src/librustc_ast_passes/ast_validation.rs

   1 // Validate AST before lowering it to HIR.
   2 //
   3 // This pass is supposed to catch things that fit into AST data structures,
   4 // but not permitted by the language. It runs after expansion when AST is frozen,
   5 // so it can check for erroneous constructions produced by syntax extensions.
   6 // This pass is supposed to perform only simple checks not requiring name resolution
   7 // or type checking or some other kind of complex analysis.
   8
   9 use itertools::{Either, Itertools};
  10 use rustc_ast::ptr::P;
  11 use rustc_ast::visit::{self, AssocCtxt, FnCtxt, FnKind, Visitor};
  12 use rustc_ast::walk_list;
  13 use rustc_ast::*;
  14 use rustc_ast_pretty::pprust;
  15 use rustc_data_structures::fx::FxHashMap;
  16 use rustc_errors::{error_code, pluralize, struct_span_err, Applicability};
  17 use rustc_parse::validate_attr;
  18 use rustc_session::lint::builtin::PATTERNS_IN_FNS_WITHOUT_BODY;
  19 use rustc_session::lint::LintBuffer;
  20 use rustc_session::Session;
  21 use rustc_span::symbol::{kw, sym, Ident};
  22 use rustc_span::Span;
  23 use std::mem;
  24 use std::ops::DerefMut;
  25
  26 const MORE_EXTERN: &str =
  27     "for more information, visit https://doc.rust-lang.org/std/keyword.extern.html";
  28
  29 /// Is `self` allowed semantically as the first parameter in an `FnDecl`?
  30 enum SelfSemantic {
  31     Yes,
  32     No,
  33 }
  34
  35 /// A syntactic context that disallows certain kinds of bounds (e.g., `?Trait` or `?const Trait`).
  36 #[derive(Clone, Copy)]
  37 enum BoundContext {
  38     ImplTrait,
  39     TraitBounds,
  40     TraitObject,
  41 }
  42
  43 impl BoundContext {
  44     fn description(&self) -> &'static str {
  45         match self {
  46             Self::ImplTrait => "`impl Trait`",
  47             Self::TraitBounds => "supertraits",
  48             Self::TraitObject => "trait objects",
  49         }
  50     }
  51 }
  52
  53 struct AstValidator<'a> {
  54     session: &'a Session,
  55
  56     /// The span of the `extern` in an `extern { ... }` block, if any.
  57     extern_mod: Option<&'a Item>,
  58
  59     /// Are we inside a trait impl?
  60     in_trait_impl: bool,
  61
  62     has_proc_macro_decls: bool,
  63
  64     /// Used to ban nested `impl Trait`, e.g., `impl Into<impl Debug>`.
  65     /// Nested `impl Trait` _is_ allowed in associated type position,
  66     /// e.g., `impl Iterator<Item = impl Debug>`.
  67     outer_impl_trait: Option<Span>,
  68
  69     /// Keeps track of the `BoundContext` as we recurse.
  70     ///
  71     /// This is used to forbid `?const Trait` bounds in, e.g.,
  72     /// `impl Iterator<Item = Box<dyn ?const Trait>`.
  73     bound_context: Option<BoundContext>,
  74
  75     /// Used to ban `impl Trait` in path projections like `<impl Iterator>::Item`
  76     /// or `Foo::Bar<impl Trait>`
  77     is_impl_trait_banned: bool,
  78
  79     /// Used to ban associated type bounds (i.e., `Type<AssocType: Bounds>`) in
  80     /// certain positions.
  81     is_assoc_ty_bound_banned: bool,
  82
  83     lint_buffer: &'a mut LintBuffer,
  84 }
  85
  86 impl<'a> AstValidator<'a> {
  87     fn with_in_trait_impl(&mut self, is_in: bool, f: impl FnOnce(&mut Self)) {
  88         let old = mem::replace(&mut self.in_trait_impl, is_in);
  89         f(self);
  90         self.in_trait_impl = old;
  91     }
  92
  93     fn with_banned_impl_trait(&mut self, f: impl FnOnce(&mut Self)) {
  94         let old = mem::replace(&mut self.is_impl_trait_banned, true);
  95         f(self);
  96         self.is_impl_trait_banned = old;
  97     }
  98
  99     fn with_banned_assoc_ty_bound(&mut self, f: impl FnOnce(&mut Self)) {
 100         let old = mem::replace(&mut self.is_assoc_ty_bound_banned, true);
 101         f(self);
 102         self.is_assoc_ty_bound_banned = old;
 103     }
 104
 105     fn with_impl_trait(&mut self, outer: Option<Span>, f: impl FnOnce(&mut Self)) {
 106         let old = mem::replace(&mut self.outer_impl_trait, outer);
 107         if outer.is_some() {
 108             self.with_bound_context(BoundContext::ImplTrait, |this| f(this));
 109         } else {
 110             f(self)
 111         }
 112         self.outer_impl_trait = old;
 113     }
 114
 115     fn with_bound_context(&mut self, ctx: BoundContext, f: impl FnOnce(&mut Self)) {
 116         let old = self.bound_context.replace(ctx);
 117         f(self);
 118         self.bound_context = old;
 119     }
 120
 121     fn visit_assoc_ty_constraint_from_generic_args(&mut self, constraint: &'a AssocTyConstraint) {
 122         match constraint.kind {
 123             AssocTyConstraintKind::Equality { .. } => {}
 124             AssocTyConstraintKind::Bound { .. } => {
 125                 if self.is_assoc_ty_bound_banned {
 126                     self.err_handler().span_err(
 127                         constraint.span,
 128                         "associated type bounds are not allowed within structs, enums, or unions",
 129                     );
 130                 }
 131             }
 132         }
 133         self.visit_assoc_ty_constraint(constraint);
 134     }
 135
 136     // Mirrors `visit::walk_ty`, but tracks relevant state.
 137     fn walk_ty(&mut self, t: &'a Ty) {
 138         match t.kind {
 139             TyKind::ImplTrait(..) => {
 140                 self.with_impl_trait(Some(t.span), |this| visit::walk_ty(this, t))
 141             }
 142             TyKind::TraitObject(..) => {
 143                 self.with_bound_context(BoundContext::TraitObject, |this| visit::walk_ty(this, t));
 144             }
 145             TyKind::Path(ref qself, ref path) => {
 146                 // We allow these:
 147                 //  - `Option<impl Trait>`
 148                 //  - `option::Option<impl Trait>`
 149                 //  - `option::Option<T>::Foo<impl Trait>
 150                 //
 151                 // But not these:
 152                 //  - `<impl Trait>::Foo`
 153                 //  - `option::Option<impl Trait>::Foo`.
 154                 //
 155                 // To implement this, we disallow `impl Trait` from `qself`
 156                 // (for cases like `<impl Trait>::Foo>`)
 157                 // but we allow `impl Trait` in `GenericArgs`
 158                 // iff there are no more PathSegments.
 159                 if let Some(ref qself) = *qself {
 160                     // `impl Trait` in `qself` is always illegal
 161                     self.with_banned_impl_trait(|this| this.visit_ty(&qself.ty));
 162                 }
 163
 164                 // Note that there should be a call to visit_path here,
 165                 // so if any logic is added to process `Path`s a call to it should be
 166                 // added both in visit_path and here. This code mirrors visit::walk_path.
