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