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