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, LitKind, NestedMetaItem};
  12 use rustc_errors::{pluralize, 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::{
  17     self, FnSig, ForeignItem, ForeignItemKind, HirId, Item, ItemKind, TraitItem, CRATE_HIR_ID,
  18 };
  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, Symbol};
  23 use rustc_span::{Span, DUMMY_SP};
  24
  25 pub(crate) fn target_from_impl_item<'tcx>(
  26     tcx: TyCtxt<'tcx>,
  27     impl_item: &hir::ImplItem<'_>,
  28 ) -> Target {
  29     match impl_item.kind {
  30         hir::ImplItemKind::Const(..) => Target::AssocConst,
  31         hir::ImplItemKind::Fn(..) => {
  32             let parent_hir_id = tcx.hir().get_parent_item(impl_item.hir_id);
  33             let containing_item = tcx.hir().expect_item(parent_hir_id);
  34             let containing_impl_is_for_trait = match &containing_item.kind {
  35                 hir::ItemKind::Impl { ref of_trait, .. } => of_trait.is_some(),
  36                 _ => bug!("parent of an ImplItem must be an Impl"),
  37             };
  38             if containing_impl_is_for_trait {
  39                 Target::Method(MethodKind::Trait { body: true })
  40             } else {
  41                 Target::Method(MethodKind::Inherent)
  42             }
  43         }
  44         hir::ImplItemKind::TyAlias(..) => Target::AssocTy,
  45     }
  46 }
  47
  48 #[derive(Clone, Copy)]
  49 enum ItemLike<'tcx> {
  50     Item(&'tcx Item<'tcx>),
  51     ForeignItem(&'tcx ForeignItem<'tcx>),
  52 }
  53
  54 struct CheckAttrVisitor<'tcx> {
  55     tcx: TyCtxt<'tcx>,
  56 }
  57
  58 impl CheckAttrVisitor<'tcx> {
  59     /// Checks any attribute.
  60     fn check_attributes(
  61         &self,
  62         hir_id: HirId,
  63         attrs: &'hir [Attribute],
  64         span: &Span,
  65         target: Target,
  66         item: Option<ItemLike<'_>>,
  67     ) {
  68         let mut is_valid = true;
  69         for attr in attrs {
  70             is_valid &= if self.tcx.sess.check_name(attr, sym::inline) {
  71                 self.check_inline(hir_id, attr, span, target)
  72             } else if self.tcx.sess.check_name(attr, sym::non_exhaustive) {
  73                 self.check_non_exhaustive(attr, span, target)
  74             } else if self.tcx.sess.check_name(attr, sym::marker) {
  75                 self.check_marker(attr, span, target)
  76             } else if self.tcx.sess.check_name(attr, sym::target_feature) {
  77                 self.check_target_feature(hir_id, attr, span, target)
  78             } else if self.tcx.sess.check_name(attr, sym::track_caller) {
  79                 self.check_track_caller(&attr.span, attrs, span, target)
  80             } else if self.tcx.sess.check_name(attr, sym::doc) {
  81                 self.check_doc_alias(attr, hir_id, target)
  82             } else if self.tcx.sess.check_name(attr, sym::no_link) {
  83                 self.check_no_link(&attr, span, target)
  84             } else if self.tcx.sess.check_name(attr, sym::export_name) {
  85                 self.check_export_name(&attr, span, target)
  86             } else if self.tcx.sess.check_name(attr, sym::rustc_args_required_const) {
  87                 self.check_rustc_args_required_const(&attr, span, target, item)
  88             } else {
  89                 // lint-only checks
  90                 if self.tcx.sess.check_name(attr, sym::cold) {
  91                     self.check_cold(hir_id, attr, span, target);
  92                 } else if self.tcx.sess.check_name(attr, sym::link_name) {
  93                     self.check_link_name(hir_id, attr, span, target);
  94                 } else if self.tcx.sess.check_name(attr, sym::link_section) {
  95                     self.check_link_section(hir_id, attr, span, target);
  96                 } else if self.tcx.sess.check_name(attr, sym::no_mangle) {
  97                     self.check_no_mangle(hir_id, attr, span, target);
  98                 }
  99                 true
 100             };
 101         }
 102
 103         if !is_valid {
 104             return;
 105         }
 106
 107         if matches!(target, Target::Fn | Target::Method(_) | Target::ForeignFn) {
 108             self.tcx.ensure().codegen_fn_attrs(self.tcx.hir().local_def_id(hir_id));
 109         }
 110
 111         self.check_repr(attrs, span, target, item, hir_id);
 112         self.check_used(attrs, target);
 113     }
 114
 115     /// Checks if an `#[inline]` is applied to a function or a closure. Returns `true` if valid.
 116     fn check_inline(&self, hir_id: HirId, attr: &Attribute, span: &Span, target: Target) -> bool {
 117         match target {
 118             Target::Fn
 119             | Target::Closure
 120             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
 121             Target::Method(MethodKind::Trait { body: false }) | Target::ForeignFn => {
 122                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
 123                     lint.build("`#[inline]` is ignored on function prototypes").emit()
 124                 });
 125                 true
 126             }
 127             // FIXME(#65833): We permit associated consts to have an `#[inline]` attribute with
 128             // just a lint, because we previously erroneously allowed it and some crates used it
 129             // accidentally, to to be compatible with crates depending on them, we can't throw an
 130             // error here.
