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::source_map::Spanned;
  17 use rustc_span::symbol::{kw, sym};
  18 use rustc_span::Span;
  19 use std::mem;
  20 use syntax::ast::*;
  21 use syntax::attr;
  22 use syntax::expand::is_proc_macro_attr;
  23 use syntax::visit::{self, AssocCtxt, FnCtxt, FnKind, Visitor};
  24 use syntax::walk_list;
  25
  26 /// Is `self` allowed semantically as the first parameter in an `FnDecl`?
  27 enum SelfSemantic {
  28     Yes,
  29     No,
  30 }
  31
  32 /// A syntactic context that disallows certain kinds of bounds (e.g., `?Trait` or `?const Trait`).
  33 #[derive(Clone, Copy)]
  34 enum BoundContext {
  35     ImplTrait,
  36     TraitBounds,
  37     TraitObject,
  38 }
  39
  40 impl BoundContext {
  41     fn description(&self) -> &'static str {
  42         match self {
  43             Self::ImplTrait => "`impl Trait`",
  44             Self::TraitBounds => "supertraits",
  45             Self::TraitObject => "trait objects",
  46         }
  47     }
  48 }
  49
  50 struct AstValidator<'a> {
  51     session: &'a Session,
  52
  53     /// The span of the `extern` in an `extern { ... }` block, if any.
  54     extern_mod: Option<&'a Item>,
  55
  56     /// Are we inside a trait impl?
  57     in_trait_impl: bool,
  58
  59     has_proc_macro_decls: bool,
  60
  61     /// Used to ban nested `impl Trait`, e.g., `impl Into<impl Debug>`.
  62     /// Nested `impl Trait` _is_ allowed in associated type position,
  63     /// e.g., `impl Iterator<Item = impl Debug>`.
  64     outer_impl_trait: Option<Span>,
  65
  66     /// Keeps track of the `BoundContext` as we recurse.
  67     ///
  68     /// This is used to forbid `?const Trait` bounds in, e.g.,
  69     /// `impl Iterator<Item = Box<dyn ?const Trait>`.
  70     bound_context: Option<BoundContext>,
  71
  72     /// Used to ban `impl Trait` in path projections like `<impl Iterator>::Item`
  73     /// or `Foo::Bar<impl Trait>`
  74     is_impl_trait_banned: bool,
  75
  76     /// Used to ban associated type bounds (i.e., `Type<AssocType: Bounds>`) in
  77     /// certain positions.
  78     is_assoc_ty_bound_banned: bool,
  79
  80     lint_buffer: &'a mut LintBuffer,
  81 }
  82
  83 impl<'a> AstValidator<'a> {
  84     fn with_in_trait_impl(&mut self, is_in: bool, f: impl FnOnce(&mut Self)) {
  85         let old = mem::replace(&mut self.in_trait_impl, is_in);
  86         f(self);
  87         self.in_trait_impl = old;
  88     }
  89
  90     fn with_banned_impl_trait(&mut self, f: impl FnOnce(&mut Self)) {
  91         let old = mem::replace(&mut self.is_impl_trait_banned, true);
  92         f(self);
  93         self.is_impl_trait_banned = old;
  94     }
  95
  96     fn with_banned_assoc_ty_bound(&mut self, f: impl FnOnce(&mut Self)) {
  97         let old = mem::replace(&mut self.is_assoc_ty_bound_banned, true);
  98         f(self);
  99         self.is_assoc_ty_bound_banned = old;
 100     }
 101
 102     fn with_impl_trait(&mut self, outer: Option<Span>, f: impl FnOnce(&mut Self)) {
 103         let old = mem::replace(&mut self.outer_impl_trait, outer);
 104         if outer.is_some() {
 105             self.with_bound_context(BoundContext::ImplTrait, |this| f(this));
 106         } else {
 107             f(self)
 108         }
 109         self.outer_impl_trait = old;
 110     }
 111
 112     fn with_bound_context(&mut self, ctx: BoundContext, f: impl FnOnce(&mut Self)) {
 113         let old = self.bound_context.replace(ctx);
 114         f(self);
 115         self.bound_context = old;
 116     }
 117
 118     fn visit_assoc_ty_constraint_from_generic_args(&mut self, constraint: &'a AssocTyConstraint) {
 119         match constraint.kind {
 120             AssocTyConstraintKind::Equality { .. } => {}
 121             AssocTyConstraintKind::Bound { .. } => {
 122                 if self.is_assoc_ty_bound_banned {
 123                     self.err_handler().span_err(
 124                         constraint.span,
 125                         "associated type bounds are not allowed within structs, enums, or unions",
 126                     );
 127                 }
 128             }
 129         }
 130         self.visit_assoc_ty_constraint(constraint);
 131     }
 132
 133     // Mirrors `visit::walk_ty`, but tracks relevant state.
 134     fn walk_ty(&mut self, t: &'a Ty) {
 135         match t.kind {
 136             TyKind::ImplTrait(..) => {
 137                 self.with_impl_trait(Some(t.span), |this| visit::walk_ty(this, t))
 138             }
 139             TyKind::TraitObject(..) => {
 140                 self.with_bound_context(BoundContext::TraitObject, |this| visit::walk_ty(this, t));
 141             }
 142             TyKind::Path(ref qself, ref path) => {
 143                 // We allow these:
 144                 //  - `Option<impl Trait>`
 145                 //  - `option::Option<impl Trait>`
 146                 //  - `option::Option<T>::Foo<impl Trait>
 147                 //
 148                 // But not these:
 149                 //  - `<impl Trait>::Foo`
 150                 //  - `option::Option<impl Trait>::Foo`.
