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<'_>) {
 588         self.check_missing_docs_attrs(
 589             cx,
 590             CRATE_DEF_ID,
 591             cx.tcx.def_span(CRATE_DEF_ID),
 592             "the",
 593             "crate",
 594         );
 595     }
 596
 597     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 598         match it.kind {
 599             hir::ItemKind::Trait(.., trait_item_refs) => {
 600                 // Issue #11592: traits are always considered exported, even when private.
 601                 if let hir::VisibilityKind::Inherited = it.vis.node {
 602                     self.private_traits.insert(it.hir_id());
 603                     for trait_item_ref in trait_item_refs {
 604                         self.private_traits.insert(trait_item_ref.id.hir_id());
 605                     }
 606                     return;
 607                 }
 608             }
 609             hir::ItemKind::Impl(hir::Impl { of_trait: Some(ref trait_ref), items, .. }) => {
 610                 // If the trait is private, add the impl items to `private_traits` so they don't get
 611                 // reported for missing docs.
 612                 let real_trait = trait_ref.path.res.def_id();
 613                 if let Some(def_id) = real_trait.as_local() {
 614                     let hir_id = cx.tcx.hir().local_def_id_to_hir_id(def_id);
 615                     if let Some(Node::Item(item)) = cx.tcx.hir().find(hir_id) {
 616                         if let hir::VisibilityKind::Inherited = item.vis.node {
 617                             for impl_item_ref in items {
 618                                 self.private_traits.insert(impl_item_ref.id.hir_id());
 619                             }
 620                         }
 621                     }
 622                 }
 623                 return;
 624             }
 625
 626             hir::ItemKind::TyAlias(..)
 627             | hir::ItemKind::Fn(..)
 628             | hir::ItemKind::Macro(..)
 629             | hir::ItemKind::Mod(..)
 630             | hir::ItemKind::Enum(..)
 631             | hir::ItemKind::Struct(..)
 632             | hir::ItemKind::Union(..)
 633             | hir::ItemKind::Const(..)
 634             | hir::ItemKind::Static(..) => {}
 635
 636             _ => return,
 637         };
 638
 639         let (article, desc) = cx.tcx.article_and_description(it.def_id.to_def_id());
 640
 641         self.check_missing_docs_attrs(cx, it.def_id, it.span, article, desc);
 642     }
 643
 644     fn check_trait_item(&mut self, cx: &LateContext<'_>, trait_item: &hir::TraitItem<'_>) {
 645         if self.private_traits.contains(&trait_item.hir_id()) {
 646             return;
 647         }
 648
 649         let (article, desc) = cx.tcx.article_and_description(trait_item.def_id.to_def_id());
 650
 651         self.check_missing_docs_attrs(cx, trait_item.def_id, trait_item.span, article, desc);
 652     }
 653
 654     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
 655         // If the method is an impl for a trait, don't doc.
 656         if method_context(cx, impl_item.hir_id()) == MethodLateContext::TraitImpl {
 657             return;
 658         }
 659
 660         // If the method is an impl for an item with docs_hidden, don't doc.
 661         if method_context(cx, impl_item.hir_id()) == MethodLateContext::PlainImpl {
 662             let parent = cx.tcx.hir().get_parent_did(impl_item.hir_id());
 663             let impl_ty = cx.tcx.type_of(parent);
 664             let outerdef = match impl_ty.kind() {
 665                 ty::Adt(def, _) => Some(def.did),
 666                 ty::Foreign(def_id) => Some(*def_id),
 667                 _ => None,
 668             };
 669             let is_hidden = match outerdef {
 670                 Some(id) => cx.tcx.is_doc_hidden(id),
 671                 None => false,
 672             };
 673             if is_hidden {
 674                 return;
 675             }
 676         }
 677
 678         let (article, desc) = cx.tcx.article_and_description(impl_item.def_id.to_def_id());
 679         self.check_missing_docs_attrs(cx, impl_item.def_id, impl_item.span, article, desc);
 680     }
 681
 682     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'_>) {
 683         let (article, desc) = cx.tcx.article_and_description(foreign_item.def_id.to_def_id());
 684         self.check_missing_docs_attrs(cx, foreign_item.def_id, foreign_item.span, article, desc);
 685     }
 686
 687     fn check_field_def(&mut self, cx: &LateContext<'_>, sf: &hir::FieldDef<'_>) {
 688         if !sf.is_positional() {
 689             let def_id = cx.tcx.hir().local_def_id(sf.hir_id);
 690             self.check_missing_docs_attrs(cx, def_id, sf.span, "a", "struct field")
 691         }
 692     }
 693
 694     fn check_variant(&mut self, cx: &LateContext<'_>, v: &hir::Variant<'_>) {
 695         self.check_missing_docs_attrs(cx, cx.tcx.hir().local_def_id(v.id), v.span, "a", "variant");
 696     }
 697 }
 698
 699 declare_lint! {
 700     /// The `missing_copy_implementations` lint detects potentially-forgotten
 701     /// implementations of [`Copy`].
 702     ///
 703     /// [`Copy`]: https://doc.rust-lang.org/std/marker/trait.Copy.html
 704     ///
 705     /// ### Example
 706     ///
 707     /// ```rust,compile_fail
 708     /// #![deny(missing_copy_implementations)]
 709     /// pub struct Foo {
 710     ///     pub field: i32
 711     /// }
 712     /// # fn main() {}
 713     /// ```
 714     ///
 715     /// {{produces}}
 716     ///
 717     /// ### Explanation
 718     ///
 719     /// Historically (before 1.0), types were automatically marked as `Copy`
 720     /// if possible. This was changed so that it required an explicit opt-in
 721     /// by implementing the `Copy` trait. As part of this change, a lint was
 722     /// added to alert if a copyable type was not marked `Copy`.
 723     ///
 724     /// This lint is "allow" by default because this code isn't bad; it is
 725     /// common to write newtypes like this specifically so that a `Copy` type
 726     /// is no longer `Copy`. `Copy` types can result in unintended copies of
 727     /// large data which can impact performance.
 728     pub MISSING_COPY_IMPLEMENTATIONS,
 729     Allow,
 730     "detects potentially-forgotten implementations of `Copy`"
 731 }
 732
 733 declare_lint_pass!(MissingCopyImplementations => [MISSING_COPY_IMPLEMENTATIONS]);
 734
 735 impl<'tcx> LateLintPass<'tcx> for MissingCopyImplementations {
 736     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 737         if !cx.access_levels.is_reachable(item.def_id) {
 738             return;
 739         }
 740         let (def, ty) = match item.kind {
 741             hir::ItemKind::Struct(_, ref ast_generics) => {
 742                 if !ast_generics.params.is_empty() {
 743                     return;
 744                 }
 745                 let def = cx.tcx.adt_def(item.def_id);
 746                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 747             }
 748             hir::ItemKind::Union(_, ref ast_generics) => {
 749                 if !ast_generics.params.is_empty() {
 750                     return;
 751                 }
 752                 let def = cx.tcx.adt_def(item.def_id);
 753                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 754             }
 755             hir::ItemKind::Enum(_, ref ast_generics) => {
 756                 if !ast_generics.params.is_empty() {
 757                     return;
 758                 }
 759                 let def = cx.tcx.adt_def(item.def_id);
 760                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 761             }
 762             _ => return,
 763         };
 764         if def.has_dtor(cx.tcx) {
 765             return;
 766         }
 767         let param_env = ty::ParamEnv::empty();
 768         if ty.is_copy_modulo_regions(cx.tcx.at(item.span), param_env) {
 769             return;
 770         }
 771         if can_type_implement_copy(cx.tcx, param_env, ty).is_ok() {
 772             cx.struct_span_lint(MISSING_COPY_IMPLEMENTATIONS, item.span, |lint| {
 773                 lint.build(
 774                     "type could implement `Copy`; consider adding `impl \
 775                           Copy`",
 776                 )
 777                 .emit()
 778             })
 779         }
 780     }
 781 }
 782
 783 declare_lint! {
 784     /// The `missing_debug_implementations` lint detects missing
 785     /// implementations of [`fmt::Debug`].
 786     ///
 787     /// [`fmt::Debug`]: https://doc.rust-lang.org/std/fmt/trait.Debug.html
 788     ///
 789     /// ### Example
 790     ///
 791     /// ```rust,compile_fail
 792     /// #![deny(missing_debug_implementations)]
 793     /// pub struct Foo;
 794     /// # fn main() {}
 795     /// ```
 796     ///
 797     /// {{produces}}
 798     ///
 799     /// ### Explanation
 800     ///
 801     /// Having a `Debug` implementation on all types can assist with
 802     /// debugging, as it provides a convenient way to format and display a
 803     /// value. Using the `#[derive(Debug)]` attribute will automatically
 804     /// generate a typical implementation, or a custom implementation can be
 805     /// added by manually implementing the `Debug` trait.
 806     ///
 807     /// This lint is "allow" by default because adding `Debug` to all types can
 808     /// have a negative impact on compile time and code size. It also requires
 809     /// boilerplate to be added to every type, which can be an impediment.
 810     MISSING_DEBUG_IMPLEMENTATIONS,
 811     Allow,
 812     "detects missing implementations of Debug"
 813 }
 814
 815 #[derive(Default)]
 816 pub struct MissingDebugImplementations {
 817     impling_types: Option<LocalDefIdSet>,
 818 }
 819
 820 impl_lint_pass!(MissingDebugImplementations => [MISSING_DEBUG_IMPLEMENTATIONS]);
 821
 822 impl<'tcx> LateLintPass<'tcx> for MissingDebugImplementations {
 823     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 824         if !cx.access_levels.is_reachable(item.def_id) {
 825             return;
 826         }
 827
 828         match item.kind {
 829             hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) | hir::ItemKind::Enum(..) => {}
 830             _ => return,
 831         }
 832
 833         let debug = match cx.tcx.get_diagnostic_item(sym::Debug) {
 834             Some(debug) => debug,
 835             None => return,
 836         };
 837
 838         if self.impling_types.is_none() {
 839             let mut impls = LocalDefIdSet::default();
 840             cx.tcx.for_each_impl(debug, |d| {
 841                 if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() {
 842                     if let Some(def_id) = ty_def.did.as_local() {
 843                         impls.insert(def_id);
 844                     }
 845                 }
 846             });
 847
 848             self.impling_types = Some(impls);
 849             debug!("{:?}", self.impling_types);
 850         }
 851
 852         if !self.impling_types.as_ref().unwrap().contains(&item.def_id) {
 853             cx.struct_span_lint(MISSING_DEBUG_IMPLEMENTATIONS, item.span, |lint| {
 854                 lint.build(&format!(
 855                     "type does not implement `{}`; consider adding `#[derive(Debug)]` \
 856                      or a manual implementation",
 857                     cx.tcx.def_path_str(debug)
 858                 ))
 859                 .emit()
 860             });
 861         }
 862     }
 863 }
 864
 865 declare_lint! {
 866     /// The `anonymous_parameters` lint detects anonymous parameters in trait
 867     /// definitions.
 868     ///
 869     /// ### Example
 870     ///
 871     /// ```rust,edition2015,compile_fail
 872     /// #![deny(anonymous_parameters)]
 873     /// // edition 2015
 874     /// pub trait Foo {
 875     ///     fn foo(usize);
 876     /// }
 877     /// fn main() {}
 878     /// ```
 879     ///
 880     /// {{produces}}
 881     ///
 882     /// ### Explanation
 883     ///
 884     /// This syntax is mostly a historical accident, and can be worked around
 885     /// quite easily by adding an `_` pattern or a descriptive identifier:
 886     ///
 887     /// ```rust
 888     /// trait Foo {
 889     ///     fn foo(_: usize);
 890     /// }
 891     /// ```
 892     ///
 893     /// This syntax is now a hard error in the 2018 edition. In the 2015
 894     /// edition, this lint is "warn" by default. This lint
 895     /// enables the [`cargo fix`] tool with the `--edition` flag to
 896     /// automatically transition old code from the 2015 edition to 2018. The
 897     /// tool will run this lint and automatically apply the
 898     /// suggested fix from the compiler (which is to add `_` to each
 899     /// parameter). This provides a completely automated way to update old
 900     /// code for a new edition. See [issue #41686] for more details.
 901     ///
 902     /// [issue #41686]: https://github.com/rust-lang/rust/issues/41686
 903     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
 904     pub ANONYMOUS_PARAMETERS,
 905     Warn,
 906     "detects anonymous parameters",
 907     @future_incompatible = FutureIncompatibleInfo {
 908         reference: "issue #41686 <https://github.com/rust-lang/rust/issues/41686>",
 909         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
 910     };
 911 }
 912
 913 declare_lint_pass!(
 914     /// Checks for use of anonymous parameters (RFC 1685).