 131             Target::AssocConst => {
 132                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
 133                     lint.build("`#[inline]` is ignored on constants")
 134                         .warn(
 135                             "this was previously accepted by the compiler but is \
 136                              being phased out; it will become a hard error in \
 137                              a future release!",
 138                         )
 139                         .note(
 140                             "see issue #65833 <https://github.com/rust-lang/rust/issues/65833> \
 141                              for more information",
 142                         )
 143                         .emit();
 144                 });
 145                 true
 146             }
 147             _ => {
 148                 struct_span_err!(
 149                     self.tcx.sess,
 150                     attr.span,
 151                     E0518,
 152                     "attribute should be applied to function or closure",
 153                 )
 154                 .span_label(*span, "not a function or closure")
 155                 .emit();
 156                 false
 157             }
 158         }
 159     }
 160
 161     /// Checks if a `#[track_caller]` is applied to a non-naked function. Returns `true` if valid.
 162     fn check_track_caller(
 163         &self,
 164         attr_span: &Span,
 165         attrs: &'hir [Attribute],
 166         span: &Span,
 167         target: Target,
 168     ) -> bool {
 169         match target {
 170             _ if self.tcx.sess.contains_name(attrs, sym::naked) => {
 171                 struct_span_err!(
 172                     self.tcx.sess,
 173                     *attr_span,
 174                     E0736,
 175                     "cannot use `#[track_caller]` with `#[naked]`",
 176                 )
 177                 .emit();
 178                 false
 179             }
 180             Target::Fn | Target::Method(..) | Target::ForeignFn | Target::Closure => true,
 181             _ => {
 182                 struct_span_err!(
 183                     self.tcx.sess,
 184                     *attr_span,
 185                     E0739,
 186                     "attribute should be applied to function"
 187                 )
 188                 .span_label(*span, "not a function")
 189                 .emit();
 190                 false
 191             }
 192         }
 193     }
 194
 195     /// Checks if the `#[non_exhaustive]` attribute on an `item` is valid. Returns `true` if valid.
 196     fn check_non_exhaustive(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 197         match target {
 198             Target::Struct | Target::Enum => true,
 199             _ => {
 200                 struct_span_err!(
 201                     self.tcx.sess,
 202                     attr.span,
 203                     E0701,
 204                     "attribute can only be applied to a struct or enum"
 205                 )
 206                 .span_label(*span, "not a struct or enum")
 207                 .emit();
 208                 false
 209             }
 210         }
 211     }
 212
 213     /// Checks if the `#[marker]` attribute on an `item` is valid. Returns `true` if valid.
 214     fn check_marker(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 215         match target {
 216             Target::Trait => true,
 217             _ => {
 218                 self.tcx
 219                     .sess
 220                     .struct_span_err(attr.span, "attribute can only be applied to a trait")
 221                     .span_label(*span, "not a trait")
 222                     .emit();
 223                 false
 224             }
 225         }
 226     }
 227
 228     /// Checks if the `#[target_feature]` attribute on `item` is valid. Returns `true` if valid.
 229     fn check_target_feature(
 230         &self,
 231         hir_id: HirId,
 232         attr: &Attribute,
 233         span: &Span,
 234         target: Target,
 235     ) -> bool {
 236         match target {
 237             Target::Fn
 238             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
 239             // FIXME: #[target_feature] was previously erroneously allowed on statements and some
 240             // crates used this, so only emit a warning.
