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