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, FatalError};
  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 = defaultness {
 404             self.err_handler()
 405                 .struct_span_err(span, "`default` is only allowed on items in `impl` definitions")
 406                 .emit();
 407         }
 408     }
 409
 410     fn error_item_without_body(&self, sp: Span, ctx: &str, msg: &str, sugg: &str) {
 411         self.err_handler()
 412             .struct_span_err(sp, msg)
 413             .span_suggestion(
 414                 self.session.source_map().end_point(sp),
 415                 &format!("provide a definition for the {}", ctx),
 416                 sugg.to_string(),
 417                 Applicability::HasPlaceholders,
 418             )
 419             .emit();
 420     }
 421
 422     fn check_impl_item_provided<T>(&self, sp: Span, body: &Option<T>, ctx: &str, sugg: &str) {
 423         if body.is_none() {
 424             let msg = format!("associated {} in `impl` without body", ctx);
 425             self.error_item_without_body(sp, ctx, &msg, sugg);
 426         }
 427     }
 428
 429     fn check_type_no_bounds(&self, bounds: &[GenericBound], ctx: &str) {
 430         let span = match bounds {
 431             [] => return,
 432             [b0] => b0.span(),
 433             [b0, .., bl] => b0.span().to(bl.span()),
 434         };
 435         self.err_handler()
 436             .struct_span_err(span, &format!("bounds on `type`s in {} have no effect", ctx))
 437             .emit();
 438     }
 439
 440     fn check_foreign_ty_genericless(&self, generics: &Generics) {
 441         let cannot_have = |span, descr, remove_descr| {
 442             self.err_handler()
 443                 .struct_span_err(
 444                     span,
 445                     &format!("`type`s inside `extern` blocks cannot have {}", descr),
 446                 )
 447                 .span_suggestion(
 448                     span,
 449                     &format!("remove the {}", remove_descr),
 450                     String::new(),
 451                     Applicability::MaybeIncorrect,
 452                 )
 453                 .span_label(self.current_extern_span(), "`extern` block begins here")
 454                 .note(MORE_EXTERN)
 455                 .emit();
 456         };
 457
 458         if !generics.params.is_empty() {
 459             cannot_have(generics.span, "generic parameters", "generic parameters");
 460         }
 461
 462         if !generics.where_clause.predicates.is_empty() {
 463             cannot_have(generics.where_clause.span, "`where` clauses", "`where` clause");
 464         }
 465     }
 466
 467     fn check_foreign_kind_bodyless(&self, ident: Ident, kind: &str, body: Option<Span>) {
 468         let body = match body {
 469             None => return,
 470             Some(body) => body,
 471         };
 472         self.err_handler()
 473             .struct_span_err(ident.span, &format!("incorrect `{}` inside `extern` block", kind))
 474             .span_label(ident.span, "cannot have a body")
 475             .span_label(body, "the invalid body")
 476             .span_label(
 477                 self.current_extern_span(),
 478                 format!(
 479                     "`extern` blocks define existing foreign {0}s and {0}s \
 480                     inside of them cannot have a body",
 481                     kind
 482                 ),
 483             )
 484             .note(MORE_EXTERN)
 485             .emit();
 486     }
 487
 488     /// An `fn` in `extern { ... }` cannot have a body `{ ... }`.
 489     fn check_foreign_fn_bodyless(&self, ident: Ident, body: Option<&Block>) {
 490         let body = match body {
 491             None => return,
 492             Some(body) => body,
 493         };
 494         self.err_handler()
 495             .struct_span_err(ident.span, "incorrect function inside `extern` block")
 496             .span_label(ident.span, "cannot have a body")
 497             .span_suggestion(
 498                 body.span,
 499                 "remove the invalid body",
 500                 ";".to_string(),
 501                 Applicability::MaybeIncorrect,
 502             )
 503             .help(
 504                 "you might have meant to write a function accessible through FFI, \
 505                 which can be done by writing `extern fn` outside of the `extern` block",
 506             )
 507             .span_label(
 508                 self.current_extern_span(),
 509                 "`extern` blocks define existing foreign functions and functions \
 510                 inside of them cannot have a body",
 511             )
 512             .note(MORE_EXTERN)
 513             .emit();
 514     }
 515
 516     fn current_extern_span(&self) -> Span {
 517         self.session.source_map().def_span(self.extern_mod.unwrap().span)
 518     }
 519
 520     /// An `fn` in `extern { ... }` cannot have qualfiers, e.g. `async fn`.
