compiler/rustc_ast_passes/src/ast_validation.rs

   1 // Validate AST before lowering it to HIR.
   2 //
   3 // This pass is supposed to catch things that fit into AST data structures,
   4 // but not permitted by the language. It runs after expansion when AST is frozen,
   5 // so it can check for erroneous constructions produced by syntax extensions.
   6 // This pass is supposed to perform only simple checks not requiring name resolution
   7 // or type checking or some other kind of complex analysis.
   8
   9 use itertools::{Either, Itertools};
  10 use rustc_ast::ptr::P;
  11 use rustc_ast::visit::{self, AssocCtxt, FnCtxt, FnKind, Visitor};
  12 use rustc_ast::walk_list;
  13 use rustc_ast::*;
  14 use rustc_ast_pretty::pprust::{self, State};
  15 use rustc_data_structures::fx::FxHashMap;
  16 use rustc_errors::{error_code, pluralize, struct_span_err, Applicability};
  17 use rustc_parse::validate_attr;
  18 use rustc_session::lint::builtin::{
  19     DEPRECATED_WHERE_CLAUSE_LOCATION, MISSING_ABI, PATTERNS_IN_FNS_WITHOUT_BODY,
  20 };
  21 use rustc_session::lint::{BuiltinLintDiagnostics, LintBuffer};
  22 use rustc_session::Session;
  23 use rustc_span::source_map::Spanned;
  24 use rustc_span::symbol::{kw, sym, Ident};
  25 use rustc_span::Span;
  26 use rustc_target::spec::abi;
  27 use std::mem;
  28 use std::ops::{Deref, DerefMut};
  29
  30 const MORE_EXTERN: &str =
  31     "for more information, visit https://doc.rust-lang.org/std/keyword.extern.html";
  32
  33 /// Is `self` allowed semantically as the first parameter in an `FnDecl`?
  34 enum SelfSemantic {
  35     Yes,
  36     No,
  37 }
  38
  39 struct AstValidator<'a> {
  40     session: &'a Session,
  41
  42     /// The span of the `extern` in an `extern { ... }` block, if any.
  43     extern_mod: Option<&'a Item>,
  44
  45     /// Are we inside a trait impl?
  46     in_trait_impl: bool,
  47
  48     in_const_trait_impl: bool,
  49
  50     has_proc_macro_decls: bool,
  51
  52     /// Used to ban nested `impl Trait`, e.g., `impl Into<impl Debug>`.
  53     /// Nested `impl Trait` _is_ allowed in associated type position,
  54     /// e.g., `impl Iterator<Item = impl Debug>`.
  55     outer_impl_trait: Option<Span>,
  56
  57     is_tilde_const_allowed: bool,
  58
  59     /// Used to ban `impl Trait` in path projections like `<impl Iterator>::Item`
  60     /// or `Foo::Bar<impl Trait>`
  61     is_impl_trait_banned: bool,
  62
  63     /// Used to ban associated type bounds (i.e., `Type<AssocType: Bounds>`) in
  64     /// certain positions.
  65     is_assoc_ty_bound_banned: bool,
  66
  67     /// See [ForbiddenLetReason]
  68     forbidden_let_reason: Option<ForbiddenLetReason>,
  69
  70     lint_buffer: &'a mut LintBuffer,
  71 }
  72
  73 impl<'a> AstValidator<'a> {
  74     fn with_in_trait_impl(
  75         &mut self,
  76         is_in: bool,
  77         constness: Option<Const>,
  78         f: impl FnOnce(&mut Self),
  79     ) {
  80         let old = mem::replace(&mut self.in_trait_impl, is_in);
  81         let old_const =
  82             mem::replace(&mut self.in_const_trait_impl, matches!(constness, Some(Const::Yes(_))));
  83         f(self);
  84         self.in_trait_impl = old;
  85         self.in_const_trait_impl = old_const;
  86     }
  87
  88     fn with_banned_impl_trait(&mut self, f: impl FnOnce(&mut Self)) {
  89         let old = mem::replace(&mut self.is_impl_trait_banned, true);
  90         f(self);
  91         self.is_impl_trait_banned = old;
  92     }
  93
  94     fn with_tilde_const_allowed(&mut self, f: impl FnOnce(&mut Self)) {
  95         let old = mem::replace(&mut self.is_tilde_const_allowed, true);
  96         f(self);
  97         self.is_tilde_const_allowed = old;
  98     }
  99
 100     fn with_banned_tilde_const(&mut self, f: impl FnOnce(&mut Self)) {
 101         let old = mem::replace(&mut self.is_tilde_const_allowed, false);
 102         f(self);
 103         self.is_tilde_const_allowed = old;
 104     }
 105
 106     fn with_let_management(
 107         &mut self,
 108         forbidden_let_reason: Option<ForbiddenLetReason>,
 109         f: impl FnOnce(&mut Self, Option<ForbiddenLetReason>),
 110     ) {
 111         let old = mem::replace(&mut self.forbidden_let_reason, forbidden_let_reason);
 112         f(self, old);
 113         self.forbidden_let_reason = old;
 114     }
 115
 116     /// Emits an error banning the `let` expression provided in the given location.
 117     fn ban_let_expr(&self, expr: &'a Expr, forbidden_let_reason: ForbiddenLetReason) {
 118         let sess = &self.session;
 119         if sess.opts.unstable_features.is_nightly_build() {
 120             let err = "`let` expressions are not supported here";
 121             let mut diag = sess.struct_span_err(expr.span, err);
 122             diag.note("only supported directly in conditions of `if` and `while` expressions");
 123             diag.note("as well as when nested within `&&` and parentheses in those conditions");
 124             if let ForbiddenLetReason::ForbiddenWithOr(span) = forbidden_let_reason {
 125                 diag.span_note(span, "`||` operators are not allowed in let chain expressions");
 126             }
 127             diag.emit();
 128         } else {
 129             sess.struct_span_err(expr.span, "expected expression, found statement (`let`)")
 130                 .note("variable declaration using `let` is a statement")
 131                 .emit();
 132         }
 133     }
 134
 135     fn check_gat_where(
 136         &mut self,
 137         id: NodeId,
 138         before_predicates: &[WherePredicate],
 139         where_clauses: (ast::TyAliasWhereClause, ast::TyAliasWhereClause),
 140     ) {
 141         if !before_predicates.is_empty() {
 142             let mut state = State::new();
 143             if !where_clauses.1.0 {
 144                 state.space();
 145                 state.word_space("where");
 146             } else {
 147                 state.word_space(",");
 148             }
 149             let mut first = true;
 150             for p in before_predicates.iter() {
 151                 if !first {
 152                     state.word_space(",");
 153                 }
 154                 first = false;
 155                 state.print_where_predicate(p);
 156             }
 157             let suggestion = state.s.eof();
 158             self.lint_buffer.buffer_lint_with_diagnostic(
 159                 DEPRECATED_WHERE_CLAUSE_LOCATION,
 160                 id,
 161                 where_clauses.0.1,
 162                 "where clause not allowed here",
 163                 BuiltinLintDiagnostics::DeprecatedWhereclauseLocation(
 164                     where_clauses.1.1.shrink_to_hi(),
 165                     suggestion,
 166                 ),
 167             );
 168         }
 169     }
 170
 171     fn with_banned_assoc_ty_bound(&mut self, f: impl FnOnce(&mut Self)) {
 172         let old = mem::replace(&mut self.is_assoc_ty_bound_banned, true);
 173         f(self);
 174         self.is_assoc_ty_bound_banned = old;
 175     }
 176
 177     fn with_impl_trait(&mut self, outer: Option<Span>, f: impl FnOnce(&mut Self)) {
 178         let old = mem::replace(&mut self.outer_impl_trait, outer);
 179         if outer.is_some() {
 180             self.with_banned_tilde_const(f);
 181         } else {
 182             f(self);
 183         }
 184         self.outer_impl_trait = old;
 185     }
 186
 187     fn visit_assoc_constraint_from_generic_args(&mut self, constraint: &'a AssocConstraint) {
 188         match constraint.kind {
 189             AssocConstraintKind::Equality { .. } => {}
 190             AssocConstraintKind::Bound { .. } => {
 191                 if self.is_assoc_ty_bound_banned {
 192                     self.err_handler().span_err(
 193                         constraint.span,
 194                         "associated type bounds are not allowed within structs, enums, or unions",
 195                     );
 196                 }
 197             }
 198         }
 199         self.visit_assoc_constraint(constraint);
 200     }
 201
 202     // Mirrors `visit::walk_ty`, but tracks relevant state.
 203     fn walk_ty(&mut self, t: &'a Ty) {
 204         match t.kind {
 205             TyKind::ImplTrait(..) => {
 206                 self.with_impl_trait(Some(t.span), |this| visit::walk_ty(this, t))
 207             }
 208             TyKind::TraitObject(..) => self.with_banned_tilde_const(|this| visit::walk_ty(this, t)),
 209             TyKind::Path(ref qself, ref path) => {
 210                 // We allow these:
 211                 //  - `Option<impl Trait>`
 212                 //  - `option::Option<impl Trait>`
 213                 //  - `option::Option<T>::Foo<impl Trait>
 214                 //
 215                 // But not these:
 216                 //  - `<impl Trait>::Foo`
 217                 //  - `option::Option<impl Trait>::Foo`.
