1 // Validate AST before lowering it to HIR.
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.
11 use rustc_ast::expand::is_proc_macro_attr;
12 use rustc_ast::ptr::P;
13 use rustc_ast::visit::{self, AssocCtxt, FnCtxt, FnKind, Visitor};
14 use rustc_ast::walk_list;
15 use rustc_ast_pretty::pprust;
16 use rustc_data_structures::fx::FxHashMap;
17 use rustc_errors::{error_code, struct_span_err, Applicability};
18 use rustc_parse::validate_attr;
19 use rustc_session::lint::builtin::PATTERNS_IN_FNS_WITHOUT_BODY;
20 use rustc_session::lint::LintBuffer;
21 use rustc_session::Session;
22 use rustc_span::symbol::{kw, sym};
26 const MORE_EXTERN: &str =
27 "for more information, visit https://doc.rust-lang.org/std/keyword.extern.html";
29 /// Is `self` allowed semantically as the first parameter in an `FnDecl`?
35 /// A syntactic context that disallows certain kinds of bounds (e.g., `?Trait` or `?const Trait`).
36 #[derive(Clone, Copy)]
44 fn description(&self) -> &'static str {
46 Self::ImplTrait => "`impl Trait`",
47 Self::TraitBounds => "supertraits",
48 Self::TraitObject => "trait objects",
53 struct AstValidator<'a> {
56 /// The span of the `extern` in an `extern { ... }` block, if any.
57 extern_mod: Option<&'a Item>,
59 /// Are we inside a trait impl?
62 has_proc_macro_decls: bool,
64 /// Used to ban nested `impl Trait`, e.g., `impl Into<impl Debug>`.
65 /// Nested `impl Trait` _is_ allowed in associated type position,
66 /// e.g., `impl Iterator<Item = impl Debug>`.
67 outer_impl_trait: Option<Span>,
69 /// Keeps track of the `BoundContext` as we recurse.
71 /// This is used to forbid `?const Trait` bounds in, e.g.,
72 /// `impl Iterator<Item = Box<dyn ?const Trait>`.
73 bound_context: Option<BoundContext>,
75 /// Used to ban `impl Trait` in path projections like `<impl Iterator>::Item`
76 /// or `Foo::Bar<impl Trait>`
77 is_impl_trait_banned: bool,
79 /// Used to ban associated type bounds (i.e., `Type<AssocType: Bounds>`) in
80 /// certain positions.
81 is_assoc_ty_bound_banned: bool,
83 lint_buffer: &'a mut LintBuffer,
86 impl<'a> AstValidator<'a> {
87 fn with_in_trait_impl(&mut self, is_in: bool, f: impl FnOnce(&mut Self)) {
88 let old = mem::replace(&mut self.in_trait_impl, is_in);
90 self.in_trait_impl = old;
93 fn with_banned_impl_trait(&mut self, f: impl FnOnce(&mut Self)) {
94 let old = mem::replace(&mut self.is_impl_trait_banned, true);
96 self.is_impl_trait_banned = old;
99 fn with_banned_assoc_ty_bound(&mut self, f: impl FnOnce(&mut Self)) {
100 let old = mem::replace(&mut self.is_assoc_ty_bound_banned, true);
102 self.is_assoc_ty_bound_banned = old;
105 fn with_impl_trait(&mut self, outer: Option<Span>, f: impl FnOnce(&mut Self)) {
106 let old = mem::replace(&mut self.outer_impl_trait, outer);
108 self.with_bound_context(BoundContext::ImplTrait, |this| f(this));
112 self.outer_impl_trait = old;
115 fn with_bound_context(&mut self, ctx: BoundContext, f: impl FnOnce(&mut Self)) {
116 let old = self.bound_context.replace(ctx);
118 self.bound_context = old;
121 fn visit_assoc_ty_constraint_from_generic_args(&mut self, constraint: &'a AssocTyConstraint) {
122 match constraint.kind {
123 AssocTyConstraintKind::Equality { .. } => {}
124 AssocTyConstraintKind::Bound { .. } => {
125 if self.is_assoc_ty_bound_banned {
126 self.err_handler().span_err(
128 "associated type bounds are not allowed within structs, enums, or unions",
133 self.visit_assoc_ty_constraint(constraint);
136 // Mirrors `visit::walk_ty`, but tracks relevant state.
137 fn walk_ty(&mut self, t: &'a Ty) {
139 TyKind::ImplTrait(..) => {
140 self.with_impl_trait(Some(t.span), |this| visit::walk_ty(this, t))
142 TyKind::TraitObject(..) => {
143 self.with_bound_context(BoundContext::TraitObject, |this| visit::walk_ty(this, t));
145 TyKind::Path(ref qself, ref path) => {
147 // - `Option<impl Trait>`
148 // - `option::Option<impl Trait>`
149 // - `option::Option<T>::Foo<impl Trait>
152 // - `<impl Trait>::Foo`
153 // - `option::Option<impl Trait>::Foo`.
