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::DefId;
  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 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::Fn(..) => {
  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"),
  33             };
  34             if containing_impl_is_for_trait {
  35                 Target::Method(MethodKind::Trait { body: true })
  36             } else {
  37                 Target::Method(MethodKind::Inherent)
  38             }
  39         }
  40         hir::ImplItemKind::TyAlias(..) | hir::ImplItemKind::OpaqueTy(..) => Target::AssocTy,
  41     }
  42 }
  43
  44 struct CheckAttrVisitor<'tcx> {
  45     tcx: TyCtxt<'tcx>,
  46 }
  47
  48 impl CheckAttrVisitor<'tcx> {
  49     /// Checks any attribute.
  50     fn check_attributes(
  51         &self,
  52         hir_id: HirId,
  53         attrs: &'hir [Attribute],
  54         span: &Span,
  55         target: Target,
  56         item: Option<&Item<'_>>,
  57     ) {
  58         let mut is_valid = true;
  59         for attr in attrs {
  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)
  70             } else {
  71                 true
  72             };
  73         }
  74
  75         if !is_valid {
  76             return;
  77         }
  78
  79         if target == Target::Fn {
  80             self.tcx.codegen_fn_attrs(self.tcx.hir().local_def_id(hir_id));
  81         }
  82
  83         self.check_repr(attrs, span, target, item, hir_id);
  84         self.check_used(attrs, target);
  85     }
  86
  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 {
  89         match target {
  90             Target::Fn
  91             | Target::Closure
  92             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
  93             Target::Method(MethodKind::Trait { body: false }) | Target::ForeignFn => {
  94                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
  95                     lint.build("`#[inline]` is ignored on function prototypes").emit()
  96                 });
  97                 true
  98             }
  99             // FIXME(#65833): We permit associated consts to have an `#[inline]` attribute with
 100             // just a lint, because we previously erroneously allowed it and some crates used it
 101             // accidentally, to to be compatible with crates depending on them, we can't throw an
 102             // error here.
 103             Target::AssocConst => {
 104                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
 105                     lint.build("`#[inline]` is ignored on constants")
 106                         .warn(
 107                             "this was previously accepted by the compiler but is \
 108                                being phased out; it will become a hard error in \
 109                                a future release!",
 110                         )
 111                         .note(
 112                             "see issue #65833 <https://github.com/rust-lang/rust/issues/65833> \
 113                                  for more information",
 114                         )
 115                         .emit();
 116                 });
 117                 true
 118             }
 119             _ => {
 120                 struct_span_err!(
 121                     self.tcx.sess,
 122                     attr.span,
 123                     E0518,
 124                     "attribute should be applied to function or closure",
 125                 )
 126                 .span_label(*span, "not a function or closure")
 127                 .emit();
 128                 false
 129             }
 130         }
 131     }
 132
 133     /// Checks if a `#[track_caller]` is applied to a non-naked function. Returns `true` if valid.
 134     fn check_track_caller(
 135         &self,
 136         attr_span: &Span,
 137         attrs: &'hir [Attribute],
 138         span: &Span,
 139         target: Target,
 140     ) -> bool {
 141         match target {
 142             _ if attr::contains_name(attrs, sym::naked) => {
 143                 struct_span_err!(
 144                     self.tcx.sess,
 145                     *attr_span,
 146                     E0736,
 147                     "cannot use `#[track_caller]` with `#[naked]`",
 148                 )
 149                 .emit();
 150                 false
 151             }
 152             Target::Fn | Target::Method(..) | Target::ForeignFn => true,
 153             _ => {
 154                 struct_span_err!(
 155                     self.tcx.sess,
 156                     *attr_span,
 157                     E0739,
 158                     "attribute should be applied to function"
 159                 )
 160                 .span_label(*span, "not a function")
 161                 .emit();
 162                 false
 163             }
 164         }
 165     }
 166
 167     /// Checks if the `#[non_exhaustive]` attribute on an `item` is valid. Returns `true` if valid.
 168     fn check_non_exhaustive(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 169         match target {
 170             Target::Struct | Target::Enum => true,
 171             _ => {
 172                 struct_span_err!(
 173                     self.tcx.sess,
 174                     attr.span,
 175                     E0701,
 176                     "attribute can only be applied to a struct or enum"
 177                 )
 178                 .span_label(*span, "not a struct or enum")
 179                 .emit();
 180                 false
 181             }
 182         }
 183     }
 184
 185     /// Checks if the `#[marker]` attribute on an `item` is valid. Returns `true` if valid.
 186     fn check_marker(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 187         match target {
 188             Target::Trait => true,
 189             _ => {
 190                 self.tcx
 191                     .sess
 192                     .struct_span_err(attr.span, "attribute can only be applied to a trait")
 193                     .span_label(*span, "not a trait")
 194                     .emit();
 195                 false
 196             }
 197         }
 198     }
 199
 200     /// Checks if the `#[target_feature]` attribute on `item` is valid. Returns `true` if valid.
