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::map::Map;
   8 use rustc::ty::query::Providers;
   9 use rustc::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::DUMMY_HIR_ID;
  18 use rustc_hir::{self, HirId, Item, ItemKind, TraitItem};
  19 use rustc_hir::{MethodKind, Target};
  20 use rustc_session::lint::builtin::{CONFLICTING_REPR_HINTS, UNUSED_ATTRIBUTES};
  21 use rustc_session::parse::feature_err;
  22 use rustc_span::symbol::sym;
  23 use rustc_span::Span;
  24
  25 fn target_from_impl_item<'tcx>(tcx: TyCtxt<'tcx>, impl_item: &hir::ImplItem<'_>) -> Target {
  26     match impl_item.kind {
  27         hir::ImplItemKind::Const(..) => Target::AssocConst,
  28         hir::ImplItemKind::Method(..) => {
  29             let parent_hir_id = tcx.hir().get_parent_item(impl_item.hir_id);
  30             let containing_item = tcx.hir().expect_item(parent_hir_id);
  31             let containing_impl_is_for_trait = match &containing_item.kind {
  32                 hir::ItemKind::Impl { ref of_trait, .. } => of_trait.is_some(),
  33                 _ => bug!("parent of an ImplItem must be an Impl"),
  34             };
  35             if containing_impl_is_for_trait {
  36                 Target::Method(MethodKind::Trait { body: true })
  37             } else {
  38                 Target::Method(MethodKind::Inherent)
  39             }
  40         }
  41         hir::ImplItemKind::TyAlias(..) | hir::ImplItemKind::OpaqueTy(..) => Target::AssocTy,
  42     }
  43 }
  44
  45 struct CheckAttrVisitor<'tcx> {
  46     tcx: TyCtxt<'tcx>,
  47 }
  48
  49 impl CheckAttrVisitor<'tcx> {
  50     /// Checks any attribute.
  51     fn check_attributes(
  52         &self,
  53         hir_id: HirId,
  54         attrs: &'hir [Attribute],
  55         span: &Span,
  56         target: Target,
  57         item: Option<&Item<'_>>,
  58     ) {
  59         let mut is_valid = true;
  60         for attr in attrs {
  61             is_valid &= if attr.check_name(sym::inline) {
  62                 self.check_inline(hir_id, attr, span, target)
  63             } else if attr.check_name(sym::non_exhaustive) {
  64                 self.check_non_exhaustive(attr, span, target)
  65             } else if attr.check_name(sym::marker) {
  66                 self.check_marker(attr, span, target)
  67             } else if attr.check_name(sym::target_feature) {
  68                 self.check_target_feature(attr, span, target)
  69             } else if attr.check_name(sym::track_caller) {
  70                 self.check_track_caller(&attr.span, attrs, span, target)
  71             } else {
  72                 true
  73             };
  74         }
  75
  76         if !is_valid {
  77             return;
  78         }
  79
  80         if target == Target::Fn {
  81             self.tcx.codegen_fn_attrs(self.tcx.hir().local_def_id(hir_id));
  82         }
  83
  84         self.check_repr(attrs, span, target, item, hir_id);
  85         self.check_used(attrs, target);
  86     }
  87
  88     /// Checks if an `#[inline]` is applied to a function or a closure. Returns `true` if valid.
  89     fn check_inline(&self, hir_id: HirId, attr: &Attribute, span: &Span, target: Target) -> bool {
  90         match target {
  91             Target::Fn
  92             | Target::Closure
  93             | Target::Method(MethodKind::Trait { body: true })
  94             | Target::Method(MethodKind::Inherent) => true,
  95             Target::Method(MethodKind::Trait { body: false }) | Target::ForeignFn => {
  96                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
  97                     lint.build("`#[inline]` is ignored on function prototypes").emit()
  98                 });
  99                 true
 100             }
 101             // FIXME(#65833): We permit associated consts to have an `#[inline]` attribute with
 102             // just a lint, because we previously erroneously allowed it and some crates used it
 103             // accidentally, to to be compatible with crates depending on them, we can't throw an
 104             // error here.