155 // To implement this, we disallow `impl Trait` from `qself`
156 // (for cases like `<impl Trait>::Foo>`)
157 // but we allow `impl Trait` in `GenericArgs`
158 // iff there are no more PathSegments.
159 if let Some(ref qself) = *qself {
160 // `impl Trait` in `qself` is always illegal
161 self.with_banned_impl_trait(|this| this.visit_ty(&qself.ty));
164 // Note that there should be a call to visit_path here,
165 // so if any logic is added to process `Path`s a call to it should be
166 // added both in visit_path and here. This code mirrors visit::walk_path.
167 for (i, segment) in path.segments.iter().enumerate() {
168 // Allow `impl Trait` iff we're on the final path segment
169 if i == path.segments.len() - 1 {
170 self.visit_path_segment(path.span, segment);
172 self.with_banned_impl_trait(|this| {
173 this.visit_path_segment(path.span, segment)
178 _ => visit::walk_ty(self, t),
182 fn err_handler(&self) -> &rustc_errors::Handler {
183 &self.session.diagnostic()
186 fn check_lifetime(&self, ident: Ident) {
187 let valid_names = [kw::UnderscoreLifetime, kw::StaticLifetime, kw::Invalid];
188 if !valid_names.contains(&ident.name) && ident.without_first_quote().is_reserved() {
189 self.err_handler().span_err(ident.span, "lifetimes cannot use keyword names");
193 fn check_label(&self, ident: Ident) {
194 if ident.without_first_quote().is_reserved() {
196 .span_err(ident.span, &format!("invalid label name `{}`", ident.name));
200 fn invalid_visibility(&self, vis: &Visibility, note: Option<&str>) {
201 if let VisibilityKind::Inherited = vis.node {
206 struct_span_err!(self.session, vis.span, E0449, "unnecessary visibility qualifier");
207 if vis.node.is_pub() {
208 err.span_label(vis.span, "`pub` not permitted here because it's implied");
210 if let Some(note) = note {
216 fn check_decl_no_pat(decl: &FnDecl, mut report_err: impl FnMut(Span, bool)) {
217 for Param { pat, .. } in &decl.inputs {
219 PatKind::Ident(BindingMode::ByValue(Mutability::Not), _, None) | PatKind::Wild => {}
220 PatKind::Ident(BindingMode::ByValue(Mutability::Mut), _, None) => {
221 report_err(pat.span, true)
223 _ => report_err(pat.span, false),
228 fn check_trait_fn_not_async(&self, fn_span: Span, asyncness: Async) {
229 if let Async::Yes { span, .. } = asyncness {
234 "functions in traits cannot be declared `async`"
236 .span_label(span, "`async` because of this")
237 .note("`async` trait functions are not currently supported")
238 .note("consider using the `async-trait` crate: https://crates.io/crates/async-trait")
243 fn check_trait_fn_not_const(&self, constness: Const) {
244 if let Const::Yes(span) = constness {
249 "functions in traits cannot be declared const"
251 .span_label(span, "functions in traits cannot be const")
256 // FIXME(ecstaticmorse): Instead, use `bound_context` to check this in `visit_param_bound`.
257 fn no_questions_in_bounds(&self, bounds: &GenericBounds, where_: &str, is_trait: bool) {
258 for bound in bounds {
259 if let GenericBound::Trait(ref poly, TraitBoundModifier::Maybe) = *bound {
260 let mut err = self.err_handler().struct_span_err(
262 &format!("`?Trait` is not permitted in {}", where_),
265 let path_str = pprust::path_to_string(&poly.trait_ref.path);
266 err.note(&format!("traits are `?{}` by default", path_str));
273 /// Matches `'-' lit | lit (cf. parser::Parser::parse_literal_maybe_minus)`,
274 /// or paths for ranges.
276 // FIXME: do we want to allow `expr -> pattern` conversion to create path expressions?
277 // That means making this work:
279 // ```rust,ignore (FIXME)
288 fn check_expr_within_pat(&self, expr: &Expr, allow_paths: bool) {
290 ExprKind::Lit(..) | ExprKind::Err => {}
291 ExprKind::Path(..) if allow_paths => {}
292 ExprKind::Unary(UnOp::Neg, ref inner) if matches!(inner.kind, ExprKind::Lit(_)) => {}
293 _ => self.err_handler().span_err(
295 "arbitrary expressions aren't allowed \
301 fn check_late_bound_lifetime_defs(&self, params: &[GenericParam]) {
302 // Check only lifetime parameters are present and that the lifetime
303 // parameters that are present have no bounds.