 167                 for (i, segment) in path.segments.iter().enumerate() {
 168                     // Allow `impl Trait` iff we're on the final path segment
 169                     if i == path.segments.len() - 1 {
 170                         self.visit_path_segment(path.span, segment);
 171                     } else {
 172                         self.with_banned_impl_trait(|this| {
 173                             this.visit_path_segment(path.span, segment)
 174                         });
 175                     }
 176                 }
 177             }
 178             _ => visit::walk_ty(self, t),
 179         }
 180     }
 181
 182     fn err_handler(&self) -> &rustc_errors::Handler {
 183         &self.session.diagnostic()
 184     }
 185
 186     fn check_lifetime(&self, ident: Ident) {
 187         let valid_names = [kw::UnderscoreLifetime, kw::StaticLifetime, kw::Invalid];
 188         if !valid_names.contains(&ident.name) && ident.without_first_quote().is_reserved() {
 189             self.err_handler().span_err(ident.span, "lifetimes cannot use keyword names");
 190         }
 191     }
 192
 193     fn check_label(&self, ident: Ident) {
 194         if ident.without_first_quote().is_reserved() {
 195             self.err_handler()
 196                 .span_err(ident.span, &format!("invalid label name `{}`", ident.name));
 197         }
 198     }
 199
 200     fn invalid_visibility(&self, vis: &Visibility, note: Option<&str>) {
 201         if let VisibilityKind::Inherited = vis.node {
 202             return;
 203         }
 204
 205         let mut err =
 206             struct_span_err!(self.session, vis.span, E0449, "unnecessary visibility qualifier");
 207         if vis.node.is_pub() {
 208             err.span_label(vis.span, "`pub` not permitted here because it's implied");
 209         }
 210         if let Some(note) = note {
 211             err.note(note);
 212         }
 213         err.emit();
 214     }
 215
 216     fn check_decl_no_pat(decl: &FnDecl, mut report_err: impl FnMut(Span, bool)) {
 217         for Param { pat, .. } in &decl.inputs {
 218             match pat.kind {
 219                 PatKind::Ident(BindingMode::ByValue(Mutability::Not), _, None) | PatKind::Wild => {}
 220                 PatKind::Ident(BindingMode::ByValue(Mutability::Mut), _, None) => {
 221                     report_err(pat.span, true)
 222                 }
 223                 _ => report_err(pat.span, false),
 224             }
 225         }
 226     }
 227
 228     fn check_trait_fn_not_async(&self, fn_span: Span, asyncness: Async) {
 229         if let Async::Yes { span, .. } = asyncness {
 230             struct_span_err!(
 231                 self.session,
 232                 fn_span,
 233                 E0706,
 234                 "functions in traits cannot be declared `async`"
 235             )
 236             .span_label(span, "`async` because of this")
 237             .note("`async` trait functions are not currently supported")
 238             .note("consider using the `async-trait` crate: https://crates.io/crates/async-trait")
 239             .emit();
 240         }
 241     }
 242
 243     fn check_trait_fn_not_const(&self, constness: Const) {
 244         if let Const::Yes(span) = constness {
 245             struct_span_err!(
 246                 self.session,
 247                 span,
 248                 E0379,
 249                 "functions in traits cannot be declared const"
 250             )
 251             .span_label(span, "functions in traits cannot be const")
 252             .emit();
 253         }
 254     }
 255
 256     // FIXME(ecstaticmorse): Instead, use `bound_context` to check this in `visit_param_bound`.
 257     fn no_questions_in_bounds(&self, bounds: &GenericBounds, where_: &str, is_trait: bool) {
 258         for bound in bounds {
 259             if let GenericBound::Trait(ref poly, TraitBoundModifier::Maybe) = *bound {
 260                 let mut err = self.err_handler().struct_span_err(
 261                     poly.span,
 262                     &format!("`?Trait` is not permitted in {}", where_),
 263                 );
 264                 if is_trait {
 265                     let path_str = pprust::path_to_string(&poly.trait_ref.path);
 266                     err.note(&format!("traits are `?{}` by default", path_str));
 267                 }
 268                 err.emit();
 269             }
 270         }
 271     }
 272
 273     /// Matches `'-' lit | lit (cf. parser::Parser::parse_literal_maybe_minus)`,
 274     /// or paths for ranges.
 275     //
 276     // FIXME: do we want to allow `expr -> pattern` conversion to create path expressions?
 277     // That means making this work:
 278     //
 279     // ```rust,ignore (FIXME)
 280     // struct S;
 281     // macro_rules! m {
 282     //     ($a:expr) => {
 283     //         let $a = S;
 284     //     }
 285     // }
 286     // m!(S);
 287     // ```
 288     fn check_expr_within_pat(&self, expr: &Expr, allow_paths: bool) {
 289         match expr.kind {
 290             ExprKind::Lit(..) | ExprKind::Err => {}
 291             ExprKind::Path(..) if allow_paths => {}
 292             ExprKind::Unary(UnOp::Neg, ref inner) if matches!(inner.kind, ExprKind::Lit(_)) => {}
 293             _ => self.err_handler().span_err(
 294                 expr.span,
 295                 "arbitrary expressions aren't allowed \
 296                                                          in patterns",
 297             ),
 298         }
 299     }
 300
 301     fn check_late_bound_lifetime_defs(&self, params: &[GenericParam]) {
 302         // Check only lifetime parameters are present and that the lifetime
 303         // parameters that are present have no bounds.
