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, BuiltinAttribute, GateIssue, Stability};
  36 use rustc_hir as hir;
  37 use rustc_hir::def::{DefKind, Res};
  38 use rustc_hir::def_id::{DefId, LocalDefId, LocalDefIdSet, CRATE_DEF_ID};
  39 use rustc_hir::{ForeignItemKind, GenericParamKind, PatKind};
  40 use rustc_hir::{HirId, Node};
  41 use rustc_index::vec::Idx;
  42 use rustc_middle::lint::LintDiagnosticBuilder;
  43 use rustc_middle::ty::layout::{LayoutError, LayoutOf};
  44 use rustc_middle::ty::print::with_no_trimmed_paths;
  45 use rustc_middle::ty::subst::{GenericArgKind, Subst};
  46 use rustc_middle::ty::Instance;
  47 use rustc_middle::ty::{self, Ty, TyCtxt};
  48 use rustc_session::lint::{BuiltinLintDiagnostics, FutureIncompatibilityReason};
  49 use rustc_span::edition::Edition;
  50 use rustc_span::source_map::Spanned;
  51 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  52 use rustc_span::{BytePos, InnerSpan, MultiSpan, Span};
  53 use rustc_target::abi::VariantIdx;
  54 use rustc_trait_selection::traits::misc::can_type_implement_copy;
  55
  56 use crate::nonstandard_style::{method_context, MethodLateContext};
  57
  58 use std::fmt::Write;
  59 use tracing::{debug, trace};
  60
  61 // hardwired lints from librustc_middle
  62 pub use rustc_session::lint::builtin::*;
  63
  64 declare_lint! {
  65     /// The `while_true` lint detects `while true { }`.
  66     ///
  67     /// ### Example
  68     ///
  69     /// ```rust,no_run
  70     /// while true {
  71     ///
  72     /// }
  73     /// ```
  74     ///
  75     /// {{produces}}
  76     ///
  77     /// ### Explanation
  78     ///
  79     /// `while true` should be replaced with `loop`. A `loop` expression is
  80     /// the preferred way to write an infinite loop because it more directly
  81     /// expresses the intent of the loop.
  82     WHILE_TRUE,
  83     Warn,
  84     "suggest using `loop { }` instead of `while true { }`"
  85 }
  86
  87 declare_lint_pass!(WhileTrue => [WHILE_TRUE]);
  88
  89 /// Traverse through any amount of parenthesis and return the first non-parens expression.
  90 fn pierce_parens(mut expr: &ast::Expr) -> &ast::Expr {
  91     while let ast::ExprKind::Paren(sub) = &expr.kind {
  92         expr = sub;
  93     }
  94     expr
  95 }
  96
  97 impl EarlyLintPass for WhileTrue {
  98     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
  99         if let ast::ExprKind::While(cond, _, label) = &e.kind {
 100             if let ast::ExprKind::Lit(ref lit) = pierce_parens(cond).kind {
 101                 if let ast::LitKind::Bool(true) = lit.kind {
 102                     if !lit.span.from_expansion() {
 103                         let msg = "denote infinite loops with `loop { ... }`";
 104                         let condition_span = e.span.with_hi(cond.span.hi());
 105                         cx.struct_span_lint(WHILE_TRUE, condition_span, |lint| {
 106                             lint.build(msg)
 107                                 .span_suggestion_short(
 108                                     condition_span,
 109                                     "use `loop`",
 110                                     format!(
 111                                         "{}loop",
 112                                         label.map_or_else(String::new, |label| format!(
 113                                             "{}: ",
 114                                             label.ident,
 115                                         ))
 116                                     ),
 117                                     Applicability::MachineApplicable,
 118                                 )
 119                                 .emit();
 120                         })
 121                     }
 122                 }
 123             }
 124         }
 125     }
 126 }
 127
 128 declare_lint! {
 129     /// The `box_pointers` lints use of the Box type.
 130     ///
 131     /// ### Example
 132     ///
 133     /// ```rust,compile_fail
 134     /// #![deny(box_pointers)]
 135     /// struct Foo {
 136     ///     x: Box<isize>,
 137     /// }
 138     /// ```
 139     ///
 140     /// {{produces}}
 141     ///
 142     /// ### Explanation
 143     ///
 144     /// This lint is mostly historical, and not particularly useful. `Box<T>`
 145     /// used to be built into the language, and the only way to do heap
 146     /// allocation. Today's Rust can call into other allocators, etc.
 147     BOX_POINTERS,
 148     Allow,
 149     "use of owned (Box type) heap memory"
 150 }
 151
 152 declare_lint_pass!(BoxPointers => [BOX_POINTERS]);
 153
 154 impl BoxPointers {
 155     fn check_heap_type<'tcx>(&self, cx: &LateContext<'tcx>, span: Span, ty: Ty<'tcx>) {
 156         for leaf in ty.walk(cx.tcx) {
 157             if let GenericArgKind::Type(leaf_ty) = leaf.unpack() {
 158                 if leaf_ty.is_box() {
 159                     cx.struct_span_lint(BOX_POINTERS, span, |lint| {
 160                         lint.build(&format!("type uses owned (Box type) pointers: {}", ty)).emit()
 161                     });
 162                 }
 163             }
 164         }
 165     }
 166 }
 167
 168 impl<'tcx> LateLintPass<'tcx> for BoxPointers {
 169     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 170         match it.kind {
 171             hir::ItemKind::Fn(..)
 172             | hir::ItemKind::TyAlias(..)
 173             | hir::ItemKind::Enum(..)
 174             | hir::ItemKind::Struct(..)
 175             | hir::ItemKind::Union(..) => {
 176                 self.check_heap_type(cx, it.span, cx.tcx.type_of(it.def_id))
 177             }
 178             _ => (),
 179         }
 180
 181         // If it's a struct, we also have to check the fields' types
 182         match it.kind {
 183             hir::ItemKind::Struct(ref struct_def, _) | hir::ItemKind::Union(ref struct_def, _) => {
 184                 for struct_field in struct_def.fields() {
 185                     let def_id = cx.tcx.hir().local_def_id(struct_field.hir_id);
 186                     self.check_heap_type(cx, struct_field.span, cx.tcx.type_of(def_id));
 187                 }
 188             }
 189             _ => (),
 190         }
 191     }
 192
 193     fn check_expr(&mut self, cx: &LateContext<'_>, e: &hir::Expr<'_>) {
 194         let ty = cx.typeck_results().node_type(e.hir_id);
 195         self.check_heap_type(cx, e.span, ty);
 196     }
 197 }
 198
 199 declare_lint! {
 200     /// The `non_shorthand_field_patterns` lint detects using `Struct { x: x }`
 201     /// instead of `Struct { x }` in a pattern.
 202     ///
 203     /// ### Example
 204     ///
 205     /// ```rust
 206     /// struct Point {
 207     ///     x: i32,
 208     ///     y: i32,
 209     /// }
 210     ///
 211     ///
 212     /// fn main() {
 213     ///     let p = Point {
 214     ///         x: 5,
 215     ///         y: 5,
 216     ///     };
 217     ///
 218     ///     match p {
 219     ///         Point { x: x, y: y } => (),
 220     ///     }
 221     /// }
 222     /// ```
 223     ///
 224     /// {{produces}}
 225     ///
 226     /// ### Explanation
 227     ///
 228     /// The preferred style is to avoid the repetition of specifying both the
 229     /// field name and the binding name if both identifiers are the same.
 230     NON_SHORTHAND_FIELD_PATTERNS,
 231     Warn,
 232     "using `Struct { x: x }` instead of `Struct { x }` in a pattern"
 233 }
 234
 235 declare_lint_pass!(NonShorthandFieldPatterns => [NON_SHORTHAND_FIELD_PATTERNS]);
 236
 237 impl<'tcx> LateLintPass<'tcx> for NonShorthandFieldPatterns {
 238     fn check_pat(&mut self, cx: &LateContext<'_>, pat: &hir::Pat<'_>) {
 239         if let PatKind::Struct(ref qpath, field_pats, _) = pat.kind {
 240             let variant = cx
 241                 .typeck_results()
 242                 .pat_ty(pat)
 243                 .ty_adt_def()
 244                 .expect("struct pattern type is not an ADT")
 245                 .variant_of_res(cx.qpath_res(qpath, pat.hir_id));
 246             for fieldpat in field_pats {
 247                 if fieldpat.is_shorthand {
 248                     continue;
 249                 }
 250                 if fieldpat.span.from_expansion() {
 251                     // Don't lint if this is a macro expansion: macro authors
 252                     // shouldn't have to worry about this kind of style issue
 253                     // (Issue #49588)
 254                     continue;
 255                 }
 256                 if let PatKind::Binding(binding_annot, _, ident, None) = fieldpat.pat.kind {
 257                     if cx.tcx.find_field_index(ident, &variant)
 258                         == Some(cx.tcx.field_index(fieldpat.hir_id, cx.typeck_results()))
 259                     {
 260                         cx.struct_span_lint(NON_SHORTHAND_FIELD_PATTERNS, fieldpat.span, |lint| {
 261                             let mut err = lint
 262                                 .build(&format!("the `{}:` in this pattern is redundant", ident));
 263                             let binding = match binding_annot {
 264                                 hir::BindingAnnotation::Unannotated => None,
 265                                 hir::BindingAnnotation::Mutable => Some("mut"),
 266                                 hir::BindingAnnotation::Ref => Some("ref"),
 267                                 hir::BindingAnnotation::RefMut => Some("ref mut"),
 268                             };
 269                             let ident = if let Some(binding) = binding {
 270                                 format!("{} {}", binding, ident)
 271                             } else {
 272                                 ident.to_string()
 273                             };
 274                             err.span_suggestion(
 275                                 fieldpat.span,
 276                                 "use shorthand field pattern",
 277                                 ident,
 278                                 Applicability::MachineApplicable,
 279                             );
 280                             err.emit();
 281                         });
 282                     }
 283                 }
 284             }
 285         }
 286     }
 287 }
 288
 289 declare_lint! {
 290     /// The `unsafe_code` lint catches usage of `unsafe` code.
 291     ///
 292     /// ### Example
 293     ///
 294     /// ```rust,compile_fail
 295     /// #![deny(unsafe_code)]
 296     /// fn main() {
 297     ///     unsafe {
 298     ///
 299     ///     }
 300     /// }
 301     /// ```
 302     ///
 303     /// {{produces}}
 304     ///
 305     /// ### Explanation
 306     ///
 307     /// This lint is intended to restrict the usage of `unsafe`, which can be
 308     /// difficult to use correctly.
 309     UNSAFE_CODE,
 310     Allow,
 311     "usage of `unsafe` code"
 312 }
 313
 314 declare_lint_pass!(UnsafeCode => [UNSAFE_CODE]);
 315
 316 impl UnsafeCode {
 317     fn report_unsafe(
 318         &self,
 319         cx: &EarlyContext<'_>,
 320         span: Span,
 321         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
 322     ) {
 323         // This comes from a macro that has `#[allow_internal_unsafe]`.
 324         if span.allows_unsafe() {
 325             return;
 326         }
 327
 328         cx.struct_span_lint(UNSAFE_CODE, span, decorate);
 329     }
 330
 331     fn report_overriden_symbol_name(&self, cx: &EarlyContext<'_>, span: Span, msg: &str) {
 332         self.report_unsafe(cx, span, |lint| {
 333             lint.build(msg)
 334                 .note(
 335                     "the linker's behavior with multiple libraries exporting duplicate symbol \
 336                     names is undefined and Rust cannot provide guarantees when you manually \
 337                     override them",
 338                 )
 339                 .emit();
 340         })
 341     }
 342 }
 343
 344 impl EarlyLintPass for UnsafeCode {
 345     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 346         if attr.has_name(sym::allow_internal_unsafe) {
 347             self.report_unsafe(cx, attr.span, |lint| {
 348                 lint.build(
 349                     "`allow_internal_unsafe` allows defining \
 350                                                macros using unsafe without triggering \
 351                                                the `unsafe_code` lint at their call site",
 352                 )
 353                 .emit()
 354             });
 355         }
 356     }
 357
 358     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
 359         if let ast::ExprKind::Block(ref blk, _) = e.kind {
 360             // Don't warn about generated blocks; that'll just pollute the output.
 361             if blk.rules == ast::BlockCheckMode::Unsafe(ast::UserProvided) {
 362                 self.report_unsafe(cx, blk.span, |lint| {
 363                     lint.build("usage of an `unsafe` block").emit()
 364                 });
 365             }
 366         }
 367     }
 368
 369     fn check_item(&mut self, cx: &EarlyContext<'_>, it: &ast::Item) {
 370         match it.kind {
 371             ast::ItemKind::Trait(box ast::Trait { unsafety: ast::Unsafe::Yes(_), .. }) => self
 372                 .report_unsafe(cx, it.span, |lint| {
 373                     lint.build("declaration of an `unsafe` trait").emit()
 374                 }),
 375
 376             ast::ItemKind::Impl(box ast::Impl { unsafety: ast::Unsafe::Yes(_), .. }) => self
 377                 .report_unsafe(cx, it.span, |lint| {
 378                     lint.build("implementation of an `unsafe` trait").emit()
 379                 }),
 380
 381             ast::ItemKind::Fn(..) => {
 382                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
 383                     self.report_overriden_symbol_name(
 384                         cx,
 385                         attr.span,
 386                         "declaration of a `no_mangle` function",
 387                     );
 388                 }
 389                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::export_name) {
 390                     self.report_overriden_symbol_name(
 391                         cx,
 392                         attr.span,
 393                         "declaration of a function with `export_name`",
 394                     );
 395                 }
 396             }
 397
 398             ast::ItemKind::Static(..) => {
 399                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
 400                     self.report_overriden_symbol_name(
 401                         cx,
 402                         attr.span,
 403                         "declaration of a `no_mangle` static",
 404                     );
 405                 }
 406                 if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::export_name) {
 407                     self.report_overriden_symbol_name(
 408                         cx,
 409                         attr.span,
 410                         "declaration of a static with `export_name`",
 411                     );
 412                 }
 413             }
 414
 415             _ => {}
 416         }
 417     }
 418
 419     fn check_impl_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
 420         if let ast::AssocItemKind::Fn(..) = it.kind {
 421             if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
 422                 self.report_overriden_symbol_name(
 423                     cx,
 424                     attr.span,
 425                     "declaration of a `no_mangle` method",
 426                 );
 427             }
 428             if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::export_name) {
 429                 self.report_overriden_symbol_name(
 430                     cx,
 431                     attr.span,
 432                     "declaration of a method with `export_name`",
 433                 );
 434             }
 435         }
 436     }
 437
 438     fn check_fn(&mut self, cx: &EarlyContext<'_>, fk: FnKind<'_>, span: Span, _: ast::NodeId) {
 439         if let FnKind::Fn(
 440             ctxt,
 441             _,
 442             ast::FnSig { header: ast::FnHeader { unsafety: ast::Unsafe::Yes(_), .. }, .. },
 443             _,
 444             body,
 445         ) = fk
 446         {
 447             let msg = match ctxt {
 448                 FnCtxt::Foreign => return,
 449                 FnCtxt::Free => "declaration of an `unsafe` function",
 450                 FnCtxt::Assoc(_) if body.is_none() => "declaration of an `unsafe` method",
 451                 FnCtxt::Assoc(_) => "implementation of an `unsafe` method",
 452             };
 453             self.report_unsafe(cx, span, |lint| lint.build(msg).emit());
 454         }
 455     }
 456 }
 457
 458 declare_lint! {
 459     /// The `missing_docs` lint detects missing documentation for public items.