304 let non_lt_param_spans: Vec<_> = params
306 .filter_map(|param| match param.kind {
307 GenericParamKind::Lifetime { .. } => {
308 if !param.bounds.is_empty() {
309 let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
311 .span_err(spans, "lifetime bounds cannot be used in this context");
315 _ => Some(param.ident.span),
318 if !non_lt_param_spans.is_empty() {
319 self.err_handler().span_err(
321 "only lifetime parameters can be used in this context",
326 fn check_fn_decl(&self, fn_decl: &FnDecl, self_semantic: SelfSemantic) {
327 self.check_decl_cvaradic_pos(fn_decl);
328 self.check_decl_attrs(fn_decl);
329 self.check_decl_self_param(fn_decl, self_semantic);
332 fn check_decl_cvaradic_pos(&self, fn_decl: &FnDecl) {
333 match &*fn_decl.inputs {
334 [Param { ty, span, .. }] => {
335 if let TyKind::CVarArgs = ty.kind {
336 self.err_handler().span_err(
338 "C-variadic function must be declared with at least one named argument",
343 for Param { ty, span, .. } in ps {
344 if let TyKind::CVarArgs = ty.kind {
345 self.err_handler().span_err(
347 "`...` must be the last argument of a C-variadic function",
356 fn check_decl_attrs(&self, fn_decl: &FnDecl) {
360 .flat_map(|i| i.attrs.as_ref())
362 let arr = [sym::allow, sym::cfg, sym::cfg_attr, sym::deny, sym::forbid, sym::warn];
363 !arr.contains(&attr.name_or_empty()) && rustc_attr::is_builtin_attr(attr)
366 if attr.is_doc_comment() {
370 "documentation comments cannot be applied to function parameters",
372 .span_label(attr.span, "doc comments are not allowed here")
375 self.err_handler().span_err(
377 "allow, cfg, cfg_attr, deny, \
378 forbid, and warn are the only allowed built-in attributes in function parameters",
384 fn check_decl_self_param(&self, fn_decl: &FnDecl, self_semantic: SelfSemantic) {
385 if let (SelfSemantic::No, [param, ..]) = (self_semantic, &*fn_decl.inputs) {
390 "`self` parameter is only allowed in associated functions",
392 .span_label(param.span, "not semantically valid as function parameter")
393 .note("associated functions are those in `impl` or `trait` definitions")
399 fn check_defaultness(&self, span: Span, defaultness: Defaultness) {
400 if let Defaultness::Default(def_span) = defaultness {
401 let span = self.session.source_map().guess_head_span(span);
403 .struct_span_err(span, "`default` is only allowed on items in `impl` definitions")
404 .span_label(def_span, "`default` because of this")
409 fn error_item_without_body(&self, sp: Span, ctx: &str, msg: &str, sugg: &str) {
411 .struct_span_err(sp, msg)
413 self.session.source_map().end_point(sp),
414 &format!("provide a definition for the {}", ctx),
416 Applicability::HasPlaceholders,
421 fn check_impl_item_provided<T>(&self, sp: Span, body: &Option<T>, ctx: &str, sugg: &str) {
423 let msg = format!("associated {} in `impl` without body", ctx);
424 self.error_item_without_body(sp, ctx, &msg, sugg);
428 fn check_type_no_bounds(&self, bounds: &[GenericBound], ctx: &str) {
429 let span = match bounds {
432 [b0, .., bl] => b0.span().to(bl.span()),
435 .struct_span_err(span, &format!("bounds on `type`s in {} have no effect", ctx))
439 fn check_foreign_ty_genericless(&self, generics: &Generics) {
440 let cannot_have = |span, descr, remove_descr| {
444 &format!("`type`s inside `extern` blocks cannot have {}", descr),
448 &format!("remove the {}", remove_descr),
450 Applicability::MaybeIncorrect,
452 .span_label(self.current_extern_span(), "`extern` block begins here")
457 if !generics.params.is_empty() {
458 cannot_have(generics.span, "generic parameters", "generic parameters");
461 if !generics.where_clause.predicates.is_empty() {
462 cannot_have(generics.where_clause.span, "`where` clauses", "`where` clause");
466 fn check_foreign_kind_bodyless(&self, ident: Ident, kind: &str, body: Option<Span>) {
467 let body = match body {
472 .struct_span_err(ident.span, &format!("incorrect `{}` inside `extern` block", kind))
473 .span_label(ident.span, "cannot have a body")
474 .span_label(body, "the invalid body")
476 self.current_extern_span(),
478 "`extern` blocks define existing foreign {0}s and {0}s \
479 inside of them cannot have a body",
487 /// An `fn` in `extern { ... }` cannot have a body `{ ... }`.