 218                 //
 219                 // To implement this, we disallow `impl Trait` from `qself`
 220                 // (for cases like `<impl Trait>::Foo>`)
 221                 // but we allow `impl Trait` in `GenericArgs`
 222                 // iff there are no more PathSegments.
 223                 if let Some(ref qself) = *qself {
 224                     // `impl Trait` in `qself` is always illegal
 225                     self.with_banned_impl_trait(|this| this.visit_ty(&qself.ty));
 226                 }
 227
 228                 // Note that there should be a call to visit_path here,
 229                 // so if any logic is added to process `Path`s a call to it should be
 230                 // added both in visit_path and here. This code mirrors visit::walk_path.
 231                 for (i, segment) in path.segments.iter().enumerate() {
 232                     // Allow `impl Trait` iff we're on the final path segment
 233                     if i == path.segments.len() - 1 {
 234                         self.visit_path_segment(path.span, segment);
 235                     } else {
 236                         self.with_banned_impl_trait(|this| {
 237                             this.visit_path_segment(path.span, segment)
 238                         });
 239                     }
 240                 }
 241             }
 242             _ => visit::walk_ty(self, t),
 243         }
 244     }
 245
 246     fn visit_struct_field_def(&mut self, field: &'a FieldDef) {
 247         if let Some(ident) = field.ident {
 248             if ident.name == kw::Underscore {
 249                 self.visit_vis(&field.vis);
 250                 self.visit_ident(ident);
 251                 self.visit_ty_common(&field.ty);
 252                 self.walk_ty(&field.ty);
 253                 walk_list!(self, visit_attribute, &field.attrs);
 254                 return;
 255             }
 256         }
 257         self.visit_field_def(field);
 258     }
 259
 260     fn err_handler(&self) -> &rustc_errors::Handler {
 261         &self.session.diagnostic()
 262     }
 263
 264     fn check_lifetime(&self, ident: Ident) {
 265         let valid_names = [kw::UnderscoreLifetime, kw::StaticLifetime, kw::Empty];
 266         if !valid_names.contains(&ident.name) && ident.without_first_quote().is_reserved() {
 267             self.err_handler().span_err(ident.span, "lifetimes cannot use keyword names");
 268         }
 269     }
 270
 271     fn check_label(&self, ident: Ident) {
 272         if ident.without_first_quote().is_reserved() {
 273             self.err_handler()
 274                 .span_err(ident.span, &format!("invalid label name `{}`", ident.name));
 275         }
 276     }
 277
 278     fn invalid_visibility(&self, vis: &Visibility, note: Option<&str>) {
 279         if let VisibilityKind::Inherited = vis.kind {
 280             return;
 281         }
 282
 283         let mut err =
 284             struct_span_err!(self.session, vis.span, E0449, "unnecessary visibility qualifier");
 285         if vis.kind.is_pub() {
 286             err.span_label(vis.span, "`pub` not permitted here because it's implied");
 287         }
 288         if let Some(note) = note {
 289             err.note(note);
 290         }
 291         err.emit();
 292     }
 293
 294     fn check_decl_no_pat(decl: &FnDecl, mut report_err: impl FnMut(Span, Option<Ident>, bool)) {
 295         for Param { pat, .. } in &decl.inputs {
 296             match pat.kind {
 297                 PatKind::Ident(BindingMode::ByValue(Mutability::Not), _, None) | PatKind::Wild => {}
 298                 PatKind::Ident(BindingMode::ByValue(Mutability::Mut), ident, None) => {
 299                     report_err(pat.span, Some(ident), true)
 300                 }
 301                 _ => report_err(pat.span, None, false),
 302             }
 303         }
 304     }
 305
 306     fn check_trait_fn_not_async(&self, fn_span: Span, asyncness: Async) {
 307         if let Async::Yes { span, .. } = asyncness {
 308             struct_span_err!(
 309                 self.session,
 310                 fn_span,
 311                 E0706,
 312                 "functions in traits cannot be declared `async`"
 313             )
 314             .span_label(span, "`async` because of this")
 315             .note("`async` trait functions are not currently supported")
 316             .note("consider using the `async-trait` crate: https://crates.io/crates/async-trait")
 317             .emit();
 318         }
 319     }
 320
 321     fn check_trait_fn_not_const(&self, constness: Const) {
 322         if let Const::Yes(span) = constness {
 323             struct_span_err!(
 324                 self.session,
 325                 span,
 326                 E0379,
 327                 "functions in traits cannot be declared const"
 328             )
 329             .span_label(span, "functions in traits cannot be const")
 330             .emit();
 331         }
 332     }
 333
 334     // FIXME(ecstaticmorse): Instead, use `bound_context` to check this in `visit_param_bound`.
 335     fn no_questions_in_bounds(&self, bounds: &GenericBounds, where_: &str, is_trait: bool) {
 336         for bound in bounds {
 337             if let GenericBound::Trait(ref poly, TraitBoundModifier::Maybe) = *bound {
 338                 let mut err = self.err_handler().struct_span_err(
 339                     poly.span,
 340                     &format!("`?Trait` is not permitted in {}", where_),
 341                 );
 342                 if is_trait {
 343                     let path_str = pprust::path_to_string(&poly.trait_ref.path);
 344                     err.note(&format!("traits are `?{}` by default", path_str));
 345                 }
 346                 err.emit();
 347             }
 348         }
 349     }
 350
 351     fn check_late_bound_lifetime_defs(&self, params: &[GenericParam]) {
 352         // Check only lifetime parameters are present and that the lifetime
 353         // parameters that are present have no bounds.
 354         let non_lt_param_spans: Vec<_> = params
 355             .iter()
 356             .filter_map(|param| match param.kind {
 357                 GenericParamKind::Lifetime { .. } => {
 358                     if !param.bounds.is_empty() {
 359                         let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
 360                         self.err_handler()
 361                             .span_err(spans, "lifetime bounds cannot be used in this context");
 362                     }
 363                     None
 364                 }
 365                 _ => Some(param.ident.span),
 366             })
 367             .collect();
 368         if !non_lt_param_spans.is_empty() {
 369             self.err_handler().span_err(
 370                 non_lt_param_spans,
 371                 "only lifetime parameters can be used in this context",
 372             );
 373         }
 374     }
 375
 376     fn check_fn_decl(&self, fn_decl: &FnDecl, self_semantic: SelfSemantic) {
 377         self.check_decl_num_args(fn_decl);
 378         self.check_decl_cvaradic_pos(fn_decl);
 379         self.check_decl_attrs(fn_decl);
 380         self.check_decl_self_param(fn_decl, self_semantic);
 381     }
 382
 383     /// Emits fatal error if function declaration has more than `u16::MAX` arguments
 384     /// Error is fatal to prevent errors during typechecking
 385     fn check_decl_num_args(&self, fn_decl: &FnDecl) {
 386         let max_num_args: usize = u16::MAX.into();
 387         if fn_decl.inputs.len() > max_num_args {
 388             let Param { span, .. } = fn_decl.inputs[0];
 389             self.err_handler().span_fatal(
 390                 span,
 391                 &format!("function can not have more than {} arguments", max_num_args),
 392             );
 393         }
 394     }
 395
 396     fn check_decl_cvaradic_pos(&self, fn_decl: &FnDecl) {
 397         match &*fn_decl.inputs {
 398             [Param { ty, span, .. }] => {
 399                 if let TyKind::CVarArgs = ty.kind {
 400                     self.err_handler().span_err(
 401                         *span,
 402                         "C-variadic function must be declared with at least one named argument",
 403                     );
 404                 }
 405             }
 406             [ps @ .., _] => {
 407                 for Param { ty, span, .. } in ps {
 408                     if let TyKind::CVarArgs = ty.kind {
 409                         self.err_handler().span_err(
 410                             *span,
 411                             "`...` must be the last argument of a C-variadic function",
 412                         );
 413                     }
 414                 }
 415             }
 416             _ => {}
 417         }
 418     }
 419
 420     fn check_decl_attrs(&self, fn_decl: &FnDecl) {
 421         fn_decl
 422             .inputs
 423             .iter()
 424             .flat_map(|i| i.attrs.as_ref())
 425             .filter(|attr| {
 426                 let arr = [sym::allow, sym::cfg, sym::cfg_attr, sym::deny, sym::forbid, sym::warn];
 427                 !arr.contains(&attr.name_or_empty()) && rustc_attr::is_builtin_attr(attr)
 428             })
 429             .for_each(|attr| {
 430                 if attr.is_doc_comment() {
 431                     self.err_handler()
 432                         .struct_span_err(
 433                             attr.span,
 434                             "documentation comments cannot be applied to function parameters",
 435                         )
 436                         .span_label(attr.span, "doc comments are not allowed here")
 437                         .emit();
 438                 } else {
 439                     self.err_handler().span_err(
 440                         attr.span,
 441                         "allow, cfg, cfg_attr, deny, \
 442                 forbid, and warn are the only allowed built-in attributes in function parameters",
 443                     );
 444                 }
 445             });
 446     }
 447
 448     fn check_decl_self_param(&self, fn_decl: &FnDecl, self_semantic: SelfSemantic) {
 449         if let (SelfSemantic::No, [param, ..]) = (self_semantic, &*fn_decl.inputs) {
 450             if param.is_self() {
 451                 self.err_handler()
 452                     .struct_span_err(
 453                         param.span,
 454                         "`self` parameter is only allowed in associated functions",
 455                     )
 456                     .span_label(param.span, "not semantically valid as function parameter")
 457                     .note("associated functions are those in `impl` or `trait` definitions")
 458                     .emit();
 459             }
 460         }
 461     }
 462
 463     fn check_defaultness(&self, span: Span, defaultness: Defaultness) {
 464         if let Defaultness::Default(def_span) = defaultness {
 465             let span = self.session.source_map().guess_head_span(span);
 466             self.err_handler()
 467                 .struct_span_err(span, "`default` is only allowed on items in trait impls")
 468                 .span_label(def_span, "`default` because of this")
 469                 .emit();
 470         }
 471     }
 472
 473     fn error_item_without_body(&self, sp: Span, ctx: &str, msg: &str, sugg: &str) {