 460     ///
 461     /// ### Example
 462     ///
 463     /// ```rust,compile_fail
 464     /// #![deny(missing_docs)]
 465     /// pub fn foo() {}
 466     /// ```
 467     ///
 468     /// {{produces}}
 469     ///
 470     /// ### Explanation
 471     ///
 472     /// This lint is intended to ensure that a library is well-documented.
 473     /// Items without documentation can be difficult for users to understand
 474     /// how to use properly.
 475     ///
 476     /// This lint is "allow" by default because it can be noisy, and not all
 477     /// projects may want to enforce everything to be documented.
 478     pub MISSING_DOCS,
 479     Allow,
 480     "detects missing documentation for public members",
 481     report_in_external_macro
 482 }
 483
 484 pub struct MissingDoc {
 485     /// Stack of whether `#[doc(hidden)]` is set at each level which has lint attributes.
 486     doc_hidden_stack: Vec<bool>,
 487
 488     /// Private traits or trait items that leaked through. Don't check their methods.
 489     private_traits: FxHashSet<hir::HirId>,
 490 }
 491
 492 impl_lint_pass!(MissingDoc => [MISSING_DOCS]);
 493
 494 fn has_doc(attr: &ast::Attribute) -> bool {
 495     if attr.is_doc_comment() {
 496         return true;
 497     }
 498
 499     if !attr.has_name(sym::doc) {
 500         return false;
 501     }
 502
 503     if attr.value_str().is_some() {
 504         return true;
 505     }
 506
 507     if let Some(list) = attr.meta_item_list() {
 508         for meta in list {
 509             if meta.has_name(sym::hidden) {
 510                 return true;
 511             }
 512         }
 513     }
 514
 515     false
 516 }
 517
 518 impl MissingDoc {
 519     pub fn new() -> MissingDoc {
 520         MissingDoc { doc_hidden_stack: vec![false], private_traits: FxHashSet::default() }
 521     }
 522
 523     fn doc_hidden(&self) -> bool {
 524         *self.doc_hidden_stack.last().expect("empty doc_hidden_stack")
 525     }
 526
 527     fn check_missing_docs_attrs(
 528         &self,
 529         cx: &LateContext<'_>,
 530         def_id: LocalDefId,
 531         sp: Span,
 532         article: &'static str,
 533         desc: &'static str,
 534     ) {
 535         // If we're building a test harness, then warning about
 536         // documentation is probably not really relevant right now.
 537         if cx.sess().opts.test {
 538             return;
 539         }
 540
 541         // `#[doc(hidden)]` disables missing_docs check.
 542         if self.doc_hidden() {
 543             return;
 544         }
 545
 546         // Only check publicly-visible items, using the result from the privacy pass.
 547         // It's an option so the crate root can also use this function (it doesn't
 548         // have a `NodeId`).
 549         if def_id != CRATE_DEF_ID {
 550             if !cx.access_levels.is_exported(def_id) {
 551                 return;
 552             }
 553         }
 554
 555         let attrs = cx.tcx.get_attrs(def_id.to_def_id());
 556         let has_doc = attrs.iter().any(has_doc);
 557         if !has_doc {
 558             cx.struct_span_lint(
 559                 MISSING_DOCS,
 560                 cx.tcx.sess.source_map().guess_head_span(sp),
 561                 |lint| {
 562                     lint.build(&format!("missing documentation for {} {}", article, desc)).emit()
 563                 },
 564             );
 565         }
 566     }
 567 }
 568
 569 impl<'tcx> LateLintPass<'tcx> for MissingDoc {
 570     fn enter_lint_attrs(&mut self, _cx: &LateContext<'_>, attrs: &[ast::Attribute]) {
 571         let doc_hidden = self.doc_hidden()
 572             || attrs.iter().any(|attr| {
 573                 attr.has_name(sym::doc)
 574                     && match attr.meta_item_list() {
 575                         None => false,
 576                         Some(l) => attr::list_contains_name(&l, sym::hidden),
 577                     }
 578             });
 579         self.doc_hidden_stack.push(doc_hidden);
 580     }
 581
 582     fn exit_lint_attrs(&mut self, _: &LateContext<'_>, _attrs: &[ast::Attribute]) {
 583         self.doc_hidden_stack.pop().expect("empty doc_hidden_stack");
 584     }
 585
 586     fn check_crate(&mut self, cx: &LateContext<'_>) {
 587         self.check_missing_docs_attrs(
 588             cx,
 589             CRATE_DEF_ID,
 590             cx.tcx.def_span(CRATE_DEF_ID),
 591             "the",
 592             "crate",
 593         );
 594     }
 595
 596     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 597         match it.kind {
 598             hir::ItemKind::Trait(.., trait_item_refs) => {
 599                 // Issue #11592: traits are always considered exported, even when private.
 600                 if let hir::VisibilityKind::Inherited = it.vis.node {
 601                     self.private_traits.insert(it.hir_id());
 602                     for trait_item_ref in trait_item_refs {
 603                         self.private_traits.insert(trait_item_ref.id.hir_id());
 604                     }
 605                     return;
 606                 }
 607             }
 608             hir::ItemKind::Impl(hir::Impl { of_trait: Some(ref trait_ref), items, .. }) => {
 609                 // If the trait is private, add the impl items to `private_traits` so they don't get
 610                 // reported for missing docs.
 611                 let real_trait = trait_ref.path.res.def_id();
 612                 if let Some(def_id) = real_trait.as_local() {
 613                     let hir_id = cx.tcx.hir().local_def_id_to_hir_id(def_id);
 614                     if let Some(Node::Item(item)) = cx.tcx.hir().find(hir_id) {
 615                         if let hir::VisibilityKind::Inherited = item.vis.node {
 616                             for impl_item_ref in items {
 617                                 self.private_traits.insert(impl_item_ref.id.hir_id());
 618                             }
 619                         }
 620                     }
 621                 }
 622                 return;
 623             }
 624
 625             hir::ItemKind::TyAlias(..)
 626             | hir::ItemKind::Fn(..)
 627             | hir::ItemKind::Macro(..)
 628             | hir::ItemKind::Mod(..)
 629             | hir::ItemKind::Enum(..)
 630             | hir::ItemKind::Struct(..)
 631             | hir::ItemKind::Union(..)
 632             | hir::ItemKind::Const(..)
 633             | hir::ItemKind::Static(..) => {}
 634
 635             _ => return,
 636         };
 637
 638         let (article, desc) = cx.tcx.article_and_description(it.def_id.to_def_id());
 639
 640         self.check_missing_docs_attrs(cx, it.def_id, it.span, article, desc);
 641     }
 642
 643     fn check_trait_item(&mut self, cx: &LateContext<'_>, trait_item: &hir::TraitItem<'_>) {
 644         if self.private_traits.contains(&trait_item.hir_id()) {
 645             return;
 646         }
 647
 648         let (article, desc) = cx.tcx.article_and_description(trait_item.def_id.to_def_id());
 649
 650         self.check_missing_docs_attrs(cx, trait_item.def_id, trait_item.span, article, desc);
 651     }
 652
 653     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
 654         // If the method is an impl for a trait, don't doc.
 655         if method_context(cx, impl_item.hir_id()) == MethodLateContext::TraitImpl {
 656             return;
 657         }
 658
 659         // If the method is an impl for an item with docs_hidden, don't doc.
 660         if method_context(cx, impl_item.hir_id()) == MethodLateContext::PlainImpl {
 661             let parent = cx.tcx.hir().get_parent_did(impl_item.hir_id());
 662             let impl_ty = cx.tcx.type_of(parent);
 663             let outerdef = match impl_ty.kind() {
 664                 ty::Adt(def, _) => Some(def.did),
 665                 ty::Foreign(def_id) => Some(*def_id),
 666                 _ => None,
 667             };
 668             let is_hidden = match outerdef {
 669                 Some(id) => cx.tcx.is_doc_hidden(id),
 670                 None => false,
 671             };
 672             if is_hidden {
 673                 return;
 674             }
 675         }
 676
 677         let (article, desc) = cx.tcx.article_and_description(impl_item.def_id.to_def_id());
 678         self.check_missing_docs_attrs(cx, impl_item.def_id, impl_item.span, article, desc);
 679     }
 680
 681     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'_>) {
 682         let (article, desc) = cx.tcx.article_and_description(foreign_item.def_id.to_def_id());
 683         self.check_missing_docs_attrs(cx, foreign_item.def_id, foreign_item.span, article, desc);
 684     }
 685
 686     fn check_field_def(&mut self, cx: &LateContext<'_>, sf: &hir::FieldDef<'_>) {
 687         if !sf.is_positional() {
 688             let def_id = cx.tcx.hir().local_def_id(sf.hir_id);
 689             self.check_missing_docs_attrs(cx, def_id, sf.span, "a", "struct field")
 690         }
 691     }
 692
 693     fn check_variant(&mut self, cx: &LateContext<'_>, v: &hir::Variant<'_>) {
 694         self.check_missing_docs_attrs(cx, cx.tcx.hir().local_def_id(v.id), v.span, "a", "variant");
 695     }
 696 }
 697
 698 declare_lint! {
 699     /// The `missing_copy_implementations` lint detects potentially-forgotten
 700     /// implementations of [`Copy`].
 701     ///
 702     /// [`Copy`]: https://doc.rust-lang.org/std/marker/trait.Copy.html
 703     ///
 704     /// ### Example
 705     ///
 706     /// ```rust,compile_fail
 707     /// #![deny(missing_copy_implementations)]
 708     /// pub struct Foo {
 709     ///     pub field: i32
 710     /// }
 711     /// # fn main() {}
 712     /// ```
 713     ///
 714     /// {{produces}}
 715     ///
 716     /// ### Explanation
 717     ///
 718     /// Historically (before 1.0), types were automatically marked as `Copy`
 719     /// if possible. This was changed so that it required an explicit opt-in
 720     /// by implementing the `Copy` trait. As part of this change, a lint was
 721     /// added to alert if a copyable type was not marked `Copy`.
 722     ///
 723     /// This lint is "allow" by default because this code isn't bad; it is
 724     /// common to write newtypes like this specifically so that a `Copy` type
 725     /// is no longer `Copy`. `Copy` types can result in unintended copies of
 726     /// large data which can impact performance.
 727     pub MISSING_COPY_IMPLEMENTATIONS,
 728     Allow,
 729     "detects potentially-forgotten implementations of `Copy`"
 730 }
 731
 732 declare_lint_pass!(MissingCopyImplementations => [MISSING_COPY_IMPLEMENTATIONS]);
 733
 734 impl<'tcx> LateLintPass<'tcx> for MissingCopyImplementations {
 735     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 736         if !cx.access_levels.is_reachable(item.def_id) {
 737             return;
 738         }
 739         let (def, ty) = match item.kind {
 740             hir::ItemKind::Struct(_, ref ast_generics) => {
 741                 if !ast_generics.params.is_empty() {
 742                     return;
 743                 }
 744                 let def = cx.tcx.adt_def(item.def_id);
 745                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 746             }
 747             hir::ItemKind::Union(_, ref ast_generics) => {
 748                 if !ast_generics.params.is_empty() {
 749                     return;
 750                 }
 751                 let def = cx.tcx.adt_def(item.def_id);
 752                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 753             }
 754             hir::ItemKind::Enum(_, ref ast_generics) => {
 755                 if !ast_generics.params.is_empty() {
 756                     return;
 757                 }
 758                 let def = cx.tcx.adt_def(item.def_id);
 759                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 760             }
 761             _ => return,
 762         };
 763         if def.has_dtor(cx.tcx) {
 764             return;
 765         }
 766         let param_env = ty::ParamEnv::empty();
 767         if ty.is_copy_modulo_regions(cx.tcx.at(item.span), param_env) {
 768             return;
 769         }
 770         if can_type_implement_copy(cx.tcx, param_env, ty).is_ok() {
 771             cx.struct_span_lint(MISSING_COPY_IMPLEMENTATIONS, item.span, |lint| {
 772                 lint.build(
 773                     "type could implement `Copy`; consider adding `impl \
 774                           Copy`",
 775                 )
 776                 .emit()
 777             })
 778         }
 779     }
 780 }
 781
 782 declare_lint! {
 783     /// The `missing_debug_implementations` lint detects missing
 784     /// implementations of [`fmt::Debug`].
 785     ///
 786     /// [`fmt::Debug`]: https://doc.rust-lang.org/std/fmt/trait.Debug.html
 787     ///
 788     /// ### Example
 789     ///
 790     /// ```rust,compile_fail
 791     /// #![deny(missing_debug_implementations)]
 792     /// pub struct Foo;
 793     /// # fn main() {}
 794     /// ```
 795     ///
 796     /// {{produces}}
 797     ///
 798     /// ### Explanation
 799     ///
 800     /// Having a `Debug` implementation on all types can assist with
 801     /// debugging, as it provides a convenient way to format and display a
 802     /// value. Using the `#[derive(Debug)]` attribute will automatically
 803     /// generate a typical implementation, or a custom implementation can be
 804     /// added by manually implementing the `Debug` trait.
 805     ///
 806     /// This lint is "allow" by default because adding `Debug` to all types can
 807     /// have a negative impact on compile time and code size. It also requires
 808     /// boilerplate to be added to every type, which can be an impediment.
 809     MISSING_DEBUG_IMPLEMENTATIONS,
 810     Allow,
 811     "detects missing implementations of Debug"
 812 }
 813
 814 #[derive(Default)]
 815 pub struct MissingDebugImplementations {
 816     impling_types: Option<LocalDefIdSet>,
 817 }
 818
 819 impl_lint_pass!(MissingDebugImplementations => [MISSING_DEBUG_IMPLEMENTATIONS]);
 820
 821 impl<'tcx> LateLintPass<'tcx> for MissingDebugImplementations {
 822     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
 823         if !cx.access_levels.is_reachable(item.def_id) {
 824             return;
 825         }
 826
 827         match item.kind {
 828             hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) | hir::ItemKind::Enum(..) => {}
 829             _ => return,
 830         }
 831
 832         let debug = match cx.tcx.get_diagnostic_item(sym::Debug) {
 833             Some(debug) => debug,
 834             None => return,
 835         };
 836
 837         if self.impling_types.is_none() {
 838             let mut impls = LocalDefIdSet::default();
 839             cx.tcx.for_each_impl(debug, |d| {
 840                 if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() {
 841                     if let Some(def_id) = ty_def.did.as_local() {
 842                         impls.insert(def_id);
 843                     }
 844                 }
 845             });
 846
 847             self.impling_types = Some(impls);
 848             debug!("{:?}", self.impling_types);
 849         }
 850
 851         if !self.impling_types.as_ref().unwrap().contains(&item.def_id) {
 852             cx.struct_span_lint(MISSING_DEBUG_IMPLEMENTATIONS, item.span, |lint| {
 853                 lint.build(&format!(
 854                     "type does not implement `{}`; consider adding `#[derive(Debug)]` \
 855                      or a manual implementation",
 856                     cx.tcx.def_path_str(debug)
 857                 ))
 858                 .emit()
 859             });
 860         }
 861     }
 862 }
 863
 864 declare_lint! {
 865     /// The `anonymous_parameters` lint detects anonymous parameters in trait
 866     /// definitions.