488 fn check_foreign_fn_bodyless(&self, ident: Ident, body: Option<&Block>) {
489 let body = match body {
494 .struct_span_err(ident.span, "incorrect function inside `extern` block")
495 .span_label(ident.span, "cannot have a body")
498 "remove the invalid body",
500 Applicability::MaybeIncorrect,
503 "you might have meant to write a function accessible through FFI, \
504 which can be done by writing `extern fn` outside of the `extern` block",
507 self.current_extern_span(),
508 "`extern` blocks define existing foreign functions and functions \
509 inside of them cannot have a body",
515 fn current_extern_span(&self) -> Span {
516 self.session.source_map().guess_head_span(self.extern_mod.unwrap().span)
519 /// An `fn` in `extern { ... }` cannot have qualfiers, e.g. `async fn`.
520 fn check_foreign_fn_headerless(&self, ident: Ident, span: Span, header: FnHeader) {
521 if header.has_qualifiers() {
523 .struct_span_err(ident.span, "functions in `extern` blocks cannot have qualifiers")
524 .span_label(self.current_extern_span(), "in this `extern` block")
526 span.until(ident.span.shrink_to_lo()),
527 "remove the qualifiers",
529 Applicability::MaybeIncorrect,
535 /// Reject C-varadic type unless the function is foreign,
536 /// or free and `unsafe extern "C"` semantically.
537 fn check_c_varadic_type(&self, fk: FnKind<'a>) {
538 match (fk.ctxt(), fk.header()) {
539 (Some(FnCtxt::Foreign), _) => return,
540 (Some(FnCtxt::Free), Some(header)) => match header.ext {
541 Extern::Explicit(StrLit { symbol_unescaped: sym::C, .. }) | Extern::Implicit
542 if matches!(header.unsafety, Unsafe::Yes(_)) =>
551 for Param { ty, span, .. } in &fk.decl().inputs {
552 if let TyKind::CVarArgs = ty.kind {
556 "only foreign or `unsafe extern \"C\" functions may be C-variadic",
563 /// We currently do not permit const generics in `const fn`,
564 /// as this is tantamount to allowing compile-time dependent typing.
566 /// FIXME(const_generics): Is this really true / necessary? Discuss with @varkor.
567 /// At any rate, the restriction feels too syntactic. Consider moving it to e.g. typeck.
568 fn check_const_fn_const_generic(&self, span: Span, sig: &FnSig, generics: &Generics) {
569 if let Const::Yes(const_span) = sig.header.constness {
570 // Look for const generics and error if we find any.
571 for param in &generics.params {
572 if let GenericParamKind::Const { .. } = param.kind {
576 "const parameters are not permitted in const functions",
578 .span_label(const_span, "`const` because of this")
585 fn check_item_named(&self, ident: Ident, kind: &str) {
586 if ident.name != kw::Underscore {
590 .struct_span_err(ident.span, &format!("`{}` items in this context need a name", kind))
591 .span_label(ident.span, format!("`_` is not a valid name for this `{}` item", kind))
595 fn deny_generic_params(&self, generics: &Generics, ident_span: Span) {
596 if !generics.params.is_empty() {
601 "auto traits cannot have generic parameters"
603 .span_label(ident_span, "auto trait cannot have generic parameters")
606 "remove the parameters",
608 Applicability::MachineApplicable,
614 fn deny_super_traits(&self, bounds: &GenericBounds, ident_span: Span) {
615 if let [first @ last] | [first, .., last] = &bounds[..] {
616 let span = first.span().to(last.span());
617 struct_span_err!(self.session, span, E0568, "auto traits cannot have super traits")
618 .span_label(ident_span, "auto trait cannot have super traits")
621 "remove the super traits",
623 Applicability::MachineApplicable,
629 fn deny_items(&self, trait_items: &[P<AssocItem>], ident_span: Span) {
630 if !trait_items.is_empty() {
631 let spans: Vec<_> = trait_items.iter().map(|i| i.ident.span).collect();
636 "auto traits cannot have methods or associated items"
638 .span_label(ident_span, "auto trait cannot have items")
643 /// Enforce generic args coming before constraints in `<...>` of a path segment.
644 fn check_generic_args_before_constraints(&self, data: &AngleBracketedArgs) {
645 // Early exit in case it's partitioned as it should be.
646 if data.args.iter().is_partitioned(|arg| matches!(arg, AngleBracketedArg::Arg(_))) {
649 // Find all generic argument coming after the first constraint...
