compiler/rustc_passes/src/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(hir_id, 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 if self.tcx.sess.check_name(attr, sym::no_link) {
  75                 self.check_no_link(&attr, span, target)
  76             } else if self.tcx.sess.check_name(attr, sym::export_name) {
  77                 self.check_export_name(&attr, span, target)
  78             } else {
  79                 // lint-only checks
  80                 if self.tcx.sess.check_name(attr, sym::cold) {
  81                     self.check_cold(hir_id, attr, span, target);
  82                 } else if self.tcx.sess.check_name(attr, sym::link_name) {
  83                     self.check_link_name(hir_id, attr, span, target);
  84                 } else if self.tcx.sess.check_name(attr, sym::link_section) {
  85                     self.check_link_section(hir_id, attr, span, target);
  86                 }
  87                 true
  88             };
  89         }
  90
  91         if !is_valid {
  92             return;
  93         }
  94
  95         if matches!(target, Target::Fn | Target::Method(_) | Target::ForeignFn) {
  96             self.tcx.ensure().codegen_fn_attrs(self.tcx.hir().local_def_id(hir_id));
  97         }
  98
  99         self.check_repr(attrs, span, target, item, hir_id);
 100         self.check_used(attrs, target);
 101     }
 102
 103     /// Checks if an `#[inline]` is applied to a function or a closure. Returns `true` if valid.
 104     fn check_inline(&self, hir_id: HirId, attr: &Attribute, span: &Span, target: Target) -> bool {
 105         match target {
 106             Target::Fn
 107             | Target::Closure
 108             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
 109             Target::Method(MethodKind::Trait { body: false }) | Target::ForeignFn => {
 110                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
 111                     lint.build("`#[inline]` is ignored on function prototypes").emit()
 112                 });
 113                 true
 114             }
 115             // FIXME(#65833): We permit associated consts to have an `#[inline]` attribute with
 116             // just a lint, because we previously erroneously allowed it and some crates used it
 117             // accidentally, to to be compatible with crates depending on them, we can't throw an
 118             // error here.
 119             Target::AssocConst => {
 120                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
 121                     lint.build("`#[inline]` is ignored on constants")
 122                         .warn(
 123                             "this was previously accepted by the compiler but is \
 124                              being phased out; it will become a hard error in \
 125                              a future release!",
 126                         )
 127                         .note(
 128                             "see issue #65833 <https://github.com/rust-lang/rust/issues/65833> \
 129                              for more information",
 130                         )
 131                         .emit();
 132                 });
 133                 true
 134             }
 135             _ => {
 136                 struct_span_err!(
 137                     self.tcx.sess,
 138                     attr.span,
 139                     E0518,
 140                     "attribute should be applied to function or closure",
 141                 )
 142                 .span_label(*span, "not a function or closure")
 143                 .emit();
 144                 false
 145             }
 146         }
 147     }
 148
 149     /// Checks if a `#[track_caller]` is applied to a non-naked function. Returns `true` if valid.
 150     fn check_track_caller(
 151         &self,
 152         attr_span: &Span,
 153         attrs: &'hir [Attribute],
 154         span: &Span,
 155         target: Target,
 156     ) -> bool {
 157         match target {
 158             _ if self.tcx.sess.contains_name(attrs, sym::naked) => {
 159                 struct_span_err!(
 160                     self.tcx.sess,
 161                     *attr_span,
 162                     E0736,
 163                     "cannot use `#[track_caller]` with `#[naked]`",
 164                 )
 165                 .emit();
 166                 false
 167             }
 168             Target::Fn | Target::Method(..) | Target::ForeignFn | Target::Closure => true,
 169             _ => {
 170                 struct_span_err!(
 171                     self.tcx.sess,
 172                     *attr_span,
 173                     E0739,
 174                     "attribute should be applied to function"
 175                 )
 176                 .span_label(*span, "not a function")
 177                 .emit();
 178                 false
 179             }
 180         }
 181     }
 182
 183     /// Checks if the `#[non_exhaustive]` attribute on an `item` is valid. Returns `true` if valid.
 184     fn check_non_exhaustive(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 185         match target {
 186             Target::Struct | Target::Enum => true,
 187             _ => {
 188                 struct_span_err!(
 189                     self.tcx.sess,
 190                     attr.span,
 191                     E0701,
 192                     "attribute can only be applied to a struct or enum"
 193                 )
 194                 .span_label(*span, "not a struct or enum")
 195                 .emit();
 196                 false
 197             }
 198         }
 199     }
 200
 201     /// Checks if the `#[marker]` attribute on an `item` is valid. Returns `true` if valid.
