIssue, Stability};
  37 use rustc_hir as hir;
  38 use rustc_hir::def::{DefKind, Res};
  39 use rustc_hir::def_id::{DefId, LocalDefId, LocalDefIdSet, CRATE_DEF_ID};
  40 use rustc_hir::{ForeignItemKind, GenericParamKind, PatKind};
  41 use rustc_hir::{HirId, Node};
  42 use rustc_index::vec::Idx;
  43 use rustc_middle::lint::LintDiagnosticBuilder;
  44 use rustc_middle::ty::layout::{LayoutError, LayoutOf};
  45 use rustc_middle::ty::print::with_no_trimmed_paths;
  46 use rustc_middle::ty::subst::{GenericArgKind, Subst};
  47 use rustc_middle::ty::Instance;
  48 use rustc_middle::ty::{self, Ty, TyCtxt};
  49 use rustc_session::lint::{BuiltinLintDiagnostics, FutureIncompatibilityReason};
  50 use rustc_span::edition::Edition;
  51 use rustc_span::source_map::Spanned;
  52 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  53 use rustc_span::{BytePos, InnerSpan, MultiSpan, Span};
  54 use rustc_target::abi::VariantIdx;
  55 use rustc_trait_selection::traits::misc::can_type_implement_copy;
  56
  57 use crate::nonstandard_style::{method_context, MethodLateContext};
  58
  59 use std::fmt::Write;
  60 use tracing::{debug, trace};
  61
  62 // hardwired lints from librustc_middle
  63 pub use rustc_session::lint::builtin::*;
  64
  65 declare_lint! {
  66     /// The `while_true` lint detects `while true { }`.
  67     ///
  68     /// ### Example
  69     ///
  70     /// ```rust,no_run
  71     /// while true {
  72     ///
  73     /// }
  74     /// ```
  75     ///
  76     /// {{produces}}
  77     ///
  78     /// ### Explanation
  79     ///
  80     /// `while true` should be replaced with `loop`. A `loop` expression is
  81     /// the preferred way to write an infinite loop because it more directly
  82     /// expresses the intent of the loop.
  83     WHILE_TRUE,
  84     Warn,
  85     "suggest using `loop { }` instead of `while true { }`"
  86 }
  87
  88 declare_lint_pass!(WhileTrue => [WHILE_TRUE]);
  89
  90 /// Traverse through any amount of parenthesis and return the first non-parens expression.
  91 fn pierce_parens(mut expr: &ast::Expr) -> &ast::Expr {
  92     while let ast::ExprKind::Paren(sub) = &expr.kind {
  93         expr = sub;
  94     }
  95     expr
  96 }
  97
  98 impl EarlyLintPass for WhileTrue {
  99     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
 100         if let ast::ExprKind::While(cond, _, label) = &e.kind {
 101             if let ast::ExprKind::Lit(ref lit) = pierce_parens(cond).kind {
 102                 if let ast::LitKind::Bool(true) = lit.kind {
 103                     if !lit.span.from_expansion() {
 104                         let msg = "denote infinite loops with `loop { ... }`";
 105                         let condition_span = e.span.with_hi(cond.span.hi());
 106                         cx.struct_span_lint(WHILE_TRUE, condition_span, |lint| {
 107                             lint.build(msg)
 108                                 .span_suggestion_short(
 109                                     condition_span,
 110                                     "use `loop`",
 111                                     format!(
 112                                         "{}loop",
 113                                         label.map_or_else(String::new, |label| format!(
 114                                             "{}: ",
 115                                             label.ident,
 116                                         ))
 117                                     ),
 118                                     Applicability::MachineApplicable,
 119                                 )
 120                                 .emit();
 121                         })
 122                     }
 123                 }
 124             }
 125         }
 126     }
 127 }
 128
 129 declare_lint! {
 130     /// The `box_pointers` lints use of the Box type.
 131     ///
 132     /// ### Example
 133     ///
 134     /// ```rust,compile_fail
 135     /// #![deny(box_pointers)]
 136     /// struct Foo {
 137     ///     x: Box<isize>,
 138     /// }
 139     /// ```
 140     ///
 141     /// {{produces}}
 142     ///
 143     /// ### Explanation
 144     ///
 145     /// This lint is mostly historical, and not particularly useful. `Box<T>`
 146     /// used to be built into the language, and the only way to do heap
 147     /// allocation. Today's Rust can call into other allocators, etc.
 148     BOX_POINTERS,
 149     Allow,
 150     "use of owned (Box type) heap memory"
 151 }
 152
 153 declare_lint_pass!(BoxPointers => [BOX_POINTERS]);
 154
 155 impl BoxPointers {
 156     fn check_heap_type<'tcx>(&self, cx: &LateContext<'tcx>, span: Span, ty: Ty<'tcx>) {
 157         for leaf in ty.walk(cx.tcx) {
 158             if let GenericArgKind::Type(leaf_ty) = leaf.unpack() {
 159                 if leaf_ty.is_box() {
 160                     cx.struct_span_lint(BOX_POINTERS, span, |lint| {
 161                         lint.build(&format!("type uses owned (Box type) pointers: {}", ty)).emit()
 162                     });
 163                 }
 164             }
 165         }
 166     }
 167 }
 168
 169 impl<'tcx> LateLintPass<'tcx> for BoxPointers {
 170     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 171         match it.kind {
 172             hir::ItemKind::Fn(..)
 173             | hir::ItemKind::TyAlias(..)
 174             | hir::ItemKind::Enum(..)
 175             | hir::ItemKind::Struct(..)
 176             | hir::ItemKind::Union(..) => {
 177                 self.check_heap_type(cx, it.span, cx.tcx.type_of(it.def_id))
 178             }
 179             _ => (),
 180         }
 181
 182         // If it's a struct, we also have to check the fields' types
 183         match it.kind {
 184             hir::ItemKind::Struct(ref struct_def, _) | hir::ItemKind::Union(ref struct_def, _) => {
 185                 for struct_field in struct_def.fields() {
 186                     let def_id = cx.tcx.hir().local_def_id(struct_field.hir_id);
 187                     self.check_heap_type(cx, struct_field.span, cx.tcx.type_of(def_id));
 188                 }
 189             }
 190             _ => (),
 191         }
 192     }
 193
 194     fn check_expr(&mut self, cx: &LateContext<'_>, e: &hir::Expr<'_>) {
 195         let ty = cx.typeck_results().node_type(e.hir_id);
 196         self.check_heap_type(cx, e.span, ty);
 197     }
 198 }
 199
 200 declare_lint! {
 201     /// The `non_shorthand_field_patterns` lint detects using `Struct { x: x }`
 202     /// instead of `Struct { x }` in a pattern.
 203     ///
 204     /// ### Example
 205     ///
 206     /// ```rust
 207     /// struct Point {
 208     ///     x: i32,
 209     ///     y: i32,
 210     /// }
 211     ///
 212     ///
 213     /// fn main() {
 214     ///     let p = Point {
 215     ///         x: 5,
 216     ///         y: 5,
 217     ///     };
 218     ///
 219     ///     match p {
 220     ///         Point { x: x, y: y } => (),
 221     ///     }
 222     /// }
 223     /// ```
 224     ///
 225     /// {{produces}}
 226     ///
 227     /// ### Explanation
 228     ///
 229     /// The preferred style is to avoid the repetition of specifying both the
 230     /// field name and the binding name if both identifiers are the same.
 231     NON_SHORTHAND_FIELD_PATTERNS,
 232     Warn,
 233     "using `Struct { x: x }` instead of `Struct { x }` in a pattern"
 234 }
 235
 236 declare_lint_pass!(NonShorthandFieldPatterns => [NON_SHORTHAND_FIELD_PATTERNS]);
 237
 238 impl<'tcx> LateLintPass<'tcx> for NonShorthandFieldPatterns {
 239     fn check_pat(&mut self, cx: &LateContext<'_>, pat: &hir::Pat<'_>) {
 240         if let PatKind::Struct(ref qpath, field_pats, _) = pat.kind {
 241             let variant = cx
 242                 .typeck_results()
 243                 .pat_ty(pat)
 244                 .ty_adt_def()
 245                 .expect("struct pattern type is not an ADT")
 246                 .variant_of_res(cx.qpath_res(qpath, pat.hir_id));
 247             for fieldpat in field_pats {
 248                 if fieldpat.is_shorthand {
 249                     continue;
 250                 }
 251                 if fieldpat.span.from_expansion() {
 252                     // Don't lint if this is a macro expansion: macro authors
 253                     // shouldn't have to worry about this kind of style issue
 254                     // (Issue #49588)
 255                     continue;
 256                 }
 257                 if let PatKind::Binding(binding_annot, _, ident, None) = fieldpat.pat.kind {
 258                     if cx.tcx.find_field_index(ident, &variant)
 259                         == Some(cx.tcx.field_index(fieldpat.hir_id, cx.typeck_results()))
 260                     {
 261                         cx.struct_span_lint(NON_SHORTHAND_FIELD_PATTERNS, fieldpat.span, |lint| {
 262                             let mut err = lint
 263                                 .build(&format!("the `{}:` in this pattern is redundant", ident));
 264                             let binding = match binding_annot {
 265                                 hir::BindingAnnotation::Unannotated => None,
 266                                 hir::BindingAnnotation::Mutable => Some("mut"),
 267                                 hir::BindingAnnotation::Ref => Some("ref"),
 268                                 hir::BindingAnnotation::RefMut => Some("ref mut"),
 269                             };
 270                             let ident = if let Some(binding) = binding {
 271                                 format!("{} {}", binding, ident)
 272                             } else {
 273                                 ident.to_string()
 274                             };
 275                             err.span_suggestion(
 276                                 fieldpat.span,
 277                                 "use shorthand field pattern",
 278                                 ident,
 279                                 Applicability::MachineApplicable,
 280                             );
 281                             err.emit();
 282                         });
 283                     }
 284                 }
 285             }
 286         }
 287     }
 288 }
 289
 290 declare_lint! {
 291     /// The `unsafe_code` lint catches usage of `unsafe` code.
 292     ///
 293     /// ### Example
 294     ///
 295     /// ```rust,compile_fail
 296     /// #![deny(unsafe_code)]
 297     /// fn main() {
 298     ///     unsafe {
 299     ///
 300     ///     }
 301     /// }
 302     /// ```
 303     ///
 304     /// {{produces}}
 305     ///
 306     /// ### Explanation
 307     ///
 308     /// This lint is intended to restrict the usage of `unsafe`, which can be
 309     /// difficult to use correctly.
 310     UNSAFE_CODE,
 311     Allow,
 312     "usage of `unsafe` code"
 313 }
 314
 315 declare_lint_pass!(UnsafeCode => [UNSAFE_CODE]);
 316
 317 impl UnsafeCode {
 318     fn report_unsafe(
 319         &self,
 320         cx: &EarlyContext<'_>,
 321         span: Span,
 322         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
 323     ) {
 324         // This comes from a macro that has `#[allow_internal_unsafe]`.
 325         if span.allows_unsafe() {
 326             return;
 327         }
 328
 329         cx.struct_span_lint(UNSAFE_CODE, span, decorate);
 330     }
 331
 332     fn report_overriden_symbol_name(&self, cx: &EarlyContext<'_>, span: Span, msg: &str) {
 333         self.report_unsafe(cx, span, |lint| {
 334             lint.build(msg)
 335                 .note(
 336                     "the linker's behavior with multiple libraries exporting duplicate symbol \
 337                     names is undefined and Rust cannot provide guarantees when you manually \
 338                     override them",
 339                 )
 340                 .emit();
 341         })
 342     }
 343 }
 344
 345 impl EarlyLintPass for UnsafeCode {
 346     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 347         if attr.has_name(sym::allow_internal_unsafe) {
 348             self.report_unsafe(cx, attr.span, |lint| {
 349                 lint.build(
 350                     "`allow_internal_unsafe` allows defining \
 351                                                macros using unsafe without triggering \
 352                                                the `unsafe_code` lint at their call site",
 353                 )
 354                 .emit()
 355             });
 356         }
 357     }
 358
 359     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
 360         if let ast::ExprKind::Block(ref blk, _) = e.kind {
 361             // Don't warn about generated blocks; that'll just pollute the output.
 362             if blk.rules == ast::BlockCheckMode::Unsafe(ast::UserProvided) {
 363                 self.report_unsafe(cx, blk.span, |lint| {
 364                     lint.build("usage of an `unsafe` block").emit()
 365                 });
 366             }
 367         }
 368     }
 369
 370     fn check_item(&mut self, cx: &EarlyContext<'_>, it: &ast::Item) {
 371         match it.kind {
 372             ast::ItemKind::Trait(box ast::TraitKind(_, ast::Unsafe::Yes(_), ..)) => self
 373                 .report_unsafe(cx, it.span, |lint| {
 374                     lint.build("declaration of an `unsafe` trait").emit()
 375                 }),
 376
 377             ast::ItemKind::Impl(box ast::ImplKind { unsafety: ast::Unsafe::Yes(_), .. }) => self
 378                 .report_unsafe(cx, it.span, |lint| {
 379                     lint.build("implementation of an `unsafe` trait").emit()
 380                 }),
 381
 382             ast::ItemKind::Fn(..) => {
 383                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
 384                     self.report_overriden_symbol_name(
 385                         cx,
 386                         attr.span,
 387                         "declaration of a `no_mangle` function",
 388                     );
 389                 }
 390                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::export_name) {
 391                     self.report_overriden_symbol_name(
 392                         cx,
 393                         attr.span,
 394                         "declaration of a function with `export_name`",
 395                     );
 396                 }
 397             }
 398
 399             ast::ItemKind::Static(..) => {
 400                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
 401                     self.report_overriden_symbol_name(
 402                         cx,
 403                         attr.span,
 404                         "declaration of a `no_mangle` static",
 405                     );
 406                 }
 407                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::export_name) {
 408                     self.report_overriden_symbol_name(
 409                         cx,
 410                         attr.span,
 411                         "declaration of a static with `export_name`",
 412                     );
 413                 }
 414             }
 415
 416             _ => {}
 417         }
 418     }
 419
 420     fn check_impl_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
 421         if let ast::AssocItemKind::Fn(..) = it.kind {
 422             if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
 423                 self.report_overriden_symbol_name(
 424                     cx,
 425                     attr.span,
 426                     "declaration of a `no_mangle` method",
 427                 );
 428             }
 429             if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::export_name) {
 430                 self.report_overriden_symbol_name(
 431                     cx,
 432                     attr.span,
 433                     "declaration of a method with `export_name`",
 434                 );
 435             }
 436         }
 437     }
 438
 439     fn check_fn(&mut self, cx: &EarlyContext<'_>, fk: FnKind<'_>, span: Span, _: ast::NodeId) {
 440         if let FnKind::Fn(
 441             ctxt,
 442             _,
 443             ast::FnSig { header: ast::FnHeader { unsafety: ast::Unsafe::Yes(_), .. }, .. },
 444             _,
 445             body,
 446         ) = fk
 447         {
 448             let msg = match ctxt {
 449                 FnCtxt::Foreign => return,
 450                 FnCtxt::Free => "declaration of an `unsafe` function",
 451                 FnCtxt::Assoc(_) if body.is_none() => "declaration of an `unsafe` method",
 452                 FnCtxt::Assoc(_) => "implementation of an `unsafe` method",
 453             };
 454             self.report_unsafe(cx, span, |lint| lint.build(msg).emit());
 455         }
 456     }
 457 }
 458
 459 declare_lint! {
 460     /// The `missing_docs` lint detects missing documentation for public items.