650 let mut misplaced_args = Vec::new();
651 let mut first = None;
652 for arg in &data.args {
654 (AngleBracketedArg::Arg(a), Some(_)) => misplaced_args.push(a.span()),
655 (AngleBracketedArg::Constraint(c), None) => first = Some(c.span),
656 (AngleBracketedArg::Arg(_), None) | (AngleBracketedArg::Constraint(_), Some(_)) => {
660 // ...and then error:
663 misplaced_args.clone(),
664 "generic arguments must come before the first constraint",
666 .span_label(first.unwrap(), "the first constraint is provided here")
667 .span_labels(misplaced_args, "generic argument")
672 /// Checks that generic parameters are in the correct order,
673 /// which is lifetimes, then types and then consts. (`<'a, T, const N: usize>`)
674 fn validate_generic_param_order<'a>(
676 handler: &rustc_errors::Handler,
677 generics: impl Iterator<Item = (ParamKindOrd, Option<&'a [GenericBound]>, Span, Option<String>)>,
680 let mut max_param: Option<ParamKindOrd> = None;
681 let mut out_of_order = FxHashMap::default();
682 let mut param_idents = vec![];
684 for (kind, bounds, span, ident) in generics {
685 if let Some(ident) = ident {
686 param_idents.push((kind, bounds, param_idents.len(), ident));
688 let max_param = &mut max_param;
690 Some(max_param) if *max_param > kind => {
691 let entry = out_of_order.entry(kind).or_insert((*max_param, vec![]));
694 Some(_) | None => *max_param = Some(kind),
698 let mut ordered_params = "<".to_string();
699 if !out_of_order.is_empty() {
700 param_idents.sort_by_key(|&(po, _, i, _)| (po, i));
701 let mut first = true;
702 for (_, bounds, _, ident) in param_idents {
704 ordered_params += ", ";
706 ordered_params += &ident;
707 if let Some(bounds) = bounds {
708 if !bounds.is_empty() {
709 ordered_params += ": ";
710 ordered_params += &pprust::bounds_to_string(&bounds);
716 ordered_params += ">";
718 for (param_ord, (max_param, spans)) in &out_of_order {
720 handler.struct_span_err(
723 "{} parameters must be declared prior to {} parameters",
724 param_ord, max_param,
730 "reorder the parameters: lifetimes, then types{}",
731 if sess.features_untracked().const_generics { ", then consts" } else { "" },
733 ordered_params.clone(),
734 Applicability::MachineApplicable,
740 impl<'a> Visitor<'a> for AstValidator<'a> {
741 fn visit_attribute(&mut self, attr: &Attribute) {
742 validate_attr::check_meta(&self.session.parse_sess, attr);
745 fn visit_expr(&mut self, expr: &'a Expr) {
747 ExprKind::LlvmInlineAsm(..) if !self.session.target.target.options.allow_asm => {
752 "llvm_asm! is unsupported on this target"
759 visit::walk_expr(self, expr);
762 fn visit_ty(&mut self, ty: &'a Ty) {
764 TyKind::BareFn(ref bfty) => {
765 self.check_fn_decl(&bfty.decl, SelfSemantic::No);
766 Self::check_decl_no_pat(&bfty.decl, |span, _| {
771 "patterns aren't allowed in function pointer types"
775 self.check_late_bound_lifetime_defs(&bfty.generic_params);
777 TyKind::TraitObject(ref bounds, ..) => {
778 let mut any_lifetime_bounds = false;
779 for bound in bounds {
780 if let GenericBound::Outlives(ref lifetime) = *bound {
781 if any_lifetime_bounds {
786 "only a single explicit lifetime bound is permitted"
791 any_lifetime_bounds = true;
794 self.no_questions_in_bounds(bounds, "trait object types", false);
796 TyKind::ImplTrait(_, ref bounds) => {
797 if self.is_impl_trait_banned {
802 "`impl Trait` is not allowed in path parameters"
807 if let Some(outer_impl_trait_sp) = self.outer_impl_trait {
812 "nested `impl Trait` is not allowed"
814 .span_label(outer_impl_trait_sp, "outer `impl Trait`")
815 .span_label(ty.span, "nested `impl Trait` here")
821 .any(|b| if let GenericBound::Trait(..) = *b { true } else { false })
823 self.err_handler().span_err(ty.span, "at least one trait must be specified");
835 fn visit_label(&mut self, label: &'a Label) {
836 self.check_label(label.ident);
837 visit::walk_label(self, label);
840 fn visit_lifetime(&mut self, lifetime: &'a Lifetime) {
841 self.check_lifetime(lifetime.ident);
842 visit::walk_lifetime(self, lifetime);
845 fn visit_item(&mut self, item: &'a Item) {
846 if item.attrs.iter().any(|attr| is_proc_macro_attr(attr)) {
847 self.has_proc_macro_decls = true;
857 of_trait: Some(ref t),
861 self.with_in_trait_impl(true, |this| {
862 this.invalid_visibility(&item.vis, None);
863 if let TyKind::Err = self_ty.kind {
867 "`impl Trait for .. {}` is an obsolete syntax",
869 .help("use `auto trait Trait {}` instead")
872 if let (Unsafe::Yes(span), ImplPolarity::Negative(sp)) = (unsafety, polarity) {
877 "negative impls cannot be unsafe"
879 .span_label(sp, "negative because of this")
880 .span_label(span, "unsafe because of this")
884 visit::walk_item(this, item);
886 return; // Avoid visiting again.