 201     fn check_target_feature(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 202         match target {
 203             Target::Fn
 204             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
 205             _ => {
 206                 self.tcx
 207                     .sess
 208                     .struct_span_err(attr.span, "attribute should be applied to a function")
 209                     .span_label(*span, "not a function")
 210                     .emit();
 211                 false
 212             }
 213         }
 214     }
 215
 216     /// Checks if the `#[repr]` attributes on `item` are valid.
 217     fn check_repr(
 218         &self,
 219         attrs: &'hir [Attribute],
 220         span: &Span,
 221         target: Target,
 222         item: Option<&Item<'_>>,
 223         hir_id: HirId,
 224     ) {
 225         // Extract the names of all repr hints, e.g., [foo, bar, align] for:
 226         // ```
 227         // #[repr(foo)]
 228         // #[repr(bar, align(8))]
 229         // ```
 230         let hints: Vec<_> = attrs
 231             .iter()
 232             .filter(|attr| attr.check_name(sym::repr))
 233             .filter_map(|attr| attr.meta_item_list())
 234             .flatten()
 235             .collect();
 236
 237         let mut int_reprs = 0;
 238         let mut is_c = false;
 239         let mut is_simd = false;
 240         let mut is_transparent = false;
 241
 242         for hint in &hints {
 243             let (article, allowed_targets) = match hint.name_or_empty() {
 244                 name @ sym::C | name @ sym::align => {
 245                     is_c |= name == sym::C;
 246                     match target {
 247                         Target::Struct | Target::Union | Target::Enum => continue,
 248                         _ => ("a", "struct, enum, or union"),
 249                     }
 250                 }
 251                 sym::packed => {
 252                     if target != Target::Struct && target != Target::Union {
 253                         ("a", "struct or union")
 254                     } else {
 255                         continue;
 256                     }
 257                 }
 258                 sym::simd => {
 259                     is_simd = true;
 260                     if target != Target::Struct { ("a", "struct") } else { continue }
 261                 }
 262                 sym::transparent => {
 263                     is_transparent = true;
 264                     match target {
 265                         Target::Struct | Target::Union | Target::Enum => continue,
 266                         _ => ("a", "struct, enum, or union"),
 267                     }
 268                 }
 269                 sym::no_niche => {
 270                     if !self.tcx.features().enabled(sym::no_niche) {
 271                         feature_err(
 272                             &self.tcx.sess.parse_sess,
 273                             sym::no_niche,
 274                             hint.span(),
 275                             "the attribute `repr(no_niche)` is currently unstable",
 276                         )
 277                         .emit();
 278                     }
 279                     match target {
 280                         Target::Struct | Target::Enum => continue,
 281                         _ => ("a", "struct or enum"),
 282                     }
 283                 }
 284                 sym::i8
 285                 | sym::u8
 286                 | sym::i16
 287                 | sym::u16
 288                 | sym::i32
 289                 | sym::u32
 290                 | sym::i64
 291                 | sym::u64
 292                 | sym::isize
 293                 | sym::usize => {
 294                     int_reprs += 1;
 295                     if target != Target::Enum { ("an", "enum") } else { continue }
 296                 }
 297                 _ => continue,
 298             };
 299             self.emit_repr_error(
 300                 hint.span(),
 301                 *span,
 302                 &format!("attribute should be applied to {}", allowed_targets),
 303                 &format!("not {} {}", article, allowed_targets),
 304             )
 305         }
 306
 307         // Just point at all repr hints if there are any incompatibilities.
 308         // This is not ideal, but tracking precisely which ones are at fault is a huge hassle.
 309         let hint_spans = hints.iter().map(|hint| hint.span());
 310
 311         // Error on repr(transparent, <anything else apart from no_niche>).