 202     fn check_marker(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 203         match target {
 204             Target::Trait => true,
 205             _ => {
 206                 self.tcx
 207                     .sess
 208                     .struct_span_err(attr.span, "attribute can only be applied to a trait")
 209                     .span_label(*span, "not a trait")
 210                     .emit();
 211                 false
 212             }
 213         }
 214     }
 215
 216     /// Checks if the `#[target_feature]` attribute on `item` is valid. Returns `true` if valid.
 217     fn check_target_feature(
 218         &self,
 219         hir_id: HirId,
 220         attr: &Attribute,
 221         span: &Span,
 222         target: Target,
 223     ) -> bool {
 224         match target {
 225             Target::Fn
 226             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
 227             // FIXME: #[target_feature] was previously erroneously allowed on statements and some
 228             // crates used this, so only emit a warning.
 229             Target::Statement => {
 230                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
 231                     lint.build("attribute should be applied to a function")
 232                         .warn(
 233                             "this was previously accepted by the compiler but is \
 234                              being phased out; it will become a hard error in \
 235                              a future release!",
 236                         )
 237                         .span_label(*span, "not a function")
 238                         .emit();
 239                 });
 240                 true
 241             }
 242             _ => {
 243                 self.tcx
 244                     .sess
 245                     .struct_span_err(attr.span, "attribute should be applied to a function")
 246                     .span_label(*span, "not a function")
 247                     .emit();
 248                 false
 249             }
 250         }
 251     }
 252
 253     fn check_doc_alias(&self, attr: &Attribute, hir_id: HirId, target: Target) -> bool {
 254         if let Some(mi) = attr.meta() {
 255             if let Some(list) = mi.meta_item_list() {
 256                 for meta in list {
 257                     if meta.has_name(sym::alias) {
 258                         if !meta.is_value_str()
 259                             || meta
 260                                 .value_str()
 261                                 .map(|s| s.to_string())
 262                                 .unwrap_or_else(String::new)
 263                                 .is_empty()
 264                         {
 265                             self.tcx
 266                                 .sess
 267                                 .struct_span_err(
 268                                     meta.span(),
 269                                     "doc alias attribute expects a string: #[doc(alias = \"0\")]",
 270                                 )
 271                                 .emit();
 272                             return false;
 273                         }
 274                         if let Some(err) = match target {
 275                             Target::Impl => Some("implementation block"),
 276                             Target::ForeignMod => Some("extern block"),
 277                             Target::AssocTy => {
 278                                 let parent_hir_id = self.tcx.hir().get_parent_item(hir_id);
 279                                 let containing_item = self.tcx.hir().expect_item(parent_hir_id);
 280                                 if Target::from_item(containing_item) == Target::Impl {
 281                                     Some("type alias in implementation block")
 282                                 } else {
 283                                     None
 284                                 }
 285                             }
 286                             Target::AssocConst => {
 287                                 let parent_hir_id = self.tcx.hir().get_parent_item(hir_id);
 288                                 let containing_item = self.tcx.hir().expect_item(parent_hir_id);
 289                                 // We can't link to trait impl's consts.
 290                                 let err = "associated constant in trait implementation block";
 291                                 match containing_item.kind {
 292                                     ItemKind::Impl { of_trait: Some(_), .. } => Some(err),
 293                                     _ => None,
 294                                 }
 295                             }
 296                             _ => None,
 297                         } {
 298                             self.tcx
 299                                 .sess
 300                                 .struct_span_err(
 301                                     meta.span(),
 302                                     &format!("`#[doc(alias = \"...\")]` isn't allowed on {}", err),
 303                                 )
 304                                 .emit();
 305                         }
 306                     }
 307                 }
 308             }
 309         }
 310         true
 311     }
 312
 313     /// Checks if `#[cold]` is applied to a non-function. Returns `true` if valid.
 314     fn check_cold(&self, hir_id: HirId, attr: &Attribute, span: &Span, target: Target) {
 315         match target {
 316             Target::Fn | Target::Method(..) | Target::ForeignFn | Target::Closure => {}
 317             _ => {
 318                 // FIXME: #[cold] was previously allowed on non-functions and some crates used
 319                 // this, so only emit a warning.