 521     fn check_foreign_fn_headerless(&self, ident: Ident, span: Span, header: FnHeader) {
 522         if header.has_qualifiers() {
 523             self.err_handler()
 524                 .struct_span_err(ident.span, "functions in `extern` blocks cannot have qualifiers")
 525                 .span_label(self.current_extern_span(), "in this `extern` block")
 526                 .span_suggestion(
 527                     span.until(ident.span.shrink_to_lo()),
 528                     "remove the qualifiers",
 529                     "fn ".to_string(),
 530                     Applicability::MaybeIncorrect,
 531                 )
 532                 .emit();
 533         }
 534     }
 535
 536     /// Reject C-varadic type unless the function is foreign,
 537     /// or free and `unsafe extern "C"` semantically.
 538     fn check_c_varadic_type(&self, fk: FnKind<'a>) {
 539         match (fk.ctxt(), fk.header()) {
 540             (Some(FnCtxt::Foreign), _) => return,
 541             (Some(FnCtxt::Free), Some(header)) => match header.ext {
 542                 Extern::Explicit(StrLit { symbol_unescaped: sym::C, .. }) | Extern::Implicit
 543                     if matches!(header.unsafety, Unsafe::Yes(_)) =>
 544                 {
 545                     return;
 546                 }
 547                 _ => {}
 548             },
 549             _ => {}
 550         };
 551
 552         for Param { ty, span, .. } in &fk.decl().inputs {
 553             if let TyKind::CVarArgs = ty.kind {
 554                 self.err_handler()
 555                     .struct_span_err(
 556                         *span,
 557                         "only foreign or `unsafe extern \"C\" functions may be C-variadic",
 558                     )
 559                     .emit();
 560             }
 561         }
 562     }
 563
 564     /// We currently do not permit const generics in `const fn`,
 565     /// as this is tantamount to allowing compile-time dependent typing.
 566     ///
 567     /// FIXME(const_generics): Is this really true / necessary? Discuss with @varkor.
 568     /// At any rate, the restriction feels too syntactic. Consider moving it to e.g. typeck.
 569     fn check_const_fn_const_generic(&self, span: Span, sig: &FnSig, generics: &Generics) {
 570         if let Const::Yes(const_span) = sig.header.constness {
 571             // Look for const generics and error if we find any.
 572             for param in &generics.params {
 573                 if let GenericParamKind::Const { .. } = param.kind {
 574                     self.err_handler()
 575                         .struct_span_err(
 576                             span,
 577                             "const parameters are not permitted in const functions",
 578                         )
 579                         .span_label(const_span, "`const` because of this")
 580                         .emit();
 581                 }
 582             }
 583         }
 584     }
 585
 586     fn check_item_named(&self, ident: Ident, kind: &str) {
 587         if ident.name != kw::Underscore {
 588             return;
 589         }
 590         self.err_handler()
 591             .struct_span_err(ident.span, &format!("`{}` items in this context need a name", kind))
 592             .span_label(ident.span, format!("`_` is not a valid name for this `{}` item", kind))
 593             .emit();
 594     }
 595 }
 596
 597 enum GenericPosition {
 598     Param,
 599     Arg,
 600 }
 601
 602 fn validate_generics_order<'a>(
 603     sess: &Session,
 604     handler: &rustc_errors::Handler,
 605     generics: impl Iterator<Item = (ParamKindOrd, Option<&'a [GenericBound]>, Span, Option<String>)>,
 606     pos: GenericPosition,
 607     span: Span,
 608 ) {
 609     let mut max_param: Option<ParamKindOrd> = None;
 610     let mut out_of_order = FxHashMap::default();
 611     let mut param_idents = vec![];
 612     let mut found_type = false;
 613     let mut found_const = false;
 614
 615     for (kind, bounds, span, ident) in generics {
 616         if let Some(ident) = ident {
 617             param_idents.push((kind, bounds, param_idents.len(), ident));
 618         }
 619         let max_param = &mut max_param;
 620         match max_param {
 621             Some(max_param) if *max_param > kind => {
