src/librustc_passes/check_attr.rs

   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
   5 //! item.
   6
   7 use rustc_middle::hir::map::Map;
   8 use rustc_middle::ty::query::Providers;
   9 use rustc_middle::ty::TyCtxt;
  10
  11 use rustc_ast::ast::{Attribute, NestedMetaItem};
  12 use rustc_ast::attr;
  13 use rustc_errors::struct_span_err;
  14 use rustc_hir as hir;
  15 use rustc_hir::def_id::LocalDefId;
  16 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
  17 use rustc_hir::{self, HirId, Item, ItemKind, TraitItem};
  18 use rustc_hir::{MethodKind, Target};
  19 use rustc_session::lint::builtin::{CONFLICTING_REPR_HINTS, UNUSED_ATTRIBUTES};
  20 use rustc_session::parse::feature_err;
  21 use rustc_span::symbol::sym;
  22 use rustc_span::Span;
  23
  24 pub(crate) fn target_from_impl_item<'tcx>(
  25     tcx: TyCtxt<'tcx>,
  26     impl_item: &hir::ImplItem<'_>,
  27 ) -> Target {
  28     match impl_item.kind {
  29         hir::ImplItemKind::Const(..) => Target::AssocConst,
  30         hir::ImplItemKind::Fn(..) => {
  31             let parent_hir_id = tcx.hir().get_parent_item(impl_item.hir_id);
  32             let containing_item = tcx.hir().expect_item(parent_hir_id);
  33             let containing_impl_is_for_trait = match &containing_item.kind {
  34                 hir::ItemKind::Impl { ref of_trait, .. } => of_trait.is_some(),
  35                 _ => bug!("parent of an ImplItem must be an Impl"),
  36             };
  37             if containing_impl_is_for_trait {
  38                 Target::Method(MethodKind::Trait { body: true })
  39             } else {
  40                 Target::Method(MethodKind::Inherent)
  41             }
  42         }
  43         hir::ImplItemKind::TyAlias(..) => Target::AssocTy,
  44     }
  45 }
  46
  47 struct CheckAttrVisitor<'tcx> {
  48     tcx: TyCtxt<'tcx>,
  49 }
  50
  51 impl CheckAttrVisitor<'tcx> {
  52     /// Checks any attribute.
  53     fn check_attributes(
  54         &self,
  55         hir_id: HirId,
  56         attrs: &'hir [Attribute],
  57         span: &Span,
  58         target: Target,
  59         item: Option<&Item<'_>>,
  60     ) {
  61         let mut is_valid = true;
  62         for attr in attrs {
  63             is_valid &= if attr.check_name(sym::inline) {
  64                 self.check_inline(hir_id, attr, span, target)
  65             } else if attr.check_name(sym::non_exhaustive) {
  66                 self.check_non_exhaustive(attr, span, target)
  67             } else if attr.check_name(sym::marker) {
  68                 self.check_marker(attr, span, target)
  69             } else if attr.check_name(sym::target_feature) {
  70                 self.check_target_feature(attr, span, target)
  71             } else if attr.check_name(sym::track_caller) {
  72                 self.check_track_caller(&attr.span, attrs, span, target)
  73             } else {
  74                 true
  75             };
  76         }
  77
  78         if !is_valid {
  79             return;
  80         }
  81
  82         if matches!(target, Target::Fn | Target::Method(_) | Target::ForeignFn) {
  83             self.tcx.ensure().codegen_fn_attrs(self.tcx.hir().local_def_id(hir_id));
  84         }
  85
  86         self.check_repr(attrs, span, target, item, hir_id);
  87         self.check_used(attrs, target);
  88     }
  89
  90     /// Checks if an `#[inline]` is applied to a function or a closure. Returns `true` if valid.
  91     fn check_inline(&self, hir_id: HirId, attr: &Attribute, span: &Span, target: Target) -> bool {
  92         match target {
  93             Target::Fn
  94             | Target::Closure
  95             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
  96             Target::Method(MethodKind::Trait { body: false }) | Target::ForeignFn => {
  97                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
  98                     lint.build("`#[inline]` is ignored on function prototypes").emit()
  99                 });
 100                 true
 101             }
 102             // FIXME(#65833): We permit associated consts to have an `#[inline]` attribute with
 103             // just a lint, because we previously erroneously allowed it and some crates used it
 104             // accidentally, to to be compatible with crates depending on them, we can't throw an
 105             // error here.