 474         self.err_handler()
 475             .struct_span_err(sp, msg)
 476             .span_suggestion(
 477                 self.session.source_map().end_point(sp),
 478                 &format!("provide a definition for the {}", ctx),
 479                 sugg.to_string(),
 480                 Applicability::HasPlaceholders,
 481             )
 482             .emit();
 483     }
 484
 485     fn check_impl_item_provided<T>(&self, sp: Span, body: &Option<T>, ctx: &str, sugg: &str) {
 486         if body.is_none() {
 487             let msg = format!("associated {} in `impl` without body", ctx);
 488             self.error_item_without_body(sp, ctx, &msg, sugg);
 489         }
 490     }
 491
 492     fn check_type_no_bounds(&self, bounds: &[GenericBound], ctx: &str) {
 493         let span = match bounds {
 494             [] => return,
 495             [b0] => b0.span(),
 496             [b0, .., bl] => b0.span().to(bl.span()),
 497         };
 498         self.err_handler()
 499             .struct_span_err(span, &format!("bounds on `type`s in {} have no effect", ctx))
 500             .emit();
 501     }
 502
 503     fn check_foreign_ty_genericless(&self, generics: &Generics, where_span: Span) {
 504         let cannot_have = |span, descr, remove_descr| {
 505             self.err_handler()
 506                 .struct_span_err(
 507                     span,
 508                     &format!("`type`s inside `extern` blocks cannot have {}", descr),
 509                 )
 510                 .span_suggestion(
 511                     span,
 512                     &format!("remove the {}", remove_descr),
 513                     String::new(),
 514                     Applicability::MaybeIncorrect,
 515                 )
 516                 .span_label(self.current_extern_span(), "`extern` block begins here")
 517                 .note(MORE_EXTERN)
 518                 .emit();
 519         };
 520
 521         if !generics.params.is_empty() {
 522             cannot_have(generics.span, "generic parameters", "generic parameters");
 523         }
 524
 525         if !generics.where_clause.predicates.is_empty() {
 526             cannot_have(where_span, "`where` clauses", "`where` clause");
 527         }
 528     }
 529
 530     fn check_foreign_kind_bodyless(&self, ident: Ident, kind: &str, body: Option<Span>) {
 531         let Some(body) = body else {
 532             return;
 533         };
 534         self.err_handler()
 535             .struct_span_err(ident.span, &format!("incorrect `{}` inside `extern` block", kind))
 536             .span_label(ident.span, "cannot have a body")
 537             .span_label(body, "the invalid body")
 538             .span_label(
 539                 self.current_extern_span(),
 540                 format!(
 541                     "`extern` blocks define existing foreign {0}s and {0}s \
 542                     inside of them cannot have a body",
 543                     kind
 544                 ),
 545             )
 546             .note(MORE_EXTERN)
 547             .emit();
 548     }
 549
 550     /// An `fn` in `extern { ... }` cannot have a body `{ ... }`.
 551     fn check_foreign_fn_bodyless(&self, ident: Ident, body: Option<&Block>) {
 552         let Some(body) = body else {
 553             return;
 554         };
 555         self.err_handler()
 556             .struct_span_err(ident.span, "incorrect function inside `extern` block")
 557             .span_label(ident.span, "cannot have a body")
 558             .span_suggestion(
 559                 body.span,
 560                 "remove the invalid body",
 561                 ";".to_string(),
 562                 Applicability::MaybeIncorrect,
 563             )
 564             .help(
 565                 "you might have meant to write a function accessible through FFI, \
 566                 which can be done by writing `extern fn` outside of the `extern` block",
 567             )
 568             .span_label(
 569                 self.current_extern_span(),
 570                 "`extern` blocks define existing foreign functions and functions \
 571                 inside of them cannot have a body",
 572             )
 573             .note(MORE_EXTERN)
 574             .emit();
 575     }
 576
 577     fn current_extern_span(&self) -> Span {
 578         self.session.source_map().guess_head_span(self.extern_mod.unwrap().span)
 579     }
 580
 581     /// An `fn` in `extern { ... }` cannot have qualifiers, e.g. `async fn`.
 582     fn check_foreign_fn_headerless(&self, ident: Ident, span: Span, header: FnHeader) {
 583         if header.has_qualifiers() {
 584             self.err_handler()
 585                 .struct_span_err(ident.span, "functions in `extern` blocks cannot have qualifiers")
 586                 .span_label(self.current_extern_span(), "in this `extern` block")
 587                 .span_suggestion_verbose(
 588                     span.until(ident.span.shrink_to_lo()),
 589                     "remove the qualifiers",
 590                     "fn ".to_string(),
 591                     Applicability::MaybeIncorrect,
 592                 )
 593                 .emit();
 594         }
 595     }
 596
 597     /// An item in `extern { ... }` cannot use non-ascii identifier.
 598     fn check_foreign_item_ascii_only(&self, ident: Ident) {
 599         if !ident.as_str().is_ascii() {
 600             let n = 83942;
 601             self.err_handler()
 602                 .struct_span_err(
 603                     ident.span,
 604                     "items in `extern` blocks cannot use non-ascii identifiers",
 605                 )
 606                 .span_label(self.current_extern_span(), "in this `extern` block")
 607                 .note(&format!(
 608                     "this limitation may be lifted in the future; see issue #{} <https://github.com/rust-lang/rust/issues/{}> for more information",
 609                     n, n,
 610                 ))
 611                 .emit();
 612         }
 613     }
 614
 615     /// Reject C-varadic type unless the function is foreign,
 616     /// or free and `unsafe extern "C"` semantically.
 617     fn check_c_varadic_type(&self, fk: FnKind<'a>) {
 618         match (fk.ctxt(), fk.header()) {
 619             (Some(FnCtxt::Foreign), _) => return,
 620             (Some(FnCtxt::Free), Some(header)) => match header.ext {
 621                 Extern::Explicit(StrLit { symbol_unescaped: sym::C, .. }) | Extern::Implicit
 622                     if matches!(header.unsafety, Unsafe::Yes(_)) =>
 623                 {
 624                     return;
 625                 }
 626                 _ => {}
 627             },
 628             _ => {}
 629         };
 630
 631         for Param { ty, span, .. } in &fk.decl().inputs {
 632             if let TyKind::CVarArgs = ty.kind {
 633                 self.err_handler()
 634                     .struct_span_err(
 635                         *span,
 636                         "only foreign or `unsafe extern \"C\"` functions may be C-variadic",
 637                     )
 638                     .emit();
 639             }
 640         }
 641     }
 642
 643     fn check_item_named(&self, ident: Ident, kind: &str) {
 644         if ident.name != kw::Underscore {
 645             return;
 646         }
 647         self.err_handler()
 648             .struct_span_err(ident.span, &format!("`{}` items in this context need a name", kind))
 649             .span_label(ident.span, format!("`_` is not a valid name for this `{}` item", kind))
 650             .emit();
 651     }
 652
 653     fn check_nomangle_item_asciionly(&self, ident: Ident, item_span: Span) {
 654         if ident.name.as_str().is_ascii() {
 655             return;
 656         }
 657         let head_span = self.session.source_map().guess_head_span(item_span);
 658         struct_span_err!(
 659             self.session,
 660             head_span,
 661             E0754,
 662             "`#[no_mangle]` requires ASCII identifier"
 663         )
 664         .emit();
 665     }
 666
 667     fn check_mod_file_item_asciionly(&self, ident: Ident) {
 668         if ident.name.as_str().is_ascii() {
 669             return;
 670         }
 671         struct_span_err!(
 672             self.session,
 673             ident.span,
 674             E0754,
 675             "trying to load file for module `{}` with non-ascii identifier name",
 676             ident.name
 677         )
 678         .help("consider using `#[path]` attribute to specify filesystem path")
 679         .emit();
 680     }
 681
 682     fn deny_generic_params(&self, generics: &Generics, ident_span: Span) {
 683         if !generics.params.is_empty() {
 684             struct_span_err!(
 685                 self.session,
 686                 generics.span,
 687                 E0567,
 688                 "auto traits cannot have generic parameters"
 689             )
 690             .span_label(ident_span, "auto trait cannot have generic parameters")
 691             .span_suggestion(
 692                 generics.span,
 693                 "remove the parameters",
 694                 String::new(),
 695                 Applicability::MachineApplicable,
 696             )
 697             .emit();
 698         }
 699     }
 700
 701     fn emit_e0568(&self, span: Span, ident_span: Span) {
 702         struct_span_err!(
 703             self.session,
 704             span,
 705             E0568,
 706             "auto traits cannot have super traits or lifetime bounds"
 707         )
 708         .span_label(ident_span, "auto trait cannot have super traits or lifetime bounds")
 709         .span_suggestion(
 710             span,
 711             "remove the super traits or lifetime bounds",
 712             String::new(),
 713             Applicability::MachineApplicable,
 714         )
 715         .emit();
 716     }
 717
 718     fn deny_super_traits(&self, bounds: &GenericBounds, ident_span: Span) {
 719         if let [.., last] = &bounds[..] {
 720             let span = ident_span.shrink_to_hi().to(last.span());
 721             self.emit_e0568(span, ident_span);
 722         }
 723     }
 724
 725     fn deny_where_clause(&self, where_clause: &WhereClause, ident_span: Span) {
 726         if !where_clause.predicates.is_empty() {
 727             self.emit_e0568(where_clause.span, ident_span);
 728         }
 729     }
 730
 731     fn deny_items(&self, trait_items: &[P<AssocItem>], ident_span: Span) {
 732         if !trait_items.is_empty() {
 733             let spans: Vec<_> = trait_items.iter().map(|i| i.ident.span).collect();
 734             let total_span = trait_items.first().unwrap().span.to(trait_items.last().unwrap().span);
 735             struct_span_err!(
 736                 self.session,
 737                 spans,
 738                 E0380,
 739                 "auto traits cannot have associated items"
 740             )
 741             .span_suggestion(
 742                 total_span,
 743                 "remove these associated items",
 744                 String::new(),
 745                 Applicability::MachineApplicable,
 746             )
 747             .span_label(ident_span, "auto trait cannot have associated items")
 748             .emit();
 749         }
 750     }
 751
 752     fn correct_generic_order_suggestion(&self, data: &AngleBracketedArgs) -> String {
 753         // Lifetimes always come first.