 622                 let entry = out_of_order.entry(kind).or_insert((*max_param, vec![]));
 623                 entry.1.push(span);
 624             }
 625             Some(_) | None => *max_param = Some(kind),
 626         };
 627         match kind {
 628             ParamKindOrd::Type => found_type = true,
 629             ParamKindOrd::Const => found_const = true,
 630             _ => {}
 631         }
 632     }
 633
 634     let mut ordered_params = "<".to_string();
 635     if !out_of_order.is_empty() {
 636         param_idents.sort_by_key(|&(po, _, i, _)| (po, i));
 637         let mut first = true;
 638         for (_, bounds, _, ident) in param_idents {
 639             if !first {
 640                 ordered_params += ", ";
 641             }
 642             ordered_params += &ident;
 643             if let Some(bounds) = bounds {
 644                 if !bounds.is_empty() {
 645                     ordered_params += ": ";
 646                     ordered_params += &pprust::bounds_to_string(&bounds);
 647                 }
 648             }
 649             first = false;
 650         }
 651     }
 652     ordered_params += ">";
 653
 654     let pos_str = match pos {
 655         GenericPosition::Param => "parameter",
 656         GenericPosition::Arg => "argument",
 657     };
 658
 659     for (param_ord, (max_param, spans)) in &out_of_order {
 660         let mut err = handler.struct_span_err(
 661             spans.clone(),
 662             &format!(
 663                 "{} {pos}s must be declared prior to {} {pos}s",
 664                 param_ord,
 665                 max_param,
 666                 pos = pos_str,
 667             ),
 668         );
 669         if let GenericPosition::Param = pos {
 670             err.span_suggestion(
 671                 span,
 672                 &format!(
 673                     "reorder the {}s: lifetimes, then types{}",
 674                     pos_str,
 675                     if sess.features_untracked().const_generics { ", then consts" } else { "" },
 676                 ),
 677                 ordered_params.clone(),
 678                 Applicability::MachineApplicable,
 679             );
 680         }
 681         err.emit();
 682     }
 683
 684     // FIXME(const_generics): we shouldn't have to abort here at all, but we currently get ICEs
 685     // if we don't. Const parameters and type parameters can currently conflict if they
 686     // are out-of-order.
 687     if !out_of_order.is_empty() && found_type && found_const {
 688         FatalError.raise();
 689     }
 690 }
 691
 692 impl<'a> Visitor<'a> for AstValidator<'a> {
 693     fn visit_attribute(&mut self, attr: &Attribute) {
 694         validate_attr::check_meta(&self.session.parse_sess, attr);
 695     }
 696
 697     fn visit_expr(&mut self, expr: &'a Expr) {
 698         match &expr.kind {
 699             ExprKind::InlineAsm(..) if !self.session.target.target.options.allow_asm => {
 700                 struct_span_err!(
 701                     self.session,
 702                     expr.span,
 703                     E0472,
 704                     "asm! is unsupported on this target"
 705                 )
 706                 .emit();
 707             }
 708             _ => {}
 709         }
 710
 711         visit::walk_expr(self, expr);
 712     }
 713
 714     fn visit_ty(&mut self, ty: &'a Ty) {
 715         match ty.kind {
 716             TyKind::BareFn(ref bfty) => {
 717                 self.check_fn_decl(&bfty.decl, SelfSemantic::No);
 718                 Self::check_decl_no_pat(&bfty.decl, |span, _| {
 719                     struct_span_err!(
 720                         self.session,
 721                         span,
 722                         E0561,
 723                         "patterns aren't allowed in function pointer types"
 724                     )
 725                     .emit();
 726                 });
 727                 self.check_late_bound_lifetime_defs(&bfty.generic_params);
 728             }
 729             TyKind::TraitObject(ref bounds, ..) => {
 730                 let mut any_lifetime_bounds = false;
 731                 for bound in bounds {
 732                     if let GenericBound::Outlives(ref lifetime) = *bound {
