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         let (article, desc) = cx.tcx.article_and_description(impl_item.def_id.to_def_id());
 661         self.check_missing_docs_attrs(cx, impl_item.def_id, impl_item.span, article, desc);
 662     }
 663
 664     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'_>) {
 665         let (article, desc) = cx.tcx.article_and_description(foreign_item.def_id.to_def_id());
 666         self.check_missing_docs_attrs(cx, foreign_item.def_id, foreign_item.span, article, desc);
 667     }
 668
 669     fn check_field_def(&mut self, cx: &LateContext<'_>, sf: &hir::FieldDef<'_>) {
 670         if !sf.is_positional() {
 671             let def_id = cx.tcx.hir().local_def_id(sf.hir_id);
 672             self.check_missing_docs_attrs(cx, def_id, sf.span, "a", "struct field")
 673         }
 674     }
 675
 676     fn check_variant(&mut self, cx: &LateContext<'_>, v: &hir::Variant<'_>) {
 677         self.check_missing_docs_attrs(cx, cx.tcx.hir().local_def_id(v.id), v.span, "a", "variant");
 678     }
 679 }
 680
 681 declare_lint! {
 682     /// The `missing_copy_implementations` lint detects potentially-forgotten
 683     /// implementations of [`Copy`].
 684     ///
 685     /// [`Copy`]: https://doc.rust-lang.org/std/marker/trait.Copy.html
 686     ///
 687     /// ### Example
 688     ///
 689     /// ```rust,compile_fail
 690     /// #![deny(missing_copy_implementations)]
 691     /// pub struct Foo {
 692     ///     pub field: i32
 693     /// }
 694     /// # fn main() {}
 695     /// ```
 696     ///
 697     /// {{produces}}
 698     ///
 699     /// ### Explanation
 700     ///
 701     /// Historically (before 1.0), types were automatically marked as `Copy`
 702     /// if possible. This was changed so that it required an explicit opt-in
 703     /// by implementing the `Copy` trait. As part of this change, a lint was
 704     /// added to alert if a copyable type was not marked `Copy`.
 705     ///
 706     /// This lint is "allow" by default because this code isn't bad; it is
 707     /// common to write newtypes like this specifically so that a `Copy` type
 708     /// is no longer `Copy`. `Copy` types can result in unintended copies of
 709     /// large data which can impact performance.
 710     pub MISSING_COPY_IMPLEMENTATIONS,
 711     Allow,
 712     "detects potentially-forgotten implementations of `Copy`"
 713 }
 714
 715 declare_lint_pass!(MissingCopyImplementations => [MISSING_COPY_IMPLEMENTATIONS]);
 716
 717 impl<'tcx> LateLintPass<'tcx> for MissingCopyImplementations {
 718     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 719         if !cx.access_levels.is_reachable(item.def_id) {
 720             return;
 721         }
 722         let (def, ty) = match item.kind {
 723             hir::ItemKind::Struct(_, ref ast_generics) => {
 724                 if !ast_generics.params.is_empty() {
 725                     return;
 726                 }
 727                 let def = cx.tcx.adt_def(item.def_id);
 728                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 729             }
 730             hir::ItemKind::Union(_, ref ast_generics) => {
 731                 if !ast_generics.params.is_empty() {
 732                     return;
 733                 }
 734                 let def = cx.tcx.adt_def(item.def_id);
 735                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 736             }
 737             hir::ItemKind::Enum(_, ref ast_generics) => {
 738                 if !ast_generics.params.is_empty() {
 739                     return;
 740                 }
 741                 let def = cx.tcx.adt_def(item.def_id);
 742                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 743             }
 744             _ => return,
 745         };
 746         if def.has_dtor(cx.tcx) {
 747             return;
 748         }
 749         let param_env = ty::ParamEnv::empty();
 750         if ty.is_copy_modulo_regions(cx.tcx.at(item.span), param_env) {
 751             return;
 752         }
 753         if can_type_implement_copy(cx.tcx, param_env, ty).is_ok() {
 754             cx.struct_span_lint(MISSING_COPY_IMPLEMENTATIONS, item.span, |lint| {
 755                 lint.build(
 756                     "type could implement `Copy`; consider adding `impl \
 757                           Copy`",
 758                 )
 759                 .emit()
 760             })
 761         }
 762     }
 763 }
 764
 765 declare_lint! {
 766     /// The `missing_debug_implementations` lint detects missing
 767     /// implementations of [`fmt::Debug`].
 768     ///
 769     /// [`fmt::Debug`]: https://doc.rust-lang.org/std/fmt/trait.Debug.html
 770     ///
 771     /// ### Example
 772     ///
 773     /// ```rust,compile_fail
 774     /// #![deny(missing_debug_implementations)]
 775     /// pub struct Foo;
 776     /// # fn main() {}
 777     /// ```
 778     ///
 779     /// {{produces}}
 780     ///
 781     /// ### Explanation
 782     ///
 783     /// Having a `Debug` implementation on all types can assist with
 784     /// debugging, as it provides a convenient way to format and display a
 785     /// value. Using the `#[derive(Debug)]` attribute will automatically
 786     /// generate a typical implementation, or a custom implementation can be
 787     /// added by manually implementing the `Debug` trait.
 788     ///
 789     /// This lint is "allow" by default because adding `Debug` to all types can
 790     /// have a negative impact on compile time and code size. It also requires
 791     /// boilerplate to be added to every type, which can be an impediment.
 792     MISSING_DEBUG_IMPLEMENTATIONS,
 793     Allow,
 794     "detects missing implementations of Debug"
 795 }
 796
 797 #[derive(Default)]
 798 pub struct MissingDebugImplementations {
 799     impling_types: Option<LocalDefIdSet>,
 800 }
 801
 802 impl_lint_pass!(MissingDebugImplementations => [MISSING_DEBUG_IMPLEMENTATIONS]);
 803
 804 impl<'tcx> LateLintPass<'tcx> for MissingDebugImplementations {
 805     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 806         if !cx.access_levels.is_reachable(item.def_id) {
 807             return;
 808         }
 809
 810         match item.kind {
 811             hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) | hir::ItemKind::Enum(..) => {}
 812             _ => return,
 813         }
 814
 815         let debug = match cx.tcx.get_diagnostic_item(sym::debug_trait) {
 816             Some(debug) => debug,
 817             None => return,
 818         };
 819
 820         if self.impling_types.is_none() {
 821             let mut impls = LocalDefIdSet::default();
 822             cx.tcx.for_each_impl(debug, |d| {
 823                 if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() {
 824                     if let Some(def_id) = ty_def.did.as_local() {
 825                         impls.insert(def_id);
 826                     }
 827                 }
 828             });
 829
 830             self.impling_types = Some(impls);
 831             debug!("{:?}", self.impling_types);
 832         }
 833
 834         if !self.impling_types.as_ref().unwrap().contains(&item.def_id) {
 835             cx.struct_span_lint(MISSING_DEBUG_IMPLEMENTATIONS, item.span, |lint| {
 836                 lint.build(&format!(
 837                     "type does not implement `{}`; consider adding `#[derive(Debug)]` \
 838                      or a manual implementation",
 839                     cx.tcx.def_path_str(debug)
 840                 ))
 841                 .emit()
 842             });
 843         }
 844     }
 845 }
 846
 847 declare_lint! {
 848     /// The `anonymous_parameters` lint detects anonymous parameters in trait
 849     /// definitions.
 850     ///
 851     /// ### Example
 852     ///
 853     /// ```rust,edition2015,compile_fail
 854     /// #![deny(anonymous_parameters)]
 855     /// // edition 2015
 856     /// pub trait Foo {
 857     ///     fn foo(usize);
 858     /// }
 859     /// fn main() {}
 860     /// ```
 861     ///
 862     /// {{produces}}
 863     ///
 864     /// ### Explanation
 865     ///
 866     /// This syntax is mostly a historical accident, and can be worked around
 867     /// quite easily by adding an `_` pattern or a descriptive identifier:
 868     ///
 869     /// ```rust
 870     /// trait Foo {
 871     ///     fn foo(_: usize);
 872     /// }
 873     /// ```
 874     ///
 875     /// This syntax is now a hard error in the 2018 edition. In the 2015
 876     /// edition, this lint is "warn" by default. This lint
 877     /// enables the [`cargo fix`] tool with the `--edition` flag to
 878     /// automatically transition old code from the 2015 edition to 2018. The
 879     /// tool will run this lint and automatically apply the
 880     /// suggested fix from the compiler (which is to add `_` to each
 881     /// parameter). This provides a completely automated way to update old
 882     /// code for a new edition. See [issue #41686] for more details.
 883     ///
 884     /// [issue #41686]: https://github.com/rust-lang/rust/issues/41686
 885     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
 886     pub ANONYMOUS_PARAMETERS,
 887     Warn,
 888     "detects anonymous parameters",
 889     @future_incompatible = FutureIncompatibleInfo {
 890         reference: "issue #41686 <https://github.com/rust-lang/rust/issues/41686>",
 891         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
 892     };
 893 }
 894
 895 declare_lint_pass!(
 896     /// Checks for use of anonymous parameters (RFC 1685).
 897     AnonymousParameters => [ANONYMOUS_PARAMETERS]
 898 );
 899
 900 impl EarlyLintPass for AnonymousParameters {
 901     fn check_trait_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
 902         if cx.sess.edition() != Edition::Edition2015 {
 903             // This is a hard error in future editions; avoid linting and erroring
 904             return;
 905         }
 906         if let ast::AssocItemKind::Fn(box FnKind(_, ref sig, _, _)) = it.kind {
 907             for arg in sig.decl.inputs.iter() {
 908                 if let ast::PatKind::Ident(_, ident, None) = arg.pat.kind {
 909                     if ident.name == kw::Empty {
 910                         cx.struct_span_lint(ANONYMOUS_PARAMETERS, arg.pat.span, |lint| {
 911                             let ty_snip = cx.sess.source_map().span_to_snippet(arg.ty.span);
 912
 913                             let (ty_snip, appl) = if let Ok(ref snip) = ty_snip {
 914                                 (snip.as_str(), Applicability::MachineApplicable)
 915                             } else {
 916                                 ("<type>", Applicability::HasPlaceholders)
 917                             };
 918
 919                             lint.build(
 920                                 "anonymous parameters are deprecated and will be \
 921                                      removed in the next edition.",
 922                             )
 923                             .span_suggestion(
 924                                 arg.pat.span,
 925                                 "try naming the parameter or explicitly \
 926                                             ignoring it",
 927                                 format!("_: {}", ty_snip),
 928                                 appl,
 929                             )
 930                             .emit();
 931                         })
 932                     }
 933                 }
 934             }
 935         }
 936     }
 937 }
 938
 939 /// Check for use of attributes which have been deprecated.
 940 #[derive(Clone)]
 941 pub struct DeprecatedAttr {
 942     // This is not free to compute, so we want to keep it around, rather than
 943     // compute it for every attribute.
 944     depr_attrs: Vec<&'static (Symbol, AttributeType, AttributeTemplate, AttributeGate)>,
 945 }
 946
 947 impl_lint_pass!(DeprecatedAttr => []);
 948
 949 impl DeprecatedAttr {
 950     pub fn new() -> DeprecatedAttr {
 951         DeprecatedAttr { depr_attrs: deprecated_attributes() }
 952     }
 953 }
 954
 955 fn lint_deprecated_attr(
 956     cx: &EarlyContext<'_>,
 957     attr: &ast::Attribute,
 958     msg: &str,
 959     suggestion: Option<&str>,
 960 ) {
 961     cx.struct_span_lint(DEPRECATED, attr.span, |lint| {
 962         lint.build(msg)
 963             .span_suggestion_short(
 964                 attr.span,
 965                 suggestion.unwrap_or("remove this attribute"),
 966                 String::new(),
 967                 Applicability::MachineApplicable,
 968             )
 969             .emit();
 970     })
 971 }
 972
 973 impl EarlyLintPass for DeprecatedAttr {
 974     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 975         for &&(n, _, _, ref g) in &self.depr_attrs {
 976             if attr.ident().map(|ident| ident.name) == Some(n) {
 977                 if let &AttributeGate::Gated(
 978                     Stability::Deprecated(link, suggestion),
 979                     name,
 980                     reason,
 981                     _,
 982                 ) = g
 983                 {
 984                     let msg =
 985                         format!("use of deprecated attribute `{}`: {}. See {}", name, reason, link);
 986                     lint_deprecated_attr(cx, attr, &msg, suggestion);
 987                 }
 988                 return;
 989             }
 990         }
 991         if attr.has_name(sym::no_start) || attr.has_name(sym::crate_id) {
 992             let path_str = pprust::path_to_string(&attr.get_normal_item().path);
 993             let msg = format!("use of deprecated attribute `{}`: no longer used.", path_str);
 994             lint_deprecated_attr(cx, attr, &msg, None);
 995         }
 996     }
 997 }
 998
 999 fn warn_if_doc(cx: &EarlyContext<'_>, node_span: Span, node_kind: &str, attrs: &[ast::Attribute]) {
1000     use rustc_ast::token::CommentKind;
1001
1002     let mut attrs = attrs.iter().peekable();
1003
1004     // Accumulate a single span for sugared doc comments.