 461     ///
 462     /// ### Example
 463     ///
 464     /// ```rust,compile_fail
 465     /// #![deny(missing_docs)]
 466     /// pub fn foo() {}
 467     /// ```
 468     ///
 469     /// {{produces}}
 470     ///
 471     /// ### Explanation
 472     ///
 473     /// This lint is intended to ensure that a library is well-documented.
 474     /// Items without documentation can be difficult for users to understand
 475     /// how to use properly.
 476     ///
 477     /// This lint is "allow" by default because it can be noisy, and not all
 478     /// projects may want to enforce everything to be documented.
 479     pub MISSING_DOCS,
 480     Allow,
 481     "detects missing documentation for public members",
 482     report_in_external_macro
 483 }
 484
 485 pub struct MissingDoc {
 486     /// Stack of whether `#[doc(hidden)]` is set at each level which has lint attributes.
 487     doc_hidden_stack: Vec<bool>,
 488
 489     /// Private traits or trait items that leaked through. Don't check their methods.
 490     private_traits: FxHashSet<hir::HirId>,
 491 }
 492
 493 impl_lint_pass!(MissingDoc => [MISSING_DOCS]);
 494
 495 fn has_doc(attr: &ast::Attribute) -> bool {
 496     if attr.is_doc_comment() {
 497         return true;
 498     }
 499
 500     if !attr.has_name(sym::doc) {
 501         return false;
 502     }
 503
 504     if attr.value_str().is_some() {
 505         return true;
 506     }
 507
 508     if let Some(list) = attr.meta_item_list() {
 509         for meta in list {
 510             if meta.has_name(sym::hidden) {
 511                 return true;
 512             }
 513         }
 514     }
 515
 516     false
 517 }
 518
 519 impl MissingDoc {
 520     pub fn new() -> MissingDoc {
 521         MissingDoc { doc_hidden_stack: vec![false], private_traits: FxHashSet::default() }
 522     }
 523
 524     fn doc_hidden(&self) -> bool {
 525         *self.doc_hidden_stack.last().expect("empty doc_hidden_stack")
 526     }
 527
 528     fn check_missing_docs_attrs(
 529         &self,
 530         cx: &LateContext<'_>,
 531         def_id: LocalDefId,
 532         sp: Span,
 533         article: &'static str,
 534         desc: &'static str,
 535     ) {
 536         // If we're building a test harness, then warning about
 537         // documentation is probably not really relevant right now.
 538         if cx.sess().opts.test {
 539             return;
 540         }
 541
 542         // `#[doc(hidden)]` disables missing_docs check.
 543         if self.doc_hidden() {
 544             return;
 545         }
 546
 547         // Only check publicly-visible items, using the result from the privacy pass.
 548         // It's an option so the crate root can also use this function (it doesn't
 549         // have a `NodeId`).
 550         if def_id != CRATE_DEF_ID {
 551             if !cx.access_levels.is_exported(def_id) {
 552                 return;
 553             }
 554         }
 555
 556         let attrs = cx.tcx.get_attrs(def_id.to_def_id());
 557         let has_doc = attrs.iter().any(has_doc);
 558         if !has_doc {
 559             cx.struct_span_lint(
 560                 MISSING_DOCS,
 561                 cx.tcx.sess.source_map().guess_head_span(sp),
 562                 |lint| {
 563                     lint.build(&format!("missing documentation for {} {}", article, desc)).emit()
 564                 },
 565             );
 566         }
 567     }
 568 }
 569
 570 impl<'tcx> LateLintPass<'tcx> for MissingDoc {
 571     fn enter_lint_attrs(&mut self, _cx: &LateContext<'_>, attrs: &[ast::Attribute]) {
 572         let doc_hidden = self.doc_hidden()
 573             || attrs.iter().any(|attr| {
 574                 attr.has_name(sym::doc)
 575                     && match attr.meta_item_list() {
 576                         None => false,
 577                         Some(l) => attr::list_contains_name(&l, sym::hidden),
 578                     }
 579             });
 580         self.doc_hidden_stack.push(doc_hidden);
 581     }
 582
 583     fn exit_lint_attrs(&mut self, _: &LateContext<'_>, _attrs: &[ast::Attribute]) {
 584         self.doc_hidden_stack.pop().expect("empty doc_hidden_stack");
 585     }
 586
 587     fn check_crate(&mut self, cx: &LateContext<'_>, krate: &hir::Crate<'_>) {
 588         self.check_missing_docs_attrs(cx, CRATE_DEF_ID, krate.module().inner, "the", "crate");
 589     }
 590
 591     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 592         match it.kind {
 593             hir::ItemKind::Trait(.., trait_item_refs) => {
 594                 // Issue #11592: traits are always considered exported, even when private.
 595                 if let hir::VisibilityKind::Inherited = it.vis.node {
 596                     self.private_traits.insert(it.hir_id());
 597                     for trait_item_ref in trait_item_refs {
 598                         self.private_traits.insert(trait_item_ref.id.hir_id());
 599                     }
 600                     return;
 601                 }
 602             }
 603             hir::ItemKind::Impl(hir::Impl { of_trait: Some(ref trait_ref), items, .. }) => {
 604                 // If the trait is private, add the impl items to `private_traits` so they don't get
 605                 // reported for missing docs.
 606                 let real_trait = trait_ref.path.res.def_id();
 607                 if let Some(def_id) = real_trait.as_local() {
 608                     let hir_id = cx.tcx.hir().local_def_id_to_hir_id(def_id);
 609                     if let Some(Node::Item(item)) = cx.tcx.hir().find(hir_id) {
 610                         if let hir::VisibilityKind::Inherited = item.vis.node {
 611                             for impl_item_ref in items {
 612                                 self.private_traits.insert(impl_item_ref.id.hir_id());
 613                             }
 614                         }
 615                     }
 616                 }
 617                 return;
 618             }
 619
 620             hir::ItemKind::TyAlias(..)
 621             | hir::ItemKind::Fn(..)
 622             | hir::ItemKind::Macro(..)
 623             | hir::ItemKind::Mod(..)
 624             | hir::ItemKind::Enum(..)
 625             | hir::ItemKind::Struct(..)
 626             | hir::ItemKind::Union(..)
 627             | hir::ItemKind::Const(..)
 628             | hir::ItemKind::Static(..) => {}
 629
 630             _ => return,
 631         };
 632
 633         let (article, desc) = cx.tcx.article_and_description(it.def_id.to_def_id());
 634
 635         self.check_missing_docs_attrs(cx, it.def_id, it.span, article, desc);
 636     }
 637
 638     fn check_trait_item(&mut self, cx: &LateContext<'_>, trait_item: &hir::TraitItem<'_>) {
 639         if self.private_traits.contains(&trait_item.hir_id()) {
 640             return;
 641         }
 642
 643         let (article, desc) = cx.tcx.article_and_description(trait_item.def_id.to_def_id());
 644
 645         self.check_missing_docs_attrs(cx, trait_item.def_id, trait_item.span, article, desc);
 646     }
 647
 648     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
 649         // If the method is an impl for a trait, don't doc.
 650         if method_context(cx, impl_item.hir_id()) == MethodLateContext::TraitImpl {
 651             return;
 652         }
 653
 654         let (article, desc) = cx.tcx.article_and_description(impl_item.def_id.to_def_id());
 655         self.check_missing_docs_attrs(cx, impl_item.def_id, impl_item.span, article, desc);
 656     }
 657
 658     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'_>) {
 659         let (article, desc) = cx.tcx.article_and_description(foreign_item.def_id.to_def_id());
 660         self.check_missing_docs_attrs(cx, foreign_item.def_id, foreign_item.span, article, desc);
 661     }
 662
 663     fn check_field_def(&mut self, cx: &LateContext<'_>, sf: &hir::FieldDef<'_>) {
 664         if !sf.is_positional() {
 665             let def_id = cx.tcx.hir().local_def_id(sf.hir_id);
 666             self.check_missing_docs_attrs(cx, def_id, sf.span, "a", "struct field")
 667         }
 668     }
 669
 670     fn check_variant(&mut self, cx: &LateContext<'_>, v: &hir::Variant<'_>) {
 671         self.check_missing_docs_attrs(cx, cx.tcx.hir().local_def_id(v.id), v.span, "a", "variant");
 672     }
 673 }
 674
 675 declare_lint! {
 676     /// The `missing_copy_implementations` lint detects potentially-forgotten
 677     /// implementations of [`Copy`].
 678     ///
 679     /// [`Copy`]: https://doc.rust-lang.org/std/marker/trait.Copy.html
 680     ///
 681     /// ### Example
 682     ///
 683     /// ```rust,compile_fail
 684     /// #![deny(missing_copy_implementations)]
 685     /// pub struct Foo {
 686     ///     pub field: i32
 687     /// }
 688     /// # fn main() {}
 689     /// ```
 690     ///
 691     /// {{produces}}
 692     ///
 693     /// ### Explanation
 694     ///
 695     /// Historically (before 1.0), types were automatically marked as `Copy`
 696     /// if possible. This was changed so that it required an explicit opt-in
 697     /// by implementing the `Copy` trait. As part of this change, a lint was
 698     /// added to alert if a copyable type was not marked `Copy`.
 699     ///
 700     /// This lint is "allow" by default because this code isn't bad; it is
 701     /// common to write newtypes like this specifically so that a `Copy` type
 702     /// is no longer `Copy`. `Copy` types can result in unintended copies of
 703     /// large data which can impact performance.
 704     pub MISSING_COPY_IMPLEMENTATIONS,
 705     Allow,
 706     "detects potentially-forgotten implementations of `Copy`"
 707 }
 708
 709 declare_lint_pass!(MissingCopyImplementations => [MISSING_COPY_IMPLEMENTATIONS]);
 710
 711 impl<'tcx> LateLintPass<'tcx> for MissingCopyImplementations {
 712     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 713         if !cx.access_levels.is_reachable(item.def_id) {
 714             return;
 715         }
 716         let (def, ty) = match item.kind {
 717             hir::ItemKind::Struct(_, ref ast_generics) => {
 718                 if !ast_generics.params.is_empty() {
 719                     return;
 720                 }
 721                 let def = cx.tcx.adt_def(item.def_id);
 722                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 723             }
 724             hir::ItemKind::Union(_, ref ast_generics) => {
 725                 if !ast_generics.params.is_empty() {
 726                     return;
 727                 }
 728                 let def = cx.tcx.adt_def(item.def_id);
 729                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 730             }
 731             hir::ItemKind::Enum(_, ref ast_generics) => {
 732                 if !ast_generics.params.is_empty() {
 733                     return;
 734                 }
 735                 let def = cx.tcx.adt_def(item.def_id);
 736                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 737             }
 738             _ => return,
 739         };
 740         if def.has_dtor(cx.tcx) {
 741             return;
 742         }
 743         let param_env = ty::ParamEnv::empty();
 744         if ty.is_copy_modulo_regions(cx.tcx.at(item.span), param_env) {
 745             return;
 746         }
 747         if can_type_implement_copy(cx.tcx, param_env, ty).is_ok() {
 748             cx.struct_span_lint(MISSING_COPY_IMPLEMENTATIONS, item.span, |lint| {
 749                 lint.build(
 750                     "type could implement `Copy`; consider adding `impl \
 751                           Copy`",
 752                 )
 753                 .emit()
 754             })
 755         }
 756     }
 757 }
 758
 759 declare_lint! {
 760     /// The `missing_debug_implementations` lint detects missing
 761     /// implementations of [`fmt::Debug`].
 762     ///
 763     /// [`fmt::Debug`]: https://doc.rust-lang.org/std/fmt/trait.Debug.html
 764     ///
 765     /// ### Example
 766     ///
 767     /// ```rust,compile_fail
 768     /// #![deny(missing_debug_implementations)]
 769     /// pub struct Foo;
 770     /// # fn main() {}
 771     /// ```
 772     ///
 773     /// {{produces}}
 774     ///
 775     /// ### Explanation
 776     ///
 777     /// Having a `Debug` implementation on all types can assist with
 778     /// debugging, as it provides a convenient way to format and display a
 779     /// value. Using the `#[derive(Debug)]` attribute will automatically
 780     /// generate a typical implementation, or a custom implementation can be
 781     /// added by manually implementing the `Debug` trait.
 782     ///
 783     /// This lint is "allow" by default because adding `Debug` to all types can
 784     /// have a negative impact on compile time and code size. It also requires
 785     /// boilerplate to be added to every type, which can be an impediment.
 786     MISSING_DEBUG_IMPLEMENTATIONS,
 787     Allow,
 788     "detects missing implementations of Debug"
 789 }
 790
 791 #[derive(Default)]
 792 pub struct MissingDebugImplementations {
 793     impling_types: Option<LocalDefIdSet>,
 794 }
 795
 796 impl_lint_pass!(MissingDebugImplementations => [MISSING_DEBUG_IMPLEMENTATIONS]);
 797
 798 impl<'tcx> LateLintPass<'tcx> for MissingDebugImplementations {
 799     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 800         if !cx.access_levels.is_reachable(item.def_id) {
 801             return;
 802         }
 803
 804         match item.kind {
 805             hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) | hir::ItemKind::Enum(..) => {}
 806             _ => return,
 807         }
 808
 809         let debug = match cx.tcx.get_diagnostic_item(sym::debug_trait) {
 810             Some(debug) => debug,
 811             None => return,
 812         };
 813
 814         if self.impling_types.is_none() {
 815             let mut impls = LocalDefIdSet::default();
 816             cx.tcx.for_each_impl(debug, |d| {
 817                 if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() {
 818                     if let Some(def_id) = ty_def.did.as_local() {
 819                         impls.insert(def_id);
 820                     }
 821                 }
 822             });
 823
 824             self.impling_types = Some(impls);
 825             debug!("{:?}", self.impling_types);
 826         }
 827
 828         if !self.impling_types.as_ref().unwrap().contains(&item.def_id) {
 829             cx.struct_span_lint(MISSING_DEBUG_IMPLEMENTATIONS, item.span, |lint| {
 830                 lint.build(&format!(
 831                     "type does not implement `{}`; consider adding `#[derive(Debug)]` \
 832                      or a manual implementation",
 833                     cx.tcx.def_path_str(debug)
 834                 ))
 835                 .emit()
 836             });
 837         }
 838     }
 839 }
 840
 841 declare_lint! {
 842     /// The `anonymous_parameters` lint detects anonymous parameters in trait
 843     /// definitions.
 844     ///
 845     /// ### Example
 846     ///
 847     /// ```rust,edition2015,compile_fail
 848     /// #![deny(anonymous_parameters)]
 849     /// // edition 2015
 850     /// pub trait Foo {
 851     ///     fn foo(usize);
 852     /// }
 853     /// fn main() {}
 854     /// ```
 855     ///
 856     /// {{produces}}
 857     ///
 858     /// ### Explanation
 859     ///
 860     /// This syntax is mostly a historical accident, and can be worked around
 861     /// quite easily by adding an `_` pattern or a descriptive identifier:
 862     ///
 863     /// ```rust
 864     /// trait Foo {
 865     ///     fn foo(_: usize);
 866     /// }
 867     /// ```
 868     ///
 869     /// This syntax is now a hard error in the 2018 edition. In the 2015
 870     /// edition, this lint is "warn" by default. This lint
 871     /// enables the [`cargo fix`] tool with the `--edition` flag to
 872     /// automatically transition old code from the 2015 edition to 2018. The
 873     /// tool will run this lint and automatically apply the
 874     /// suggested fix from the compiler (which is to add `_` to each
 875     /// parameter). This provides a completely automated way to update old
 876     /// code for a new edition. See [issue #41686] for more details.