 915     AnonymousParameters => [ANONYMOUS_PARAMETERS]
 916 );
 917
 918 impl EarlyLintPass for AnonymousParameters {
 919     fn check_trait_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
 920         if cx.sess.edition() != Edition::Edition2015 {
 921             // This is a hard error in future editions; avoid linting and erroring
 922             return;
 923         }
 924         if let ast::AssocItemKind::Fn(box FnKind(_, ref sig, _, _)) = it.kind {
 925             for arg in sig.decl.inputs.iter() {
 926                 if let ast::PatKind::Ident(_, ident, None) = arg.pat.kind {
 927                     if ident.name == kw::Empty {
 928                         cx.struct_span_lint(ANONYMOUS_PARAMETERS, arg.pat.span, |lint| {
 929                             let ty_snip = cx.sess.source_map().span_to_snippet(arg.ty.span);
 930
 931                             let (ty_snip, appl) = if let Ok(ref snip) = ty_snip {
 932                                 (snip.as_str(), Applicability::MachineApplicable)
 933                             } else {
 934                                 ("<type>", Applicability::HasPlaceholders)
 935                             };
 936
 937                             lint.build(
 938                                 "anonymous parameters are deprecated and will be \
 939                                      removed in the next edition",
 940                             )
 941                             .span_suggestion(
 942                                 arg.pat.span,
 943                                 "try naming the parameter or explicitly \
 944                                             ignoring it",
 945                                 format!("_: {}", ty_snip),
 946                                 appl,
 947                             )
 948                             .emit();
 949                         })
 950                     }
 951                 }
 952             }
 953         }
 954     }
 955 }
 956
 957 /// Check for use of attributes which have been deprecated.
 958 #[derive(Clone)]
 959 pub struct DeprecatedAttr {
 960     // This is not free to compute, so we want to keep it around, rather than
 961     // compute it for every attribute.
 962     depr_attrs: Vec<&'static (Symbol, AttributeType, AttributeTemplate, AttributeGate)>,
 963 }
 964
 965 impl_lint_pass!(DeprecatedAttr => []);
 966
 967 impl DeprecatedAttr {
 968     pub fn new() -> DeprecatedAttr {
 969         DeprecatedAttr { depr_attrs: deprecated_attributes() }
 970     }
 971 }
 972
 973 fn lint_deprecated_attr(
 974     cx: &EarlyContext<'_>,
 975     attr: &ast::Attribute,
 976     msg: &str,
 977     suggestion: Option<&str>,
 978 ) {
 979     cx.struct_span_lint(DEPRECATED, attr.span, |lint| {
 980         lint.build(msg)
 981             .span_suggestion_short(
 982                 attr.span,
 983                 suggestion.unwrap_or("remove this attribute"),
 984                 String::new(),
 985                 Applicability::MachineApplicable,
 986             )
 987             .emit();
 988     })
 989 }
 990
 991 impl EarlyLintPass for DeprecatedAttr {
 992     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 993         for &&(n, _, _, ref g) in &self.depr_attrs {
 994             if attr.ident().map(|ident| ident.name) == Some(n) {
 995                 if let &AttributeGate::Gated(
 996                     Stability::Deprecated(link, suggestion),
 997                     name,
 998                     reason,
 999                     _,
1000                 ) = g
1001                 {
1002                     let msg =
1003                         format!("use of deprecated attribute `{}`: {}. See {}", name, reason, link);
1004                     lint_deprecated_attr(cx, attr, &msg, suggestion);
1005                 }
1006                 return;
1007             }
1008         }
1009         if attr.has_name(sym::no_start) || attr.has_name(sym::crate_id) {
1010             let path_str = pprust::path_to_string(&attr.get_normal_item().path);
1011             let msg = format!("use of deprecated attribute `{}`: no longer used.", path_str);
1012             lint_deprecated_attr(cx, attr, &msg, None);
1013         }
1014     }
1015 }
1016
1017 fn warn_if_doc(cx: &EarlyContext<'_>, node_span: Span, node_kind: &str, attrs: &[ast::Attribute]) {
1018     use rustc_ast::token::CommentKind;
1019
1020     let mut attrs = attrs.iter().peekable();
1021
1022     // Accumulate a single span for sugared doc comments.
1023     let mut sugared_span: Option<Span> = None;
1024
1025     while let Some(attr) = attrs.next() {
1026         let is_doc_comment = attr.is_doc_comment();
1027         if is_doc_comment {
1028             sugared_span =
1029                 Some(sugared_span.map_or(attr.span, |span| span.with_hi(attr.span.hi())));
1030         }
1031
1032         if attrs.peek().map_or(false, |next_attr| next_attr.is_doc_comment()) {
1033             continue;
1034         }
1035
1036         let span = sugared_span.take().unwrap_or(attr.span);
1037
1038         if is_doc_comment || attr.has_name(sym::doc) {
1039             cx.struct_span_lint(UNUSED_DOC_COMMENTS, span, |lint| {
1040                 let mut err = lint.build("unused doc comment");
1041                 err.span_label(
1042                     node_span,
1043                     format!("rustdoc does not generate documentation for {}", node_kind),
1044                 );
1045                 match attr.kind {
1046                     AttrKind::DocComment(CommentKind::Line, _) | AttrKind::Normal(..) => {
1047                         err.help("use `//` for a plain comment");
1048                     }
1049                     AttrKind::DocComment(CommentKind::Block, _) => {
1050                         err.help("use `/* */` for a plain comment");
1051                     }
1052                 }
1053                 err.emit();
1054             });
1055         }
1056     }
1057 }
1058
1059 impl EarlyLintPass for UnusedDocComment {
1060     fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &ast::Stmt) {
1061         let kind = match stmt.kind {
1062             ast::StmtKind::Local(..) => "statements",
1063             // Disabled pending discussion in #78306
1064             ast::StmtKind::Item(..) => return,
1065             // expressions will be reported by `check_expr`.
1066             ast::StmtKind::Empty
1067             | ast::StmtKind::Semi(_)
1068             | ast::StmtKind::Expr(_)
1069             | ast::StmtKind::MacCall(_) => return,
1070         };
1071
1072         warn_if_doc(cx, stmt.span, kind, stmt.kind.attrs());
1073     }
1074
1075     fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) {
1076         let arm_span = arm.pat.span.with_hi(arm.body.span.hi());
1077         warn_if_doc(cx, arm_span, "match arms", &arm.attrs);
1078     }
1079
1080     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
1081         warn_if_doc(cx, expr.span, "expressions", &expr.attrs);
1082     }
1083 }
1084
1085 declare_lint! {
1086     /// The `no_mangle_const_items` lint detects any `const` items with the
1087     /// [`no_mangle` attribute].
1088     ///
1089     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1090     ///
1091     /// ### Example
1092     ///
1093     /// ```rust,compile_fail
1094     /// #[no_mangle]
1095     /// const FOO: i32 = 5;
1096     /// ```
1097     ///
1098     /// {{produces}}
1099     ///
1100     /// ### Explanation
1101     ///
1102     /// Constants do not have their symbols exported, and therefore, this
1103     /// probably means you meant to use a [`static`], not a [`const`].
1104     ///
1105     /// [`static`]: https://doc.rust-lang.org/reference/items/static-items.html
1106     /// [`const`]: https://doc.rust-lang.org/reference/items/constant-items.html
1107     NO_MANGLE_CONST_ITEMS,
1108     Deny,
1109     "const items will not have their symbols exported"
1110 }
1111
1112 declare_lint! {
1113     /// The `no_mangle_generic_items` lint detects generic items that must be
1114     /// mangled.
1115     ///
1116     /// ### Example
1117     ///
1118     /// ```rust
1119     /// #[no_mangle]
1120     /// fn foo<T>(t: T) {
1121     ///
1122     /// }
1123     /// ```
1124     ///
1125     /// {{produces}}
1126     ///
1127     /// ### Explanation
1128     ///
1129     /// A function with generics must have its symbol mangled to accommodate
1130     /// the generic parameter. The [`no_mangle` attribute] has no effect in
1131     /// this situation, and should be removed.
1132     ///
1133     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1134     NO_MANGLE_GENERIC_ITEMS,
1135     Warn,
1136     "generic items must be mangled"
1137 }
1138
1139 declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS, NO_MANGLE_GENERIC_ITEMS]);
1140
1141 impl<'tcx> LateLintPass<'tcx> for InvalidNoMangleItems {
1142     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1143         let attrs = cx.tcx.hir().attrs(it.hir_id());
1144         let check_no_mangle_on_generic_fn = |no_mangle_attr: &ast::Attribute,
1145                                              impl_generics: Option<&hir::Generics<'_>>,
1146                                              generics: &hir::Generics<'_>,
1147                                              span| {
1148             for param in
1149                 generics.params.iter().chain(impl_generics.map(|g| g.params).into_iter().flatten())
1150             {
1151                 match param.kind {
1152                     GenericParamKind::Lifetime { .. } => {}
1153                     GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1154                         cx.struct_span_lint(NO_MANGLE_GENERIC_ITEMS, span, |lint| {
1155                             lint.build("functions generic over types or consts must be mangled")
1156                                 .span_suggestion_short(
1157                                     no_mangle_attr.span,
1158                                     "remove this attribute",
1159                                     String::new(),
1160                                     // Use of `#[no_mangle]` suggests FFI intent; correct
1161                                     // fix may be to monomorphize source by hand
1162                                     Applicability::MaybeIncorrect,
1163                                 )
1164                                 .emit();
1165                         });
1166                         break;
1167                     }
1168                 }
1169             }
1170         };
1171         match it.kind {
1172             hir::ItemKind::Fn(.., ref generics, _) => {
1173                 if let Some(no_mangle_attr) = cx.sess().find_by_name(attrs, sym::no_mangle) {
1174                     check_no_mangle_on_generic_fn(no_mangle_attr, None, generics, it.span);
1175                 }
1176             }
1177             hir::ItemKind::Const(..) => {
1178                 if cx.sess().contains_name(attrs, sym::no_mangle) {
1179                     // Const items do not refer to a particular location in memory, and therefore
1180                     // don't have anything to attach a symbol to
1181                     cx.struct_span_lint(NO_MANGLE_CONST_ITEMS, it.span, |lint| {
1182                         let msg = "const items should never be `#[no_mangle]`";
1183                         let mut err = lint.build(msg);
1184
1185                         // account for "pub const" (#45562)
1186                         let start = cx
1187                             .tcx
1188                             .sess
1189                             .source_map()
1190                             .span_to_snippet(it.span)
1191                             .map(|snippet| snippet.find("const").unwrap_or(0))
1192                             .unwrap_or(0) as u32;
1193                         // `const` is 5 chars
1194                         let const_span = it.span.with_hi(BytePos(it.span.lo().0 + start + 5));
1195                         err.span_suggestion(
1196                             const_span,
1197                             "try a static value",
1198                             "pub static".to_owned(),
1199                             Applicability::MachineApplicable,
1200                         );
1201                         err.emit();
1202                     });
1203                 }
1204             }
1205             hir::ItemKind::Impl(hir::Impl { ref generics, items, .. }) => {
1206                 for it in items {
1207                     if let hir::AssocItemKind::Fn { .. } = it.kind {
1208                         if let Some(no_mangle_attr) = cx
1209                             .sess()
1210                             .find_by_name(cx.tcx.hir().attrs(it.id.hir_id()), sym::no_mangle)
1211                         {
1212                             check_no_mangle_on_generic_fn(
1213                                 no_mangle_attr,
1214                                 Some(generics),
1215                                 cx.tcx.hir().get_generics(it.id.def_id.to_def_id()).unwrap(),
1216                                 it.span,
1217                             );
1218                         }
1219                     }
1220                 }
1221             }
1222             _ => {}
1223         }
1224     }
1225 }
1226
1227 declare_lint! {
1228     /// The `mutable_transmutes` lint catches transmuting from `&T` to `&mut
1229     /// T` because it is [undefined behavior].
1230     ///
1231     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1232     ///
1233     /// ### Example
1234     ///
1235     /// ```rust,compile_fail
1236     /// unsafe {
1237     ///     let y = std::mem::transmute::<&i32, &mut i32>(&5);
1238     /// }
1239     /// ```
1240     ///
1241     /// {{produces}}
1242     ///
1243     /// ### Explanation
1244     ///
1245     /// Certain assumptions are made about aliasing of data, and this transmute
1246     /// violates those assumptions. Consider using [`UnsafeCell`] instead.