 304         let non_lt_param_spans: Vec<_> = params
 305             .iter()
 306             .filter_map(|param| match param.kind {
 307                 GenericParamKind::Lifetime { .. } => {
 308                     if !param.bounds.is_empty() {
 309                         let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
 310                         self.err_handler()
 311                             .span_err(spans, "lifetime bounds cannot be used in this context");
 312                     }
 313                     None
 314                 }
 315                 _ => Some(param.ident.span),
 316             })
 317             .collect();
 318         if !non_lt_param_spans.is_empty() {
 319             self.err_handler().span_err(
 320                 non_lt_param_spans,
 321                 "only lifetime parameters can be used in this context",
 322             );
 323         }
 324     }
 325
 326     fn check_fn_decl(&self, fn_decl: &FnDecl, self_semantic: SelfSemantic) {
 327         self.check_decl_cvaradic_pos(fn_decl);
 328         self.check_decl_attrs(fn_decl);
 329         self.check_decl_self_param(fn_decl, self_semantic);
 330     }
 331
 332     fn check_decl_cvaradic_pos(&self, fn_decl: &FnDecl) {
 333         match &*fn_decl.inputs {
 334             [Param { ty, span, .. }] => {
 335                 if let TyKind::CVarArgs = ty.kind {
 336                     self.err_handler().span_err(
 337                         *span,
 338                         "C-variadic function must be declared with at least one named argument",
 339                     );
 340                 }
 341             }
 342             [ps @ .., _] => {
 343                 for Param { ty, span, .. } in ps {
 344                     if let TyKind::CVarArgs = ty.kind {
 345                         self.err_handler().span_err(
 346                             *span,
 347                             "`...` must be the last argument of a C-variadic function",
 348                         );
 349                     }
 350                 }
 351             }
 352             _ => {}
 353         }
 354     }
 355
 356     fn check_decl_attrs(&self, fn_decl: &FnDecl) {
 357         fn_decl
 358             .inputs
 359             .iter()
 360             .flat_map(|i| i.attrs.as_ref())
 361             .filter(|attr| {
 362                 let arr = [sym::allow, sym::cfg, sym::cfg_attr, sym::deny, sym::forbid, sym::warn];
 363                 !arr.contains(&attr.name_or_empty()) && rustc_attr::is_builtin_attr(attr)
 364             })
 365             .for_each(|attr| {
 366                 if attr.is_doc_comment() {
 367                     self.err_handler()
 368                         .struct_span_err(
 369                             attr.span,
 370                             "documentation comments cannot be applied to function parameters",
 371                         )
 372                         .span_label(attr.span, "doc comments are not allowed here")
 373                         .emit();
 374                 } else {
 375                     self.err_handler().span_err(
 376                         attr.span,
 377                         "allow, cfg, cfg_attr, deny, \
 378                 forbid, and warn are the only allowed built-in attributes in function parameters",
 379                     )
 380                 }
 381             });
 382     }
 383
 384     fn check_decl_self_param(&self, fn_decl: &FnDecl, self_semantic: SelfSemantic) {
 385         if let (SelfSemantic::No, [param, ..]) = (self_semantic, &*fn_decl.inputs) {
 386             if param.is_self() {
 387                 self.err_handler()
 388                     .struct_span_err(
 389                         param.span,
 390                         "`self` parameter is only allowed in associated functions",
 391                     )
 392                     .span_label(param.span, "not semantically valid as function parameter")
 393                     .note("associated functions are those in `impl` or `trait` definitions")
 394                     .emit();
 395             }
 396         }
 397     }
 398
 399     fn check_defaultness(&self, span: Span, defaultness: Defaultness) {
 400         if let Defaultness::Default(def_span) = defaultness {
 401             let span = self.session.source_map().guess_head_span(span);
 402             self.err_handler()
 403                 .struct_span_err(span, "`default` is only allowed on items in `impl` definitions")
 404                 .span_label(def_span, "`default` because of this")
 405                 .emit();
 406         }
 407     }
 408
 409     fn error_item_without_body(&self, sp: Span, ctx: &str, msg: &str, sugg: &str) {
 410         self.err_handler()
 411             .struct_span_err(sp, msg)
 412             .span_suggestion(
 413                 self.session.source_map().end_point(sp),
 414                 &format!("provide a definition for the {}", ctx),
 415                 sugg.to_string(),
 416                 Applicability::HasPlaceholders,
 417             )
 418             .emit();
 419     }
 420
 421     fn check_impl_item_provided<T>(&self, sp: Span, body: &Option<T>, ctx: &str, sugg: &str) {
 422         if body.is_none() {
 423             let msg = format!("associated {} in `impl` without body", ctx);
 424             self.error_item_without_body(sp, ctx, &msg, sugg);
 425         }
 426     }
 427
 428     fn check_type_no_bounds(&self, bounds: &[GenericBound], ctx: &str) {
 429         let span = match bounds {
 430             [] => return,
 431             [b0] => b0.span(),
 432             [b0, .., bl] => b0.span().to(bl.span()),
 433         };
 434         self.err_handler()
 435             .struct_span_err(span, &format!("bounds on `type`s in {} have no effect", ctx))
 436             .emit();
 437     }
 438
 439     fn check_foreign_ty_genericless(&self, generics: &Generics) {
 440         let cannot_have = |span, descr, remove_descr| {
 441             self.err_handler()
 442                 .struct_span_err(
 443                     span,
 444                     &format!("`type`s inside `extern` blocks cannot have {}", descr),
 445                 )
 446                 .span_suggestion(
 447                     span,
 448                     &format!("remove the {}", remove_descr),
 449                     String::new(),
 450                     Applicability::MaybeIncorrect,
 451                 )
 452                 .span_label(self.current_extern_span(), "`extern` block begins here")
 453                 .note(MORE_EXTERN)
 454                 .emit();
 455         };
 456
 457         if !generics.params.is_empty() {
 458             cannot_have(generics.span, "generic parameters", "generic parameters");
 459         }
 460
 461         if !generics.where_clause.predicates.is_empty() {
 462             cannot_have(generics.where_clause.span, "`where` clauses", "`where` clause");
 463         }
 464     }
 465
 466     fn check_foreign_kind_bodyless(&self, ident: Ident, kind: &str, body: Option<Span>) {
 467         let body = match body {
 468             None => return,
 469             Some(body) => body,
 470         };
 471         self.err_handler()
 472             .struct_span_err(ident.span, &format!("incorrect `{}` inside `extern` block", kind))
 473             .span_label(ident.span, "cannot have a body")
 474             .span_label(body, "the invalid body")
 475             .span_label(
 476                 self.current_extern_span(),
 477                 format!(
 478                     "`extern` blocks define existing foreign {0}s and {0}s \
 479                     inside of them cannot have a body",
 480                     kind
 481                 ),
 482             )
 483             .note(MORE_EXTERN)
 484             .emit();
 485     }
 486
 487     /// An `fn` in `extern { ... }` cannot have a body `{ ... }`.
 488     fn check_foreign_fn_bodyless(&self, ident: Ident, body: Option<&Block>) {
 489         let body = match body {
 490             None => return,
 491             Some(body) => body,
 492         };
 493         self.err_handler()
 494             .struct_span_err(ident.span, "incorrect function inside `extern` block")
 495             .span_label(ident.span, "cannot have a body")
 496             .span_suggestion(
 497                 body.span,
 498                 "remove the invalid body",
 499                 ";".to_string(),
 500                 Applicability::MaybeIncorrect,
 501             )
 502             .help(
 503                 "you might have meant to write a function accessible through FFI, \
 504                 which can be done by writing `extern fn` outside of the `extern` block",
 505             )
 506             .span_label(
 507                 self.current_extern_span(),
 508                 "`extern` blocks define existing foreign functions and functions \
 509                 inside of them cannot have a body",
 510             )
 511             .note(MORE_EXTERN)
 512             .emit();
 513     }
 514
 515     fn current_extern_span(&self) -> Span {
 516         self.session.source_map().guess_head_span(self.extern_mod.unwrap().span)
 517     }
 518
 519     /// An `fn` in `extern { ... }` cannot have qualfiers, e.g. `async fn`.
 520     fn check_foreign_fn_headerless(&self, ident: Ident, span: Span, header: FnHeader) {
 521         if header.has_qualifiers() {
 522             self.err_handler()
 523                 .struct_span_err(ident.span, "functions in `extern` blocks cannot have qualifiers")
 524                 .span_label(self.current_extern_span(), "in this `extern` block")
 525                 .span_suggestion(
 526                     span.until(ident.span.shrink_to_lo()),
 527                     "remove the qualifiers",
 528                     "fn ".to_string(),
 529                     Applicability::MaybeIncorrect,
 530                 )
 531                 .emit();
 532         }
 533     }
 534
 535     /// Reject C-varadic type unless the function is foreign,
 536     /// or free and `unsafe extern "C"` semantically.