 733                         if any_lifetime_bounds {
 734                             struct_span_err!(
 735                                 self.session,
 736                                 lifetime.ident.span,
 737                                 E0226,
 738                                 "only a single explicit lifetime bound is permitted"
 739                             )
 740                             .emit();
 741                             break;
 742                         }
 743                         any_lifetime_bounds = true;
 744                     }
 745                 }
 746                 self.no_questions_in_bounds(bounds, "trait object types", false);
 747             }
 748             TyKind::ImplTrait(_, ref bounds) => {
 749                 if self.is_impl_trait_banned {
 750                     struct_span_err!(
 751                         self.session,
 752                         ty.span,
 753                         E0667,
 754                         "`impl Trait` is not allowed in path parameters"
 755                     )
 756                     .emit();
 757                 }
 758
 759                 if let Some(outer_impl_trait_sp) = self.outer_impl_trait {
 760                     struct_span_err!(
 761                         self.session,
 762                         ty.span,
 763                         E0666,
 764                         "nested `impl Trait` is not allowed"
 765                     )
 766                     .span_label(outer_impl_trait_sp, "outer `impl Trait`")
 767                     .span_label(ty.span, "nested `impl Trait` here")
 768                     .emit();
 769                 }
 770
 771                 if !bounds
 772                     .iter()
 773                     .any(|b| if let GenericBound::Trait(..) = *b { true } else { false })
 774                 {
 775                     self.err_handler().span_err(ty.span, "at least one trait must be specified");
 776                 }
 777
 778                 self.walk_ty(ty);
 779                 return;
 780             }
 781             _ => {}
 782         }
 783
 784         self.walk_ty(ty)
 785     }
 786
 787     fn visit_label(&mut self, label: &'a Label) {
 788         self.check_label(label.ident);
 789         visit::walk_label(self, label);
 790     }
 791
 792     fn visit_lifetime(&mut self, lifetime: &'a Lifetime) {
 793         self.check_lifetime(lifetime.ident);
 794         visit::walk_lifetime(self, lifetime);
 795     }
 796
 797     fn visit_item(&mut self, item: &'a Item) {
 798         if item.attrs.iter().any(|attr| is_proc_macro_attr(attr)) {
 799             self.has_proc_macro_decls = true;
 800         }
 801
 802         match item.kind {
 803             ItemKind::Impl {
 804                 unsafety,
 805                 polarity,
 806                 defaultness: _,
 807                 constness: _,
 808                 generics: _,
 809                 of_trait: Some(_),
 810                 ref self_ty,
 811                 items: _,
 812             } => {
 813                 self.with_in_trait_impl(true, |this| {
 814                     this.invalid_visibility(&item.vis, None);
 815                     if let TyKind::Err = self_ty.kind {
 816                         this.err_handler()
 817                             .struct_span_err(
 818                                 item.span,
 819                                 "`impl Trait for .. {}` is an obsolete syntax",
 820                             )
 821                             .help("use `auto trait Trait {}` instead")
 822                             .emit();
 823                     }
 824                     if let (Unsafe::Yes(span), ImplPolarity::Negative) = (unsafety, polarity) {
 825                         struct_span_err!(
 826                             this.session,
 827                             item.span,
 828                             E0198,
 829                             "negative impls cannot be unsafe"
 830                         )
 831                         .span_label(span, "unsafe because of this")
 832                         .emit();
 833                     }
 834
 835                     visit::walk_item(this, item);
 836                 });
 837                 return; // Avoid visiting again.