 754         let lt_sugg = data.args.iter().filter_map(|arg| match arg {
 755             AngleBracketedArg::Arg(lt @ GenericArg::Lifetime(_)) => {
 756                 Some(pprust::to_string(|s| s.print_generic_arg(lt)))
 757             }
 758             _ => None,
 759         });
 760         let args_sugg = data.args.iter().filter_map(|a| match a {
 761             AngleBracketedArg::Arg(GenericArg::Lifetime(_)) | AngleBracketedArg::Constraint(_) => {
 762                 None
 763             }
 764             AngleBracketedArg::Arg(arg) => Some(pprust::to_string(|s| s.print_generic_arg(arg))),
 765         });
 766         // Constraints always come last.
 767         let constraint_sugg = data.args.iter().filter_map(|a| match a {
 768             AngleBracketedArg::Arg(_) => None,
 769             AngleBracketedArg::Constraint(c) => {
 770                 Some(pprust::to_string(|s| s.print_assoc_constraint(c)))
 771             }
 772         });
 773         format!(
 774             "<{}>",
 775             lt_sugg.chain(args_sugg).chain(constraint_sugg).collect::<Vec<String>>().join(", ")
 776         )
 777     }
 778
 779     /// Enforce generic args coming before constraints in `<...>` of a path segment.
 780     fn check_generic_args_before_constraints(&self, data: &AngleBracketedArgs) {
 781         // Early exit in case it's partitioned as it should be.
 782         if data.args.iter().is_partitioned(|arg| matches!(arg, AngleBracketedArg::Arg(_))) {
 783             return;
 784         }
 785         // Find all generic argument coming after the first constraint...
 786         let (constraint_spans, arg_spans): (Vec<Span>, Vec<Span>) =
 787             data.args.iter().partition_map(|arg| match arg {
 788                 AngleBracketedArg::Constraint(c) => Either::Left(c.span),
 789                 AngleBracketedArg::Arg(a) => Either::Right(a.span()),
 790             });
 791         let args_len = arg_spans.len();
 792         let constraint_len = constraint_spans.len();
 793         // ...and then error:
 794         self.err_handler()
 795             .struct_span_err(
 796                 arg_spans.clone(),
 797                 "generic arguments must come before the first constraint",
 798             )
 799             .span_label(constraint_spans[0], &format!("constraint{}", pluralize!(constraint_len)))
 800             .span_label(
 801                 *arg_spans.iter().last().unwrap(),
 802                 &format!("generic argument{}", pluralize!(args_len)),
 803             )
 804             .span_labels(constraint_spans, "")
 805             .span_labels(arg_spans, "")
 806             .span_suggestion_verbose(
 807                 data.span,
 808                 &format!(
 809                     "move the constraint{} after the generic argument{}",
 810                     pluralize!(constraint_len),
 811                     pluralize!(args_len)
 812                 ),
 813                 self.correct_generic_order_suggestion(&data),
 814                 Applicability::MachineApplicable,
 815             )
 816             .emit();
 817     }
 818
 819     fn visit_ty_common(&mut self, ty: &'a Ty) {
 820         match ty.kind {
 821             TyKind::BareFn(ref bfty) => {
 822                 self.check_fn_decl(&bfty.decl, SelfSemantic::No);
 823                 Self::check_decl_no_pat(&bfty.decl, |span, _, _| {
 824                     struct_span_err!(
 825                         self.session,
 826                         span,
 827                         E0561,
 828                         "patterns aren't allowed in function pointer types"
 829                     )
 830                     .emit();
 831                 });
 832                 self.check_late_bound_lifetime_defs(&bfty.generic_params);
 833                 if let Extern::Implicit = bfty.ext {
 834                     let sig_span = self.session.source_map().next_point(ty.span.shrink_to_lo());
 835                     self.maybe_lint_missing_abi(sig_span, ty.id);
 836                 }
 837             }
 838             TyKind::TraitObject(ref bounds, ..) => {
 839                 let mut any_lifetime_bounds = false;
 840                 for bound in bounds {
 841                     if let GenericBound::Outlives(ref lifetime) = *bound {
 842                         if any_lifetime_bounds {
 843                             struct_span_err!(
 844                                 self.session,
 845                                 lifetime.ident.span,
 846                                 E0226,
 847                                 "only a single explicit lifetime bound is permitted"
 848                             )
 849                             .emit();
 850                             break;
 851                         }
 852                         any_lifetime_bounds = true;
 853                     }
 854                 }
 855                 self.no_questions_in_bounds(bounds, "trait object types", false);
 856             }
 857             TyKind::ImplTrait(_, ref bounds) => {
 858                 if self.is_impl_trait_banned {
 859                     struct_span_err!(
 860                         self.session,
 861                         ty.span,
 862                         E0667,
 863                         "`impl Trait` is not allowed in path parameters"
 864                     )
 865                     .emit();
 866                 }
 867
 868                 if let Some(outer_impl_trait_sp) = self.outer_impl_trait {
 869                     struct_span_err!(
 870                         self.session,
 871                         ty.span,
 872                         E0666,
 873                         "nested `impl Trait` is not allowed"
 874                     )
 875                     .span_label(outer_impl_trait_sp, "outer `impl Trait`")
 876                     .span_label(ty.span, "nested `impl Trait` here")
 877                     .emit();
 878                 }
 879
 880                 if !bounds.iter().any(|b| matches!(b, GenericBound::Trait(..))) {
 881                     self.err_handler().span_err(ty.span, "at least one trait must be specified");
 882                 }
 883             }
 884             _ => {}
 885         }
 886     }
 887
 888     fn maybe_lint_missing_abi(&mut self, span: Span, id: NodeId) {
 889         // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
 890         // call site which do not have a macro backtrace. See #61963.