 105             Target::AssocConst => {
 106                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
 107                     lint.build("`#[inline]` is ignored on constants")
 108                         .warn(
 109                             "this was previously accepted by the compiler but is \
 110                                being phased out; it will become a hard error in \
 111                                a future release!",
 112                         )
 113                         .note(
 114                             "see issue #65833 <https://github.com/rust-lang/rust/issues/65833> \
 115                                  for more information",
 116                         )
 117                         .emit();
 118                 });
 119                 true
 120             }
 121             _ => {
 122                 struct_span_err!(
 123                     self.tcx.sess,
 124                     attr.span,
 125                     E0518,
 126                     "attribute should be applied to function or closure",
 127                 )
 128                 .span_label(*span, "not a function or closure")
 129                 .emit();
 130                 false
 131             }
 132         }
 133     }
 134
 135     /// Checks if a `#[track_caller]` is applied to a non-naked function. Returns `true` if valid.
 136     fn check_track_caller(
 137         &self,
 138         attr_span: &Span,
 139         attrs: &'hir [Attribute],
 140         span: &Span,
 141         target: Target,
 142     ) -> bool {
 143         match target {
 144             Target::Fn if attr::contains_name(attrs, sym::naked) => {
 145                 struct_span_err!(
 146                     self.tcx.sess,
 147                     *attr_span,
 148                     E0736,
 149                     "cannot use `#[track_caller]` with `#[naked]`",
 150                 )
 151                 .emit();
 152                 false
 153             }
 154             Target::Fn | Target::Method(MethodKind::Inherent) => true,
 155             Target::Method(_) => {
 156                 struct_span_err!(
 157                     self.tcx.sess,
 158                     *attr_span,
 159                     E0738,
 160                     "`#[track_caller]` may not be used on trait methods",
 161                 )
 162                 .emit();
 163                 false
 164             }
 165             _ => {
 166                 struct_span_err!(
 167                     self.tcx.sess,
 168                     *attr_span,
 169                     E0739,
 170                     "attribute should be applied to function"
 171                 )
 172                 .span_label(*span, "not a function")
 173                 .emit();
 174                 false
 175             }
 176         }
 177     }
 178
 179     /// Checks if the `#[non_exhaustive]` attribute on an `item` is valid. Returns `true` if valid.
 180     fn check_non_exhaustive(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 181         match target {
 182             Target::Struct | Target::Enum => true,
 183             _ => {
 184                 struct_span_err!(
 185                     self.tcx.sess,
 186                     attr.span,
 187                     E0701,
 188                     "attribute can only be applied to a struct or enum"
 189                 )
 190                 .span_label(*span, "not a struct or enum")
 191                 .emit();
 192                 false
 193             }
 194         }
 195     }
 196
 197     /// Checks if the `#[marker]` attribute on an `item` is valid. Returns `true` if valid.
 198     fn check_marker(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 199         match target {
 200             Target::Trait => true,
 201             _ => {
 202                 self.tcx
 203                     .sess
 204                     .struct_span_err(attr.span, "attribute can only be applied to a trait")
 205                     .span_label(*span, "not a trait")
 206                     .emit();
 207                 false
 208             }
 209         }
 210     }
 211
 212     /// Checks if the `#[target_feature]` attribute on `item` is valid. Returns `true` if valid.
 213     fn check_target_feature(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 214         match target {
 215             Target::Fn
 216             | Target::Method(MethodKind::Trait { body: true })
 217             | Target::Method(MethodKind::Inherent) => true,
 218             _ => {
 219                 self.tcx
 220                     .sess
 221                     .struct_span_err(attr.span, "attribute should be applied to a function")
 222                     .span_label(*span, "not a function")
 223                     .emit();
 224                 false
 225             }
 226         }
 227     }
 228
 229     /// Checks if the `#[repr]` attributes on `item` are valid.