 838             }
 839             ItemKind::Impl {
 840                 unsafety,
 841                 polarity,
 842                 defaultness,
 843                 constness,
 844                 generics: _,
 845                 of_trait: None,
 846                 self_ty: _,
 847                 items: _,
 848             } => {
 849                 self.invalid_visibility(
 850                     &item.vis,
 851                     Some("place qualifiers on individual impl items instead"),
 852                 );
 853                 if let Unsafe::Yes(span) = unsafety {
 854                     struct_span_err!(
 855                         self.session,
 856                         item.span,
 857                         E0197,
 858                         "inherent impls cannot be unsafe"
 859                     )
 860                     .span_label(span, "unsafe because of this")
 861                     .emit();
 862                 }
 863                 if polarity == ImplPolarity::Negative {
 864                     self.err_handler().span_err(item.span, "inherent impls cannot be negative");
 865                 }
 866                 if defaultness == Defaultness::Default {
 867                     self.err_handler()
 868                         .struct_span_err(item.span, "inherent impls cannot be default")
 869                         .note("only trait implementations may be annotated with default")
 870                         .emit();
 871                 }
 872                 if let Const::Yes(span) = constness {
 873                     self.err_handler()
 874                         .struct_span_err(item.span, "inherent impls cannot be `const`")
 875                         .span_label(span, "`const` because of this")
 876                         .note("only trait implementations may be annotated with `const`")
 877                         .emit();
 878                 }
 879             }
 880             ItemKind::Fn(ref sig, ref generics, ref body) => {
 881                 self.check_const_fn_const_generic(item.span, sig, generics);
 882
 883                 if body.is_none() {
 884                     let msg = "free function without a body";
 885                     self.error_item_without_body(item.span, "function", msg, " { <body> }");
 886                 }
 887             }
 888             ItemKind::ForeignMod(_) => {
 889                 let old_item = mem::replace(&mut self.extern_mod, Some(item));
 890                 self.invalid_visibility(
 891                     &item.vis,
 892                     Some("place qualifiers on individual foreign items instead"),
 893                 );
 894                 visit::walk_item(self, item);
 895                 self.extern_mod = old_item;
 896                 return; // Avoid visiting again.
 897             }
 898             ItemKind::Enum(ref def, _) => {
 899                 for variant in &def.variants {
 900                     self.invalid_visibility(&variant.vis, None);
 901                     for field in variant.data.fields() {
 902                         self.invalid_visibility(&field.vis, None);
 903                     }
 904                 }
 905             }
 906             ItemKind::Trait(is_auto, _, ref generics, ref bounds, ref trait_items) => {
 907                 if is_auto == IsAuto::Yes {
 908                     // Auto traits cannot have generics, super traits nor contain items.
 909                     if !generics.params.is_empty() {
 910                         struct_span_err!(
 911                             self.session,
 912                             item.span,
 913                             E0567,
 914                             "auto traits cannot have generic parameters"
 915                         )
 916                         .emit();
 917                     }
 918                     if !bounds.is_empty() {
 919                         struct_span_err!(
 920                             self.session,
 921                             item.span,
 922                             E0568,
 923                             "auto traits cannot have super traits"
 924                         )
 925                         .emit();
 926                     }
 927                     if !trait_items.is_empty() {
 928                         struct_span_err!(
 929                             self.session,
 930                             item.span,
 931                             E0380,
 932                             "auto traits cannot have methods or associated items"
 933                         )
 934                         .emit();
 935                     }
 936                 }
 937                 self.no_questions_in_bounds(bounds, "supertraits", true);
 938
 939                 // Equivalent of `visit::walk_item` for `ItemKind::Trait` that inserts a bound
 940                 // context for the supertraits.
 941                 self.visit_vis(&item.vis);
 942                 self.visit_ident(item.ident);
 943                 self.visit_generics(generics);
 944                 self.with_bound_context(BoundContext::TraitBounds, |this| {
 945                     walk_list!(this, visit_param_bound, bounds);
 946                 });
 947                 walk_list!(self, visit_assoc_item, trait_items, AssocCtxt::Trait);
 948                 walk_list!(self, visit_attribute, &item.attrs);
 949                 return;
 950             }
 951             ItemKind::Mod(_) => {
 952                 // Ensure that `path` attributes on modules are recorded as used (cf. issue #35584).