1005     let mut sugared_span: Option<Span> = None;
1006
1007     while let Some(attr) = attrs.next() {
1008         let is_doc_comment = attr.is_doc_comment();
1009         if is_doc_comment {
1010             sugared_span =
1011                 Some(sugared_span.map_or(attr.span, |span| span.with_hi(attr.span.hi())));
1012         }
1013
1014         if attrs.peek().map_or(false, |next_attr| next_attr.is_doc_comment()) {
1015             continue;
1016         }
1017
1018         let span = sugared_span.take().unwrap_or(attr.span);
1019
1020         if is_doc_comment || attr.has_name(sym::doc) {
1021             cx.struct_span_lint(UNUSED_DOC_COMMENTS, span, |lint| {
1022                 let mut err = lint.build("unused doc comment");
1023                 err.span_label(
1024                     node_span,
1025                     format!("rustdoc does not generate documentation for {}", node_kind),
1026                 );
1027                 match attr.kind {
1028                     AttrKind::DocComment(CommentKind::Line, _) | AttrKind::Normal(..) => {
1029                         err.help("use `//` for a plain comment");
1030                     }
1031                     AttrKind::DocComment(CommentKind::Block, _) => {
1032                         err.help("use `/* */` for a plain comment");
1033                     }
1034                 }
1035                 err.emit();
1036             });
1037         }
1038     }
1039 }
1040
1041 impl EarlyLintPass for UnusedDocComment {
1042     fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &ast::Stmt) {
1043         let kind = match stmt.kind {
1044             ast::StmtKind::Local(..) => "statements",
1045             // Disabled pending discussion in #78306
1046             ast::StmtKind::Item(..) => return,
1047             // expressions will be reported by `check_expr`.
1048             ast::StmtKind::Empty
1049             | ast::StmtKind::Semi(_)
1050             | ast::StmtKind::Expr(_)
1051             | ast::StmtKind::MacCall(_) => return,
1052         };
1053
1054         warn_if_doc(cx, stmt.span, kind, stmt.kind.attrs());
1055     }
1056
1057     fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) {
1058         let arm_span = arm.pat.span.with_hi(arm.body.span.hi());
1059         warn_if_doc(cx, arm_span, "match arms", &arm.attrs);
1060     }
1061
1062     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
1063         warn_if_doc(cx, expr.span, "expressions", &expr.attrs);
1064     }
1065 }
1066
1067 declare_lint! {
1068     /// The `no_mangle_const_items` lint detects any `const` items with the
1069     /// [`no_mangle` attribute].
1070     ///
1071     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1072     ///
1073     /// ### Example
1074     ///
1075     /// ```rust,compile_fail
1076     /// #[no_mangle]
1077     /// const FOO: i32 = 5;
1078     /// ```
1079     ///
1080     /// {{produces}}
1081     ///
1082     /// ### Explanation
1083     ///
1084     /// Constants do not have their symbols exported, and therefore, this
1085     /// probably means you meant to use a [`static`], not a [`const`].
1086     ///
1087     /// [`static`]: https://doc.rust-lang.org/reference/items/static-items.html
1088     /// [`const`]: https://doc.rust-lang.org/reference/items/constant-items.html
1089     NO_MANGLE_CONST_ITEMS,
1090     Deny,
1091     "const items will not have their symbols exported"
1092 }
1093
1094 declare_lint! {
1095     /// The `no_mangle_generic_items` lint detects generic items that must be
1096     /// mangled.
1097     ///
1098     /// ### Example
1099     ///
1100     /// ```rust
1101     /// #[no_mangle]
1102     /// fn foo<T>(t: T) {
1103     ///
1104     /// }
1105     /// ```
1106     ///
1107     /// {{produces}}
1108     ///
1109     /// ### Explanation
1110     ///
1111     /// A function with generics must have its symbol mangled to accommodate
1112     /// the generic parameter. The [`no_mangle` attribute] has no effect in
1113     /// this situation, and should be removed.
1114     ///
1115     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1116     NO_MANGLE_GENERIC_ITEMS,
1117     Warn,
1118     "generic items must be mangled"
1119 }
1120
1121 declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS, NO_MANGLE_GENERIC_ITEMS]);
1122
1123 impl<'tcx> LateLintPass<'tcx> for InvalidNoMangleItems {
1124     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1125         let attrs = cx.tcx.hir().attrs(it.hir_id());
1126         let check_no_mangle_on_generic_fn = |no_mangle_attr: &ast::Attribute,
1127                                              impl_generics: Option<&hir::Generics<'_>>,
1128                                              generics: &hir::Generics<'_>,
1129                                              span| {
1130             for param in
1131                 generics.params.iter().chain(impl_generics.map(|g| g.params).into_iter().flatten())
1132             {
1133                 match param.kind {
1134                     GenericParamKind::Lifetime { .. } => {}
1135                     GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1136                         cx.struct_span_lint(NO_MANGLE_GENERIC_ITEMS, span, |lint| {
1137                             lint.build("functions generic over types or consts must be mangled")
1138                                 .span_suggestion_short(
1139                                     no_mangle_attr.span,
1140                                     "remove this attribute",
1141                                     String::new(),
1142                                     // Use of `#[no_mangle]` suggests FFI intent; correct
1143                                     // fix may be to monomorphize source by hand
1144                                     Applicability::MaybeIncorrect,
1145                                 )
1146                                 .emit();
1147                         });
1148                         break;
1149                     }
1150                 }
1151             }
1152         };
1153         match it.kind {
1154             hir::ItemKind::Fn(.., ref generics, _) => {
1155                 if let Some(no_mangle_attr) = cx.sess().find_by_name(attrs, sym::no_mangle) {
1156                     check_no_mangle_on_generic_fn(no_mangle_attr, None, generics, it.span);
1157                 }
1158             }
1159             hir::ItemKind::Const(..) => {
1160                 if cx.sess().contains_name(attrs, sym::no_mangle) {
1161                     // Const items do not refer to a particular location in memory, and therefore
1162                     // don't have anything to attach a symbol to
1163                     cx.struct_span_lint(NO_MANGLE_CONST_ITEMS, it.span, |lint| {
1164                         let msg = "const items should never be `#[no_mangle]`";
1165                         let mut err = lint.build(msg);
1166
1167                         // account for "pub const" (#45562)
1168                         let start = cx
1169                             .tcx
1170                             .sess
1171                             .source_map()
1172                             .span_to_snippet(it.span)
1173                             .map(|snippet| snippet.find("const").unwrap_or(0))
1174                             .unwrap_or(0) as u32;
1175                         // `const` is 5 chars
1176                         let const_span = it.span.with_hi(BytePos(it.span.lo().0 + start + 5));
1177                         err.span_suggestion(
1178                             const_span,
1179                             "try a static value",
1180                             "pub static".to_owned(),
1181                             Applicability::MachineApplicable,
1182                         );
1183                         err.emit();
1184                     });
1185                 }
1186             }
1187             hir::ItemKind::Impl(hir::Impl { ref generics, items, .. }) => {
1188                 for it in items {
1189                     if let hir::AssocItemKind::Fn { .. } = it.kind {
1190                         if let Some(no_mangle_attr) = cx
1191                             .sess()
1192                             .find_by_name(cx.tcx.hir().attrs(it.id.hir_id()), sym::no_mangle)
1193                         {
1194                             check_no_mangle_on_generic_fn(
1195                                 no_mangle_attr,
1196                                 Some(generics),
1197                                 cx.tcx.hir().get_generics(it.id.def_id.to_def_id()).unwrap(),
1198                                 it.span,
1199                             );
1200                         }
1201                     }
1202                 }
1203             }
1204             _ => {}
1205         }
1206     }
1207 }
1208
1209 declare_lint! {
1210     /// The `mutable_transmutes` lint catches transmuting from `&T` to `&mut
1211     /// T` because it is [undefined behavior].
1212     ///
1213     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1214     ///
1215     /// ### Example
1216     ///
1217     /// ```rust,compile_fail
1218     /// unsafe {
1219     ///     let y = std::mem::transmute::<&i32, &mut i32>(&5);
1220     /// }
1221     /// ```
1222     ///
1223     /// {{produces}}
1224     ///
1225     /// ### Explanation
1226     ///
1227     /// Certain assumptions are made about aliasing of data, and this transmute
1228     /// violates those assumptions. Consider using [`UnsafeCell`] instead.
1229     ///
1230     /// [`UnsafeCell`]: https://doc.rust-lang.org/std/cell/struct.UnsafeCell.html
1231     MUTABLE_TRANSMUTES,
1232     Deny,
1233     "mutating transmuted &mut T from &T may cause undefined behavior"
1234 }
1235
1236 declare_lint_pass!(MutableTransmutes => [MUTABLE_TRANSMUTES]);
1237
1238 impl<'tcx> LateLintPass<'tcx> for MutableTransmutes {
1239     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &hir::Expr<'_>) {
1240         use rustc_target::spec::abi::Abi::RustIntrinsic;
1241         if let Some((&ty::Ref(_, _, from_mt), &ty::Ref(_, _, to_mt))) =
1242             get_transmute_from_to(cx, expr).map(|(ty1, ty2)| (ty1.kind(), ty2.kind()))
1243         {
1244             if to_mt == hir::Mutability::Mut && from_mt == hir::Mutability::Not {
1245                 let msg = "mutating transmuted &mut T from &T may cause undefined behavior, \
1246                                consider instead using an UnsafeCell";
1247                 cx.struct_span_lint(MUTABLE_TRANSMUTES, expr.span, |lint| lint.build(msg).emit());
1248             }
1249         }
1250
1251         fn get_transmute_from_to<'tcx>(
1252             cx: &LateContext<'tcx>,
1253             expr: &hir::Expr<'_>,
1254         ) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
1255             let def = if let hir::ExprKind::Path(ref qpath) = expr.kind {
1256                 cx.qpath_res(qpath, expr.hir_id)
1257             } else {
1258                 return None;
1259             };
1260             if let Res::Def(DefKind::Fn, did) = def {
1261                 if !def_id_is_transmute(cx, did) {
1262                     return None;
1263                 }
1264                 let sig = cx.typeck_results().node_type(expr.hir_id).fn_sig(cx.tcx);
1265                 let from = sig.inputs().skip_binder()[0];
1266                 let to = sig.output().skip_binder();
1267                 return Some((from, to));
1268             }
1269             None
1270         }
1271
1272         fn def_id_is_transmute(cx: &LateContext<'_>, def_id: DefId) -> bool {
1273             cx.tcx.fn_sig(def_id).abi() == RustIntrinsic
1274                 && cx.tcx.item_name(def_id) == sym::transmute
1275         }
1276     }
1277 }
1278
1279 declare_lint! {
1280     /// The `unstable_features` is deprecated and should no longer be used.
1281     UNSTABLE_FEATURES,
1282     Allow,
1283     "enabling unstable features (deprecated. do not use)"
1284 }
1285
1286 declare_lint_pass!(
1287     /// Forbids using the `#[feature(...)]` attribute
1288     UnstableFeatures => [UNSTABLE_FEATURES]
1289 );
1290
1291 impl<'tcx> LateLintPass<'tcx> for UnstableFeatures {
1292     fn check_attribute(&mut self, cx: &LateContext<'_>, attr: &ast::Attribute) {
1293         if attr.has_name(sym::feature) {
1294             if let Some(items) = attr.meta_item_list() {
1295                 for item in items {
1296                     cx.struct_span_lint(UNSTABLE_FEATURES, item.span(), |lint| {
1297                         lint.build("unstable feature").emit()
1298                     });
1299                 }
1300             }
1301         }
1302     }
1303 }
1304
1305 declare_lint! {
1306     /// The `unreachable_pub` lint triggers for `pub` items not reachable from
1307     /// the crate root.
1308     ///
1309     /// ### Example
1310     ///
1311     /// ```rust,compile_fail
1312     /// #![deny(unreachable_pub)]
1313     /// mod foo {
1314     ///     pub mod bar {
1315     ///
1316     ///     }
1317     /// }
1318     /// ```
1319     ///
1320     /// {{produces}}
1321     ///
1322     /// ### Explanation
1323     ///
1324     /// A bare `pub` visibility may be misleading if the item is not actually
1325     /// publicly exported from the crate. The `pub(crate)` visibility is
1326     /// recommended to be used instead, which more clearly expresses the intent
1327     /// that the item is only visible within its own crate.