 867     ///
 868     /// ### Example
 869     ///
 870     /// ```rust,edition2015,compile_fail
 871     /// #![deny(anonymous_parameters)]
 872     /// // edition 2015
 873     /// pub trait Foo {
 874     ///     fn foo(usize);
 875     /// }
 876     /// fn main() {}
 877     /// ```
 878     ///
 879     /// {{produces}}
 880     ///
 881     /// ### Explanation
 882     ///
 883     /// This syntax is mostly a historical accident, and can be worked around
 884     /// quite easily by adding an `_` pattern or a descriptive identifier:
 885     ///
 886     /// ```rust
 887     /// trait Foo {
 888     ///     fn foo(_: usize);
 889     /// }
 890     /// ```
 891     ///
 892     /// This syntax is now a hard error in the 2018 edition. In the 2015
 893     /// edition, this lint is "warn" by default. This lint
 894     /// enables the [`cargo fix`] tool with the `--edition` flag to
 895     /// automatically transition old code from the 2015 edition to 2018. The
 896     /// tool will run this lint and automatically apply the
 897     /// suggested fix from the compiler (which is to add `_` to each
 898     /// parameter). This provides a completely automated way to update old
 899     /// code for a new edition. See [issue #41686] for more details.
 900     ///
 901     /// [issue #41686]: https://github.com/rust-lang/rust/issues/41686
 902     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
 903     pub ANONYMOUS_PARAMETERS,
 904     Warn,
 905     "detects anonymous parameters",
 906     @future_incompatible = FutureIncompatibleInfo {
 907         reference: "issue #41686 <https://github.com/rust-lang/rust/issues/41686>",
 908         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
 909     };
 910 }
 911
 912 declare_lint_pass!(
 913     /// Checks for use of anonymous parameters (RFC 1685).
 914     AnonymousParameters => [ANONYMOUS_PARAMETERS]
 915 );
 916
 917 impl EarlyLintPass for AnonymousParameters {
 918     fn check_trait_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
 919         if cx.sess.edition() != Edition::Edition2015 {
 920             // This is a hard error in future editions; avoid linting and erroring
 921             return;
 922         }
 923         if let ast::AssocItemKind::Fn(box Fn { ref sig, .. }) = it.kind {
 924             for arg in sig.decl.inputs.iter() {
 925                 if let ast::PatKind::Ident(_, ident, None) = arg.pat.kind {
 926                     if ident.name == kw::Empty {
 927                         cx.struct_span_lint(ANONYMOUS_PARAMETERS, arg.pat.span, |lint| {
 928                             let ty_snip = cx.sess.source_map().span_to_snippet(arg.ty.span);
 929
 930                             let (ty_snip, appl) = if let Ok(ref snip) = ty_snip {
 931                                 (snip.as_str(), Applicability::MachineApplicable)
 932                             } else {
 933                                 ("<type>", Applicability::HasPlaceholders)
 934                             };
 935
 936                             lint.build(
 937                                 "anonymous parameters are deprecated and will be \
 938                                      removed in the next edition",
 939                             )
 940                             .span_suggestion(
 941                                 arg.pat.span,
 942                                 "try naming the parameter or explicitly \
 943                                             ignoring it",
 944                                 format!("_: {}", ty_snip),
 945                                 appl,
 946                             )
 947                             .emit();
 948                         })
 949                     }
 950                 }
 951             }
 952         }
 953     }
 954 }
 955
 956 /// Check for use of attributes which have been deprecated.
 957 #[derive(Clone)]
 958 pub struct DeprecatedAttr {
 959     // This is not free to compute, so we want to keep it around, rather than
 960     // compute it for every attribute.
 961     depr_attrs: Vec<&'static BuiltinAttribute>,
 962 }
 963
 964 impl_lint_pass!(DeprecatedAttr => []);
 965
 966 impl DeprecatedAttr {
 967     pub fn new() -> DeprecatedAttr {
 968         DeprecatedAttr { depr_attrs: deprecated_attributes() }
 969     }
 970 }
 971
 972 fn lint_deprecated_attr(
 973     cx: &EarlyContext<'_>,
 974     attr: &ast::Attribute,
 975     msg: &str,
 976     suggestion: Option<&str>,
 977 ) {
 978     cx.struct_span_lint(DEPRECATED, attr.span, |lint| {
 979         lint.build(msg)
 980             .span_suggestion_short(
 981                 attr.span,
 982                 suggestion.unwrap_or("remove this attribute"),
 983                 String::new(),
 984                 Applicability::MachineApplicable,
 985             )
 986             .emit();
 987     })
 988 }
 989
 990 impl EarlyLintPass for DeprecatedAttr {
 991     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 992         for BuiltinAttribute { name, gate, .. } in &self.depr_attrs {
 993             if attr.ident().map(|ident| ident.name) == Some(*name) {
 994                 if let &AttributeGate::Gated(
 995                     Stability::Deprecated(link, suggestion),
 996                     name,
 997                     reason,
 998                     _,
 999                 ) = gate
1000                 {
1001                     let msg =
1002                         format!("use of deprecated attribute `{}`: {}. See {}", name, reason, link);
1003                     lint_deprecated_attr(cx, attr, &msg, suggestion);
1004                 }
1005                 return;
1006             }
1007         }
1008         if attr.has_name(sym::no_start) || attr.has_name(sym::crate_id) {
1009             let path_str = pprust::path_to_string(&attr.get_normal_item().path);
1010             let msg = format!("use of deprecated attribute `{}`: no longer used.", path_str);
1011             lint_deprecated_attr(cx, attr, &msg, None);
1012         }
1013     }
1014 }
1015
1016 fn warn_if_doc(cx: &EarlyContext<'_>, node_span: Span, node_kind: &str, attrs: &[ast::Attribute]) {
1017     use rustc_ast::token::CommentKind;
1018
1019     let mut attrs = attrs.iter().peekable();
1020
1021     // Accumulate a single span for sugared doc comments.
1022     let mut sugared_span: Option<Span> = None;
1023
1024     while let Some(attr) = attrs.next() {
1025         let is_doc_comment = attr.is_doc_comment();
1026         if is_doc_comment {
1027             sugared_span =
1028                 Some(sugared_span.map_or(attr.span, |span| span.with_hi(attr.span.hi())));
1029         }
1030
1031         if attrs.peek().map_or(false, |next_attr| next_attr.is_doc_comment()) {
1032             continue;
1033         }
1034
1035         let span = sugared_span.take().unwrap_or(attr.span);
1036
1037         if is_doc_comment || attr.has_name(sym::doc) {
1038             cx.struct_span_lint(UNUSED_DOC_COMMENTS, span, |lint| {
1039                 let mut err = lint.build("unused doc comment");
1040                 err.span_label(
1041                     node_span,
1042                     format!("rustdoc does not generate documentation for {}", node_kind),
1043                 );
1044                 match attr.kind {
1045                     AttrKind::DocComment(CommentKind::Line, _) | AttrKind::Normal(..) => {
1046                         err.help("use `//` for a plain comment");
1047                     }
1048                     AttrKind::DocComment(CommentKind::Block, _) => {
1049                         err.help("use `/* */` for a plain comment");
1050                     }
1051                 }
1052                 err.emit();
1053             });
1054         }
1055     }
1056 }
1057
1058 impl EarlyLintPass for UnusedDocComment {
1059     fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &ast::Stmt) {
1060         let kind = match stmt.kind {
1061             ast::StmtKind::Local(..) => "statements",
1062             // Disabled pending discussion in #78306
1063             ast::StmtKind::Item(..) => return,
1064             // expressions will be reported by `check_expr`.
1065             ast::StmtKind::Empty
1066             | ast::StmtKind::Semi(_)
1067             | ast::StmtKind::Expr(_)
1068             | ast::StmtKind::MacCall(_) => return,
1069         };
1070
1071         warn_if_doc(cx, stmt.span, kind, stmt.kind.attrs());
1072     }
1073
1074     fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) {
1075         let arm_span = arm.pat.span.with_hi(arm.body.span.hi());
1076         warn_if_doc(cx, arm_span, "match arms", &arm.attrs);
1077     }
1078
1079     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
1080         warn_if_doc(cx, expr.span, "expressions", &expr.attrs);
1081     }
1082
1083     fn check_generic_param(&mut self, cx: &EarlyContext<'_>, param: &ast::GenericParam) {
1084         warn_if_doc(cx, param.ident.span, "generic parameters", &param.attrs);
1085     }
1086 }
1087
1088 declare_lint! {
1089     /// The `no_mangle_const_items` lint detects any `const` items with the
1090     /// [`no_mangle` attribute].
1091     ///
1092     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1093     ///
1094     /// ### Example
1095     ///
1096     /// ```rust,compile_fail
1097     /// #[no_mangle]
1098     /// const FOO: i32 = 5;
1099     /// ```
1100     ///
1101     /// {{produces}}
1102     ///
1103     /// ### Explanation
1104     ///
1105     /// Constants do not have their symbols exported, and therefore, this
1106     /// probably means you meant to use a [`static`], not a [`const`].
1107     ///
1108     /// [`static`]: https://doc.rust-lang.org/reference/items/static-items.html
1109     /// [`const`]: https://doc.rust-lang.org/reference/items/constant-items.html
1110     NO_MANGLE_CONST_ITEMS,
1111     Deny,
1112     "const items will not have their symbols exported"
1113 }
1114
1115 declare_lint! {
1116     /// The `no_mangle_generic_items` lint detects generic items that must be
1117     /// mangled.
1118     ///
1119     /// ### Example
1120     ///
1121     /// ```rust
1122     /// #[no_mangle]
1123     /// fn foo<T>(t: T) {
1124     ///
1125     /// }
1126     /// ```
1127     ///
1128     /// {{produces}}
1129     ///
1130     /// ### Explanation
1131     ///
1132     /// A function with generics must have its symbol mangled to accommodate
1133     /// the generic parameter. The [`no_mangle` attribute] has no effect in
1134     /// this situation, and should be removed.
1135     ///
1136     /// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
1137     NO_MANGLE_GENERIC_ITEMS,
1138     Warn,
1139     "generic items must be mangled"
1140 }
1141
1142 declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS, NO_MANGLE_GENERIC_ITEMS]);
1143
1144 impl<'tcx> LateLintPass<'tcx> for InvalidNoMangleItems {
1145     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1146         let attrs = cx.tcx.hir().attrs(it.hir_id());
1147         let check_no_mangle_on_generic_fn = |no_mangle_attr: &ast::Attribute,
1148                                              impl_generics: Option<&hir::Generics<'_>>,
1149                                              generics: &hir::Generics<'_>,
1150                                              span| {
1151             for param in
1152                 generics.params.iter().chain(impl_generics.map(|g| g.params).into_iter().flatten())
1153             {
1154                 match param.kind {
1155                     GenericParamKind::Lifetime { .. } => {}
1156                     GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1157                         cx.struct_span_lint(NO_MANGLE_GENERIC_ITEMS, span, |lint| {
1158                             lint.build("functions generic over types or consts must be mangled")
1159                                 .span_suggestion_short(
1160                                     no_mangle_attr.span,
1161                                     "remove this attribute",
1162                                     String::new(),
1163                                     // Use of `#[no_mangle]` suggests FFI intent; correct
1164                                     // fix may be to monomorphize source by hand
1165                                     Applicability::MaybeIncorrect,
1166                                 )
1167                                 .emit();
1168                         });
1169                         break;
1170                     }
1171                 }
1172             }
1173         };
1174         match it.kind {
1175             hir::ItemKind::Fn(.., ref generics, _) => {
1176                 if let Some(no_mangle_attr) = cx.sess().find_by_name(attrs, sym::no_mangle) {
1177                     check_no_mangle_on_generic_fn(no_mangle_attr, None, generics, it.span);
1178                 }
1179             }
1180             hir::ItemKind::Const(..) => {
1181                 if cx.sess().contains_name(attrs, sym::no_mangle) {
1182                     // Const items do not refer to a particular location in memory, and therefore
1183                     // don't have anything to attach a symbol to
1184                     cx.struct_span_lint(NO_MANGLE_CONST_ITEMS, it.span, |lint| {
1185                         let msg = "const items should never be `#[no_mangle]`";
1186                         let mut err = lint.build(msg);
1187
1188                         // account for "pub const" (#45562)
1189                         let start = cx
1190                             .tcx
1191                             .sess
1192                             .source_map()
1193                             .span_to_snippet(it.span)
1194                             .map(|snippet| snippet.find("const").unwrap_or(0))
1195                             .unwrap_or(0) as u32;
1196                         // `const` is 5 chars
1197                         let const_span = it.span.with_hi(BytePos(it.span.lo().0 + start + 5));
1198                         err.span_suggestion(
1199                             const_span,
1200                             "try a static value",
1201                             "pub static".to_owned(),
1202                             Applicability::MachineApplicable,
1203                         );
1204                         err.emit();
1205                     });
1206                 }
1207             }
1208             hir::ItemKind::Impl(hir::Impl { ref generics, items, .. }) => {
1209                 for it in items {
1210                     if let hir::AssocItemKind::Fn { .. } = it.kind {
1211                         if let Some(no_mangle_attr) = cx
1212                             .sess()
1213                             .find_by_name(cx.tcx.hir().attrs(it.id.hir_id()), sym::no_mangle)
1214                         {
1215                             check_no_mangle_on_generic_fn(
1216                                 no_mangle_attr,
1217                                 Some(generics),
1218                                 cx.tcx.hir().get_generics(it.id.def_id.to_def_id()).unwrap(),
1219                                 it.span,
1220                             );
1221                         }
1222                     }
1223                 }
1224             }
1225             _ => {}
1226         }
1227     }
1228 }
1229
1230 declare_lint! {
1231     /// The `mutable_transmutes` lint catches transmuting from `&T` to `&mut
1232     /// T` because it is [undefined behavior].
1233     ///
1234     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1235     ///
1236     /// ### Example
1237     ///
1238     /// ```rust,compile_fail
1239     /// unsafe {
1240     ///     let y = std::mem::transmute::<&i32, &mut i32>(&5);
1241     /// }
1242     /// ```
1243     ///
1244     /// {{produces}}
1245     ///
1246     /// ### Explanation
1247     ///
1248     /// Certain assumptions are made about aliasing of data, and this transmute
1249     /// violates those assumptions. Consider using [`UnsafeCell`] instead.
1250     ///
1251     /// [`UnsafeCell`]: https://doc.rust-lang.org/std/cell/struct.UnsafeCell.html
1252     MUTABLE_TRANSMUTES,
1253     Deny,
1254     "mutating transmuted &mut T from &T may cause undefined behavior"
1255 }
1256
1257 declare_lint_pass!(MutableTransmutes => [MUTABLE_TRANSMUTES]);
1258
1259 impl<'tcx> LateLintPass<'tcx> for MutableTransmutes {
1260     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &hir::Expr<'_>) {
1261         use rustc_target::spec::abi::Abi::RustIntrinsic;
1262         if let Some((&ty::Ref(_, _, from_mt), &ty::Ref(_, _, to_mt))) =
1263             get_transmute_from_to(cx, expr).map(|(ty1, ty2)| (ty1.kind(), ty2.kind()))
1264         {
1265             if to_mt == hir::Mutability::Mut && from_mt == hir::Mutability::Not {
1266                 let msg = "mutating transmuted &mut T from &T may cause undefined behavior, \
1267                                consider instead using an UnsafeCell";
1268                 cx.struct_span_lint(MUTABLE_TRANSMUTES, expr.span, |lint| lint.build(msg).emit());
1269             }
1270         }
1271
1272         fn get_transmute_from_to<'tcx>(
1273             cx: &LateContext<'tcx>,
1274             expr: &hir::Expr<'_>,
1275         ) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
1276             let def = if let hir::ExprKind::Path(ref qpath) = expr.kind {
1277                 cx.qpath_res(qpath, expr.hir_id)
1278             } else {
1279                 return None;
1280             };
1281             if let Res::Def(DefKind::Fn, did) = def {
1282                 if !def_id_is_transmute(cx, did) {
1283                     return None;
1284                 }
1285                 let sig = cx.typeck_results().node_type(expr.hir_id).fn_sig(cx.tcx);
1286                 let from = sig.inputs().skip_binder()[0];
1287                 let to = sig.output().skip_binder();
1288                 return Some((from, to));
1289             }
1290             None
1291         }
1292
1293         fn def_id_is_transmute(cx: &LateContext<'_>, def_id: DefId) -> bool {
1294             cx.tcx.fn_sig(def_id).abi() == RustIntrinsic
1295                 && cx.tcx.item_name(def_id) == sym::transmute
1296         }
1297     }
1298 }
1299
1300 declare_lint! {
1301     /// The `unstable_features` is deprecated and should no longer be used.