 230     fn check_repr(
 231         &self,
 232         attrs: &'hir [Attribute],
 233         span: &Span,
 234         target: Target,
 235         item: Option<&Item<'_>>,
 236         hir_id: HirId,
 237     ) {
 238         // Extract the names of all repr hints, e.g., [foo, bar, align] for:
 239         // ```
 240         // #[repr(foo)]
 241         // #[repr(bar, align(8))]
 242         // ```
 243         let hints: Vec<_> = attrs
 244             .iter()
 245             .filter(|attr| attr.check_name(sym::repr))
 246             .filter_map(|attr| attr.meta_item_list())
 247             .flatten()
 248             .collect();
 249
 250         let mut int_reprs = 0;
 251         let mut is_c = false;
 252         let mut is_simd = false;
 253         let mut is_transparent = false;
 254
 255         for hint in &hints {
 256             let (article, allowed_targets) = match hint.name_or_empty() {
 257                 name @ sym::C | name @ sym::align => {
 258                     is_c |= name == sym::C;
 259                     match target {
 260                         Target::Struct | Target::Union | Target::Enum => continue,
 261                         _ => ("a", "struct, enum, or union"),
 262                     }
 263                 }
 264                 sym::packed => {
 265                     if target != Target::Struct && target != Target::Union {
 266                         ("a", "struct or union")
 267                     } else {
 268                         continue;
 269                     }
 270                 }
 271                 sym::simd => {
 272                     is_simd = true;
 273                     if target != Target::Struct { ("a", "struct") } else { continue }
 274                 }
 275                 sym::transparent => {
 276                     is_transparent = true;
 277                     match target {
 278                         Target::Struct | Target::Union | Target::Enum => continue,
 279                         _ => ("a", "struct, enum, or union"),
 280                     }
 281                 }
 282                 sym::no_niche => {
 283                     if !self.tcx.features().enabled(sym::no_niche) {
 284                         feature_err(
 285                             &self.tcx.sess.parse_sess,
 286                             sym::no_niche,
 287                             hint.span(),
 288                             "the attribute `repr(no_niche)` is currently unstable",
 289                         )
 290                         .emit();
 291                     }
 292                     match target {
 293                         Target::Struct | Target::Enum => continue,
 294                         _ => ("a", "struct or enum"),
 295                     }
 296                 }
 297                 sym::i8
 298                 | sym::u8
 299                 | sym::i16
 300                 | sym::u16
 301                 | sym::i32
 302                 | sym::u32
 303                 | sym::i64
 304                 | sym::u64
 305                 | sym::isize
 306                 | sym::usize => {
 307                     int_reprs += 1;
 308                     if target != Target::Enum { ("an", "enum") } else { continue }
 309                 }
 310                 _ => continue,
 311             };
 312             self.emit_repr_error(
 313                 hint.span(),
 314                 *span,
 315                 &format!("attribute should be applied to {}", allowed_targets),
 316                 &format!("not {} {}", article, allowed_targets),
 317             )
 318         }
 319
 320         // Just point at all repr hints if there are any incompatibilities.
 321         // This is not ideal, but tracking precisely which ones are at fault is a huge hassle.
 322         let hint_spans = hints.iter().map(|hint| hint.span());
 323
 324         // Error on repr(transparent, <anything else apart from no_niche>).
 325         let non_no_niche = |hint: &&NestedMetaItem| hint.name_or_empty() != sym::no_niche;
 326         let non_no_niche_count = hints.iter().filter(non_no_niche).count();
 327         if is_transparent && non_no_niche_count > 1 {
 328             let hint_spans: Vec<_> = hint_spans.clone().collect();
 329             struct_span_err!(
 330                 self.tcx.sess,
 331                 hint_spans,
 332                 E0692,
 333                 "transparent {} cannot have other repr hints",
 334                 target
 335             )
 336             .emit();
 337         }
 338         // Warn on repr(u8, u16), repr(C, simd), and c-like-enum-repr(C, u8)
 339         if (int_reprs > 1)
 340             || (is_simd && is_c)
 341             || (int_reprs == 1 && is_c && item.map_or(false, |item| is_c_like_enum(item)))
 342         {
 343             self.tcx.struct_span_lint_hir(
 344                 CONFLICTING_REPR_HINTS,
 345                 hir_id,
 346                 hint_spans.collect::<Vec<Span>>(),
 347                 |lint| {
 348                     lint.build("conflicting representation hints")