 877     ///
 878     /// [issue #41686]: https://github.com/rust-lang/rust/issues/41686
 879     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
 880     pub ANONYMOUS_PARAMETERS,
 881     Warn,
 882     "detects anonymous parameters",
 883     @future_incompatible = FutureIncompatibleInfo {
 884         reference: "issue #41686 <https://github.com/rust-lang/rust/issues/41686>",
 885         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
 886     };
 887 }
 888
 889 declare_lint_pass!(
 890     /// Checks for use of anonymous parameters (RFC 1685).
 891     AnonymousParameters => [ANONYMOUS_PARAMETERS]
 892 );
 893
 894 impl EarlyLintPass for AnonymousParameters {
 895     fn check_trait_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
 896         if cx.sess.edition() != Edition::Edition2015 {
 897             // This is a hard error in future editions; avoid linting and erroring
 898             return;
 899         }
 900         if let ast::AssocItemKind::Fn(box FnKind(_, ref sig, _, _)) = it.kind {
 901             for arg in sig.decl.inputs.iter() {
 902                 if let ast::PatKind::Ident(_, ident, None) = arg.pat.kind {
 903                     if ident.name == kw::Empty {
 904                         cx.struct_span_lint(ANONYMOUS_PARAMETERS, arg.pat.span, |lint| {
 905                             let ty_snip = cx.sess.source_map().span_to_snippet(arg.ty.span);
 906
 907                             let (ty_snip, appl) = if let Ok(ref snip) = ty_snip {
 908                                 (snip.as_str(), Applicability::MachineApplicable)
 909                             } else {
 910                                 ("<type>", Applicability::HasPlaceholders)
 911                             };
 912
 913                             lint.build(
 914                                 "anonymous parameters are deprecated and will be \
 915                                      removed in the next edition.",
 916                             )
 917                             .span_suggestion(
 918                                 arg.pat.span,
 919                                 "try naming the parameter or explicitly \
 920                                             ignoring it",
 921                                 format!("_: {}", ty_snip),
 922                                 appl,
 923                             )
 924                             .emit();
 925                         })
 926                     }
 927                 }
 928             }
 929         }
 930     }
 931 }
 932
 933 /// Check for use of attributes which have been deprecated.
 934 #[derive(Clone)]
 935 pub struct DeprecatedAttr {
 936     // This is not free to compute, so we want to keep it around, rather than
 937     // compute it for every attribute.
 938     depr_attrs: Vec<&'static (Symbol, AttributeType, AttributeTemplate, AttributeGate)>,
 939 }
 940
 941 impl_lint_pass!(DeprecatedAttr => []);
 942
 943 impl DeprecatedAttr {
 944     pub fn new() -> DeprecatedAttr {
 945         DeprecatedAttr { depr_attrs: deprecated_attributes() }
 946     }
 947 }
 948
 949 fn lint_deprecated_attr(
 950     cx: &EarlyContext<'_>,
 951     attr: &ast::Attribute,
 952     msg: &str,
 953     suggestion: Option<&str>,
 954 ) {
 955     cx.struct_span_lint(DEPRECATED, attr.span, |lint| {
 956         lint.build(msg)
 957             .span_suggestion_short(
 958                 attr.span,
 959                 suggestion.unwrap_or("remove this attribute"),
 960                 String::new(),
 961                 Applicability::MachineApplicable,
 962             )
 963             .emit();
 964     })
 965 }
 966
 967 impl EarlyLintPass for DeprecatedAttr {
 968     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 969         for &&(n, _, _, ref g) in &self.depr_attrs {
 970             if attr.ident().map(|ident| ident.name) == Some(n) {
 971                 if let &AttributeGate::Gated(
 972                     Stability::Deprecated(link, suggestion),
 973                     name,
 974                     reason,
 975                     _,
 976                 ) = g
 977                 {
 978                     let msg =
 979                         format!("use of deprecated attribute `{}`: {}. See {}", name, reason, link);
 980                     lint_deprecated_attr(cx, attr, &msg, suggestion);
 981                 }
 982                 return;
 983             }
 984         }
 985         if attr.has_name(sym::no_start) || attr.has_name(sym::crate_id) {
 986             let path_str = pprust::path_to_string(&attr.get_normal_item().path);
 987             let msg = format!("use of deprecated attribute `{}`: no longer used.", path_str);
 988             lint_deprecated_attr(cx, attr, &msg, None);
 989         }
 990     }
 991 }
 992
 993 fn warn_if_doc(cx: &EarlyContext<'_>, node_span: Span, node_kind: &str, attrs: &[ast::Attribute]) {
 994     use rustc_ast::token::CommentKind;
 995
 996     let mut attrs = attrs.iter().peekable();
 997
 998     // Accumulate a single span for sugared doc comments.
 999     let mut sugared_span: Option<Span> = None;
1000
1001     while let Some(attr) = attrs.next() {
1002         let is_doc_comment = attr.is_doc_comment();
1003         if is_doc_comment {
1004             sugared_span =
1005                 Some(sugared_span.map_or(attr.span, |span| span.with_hi(attr.span.hi())));
1006         }
1007
1008         if attrs.peek().map_or(false, |next_attr| next_attr.is_doc_comment()) {
1009             continue;
1010         }
1011
1012         let span = sugared_span.take().unwrap_or(attr.span);
1013
1014         if is_doc_comment || attr.has_name(sym::doc) {
1015             cx.struct_span_lint(UNUSED_DOC_COMMENTS, span, |lint| {
1016                 let mut err = lint.build("unused doc comment");
1017                 err.span_label(
1018                     node_span,
1019                     format!("rustdoc does not generate documentation for {}", node_kind),
1020                 );
1021                 match attr.kind {
1022                     AttrKind::DocComment(CommentKind::Line, _) | AttrKind::Normal(..) => {
1023                         err.help("use `//` for a plain comment");
1024                     }
1025                     AttrKind::DocComment(CommentKind::Block, _) => {
1026                         err.help("use `/* */` for a plain comment");
1027                     }
1028                 }
1029                 err.emit();
1030             });
1031         }
1032     }
1033 }
1034
1035 impl EarlyLintPass for UnusedDocComment {
1036     fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &ast::Stmt) {
1037         let kind = match stmt.kind {
1038             ast::StmtKind::Local(..) => "statements",
1039             // Disabled pending discussion in #78306
1040             ast::StmtKind::Item(..) => return,
1041             // expressions will be reported by `check_expr`.
1042             ast::StmtKind::Empty
1043             | ast::StmtKind::Semi(_)
1044             | ast::StmtKind::Expr(_)
1045             | ast::StmtKind::MacCall(_) => return,
1046         };
1047
1048         warn_if_doc(cx, stmt.span, kind, stmt.kind.attrs());
1049     }
1050
1051     fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) {
1052         let arm_span = arm.pat.span.with_hi(arm.body.span.hi());
1053         warn_if_doc(cx, arm_span, "match arms", &arm.attrs);
1054     }
1055
1056     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
1057         warn_if_doc(cx, expr.span, "expressions", &expr.attrs);
1058     }
1059 }
1060
1061 declare_lint! {
1062     /// The `no_mangle_const_items` lint detects any `const` items with the
1063     /// [`no_mangle` attribute].
1064     ///
1065     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1066     ///
1067     /// ### Example
1068     ///
1069     /// ```rust,compile_fail
1070     /// #[no_mangle]
1071     /// const FOO: i32 = 5;
1072     /// ```
1073     ///
1074     /// {{produces}}
1075     ///
1076     /// ### Explanation
1077     ///
1078     /// Constants do not have their symbols exported, and therefore, this
1079     /// probably means you meant to use a [`static`], not a [`const`].
1080     ///
1081     /// [`static`]: https://doc.rust-lang.org/reference/items/static-items.html
1082     /// [`const`]: https://doc.rust-lang.org/reference/items/constant-items.html
1083     NO_MANGLE_CONST_ITEMS,
1084     Deny,
1085     "const items will not have their symbols exported"
1086 }
1087
1088 declare_lint! {
1089     /// The `no_mangle_generic_items` lint detects generic items that must be
1090     /// mangled.
1091     ///
1092     /// ### Example
1093     ///
1094     /// ```rust
1095     /// #[no_mangle]
1096     /// fn foo<T>(t: T) {
1097     ///
1098     /// }
1099     /// ```
1100     ///
1101     /// {{produces}}
1102     ///
1103     /// ### Explanation
1104     ///
1105     /// A function with generics must have its symbol mangled to accommodate
1106     /// the generic parameter. The [`no_mangle` attribute] has no effect in
1107     /// this situation, and should be removed.
1108     ///
1109     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1110     NO_MANGLE_GENERIC_ITEMS,
1111     Warn,
1112     "generic items must be mangled"
1113 }
1114
1115 declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS, NO_MANGLE_GENERIC_ITEMS]);
1116
1117 impl<'tcx> LateLintPass<'tcx> for InvalidNoMangleItems {
1118     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1119         let attrs = cx.tcx.hir().attrs(it.hir_id());
1120         let check_no_mangle_on_generic_fn = |no_mangle_attr: &ast::Attribute,
1121                                              impl_generics: Option<&hir::Generics<'_>>,
1122                                              generics: &hir::Generics<'_>,
1123                                              span| {
1124             for param in
1125                 generics.params.iter().chain(impl_generics.map(|g| g.params).into_iter().flatten())
1126             {
1127                 match param.kind {
1128                     GenericParamKind::Lifetime { .. } => {}
1129                     GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1130                         cx.struct_span_lint(NO_MANGLE_GENERIC_ITEMS, span, |lint| {
1131                             lint.build("functions generic over types or consts must be mangled")
1132                                 .span_suggestion_short(
1133                                     no_mangle_attr.span,
1134                                     "remove this attribute",
1135                                     String::new(),
1136                                     // Use of `#[no_mangle]` suggests FFI intent; correct
1137                                     // fix may be to monomorphize source by hand
1138                                     Applicability::MaybeIncorrect,
1139                                 )
1140                                 .emit();
1141                         });
1142                         break;
1143                     }
1144                 }
1145             }
1146         };
1147         match it.kind {
1148             hir::ItemKind::Fn(.., ref generics, _) => {
1149                 if let Some(no_mangle_attr) = cx.sess().find_by_name(attrs, sym::no_mangle) {
1150                     check_no_mangle_on_generic_fn(no_mangle_attr, None, generics, it.span);
1151                 }
1152             }
1153             hir::ItemKind::Const(..) => {
1154                 if cx.sess().contains_name(attrs, sym::no_mangle) {
1155                     // Const items do not refer to a particular location in memory, and therefore
1156                     // don't have anything to attach a symbol to
1157                     cx.struct_span_lint(NO_MANGLE_CONST_ITEMS, it.span, |lint| {
1158                         let msg = "const items should never be `#[no_mangle]`";
1159                         let mut err = lint.build(msg);
1160
1161                         // account for "pub const" (#45562)
1162                         let start = cx
1163                             .tcx
1164                             .sess
1165                             .source_map()
1166                             .span_to_snippet(it.span)
1167                             .map(|snippet| snippet.find("const").unwrap_or(0))
1168                             .unwrap_or(0) as u32;
1169                         // `const` is 5 chars
1170                         let const_span = it.span.with_hi(BytePos(it.span.lo().0 + start + 5));
1171                         err.span_suggestion(
1172                             const_span,
1173                             "try a static value",
1174                             "pub static".to_owned(),
1175                             Applicability::MachineApplicable,
1176                         );
1177                         err.emit();
1178                     });
1179                 }
1180             }
1181             hir::ItemKind::Impl(hir::Impl { ref generics, items, .. }) => {
1182                 for it in items {
1183                     if let hir::AssocItemKind::Fn { .. } = it.kind {
1184                         if let Some(no_mangle_attr) = cx
1185                             .sess()
1186                             .find_by_name(cx.tcx.hir().attrs(it.id.hir_id()), sym::no_mangle)
1187                         {
1188                             check_no_mangle_on_generic_fn(
1189                                 no_mangle_attr,
1190                                 Some(generics),
1191                                 cx.tcx.hir().get_generics(it.id.def_id.to_def_id()).unwrap(),
1192                                 it.span,
1193                             );
1194                         }
1195                     }
1196                 }
1197             }
1198             _ => {}
1199         }
1200     }
1201 }
1202
1203 declare_lint! {
1204     /// The `mutable_transmutes` lint catches transmuting from `&T` to `&mut
1205     /// T` because it is [undefined behavior].
1206     ///
1207     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1208     ///
1209     /// ### Example
1210     ///
1211     /// ```rust,compile_fail
1212     /// unsafe {
1213     ///     let y = std::mem::transmute::<&i32, &mut i32>(&5);
1214     /// }
1215     /// ```
1216     ///
1217     /// {{produces}}
1218     ///
1219     /// ### Explanation
1220     ///
1221     /// Certain assumptions are made about aliasing of data, and this transmute
1222     /// violates those assumptions. Consider using [`UnsafeCell`] instead.
1223     ///
1224     /// [`UnsafeCell`]: https://doc.rust-lang.org/std/cell/struct.UnsafeCell.html
1225     MUTABLE_TRANSMUTES,
1226     Deny,
1227     "mutating transmuted &mut T from &T may cause undefined behavior"
1228 }
1229
1230 declare_lint_pass!(MutableTransmutes => [MUTABLE_TRANSMUTES]);
1231
1232 impl<'tcx> LateLintPass<'tcx> for MutableTransmutes {
1233     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &hir::Expr<'_>) {
1234         use rustc_target::spec::abi::Abi::RustIntrinsic;
1235         if let Some((&ty::Ref(_, _, from_mt), &ty::Ref(_, _, to_mt))) =
1236             get_transmute_from_to(cx, expr).map(|(ty1, ty2)| (ty1.kind(), ty2.kind()))
1237         {
1238             if to_mt == hir::Mutability::Mut && from_mt == hir::Mutability::Not {
1239                 let msg = "mutating transmuted &mut T from &T may cause undefined behavior, \
1240                                consider instead using an UnsafeCell";
1241                 cx.struct_span_lint(MUTABLE_TRANSMUTES, expr.span, |lint| lint.build(msg).emit());
1242             }
1243         }
1244
1245         fn get_transmute_from_to<'tcx>(
1246             cx: &LateContext<'tcx>,
1247             expr: &hir::Expr<'_>,
1248         ) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
1249             let def = if let hir::ExprKind::Path(ref qpath) = expr.kind {
1250                 cx.qpath_res(qpath, expr.hir_id)
1251             } else {
1252                 return None;
1253             };
1254             if let Res::Def(DefKind::Fn, did) = def {
1255                 if !def_id_is_transmute(cx, did) {
1256                     return None;
1257                 }
1258                 let sig = cx.typeck_results().node_type(expr.hir_id).fn_sig(cx.tcx);
1259                 let from = sig.inputs().skip_binder()[0];
1260                 let to = sig.output().skip_binder();
1261                 return Some((from, to));
1262             }
1263             None
1264         }
1265
1266         fn def_id_is_transmute(cx: &LateContext<'_>, def_id: DefId) -> bool {
1267             cx.tcx.fn_sig(def_id).abi() == RustIntrinsic
1268                 && cx.tcx.item_name(def_id) == sym::transmute
1269         }
1270     }
1271 }
1272
1273 declare_lint! {
1274     /// The `unstable_features` is deprecated and should no longer be used.