 106             Target::AssocConst => {
 107                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
 108                     lint.build("`#[inline]` is ignored on constants")
 109                         .warn(
 110                             "this was previously accepted by the compiler but is \
 111                                being phased out; it will become a hard error in \
 112                                a future release!",
 113                         )
 114                         .note(
 115                             "see issue #65833 <https://github.com/rust-lang/rust/issues/65833> \
 116                                  for more information",
 117                         )
 118                         .emit();
 119                 });
 120                 true
 121             }
 122             _ => {
 123                 struct_span_err!(
 124                     self.tcx.sess,
 125                     attr.span,
 126                     E0518,
 127                     "attribute should be applied to function or closure",
 128                 )
 129                 .span_label(*span, "not a function or closure")
 130                 .emit();
 131                 false
 132             }
 133         }
 134     }
 135
 136     /// Checks if a `#[track_caller]` is applied to a non-naked function. Returns `true` if valid.
 137     fn check_track_caller(
 138         &self,
 139         attr_span: &Span,
 140         attrs: &'hir [Attribute],
 141         span: &Span,
 142         target: Target,
 143     ) -> bool {
 144         match target {
 145             _ if attr::contains_name(attrs, sym::naked) => {
 146                 struct_span_err!(
 147                     self.tcx.sess,
 148                     *attr_span,
 149                     E0736,
 150                     "cannot use `#[track_caller]` with `#[naked]`",
 151                 )
 152                 .emit();
 153                 false
 154             }
 155             Target::Fn | Target::Method(..) | Target::ForeignFn => true,
 156             _ => {
 157                 struct_span_err!(
 158                     self.tcx.sess,
 159                     *attr_span,
 160                     E0739,
 161                     "attribute should be applied to function"
 162                 )
 163                 .span_label(*span, "not a function")
 164                 .emit();
 165                 false
 166             }
 167         }
 168     }
 169
 170     /// Checks if the `#[non_exhaustive]` attribute on an `item` is valid. Returns `true` if valid.
 171     fn check_non_exhaustive(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 172         match target {
 173             Target::Struct | Target::Enum => true,
 174             _ => {
 175                 struct_span_err!(
 176                     self.tcx.sess,
 177                     attr.span,
 178                     E0701,
 179                     "attribute can only be applied to a struct or enum"
 180                 )
 181                 .span_label(*span, "not a struct or enum")
 182                 .emit();
 183                 false
 184             }
 185         }
 186     }
 187
 188     /// Checks if the `#[marker]` attribute on an `item` is valid. Returns `true` if valid.
 189     fn check_marker(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 190         match target {
 191             Target::Trait => true,
 192             _ => {
 193                 self.tcx
 194                     .sess
 195                     .struct_span_err(attr.span, "attribute can only be applied to a trait")
 196                     .span_label(*span, "not a trait")
 197                     .emit();
 198                 false
 199             }
 200         }
 201     }
 202
 203     /// Checks if the `#[target_feature]` attribute on `item` is valid. Returns `true` if valid.
 204     fn check_target_feature(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 205         match target {
 206             Target::Fn
 207             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
 208             _ => {
 209                 self.tcx
 210                     .sess
 211                     .struct_span_err(attr.span, "attribute should be applied to a function")
 212                     .span_label(*span, "not a function")
 213                     .emit();
 214                 false
 215             }
 216         }
 217     }
 218
 219     /// Checks if the `#[repr]` attributes on `item` are valid.