1302     UNSTABLE_FEATURES,
1303     Allow,
1304     "enabling unstable features (deprecated. do not use)"
1305 }
1306
1307 declare_lint_pass!(
1308     /// Forbids using the `#[feature(...)]` attribute
1309     UnstableFeatures => [UNSTABLE_FEATURES]
1310 );
1311
1312 impl<'tcx> LateLintPass<'tcx> for UnstableFeatures {
1313     fn check_attribute(&mut self, cx: &LateContext<'_>, attr: &ast::Attribute) {
1314         if attr.has_name(sym::feature) {
1315             if let Some(items) = attr.meta_item_list() {
1316                 for item in items {
1317                     cx.struct_span_lint(UNSTABLE_FEATURES, item.span(), |lint| {
1318                         lint.build("unstable feature").emit()
1319                     });
1320                 }
1321             }
1322         }
1323     }
1324 }
1325
1326 declare_lint! {
1327     /// The `unreachable_pub` lint triggers for `pub` items not reachable from
1328     /// the crate root.
1329     ///
1330     /// ### Example
1331     ///
1332     /// ```rust,compile_fail
1333     /// #![deny(unreachable_pub)]
1334     /// mod foo {
1335     ///     pub mod bar {
1336     ///
1337     ///     }
1338     /// }
1339     /// ```
1340     ///
1341     /// {{produces}}
1342     ///
1343     /// ### Explanation
1344     ///
1345     /// A bare `pub` visibility may be misleading if the item is not actually
1346     /// publicly exported from the crate. The `pub(crate)` visibility is
1347     /// recommended to be used instead, which more clearly expresses the intent
1348     /// that the item is only visible within its own crate.
1349     ///
1350     /// This lint is "allow" by default because it will trigger for a large
1351     /// amount existing Rust code, and has some false-positives. Eventually it
1352     /// is desired for this to become warn-by-default.
1353     pub UNREACHABLE_PUB,
1354     Allow,
1355     "`pub` items not reachable from crate root"
1356 }
1357
1358 declare_lint_pass!(
1359     /// Lint for items marked `pub` that aren't reachable from other crates.
1360     UnreachablePub => [UNREACHABLE_PUB]
1361 );
1362
1363 impl UnreachablePub {
1364     fn perform_lint(
1365         &self,
1366         cx: &LateContext<'_>,
1367         what: &str,
1368         def_id: LocalDefId,
1369         vis: &hir::Visibility<'_>,
1370         span: Span,
1371         exportable: bool,
1372     ) {
1373         let mut applicability = Applicability::MachineApplicable;
1374         match vis.node {
1375             hir::VisibilityKind::Public if !cx.access_levels.is_reachable(def_id) => {
1376                 if span.from_expansion() {
1377                     applicability = Applicability::MaybeIncorrect;
1378                 }
1379                 let def_span = cx.tcx.sess.source_map().guess_head_span(span);
1380                 cx.struct_span_lint(UNREACHABLE_PUB, def_span, |lint| {
1381                     let mut err = lint.build(&format!("unreachable `pub` {}", what));
1382                     let replacement = if cx.tcx.features().crate_visibility_modifier {
1383                         "crate"
1384                     } else {
1385                         "pub(crate)"
1386                     }
1387                     .to_owned();
1388
1389                     err.span_suggestion(
1390                         vis.span,
1391                         "consider restricting its visibility",
1392                         replacement,
1393                         applicability,
1394                     );
1395                     if exportable {
1396                         err.help("or consider exporting it for use by other crates");
1397                     }
1398                     err.emit();
1399                 });
1400             }
1401             _ => {}
1402         }
1403     }
1404 }
1405
1406 impl<'tcx> LateLintPass<'tcx> for UnreachablePub {
1407     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1408         self.perform_lint(cx, "item", item.def_id, &item.vis, item.span, true);
1409     }
1410
1411     fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'tcx>) {
1412         self.perform_lint(
1413             cx,
1414             "item",
1415             foreign_item.def_id,
1416             &foreign_item.vis,
1417             foreign_item.span,
1418             true,
1419         );
1420     }
1421
1422     fn check_field_def(&mut self, cx: &LateContext<'_>, field: &hir::FieldDef<'_>) {
1423         let def_id = cx.tcx.hir().local_def_id(field.hir_id);
1424         self.perform_lint(cx, "field", def_id, &field.vis, field.span, false);
1425     }
1426
1427     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
1428         self.perform_lint(cx, "item", impl_item.def_id, &impl_item.vis, impl_item.span, false);
1429     }
1430 }
1431
1432 declare_lint! {
1433     /// The `type_alias_bounds` lint detects bounds in type aliases.
1434     ///
1435     /// ### Example
1436     ///
1437     /// ```rust
1438     /// type SendVec<T: Send> = Vec<T>;
1439     /// ```
1440     ///
1441     /// {{produces}}
1442     ///
1443     /// ### Explanation
1444     ///
1445     /// The trait bounds in a type alias are currently ignored, and should not
1446     /// be included to avoid confusion. This was previously allowed
1447     /// unintentionally; this may become a hard error in the future.
1448     TYPE_ALIAS_BOUNDS,
1449     Warn,
1450     "bounds in type aliases are not enforced"
1451 }
1452
1453 declare_lint_pass!(
1454     /// Lint for trait and lifetime bounds in type aliases being mostly ignored.
1455     /// They are relevant when using associated types, but otherwise neither checked
1456     /// at definition site nor enforced at use site.
1457     TypeAliasBounds => [TYPE_ALIAS_BOUNDS]
1458 );
1459
1460 impl TypeAliasBounds {
1461     fn is_type_variable_assoc(qpath: &hir::QPath<'_>) -> bool {
1462         match *qpath {
1463             hir::QPath::TypeRelative(ref ty, _) => {
1464                 // If this is a type variable, we found a `T::Assoc`.
1465                 match ty.kind {
1466                     hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
1467                         matches!(path.res, Res::Def(DefKind::TyParam, _))
1468                     }
1469                     _ => false,
1470                 }
1471             }
1472             hir::QPath::Resolved(..) | hir::QPath::LangItem(..) => false,
1473         }
1474     }
1475
1476     fn suggest_changing_assoc_types(ty: &hir::Ty<'_>, err: &mut DiagnosticBuilder<'_>) {
1477         // Access to associates types should use `<T as Bound>::Assoc`, which does not need a
1478         // bound.  Let's see if this type does that.
1479
1480         // We use a HIR visitor to walk the type.
1481         use rustc_hir::intravisit::{self, Visitor};
1482         struct WalkAssocTypes<'a, 'db> {
1483             err: &'a mut DiagnosticBuilder<'db>,
1484         }
1485         impl<'a, 'db, 'v> Visitor<'v> for WalkAssocTypes<'a, 'db> {
1486             type Map = intravisit::ErasedMap<'v>;
1487
1488             fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1489                 intravisit::NestedVisitorMap::None
1490             }
1491
1492             fn visit_qpath(&mut self, qpath: &'v hir::QPath<'v>, id: hir::HirId, span: Span) {
1493                 if TypeAliasBounds::is_type_variable_assoc(qpath) {
1494                     self.err.span_help(
1495                         span,
1496                         "use fully disambiguated paths (i.e., `<T as Trait>::Assoc`) to refer to \
1497                          associated types in type aliases",
1498                     );
1499                 }
1500                 intravisit::walk_qpath(self, qpath, id, span)
1501             }
1502         }
1503
1504         // Let's go for a walk!
1505         let mut visitor = WalkAssocTypes { err };
1506         visitor.visit_ty(ty);
1507     }
1508 }
1509
1510 impl<'tcx> LateLintPass<'tcx> for TypeAliasBounds {
1511     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1512         let (ty, type_alias_generics) = match item.kind {
1513             hir::ItemKind::TyAlias(ref ty, ref generics) => (&*ty, generics),
1514             _ => return,
1515         };
1516         if let hir::TyKind::OpaqueDef(..) = ty.kind {
1517             // Bounds are respected for `type X = impl Trait`
1518             return;
1519         }
1520         let mut suggested_changing_assoc_types = false;
1521         // There must not be a where clause
1522         if !type_alias_generics.where_clause.predicates.is_empty() {
1523             cx.lint(
1524                 TYPE_ALIAS_BOUNDS,
1525                 |lint| {
1526                     let mut err = lint.build("where clauses are not enforced in type aliases");
1527                     let spans: Vec<_> = type_alias_generics
1528                         .where_clause
1529                         .predicates
1530                         .iter()
1531                         .map(|pred| pred.span())
1532                         .collect();
1533                     err.set_span(spans);
1534                     err.span_suggestion(
1535                         type_alias_generics.where_clause.span_for_predicates_or_empty_place(),
1536                         "the clause will not be checked when the type alias is used, and should be removed",
1537                         String::new(),
1538                         Applicability::MachineApplicable,
1539                     );
1540                     if !suggested_changing_assoc_types {
1541                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1542                         suggested_changing_assoc_types = true;
1543                     }
1544                     err.emit();
1545                 },
1546             );
1547         }
1548         // The parameters must not have bounds
1549         for param in type_alias_generics.params.iter() {
1550             let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
1551             let suggestion = spans
1552                 .iter()
1553                 .map(|sp| {
1554                     let start = param.span.between(*sp); // Include the `:` in `T: Bound`.
1555                     (start.to(*sp), String::new())
1556                 })
1557                 .collect();
1558             if !spans.is_empty() {
1559                 cx.struct_span_lint(TYPE_ALIAS_BOUNDS, spans, |lint| {
1560                     let mut err =
1561                         lint.build("bounds on generic parameters are not enforced in type aliases");
1562                     let msg = "the bound will not be checked when the type alias is used, \
1563                                    and should be removed";
1564                     err.multipart_suggestion(&msg, suggestion, Applicability::MachineApplicable);
1565                     if !suggested_changing_assoc_types {
1566                         TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1567                         suggested_changing_assoc_types = true;
1568                     }
1569                     err.emit();
1570                 });
1571             }
1572         }
1573     }
1574 }
1575
1576 declare_lint_pass!(
1577     /// Lint constants that are erroneous.
1578     /// Without this lint, we might not get any diagnostic if the constant is
1579     /// unused within this crate, even though downstream crates can't use it
1580     /// without producing an error.
1581     UnusedBrokenConst => []
1582 );
1583
1584 impl<'tcx> LateLintPass<'tcx> for UnusedBrokenConst {
1585     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1586         match it.kind {
1587             hir::ItemKind::Const(_, body_id) => {
1588                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1589                 // trigger the query once for all constants since that will already report the errors
1590                 // FIXME: Use ensure here
1591                 let _ = cx.tcx.const_eval_poly(def_id);
1592             }
1593             hir::ItemKind::Static(_, _, body_id) => {
1594                 let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
1595                 // FIXME: Use ensure here
1596                 let _ = cx.tcx.eval_static_initializer(def_id);
1597             }
1598             _ => {}
1599         }
1600     }
1601 }
1602
1603 declare_lint! {
1604     /// The `trivial_bounds` lint detects trait bounds that don't depend on
1605     /// any type parameters.
1606     ///
1607     /// ### Example
1608     ///
1609     /// ```rust
1610     /// #![feature(trivial_bounds)]
1611     /// pub struct A where i32: Copy;
1612     /// ```
1613     ///
1614     /// {{produces}}
1615     ///
1616     /// ### Explanation
1617     ///
1618     /// Usually you would not write a trait bound that you know is always
1619     /// true, or never true. However, when using macros, the macro may not
1620     /// know whether or not the constraint would hold or not at the time when
1621     /// generating the code. Currently, the compiler does not alert you if the
1622     /// constraint is always true, and generates an error if it is never true.
1623     /// The `trivial_bounds` feature changes this to be a warning in both
1624     /// cases, giving macros more freedom and flexibility to generate code,
1625     /// while still providing a signal when writing non-macro code that
1626     /// something is amiss.
1627     ///
1628     /// See [RFC 2056] for more details. This feature is currently only
1629     /// available on the nightly channel, see [tracking issue #48214].
1630     ///
1631     /// [RFC 2056]: https://github.com/rust-lang/rfcs/blob/master/text/2056-allow-trivial-where-clause-constraints.md
1632     /// [tracking issue #48214]: https://github.com/rust-lang/rust/issues/48214
1633     TRIVIAL_BOUNDS,
1634     Warn,
1635     "these bounds don't depend on an type parameters"
1636 }
1637
1638 declare_lint_pass!(
1639     /// Lint for trait and lifetime bounds that don't depend on type parameters
1640     /// which either do nothing, or stop the item from being used.
1641     TrivialConstraints => [TRIVIAL_BOUNDS]
1642 );
1643
1644 impl<'tcx> LateLintPass<'tcx> for TrivialConstraints {
1645     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
1646         use rustc_middle::ty::fold::TypeFoldable;
1647         use rustc_middle::ty::PredicateKind::*;
1648
1649         if cx.tcx.features().trivial_bounds {
1650             let predicates = cx.tcx.predicates_of(item.def_id);
1651             for &(predicate, span) in predicates.predicates {
1652                 let predicate_kind_name = match predicate.kind().skip_binder() {
1653                     Trait(..) => "trait",
1654                     TypeOutlives(..) |
1655                     RegionOutlives(..) => "lifetime",
1656
1657                     // Ignore projections, as they can only be global
1658                     // if the trait bound is global
1659                     Projection(..) |
1660                     // Ignore bounds that a user can't type
1661                     WellFormed(..) |
1662                     ObjectSafe(..) |
1663                     ClosureKind(..) |
1664                     Subtype(..) |
1665                     Coerce(..) |
1666                     ConstEvaluatable(..) |
1667                     ConstEquate(..) |
1668                     TypeWellFormedFromEnv(..) => continue,
1669                 };
1670                 if predicate.is_global(cx.tcx) {
1671                     cx.struct_span_lint(TRIVIAL_BOUNDS, span, |lint| {
1672                         lint.build(&format!(
1673                             "{} bound {} does not depend on any type \
1674                                 or lifetime parameters",
1675                             predicate_kind_name, predicate
1676                         ))
1677                         .emit()
1678                     });
1679                 }
1680             }
1681         }
1682     }
1683 }
1684
1685 declare_lint_pass!(
1686     /// Does nothing as a lint pass, but registers some `Lint`s
1687     /// which are used by other parts of the compiler.
1688     SoftLints => [
1689         WHILE_TRUE,
1690         BOX_POINTERS,
1691         NON_SHORTHAND_FIELD_PATTERNS,
1692         UNSAFE_CODE,
1693         MISSING_DOCS,
1694         MISSING_COPY_IMPLEMENTATIONS,
1695         MISSING_DEBUG_IMPLEMENTATIONS,
1696         ANONYMOUS_PARAMETERS,
1697         UNUSED_DOC_COMMENTS,
1698         NO_MANGLE_CONST_ITEMS,
1699         NO_MANGLE_GENERIC_ITEMS,
1700         MUTABLE_TRANSMUTES,
1701         UNSTABLE_FEATURES,
1702         UNREACHABLE_PUB,
1703         TYPE_ALIAS_BOUNDS,
1704         TRIVIAL_BOUNDS
1705     ]
1706 );
1707
1708 declare_lint! {
1709     /// The `ellipsis_inclusive_range_patterns` lint detects the [`...` range
1710     /// pattern], which is deprecated.