898 let error = |annotation_span, annotation| {
899 let mut err = self.err_handler().struct_span_err(
901 &format!("inherent impls cannot be {}", annotation),
903 err.span_label(annotation_span, &format!("{} because of this", annotation));
904 err.span_label(self_ty.span, "inherent impl for this type");
908 self.invalid_visibility(
910 Some("place qualifiers on individual impl items instead"),
912 if let Unsafe::Yes(span) = unsafety {
913 error(span, "unsafe").code(error_code!(E0197)).emit();
915 if let ImplPolarity::Negative(span) = polarity {
916 error(span, "negative").emit();
918 if let Defaultness::Default(def_span) = defaultness {
919 error(def_span, "`default`")
920 .note("only trait implementations may be annotated with `default`")
923 if let Const::Yes(span) = constness {
924 error(span, "`const`")
925 .note("only trait implementations may be annotated with `const`")
929 ItemKind::Fn(def, ref sig, ref generics, ref body) => {
930 self.check_defaultness(item.span, def);
931 self.check_const_fn_const_generic(item.span, sig, generics);
934 let msg = "free function without a body";
935 self.error_item_without_body(item.span, "function", msg, " { <body> }");
938 ItemKind::ForeignMod(_) => {
939 let old_item = mem::replace(&mut self.extern_mod, Some(item));
940 self.invalid_visibility(
942 Some("place qualifiers on individual foreign items instead"),
944 visit::walk_item(self, item);
945 self.extern_mod = old_item;
946 return; // Avoid visiting again.
948 ItemKind::Enum(ref def, _) => {
949 for variant in &def.variants {
950 self.invalid_visibility(&variant.vis, None);
951 for field in variant.data.fields() {
952 self.invalid_visibility(&field.vis, None);
956 ItemKind::Trait(is_auto, _, ref generics, ref bounds, ref trait_items) => {
957 if is_auto == IsAuto::Yes {
958 // Auto traits cannot have generics, super traits nor contain items.
959 self.deny_generic_params(generics, item.ident.span);
960 self.deny_super_traits(bounds, item.ident.span);
961 self.deny_items(trait_items, item.ident.span);
963 self.no_questions_in_bounds(bounds, "supertraits", true);
965 // Equivalent of `visit::walk_item` for `ItemKind::Trait` that inserts a bound
966 // context for the supertraits.
967 self.visit_vis(&item.vis);
968 self.visit_ident(item.ident);
969 self.visit_generics(generics);
970 self.with_bound_context(BoundContext::TraitBounds, |this| {
971 walk_list!(this, visit_param_bound, bounds);
973 walk_list!(self, visit_assoc_item, trait_items, AssocCtxt::Trait);
974 walk_list!(self, visit_attribute, &item.attrs);
977 ItemKind::Mod(_) => {
978 // Ensure that `path` attributes on modules are recorded as used (cf. issue #35584).
979 attr::first_attr_value_str_by_name(&item.attrs, sym::path);
981 ItemKind::Union(ref vdata, _) => {
982 if let VariantData::Tuple(..) | VariantData::Unit(..) = vdata {
984 .span_err(item.span, "tuple and unit unions are not permitted");
986 if vdata.fields().is_empty() {
987 self.err_handler().span_err(item.span, "unions cannot have zero fields");
990 ItemKind::Const(def, .., None) => {
991 self.check_defaultness(item.span, def);
992 let msg = "free constant item without body";
993 self.error_item_without_body(item.span, "constant", msg, " = <expr>;");
995 ItemKind::Static(.., None) => {
996 let msg = "free static item without body";
997 self.error_item_without_body(item.span, "static", msg, " = <expr>;");
999 ItemKind::TyAlias(def, _, ref bounds, ref body) => {
1000 self.check_defaultness(item.span, def);
1002 let msg = "free type alias without body";
1003 self.error_item_without_body(item.span, "type", msg, " = <type>;");
1005 self.check_type_no_bounds(bounds, "this context");
1010 visit::walk_item(self, item)
1013 fn visit_foreign_item(&mut self, fi: &'a ForeignItem) {
1015 ForeignItemKind::Fn(def, sig, _, body) => {
1016 self.check_defaultness(fi.span, *def);
1017 self.check_foreign_fn_bodyless(fi.ident, body.as_deref());
1018 self.check_foreign_fn_headerless(fi.ident, fi.span, sig.header);
1020 ForeignItemKind::TyAlias(def, generics, bounds, body) => {
1021 self.check_defaultness(fi.span, *def);
1022 self.check_foreign_kind_bodyless(fi.ident, "type", body.as_ref().map(|b| b.span));
1023 self.check_type_no_bounds(bounds, "`extern` blocks");
1024 self.check_foreign_ty_genericless(generics);
1026 ForeignItemKind::Static(_, _, body) => {
1027 self.check_foreign_kind_bodyless(fi.ident, "static", body.as_ref().map(|b| b.span));
1029 ForeignItemKind::MacCall(..) => {}
1032 visit::walk_foreign_item(self, fi)
1035 // Mirrors `visit::walk_generic_args`, but tracks relevant state.
