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::{Attribute, NestedMetaItem};
  12 use rustc_errors::struct_span_err;
  13 use rustc_hir as hir;
  14 use rustc_hir::def_id::LocalDefId;
  15 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
  16 use rustc_hir::{self, HirId, Item, ItemKind, TraitItem};
  17 use rustc_hir::{MethodKind, Target};
  18 use rustc_session::lint::builtin::{CONFLICTING_REPR_HINTS, UNUSED_ATTRIBUTES};
  19 use rustc_session::parse::feature_err;
  20 use rustc_span::symbol::sym;
  21 use rustc_span::Span;
  22
  23 pub(crate) fn target_from_impl_item<'tcx>(
  24     tcx: TyCtxt<'tcx>,
  25     impl_item: &hir::ImplItem<'_>,
  26 ) -> Target {
  27     match impl_item.kind {
  28         hir::ImplItemKind::Const(..) => Target::AssocConst,
  29         hir::ImplItemKind::Fn(..) => {
  30             let parent_hir_id = tcx.hir().get_parent_item(impl_item.hir_id);
  31             let containing_item = tcx.hir().expect_item(parent_hir_id);
  32             let containing_impl_is_for_trait = match &containing_item.kind {
  33                 hir::ItemKind::Impl { ref of_trait, .. } => of_trait.is_some(),
  34                 _ => bug!("parent of an ImplItem must be an Impl"),
  35             };
  36             if containing_impl_is_for_trait {
  37                 Target::Method(MethodKind::Trait { body: true })
  38             } else {
  39                 Target::Method(MethodKind::Inherent)
  40             }
  41         }
  42         hir::ImplItemKind::TyAlias(..) => Target::AssocTy,
  43     }
  44 }
  45
  46 struct CheckAttrVisitor<'tcx> {
  47     tcx: TyCtxt<'tcx>,
  48 }
  49
  50 impl CheckAttrVisitor<'tcx> {
  51     /// Checks any attribute.
  52     fn check_attributes(
  53         &self,
  54         hir_id: HirId,
  55         attrs: &'hir [Attribute],
  56         span: &Span,
  57         target: Target,
  58         item: Option<&Item<'_>>,
  59     ) {
  60         let mut is_valid = true;
  61         for attr in attrs {
  62             is_valid &= if self.tcx.sess.check_name(attr, sym::inline) {
  63                 self.check_inline(hir_id, attr, span, target)
  64             } else if self.tcx.sess.check_name(attr, sym::non_exhaustive) {
  65                 self.check_non_exhaustive(attr, span, target)
  66             } else if self.tcx.sess.check_name(attr, sym::marker) {
  67                 self.check_marker(attr, span, target)
  68             } else if self.tcx.sess.check_name(attr, sym::target_feature) {
  69                 self.check_target_feature(attr, span, target)
  70             } else if self.tcx.sess.check_name(attr, sym::track_caller) {
  71                 self.check_track_caller(&attr.span, attrs, span, target)
  72             } else if self.tcx.sess.check_name(attr, sym::doc) {
  73                 self.check_doc_alias(attr, hir_id, target)
  74             } else {
  75                 true
  76             };
  77         }
  78
  79         if !is_valid {
  80             return;
  81         }
  82
  83         if matches!(target, Target::Fn | Target::Method(_) | Target::ForeignFn) {
  84             self.tcx.ensure().codegen_fn_attrs(self.tcx.hir().local_def_id(hir_id));
  85         }
  86
  87         self.check_repr(attrs, span, target, item, hir_id);
  88         self.check_used(attrs, target);
  89     }
  90
  91     /// Checks if an `#[inline]` is applied to a function or a closure. Returns `true` if valid.
  92     fn check_inline(&self, hir_id: HirId, attr: &Attribute, span: &Span, target: Target) -> bool {
  93         match target {
  94             Target::Fn
  95             | Target::Closure
  96             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
  97             Target::Method(MethodKind::Trait { body: false }) | Target::ForeignFn => {
  98                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
  99                     lint.build("`#[inline]` is ignored on function prototypes").emit()
 100                 });
 101                 true
 102             }
 103             // FIXME(#65833): We permit associated consts to have an `#[inline]` attribute with
 104             // just a lint, because we previously erroneously allowed it and some crates used it
 105             // accidentally, to to be compatible with crates depending on them, we can't throw an
 106             // error here.
 107             Target::AssocConst => {
 108                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
 109                     lint.build("`#[inline]` is ignored on constants")
 110                         .warn(
 111                             "this was previously accepted by the compiler but is \
 112                                being phased out; it will become a hard error in \
 113                                a future release!",
 114                         )
 115                         .note(
 116                             "see issue #65833 <https://github.com/rust-lang/rust/issues/65833> \
 117                                  for more information",
 118                         )
 119                         .emit();
 120                 });
 121                 true
 122             }
 123             _ => {
 124                 struct_span_err!(
 125                     self.tcx.sess,
 126                     attr.span,
 127                     E0518,
 128                     "attribute should be applied to function or closure",
 129                 )
 130                 .span_label(*span, "not a function or closure")
 131                 .emit();
 132                 false
 133             }
 134         }
 135     }
 136
 137     /// Checks if a `#[track_caller]` is applied to a non-naked function. Returns `true` if valid.