1328     ///
1329     /// This lint is "allow" by default because it will trigger for a large
1330     /// amount existing Rust code, and has some false-positives. Eventually it
1331     /// is desired for this to become warn-by-default.
1332     pub UNREACHABLE_PUB,
1333     Allow,
1334     "`pub` items not reachable from crate root"
1335 }
1336
1337 declare_lint_pass!(
1338     /// Lint for items marked `pub` that aren't reachable from other crates.
1339     UnreachablePub => [UNREACHABLE_PUB]
1340 );
1341
1342 impl UnreachablePub {
1343     fn perform_lint(
1344         &self,
1345         cx: &LateContext<'_>,
1346         what: &str,
1347         def_id: LocalDefId,
1348         vis: &hir::Visibility<'_>,
1349         span: Span,
1350         exportable: bool,
1351     ) {
1352         let mut applicability = Applicability::MachineApplicable;
1353         match vis.node {
1354             hir::VisibilityKind::Public if !cx.access_levels.is_reachable(def_id) => {
1355                 if span.from_expansion() {
1356                     applicability = Applicability::MaybeIncorrect;
1357                 }
1358                 let def_span = cx.tcx.sess.source_map().guess_head_span(span);
1359                 cx.struct_span_lint(UNREACHABLE_PUB, def_span, |lint| {
1360                     let mut err = lint.build(&format!("unreachable `pub` {}", what));
1361                     let replacement = if cx.tcx.features().crate_visibility_modifier {
1362                         "crate"
1363                     } else {
1364                         "pub(crate)"
1365                     }
1366                     .to_owned();
1367
1368                     err.span_suggestion(
1369                         vis.span,
1370                         "consider restricting its visibility",
1371                         replacement,
1372                         applicability,
1373                     );
1374                     if exportable {
1375                         err.help("or consider exporting it for use by other crates");
1376                     }
1377                     err.emit();
1378                 });
1379             }
1380             _ => {}
1381         }
1382     }
1383 }
1384
1385 impl<'tcx> LateLintPass<'tcx> for UnreachablePub {
1386     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1387         self.perform_lint(cx, "item", item.def_id, &item.vis, item.span, true);
1388     }
1389
1390     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'tcx>) {
1391         self.perform_lint(
1392             cx,
1393             "item",
1394             foreign_item.def_id,
1395             &foreign_item.vis,
1396             foreign_item.span,
1397             true,
1398         );
1399     }
1400
1401     fn check_field_def(&mut self, cx: &LateContext<'_>, field: &hir::FieldDef<'_>) {
1402         let def_id = cx.tcx.hir().local_def_id(field.hir_id);
1403         self.perform_lint(cx, "field", def_id, &field.vis, field.span, false);
1404     }
1405
1406     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
1407         self.perform_lint(cx, "item", impl_item.def_id, &impl_item.vis, impl_item.span, false);
1408     }
1409 }
1410
1411 declare_lint! {
1412     /// The `type_alias_bounds` lint detects bounds in type aliases.
1413     ///
1414     /// ### Example
1415     ///
1416     /// ```rust
1417     /// type SendVec<T: Send> = Vec<T>;
1418     /// ```
1419     ///
1420     /// {{produces}}
1421     ///
1422     /// ### Explanation
1423     ///
1424     /// The trait bounds in a type alias are currently ignored, and should not
1425     /// be included to avoid confusion. This was previously allowed
1426     /// unintentionally; this may become a hard error in the future.
1427     TYPE_ALIAS_BOUNDS,
1428     Warn,
1429     "bounds in type aliases are not enforced"
1430 }
1431
1432 declare_lint_pass!(
1433     /// Lint for trait and lifetime bounds in type aliases being mostly ignored.
1434     /// They are relevant when using associated types, but otherwise neither checked
1435     /// at definition site nor enforced at use site.
1436     TypeAliasBounds => [TYPE_ALIAS_BOUNDS]
1437 );
1438
1439 impl TypeAliasBounds {
1440     fn is_type_variable_assoc(qpath: &hir::QPath<'_>) -> bool {
1441         match *qpath {
1442             hir::QPath::TypeRelative(ref ty, _) => {
1443                 // If this is a type variable, we found a `T::Assoc`.
1444                 match ty.kind {
1445                     hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
1446                         matches!(path.res, Res::Def(DefKind::TyParam, _))
1447                     }
1448                     _ => false,
1449                 }
1450             }
1451             hir::QPath::Resolved(..) | hir::QPath::LangItem(..) => false,
1452         }
1453     }
1454
1455     fn suggest_changing_assoc_types(ty: &hir::Ty<'_>, err: &mut DiagnosticBuilder<'_>) {
1456         // Access to associates types should use `<T as Bound>::Assoc`, which does not need a
1457         // bound.  Let's see if this type does that.
1458
1459         // We use a HIR visitor to walk the type.
1460         use rustc_hir::intravisit::{self, Visitor};
1461         struct WalkAssocTypes<'a, 'db> {
1462             err: &'a mut DiagnosticBuilder<'db>,
1463         }
1464         impl<'a, 'db, 'v> Visitor<'v> for WalkAssocTypes<'a, 'db> {
1465             type Map = intravisit::ErasedMap<'v>;
1466
1467             fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1468                 intravisit::NestedVisitorMap::None
1469             }
1470
1471             fn visit_qpath(&mut self, qpath: &'v hir::QPath<'v>, id: hir::HirId, span: Span) {
1472                 if TypeAliasBounds::is_type_variable_assoc(qpath) {
1473                     self.err.span_help(
1474                         span,
1475                         "use fully disambiguated paths (i.e., `<T as Trait>::Assoc`) to refer to \
1476                          associated types in type aliases",
1477                     );
1478                 }
1479                 intravisit::walk_qpath(self, qpath, id, span)
1480             }
1481         }
1482
1483         // Let's go for a walk!
1484         let mut visitor = WalkAssocTypes { err };
1485         visitor.visit_ty(ty);
1486     }
1487 }
1488
1489 impl<'tcx> LateLintPass<'tcx> for TypeAliasBounds {
1490     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1491         let (ty, type_alias_generics) = match item.kind {
1492             hir::ItemKind::TyAlias(ref ty, ref generics) => (&*ty, generics),
1493             _ => return,
1494         };
1495         if let hir::TyKind::OpaqueDef(..) = ty.kind {
1496             // Bounds are respected for `type X = impl Trait`
1497             return;
1498         }
1499         let mut suggested_changing_assoc_types = false;
1500         // There must not be a where clause
1501         if !type_alias_generics.where_clause.predicates.is_empty() {
1502             cx.lint(
1503                 TYPE_ALIAS_BOUNDS,
1504                 |lint| {
1505                     let mut err = lint.build("where clauses are not enforced in type aliases");
1506                     let spans: Vec<_> = type_alias_generics
1507                         .where_clause
1508                         .predicates
1509                         .iter()
1510                         .map(|pred| pred.span())
1511                         .collect();
1512                     err.set_span(spans);
1513                     err.span_suggestion(
1514                         type_alias_generics.where_clause.span_for_predicates_or_empty_place(),
1515                         "the clause will not be checked when the type alias is used, and should be removed",
1516                         String::new(),
1517                         Applicability::MachineApplicable,
1518                     );
1519                     if !suggested_changing_assoc_types {
1520                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1521                         suggested_changing_assoc_types = true;
1522                     }
1523                     err.emit();
1524                 },
1525             );
1526         }
1527         // The parameters must not have bounds
1528         for param in type_alias_generics.params.iter() {
1529             let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
1530             let suggestion = spans
1531                 .iter()
1532                 .map(|sp| {
1533                     let start = param.span.between(*sp); // Include the `:` in `T: Bound`.
1534                     (start.to(*sp), String::new())
1535                 })
1536                 .collect();
1537             if !spans.is_empty() {
1538                 cx.struct_span_lint(TYPE_ALIAS_BOUNDS, spans, |lint| {
1539                     let mut err =
1540                         lint.build("bounds on generic parameters are not enforced in type aliases");
1541                     let msg = "the bound will not be checked when the type alias is used, \
1542                                    and should be removed";
1543                     err.multipart_suggestion(&msg, suggestion, Applicability::MachineApplicable);
1544                     if !suggested_changing_assoc_types {
1545                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1546                         suggested_changing_assoc_types = true;
1547                     }
1548                     err.emit();
1549                 });
1550             }
1551         }
1552     }
1553 }
1554
1555 declare_lint_pass!(
1556     /// Lint constants that are erroneous.
1557     /// Without this lint, we might not get any diagnostic if the constant is
1558     /// unused within this crate, even though downstream crates can't use it
1559     /// without producing an error.
1560     UnusedBrokenConst => []
1561 );
1562
1563 impl<'tcx> LateLintPass<'tcx> for UnusedBrokenConst {
1564     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1565         match it.kind {
1566             hir::ItemKind::Const(_, body_id) => {
1567                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1568                 // trigger the query once for all constants since that will already report the errors
1569                 // FIXME: Use ensure here
1570                 let _ = cx.tcx.const_eval_poly(def_id);
1571             }
1572             hir::ItemKind::Static(_, _, body_id) => {
1573                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1574                 // FIXME: Use ensure here
1575                 let _ = cx.tcx.eval_static_initializer(def_id);
1576             }
1577             _ => {}
1578         }
1579     }
1580 }
1581
1582 declare_lint! {
1583     /// The `trivial_bounds` lint detects trait bounds that don't depend on
1584     /// any type parameters.
1585     ///
1586     /// ### Example
1587     ///
1588     /// ```rust
1589     /// #![feature(trivial_bounds)]
1590     /// pub struct A where i32: Copy;
1591     /// ```
1592     ///
1593     /// {{produces}}
1594     ///
1595     /// ### Explanation
1596     ///
1597     /// Usually you would not write a trait bound that you know is always
1598     /// true, or never true. However, when using macros, the macro may not
1599     /// know whether or not the constraint would hold or not at the time when
1600     /// generating the code. Currently, the compiler does not alert you if the
1601     /// constraint is always true, and generates an error if it is never true.
1602     /// The `trivial_bounds` feature changes this to be a warning in both
1603     /// cases, giving macros more freedom and flexibility to generate code,
1604     /// while still providing a signal when writing non-macro code that
1605     /// something is amiss.
1606     ///
1607     /// See [RFC 2056] for more details. This feature is currently only
1608     /// available on the nightly channel, see [tracking issue #48214].
1609     ///
1610     /// [RFC 2056]: https://github.com/rust-lang/rfcs/blob/master/text/2056-allow-trivial-where-clause-constraints.md
1611     /// [tracking issue #48214]: https://github.com/rust-lang/rust/issues/48214
1612     TRIVIAL_BOUNDS,
1613     Warn,
1614     "these bounds don't depend on an type parameters"
1615 }
1616
1617 declare_lint_pass!(
1618     /// Lint for trait and lifetime bounds that don't depend on type parameters
1619     /// which either do nothing, or stop the item from being used.
1620     TrivialConstraints => [TRIVIAL_BOUNDS]
1621 );
1622
1623 impl<'tcx> LateLintPass<'tcx> for TrivialConstraints {
1624     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
1625         use rustc_middle::ty::fold::TypeFoldable;
1626         use rustc_middle::ty::PredicateKind::*;
1627
1628         if cx.tcx.features().trivial_bounds {
1629             let predicates = cx.tcx.predicates_of(item.def_id);
1630             for &(predicate, span) in predicates.predicates {
1631                 let predicate_kind_name = match predicate.kind().skip_binder() {
1632                     Trait(..) => "Trait",
1633                     TypeOutlives(..) |
1634                     RegionOutlives(..) => "Lifetime",
1635
1636                     // Ignore projections, as they can only be global
1637                     // if the trait bound is global
1638                     Projection(..) |
1639                     // Ignore bounds that a user can't type
1640                     WellFormed(..) |
1641                     ObjectSafe(..) |
1642                     ClosureKind(..) |
1643                     Subtype(..) |
1644                     Coerce(..) |
1645                     ConstEvaluatable(..) |
1646                     ConstEquate(..) |
1647                     TypeWellFormedFromEnv(..) => continue,
1648                 };
1649                 if predicate.is_global(cx.tcx) {
1650                     cx.struct_span_lint(TRIVIAL_BOUNDS, span, |lint| {
1651                         lint.build(&format!(
1652                             "{} bound {} does not depend on any type \
1653                                 or lifetime parameters",
1654                             predicate_kind_name, predicate
1655                         ))
1656                         .emit()
1657                     });
1658                 }
1659             }
1660         }
1661     }
1662 }
1663
1664 declare_lint_pass!(
1665     /// Does nothing as a lint pass, but registers some `Lint`s
1666     /// which are used by other parts of the compiler.
