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::hir::check_attr::{MethodKind, Target};
   8 use rustc::hir::map::Map;
   9 use rustc::ty::query::Providers;
  10 use rustc::ty::TyCtxt;
  11
  12 use rustc_errors::struct_span_err;
  13 use rustc_hir as hir;
  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;
  20 use rustc_span::Span;
  21 use syntax::ast::Attribute;
  22 use syntax::attr;
  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::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"),
  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 })
  93             | Target::Method(MethodKind::Inherent) => true,
  94             Target::Method(MethodKind::Trait { body: false }) | Target::ForeignFn => {
  95                 self.tcx
  96                     .struct_span_lint_hir(
  97                         UNUSED_ATTRIBUTES,
  98                         hir_id,
  99                         attr.span,
 100                         "`#[inline]` is ignored on function prototypes",
 101                     )
 102                     .emit();
 103                 true
 104             }
 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
 108             // error here.
 109             Target::AssocConst => {
 110                 self.tcx
 111                     .struct_span_lint_hir(
 112                         UNUSED_ATTRIBUTES,
 113                         hir_id,
 114                         attr.span,
 115                         "`#[inline]` is ignored on constants",
 116                     )
 117                     .warn(
 118                         "this was previously accepted by the compiler but is \
 119                        being phased out; it will become a hard error in \
 120                        a future release!",
 121                     )
 122                     .note(
 123                         "for more information, see issue #65833 \
 124                        <https://github.com/rust-lang/rust/issues/65833>",
 125                     )
 126                     .emit();
 127                 true
 128             }
 129             _ => {
 130                 struct_span_err!(
 131                     self.tcx.sess,
 132                     attr.span,
 133                     E0518,
 134                     "attribute should be applied to function or closure",
 135                 )
 136                 .span_label(*span, "not a function or closure")
 137                 .emit();
 138                 false
 139             }
 140         }
 141     }
 142
 143     /// Checks if a `#[track_caller]` is applied to a non-naked function. Returns `true` if valid.
 144     fn check_track_caller(
 145         &self,
 146         attr_span: &Span,
 147         attrs: &'hir [Attribute],
 148         span: &Span,
 149         target: Target,
 150     ) -> bool {
 151         match target {
 152             Target::Fn if attr::contains_name(attrs, sym::naked) => {
 153                 struct_span_err!(
 154                     self.tcx.sess,
 155                     *attr_span,
 156                     E0736,
 157                     "cannot use `#[track_caller]` with `#[naked]`",
 158                 )
 159                 .emit();
 160                 false
 161             }
 162             Target::Fn | Target::Method(MethodKind::Inherent) => true,
 163             Target::Method(_) => {
 164                 struct_span_err!(
 165                     self.tcx.sess,
 166                     *attr_span,
 167                     E0738,
 168                     "`#[track_caller]` may not be used on trait methods",
 169                 )
 170                 .emit();
 171                 false
 172             }
 173             _ => {
 174                 struct_span_err!(
 175                     self.tcx.sess,
 176                     *attr_span,
 177                     E0739,
 178                     "attribute should be applied to function"
 179                 )
 180                 .span_label(*span, "not a function")
 181                 .emit();
 182                 false
 183             }
 184         }
 185     }
 186
 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 {
 189         match target {
 190             Target::Struct | Target::Enum => true,
 191             _ => {
 192                 struct_span_err!(
 193                     self.tcx.sess,
 194                     attr.span,
 195                     E0701,
 196                     "attribute can only be applied to a struct or enum"
 197                 )
 198                 .span_label(*span, "not a struct or enum")
 199                 .emit();
 200                 false
 201             }
 202         }
 203     }
 204
 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 {
 207         match target {
 208             Target::Trait => true,
 209             _ => {
 210                 self.tcx
 211                     .sess
 212                     .struct_span_err(attr.span, "attribute can only be applied to a trait")
 213                     .span_label(*span, "not a trait")
 214                     .emit();
 215                 false
 216             }
 217         }
 218     }
 219
 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 {
 222         match target {
 223             Target::Fn
 224             | Target::Method(MethodKind::Trait { body: true })
 225             | Target::Method(MethodKind::Inherent) => true,
 226             _ => {
 227                 self.tcx
 228                     .sess
 229                     .struct_span_err(attr.span, "attribute should be applied to a function")
 230                     .span_label(*span, "not a function")
 231                     .emit();
 232                 false
 233             }
 234         }
 235     }
 236
 237     /// Checks if the `#[repr]` attributes on `item` are valid.