 537     fn check_c_varadic_type(&self, fk: FnKind<'a>) {
 538         match (fk.ctxt(), fk.header()) {
 539             (Some(FnCtxt::Foreign), _) => return,
 540             (Some(FnCtxt::Free), Some(header)) => match header.ext {
 541                 Extern::Explicit(StrLit { symbol_unescaped: sym::C, .. }) | Extern::Implicit
 542                     if matches!(header.unsafety, Unsafe::Yes(_)) =>
 543                 {
 544                     return;
 545                 }
 546                 _ => {}
 547             },
 548             _ => {}
 549         };
 550
 551         for Param { ty, span, .. } in &fk.decl().inputs {
 552             if let TyKind::CVarArgs = ty.kind {
 553                 self.err_handler()
 554                     .struct_span_err(
 555                         *span,
 556                         "only foreign or `unsafe extern \"C\" functions may be C-variadic",
 557                     )
 558                     .emit();
 559             }
 560         }
 561     }
 562
 563     fn check_item_named(&self, ident: Ident, kind: &str) {
 564         if ident.name != kw::Underscore {
 565             return;
 566         }
 567         self.err_handler()
 568             .struct_span_err(ident.span, &format!("`{}` items in this context need a name", kind))
 569             .span_label(ident.span, format!("`_` is not a valid name for this `{}` item", kind))
 570             .emit();
 571     }
 572
 573     fn check_nomangle_item_asciionly(&self, ident: Ident, item_span: Span) {
 574         if ident.name.as_str().is_ascii() {
 575             return;
 576         }
 577         let head_span = self.session.source_map().guess_head_span(item_span);
 578         struct_span_err!(
 579             self.session,
 580             head_span,
 581             E0754,
 582             "`#[no_mangle]` requires ASCII identifier"
 583         )
 584         .emit();
 585     }
 586
 587     fn check_mod_file_item_asciionly(&self, ident: Ident) {
 588         if ident.name.as_str().is_ascii() {
 589             return;
 590         }
 591         struct_span_err!(
 592             self.session,
 593             ident.span,
 594             E0754,
 595             "trying to load file for module `{}` with non ascii identifer name",
 596             ident.name
 597         )
 598         .help("consider using `#[path]` attribute to specify filesystem path")
 599         .emit();
 600     }
 601
 602     fn deny_generic_params(&self, generics: &Generics, ident_span: Span) {
 603         if !generics.params.is_empty() {
 604             struct_span_err!(
 605                 self.session,
 606                 generics.span,
 607                 E0567,
 608                 "auto traits cannot have generic parameters"
 609             )
 610             .span_label(ident_span, "auto trait cannot have generic parameters")
 611             .span_suggestion(
 612                 generics.span,
 613                 "remove the parameters",
 614                 String::new(),
 615                 Applicability::MachineApplicable,
 616             )
 617             .emit();
 618         }
 619     }
 620
 621     fn deny_super_traits(&self, bounds: &GenericBounds, ident_span: Span) {
 622         if let [first @ last] | [first, .., last] = &bounds[..] {
 623             let span = first.span().to(last.span());
 624             struct_span_err!(self.session, span, E0568, "auto traits cannot have super traits")
 625                 .span_label(ident_span, "auto trait cannot have super traits")
 626                 .span_suggestion(
 627                     span,
 628                     "remove the super traits",
 629                     String::new(),
 630                     Applicability::MachineApplicable,
 631                 )
 632                 .emit();
 633         }
 634     }
 635
 636     fn deny_items(&self, trait_items: &[P<AssocItem>], ident_span: Span) {
 637         if !trait_items.is_empty() {
 638             let spans: Vec<_> = trait_items.iter().map(|i| i.ident.span).collect();
 639             struct_span_err!(
 640                 self.session,
 641                 spans,
 642                 E0380,
 643                 "auto traits cannot have methods or associated items"
 644             )
 645             .span_label(ident_span, "auto trait cannot have items")
 646             .emit();
 647         }
 648     }
 649
 650     fn correct_generic_order_suggestion(&self, data: &AngleBracketedArgs) -> String {
 651         // Lifetimes always come first.
 652         let lt_sugg = data.args.iter().filter_map(|arg| match arg {
 653             AngleBracketedArg::Arg(lt @ GenericArg::Lifetime(_)) => {
 654                 Some(pprust::to_string(|s| s.print_generic_arg(lt)))
 655             }
 656             _ => None,
 657         });
 658         let args_sugg = data.args.iter().filter_map(|a| match a {
 659             AngleBracketedArg::Arg(GenericArg::Lifetime(_)) | AngleBracketedArg::Constraint(_) => {
 660                 None
 661             }
 662             AngleBracketedArg::Arg(arg) => Some(pprust::to_string(|s| s.print_generic_arg(arg))),
 663         });
 664         // Constraints always come last.
 665         let constraint_sugg = data.args.iter().filter_map(|a| match a {
 666             AngleBracketedArg::Arg(_) => None,
 667             AngleBracketedArg::Constraint(c) => {
 668                 Some(pprust::to_string(|s| s.print_assoc_constraint(c)))
 669             }
 670         });
 671         format!(
 672             "<{}>",
 673             lt_sugg.chain(args_sugg).chain(constraint_sugg).collect::<Vec<String>>().join(", ")
 674         )
 675     }
 676
 677     /// Enforce generic args coming before constraints in `<...>` of a path segment.
 678     fn check_generic_args_before_constraints(&self, data: &AngleBracketedArgs) {
 679         // Early exit in case it's partitioned as it should be.
 680         if data.args.iter().is_partitioned(|arg| matches!(arg, AngleBracketedArg::Arg(_))) {
 681             return;
 682         }
 683         // Find all generic argument coming after the first constraint...