 151                 //
 152                 // To implement this, we disallow `impl Trait` from `qself`
 153                 // (for cases like `<impl Trait>::Foo>`)
 154                 // but we allow `impl Trait` in `GenericArgs`
 155                 // iff there are no more PathSegments.
 156                 if let Some(ref qself) = *qself {
 157                     // `impl Trait` in `qself` is always illegal
 158                     self.with_banned_impl_trait(|this| this.visit_ty(&qself.ty));
 159                 }
 160
 161                 // Note that there should be a call to visit_path here,
 162                 // so if any logic is added to process `Path`s a call to it should be
 163                 // added both in visit_path and here. This code mirrors visit::walk_path.
 164                 for (i, segment) in path.segments.iter().enumerate() {
 165                     // Allow `impl Trait` iff we're on the final path segment
 166                     if i == path.segments.len() - 1 {
 167                         self.visit_path_segment(path.span, segment);
 168                     } else {
 169                         self.with_banned_impl_trait(|this| {
 170                             this.visit_path_segment(path.span, segment)
 171                         });
 172                     }
 173                 }
 174             }
 175             _ => visit::walk_ty(self, t),
 176         }
 177     }
 178
 179     fn err_handler(&self) -> &rustc_errors::Handler {
 180         &self.session.diagnostic()
 181     }
 182
 183     fn check_lifetime(&self, ident: Ident) {
 184         let valid_names = [kw::UnderscoreLifetime, kw::StaticLifetime, kw::Invalid];
 185         if !valid_names.contains(&ident.name) && ident.without_first_quote().is_reserved() {
 186             self.err_handler().span_err(ident.span, "lifetimes cannot use keyword names");
 187         }
 188     }
 189
 190     fn check_label(&self, ident: Ident) {
 191         if ident.without_first_quote().is_reserved() {
 192             self.err_handler()
 193                 .span_err(ident.span, &format!("invalid label name `{}`", ident.name));
 194         }
 195     }
 196
 197     fn invalid_visibility(&self, vis: &Visibility, note: Option<&str>) {
 198         if let VisibilityKind::Inherited = vis.node {
 199             return;
 200         }
 201
 202         let mut err =
 203             struct_span_err!(self.session, vis.span, E0449, "unnecessary visibility qualifier");
 204         if vis.node.is_pub() {
 205             err.span_label(vis.span, "`pub` not permitted here because it's implied");
 206         }
 207         if let Some(note) = note {
 208             err.note(note);
 209         }
 210         err.emit();
 211     }
 212
 213     fn check_decl_no_pat(decl: &FnDecl, mut report_err: impl FnMut(Span, bool)) {
 214         for Param { pat, .. } in &decl.inputs {
 215             match pat.kind {
 216                 PatKind::Ident(BindingMode::ByValue(Mutability::Not), _, None) | PatKind::Wild => {}
 217                 PatKind::Ident(BindingMode::ByValue(Mutability::Mut), _, None) => {
 218                     report_err(pat.span, true)
 219                 }
 220                 _ => report_err(pat.span, false),
 221             }
 222         }
 223     }
 224
 225     fn check_trait_fn_not_async(&self, span: Span, asyncness: IsAsync) {
 226         if asyncness.is_async() {
 227             struct_span_err!(self.session, span, E0706, "trait fns cannot be declared `async`")
 228                 .note("`async` trait functions are not currently supported")
 229                 .note(
 230                     "consider using the `async-trait` crate: \
 231                        https://crates.io/crates/async-trait",
 232                 )
 233                 .emit();
 234         }
 235     }
 236
 237     fn check_trait_fn_not_const(&self, constness: Spanned<Constness>) {
 238         if constness.node == Constness::Const {
 239             struct_span_err!(
 240                 self.session,
 241                 constness.span,
 242                 E0379,
 243                 "trait fns cannot be declared const"
 244             )
 245             .span_label(constness.span, "trait fns cannot be const")
 246             .emit();
 247         }
 248     }
 249
 250     // FIXME(ecstaticmorse): Instead, use `bound_context` to check this in `visit_param_bound`.
 251     fn no_questions_in_bounds(&self, bounds: &GenericBounds, where_: &str, is_trait: bool) {
 252         for bound in bounds {
 253             if let GenericBound::Trait(ref poly, TraitBoundModifier::Maybe) = *bound {
 254                 let mut err = self.err_handler().struct_span_err(
 255                     poly.span,
 256                     &format!("`?Trait` is not permitted in {}", where_),
 257                 );
 258                 if is_trait {
 259                     let path_str = pprust::path_to_string(&poly.trait_ref.path);
 260                     err.note(&format!("traits are `?{}` by default", path_str));
 261                 }
 262                 err.emit();
 263             }
 264         }
 265     }
 266
 267     /// Matches `'-' lit | lit (cf. parser::Parser::parse_literal_maybe_minus)`,
 268     /// or paths for ranges.
 269     //
 270     // FIXME: do we want to allow `expr -> pattern` conversion to create path expressions?
 271     // That means making this work:
 272     //
 273     // ```rust,ignore (FIXME)
 274     // struct S;
 275     // macro_rules! m {
 276     //     ($a:expr) => {
 277     //         let $a = S;
 278     //     }
 279     // }
 280     // m!(S);
 281     // ```
 282     fn check_expr_within_pat(&self, expr: &Expr, allow_paths: bool) {
 283         match expr.kind {
 284             ExprKind::Lit(..) | ExprKind::Err => {}
 285             ExprKind::Path(..) if allow_paths => {}
 286             ExprKind::Unary(UnOp::Neg, ref inner)
 287                 if match inner.kind {
 288                     ExprKind::Lit(_) => true,
 289                     _ => false,
 290                 } => {}
 291             _ => self.err_handler().span_err(
 292                 expr.span,
 293                 "arbitrary expressions aren't allowed \
 294                                                          in patterns",
 295             ),
 296         }
 297     }
 298
 299     fn check_late_bound_lifetime_defs(&self, params: &[GenericParam]) {
 300         // Check only lifetime parameters are present and that the lifetime
 301         // parameters that are present have no bounds.