1247     ///
1248     /// [`UnsafeCell`]: https://doc.rust-lang.org/std/cell/struct.UnsafeCell.html
1249     MUTABLE_TRANSMUTES,
1250     Deny,
1251     "mutating transmuted &mut T from &T may cause undefined behavior"
1252 }
1253
1254 declare_lint_pass!(MutableTransmutes => [MUTABLE_TRANSMUTES]);
1255
1256 impl<'tcx> LateLintPass<'tcx> for MutableTransmutes {
1257     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &hir::Expr<'_>) {
1258         use rustc_target::spec::abi::Abi::RustIntrinsic;
1259         if let Some((&ty::Ref(_, _, from_mt), &ty::Ref(_, _, to_mt))) =
1260             get_transmute_from_to(cx, expr).map(|(ty1, ty2)| (ty1.kind(), ty2.kind()))
1261         {
1262             if to_mt == hir::Mutability::Mut && from_mt == hir::Mutability::Not {
1263                 let msg = "mutating transmuted &mut T from &T may cause undefined behavior, \
1264                                consider instead using an UnsafeCell";
1265                 cx.struct_span_lint(MUTABLE_TRANSMUTES, expr.span, |lint| lint.build(msg).emit());
1266             }
1267         }
1268
1269         fn get_transmute_from_to<'tcx>(
1270             cx: &LateContext<'tcx>,
1271             expr: &hir::Expr<'_>,
1272         ) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
1273             let def = if let hir::ExprKind::Path(ref qpath) = expr.kind {
1274                 cx.qpath_res(qpath, expr.hir_id)
1275             } else {
1276                 return None;
1277             };
1278             if let Res::Def(DefKind::Fn, did) = def {
1279                 if !def_id_is_transmute(cx, did) {
1280                     return None;
1281                 }
1282                 let sig = cx.typeck_results().node_type(expr.hir_id).fn_sig(cx.tcx);
1283                 let from = sig.inputs().skip_binder()[0];
1284                 let to = sig.output().skip_binder();
1285                 return Some((from, to));
1286             }
1287             None
1288         }
1289
1290         fn def_id_is_transmute(cx: &LateContext<'_>, def_id: DefId) -> bool {
1291             cx.tcx.fn_sig(def_id).abi() == RustIntrinsic
1292                 && cx.tcx.item_name(def_id) == sym::transmute
1293         }
1294     }
1295 }
1296
1297 declare_lint! {
1298     /// The `unstable_features` is deprecated and should no longer be used.
1299     UNSTABLE_FEATURES,
1300     Allow,
1301     "enabling unstable features (deprecated. do not use)"
1302 }
1303
1304 declare_lint_pass!(
1305     /// Forbids using the `#[feature(...)]` attribute
1306     UnstableFeatures => [UNSTABLE_FEATURES]
1307 );
1308
1309 impl<'tcx> LateLintPass<'tcx> for UnstableFeatures {
1310     fn check_attribute(&mut self, cx: &LateContext<'_>, attr: &ast::Attribute) {
1311         if attr.has_name(sym::feature) {
1312             if let Some(items) = attr.meta_item_list() {
1313                 for item in items {
1314                     cx.struct_span_lint(UNSTABLE_FEATURES, item.span(), |lint| {
1315                         lint.build("unstable feature").emit()
1316                     });
1317                 }
1318             }
1319         }
1320     }
1321 }
1322
1323 declare_lint! {
1324     /// The `unreachable_pub` lint triggers for `pub` items not reachable from
1325     /// the crate root.
1326     ///
1327     /// ### Example
1328     ///
1329     /// ```rust,compile_fail
1330     /// #![deny(unreachable_pub)]
1331     /// mod foo {
1332     ///     pub mod bar {
1333     ///
1334     ///     }
1335     /// }
1336     /// ```
1337     ///
1338     /// {{produces}}
1339     ///
1340     /// ### Explanation
1341     ///
1342     /// A bare `pub` visibility may be misleading if the item is not actually
1343     /// publicly exported from the crate. The `pub(crate)` visibility is
1344     /// recommended to be used instead, which more clearly expresses the intent
1345     /// that the item is only visible within its own crate.
1346     ///
1347     /// This lint is "allow" by default because it will trigger for a large
1348     /// amount existing Rust code, and has some false-positives. Eventually it
1349     /// is desired for this to become warn-by-default.
1350     pub UNREACHABLE_PUB,
1351     Allow,
1352     "`pub` items not reachable from crate root"
1353 }
1354
1355 declare_lint_pass!(
1356     /// Lint for items marked `pub` that aren't reachable from other crates.
1357     UnreachablePub => [UNREACHABLE_PUB]
1358 );
1359
1360 impl UnreachablePub {
1361     fn perform_lint(
1362         &self,
1363         cx: &LateContext<'_>,
1364         what: &str,
1365         def_id: LocalDefId,
1366         vis: &hir::Visibility<'_>,
1367         span: Span,
1368         exportable: bool,
1369     ) {
1370         let mut applicability = Applicability::MachineApplicable;
1371         match vis.node {
1372             hir::VisibilityKind::Public if !cx.access_levels.is_reachable(def_id) => {
1373                 if span.from_expansion() {
1374                     applicability = Applicability::MaybeIncorrect;
1375                 }
1376                 let def_span = cx.tcx.sess.source_map().guess_head_span(span);
1377                 cx.struct_span_lint(UNREACHABLE_PUB, def_span, |lint| {
1378                     let mut err = lint.build(&format!("unreachable `pub` {}", what));
1379                     let replacement = if cx.tcx.features().crate_visibility_modifier {
1380                         "crate"
1381                     } else {
1382                         "pub(crate)"
1383                     }
1384                     .to_owned();
1385
1386                     err.span_suggestion(
1387                         vis.span,
1388                         "consider restricting its visibility",
1389                         replacement,
1390                         applicability,
1391                     );
1392                     if exportable {
1393                         err.help("or consider exporting it for use by other crates");
1394                     }
1395                     err.emit();
1396                 });
1397             }
1398             _ => {}
1399         }
1400     }
1401 }
1402
1403 impl<'tcx> LateLintPass<'tcx> for UnreachablePub {
1404     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1405         self.perform_lint(cx, "item", item.def_id, &item.vis, item.span, true);
1406     }
1407
1408     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'tcx>) {
1409         self.perform_lint(
1410             cx,
1411             "item",
1412             foreign_item.def_id,
1413             &foreign_item.vis,
1414             foreign_item.span,
1415             true,
1416         );
1417     }
1418
1419     fn check_field_def(&mut self, cx: &LateContext<'_>, field: &hir::FieldDef<'_>) {
1420         let def_id = cx.tcx.hir().local_def_id(field.hir_id);
1421         self.perform_lint(cx, "field", def_id, &field.vis, field.span, false);
1422     }
1423
1424     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
1425         self.perform_lint(cx, "item", impl_item.def_id, &impl_item.vis, impl_item.span, false);
1426     }
1427 }
1428
1429 declare_lint! {
1430     /// The `type_alias_bounds` lint detects bounds in type aliases.
1431     ///
1432     /// ### Example
1433     ///
1434     /// ```rust
1435     /// type SendVec<T: Send> = Vec<T>;
1436     /// ```
1437     ///
1438     /// {{produces}}
1439     ///
1440     /// ### Explanation
1441     ///
1442     /// The trait bounds in a type alias are currently ignored, and should not
1443     /// be included to avoid confusion. This was previously allowed
1444     /// unintentionally; this may become a hard error in the future.
1445     TYPE_ALIAS_BOUNDS,
1446     Warn,
1447     "bounds in type aliases are not enforced"
1448 }
1449
1450 declare_lint_pass!(
1451     /// Lint for trait and lifetime bounds in type aliases being mostly ignored.
1452     /// They are relevant when using associated types, but otherwise neither checked
1453     /// at definition site nor enforced at use site.
1454     TypeAliasBounds => [TYPE_ALIAS_BOUNDS]
1455 );
1456
1457 impl TypeAliasBounds {
1458     fn is_type_variable_assoc(qpath: &hir::QPath<'_>) -> bool {
1459         match *qpath {
1460             hir::QPath::TypeRelative(ref ty, _) => {
1461                 // If this is a type variable, we found a `T::Assoc`.
1462                 match ty.kind {
1463                     hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
1464                         matches!(path.res, Res::Def(DefKind::TyParam, _))
1465                     }
1466                     _ => false,
1467                 }
1468             }
1469             hir::QPath::Resolved(..) | hir::QPath::LangItem(..) => false,
1470         }
1471     }
1472
1473     fn suggest_changing_assoc_types(ty: &hir::Ty<'_>, err: &mut DiagnosticBuilder<'_>) {
1474         // Access to associates types should use `<T as Bound>::Assoc`, which does not need a
1475         // bound.  Let's see if this type does that.
1476
1477         // We use a HIR visitor to walk the type.
1478         use rustc_hir::intravisit::{self, Visitor};
1479         struct WalkAssocTypes<'a, 'db> {
1480             err: &'a mut DiagnosticBuilder<'db>,
1481         }
1482         impl<'a, 'db, 'v> Visitor<'v> for WalkAssocTypes<'a, 'db> {
1483             type Map = intravisit::ErasedMap<'v>;
1484
1485             fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1486                 intravisit::NestedVisitorMap::None
1487             }
1488
1489             fn visit_qpath(&mut self, qpath: &'v hir::QPath<'v>, id: hir::HirId, span: Span) {
1490                 if TypeAliasBounds::is_type_variable_assoc(qpath) {
1491                     self.err.span_help(
1492                         span,
1493                         "use fully disambiguated paths (i.e., `<T as Trait>::Assoc`) to refer to \
1494                          associated types in type aliases",
1495                     );
1496                 }
1497                 intravisit::walk_qpath(self, qpath, id, span)
1498             }
1499         }
1500
1501         // Let's go for a walk!
1502         let mut visitor = WalkAssocTypes { err };
1503         visitor.visit_ty(ty);
1504     }
1505 }
1506
1507 impl<'tcx> LateLintPass<'tcx> for TypeAliasBounds {
1508     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1509         let (ty, type_alias_generics) = match item.kind {
1510             hir::ItemKind::TyAlias(ref ty, ref generics) => (&*ty, generics),
1511             _ => return,
1512         };
1513         if let hir::TyKind::OpaqueDef(..) = ty.kind {
1514             // Bounds are respected for `type X = impl Trait`
1515             return;
1516         }
1517         let mut suggested_changing_assoc_types = false;
1518         // There must not be a where clause
1519         if !type_alias_generics.where_clause.predicates.is_empty() {
1520             cx.lint(
1521                 TYPE_ALIAS_BOUNDS,
1522                 |lint| {
1523                     let mut err = lint.build("where clauses are not enforced in type aliases");
1524                     let spans: Vec<_> = type_alias_generics
1525                         .where_clause
1526                         .predicates
1527                         .iter()
1528                         .map(|pred| pred.span())
1529                         .collect();
1530                     err.set_span(spans);
1531                     err.span_suggestion(
1532                         type_alias_generics.where_clause.span_for_predicates_or_empty_place(),
1533                         "the clause will not be checked when the type alias is used, and should be removed",
1534                         String::new(),
1535                         Applicability::MachineApplicable,
1536                     );
1537                     if !suggested_changing_assoc_types {
1538                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1539                         suggested_changing_assoc_types = true;
1540                     }
1541                     err.emit();
1542                 },
1543             );
1544         }
1545         // The parameters must not have bounds
1546         for param in type_alias_generics.params.iter() {
1547             let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
1548             let suggestion = spans
1549                 .iter()
1550                 .map(|sp| {
1551                     let start = param.span.between(*sp); // Include the `:` in `T: Bound`.
1552                     (start.to(*sp), String::new())
1553                 })
1554                 .collect();
1555             if !spans.is_empty() {
1556                 cx.struct_span_lint(TYPE_ALIAS_BOUNDS, spans, |lint| {
1557                     let mut err =
1558                         lint.build("bounds on generic parameters are not enforced in type aliases");
1559                     let msg = "the bound will not be checked when the type alias is used, \
1560                                    and should be removed";
1561                     err.multipart_suggestion(&msg, suggestion, Applicability::MachineApplicable);
1562                     if !suggested_changing_assoc_types {
1563                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1564                         suggested_changing_assoc_types = true;
1565                     }
1566                     err.emit();
1567                 });
1568             }
1569         }
1570     }
1571 }
1572
1573 declare_lint_pass!(
1574     /// Lint constants that are erroneous.
1575     /// Without this lint, we might not get any diagnostic if the constant is
1576     /// unused within this crate, even though downstream crates can't use it
1577     /// without producing an error.
1578     UnusedBrokenConst => []
1579 );
1580
1581 impl<'tcx> LateLintPass<'tcx> for UnusedBrokenConst {
1582     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1583         match it.kind {
1584             hir::ItemKind::Const(_, body_id) => {
1585                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1586                 // trigger the query once for all constants since that will already report the errors
1587                 // FIXME: Use ensure here
1588                 let _ = cx.tcx.const_eval_poly(def_id);
1589             }
1590             hir::ItemKind::Static(_, _, body_id) => {
1591                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1592                 // FIXME: Use ensure here
1593                 let _ = cx.tcx.eval_static_initializer(def_id);
1594             }
1595             _ => {}
1596         }
1597     }
1598 }
1599
1600 declare_lint! {
1601     /// The `trivial_bounds` lint detects trait bounds that don't depend on
1602     /// any type parameters.
1603     ///
1604     /// ### Example
1605     ///
1606     /// ```rust
1607     /// #![feature(trivial_bounds)]
1608     /// pub struct A where i32: Copy;
1609     /// ```
1610     ///
1611     /// {{produces}}
1612     ///
1613     /// ### Explanation
1614     ///
1615     /// Usually you would not write a trait bound that you know is always
1616     /// true, or never true. However, when using macros, the macro may not
1617     /// know whether or not the constraint would hold or not at the time when
1618     /// generating the code. Currently, the compiler does not alert you if the
1619     /// constraint is always true, and generates an error if it is never true.