 891         let is_macro_callsite = self
 892             .session
 893             .source_map()
 894             .span_to_snippet(span)
 895             .map(|snippet| snippet.starts_with("#["))
 896             .unwrap_or(true);
 897         if !is_macro_callsite {
 898             self.lint_buffer.buffer_lint_with_diagnostic(
 899                 MISSING_ABI,
 900                 id,
 901                 span,
 902                 "extern declarations without an explicit ABI are deprecated",
 903                 BuiltinLintDiagnostics::MissingAbi(span, abi::Abi::FALLBACK),
 904             )
 905         }
 906     }
 907 }
 908
 909 /// Checks that generic parameters are in the correct order,
 910 /// which is lifetimes, then types and then consts. (`<'a, T, const N: usize>`)
 911 fn validate_generic_param_order(
 912     handler: &rustc_errors::Handler,
 913     generics: &[GenericParam],
 914     span: Span,
 915 ) {
 916     let mut max_param: Option<ParamKindOrd> = None;
 917     let mut out_of_order = FxHashMap::default();
 918     let mut param_idents = Vec::with_capacity(generics.len());
 919
 920     for (idx, param) in generics.iter().enumerate() {
 921         let ident = param.ident;
 922         let (kind, bounds, span) = (&param.kind, &param.bounds, ident.span);
 923         let (ord_kind, ident) = match &param.kind {
 924             GenericParamKind::Lifetime => (ParamKindOrd::Lifetime, ident.to_string()),
 925             GenericParamKind::Type { default: _ } => (ParamKindOrd::Type, ident.to_string()),
 926             GenericParamKind::Const { ref ty, kw_span: _, default: _ } => {
 927                 let ty = pprust::ty_to_string(ty);
 928                 (ParamKindOrd::Const, format!("const {}: {}", ident, ty))
 929             }
 930         };
 931         param_idents.push((kind, ord_kind, bounds, idx, ident));
 932         match max_param {
 933             Some(max_param) if max_param > ord_kind => {
 934                 let entry = out_of_order.entry(ord_kind).or_insert((max_param, vec![]));
 935                 entry.1.push(span);
 936             }
 937             Some(_) | None => max_param = Some(ord_kind),
 938         };
 939     }
 940
 941     if !out_of_order.is_empty() {
 942         let mut ordered_params = "<".to_string();
 943         param_idents.sort_by_key(|&(_, po, _, i, _)| (po, i));
 944         let mut first = true;
 945         for (kind, _, bounds, _, ident) in param_idents {
 946             if !first {
 947                 ordered_params += ", ";
 948             }
 949             ordered_params += &ident;
 950
 951             if !bounds.is_empty() {
 952                 ordered_params += ": ";
 953                 ordered_params += &pprust::bounds_to_string(&bounds);
 954             }
 955
 956             match kind {
 957                 GenericParamKind::Type { default: Some(default) } => {
 958                     ordered_params += " = ";
 959                     ordered_params += &pprust::ty_to_string(default);
 960                 }
 961                 GenericParamKind::Type { default: None } => (),
 962                 GenericParamKind::Lifetime => (),
 963                 GenericParamKind::Const { ty: _, kw_span: _, default: Some(default) } => {
 964                     ordered_params += " = ";
 965                     ordered_params += &pprust::expr_to_string(&*default.value);
 966                 }
 967                 GenericParamKind::Const { ty: _, kw_span: _, default: None } => (),
 968             }
 969             first = false;
 970         }
 971
 972         ordered_params += ">";
 973
 974         for (param_ord, (max_param, spans)) in &out_of_order {
 975             let mut err = handler.struct_span_err(
 976                 spans.clone(),
 977                 &format!(
 978                     "{} parameters must be declared prior to {} parameters",
 979                     param_ord, max_param,
 980                 ),
 981             );
 982             err.span_suggestion(
 983                 span,
 984                 "reorder the parameters: lifetimes, then consts and types",
 985                 ordered_params.clone(),
 986                 Applicability::MachineApplicable,
 987             );
 988             err.emit();
 989         }
 990     }
 991 }
 992
 993 impl<'a> Visitor<'a> for AstValidator<'a> {
 994     fn visit_attribute(&mut self, attr: &Attribute) {
 995         validate_attr::check_meta(&self.session.parse_sess, attr);
 996     }
 997
 998     fn visit_expr(&mut self, expr: &'a Expr) {
 999         self.with_let_management(Some(ForbiddenLetReason::GenericForbidden), |this, forbidden_let_reason| {
1000             match &expr.kind {
1001                 ExprKind::Binary(Spanned { node: BinOpKind::Or, span }, lhs, rhs) => {
1002                     let forbidden_let_reason = Some(ForbiddenLetReason::ForbiddenWithOr(*span));
1003                     this.with_let_management(forbidden_let_reason, |this, _| this.visit_expr(lhs));
1004                     this.with_let_management(forbidden_let_reason, |this, _| this.visit_expr(rhs));
1005                 }
1006                 ExprKind::If(cond, then, opt_else) => {
1007                     this.visit_block(then);
1008                     walk_list!(this, visit_expr, opt_else);
1009                     this.with_let_management(None, |this, _| this.visit_expr(cond));
1010                     return;
1011                 }
1012                 ExprKind::Let(..) if let Some(elem) = forbidden_let_reason => {
1013                     this.ban_let_expr(expr, elem);
1014                 },
1015                 ExprKind::Match(scrutinee, arms) => {
1016                     this.visit_expr(scrutinee);
1017                     for arm in arms {
1018                         this.visit_expr(&arm.body);
1019                         this.visit_pat(&arm.pat);
1020                         walk_list!(this, visit_attribute, &arm.attrs);
1021                         if let Some(guard) = &arm.guard && let ExprKind::Let(_, guard_expr, _) = &guard.kind {
1022                             this.with_let_management(None, |this, _| {
1023                                 this.visit_expr(guard_expr)
1024                             });
1025                             return;
1026                         }
1027                     }
1028                 }
1029                 ExprKind::Paren(_) | ExprKind::Binary(Spanned { node: BinOpKind::And, .. }, ..) => {
1030                     this.with_let_management(forbidden_let_reason, |this, _| visit::walk_expr(this, expr));
1031                     return;
1032                 }
1033                 ExprKind::While(cond, then, opt_label) => {
1034                     walk_list!(this, visit_label, opt_label);
1035                     this.visit_block(then);
1036                     this.with_let_management(None, |this, _| this.visit_expr(cond));
1037                     return;
1038                 }
1039                 _ => visit::walk_expr(this, expr),
1040             }
1041         });
1042     }
1043
1044     fn visit_ty(&mut self, ty: &'a Ty) {
1045         self.visit_ty_common(ty);
1046         self.walk_ty(ty)
1047     }
1048
1049     fn visit_label(&mut self, label: &'a Label) {
1050         self.check_label(label.ident);
1051         visit::walk_label(self, label);
1052     }
1053
1054     fn visit_lifetime(&mut self, lifetime: &'a Lifetime) {
1055         self.check_lifetime(lifetime.ident);
1056         visit::walk_lifetime(self, lifetime);
1057     }
1058
1059     fn visit_field_def(&mut self, s: &'a FieldDef) {
1060         visit::walk_field_def(self, s)
1061     }
1062
1063     fn visit_item(&mut self, item: &'a Item) {
1064         if item.attrs.iter().any(|attr| self.session.is_proc_macro_attr(attr)) {
1065             self.has_proc_macro_decls = true;
1066         }
1067
1068         if self.session.contains_name(&item.attrs, sym::no_mangle) {
1069             self.check_nomangle_item_asciionly(item.ident, item.span);
1070         }
1071
1072         match item.kind {
1073             ItemKind::Impl(box Impl {
1074                 unsafety,
1075                 polarity,
1076                 defaultness: _,
1077                 constness,
1078                 ref generics,
1079                 of_trait: Some(ref t),
1080                 ref self_ty,
1081                 ref items,
1082             }) => {
1083                 self.with_in_trait_impl(true, Some(constness), |this| {
1084                     this.invalid_visibility(&item.vis, None);
1085                     if let TyKind::Err = self_ty.kind {
1086                         this.err_handler()
1087                             .struct_span_err(
1088                                 item.span,
1089                                 "`impl Trait for .. {}` is an obsolete syntax",
1090                             )
1091                             .help("use `auto trait Trait {}` instead")
1092                             .emit();
1093                     }
1094                     if let (Unsafe::Yes(span), ImplPolarity::Negative(sp)) = (unsafety, polarity) {
1095                         struct_span_err!(
1096                             this.session,
1097                             sp.to(t.path.span),
1098                             E0198,
1099                             "negative impls cannot be unsafe"
1100                         )
1101                         .span_label(sp, "negative because of this")
1102                         .span_label(span, "unsafe because of this")
1103                         .emit();
1104                     }
1105
1106                     this.visit_vis(&item.vis);
1107                     this.visit_ident(item.ident);
1108                     if let Const::Yes(_) = constness {
1109                         this.with_tilde_const_allowed(|this| this.visit_generics(generics));
1110                     } else {
1111                         this.visit_generics(generics);
1112                     }
1113                     this.visit_trait_ref(t);
1114                     this.visit_ty(self_ty);
1115
1116                     walk_list!(this, visit_assoc_item, items, AssocCtxt::Impl);
1117                 });
1118                 return; // Avoid visiting again.