 953                 attr::first_attr_value_str_by_name(&item.attrs, sym::path);
 954             }
 955             ItemKind::Union(ref vdata, _) => {
 956                 if let VariantData::Tuple(..) | VariantData::Unit(..) = vdata {
 957                     self.err_handler()
 958                         .span_err(item.span, "tuple and unit unions are not permitted");
 959                 }
 960                 if vdata.fields().is_empty() {
 961                     self.err_handler().span_err(item.span, "unions cannot have zero fields");
 962                 }
 963             }
 964             ItemKind::Const(.., None) => {
 965                 let msg = "free constant item without body";
 966                 self.error_item_without_body(item.span, "constant", msg, " = <expr>;");
 967             }
 968             ItemKind::Static(.., None) => {
 969                 let msg = "free static item without body";
 970                 self.error_item_without_body(item.span, "static", msg, " = <expr>;");
 971             }
 972             _ => {}
 973         }
 974
 975         visit::walk_item(self, item)
 976     }
 977
 978     fn visit_foreign_item(&mut self, fi: &'a ForeignItem) {
 979         match &fi.kind {
 980             ForeignItemKind::Fn(sig, _, body) => {
 981                 self.check_foreign_fn_bodyless(fi.ident, body.as_deref());
 982                 self.check_foreign_fn_headerless(fi.ident, fi.span, sig.header);
 983             }
 984             ForeignItemKind::TyAlias(generics, bounds, body) => {
 985                 self.check_foreign_kind_bodyless(fi.ident, "type", body.as_ref().map(|b| b.span));
 986                 self.check_type_no_bounds(bounds, "`extern` blocks");
 987                 self.check_foreign_ty_genericless(generics);
 988             }
 989             ForeignItemKind::Static(_, _, body) => {
 990                 self.check_foreign_kind_bodyless(fi.ident, "static", body.as_ref().map(|b| b.span));
 991             }
 992             ForeignItemKind::Const(..) | ForeignItemKind::Macro(..) => {}
 993         }
 994
 995         visit::walk_foreign_item(self, fi)
 996     }
 997
 998     // Mirrors `visit::walk_generic_args`, but tracks relevant state.
 999     fn visit_generic_args(&mut self, _: Span, generic_args: &'a GenericArgs) {
1000         match *generic_args {
1001             GenericArgs::AngleBracketed(ref data) => {
1002                 walk_list!(self, visit_generic_arg, &data.args);
1003                 validate_generics_order(
1004                     self.session,
1005                     self.err_handler(),
1006                     data.args.iter().map(|arg| {
1007                         (
1008                             match arg {
1009                                 GenericArg::Lifetime(..) => ParamKindOrd::Lifetime,
1010                                 GenericArg::Type(..) => ParamKindOrd::Type,
1011                                 GenericArg::Const(..) => ParamKindOrd::Const,
1012                             },
1013                             None,
1014                             arg.span(),
1015                             None,
1016                         )
1017                     }),
1018                     GenericPosition::Arg,
1019                     generic_args.span(),
1020                 );
1021
1022                 // Type bindings such as `Item = impl Debug` in `Iterator<Item = Debug>`
1023                 // are allowed to contain nested `impl Trait`.
1024                 self.with_impl_trait(None, |this| {
1025                     walk_list!(
1026                         this,
1027                         visit_assoc_ty_constraint_from_generic_args,
1028                         &data.constraints
1029                     );
1030                 });
1031             }
1032             GenericArgs::Parenthesized(ref data) => {
1033                 walk_list!(self, visit_ty, &data.inputs);
1034                 if let FnRetTy::Ty(ty) = &data.output {
1035                     // `-> Foo` syntax is essentially an associated type binding,
1036                     // so it is also allowed to contain nested `impl Trait`.
