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