1667     SoftLints => [
1668         WHILE_TRUE,
1669         BOX_POINTERS,
1670         NON_SHORTHAND_FIELD_PATTERNS,
1671         UNSAFE_CODE,
1672         MISSING_DOCS,
1673         MISSING_COPY_IMPLEMENTATIONS,
1674         MISSING_DEBUG_IMPLEMENTATIONS,
1675         ANONYMOUS_PARAMETERS,
1676         UNUSED_DOC_COMMENTS,
1677         NO_MANGLE_CONST_ITEMS,
1678         NO_MANGLE_GENERIC_ITEMS,
1679         MUTABLE_TRANSMUTES,
1680         UNSTABLE_FEATURES,
1681         UNREACHABLE_PUB,
1682         TYPE_ALIAS_BOUNDS,
1683         TRIVIAL_BOUNDS
1684     ]
1685 );
1686
1687 declare_lint! {
1688     /// The `ellipsis_inclusive_range_patterns` lint detects the [`...` range
1689     /// pattern], which is deprecated.
1690     ///
1691     /// [`...` range pattern]: https://doc.rust-lang.org/reference/patterns.html#range-patterns
1692     ///
1693     /// ### Example
1694     ///
1695     /// ```rust,edition2018
1696     /// let x = 123;
1697     /// match x {
1698     ///     0...100 => {}
1699     ///     _ => {}
1700     /// }
1701     /// ```
1702     ///
1703     /// {{produces}}
1704     ///
1705     /// ### Explanation
1706     ///
1707     /// The `...` range pattern syntax was changed to `..=` to avoid potential
1708     /// confusion with the [`..` range expression]. Use the new form instead.
1709     ///
1710     /// [`..` range expression]: https://doc.rust-lang.org/reference/expressions/range-expr.html
1711     pub ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
1712     Warn,
1713     "`...` range patterns are deprecated",
1714     @future_incompatible = FutureIncompatibleInfo {
1715         reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>",
1716         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
1717     };
1718 }
1719
1720 #[derive(Default)]
1721 pub struct EllipsisInclusiveRangePatterns {
1722     /// If `Some(_)`, suppress all subsequent pattern
1723     /// warnings for better diagnostics.
1724     node_id: Option<ast::NodeId>,
1725 }
1726
1727 impl_lint_pass!(EllipsisInclusiveRangePatterns => [ELLIPSIS_INCLUSIVE_RANGE_PATTERNS]);
1728
1729 impl EarlyLintPass for EllipsisInclusiveRangePatterns {
1730     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &ast::Pat) {
1731         if self.node_id.is_some() {
1732             // Don't recursively warn about patterns inside range endpoints.
1733             return;
1734         }
1735
1736         use self::ast::{PatKind, RangeSyntax::DotDotDot};
1737
1738         /// If `pat` is a `...` pattern, return the start and end of the range, as well as the span
1739         /// corresponding to the ellipsis.
1740         fn matches_ellipsis_pat(pat: &ast::Pat) -> Option<(Option<&Expr>, &Expr, Span)> {
1741             match &pat.kind {
1742                 PatKind::Range(
1743                     a,
1744                     Some(b),
1745                     Spanned { span, node: RangeEnd::Included(DotDotDot) },
1746                 ) => Some((a.as_deref(), b, *span)),
1747                 _ => None,
1748             }
1749         }
1750
1751         let (parenthesise, endpoints) = match &pat.kind {
1752             PatKind::Ref(subpat, _) => (true, matches_ellipsis_pat(&subpat)),
1753             _ => (false, matches_ellipsis_pat(pat)),
1754         };
1755
1756         if let Some((start, end, join)) = endpoints {
1757             let msg = "`...` range patterns are deprecated";
1758             let suggestion = "use `..=` for an inclusive range";
1759             if parenthesise {
1760                 self.node_id = Some(pat.id);
1761                 let end = expr_to_string(&end);
1762                 let replace = match start {
1763                     Some(start) => format!("&({}..={})", expr_to_string(&start), end),
1764                     None => format!("&(..={})", end),
1765                 };
1766                 if join.edition() >= Edition::Edition2021 {
1767                     let mut err =
1768                         rustc_errors::struct_span_err!(cx.sess, pat.span, E0783, "{}", msg,);
1769                     err.span_suggestion(
1770                         pat.span,
1771                         suggestion,
1772                         replace,
1773                         Applicability::MachineApplicable,
1774                     )
1775                     .emit();
1776                 } else {
1777                     cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, pat.span, |lint| {
1778                         lint.build(msg)
1779                             .span_suggestion(
1780                                 pat.span,
1781                                 suggestion,
1782                                 replace,
1783                                 Applicability::MachineApplicable,
1784                             )
1785                             .emit();
1786                     });
1787                 }
1788             } else {
1789                 let replace = "..=".to_owned();
1790                 if join.edition() >= Edition::Edition2021 {
1791                     let mut err =
1792                         rustc_errors::struct_span_err!(cx.sess, pat.span, E0783, "{}", msg,);
1793                     err.span_suggestion_short(
1794                         join,
1795                         suggestion,
1796                         replace,
1797                         Applicability::MachineApplicable,
1798                     )
1799                     .emit();
1800                 } else {
1801                     cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, join, |lint| {
1802                         lint.build(msg)
1803                             .span_suggestion_short(
1804                                 join,
1805                                 suggestion,
1806                                 replace,
1807                                 Applicability::MachineApplicable,
1808                             )
1809                             .emit();
1810                     });
1811                 }
1812             };
1813         }
1814     }
1815
1816     fn check_pat_post(&mut self, _cx: &EarlyContext<'_>, pat: &ast::Pat) {
1817         if let Some(node_id) = self.node_id {
1818             if pat.id == node_id {
1819                 self.node_id = None
1820             }
1821         }
1822     }
1823 }
1824
1825 declare_lint! {
1826     /// The `unnameable_test_items` lint detects [`#[test]`][test] functions
1827     /// that are not able to be run by the test harness because they are in a
1828     /// position where they are not nameable.
1829     ///
1830     /// [test]: https://doc.rust-lang.org/reference/attributes/testing.html#the-test-attribute
1831     ///
1832     /// ### Example
1833     ///
1834     /// ```rust,test
1835     /// fn main() {
1836     ///     #[test]
1837     ///     fn foo() {
1838     ///         // This test will not fail because it does not run.
1839     ///         assert_eq!(1, 2);
1840     ///     }
1841     /// }
1842     /// ```
1843     ///
1844     /// {{produces}}
1845     ///
1846     /// ### Explanation
1847     ///
1848     /// In order for the test harness to run a test, the test function must be
1849     /// located in a position where it can be accessed from the crate root.
1850     /// This generally means it must be defined in a module, and not anywhere
1851     /// else such as inside another function. The compiler previously allowed
1852     /// this without an error, so a lint was added as an alert that a test is
1853     /// not being used. Whether or not this should be allowed has not yet been
1854     /// decided, see [RFC 2471] and [issue #36629].
1855     ///
1856     /// [RFC 2471]: https://github.com/rust-lang/rfcs/pull/2471#issuecomment-397414443
1857     /// [issue #36629]: https://github.com/rust-lang/rust/issues/36629
1858     UNNAMEABLE_TEST_ITEMS,
1859     Warn,
1860     "detects an item that cannot be named being marked as `#[test_case]`",
1861     report_in_external_macro
1862 }
1863
1864 pub struct UnnameableTestItems {
1865     boundary: Option<LocalDefId>, // Id of the item under which things are not nameable
1866     items_nameable: bool,
1867 }
1868
1869 impl_lint_pass!(UnnameableTestItems => [UNNAMEABLE_TEST_ITEMS]);
1870
1871 impl UnnameableTestItems {
1872     pub fn new() -> Self {
1873         Self { boundary: None, items_nameable: true }
1874     }
1875 }
1876
1877 impl<'tcx> LateLintPass<'tcx> for UnnameableTestItems {
1878     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1879         if self.items_nameable {
1880             if let hir::ItemKind::Mod(..) = it.kind {
1881             } else {
1882                 self.items_nameable = false;
1883                 self.boundary = Some(it.def_id);
1884             }
1885             return;
1886         }
1887
1888         let attrs = cx.tcx.hir().attrs(it.hir_id());
1889         if let Some(attr) = cx.sess().find_by_name(attrs, sym::rustc_test_marker) {
1890             cx.struct_span_lint(UNNAMEABLE_TEST_ITEMS, attr.span, |lint| {
1891                 lint.build("cannot test inner items").emit()
1892             });
1893         }
1894     }
1895
1896     fn check_item_post(&mut self, _cx: &LateContext<'_>, it: &hir::Item<'_>) {
1897         if !self.items_nameable && self.boundary == Some(it.def_id) {
1898             self.items_nameable = true;
1899         }
1900     }
1901 }
1902
1903 declare_lint! {
1904     /// The `keyword_idents` lint detects edition keywords being used as an
1905     /// identifier.
1906     ///
1907     /// ### Example
1908     ///
1909     /// ```rust,edition2015,compile_fail
1910     /// #![deny(keyword_idents)]
1911     /// // edition 2015
1912     /// fn dyn() {}
1913     /// ```
1914     ///
1915     /// {{produces}}
1916     ///
1917     /// ### Explanation
1918     ///
1919     /// Rust [editions] allow the language to evolve without breaking
1920     /// backwards compatibility. This lint catches code that uses new keywords
1921     /// that are added to the language that are used as identifiers (such as a
1922     /// variable name, function name, etc.). If you switch the compiler to a
1923     /// new edition without updating the code, then it will fail to compile if
1924     /// you are using a new keyword as an identifier.
1925     ///
1926     /// You can manually change the identifiers to a non-keyword, or use a
1927     /// [raw identifier], for example `r#dyn`, to transition to a new edition.
1928     ///
1929     /// This lint solves the problem automatically. It is "allow" by default
1930     /// because the code is perfectly valid in older editions. The [`cargo
1931     /// fix`] tool with the `--edition` flag will switch this lint to "warn"
1932     /// and automatically apply the suggested fix from the compiler (which is
1933     /// to use a raw identifier). This provides a completely automated way to
1934     /// update old code for a new edition.
1935     ///
1936     /// [editions]: https://doc.rust-lang.org/edition-guide/
1937     /// [raw identifier]: https://doc.rust-lang.org/reference/identifiers.html
1938     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
1939     pub KEYWORD_IDENTS,
1940     Allow,
1941     "detects edition keywords being used as an identifier",
1942     @future_incompatible = FutureIncompatibleInfo {
1943         reference: "issue #49716 <https://github.com/rust-lang/rust/issues/49716>",
1944         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
1945     };
1946 }
1947
1948 declare_lint_pass!(
1949     /// Check for uses of edition keywords used as an identifier.
1950     KeywordIdents => [KEYWORD_IDENTS]
1951 );
1952
1953 struct UnderMacro(bool);
1954
1955 impl KeywordIdents {
1956     fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: TokenStream) {
1957         for tt in tokens.into_trees() {
1958             match tt {
1959                 // Only report non-raw idents.
1960                 TokenTree::Token(token) => {
1961                     if let Some((ident, false)) = token.ident() {
1962                         self.check_ident_token(cx, UnderMacro(true), ident);
1963                     }
1964                 }
1965                 TokenTree::Delimited(_, _, tts) => self.check_tokens(cx, tts),
1966             }
1967         }
1968     }
1969
1970     fn check_ident_token(
1971         &mut self,
1972         cx: &EarlyContext<'_>,
1973         UnderMacro(under_macro): UnderMacro,
1974         ident: Ident,
1975     ) {
1976         let next_edition = match cx.sess.edition() {
1977             Edition::Edition2015 => {
1978                 match ident.name {
1979                     kw::Async | kw::Await | kw::Try => Edition::Edition2018,
1980
1981                     // rust-lang/rust#56327: Conservatively do not
1982                     // attempt to report occurrences of `dyn` within
1983                     // macro definitions or invocations, because `dyn`
1984                     // can legitimately occur as a contextual keyword
1985                     // in 2015 code denoting its 2018 meaning, and we
1986                     // do not want rustfix to inject bugs into working
1987                     // code by rewriting such occurrences.
1988                     //
1989                     // But if we see `dyn` outside of a macro, we know
1990                     // its precise role in the parsed AST and thus are
1991                     // assured this is truly an attempt to use it as
1992                     // an identifier.
1993                     kw::Dyn if !under_macro => Edition::Edition2018,
1994
1995                     _ => return,
1996                 }
1997             }
1998
1999             // There are no new keywords yet for the 2018 edition and beyond.