1711     ///
1712     /// [`...` range pattern]: https://doc.rust-lang.org/reference/patterns.html#range-patterns
1713     ///
1714     /// ### Example
1715     ///
1716     /// ```rust,edition2018
1717     /// let x = 123;
1718     /// match x {
1719     ///     0...100 => {}
1720     ///     _ => {}
1721     /// }
1722     /// ```
1723     ///
1724     /// {{produces}}
1725     ///
1726     /// ### Explanation
1727     ///
1728     /// The `...` range pattern syntax was changed to `..=` to avoid potential
1729     /// confusion with the [`..` range expression]. Use the new form instead.
1730     ///
1731     /// [`..` range expression]: https://doc.rust-lang.org/reference/expressions/range-expr.html
1732     pub ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
1733     Warn,
1734     "`...` range patterns are deprecated",
1735     @future_incompatible = FutureIncompatibleInfo {
1736         reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>",
1737         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
1738     };
1739 }
1740
1741 #[derive(Default)]
1742 pub struct EllipsisInclusiveRangePatterns {
1743     /// If `Some(_)`, suppress all subsequent pattern
1744     /// warnings for better diagnostics.
1745     node_id: Option<ast::NodeId>,
1746 }
1747
1748 impl_lint_pass!(EllipsisInclusiveRangePatterns => [ELLIPSIS_INCLUSIVE_RANGE_PATTERNS]);
1749
1750 impl EarlyLintPass for EllipsisInclusiveRangePatterns {
1751     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &ast::Pat) {
1752         if self.node_id.is_some() {
1753             // Don't recursively warn about patterns inside range endpoints.
1754             return;
1755         }
1756
1757         use self::ast::{PatKind, RangeSyntax::DotDotDot};
1758
1759         /// If `pat` is a `...` pattern, return the start and end of the range, as well as the span
1760         /// corresponding to the ellipsis.
1761         fn matches_ellipsis_pat(pat: &ast::Pat) -> Option<(Option<&Expr>, &Expr, Span)> {
1762             match &pat.kind {
1763                 PatKind::Range(
1764                     a,
1765                     Some(b),
1766                     Spanned { span, node: RangeEnd::Included(DotDotDot) },
1767                 ) => Some((a.as_deref(), b, *span)),
1768                 _ => None,
1769             }
1770         }
1771
1772         let (parenthesise, endpoints) = match &pat.kind {
1773             PatKind::Ref(subpat, _) => (true, matches_ellipsis_pat(&subpat)),
1774             _ => (false, matches_ellipsis_pat(pat)),
1775         };
1776
1777         if let Some((start, end, join)) = endpoints {
1778             let msg = "`...` range patterns are deprecated";
1779             let suggestion = "use `..=` for an inclusive range";
1780             if parenthesise {
1781                 self.node_id = Some(pat.id);
1782                 let end = expr_to_string(&end);
1783                 let replace = match start {
1784                     Some(start) => format!("&({}..={})", expr_to_string(&start), end),
1785                     None => format!("&(..={})", end),
1786                 };
1787                 if join.edition() >= Edition::Edition2021 {
1788                     let mut err =
1789                         rustc_errors::struct_span_err!(cx.sess, pat.span, E0783, "{}", msg,);
1790                     err.span_suggestion(
1791                         pat.span,
1792                         suggestion,
1793                         replace,
1794                         Applicability::MachineApplicable,
1795                     )
1796                     .emit();
1797                 } else {
1798                     cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, pat.span, |lint| {
1799                         lint.build(msg)
1800                             .span_suggestion(
1801                                 pat.span,
1802                                 suggestion,
1803                                 replace,
1804                                 Applicability::MachineApplicable,
1805                             )
1806                             .emit();
1807                     });
1808                 }
1809             } else {
1810                 let replace = "..=".to_owned();
1811                 if join.edition() >= Edition::Edition2021 {
1812                     let mut err =
1813                         rustc_errors::struct_span_err!(cx.sess, pat.span, E0783, "{}", msg,);
1814                     err.span_suggestion_short(
1815                         join,
1816                         suggestion,
1817                         replace,
1818                         Applicability::MachineApplicable,
1819                     )
1820                     .emit();
1821                 } else {
1822                     cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, join, |lint| {
1823                         lint.build(msg)
1824                             .span_suggestion_short(
1825                                 join,
1826                                 suggestion,
1827                                 replace,
1828                                 Applicability::MachineApplicable,
1829                             )
1830                             .emit();
1831                     });
1832                 }
1833             };
1834         }
1835     }
1836
1837     fn check_pat_post(&mut self, _cx: &EarlyContext<'_>, pat: &ast::Pat) {
1838         if let Some(node_id) = self.node_id {
1839             if pat.id == node_id {
1840                 self.node_id = None
1841             }
1842         }
1843     }
1844 }
1845
1846 declare_lint! {
1847     /// The `unnameable_test_items` lint detects [`#[test]`][test] functions
1848     /// that are not able to be run by the test harness because they are in a
1849     /// position where they are not nameable.
1850     ///
1851     /// [test]: https://doc.rust-lang.org/reference/attributes/testing.html#the-test-attribute
1852     ///
1853     /// ### Example
1854     ///
1855     /// ```rust,test
1856     /// fn main() {
1857     ///     #[test]
1858     ///     fn foo() {
1859     ///         // This test will not fail because it does not run.
1860     ///         assert_eq!(1, 2);
1861     ///     }
1862     /// }
1863     /// ```
1864     ///
1865     /// {{produces}}
1866     ///
1867     /// ### Explanation
1868     ///
1869     /// In order for the test harness to run a test, the test function must be
1870     /// located in a position where it can be accessed from the crate root.
1871     /// This generally means it must be defined in a module, and not anywhere
1872     /// else such as inside another function. The compiler previously allowed
1873     /// this without an error, so a lint was added as an alert that a test is
1874     /// not being used. Whether or not this should be allowed has not yet been
1875     /// decided, see [RFC 2471] and [issue #36629].
1876     ///
1877     /// [RFC 2471]: https://github.com/rust-lang/rfcs/pull/2471#issuecomment-397414443
1878     /// [issue #36629]: https://github.com/rust-lang/rust/issues/36629
1879     UNNAMEABLE_TEST_ITEMS,
1880     Warn,
1881     "detects an item that cannot be named being marked as `#[test_case]`",
1882     report_in_external_macro
1883 }
1884
1885 pub struct UnnameableTestItems {
1886     boundary: Option<LocalDefId>, // Id of the item under which things are not nameable
1887     items_nameable: bool,
1888 }
1889
1890 impl_lint_pass!(UnnameableTestItems => [UNNAMEABLE_TEST_ITEMS]);
1891
1892 impl UnnameableTestItems {
1893     pub fn new() -> Self {
1894         Self { boundary: None, items_nameable: true }
1895     }
1896 }
1897
1898 impl<'tcx> LateLintPass<'tcx> for UnnameableTestItems {
1899     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1900         if self.items_nameable {
1901             if let hir::ItemKind::Mod(..) = it.kind {
1902             } else {
1903                 self.items_nameable = false;
1904                 self.boundary = Some(it.def_id);
1905             }
1906             return;
1907         }
1908
1909         let attrs = cx.tcx.hir().attrs(it.hir_id());
1910         if let Some(attr) = cx.sess().find_by_name(attrs, sym::rustc_test_marker) {
1911             cx.struct_span_lint(UNNAMEABLE_TEST_ITEMS, attr.span, |lint| {
1912                 lint.build("cannot test inner items").emit()
1913             });
1914         }
1915     }
1916
1917     fn check_item_post(&mut self, _cx: &LateContext<'_>, it: &hir::Item<'_>) {
1918         if !self.items_nameable && self.boundary == Some(it.def_id) {
1919             self.items_nameable = true;
1920         }
1921     }
1922 }
1923
1924 declare_lint! {
1925     /// The `keyword_idents` lint detects edition keywords being used as an
1926     /// identifier.
1927     ///
1928     /// ### Example
1929     ///
1930     /// ```rust,edition2015,compile_fail
1931     /// #![deny(keyword_idents)]
1932     /// // edition 2015
1933     /// fn dyn() {}
1934     /// ```
1935     ///
1936     /// {{produces}}
1937     ///
1938     /// ### Explanation
1939     ///
1940     /// Rust [editions] allow the language to evolve without breaking
1941     /// backwards compatibility. This lint catches code that uses new keywords
1942     /// that are added to the language that are used as identifiers (such as a
1943     /// variable name, function name, etc.). If you switch the compiler to a
1944     /// new edition without updating the code, then it will fail to compile if
1945     /// you are using a new keyword as an identifier.
1946     ///
1947     /// You can manually change the identifiers to a non-keyword, or use a
1948     /// [raw identifier], for example `r#dyn`, to transition to a new edition.
1949     ///
1950     /// This lint solves the problem automatically. It is "allow" by default
1951     /// because the code is perfectly valid in older editions. The [`cargo
1952     /// fix`] tool with the `--edition` flag will switch this lint to "warn"
1953     /// and automatically apply the suggested fix from the compiler (which is
1954     /// to use a raw identifier). This provides a completely automated way to
1955     /// update old code for a new edition.
1956     ///
1957     /// [editions]: https://doc.rust-lang.org/edition-guide/
1958     /// [raw identifier]: https://doc.rust-lang.org/reference/identifiers.html
1959     /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
1960     pub KEYWORD_IDENTS,
1961     Allow,
1962     "detects edition keywords being used as an identifier",
1963     @future_incompatible = FutureIncompatibleInfo {
1964         reference: "issue #49716 <https://github.com/rust-lang/rust/issues/49716>",
1965         reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
1966     };
1967 }
1968
1969 declare_lint_pass!(
1970     /// Check for uses of edition keywords used as an identifier.
1971     KeywordIdents => [KEYWORD_IDENTS]
1972 );
1973
1974 struct UnderMacro(bool);
1975
1976 impl KeywordIdents {
1977     fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: TokenStream) {
1978         for tt in tokens.into_trees() {
1979             match tt {
1980                 // Only report non-raw idents.
1981                 TokenTree::Token(token) => {
1982                     if let Some((ident, false)) = token.ident() {
1983                         self.check_ident_token(cx, UnderMacro(true), ident);
1984                     }
1985                 }
1986                 TokenTree::Delimited(_, _, tts) => self.check_tokens(cx, tts),
1987             }
1988         }
1989     }
1990
1991     fn check_ident_token(
1992         &mut self,
1993         cx: &EarlyContext<'_>,
1994         UnderMacro(under_macro): UnderMacro,
1995         ident: Ident,
1996     ) {
1997         let next_edition = match cx.sess.edition() {
1998             Edition::Edition2015 => {
1999                 match ident.name {
2000                     kw::Async | kw::Await | kw::Try => Edition::Edition2018,
2001
2002                     // rust-lang/rust#56327: Conservatively do not
2003                     // attempt to report occurrences of `dyn` within
2004                     // macro definitions or invocations, because `dyn`
2005                     // can legitimately occur as a contextual keyword
2006                     // in 2015 code denoting its 2018 meaning, and we
2007                     // do not want rustfix to inject bugs into working
2008                     // code by rewriting such occurrences.
2009                     //
2010                     // But if we see `dyn` outside of a macro, we know
2011                     // its precise role in the parsed AST and thus are
2012                     // assured this is truly an attempt to use it as
2013                     // an identifier.
2014                     kw::Dyn if !under_macro => Edition::Edition2018,
2015
2016                     _ => return,
2017                 }
2018             }
2019
2020             // There are no new keywords yet for the 2018 edition and beyond.
2021             _ => return,
2022         };
2023
2024         // Don't lint `r#foo`.
2025         if cx.sess.parse_sess.raw_identifier_spans.borrow().contains(&ident.span) {
2026             return;
2027         }
2028
2029         cx.struct_span_lint(KEYWORD_IDENTS, ident.span, |lint| {
2030             lint.build(&format!("`{}` is a keyword in the {} edition", ident, next_edition))
2031                 .span_suggestion(
2032                     ident.span,
2033                     "you can use a raw identifier to stay compatible",
2034                     format!("r#{}", ident),
2035                     Applicability::MachineApplicable,
2036                 )
2037                 .emit()
2038         });
2039     }
2040 }
2041
2042 impl EarlyLintPass for KeywordIdents {
2043     fn check_mac_def(&mut self, cx: &EarlyContext<'_>, mac_def: &ast::MacroDef, _id: ast::NodeId) {
2044         self.check_tokens(cx, mac_def.body.inner_tokens());
2045     }
2046     fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::MacCall) {
2047         self.check_tokens(cx, mac.args.inner_tokens());
2048     }
2049     fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: Ident) {
2050         self.check_ident_token(cx, UnderMacro(false), ident);
2051     }
2052 }
2053
2054 declare_lint_pass!(ExplicitOutlivesRequirements => [EXPLICIT_OUTLIVES_REQUIREMENTS]);
2055
2056 impl ExplicitOutlivesRequirements {
2057     fn lifetimes_outliving_lifetime<'tcx>(
2058         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2059         index: u32,
2060     ) -> Vec<ty::Region<'tcx>> {
2061         inferred_outlives
2062             .iter()
2063             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
2064                 ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => match a {
2065                     ty::ReEarlyBound(ebr) if ebr.index == index => Some(b),
2066                     _ => None,
2067                 },
2068                 _ => None,
2069             })
2070             .collect()
2071     }
2072
2073     fn lifetimes_outliving_type<'tcx>(
2074         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2075         index: u32,
2076     ) -> Vec<ty::Region<'tcx>> {
2077         inferred_outlives
2078             .iter()
2079             .filter_map(|(pred, _)| match pred.kind().skip_binder() {
2080                 ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
2081                     a.is_param(index).then_some(b)
2082                 }
2083                 _ => None,
2084             })
2085             .collect()
2086     }
2087
2088     fn collect_outlived_lifetimes<'tcx>(
2089         &self,
2090         param: &'tcx hir::GenericParam<'tcx>,
2091         tcx: TyCtxt<'tcx>,
2092         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
2093         ty_generics: &'tcx ty::Generics,
2094     ) -> Vec<ty::Region<'tcx>> {
2095         let index =
2096             ty_generics.param_def_id_to_index[&tcx.hir().local_def_id(param.hir_id).to_def_id()];
2097
2098         match param.kind {
2099             hir::GenericParamKind::Lifetime { .. } => {
2100                 Self::lifetimes_outliving_lifetime(inferred_outlives, index)
2101             }
2102             hir::GenericParamKind::Type { .. } => {
2103                 Self::lifetimes_outliving_type(inferred_outlives, index)
2104             }
2105             hir::GenericParamKind::Const { .. } => Vec::new(),
2106         }
2107     }
2108
2109     fn collect_outlives_bound_spans<'tcx>(
2110         &self,
2111         tcx: TyCtxt<'tcx>,
2112         bounds: &hir::GenericBounds<'_>,
2113         inferred_outlives: &[ty::Region<'tcx>],
2114         infer_static: bool,
2115     ) -> Vec<(usize, Span)> {
2116         use rustc_middle::middle::resolve_lifetime::Region;
2117
2118         bounds
2119             .iter()
2120             .enumerate()
2121             .filter_map(|(i, bound)| {
2122                 if let hir::GenericBound::Outlives(lifetime) = bound {
2123                     let is_inferred = match tcx.named_region(lifetime.hir_id) {
2124                         Some(Region::Static) if infer_static => {
2125                             inferred_outlives.iter().any(|r| matches!(r, ty::ReStatic))
2126                         }
2127                         Some(Region::EarlyBound(index, ..)) => inferred_outlives.iter().any(|r| {
2128                             if let ty::ReEarlyBound(ebr) = r { ebr.index == index } else { false }
2129                         }),
2130                         _ => false,
2131                     };
2132                     is_inferred.then_some((i, bound.span()))
2133                 } else {
2134                     None
2135                 }
2136             })
2137             .collect()
2138     }
2139
2140     fn consolidate_outlives_bound_spans(
2141         &self,
2142         lo: Span,
2143         bounds: &hir::GenericBounds<'_>,
2144         bound_spans: Vec<(usize, Span)>,
2145     ) -> Vec<Span> {
2146         if bounds.is_empty() {
2147             return Vec::new();
2148         }
2149         if bound_spans.len() == bounds.len() {
2150             let (_, last_bound_span) = bound_spans[bound_spans.len() - 1];
2151             // If all bounds are inferable, we want to delete the colon, so
2152             // start from just after the parameter (span passed as argument)
2153             vec![lo.to(last_bound_span)]
2154         } else {
2155             let mut merged = Vec::new();
2156             let mut last_merged_i = None;
2157
2158             let mut from_start = true;
2159             for (i, bound_span) in bound_spans {
2160                 match last_merged_i {
2161                     // If the first bound is inferable, our span should also eat the leading `+`.