 302         let non_lt_param_spans: Vec<_> = params
 303             .iter()
 304             .filter_map(|param| match param.kind {
 305                 GenericParamKind::Lifetime { .. } => {
 306                     if !param.bounds.is_empty() {
 307                         let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
 308                         self.err_handler()
 309                             .span_err(spans, "lifetime bounds cannot be used in this context");
 310                     }
 311                     None
 312                 }
 313                 _ => Some(param.ident.span),
 314             })
 315             .collect();
 316         if !non_lt_param_spans.is_empty() {
 317             self.err_handler().span_err(
 318                 non_lt_param_spans,
 319                 "only lifetime parameters can be used in this context",
 320             );
 321         }
 322     }
 323
 324     fn check_fn_decl(&self, fn_decl: &FnDecl, self_semantic: SelfSemantic) {
 325         self.check_decl_cvaradic_pos(fn_decl);
 326         self.check_decl_attrs(fn_decl);
 327         self.check_decl_self_param(fn_decl, self_semantic);
 328     }
 329
 330     fn check_decl_cvaradic_pos(&self, fn_decl: &FnDecl) {
 331         match &*fn_decl.inputs {
 332             [Param { ty, span, .. }] => {
 333                 if let TyKind::CVarArgs = ty.kind {
 334                     self.err_handler().span_err(
 335                         *span,
 336                         "C-variadic function must be declared with at least one named argument",
 337                     );
 338                 }
 339             }
 340             [ps @ .., _] => {
 341                 for Param { ty, span, .. } in ps {
 342                     if let TyKind::CVarArgs = ty.kind {
 343                         self.err_handler().span_err(
 344                             *span,
 345                             "`...` must be the last argument of a C-variadic function",
 346                         );
 347                     }
 348                 }
 349             }
 350             _ => {}
 351         }
 352     }
 353
 354     fn check_decl_attrs(&self, fn_decl: &FnDecl) {
 355         fn_decl
 356             .inputs
 357             .iter()
 358             .flat_map(|i| i.attrs.as_ref())
 359             .filter(|attr| {
 360                 let arr = [sym::allow, sym::cfg, sym::cfg_attr, sym::deny, sym::forbid, sym::warn];
 361                 !arr.contains(&attr.name_or_empty()) && rustc_attr::is_builtin_attr(attr)
 362             })
 363             .for_each(|attr| {
 364                 if attr.is_doc_comment() {
 365                     self.err_handler()
 366                         .struct_span_err(
 367                             attr.span,
 368                             "documentation comments cannot be applied to function parameters",
 369                         )
 370                         .span_label(attr.span, "doc comments are not allowed here")
 371                         .emit();
 372                 } else {
 373                     self.err_handler().span_err(
 374                         attr.span,
 375                         "allow, cfg, cfg_attr, deny, \
 376                 forbid, and warn are the only allowed built-in attributes in function parameters",
 377                     )
 378                 }
 379             });
 380     }
 381
 382     fn check_decl_self_param(&self, fn_decl: &FnDecl, self_semantic: SelfSemantic) {
 383         if let (SelfSemantic::No, [param, ..]) = (self_semantic, &*fn_decl.inputs) {
 384             if param.is_self() {
 385                 self.err_handler()
 386                     .struct_span_err(
 387                         param.span,
 388                         "`self` parameter is only allowed in associated functions",
 389                     )
 390                     .span_label(param.span, "not semantically valid as function parameter")
 391                     .note("associated functions are those in `impl` or `trait` definitions")
 392                     .emit();
 393             }
 394         }
 395     }
 396
 397     fn check_defaultness(&self, span: Span, defaultness: Defaultness) {
 398         if let Defaultness::Default = defaultness {
 399             self.err_handler()
 400                 .struct_span_err(span, "`default` is only allowed on items in `impl` definitions")
 401                 .emit();
 402         }
 403     }
 404
 405     fn error_item_without_body(&self, sp: Span, ctx: &str, msg: &str, sugg: &str) {
 406         self.err_handler()
 407             .struct_span_err(sp, msg)
 408             .span_suggestion(
 409                 self.session.source_map().end_point(sp),
 410                 &format!("provide a definition for the {}", ctx),
 411                 sugg.to_string(),
 412                 Applicability::HasPlaceholders,
 413             )
 414             .emit();
 415     }
 416
 417     fn check_impl_item_provided<T>(&self, sp: Span, body: &Option<T>, ctx: &str, sugg: &str) {
 418         if body.is_none() {
 419             let msg = format!("associated {} in `impl` without body", ctx);
 420             self.error_item_without_body(sp, ctx, &msg, sugg);
 421         }
 422     }
 423
 424     fn check_impl_assoc_type_no_bounds(&self, bounds: &[GenericBound]) {
 425         let span = match bounds {
 426             [] => return,
 427             [b0] => b0.span(),
 428             [b0, .., bl] => b0.span().to(bl.span()),
 429         };
 430         self.err_handler()
 431             .struct_span_err(span, "bounds on associated `type`s in `impl`s have no effect")
 432             .emit();
 433     }
 434
 435     /// An `fn` in `extern { ... }` cannot have a body `{ ... }`.