 684         let (constraint_spans, arg_spans): (Vec<Span>, Vec<Span>) =
 685             data.args.iter().partition_map(|arg| match arg {
 686                 AngleBracketedArg::Constraint(c) => Either::Left(c.span),
 687                 AngleBracketedArg::Arg(a) => Either::Right(a.span()),
 688             });
 689         let args_len = arg_spans.len();
 690         let constraint_len = constraint_spans.len();
 691         // ...and then error:
 692         self.err_handler()
 693             .struct_span_err(
 694                 arg_spans.clone(),
 695                 "generic arguments must come before the first constraint",
 696             )
 697             .span_label(constraint_spans[0], &format!("constraint{}", pluralize!(constraint_len)))
 698             .span_label(
 699                 *arg_spans.iter().last().unwrap(),
 700                 &format!("generic argument{}", pluralize!(args_len)),
 701             )
 702             .span_labels(constraint_spans, "")
 703             .span_labels(arg_spans, "")
 704             .span_suggestion_verbose(
 705                 data.span,
 706                 &format!(
 707                     "move the constraint{} after the generic argument{}",
 708                     pluralize!(constraint_len),
 709                     pluralize!(args_len)
 710                 ),
 711                 self.correct_generic_order_suggestion(&data),
 712                 Applicability::MachineApplicable,
 713             )
 714             .emit();
 715     }
 716 }
 717
 718 /// Checks that generic parameters are in the correct order,
 719 /// which is lifetimes, then types and then consts. (`<'a, T, const N: usize>`)
 720 fn validate_generic_param_order<'a>(
 721     sess: &Session,
 722     handler: &rustc_errors::Handler,
 723     generics: impl Iterator<Item = (ParamKindOrd, Option<&'a [GenericBound]>, Span, Option<String>)>,
 724     span: Span,
 725 ) {
 726     let mut max_param: Option<ParamKindOrd> = None;
 727     let mut out_of_order = FxHashMap::default();
 728     let mut param_idents = vec![];
 729
 730     for (kind, bounds, span, ident) in generics {
 731         if let Some(ident) = ident {
 732             param_idents.push((kind, bounds, param_idents.len(), ident));
 733         }
 734         let max_param = &mut max_param;
 735         match max_param {
 736             Some(max_param) if *max_param > kind => {
 737                 let entry = out_of_order.entry(kind).or_insert((*max_param, vec![]));
 738                 entry.1.push(span);
 739             }
 740             Some(_) | None => *max_param = Some(kind),
 741         };
 742     }
 743
 744     let mut ordered_params = "<".to_string();
 745     if !out_of_order.is_empty() {
 746         param_idents.sort_by_key(|&(po, _, i, _)| (po, i));
 747         let mut first = true;
 748         for (_, bounds, _, ident) in param_idents {
 749             if !first {
 750                 ordered_params += ", ";
 751             }
 752             ordered_params += &ident;
 753             if let Some(bounds) = bounds {
 754                 if !bounds.is_empty() {
 755                     ordered_params += ": ";
 756                     ordered_params += &pprust::bounds_to_string(&bounds);
 757                 }
 758             }
 759             first = false;
 760         }
 761     }
 762     ordered_params += ">";
 763
 764     for (param_ord, (max_param, spans)) in &out_of_order {
 765         let mut err =
 766             handler.struct_span_err(
 767                 spans.clone(),
 768                 &format!(
 769                     "{} parameters must be declared prior to {} parameters",
 770                     param_ord, max_param,
 771                 ),
 772             );
 773         err.span_suggestion(
 774             span,
 775             &format!(
 776                 "reorder the parameters: lifetimes{}",
 777                 if sess.features_untracked().const_generics {
 778                     ", then consts and types"
 779                 } else if sess.features_untracked().min_const_generics {
 780                     ", then types, then consts"
 781                 } else {
 782                     ", then types"
 783                 },
 784             ),
 785             ordered_params.clone(),
 786             Applicability::MachineApplicable,
 787         );
 788         err.emit();
 789     }
 790 }
 791
 792 impl<'a> Visitor<'a> for AstValidator<'a> {
 793     fn visit_attribute(&mut self, attr: &Attribute) {
 794         validate_attr::check_meta(&self.session.parse_sess, attr);
 795     }
 796
 797     fn visit_expr(&mut self, expr: &'a Expr) {
 798         match &expr.kind {
 799             ExprKind::LlvmInlineAsm(..) if !self.session.target.target.options.allow_asm => {
 800                 struct_span_err!(
 801                     self.session,
 802                     expr.span,
 803                     E0472,
 804                     "llvm_asm! is unsupported on this target"
 805                 )
 806                 .emit();
 807             }
 808             _ => {}
 809         }
 810
 811         visit::walk_expr(self, expr);
 812     }
 813
 814     fn visit_ty(&mut self, ty: &'a Ty) {
 815         match ty.kind {
 816             TyKind::BareFn(ref bfty) => {
 817                 self.check_fn_decl(&bfty.decl, SelfSemantic::No);
 818                 Self::check_decl_no_pat(&bfty.decl, |span, _| {
 819                     struct_span_err!(
 820                         self.session,
 821                         span,
 822                         E0561,
 823                         "patterns aren't allowed in function pointer types"
 824                     )
 825                     .emit();
 826                 });
 827                 self.check_late_bound_lifetime_defs(&bfty.generic_params);
 828             }
 829             TyKind::TraitObject(ref bounds, ..) => {
 830                 let mut any_lifetime_bounds = false;
 831                 for bound in bounds {
 832                     if let GenericBound::Outlives(ref lifetime) = *bound {
 833                         if any_lifetime_bounds {
 834                             struct_span_err!(
 835                                 self.session,
 836                                 lifetime.ident.span,
 837                                 E0226,
 838                                 "only a single explicit lifetime bound is permitted"
 839                             )
 840                             .emit();
 841                             break;
 842                         }
 843                         any_lifetime_bounds = true;
 844                     }
 845                 }
 846                 self.no_questions_in_bounds(bounds, "trait object types", false);
 847             }
 848             TyKind::ImplTrait(_, ref bounds) => {
 849                 if self.is_impl_trait_banned {
 850                     struct_span_err!(
 851                         self.session,
 852                         ty.span,
 853                         E0667,
 854                         "`impl Trait` is not allowed in path parameters"
 855                     )
 856                     .emit();
 857                 }
 858
 859                 if let Some(outer_impl_trait_sp) = self.outer_impl_trait {
 860                     struct_span_err!(
 861                         self.session,
 862                         ty.span,
 863                         E0666,
 864                         "nested `impl Trait` is not allowed"
 865                     )
 866                     .span_label(outer_impl_trait_sp, "outer `impl Trait`")
 867                     .span_label(ty.span, "nested `impl Trait` here")
 868                     .emit();
 869                 }
 870
 871                 if !bounds
 872                     .iter()
 873                     .any(|b| if let GenericBound::Trait(..) = *b { true } else { false })
 874                 {
 875                     self.err_handler().span_err(ty.span, "at least one trait must be specified");
 876                 }
 877
 878                 self.walk_ty(ty);
 879                 return;
 880             }
 881             _ => {}
 882         }
 883
 884         self.walk_ty(ty)
 885     }
 886
 887     fn visit_label(&mut self, label: &'a Label) {
 888         self.check_label(label.ident);
 889         visit::walk_label(self, label);
 890     }
 891
 892     fn visit_lifetime(&mut self, lifetime: &'a Lifetime) {
 893         self.check_lifetime(lifetime.ident);
 894         visit::walk_lifetime(self, lifetime);
 895     }
 896
 897     fn visit_item(&mut self, item: &'a Item) {
 898         if item.attrs.iter().any(|attr| self.session.is_proc_macro_attr(attr)) {
 899             self.has_proc_macro_decls = true;
 900         }
 901
 902         if self.session.contains_name(&item.attrs, sym::no_mangle) {
 903             self.check_nomangle_item_asciionly(item.ident, item.span);
 904         }
 905
 906         match item.kind {
 907             ItemKind::Impl {
 908                 unsafety,
 909                 polarity,
 910                 defaultness: _,
 911                 constness: _,
 912                 generics: _,
 913                 of_trait: Some(ref t),
 914                 ref self_ty,
 915                 items: _,
 916             } => {
 917                 self.with_in_trait_impl(true, |this| {
 918                     this.invalid_visibility(&item.vis, None);
 919                     if let TyKind::Err = self_ty.kind {
 920                         this.err_handler()
 921                             .struct_span_err(
 922                                 item.span,
 923                                 "`impl Trait for .. {}` is an obsolete syntax",
 924                             )
 925                             .help("use `auto trait Trait {}` instead")
 926                             .emit();
 927                     }
 928                     if let (Unsafe::Yes(span), ImplPolarity::Negative(sp)) = (unsafety, polarity) {
 929                         struct_span_err!(
 930                             this.session,
 931                             sp.to(t.path.span),
 932                             E0198,
 933                             "negative impls cannot be unsafe"
 934                         )
 935                         .span_label(sp, "negative because of this")
 936                         .span_label(span, "unsafe because of this")
 937                         .emit();
 938                     }
 939
 940                     visit::walk_item(this, item);
 941                 });
 942                 return; // Avoid visiting again.