1036 fn visit_generic_args(&mut self, _: Span, generic_args: &'a GenericArgs) {
1037 match *generic_args {
1038 GenericArgs::AngleBracketed(ref data) => {
1039 self.check_generic_args_before_constraints(data);
1041 for arg in &data.args {
1043 AngleBracketedArg::Arg(arg) => self.visit_generic_arg(arg),
1044 // Type bindings such as `Item = impl Debug` in `Iterator<Item = Debug>`
1045 // are allowed to contain nested `impl Trait`.
1046 AngleBracketedArg::Constraint(constraint) => {
1047 self.with_impl_trait(None, |this| {
1048 this.visit_assoc_ty_constraint_from_generic_args(constraint);
1054 GenericArgs::Parenthesized(ref data) => {
1055 walk_list!(self, visit_ty, &data.inputs);
1056 if let FnRetTy::Ty(ty) = &data.output {
1057 // `-> Foo` syntax is essentially an associated type binding,
1058 // so it is also allowed to contain nested `impl Trait`.
1059 self.with_impl_trait(None, |this| this.visit_ty(ty));
1065 fn visit_generics(&mut self, generics: &'a Generics) {
1066 let mut prev_ty_default = None;
1067 for param in &generics.params {
1068 if let GenericParamKind::Type { ref default, .. } = param.kind {
1069 if default.is_some() {
1070 prev_ty_default = Some(param.ident.span);
1071 } else if let Some(span) = prev_ty_default {
1073 .span_err(span, "type parameters with a default must be trailing");
1079 validate_generic_param_order(
1082 generics.params.iter().map(|param| {
1083 let ident = Some(param.ident.to_string());
1084 let (kind, ident) = match ¶m.kind {
1085 GenericParamKind::Lifetime { .. } => (ParamKindOrd::Lifetime, ident),
1086 GenericParamKind::Type { .. } => (ParamKindOrd::Type, ident),
1087 GenericParamKind::Const { ref ty } => {
1088 let ty = pprust::ty_to_string(ty);
1089 (ParamKindOrd::Const, Some(format!("const {}: {}", param.ident, ty)))
1092 (kind, Some(&*param.bounds), param.ident.span, ident)
1097 for predicate in &generics.where_clause.predicates {
1098 if let WherePredicate::EqPredicate(ref predicate) = *predicate {
1102 "equality constraints are not yet supported in `where` clauses",
1104 .span_label(predicate.span, "not supported")
1106 "see issue #20041 <https://github.com/rust-lang/rust/issues/20041> \
1107 for more information",
1113 visit::walk_generics(self, generics)
1116 fn visit_generic_param(&mut self, param: &'a GenericParam) {
1117 if let GenericParamKind::Lifetime { .. } = param.kind {
1118 self.check_lifetime(param.ident);
1120 visit::walk_generic_param(self, param);
1123 fn visit_param_bound(&mut self, bound: &'a GenericBound) {
1125 GenericBound::Trait(_, TraitBoundModifier::MaybeConst) => {
1126 if let Some(ctx) = self.bound_context {
1127 let msg = format!("`?const` is not permitted in {}", ctx.description());
1128 self.err_handler().span_err(bound.span(), &msg);
1132 GenericBound::Trait(_, TraitBoundModifier::MaybeConstMaybe) => {
1134 .span_err(bound.span(), "`?const` and `?` are mutually exclusive");
1140 visit::walk_param_bound(self, bound)
1143 fn visit_pat(&mut self, pat: &'a Pat) {
1145 PatKind::Lit(ref expr) => {
1146 self.check_expr_within_pat(expr, false);
1148 PatKind::Range(ref start, ref end, _) => {
1149 if let Some(expr) = start {
1150 self.check_expr_within_pat(expr, true);
1152 if let Some(expr) = end {
1153 self.check_expr_within_pat(expr, true);
1159 visit::walk_pat(self, pat)
1162 fn visit_where_predicate(&mut self, p: &'a WherePredicate) {
1163 if let &WherePredicate::BoundPredicate(ref bound_predicate) = p {
1164 // A type binding, eg `for<'c> Foo: Send+Clone+'c`
1165 self.check_late_bound_lifetime_defs(&bound_predicate.bound_generic_params);
1167 visit::walk_where_predicate(self, p);
1170 fn visit_poly_trait_ref(&mut self, t: &'a PolyTraitRef, m: &'a TraitBoundModifier) {
1171 self.check_late_bound_lifetime_defs(&t.bound_generic_params);
1172 visit::walk_poly_trait_ref(self, t, m);
1175 fn visit_variant_data(&mut self, s: &'a VariantData) {
1176 self.with_banned_assoc_ty_bound(|this| visit::walk_struct_def(this, s))
1181 enum_definition: &'a EnumDef,
1182 generics: &'a Generics,
1186 self.with_banned_assoc_ty_bound(|this| {
1187 visit::walk_enum_def(this, enum_definition, generics, item_id)
1191 fn visit_fn(&mut self, fk: FnKind<'a>, span: Span, id: NodeId) {
1192 // Only associated `fn`s can have `self` parameters.