 436     fn check_foreign_fn_bodyless(&self, ident: Ident, body: Option<&Block>) {
 437         let body = match body {
 438             None => return,
 439             Some(body) => body,
 440         };
 441         self.err_handler()
 442             .struct_span_err(ident.span, "incorrect function inside `extern` block")
 443             .span_label(ident.span, "cannot have a body")
 444             .span_suggestion(
 445                 body.span,
 446                 "remove the invalid body",
 447                 ";".to_string(),
 448                 Applicability::MaybeIncorrect,
 449             )
 450             .help(
 451                 "you might have meant to write a function accessible through FFI, \
 452                 which can be done by writing `extern fn` outside of the `extern` block",
 453             )
 454             .span_label(
 455                 self.current_extern_span(),
 456                 "`extern` blocks define existing foreign functions and functions \
 457                 inside of them cannot have a body",
 458             )
 459             .note("for more information, visit https://doc.rust-lang.org/std/keyword.extern.html")
 460             .emit();
 461     }
 462
 463     fn current_extern_span(&self) -> Span {
 464         self.session.source_map().def_span(self.extern_mod.unwrap().span)
 465     }
 466
 467     /// An `fn` in `extern { ... }` cannot have qualfiers, e.g. `async fn`.
 468     fn check_foreign_fn_headerless(&self, ident: Ident, span: Span, header: FnHeader) {
 469         if header.has_qualifiers() {
 470             self.err_handler()
 471                 .struct_span_err(ident.span, "functions in `extern` blocks cannot have qualifiers")
 472                 .span_label(self.current_extern_span(), "in this `extern` block")
 473                 .span_suggestion(
 474                     span.until(ident.span.shrink_to_lo()),
 475                     "remove the qualifiers",
 476                     "fn ".to_string(),
 477                     Applicability::MaybeIncorrect,
 478                 )
 479                 .emit();
 480         }
 481     }
 482
 483     /// Reject C-varadic type unless the function is foreign,
 484     /// or free and `unsafe extern "C"` semantically.
 485     fn check_c_varadic_type(&self, fk: FnKind<'a>) {
 486         match (fk.ctxt(), fk.header()) {
 487             (Some(FnCtxt::Foreign), _) => return,
 488             (Some(FnCtxt::Free), Some(header)) => match header.ext {
 489                 Extern::Explicit(StrLit { symbol_unescaped: sym::C, .. }) | Extern::Implicit
 490                     if header.unsafety == Unsafety::Unsafe =>
 491                 {
 492                     return;
 493                 }
 494                 _ => {}
 495             },
 496             _ => {}
 497         };
 498
 499         for Param { ty, span, .. } in &fk.decl().inputs {
 500             if let TyKind::CVarArgs = ty.kind {
 501                 self.err_handler()
 502                     .struct_span_err(
 503                         *span,
 504                         "only foreign or `unsafe extern \"C\" functions may be C-variadic",
 505                     )
 506                     .emit();
 507             }
 508         }
 509     }
 510
 511     /// We currently do not permit const generics in `const fn`,
 512     /// as this is tantamount to allowing compile-time dependent typing.
 513     ///
 514     /// FIXME(const_generics): Is this really true / necessary? Discuss with @varkor.
 515     /// At any rate, the restriction feels too syntactic. Consider moving it to e.g. typeck.
 516     fn check_const_fn_const_generic(&self, span: Span, sig: &FnSig, generics: &Generics) {
 517         if sig.header.constness.node == Constness::Const {
 518             // Look for const generics and error if we find any.
 519             for param in &generics.params {
 520                 if let GenericParamKind::Const { .. } = param.kind {
 521                     self.err_handler()
 522                         .struct_span_err(span, "const parameters are not permitted in `const fn`")
 523                         .emit();
 524                 }
 525             }
 526         }
 527     }
 528 }
 529
 530 enum GenericPosition {
 531     Param,
 532     Arg,
 533 }
 534
 535 fn validate_generics_order<'a>(
 536     sess: &Session,
 537     handler: &rustc_errors::Handler,
 538     generics: impl Iterator<Item = (ParamKindOrd, Option<&'a [GenericBound]>, Span, Option<String>)>,
 539     pos: GenericPosition,
 540     span: Span,
 541 ) {
 542     let mut max_param: Option<ParamKindOrd> = None;
 543     let mut out_of_order = FxHashMap::default();
 544     let mut param_idents = vec![];
 545     let mut found_type = false;
 546     let mut found_const = false;
 547
 548     for (kind, bounds, span, ident) in generics {
 549         if let Some(ident) = ident {
 550             param_idents.push((kind, bounds, param_idents.len(), ident));
 551         }
 552         let max_param = &mut max_param;
 553         match max_param {
 554             Some(max_param) if *max_param > kind => {
 555                 let entry = out_of_order.entry(kind).or_insert((*max_param, vec![]));
 556                 entry.1.push(span);
 557             }
 558             Some(_) | None => *max_param = Some(kind),
 559         };
 560         match kind {
 561             ParamKindOrd::Type => found_type = true,
 562             ParamKindOrd::Const => found_const = true,
 563             _ => {}
 564         }
 565     }
 566
 567     let mut ordered_params = "<".to_string();
 568     if !out_of_order.is_empty() {
 569         param_idents.sort_by_key(|&(po, _, i, _)| (po, i));
 570         let mut first = true;
 571         for (_, bounds, _, ident) in param_idents {
 572             if !first {
 573                 ordered_params += ", ";
 574             }
 575             ordered_params += &ident;
 576             if let Some(bounds) = bounds {
 577                 if !bounds.is_empty() {
 578                     ordered_params += ": ";
 579                     ordered_params += &pprust::bounds_to_string(&bounds);
 580                 }
 581             }
 582             first = false;
 583         }
 584     }
 585     ordered_params += ">";
 586
 587     let pos_str = match pos {
 588         GenericPosition::Param => "parameter",
 589         GenericPosition::Arg => "argument",
 590     };
 591
 592     for (param_ord, (max_param, spans)) in &out_of_order {
 593         let mut err = handler.struct_span_err(
 594             spans.clone(),
 595             &format!(
 596                 "{} {pos}s must be declared prior to {} {pos}s",
 597                 param_ord,
 598                 max_param,
 599                 pos = pos_str,
 600             ),
 601         );
 602         if let GenericPosition::Param = pos {
 603             err.span_suggestion(
 604                 span,
 605                 &format!(
 606                     "reorder the {}s: lifetimes, then types{}",
 607                     pos_str,
 608                     if sess.features_untracked().const_generics { ", then consts" } else { "" },
 609                 ),
 610                 ordered_params.clone(),
 611                 Applicability::MachineApplicable,
 612             );
 613         }
 614         err.emit();
 615     }
 616
 617     // FIXME(const_generics): we shouldn't have to abort here at all, but we currently get ICEs
 618     // if we don't. Const parameters and type parameters can currently conflict if they
 619     // are out-of-order.