1275     UNSTABLE_FEATURES,
1276     Allow,
1277     "enabling unstable features (deprecated. do not use)"
1278 }
1279
1280 declare_lint_pass!(
1281     /// Forbids using the `#[feature(...)]` attribute
1282     UnstableFeatures => [UNSTABLE_FEATURES]
1283 );
1284
1285 impl<'tcx> LateLintPass<'tcx> for UnstableFeatures {
1286     fn check_attribute(&mut self, cx: &LateContext<'_>, attr: &ast::Attribute) {
1287         if attr.has_name(sym::feature) {
1288             if let Some(items) = attr.meta_item_list() {
1289                 for item in items {
1290                     cx.struct_span_lint(UNSTABLE_FEATURES, item.span(), |lint| {
1291                         lint.build("unstable feature").emit()
1292                     });
1293                 }
1294             }
1295         }
1296     }
1297 }
1298
1299 declare_lint! {
1300     /// The `unreachable_pub` lint triggers for `pub` items not reachable from
1301     /// the crate root.
1302     ///
1303     /// ### Example
1304     ///
1305     /// ```rust,compile_fail
1306     /// #![deny(unreachable_pub)]
1307     /// mod foo {
1308     ///     pub mod bar {
1309     ///
1310     ///     }
1311     /// }
1312     /// ```
1313     ///
1314     /// {{produces}}
1315     ///
1316     /// ### Explanation
1317     ///
1318     /// A bare `pub` visibility may be misleading if the item is not actually
1319     /// publicly exported from the crate. The `pub(crate)` visibility is
1320     /// recommended to be used instead, which more clearly expresses the intent
1321     /// that the item is only visible within its own crate.
1322     ///
1323     /// This lint is "allow" by default because it will trigger for a large
1324     /// amount existing Rust code, and has some false-positives. Eventually it
1325     /// is desired for this to become warn-by-default.
1326     pub UNREACHABLE_PUB,
1327     Allow,
1328     "`pub` items not reachable from crate root"
1329 }
1330
1331 declare_lint_pass!(
1332     /// Lint for items marked `pub` that aren't reachable from other crates.
1333     UnreachablePub => [UNREACHABLE_PUB]
1334 );
1335
1336 impl UnreachablePub {
1337     fn perform_lint(
1338         &self,
1339         cx: &LateContext<'_>,
1340         what: &str,
1341         def_id: LocalDefId,
1342         vis: &hir::Visibility<'_>,
1343         span: Span,
1344         exportable: bool,
1345     ) {
1346         let mut applicability = Applicability::MachineApplicable;
1347         match vis.node {
1348             hir::VisibilityKind::Public if !cx.access_levels.is_reachable(def_id) => {
1349                 if span.from_expansion() {
1350                     applicability = Applicability::MaybeIncorrect;
1351                 }
1352                 let def_span = cx.tcx.sess.source_map().guess_head_span(span);
1353                 cx.struct_span_lint(UNREACHABLE_PUB, def_span, |lint| {
1354                     let mut err = lint.build(&format!("unreachable `pub` {}", what));
1355                     let replacement = if cx.tcx.features().crate_visibility_modifier {
1356                         "crate"
1357                     } else {
1358                         "pub(crate)"
1359                     }
1360                     .to_owned();
1361
1362                     err.span_suggestion(
1363                         vis.span,
1364                         "consider restricting its visibility",
1365                         replacement,
1366                         applicability,
1367                     );
1368                     if exportable {
1369                         err.help("or consider exporting it for use by other crates");
1370                     }
1371                     err.emit();
1372                 });
1373             }
1374             _ => {}
1375         }
1376     }
1377 }
1378
1379 impl<'tcx> LateLintPass<'tcx> for UnreachablePub {
1380     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1381         self.perform_lint(cx, "item", item.def_id, &item.vis, item.span, true);
1382     }
1383
1384     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'tcx>) {
1385         self.perform_lint(
1386             cx,
1387             "item",
1388             foreign_item.def_id,
1389             &foreign_item.vis,
1390             foreign_item.span,
1391             true,
1392         );
1393     }
1394
1395     fn check_field_def(&mut self, cx: &LateContext<'_>, field: &hir::FieldDef<'_>) {
1396         let def_id = cx.tcx.hir().local_def_id(field.hir_id);
1397         self.perform_lint(cx, "field", def_id, &field.vis, field.span, false);
1398     }
1399
1400     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
1401         self.perform_lint(cx, "item", impl_item.def_id, &impl_item.vis, impl_item.span, false);
1402     }
1403 }
1404
1405 declare_lint! {
1406     /// The `type_alias_bounds` lint detects bounds in type aliases.
1407     ///
1408     /// ### Example
1409     ///
1410     /// ```rust
1411     /// type SendVec<T: Send> = Vec<T>;
1412     /// ```
1413     ///
1414     /// {{produces}}
1415     ///
1416     /// ### Explanation
1417     ///
1418     /// The trait bounds in a type alias are currently ignored, and should not
1419     /// be included to avoid confusion. This was previously allowed
1420     /// unintentionally; this may become a hard error in the future.
1421     TYPE_ALIAS_BOUNDS,
1422     Warn,
1423     "bounds in type aliases are not enforced"
1424 }
1425
1426 declare_lint_pass!(
1427     /// Lint for trait and lifetime bounds in type aliases being mostly ignored.
1428     /// They are relevant when using associated types, but otherwise neither checked
1429     /// at definition site nor enforced at use site.
1430     TypeAliasBounds => [TYPE_ALIAS_BOUNDS]
1431 );
1432
1433 impl TypeAliasBounds {
1434     fn is_type_variable_assoc(qpath: &hir::QPath<'_>) -> bool {
1435         match *qpath {
1436             hir::QPath::TypeRelative(ref ty, _) => {
1437                 // If this is a type variable, we found a `T::Assoc`.
1438                 match ty.kind {
1439                     hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
1440                         matches!(path.res, Res::Def(DefKind::TyParam, _))
1441                     }
1442                     _ => false,
1443                 }
1444             }
1445             hir::QPath::Resolved(..) | hir::QPath::LangItem(..) => false,
1446         }
1447     }
1448
1449     fn suggest_changing_assoc_types(ty: &hir::Ty<'_>, err: &mut DiagnosticBuilder<'_>) {
1450         // Access to associates types should use `<T as Bound>::Assoc`, which does not need a
1451         // bound.  Let's see if this type does that.
1452
1453         // We use a HIR visitor to walk the type.
1454         use rustc_hir::intravisit::{self, Visitor};
1455         struct WalkAssocTypes<'a, 'db> {
1456             err: &'a mut DiagnosticBuilder<'db>,
1457         }
1458         impl<'a, 'db, 'v> Visitor<'v> for WalkAssocTypes<'a, 'db> {
1459             type Map = intravisit::ErasedMap<'v>;
1460
1461             fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1462                 intravisit::NestedVisitorMap::None
1463             }
1464
1465             fn visit_qpath(&mut self, qpath: &'v hir::QPath<'v>, id: hir::HirId, span: Span) {
1466                 if TypeAliasBounds::is_type_variable_assoc(qpath) {
1467                     self.err.span_help(
1468                         span,
1469                         "use fully disambiguated paths (i.e., `<T as Trait>::Assoc`) to refer to \
1470                          associated types in type aliases",
1471                     );
1472                 }
1473                 intravisit::walk_qpath(self, qpath, id, span)
1474             }
1475         }
1476
1477         // Let's go for a walk!
1478         let mut visitor = WalkAssocTypes { err };
1479         visitor.visit_ty(ty);
1480     }
1481 }
1482
1483 impl<'tcx> LateLintPass<'tcx> for TypeAliasBounds {
1484     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1485         let (ty, type_alias_generics) = match item.kind {
1486             hir::ItemKind::TyAlias(ref ty, ref generics) => (&*ty, generics),
1487             _ => return,
1488         };
1489         if let hir::TyKind::OpaqueDef(..) = ty.kind {
1490             // Bounds are respected for `type X = impl Trait`
1491             return;
1492         }
1493         let mut suggested_changing_assoc_types = false;
1494         // There must not be a where clause
1495         if !type_alias_generics.where_clause.predicates.is_empty() {
1496             cx.lint(
1497                 TYPE_ALIAS_BOUNDS,
1498                 |lint| {
1499                     let mut err = lint.build("where clauses are not enforced in type aliases");
1500                     let spans: Vec<_> = type_alias_generics
1501                         .where_clause
1502                         .predicates
1503                         .iter()
1504                         .map(|pred| pred.span())
1505                         .collect();
1506                     err.set_span(spans);
1507                     err.span_suggestion(
1508                         type_alias_generics.where_clause.span_for_predicates_or_empty_place(),
1509                         "the clause will not be checked when the type alias is used, and should be removed",
1510                         String::new(),
1511                         Applicability::MachineApplicable,
1512                     );
1513                     if !suggested_changing_assoc_types {
1514                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1515                         suggested_changing_assoc_types = true;
1516                     }
1517                     err.emit();
1518                 },
1519             );
1520         }
1521         // The parameters must not have bounds
1522         for param in type_alias_generics.params.iter() {
1523             let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
1524             let suggestion = spans
1525                 .iter()
1526                 .map(|sp| {
1527                     let start = param.span.between(*sp); // Include the `:` in `T: Bound`.
1528                     (start.to(*sp), String::new())
1529                 })
1530                 .collect();
1531             if !spans.is_empty() {
1532                 cx.struct_span_lint(TYPE_ALIAS_BOUNDS, spans, |lint| {
1533                     let mut err =
1534                         lint.build("bounds on generic parameters are not enforced in type aliases");
1535                     let msg = "the bound will not be checked when the type alias is used, \
1536                                    and should be removed";
1537                     err.multipart_suggestion(&msg, suggestion, Applicability::MachineApplicable);
1538                     if !suggested_changing_assoc_types {
1539                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1540                         suggested_changing_assoc_types = true;
1541                     }
1542                     err.emit();
1543                 });
1544             }
1545         }
1546     }
1547 }
1548
1549 declare_lint_pass!(
1550     /// Lint constants that are erroneous.
1551     /// Without this lint, we might not get any diagnostic if the constant is
1552     /// unused within this crate, even though downstream crates can't use it
1553     /// without producing an error.
1554     UnusedBrokenConst => []
1555 );
1556
1557 impl<'tcx> LateLintPass<'tcx> for UnusedBrokenConst {
1558     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1559         match it.kind {
1560             hir::ItemKind::Const(_, body_id) => {
1561                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1562                 // trigger the query once for all constants since that will already report the errors
1563                 // FIXME: Use ensure here
1564                 let _ = cx.tcx.const_eval_poly(def_id);
1565             }
1566             hir::ItemKind::Static(_, _, body_id) => {
1567                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1568                 // FIXME: Use ensure here
1569                 let _ = cx.tcx.eval_static_initializer(def_id);
1570             }
1571             _ => {}
1572         }
1573     }
1574 }
1575
1576 declare_lint! {
1577     /// The `trivial_bounds` lint detects trait bounds that don't depend on
1578     /// any type parameters.
1579     ///
1580     /// ### Example
1581     ///
1582     /// ```rust
1583     /// #![feature(trivial_bounds)]
1584     /// pub struct A where i32: Copy;
1585     /// ```
1586     ///
1587     /// {{produces}}
1588     ///
1589     /// ### Explanation
1590     ///
1591     /// Usually you would not write a trait bound that you know is always
1592     /// true, or never true. However, when using macros, the macro may not
1593     /// know whether or not the constraint would hold or not at the time when
1594     /// generating the code. Currently, the compiler does not alert you if the
1595     /// constraint is always true, and generates an error if it is never true.
1596     /// The `trivial_bounds` feature changes this to be a warning in both
1597     /// cases, giving macros more freedom and flexibility to generate code,
1598     /// while still providing a signal when writing non-macro code that
1599     /// something is amiss.
1600     ///
1601     /// See [RFC 2056] for more details. This feature is currently only
1602     /// available on the nightly channel, see [tracking issue #48214].
1603     ///
1604     /// [RFC 2056]: https://github.com/rust-lang/rfcs/blob/master/text/2056-allow-trivial-where-clause-constraints.md
1605     /// [tracking issue #48214]: https://github.com/rust-lang/rust/issues/48214
1606     TRIVIAL_BOUNDS,
1607     Warn,
1608     "these bounds don't depend on an type parameters"
1609 }
1610
1611 declare_lint_pass!(
1612     /// Lint for trait and lifetime bounds that don't depend on type parameters
1613     /// which either do nothing, or stop the item from being used.
1614     TrivialConstraints => [TRIVIAL_BOUNDS]
1615 );
1616
1617 impl<'tcx> LateLintPass<'tcx> for TrivialConstraints {
1618     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
1619         use rustc_middle::ty::fold::TypeFoldable;
1620         use rustc_middle::ty::PredicateKind::*;
1621
1622         if cx.tcx.features().trivial_bounds {
1623             let predicates = cx.tcx.predicates_of(item.def_id);
1624             for &(predicate, span) in predicates.predicates {
1625                 let predicate_kind_name = match predicate.kind().skip_binder() {
1626                     Trait(..) => "Trait",
1627                     TypeOutlives(..) |
1628                     RegionOutlives(..) => "Lifetime",
1629
1630                     // Ignore projections, as they can only be global
1631                     // if the trait bound is global
1632                     Projection(..) |
1633                     // Ignore bounds that a user can't type
1634                     WellFormed(..) |
1635                     ObjectSafe(..) |
1636                     ClosureKind(..) |
1637                     Subtype(..) |
1638                     Coerce(..) |
1639                     ConstEvaluatable(..) |
1640                     ConstEquate(..) |
1641                     TypeWellFormedFromEnv(..) => continue,
1642                 };
1643                 if predicate.is_global(cx.tcx) {
1644                     cx.struct_span_lint(TRIVIAL_BOUNDS, span, |lint| {
1645                         lint.build(&format!(
1646                             "{} bound {} does not depend on any type \
1647                                 or lifetime parameters",
1648                             predicate_kind_name, predicate
1649                         ))
1650                         .emit()
1651                     });
1652                 }
1653             }
1654         }
1655     }
1656 }
1657
1658 declare_lint_pass!(
1659     /// Does nothing as a lint pass, but registers some `Lint`s
1660     /// which are used by other parts of the compiler.
1661     SoftLints => [
1662         WHILE_TRUE,
1663         BOX_POINTERS,
1664         NON_SHORTHAND_FIELD_PATTERNS,
1665         UNSAFE_CODE,
1666         MISSING_DOCS,
1667         MISSING_COPY_IMPLEMENTATIONS,
1668         MISSING_DEBUG_IMPLEMENTATIONS,
1669         ANONYMOUS_PARAMETERS,
1670         UNUSED_DOC_COMMENTS,
1671         NO_MANGLE_CONST_ITEMS,
1672         NO_MANGLE_GENERIC_ITEMS,
1673         MUTABLE_TRANSMUTES,
1674         UNSTABLE_FEATURES,
1675         UNREACHABLE_PUB,
1676         TYPE_ALIAS_BOUNDS,
1677         TRIVIAL_BOUNDS
1678     ]
1679 );
1680
1681 declare_lint! {
1682     /// The `ellipsis_inclusive_range_patterns` lint detects the [`...` range
1683     /// pattern], which is deprecated.