1620     /// The `trivial_bounds` feature changes this to be a warning in both
1621     /// cases, giving macros more freedom and flexibility to generate code,
1622     /// while still providing a signal when writing non-macro code that
1623     /// something is amiss.
1624     ///
1625     /// See [RFC 2056] for more details. This feature is currently only
1626     /// available on the nightly channel, see [tracking issue #48214].
1627     ///
1628     /// [RFC 2056]: https://github.com/rust-lang/rfcs/blob/master/text/2056-allow-trivial-where-clause-constraints.md
1629     /// [tracking issue #48214]: https://github.com/rust-lang/rust/issues/48214
1630     TRIVIAL_BOUNDS,
1631     Warn,
1632     "these bounds don't depend on an type parameters"
1633 }
1634
1635 declare_lint_pass!(
1636     /// Lint for trait and lifetime bounds that don't depend on type parameters
1637     /// which either do nothing, or stop the item from being used.
1638     TrivialConstraints => [TRIVIAL_BOUNDS]
1639 );
1640
1641 impl<'tcx> LateLintPass<'tcx> for TrivialConstraints {
1642     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
1643         use rustc_middle::ty::fold::TypeFoldable;
1644         use rustc_middle::ty::PredicateKind::*;
1645
1646         if cx.tcx.features().trivial_bounds {
1647             let predicates = cx.tcx.predicates_of(item.def_id);
1648             for &(predicate, span) in predicates.predicates {
1649                 let predicate_kind_name = match predicate.kind().skip_binder() {
1650                     Trait(..) => "trait",
1651                     TypeOutlives(..) |
1652                     RegionOutlives(..) => "lifetime",
1653
1654                     // Ignore projections, as they can only be global
1655                     // if the trait bound is global
1656                     Projection(..) |
1657                     // Ignore bounds that a user can't type
1658                     WellFormed(..) |
1659                     ObjectSafe(..) |
1660                     ClosureKind(..) |
1661                     Subtype(..) |
1662                     Coerce(..) |
1663                     ConstEvaluatable(..) |
1664                     ConstEquate(..) |
1665                     TypeWellFormedFromEnv(..) => continue,
1666                 };
1667                 if predicate.is_global(cx.tcx) {
1668                     cx.struct_span_lint(TRIVIAL_BOUNDS, span, |lint| {
1669                         lint.build(&format!(
1670                             "{} bound {} does not depend on any type \
1671                                 or lifetime parameters",
1672                             predicate_kind_name, predicate
1673                         ))
1674                         .emit()
1675                     });
1676                 }
1677             }
1678         }
1679     }
1680 }
1681
1682 declare_lint_pass!(
1683     /// Does nothing as a lint pass, but registers some `Lint`s
1684     /// which are used by other parts of the compiler.
1685     SoftLints => [
1686         WHILE_TRUE,
1687         BOX_POINTERS,
1688         NON_SHORTHAND_FIELD_PATTERNS,
1689         UNSAFE_CODE,
1690         MISSING_DOCS,
1691         MISSING_COPY_IMPLEMENTATIONS,
1692         MISSING_DEBUG_IMPLEMENTATIONS,
1693         ANONYMOUS_PARAMETERS,
1694         UNUSED_DOC_COMMENTS,
1695         NO_MANGLE_CONST_ITEMS,
1696         NO_MANGLE_GENERIC_ITEMS,
1697         MUTABLE_TRANSMUTES,
1698         UNSTABLE_FEATURES,
1699         UNREACHABLE_PUB,
1700         TYPE_ALIAS_BOUNDS,
1701         TRIVIAL_BOUNDS
1702     ]
1703 );
1704
1705 declare_lint! {
1706     /// The `ellipsis_inclusive_range_patterns` lint detects the [`...` range
1707     /// pattern], which is deprecated.
1708     ///
1709     /// [`...` range pattern]: https://doc.rust-lang.org/reference/patterns.html#range-patterns
1710     ///
1711     /// ### Example
1712     ///
1713     /// ```rust,edition2018
1714     /// let x = 123;
1715     /// match x {
1716     ///     0...100 => {}
1717     ///     _ => {}
1718     /// }
1719     /// ```
1720     ///
1721     /// {{produces}}
1722     ///
1723     /// ### Explanation
1724     ///
1725     /// The `...` range pattern syntax was changed to `..=` to avoid potential
1726     /// confusion with the [`..` range expression]. Use the new form instead.
1727     ///
1728     /// [`..` range expression]: https://doc.rust-lang.org/reference/expressions/range-expr.html
1729     pub ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
1730     Warn,
1731     "`...` range patterns are deprecated",
1732     @future_incompatible = FutureIncompatibleInfo {
1733         reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>",
1734         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
1735     };
1736 }
1737
1738 #[derive(Default)]
1739 pub struct EllipsisInclusiveRangePatterns {
1740     /// If `Some(_)`, suppress all subsequent pattern
1741     /// warnings for better diagnostics.
1742     node_id: Option<ast::NodeId>,
1743 }
1744
1745 impl_lint_pass!(EllipsisInclusiveRangePatterns => [ELLIPSIS_INCLUSIVE_RANGE_PATTERNS]);
1746
1747 impl EarlyLintPass for EllipsisInclusiveRangePatterns {
1748     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &ast::Pat) {
1749         if self.node_id.is_some() {
1750             // Don't recursively warn about patterns inside range endpoints.
1751             return;
1752         }
1753
1754         use self::ast::{PatKind, RangeSyntax::DotDotDot};
1755
1756         /// If `pat` is a `...` pattern, return the start and end of the range, as well as the span
1757         /// corresponding to the ellipsis.
1758         fn matches_ellipsis_pat(pat: &ast::Pat) -> Option<(Option<&Expr>, &Expr, Span)> {
1759             match &pat.kind {
1760                 PatKind::Range(
1761                     a,
1762                     Some(b),
1763                     Spanned { span, node: RangeEnd::Included(DotDotDot) },
1764                 ) => Some((a.as_deref(), b, *span)),
1765                 _ => None,
1766             }
1767         }
1768
1769         let (parenthesise, endpoints) = match &pat.kind {
1770             PatKind::Ref(subpat, _) => (true, matches_ellipsis_pat(&subpat)),
1771             _ => (false, matches_ellipsis_pat(pat)),
1772         };
1773
1774         if let Some((start, end, join)) = endpoints {
1775             let msg = "`...` range patterns are deprecated";
1776             let suggestion = "use `..=` for an inclusive range";
1777             if parenthesise {
1778                 self.node_id = Some(pat.id);
1779                 let end = expr_to_string(&end);
1780                 let replace = match start {
1781                     Some(start) => format!("&({}..={})", expr_to_string(&start), end),
1782                     None => format!("&(..={})", end),
1783                 };
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(
1788                         pat.span,
1789                         suggestion,
1790                         replace,
1791                         Applicability::MachineApplicable,
1792                     )
1793                     .emit();
1794                 } else {
1795                     cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, pat.span, |lint| {
1796                         lint.build(msg)
1797                             .span_suggestion(
1798                                 pat.span,
1799                                 suggestion,
1800                                 replace,
1801                                 Applicability::MachineApplicable,
1802                             )
1803                             .emit();
1804                     });
1805                 }
1806             } else {
1807                 let replace = "..=".to_owned();
1808                 if join.edition() >= Edition::Edition2021 {
1809                     let mut err =
1810                         rustc_errors::struct_span_err!(cx.sess, pat.span, E0783, "{}", msg,);
1811                     err.span_suggestion_short(
1812                         join,
1813                         suggestion,
1814                         replace,
1815                         Applicability::MachineApplicable,
1816                     )
1817                     .emit();
1818                 } else {
1819                     cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, join, |lint| {
1820                         lint.build(msg)
1821                             .span_suggestion_short(
1822                                 join,
1823                                 suggestion,
1824                                 replace,
1825                                 Applicability::MachineApplicable,
1826                             )
1827                             .emit();
1828                     });
1829                 }
1830             };
1831         }
1832     }
1833
1834     fn check_pat_post(&mut self, _cx: &EarlyContext<'_>, pat: &ast::Pat) {
1835         if let Some(node_id) = self.node_id {
1836             if pat.id == node_id {
1837                 self.node_id = None
1838             }
1839         }
1840     }
1841 }
1842
1843 declare_lint! {
1844     /// The `unnameable_test_items` lint detects [`#[test]`][test] functions
1845     /// that are not able to be run by the test harness because they are in a
1846     /// position where they are not nameable.
1847     ///
1848     /// [test]: https://doc.rust-lang.org/reference/attributes/testing.html#the-test-attribute
1849     ///
1850     /// ### Example
1851     ///
1852     /// ```rust,test
1853     /// fn main() {
1854     ///     #[test]
1855     ///     fn foo() {
1856     ///         // This test will not fail because it does not run.
1857     ///         assert_eq!(1, 2);
1858     ///     }
1859     /// }
1860     /// ```
1861     ///
1862     /// {{produces}}
1863     ///
1864     /// ### Explanation
1865     ///
1866     /// In order for the test harness to run a test, the test function must be
1867     /// located in a position where it can be accessed from the crate root.
1868     /// This generally means it must be defined in a module, and not anywhere
1869     /// else such as inside another function. The compiler previously allowed
1870     /// this without an error, so a lint was added as an alert that a test is
1871     /// not being used. Whether or not this should be allowed has not yet been
1872     /// decided, see [RFC 2471] and [issue #36629].
1873     ///
1874     /// [RFC 2471]: https://github.com/rust-lang/rfcs/pull/2471#issuecomment-397414443
1875     /// [issue #36629]: https://github.com/rust-lang/rust/issues/36629
1876     UNNAMEABLE_TEST_ITEMS,
1877     Warn,
1878     "detects an item that cannot be named being marked as `#[test_case]`",
1879     report_in_external_macro
1880 }
1881
1882 pub struct UnnameableTestItems {
1883     boundary: Option<LocalDefId>, // Id of the item under which things are not nameable
1884     items_nameable: bool,
1885 }
1886
1887 impl_lint_pass!(UnnameableTestItems => [UNNAMEABLE_TEST_ITEMS]);
1888
1889 impl UnnameableTestItems {
1890     pub fn new() -> Self {
1891         Self { boundary: None, items_nameable: true }
1892     }
1893 }
1894
1895 impl<'tcx> LateLintPass<'tcx> for UnnameableTestItems {
1896     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1897         if self.items_nameable {
1898             if let hir::ItemKind::Mod(..) = it.kind {
1899             } else {
1900                 self.items_nameable = false;
1901                 self.boundary = Some(it.def_id);
1902             }
1903             return;
1904         }
1905
1906         let attrs = cx.tcx.hir().attrs(it.hir_id());
1907         if let Some(attr) = cx.sess().find_by_name(attrs, sym::rustc_test_marker) {
1908             cx.struct_span_lint(UNNAMEABLE_TEST_ITEMS, attr.span, |lint| {
1909                 lint.build("cannot test inner items").emit()
1910             });
1911         }
1912     }
1913
1914     fn check_item_post(&mut self, _cx: &LateContext<'_>, it: &hir::Item<'_>) {
1915         if !self.items_nameable && self.boundary == Some(it.def_id) {
1916             self.items_nameable = true;
1917         }
1918     }
1919 }
1920
1921 declare_lint! {
1922     /// The `keyword_idents` lint detects edition keywords being used as an
1923     /// identifier.
1924     ///
1925     /// ### Example
1926     ///
1927     /// ```rust,edition2015,compile_fail
1928     /// #![deny(keyword_idents)]
1929     /// // edition 2015
1930     /// fn dyn() {}
1931     /// ```
1932     ///
1933     /// {{produces}}
1934     ///
1935     /// ### Explanation
1936     ///
1937     /// Rust [editions] allow the language to evolve without breaking
1938     /// backwards compatibility. This lint catches code that uses new keywords
1939     /// that are added to the language that are used as identifiers (such as a
1940     /// variable name, function name, etc.). If you switch the compiler to a
1941     /// new edition without updating the code, then it will fail to compile if
1942     /// you are using a new keyword as an identifier.
1943     ///
1944     /// You can manually change the identifiers to a non-keyword, or use a
1945     /// [raw identifier], for example `r#dyn`, to transition to a new edition.
1946     ///
1947     /// This lint solves the problem automatically. It is "allow" by default
1948     /// because the code is perfectly valid in older editions. The [`cargo
1949     /// fix`] tool with the `--edition` flag will switch this lint to "warn"
1950     /// and automatically apply the suggested fix from the compiler (which is
1951     /// to use a raw identifier). This provides a completely automated way to
1952     /// update old code for a new edition.
1953     ///
1954     /// [editions]: https://doc.rust-lang.org/edition-guide/
1955     /// [raw identifier]: https://doc.rust-lang.org/reference/identifiers.html
1956     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
1957     pub KEYWORD_IDENTS,
1958     Allow,
1959     "detects edition keywords being used as an identifier",
1960     @future_incompatible = FutureIncompatibleInfo {
1961         reference: "issue #49716 <https://github.com/rust-lang/rust/issues/49716>",
1962         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
1963     };
1964 }
1965
1966 declare_lint_pass!(
1967     /// Check for uses of edition keywords used as an identifier.