 320                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
 321                     lint.build("attribute should be applied to a function")
 322                         .warn(
 323                             "this was previously accepted by the compiler but is \
 324                              being phased out; it will become a hard error in \
 325                              a future release!",
 326                         )
 327                         .span_label(*span, "not a function")
 328                         .emit();
 329                 });
 330             }
 331         }
 332     }
 333
 334     /// Checks if `#[link_name]` is applied to an item other than a foreign function or static.
 335     fn check_link_name(&self, hir_id: HirId, attr: &Attribute, span: &Span, target: Target) {
 336         match target {
 337             Target::ForeignFn | Target::ForeignStatic => {}
 338             _ => {
 339                 // FIXME: #[cold] was previously allowed on non-functions/statics and some crates
 340                 // used this, so only emit a warning.
 341                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
 342                     let mut diag =
 343                         lint.build("attribute should be applied to a foreign function or static");
 344                     diag.warn(
 345                         "this was previously accepted by the compiler but is \
 346                          being phased out; it will become a hard error in \
 347                          a future release!",
 348                     );
 349
 350                     // See issue #47725
 351                     if let Target::ForeignMod = target {
 352                         if let Some(value) = attr.value_str() {
 353                             diag.span_help(
 354                                 attr.span,
 355                                 &format!(r#"try `#[link(name = "{}")]` instead"#, value),
 356                             );
 357                         } else {
 358                             diag.span_help(attr.span, r#"try `#[link(name = "...")]` instead"#);
 359                         }
 360                     }
 361
 362                     diag.span_label(*span, "not a foreign function or static");
 363                     diag.emit();
 364                 });
 365             }
 366         }
 367     }
 368
 369     /// Checks if `#[no_link]` is applied to an `extern crate`. Returns `true` if valid.
 370     fn check_no_link(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 371         if target == Target::ExternCrate {
 372             true
 373         } else {
 374             self.tcx
 375                 .sess
 376                 .struct_span_err(attr.span, "attribute should be applied to an `extern crate` item")
 377                 .span_label(*span, "not an `extern crate` item")
 378                 .emit();
 379             false
 380         }
 381     }
 382
 383     /// Checks if `#[export_name]` is applied to a function or static. Returns `true` if valid.
 384     fn check_export_name(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 385         match target {
 386             Target::Static | Target::Fn | Target::Method(..) => true,
 387             _ => {
 388                 self.tcx
 389                     .sess
 390                     .struct_span_err(
 391                         attr.span,
 392                         "attribute should be applied to a function or static",
 393                     )
 394                     .span_label(*span, "not a function or static")
 395                     .emit();
 396                 false
 397             }
 398         }
 399     }
 400
 401     /// Checks if `#[link_section]` is applied to a function or static.
 402     fn check_link_section(&self, hir_id: HirId, attr: &Attribute, span: &Span, target: Target) {
 403         match target {
 404             Target::Static | Target::Fn | Target::Method(..) => {}
 405             _ => {
 406                 // FIXME: #[link_section] was previously allowed on non-functions/statics and some
 407                 // crates used this, so only emit a warning.
 408                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
 409                     lint.build("attribute should be applied to a function or static")
 410                         .warn(
 411                             "this was previously accepted by the compiler but is \
 412                              being phased out; it will become a hard error in \
 413                              a future release!",
 414                         )
 415                         .span_label(*span, "not a function or static")
 416                         .emit();
 417                 });
 418             }
 419         }
 420     }
 421
 422     /// Checks if the `#[repr]` attributes on `item` are valid.