2162                     None if i == 0 => {
2163                         merged.push(bound_span.to(bounds[1].span().shrink_to_lo()));
2164                         last_merged_i = Some(0);
2165                     }
2166                     // If consecutive bounds are inferable, merge their spans
2167                     Some(h) if i == h + 1 => {
2168                         if let Some(tail) = merged.last_mut() {
2169                             // Also eat the trailing `+` if the first
2170                             // more-than-one bound is inferable
2171                             let to_span = if from_start && i < bounds.len() {
2172                                 bounds[i + 1].span().shrink_to_lo()
2173                             } else {
2174                                 bound_span
2175                             };
2176                             *tail = tail.to(to_span);
2177                             last_merged_i = Some(i);
2178                         } else {
2179                             bug!("another bound-span visited earlier");
2180                         }
2181                     }
2182                     _ => {
2183                         // When we find a non-inferable bound, subsequent inferable bounds
2184                         // won't be consecutive from the start (and we'll eat the leading
2185                         // `+` rather than the trailing one)
2186                         from_start = false;
2187                         merged.push(bounds[i - 1].span().shrink_to_hi().to(bound_span));
2188                         last_merged_i = Some(i);
2189                     }
2190                 }
2191             }
2192             merged
2193         }
2194     }
2195 }
2196
2197 impl<'tcx> LateLintPass<'tcx> for ExplicitOutlivesRequirements {
2198     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
2199         use rustc_middle::middle::resolve_lifetime::Region;
2200
2201         let infer_static = cx.tcx.features().infer_static_outlives_requirements;
2202         let def_id = item.def_id;
2203         if let hir::ItemKind::Struct(_, ref hir_generics)
2204         | hir::ItemKind::Enum(_, ref hir_generics)
2205         | hir::ItemKind::Union(_, ref hir_generics) = item.kind
2206         {
2207             let inferred_outlives = cx.tcx.inferred_outlives_of(def_id);
2208             if inferred_outlives.is_empty() {
2209                 return;
2210             }
2211
2212             let ty_generics = cx.tcx.generics_of(def_id);
2213
2214             let mut bound_count = 0;
2215             let mut lint_spans = Vec::new();
2216
2217             for param in hir_generics.params {
2218                 let has_lifetime_bounds = param
2219                     .bounds
2220                     .iter()
2221                     .any(|bound| matches!(bound, hir::GenericBound::Outlives(_)));
2222                 if !has_lifetime_bounds {
2223                     continue;
2224                 }
2225
2226                 let relevant_lifetimes =
2227                     self.collect_outlived_lifetimes(param, cx.tcx, inferred_outlives, ty_generics);
2228                 if relevant_lifetimes.is_empty() {
2229                     continue;
2230                 }
2231
2232                 let bound_spans = self.collect_outlives_bound_spans(
2233                     cx.tcx,
2234                     &param.bounds,
2235                     &relevant_lifetimes,
2236                     infer_static,
2237                 );
2238                 bound_count += bound_spans.len();
2239                 lint_spans.extend(self.consolidate_outlives_bound_spans(
2240                     param.span.shrink_to_hi(),
2241                     &param.bounds,
2242                     bound_spans,
2243                 ));
2244             }
2245
2246             let mut where_lint_spans = Vec::new();
2247             let mut dropped_predicate_count = 0;
2248             let num_predicates = hir_generics.where_clause.predicates.len();
2249             for (i, where_predicate) in hir_generics.where_clause.predicates.iter().enumerate() {
2250                 let (relevant_lifetimes, bounds, span) = match where_predicate {
2251                     hir::WherePredicate::RegionPredicate(predicate) => {
2252                         if let Some(Region::EarlyBound(index, ..)) =
2253                             cx.tcx.named_region(predicate.lifetime.hir_id)
2254                         {
2255                             (
2256                                 Self::lifetimes_outliving_lifetime(inferred_outlives, index),
2257                                 &predicate.bounds,
2258                                 predicate.span,
2259                             )
2260                         } else {
2261                             continue;
2262                         }
2263                     }
2264                     hir::WherePredicate::BoundPredicate(predicate) => {
2265                         // FIXME we can also infer bounds on associated types,
2266                         // and should check for them here.
2267                         match predicate.bounded_ty.kind {
2268                             hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
2269                                 if let Res::Def(DefKind::TyParam, def_id) = path.res {
2270                                     let index = ty_generics.param_def_id_to_index[&def_id];
2271                                     (
2272                                         Self::lifetimes_outliving_type(inferred_outlives, index),
2273                                         &predicate.bounds,
2274                                         predicate.span,
2275                                     )
2276                                 } else {
2277                                     continue;
2278                                 }
2279                             }
2280                             _ => {
2281                                 continue;
2282                             }
2283                         }
2284                     }
2285                     _ => continue,
2286                 };
2287                 if relevant_lifetimes.is_empty() {
2288                     continue;
2289                 }
2290
2291                 let bound_spans = self.collect_outlives_bound_spans(
2292                     cx.tcx,
2293                     bounds,
2294                     &relevant_lifetimes,
2295                     infer_static,
2296                 );
2297                 bound_count += bound_spans.len();
2298
2299                 let drop_predicate = bound_spans.len() == bounds.len();
2300                 if drop_predicate {
2301                     dropped_predicate_count += 1;
2302                 }
2303
2304                 // If all the bounds on a predicate were inferable and there are
2305                 // further predicates, we want to eat the trailing comma.
2306                 if drop_predicate && i + 1 < num_predicates {
2307                     let next_predicate_span = hir_generics.where_clause.predicates[i + 1].span();
2308                     where_lint_spans.push(span.to(next_predicate_span.shrink_to_lo()));
2309                 } else {
2310                     where_lint_spans.extend(self.consolidate_outlives_bound_spans(
2311                         span.shrink_to_lo(),
2312                         bounds,
2313                         bound_spans,
2314                     ));
2315                 }
2316             }
2317
2318             // If all predicates are inferable, drop the entire clause
2319             // (including the `where`)
2320             if num_predicates > 0 && dropped_predicate_count == num_predicates {
2321                 let where_span = hir_generics
2322                     .where_clause
2323                     .span()
2324                     .expect("span of (nonempty) where clause should exist");
2325                 // Extend the where clause back to the closing `>` of the
2326                 // generics, except for tuple struct, which have the `where`
2327                 // after the fields of the struct.
2328                 let full_where_span =
2329                     if let hir::ItemKind::Struct(hir::VariantData::Tuple(..), _) = item.kind {
2330                         where_span
2331                     } else {
2332                         hir_generics.span.shrink_to_hi().to(where_span)
2333                     };
2334                 lint_spans.push(full_where_span);
2335             } else {
2336                 lint_spans.extend(where_lint_spans);
2337             }
2338
2339             if !lint_spans.is_empty() {
2340                 cx.struct_span_lint(EXPLICIT_OUTLIVES_REQUIREMENTS, lint_spans.clone(), |lint| {
2341                     lint.build("outlives requirements can be inferred")
2342                         .multipart_suggestion(
2343                             if bound_count == 1 {
2344                                 "remove this bound"
2345                             } else {
2346                                 "remove these bounds"
2347                             },
2348                             lint_spans
2349                                 .into_iter()
2350                                 .map(|span| (span, "".to_owned()))
2351                                 .collect::<Vec<_>>(),
2352                             Applicability::MachineApplicable,
2353                         )
2354                         .emit();
2355                 });
2356             }
2357         }
2358     }
2359 }
2360
2361 declare_lint! {
2362     /// The `incomplete_features` lint detects unstable features enabled with
2363     /// the [`feature` attribute] that may function improperly in some or all
2364     /// cases.
2365     ///
2366     /// [`feature` attribute]: https://doc.rust-lang.org/nightly/unstable-book/
2367     ///
2368     /// ### Example
2369     ///
2370     /// ```rust
2371     /// #![feature(generic_const_exprs)]
2372     /// ```
2373     ///
2374     /// {{produces}}
2375     ///
2376     /// ### Explanation
2377     ///
2378     /// Although it is encouraged for people to experiment with unstable
2379     /// features, some of them are known to be incomplete or faulty. This lint
2380     /// is a signal that the feature has not yet been finished, and you may
2381     /// experience problems with it.
2382     pub INCOMPLETE_FEATURES,
2383     Warn,
2384     "incomplete features that may function improperly in some or all cases"
2385 }
2386
2387 declare_lint_pass!(
2388     /// Check for used feature gates in `INCOMPLETE_FEATURES` in `rustc_feature/src/active.rs`.
2389     IncompleteFeatures => [INCOMPLETE_FEATURES]
2390 );
2391
2392 impl EarlyLintPass for IncompleteFeatures {
2393     fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
2394         let features = cx.sess.features_untracked();
2395         features
2396             .declared_lang_features
2397             .iter()
2398             .map(|(name, span, _)| (name, span))
2399             .chain(features.declared_lib_features.iter().map(|(name, span)| (name, span)))
2400             .filter(|(&name, _)| features.incomplete(name))
2401             .for_each(|(&name, &span)| {
2402                 cx.struct_span_lint(INCOMPLETE_FEATURES, span, |lint| {
2403                     let mut builder = lint.build(&format!(
2404                         "the feature `{}` is incomplete and may not be safe to use \
2405                          and/or cause compiler crashes",
2406                         name,
2407                     ));
2408                     if let Some(n) = rustc_feature::find_feature_issue(name, GateIssue::Language) {
2409                         builder.note(&format!(
2410                             "see issue #{} <https://github.com/rust-lang/rust/issues/{}> \
2411                              for more information",
2412                             n, n,
2413                         ));
2414                     }
2415                     if HAS_MIN_FEATURES.contains(&name) {
2416                         builder.help(&format!(
2417                             "consider using `min_{}` instead, which is more stable and complete",
2418                             name,
2419                         ));
2420                     }
2421                     builder.emit();
2422                 })
2423             });
2424     }
2425 }
2426
2427 const HAS_MIN_FEATURES: &[Symbol] = &[sym::specialization];
2428
2429 declare_lint! {
2430     /// The `invalid_value` lint detects creating a value that is not valid,
2431     /// such as a null reference.
2432     ///
2433     /// ### Example
2434     ///
2435     /// ```rust,no_run
2436     /// # #![allow(unused)]
2437     /// unsafe {
2438     ///     let x: &'static i32 = std::mem::zeroed();
2439     /// }
2440     /// ```
2441     ///
2442     /// {{produces}}
2443     ///
2444     /// ### Explanation
2445     ///
2446     /// In some situations the compiler can detect that the code is creating
2447     /// an invalid value, which should be avoided.
2448     ///
2449     /// In particular, this lint will check for improper use of
2450     /// [`mem::zeroed`], [`mem::uninitialized`], [`mem::transmute`], and
2451     /// [`MaybeUninit::assume_init`] that can cause [undefined behavior]. The
2452     /// lint should provide extra information to indicate what the problem is
2453     /// and a possible solution.
2454     ///
2455     /// [`mem::zeroed`]: https://doc.rust-lang.org/std/mem/fn.zeroed.html
2456     /// [`mem::uninitialized`]: https://doc.rust-lang.org/std/mem/fn.uninitialized.html
2457     /// [`mem::transmute`]: https://doc.rust-lang.org/std/mem/fn.transmute.html
2458     /// [`MaybeUninit::assume_init`]: https://doc.rust-lang.org/std/mem/union.MaybeUninit.html#method.assume_init
2459     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
2460     pub INVALID_VALUE,
2461     Warn,
2462     "an invalid value is being created (such as a null reference)"
2463 }
2464
2465 declare_lint_pass!(InvalidValue => [INVALID_VALUE]);
2466
2467 impl<'tcx> LateLintPass<'tcx> for InvalidValue {
2468     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
2469         #[derive(Debug, Copy, Clone, PartialEq)]
2470         enum InitKind {
2471             Zeroed,
2472             Uninit,
2473         }
2474
2475         /// Information about why a type cannot be initialized this way.
2476         /// Contains an error message and optionally a span to point at.
2477         type InitError = (String, Option<Span>);
2478
2479         /// Test if this constant is all-0.
2480         fn is_zero(expr: &hir::Expr<'_>) -> bool {
2481             use hir::ExprKind::*;
2482             use rustc_ast::LitKind::*;
2483             match &expr.kind {
2484                 Lit(lit) => {
2485                     if let Int(i, _) = lit.node {
2486                         i == 0
2487                     } else {
2488                         false
2489                     }
2490                 }
2491                 Tup(tup) => tup.iter().all(is_zero),
2492                 _ => false,
2493             }
2494         }
2495
2496         /// Determine if this expression is a "dangerous initialization".
2497         fn is_dangerous_init(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> Option<InitKind> {
2498             if let hir::ExprKind::Call(ref path_expr, ref args) = expr.kind {
2499                 // Find calls to `mem::{uninitialized,zeroed}` methods.
2500                 if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2501                     let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2502                     match cx.tcx.get_diagnostic_name(def_id) {
2503                         Some(sym::mem_zeroed) => return Some(InitKind::Zeroed),
2504                         Some(sym::mem_uninitialized) => return Some(InitKind::Uninit),
2505                         Some(sym::transmute) if is_zero(&args[0]) => return Some(InitKind::Zeroed),
2506                         _ => {}
2507                     }
2508                 }
2509             } else if let hir::ExprKind::MethodCall(_, _, ref args, _) = expr.kind {
2510                 // Find problematic calls to `MaybeUninit::assume_init`.
2511                 let def_id = cx.typeck_results().type_dependent_def_id(expr.hir_id)?;
2512                 if cx.tcx.is_diagnostic_item(sym::assume_init, def_id) {
2513                     // This is a call to *some* method named `assume_init`.
2514                     // See if the `self` parameter is one of the dangerous constructors.