 620     if !out_of_order.is_empty() && found_type && found_const {
 621         FatalError.raise();
 622     }
 623 }
 624
 625 impl<'a> Visitor<'a> for AstValidator<'a> {
 626     fn visit_attribute(&mut self, attr: &Attribute) {
 627         validate_attr::check_meta(&self.session.parse_sess, attr);
 628     }
 629
 630     fn visit_expr(&mut self, expr: &'a Expr) {
 631         match &expr.kind {
 632             ExprKind::InlineAsm(..) if !self.session.target.target.options.allow_asm => {
 633                 struct_span_err!(
 634                     self.session,
 635                     expr.span,
 636                     E0472,
 637                     "asm! is unsupported on this target"
 638                 )
 639                 .emit();
 640             }
 641             _ => {}
 642         }
 643
 644         visit::walk_expr(self, expr);
 645     }
 646
 647     fn visit_ty(&mut self, ty: &'a Ty) {
 648         match ty.kind {
 649             TyKind::BareFn(ref bfty) => {
 650                 self.check_fn_decl(&bfty.decl, SelfSemantic::No);
 651                 Self::check_decl_no_pat(&bfty.decl, |span, _| {
 652                     struct_span_err!(
 653                         self.session,
 654                         span,
 655                         E0561,
 656                         "patterns aren't allowed in function pointer types"
 657                     )
 658                     .emit();
 659                 });
 660                 self.check_late_bound_lifetime_defs(&bfty.generic_params);
 661             }
 662             TyKind::TraitObject(ref bounds, ..) => {
 663                 let mut any_lifetime_bounds = false;
 664                 for bound in bounds {
 665                     if let GenericBound::Outlives(ref lifetime) = *bound {
 666                         if any_lifetime_bounds {
 667                             struct_span_err!(
 668                                 self.session,
 669                                 lifetime.ident.span,
 670                                 E0226,
 671                                 "only a single explicit lifetime bound is permitted"
 672                             )
 673                             .emit();
 674                             break;
 675                         }
 676                         any_lifetime_bounds = true;
 677                     }
 678                 }
 679                 self.no_questions_in_bounds(bounds, "trait object types", false);
 680             }
 681             TyKind::ImplTrait(_, ref bounds) => {
 682                 if self.is_impl_trait_banned {
 683                     struct_span_err!(
 684                         self.session,
 685                         ty.span,
 686                         E0667,
 687                         "`impl Trait` is not allowed in path parameters"
 688                     )
 689                     .emit();
 690                 }
 691
 692                 if let Some(outer_impl_trait_sp) = self.outer_impl_trait {
 693                     struct_span_err!(
 694                         self.session,
 695                         ty.span,
 696                         E0666,
 697                         "nested `impl Trait` is not allowed"
 698                     )
 699                     .span_label(outer_impl_trait_sp, "outer `impl Trait`")
 700                     .span_label(ty.span, "nested `impl Trait` here")
 701                     .emit();
 702                 }
 703
 704                 if !bounds
 705                     .iter()
 706                     .any(|b| if let GenericBound::Trait(..) = *b { true } else { false })
 707                 {
 708                     self.err_handler().span_err(ty.span, "at least one trait must be specified");
 709                 }
 710
 711                 self.walk_ty(ty);
 712                 return;
 713             }
 714             _ => {}
 715         }
 716
 717         self.walk_ty(ty)
 718     }
 719
 720     fn visit_label(&mut self, label: &'a Label) {
 721         self.check_label(label.ident);
 722         visit::walk_label(self, label);
 723     }
 724
 725     fn visit_lifetime(&mut self, lifetime: &'a Lifetime) {
 726         self.check_lifetime(lifetime.ident);
 727         visit::walk_lifetime(self, lifetime);
 728     }
 729
 730     fn visit_item(&mut self, item: &'a Item) {
 731         if item.attrs.iter().any(|attr| is_proc_macro_attr(attr)) {
 732             self.has_proc_macro_decls = true;
 733         }
 734
 735         match item.kind {
 736             ItemKind::Impl {
 737                 unsafety,
 738                 polarity,
 739                 defaultness: _,
 740                 constness: _,
 741                 generics: _,
 742                 of_trait: Some(_),
 743                 ref self_ty,
 744                 items: _,
 745             } => {
 746                 self.with_in_trait_impl(true, |this| {
 747                     this.invalid_visibility(&item.vis, None);
 748                     if let TyKind::Err = self_ty.kind {
 749                         this.err_handler()
 750                             .struct_span_err(
 751                                 item.span,
 752                                 "`impl Trait for .. {}` is an obsolete syntax",
 753                             )
 754                             .help("use `auto trait Trait {}` instead")
 755                             .emit();
 756                     }
 757                     if unsafety == Unsafety::Unsafe && polarity == ImplPolarity::Negative {
 758                         struct_span_err!(
 759                             this.session,
 760                             item.span,
 761                             E0198,
 762                             "negative impls cannot be unsafe"
 763                         )
 764                         .emit();
 765                     }
 766
 767                     visit::walk_item(this, item);
 768                 });
 769                 return; // Avoid visiting again.