1037                     self.with_impl_trait(None, |this| this.visit_ty(ty));
1038                 }
1039             }
1040         }
1041     }
1042
1043     fn visit_generics(&mut self, generics: &'a Generics) {
1044         let mut prev_ty_default = None;
1045         for param in &generics.params {
1046             if let GenericParamKind::Type { ref default, .. } = param.kind {
1047                 if default.is_some() {
1048                     prev_ty_default = Some(param.ident.span);
1049                 } else if let Some(span) = prev_ty_default {
1050                     self.err_handler()
1051                         .span_err(span, "type parameters with a default must be trailing");
1052                     break;
1053                 }
1054             }
1055         }
1056
1057         validate_generics_order(
1058             self.session,
1059             self.err_handler(),
1060             generics.params.iter().map(|param| {
1061                 let ident = Some(param.ident.to_string());
1062                 let (kind, ident) = match &param.kind {
1063                     GenericParamKind::Lifetime { .. } => (ParamKindOrd::Lifetime, ident),
1064                     GenericParamKind::Type { .. } => (ParamKindOrd::Type, ident),
1065                     GenericParamKind::Const { ref ty } => {
1066                         let ty = pprust::ty_to_string(ty);
1067                         (ParamKindOrd::Const, Some(format!("const {}: {}", param.ident, ty)))
1068                     }
1069                 };
1070                 (kind, Some(&*param.bounds), param.ident.span, ident)
1071             }),
1072             GenericPosition::Param,
1073             generics.span,
1074         );
1075
1076         for predicate in &generics.where_clause.predicates {
1077             if let WherePredicate::EqPredicate(ref predicate) = *predicate {
1078                 self.err_handler()
1079                     .struct_span_err(
1080                         predicate.span,
1081                         "equality constraints are not yet supported in `where` clauses",
1082                     )
1083                     .span_label(predicate.span, "not supported")
1084                     .note(
1085                         "see issue #20041 <https://github.com/rust-lang/rust/issues/20041> \
1086                          for more information",
1087                     )
1088                     .emit();
1089             }
1090         }
1091
1092         visit::walk_generics(self, generics)
1093     }
1094
1095     fn visit_generic_param(&mut self, param: &'a GenericParam) {
1096         if let GenericParamKind::Lifetime { .. } = param.kind {
1097             self.check_lifetime(param.ident);
1098         }
1099         visit::walk_generic_param(self, param);
1100     }
1101
1102     fn visit_param_bound(&mut self, bound: &'a GenericBound) {
1103         match bound {
1104             GenericBound::Trait(_, TraitBoundModifier::MaybeConst) => {
1105                 if let Some(ctx) = self.bound_context {
1106                     let msg = format!("`?const` is not permitted in {}", ctx.description());
1107                     self.err_handler().span_err(bound.span(), &msg);
1108                 }
1109             }
1110
1111             GenericBound::Trait(_, TraitBoundModifier::MaybeConstMaybe) => {
1112                 self.err_handler()
1113                     .span_err(bound.span(), "`?const` and `?` are mutually exclusive");
1114             }
1115
1116             _ => {}
1117         }
1118
1119         visit::walk_param_bound(self, bound)
1120     }
1121
1122     fn visit_pat(&mut self, pat: &'a Pat) {
1123         match pat.kind {
1124             PatKind::Lit(ref expr) => {
1125                 self.check_expr_within_pat(expr, false);
1126             }
1127             PatKind::Range(ref start, ref end, _) => {
1128                 if let Some(expr) = start {
1129                     self.check_expr_within_pat(expr, true);
1130                 }
1131                 if let Some(expr) = end {
1132                     self.check_expr_within_pat(expr, true);
1133                 }
1134             }
1135             _ => {}
1136         }
1137
1138         visit::walk_pat(self, pat)
1139     }
1140
1141     fn visit_where_predicate(&mut self, p: &'a WherePredicate) {
1142         if let &WherePredicate::BoundPredicate(ref bound_predicate) = p {
1143             // A type binding, eg `for<'c> Foo: Send+Clone+'c`
1144             self.check_late_bound_lifetime_defs(&bound_predicate.bound_generic_params);
1145         }
1146         visit::walk_where_predicate(self, p);
1147     }
1148
1149     fn visit_poly_trait_ref(&mut self, t: &'a PolyTraitRef, m: &'a TraitBoundModifier) {
1150         self.check_late_bound_lifetime_defs(&t.bound_generic_params);
1151         visit::walk_poly_trait_ref(self, t, m);
1152     }
1153
1154     fn visit_variant_data(&mut self, s: &'a VariantData) {
1155         self.with_banned_assoc_ty_bound(|this| visit::walk_struct_def(this, s))
1156     }
1157
1158     fn visit_enum_def(
1159         &mut self,
1160         enum_definition: &'a EnumDef,
1161         generics: &'a Generics,
1162         item_id: NodeId,
1163         _: Span,
1164     ) {
1165         self.with_banned_assoc_ty_bound(|this| {
1166             visit::walk_enum_def(this, enum_definition, generics, item_id)
1167         })
1168     }
1169
1170     fn visit_fn(&mut self, fk: FnKind<'a>, span: Span, id: NodeId) {
1171         // Only associated `fn`s can have `self` parameters.