 138     fn check_track_caller(
 139         &self,
 140         attr_span: &Span,
 141         attrs: &'hir [Attribute],
 142         span: &Span,
 143         target: Target,
 144     ) -> bool {
 145         match target {
 146             _ if self.tcx.sess.contains_name(attrs, sym::naked) => {
 147                 struct_span_err!(
 148                     self.tcx.sess,
 149                     *attr_span,
 150                     E0736,
 151                     "cannot use `#[track_caller]` with `#[naked]`",
 152                 )
 153                 .emit();
 154                 false
 155             }
 156             Target::Fn | Target::Method(..) | Target::ForeignFn => true,
 157             _ => {
 158                 struct_span_err!(
 159                     self.tcx.sess,
 160                     *attr_span,
 161                     E0739,
 162                     "attribute should be applied to function"
 163                 )
 164                 .span_label(*span, "not a function")
 165                 .emit();
 166                 false
 167             }
 168         }
 169     }
 170
 171     /// Checks if the `#[non_exhaustive]` attribute on an `item` is valid. Returns `true` if valid.
 172     fn check_non_exhaustive(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 173         match target {
 174             Target::Struct | Target::Enum => true,
 175             _ => {
 176                 struct_span_err!(
 177                     self.tcx.sess,
 178                     attr.span,
 179                     E0701,
 180                     "attribute can only be applied to a struct or enum"
 181                 )
 182                 .span_label(*span, "not a struct or enum")
 183                 .emit();
 184                 false
 185             }
 186         }
 187     }
 188
 189     /// Checks if the `#[marker]` attribute on an `item` is valid. Returns `true` if valid.
 190     fn check_marker(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 191         match target {
 192             Target::Trait => true,
 193             _ => {
 194                 self.tcx
 195                     .sess
 196                     .struct_span_err(attr.span, "attribute can only be applied to a trait")
 197                     .span_label(*span, "not a trait")
 198                     .emit();
 199                 false
 200             }
 201         }
 202     }
 203
 204     /// Checks if the `#[target_feature]` attribute on `item` is valid. Returns `true` if valid.
 205     fn check_target_feature(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 206         match target {
 207             Target::Fn
 208             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
 209             _ => {
 210                 self.tcx
 211                     .sess
 212                     .struct_span_err(attr.span, "attribute should be applied to a function")
 213                     .span_label(*span, "not a function")
 214                     .emit();
 215                 false
 216             }
 217         }
 218     }
 219
 220     fn check_doc_alias(&self, attr: &Attribute, hir_id: HirId, target: Target) -> bool {
 221         if let Some(mi) = attr.meta() {
 222             if let Some(list) = mi.meta_item_list() {
 223                 for meta in list {
 224                     if meta.has_name(sym::alias) {
 225                         if !meta.is_value_str()
 226                             || meta
 227                                 .value_str()
 228                                 .map(|s| s.to_string())
 229                                 .unwrap_or_else(String::new)
 230                                 .is_empty()
 231                         {
 232                             self.tcx
 233                                 .sess
 234                                 .struct_span_err(
 235                                     meta.span(),
 236                                     "doc alias attribute expects a string: #[doc(alias = \"0\")]",
 237                                 )
 238                                 .emit();
 239                             return false;
 240                         }
 241                         if let Some(err) = match target {
 242                             Target::Impl => Some("implementation block"),
 243                             Target::ForeignMod => Some("extern block"),
 244                             Target::AssocTy => {
 245                                 let parent_hir_id = self.tcx.hir().get_parent_item(hir_id);
 246                                 let containing_item = self.tcx.hir().expect_item(parent_hir_id);
 247                                 if Target::from_item(containing_item) == Target::Impl {
 248                                     Some("type alias in implementation block")
 249                                 } else {
 250                                     None
 251                                 }
 252                             }
 253                             _ => None,
 254                         } {
 255                             self.tcx
 256                                 .sess
 257                                 .struct_span_err(
 258                                     meta.span(),
 259                                     &format!("`#[doc(alias = \"...\")]` isn't allowed on {}", err,),
 260                                 )
 261                                 .emit();
 262                         }
 263                     }
 264                 }
 265             }
 266         }
 267         true
 268     }
 269
 270     /// Checks if the `#[repr]` attributes on `item` are valid.