2000             _ => return,
2001         };
2002
2003         // Don't lint `r#foo`.
2004         if cx.sess.parse_sess.raw_identifier_spans.borrow().contains(&ident.span) {
2005             return;
2006         }
2007
2008         cx.struct_span_lint(KEYWORD_IDENTS, ident.span, |lint| {
2009             lint.build(&format!("`{}` is a keyword in the {} edition", ident, next_edition))
2010                 .span_suggestion(
2011                     ident.span,
2012                     "you can use a raw identifier to stay compatible",
2013                     format!("r#{}", ident),
2014                     Applicability::MachineApplicable,
2015                 )
2016                 .emit()
2017         });
2018     }
2019 }
2020
2021 impl EarlyLintPass for KeywordIdents {
2022     fn check_mac_def(&mut self, cx: &EarlyContext<'_>, mac_def: &ast::MacroDef, _id: ast::NodeId) {
2023         self.check_tokens(cx, mac_def.body.inner_tokens());
2024     }
2025     fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::MacCall) {
2026         self.check_tokens(cx, mac.args.inner_tokens());
2027     }
2028     fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: Ident) {
2029         self.check_ident_token(cx, UnderMacro(false), ident);
2030     }
2031 }
2032
2033 declare_lint_pass!(ExplicitOutlivesRequirements => [EXPLICIT_OUTLIVES_REQUIREMENTS]);
2034
2035 impl ExplicitOutlivesRequirements {
2036     fn lifetimes_outliving_lifetime<'tcx>(
2037         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2038         index: u32,
2039     ) -> Vec<ty::Region<'tcx>> {
2040         inferred_outlives
2041             .iter()
2042             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
2043                 ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => match a {
2044                     ty::ReEarlyBound(ebr) if ebr.index == index => Some(b),
2045                     _ => None,
2046                 },
2047                 _ => None,
2048             })
2049             .collect()
2050     }
2051
2052     fn lifetimes_outliving_type<'tcx>(
2053         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2054         index: u32,
2055     ) -> Vec<ty::Region<'tcx>> {
2056         inferred_outlives
2057             .iter()
2058             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
2059                 ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
2060                     a.is_param(index).then_some(b)
2061                 }
2062                 _ => None,
2063             })
2064             .collect()
2065     }
2066
2067     fn collect_outlived_lifetimes<'tcx>(
2068         &self,
2069         param: &'tcx hir::GenericParam<'tcx>,
2070         tcx: TyCtxt<'tcx>,
2071         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2072         ty_generics: &'tcx ty::Generics,
2073     ) -> Vec<ty::Region<'tcx>> {
2074         let index =
2075             ty_generics.param_def_id_to_index[&tcx.hir().local_def_id(param.hir_id).to_def_id()];
2076
2077         match param.kind {
2078             hir::GenericParamKind::Lifetime { .. } => {
2079                 Self::lifetimes_outliving_lifetime(inferred_outlives, index)
2080             }
2081             hir::GenericParamKind::Type { .. } => {
2082                 Self::lifetimes_outliving_type(inferred_outlives, index)
2083             }
2084             hir::GenericParamKind::Const { .. } => Vec::new(),
2085         }
2086     }
2087
2088     fn collect_outlives_bound_spans<'tcx>(
2089         &self,
2090         tcx: TyCtxt<'tcx>,
2091         bounds: &hir::GenericBounds<'_>,
2092         inferred_outlives: &[ty::Region<'tcx>],
2093         infer_static: bool,
2094     ) -> Vec<(usize, Span)> {
2095         use rustc_middle::middle::resolve_lifetime::Region;
2096
2097         bounds
2098             .iter()
2099             .enumerate()
2100             .filter_map(|(i, bound)| {
2101                 if let hir::GenericBound::Outlives(lifetime) = bound {
2102                     let is_inferred = match tcx.named_region(lifetime.hir_id) {
2103                         Some(Region::Static) if infer_static => {
2104                             inferred_outlives.iter().any(|r| matches!(r, ty::ReStatic))
2105                         }
2106                         Some(Region::EarlyBound(index, ..)) => inferred_outlives.iter().any(|r| {
2107                             if let ty::ReEarlyBound(ebr) = r { ebr.index == index } else { false }
2108                         }),
2109                         _ => false,
2110                     };
2111                     is_inferred.then_some((i, bound.span()))
2112                 } else {
2113                     None
2114                 }
2115             })
2116             .collect()
2117     }
2118
2119     fn consolidate_outlives_bound_spans(
2120         &self,
2121         lo: Span,
2122         bounds: &hir::GenericBounds<'_>,
2123         bound_spans: Vec<(usize, Span)>,
2124     ) -> Vec<Span> {
2125         if bounds.is_empty() {
2126             return Vec::new();
2127         }
2128         if bound_spans.len() == bounds.len() {
2129             let (_, last_bound_span) = bound_spans[bound_spans.len() - 1];
2130             // If all bounds are inferable, we want to delete the colon, so
2131             // start from just after the parameter (span passed as argument)
2132             vec![lo.to(last_bound_span)]
2133         } else {
2134             let mut merged = Vec::new();
2135             let mut last_merged_i = None;
2136
2137             let mut from_start = true;
2138             for (i, bound_span) in bound_spans {
2139                 match last_merged_i {
2140                     // If the first bound is inferable, our span should also eat the leading `+`.
2141                     None if i == 0 => {
2142                         merged.push(bound_span.to(bounds[1].span().shrink_to_lo()));
2143                         last_merged_i = Some(0);
2144                     }
2145                     // If consecutive bounds are inferable, merge their spans
2146                     Some(h) if i == h + 1 => {
2147                         if let Some(tail) = merged.last_mut() {
2148                             // Also eat the trailing `+` if the first
2149                             // more-than-one bound is inferable
2150                             let to_span = if from_start && i < bounds.len() {
2151                                 bounds[i + 1].span().shrink_to_lo()
2152                             } else {
2153                                 bound_span
2154                             };
2155                             *tail = tail.to(to_span);
2156                             last_merged_i = Some(i);
2157                         } else {
2158                             bug!("another bound-span visited earlier");
2159                         }
2160                     }
2161                     _ => {
2162                         // When we find a non-inferable bound, subsequent inferable bounds
2163                         // won't be consecutive from the start (and we'll eat the leading
2164                         // `+` rather than the trailing one)
2165                         from_start = false;
2166                         merged.push(bounds[i - 1].span().shrink_to_hi().to(bound_span));
2167                         last_merged_i = Some(i);
2168                     }
2169                 }
2170             }
2171             merged
2172         }
2173     }
2174 }
2175
2176 impl<'tcx> LateLintPass<'tcx> for ExplicitOutlivesRequirements {
2177     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
2178         use rustc_middle::middle::resolve_lifetime::Region;
2179
2180         let infer_static = cx.tcx.features().infer_static_outlives_requirements;
2181         let def_id = item.def_id;
2182         if let hir::ItemKind::Struct(_, ref hir_generics)
2183         | hir::ItemKind::Enum(_, ref hir_generics)
2184         | hir::ItemKind::Union(_, ref hir_generics) = item.kind
2185         {
2186             let inferred_outlives = cx.tcx.inferred_outlives_of(def_id);
2187             if inferred_outlives.is_empty() {
2188                 return;
2189             }
2190
2191             let ty_generics = cx.tcx.generics_of(def_id);
2192
2193             let mut bound_count = 0;
2194             let mut lint_spans = Vec::new();
2195
2196             for param in hir_generics.params {
2197                 let has_lifetime_bounds = param
2198                     .bounds
2199                     .iter()
2200                     .any(|bound| matches!(bound, hir::GenericBound::Outlives(_)));
2201                 if !has_lifetime_bounds {
2202                     continue;
2203                 }
2204
2205                 let relevant_lifetimes =
2206                     self.collect_outlived_lifetimes(param, cx.tcx, inferred_outlives, ty_generics);
2207                 if relevant_lifetimes.is_empty() {
2208                     continue;
2209                 }
2210
2211                 let bound_spans = self.collect_outlives_bound_spans(
2212                     cx.tcx,
2213                     &param.bounds,
2214                     &relevant_lifetimes,
2215                     infer_static,
2216                 );
2217                 bound_count += bound_spans.len();
2218                 lint_spans.extend(self.consolidate_outlives_bound_spans(
2219                     param.span.shrink_to_hi(),
2220                     &param.bounds,
2221                     bound_spans,
2222                 ));
2223             }
2224
2225             let mut where_lint_spans = Vec::new();
2226             let mut dropped_predicate_count = 0;
2227             let num_predicates = hir_generics.where_clause.predicates.len();
2228             for (i, where_predicate) in hir_generics.where_clause.predicates.iter().enumerate() {
2229                 let (relevant_lifetimes, bounds, span) = match where_predicate {
2230                     hir::WherePredicate::RegionPredicate(predicate) => {
2231                         if let Some(Region::EarlyBound(index, ..)) =
2232                             cx.tcx.named_region(predicate.lifetime.hir_id)
2233                         {
2234                             (
2235                                 Self::lifetimes_outliving_lifetime(inferred_outlives, index),
2236                                 &predicate.bounds,
2237                                 predicate.span,
2238                             )
2239                         } else {
2240                             continue;
2241                         }
2242                     }
2243                     hir::WherePredicate::BoundPredicate(predicate) => {
2244                         // FIXME we can also infer bounds on associated types,
2245                         // and should check for them here.
2246                         match predicate.bounded_ty.kind {
2247                             hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
2248                                 if let Res::Def(DefKind::TyParam, def_id) = path.res {
2249                                     let index = ty_generics.param_def_id_to_index[&def_id];
2250                                     (
2251                                         Self::lifetimes_outliving_type(inferred_outlives, index),
2252                                         &predicate.bounds,
2253                                         predicate.span,
2254                                     )
2255                                 } else {
2256                                     continue;
2257                                 }
2258                             }
2259                             _ => {
2260                                 continue;
2261                             }
2262                         }
2263                     }
2264                     _ => continue,
2265                 };
2266                 if relevant_lifetimes.is_empty() {
2267                     continue;
2268                 }
2269
2270                 let bound_spans = self.collect_outlives_bound_spans(
2271                     cx.tcx,
2272                     bounds,
2273                     &relevant_lifetimes,
2274                     infer_static,
2275                 );
2276                 bound_count += bound_spans.len();
2277
2278                 let drop_predicate = bound_spans.len() == bounds.len();
2279                 if drop_predicate {
2280                     dropped_predicate_count += 1;
2281                 }
2282
2283                 // If all the bounds on a predicate were inferable and there are
2284                 // further predicates, we want to eat the trailing comma.
2285                 if drop_predicate && i + 1 < num_predicates {
2286                     let next_predicate_span = hir_generics.where_clause.predicates[i + 1].span();
2287                     where_lint_spans.push(span.to(next_predicate_span.shrink_to_lo()));
2288                 } else {
2289                     where_lint_spans.extend(self.consolidate_outlives_bound_spans(
2290                         span.shrink_to_lo(),
2291                         bounds,
2292                         bound_spans,
2293                     ));
2294                 }
2295             }
2296
2297             // If all predicates are inferable, drop the entire clause
2298             // (including the `where`)
2299             if num_predicates > 0 && dropped_predicate_count == num_predicates {
2300                 let where_span = hir_generics
2301                     .where_clause
2302                     .span()
2303                     .expect("span of (nonempty) where clause should exist");
2304                 // Extend the where clause back to the closing `>` of the
2305                 // generics, except for tuple struct, which have the `where`
2306                 // after the fields of the struct.
2307                 let full_where_span =
2308                     if let hir::ItemKind::Struct(hir::VariantData::Tuple(..), _) = item.kind {
2309                         where_span
2310                     } else {
2311                         hir_generics.span.shrink_to_hi().to(where_span)
2312                     };
2313                 lint_spans.push(full_where_span);
2314             } else {
2315                 lint_spans.extend(where_lint_spans);
2316             }
2317
2318             if !lint_spans.is_empty() {
2319                 cx.struct_span_lint(EXPLICIT_OUTLIVES_REQUIREMENTS, lint_spans.clone(), |lint| {
2320                     lint.build("outlives requirements can be inferred")
2321                         .multipart_suggestion(
2322                             if bound_count == 1 {
2323                                 "remove this bound"
2324                             } else {
2325                                 "remove these bounds"
2326                             },
2327                             lint_spans
2328                                 .into_iter()
2329                                 .map(|span| (span, "".to_owned()))
2330                                 .collect::<Vec<_>>(),
2331                             Applicability::MachineApplicable,
2332                         )
2333                         .emit();
2334                 });
2335             }
2336         }
2337     }
2338 }
2339
2340 declare_lint! {
2341     /// The `incomplete_features` lint detects unstable features enabled with
2342     /// the [`feature` attribute] that may function improperly in some or all
2343     /// cases.