 423     fn check_repr(
 424         &self,
 425         attrs: &'hir [Attribute],
 426         span: &Span,
 427         target: Target,
 428         item: Option<&Item<'_>>,
 429         hir_id: HirId,
 430     ) {
 431         // Extract the names of all repr hints, e.g., [foo, bar, align] for:
 432         // ```
 433         // #[repr(foo)]
 434         // #[repr(bar, align(8))]
 435         // ```
 436         let hints: Vec<_> = attrs
 437             .iter()
 438             .filter(|attr| self.tcx.sess.check_name(attr, sym::repr))
 439             .filter_map(|attr| attr.meta_item_list())
 440             .flatten()
 441             .collect();
 442
 443         let mut int_reprs = 0;
 444         let mut is_c = false;
 445         let mut is_simd = false;
 446         let mut is_transparent = false;
 447
 448         for hint in &hints {
 449             let (article, allowed_targets) = match hint.name_or_empty() {
 450                 name @ sym::C | name @ sym::align => {
 451                     is_c |= name == sym::C;
 452                     match target {
 453                         Target::Struct | Target::Union | Target::Enum => continue,
 454                         _ => ("a", "struct, enum, or union"),
 455                     }
 456                 }
 457                 sym::packed => {
 458                     if target != Target::Struct && target != Target::Union {
 459                         ("a", "struct or union")
 460                     } else {
 461                         continue;
 462                     }
 463                 }
 464                 sym::simd => {
 465                     is_simd = true;
 466                     if target != Target::Struct {
 467                         ("a", "struct")
 468                     } else {
 469                         continue;
 470                     }
 471                 }
 472                 sym::transparent => {
 473                     is_transparent = true;
 474                     match target {
 475                         Target::Struct | Target::Union | Target::Enum => continue,
 476                         _ => ("a", "struct, enum, or union"),
 477                     }
 478                 }
 479                 sym::no_niche => {
 480                     if !self.tcx.features().enabled(sym::no_niche) {
 481                         feature_err(
 482                             &self.tcx.sess.parse_sess,
 483                             sym::no_niche,
 484                             hint.span(),
 485                             "the attribute `repr(no_niche)` is currently unstable",
 486                         )
 487                         .emit();
 488                     }
 489                     match target {
 490                         Target::Struct | Target::Enum => continue,
 491                         _ => ("a", "struct or enum"),
 492                     }
 493                 }
 494                 sym::i8
 495                 | sym::u8
 496                 | sym::i16
 497                 | sym::u16
 498                 | sym::i32
 499                 | sym::u32
 500                 | sym::i64
 501                 | sym::u64
 502                 | sym::i128
 503                 | sym::u128
 504                 | sym::isize
 505                 | sym::usize => {
 506                     int_reprs += 1;
 507                     if target != Target::Enum {
 508                         ("an", "enum")
 509                     } else {
 510                         continue;
 511                     }
 512                 }
 513                 _ => continue,
 514             };
 515             self.emit_repr_error(
 516                 hint.span(),
 517                 *span,
 518                 &format!("attribute should be applied to {}", allowed_targets),
 519                 &format!("not {} {}", article, allowed_targets),
 520             )
 521         }
 522
 523         // Just point at all repr hints if there are any incompatibilities.
 524         // This is not ideal, but tracking precisely which ones are at fault is a huge hassle.
 525         let hint_spans = hints.iter().map(|hint| hint.span());
 526
 527         // Error on repr(transparent, <anything else apart from no_niche>).
 528         let non_no_niche = |hint: &&NestedMetaItem| hint.name_or_empty() != sym::no_niche;
 529         let non_no_niche_count = hints.iter().filter(non_no_niche).count();
 530         if is_transparent && non_no_niche_count > 1 {
 531             let hint_spans: Vec<_> = hint_spans.clone().collect();
 532             struct_span_err!(
 533                 self.tcx.sess,
 534                 hint_spans,
 535                 E0692,
 536                 "transparent {} cannot have other repr hints",
 537                 target
 538             )
 539             .emit();
 540         }
 541         // Warn on repr(u8, u16), repr(C, simd), and c-like-enum-repr(C, u8)
 542         if (int_reprs > 1)
 543             || (is_simd && is_c)
 544             || (int_reprs == 1 && is_c && item.map_or(false, |item| is_c_like_enum(item)))
 545         {
 546             self.tcx.struct_span_lint_hir(
 547                 CONFLICTING_REPR_HINTS,
 548                 hir_id,
 549                 hint_spans.collect::<Vec<Span>>(),