 238     fn check_repr(
 239         &self,
 240         attrs: &'hir [Attribute],
 241         span: &Span,
 242         target: Target,
 243         item: Option<&Item<'_>>,
 244         hir_id: HirId,
 245     ) {
 246         // Extract the names of all repr hints, e.g., [foo, bar, align] for:
 247         // ```
 248         // #[repr(foo)]
 249         // #[repr(bar, align(8))]
 250         // ```
 251         let hints: Vec<_> = attrs
 252             .iter()
 253             .filter(|attr| attr.check_name(sym::repr))
 254             .filter_map(|attr| attr.meta_item_list())
 255             .flatten()
 256             .collect();
 257
 258         let mut int_reprs = 0;
 259         let mut is_c = false;
 260         let mut is_simd = false;
 261         let mut is_transparent = false;
 262
 263         for hint in &hints {
 264             let (article, allowed_targets) = match hint.name_or_empty() {
 265                 name @ sym::C | name @ sym::align => {
 266                     is_c |= name == sym::C;
 267                     match target {
 268                         Target::Struct | Target::Union | Target::Enum => continue,
 269                         _ => ("a", "struct, enum, or union"),
 270                     }
 271                 }
 272                 sym::packed => {
 273                     if target != Target::Struct && target != Target::Union {
 274                         ("a", "struct or union")
 275                     } else {
 276                         continue;
 277                     }
 278                 }
 279                 sym::simd => {
 280                     is_simd = true;
 281                     if target != Target::Struct { ("a", "struct") } else { continue }
 282                 }
 283                 sym::transparent => {
 284                     is_transparent = true;
 285                     match target {
 286                         Target::Struct | Target::Union | Target::Enum => continue,
 287                         _ => ("a", "struct, enum, or union"),
 288                     }
 289                 }
 290                 sym::i8
 291                 | sym::u8
 292                 | sym::i16
 293                 | sym::u16
 294                 | sym::i32
 295                 | sym::u32
 296                 | sym::i64
 297                 | sym::u64
 298                 | sym::isize
 299                 | sym::usize => {
 300                     int_reprs += 1;
 301                     if target != Target::Enum { ("an", "enum") } else { continue }
 302                 }
 303                 _ => continue,
 304             };
 305             self.emit_repr_error(
 306                 hint.span(),
 307                 *span,
 308                 &format!("attribute should be applied to {}", allowed_targets),
 309                 &format!("not {} {}", article, allowed_targets),
 310             )
 311         }
 312
 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());
 316
 317         // Error on repr(transparent, <anything else>).
 318         if is_transparent && hints.len() > 1 {
 319             let hint_spans: Vec<_> = hint_spans.clone().collect();
 320             struct_span_err!(
 321                 self.tcx.sess,
 322                 hint_spans,
 323                 E0692,
 324                 "transparent {} cannot have other repr hints",
 325                 target
 326             )
 327             .emit();
 328         }
 329         // Warn on repr(u8, u16), repr(C, simd), and c-like-enum-repr(C, u8)
 330         if (int_reprs > 1)
 331             || (is_simd && is_c)
 332             || (int_reprs == 1 && is_c && item.map_or(false, |item| is_c_like_enum(item)))
 333         {
 334             self.tcx
 335                 .struct_span_lint_hir(
 336                     CONFLICTING_REPR_HINTS,
 337                     hir_id,
 338                     hint_spans.collect::<Vec<Span>>(),
 339                     "conflicting representation hints",
 340                 )
 341                 .code(rustc_errors::error_code!(E0566))
 342                 .emit();
 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(DUMMY_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(DUMMY_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     }
 396
 397     fn check_used(&self, attrs: &'hir [Attribute], target: Target) {
 398         for attr in attrs {
 399             if attr.check_name(sym::used) && target != Target::Static {
 400                 self.tcx
 401                     .sess
 402                     .span_err(attr.span, "attribute must be applied to a `static` variable");
 403             }
 404         }
 405     }
 406 }
 407
 408 impl Visitor<'tcx> for CheckAttrVisitor<'tcx> {
 409     type Map = Map<'tcx>;
 410
 411     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, Self::Map> {
 412         NestedVisitorMap::OnlyBodies(&self.tcx.hir())
 413     }
 414
 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)
 419     }
 420
 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)
 425     }
 426
 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)
 431     }
 432
 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)
 437     }
 438
 439     fn visit_stmt(&mut self, stmt: &'tcx hir::Stmt<'tcx>) {
 440         self.check_stmt_attributes(stmt);
 441         intravisit::walk_stmt(self, stmt)
 442     }
 443
 444     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
 445         self.check_expr_attributes(expr);
 446         intravisit::walk_expr(self, expr)
 447     }
 448 }
 449
 450 fn is_c_like_enum(item: &Item<'_>) -> bool {
 451     if let ItemKind::Enum(ref def, _) = item.kind {
 452         for variant in def.variants {
 453             match variant.data {
 454                 hir::VariantData::Unit(..) => { /* continue */ }
 455                 _ => return false,
 456             }
 457         }
 458         true
 459     } else {
 460         false
 461     }
 462 }
 463
 464 fn check_mod_attrs(tcx: TyCtxt<'_>, module_def_id: DefId) {
 465     tcx.hir()
 466         .visit_item_likes_in_module(module_def_id, &mut CheckAttrVisitor { tcx }.as_deep_visitor());
 467 }
 468
 469 pub(crate) fn provide(providers: &mut Providers<'_>) {
 470     *providers = Providers { check_mod_attrs, ..*providers };
 471 }