1 //! This module implements some validity checks for attributes.
2 //! In particular it verifies that `#[inline]` and `#[repr]` attributes are
3 //! attached to items that actually support them and if there are
4 //! conflicts between multiple such attributes attached to the same
7 use rustc::hir::check_attr::{MethodKind, Target};
8 use rustc::hir::map::Map;
9 use rustc::ty::query::Providers;
10 use rustc::ty::TyCtxt;
12 use rustc_errors::struct_span_err;
14 use rustc_hir::def_id::DefId;
15 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
16 use rustc_hir::DUMMY_HIR_ID;
17 use rustc_hir::{self, HirId, Item, ItemKind, TraitItem};
18 use rustc_session::lint::builtin::{CONFLICTING_REPR_HINTS, UNUSED_ATTRIBUTES};
19 use rustc_span::symbol::sym;
21 use syntax::ast::Attribute;
24 fn target_from_impl_item<'tcx>(tcx: TyCtxt<'tcx>, impl_item: &hir::ImplItem<'_>) -> Target {
25 match impl_item.kind {
26 hir::ImplItemKind::Const(..) => Target::AssocConst,
27 hir::ImplItemKind::Method(..) => {
28 let parent_hir_id = tcx.hir().get_parent_item(impl_item.hir_id);
29 let containing_item = tcx.hir().expect_item(parent_hir_id);
30 let containing_impl_is_for_trait = match &containing_item.kind {
31 hir::ItemKind::Impl { ref of_trait, .. } => of_trait.is_some(),
32 _ => bug!("parent of an ImplItem must be an Impl"),
34 if containing_impl_is_for_trait {
35 Target::Method(MethodKind::Trait { body: true })
37 Target::Method(MethodKind::Inherent)
40 hir::ImplItemKind::TyAlias(..) | hir::ImplItemKind::OpaqueTy(..) => Target::AssocTy,
44 struct CheckAttrVisitor<'tcx> {
48 impl CheckAttrVisitor<'tcx> {
49 /// Checks any attribute.
53 attrs: &'hir [Attribute],
56 item: Option<&Item<'_>>,
58 let mut is_valid = true;
60 is_valid &= if attr.check_name(sym::inline) {
61 self.check_inline(hir_id, attr, span, target)
62 } else if attr.check_name(sym::non_exhaustive) {
63 self.check_non_exhaustive(attr, span, target)
64 } else if attr.check_name(sym::marker) {
65 self.check_marker(attr, span, target)
66 } else if attr.check_name(sym::target_feature) {
67 self.check_target_feature(attr, span, target)
68 } else if attr.check_name(sym::track_caller) {
69 self.check_track_caller(&attr.span, attrs, span, target)
79 if target == Target::Fn {
80 self.tcx.codegen_fn_attrs(self.tcx.hir().local_def_id(hir_id));
83 self.check_repr(attrs, span, target, item, hir_id);
84 self.check_used(attrs, target);
87 /// Checks if an `#[inline]` is applied to a function or a closure. Returns `true` if valid.
88 fn check_inline(&self, hir_id: HirId, attr: &Attribute, span: &Span, target: Target) -> bool {
92 | Target::Method(MethodKind::Trait { body: true })
93 | Target::Method(MethodKind::Inherent) => true,
94 Target::Method(MethodKind::Trait { body: false }) | Target::ForeignFn => {
96 .struct_span_lint_hir(
100 "`#[inline]` is ignored on function prototypes",
105 // FIXME(#65833): We permit associated consts to have an `#[inline]` attribute with
106 // just a lint, because we previously erroneously allowed it and some crates used it
107 // accidentally, to to be compatible with crates depending on them, we can't throw an
109 Target::AssocConst => {
111 .struct_span_lint_hir(
115 "`#[inline]` is ignored on constants",
118 "this was previously accepted by the compiler but is \
119 being phased out; it will become a hard error in \
123 "for more information, see issue #65833 \
124 <https://github.com/rust-lang/rust/issues/65833>",
134 "attribute should be applied to function or closure",
136 .span_label(*span, "not a function or closure")
143 /// Checks if a `#[track_caller]` is applied to a non-naked function. Returns `true` if valid.
144 fn check_track_caller(
147 attrs: &'hir [Attribute],
152 Target::Fn if attr::contains_name(attrs, sym::naked) => {
157 "cannot use `#[track_caller]` with `#[naked]`",
162 Target::Fn | Target::Method(MethodKind::Inherent) => true,
163 Target::Method(_) => {
168 "`#[track_caller]` may not be used on trait methods",
178 "attribute should be applied to function"
180 .span_label(*span, "not a function")
187 /// Checks if the `#[non_exhaustive]` attribute on an `item` is valid. Returns `true` if valid.
188 fn check_non_exhaustive(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
190 Target::Struct | Target::Enum => true,
196 "attribute can only be applied to a struct or enum"
198 .span_label(*span, "not a struct or enum")
205 /// Checks if the `#[marker]` attribute on an `item` is valid. Returns `true` if valid.
206 fn check_marker(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
208 Target::Trait => true,
212 .struct_span_err(attr.span, "attribute can only be applied to a trait")
213 .span_label(*span, "not a trait")
220 /// Checks if the `#[target_feature]` attribute on `item` is valid. Returns `true` if valid.
221 fn check_target_feature(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
224 | Target::Method(MethodKind::Trait { body: true })
225 | Target::Method(MethodKind::Inherent) => true,
229 .struct_span_err(attr.span, "attribute should be applied to a function")
230 .span_label(*span, "not a function")
237 /// Checks if the `#[repr]` attributes on `item` are valid.
