src/librustc_ast_passes/ast_validation.rs

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