 943             }
 944             ItemKind::Impl {
 945                 unsafety,
 946                 polarity,
 947                 defaultness,
 948                 constness,
 949                 generics: _,
 950                 of_trait: None,
 951                 ref self_ty,
 952                 items: _,
 953             } => {
 954                 let error = |annotation_span, annotation| {
 955                     let mut err = self.err_handler().struct_span_err(
 956                         self_ty.span,
 957                         &format!("inherent impls cannot be {}", annotation),
 958                     );
 959                     err.span_label(annotation_span, &format!("{} because of this", annotation));
 960                     err.span_label(self_ty.span, "inherent impl for this type");
 961                     err
 962                 };
 963
 964                 self.invalid_visibility(
 965                     &item.vis,
 966                     Some("place qualifiers on individual impl items instead"),
 967                 );
 968                 if let Unsafe::Yes(span) = unsafety {
 969                     error(span, "unsafe").code(error_code!(E0197)).emit();
 970                 }
 971                 if let ImplPolarity::Negative(span) = polarity {
 972                     error(span, "negative").emit();
 973                 }
 974                 if let Defaultness::Default(def_span) = defaultness {
 975                     error(def_span, "`default`")
 976                         .note("only trait implementations may be annotated with `default`")
 977                         .emit();
 978                 }
 979                 if let Const::Yes(span) = constness {
 980                     error(span, "`const`")
 981                         .note("only trait implementations may be annotated with `const`")
 982                         .emit();
 983                 }
 984             }
 985             ItemKind::Fn(def, _, _, ref body) => {
 986                 self.check_defaultness(item.span, def);
 987
 988                 if body.is_none() {
 989                     let msg = "free function without a body";
 990                     self.error_item_without_body(item.span, "function", msg, " { <body> }");
 991                 }
 992             }
 993             ItemKind::ForeignMod(_) => {
 994                 let old_item = mem::replace(&mut self.extern_mod, Some(item));
 995                 self.invalid_visibility(
 996                     &item.vis,
 997                     Some("place qualifiers on individual foreign items instead"),
 998                 );
 999                 visit::walk_item(self, item);
1000                 self.extern_mod = old_item;
1001                 return; // Avoid visiting again.
1002             }
1003             ItemKind::Enum(ref def, _) => {
1004                 for variant in &def.variants {
1005                     self.invalid_visibility(&variant.vis, None);
1006                     for field in variant.data.fields() {
1007                         self.invalid_visibility(&field.vis, None);
1008                     }
1009                 }
1010             }
1011             ItemKind::Trait(is_auto, _, ref generics, ref bounds, ref trait_items) => {
1012                 if is_auto == IsAuto::Yes {
1013                     // Auto traits cannot have generics, super traits nor contain items.
1014                     self.deny_generic_params(generics, item.ident.span);
1015                     self.deny_super_traits(bounds, item.ident.span);
1016                     self.deny_items(trait_items, item.ident.span);
1017                 }
1018                 self.no_questions_in_bounds(bounds, "supertraits", true);
1019
1020                 // Equivalent of `visit::walk_item` for `ItemKind::Trait` that inserts a bound
1021                 // context for the supertraits.
1022                 self.visit_vis(&item.vis);
1023                 self.visit_ident(item.ident);
1024                 self.visit_generics(generics);
1025                 self.with_bound_context(BoundContext::TraitBounds, |this| {
1026                     walk_list!(this, visit_param_bound, bounds);
1027                 });
1028                 walk_list!(self, visit_assoc_item, trait_items, AssocCtxt::Trait);
1029                 walk_list!(self, visit_attribute, &item.attrs);
1030                 return;
1031             }
1032             ItemKind::Mod(Mod { inline, .. }) => {
1033                 // Ensure that `path` attributes on modules are recorded as used (cf. issue #35584).
1034                 if !inline && !self.session.contains_name(&item.attrs, sym::path) {
1035                     self.check_mod_file_item_asciionly(item.ident);
1036                 }
1037             }
1038             ItemKind::Union(ref vdata, _) => {
1039                 if let VariantData::Tuple(..) | VariantData::Unit(..) = vdata {
1040                     self.err_handler()
1041                         .span_err(item.span, "tuple and unit unions are not permitted");
1042                 }
1043                 if vdata.fields().is_empty() {
1044                     self.err_handler().span_err(item.span, "unions cannot have zero fields");
1045                 }
1046             }
1047             ItemKind::Const(def, .., None) => {
1048                 self.check_defaultness(item.span, def);
1049                 let msg = "free constant item without body";
1050                 self.error_item_without_body(item.span, "constant", msg, " = <expr>;");
1051             }
1052             ItemKind::Static(.., None) => {
1053                 let msg = "free static item without body";
1054                 self.error_item_without_body(item.span, "static", msg, " = <expr>;");
1055             }
1056             ItemKind::TyAlias(def, _, ref bounds, ref body) => {
1057                 self.check_defaultness(item.span, def);
1058                 if body.is_none() {
1059                     let msg = "free type alias without body";
1060                     self.error_item_without_body(item.span, "type", msg, " = <type>;");
1061                 }
1062                 self.check_type_no_bounds(bounds, "this context");
1063             }
1064             _ => {}
1065         }
1066
1067         visit::walk_item(self, item)
1068     }
1069
1070     fn visit_foreign_item(&mut self, fi: &'a ForeignItem) {
1071         match &fi.kind {
1072             ForeignItemKind::Fn(def, sig, _, body) => {
1073                 self.check_defaultness(fi.span, *def);
1074                 self.check_foreign_fn_bodyless(fi.ident, body.as_deref());
1075                 self.check_foreign_fn_headerless(fi.ident, fi.span, sig.header);
1076             }
1077             ForeignItemKind::TyAlias(def, generics, bounds, body) => {
1078                 self.check_defaultness(fi.span, *def);
1079                 self.check_foreign_kind_bodyless(fi.ident, "type", body.as_ref().map(|b| b.span));
1080                 self.check_type_no_bounds(bounds, "`extern` blocks");
1081                 self.check_foreign_ty_genericless(generics);
1082             }
1083             ForeignItemKind::Static(_, _, body) => {
1084                 self.check_foreign_kind_bodyless(fi.ident, "static", body.as_ref().map(|b| b.span));
1085             }
1086             ForeignItemKind::MacCall(..) => {}
1087         }
1088
1089         visit::walk_foreign_item(self, fi)
1090     }
1091
1092     // Mirrors `visit::walk_generic_args`, but tracks relevant state.