1119             }
1120             ItemKind::Impl(box Impl {
1121                 unsafety,
1122                 polarity,
1123                 defaultness,
1124                 constness,
1125                 generics: _,
1126                 of_trait: None,
1127                 ref self_ty,
1128                 items: _,
1129             }) => {
1130                 let error = |annotation_span, annotation| {
1131                     let mut err = self.err_handler().struct_span_err(
1132                         self_ty.span,
1133                         &format!("inherent impls cannot be {}", annotation),
1134                     );
1135                     err.span_label(annotation_span, &format!("{} because of this", annotation));
1136                     err.span_label(self_ty.span, "inherent impl for this type");
1137                     err
1138                 };
1139
1140                 self.invalid_visibility(
1141                     &item.vis,
1142                     Some("place qualifiers on individual impl items instead"),
1143                 );
1144                 if let Unsafe::Yes(span) = unsafety {
1145                     error(span, "unsafe").code(error_code!(E0197)).emit();
1146                 }
1147                 if let ImplPolarity::Negative(span) = polarity {
1148                     error(span, "negative").emit();
1149                 }
1150                 if let Defaultness::Default(def_span) = defaultness {
1151                     error(def_span, "`default`")
1152                         .note("only trait implementations may be annotated with `default`")
1153                         .emit();
1154                 }
1155                 if let Const::Yes(span) = constness {
1156                     error(span, "`const`")
1157                         .note("only trait implementations may be annotated with `const`")
1158                         .emit();
1159                 }
1160             }
1161             ItemKind::Fn(box Fn { defaultness, ref sig, ref generics, ref body }) => {
1162                 self.check_defaultness(item.span, defaultness);
1163
1164                 if body.is_none() {
1165                     let msg = "free function without a body";
1166                     self.error_item_without_body(item.span, "function", msg, " { <body> }");
1167                 }
1168                 self.visit_vis(&item.vis);
1169                 self.visit_ident(item.ident);
1170                 if let Const::Yes(_) = sig.header.constness {
1171                     self.with_tilde_const_allowed(|this| this.visit_generics(generics));
1172                 } else {
1173                     self.visit_generics(generics);
1174                 }
1175                 let kind = FnKind::Fn(FnCtxt::Free, item.ident, sig, &item.vis, body.as_deref());
1176                 self.visit_fn(kind, item.span, item.id);
1177                 walk_list!(self, visit_attribute, &item.attrs);
1178                 return; // Avoid visiting again.
1179             }
1180             ItemKind::ForeignMod(ForeignMod { abi, unsafety, .. }) => {
1181                 let old_item = mem::replace(&mut self.extern_mod, Some(item));
1182                 self.invalid_visibility(
1183                     &item.vis,
1184                     Some("place qualifiers on individual foreign items instead"),
1185                 );
1186                 if let Unsafe::Yes(span) = unsafety {
1187                     self.err_handler().span_err(span, "extern block cannot be declared unsafe");
1188                 }
1189                 if abi.is_none() {
1190                     self.maybe_lint_missing_abi(item.span, item.id);
1191                 }
1192                 visit::walk_item(self, item);
1193                 self.extern_mod = old_item;
1194                 return; // Avoid visiting again.
1195             }
1196             ItemKind::Enum(ref def, _) => {
1197                 for variant in &def.variants {
1198                     self.invalid_visibility(&variant.vis, None);
1199                     for field in variant.data.fields() {
1200                         self.invalid_visibility(&field.vis, None);
1201                     }
1202                 }
1203             }
1204             ItemKind::Trait(box Trait { is_auto, ref generics, ref bounds, ref items, .. }) => {
1205                 if is_auto == IsAuto::Yes {
1206                     // Auto traits cannot have generics, super traits nor contain items.
1207                     self.deny_generic_params(generics, item.ident.span);
1208                     self.deny_super_traits(bounds, item.ident.span);
1209                     self.deny_where_clause(&generics.where_clause, item.ident.span);
1210                     self.deny_items(items, item.ident.span);
1211                 }
1212                 self.no_questions_in_bounds(bounds, "supertraits", true);
1213
1214                 // Equivalent of `visit::walk_item` for `ItemKind::Trait` that inserts a bound
1215                 // context for the supertraits.
1216                 self.visit_vis(&item.vis);
1217                 self.visit_ident(item.ident);
1218                 self.visit_generics(generics);
1219                 self.with_banned_tilde_const(|this| walk_list!(this, visit_param_bound, bounds));
1220                 walk_list!(self, visit_assoc_item, items, AssocCtxt::Trait);
1221                 walk_list!(self, visit_attribute, &item.attrs);
1222                 return;
1223             }
1224             ItemKind::Mod(unsafety, ref mod_kind) => {
1225                 if let Unsafe::Yes(span) = unsafety {
1226                     self.err_handler().span_err(span, "module cannot be declared unsafe");
1227                 }
1228                 // Ensure that `path` attributes on modules are recorded as used (cf. issue #35584).
1229                 if !matches!(mod_kind, ModKind::Loaded(_, Inline::Yes, _))
1230                     && !self.session.contains_name(&item.attrs, sym::path)
1231                 {
1232                     self.check_mod_file_item_asciionly(item.ident);
1233                 }
1234             }
1235             ItemKind::Struct(ref vdata, ref generics) => match vdata {
1236                 // Duplicating the `Visitor` logic allows catching all cases
1237                 // of `Anonymous(Struct, Union)` outside of a field struct or union.
1238                 //
1239                 // Inside `visit_ty` the validator catches every `Anonymous(Struct, Union)` it
1240                 // encounters, and only on `ItemKind::Struct` and `ItemKind::Union`
1241                 // it uses `visit_ty_common`, which doesn't contain that specific check.
1242                 VariantData::Struct(ref fields, ..) => {
1243                     self.visit_vis(&item.vis);
1244                     self.visit_ident(item.ident);
1245                     self.visit_generics(generics);
1246                     self.with_banned_assoc_ty_bound(|this| {
1247                         walk_list!(this, visit_struct_field_def, fields);
1248                     });
1249                     walk_list!(self, visit_attribute, &item.attrs);
1250                     return;
1251                 }
1252                 _ => {}
1253             },
1254             ItemKind::Union(ref vdata, ref generics) => {
1255                 if vdata.fields().is_empty() {
1256                     self.err_handler().span_err(item.span, "unions cannot have zero fields");
1257                 }
1258                 match vdata {
1259                     VariantData::Struct(ref fields, ..) => {
1260                         self.visit_vis(&item.vis);
1261                         self.visit_ident(item.ident);
1262                         self.visit_generics(generics);
1263                         self.with_banned_assoc_ty_bound(|this| {
1264                             walk_list!(this, visit_struct_field_def, fields);
1265                         });
1266                         walk_list!(self, visit_attribute, &item.attrs);
1267                         return;
1268                     }
1269                     _ => {}
1270                 }
1271             }
1272             ItemKind::Const(def, .., None) => {
1273                 self.check_defaultness(item.span, def);
1274                 let msg = "free constant item without body";
1275                 self.error_item_without_body(item.span, "constant", msg, " = <expr>;");
1276             }
1277             ItemKind::Static(.., None) => {
1278                 let msg = "free static item without body";
1279                 self.error_item_without_body(item.span, "static", msg, " = <expr>;");
1280             }
1281             ItemKind::TyAlias(box TyAlias {
1282                 defaultness,
1283                 where_clauses,
1284                 ref bounds,
1285                 ref ty,
1286                 ..
1287             }) => {
1288                 self.check_defaultness(item.span, defaultness);
1289                 if ty.is_none() {
1290                     let msg = "free type alias without body";
1291                     self.error_item_without_body(item.span, "type", msg, " = <type>;");
1292                 }
1293                 self.check_type_no_bounds(bounds, "this context");
1294                 if where_clauses.1.0 {
1295                     let mut err = self.err_handler().struct_span_err(
1296                         where_clauses.1.1,
1297                         "where clauses are not allowed after the type for type aliases",
1298                     );
1299                     err.note(
1300                         "see issue #89122 <https://github.com/rust-lang/rust/issues/89122> for more information",
1301                     );
1302                     err.emit();
1303                 }
1304             }
1305             _ => {}
1306         }
1307
1308         visit::walk_item(self, item);
1309     }
1310
1311     fn visit_foreign_item(&mut self, fi: &'a ForeignItem) {
1312         match &fi.kind {
1313             ForeignItemKind::Fn(box Fn { defaultness, sig, body, .. }) => {
1314                 self.check_defaultness(fi.span, *defaultness);
1315                 self.check_foreign_fn_bodyless(fi.ident, body.as_deref());
1316                 self.check_foreign_fn_headerless(fi.ident, fi.span, sig.header);
1317                 self.check_foreign_item_ascii_only(fi.ident);
1318             }
1319             ForeignItemKind::TyAlias(box TyAlias {
1320                 defaultness,
1321                 generics,
1322                 where_clauses,
1323                 bounds,
1324                 ty,
1325                 ..
1326             }) => {
1327                 self.check_defaultness(fi.span, *defaultness);
1328                 self.check_foreign_kind_bodyless(fi.ident, "type", ty.as_ref().map(|b| b.span));
1329                 self.check_type_no_bounds(bounds, "`extern` blocks");
1330                 self.check_foreign_ty_genericless(generics, where_clauses.0.1);
1331                 self.check_foreign_item_ascii_only(fi.ident);
1332             }
1333             ForeignItemKind::Static(_, _, body) => {
1334                 self.check_foreign_kind_bodyless(fi.ident, "static", body.as_ref().map(|b| b.span));
1335                 self.check_foreign_item_ascii_only(fi.ident);
1336             }
1337             ForeignItemKind::MacCall(..) => {}
1338         }
1339
1340         visit::walk_foreign_item(self, fi)
1341     }
1342
1343     // Mirrors `visit::walk_generic_args`, but tracks relevant state.
1344     fn visit_generic_args(&mut self, _: Span, generic_args: &'a GenericArgs) {
1345         match *generic_args {
1346             GenericArgs::AngleBracketed(ref data) => {
1347                 self.check_generic_args_before_constraints(data);
1348
1349                 for arg in &data.args {
1350                     match arg {
1351                         AngleBracketedArg::Arg(arg) => self.visit_generic_arg(arg),
1352                         // Type bindings such as `Item = impl Debug` in `Iterator<Item = Debug>`
1353                         // are allowed to contain nested `impl Trait`.