1684     ///
1685     /// [`...` range pattern]: https://doc.rust-lang.org/reference/patterns.html#range-patterns
1686     ///
1687     /// ### Example
1688     ///
1689     /// ```rust
1690     /// let x = 123;
1691     /// match x {
1692     ///     0...100 => {}
1693     ///     _ => {}
1694     /// }
1695     /// ```
1696     ///
1697     /// {{produces}}
1698     ///
1699     /// ### Explanation
1700     ///
1701     /// The `...` range pattern syntax was changed to `..=` to avoid potential
1702     /// confusion with the [`..` range expression]. Use the new form instead.
1703     ///
1704     /// [`..` range expression]: https://doc.rust-lang.org/reference/expressions/range-expr.html
1705     pub ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
1706     Warn,
1707     "`...` range patterns are deprecated",
1708     @future_incompatible = FutureIncompatibleInfo {
1709         reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>",
1710         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
1711     };
1712 }
1713
1714 #[derive(Default)]
1715 pub struct EllipsisInclusiveRangePatterns {
1716     /// If `Some(_)`, suppress all subsequent pattern
1717     /// warnings for better diagnostics.
1718     node_id: Option<ast::NodeId>,
1719 }
1720
1721 impl_lint_pass!(EllipsisInclusiveRangePatterns => [ELLIPSIS_INCLUSIVE_RANGE_PATTERNS]);
1722
1723 impl EarlyLintPass for EllipsisInclusiveRangePatterns {
1724     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &ast::Pat) {
1725         if self.node_id.is_some() {
1726             // Don't recursively warn about patterns inside range endpoints.
1727             return;
1728         }
1729
1730         use self::ast::{PatKind, RangeSyntax::DotDotDot};
1731
1732         /// If `pat` is a `...` pattern, return the start and end of the range, as well as the span
1733         /// corresponding to the ellipsis.
1734         fn matches_ellipsis_pat(pat: &ast::Pat) -> Option<(Option<&Expr>, &Expr, Span)> {
1735             match &pat.kind {
1736                 PatKind::Range(
1737                     a,
1738                     Some(b),
1739                     Spanned { span, node: RangeEnd::Included(DotDotDot) },
1740                 ) => Some((a.as_deref(), b, *span)),
1741                 _ => None,
1742             }
1743         }
1744
1745         let (parenthesise, endpoints) = match &pat.kind {
1746             PatKind::Ref(subpat, _) => (true, matches_ellipsis_pat(&subpat)),
1747             _ => (false, matches_ellipsis_pat(pat)),
1748         };
1749
1750         if let Some((start, end, join)) = endpoints {
1751             let msg = "`...` range patterns are deprecated";
1752             let suggestion = "use `..=` for an inclusive range";
1753             if parenthesise {
1754                 self.node_id = Some(pat.id);
1755                 let end = expr_to_string(&end);
1756                 let replace = match start {
1757                     Some(start) => format!("&({}..={})", expr_to_string(&start), end),
1758                     None => format!("&(..={})", end),
1759                 };
1760                 if join.edition() >= Edition::Edition2021 {
1761                     let mut err =
1762                         rustc_errors::struct_span_err!(cx.sess, pat.span, E0783, "{}", msg,);
1763                     err.span_suggestion(
1764                         pat.span,
1765                         suggestion,
1766                         replace,
1767                         Applicability::MachineApplicable,
1768                     )
1769                     .emit();
1770                 } else {
1771                     cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, pat.span, |lint| {
1772                         lint.build(msg)
1773                             .span_suggestion(
1774                                 pat.span,
1775                                 suggestion,
1776                                 replace,
1777                                 Applicability::MachineApplicable,
1778                             )
1779                             .emit();
1780                     });
1781                 }
1782             } else {
1783                 let replace = "..=".to_owned();
1784                 if join.edition() >= Edition::Edition2021 {
1785                     let mut err =
1786                         rustc_errors::struct_span_err!(cx.sess, pat.span, E0783, "{}", msg,);
1787                     err.span_suggestion_short(
1788                         join,
1789                         suggestion,
1790                         replace,
1791                         Applicability::MachineApplicable,
1792                     )
1793                     .emit();
1794                 } else {
1795                     cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, join, |lint| {
1796                         lint.build(msg)
1797                             .span_suggestion_short(
1798                                 join,
1799                                 suggestion,
1800                                 replace,
1801                                 Applicability::MachineApplicable,
1802                             )
1803                             .emit();
1804                     });
1805                 }
1806             };
1807         }
1808     }
1809
1810     fn check_pat_post(&mut self, _cx: &EarlyContext<'_>, pat: &ast::Pat) {
1811         if let Some(node_id) = self.node_id {
1812             if pat.id == node_id {
1813                 self.node_id = None
1814             }
1815         }
1816     }
1817 }
1818
1819 declare_lint! {
1820     /// The `unnameable_test_items` lint detects [`#[test]`][test] functions
1821     /// that are not able to be run by the test harness because they are in a
1822     /// position where they are not nameable.
1823     ///
1824     /// [test]: https://doc.rust-lang.org/reference/attributes/testing.html#the-test-attribute
1825     ///
1826     /// ### Example
1827     ///
1828     /// ```rust,test
1829     /// fn main() {
1830     ///     #[test]
1831     ///     fn foo() {
1832     ///         // This test will not fail because it does not run.
1833     ///         assert_eq!(1, 2);
1834     ///     }
1835     /// }
1836     /// ```
1837     ///
1838     /// {{produces}}
1839     ///
1840     /// ### Explanation
1841     ///
1842     /// In order for the test harness to run a test, the test function must be
1843     /// located in a position where it can be accessed from the crate root.
1844     /// This generally means it must be defined in a module, and not anywhere
1845     /// else such as inside another function. The compiler previously allowed
1846     /// this without an error, so a lint was added as an alert that a test is
1847     /// not being used. Whether or not this should be allowed has not yet been
1848     /// decided, see [RFC 2471] and [issue #36629].
1849     ///
1850     /// [RFC 2471]: https://github.com/rust-lang/rfcs/pull/2471#issuecomment-397414443
1851     /// [issue #36629]: https://github.com/rust-lang/rust/issues/36629
1852     UNNAMEABLE_TEST_ITEMS,
1853     Warn,
1854     "detects an item that cannot be named being marked as `#[test_case]`",
1855     report_in_external_macro
1856 }
1857
1858 pub struct UnnameableTestItems {
1859     boundary: Option<LocalDefId>, // Id of the item under which things are not nameable
1860     items_nameable: bool,
1861 }
1862
1863 impl_lint_pass!(UnnameableTestItems => [UNNAMEABLE_TEST_ITEMS]);
1864
1865 impl UnnameableTestItems {
1866     pub fn new() -> Self {
1867         Self { boundary: None, items_nameable: true }
1868     }
1869 }
1870
1871 impl<'tcx> LateLintPass<'tcx> for UnnameableTestItems {
1872     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1873         if self.items_nameable {
1874             if let hir::ItemKind::Mod(..) = it.kind {
1875             } else {
1876                 self.items_nameable = false;
1877                 self.boundary = Some(it.def_id);
1878             }
1879             return;
1880         }
1881
1882         let attrs = cx.tcx.hir().attrs(it.hir_id());
1883         if let Some(attr) = cx.sess().find_by_name(attrs, sym::rustc_test_marker) {
1884             cx.struct_span_lint(UNNAMEABLE_TEST_ITEMS, attr.span, |lint| {
1885                 lint.build("cannot test inner items").emit()
1886             });
1887         }
1888     }
1889
1890     fn check_item_post(&mut self, _cx: &LateContext<'_>, it: &hir::Item<'_>) {
1891         if !self.items_nameable && self.boundary == Some(it.def_id) {
1892             self.items_nameable = true;
1893         }
1894     }
1895 }
1896
1897 declare_lint! {
1898     /// The `keyword_idents` lint detects edition keywords being used as an
1899     /// identifier.
1900     ///
1901     /// ### Example
1902     ///
1903     /// ```rust,edition2015,compile_fail
1904     /// #![deny(keyword_idents)]
1905     /// // edition 2015
1906     /// fn dyn() {}
1907     /// ```
1908     ///
1909     /// {{produces}}
1910     ///
1911     /// ### Explanation
1912     ///
1913     /// Rust [editions] allow the language to evolve without breaking
1914     /// backwards compatibility. This lint catches code that uses new keywords
1915     /// that are added to the language that are used as identifiers (such as a
1916     /// variable name, function name, etc.). If you switch the compiler to a
1917     /// new edition without updating the code, then it will fail to compile if
1918     /// you are using a new keyword as an identifier.
1919     ///
1920     /// You can manually change the identifiers to a non-keyword, or use a
1921     /// [raw identifier], for example `r#dyn`, to transition to a new edition.
1922     ///
1923     /// This lint solves the problem automatically. It is "allow" by default
1924     /// because the code is perfectly valid in older editions. The [`cargo
1925     /// fix`] tool with the `--edition` flag will switch this lint to "warn"
1926     /// and automatically apply the suggested fix from the compiler (which is
1927     /// to use a raw identifier). This provides a completely automated way to
1928     /// update old code for a new edition.
1929     ///
1930     /// [editions]: https://doc.rust-lang.org/edition-guide/
1931     /// [raw identifier]: https://doc.rust-lang.org/reference/identifiers.html
1932     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
1933     pub KEYWORD_IDENTS,
1934     Allow,
1935     "detects edition keywords being used as an identifier",
1936     @future_incompatible = FutureIncompatibleInfo {
1937         reference: "issue #49716 <https://github.com/rust-lang/rust/issues/49716>",
1938         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
1939     };
1940 }
1941
1942 declare_lint_pass!(
1943     /// Check for uses of edition keywords used as an identifier.
1944     KeywordIdents => [KEYWORD_IDENTS]
1945 );
1946
1947 struct UnderMacro(bool);
1948
1949 impl KeywordIdents {
1950     fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: TokenStream) {
1951         for tt in tokens.into_trees() {
1952             match tt {
1953                 // Only report non-raw idents.
1954                 TokenTree::Token(token) => {
1955                     if let Some((ident, false)) = token.ident() {
1956                         self.check_ident_token(cx, UnderMacro(true), ident);
1957                     }
1958                 }
1959                 TokenTree::Delimited(_, _, tts) => self.check_tokens(cx, tts),
1960             }
1961         }
1962     }
1963
1964     fn check_ident_token(
1965         &mut self,
1966         cx: &EarlyContext<'_>,
1967         UnderMacro(under_macro): UnderMacro,
1968         ident: Ident,
1969     ) {
1970         let next_edition = match cx.sess.edition() {
1971             Edition::Edition2015 => {
1972                 match ident.name {
1973                     kw::Async | kw::Await | kw::Try => Edition::Edition2018,
1974
1975                     // rust-lang/rust#56327: Conservatively do not
1976                     // attempt to report occurrences of `dyn` within
1977                     // macro definitions or invocations, because `dyn`
1978                     // can legitimately occur as a contextual keyword
1979                     // in 2015 code denoting its 2018 meaning, and we
1980                     // do not want rustfix to inject bugs into working
1981                     // code by rewriting such occurrences.
1982                     //
1983                     // But if we see `dyn` outside of a macro, we know
1984                     // its precise role in the parsed AST and thus are
1985                     // assured this is truly an attempt to use it as
1986                     // an identifier.
1987                     kw::Dyn if !under_macro => Edition::Edition2018,
1988
1989                     _ => return,
1990                 }
1991             }
1992
1993             // There are no new keywords yet for the 2018 edition and beyond.
1994             _ => return,
1995         };
1996
1997         // Don't lint `r#foo`.
1998         if cx.sess.parse_sess.raw_identifier_spans.borrow().contains(&ident.span) {
1999             return;
2000         }
2001
2002         cx.struct_span_lint(KEYWORD_IDENTS, ident.span, |lint| {
2003             lint.build(&format!("`{}` is a keyword in the {} edition", ident, next_edition))
2004                 .span_suggestion(
2005                     ident.span,
2006                     "you can use a raw identifier to stay compatible",
2007                     format!("r#{}", ident),
2008                     Applicability::MachineApplicable,
2009                 )
2010                 .emit()
2011         });
2012     }
2013 }
2014
2015 impl EarlyLintPass for KeywordIdents {
2016     fn check_mac_def(&mut self, cx: &EarlyContext<'_>, mac_def: &ast::MacroDef, _id: ast::NodeId) {
2017         self.check_tokens(cx, mac_def.body.inner_tokens());
2018     }
2019     fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::MacCall) {
2020         self.check_tokens(cx, mac.args.inner_tokens());
2021     }
2022     fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: Ident) {
2023         self.check_ident_token(cx, UnderMacro(false), ident);
2024     }
2025 }
2026
2027 declare_lint_pass!(ExplicitOutlivesRequirements => [EXPLICIT_OUTLIVES_REQUIREMENTS]);
2028
2029 impl ExplicitOutlivesRequirements {
2030     fn lifetimes_outliving_lifetime<'tcx>(
2031         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2032         index: u32,
2033     ) -> Vec<ty::Region<'tcx>> {
2034         inferred_outlives
2035             .iter()
2036             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
2037                 ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => match a {
2038                     ty::ReEarlyBound(ebr) if ebr.index == index => Some(b),
2039                     _ => None,
2040                 },
2041                 _ => None,
2042             })
2043             .collect()
2044     }
2045
2046     fn lifetimes_outliving_type<'tcx>(
2047         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2048         index: u32,
2049     ) -> Vec<ty::Region<'tcx>> {
2050         inferred_outlives
2051             .iter()
2052             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
2053                 ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
2054                     a.is_param(index).then_some(b)
2055                 }
2056                 _ => None,
2057             })
2058             .collect()
2059     }
2060
2061     fn collect_outlived_lifetimes<'tcx>(
2062         &self,
2063         param: &'tcx hir::GenericParam<'tcx>,
2064         tcx: TyCtxt<'tcx>,
2065         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2066         ty_generics: &'tcx ty::Generics,
2067     ) -> Vec<ty::Region<'tcx>> {
2068         let index =
2069             ty_generics.param_def_id_to_index[&tcx.hir().local_def_id(param.hir_id).to_def_id()];
2070
2071         match param.kind {
2072             hir::GenericParamKind::Lifetime { .. } => {
2073                 Self::lifetimes_outliving_lifetime(inferred_outlives, index)
2074             }
2075             hir::GenericParamKind::Type { .. } => {
2076                 Self::lifetimes_outliving_type(inferred_outlives, index)
2077             }
2078             hir::GenericParamKind::Const { .. } => Vec::new(),
2079         }
2080     }
2081
2082     fn collect_outlives_bound_spans<'tcx>(
2083         &self,
2084         tcx: TyCtxt<'tcx>,
2085         bounds: &hir::GenericBounds<'_>,
2086         inferred_outlives: &[ty::Region<'tcx>],
2087         infer_static: bool,
2088     ) -> Vec<(usize, Span)> {
2089         use rustc_middle::middle::resolve_lifetime::Region;
2090
2091         bounds
2092             .iter()
2093             .enumerate()
2094             .filter_map(|(i, bound)| {
2095                 if let hir::GenericBound::Outlives(lifetime) = bound {
2096                     let is_inferred = match tcx.named_region(lifetime.hir_id) {
2097                         Some(Region::Static) if infer_static => {
2098                             inferred_outlives.iter().any(|r| matches!(r, ty::ReStatic))
2099                         }
2100                         Some(Region::EarlyBound(index, ..)) => inferred_outlives.iter().any(|r| {
2101                             if let ty::ReEarlyBound(ebr) = r { ebr.index == index } else { false }
2102                         }),
2103                         _ => false,
2104                     };
2105                     is_inferred.then_some((i, bound.span()))
2106                 } else {
2107                     None
2108                 }
2109             })
2110             .collect()
2111     }
2112
2113     fn consolidate_outlives_bound_spans(
2114         &self,
2115         lo: Span,
2116         bounds: &hir::GenericBounds<'_>,
2117         bound_spans: Vec<(usize, Span)>,
2118     ) -> Vec<Span> {
2119         if bounds.is_empty() {
2120             return Vec::new();
2121         }
2122         if bound_spans.len() == bounds.len() {
2123             let (_, last_bound_span) = bound_spans[bound_spans.len() - 1];
2124             // If all bounds are inferable, we want to delete the colon, so
2125             // start from just after the parameter (span passed as argument)
2126             vec![lo.to(last_bound_span)]
2127         } else {
2128             let mut merged = Vec::new();
2129             let mut last_merged_i = None;
2130
2131             let mut from_start = true;
2132             for (i, bound_span) in bound_spans {
2133                 match last_merged_i {
2134                     // If the first bound is inferable, our span should also eat the leading `+`.