2515                     if let hir::ExprKind::Call(ref path_expr, _) = args[0].kind {
2516                         if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
2517                             let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
2518                             match cx.tcx.get_diagnostic_name(def_id) {
2519                                 Some(sym::maybe_uninit_zeroed) => return Some(InitKind::Zeroed),
2520                                 Some(sym::maybe_uninit_uninit) => return Some(InitKind::Uninit),
2521                                 _ => {}
2522                             }
2523                         }
2524                     }
2525                 }
2526             }
2527
2528             None
2529         }
2530
2531         /// Test if this enum has several actually "existing" variants.
2532         /// Zero-sized uninhabited variants do not always have a tag assigned and thus do not "exist".
2533         fn is_multi_variant(adt: &ty::AdtDef) -> bool {
2534             // As an approximation, we only count dataless variants. Those are definitely inhabited.
2535             let existing_variants = adt.variants.iter().filter(|v| v.fields.is_empty()).count();
2536             existing_variants > 1
2537         }
2538
2539         /// Return `Some` only if we are sure this type does *not*
2540         /// allow zero initialization.
2541         fn ty_find_init_error<'tcx>(
2542             tcx: TyCtxt<'tcx>,
2543             ty: Ty<'tcx>,
2544             init: InitKind,
2545         ) -> Option<InitError> {
2546             use rustc_middle::ty::TyKind::*;
2547             match ty.kind() {
2548                 // Primitive types that don't like 0 as a value.
2549                 Ref(..) => Some(("references must be non-null".to_string(), None)),
2550                 Adt(..) if ty.is_box() => Some(("`Box` must be non-null".to_string(), None)),
2551                 FnPtr(..) => Some(("function pointers must be non-null".to_string(), None)),
2552                 Never => Some(("the `!` type has no valid value".to_string(), None)),
2553                 RawPtr(tm) if matches!(tm.ty.kind(), Dynamic(..)) =>
2554                 // raw ptr to dyn Trait
2555                 {
2556                     Some(("the vtable of a wide raw pointer must be non-null".to_string(), None))
2557                 }
2558                 // Primitive types with other constraints.
2559                 Bool if init == InitKind::Uninit => {
2560                     Some(("booleans must be either `true` or `false`".to_string(), None))
2561                 }
2562                 Char if init == InitKind::Uninit => {
2563                     Some(("characters must be a valid Unicode codepoint".to_string(), None))
2564                 }
2565                 // Recurse and checks for some compound types.
2566                 Adt(adt_def, substs) if !adt_def.is_union() => {
2567                     // First check if this ADT has a layout attribute (like `NonNull` and friends).
2568                     use std::ops::Bound;
2569                     match tcx.layout_scalar_valid_range(adt_def.did) {
2570                         // We exploit here that `layout_scalar_valid_range` will never
2571                         // return `Bound::Excluded`.  (And we have tests checking that we
2572                         // handle the attribute correctly.)
2573                         (Bound::Included(lo), _) if lo > 0 => {
2574                             return Some((format!("`{}` must be non-null", ty), None));
2575                         }
2576                         (Bound::Included(_), _) | (_, Bound::Included(_))
2577                             if init == InitKind::Uninit =>
2578                         {
2579                             return Some((
2580                                 format!(
2581                                     "`{}` must be initialized inside its custom valid range",
2582                                     ty,
2583                                 ),
2584                                 None,
2585                             ));
2586                         }
2587                         _ => {}
2588                     }
2589                     // Now, recurse.
2590                     match adt_def.variants.len() {
2591                         0 => Some(("enums with no variants have no valid value".to_string(), None)),
2592                         1 => {
2593                             // Struct, or enum with exactly one variant.
2594                             // Proceed recursively, check all fields.
2595                             let variant = &adt_def.variants[VariantIdx::from_u32(0)];
2596                             variant.fields.iter().find_map(|field| {
2597                                 ty_find_init_error(tcx, field.ty(tcx, substs), init).map(
2598                                     |(mut msg, span)| {
2599                                         if span.is_none() {
2600                                             // Point to this field, should be helpful for figuring
2601                                             // out where the source of the error is.
2602                                             let span = tcx.def_span(field.did);
2603                                             write!(
2604                                                 &mut msg,
2605                                                 " (in this {} field)",
2606                                                 adt_def.descr()
2607                                             )
2608                                             .unwrap();
2609                                             (msg, Some(span))
2610                                         } else {
2611                                             // Just forward.
2612                                             (msg, span)
2613                                         }
2614                                     },
2615                                 )
2616                             })
2617                         }
2618                         // Multi-variant enum.
2619                         _ => {
2620                             if init == InitKind::Uninit && is_multi_variant(adt_def) {
2621                                 let span = tcx.def_span(adt_def.did);
2622                                 Some((
2623                                     "enums have to be initialized to a variant".to_string(),
2624                                     Some(span),
2625                                 ))
2626                             } else {
2627                                 // In principle, for zero-initialization we could figure out which variant corresponds
2628                                 // to tag 0, and check that... but for now we just accept all zero-initializations.
2629                                 None
2630                             }
2631                         }
2632                     }
2633                 }
2634                 Tuple(..) => {
2635                     // Proceed recursively, check all fields.
2636                     ty.tuple_fields().find_map(|field| ty_find_init_error(tcx, field, init))
2637                 }
2638                 // Conservative fallback.
2639                 _ => None,
2640             }
2641         }
2642
2643         if let Some(init) = is_dangerous_init(cx, expr) {
2644             // This conjures an instance of a type out of nothing,
2645             // using zeroed or uninitialized memory.
2646             // We are extremely conservative with what we warn about.
2647             let conjured_ty = cx.typeck_results().expr_ty(expr);
2648             if let Some((msg, span)) =
2649                 with_no_trimmed_paths(|| ty_find_init_error(cx.tcx, conjured_ty, init))
2650             {
2651                 cx.struct_span_lint(INVALID_VALUE, expr.span, |lint| {
2652                     let mut err = lint.build(&format!(
2653                         "the type `{}` does not permit {}",
2654                         conjured_ty,
2655                         match init {
2656                             InitKind::Zeroed => "zero-initialization",
2657                             InitKind::Uninit => "being left uninitialized",
2658                         },
2659                     ));
2660                     err.span_label(expr.span, "this code causes undefined behavior when executed");
2661                     err.span_label(
2662                         expr.span,
2663                         "help: use `MaybeUninit<T>` instead, \
2664                             and only call `assume_init` after initialization is done",
2665                     );
2666                     if let Some(span) = span {
2667                         err.span_note(span, &msg);
2668                     } else {
2669                         err.note(&msg);
2670                     }
2671                     err.emit();
2672                 });
2673             }
2674         }
2675     }
2676 }
2677
2678 declare_lint! {
2679     /// The `clashing_extern_declarations` lint detects when an `extern fn`
2680     /// has been declared with the same name but different types.
2681     ///
2682     /// ### Example
2683     ///
2684     /// ```rust
2685     /// mod m {
2686     ///     extern "C" {
2687     ///         fn foo();
2688     ///     }
2689     /// }
2690     ///
2691     /// extern "C" {
2692     ///     fn foo(_: u32);
2693     /// }
2694     /// ```
2695     ///
2696     /// {{produces}}
2697     ///
2698     /// ### Explanation
2699     ///
2700     /// Because two symbols of the same name cannot be resolved to two
2701     /// different functions at link time, and one function cannot possibly
2702     /// have two types, a clashing extern declaration is almost certainly a
2703     /// mistake. Check to make sure that the `extern` definitions are correct
2704     /// and equivalent, and possibly consider unifying them in one location.
2705     ///
2706     /// This lint does not run between crates because a project may have
2707     /// dependencies which both rely on the same extern function, but declare
2708     /// it in a different (but valid) way. For example, they may both declare
2709     /// an opaque type for one or more of the arguments (which would end up
2710     /// distinct types), or use types that are valid conversions in the
2711     /// language the `extern fn` is defined in. In these cases, the compiler
2712     /// can't say that the clashing declaration is incorrect.
2713     pub CLASHING_EXTERN_DECLARATIONS,
2714     Warn,
2715     "detects when an extern fn has been declared with the same name but different types"
2716 }
2717
2718 pub struct ClashingExternDeclarations {
2719     /// Map of function symbol name to the first-seen hir id for that symbol name.. If seen_decls
2720     /// contains an entry for key K, it means a symbol with name K has been seen by this lint and
2721     /// the symbol should be reported as a clashing declaration.
2722     // FIXME: Technically, we could just store a &'tcx str here without issue; however, the
2723     // `impl_lint_pass` macro doesn't currently support lints parametric over a lifetime.
2724     seen_decls: FxHashMap<Symbol, HirId>,
2725 }
2726
2727 /// Differentiate between whether the name for an extern decl came from the link_name attribute or
2728 /// just from declaration itself. This is important because we don't want to report clashes on
2729 /// symbol name if they don't actually clash because one or the other links against a symbol with a
2730 /// different name.
2731 enum SymbolName {
2732     /// The name of the symbol + the span of the annotation which introduced the link name.
2733     Link(Symbol, Span),
2734     /// No link name, so just the name of the symbol.
2735     Normal(Symbol),
2736 }
2737
2738 impl SymbolName {
2739     fn get_name(&self) -> Symbol {
2740         match self {
2741             SymbolName::Link(s, _) | SymbolName::Normal(s) => *s,
2742         }
2743     }
2744 }
2745
2746 impl ClashingExternDeclarations {
2747     crate fn new() -> Self {
2748         ClashingExternDeclarations { seen_decls: FxHashMap::default() }
2749     }
2750     /// Insert a new foreign item into the seen set. If a symbol with the same name already exists
2751     /// for the item, return its HirId without updating the set.
2752     fn insert(&mut self, tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> Option<HirId> {
2753         let did = fi.def_id.to_def_id();
2754         let instance = Instance::new(did, ty::List::identity_for_item(tcx, did));
2755         let name = Symbol::intern(tcx.symbol_name(instance).name);
2756         if let Some(&hir_id) = self.seen_decls.get(&name) {
2757             // Avoid updating the map with the new entry when we do find a collision. We want to
2758             // make sure we're always pointing to the first definition as the previous declaration.
2759             // This lets us avoid emitting "knock-on" diagnostics.
2760             Some(hir_id)
2761         } else {
2762             self.seen_decls.insert(name, fi.hir_id())
2763         }
2764     }
2765
2766     /// Get the name of the symbol that's linked against for a given extern declaration. That is,
2767     /// the name specified in a #[link_name = ...] attribute if one was specified, else, just the
2768     /// symbol's name.
2769     fn name_of_extern_decl(tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> SymbolName {
2770         if let Some((overridden_link_name, overridden_link_name_span)) =
2771             tcx.codegen_fn_attrs(fi.def_id).link_name.map(|overridden_link_name| {
2772                 // FIXME: Instead of searching through the attributes again to get span
2773                 // information, we could have codegen_fn_attrs also give span information back for
2774                 // where the attribute was defined. However, until this is found to be a
2775                 // bottleneck, this does just fine.
2776                 (
2777                     overridden_link_name,
2778                     tcx.get_attrs(fi.def_id.to_def_id())
2779                         .iter()
2780                         .find(|at| at.has_name(sym::link_name))
2781                         .unwrap()
2782                         .span,
2783                 )
2784             })
2785         {
2786             SymbolName::Link(overridden_link_name, overridden_link_name_span)
2787         } else {
2788             SymbolName::Normal(fi.ident.name)
2789         }
2790     }
2791
2792     /// Checks whether two types are structurally the same enough that the declarations shouldn't
2793     /// clash. We need this so we don't emit a lint when two modules both declare an extern struct,
2794     /// with the same members (as the declarations shouldn't clash).
2795     fn structurally_same_type<'tcx>(
2796         cx: &LateContext<'tcx>,
2797         a: Ty<'tcx>,
2798         b: Ty<'tcx>,
2799         ckind: CItemKind,
2800     ) -> bool {
2801         fn structurally_same_type_impl<'tcx>(
2802             seen_types: &mut FxHashSet<(Ty<'tcx>, Ty<'tcx>)>,
2803             cx: &LateContext<'tcx>,
2804             a: Ty<'tcx>,
2805             b: Ty<'tcx>,
2806             ckind: CItemKind,
2807         ) -> bool {
2808             debug!("structurally_same_type_impl(cx, a = {:?}, b = {:?})", a, b);
2809             let tcx = cx.tcx;
2810
2811             // Given a transparent newtype, reach through and grab the inner
2812             // type unless the newtype makes the type non-null.
2813             let non_transparent_ty = |ty: Ty<'tcx>| -> Ty<'tcx> {
2814                 let mut ty = ty;
2815                 loop {
2816                     if let ty::Adt(def, substs) = *ty.kind() {
2817                         let is_transparent = def.subst(tcx, substs).repr.transparent();
2818                         let is_non_null = crate::types::nonnull_optimization_guaranteed(tcx, &def);
2819                         debug!(
2820                             "non_transparent_ty({:?}) -- type is transparent? {}, type is non-null? {}",
2821                             ty, is_transparent, is_non_null
2822                         );
2823                         if is_transparent && !is_non_null {
2824                             debug_assert!(def.variants.len() == 1);
2825                             let v = &def.variants[VariantIdx::new(0)];
2826                             ty = transparent_newtype_field(tcx, v)
2827                                 .expect(
2828                                     "single-variant transparent structure with zero-sized field",
2829                                 )
2830                                 .ty(tcx, substs);
2831                             continue;
2832                         }
2833                     }
2834                     debug!("non_transparent_ty -> {:?}", ty);
2835                     return ty;
2836                 }
2837             };
2838
2839             let a = non_transparent_ty(a);
2840             let b = non_transparent_ty(b);
2841
2842             if !seen_types.insert((a, b)) {
2843                 // We've encountered a cycle. There's no point going any further -- the types are
2844                 // structurally the same.
2845                 return true;
2846             }
2847             let tcx = cx.tcx;
2848             if a == b || rustc_middle::ty::TyS::same_type(a, b) {
2849                 // All nominally-same types are structurally same, too.
2850                 true
2851             } else {
2852                 // Do a full, depth-first comparison between the two.
2853                 use rustc_middle::ty::TyKind::*;
2854                 let a_kind = a.kind();
2855                 let b_kind = b.kind();
2856
2857                 let compare_layouts = |a, b| -> Result<bool, LayoutError<'tcx>> {
2858                     debug!("compare_layouts({:?}, {:?})", a, b);
2859                     let a_layout = &cx.layout_of(a)?.layout.abi;
2860                     let b_layout = &cx.layout_of(b)?.layout.abi;
2861                     debug!(
2862                         "comparing layouts: {:?} == {:?} = {}",
2863                         a_layout,
2864                         b_layout,
2865                         a_layout == b_layout
2866                     );
2867                     Ok(a_layout == b_layout)
2868                 };
2869
2870                 #[allow(rustc::usage_of_ty_tykind)]
2871                 let is_primitive_or_pointer = |kind: &ty::TyKind<'_>| {
2872                     kind.is_primitive() || matches!(kind, RawPtr(..) | Ref(..))
2873                 };
2874
2875                 ensure_sufficient_stack(|| {
2876                     match (a_kind, b_kind) {
2877                         (Adt(a_def, a_substs), Adt(b_def, b_substs)) => {
2878                             let a = a.subst(cx.tcx, a_substs);
2879                             let b = b.subst(cx.tcx, b_substs);
2880                             debug!("Comparing {:?} and {:?}", a, b);
2881
2882                             // We can immediately rule out these types as structurally same if
2883                             // their layouts differ.
2884                             match compare_layouts(a, b) {
2885                                 Ok(false) => return false,
2886                                 _ => (), // otherwise, continue onto the full, fields comparison
2887                             }
2888
2889                             // Grab a flattened representation of all fields.