1968     KeywordIdents => [KEYWORD_IDENTS]
1969 );
1970
1971 struct UnderMacro(bool);
1972
1973 impl KeywordIdents {
1974     fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: TokenStream) {
1975         for tt in tokens.into_trees() {
1976             match tt {
1977                 // Only report non-raw idents.
1978                 TokenTree::Token(token) => {
1979                     if let Some((ident, false)) = token.ident() {
1980                         self.check_ident_token(cx, UnderMacro(true), ident);
1981                     }
1982                 }
1983                 TokenTree::Delimited(_, _, tts) => self.check_tokens(cx, tts),
1984             }
1985         }
1986     }
1987
1988     fn check_ident_token(
1989         &mut self,
1990         cx: &EarlyContext<'_>,
1991         UnderMacro(under_macro): UnderMacro,
1992         ident: Ident,
1993     ) {
1994         let next_edition = match cx.sess.edition() {
1995             Edition::Edition2015 => {
1996                 match ident.name {
1997                     kw::Async | kw::Await | kw::Try => Edition::Edition2018,
1998
1999                     // rust-lang/rust#56327: Conservatively do not
2000                     // attempt to report occurrences of `dyn` within
2001                     // macro definitions or invocations, because `dyn`
2002                     // can legitimately occur as a contextual keyword
2003                     // in 2015 code denoting its 2018 meaning, and we
2004                     // do not want rustfix to inject bugs into working
2005                     // code by rewriting such occurrences.
2006                     //
2007                     // But if we see `dyn` outside of a macro, we know
2008                     // its precise role in the parsed AST and thus are
2009                     // assured this is truly an attempt to use it as
2010                     // an identifier.
2011                     kw::Dyn if !under_macro => Edition::Edition2018,
2012
2013                     _ => return,
2014                 }
2015             }
2016
2017             // There are no new keywords yet for the 2018 edition and beyond.
2018             _ => return,
2019         };
2020
2021         // Don't lint `r#foo`.
2022         if cx.sess.parse_sess.raw_identifier_spans.borrow().contains(&ident.span) {
2023             return;
2024         }
2025
2026         cx.struct_span_lint(KEYWORD_IDENTS, ident.span, |lint| {
2027             lint.build(&format!("`{}` is a keyword in the {} edition", ident, next_edition))
2028                 .span_suggestion(
2029                     ident.span,
2030                     "you can use a raw identifier to stay compatible",
2031                     format!("r#{}", ident),
2032                     Applicability::MachineApplicable,
2033                 )
2034                 .emit()
2035         });
2036     }
2037 }
2038
2039 impl EarlyLintPass for KeywordIdents {
2040     fn check_mac_def(&mut self, cx: &EarlyContext<'_>, mac_def: &ast::MacroDef, _id: ast::NodeId) {
2041         self.check_tokens(cx, mac_def.body.inner_tokens());
2042     }
2043     fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::MacCall) {
2044         self.check_tokens(cx, mac.args.inner_tokens());
2045     }
2046     fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: Ident) {
2047         self.check_ident_token(cx, UnderMacro(false), ident);
2048     }
2049 }
2050
2051 declare_lint_pass!(ExplicitOutlivesRequirements => [EXPLICIT_OUTLIVES_REQUIREMENTS]);
2052
2053 impl ExplicitOutlivesRequirements {
2054     fn lifetimes_outliving_lifetime<'tcx>(
2055         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2056         index: u32,
2057     ) -> Vec<ty::Region<'tcx>> {
2058         inferred_outlives
2059             .iter()
2060             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
2061                 ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => match a {
2062                     ty::ReEarlyBound(ebr) if ebr.index == index => Some(b),
2063                     _ => None,
2064                 },
2065                 _ => None,
2066             })
2067             .collect()
2068     }
2069
2070     fn lifetimes_outliving_type<'tcx>(
2071         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2072         index: u32,
2073     ) -> Vec<ty::Region<'tcx>> {
2074         inferred_outlives
2075             .iter()
2076             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
2077                 ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
2078                     a.is_param(index).then_some(b)
2079                 }
2080                 _ => None,
2081             })
2082             .collect()
2083     }
2084
2085     fn collect_outlived_lifetimes<'tcx>(
2086         &self,
2087         param: &'tcx hir::GenericParam<'tcx>,
2088         tcx: TyCtxt<'tcx>,
2089         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2090         ty_generics: &'tcx ty::Generics,
2091     ) -> Vec<ty::Region<'tcx>> {
2092         let index =
2093             ty_generics.param_def_id_to_index[&tcx.hir().local_def_id(param.hir_id).to_def_id()];
2094
2095         match param.kind {
2096             hir::GenericParamKind::Lifetime { .. } => {
2097                 Self::lifetimes_outliving_lifetime(inferred_outlives, index)
2098             }
2099             hir::GenericParamKind::Type { .. } => {
2100                 Self::lifetimes_outliving_type(inferred_outlives, index)
2101             }
2102             hir::GenericParamKind::Const { .. } => Vec::new(),
2103         }
2104     }
2105
2106     fn collect_outlives_bound_spans<'tcx>(
2107         &self,
2108         tcx: TyCtxt<'tcx>,
2109         bounds: &hir::GenericBounds<'_>,
2110         inferred_outlives: &[ty::Region<'tcx>],
2111         infer_static: bool,
2112     ) -> Vec<(usize, Span)> {
2113         use rustc_middle::middle::resolve_lifetime::Region;
2114
2115         bounds
2116             .iter()
2117             .enumerate()
2118             .filter_map(|(i, bound)| {
2119                 if let hir::GenericBound::Outlives(lifetime) = bound {
2120                     let is_inferred = match tcx.named_region(lifetime.hir_id) {
2121                         Some(Region::Static) if infer_static => {
2122                             inferred_outlives.iter().any(|r| matches!(r, ty::ReStatic))
2123                         }
2124                         Some(Region::EarlyBound(index, ..)) => inferred_outlives.iter().any(|r| {
2125                             if let ty::ReEarlyBound(ebr) = r { ebr.index == index } else { false }
2126                         }),
2127                         _ => false,
2128                     };
2129                     is_inferred.then_some((i, bound.span()))
2130                 } else {
2131                     None
2132                 }
2133             })
2134             .collect()
2135     }
2136
2137     fn consolidate_outlives_bound_spans(
2138         &self,
2139         lo: Span,
2140         bounds: &hir::GenericBounds<'_>,
2141         bound_spans: Vec<(usize, Span)>,
2142     ) -> Vec<Span> {
2143         if bounds.is_empty() {
2144             return Vec::new();
2145         }
2146         if bound_spans.len() == bounds.len() {
2147             let (_, last_bound_span) = bound_spans[bound_spans.len() - 1];
2148             // If all bounds are inferable, we want to delete the colon, so
2149             // start from just after the parameter (span passed as argument)
2150             vec![lo.to(last_bound_span)]
2151         } else {
2152             let mut merged = Vec::new();
2153             let mut last_merged_i = None;
2154
2155             let mut from_start = true;
2156             for (i, bound_span) in bound_spans {
2157                 match last_merged_i {
2158                     // If the first bound is inferable, our span should also eat the leading `+`.
2159                     None if i == 0 => {
2160                         merged.push(bound_span.to(bounds[1].span().shrink_to_lo()));
2161                         last_merged_i = Some(0);
2162                     }
2163                     // If consecutive bounds are inferable, merge their spans
2164                     Some(h) if i == h + 1 => {
2165                         if let Some(tail) = merged.last_mut() {
2166                             // Also eat the trailing `+` if the first
2167                             // more-than-one bound is inferable
2168                             let to_span = if from_start && i < bounds.len() {
2169                                 bounds[i + 1].span().shrink_to_lo()
2170                             } else {
2171                                 bound_span
2172                             };
2173                             *tail = tail.to(to_span);
2174                             last_merged_i = Some(i);
2175                         } else {
2176                             bug!("another bound-span visited earlier");
2177                         }
2178                     }
2179                     _ => {
2180                         // When we find a non-inferable bound, subsequent inferable bounds
2181                         // won't be consecutive from the start (and we'll eat the leading
2182                         // `+` rather than the trailing one)
2183                         from_start = false;
2184                         merged.push(bounds[i - 1].span().shrink_to_hi().to(bound_span));
2185                         last_merged_i = Some(i);
2186                     }
2187                 }
2188             }
2189             merged
2190         }
2191     }
2192 }
2193
2194 impl<'tcx> LateLintPass<'tcx> for ExplicitOutlivesRequirements {
2195     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
2196         use rustc_middle::middle::resolve_lifetime::Region;
2197
2198         let infer_static = cx.tcx.features().infer_static_outlives_requirements;
2199         let def_id = item.def_id;
2200         if let hir::ItemKind::Struct(_, ref hir_generics)
2201         | hir::ItemKind::Enum(_, ref hir_generics)
2202         | hir::ItemKind::Union(_, ref hir_generics) = item.kind
2203         {
2204             let inferred_outlives = cx.tcx.inferred_outlives_of(def_id);
2205             if inferred_outlives.is_empty() {
2206                 return;
2207             }
2208
2209             let ty_generics = cx.tcx.generics_of(def_id);
2210
2211             let mut bound_count = 0;
2212             let mut lint_spans = Vec::new();
2213
2214             for param in hir_generics.params {
2215                 let has_lifetime_bounds = param
2216                     .bounds
2217                     .iter()
2218                     .any(|bound| matches!(bound, hir::GenericBound::Outlives(_)));
2219                 if !has_lifetime_bounds {
2220                     continue;
2221                 }
2222
2223                 let relevant_lifetimes =
2224                     self.collect_outlived_lifetimes(param, cx.tcx, inferred_outlives, ty_generics);
2225                 if relevant_lifetimes.is_empty() {
2226                     continue;
2227                 }
2228
2229                 let bound_spans = self.collect_outlives_bound_spans(
2230                     cx.tcx,
2231                     &param.bounds,
2232                     &relevant_lifetimes,
2233                     infer_static,
2234                 );
2235                 bound_count += bound_spans.len();
2236                 lint_spans.extend(self.consolidate_outlives_bound_spans(
2237                     param.span.shrink_to_hi(),
2238                     &param.bounds,
2239                     bound_spans,
2240                 ));
2241             }
2242
2243             let mut where_lint_spans = Vec::new();
2244             let mut dropped_predicate_count = 0;
2245             let num_predicates = hir_generics.where_clause.predicates.len();
2246             for (i, where_predicate) in hir_generics.where_clause.predicates.iter().enumerate() {
2247                 let (relevant_lifetimes, bounds, span) = match where_predicate {
2248                     hir::WherePredicate::RegionPredicate(predicate) => {
2249                         if let Some(Region::EarlyBound(index, ..)) =
2250                             cx.tcx.named_region(predicate.lifetime.hir_id)
2251                         {
2252                             (
2253                                 Self::lifetimes_outliving_lifetime(inferred_outlives, index),
2254                                 &predicate.bounds,
2255                                 predicate.span,
2256                             )
2257                         } else {
2258                             continue;
2259                         }
2260                     }
2261                     hir::WherePredicate::BoundPredicate(predicate) => {
2262                         // FIXME we can also infer bounds on associated types,
2263                         // and should check for them here.
2264                         match predicate.bounded_ty.kind {
2265                             hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
2266                                 if let Res::Def(DefKind::TyParam, def_id) = path.res {
2267                                     let index = ty_generics.param_def_id_to_index[&def_id];
2268                                     (
2269                                         Self::lifetimes_outliving_type(inferred_outlives, index),
2270                                         &predicate.bounds,
2271                                         predicate.span,
2272                                     )
2273                                 } else {
2274                                     continue;
2275                                 }
2276                             }
2277                             _ => {
2278                                 continue;
2279                             }
2280                         }
2281                     }
2282                     _ => continue,
2283                 };
2284                 if relevant_lifetimes.is_empty() {
2285                     continue;
2286                 }
2287
2288                 let bound_spans = self.collect_outlives_bound_spans(
2289                     cx.tcx,
2290                     bounds,
2291                     &relevant_lifetimes,
2292                     infer_static,
2293                 );
2294                 bound_count += bound_spans.len();
2295
2296                 let drop_predicate = bound_spans.len() == bounds.len();
2297                 if drop_predicate {
2298                     dropped_predicate_count += 1;
2299                 }
2300
2301                 // If all the bounds on a predicate were inferable and there are
2302                 // further predicates, we want to eat the trailing comma.
2303                 if drop_predicate && i + 1 < num_predicates {
2304                     let next_predicate_span = hir_generics.where_clause.predicates[i + 1].span();
2305                     where_lint_spans.push(span.to(next_predicate_span.shrink_to_lo()));
2306                 } else {
2307                     where_lint_spans.extend(self.consolidate_outlives_bound_spans(
2308                         span.shrink_to_lo(),
2309                         bounds,
2310                         bound_spans,
2311                     ));
2312                 }
2313             }
2314
2315             // If all predicates are inferable, drop the entire clause
2316             // (including the `where`)
2317             if num_predicates > 0 && dropped_predicate_count == num_predicates {
2318                 let where_span = hir_generics
2319                     .where_clause
2320                     .span()
2321                     .expect("span of (nonempty) where clause should exist");
2322                 // Extend the where clause back to the closing `>` of the
2323                 // generics, except for tuple struct, which have the `where`
2324                 // after the fields of the struct.
