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