 550                 |lint| {
 551                     lint.build("conflicting representation hints")
 552                         .code(rustc_errors::error_code!(E0566))
 553                         .emit();
 554                 },
 555             );
 556         }
 557     }
 558
 559     fn emit_repr_error(
 560         &self,
 561         hint_span: Span,
 562         label_span: Span,
 563         hint_message: &str,
 564         label_message: &str,
 565     ) {
 566         struct_span_err!(self.tcx.sess, hint_span, E0517, "{}", hint_message)
 567             .span_label(label_span, label_message)
 568             .emit();
 569     }
 570
 571     fn check_stmt_attributes(&self, stmt: &hir::Stmt<'_>) {
 572         // When checking statements ignore expressions, they will be checked later
 573         if let hir::StmtKind::Local(ref l) = stmt.kind {
 574             self.check_attributes(l.hir_id, &l.attrs, &stmt.span, Target::Statement, None);
 575             for attr in l.attrs.iter() {
 576                 if self.tcx.sess.check_name(attr, sym::repr) {
 577                     self.emit_repr_error(
 578                         attr.span,
 579                         stmt.span,
 580                         "attribute should not be applied to a statement",
 581                         "not a struct, enum, or union",
 582                     );
 583                 }
 584             }
 585         }
 586     }
 587
 588     fn check_expr_attributes(&self, expr: &hir::Expr<'_>) {
 589         let target = match expr.kind {
 590             hir::ExprKind::Closure(..) => Target::Closure,
 591             _ => Target::Expression,
 592         };
 593         self.check_attributes(expr.hir_id, &expr.attrs, &expr.span, target, None);
 594         for attr in expr.attrs.iter() {
 595             if self.tcx.sess.check_name(attr, sym::repr) {
 596                 self.emit_repr_error(
 597                     attr.span,
 598                     expr.span,
 599                     "attribute should not be applied to an expression",
 600                     "not defining a struct, enum, or union",
 601                 );
 602             }
 603         }
 604         if target == Target::Closure {
 605             self.tcx.ensure().codegen_fn_attrs(self.tcx.hir().local_def_id(expr.hir_id));
 606         }
 607     }
 608
 609     fn check_used(&self, attrs: &'hir [Attribute], target: Target) {
 610         for attr in attrs {
 611             if self.tcx.sess.check_name(attr, sym::used) && target != Target::Static {
 612                 self.tcx
 613                     .sess
 614                     .span_err(attr.span, "attribute must be applied to a `static` variable");
 615             }
 616         }
 617     }
 618 }
 619
 620 impl Visitor<'tcx> for CheckAttrVisitor<'tcx> {
 621     type Map = Map<'tcx>;
 622
 623     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 624         NestedVisitorMap::OnlyBodies(self.tcx.hir())
 625     }
 626
 627     fn visit_item(&mut self, item: &'tcx Item<'tcx>) {
 628         let target = Target::from_item(item);
 629         self.check_attributes(item.hir_id, item.attrs, &item.span, target, Some(item));
 630         intravisit::walk_item(self, item)
 631     }
 632
 633     fn visit_trait_item(&mut self, trait_item: &'tcx TraitItem<'tcx>) {
 634         let target = Target::from_trait_item(trait_item);
 635         self.check_attributes(trait_item.hir_id, &trait_item.attrs, &trait_item.span, target, None);
 636         intravisit::walk_trait_item(self, trait_item)
 637     }
 638
 639     fn visit_foreign_item(&mut self, f_item: &'tcx hir::ForeignItem<'tcx>) {
 640         let target = Target::from_foreign_item(f_item);
 641         self.check_attributes(f_item.hir_id, &f_item.attrs, &f_item.span, target, None);
 642         intravisit::walk_foreign_item(self, f_item)
 643     }
 644
 645     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
 646         let target = target_from_impl_item(self.tcx, impl_item);
 647         self.check_attributes(impl_item.hir_id, &impl_item.attrs, &impl_item.span, target, None);
 648         intravisit::walk_impl_item(self, impl_item)
 649     }
 650
 651     fn visit_stmt(&mut self, stmt: &'tcx hir::Stmt<'tcx>) {
 652         self.check_stmt_attributes(stmt);
 653         intravisit::walk_stmt(self, stmt)
 654     }
 655
 656     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
 657         self.check_expr_attributes(expr);
 658         intravisit::walk_expr(self, expr)
 659     }
 660 }
 661
 662 fn is_c_like_enum(item: &Item<'_>) -> bool {
 663     if let ItemKind::Enum(ref def, _) = item.kind {
 664         for variant in def.variants {
 665             match variant.data {
 666                 hir::VariantData::Unit(..) => { /* continue */ }
 667                 _ => return false,
 668             }
 669         }
 670         true
 671     } else {
 672         false
 673     }
 674 }
 675
 676 fn check_mod_attrs(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
 677     tcx.hir()
 678         .visit_item_likes_in_module(module_def_id, &mut CheckAttrVisitor { tcx }.as_deep_visitor());
 679 }
 680
 681 pub(crate) fn provide(providers: &mut Providers) {
 682     *providers = Providers { check_mod_attrs, ..*providers };
 683 }