 220     fn check_repr(
 221         &self,
 222         attrs: &'hir [Attribute],
 223         span: &Span,
 224         target: Target,
 225         item: Option<&Item<'_>>,
 226         hir_id: HirId,
 227     ) {
 228         // Extract the names of all repr hints, e.g., [foo, bar, align] for:
 229         // ```
 230         // #[repr(foo)]
 231         // #[repr(bar, align(8))]
 232         // ```
 233         let hints: Vec<_> = attrs
 234             .iter()
 235             .filter(|attr| attr.check_name(sym::repr))
 236             .filter_map(|attr| attr.meta_item_list())
 237             .flatten()
 238             .collect();
 239
 240         let mut int_reprs = 0;
 241         let mut is_c = false;
 242         let mut is_simd = false;
 243         let mut is_transparent = false;
 244
 245         for hint in &hints {
 246             let (article, allowed_targets) = match hint.name_or_empty() {
 247                 name @ sym::C | name @ sym::align => {
 248                     is_c |= name == sym::C;
 249                     match target {
 250                         Target::Struct | Target::Union | Target::Enum => continue,
 251                         _ => ("a", "struct, enum, or union"),
 252                     }
 253                 }
 254                 sym::packed => {
 255                     if target != Target::Struct && target != Target::Union {
 256                         ("a", "struct or union")
 257                     } else {
 258                         continue;
 259                     }
 260                 }
 261                 sym::simd => {
 262                     is_simd = true;
 263                     if target != Target::Struct { ("a", "struct") } else { continue }
 264                 }
 265                 sym::transparent => {
 266                     is_transparent = true;
 267                     match target {
 268                         Target::Struct | Target::Union | Target::Enum => continue,
 269                         _ => ("a", "struct, enum, or union"),
 270                     }
 271                 }
 272                 sym::no_niche => {
 273                     if !self.tcx.features().enabled(sym::no_niche) {
 274                         feature_err(
 275                             &self.tcx.sess.parse_sess,
 276                             sym::no_niche,
 277                             hint.span(),
 278                             "the attribute `repr(no_niche)` is currently unstable",
 279                         )
 280                         .emit();
 281                     }
 282                     match target {
 283                         Target::Struct | Target::Enum => continue,
 284                         _ => ("a", "struct or enum"),
 285                     }
 286                 }
 287                 sym::i8
 288                 | sym::u8
 289                 | sym::i16
 290                 | sym::u16
 291                 | sym::i32
 292                 | sym::u32
 293                 | sym::i64
 294                 | sym::u64
 295                 | sym::isize
 296                 | sym::usize => {
 297                     int_reprs += 1;
 298                     if target != Target::Enum { ("an", "enum") } else { continue }
 299                 }
 300                 _ => continue,
 301             };
 302             self.emit_repr_error(
 303                 hint.span(),
 304                 *span,
 305                 &format!("attribute should be applied to {}", allowed_targets),
 306                 &format!("not {} {}", article, allowed_targets),
 307             )
 308         }
 309
 310         // Just point at all repr hints if there are any incompatibilities.
 311         // This is not ideal, but tracking precisely which ones are at fault is a huge hassle.
 312         let hint_spans = hints.iter().map(|hint| hint.span());
 313
 314         // Error on repr(transparent, <anything else apart from no_niche>).
 315         let non_no_niche = |hint: &&NestedMetaItem| hint.name_or_empty() != sym::no_niche;
 316         let non_no_niche_count = hints.iter().filter(non_no_niche).count();
 317         if is_transparent && non_no_niche_count > 1 {
 318             let hint_spans: Vec<_> = hint_spans.clone().collect();
 319             struct_span_err!(
 320                 self.tcx.sess,
 321                 hint_spans,
 322                 E0692,
 323                 "transparent {} cannot have other repr hints",
 324                 target
 325             )
 326             .emit();
 327         }
 328         // Warn on repr(u8, u16), repr(C, simd), and c-like-enum-repr(C, u8)
 329         if (int_reprs > 1)
 330             || (is_simd && is_c)
 331             || (int_reprs == 1 && is_c && item.map_or(false, |item| is_c_like_enum(item)))
 332         {
 333             self.tcx.struct_span_lint_hir(
 334                 CONFLICTING_REPR_HINTS,
 335                 hir_id,
 336                 hint_spans.collect::<Vec<Span>>(),
 337                 |lint| {