2890                             let a_fields = a_def.variants.iter().flat_map(|v| v.fields.iter());
2891                             let b_fields = b_def.variants.iter().flat_map(|v| v.fields.iter());
2892
2893                             // Perform a structural comparison for each field.
2894                             a_fields.eq_by(
2895                                 b_fields,
2896                                 |&ty::FieldDef { did: a_did, .. },
2897                                  &ty::FieldDef { did: b_did, .. }| {
2898                                     structurally_same_type_impl(
2899                                         seen_types,
2900                                         cx,
2901                                         tcx.type_of(a_did),
2902                                         tcx.type_of(b_did),
2903                                         ckind,
2904                                     )
2905                                 },
2906                             )
2907                         }
2908                         (Array(a_ty, a_const), Array(b_ty, b_const)) => {
2909                             // For arrays, we also check the constness of the type.
2910                             a_const.val == b_const.val
2911                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2912                         }
2913                         (Slice(a_ty), Slice(b_ty)) => {
2914                             structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2915                         }
2916                         (RawPtr(a_tymut), RawPtr(b_tymut)) => {
2917                             a_tymut.mutbl == b_tymut.mutbl
2918                                 && structurally_same_type_impl(
2919                                     seen_types,
2920                                     cx,
2921                                     &a_tymut.ty,
2922                                     &b_tymut.ty,
2923                                     ckind,
2924                                 )
2925                         }
2926                         (Ref(_a_region, a_ty, a_mut), Ref(_b_region, b_ty, b_mut)) => {
2927                             // For structural sameness, we don't need the region to be same.
2928                             a_mut == b_mut
2929                                 && structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2930                         }
2931                         (FnDef(..), FnDef(..)) => {
2932                             let a_poly_sig = a.fn_sig(tcx);
2933                             let b_poly_sig = b.fn_sig(tcx);
2934
2935                             // As we don't compare regions, skip_binder is fine.
2936                             let a_sig = a_poly_sig.skip_binder();
2937                             let b_sig = b_poly_sig.skip_binder();
2938
2939                             (a_sig.abi, a_sig.unsafety, a_sig.c_variadic)
2940                                 == (b_sig.abi, b_sig.unsafety, b_sig.c_variadic)
2941                                 && a_sig.inputs().iter().eq_by(b_sig.inputs().iter(), |a, b| {
2942                                     structurally_same_type_impl(seen_types, cx, a, b, ckind)
2943                                 })
2944                                 && structurally_same_type_impl(
2945                                     seen_types,
2946                                     cx,
2947                                     a_sig.output(),
2948                                     b_sig.output(),
2949                                     ckind,
2950                                 )
2951                         }
2952                         (Tuple(a_substs), Tuple(b_substs)) => {
2953                             a_substs.types().eq_by(b_substs.types(), |a_ty, b_ty| {
2954                                 structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
2955                             })
2956                         }
2957                         // For these, it's not quite as easy to define structural-sameness quite so easily.
2958                         // For the purposes of this lint, take the conservative approach and mark them as
2959                         // not structurally same.
2960                         (Dynamic(..), Dynamic(..))
2961                         | (Error(..), Error(..))
2962                         | (Closure(..), Closure(..))
2963                         | (Generator(..), Generator(..))
2964                         | (GeneratorWitness(..), GeneratorWitness(..))
2965                         | (Projection(..), Projection(..))
2966                         | (Opaque(..), Opaque(..)) => false,
2967
2968                         // These definitely should have been caught above.
2969                         (Bool, Bool) | (Char, Char) | (Never, Never) | (Str, Str) => unreachable!(),
2970
2971                         // An Adt and a primitive or pointer type. This can be FFI-safe if non-null
2972                         // enum layout optimisation is being applied.
2973                         (Adt(..), other_kind) | (other_kind, Adt(..))
2974                             if is_primitive_or_pointer(other_kind) =>
2975                         {
2976                             let (primitive, adt) =
2977                                 if is_primitive_or_pointer(a.kind()) { (a, b) } else { (b, a) };
2978                             if let Some(ty) = crate::types::repr_nullable_ptr(cx, adt, ckind) {
2979                                 ty == primitive
2980                             } else {
2981                                 compare_layouts(a, b).unwrap_or(false)
2982                             }
2983                         }
2984                         // Otherwise, just compare the layouts. This may fail to lint for some
2985                         // incompatible types, but at the very least, will stop reads into
2986                         // uninitialised memory.
2987                         _ => compare_layouts(a, b).unwrap_or(false),
2988                     }
2989                 })
2990             }
2991         }
2992         let mut seen_types = FxHashSet::default();
2993         structurally_same_type_impl(&mut seen_types, cx, a, b, ckind)
2994     }
2995 }
2996
2997 impl_lint_pass!(ClashingExternDeclarations => [CLASHING_EXTERN_DECLARATIONS]);
2998
2999 impl<'tcx> LateLintPass<'tcx> for ClashingExternDeclarations {
3000     fn check_foreign_item(&mut self, cx: &LateContext<'tcx>, this_fi: &hir::ForeignItem<'_>) {
3001         trace!("ClashingExternDeclarations: check_foreign_item: {:?}", this_fi);
3002         if let ForeignItemKind::Fn(..) = this_fi.kind {
3003             let tcx = cx.tcx;
3004             if let Some(existing_hid) = self.insert(tcx, this_fi) {
3005                 let existing_decl_ty = tcx.type_of(tcx.hir().local_def_id(existing_hid));
3006                 let this_decl_ty = tcx.type_of(this_fi.def_id);
3007                 debug!(
3008                     "ClashingExternDeclarations: Comparing existing {:?}: {:?} to this {:?}: {:?}",
3009                     existing_hid, existing_decl_ty, this_fi.def_id, this_decl_ty
3010                 );
3011                 // Check that the declarations match.
3012                 if !Self::structurally_same_type(
3013                     cx,
3014                     existing_decl_ty,
3015                     this_decl_ty,
3016                     CItemKind::Declaration,
3017                 ) {
3018                     let orig_fi = tcx.hir().expect_foreign_item(existing_hid.expect_owner());
3019                     let orig = Self::name_of_extern_decl(tcx, orig_fi);
3020
3021                     // We want to ensure that we use spans for both decls that include where the
3022                     // name was defined, whether that was from the link_name attribute or not.
3023                     let get_relevant_span =
3024                         |fi: &hir::ForeignItem<'_>| match Self::name_of_extern_decl(tcx, fi) {
3025                             SymbolName::Normal(_) => fi.span,
3026                             SymbolName::Link(_, annot_span) => fi.span.to(annot_span),
3027                         };
3028                     // Finally, emit the diagnostic.
3029                     tcx.struct_span_lint_hir(
3030                         CLASHING_EXTERN_DECLARATIONS,
3031                         this_fi.hir_id(),
3032                         get_relevant_span(this_fi),
3033                         |lint| {
3034                             let mut expected_str = DiagnosticStyledString::new();
3035                             expected_str.push(existing_decl_ty.fn_sig(tcx).to_string(), false);
3036                             let mut found_str = DiagnosticStyledString::new();
3037                             found_str.push(this_decl_ty.fn_sig(tcx).to_string(), true);
3038
3039                             lint.build(&format!(
3040                                 "`{}` redeclare{} with a different signature",
3041                                 this_fi.ident.name,
3042                                 if orig.get_name() == this_fi.ident.name {
3043                                     "d".to_string()
3044                                 } else {
3045                                     format!("s `{}`", orig.get_name())
3046                                 }
3047                             ))
3048                             .span_label(
3049                                 get_relevant_span(orig_fi),
3050                                 &format!("`{}` previously declared here", orig.get_name()),
3051                             )
3052                             .span_label(
3053                                 get_relevant_span(this_fi),
3054                                 "this signature doesn't match the previous declaration",
3055                             )
3056                             .note_expected_found(&"", expected_str, &"", found_str)
3057                             .emit()
3058                         },
3059                     );
3060                 }
3061             }
3062         }
3063     }
3064 }
3065
3066 declare_lint! {
3067     /// The `deref_nullptr` lint detects when an null pointer is dereferenced,
3068     /// which causes [undefined behavior].
3069     ///
3070     /// ### Example
3071     ///
3072     /// ```rust,no_run
3073     /// # #![allow(unused)]
3074     /// use std::ptr;
3075     /// unsafe {
3076     ///     let x = &*ptr::null::<i32>();
3077     ///     let x = ptr::addr_of!(*ptr::null::<i32>());
3078     ///     let x = *(0 as *const i32);
3079     /// }
3080     /// ```
3081     ///
3082     /// {{produces}}
3083     ///
3084     /// ### Explanation
3085     ///
3086     /// Dereferencing a null pointer causes [undefined behavior] even as a place expression,
3087     /// like `&*(0 as *const i32)` or `addr_of!(*(0 as *const i32))`.
3088     ///
3089     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
3090     pub DEREF_NULLPTR,
3091     Warn,
3092     "detects when an null pointer is dereferenced"
3093 }
3094
3095 declare_lint_pass!(DerefNullPtr => [DEREF_NULLPTR]);
3096
3097 impl<'tcx> LateLintPass<'tcx> for DerefNullPtr {
3098     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
3099         /// test if expression is a null ptr
3100         fn is_null_ptr(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> bool {
3101             match &expr.kind {
3102                 rustc_hir::ExprKind::Cast(ref expr, ref ty) => {
3103                     if let rustc_hir::TyKind::Ptr(_) = ty.kind {
3104                         return is_zero(expr) || is_null_ptr(cx, expr);
3105                     }
3106                 }
3107                 // check for call to `core::ptr::null` or `core::ptr::null_mut`
3108                 rustc_hir::ExprKind::Call(ref path, _) => {
3109                     if let rustc_hir::ExprKind::Path(ref qpath) = path.kind {
3110                         if let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id() {
3111                             return matches!(
3112                                 cx.tcx.get_diagnostic_name(def_id),
3113                                 Some(sym::ptr_null | sym::ptr_null_mut)
3114                             );
3115                         }
3116                     }
3117                 }
3118                 _ => {}
3119             }
3120             false
3121         }
3122
3123         /// test if expression is the literal `0`
3124         fn is_zero(expr: &hir::Expr<'_>) -> bool {
3125             match &expr.kind {
3126                 rustc_hir::ExprKind::Lit(ref lit) => {
3127                     if let LitKind::Int(a, _) = lit.node {
3128                         return a == 0;
3129                     }
3130                 }
3131                 _ => {}
3132             }
3133             false
3134         }
3135
3136         if let rustc_hir::ExprKind::Unary(rustc_hir::UnOp::Deref, expr_deref) = expr.kind {
3137             if is_null_ptr(cx, expr_deref) {
3138                 cx.struct_span_lint(DEREF_NULLPTR, expr.span, |lint| {
3139                     let mut err = lint.build("dereferencing a null pointer");
3140                     err.span_label(expr.span, "this code causes undefined behavior when executed");
3141                     err.emit();
3142                 });
3143             }
3144         }
3145     }
3146 }
3147
3148 declare_lint! {
3149     /// The `named_asm_labels` lint detects the use of named labels in the
3150     /// inline `asm!` macro.
3151     ///
3152     /// ### Example
3153     ///
3154     /// ```rust,compile_fail
3155     /// #![feature(asm)]
3156     /// fn main() {
3157     ///     unsafe {
3158     ///         asm!("foo: bar");
3159     ///     }
3160     /// }
3161     /// ```
3162     ///
3163     /// {{produces}}
3164     ///
3165     /// ### Explanation
3166     ///
3167     /// LLVM is allowed to duplicate inline assembly blocks for any
3168     /// reason, for example when it is in a function that gets inlined. Because
3169     /// of this, GNU assembler [local labels] *must* be used instead of labels
3170     /// with a name. Using named labels might cause assembler or linker errors.
3171     ///
3172     /// See the [unstable book] for more details.
3173     ///
3174     /// [local labels]: https://sourceware.org/binutils/docs/as/Symbol-Names.html#Local-Labels
3175     /// [unstable book]: https://doc.rust-lang.org/nightly/unstable-book/library-features/asm.html#labels
3176     pub NAMED_ASM_LABELS,
3177     Deny,
3178     "named labels in inline assembly",
3179 }
3180
3181 declare_lint_pass!(NamedAsmLabels => [NAMED_ASM_LABELS]);
3182
3183 impl<'tcx> LateLintPass<'tcx> for NamedAsmLabels {
3184     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
3185         if let hir::Expr {
3186             kind: hir::ExprKind::InlineAsm(hir::InlineAsm { template_strs, .. }),
3187             ..
3188         } = expr
3189         {
3190             for (template_sym, template_snippet, template_span) in template_strs.iter() {
3191                 let template_str = &template_sym.as_str();
3192                 let find_label_span = |needle: &str| -> Option<Span> {
3193                     if let Some(template_snippet) = template_snippet {
3194                         let snippet = template_snippet.as_str();
3195                         if let Some(pos) = snippet.find(needle) {
3196                             let end = pos
3197                                 + snippet[pos..]
3198                                     .find(|c| c == ':')
3199                                     .unwrap_or(snippet[pos..].len() - 1);
3200                             let inner = InnerSpan::new(pos, end);
3201                             return Some(template_span.from_inner(inner));
3202                         }
3203                     }
3204
3205                     None
3206                 };
3207
3208                 let mut found_labels = Vec::new();
3209
3210                 // A semicolon might not actually be specified as a separator for all targets, but it seems like LLVM accepts it always
3211                 let statements = template_str.split(|c| matches!(c, '\n' | ';'));
3212                 for statement in statements {
3213                     // If there's a comment, trim it from the statement
3214                     let statement = statement.find("//").map_or(statement, |idx| &statement[..idx]);
3215                     let mut start_idx = 0;
3216                     for (idx, _) in statement.match_indices(':') {
3217                         let possible_label = statement[start_idx..idx].trim();
3218                         let mut chars = possible_label.chars();
3219                         if let Some(c) = chars.next() {
3220                             // A label starts with an alphabetic character or . or _ and continues with alphanumeric characters, _, or $
3221                             if (c.is_alphabetic() || matches!(c, '.' | '_'))
3222                                 && chars.all(|c| c.is_alphanumeric() || matches!(c, '_' | '$'))
3223                             {
3224                                 found_labels.push(possible_label);
3225                             } else {
3226                                 // If we encounter a non-label, there cannot be any further labels, so stop checking
3227                                 break;
3228                             }
3229                         } else {
3230                             // Empty string means a leading ':' in this section, which is not a label
3231                             break;
3232                         }
3233
3234                         start_idx = idx + 1;
3235                     }
3236                 }
3237
3238                 debug!("NamedAsmLabels::check_expr(): found_labels: {:#?}", &found_labels);
3239
3240                 if found_labels.len() > 0 {
3241                     let spans = found_labels
3242                         .into_iter()
3243                         .filter_map(|label| find_label_span(label))
3244                         .collect::<Vec<Span>>();
3245                     // If there were labels but we couldn't find a span, combine the warnings and use the template span
3246                     let target_spans: MultiSpan =
3247                         if spans.len() > 0 { spans.into() } else { (*template_span).into() };
3248
3249                     cx.lookup_with_diagnostics(
3250                             NAMED_ASM_LABELS,
3251                             Some(target_spans),
3252                             |diag| {
3253                                 let mut err =
3254                                     diag.build("avoid using named labels in inline assembly");
3255                                 err.emit();
3256                             },
3257                             BuiltinLintDiagnostics::NamedAsmLabel(
3258                                 "only local labels of the form `<number>:` should be used in inline asm"
3259                                     .to_string(),
3260                             ),
3261                         );
3262                 }
3263             }
3264         }
3265     }
3266 }