2344     ///
2345     /// [`feature` attribute]: https://doc.rust-lang.org/nightly/unstable-book/
2346     ///
2347     /// ### Example
2348     ///
2349     /// ```rust
2350     /// #![feature(generic_const_exprs)]
2351     /// ```
2352     ///
2353     /// {{produces}}
2354     ///
2355     /// ### Explanation
2356     ///
2357     /// Although it is encouraged for people to experiment with unstable
2358     /// features, some of them are known to be incomplete or faulty. This lint
2359     /// is a signal that the feature has not yet been finished, and you may
2360     /// experience problems with it.
2361     pub INCOMPLETE_FEATURES,
2362     Warn,
2363     "incomplete features that may function improperly in some or all cases"
2364 }
2365
2366 declare_lint_pass!(
2367     /// Check for used feature gates in `INCOMPLETE_FEATURES` in `rustc_feature/src/active.rs`.
2368     IncompleteFeatures => [INCOMPLETE_FEATURES]
2369 );
2370
2371 impl EarlyLintPass for IncompleteFeatures {
2372     fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
2373         let features = cx.sess.features_untracked();
2374         features
2375             .declared_lang_features
2376             .iter()
2377             .map(|(name, span, _)| (name, span))
2378             .chain(features.declared_lib_features.iter().map(|(name, span)| (name, span)))
2379             .filter(|(&name, _)| features.incomplete(name))
2380             .for_each(|(&name, &span)| {
2381                 cx.struct_span_lint(INCOMPLETE_FEATURES, span, |lint| {
2382                     let mut builder = lint.build(&format!(
2383                         "the feature `{}` is incomplete and may not be safe to use \
2384                          and/or cause compiler crashes",
2385                         name,
2386                     ));
2387                     if let Some(n) = rustc_feature::find_feature_issue(name, GateIssue::Language) {
2388                         builder.note(&format!(
2389                             "see issue #{} <https://github.com/rust-lang/rust/issues/{}> \
2390                              for more information",
2391                             n, n,
2392                         ));
2393                     }
2394                     if HAS_MIN_FEATURES.contains(&name) {
2395                         builder.help(&format!(
2396                             "consider using `min_{}` instead, which is more stable and complete",
2397                             name,
2398                         ));
2399                     }
2400                     builder.emit();
2401                 })
2402             });
2403     }
2404 }
2405
2406 const HAS_MIN_FEATURES: &[Symbol] = &[sym::specialization];
2407
2408 declare_lint! {
2409     /// The `invalid_value` lint detects creating a value that is not valid,
2410     /// such as a null reference.
2411     ///
2412     /// ### Example
2413     ///
2414     /// ```rust,no_run
2415     /// # #![allow(unused)]
2416     /// unsafe {
2417     ///     let x: &'static i32 = std::mem::zeroed();
2418     /// }
2419     /// ```
2420     ///
2421     /// {{produces}}
2422     ///
2423     /// ### Explanation
2424     ///
2425     /// In some situations the compiler can detect that the code is creating
2426     /// an invalid value, which should be avoided.
2427     ///
2428     /// In particular, this lint will check for improper use of
2429     /// [`mem::zeroed`], [`mem::uninitialized`], [`mem::transmute`], and
2430     /// [`MaybeUninit::assume_init`] that can cause [undefined behavior]. The
2431     /// lint should provide extra information to indicate what the problem is
2432     /// and a possible solution.
2433     ///
2434     /// [`mem::zeroed`]: https://doc.rust-lang.org/std/mem/fn.zeroed.html
2435     /// [`mem::uninitialized`]: https://doc.rust-lang.org/std/mem/fn.uninitialized.html
2436     /// [`mem::transmute`]: https://doc.rust-lang.org/std/mem/fn.transmute.html
2437     /// [`MaybeUninit::assume_init`]: https://doc.rust-lang.org/std/mem/union.MaybeUninit.html#method.assume_init
2438     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
2439     pub INVALID_VALUE,
2440     Warn,
2441     "an invalid value is being created (such as a null reference)"
2442 }
2443
2444 declare_lint_pass!(InvalidValue => [INVALID_VALUE]);
2445
2446 impl<'tcx> LateLintPass<'tcx> for InvalidValue {
2447     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
2448         #[derive(Debug, Copy, Clone, PartialEq)]
2449         enum InitKind {
2450             Zeroed,
2451             Uninit,
2452         }
2453
2454         /// Information about why a type cannot be initialized this way.
2455         /// Contains an error message and optionally a span to point at.
2456         type InitError = (String, Option<Span>);
2457
2458         /// Test if this constant is all-0.
2459         fn is_zero(expr: &hir::Expr<'_>) -> bool {
2460             use hir::ExprKind::*;
2461             use rustc_ast::LitKind::*;
2462             match &expr.kind {
2463                 Lit(lit) => {
2464                     if let Int(i, _) = lit.node {
2465                         i == 0
2466                     } else {
2467                         false
2468                     }
2469                 }
2470                 Tup(tup) => tup.iter().all(is_zero),
2471                 _ => false,
2472             }
2473         }
2474
2475         /// Determine if this expression is a "dangerous initialization".
2476         fn is_dangerous_init(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> Option<InitKind> {
2477             if let hir::ExprKind::Call(ref path_expr, ref args) = expr.kind {
2478                 // Find calls to `mem::{uninitialized,zeroed}` methods.
2479                 if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2480                     let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2481
2482                     if cx.tcx.is_diagnostic_item(sym::mem_zeroed, def_id) {
2483                         return Some(InitKind::Zeroed);
2484                     } else if cx.tcx.is_diagnostic_item(sym::mem_uninitialized, def_id) {
2485                         return Some(InitKind::Uninit);
2486                     } else if cx.tcx.is_diagnostic_item(sym::transmute, def_id) && is_zero(&args[0])
2487                     {
2488                         return Some(InitKind::Zeroed);
2489                     }
2490                 }
2491             } else if let hir::ExprKind::MethodCall(_, _, ref args, _) = expr.kind {
2492                 // Find problematic calls to `MaybeUninit::assume_init`.
2493                 let def_id = cx.typeck_results().type_dependent_def_id(expr.hir_id)?;
2494                 if cx.tcx.is_diagnostic_item(sym::assume_init, def_id) {
2495                     // This is a call to *some* method named `assume_init`.
2496                     // See if the `self` parameter is one of the dangerous constructors.
2497                     if let hir::ExprKind::Call(ref path_expr, _) = args[0].kind {
2498                         if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2499                             let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2500
2501                             if cx.tcx.is_diagnostic_item(sym::maybe_uninit_zeroed, def_id) {
2502                                 return Some(InitKind::Zeroed);
2503                             } else if cx.tcx.is_diagnostic_item(sym::maybe_uninit_uninit, def_id) {
2504                                 return Some(InitKind::Uninit);
2505                             }
2506                         }
2507                     }
2508                 }
2509             }
2510
2511             None
2512         }
2513
2514         /// Test if this enum has several actually "existing" variants.
2515         /// Zero-sized uninhabited variants do not always have a tag assigned and thus do not "exist".
2516         fn is_multi_variant(adt: &ty::AdtDef) -> bool {
2517             // As an approximation, we only count dataless variants. Those are definitely inhabited.
2518             let existing_variants = adt.variants.iter().filter(|v| v.fields.is_empty()).count();
2519             existing_variants > 1
2520         }
2521
2522         /// Return `Some` only if we are sure this type does *not*
2523         /// allow zero initialization.
2524         fn ty_find_init_error<'tcx>(
2525             tcx: TyCtxt<'tcx>,
2526             ty: Ty<'tcx>,
2527             init: InitKind,
2528         ) -> Option<InitError> {
2529             use rustc_middle::ty::TyKind::*;
2530             match ty.kind() {
2531                 // Primitive types that don't like 0 as a value.
2532                 Ref(..) => Some(("references must be non-null".to_string(), None)),
2533                 Adt(..) if ty.is_box() => Some(("`Box` must be non-null".to_string(), None)),
2534                 FnPtr(..) => Some(("function pointers must be non-null".to_string(), None)),
2535                 Never => Some(("the `!` type has no valid value".to_string(), None)),
2536                 RawPtr(tm) if matches!(tm.ty.kind(), Dynamic(..)) =>
2537                 // raw ptr to dyn Trait
2538                 {
2539                     Some(("the vtable of a wide raw pointer must be non-null".to_string(), None))
2540                 }
2541                 // Primitive types with other constraints.
2542                 Bool if init == InitKind::Uninit => {
2543                     Some(("booleans must be either `true` or `false`".to_string(), None))
2544                 }
2545                 Char if init == InitKind::Uninit => {
2546                     Some(("characters must be a valid Unicode codepoint".to_string(), None))
2547                 }
2548                 // Recurse and checks for some compound types.
2549                 Adt(adt_def, substs) if !adt_def.is_union() => {
2550                     // First check if this ADT has a layout attribute (like `NonNull` and friends).
2551                     use std::ops::Bound;
2552                     match tcx.layout_scalar_valid_range(adt_def.did) {
2553                         // We exploit here that `layout_scalar_valid_range` will never
2554                         // return `Bound::Excluded`.  (And we have tests checking that we
2555                         // handle the attribute correctly.)
2556                         (Bound::Included(lo), _) if lo > 0 => {
2557                             return Some((format!("`{}` must be non-null", ty), None));
2558                         }
2559                         (Bound::Included(_), _) | (_, Bound::Included(_))
2560                             if init == InitKind::Uninit =>
2561                         {
2562                             return Some((
2563                                 format!(
2564                                     "`{}` must be initialized inside its custom valid range",
2565                                     ty,
2566                                 ),
2567                                 None,
2568                             ));
2569                         }
2570                         _ => {}
2571                     }
2572                     // Now, recurse.
2573                     match adt_def.variants.len() {
2574                         0 => Some(("enums with no variants have no valid value".to_string(), None)),
2575                         1 => {
2576                             // Struct, or enum with exactly one variant.
2577                             // Proceed recursively, check all fields.
2578                             let variant = &adt_def.variants[VariantIdx::from_u32(0)];
2579                             variant.fields.iter().find_map(|field| {
2580                                 ty_find_init_error(tcx, field.ty(tcx, substs), init).map(
2581                                     |(mut msg, span)| {
2582                                         if span.is_none() {
2583                                             // Point to this field, should be helpful for figuring
2584                                             // out where the source of the error is.
2585                                             let span = tcx.def_span(field.did);
2586                                             write!(
2587                                                 &mut msg,
2588                                                 " (in this {} field)",
2589                                                 adt_def.descr()
2590                                             )
2591                                             .unwrap();
2592                                             (msg, Some(span))
2593                                         } else {
2594                                             // Just forward.
2595                                             (msg, span)
2596                                         }
2597                                     },
2598                                 )
2599                             })
2600                         }
2601                         // Multi-variant enum.
2602                         _ => {
2603                             if init == InitKind::Uninit && is_multi_variant(adt_def) {
2604                                 let span = tcx.def_span(adt_def.did);
2605                                 Some((
2606                                     "enums have to be initialized to a variant".to_string(),
2607                                     Some(span),
2608                                 ))
2609                             } else {
2610                                 // In principle, for zero-initialization we could figure out which variant corresponds
2611                                 // to tag 0, and check that... but for now we just accept all zero-initializations.
2612                                 None
2613                             }
2614                         }
2615                     }
2616                 }
2617                 Tuple(..) => {
2618                     // Proceed recursively, check all fields.
2619                     ty.tuple_fields().find_map(|field| ty_find_init_error(tcx, field, init))
2620                 }
2621                 // Conservative fallback.
2622                 _ => None,
2623             }
2624         }
2625
2626         if let Some(init) = is_dangerous_init(cx, expr) {
2627             // This conjures an instance of a type out of nothing,
2628             // using zeroed or uninitialized memory.
2629             // We are extremely conservative with what we warn about.
2630             let conjured_ty = cx.typeck_results().expr_ty(expr);
2631             if let Some((msg, span)) =
2632                 with_no_trimmed_paths(|| ty_find_init_error(cx.tcx, conjured_ty, init))
2633             {
2634                 cx.struct_span_lint(INVALID_VALUE, expr.span, |lint| {
2635                     let mut err = lint.build(&format!(
2636                         "the type `{}` does not permit {}",
2637                         conjured_ty,
2638                         match init {
2639                             InitKind::Zeroed => "zero-initialization",
2640                             InitKind::Uninit => "being left uninitialized",
2641                         },
2642                     ));
2643                     err.span_label(expr.span, "this code causes undefined behavior when executed");
2644                     err.span_label(
2645                         expr.span,
2646                         "help: use `MaybeUninit<T>` instead, \
2647                             and only call `assume_init` after initialization is done",
2648                     );
2649                     if let Some(span) = span {
2650                         err.span_note(span, &msg);
2651                     } else {
2652                         err.note(&msg);
2653                     }
2654                     err.emit();
2655                 });
2656             }
2657         }
2658     }
2659 }
2660
2661 declare_lint! {
2662     /// The `clashing_extern_declarations` lint detects when an `extern fn`
2663     /// has been declared with the same name but different types.