 271     fn check_repr(
 272         &self,
 273         attrs: &'hir [Attribute],
 274         span: &Span,
 275         target: Target,
 276         item: Option<&Item<'_>>,
 277         hir_id: HirId,
 278     ) {
 279         // Extract the names of all repr hints, e.g., [foo, bar, align] for:
 280         // ```
 281         // #[repr(foo)]
 282         // #[repr(bar, align(8))]
 283         // ```
 284         let hints: Vec<_> = attrs
 285             .iter()
 286             .filter(|attr| self.tcx.sess.check_name(attr, sym::repr))
 287             .filter_map(|attr| attr.meta_item_list())
 288             .flatten()
 289             .collect();
 290
 291         let mut int_reprs = 0;
 292         let mut is_c = false;
 293         let mut is_simd = false;
 294         let mut is_transparent = false;
 295
 296         for hint in &hints {
 297             let (article, allowed_targets) = match hint.name_or_empty() {
 298                 name @ sym::C | name @ sym::align => {
 299                     is_c |= name == sym::C;
 300                     match target {
 301                         Target::Struct | Target::Union | Target::Enum => continue,
 302                         _ => ("a", "struct, enum, or union"),
 303                     }
 304                 }
 305                 sym::packed => {
 306                     if target != Target::Struct && target != Target::Union {
 307                         ("a", "struct or union")
 308                     } else {
 309                         continue;
 310                     }
 311                 }
 312                 sym::simd => {
 313                     is_simd = true;
 314                     if target != Target::Struct { ("a", "struct") } else { continue }
 315                 }
 316                 sym::transparent => {
 317                     is_transparent = true;
 318                     match target {
 319                         Target::Struct | Target::Union | Target::Enum => continue,
 320                         _ => ("a", "struct, enum, or union"),
 321                     }
 322                 }
 323                 sym::no_niche => {
 324                     if !self.tcx.features().enabled(sym::no_niche) {
 325                         feature_err(
 326                             &self.tcx.sess.parse_sess,
 327                             sym::no_niche,
 328                             hint.span(),
 329                             "the attribute `repr(no_niche)` is currently unstable",
 330                         )
 331                         .emit();
 332                     }
 333                     match target {
 334                         Target::Struct | Target::Enum => continue,
 335                         _ => ("a", "struct or enum"),
 336                     }
 337                 }
 338                 sym::i8
 339                 | sym::u8
 340                 | sym::i16
 341                 | sym::u16
 342                 | sym::i32
 343                 | sym::u32
 344                 | sym::i64
 345                 | sym::u64
 346                 | sym::i128
 347                 | sym::u128
 348                 | sym::isize
 349                 | sym::usize => {
 350                     int_reprs += 1;
 351                     if target != Target::Enum { ("an", "enum") } else { continue }
 352                 }
 353                 _ => continue,
 354             };
 355             self.emit_repr_error(
 356                 hint.span(),
 357                 *span,
 358                 &format!("attribute should be applied to {}", allowed_targets),
 359                 &format!("not {} {}", article, allowed_targets),
 360             )
 361         }
 362
 363         // Just point at all repr hints if there are any incompatibilities.
 364         // This is not ideal, but tracking precisely which ones are at fault is a huge hassle.
 365         let hint_spans = hints.iter().map(|hint| hint.span());
 366
 367         // Error on repr(transparent, <anything else apart from no_niche>).
 368         let non_no_niche = |hint: &&NestedMetaItem| hint.name_or_empty() != sym::no_niche;
 369         let non_no_niche_count = hints.iter().filter(non_no_niche).count();
 370         if is_transparent && non_no_niche_count > 1 {
 371             let hint_spans: Vec<_> = hint_spans.clone().collect();
 372             struct_span_err!(
 373                 self.tcx.sess,
 374                 hint_spans,
 375                 E0692,
 376                 "transparent {} cannot have other repr hints",
 377                 target
 378             )
 379             .emit();
 380         }
 381         // Warn on repr(u8, u16), repr(C, simd), and c-like-enum-repr(C, u8)
 382         if (int_reprs > 1)
 383             || (is_simd && is_c)
 384             || (int_reprs == 1 && is_c && item.map_or(false, |item| is_c_like_enum(item)))
 385         {
 386             self.tcx.struct_span_lint_hir(
 387                 CONFLICTING_REPR_HINTS,
 388                 hir_id,
 389                 hint_spans.collect::<Vec<Span>>(),
 390                 |lint| {
 391                     lint.build("conflicting representation hints")
 392                         .code(rustc_errors::error_code!(E0566))
 393                         .emit();