2325                 let full_where_span =
2326                     if let hir::ItemKind::Struct(hir::VariantData::Tuple(..), _) = item.kind {
2327                         where_span
2328                     } else {
2329                         hir_generics.span.shrink_to_hi().to(where_span)
2330                     };
2331                 lint_spans.push(full_where_span);
2332             } else {
2333                 lint_spans.extend(where_lint_spans);
2334             }
2335
2336             if !lint_spans.is_empty() {
2337                 cx.struct_span_lint(EXPLICIT_OUTLIVES_REQUIREMENTS, lint_spans.clone(), |lint| {
2338                     lint.build("outlives requirements can be inferred")
2339                         .multipart_suggestion(
2340                             if bound_count == 1 {
2341                                 "remove this bound"
2342                             } else {
2343                                 "remove these bounds"
2344                             },
2345                             lint_spans
2346                                 .into_iter()
2347                                 .map(|span| (span, "".to_owned()))
2348                                 .collect::<Vec<_>>(),
2349                             Applicability::MachineApplicable,
2350                         )
2351                         .emit();
2352                 });
2353             }
2354         }
2355     }
2356 }
2357
2358 declare_lint! {
2359     /// The `incomplete_features` lint detects unstable features enabled with
2360     /// the [`feature` attribute] that may function improperly in some or all
2361     /// cases.
2362     ///
2363     /// [`feature` attribute]: https://doc.rust-lang.org/nightly/unstable-book/
2364     ///
2365     /// ### Example
2366     ///
2367     /// ```rust
2368     /// #![feature(generic_const_exprs)]
2369     /// ```
2370     ///
2371     /// {{produces}}
2372     ///
2373     /// ### Explanation
2374     ///
2375     /// Although it is encouraged for people to experiment with unstable
2376     /// features, some of them are known to be incomplete or faulty. This lint
2377     /// is a signal that the feature has not yet been finished, and you may
2378     /// experience problems with it.
2379     pub INCOMPLETE_FEATURES,
2380     Warn,
2381     "incomplete features that may function improperly in some or all cases"
2382 }
2383
2384 declare_lint_pass!(
2385     /// Check for used feature gates in `INCOMPLETE_FEATURES` in `rustc_feature/src/active.rs`.
2386     IncompleteFeatures => [INCOMPLETE_FEATURES]
2387 );
2388
2389 impl EarlyLintPass for IncompleteFeatures {
2390     fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
2391         let features = cx.sess.features_untracked();
2392         features
2393             .declared_lang_features
2394             .iter()
2395             .map(|(name, span, _)| (name, span))
2396             .chain(features.declared_lib_features.iter().map(|(name, span)| (name, span)))
2397             .filter(|(&name, _)| features.incomplete(name))
2398             .for_each(|(&name, &span)| {
2399                 cx.struct_span_lint(INCOMPLETE_FEATURES, span, |lint| {
2400                     let mut builder = lint.build(&format!(
2401                         "the feature `{}` is incomplete and may not be safe to use \
2402                          and/or cause compiler crashes",
2403                         name,
2404                     ));
2405                     if let Some(n) = rustc_feature::find_feature_issue(name, GateIssue::Language) {
2406                         builder.note(&format!(
2407                             "see issue #{} <https://github.com/rust-lang/rust/issues/{}> \
2408                              for more information",
2409                             n, n,
2410                         ));
2411                     }
2412                     if HAS_MIN_FEATURES.contains(&name) {
2413                         builder.help(&format!(
2414                             "consider using `min_{}` instead, which is more stable and complete",
2415                             name,
2416                         ));
2417                     }
2418                     builder.emit();
2419                 })
2420             });
2421     }
2422 }
2423
2424 const HAS_MIN_FEATURES: &[Symbol] = &[sym::specialization];
2425
2426 declare_lint! {
2427     /// The `invalid_value` lint detects creating a value that is not valid,
2428     /// such as a null reference.
2429     ///
2430     /// ### Example
2431     ///
2432     /// ```rust,no_run
2433     /// # #![allow(unused)]
2434     /// unsafe {
2435     ///     let x: &'static i32 = std::mem::zeroed();
2436     /// }
2437     /// ```
2438     ///
2439     /// {{produces}}
2440     ///
2441     /// ### Explanation
2442     ///
2443     /// In some situations the compiler can detect that the code is creating
2444     /// an invalid value, which should be avoided.
2445     ///
2446     /// In particular, this lint will check for improper use of
2447     /// [`mem::zeroed`], [`mem::uninitialized`], [`mem::transmute`], and
2448     /// [`MaybeUninit::assume_init`] that can cause [undefined behavior]. The
2449     /// lint should provide extra information to indicate what the problem is
2450     /// and a possible solution.
2451     ///
2452     /// [`mem::zeroed`]: https://doc.rust-lang.org/std/mem/fn.zeroed.html
2453     /// [`mem::uninitialized`]: https://doc.rust-lang.org/std/mem/fn.uninitialized.html
2454     /// [`mem::transmute`]: https://doc.rust-lang.org/std/mem/fn.transmute.html
2455     /// [`MaybeUninit::assume_init`]: https://doc.rust-lang.org/std/mem/union.MaybeUninit.html#method.assume_init
2456     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
2457     pub INVALID_VALUE,
2458     Warn,
2459     "an invalid value is being created (such as a null reference)"
2460 }
2461
2462 declare_lint_pass!(InvalidValue => [INVALID_VALUE]);
2463
2464 impl<'tcx> LateLintPass<'tcx> for InvalidValue {
2465     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
2466         #[derive(Debug, Copy, Clone, PartialEq)]
2467         enum InitKind {
2468             Zeroed,
2469             Uninit,
2470         }
2471
2472         /// Information about why a type cannot be initialized this way.
2473         /// Contains an error message and optionally a span to point at.
2474         type InitError = (String, Option<Span>);
2475
2476         /// Test if this constant is all-0.
2477         fn is_zero(expr: &hir::Expr<'_>) -> bool {
2478             use hir::ExprKind::*;
2479             use rustc_ast::LitKind::*;
2480             match &expr.kind {
2481                 Lit(lit) => {
2482                     if let Int(i, _) = lit.node {
2483                         i == 0
2484                     } else {
2485                         false
2486                     }
2487                 }
2488                 Tup(tup) => tup.iter().all(is_zero),
2489                 _ => false,
2490             }
2491         }
2492
2493         /// Determine if this expression is a "dangerous initialization".
2494         fn is_dangerous_init(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> Option<InitKind> {
2495             if let hir::ExprKind::Call(ref path_expr, ref args) = expr.kind {
2496                 // Find calls to `mem::{uninitialized,zeroed}` methods.
2497                 if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2498                     let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2499                     match cx.tcx.get_diagnostic_name(def_id) {
2500                         Some(sym::mem_zeroed) => return Some(InitKind::Zeroed),
2501                         Some(sym::mem_uninitialized) => return Some(InitKind::Uninit),
2502                         Some(sym::transmute) if is_zero(&args[0]) => return Some(InitKind::Zeroed),
2503                         _ => {}
2504                     }
2505                 }
2506             } else if let hir::ExprKind::MethodCall(_, _, ref args, _) = expr.kind {
2507                 // Find problematic calls to `MaybeUninit::assume_init`.
2508                 let def_id = cx.typeck_results().type_dependent_def_id(expr.hir_id)?;
2509                 if cx.tcx.is_diagnostic_item(sym::assume_init, def_id) {
2510                     // This is a call to *some* method named `assume_init`.
2511                     // See if the `self` parameter is one of the dangerous constructors.
2512                     if let hir::ExprKind::Call(ref path_expr, _) = args[0].kind {
2513                         if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2514                             let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2515                             match cx.tcx.get_diagnostic_name(def_id) {
2516                                 Some(sym::maybe_uninit_zeroed) => return Some(InitKind::Zeroed),
2517                                 Some(sym::maybe_uninit_uninit) => return Some(InitKind::Uninit),
2518                                 _ => {}
2519                             }
2520                         }
2521                     }
2522                 }
2523             }
2524
2525             None
2526         }
2527
2528         /// Test if this enum has several actually "existing" variants.
2529         /// Zero-sized uninhabited variants do not always have a tag assigned and thus do not "exist".
2530         fn is_multi_variant(adt: &ty::AdtDef) -> bool {
2531             // As an approximation, we only count dataless variants. Those are definitely inhabited.
2532             let existing_variants = adt.variants.iter().filter(|v| v.fields.is_empty()).count();
2533             existing_variants > 1
2534         }
2535
2536         /// Return `Some` only if we are sure this type does *not*
2537         /// allow zero initialization.
2538         fn ty_find_init_error<'tcx>(
2539             tcx: TyCtxt<'tcx>,
2540             ty: Ty<'tcx>,
2541             init: InitKind,
2542         ) -> Option<InitError> {
2543             use rustc_middle::ty::TyKind::*;
2544             match ty.kind() {
2545                 // Primitive types that don't like 0 as a value.
2546                 Ref(..) => Some(("references must be non-null".to_string(), None)),
2547                 Adt(..) if ty.is_box() => Some(("`Box` must be non-null".to_string(), None)),
2548                 FnPtr(..) => Some(("function pointers must be non-null".to_string(), None)),
2549                 Never => Some(("the `!` type has no valid value".to_string(), None)),
2550                 RawPtr(tm) if matches!(tm.ty.kind(), Dynamic(..)) =>
2551                 // raw ptr to dyn Trait
2552                 {
2553                     Some(("the vtable of a wide raw pointer must be non-null".to_string(), None))
2554                 }
2555                 // Primitive types with other constraints.
2556                 Bool if init == InitKind::Uninit => {
2557                     Some(("booleans must be either `true` or `false`".to_string(), None))
2558                 }
2559                 Char if init == InitKind::Uninit => {
2560                     Some(("characters must be a valid Unicode codepoint".to_string(), None))
2561                 }
2562                 // Recurse and checks for some compound types.
2563                 Adt(adt_def, substs) if !adt_def.is_union() => {
2564                     // First check if this ADT has a layout attribute (like `NonNull` and friends).
2565                     use std::ops::Bound;
2566                     match tcx.layout_scalar_valid_range(adt_def.did) {
2567                         // We exploit here that `layout_scalar_valid_range` will never
2568                         // return `Bound::Excluded`.  (And we have tests checking that we
2569                         // handle the attribute correctly.)
2570                         (Bound::Included(lo), _) if lo > 0 => {
2571                             return Some((format!("`{}` must be non-null", ty), None));
2572                         }
2573                         (Bound::Included(_), _) | (_, Bound::Included(_))
2574                             if init == InitKind::Uninit =>
2575                         {
2576                             return Some((
2577                                 format!(
2578                                     "`{}` must be initialized inside its custom valid range",
2579                                     ty,
2580                                 ),
2581                                 None,
2582                             ));
2583                         }
2584                         _ => {}
2585                     }
2586                     // Now, recurse.
2587                     match adt_def.variants.len() {
2588                         0 => Some(("enums with no variants have no valid value".to_string(), None)),
2589                         1 => {
2590                             // Struct, or enum with exactly one variant.
2591                             // Proceed recursively, check all fields.
2592                             let variant = &adt_def.variants[VariantIdx::from_u32(0)];
2593                             variant.fields.iter().find_map(|field| {
2594                                 ty_find_init_error(tcx, field.ty(tcx, substs), init).map(
2595                                     |(mut msg, span)| {
2596                                         if span.is_none() {
2597                                             // Point to this field, should be helpful for figuring
2598                                             // out where the source of the error is.
2599                                             let span = tcx.def_span(field.did);
2600                                             write!(
2601                                                 &mut msg,
2602                                                 " (in this {} field)",
2603                                                 adt_def.descr()
2604                                             )
2605                                             .unwrap();
2606                                             (msg, Some(span))
2607                                         } else {
2608                                             // Just forward.
2609                                             (msg, span)
2610                                         }
2611                                     },
2612                                 )
2613                             })
2614                         }
2615                         // Multi-variant enum.
2616                         _ => {
2617                             if init == InitKind::Uninit && is_multi_variant(adt_def) {
2618                                 let span = tcx.def_span(adt_def.did);
2619                                 Some((
2620                                     "enums have to be initialized to a variant".to_string(),
2621                                     Some(span),
2622                                 ))
2623                             } else {
2624                                 // In principle, for zero-initialization we could figure out which variant corresponds
2625                                 // to tag 0, and check that... but for now we just accept all zero-initializations.
2626                                 None
2627                             }
2628                         }
2629                     }
2630                 }
2631                 Tuple(..) => {
2632                     // Proceed recursively, check all fields.
2633                     ty.tuple_fields().find_map(|field| ty_find_init_error(tcx, field, init))
2634                 }
2635                 // Conservative fallback.
2636                 _ => None,
2637             }
2638         }
2639
2640         if let Some(init) = is_dangerous_init(cx, expr) {
2641             // This conjures an instance of a type out of nothing,
2642             // using zeroed or uninitialized memory.