1354                         AngleBracketedArg::Constraint(constraint) => {
1355                             self.with_impl_trait(None, |this| {
1356                                 this.visit_assoc_constraint_from_generic_args(constraint);
1357                             });
1358                         }
1359                     }
1360                 }
1361             }
1362             GenericArgs::Parenthesized(ref data) => {
1363                 walk_list!(self, visit_ty, &data.inputs);
1364                 if let FnRetTy::Ty(ty) = &data.output {
1365                     // `-> Foo` syntax is essentially an associated type binding,
1366                     // so it is also allowed to contain nested `impl Trait`.
1367                     self.with_impl_trait(None, |this| this.visit_ty(ty));
1368                 }
1369             }
1370         }
1371     }
1372
1373     fn visit_generics(&mut self, generics: &'a Generics) {
1374         let mut prev_param_default = None;
1375         for param in &generics.params {
1376             match param.kind {
1377                 GenericParamKind::Lifetime => (),
1378                 GenericParamKind::Type { default: Some(_), .. }
1379                 | GenericParamKind::Const { default: Some(_), .. } => {
1380                     prev_param_default = Some(param.ident.span);
1381                 }
1382                 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1383                     if let Some(span) = prev_param_default {
1384                         let mut err = self.err_handler().struct_span_err(
1385                             span,
1386                             "generic parameters with a default must be trailing",
1387                         );
1388                         err.emit();
1389                         break;
1390                     }
1391                 }
1392             }
1393         }
1394
1395         validate_generic_param_order(self.err_handler(), &generics.params, generics.span);
1396
1397         for predicate in &generics.where_clause.predicates {
1398             if let WherePredicate::EqPredicate(ref predicate) = *predicate {
1399                 deny_equality_constraints(self, predicate, generics);
1400             }
1401         }
1402         walk_list!(self, visit_generic_param, &generics.params);
1403         for predicate in &generics.where_clause.predicates {
1404             match predicate {
1405                 WherePredicate::BoundPredicate(bound_pred) => {
1406                     // A type binding, eg `for<'c> Foo: Send+Clone+'c`
1407                     self.check_late_bound_lifetime_defs(&bound_pred.bound_generic_params);
1408
1409                     // This is slightly complicated. Our representation for poly-trait-refs contains a single
1410                     // binder and thus we only allow a single level of quantification. However,
1411                     // the syntax of Rust permits quantification in two places in where clauses,
1412                     // e.g., `T: for <'a> Foo<'a>` and `for <'a, 'b> &'b T: Foo<'a>`. If both are
1413                     // defined, then error.
1414                     if !bound_pred.bound_generic_params.is_empty() {
1415                         for bound in &bound_pred.bounds {
1416                             match bound {
1417                                 GenericBound::Trait(t, _) => {
1418                                     if !t.bound_generic_params.is_empty() {
1419                                         struct_span_err!(
1420                                             self.err_handler(),
1421                                             t.span,
1422                                             E0316,
1423                                             "nested quantification of lifetimes"
1424                                         )
1425                                         .emit();
1426                                     }
1427                                 }
1428                                 GenericBound::Outlives(_) => {}
1429                             }
1430                         }
1431                     }
1432                 }
1433                 _ => {}
1434             }
1435             self.visit_where_predicate(predicate);
1436         }
1437     }
1438
1439     fn visit_generic_param(&mut self, param: &'a GenericParam) {
1440         if let GenericParamKind::Lifetime { .. } = param.kind {
1441             self.check_lifetime(param.ident);
1442         }
1443         visit::walk_generic_param(self, param);
1444     }
1445
1446     fn visit_param_bound(&mut self, bound: &'a GenericBound) {
1447         match bound {
1448             GenericBound::Trait(_, TraitBoundModifier::MaybeConst) => {
1449                 if !self.is_tilde_const_allowed {
1450                     self.err_handler()
1451                         .struct_span_err(bound.span(), "`~const` is not allowed here")
1452                         .note("only allowed on bounds on traits' associated types and functions, const fns, const impls and its associated functions")
1453                         .emit();
1454                 }
1455             }
1456
1457             GenericBound::Trait(_, TraitBoundModifier::MaybeConstMaybe) => {
1458                 self.err_handler()
1459                     .span_err(bound.span(), "`~const` and `?` are mutually exclusive");
1460             }
1461
1462             _ => {}
1463         }
1464
1465         visit::walk_param_bound(self, bound)
1466     }
1467
1468     fn visit_poly_trait_ref(&mut self, t: &'a PolyTraitRef, m: &'a TraitBoundModifier) {
1469         self.check_late_bound_lifetime_defs(&t.bound_generic_params);
1470         visit::walk_poly_trait_ref(self, t, m);
1471     }
1472
1473     fn visit_variant_data(&mut self, s: &'a VariantData) {
1474         self.with_banned_assoc_ty_bound(|this| visit::walk_struct_def(this, s))
1475     }
1476
1477     fn visit_enum_def(
1478         &mut self,
1479         enum_definition: &'a EnumDef,
1480         generics: &'a Generics,
1481         item_id: NodeId,
1482         _: Span,
1483     ) {
1484         self.with_banned_assoc_ty_bound(|this| {
1485             visit::walk_enum_def(this, enum_definition, generics, item_id)
1486         })
1487     }
1488
1489     fn visit_fn(&mut self, fk: FnKind<'a>, span: Span, id: NodeId) {
1490         // Only associated `fn`s can have `self` parameters.
1491         let self_semantic = match fk.ctxt() {
1492             Some(FnCtxt::Assoc(_)) => SelfSemantic::Yes,
1493             _ => SelfSemantic::No,
1494         };
1495         self.check_fn_decl(fk.decl(), self_semantic);
1496
1497         self.check_c_varadic_type(fk);
1498
1499         // Functions cannot both be `const async`
1500         if let Some(FnHeader {
1501             constness: Const::Yes(cspan),
1502             asyncness: Async::Yes { span: aspan, .. },
1503             ..
1504         }) = fk.header()
1505         {
1506             self.err_handler()
1507                 .struct_span_err(
1508                     vec![*cspan, *aspan],
1509                     "functions cannot be both `const` and `async`",
1510                 )
1511                 .span_label(*cspan, "`const` because of this")
1512                 .span_label(*aspan, "`async` because of this")
1513                 .span_label(span, "") // Point at the fn header.
1514                 .emit();
1515         }
1516
1517         if let FnKind::Fn(
1518             _,
1519             _,
1520             FnSig { span: sig_span, header: FnHeader { ext: Extern::Implicit, .. }, .. },
1521             _,
1522             _,
1523         ) = fk
1524         {
1525             self.maybe_lint_missing_abi(*sig_span, id);
1526         }
1527
1528         // Functions without bodies cannot have patterns.
1529         if let FnKind::Fn(ctxt, _, sig, _, None) = fk {
1530             Self::check_decl_no_pat(&sig.decl, |span, ident, mut_ident| {
1531                 let (code, msg, label) = match ctxt {
1532                     FnCtxt::Foreign => (
1533                         error_code!(E0130),
1534                         "patterns aren't allowed in foreign function declarations",
1535                         "pattern not allowed in foreign function",
1536                     ),
1537                     _ => (
1538                         error_code!(E0642),
1539                         "patterns aren't allowed in functions without bodies",
1540                         "pattern not allowed in function without body",
1541                     ),
1542                 };
1543                 if mut_ident && matches!(ctxt, FnCtxt::Assoc(_)) {
1544                     if let Some(ident) = ident {
1545                         let diag = BuiltinLintDiagnostics::PatternsInFnsWithoutBody(span, ident);
1546                         self.lint_buffer.buffer_lint_with_diagnostic(
1547                             PATTERNS_IN_FNS_WITHOUT_BODY,
1548                             id,
1549                             span,
1550                             msg,
1551                             diag,
1552                         )
1553                     }
1554                 } else {
1555                     self.err_handler()
1556                         .struct_span_err(span, msg)
1557                         .span_label(span, label)
1558                         .code(code)
1559                         .emit();
1560                 }
1561             });
1562         }
1563
1564         visit::walk_fn(self, fk, span);
1565     }
1566
1567     fn visit_assoc_item(&mut self, item: &'a AssocItem, ctxt: AssocCtxt) {
1568         if self.session.contains_name(&item.attrs, sym::no_mangle) {
1569             self.check_nomangle_item_asciionly(item.ident, item.span);
1570         }
1571
1572         if ctxt == AssocCtxt::Trait || !self.in_trait_impl {
1573             self.check_defaultness(item.span, item.kind.defaultness());
1574         }
1575
1576         if ctxt == AssocCtxt::Impl {
1577             match &item.kind {
1578                 AssocItemKind::Const(_, _, body) => {
1579                     self.check_impl_item_provided(item.span, body, "constant", " = <expr>;");
1580                 }
1581                 AssocItemKind::Fn(box Fn { body, .. }) => {
1582                     self.check_impl_item_provided(item.span, body, "function", " { <body> }");
1583                 }
1584                 AssocItemKind::TyAlias(box TyAlias {
1585                     generics,
1586                     where_clauses,
1587                     where_predicates_split,
1588                     bounds,
1589                     ty,
1590                     ..