 394                 },
 395             );
 396         }
 397     }
 398
 399     fn emit_repr_error(
 400         &self,
 401         hint_span: Span,
 402         label_span: Span,
 403         hint_message: &str,
 404         label_message: &str,
 405     ) {
 406         struct_span_err!(self.tcx.sess, hint_span, E0517, "{}", hint_message)
 407             .span_label(label_span, label_message)
 408             .emit();
 409     }
 410
 411     fn check_stmt_attributes(&self, stmt: &hir::Stmt<'_>) {
 412         // When checking statements ignore expressions, they will be checked later
 413         if let hir::StmtKind::Local(ref l) = stmt.kind {
 414             for attr in l.attrs.iter() {
 415                 if self.tcx.sess.check_name(attr, sym::inline) {
 416                     self.check_inline(l.hir_id, attr, &stmt.span, Target::Statement);
 417                 }
 418                 if self.tcx.sess.check_name(attr, sym::repr) {
 419                     self.emit_repr_error(
 420                         attr.span,
 421                         stmt.span,
 422                         "attribute should not be applied to a statement",
 423                         "not a struct, enum, or union",
 424                     );
 425                 }
 426             }
 427         }
 428     }
 429
 430     fn check_expr_attributes(&self, expr: &hir::Expr<'_>) {
 431         let target = match expr.kind {
 432             hir::ExprKind::Closure(..) => Target::Closure,
 433             _ => Target::Expression,
 434         };
 435         for attr in expr.attrs.iter() {
 436             if self.tcx.sess.check_name(attr, sym::inline) {
 437                 self.check_inline(expr.hir_id, attr, &expr.span, target);
 438             }
 439             if self.tcx.sess.check_name(attr, sym::repr) {
 440                 self.emit_repr_error(
 441                     attr.span,
 442                     expr.span,
 443                     "attribute should not be applied to an expression",
 444                     "not defining a struct, enum, or union",
 445                 );
 446             }
 447         }
 448         if target == Target::Closure {
 449             self.tcx.ensure().codegen_fn_attrs(self.tcx.hir().local_def_id(expr.hir_id));
 450         }
 451     }
 452
 453     fn check_used(&self, attrs: &'hir [Attribute], target: Target) {
 454         for attr in attrs {
 455             if self.tcx.sess.check_name(attr, sym::used) && target != Target::Static {
 456                 self.tcx
 457                     .sess
 458                     .span_err(attr.span, "attribute must be applied to a `static` variable");
 459             }
 460         }
 461     }
 462 }
 463
 464 impl Visitor<'tcx> for CheckAttrVisitor<'tcx> {
 465     type Map = Map<'tcx>;
 466
 467     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 468         NestedVisitorMap::OnlyBodies(self.tcx.hir())
 469     }
 470
 471     fn visit_item(&mut self, item: &'tcx Item<'tcx>) {
 472         let target = Target::from_item(item);
 473         self.check_attributes(item.hir_id, item.attrs, &item.span, target, Some(item));
 474         intravisit::walk_item(self, item)
 475     }
 476
 477     fn visit_trait_item(&mut self, trait_item: &'tcx TraitItem<'tcx>) {
 478         let target = Target::from_trait_item(trait_item);
 479         self.check_attributes(trait_item.hir_id, &trait_item.attrs, &trait_item.span, target, None);
 480         intravisit::walk_trait_item(self, trait_item)
 481     }
 482
 483     fn visit_foreign_item(&mut self, f_item: &'tcx hir::ForeignItem<'tcx>) {
 484         let target = Target::from_foreign_item(f_item);
 485         self.check_attributes(f_item.hir_id, &f_item.attrs, &f_item.span, target, None);
 486         intravisit::walk_foreign_item(self, f_item)
 487     }
 488
 489     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
 490         let target = target_from_impl_item(self.tcx, impl_item);
 491         self.check_attributes(impl_item.hir_id, &impl_item.attrs, &impl_item.span, target, None);
 492         intravisit::walk_impl_item(self, impl_item)
 493     }
 494
 495     fn visit_stmt(&mut self, stmt: &'tcx hir::Stmt<'tcx>) {
 496         self.check_stmt_attributes(stmt);
 497         intravisit::walk_stmt(self, stmt)
 498     }
 499
 500     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
 501         self.check_expr_attributes(expr);
 502         intravisit::walk_expr(self, expr)
 503     }
 504 }
 505
 506 fn is_c_like_enum(item: &Item<'_>) -> bool {
 507     if let ItemKind::Enum(ref def, _) = item.kind {
 508         for variant in def.variants {
 509             match variant.data {
 510                 hir::VariantData::Unit(..) => { /* continue */ }
 511                 _ => return false,
 512             }
 513         }
 514         true
 515     } else {
 516         false
 517     }
 518 }
 519
 520 fn check_mod_attrs(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
 521     tcx.hir()
 522         .visit_item_likes_in_module(module_def_id, &mut CheckAttrVisitor { tcx }.as_deep_visitor());
 523 }
 524
 525 pub(crate) fn provide(providers: &mut Providers) {
 526     *providers = Providers { check_mod_attrs, ..*providers };
 527 }