1093     fn visit_generic_args(&mut self, _: Span, generic_args: &'a GenericArgs) {
1094         match *generic_args {
1095             GenericArgs::AngleBracketed(ref data) => {
1096                 self.check_generic_args_before_constraints(data);
1097
1098                 for arg in &data.args {
1099                     match arg {
1100                         AngleBracketedArg::Arg(arg) => self.visit_generic_arg(arg),
1101                         // Type bindings such as `Item = impl Debug` in `Iterator<Item = Debug>`
1102                         // are allowed to contain nested `impl Trait`.
1103                         AngleBracketedArg::Constraint(constraint) => {
1104                             self.with_impl_trait(None, |this| {
1105                                 this.visit_assoc_ty_constraint_from_generic_args(constraint);
1106                             });
1107                         }
1108                     }
1109                 }
1110             }
1111             GenericArgs::Parenthesized(ref data) => {
1112                 walk_list!(self, visit_ty, &data.inputs);
1113                 if let FnRetTy::Ty(ty) = &data.output {
1114                     // `-> Foo` syntax is essentially an associated type binding,
1115                     // so it is also allowed to contain nested `impl Trait`.
1116                     self.with_impl_trait(None, |this| this.visit_ty(ty));
1117                 }
1118             }
1119         }
1120     }
1121
1122     fn visit_generics(&mut self, generics: &'a Generics) {
1123         let mut prev_ty_default = None;
1124         for param in &generics.params {
1125             match param.kind {
1126                 GenericParamKind::Lifetime => (),
1127                 GenericParamKind::Type { default: Some(_), .. } => {
1128                     prev_ty_default = Some(param.ident.span);
1129                 }
1130                 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1131                     if let Some(span) = prev_ty_default {
1132                         let mut err = self.err_handler().struct_span_err(
1133                             span,
1134                             "type parameters with a default must be trailing",
1135                         );
1136                         if matches!(param.kind, GenericParamKind::Const { .. }) {
1137                             err.note(
1138                                 "using type defaults and const parameters \
1139                                  in the same parameter list is currently not permitted",
1140                             );
1141                         }
1142                         err.emit();
1143                         break;
1144                     }
1145                 }
1146             }
1147         }
1148
1149         validate_generic_param_order(
1150             self.session,
1151             self.err_handler(),
1152             generics.params.iter().map(|param| {
1153                 let ident = Some(param.ident.to_string());
1154                 let (kind, ident) = match &param.kind {
1155                     GenericParamKind::Lifetime => (ParamKindOrd::Lifetime, ident),
1156                     GenericParamKind::Type { default: _ } => (ParamKindOrd::Type, ident),
1157                     GenericParamKind::Const { ref ty, kw_span: _ } => {
1158                         let ty = pprust::ty_to_string(ty);
1159                         let unordered = self.session.features_untracked().const_generics;
1160                         (
1161                             ParamKindOrd::Const { unordered },
1162                             Some(format!("const {}: {}", param.ident, ty)),
1163                         )
1164                     }
1165                 };
1166                 (kind, Some(&*param.bounds), param.ident.span, ident)
1167             }),
1168             generics.span,
1169         );
1170
1171         for predicate in &generics.where_clause.predicates {
1172             if let WherePredicate::EqPredicate(ref predicate) = *predicate {
1173                 deny_equality_constraints(self, predicate, generics);
1174             }
1175         }
1176
1177         visit::walk_generics(self, generics)
1178     }
1179
1180     fn visit_generic_param(&mut self, param: &'a GenericParam) {
1181         if let GenericParamKind::Lifetime { .. } = param.kind {
1182             self.check_lifetime(param.ident);
1183         }
1184         visit::walk_generic_param(self, param);
1185     }
1186
1187     fn visit_param_bound(&mut self, bound: &'a GenericBound) {
1188         match bound {
1189             GenericBound::Trait(_, TraitBoundModifier::MaybeConst) => {
1190                 if let Some(ctx) = self.bound_context {
1191                     let msg = format!("`?const` is not permitted in {}", ctx.description());
1192                     self.err_handler().span_err(bound.span(), &msg);
1193                 }
1194             }
1195
1196             GenericBound::Trait(_, TraitBoundModifier::MaybeConstMaybe) => {
1197                 self.err_handler()
1198                     .span_err(bound.span(), "`?const` and `?` are mutually exclusive");
1199             }
1200
1201             _ => {}
1202         }
1203
1204         visit::walk_param_bound(self, bound)
1205     }
1206
1207     fn visit_pat(&mut self, pat: &'a Pat) {
1208         match pat.kind {
1209             PatKind::Lit(ref expr) => {
1210                 self.check_expr_within_pat(expr, false);
1211             }
1212             PatKind::Range(ref start, ref end, _) => {
1213                 if let Some(expr) = start {
1214                     self.check_expr_within_pat(expr, true);
1215                 }
1216                 if let Some(expr) = end {
1217                     self.check_expr_within_pat(expr, true);
1218                 }
1219             }
1220             _ => {}
1221         }
1222
1223         visit::walk_pat(self, pat)
1224     }
1225
1226     fn visit_where_predicate(&mut self, p: &'a WherePredicate) {
1227         if let &WherePredicate::BoundPredicate(ref bound_predicate) = p {
1228             // A type binding, eg `for<'c> Foo: Send+Clone+'c`
1229             self.check_late_bound_lifetime_defs(&bound_predicate.bound_generic_params);
1230         }
1231         visit::walk_where_predicate(self, p);
1232     }
1233
1234     fn visit_poly_trait_ref(&mut self, t: &'a PolyTraitRef, m: &'a TraitBoundModifier) {
1235         self.check_late_bound_lifetime_defs(&t.bound_generic_params);
1236         visit::walk_poly_trait_ref(self, t, m);
1237     }
1238
1239     fn visit_variant_data(&mut self, s: &'a VariantData) {
1240         self.with_banned_assoc_ty_bound(|this| visit::walk_struct_def(this, s))
1241     }
1242
1243     fn visit_enum_def(
1244         &mut self,
1245         enum_definition: &'a EnumDef,
1246         generics: &'a Generics,
1247         item_id: NodeId,
1248         _: Span,
1249     ) {
1250         self.with_banned_assoc_ty_bound(|this| {
1251             visit::walk_enum_def(this, enum_definition, generics, item_id)
1252         })
1253     }
1254
1255     fn visit_fn(&mut self, fk: FnKind<'a>, span: Span, id: NodeId) {
1256         // Only associated `fn`s can have `self` parameters.
1257         let self_semantic = match fk.ctxt() {
1258             Some(FnCtxt::Assoc(_)) => SelfSemantic::Yes,
1259             _ => SelfSemantic::No,
1260         };
1261         self.check_fn_decl(fk.decl(), self_semantic);
1262
1263         self.check_c_varadic_type(fk);
1264
1265         // Functions cannot both be `const async`
1266         if let Some(FnHeader {
1267             constness: Const::Yes(cspan),
1268             asyncness: Async::Yes { span: aspan, .. },
1269             ..