 338                     lint.build("conflicting representation hints")
 339                         .code(rustc_errors::error_code!(E0566))
 340                         .emit();
 341                 },
 342             );
 343         }
 344     }
 345
 346     fn emit_repr_error(
 347         &self,
 348         hint_span: Span,
 349         label_span: Span,
 350         hint_message: &str,
 351         label_message: &str,
 352     ) {
 353         struct_span_err!(self.tcx.sess, hint_span, E0517, "{}", hint_message)
 354             .span_label(label_span, label_message)
 355             .emit();
 356     }
 357
 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(l.hir_id, attr, &stmt.span, Target::Statement);
 364                 }
 365                 if attr.check_name(sym::repr) {
 366                     self.emit_repr_error(
 367                         attr.span,
 368                         stmt.span,
 369                         "attribute should not be applied to a statement",
 370                         "not a struct, enum, or union",
 371                     );
 372                 }
 373             }
 374         }
 375     }
 376
 377     fn check_expr_attributes(&self, expr: &hir::Expr<'_>) {
 378         let target = match expr.kind {
 379             hir::ExprKind::Closure(..) => Target::Closure,
 380             _ => Target::Expression,
 381         };
 382         for attr in expr.attrs.iter() {
 383             if attr.check_name(sym::inline) {
 384                 self.check_inline(expr.hir_id, attr, &expr.span, target);
 385             }
 386             if attr.check_name(sym::repr) {
 387                 self.emit_repr_error(
 388                     attr.span,
 389                     expr.span,
 390                     "attribute should not be applied to an expression",
 391                     "not defining a struct, enum, or union",
 392                 );
 393             }
 394         }
 395         if target == Target::Closure {
 396             self.tcx.ensure().codegen_fn_attrs(self.tcx.hir().local_def_id(expr.hir_id));
 397         }
 398     }
 399
 400     fn check_used(&self, attrs: &'hir [Attribute], target: Target) {
 401         for attr in attrs {
 402             if attr.check_name(sym::used) && target != Target::Static {
 403                 self.tcx
 404                     .sess
 405                     .span_err(attr.span, "attribute must be applied to a `static` variable");
 406             }
 407         }
 408     }
 409 }
 410
 411 impl Visitor<'tcx> for CheckAttrVisitor<'tcx> {
 412     type Map = Map<'tcx>;
 413
 414     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 415         NestedVisitorMap::OnlyBodies(self.tcx.hir())
 416     }
 417
 418     fn visit_item(&mut self, item: &'tcx Item<'tcx>) {
 419         let target = Target::from_item(item);
 420         self.check_attributes(item.hir_id, item.attrs, &item.span, target, Some(item));
 421         intravisit::walk_item(self, item)
 422     }
 423
 424     fn visit_trait_item(&mut self, trait_item: &'tcx TraitItem<'tcx>) {
 425         let target = Target::from_trait_item(trait_item);
 426         self.check_attributes(trait_item.hir_id, &trait_item.attrs, &trait_item.span, target, None);
 427         intravisit::walk_trait_item(self, trait_item)
 428     }
 429
 430     fn visit_foreign_item(&mut self, f_item: &'tcx hir::ForeignItem<'tcx>) {
 431         let target = Target::from_foreign_item(f_item);
 432         self.check_attributes(f_item.hir_id, &f_item.attrs, &f_item.span, target, None);
 433         intravisit::walk_foreign_item(self, f_item)
 434     }
 435
 436     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
 437         let target = target_from_impl_item(self.tcx, impl_item);
 438         self.check_attributes(impl_item.hir_id, &impl_item.attrs, &impl_item.span, target, None);
 439         intravisit::walk_impl_item(self, impl_item)
 440     }
 441
 442     fn visit_stmt(&mut self, stmt: &'tcx hir::Stmt<'tcx>) {
 443         self.check_stmt_attributes(stmt);
 444         intravisit::walk_stmt(self, stmt)
 445     }
 446
 447     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
 448         self.check_expr_attributes(expr);
 449         intravisit::walk_expr(self, expr)
 450     }
 451 }
 452
 453 fn is_c_like_enum(item: &Item<'_>) -> bool {
 454     if let ItemKind::Enum(ref def, _) = item.kind {
 455         for variant in def.variants {
 456             match variant.data {
 457                 hir::VariantData::Unit(..) => { /* continue */ }
 458                 _ => return false,
 459             }
 460         }
 461         true
 462     } else {
 463         false
 464     }
 465 }
 466
 467 fn check_mod_attrs(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
 468     tcx.hir()
 469         .visit_item_likes_in_module(module_def_id, &mut CheckAttrVisitor { tcx }.as_deep_visitor());
 470 }
 471
 472 pub(crate) fn provide(providers: &mut Providers<'_>) {
 473     *providers = Providers { check_mod_attrs, ..*providers };
 474 }