1193 let self_semantic = match fk.ctxt() {
1194 Some(FnCtxt::Assoc(_)) => SelfSemantic::Yes,
1195 _ => SelfSemantic::No,
1197 self.check_fn_decl(fk.decl(), self_semantic);
1199 self.check_c_varadic_type(fk);
1201 // Functions cannot both be `const async`
1202 if let Some(FnHeader {
1203 constness: Const::Yes(cspan),
1204 asyncness: Async::Yes { span: aspan, .. },
1210 vec![*cspan, *aspan],
1211 "functions cannot be both `const` and `async`",
1213 .span_label(*cspan, "`const` because of this")
1214 .span_label(*aspan, "`async` because of this")
1215 .span_label(span, "") // Point at the fn header.
1219 // Functions without bodies cannot have patterns.
1220 if let FnKind::Fn(ctxt, _, sig, _, None) = fk {
1221 Self::check_decl_no_pat(&sig.decl, |span, mut_ident| {
1222 let (code, msg, label) = match ctxt {
1223 FnCtxt::Foreign => (
1225 "patterns aren't allowed in foreign function declarations",
1226 "pattern not allowed in foreign function",
1230 "patterns aren't allowed in functions without bodies",
1231 "pattern not allowed in function without body",
1234 if mut_ident && matches!(ctxt, FnCtxt::Assoc(_)) {
1235 self.lint_buffer.buffer_lint(PATTERNS_IN_FNS_WITHOUT_BODY, id, span, msg);
1238 .struct_span_err(span, msg)
1239 .span_label(span, label)
1246 visit::walk_fn(self, fk, span);
1249 fn visit_assoc_item(&mut self, item: &'a AssocItem, ctxt: AssocCtxt) {
1250 if ctxt == AssocCtxt::Trait || !self.in_trait_impl {
1251 self.check_defaultness(item.span, item.kind.defaultness());
1254 if ctxt == AssocCtxt::Impl {
1256 AssocItemKind::Const(_, _, body) => {
1257 self.check_impl_item_provided(item.span, body, "constant", " = <expr>;");
1259 AssocItemKind::Fn(_, _, _, body) => {
1260 self.check_impl_item_provided(item.span, body, "function", " { <body> }");
1262 AssocItemKind::TyAlias(_, _, bounds, body) => {
1263 self.check_impl_item_provided(item.span, body, "type", " = <type>;");
1264 self.check_type_no_bounds(bounds, "`impl`s");
1270 if ctxt == AssocCtxt::Trait || self.in_trait_impl {
1271 self.invalid_visibility(&item.vis, None);
1272 if let AssocItemKind::Fn(_, sig, _, _) = &item.kind {
1273 self.check_trait_fn_not_const(sig.header.constness);
1274 self.check_trait_fn_not_async(item.span, sig.header.asyncness);
1278 if let AssocItemKind::Const(..) = item.kind {
1279 self.check_item_named(item.ident, "const");
1282 self.with_in_trait_impl(false, |this| visit::walk_assoc_item(this, item, ctxt));
1286 pub fn check_crate(session: &Session, krate: &Crate, lints: &mut LintBuffer) -> bool {
1287 let mut validator = AstValidator {
1290 in_trait_impl: false,
1291 has_proc_macro_decls: false,
1292 outer_impl_trait: None,
1293 bound_context: None,
1294 is_impl_trait_banned: false,
1295 is_assoc_ty_bound_banned: false,
1298 visit::walk_crate(&mut validator, krate);
1300 validator.has_proc_macro_decls