 349                         .code(rustc_errors::error_code!(E0566))
 350                         .emit();
 351                 },
 352             );
 353         }
 354     }
 355
 356     fn emit_repr_error(
 357         &self,
 358         hint_span: Span,
 359         label_span: Span,
 360         hint_message: &str,
 361         label_message: &str,
 362     ) {
 363         struct_span_err!(self.tcx.sess, hint_span, E0517, "{}", hint_message)
 364             .span_label(label_span, label_message)
 365             .emit();
 366     }
 367
 368     fn check_stmt_attributes(&self, stmt: &hir::Stmt<'_>) {
 369         // When checking statements ignore expressions, they will be checked later
 370         if let hir::StmtKind::Local(ref l) = stmt.kind {
 371             for attr in l.attrs.iter() {
 372                 if attr.check_name(sym::inline) {
 373                     self.check_inline(DUMMY_HIR_ID, attr, &stmt.span, Target::Statement);
 374                 }
 375                 if attr.check_name(sym::repr) {
 376                     self.emit_repr_error(
 377                         attr.span,
 378                         stmt.span,
 379                         "attribute should not be applied to a statement",
 380                         "not a struct, enum, or union",
 381                     );
 382                 }
 383             }
 384         }
 385     }
 386
 387     fn check_expr_attributes(&self, expr: &hir::Expr<'_>) {
 388         let target = match expr.kind {
 389             hir::ExprKind::Closure(..) => Target::Closure,
 390             _ => Target::Expression,
 391         };
 392         for attr in expr.attrs.iter() {
 393             if attr.check_name(sym::inline) {
 394                 self.check_inline(DUMMY_HIR_ID, attr, &expr.span, target);
 395             }
 396             if attr.check_name(sym::repr) {
 397                 self.emit_repr_error(
 398                     attr.span,
 399                     expr.span,
 400                     "attribute should not be applied to an expression",
 401                     "not defining a struct, enum, or union",
 402                 );
 403             }
 404         }
 405     }
 406
 407     fn check_used(&self, attrs: &'hir [Attribute], target: Target) {
 408         for attr in attrs {
 409             if attr.check_name(sym::used) && target != Target::Static {
 410                 self.tcx
 411                     .sess
 412                     .span_err(attr.span, "attribute must be applied to a `static` variable");
 413             }
 414         }
 415     }
 416 }
 417
 418 impl Visitor<'tcx> for CheckAttrVisitor<'tcx> {
 419     type Map = Map<'tcx>;
 420
 421     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, Self::Map> {
 422         NestedVisitorMap::OnlyBodies(&self.tcx.hir())
 423     }
 424
 425     fn visit_item(&mut self, item: &'tcx Item<'tcx>) {
 426         let target = Target::from_item(item);
 427         self.check_attributes(item.hir_id, item.attrs, &item.span, target, Some(item));
 428         intravisit::walk_item(self, item)
 429     }
 430
 431     fn visit_trait_item(&mut self, trait_item: &'tcx TraitItem<'tcx>) {
 432         let target = Target::from_trait_item(trait_item);
 433         self.check_attributes(trait_item.hir_id, &trait_item.attrs, &trait_item.span, target, None);
 434         intravisit::walk_trait_item(self, trait_item)
 435     }
 436
 437     fn visit_foreign_item(&mut self, f_item: &'tcx hir::ForeignItem<'tcx>) {
 438         let target = Target::from_foreign_item(f_item);
 439         self.check_attributes(f_item.hir_id, &f_item.attrs, &f_item.span, target, None);
 440         intravisit::walk_foreign_item(self, f_item)
 441     }
 442
 443     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
 444         let target = target_from_impl_item(self.tcx, impl_item);
 445         self.check_attributes(impl_item.hir_id, &impl_item.attrs, &impl_item.span, target, None);
 446         intravisit::walk_impl_item(self, impl_item)
 447     }
 448
 449     fn visit_stmt(&mut self, stmt: &'tcx hir::Stmt<'tcx>) {
 450         self.check_stmt_attributes(stmt);
 451         intravisit::walk_stmt(self, stmt)
 452     }
 453
 454     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
 455         self.check_expr_attributes(expr);
 456         intravisit::walk_expr(self, expr)
 457     }
 458 }
 459
 460 fn is_c_like_enum(item: &Item<'_>) -> bool {
 461     if let ItemKind::Enum(ref def, _) = item.kind {
 462         for variant in def.variants {
 463             match variant.data {
 464                 hir::VariantData::Unit(..) => { /* continue */ }
 465                 _ => return false,
 466             }
 467         }
 468         true
 469     } else {
 470         false
 471     }
 472 }
 473
 474 fn check_mod_attrs(tcx: TyCtxt<'_>, module_def_id: DefId) {
 475     tcx.hir()
 476         .visit_item_likes_in_module(module_def_id, &mut CheckAttrVisitor { tcx }.as_deep_visitor());
 477 }
 478
 479 pub(crate) fn provide(providers: &mut Providers<'_>) {
 480     *providers = Providers { check_mod_attrs, ..*providers };
 481 }