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