240 attrs: &'hir [Attribute],
243 item: Option<&Item<'_>>,
246 // Extract the names of all repr hints, e.g., [foo, bar, align] for:
249 // #[repr(bar, align(8))]
251 let hints: Vec<_> = attrs
253 .filter(|attr| attr.check_name(sym::repr))
254 .filter_map(|attr| attr.meta_item_list())
258 let mut int_reprs = 0;
259 let mut is_c = false;
260 let mut is_simd = false;
261 let mut is_transparent = false;
264 let (article, allowed_targets) = match hint.name_or_empty() {
265 name @ sym::C | name @ sym::align => {
266 is_c |= name == sym::C;
268 Target::Struct | Target::Union | Target::Enum => continue,
269 _ => ("a", "struct, enum, or union"),
273 if target != Target::Struct && target != Target::Union {
274 ("a", "struct or union")
281 if target != Target::Struct { ("a", "struct") } else { continue }
283 sym::transparent => {
284 is_transparent = true;
286 Target::Struct | Target::Union | Target::Enum => continue,
287 _ => ("a", "struct, enum, or union"),
301 if target != Target::Enum { ("an", "enum") } else { continue }
305 self.emit_repr_error(
308 &format!("attribute should be applied to {}", allowed_targets),
309 &format!("not {} {}", article, allowed_targets),
313 // Just point at all repr hints if there are any incompatibilities.
314 // This is not ideal, but tracking precisely which ones are at fault is a huge hassle.
315 let hint_spans = hints.iter().map(|hint| hint.span());
317 // Error on repr(transparent, <anything else>).
318 if is_transparent && hints.len() > 1 {
319 let hint_spans: Vec<_> = hint_spans.clone().collect();
324 "transparent {} cannot have other repr hints",
329 // Warn on repr(u8, u16), repr(C, simd), and c-like-enum-repr(C, u8)
332 || (int_reprs == 1 && is_c && item.map_or(false, |item| is_c_like_enum(item)))
335 .struct_span_lint_hir(
336 CONFLICTING_REPR_HINTS,
338 hint_spans.collect::<Vec<Span>>(),
339 "conflicting representation hints",
341 .code(rustc_errors::error_code!(E0566))
353 struct_span_err!(self.tcx.sess, hint_span, E0517, "{}", hint_message)
354 .span_label(label_span, label_message)
358 fn check_stmt_attributes(&self, stmt: &hir::Stmt<'_>) {
359 // When checking statements ignore expressions, they will be checked later
360 if let hir::StmtKind::Local(ref l) = stmt.kind {
361 for attr in l.attrs.iter() {
362 if attr.check_name(sym::inline) {
363 self.check_inline(DUMMY_HIR_ID, attr, &stmt.span, Target::Statement);
365 if attr.check_name(sym::repr) {
366 self.emit_repr_error(
369 "attribute should not be applied to a statement",
370 "not a struct, enum, or union",
377 fn check_expr_attributes(&self, expr: &hir::Expr<'_>) {
378 let target = match expr.kind {
379 hir::ExprKind::Closure(..) => Target::Closure,
380 _ => Target::Expression,
382 for attr in expr.attrs.iter() {
383 if attr.check_name(sym::inline) {
384 self.check_inline(DUMMY_HIR_ID, attr, &expr.span, target);
386 if attr.check_name(sym::repr) {
387 self.emit_repr_error(
390 "attribute should not be applied to an expression",
391 "not defining a struct, enum, or union",
397 fn check_used(&self, attrs: &'hir [Attribute], target: Target) {
399 if attr.check_name(sym::used) && target != Target::Static {
402 .span_err(attr.span, "attribute must be applied to a `static` variable");
408 impl Visitor<'tcx> for CheckAttrVisitor<'tcx> {
409 type Map = Map<'tcx>;
411 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, Self::Map> {
412 NestedVisitorMap::OnlyBodies(&self.tcx.hir())
415 fn visit_item(&mut self, item: &'tcx Item<'tcx>) {
416 let target = Target::from_item(item);
417 self.check_attributes(item.hir_id, item.attrs, &item.span, target, Some(item));
418 intravisit::walk_item(self, item)
421 fn visit_trait_item(&mut self, trait_item: &'tcx TraitItem<'tcx>) {
422 let target = Target::from_trait_item(trait_item);
423 self.check_attributes(trait_item.hir_id, &trait_item.attrs, &trait_item.span, target, None);
424 intravisit::walk_trait_item(self, trait_item)
427 fn visit_foreign_item(&mut self, f_item: &'tcx hir::ForeignItem<'tcx>) {
428 let target = Target::from_foreign_item(f_item);
429 self.check_attributes(f_item.hir_id, &f_item.attrs, &f_item.span, target, None);
430 intravisit::walk_foreign_item(self, f_item)
433 fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
434 let target = target_from_impl_item(self.tcx, impl_item);
435 self.check_attributes(impl_item.hir_id, &impl_item.attrs, &impl_item.span, target, None);
436 intravisit::walk_impl_item(self, impl_item)
439 fn visit_stmt(&mut self, stmt: &'tcx hir::Stmt<'tcx>) {
440 self.check_stmt_attributes(stmt);
441 intravisit::walk_stmt(self, stmt)
444 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
445 self.check_expr_attributes(expr);
446 intravisit::walk_expr(self, expr)
450 fn is_c_like_enum(item: &Item<'_>) -> bool {
451 if let ItemKind::Enum(ref def, _) = item.kind {
452 for variant in def.variants {
454 hir::VariantData::Unit(..) => { /* continue */ }
464 fn check_mod_attrs(tcx: TyCtxt<'_>, module_def_id: DefId) {
466 .visit_item_likes_in_module(module_def_id, &mut CheckAttrVisitor { tcx }.as_deep_visitor());
469 pub(crate) fn provide(providers: &mut Providers<'_>) {
470 *providers = Providers { check_mod_attrs, ..*providers };