1172         let self_semantic = match fk.ctxt() {
1173             Some(FnCtxt::Assoc(_)) => SelfSemantic::Yes,
1174             _ => SelfSemantic::No,
1175         };
1176         self.check_fn_decl(fk.decl(), self_semantic);
1177
1178         self.check_c_varadic_type(fk);
1179
1180         // Functions cannot both be `const async`
1181         if let Some(FnHeader {
1182             constness: Const::Yes(cspan),
1183             asyncness: Async::Yes { span: aspan, .. },
1184             ..
1185         }) = fk.header()
1186         {
1187             self.err_handler()
1188                 .struct_span_err(span, "functions cannot be both `const` and `async`")
1189                 .span_label(*cspan, "`const` because of this")
1190                 .span_label(*aspan, "`async` because of this")
1191                 .emit();
1192         }
1193
1194         // Functions without bodies cannot have patterns.
1195         if let FnKind::Fn(ctxt, _, sig, _, None) = fk {
1196             Self::check_decl_no_pat(&sig.decl, |span, mut_ident| {
1197                 let (code, msg, label) = match ctxt {
1198                     FnCtxt::Foreign => (
1199                         error_code!(E0130),
1200                         "patterns aren't allowed in foreign function declarations",
1201                         "pattern not allowed in foreign function",
1202                     ),
1203                     _ => (
1204                         error_code!(E0642),
1205                         "patterns aren't allowed in functions without bodies",
1206                         "pattern not allowed in function without body",
1207                     ),
1208                 };
1209                 if mut_ident && matches!(ctxt, FnCtxt::Assoc(_)) {
1210                     self.lint_buffer.buffer_lint(PATTERNS_IN_FNS_WITHOUT_BODY, id, span, msg);
1211                 } else {
1212                     self.err_handler()
1213                         .struct_span_err(span, msg)
1214                         .span_label(span, label)
1215                         .code(code)
1216                         .emit();
1217                 }
1218             });
1219         }
1220
1221         visit::walk_fn(self, fk, span);
1222     }
1223
1224     fn visit_assoc_item(&mut self, item: &'a AssocItem, ctxt: AssocCtxt) {
1225         if ctxt == AssocCtxt::Trait {
1226             self.check_defaultness(item.span, item.defaultness);
1227         }
1228
1229         if ctxt == AssocCtxt::Impl {
1230             match &item.kind {
1231                 AssocItemKind::Const(_, body) => {
1232                     self.check_impl_item_provided(item.span, body, "constant", " = <expr>;");
1233                 }
1234                 AssocItemKind::Fn(_, _, body) => {
1235                     self.check_impl_item_provided(item.span, body, "function", " { <body> }");
1236                 }
1237                 AssocItemKind::TyAlias(_, bounds, body) => {
1238                     self.check_impl_item_provided(item.span, body, "type", " = <type>;");
1239                     self.check_type_no_bounds(bounds, "`impl`s");
1240                 }
1241                 _ => {}
1242             }
1243         }
1244
1245         if ctxt == AssocCtxt::Trait || self.in_trait_impl {
1246             self.invalid_visibility(&item.vis, None);
1247             if let AssocItemKind::Fn(sig, _, _) = &item.kind {
1248                 self.check_trait_fn_not_const(sig.header.constness);
1249                 self.check_trait_fn_not_async(item.span, sig.header.asyncness);
1250             }
1251         }
1252
1253         if let AssocItemKind::Const(..) = item.kind {
1254             self.check_item_named(item.ident, "const");
1255         }
1256
1257         self.with_in_trait_impl(false, |this| visit::walk_assoc_item(this, item, ctxt));
1258     }
1259 }
1260
1261 pub fn check_crate(session: &Session, krate: &Crate, lints: &mut LintBuffer) -> bool {
1262     let mut validator = AstValidator {
1263         session,
1264         extern_mod: None,
1265         in_trait_impl: false,
1266         has_proc_macro_decls: false,
1267         outer_impl_trait: None,
1268         bound_context: None,
1269         is_impl_trait_banned: false,
1270         is_assoc_ty_bound_banned: false,
1271         lint_buffer: lints,
1272     };
1273     visit::walk_crate(&mut validator, krate);
1274
1275     validator.has_proc_macro_decls
1276 }