2664     ///
2665     /// ### Example
2666     ///
2667     /// ```rust
2668     /// mod m {
2669     ///     extern "C" {
2670     ///         fn foo();
2671     ///     }
2672     /// }
2673     ///
2674     /// extern "C" {
2675     ///     fn foo(_: u32);
2676     /// }
2677     /// ```
2678     ///
2679     /// {{produces}}
2680     ///
2681     /// ### Explanation
2682     ///
2683     /// Because two symbols of the same name cannot be resolved to two
2684     /// different functions at link time, and one function cannot possibly
2685     /// have two types, a clashing extern declaration is almost certainly a
2686     /// mistake. Check to make sure that the `extern` definitions are correct
2687     /// and equivalent, and possibly consider unifying them in one location.
2688     ///
2689     /// This lint does not run between crates because a project may have
2690     /// dependencies which both rely on the same extern function, but declare
2691     /// it in a different (but valid) way. For example, they may both declare
2692     /// an opaque type for one or more of the arguments (which would end up
2693     /// distinct types), or use types that are valid conversions in the
2694     /// language the `extern fn` is defined in. In these cases, the compiler
2695     /// can't say that the clashing declaration is incorrect.
2696     pub CLASHING_EXTERN_DECLARATIONS,
2697     Warn,
2698     "detects when an extern fn has been declared with the same name but different types"
2699 }
2700
2701 pub struct ClashingExternDeclarations {
2702     /// Map of function symbol name to the first-seen hir id for that symbol name.. If seen_decls
2703     /// contains an entry for key K, it means a symbol with name K has been seen by this lint and
2704     /// the symbol should be reported as a clashing declaration.
2705     // FIXME: Technically, we could just store a &'tcx str here without issue; however, the
2706     // `impl_lint_pass` macro doesn't currently support lints parametric over a lifetime.
2707     seen_decls: FxHashMap<Symbol, HirId>,
2708 }
2709
2710 /// Differentiate between whether the name for an extern decl came from the link_name attribute or
2711 /// just from declaration itself. This is important because we don't want to report clashes on
2712 /// symbol name if they don't actually clash because one or the other links against a symbol with a
2713 /// different name.
2714 enum SymbolName {
2715     /// The name of the symbol + the span of the annotation which introduced the link name.
2716     Link(Symbol, Span),
2717     /// No link name, so just the name of the symbol.
2718     Normal(Symbol),
2719 }
2720
2721 impl SymbolName {
2722     fn get_name(&self) -> Symbol {
2723         match self {
2724             SymbolName::Link(s, _) | SymbolName::Normal(s) => *s,
2725         }
2726     }
2727 }
2728
2729 impl ClashingExternDeclarations {
2730     crate fn new() -> Self {
2731         ClashingExternDeclarations { seen_decls: FxHashMap::default() }
2732     }
2733     /// Insert a new foreign item into the seen set. If a symbol with the same name already exists
2734     /// for the item, return its HirId without updating the set.
2735     fn insert(&mut self, tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> Option<HirId> {
2736         let did = fi.def_id.to_def_id();
2737         let instance = Instance::new(did, ty::List::identity_for_item(tcx, did));
2738         let name = Symbol::intern(tcx.symbol_name(instance).name);
2739         if let Some(&hir_id) = self.seen_decls.get(&name) {
2740             // Avoid updating the map with the new entry when we do find a collision. We want to
2741             // make sure we're always pointing to the first definition as the previous declaration.
2742             // This lets us avoid emitting "knock-on" diagnostics.
2743             Some(hir_id)
2744         } else {
2745             self.seen_decls.insert(name, fi.hir_id())
2746         }
2747     }
2748
2749     /// Get the name of the symbol that's linked against for a given extern declaration. That is,
2750     /// the name specified in a #[link_name = ...] attribute if one was specified, else, just the
2751     /// symbol's name.
2752     fn name_of_extern_decl(tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> SymbolName {
2753         if let Some((overridden_link_name, overridden_link_name_span)) =
2754             tcx.codegen_fn_attrs(fi.def_id).link_name.map(|overridden_link_name| {
2755                 // FIXME: Instead of searching through the attributes again to get span
2756                 // information, we could have codegen_fn_attrs also give span information back for
2757                 // where the attribute was defined. However, until this is found to be a
2758                 // bottleneck, this does just fine.
2759                 (
2760                     overridden_link_name,
2761                     tcx.get_attrs(fi.def_id.to_def_id())
2762                         .iter()
2763                         .find(|at| at.has_name(sym::link_name))
2764                         .unwrap()
2765                         .span,
2766                 )
2767             })
2768         {
2769             SymbolName::Link(overridden_link_name, overridden_link_name_span)
2770         } else {
2771             SymbolName::Normal(fi.ident.name)
2772         }
2773     }
2774
2775     /// Checks whether two types are structurally the same enough that the declarations shouldn't
2776     /// clash. We need this so we don't emit a lint when two modules both declare an extern struct,
2777     /// with the same members (as the declarations shouldn't clash).
2778     fn structurally_same_type<'tcx>(
2779         cx: &LateContext<'tcx>,
2780         a: Ty<'tcx>,
2781         b: Ty<'tcx>,
2782         ckind: CItemKind,
2783     ) -> bool {
2784         fn structurally_same_type_impl<'tcx>(
2785             seen_types: &mut FxHashSet<(Ty<'tcx>, Ty<'tcx>)>,
2786             cx: &LateContext<'tcx>,
2787             a: Ty<'tcx>,
2788             b: Ty<'tcx>,
2789             ckind: CItemKind,
2790         ) -> bool {
2791             debug!("structurally_same_type_impl(cx, a = {:?}, b = {:?})", a, b);
2792             let tcx = cx.tcx;
2793
2794             // Given a transparent newtype, reach through and grab the inner
2795             // type unless the newtype makes the type non-null.
2796             let non_transparent_ty = |ty: Ty<'tcx>| -> Ty<'tcx> {
2797                 let mut ty = ty;
2798                 loop {
2799                     if let ty::Adt(def, substs) = *ty.kind() {
2800                         let is_transparent = def.subst(tcx, substs).repr.transparent();
2801                         let is_non_null = crate::types::nonnull_optimization_guaranteed(tcx, &def);
2802                         debug!(
2803                             "non_transparent_ty({:?}) -- type is transparent? {}, type is non-null? {}",
2804                             ty, is_transparent, is_non_null
2805                         );
2806                         if is_transparent && !is_non_null {
2807                             debug_assert!(def.variants.len() == 1);
2808                             let v = &def.variants[VariantIdx::new(0)];
2809                             ty = transparent_newtype_field(tcx, v)
2810                                 .expect(
2811                                     "single-variant transparent structure with zero-sized field",
2812                                 )
2813                                 .ty(tcx, substs);
2814                             continue;
2815                         }
2816                     }
2817                     debug!("non_transparent_ty -> {:?}", ty);
2818                     return ty;
2819                 }
2820             };
2821
2822             let a = non_transparent_ty(a);
2823             let b = non_transparent_ty(b);
2824
2825             if !seen_types.insert((a, b)) {
2826                 // We've encountered a cycle. There's no point going any further -- the types are
2827                 // structurally the same.
2828                 return true;
2829             }
2830             let tcx = cx.tcx;
2831             if a == b || rustc_middle::ty::TyS::same_type(a, b) {
2832                 // All nominally-same types are structurally same, too.
2833                 true
2834             } else {
2835                 // Do a full, depth-first comparison between the two.
2836                 use rustc_middle::ty::TyKind::*;
2837                 let a_kind = a.kind();
2838                 let b_kind = b.kind();
2839
2840                 let compare_layouts = |a, b| -> Result<bool, LayoutError<'tcx>> {
2841                     debug!("compare_layouts({:?}, {:?})", a, b);
2842                     let a_layout = &cx.layout_of(a)?.layout.abi;
2843                     let b_layout = &cx.layout_of(b)?.layout.abi;
2844                     debug!(
2845                         "comparing layouts: {:?} == {:?} = {}",
2846                         a_layout,
2847                         b_layout,
2848                         a_layout == b_layout
2849                     );
2850                     Ok(a_layout == b_layout)
2851                 };
2852
2853                 #[allow(rustc::usage_of_ty_tykind)]
2854                 let is_primitive_or_pointer = |kind: &ty::TyKind<'_>| {
2855                     kind.is_primitive() || matches!(kind, RawPtr(..) | Ref(..))
2856                 };
2857
2858                 ensure_sufficient_stack(|| {
2859                     match (a_kind, b_kind) {
2860                         (Adt(a_def, a_substs), Adt(b_def, b_substs)) => {
2861                             let a = a.subst(cx.tcx, a_substs);
2862                             let b = b.subst(cx.tcx, b_substs);
2863                             debug!("Comparing {:?} and {:?}", a, b);
2864
2865                             // We can immediately rule out these types as structurally same if
2866                             // their layouts differ.
2867                             match compare_layouts(a, b) {
2868                                 Ok(false) => return false,
2869                                 _ => (), // otherwise, continue onto the full, fields comparison
2870                             }
2871
2872                             // Grab a flattened representation of all fields.
2873                             let a_fields = a_def.variants.iter().flat_map(|v| v.fields.iter());
2874                             let b_fields = b_def.variants.iter().flat_map(|v| v.fields.iter());
2875
2876                             // Perform a structural comparison for each field.
2877                             a_fields.eq_by(
2878                                 b_fields,
2879                                 |&ty::FieldDef { did: a_did, .. },
2880                                  &ty::FieldDef { did: b_did, .. }| {
2881                                     structurally_same_type_impl(
2882                                         seen_types,
2883                                         cx,
2884                                         tcx.type_of(a_did),
2885                                         tcx.type_of(b_did),
2886                                         ckind,
2887                                     )
2888                                 },
2889                             )
2890                         }
2891                         (Array(a_ty, a_const), Array(b_ty, b_const)) => {
2892                             // For arrays, we also check the constness of the type.
2893                             a_const.val == b_const.val
2894                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2895                         }
2896                         (Slice(a_ty), Slice(b_ty)) => {
2897                             structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2898                         }
2899                         (RawPtr(a_tymut), RawPtr(b_tymut)) => {
2900                             a_tymut.mutbl == b_tymut.mutbl
2901                                 && structurally_same_type_impl(
2902                                     seen_types,
2903                                     cx,
2904                                     &a_tymut.ty,
2905                                     &b_tymut.ty,
2906                                     ckind,
2907                                 )
2908                         }
2909                         (Ref(_a_region, a_ty, a_mut), Ref(_b_region, b_ty, b_mut)) => {
2910                             // For structural sameness, we don't need the region to be same.
2911                             a_mut == b_mut
2912                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2913                         }
2914                         (FnDef(..), FnDef(..)) => {
2915                             let a_poly_sig = a.fn_sig(tcx);
2916                             let b_poly_sig = b.fn_sig(tcx);
2917
2918                             // As we don't compare regions, skip_binder is fine.
2919                             let a_sig = a_poly_sig.skip_binder();
2920                             let b_sig = b_poly_sig.skip_binder();
2921
2922                             (a_sig.abi, a_sig.unsafety, a_sig.c_variadic)
2923                                 == (b_sig.abi, b_sig.unsafety, b_sig.c_variadic)
2924                                 && a_sig.inputs().iter().eq_by(b_sig.inputs().iter(), |a, b| {
2925                                     structurally_same_type_impl(seen_types, cx, a, b, ckind)
2926                                 })
2927                                 && structurally_same_type_impl(
2928                                     seen_types,
2929                                     cx,
2930                                     a_sig.output(),
2931                                     b_sig.output(),
2932                                     ckind,
2933                                 )
2934                         }
2935                         (Tuple(a_substs), Tuple(b_substs)) => {
2936                             a_substs.types().eq_by(b_substs.types(), |a_ty, b_ty| {
2937                                 structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2938                             })
2939                         }
2940                         // For these, it's not quite as easy to define structural-sameness quite so easily.
2941                         // For the purposes of this lint, take the conservative approach and mark them as
2942                         // not structurally same.
2943                         (Dynamic(..), Dynamic(..))
2944                         | (Error(..), Error(..))
2945                         | (Closure(..), Closure(..))