 312         let non_no_niche = |hint: &&NestedMetaItem| hint.name_or_empty() != sym::no_niche;
 313         let non_no_niche_count = hints.iter().filter(non_no_niche).count();
 314         if is_transparent && non_no_niche_count > 1 {
 315             let hint_spans: Vec<_> = hint_spans.clone().collect();
 316             struct_span_err!(
 317                 self.tcx.sess,
 318                 hint_spans,
 319                 E0692,
 320                 "transparent {} cannot have other repr hints",
 321                 target
 322             )
 323             .emit();
 324         }
 325         // Warn on repr(u8, u16), repr(C, simd), and c-like-enum-repr(C, u8)
 326         if (int_reprs > 1)
 327             || (is_simd && is_c)
 328             || (int_reprs == 1 && is_c && item.map_or(false, |item| is_c_like_enum(item)))
 329         {
 330             self.tcx.struct_span_lint_hir(
 331                 CONFLICTING_REPR_HINTS,
 332                 hir_id,
 333                 hint_spans.collect::<Vec<Span>>(),
 334                 |lint| {
 335                     lint.build("conflicting representation hints")
 336                         .code(rustc_errors::error_code!(E0566))
 337                         .emit();
 338                 },
 339             );
 340         }
 341     }
 342
 343     fn emit_repr_error(
 344         &self,
 345         hint_span: Span,
 346         label_span: Span,
 347         hint_message: &str,
 348         label_message: &str,
 349     ) {
 350         struct_span_err!(self.tcx.sess, hint_span, E0517, "{}", hint_message)
 351             .span_label(label_span, label_message)
 352             .emit();
 353     }
 354
 355     fn check_stmt_attributes(&self, stmt: &hir::Stmt<'_>) {
 356         // When checking statements ignore expressions, they will be checked later
 357         if let hir::StmtKind::Local(ref l) = stmt.kind {
 358             for attr in l.attrs.iter() {
 359                 if attr.check_name(sym::inline) {
 360                     self.check_inline(l.hir_id, attr, &stmt.span, Target::Statement);
 361                 }
 362                 if attr.check_name(sym::repr) {
 363                     self.emit_repr_error(
 364                         attr.span,
 365                         stmt.span,
 366                         "attribute should not be applied to a statement",
 367                         "not a struct, enum, or union",
 368                     );
 369                 }
 370             }
 371         }
 372     }
 373
 374     fn check_expr_attributes(&self, expr: &hir::Expr<'_>) {
 375         let target = match expr.kind {
 376             hir::ExprKind::Closure(..) => Target::Closure,
 377             _ => Target::Expression,
 378         };
 379         for attr in expr.attrs.iter() {
 380             if attr.check_name(sym::inline) {
 381                 self.check_inline(expr.hir_id, attr, &expr.span, target);
 382             }
 383             if attr.check_name(sym::repr) {
 384                 self.emit_repr_error(
 385                     attr.span,
 386                     expr.span,
 387                     "attribute should not be applied to an expression",
 388                     "not defining a struct, enum, or union",
 389                 );
 390             }
 391         }
 392     }
 393
 394     fn check_used(&self, attrs: &'hir [Attribute], target: Target) {
 395         for attr in attrs {
 396             if attr.check_name(sym::used) && target != Target::Static {
 397                 self.tcx
 398                     .sess
 399                     .span_err(attr.span, "attribute must be applied to a `static` variable");
 400             }
 401         }
 402     }
 403 }
 404
 405 impl Visitor<'tcx> for CheckAttrVisitor<'tcx> {
 406     type Map = Map<'tcx>;
 407
 408     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 409         NestedVisitorMap::OnlyBodies(self.tcx.hir())
 410     }
 411
 412     fn visit_item(&mut self, item: &'tcx Item<'tcx>) {
 413         let target = Target::from_item(item);
 414         self.check_attributes(item.hir_id, item.attrs, &item.span, target, Some(item));
 415         intravisit::walk_item(self, item)
 416     }
 417
 418     fn visit_trait_item(&mut self, trait_item: &'tcx TraitItem<'tcx>) {
 419         let target = Target::from_trait_item(trait_item);
 420         self.check_attributes(trait_item.hir_id, &trait_item.attrs, &trait_item.span, target, None);
 421         intravisit::walk_trait_item(self, trait_item)
 422     }
 423
 424     fn visit_foreign_item(&mut self, f_item: &'tcx hir::ForeignItem<'tcx>) {
 425         let target = Target::from_foreign_item(f_item);
 426         self.check_attributes(f_item.hir_id, &f_item.attrs, &f_item.span, target, None);
 427         intravisit::walk_foreign_item(self, f_item)
 428     }
 429
 430     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
 431         let target = target_from_impl_item(self.tcx, impl_item);
 432         self.check_attributes(impl_item.hir_id, &impl_item.attrs, &impl_item.span, target, None);
 433         intravisit::walk_impl_item(self, impl_item)
 434     }
 435
 436     fn visit_stmt(&mut self, stmt: &'tcx hir::Stmt<'tcx>) {
 437         self.check_stmt_attributes(stmt);
 438         intravisit::walk_stmt(self, stmt)
 439     }
 440
 441     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
 442         self.check_expr_attributes(expr);
 443         intravisit::walk_expr(self, expr)
 444     }
 445 }
 446
 447 fn is_c_like_enum(item: &Item<'_>) -> bool {
 448     if let ItemKind::Enum(ref def, _) = item.kind {
 449         for variant in def.variants {
 450             match variant.data {
 451                 hir::VariantData::Unit(..) => { /* continue */ }
 452                 _ => return false,
 453             }
 454         }
 455         true
 456     } else {
 457         false
 458     }
 459 }
 460
 461 fn check_mod_attrs(tcx: TyCtxt<'_>, module_def_id: DefId) {
 462     tcx.hir()
 463         .visit_item_likes_in_module(module_def_id, &mut CheckAttrVisitor { tcx }.as_deep_visitor());
 464 }
 465
 466 pub(crate) fn provide(providers: &mut Providers<'_>) {
 467     *providers = Providers { check_mod_attrs, ..*providers };
 468 }