2135                     None if i == 0 => {
2136                         merged.push(bound_span.to(bounds[1].span().shrink_to_lo()));
2137                         last_merged_i = Some(0);
2138                     }
2139                     // If consecutive bounds are inferable, merge their spans
2140                     Some(h) if i == h + 1 => {
2141                         if let Some(tail) = merged.last_mut() {
2142                             // Also eat the trailing `+` if the first
2143                             // more-than-one bound is inferable
2144                             let to_span = if from_start && i < bounds.len() {
2145                                 bounds[i + 1].span().shrink_to_lo()
2146                             } else {
2147                                 bound_span
2148                             };
2149                             *tail = tail.to(to_span);
2150                             last_merged_i = Some(i);
2151                         } else {
2152                             bug!("another bound-span visited earlier");
2153                         }
2154                     }
2155                     _ => {
2156                         // When we find a non-inferable bound, subsequent inferable bounds
2157                         // won't be consecutive from the start (and we'll eat the leading
2158                         // `+` rather than the trailing one)
2159                         from_start = false;
2160                         merged.push(bounds[i - 1].span().shrink_to_hi().to(bound_span));
2161                         last_merged_i = Some(i);
2162                     }
2163                 }
2164             }
2165             merged
2166         }
2167     }
2168 }
2169
2170 impl<'tcx> LateLintPass<'tcx> for ExplicitOutlivesRequirements {
2171     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
2172         use rustc_middle::middle::resolve_lifetime::Region;
2173
2174         let infer_static = cx.tcx.features().infer_static_outlives_requirements;
2175         let def_id = item.def_id;
2176         if let hir::ItemKind::Struct(_, ref hir_generics)
2177         | hir::ItemKind::Enum(_, ref hir_generics)
2178         | hir::ItemKind::Union(_, ref hir_generics) = item.kind
2179         {
2180             let inferred_outlives = cx.tcx.inferred_outlives_of(def_id);
2181             if inferred_outlives.is_empty() {
2182                 return;
2183             }
2184
2185             let ty_generics = cx.tcx.generics_of(def_id);
2186
2187             let mut bound_count = 0;
2188             let mut lint_spans = Vec::new();
2189
2190             for param in hir_generics.params {
2191                 let has_lifetime_bounds = param
2192                     .bounds
2193                     .iter()
2194                     .any(|bound| matches!(bound, hir::GenericBound::Outlives(_)));
2195                 if !has_lifetime_bounds {
2196                     continue;
2197                 }
2198
2199                 let relevant_lifetimes =
2200                     self.collect_outlived_lifetimes(param, cx.tcx, inferred_outlives, ty_generics);
2201                 if relevant_lifetimes.is_empty() {
2202                     continue;
2203                 }
2204
2205                 let bound_spans = self.collect_outlives_bound_spans(
2206                     cx.tcx,
2207                     &param.bounds,
2208                     &relevant_lifetimes,
2209                     infer_static,
2210                 );
2211                 bound_count += bound_spans.len();
2212                 lint_spans.extend(self.consolidate_outlives_bound_spans(
2213                     param.span.shrink_to_hi(),
2214                     &param.bounds,
2215                     bound_spans,
2216                 ));
2217             }
2218
2219             let mut where_lint_spans = Vec::new();
2220             let mut dropped_predicate_count = 0;
2221             let num_predicates = hir_generics.where_clause.predicates.len();
2222             for (i, where_predicate) in hir_generics.where_clause.predicates.iter().enumerate() {
2223                 let (relevant_lifetimes, bounds, span) = match where_predicate {
2224                     hir::WherePredicate::RegionPredicate(predicate) => {
2225                         if let Some(Region::EarlyBound(index, ..)) =
2226                             cx.tcx.named_region(predicate.lifetime.hir_id)
2227                         {
2228                             (
2229                                 Self::lifetimes_outliving_lifetime(inferred_outlives, index),
2230                                 &predicate.bounds,
2231                                 predicate.span,
2232                             )
2233                         } else {
2234                             continue;
2235                         }
2236                     }
2237                     hir::WherePredicate::BoundPredicate(predicate) => {
2238                         // FIXME we can also infer bounds on associated types,
2239                         // and should check for them here.
2240                         match predicate.bounded_ty.kind {
2241                             hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
2242                                 if let Res::Def(DefKind::TyParam, def_id) = path.res {
2243                                     let index = ty_generics.param_def_id_to_index[&def_id];
2244                                     (
2245                                         Self::lifetimes_outliving_type(inferred_outlives, index),
2246                                         &predicate.bounds,
2247                                         predicate.span,
2248                                     )
2249                                 } else {
2250                                     continue;
2251                                 }
2252                             }
2253                             _ => {
2254                                 continue;
2255                             }
2256                         }
2257                     }
2258                     _ => continue,
2259                 };
2260                 if relevant_lifetimes.is_empty() {
2261                     continue;
2262                 }
2263
2264                 let bound_spans = self.collect_outlives_bound_spans(
2265                     cx.tcx,
2266                     bounds,
2267                     &relevant_lifetimes,
2268                     infer_static,
2269                 );
2270                 bound_count += bound_spans.len();
2271
2272                 let drop_predicate = bound_spans.len() == bounds.len();
2273                 if drop_predicate {
2274                     dropped_predicate_count += 1;
2275                 }
2276
2277                 // If all the bounds on a predicate were inferable and there are
2278                 // further predicates, we want to eat the trailing comma.
2279                 if drop_predicate && i + 1 < num_predicates {
2280                     let next_predicate_span = hir_generics.where_clause.predicates[i + 1].span();
2281                     where_lint_spans.push(span.to(next_predicate_span.shrink_to_lo()));
2282                 } else {
2283                     where_lint_spans.extend(self.consolidate_outlives_bound_spans(
2284                         span.shrink_to_lo(),
2285                         bounds,
2286                         bound_spans,
2287                     ));
2288                 }
2289             }
2290
2291             // If all predicates are inferable, drop the entire clause
2292             // (including the `where`)
2293             if num_predicates > 0 && dropped_predicate_count == num_predicates {
2294                 let where_span = hir_generics
2295                     .where_clause
2296                     .span()
2297                     .expect("span of (nonempty) where clause should exist");
2298                 // Extend the where clause back to the closing `>` of the
2299                 // generics, except for tuple struct, which have the `where`
2300                 // after the fields of the struct.
2301                 let full_where_span =
2302                     if let hir::ItemKind::Struct(hir::VariantData::Tuple(..), _) = item.kind {
2303                         where_span
2304                     } else {
2305                         hir_generics.span.shrink_to_hi().to(where_span)
2306                     };
2307                 lint_spans.push(full_where_span);
2308             } else {
2309                 lint_spans.extend(where_lint_spans);
2310             }
2311
2312             if !lint_spans.is_empty() {
2313                 cx.struct_span_lint(EXPLICIT_OUTLIVES_REQUIREMENTS, lint_spans.clone(), |lint| {
2314                     lint.build("outlives requirements can be inferred")
2315                         .multipart_suggestion(
2316                             if bound_count == 1 {
2317                                 "remove this bound"
2318                             } else {
2319                                 "remove these bounds"
2320                             },
2321                             lint_spans
2322                                 .into_iter()
2323                                 .map(|span| (span, "".to_owned()))
2324                                 .collect::<Vec<_>>(),
2325                             Applicability::MachineApplicable,
2326                         )
2327                         .emit();
2328                 });
2329             }
2330         }
2331     }
2332 }
2333
2334 declare_lint! {
2335     /// The `incomplete_features` lint detects unstable features enabled with
2336     /// the [`feature` attribute] that may function improperly in some or all
2337     /// cases.
2338     ///
2339     /// [`feature` attribute]: https://doc.rust-lang.org/nightly/unstable-book/
2340     ///
2341     /// ### Example
2342     ///
2343     /// ```rust
2344     /// #![feature(generic_const_exprs)]
2345     /// ```
2346     ///
2347     /// {{produces}}
2348     ///
2349     /// ### Explanation
2350     ///
2351     /// Although it is encouraged for people to experiment with unstable
2352     /// features, some of them are known to be incomplete or faulty. This lint
2353     /// is a signal that the feature has not yet been finished, and you may
2354     /// experience problems with it.
2355     pub INCOMPLETE_FEATURES,
2356     Warn,
2357     "incomplete features that may function improperly in some or all cases"
2358 }
2359
2360 declare_lint_pass!(
2361     /// Check for used feature gates in `INCOMPLETE_FEATURES` in `rustc_feature/src/active.rs`.
2362     IncompleteFeatures => [INCOMPLETE_FEATURES]
2363 );
2364
2365 impl EarlyLintPass for IncompleteFeatures {
2366     fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
2367         let features = cx.sess.features_untracked();
2368         features
2369             .declared_lang_features
2370             .iter()
2371             .map(|(name, span, _)| (name, span))
2372             .chain(features.declared_lib_features.iter().map(|(name, span)| (name, span)))
2373             .filter(|(&name, _)| features.incomplete(name))
2374             .for_each(|(&name, &span)| {
2375                 cx.struct_span_lint(INCOMPLETE_FEATURES, span, |lint| {
2376                     let mut builder = lint.build(&format!(
2377                         "the feature `{}` is incomplete and may not be safe to use \
2378                          and/or cause compiler crashes",
2379                         name,
2380                     ));
2381                     if let Some(n) = rustc_feature::find_feature_issue(name, GateIssue::Language) {
2382                         builder.note(&format!(
2383                             "see issue #{} <https://github.com/rust-lang/rust/issues/{}> \
2384                              for more information",
2385                             n, n,
2386                         ));
2387                     }
2388                     if HAS_MIN_FEATURES.contains(&name) {
2389                         builder.help(&format!(
2390                             "consider using `min_{}` instead, which is more stable and complete",
2391                             name,
2392                         ));
2393                     }
2394                     builder.emit();
2395                 })
2396             });
2397     }
2398 }
2399
2400 const HAS_MIN_FEATURES: &[Symbol] = &[sym::specialization];
2401
2402 declare_lint! {
2403     /// The `invalid_value` lint detects creating a value that is not valid,
2404     /// such as a null reference.
2405     ///
2406     /// ### Example
2407     ///
2408     /// ```rust,no_run
2409     /// # #![allow(unused)]
2410     /// unsafe {
2411     ///     let x: &'static i32 = std::mem::zeroed();
2412     /// }
2413     /// ```
2414     ///
2415     /// {{produces}}
2416     ///
2417     /// ### Explanation
2418     ///
2419     /// In some situations the compiler can detect that the code is creating
2420     /// an invalid value, which should be avoided.
2421     ///
2422     /// In particular, this lint will check for improper use of
2423     /// [`mem::zeroed`], [`mem::uninitialized`], [`mem::transmute`], and
2424     /// [`MaybeUninit::assume_init`] that can cause [undefined behavior]. The
2425     /// lint should provide extra information to indicate what the problem is
2426     /// and a possible solution.
2427     ///
2428     /// [`mem::zeroed`]: https://doc.rust-lang.org/std/mem/fn.zeroed.html
2429     /// [`mem::uninitialized`]: https://doc.rust-lang.org/std/mem/fn.uninitialized.html
2430     /// [`mem::transmute`]: https://doc.rust-lang.org/std/mem/fn.transmute.html
2431     /// [`MaybeUninit::assume_init`]: https://doc.rust-lang.org/std/mem/union.MaybeUninit.html#method.assume_init
2432     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
2433     pub INVALID_VALUE,
2434     Warn,
2435     "an invalid value is being created (such as a null reference)"
2436 }
2437
2438 declare_lint_pass!(InvalidValue => [INVALID_VALUE]);
2439
2440 impl<'tcx> LateLintPass<'tcx> for InvalidValue {
2441     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
2442         #[derive(Debug, Copy, Clone, PartialEq)]
2443         enum InitKind {
2444             Zeroed,
2445             Uninit,
2446         }
2447
2448         /// Information about why a type cannot be initialized this way.
2449         /// Contains an error message and optionally a span to point at.
2450         type InitError = (String, Option<Span>);
2451
2452         /// Test if this constant is all-0.
2453         fn is_zero(expr: &hir::Expr<'_>) -> bool {
2454             use hir::ExprKind::*;
2455             use rustc_ast::LitKind::*;
2456             match &expr.kind {
2457                 Lit(lit) => {
2458                     if let Int(i, _) = lit.node {
2459                         i == 0
2460                     } else {
2461                         false
2462                     }
2463                 }
2464                 Tup(tup) => tup.iter().all(is_zero),
2465                 _ => false,
2466             }
2467         }
2468
2469         /// Determine if this expression is a "dangerous initialization".
2470         fn is_dangerous_init(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> Option<InitKind> {
2471             if let hir::ExprKind::Call(ref path_expr, ref args) = expr.kind {
2472                 // Find calls to `mem::{uninitialized,zeroed}` methods.
2473                 if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2474                     let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2475
2476                     if cx.tcx.is_diagnostic_item(sym::mem_zeroed, def_id) {
2477                         return Some(InitKind::Zeroed);
2478                     } else if cx.tcx.is_diagnostic_item(sym::mem_uninitialized, def_id) {
2479                         return Some(InitKind::Uninit);
2480                     } else if cx.tcx.is_diagnostic_item(sym::transmute, def_id) && is_zero(&args[0])
2481                     {
2482                         return Some(InitKind::Zeroed);
2483                     }
2484                 }
2485             } else if let hir::ExprKind::MethodCall(_, _, ref args, _) = expr.kind {
2486                 // Find problematic calls to `MaybeUninit::assume_init`.
2487                 let def_id = cx.typeck_results().type_dependent_def_id(expr.hir_id)?;
2488                 if cx.tcx.is_diagnostic_item(sym::assume_init, def_id) {
2489                     // This is a call to *some* method named `assume_init`.
2490                     // See if the `self` parameter is one of the dangerous constructors.
2491                     if let hir::ExprKind::Call(ref path_expr, _) = args[0].kind {
2492                         if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2493                             let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2494
2495                             if cx.tcx.is_diagnostic_item(sym::maybe_uninit_zeroed, def_id) {
2496                                 return Some(InitKind::Zeroed);
2497                             } else if cx.tcx.is_diagnostic_item(sym::maybe_uninit_uninit, def_id) {
2498                                 return Some(InitKind::Uninit);
2499                             }
2500                         }
2501                     }
2502                 }
2503             }
2504
2505             None
2506         }
2507
2508         /// Test if this enum has several actually "existing" variants.