 770             }
 771             ItemKind::Impl {
 772                 unsafety,
 773                 polarity,
 774                 defaultness,
 775                 constness,
 776                 generics: _,
 777                 of_trait: None,
 778                 self_ty: _,
 779                 items: _,
 780             } => {
 781                 self.invalid_visibility(
 782                     &item.vis,
 783                     Some("place qualifiers on individual impl items instead"),
 784                 );
 785                 if unsafety == Unsafety::Unsafe {
 786                     struct_span_err!(
 787                         self.session,
 788                         item.span,
 789                         E0197,
 790                         "inherent impls cannot be unsafe"
 791                     )
 792                     .emit();
 793                 }
 794                 if polarity == ImplPolarity::Negative {
 795                     self.err_handler().span_err(item.span, "inherent impls cannot be negative");
 796                 }
 797                 if defaultness == Defaultness::Default {
 798                     self.err_handler()
 799                         .struct_span_err(item.span, "inherent impls cannot be default")
 800                         .note("only trait implementations may be annotated with default")
 801                         .emit();
 802                 }
 803                 if constness == Constness::Const {
 804                     self.err_handler()
 805                         .struct_span_err(item.span, "inherent impls cannot be `const`")
 806                         .note("only trait implementations may be annotated with `const`")
 807                         .emit();
 808                 }
 809             }
 810             ItemKind::Fn(ref sig, ref generics, ref body) => {
 811                 self.check_const_fn_const_generic(item.span, sig, generics);
 812
 813                 if body.is_none() {
 814                     let msg = "free function without a body";
 815                     self.error_item_without_body(item.span, "function", msg, " { <body> }");
 816                 }
 817             }
 818             ItemKind::ForeignMod(_) => {
 819                 let old_item = mem::replace(&mut self.extern_mod, Some(item));
 820                 self.invalid_visibility(
 821                     &item.vis,
 822                     Some("place qualifiers on individual foreign items instead"),
 823                 );
 824                 visit::walk_item(self, item);
 825                 self.extern_mod = old_item;
 826                 return; // Avoid visiting again.
 827             }
 828             ItemKind::Enum(ref def, _) => {
 829                 for variant in &def.variants {
 830                     self.invalid_visibility(&variant.vis, None);
 831                     for field in variant.data.fields() {
 832                         self.invalid_visibility(&field.vis, None);
 833                     }
 834                 }
 835             }
 836             ItemKind::Trait(is_auto, _, ref generics, ref bounds, ref trait_items) => {
 837                 if is_auto == IsAuto::Yes {
 838                     // Auto traits cannot have generics, super traits nor contain items.
 839                     if !generics.params.is_empty() {
 840                         struct_span_err!(
 841                             self.session,
 842                             item.span,
 843                             E0567,
 844                             "auto traits cannot have generic parameters"
 845                         )
 846                         .emit();
 847                     }
 848                     if !bounds.is_empty() {
 849                         struct_span_err!(
 850                             self.session,
 851                             item.span,
 852                             E0568,
 853                             "auto traits cannot have super traits"
 854                         )
 855                         .emit();
 856                     }
 857                     if !trait_items.is_empty() {
 858                         struct_span_err!(
 859                             self.session,
 860                             item.span,
 861                             E0380,
 862                             "auto traits cannot have methods or associated items"
 863                         )
 864                         .emit();
 865                     }
 866                 }
 867                 self.no_questions_in_bounds(bounds, "supertraits", true);
 868
 869                 // Equivalent of `visit::walk_item` for `ItemKind::Trait` that inserts a bound
 870                 // context for the supertraits.
 871                 self.visit_vis(&item.vis);
 872                 self.visit_ident(item.ident);
 873                 self.visit_generics(generics);
 874                 self.with_bound_context(BoundContext::TraitBounds, |this| {
 875                     walk_list!(this, visit_param_bound, bounds);
 876                 });
 877                 walk_list!(self, visit_assoc_item, trait_items, AssocCtxt::Trait);
 878                 walk_list!(self, visit_attribute, &item.attrs);
 879                 return;
 880             }
 881             ItemKind::Mod(_) => {
 882                 // Ensure that `path` attributes on modules are recorded as used (cf. issue #35584).