1591                 }) => {
1592                     self.check_impl_item_provided(item.span, ty, "type", " = <type>;");
1593                     self.check_type_no_bounds(bounds, "`impl`s");
1594                     if ty.is_some() {
1595                         self.check_gat_where(
1596                             item.id,
1597                             generics.where_clause.predicates.split_at(*where_predicates_split).0,
1598                             *where_clauses,
1599                         );
1600                     }
1601                 }
1602                 _ => {}
1603             }
1604         }
1605
1606         if ctxt == AssocCtxt::Trait || self.in_trait_impl {
1607             self.invalid_visibility(&item.vis, None);
1608             if let AssocItemKind::Fn(box Fn { sig, .. }) = &item.kind {
1609                 self.check_trait_fn_not_const(sig.header.constness);
1610                 self.check_trait_fn_not_async(item.span, sig.header.asyncness);
1611             }
1612         }
1613
1614         if let AssocItemKind::Const(..) = item.kind {
1615             self.check_item_named(item.ident, "const");
1616         }
1617
1618         match item.kind {
1619             AssocItemKind::TyAlias(box TyAlias { ref generics, ref bounds, ref ty, .. })
1620                 if ctxt == AssocCtxt::Trait =>
1621             {
1622                 self.visit_vis(&item.vis);
1623                 self.visit_ident(item.ident);
1624                 walk_list!(self, visit_attribute, &item.attrs);
1625                 self.with_tilde_const_allowed(|this| {
1626                     this.visit_generics(generics);
1627                     walk_list!(this, visit_param_bound, bounds);
1628                 });
1629                 walk_list!(self, visit_ty, ty);
1630             }
1631             AssocItemKind::Fn(box Fn { ref sig, ref generics, ref body, .. })
1632                 if self.in_const_trait_impl
1633                     || ctxt == AssocCtxt::Trait
1634                     || matches!(sig.header.constness, Const::Yes(_)) =>
1635             {
1636                 self.visit_vis(&item.vis);
1637                 self.visit_ident(item.ident);
1638                 self.with_tilde_const_allowed(|this| this.visit_generics(generics));
1639                 let kind =
1640                     FnKind::Fn(FnCtxt::Assoc(ctxt), item.ident, sig, &item.vis, body.as_deref());
1641                 self.visit_fn(kind, item.span, item.id);
1642             }
1643             _ => self
1644                 .with_in_trait_impl(false, None, |this| visit::walk_assoc_item(this, item, ctxt)),
1645         }
1646     }
1647 }
1648
1649 /// When encountering an equality constraint in a `where` clause, emit an error. If the code seems
1650 /// like it's setting an associated type, provide an appropriate suggestion.
1651 fn deny_equality_constraints(
1652     this: &mut AstValidator<'_>,
1653     predicate: &WhereEqPredicate,
1654     generics: &Generics,
1655 ) {
1656     let mut err = this.err_handler().struct_span_err(
1657         predicate.span,
1658         "equality constraints are not yet supported in `where` clauses",
1659     );
1660     err.span_label(predicate.span, "not supported");
1661
1662     // Given `<A as Foo>::Bar = RhsTy`, suggest `A: Foo<Bar = RhsTy>`.
1663     if let TyKind::Path(Some(qself), full_path) = &predicate.lhs_ty.kind {
1664         if let TyKind::Path(None, path) = &qself.ty.kind {
1665             match &path.segments[..] {
1666                 [PathSegment { ident, args: None, .. }] => {
1667                     for param in &generics.params {
1668                         if param.ident == *ident {
1669                             let param = ident;
1670                             match &full_path.segments[qself.position..] {
1671                                 [PathSegment { ident, args, .. }] => {
1672                                     // Make a new `Path` from `foo::Bar` to `Foo<Bar = RhsTy>`.
1673                                     let mut assoc_path = full_path.clone();
1674                                     // Remove `Bar` from `Foo::Bar`.
1675                                     assoc_path.segments.pop();
1676                                     let len = assoc_path.segments.len() - 1;
1677                                     let gen_args = args.as_ref().map(|p| (**p).clone());
1678                                     // Build `<Bar = RhsTy>`.
1679                                     let arg = AngleBracketedArg::Constraint(AssocConstraint {
1680                                         id: rustc_ast::node_id::DUMMY_NODE_ID,
1681                                         ident: *ident,
1682                                         gen_args,
1683                                         kind: AssocConstraintKind::Equality {
1684                                             term: predicate.rhs_ty.clone().into(),
1685                                         },
1686                                         span: ident.span,
1687                                     });
1688                                     // Add `<Bar = RhsTy>` to `Foo`.
1689                                     match &mut assoc_path.segments[len].args {
1690                                         Some(args) => match args.deref_mut() {
1691                                             GenericArgs::Parenthesized(_) => continue,
1692                                             GenericArgs::AngleBracketed(args) => {
1693                                                 args.args.push(arg);
1694                                             }
1695                                         },
1696                                         empty_args => {
1697                                             *empty_args = AngleBracketedArgs {
1698                                                 span: ident.span,
1699                                                 args: vec![arg],
1700                                             }
1701                                             .into();
1702                                         }
1703                                     }
1704                                     err.span_suggestion_verbose(
1705                                         predicate.span,
1706                                         &format!(
1707                                             "if `{}` is an associated type you're trying to set, \
1708                                             use the associated type binding syntax",
1709                                             ident
1710                                         ),
1711                                         format!(
1712                                             "{}: {}",
1713                                             param,
1714                                             pprust::path_to_string(&assoc_path)
1715                                         ),
1716                                         Applicability::MaybeIncorrect,
1717                                     );
1718                                 }
1719                                 _ => {}
1720                             };
1721                         }
1722                     }
1723                 }
1724                 _ => {}
1725             }
1726         }
1727     }
1728     // Given `A: Foo, A::Bar = RhsTy`, suggest `A: Foo<Bar = RhsTy>`.
1729     if let TyKind::Path(None, full_path) = &predicate.lhs_ty.kind {
1730         if let [potential_param, potential_assoc] = &full_path.segments[..] {
1731             for param in &generics.params {
1732                 if param.ident == potential_param.ident {
1733                     for bound in &param.bounds {
1734                         if let ast::GenericBound::Trait(trait_ref, TraitBoundModifier::None) = bound
1735                         {
1736                             if let [trait_segment] = &trait_ref.trait_ref.path.segments[..] {
1737                                 let assoc = pprust::path_to_string(&ast::Path::from_ident(
1738                                     potential_assoc.ident,
1739                                 ));
1740                                 let ty = pprust::ty_to_string(&predicate.rhs_ty);
1741                                 let (args, span) = match &trait_segment.args {
1742                                     Some(args) => match args.deref() {
1743                                         ast::GenericArgs::AngleBracketed(args) => {
1744                                             let Some(arg) = args.args.last() else {
1745                                                 continue;
1746                                             };
1747                                             (
1748                                                 format!(", {} = {}", assoc, ty),
1749                                                 arg.span().shrink_to_hi(),
1750                                             )
1751                                         }
1752                                         _ => continue,
1753                                     },
1754                                     None => (
1755                                         format!("<{} = {}>", assoc, ty),
1756                                         trait_segment.span().shrink_to_hi(),
1757                                     ),
1758                                 };
1759                                 err.multipart_suggestion(
1760                                     &format!(
1761                                         "if `{}::{}` is an associated type you're trying to set, \
1762                                         use the associated type binding syntax",
1763                                         trait_segment.ident, potential_assoc.ident,
1764                                     ),
1765                                     vec![(span, args), (predicate.span, String::new())],
1766                                     Applicability::MaybeIncorrect,
1767                                 );
1768                             }
1769                         }
1770                     }
1771                 }
1772             }
1773         }
1774     }
1775     err.note(
1776         "see issue #20041 <https://github.com/rust-lang/rust/issues/20041> for more information",
1777     );
1778     err.emit();
1779 }
1780
1781 pub fn check_crate(session: &Session, krate: &Crate, lints: &mut LintBuffer) -> bool {
1782     let mut validator = AstValidator {
1783         session,
1784         extern_mod: None,
1785         in_trait_impl: false,
1786         in_const_trait_impl: false,
1787         has_proc_macro_decls: false,
1788         outer_impl_trait: None,
1789         is_tilde_const_allowed: false,
1790         is_impl_trait_banned: false,
1791         is_assoc_ty_bound_banned: false,
1792         forbidden_let_reason: Some(ForbiddenLetReason::GenericForbidden),
1793         lint_buffer: lints,
1794     };
1795     visit::walk_crate(&mut validator, krate);
1796
1797     validator.has_proc_macro_decls
1798 }
1799
1800 /// Used to forbid `let` expressions in certain syntactic locations.
1801 #[derive(Clone, Copy)]
1802 enum ForbiddenLetReason {
1803     /// A let chain with the `||` operator
1804     ForbiddenWithOr(Span),
1805     /// `let` is not valid and the source environment is not important
1806     GenericForbidden,
1807 }