2509         /// Zero-sized uninhabited variants do not always have a tag assigned and thus do not "exist".
2510         fn is_multi_variant(adt: &ty::AdtDef) -> bool {
2511             // As an approximation, we only count dataless variants. Those are definitely inhabited.
2512             let existing_variants = adt.variants.iter().filter(|v| v.fields.is_empty()).count();
2513             existing_variants > 1
2514         }
2515
2516         /// Return `Some` only if we are sure this type does *not*
2517         /// allow zero initialization.
2518         fn ty_find_init_error<'tcx>(
2519             tcx: TyCtxt<'tcx>,
2520             ty: Ty<'tcx>,
2521             init: InitKind,
2522         ) -> Option<InitError> {
2523             use rustc_middle::ty::TyKind::*;
2524             match ty.kind() {
2525                 // Primitive types that don't like 0 as a value.
2526                 Ref(..) => Some(("references must be non-null".to_string(), None)),
2527                 Adt(..) if ty.is_box() => Some(("`Box` must be non-null".to_string(), None)),
2528                 FnPtr(..) => Some(("function pointers must be non-null".to_string(), None)),
2529                 Never => Some(("the `!` type has no valid value".to_string(), None)),
2530                 RawPtr(tm) if matches!(tm.ty.kind(), Dynamic(..)) =>
2531                 // raw ptr to dyn Trait
2532                 {
2533                     Some(("the vtable of a wide raw pointer must be non-null".to_string(), None))
2534                 }
2535                 // Primitive types with other constraints.
2536                 Bool if init == InitKind::Uninit => {
2537                     Some(("booleans must be either `true` or `false`".to_string(), None))
2538                 }
2539                 Char if init == InitKind::Uninit => {
2540                     Some(("characters must be a valid Unicode codepoint".to_string(), None))
2541                 }
2542                 // Recurse and checks for some compound types.
2543                 Adt(adt_def, substs) if !adt_def.is_union() => {
2544                     // First check if this ADT has a layout attribute (like `NonNull` and friends).
2545                     use std::ops::Bound;
2546                     match tcx.layout_scalar_valid_range(adt_def.did) {
2547                         // We exploit here that `layout_scalar_valid_range` will never
2548                         // return `Bound::Excluded`.  (And we have tests checking that we
2549                         // handle the attribute correctly.)
2550                         (Bound::Included(lo), _) if lo > 0 => {
2551                             return Some((format!("`{}` must be non-null", ty), None));
2552                         }
2553                         (Bound::Included(_), _) | (_, Bound::Included(_))
2554                             if init == InitKind::Uninit =>
2555                         {
2556                             return Some((
2557                                 format!(
2558                                     "`{}` must be initialized inside its custom valid range",
2559                                     ty,
2560                                 ),
2561                                 None,
2562                             ));
2563                         }
2564                         _ => {}
2565                     }
2566                     // Now, recurse.
2567                     match adt_def.variants.len() {
2568                         0 => Some(("enums with no variants have no valid value".to_string(), None)),
2569                         1 => {
2570                             // Struct, or enum with exactly one variant.
2571                             // Proceed recursively, check all fields.
2572                             let variant = &adt_def.variants[VariantIdx::from_u32(0)];
2573                             variant.fields.iter().find_map(|field| {
2574                                 ty_find_init_error(tcx, field.ty(tcx, substs), init).map(
2575                                     |(mut msg, span)| {
2576                                         if span.is_none() {
2577                                             // Point to this field, should be helpful for figuring
2578                                             // out where the source of the error is.
2579                                             let span = tcx.def_span(field.did);
2580                                             write!(
2581                                                 &mut msg,
2582                                                 " (in this {} field)",
2583                                                 adt_def.descr()
2584                                             )
2585                                             .unwrap();
2586                                             (msg, Some(span))
2587                                         } else {
2588                                             // Just forward.
2589                                             (msg, span)
2590                                         }
2591                                     },
2592                                 )
2593                             })
2594                         }
2595                         // Multi-variant enum.
2596                         _ => {
2597                             if init == InitKind::Uninit && is_multi_variant(adt_def) {
2598                                 let span = tcx.def_span(adt_def.did);
2599                                 Some((
2600                                     "enums have to be initialized to a variant".to_string(),
2601                                     Some(span),
2602                                 ))
2603                             } else {
2604                                 // In principle, for zero-initialization we could figure out which variant corresponds
2605                                 // to tag 0, and check that... but for now we just accept all zero-initializations.
2606                                 None
2607                             }
2608                         }
2609                     }
2610                 }
2611                 Tuple(..) => {
2612                     // Proceed recursively, check all fields.
2613                     ty.tuple_fields().find_map(|field| ty_find_init_error(tcx, field, init))
2614                 }
2615                 // Conservative fallback.
2616                 _ => None,
2617             }
2618         }
2619
2620         if let Some(init) = is_dangerous_init(cx, expr) {
2621             // This conjures an instance of a type out of nothing,
2622             // using zeroed or uninitialized memory.
2623             // We are extremely conservative with what we warn about.
2624             let conjured_ty = cx.typeck_results().expr_ty(expr);
2625             if let Some((msg, span)) =
2626                 with_no_trimmed_paths(|| ty_find_init_error(cx.tcx, conjured_ty, init))
2627             {
2628                 cx.struct_span_lint(INVALID_VALUE, expr.span, |lint| {
2629                     let mut err = lint.build(&format!(
2630                         "the type `{}` does not permit {}",
2631                         conjured_ty,
2632                         match init {
2633                             InitKind::Zeroed => "zero-initialization",
2634                             InitKind::Uninit => "being left uninitialized",
2635                         },
2636                     ));
2637                     err.span_label(expr.span, "this code causes undefined behavior when executed");
2638                     err.span_label(
2639                         expr.span,
2640                         "help: use `MaybeUninit<T>` instead, \
2641                             and only call `assume_init` after initialization is done",
2642                     );
2643                     if let Some(span) = span {
2644                         err.span_note(span, &msg);
2645                     } else {
2646                         err.note(&msg);
2647                     }
2648                     err.emit();
2649                 });
2650             }
2651         }
2652     }
2653 }
2654
2655 declare_lint! {
2656     /// The `clashing_extern_declarations` lint detects when an `extern fn`
2657     /// has been declared with the same name but different types.
2658     ///
2659     /// ### Example
2660     ///
2661     /// ```rust
2662     /// mod m {
2663     ///     extern "C" {
2664     ///         fn foo();
2665     ///     }
2666     /// }
2667     ///
2668     /// extern "C" {
2669     ///     fn foo(_: u32);
2670     /// }
2671     /// ```
2672     ///
2673     /// {{produces}}
2674     ///
2675     /// ### Explanation
2676     ///
2677     /// Because two symbols of the same name cannot be resolved to two
2678     /// different functions at link time, and one function cannot possibly
2679     /// have two types, a clashing extern declaration is almost certainly a
2680     /// mistake. Check to make sure that the `extern` definitions are correct
2681     /// and equivalent, and possibly consider unifying them in one location.
2682     ///
2683     /// This lint does not run between crates because a project may have
2684     /// dependencies which both rely on the same extern function, but declare
2685     /// it in a different (but valid) way. For example, they may both declare
2686     /// an opaque type for one or more of the arguments (which would end up
2687     /// distinct types), or use types that are valid conversions in the
2688     /// language the `extern fn` is defined in. In these cases, the compiler
2689     /// can't say that the clashing declaration is incorrect.
2690     pub CLASHING_EXTERN_DECLARATIONS,
2691     Warn,
2692     "detects when an extern fn has been declared with the same name but different types"
2693 }
2694
2695 pub struct ClashingExternDeclarations {
2696     /// Map of function symbol name to the first-seen hir id for that symbol name.. If seen_decls
2697     /// contains an entry for key K, it means a symbol with name K has been seen by this lint and
2698     /// the symbol should be reported as a clashing declaration.
2699     // FIXME: Technically, we could just store a &'tcx str here without issue; however, the
2700     // `impl_lint_pass` macro doesn't currently support lints parametric over a lifetime.
2701     seen_decls: FxHashMap<Symbol, HirId>,
2702 }
2703
2704 /// Differentiate between whether the name for an extern decl came from the link_name attribute or
2705 /// just from declaration itself. This is important because we don't want to report clashes on
2706 /// symbol name if they don't actually clash because one or the other links against a symbol with a
2707 /// different name.
2708 enum SymbolName {
2709     /// The name of the symbol + the span of the annotation which introduced the link name.
2710     Link(Symbol, Span),
2711     /// No link name, so just the name of the symbol.
2712     Normal(Symbol),
2713 }
2714
2715 impl SymbolName {
2716     fn get_name(&self) -> Symbol {
2717         match self {
2718             SymbolName::Link(s, _) | SymbolName::Normal(s) => *s,
2719         }
2720     }
2721 }
2722
2723 impl ClashingExternDeclarations {
2724     crate fn new() -> Self {
2725         ClashingExternDeclarations { seen_decls: FxHashMap::default() }
2726     }
2727     /// Insert a new foreign item into the seen set. If a symbol with the same name already exists
2728     /// for the item, return its HirId without updating the set.
2729     fn insert(&mut self, tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> Option<HirId> {
2730         let did = fi.def_id.to_def_id();
2731         let instance = Instance::new(did, ty::List::identity_for_item(tcx, did));
2732         let name = Symbol::intern(tcx.symbol_name(instance).name);
2733         if let Some(&hir_id) = self.seen_decls.get(&name) {
2734             // Avoid updating the map with the new entry when we do find a collision. We want to
2735             // make sure we're always pointing to the first definition as the previous declaration.
2736             // This lets us avoid emitting "knock-on" diagnostics.
2737             Some(hir_id)
2738         } else {
2739             self.seen_decls.insert(name, fi.hir_id())
2740         }
2741     }
2742
2743     /// Get the name of the symbol that's linked against for a given extern declaration. That is,
2744     /// the name specified in a #[link_name = ...] attribute if one was specified, else, just the
2745     /// symbol's name.
2746     fn name_of_extern_decl(tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> SymbolName {
2747         if let Some((overridden_link_name, overridden_link_name_span)) =
2748             tcx.codegen_fn_attrs(fi.def_id).link_name.map(|overridden_link_name| {
2749                 // FIXME: Instead of searching through the attributes again to get span
2750                 // information, we could have codegen_fn_attrs also give span information back for
2751                 // where the attribute was defined. However, until this is found to be a
2752                 // bottleneck, this does just fine.
2753                 (
2754                     overridden_link_name,
2755                     tcx.get_attrs(fi.def_id.to_def_id())
2756                         .iter()
2757                         .find(|at| at.has_name(sym::link_name))
2758                         .unwrap()
2759                         .span,
2760                 )
2761             })
2762         {
2763             SymbolName::Link(overridden_link_name, overridden_link_name_span)
2764         } else {
2765             SymbolName::Normal(fi.ident.name)
2766         }
2767     }
2768
2769     /// Checks whether two types are structurally the same enough that the declarations shouldn't
2770     /// clash. We need this so we don't emit a lint when two modules both declare an extern struct,
2771     /// with the same members (as the declarations shouldn't clash).
2772     fn structurally_same_type<'tcx>(
2773         cx: &LateContext<'tcx>,
2774         a: Ty<'tcx>,
2775         b: Ty<'tcx>,
2776         ckind: CItemKind,
2777     ) -> bool {
2778         fn structurally_same_type_impl<'tcx>(
2779             seen_types: &mut FxHashSet<(Ty<'tcx>, Ty<'tcx>)>,
2780             cx: &LateContext<'tcx>,
2781             a: Ty<'tcx>,
2782             b: Ty<'tcx>,
2783             ckind: CItemKind,
2784         ) -> bool {
2785             debug!("structurally_same_type_impl(cx, a = {:?}, b = {:?})", a, b);
2786             let tcx = cx.tcx;
2787
2788             // Given a transparent newtype, reach through and grab the inner
2789             // type unless the newtype makes the type non-null.
2790             let non_transparent_ty = |ty: Ty<'tcx>| -> Ty<'tcx> {
2791                 let mut ty = ty;
2792                 loop {
2793                     if let ty::Adt(def, substs) = *ty.kind() {
2794                         let is_transparent = def.subst(tcx, substs).repr.transparent();
2795                         let is_non_null = crate::types::nonnull_optimization_guaranteed(tcx, &def);
2796                         debug!(
2797                             "non_transparent_ty({:?}) -- type is transparent? {}, type is non-null? {}",
2798                             ty, is_transparent, is_non_null
2799                         );
2800                         if is_transparent && !is_non_null {
2801                             debug_assert!(def.variants.len() == 1);
2802                             let v = &def.variants[VariantIdx::new(0)];
2803                             ty = transparent_newtype_field(tcx, v)
2804                                 .expect(
2805                                     "single-variant transparent structure with zero-sized field",
2806                                 )
2807                                 .ty(tcx, substs);
2808                             continue;
2809                         }
2810                     }
2811                     debug!("non_transparent_ty -> {:?}", ty);
2812                     return ty;
2813                 }
2814             };
2815
2816             let a = non_transparent_ty(a);
2817             let b = non_transparent_ty(b);
2818
2819             if !seen_types.insert((a, b)) {
2820                 // We've encountered a cycle. There's no point going any further -- the types are
2821                 // structurally the same.
2822                 return true;
2823             }
2824             let tcx = cx.tcx;
2825             if a == b || rustc_middle::ty::TyS::same_type(a, b) {
2826                 // All nominally-same types are structurally same, too.
2827                 true
2828             } else {
2829                 // Do a full, depth-first comparison between the two.
2830                 use rustc_middle::ty::TyKind::*;
2831                 let a_kind = a.kind();
2832                 let b_kind = b.kind();
2833
2834                 let compare_layouts = |a, b| -> Result<bool, LayoutError<'tcx>> {
2835                     debug!("compare_layouts({:?}, {:?})", a, b);
2836                     let a_layout = &cx.layout_of(a)?.layout.abi;
2837                     let b_layout = &cx.layout_of(b)?.layout.abi;
2838                     debug!(
2839                         "comparing layouts: {:?} == {:?} = {}",
2840                         a_layout,
2841                         b_layout,
2842                         a_layout == b_layout
2843                     );
2844                     Ok(a_layout == b_layout)
2845                 };
2846
2847                 #[allow(rustc::usage_of_ty_tykind)]
2848                 let is_primitive_or_pointer = |kind: &ty::TyKind<'_>| {
2849                     kind.is_primitive() || matches!(kind, RawPtr(..) | Ref(..))
2850                 };
2851
2852                 ensure_sufficient_stack(|| {
2853                     match (a_kind, b_kind) {
2854                         (Adt(a_def, a_substs), Adt(b_def, b_substs)) => {
2855                             let a = a.subst(cx.tcx, a_substs);
2856                             let b = b.subst(cx.tcx, b_substs);
2857                             debug!("Comparing {:?} and {:?}", a, b);
2858
2859                             // We can immediately rule out these types as structurally same if
2860                             // their layouts differ.
2861                             match compare_layouts(a, b) {
2862                                 Ok(false) => return false,
2863                                 _ => (), // otherwise, continue onto the full, fields comparison
2864                             }
2865
2866                             // Grab a flattened representation of all fields.
2867                             let a_fields = a_def.variants.iter().flat_map(|v| v.fields.iter());
2868                             let b_fields = b_def.variants.iter().flat_map(|v| v.fields.iter());
2869
2870                             // Perform a structural comparison for each field.