 883                 attr::first_attr_value_str_by_name(&item.attrs, sym::path);
 884             }
 885             ItemKind::Union(ref vdata, _) => {
 886                 if let VariantData::Tuple(..) | VariantData::Unit(..) = vdata {
 887                     self.err_handler()
 888                         .span_err(item.span, "tuple and unit unions are not permitted");
 889                 }
 890                 if vdata.fields().is_empty() {
 891                     self.err_handler().span_err(item.span, "unions cannot have zero fields");
 892                 }
 893             }
 894             _ => {}
 895         }
 896
 897         visit::walk_item(self, item)
 898     }
 899
 900     fn visit_foreign_item(&mut self, fi: &'a ForeignItem) {
 901         match &fi.kind {
 902             ForeignItemKind::Fn(sig, _, body) => {
 903                 self.check_foreign_fn_bodyless(fi.ident, body.as_deref());
 904                 self.check_foreign_fn_headerless(fi.ident, fi.span, sig.header);
 905             }
 906             ForeignItemKind::Static(..) | ForeignItemKind::Ty | ForeignItemKind::Macro(..) => {}
 907         }
 908
 909         visit::walk_foreign_item(self, fi)
 910     }
 911
 912     // Mirrors `visit::walk_generic_args`, but tracks relevant state.
 913     fn visit_generic_args(&mut self, _: Span, generic_args: &'a GenericArgs) {
 914         match *generic_args {
 915             GenericArgs::AngleBracketed(ref data) => {
 916                 walk_list!(self, visit_generic_arg, &data.args);
 917                 validate_generics_order(
 918                     self.session,
 919                     self.err_handler(),
 920                     data.args.iter().map(|arg| {
 921                         (
 922                             match arg {
 923                                 GenericArg::Lifetime(..) => ParamKindOrd::Lifetime,
 924                                 GenericArg::Type(..) => ParamKindOrd::Type,
 925                                 GenericArg::Const(..) => ParamKindOrd::Const,
 926                             },
 927                             None,
 928                             arg.span(),
 929                             None,
 930                         )
 931                     }),
 932                     GenericPosition::Arg,
 933                     generic_args.span(),
 934                 );
 935
 936                 // Type bindings such as `Item = impl Debug` in `Iterator<Item = Debug>`
 937                 // are allowed to contain nested `impl Trait`.
 938                 self.with_impl_trait(None, |this| {
 939                     walk_list!(
 940                         this,
 941                         visit_assoc_ty_constraint_from_generic_args,
 942                         &data.constraints
 943                     );
 944                 });
 945             }
 946             GenericArgs::Parenthesized(ref data) => {
 947                 walk_list!(self, visit_ty, &data.inputs);
 948                 if let FunctionRetTy::Ty(ty) = &data.output {
 949                     // `-> Foo` syntax is essentially an associated type binding,
 950                     // so it is also allowed to contain nested `impl Trait`.
 951                     self.with_impl_trait(None, |this| this.visit_ty(ty));
 952                 }
 953             }
 954         }
 955     }
 956
 957     fn visit_generics(&mut self, generics: &'a Generics) {
 958         let mut prev_ty_default = None;
 959         for param in &generics.params {
 960             if let GenericParamKind::Type { ref default, .. } = param.kind {
 961                 if default.is_some() {
 962                     prev_ty_default = Some(param.ident.span);
 963                 } else if let Some(span) = prev_ty_default {
 964                     self.err_handler()
 965                         .span_err(span, "type parameters with a default must be trailing");
 966                     break;
 967                 }
 968             }
 969         }
 970
 971         validate_generics_order(
 972             self.session,
 973             self.err_handler(),
 974             generics.params.iter().map(|param| {
 975                 let ident = Some(param.ident.to_string());
 976                 let (kind, ident) = match &param.kind {
 977                     GenericParamKind::Lifetime { .. } => (ParamKindOrd::Lifetime, ident),
 978                     GenericParamKind::Type { .. } => (ParamKindOrd::Type, ident),
 979                     GenericParamKind::Const { ref ty } => {
 980                         let ty = pprust::ty_to_string(ty);
 981                         (ParamKindOrd::Const, Some(format!("const {}: {}", param.ident, ty)))
 982                     }
 983                 };
 984                 (kind, Some(&*param.bounds), param.ident.span, ident)
 985             }),
 986             GenericPosition::Param,
 987             generics.span,
 988         );
 989
 990         for predicate in &generics.where_clause.predicates {
 991             if let WherePredicate::EqPredicate(ref predicate) = *predicate {
 992                 self.err_handler()
 993                     .struct_span_err(
 994                         predicate.span,
 995                         "equality constraints are not yet supported in `where` clauses",
 996                     )
 997                     .span_label(predicate.span, "not supported")
 998                     .note(
 999                         "for more information, see https://github.com/rust-lang/rust/issues/20041",
1000                     )
1001                     .emit();
1002             }
1003         }
1004
1005         visit::walk_generics(self, generics)
1006     }
1007
1008     fn visit_generic_param(&mut self, param: &'a GenericParam) {
1009         if let GenericParamKind::Lifetime { .. } = param.kind {
1010             self.check_lifetime(param.ident);
1011         }
1012         visit::walk_generic_param(self, param);
1013     }
1014
1015     fn visit_param_bound(&mut self, bound: &'a GenericBound) {
1016         match bound {
1017             GenericBound::Trait(_, TraitBoundModifier::MaybeConst) => {
1018                 if let Some(ctx) = self.bound_context {