2946                         | (Generator(..), Generator(..))
2947                         | (GeneratorWitness(..), GeneratorWitness(..))
2948                         | (Projection(..), Projection(..))
2949                         | (Opaque(..), Opaque(..)) => false,
2950
2951                         // These definitely should have been caught above.
2952                         (Bool, Bool) | (Char, Char) | (Never, Never) | (Str, Str) => unreachable!(),
2953
2954                         // An Adt and a primitive or pointer type. This can be FFI-safe if non-null
2955                         // enum layout optimisation is being applied.
2956                         (Adt(..), other_kind) | (other_kind, Adt(..))
2957                             if is_primitive_or_pointer(other_kind) =>
2958                         {
2959                             let (primitive, adt) =
2960                                 if is_primitive_or_pointer(a.kind()) { (a, b) } else { (b, a) };
2961                             if let Some(ty) = crate::types::repr_nullable_ptr(cx, adt, ckind) {
2962                                 ty == primitive
2963                             } else {
2964                                 compare_layouts(a, b).unwrap_or(false)
2965                             }
2966                         }
2967                         // Otherwise, just compare the layouts. This may fail to lint for some
2968                         // incompatible types, but at the very least, will stop reads into
2969                         // uninitialised memory.
2970                         _ => compare_layouts(a, b).unwrap_or(false),
2971                     }
2972                 })
2973             }
2974         }
2975         let mut seen_types = FxHashSet::default();
2976         structurally_same_type_impl(&mut seen_types, cx, a, b, ckind)
2977     }
2978 }
2979
2980 impl_lint_pass!(ClashingExternDeclarations => [CLASHING_EXTERN_DECLARATIONS]);
2981
2982 impl<'tcx> LateLintPass<'tcx> for ClashingExternDeclarations {
2983     fn check_foreign_item(&mut self, cx: &LateContext<'tcx>, this_fi: &hir::ForeignItem<'_>) {
2984         trace!("ClashingExternDeclarations: check_foreign_item: {:?}", this_fi);
2985         if let ForeignItemKind::Fn(..) = this_fi.kind {
2986             let tcx = cx.tcx;
2987             if let Some(existing_hid) = self.insert(tcx, this_fi) {
2988                 let existing_decl_ty = tcx.type_of(tcx.hir().local_def_id(existing_hid));
2989                 let this_decl_ty = tcx.type_of(this_fi.def_id);
2990                 debug!(
2991                     "ClashingExternDeclarations: Comparing existing {:?}: {:?} to this {:?}: {:?}",
2992                     existing_hid, existing_decl_ty, this_fi.def_id, this_decl_ty
2993                 );
2994                 // Check that the declarations match.
2995                 if !Self::structurally_same_type(
2996                     cx,
2997                     existing_decl_ty,
2998                     this_decl_ty,
2999                     CItemKind::Declaration,
3000                 ) {
3001                     let orig_fi = tcx.hir().expect_foreign_item(existing_hid);
3002                     let orig = Self::name_of_extern_decl(tcx, orig_fi);
3003
3004                     // We want to ensure that we use spans for both decls that include where the
3005                     // name was defined, whether that was from the link_name attribute or not.
3006                     let get_relevant_span =
3007                         |fi: &hir::ForeignItem<'_>| match Self::name_of_extern_decl(tcx, fi) {
3008                             SymbolName::Normal(_) => fi.span,
3009                             SymbolName::Link(_, annot_span) => fi.span.to(annot_span),
3010                         };
3011                     // Finally, emit the diagnostic.
3012                     tcx.struct_span_lint_hir(
3013                         CLASHING_EXTERN_DECLARATIONS,
3014                         this_fi.hir_id(),
3015                         get_relevant_span(this_fi),
3016                         |lint| {
3017                             let mut expected_str = DiagnosticStyledString::new();
3018                             expected_str.push(existing_decl_ty.fn_sig(tcx).to_string(), false);
3019                             let mut found_str = DiagnosticStyledString::new();
3020                             found_str.push(this_decl_ty.fn_sig(tcx).to_string(), true);
3021
3022                             lint.build(&format!(
3023                                 "`{}` redeclare{} with a different signature",
3024                                 this_fi.ident.name,
3025                                 if orig.get_name() == this_fi.ident.name {
3026                                     "d".to_string()
3027                                 } else {
3028                                     format!("s `{}`", orig.get_name())
3029                                 }
3030                             ))
3031                             .span_label(
3032                                 get_relevant_span(orig_fi),
3033                                 &format!("`{}` previously declared here", orig.get_name()),
3034                             )
3035                             .span_label(
3036                                 get_relevant_span(this_fi),
3037                                 "this signature doesn't match the previous declaration",
3038                             )
3039                             .note_expected_found(&"", expected_str, &"", found_str)
3040                             .emit()
3041                         },
3042                     );
3043                 }
3044             }
3045         }
3046     }
3047 }
3048
3049 declare_lint! {
3050     /// The `deref_nullptr` lint detects when an null pointer is dereferenced,
3051     /// which causes [undefined behavior].
3052     ///
3053     /// ### Example
3054     ///
3055     /// ```rust,no_run
3056     /// # #![allow(unused)]
3057     /// use std::ptr;
3058     /// unsafe {
3059     ///     let x = &*ptr::null::<i32>();
3060     ///     let x = ptr::addr_of!(*ptr::null::<i32>());
3061     ///     let x = *(0 as *const i32);
3062     /// }
3063     /// ```
3064     ///
3065     /// {{produces}}
3066     ///
3067     /// ### Explanation
3068     ///
3069     /// Dereferencing a null pointer causes [undefined behavior] even as a place expression,
3070     /// like `&*(0 as *const i32)` or `addr_of!(*(0 as *const i32))`.
3071     ///
3072     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
3073     pub DEREF_NULLPTR,
3074     Warn,
3075     "detects when an null pointer is dereferenced"
3076 }
3077
3078 declare_lint_pass!(DerefNullPtr => [DEREF_NULLPTR]);
3079
3080 impl<'tcx> LateLintPass<'tcx> for DerefNullPtr {
3081     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
3082         /// test if expression is a null ptr
3083         fn is_null_ptr(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> bool {
3084             match &expr.kind {
3085                 rustc_hir::ExprKind::Cast(ref expr, ref ty) => {
3086                     if let rustc_hir::TyKind::Ptr(_) = ty.kind {
3087                         return is_zero(expr) || is_null_ptr(cx, expr);
3088                     }
3089                 }
3090                 // check for call to `core::ptr::null` or `core::ptr::null_mut`
3091                 rustc_hir::ExprKind::Call(ref path, _) => {
3092                     if let rustc_hir::ExprKind::Path(ref qpath) = path.kind {
3093                         if let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id() {
3094                             return cx.tcx.is_diagnostic_item(sym::ptr_null, def_id)
3095                                 || cx.tcx.is_diagnostic_item(sym::ptr_null_mut, def_id);
3096                         }
3097                     }
3098                 }
3099                 _ => {}
3100             }
3101             false
3102         }
3103
3104         /// test if expression is the literal `0`
3105         fn is_zero(expr: &hir::Expr<'_>) -> bool {
3106             match &expr.kind {
3107                 rustc_hir::ExprKind::Lit(ref lit) => {
3108                     if let LitKind::Int(a, _) = lit.node {
3109                         return a == 0;
3110                     }
3111                 }
3112                 _ => {}
3113             }
3114             false
3115         }
3116
3117         if let rustc_hir::ExprKind::Unary(ref un_op, ref expr_deref) = expr.kind {
3118             if let rustc_hir::UnOp::Deref = un_op {
3119                 if is_null_ptr(cx, expr_deref) {
3120                     cx.struct_span_lint(DEREF_NULLPTR, expr.span, |lint| {
3121                         let mut err = lint.build("dereferencing a null pointer");
3122                         err.span_label(
3123                             expr.span,
3124                             "this code causes undefined behavior when executed",
3125                         );
3126                         err.emit();
3127                     });
3128                 }
3129             }
3130         }
3131     }
3132 }
3133
3134 declare_lint! {
3135     /// The `named_asm_labels` lint detects the use of named labels in the
3136     /// inline `asm!` macro.
3137     ///
3138     /// ### Example
3139     ///
3140     /// ```rust,compile_fail
3141     /// #![feature(asm)]
3142     /// fn main() {
3143     ///     unsafe {
3144     ///         asm!("foo: bar");
3145     ///     }
3146     /// }
3147     /// ```
3148     ///
3149     /// {{produces}}
3150     ///
3151     /// ### Explanation
3152     ///
3153     /// LLVM is allowed to duplicate inline assembly blocks for any
3154     /// reason, for example when it is in a function that gets inlined. Because
3155     /// of this, GNU assembler [local labels] *must* be used instead of labels
3156     /// with a name. Using named labels might cause assembler or linker errors.
3157     ///
3158     /// See the [unstable book] for more details.
3159     ///
3160     /// [local labels]: https://sourceware.org/binutils/docs/as/Symbol-Names.html#Local-Labels
3161     /// [unstable book]: https://doc.rust-lang.org/nightly/unstable-book/library-features/asm.html#labels
3162     pub NAMED_ASM_LABELS,
3163     Deny,
3164     "named labels in inline assembly",
3165 }
3166
3167 declare_lint_pass!(NamedAsmLabels => [NAMED_ASM_LABELS]);
3168
3169 impl<'tcx> LateLintPass<'tcx> for NamedAsmLabels {
3170     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
3171         if let hir::Expr {
3172             kind: hir::ExprKind::InlineAsm(hir::InlineAsm { template_strs, .. }),
3173             ..
3174         } = expr
3175         {
3176             for (template_sym, template_snippet, template_span) in template_strs.iter() {
3177                 let template_str = &template_sym.as_str();
3178                 let find_label_span = |needle: &str| -> Option<Span> {
3179                     if let Some(template_snippet) = template_snippet {
3180                         let snippet = template_snippet.as_str();
3181                         if let Some(pos) = snippet.find(needle) {
3182                             let end = pos
3183                                 + &snippet[pos..]
3184                                     .find(|c| c == ':')
3185                                     .unwrap_or(snippet[pos..].len() - 1);
3186                             let inner = InnerSpan::new(pos, end);
3187                             return Some(template_span.from_inner(inner));
3188                         }
3189                     }
3190
3191                     None
3192                 };
3193
3194                 let mut found_labels = Vec::new();
3195
3196                 // A semicolon might not actually be specified as a separator for all targets, but it seems like LLVM accepts it always
3197                 let statements = template_str.split(|c| matches!(c, '\n' | ';'));
3198                 for statement in statements {
3199                     // If there's a comment, trim it from the statement
3200                     let statement = statement.find("//").map_or(statement, |idx| &statement[..idx]);
3201                     let mut start_idx = 0;
3202                     for (idx, _) in statement.match_indices(':') {
3203                         let possible_label = statement[start_idx..idx].trim();
3204                         let mut chars = possible_label.chars();
3205                         if let Some(c) = chars.next() {
3206                             // A label starts with an alphabetic character or . or _ and continues with alphanumeric characters, _, or $
3207                             if (c.is_alphabetic() || matches!(c, '.' | '_'))
3208                                 && chars.all(|c| c.is_alphanumeric() || matches!(c, '_' | '$'))
3209                             {
3210                                 found_labels.push(possible_label);
3211                             } else {
3212                                 // If we encounter a non-label, there cannot be any further labels, so stop checking
3213                                 break;
3214                             }
3215                         } else {
3216                             // Empty string means a leading ':' in this section, which is not a label
3217                             break;
3218                         }
3219
3220                         start_idx = idx + 1;
3221                     }
3222                 }
3223
3224                 debug!("NamedAsmLabels::check_expr(): found_labels: {:#?}", &found_labels);
3225
3226                 if found_labels.len() > 0 {
3227                     let spans = found_labels
3228                         .into_iter()
3229                         .filter_map(|label| find_label_span(label))
3230                         .collect::<Vec<Span>>();
3231                     // If there were labels but we couldn't find a span, combine the warnings and use the template span
3232                     let target_spans: MultiSpan =
3233                         if spans.len() > 0 { spans.into() } else { (*template_span).into() };
3234
3235                     cx.lookup_with_diagnostics(
3236                             NAMED_ASM_LABELS,
3237                             Some(target_spans),
3238                             |diag| {
3239                                 let mut err =
3240                                     diag.build("avoid using named labels in inline assembly");
3241                                 err.emit();
3242                             },
3243                             BuiltinLintDiagnostics::NamedAsmLabel(
3244                                 "only local labels of the form `<number>:` should be used in inline asm"
3245                                     .to_string(),
3246                             ),
3247                         );
3248                 }
3249             }
3250         }
3251     }
3252 }