2643             // We are extremely conservative with what we warn about.
2644             let conjured_ty = cx.typeck_results().expr_ty(expr);
2645             if let Some((msg, span)) =
2646                 with_no_trimmed_paths(|| ty_find_init_error(cx.tcx, conjured_ty, init))
2647             {
2648                 cx.struct_span_lint(INVALID_VALUE, expr.span, |lint| {
2649                     let mut err = lint.build(&format!(
2650                         "the type `{}` does not permit {}",
2651                         conjured_ty,
2652                         match init {
2653                             InitKind::Zeroed => "zero-initialization",
2654                             InitKind::Uninit => "being left uninitialized",
2655                         },
2656                     ));
2657                     err.span_label(expr.span, "this code causes undefined behavior when executed");
2658                     err.span_label(
2659                         expr.span,
2660                         "help: use `MaybeUninit<T>` instead, \
2661                             and only call `assume_init` after initialization is done",
2662                     );
2663                     if let Some(span) = span {
2664                         err.span_note(span, &msg);
2665                     } else {
2666                         err.note(&msg);
2667                     }
2668                     err.emit();
2669                 });
2670             }
2671         }
2672     }
2673 }
2674
2675 declare_lint! {
2676     /// The `clashing_extern_declarations` lint detects when an `extern fn`
2677     /// has been declared with the same name but different types.
2678     ///
2679     /// ### Example
2680     ///
2681     /// ```rust
2682     /// mod m {
2683     ///     extern "C" {
2684     ///         fn foo();
2685     ///     }
2686     /// }
2687     ///
2688     /// extern "C" {
2689     ///     fn foo(_: u32);
2690     /// }
2691     /// ```
2692     ///
2693     /// {{produces}}
2694     ///
2695     /// ### Explanation
2696     ///
2697     /// Because two symbols of the same name cannot be resolved to two
2698     /// different functions at link time, and one function cannot possibly
2699     /// have two types, a clashing extern declaration is almost certainly a
2700     /// mistake. Check to make sure that the `extern` definitions are correct
2701     /// and equivalent, and possibly consider unifying them in one location.
2702     ///
2703     /// This lint does not run between crates because a project may have
2704     /// dependencies which both rely on the same extern function, but declare
2705     /// it in a different (but valid) way. For example, they may both declare
2706     /// an opaque type for one or more of the arguments (which would end up
2707     /// distinct types), or use types that are valid conversions in the
2708     /// language the `extern fn` is defined in. In these cases, the compiler
2709     /// can't say that the clashing declaration is incorrect.
2710     pub CLASHING_EXTERN_DECLARATIONS,
2711     Warn,
2712     "detects when an extern fn has been declared with the same name but different types"
2713 }
2714
2715 pub struct ClashingExternDeclarations {
2716     /// Map of function symbol name to the first-seen hir id for that symbol name.. If seen_decls
2717     /// contains an entry for key K, it means a symbol with name K has been seen by this lint and
2718     /// the symbol should be reported as a clashing declaration.
2719     // FIXME: Technically, we could just store a &'tcx str here without issue; however, the
2720     // `impl_lint_pass` macro doesn't currently support lints parametric over a lifetime.
2721     seen_decls: FxHashMap<Symbol, HirId>,
2722 }
2723
2724 /// Differentiate between whether the name for an extern decl came from the link_name attribute or
2725 /// just from declaration itself. This is important because we don't want to report clashes on
2726 /// symbol name if they don't actually clash because one or the other links against a symbol with a
2727 /// different name.
2728 enum SymbolName {
2729     /// The name of the symbol + the span of the annotation which introduced the link name.
2730     Link(Symbol, Span),
2731     /// No link name, so just the name of the symbol.
2732     Normal(Symbol),
2733 }
2734
2735 impl SymbolName {
2736     fn get_name(&self) -> Symbol {
2737         match self {
2738             SymbolName::Link(s, _) | SymbolName::Normal(s) => *s,
2739         }
2740     }
2741 }
2742
2743 impl ClashingExternDeclarations {
2744     crate fn new() -> Self {
2745         ClashingExternDeclarations { seen_decls: FxHashMap::default() }
2746     }
2747     /// Insert a new foreign item into the seen set. If a symbol with the same name already exists
2748     /// for the item, return its HirId without updating the set.
2749     fn insert(&mut self, tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> Option<HirId> {
2750         let did = fi.def_id.to_def_id();
2751         let instance = Instance::new(did, ty::List::identity_for_item(tcx, did));
2752         let name = Symbol::intern(tcx.symbol_name(instance).name);
2753         if let Some(&hir_id) = self.seen_decls.get(&name) {
2754             // Avoid updating the map with the new entry when we do find a collision. We want to
2755             // make sure we're always pointing to the first definition as the previous declaration.
2756             // This lets us avoid emitting "knock-on" diagnostics.
2757             Some(hir_id)
2758         } else {
2759             self.seen_decls.insert(name, fi.hir_id())
2760         }
2761     }
2762
2763     /// Get the name of the symbol that's linked against for a given extern declaration. That is,
2764     /// the name specified in a #[link_name = ...] attribute if one was specified, else, just the
2765     /// symbol's name.
2766     fn name_of_extern_decl(tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> SymbolName {
2767         if let Some((overridden_link_name, overridden_link_name_span)) =
2768             tcx.codegen_fn_attrs(fi.def_id).link_name.map(|overridden_link_name| {
2769                 // FIXME: Instead of searching through the attributes again to get span
2770                 // information, we could have codegen_fn_attrs also give span information back for
2771                 // where the attribute was defined. However, until this is found to be a
2772                 // bottleneck, this does just fine.
2773                 (
2774                     overridden_link_name,
2775                     tcx.get_attrs(fi.def_id.to_def_id())
2776                         .iter()
2777                         .find(|at| at.has_name(sym::link_name))
2778                         .unwrap()
2779                         .span,
2780                 )
2781             })
2782         {
2783             SymbolName::Link(overridden_link_name, overridden_link_name_span)
2784         } else {
2785             SymbolName::Normal(fi.ident.name)
2786         }
2787     }
2788
2789     /// Checks whether two types are structurally the same enough that the declarations shouldn't
2790     /// clash. We need this so we don't emit a lint when two modules both declare an extern struct,
2791     /// with the same members (as the declarations shouldn't clash).
2792     fn structurally_same_type<'tcx>(
2793         cx: &LateContext<'tcx>,
2794         a: Ty<'tcx>,
2795         b: Ty<'tcx>,
2796         ckind: CItemKind,
2797     ) -> bool {
2798         fn structurally_same_type_impl<'tcx>(
2799             seen_types: &mut FxHashSet<(Ty<'tcx>, Ty<'tcx>)>,
2800             cx: &LateContext<'tcx>,
2801             a: Ty<'tcx>,
2802             b: Ty<'tcx>,
2803             ckind: CItemKind,
2804         ) -> bool {
2805             debug!("structurally_same_type_impl(cx, a = {:?}, b = {:?})", a, b);
2806             let tcx = cx.tcx;
2807
2808             // Given a transparent newtype, reach through and grab the inner
2809             // type unless the newtype makes the type non-null.
2810             let non_transparent_ty = |ty: Ty<'tcx>| -> Ty<'tcx> {
2811                 let mut ty = ty;
2812                 loop {
2813                     if let ty::Adt(def, substs) = *ty.kind() {
2814                         let is_transparent = def.subst(tcx, substs).repr.transparent();
2815                         let is_non_null = crate::types::nonnull_optimization_guaranteed(tcx, &def);
2816                         debug!(
2817                             "non_transparent_ty({:?}) -- type is transparent? {}, type is non-null? {}",
2818                             ty, is_transparent, is_non_null
2819                         );
2820                         if is_transparent && !is_non_null {
2821                             debug_assert!(def.variants.len() == 1);
2822                             let v = &def.variants[VariantIdx::new(0)];
2823                             ty = transparent_newtype_field(tcx, v)
2824                                 .expect(
2825                                     "single-variant transparent structure with zero-sized field",
2826                                 )
2827                                 .ty(tcx, substs);
2828                             continue;
2829                         }
2830                     }
2831                     debug!("non_transparent_ty -> {:?}", ty);
2832                     return ty;
2833                 }
2834             };
2835
2836             let a = non_transparent_ty(a);
2837             let b = non_transparent_ty(b);
2838
2839             if !seen_types.insert((a, b)) {
2840                 // We've encountered a cycle. There's no point going any further -- the types are
2841                 // structurally the same.
2842                 return true;
2843             }
2844             let tcx = cx.tcx;
2845             if a == b || rustc_middle::ty::TyS::same_type(a, b) {
2846                 // All nominally-same types are structurally same, too.
2847                 true
2848             } else {
2849                 // Do a full, depth-first comparison between the two.
2850                 use rustc_middle::ty::TyKind::*;
2851                 let a_kind = a.kind();
2852                 let b_kind = b.kind();
2853
2854                 let compare_layouts = |a, b| -> Result<bool, LayoutError<'tcx>> {
2855                     debug!("compare_layouts({:?}, {:?})", a, b);
2856                     let a_layout = &cx.layout_of(a)?.layout.abi;
2857                     let b_layout = &cx.layout_of(b)?.layout.abi;
2858                     debug!(
2859                         "comparing layouts: {:?} == {:?} = {}",
2860                         a_layout,
2861                         b_layout,
2862                         a_layout == b_layout
2863                     );
2864                     Ok(a_layout == b_layout)
2865                 };
2866
2867                 #[allow(rustc::usage_of_ty_tykind)]
2868                 let is_primitive_or_pointer = |kind: &ty::TyKind<'_>| {
2869                     kind.is_primitive() || matches!(kind, RawPtr(..) | Ref(..))
2870                 };
2871
2872                 ensure_sufficient_stack(|| {
2873                     match (a_kind, b_kind) {
2874                         (Adt(a_def, a_substs), Adt(b_def, b_substs)) => {
2875                             let a = a.subst(cx.tcx, a_substs);
2876                             let b = b.subst(cx.tcx, b_substs);
2877                             debug!("Comparing {:?} and {:?}", a, b);
2878
2879                             // We can immediately rule out these types as structurally same if
2880                             // their layouts differ.
2881                             match compare_layouts(a, b) {
2882                                 Ok(false) => return false,
2883                                 _ => (), // otherwise, continue onto the full, fields comparison
2884                             }
2885
2886                             // Grab a flattened representation of all fields.
2887                             let a_fields = a_def.variants.iter().flat_map(|v| v.fields.iter());
2888                             let b_fields = b_def.variants.iter().flat_map(|v| v.fields.iter());
2889
2890                             // Perform a structural comparison for each field.
2891                             a_fields.eq_by(
2892                                 b_fields,
2893                                 |&ty::FieldDef { did: a_did, .. },
2894                                  &ty::FieldDef { did: b_did, .. }| {
2895                                     structurally_same_type_impl(
2896                                         seen_types,
2897                                         cx,
2898                                         tcx.type_of(a_did),
2899                                         tcx.type_of(b_did),
2900                                         ckind,
2901                                     )
2902                                 },
2903                             )
2904                         }
2905                         (Array(a_ty, a_const), Array(b_ty, b_const)) => {
2906                             // For arrays, we also check the constness of the type.
2907                             a_const.val == b_const.val
2908                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2909                         }
2910                         (Slice(a_ty), Slice(b_ty)) => {
2911                             structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2912                         }
2913                         (RawPtr(a_tymut), RawPtr(b_tymut)) => {
2914                             a_tymut.mutbl == b_tymut.mutbl
2915                                 && structurally_same_type_impl(
2916                                     seen_types,
2917                                     cx,
2918                                     &a_tymut.ty,
2919                                     &b_tymut.ty,
2920                                     ckind,
2921                                 )
2922                         }
2923                         (Ref(_a_region, a_ty, a_mut), Ref(_b_region, b_ty, b_mut)) => {
2924                             // For structural sameness, we don't need the region to be same.
2925                             a_mut == b_mut
2926                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2927                         }
2928                         (FnDef(..), FnDef(..)) => {
2929                             let a_poly_sig = a.fn_sig(tcx);
2930                             let b_poly_sig = b.fn_sig(tcx);
2931
2932                             // As we don't compare regions, skip_binder is fine.
2933                             let a_sig = a_poly_sig.skip_binder();
2934                             let b_sig = b_poly_sig.skip_binder();
2935
2936                             (a_sig.abi, a_sig.unsafety, a_sig.c_variadic)
2937                                 == (b_sig.abi, b_sig.unsafety, b_sig.c_variadic)
2938                                 && a_sig.inputs().iter().eq_by(b_sig.inputs().iter(), |a, b| {
2939                                     structurally_same_type_impl(seen_types, cx, a, b, ckind)
2940                                 })
2941                                 && structurally_same_type_impl(
2942                                     seen_types,
2943                                     cx,
2944                                     a_sig.output(),
2945                                     b_sig.output(),
2946                                     ckind,
2947                                 )
2948                         }
2949                         (Tuple(a_substs), Tuple(b_substs)) => {
2950                             a_substs.types().eq_by(b_substs.types(), |a_ty, b_ty| {
2951                                 structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2952                             })
2953                         }
2954                         // For these, it's not quite as easy to define structural-sameness quite so easily.