1019                     let msg = format!("`?const` is not permitted in {}", ctx.description());
1020                     self.err_handler().span_err(bound.span(), &msg);
1021                 }
1022             }
1023
1024             GenericBound::Trait(_, TraitBoundModifier::MaybeConstMaybe) => {
1025                 self.err_handler()
1026                     .span_err(bound.span(), "`?const` and `?` are mutually exclusive");
1027             }
1028
1029             _ => {}
1030         }
1031
1032         visit::walk_param_bound(self, bound)
1033     }
1034
1035     fn visit_pat(&mut self, pat: &'a Pat) {
1036         match pat.kind {
1037             PatKind::Lit(ref expr) => {
1038                 self.check_expr_within_pat(expr, false);
1039             }
1040             PatKind::Range(ref start, ref end, _) => {
1041                 if let Some(expr) = start {
1042                     self.check_expr_within_pat(expr, true);
1043                 }
1044                 if let Some(expr) = end {
1045                     self.check_expr_within_pat(expr, true);
1046                 }
1047             }
1048             _ => {}
1049         }
1050
1051         visit::walk_pat(self, pat)
1052     }
1053
1054     fn visit_where_predicate(&mut self, p: &'a WherePredicate) {
1055         if let &WherePredicate::BoundPredicate(ref bound_predicate) = p {
1056             // A type binding, eg `for<'c> Foo: Send+Clone+'c`
1057             self.check_late_bound_lifetime_defs(&bound_predicate.bound_generic_params);
1058         }
1059         visit::walk_where_predicate(self, p);
1060     }
1061
1062     fn visit_poly_trait_ref(&mut self, t: &'a PolyTraitRef, m: &'a TraitBoundModifier) {
1063         self.check_late_bound_lifetime_defs(&t.bound_generic_params);
1064         visit::walk_poly_trait_ref(self, t, m);
1065     }
1066
1067     fn visit_variant_data(&mut self, s: &'a VariantData) {
1068         self.with_banned_assoc_ty_bound(|this| visit::walk_struct_def(this, s))
1069     }
1070
1071     fn visit_enum_def(
1072         &mut self,
1073         enum_definition: &'a EnumDef,
1074         generics: &'a Generics,
1075         item_id: NodeId,
1076         _: Span,
1077     ) {
1078         self.with_banned_assoc_ty_bound(|this| {
1079             visit::walk_enum_def(this, enum_definition, generics, item_id)
1080         })
1081     }
1082
1083     fn visit_fn(&mut self, fk: FnKind<'a>, span: Span, id: NodeId) {
1084         // Only associated `fn`s can have `self` parameters.
1085         let self_semantic = match fk.ctxt() {
1086             Some(FnCtxt::Assoc(_)) => SelfSemantic::Yes,
1087             _ => SelfSemantic::No,
1088         };
1089         self.check_fn_decl(fk.decl(), self_semantic);
1090
1091         self.check_c_varadic_type(fk);
1092
1093         // Functions without bodies cannot have patterns.
1094         if let FnKind::Fn(ctxt, _, sig, _, None) = fk {
1095             Self::check_decl_no_pat(&sig.decl, |span, mut_ident| {
1096                 let (code, msg, label) = match ctxt {
1097                     FnCtxt::Foreign => (
1098                         error_code!(E0130),
1099                         "patterns aren't allowed in foreign function declarations",
1100                         "pattern not allowed in foreign function",
1101                     ),
1102                     _ => (
1103                         error_code!(E0642),
1104                         "patterns aren't allowed in functions without bodies",
1105                         "pattern not allowed in function without body",
1106                     ),
1107                 };
1108                 if mut_ident && matches!(ctxt, FnCtxt::Assoc(_)) {
1109                     self.lint_buffer.buffer_lint(PATTERNS_IN_FNS_WITHOUT_BODY, id, span, msg);
1110                 } else {
1111                     self.err_handler()
1112                         .struct_span_err(span, msg)
1113                         .span_label(span, label)
1114                         .code(code)
1115                         .emit();
1116                 }
1117             });
1118         }
1119
1120         visit::walk_fn(self, fk, span);
1121     }
1122
1123     fn visit_assoc_item(&mut self, item: &'a AssocItem, ctxt: AssocCtxt) {
1124         if ctxt == AssocCtxt::Trait {
1125             self.check_defaultness(item.span, item.defaultness);
1126         }
1127
1128         if ctxt == AssocCtxt::Impl {
1129             match &item.kind {
1130                 AssocItemKind::Const(_, body) => {
1131                     self.check_impl_item_provided(item.span, body, "constant", " = <expr>;");
1132                 }
1133                 AssocItemKind::Fn(_, body) => {
1134                     self.check_impl_item_provided(item.span, body, "function", " { <body> }");
1135                 }
1136                 AssocItemKind::TyAlias(bounds, body) => {
1137                     self.check_impl_item_provided(item.span, body, "type", " = <type>;");
1138                     self.check_impl_assoc_type_no_bounds(bounds);
1139                 }
1140                 _ => {}
1141             }
1142         }
1143
1144         if ctxt == AssocCtxt::Trait || self.in_trait_impl {
1145             self.invalid_visibility(&item.vis, None);
1146             if let AssocItemKind::Fn(sig, _) = &item.kind {
1147                 self.check_trait_fn_not_const(sig.header.constness);
1148                 self.check_trait_fn_not_async(item.span, sig.header.asyncness.node);
1149             }
1150         }
1151
1152         self.with_in_trait_impl(false, |this| visit::walk_assoc_item(this, item, ctxt));
1153     }
1154 }
1155
1156 pub fn check_crate(session: &Session, krate: &Crate, lints: &mut LintBuffer) -> bool {
1157     let mut validator = AstValidator {
1158         session,
1159         extern_mod: None,
1160         in_trait_impl: false,
1161         has_proc_macro_decls: false,
1162         outer_impl_trait: None,
1163         bound_context: None,
1164         is_impl_trait_banned: false,
1165         is_assoc_ty_bound_banned: false,
1166         lint_buffer: lints,
1167     };
1168     visit::walk_crate(&mut validator, krate);
1169
1170     validator.has_proc_macro_decls
1171 }