1270         }) = fk.header()
1271         {
1272             self.err_handler()
1273                 .struct_span_err(
1274                     vec![*cspan, *aspan],
1275                     "functions cannot be both `const` and `async`",
1276                 )
1277                 .span_label(*cspan, "`const` because of this")
1278                 .span_label(*aspan, "`async` because of this")
1279                 .span_label(span, "") // Point at the fn header.
1280                 .emit();
1281         }
1282
1283         // Functions without bodies cannot have patterns.
1284         if let FnKind::Fn(ctxt, _, sig, _, None) = fk {
1285             Self::check_decl_no_pat(&sig.decl, |span, mut_ident| {
1286                 let (code, msg, label) = match ctxt {
1287                     FnCtxt::Foreign => (
1288                         error_code!(E0130),
1289                         "patterns aren't allowed in foreign function declarations",
1290                         "pattern not allowed in foreign function",
1291                     ),
1292                     _ => (
1293                         error_code!(E0642),
1294                         "patterns aren't allowed in functions without bodies",
1295                         "pattern not allowed in function without body",
1296                     ),
1297                 };
1298                 if mut_ident && matches!(ctxt, FnCtxt::Assoc(_)) {
1299                     self.lint_buffer.buffer_lint(PATTERNS_IN_FNS_WITHOUT_BODY, id, span, msg);
1300                 } else {
1301                     self.err_handler()
1302                         .struct_span_err(span, msg)
1303                         .span_label(span, label)
1304                         .code(code)
1305                         .emit();
1306                 }
1307             });
1308         }
1309
1310         visit::walk_fn(self, fk, span);
1311     }
1312
1313     fn visit_assoc_item(&mut self, item: &'a AssocItem, ctxt: AssocCtxt) {
1314         if ctxt == AssocCtxt::Trait || !self.in_trait_impl {
1315             self.check_defaultness(item.span, item.kind.defaultness());
1316         }
1317
1318         if ctxt == AssocCtxt::Impl {
1319             match &item.kind {
1320                 AssocItemKind::Const(_, _, body) => {
1321                     self.check_impl_item_provided(item.span, body, "constant", " = <expr>;");
1322                 }
1323                 AssocItemKind::Fn(_, _, _, body) => {
1324                     self.check_impl_item_provided(item.span, body, "function", " { <body> }");
1325                 }
1326                 AssocItemKind::TyAlias(_, _, bounds, body) => {
1327                     self.check_impl_item_provided(item.span, body, "type", " = <type>;");
1328                     self.check_type_no_bounds(bounds, "`impl`s");
1329                 }
1330                 _ => {}
1331             }
1332         }
1333
1334         if ctxt == AssocCtxt::Trait || self.in_trait_impl {
1335             self.invalid_visibility(&item.vis, None);
1336             if let AssocItemKind::Fn(_, sig, _, _) = &item.kind {
1337                 self.check_trait_fn_not_const(sig.header.constness);
1338                 self.check_trait_fn_not_async(item.span, sig.header.asyncness);
1339             }
1340         }
1341
1342         if let AssocItemKind::Const(..) = item.kind {
1343             self.check_item_named(item.ident, "const");
1344         }
1345
1346         self.with_in_trait_impl(false, |this| visit::walk_assoc_item(this, item, ctxt));
1347     }
1348 }
1349
1350 /// When encountering an equality constraint in a `where` clause, emit an error. If the code seems
1351 /// like it's setting an associated type, provide an appropriate suggestion.
1352 fn deny_equality_constraints(
1353     this: &mut AstValidator<'_>,
1354     predicate: &WhereEqPredicate,
1355     generics: &Generics,
1356 ) {
1357     let mut err = this.err_handler().struct_span_err(
1358         predicate.span,
1359         "equality constraints are not yet supported in `where` clauses",
1360     );
1361     err.span_label(predicate.span, "not supported");
1362
1363     // Given `<A as Foo>::Bar = RhsTy`, suggest `A: Foo<Bar = RhsTy>`.
1364     if let TyKind::Path(Some(qself), full_path) = &predicate.lhs_ty.kind {
1365         if let TyKind::Path(None, path) = &qself.ty.kind {
1366             match &path.segments[..] {
1367                 [PathSegment { ident, args: None, .. }] => {
1368                     for param in &generics.params {
1369                         if param.ident == *ident {
1370                             let param = ident;
1371                             match &full_path.segments[qself.position..] {
1372                                 [PathSegment { ident, .. }] => {
1373                                     // Make a new `Path` from `foo::Bar` to `Foo<Bar = RhsTy>`.
1374                                     let mut assoc_path = full_path.clone();
1375                                     // Remove `Bar` from `Foo::Bar`.
1376                                     assoc_path.segments.pop();
1377                                     let len = assoc_path.segments.len() - 1;
1378                                     // Build `<Bar = RhsTy>`.
1379                                     let arg = AngleBracketedArg::Constraint(AssocTyConstraint {
1380                                         id: rustc_ast::node_id::DUMMY_NODE_ID,
1381                                         ident: *ident,
1382                                         kind: AssocTyConstraintKind::Equality {
1383                                             ty: predicate.rhs_ty.clone(),
1384                                         },
1385                                         span: ident.span,
1386                                     });
1387                                     // Add `<Bar = RhsTy>` to `Foo`.
1388                                     match &mut assoc_path.segments[len].args {
1389                                         Some(args) => match args.deref_mut() {
1390                                             GenericArgs::Parenthesized(_) => continue,
1391                                             GenericArgs::AngleBracketed(args) => {
1392                                                 args.args.push(arg);
1393                                             }
1394                                         },
1395                                         empty_args => {
1396                                             *empty_args = AngleBracketedArgs {
1397                                                 span: ident.span,
1398                                                 args: vec![arg],
1399                                             }
1400                                             .into();
1401                                         }
1402                                     }
1403                                     err.span_suggestion_verbose(
1404                                         predicate.span,
1405                                         &format!(
1406                                             "if `{}` is an associated type you're trying to set, \
1407                                             use the associated type binding syntax",
1408                                             ident
1409                                         ),
1410                                         format!(
1411                                             "{}: {}",
1412                                             param,
1413                                             pprust::path_to_string(&assoc_path)
1414                                         ),
1415                                         Applicability::MaybeIncorrect,
1416                                     );
1417                                 }
1418                                 _ => {}
1419                             };
1420                         }
1421                     }
1422                 }
1423                 _ => {}
1424             }
1425         }
1426     }
1427     err.note(
1428         "see issue #20041 <https://github.com/rust-lang/rust/issues/20041> for more information",
1429     );
1430     err.emit();
1431 }
1432
1433 pub fn check_crate(session: &Session, krate: &Crate, lints: &mut LintBuffer) -> bool {
1434     let mut validator = AstValidator {
1435         session,
1436         extern_mod: None,
1437         in_trait_impl: false,
1438         has_proc_macro_decls: false,
1439         outer_impl_trait: None,
1440         bound_context: None,
1441         is_impl_trait_banned: false,
1442         is_assoc_ty_bound_banned: false,
1443         lint_buffer: lints,
1444     };
1445     visit::walk_crate(&mut validator, krate);
1446
1447     validator.has_proc_macro_decls
1448 }