2955                         // For the purposes of this lint, take the conservative approach and mark them as
2956                         // not structurally same.
2957                         (Dynamic(..), Dynamic(..))
2958                         | (Error(..), Error(..))
2959                         | (Closure(..), Closure(..))
2960                         | (Generator(..), Generator(..))
2961                         | (GeneratorWitness(..), GeneratorWitness(..))
2962                         | (Projection(..), Projection(..))
2963                         | (Opaque(..), Opaque(..)) => false,
2964
2965                         // These definitely should have been caught above.
2966                         (Bool, Bool) | (Char, Char) | (Never, Never) | (Str, Str) => unreachable!(),
2967
2968                         // An Adt and a primitive or pointer type. This can be FFI-safe if non-null
2969                         // enum layout optimisation is being applied.
2970                         (Adt(..), other_kind) | (other_kind, Adt(..))
2971                             if is_primitive_or_pointer(other_kind) =>
2972                         {
2973                             let (primitive, adt) =
2974                                 if is_primitive_or_pointer(a.kind()) { (a, b) } else { (b, a) };
2975                             if let Some(ty) = crate::types::repr_nullable_ptr(cx, adt, ckind) {
2976                                 ty == primitive
2977                             } else {
2978                                 compare_layouts(a, b).unwrap_or(false)
2979                             }
2980                         }
2981                         // Otherwise, just compare the layouts. This may fail to lint for some
2982                         // incompatible types, but at the very least, will stop reads into
2983                         // uninitialised memory.
2984                         _ => compare_layouts(a, b).unwrap_or(false),
2985                     }
2986                 })
2987             }
2988         }
2989         let mut seen_types = FxHashSet::default();
2990         structurally_same_type_impl(&mut seen_types, cx, a, b, ckind)
2991     }
2992 }
2993
2994 impl_lint_pass!(ClashingExternDeclarations => [CLASHING_EXTERN_DECLARATIONS]);
2995
2996 impl<'tcx> LateLintPass<'tcx> for ClashingExternDeclarations {
2997     fn check_foreign_item(&mut self, cx: &LateContext<'tcx>, this_fi: &hir::ForeignItem<'_>) {
2998         trace!("ClashingExternDeclarations: check_foreign_item: {:?}", this_fi);
2999         if let ForeignItemKind::Fn(..) = this_fi.kind {
3000             let tcx = cx.tcx;
3001             if let Some(existing_hid) = self.insert(tcx, this_fi) {
3002                 let existing_decl_ty = tcx.type_of(tcx.hir().local_def_id(existing_hid));
3003                 let this_decl_ty = tcx.type_of(this_fi.def_id);
3004                 debug!(
3005                     "ClashingExternDeclarations: Comparing existing {:?}: {:?} to this {:?}: {:?}",
3006                     existing_hid, existing_decl_ty, this_fi.def_id, this_decl_ty
3007                 );
3008                 // Check that the declarations match.
3009                 if !Self::structurally_same_type(
3010                     cx,
3011                     existing_decl_ty,
3012                     this_decl_ty,
3013                     CItemKind::Declaration,
3014                 ) {
3015                     let orig_fi = tcx.hir().expect_foreign_item(existing_hid);
3016                     let orig = Self::name_of_extern_decl(tcx, orig_fi);
3017
3018                     // We want to ensure that we use spans for both decls that include where the
3019                     // name was defined, whether that was from the link_name attribute or not.
3020                     let get_relevant_span =
3021                         |fi: &hir::ForeignItem<'_>| match Self::name_of_extern_decl(tcx, fi) {
3022                             SymbolName::Normal(_) => fi.span,
3023                             SymbolName::Link(_, annot_span) => fi.span.to(annot_span),
3024                         };
3025                     // Finally, emit the diagnostic.
3026                     tcx.struct_span_lint_hir(
3027                         CLASHING_EXTERN_DECLARATIONS,
3028                         this_fi.hir_id(),
3029                         get_relevant_span(this_fi),
3030                         |lint| {
3031                             let mut expected_str = DiagnosticStyledString::new();
3032                             expected_str.push(existing_decl_ty.fn_sig(tcx).to_string(), false);
3033                             let mut found_str = DiagnosticStyledString::new();
3034                             found_str.push(this_decl_ty.fn_sig(tcx).to_string(), true);
3035
3036                             lint.build(&format!(
3037                                 "`{}` redeclare{} with a different signature",
3038                                 this_fi.ident.name,
3039                                 if orig.get_name() == this_fi.ident.name {
3040                                     "d".to_string()
3041                                 } else {
3042                                     format!("s `{}`", orig.get_name())
3043                                 }
3044                             ))
3045                             .span_label(
3046                                 get_relevant_span(orig_fi),
3047                                 &format!("`{}` previously declared here", orig.get_name()),
3048                             )
3049                             .span_label(
3050                                 get_relevant_span(this_fi),
3051                                 "this signature doesn't match the previous declaration",
3052                             )
3053                             .note_expected_found(&"", expected_str, &"", found_str)
3054                             .emit()
3055                         },
3056                     );
3057                 }
3058             }
3059         }
3060     }
3061 }
3062
3063 declare_lint! {
3064     /// The `deref_nullptr` lint detects when an null pointer is dereferenced,
3065     /// which causes [undefined behavior].
3066     ///
3067     /// ### Example
3068     ///
3069     /// ```rust,no_run
3070     /// # #![allow(unused)]
3071     /// use std::ptr;
3072     /// unsafe {
3073     ///     let x = &*ptr::null::<i32>();
3074     ///     let x = ptr::addr_of!(*ptr::null::<i32>());
3075     ///     let x = *(0 as *const i32);
3076     /// }
3077     /// ```
3078     ///
3079     /// {{produces}}
3080     ///
3081     /// ### Explanation
3082     ///
3083     /// Dereferencing a null pointer causes [undefined behavior] even as a place expression,
3084     /// like `&*(0 as *const i32)` or `addr_of!(*(0 as *const i32))`.
3085     ///
3086     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
3087     pub DEREF_NULLPTR,
3088     Warn,
3089     "detects when an null pointer is dereferenced"
3090 }
3091
3092 declare_lint_pass!(DerefNullPtr => [DEREF_NULLPTR]);
3093
3094 impl<'tcx> LateLintPass<'tcx> for DerefNullPtr {
3095     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
3096         /// test if expression is a null ptr
3097         fn is_null_ptr(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> bool {
3098             match &expr.kind {
3099                 rustc_hir::ExprKind::Cast(ref expr, ref ty) => {
3100                     if let rustc_hir::TyKind::Ptr(_) = ty.kind {
3101                         return is_zero(expr) || is_null_ptr(cx, expr);
3102                     }
3103                 }
3104                 // check for call to `core::ptr::null` or `core::ptr::null_mut`
3105                 rustc_hir::ExprKind::Call(ref path, _) => {
3106                     if let rustc_hir::ExprKind::Path(ref qpath) = path.kind {
3107                         if let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id() {
3108                             return matches!(
3109                                 cx.tcx.get_diagnostic_name(def_id),
3110                                 Some(sym::ptr_null | sym::ptr_null_mut)
3111                             );
3112                         }
3113                     }
3114                 }
3115                 _ => {}
3116             }
3117             false
3118         }
3119
3120         /// test if expression is the literal `0`
3121         fn is_zero(expr: &hir::Expr<'_>) -> bool {
3122             match &expr.kind {
3123                 rustc_hir::ExprKind::Lit(ref lit) => {
3124                     if let LitKind::Int(a, _) = lit.node {
3125                         return a == 0;
3126                     }
3127                 }
3128                 _ => {}
3129             }
3130             false
3131         }
3132
3133         if let rustc_hir::ExprKind::Unary(ref un_op, ref expr_deref) = expr.kind {
3134             if let rustc_hir::UnOp::Deref = un_op {
3135                 if is_null_ptr(cx, expr_deref) {
3136                     cx.struct_span_lint(DEREF_NULLPTR, expr.span, |lint| {
3137                         let mut err = lint.build("dereferencing a null pointer");
3138                         err.span_label(
3139                             expr.span,
3140                             "this code causes undefined behavior when executed",
3141                         );
3142                         err.emit();
3143                     });
3144                 }
3145             }
3146         }
3147     }
3148 }
3149
3150 declare_lint! {
3151     /// The `named_asm_labels` lint detects the use of named labels in the
3152     /// inline `asm!` macro.
3153     ///
3154     /// ### Example
3155     ///
3156     /// ```rust,compile_fail
3157     /// #![feature(asm)]
3158     /// fn main() {
3159     ///     unsafe {
3160     ///         asm!("foo: bar");
3161     ///     }
3162     /// }
3163     /// ```
3164     ///
3165     /// {{produces}}
3166     ///
3167     /// ### Explanation
3168     ///
3169     /// LLVM is allowed to duplicate inline assembly blocks for any
3170     /// reason, for example when it is in a function that gets inlined. Because
3171     /// of this, GNU assembler [local labels] *must* be used instead of labels
3172     /// with a name. Using named labels might cause assembler or linker errors.
3173     ///
3174     /// See the [unstable book] for more details.
3175     ///
3176     /// [local labels]: https://sourceware.org/binutils/docs/as/Symbol-Names.html#Local-Labels
3177     /// [unstable book]: https://doc.rust-lang.org/nightly/unstable-book/library-features/asm.html#labels
3178     pub NAMED_ASM_LABELS,
3179     Deny,
3180     "named labels in inline assembly",
3181 }
3182
3183 declare_lint_pass!(NamedAsmLabels => [NAMED_ASM_LABELS]);
3184
3185 impl<'tcx> LateLintPass<'tcx> for NamedAsmLabels {
3186     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
3187         if let hir::Expr {
3188             kind: hir::ExprKind::InlineAsm(hir::InlineAsm { template_strs, .. }),
3189             ..
3190         } = expr
3191         {
3192             for (template_sym, template_snippet, template_span) in template_strs.iter() {
3193                 let template_str = &template_sym.as_str();
3194                 let find_label_span = |needle: &str| -> Option<Span> {
3195                     if let Some(template_snippet) = template_snippet {
3196                         let snippet = template_snippet.as_str();
3197                         if let Some(pos) = snippet.find(needle) {
3198                             let end = pos
3199                                 + &snippet[pos..]
3200                                     .find(|c| c == ':')
3201                                     .unwrap_or(snippet[pos..].len() - 1);
3202                             let inner = InnerSpan::new(pos, end);
3203                             return Some(template_span.from_inner(inner));
3204                         }
3205                     }
3206
3207                     None
3208                 };
3209
3210                 let mut found_labels = Vec::new();
3211
3212                 // A semicolon might not actually be specified as a separator for all targets, but it seems like LLVM accepts it always
3213                 let statements = template_str.split(|c| matches!(c, '\n' | ';'));
3214                 for statement in statements {
3215                     // If there's a comment, trim it from the statement
3216                     let statement = statement.find("//").map_or(statement, |idx| &statement[..idx]);
3217                     let mut start_idx = 0;
3218                     for (idx, _) in statement.match_indices(':') {
3219                         let possible_label = statement[start_idx..idx].trim();
3220                         let mut chars = possible_label.chars();
3221                         if let Some(c) = chars.next() {
3222                             // A label starts with an alphabetic character or . or _ and continues with alphanumeric characters, _, or $
3223                             if (c.is_alphabetic() || matches!(c, '.' | '_'))
3224                                 && chars.all(|c| c.is_alphanumeric() || matches!(c, '_' | '$'))
3225                             {
3226                                 found_labels.push(possible_label);
3227                             } else {
3228                                 // If we encounter a non-label, there cannot be any further labels, so stop checking
3229                                 break;
3230                             }
3231                         } else {
3232                             // Empty string means a leading ':' in this section, which is not a label
3233                             break;
3234                         }
3235
3236                         start_idx = idx + 1;
3237                     }
3238                 }
3239
3240                 debug!("NamedAsmLabels::check_expr(): found_labels: {:#?}", &found_labels);
3241
3242                 if found_labels.len() > 0 {
3243                     let spans = found_labels
3244                         .into_iter()
3245                         .filter_map(|label| find_label_span(label))
3246                         .collect::<Vec<Span>>();
3247                     // If there were labels but we couldn't find a span, combine the warnings and use the template span
3248                     let target_spans: MultiSpan =
3249                         if spans.len() > 0 { spans.into() } else { (*template_span).into() };
3250
3251                     cx.lookup_with_diagnostics(
3252                             NAMED_ASM_LABELS,
3253                             Some(target_spans),
3254                             |diag| {
3255                                 let mut err =
3256                                     diag.build("avoid using named labels in inline assembly");
3257                                 err.emit();
3258                             },
3259                             BuiltinLintDiagnostics::NamedAsmLabel(
3260                                 "only local labels of the form `<number>:` should be used in inline asm"
3261                                     .to_string(),
3262                             ),
3263                         );
3264                 }
3265             }
3266         }
3267     }
3268 }