2871                             a_fields.eq_by(
2872                                 b_fields,
2873                                 |&ty::FieldDef { did: a_did, .. },
2874                                  &ty::FieldDef { did: b_did, .. }| {
2875                                     structurally_same_type_impl(
2876                                         seen_types,
2877                                         cx,
2878                                         tcx.type_of(a_did),
2879                                         tcx.type_of(b_did),
2880                                         ckind,
2881                                     )
2882                                 },
2883                             )
2884                         }
2885                         (Array(a_ty, a_const), Array(b_ty, b_const)) => {
2886                             // For arrays, we also check the constness of the type.
2887                             a_const.val == b_const.val
2888                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2889                         }
2890                         (Slice(a_ty), Slice(b_ty)) => {
2891                             structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2892                         }
2893                         (RawPtr(a_tymut), RawPtr(b_tymut)) => {
2894                             a_tymut.mutbl == b_tymut.mutbl
2895                                 && structurally_same_type_impl(
2896                                     seen_types,
2897                                     cx,
2898                                     &a_tymut.ty,
2899                                     &b_tymut.ty,
2900                                     ckind,
2901                                 )
2902                         }
2903                         (Ref(_a_region, a_ty, a_mut), Ref(_b_region, b_ty, b_mut)) => {
2904                             // For structural sameness, we don't need the region to be same.
2905                             a_mut == b_mut
2906                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2907                         }
2908                         (FnDef(..), FnDef(..)) => {
2909                             let a_poly_sig = a.fn_sig(tcx);
2910                             let b_poly_sig = b.fn_sig(tcx);
2911
2912                             // As we don't compare regions, skip_binder is fine.
2913                             let a_sig = a_poly_sig.skip_binder();
2914                             let b_sig = b_poly_sig.skip_binder();
2915
2916                             (a_sig.abi, a_sig.unsafety, a_sig.c_variadic)
2917                                 == (b_sig.abi, b_sig.unsafety, b_sig.c_variadic)
2918                                 && a_sig.inputs().iter().eq_by(b_sig.inputs().iter(), |a, b| {
2919                                     structurally_same_type_impl(seen_types, cx, a, b, ckind)
2920                                 })
2921                                 && structurally_same_type_impl(
2922                                     seen_types,
2923                                     cx,
2924                                     a_sig.output(),
2925                                     b_sig.output(),
2926                                     ckind,
2927                                 )
2928                         }
2929                         (Tuple(a_substs), Tuple(b_substs)) => {
2930                             a_substs.types().eq_by(b_substs.types(), |a_ty, b_ty| {
2931                                 structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2932                             })
2933                         }
2934                         // For these, it's not quite as easy to define structural-sameness quite so easily.
2935                         // For the purposes of this lint, take the conservative approach and mark them as
2936                         // not structurally same.
2937                         (Dynamic(..), Dynamic(..))
2938                         | (Error(..), Error(..))
2939                         | (Closure(..), Closure(..))
2940                         | (Generator(..), Generator(..))
2941                         | (GeneratorWitness(..), GeneratorWitness(..))
2942                         | (Projection(..), Projection(..))
2943                         | (Opaque(..), Opaque(..)) => false,
2944
2945                         // These definitely should have been caught above.
2946                         (Bool, Bool) | (Char, Char) | (Never, Never) | (Str, Str) => unreachable!(),
2947
2948                         // An Adt and a primitive or pointer type. This can be FFI-safe if non-null
2949                         // enum layout optimisation is being applied.
2950                         (Adt(..), other_kind) | (other_kind, Adt(..))
2951                             if is_primitive_or_pointer(other_kind) =>
2952                         {
2953                             let (primitive, adt) =
2954                                 if is_primitive_or_pointer(a.kind()) { (a, b) } else { (b, a) };
2955                             if let Some(ty) = crate::types::repr_nullable_ptr(cx, adt, ckind) {
2956                                 ty == primitive
2957                             } else {
2958                                 compare_layouts(a, b).unwrap_or(false)
2959                             }
2960                         }
2961                         // Otherwise, just compare the layouts. This may fail to lint for some
2962                         // incompatible types, but at the very least, will stop reads into
2963                         // uninitialised memory.
2964                         _ => compare_layouts(a, b).unwrap_or(false),
2965                     }
2966                 })
2967             }
2968         }
2969         let mut seen_types = FxHashSet::default();
2970         structurally_same_type_impl(&mut seen_types, cx, a, b, ckind)
2971     }
2972 }
2973
2974 impl_lint_pass!(ClashingExternDeclarations => [CLASHING_EXTERN_DECLARATIONS]);
2975
2976 impl<'tcx> LateLintPass<'tcx> for ClashingExternDeclarations {
2977     fn check_foreign_item(&mut self, cx: &LateContext<'tcx>, this_fi: &hir::ForeignItem<'_>) {
2978         trace!("ClashingExternDeclarations: check_foreign_item: {:?}", this_fi);
2979         if let ForeignItemKind::Fn(..) = this_fi.kind {
2980             let tcx = cx.tcx;
2981             if let Some(existing_hid) = self.insert(tcx, this_fi) {
2982                 let existing_decl_ty = tcx.type_of(tcx.hir().local_def_id(existing_hid));
2983                 let this_decl_ty = tcx.type_of(this_fi.def_id);
2984                 debug!(
2985                     "ClashingExternDeclarations: Comparing existing {:?}: {:?} to this {:?}: {:?}",
2986                     existing_hid, existing_decl_ty, this_fi.def_id, this_decl_ty
2987                 );
2988                 // Check that the declarations match.
2989                 if !Self::structurally_same_type(
2990                     cx,
2991                     existing_decl_ty,
2992                     this_decl_ty,
2993                     CItemKind::Declaration,
2994                 ) {
2995                     let orig_fi = tcx.hir().expect_foreign_item(existing_hid);
2996                     let orig = Self::name_of_extern_decl(tcx, orig_fi);
2997
2998                     // We want to ensure that we use spans for both decls that include where the
2999                     // name was defined, whether that was from the link_name attribute or not.
3000                     let get_relevant_span =
3001                         |fi: &hir::ForeignItem<'_>| match Self::name_of_extern_decl(tcx, fi) {
3002                             SymbolName::Normal(_) => fi.span,
3003                             SymbolName::Link(_, annot_span) => fi.span.to(annot_span),
3004                         };
3005                     // Finally, emit the diagnostic.
3006                     tcx.struct_span_lint_hir(
3007                         CLASHING_EXTERN_DECLARATIONS,
3008                         this_fi.hir_id(),
3009                         get_relevant_span(this_fi),
3010                         |lint| {
3011                             let mut expected_str = DiagnosticStyledString::new();
3012                             expected_str.push(existing_decl_ty.fn_sig(tcx).to_string(), false);
3013                             let mut found_str = DiagnosticStyledString::new();
3014                             found_str.push(this_decl_ty.fn_sig(tcx).to_string(), true);
3015
3016                             lint.build(&format!(
3017                                 "`{}` redeclare{} with a different signature",
3018                                 this_fi.ident.name,
3019                                 if orig.get_name() == this_fi.ident.name {
3020                                     "d".to_string()
3021                                 } else {
3022                                     format!("s `{}`", orig.get_name())
3023                                 }
3024                             ))
3025                             .span_label(
3026                                 get_relevant_span(orig_fi),
3027                                 &format!("`{}` previously declared here", orig.get_name()),
3028                             )
3029                             .span_label(
3030                                 get_relevant_span(this_fi),
3031                                 "this signature doesn't match the previous declaration",
3032                             )
3033                             .note_expected_found(&"", expected_str, &"", found_str)
3034                             .emit()
3035                         },
3036                     );
3037                 }
3038             }
3039         }
3040     }
3041 }
3042
3043 declare_lint! {
3044     /// The `deref_nullptr` lint detects when an null pointer is dereferenced,
3045     /// which causes [undefined behavior].
3046     ///
3047     /// ### Example
3048     ///
3049     /// ```rust,no_run
3050     /// # #![allow(unused)]
3051     /// use std::ptr;
3052     /// unsafe {
3053     ///     let x = &*ptr::null::<i32>();
3054     ///     let x = ptr::addr_of!(*ptr::null::<i32>());
3055     ///     let x = *(0 as *const i32);
3056     /// }
3057     /// ```
3058     ///
3059     /// {{produces}}
3060     ///
3061     /// ### Explanation
3062     ///
3063     /// Dereferencing a null pointer causes [undefined behavior] even as a place expression,
3064     /// like `&*(0 as *const i32)` or `addr_of!(*(0 as *const i32))`.
3065     ///
3066     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
3067     pub DEREF_NULLPTR,
3068     Warn,
3069     "detects when an null pointer is dereferenced"
3070 }
3071
3072 declare_lint_pass!(DerefNullPtr => [DEREF_NULLPTR]);
3073
3074 impl<'tcx> LateLintPass<'tcx> for DerefNullPtr {
3075     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
3076         /// test if expression is a null ptr
3077         fn is_null_ptr(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> bool {
3078             match &expr.kind {
3079                 rustc_hir::ExprKind::Cast(ref expr, ref ty) => {
3080                     if let rustc_hir::TyKind::Ptr(_) = ty.kind {
3081                         return is_zero(expr) || is_null_ptr(cx, expr);
3082                     }
3083                 }
3084                 // check for call to `core::ptr::null` or `core::ptr::null_mut`
3085                 rustc_hir::ExprKind::Call(ref path, _) => {
3086                     if let rustc_hir::ExprKind::Path(ref qpath) = path.kind {
3087                         if let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id() {
3088                             return cx.tcx.is_diagnostic_item(sym::ptr_null, def_id)
3089                                 || cx.tcx.is_diagnostic_item(sym::ptr_null_mut, def_id);
3090                         }
3091                     }
3092                 }
3093                 _ => {}
3094             }
3095             false
3096         }
3097
3098         /// test if expression is the literal `0`
3099         fn is_zero(expr: &hir::Expr<'_>) -> bool {
3100             match &expr.kind {
3101                 rustc_hir::ExprKind::Lit(ref lit) => {
3102                     if let LitKind::Int(a, _) = lit.node {
3103                         return a == 0;
3104                     }
3105                 }
3106                 _ => {}
3107             }
3108             false
3109         }
3110
3111         if let rustc_hir::ExprKind::Unary(ref un_op, ref expr_deref) = expr.kind {
3112             if let rustc_hir::UnOp::Deref = un_op {
3113                 if is_null_ptr(cx, expr_deref) {
3114                     cx.struct_span_lint(DEREF_NULLPTR, expr.span, |lint| {
3115                         let mut err = lint.build("dereferencing a null pointer");
3116                         err.span_label(
3117                             expr.span,
3118                             "this code causes undefined behavior when executed",
3119                         );
3120                         err.emit();
3121                     });
3122                 }
3123             }
3124         }
3125     }
3126 }
3127
3128 declare_lint! {
3129     /// The `named_asm_labels` lint detects the use of named labels in the
3130     /// inline `asm!` macro.
3131     ///
3132     /// ### Example
3133     ///
3134     /// ```rust,compile_fail
3135     /// #![feature(asm)]
3136     /// fn main() {
3137     ///     unsafe {
3138     ///         asm!("foo: bar");
3139     ///     }
3140     /// }
3141     /// ```
3142     ///
3143     /// {{produces}}
3144     ///
3145     /// ### Explanation
3146     ///
3147     /// LLVM is allowed to duplicate inline assembly blocks for any
3148     /// reason, for example when it is in a function that gets inlined. Because
3149     /// of this, GNU assembler [local labels] *must* be used instead of labels
3150     /// with a name. Using named labels might cause assembler or linker errors.
3151     ///
3152     /// See the [unstable book] for more details.
3153     ///
3154     /// [local labels]: https://sourceware.org/binutils/docs/as/Symbol-Names.html#Local-Labels
3155     /// [unstable book]: https://doc.rust-lang.org/nightly/unstable-book/library-features/asm.html#labels
3156     pub NAMED_ASM_LABELS,
3157     Deny,
3158     "named labels in inline assembly",
3159 }
3160
3161 declare_lint_pass!(NamedAsmLabels => [NAMED_ASM_LABELS]);
3162
3163 impl<'tcx> LateLintPass<'tcx> for NamedAsmLabels {
3164     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
3165         if let hir::Expr {
3166             kind: hir::ExprKind::InlineAsm(hir::InlineAsm { template_strs, .. }),
3167             ..
3168         } = expr
3169         {
3170             for (template_sym, template_snippet, template_span) in template_strs.iter() {
3171                 let template_str = &template_sym.as_str();
3172                 let find_label_span = |needle: &str| -> Option<Span> {
3173                     if let Some(template_snippet) = template_snippet {
3174                         let snippet = template_snippet.as_str();
3175                         if let Some(pos) = snippet.find(needle) {
3176                             let end = pos
3177                                 + &snippet[pos..]
3178                                     .find(|c| c == ':')
3179                                     .unwrap_or(snippet[pos..].len() - 1);
3180                             let inner = InnerSpan::new(pos, end);
3181                             return Some(template_span.from_inner(inner));
3182                         }
3183                     }
3184
3185                     None
3186                 };
3187
3188                 let mut found_labels = Vec::new();
3189
3190                 // A semicolon might not actually be specified as a separator for all targets, but it seems like LLVM accepts it always
3191                 let statements = template_str.split(|c| matches!(c, '\n' | ';'));
3192                 for statement in statements {
3193                     // If there's a comment, trim it from the statement
3194                     let statement = statement.find("//").map_or(statement, |idx| &statement[..idx]);
3195                     let mut start_idx = 0;
3196                     for (idx, _) in statement.match_indices(':') {
3197                         let possible_label = statement[start_idx..idx].trim();
3198                         let mut chars = possible_label.chars();
3199                         if let Some(c) = chars.next() {
3200                             // A label starts with an alphabetic character or . or _ and continues with alphanumeric characters, _, or $
3201                             if (c.is_alphabetic() || matches!(c, '.' | '_'))
3202                                 && chars.all(|c| c.is_alphanumeric() || matches!(c, '_' | '$'))
3203                             {
3204                                 found_labels.push(possible_label);
3205                             } else {
3206                                 // If we encounter a non-label, there cannot be any further labels, so stop checking
3207                                 break;
3208                             }
3209                         } else {
3210                             // Empty string means a leading ':' in this section, which is not a label
3211                             break;
3212                         }
3213
3214                         start_idx = idx + 1;
3215                     }
3216                 }
3217
3218                 debug!("NamedAsmLabels::check_expr(): found_labels: {:#?}", &found_labels);
3219
3220                 if found_labels.len() > 0 {
3221                     let spans = found_labels
3222                         .into_iter()
3223                         .filter_map(|label| find_label_span(label))
3224                         .collect::<Vec<Span>>();
3225                     // If there were labels but we couldn't find a span, combine the warnings and use the template span
3226                     let target_spans: MultiSpan =
3227                         if spans.len() > 0 { spans.into() } else { (*template_span).into() };
3228
3229                     cx.lookup_with_diagnostics(
3230                             NAMED_ASM_LABELS,
3231                             Some(target_spans),
3232                             |diag| {
3233                                 let mut err =
3234                                     diag.build("avoid using named labels in inline assembly");
3235                                 err.emit();
3236                             },
3237                             BuiltinLintDiagnostics::NamedAsmLabel(
3238                                 "only local labels of the form `<number>:` should be used in inline asm"
3239                                     .to_string(),
3240                             ),
3241                         );
3242                 }
3243             }
3244         }
3245     }
3246 }