 241             Target::Statement => {
 242                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
 243                     lint.build("attribute should be applied to a function")
 244                         .warn(
 245                             "this was previously accepted by the compiler but is \
 246                              being phased out; it will become a hard error in \
 247                              a future release!",
 248                         )
 249                         .span_label(*span, "not a function")
 250                         .emit();
 251                 });
 252                 true
 253             }
 254             _ => {
 255                 self.tcx
 256                     .sess
 257                     .struct_span_err(attr.span, "attribute should be applied to a function")
 258                     .span_label(*span, "not a function")
 259                     .emit();
 260                 false
 261             }
 262         }
 263     }
 264
 265     fn doc_alias_str_error(&self, meta: &NestedMetaItem) {
 266         self.tcx
 267             .sess
 268             .struct_span_err(
 269                 meta.span(),
 270                 "doc alias attribute expects a string: #[doc(alias = \"0\")]",
 271             )
 272             .emit();
 273     }
 274
 275     fn check_doc_alias(&self, attr: &Attribute, hir_id: HirId, target: Target) -> bool {
 276         if let Some(mi) = attr.meta() {
 277             if let Some(list) = mi.meta_item_list() {
 278                 for meta in list {
 279                     if meta.has_name(sym::alias) {
 280                         if !meta.is_value_str() {
 281                             self.doc_alias_str_error(meta);
 282                             return false;
 283                         }
 284                         let doc_alias =
 285                             meta.value_str().map(|s| s.to_string()).unwrap_or_else(String::new);
 286                         if doc_alias.is_empty() {
 287                             self.doc_alias_str_error(meta);
 288                             return false;
 289                         }
 290                         if let Some(c) = doc_alias
 291                             .chars()
 292                             .find(|&c| c == '"' || c == '\'' || (c.is_whitespace() && c != ' '))
 293                         {
 294                             self.tcx
 295                                 .sess
 296                                 .struct_span_err(
 297                                     meta.span(),
 298                                     &format!(
 299                                         "{:?} character isn't allowed in `#[doc(alias = \"...\")]`",
 300                                         c,
 301                                     ),
 302                                 )
 303                                 .emit();
 304                             return false;
 305                         }
 306                         if doc_alias.starts_with(' ') || doc_alias.ends_with(' ') {
 307                             self.tcx
 308                                 .sess
 309                                 .struct_span_err(
 310                                     meta.span(),
 311                                     "`#[doc(alias = \"...\")]` cannot start or end with ' '",
 312                                 )
 313                                 .emit();
 314                             return false;
 315                         }
 316                         if let Some(err) = match target {
 317                             Target::Impl => Some("implementation block"),
 318                             Target::ForeignMod => Some("extern block"),
 319                             Target::AssocTy => {
 320                                 let parent_hir_id = self.tcx.hir().get_parent_item(hir_id);
 321                                 let containing_item = self.tcx.hir().expect_item(parent_hir_id);
 322                                 if Target::from_item(containing_item) == Target::Impl {
 323                                     Some("type alias in implementation block")
 324                                 } else {
 325                                     None
 326                                 }
 327                             }
 328                             Target::AssocConst => {
 329                                 let parent_hir_id = self.tcx.hir().get_parent_item(hir_id);
 330                                 let containing_item = self.tcx.hir().expect_item(parent_hir_id);
 331                                 // We can't link to trait impl's consts.
 332                                 let err = "associated constant in trait implementation block";
 333                                 match containing_item.kind {
 334                                     ItemKind::Impl { of_trait: Some(_), .. } => Some(err),
 335                                     _ => None,
 336                                 }
 337                             }
 338                             _ => None,
 339                         } {
 340                             self.tcx
 341                                 .sess
 342                                 .struct_span_err(
 343                                     meta.span(),
 344                                     &format!("`#[doc(alias = \"...\")]` isn't allowed on {}", err),
 345                                 )
 346                                 .emit();
 347                             return false;
 348                         }
 349                         if CRATE_HIR_ID == hir_id {
 350                             self.tcx
 351                                 .sess
 352                                 .struct_span_err(
 353                                     meta.span(),
 354                                     "`#![doc(alias = \"...\")]` isn't allowed as a crate \
 355                                      level attribute",
 356                                 )
 357                                 .emit();
 358                             return false;
 359                         }
 360                     }
 361                 }
 362             }
 363         }
 364         true
 365     }
 366
 367     /// Checks if `#[cold]` is applied to a non-function. Returns `true` if valid.
 368     fn check_cold(&self, hir_id: HirId, attr: &Attribute, span: &Span, target: Target) {
 369         match target {
 370             Target::Fn | Target::Method(..) | Target::ForeignFn | Target::Closure => {}
 371             _ => {
 372                 // FIXME: #[cold] was previously allowed on non-functions and some crates used
 373                 // this, so only emit a warning.
 374                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
 375                     lint.build("attribute should be applied to a function")
 376                         .warn(
 377                             "this was previously accepted by the compiler but is \
 378                              being phased out; it will become a hard error in \
 379                              a future release!",
 380                         )
 381                         .span_label(*span, "not a function")
 382                         .emit();
 383                 });
 384             }
 385         }
 386     }
 387
 388     /// Checks if `#[link_name]` is applied to an item other than a foreign function or static.
 389     fn check_link_name(&self, hir_id: HirId, attr: &Attribute, span: &Span, target: Target) {
 390         match target {
 391             Target::ForeignFn | Target::ForeignStatic => {}
 392             _ => {
 393                 // FIXME: #[cold] was previously allowed on non-functions/statics and some crates
 394                 // used this, so only emit a warning.
 395                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
 396                     let mut diag =
 397                         lint.build("attribute should be applied to a foreign function or static");
 398                     diag.warn(
 399                         "this was previously accepted by the compiler but is \
 400                          being phased out; it will become a hard error in \
 401                          a future release!",
 402                     );
 403
 404                     // See issue #47725
 405                     if let Target::ForeignMod = target {
 406                         if let Some(value) = attr.value_str() {
 407                             diag.span_help(
 408                                 attr.span,
 409                                 &format!(r#"try `#[link(name = "{}")]` instead"#, value),
 410                             );
 411                         } else {
 412                             diag.span_help(attr.span, r#"try `#[link(name = "...")]` instead"#);
 413                         }
 414                     }
 415
 416                     diag.span_label(*span, "not a foreign function or static");
 417                     diag.emit();
 418                 });
 419             }
 420         }
 421     }
 422
 423     /// Checks if `#[no_link]` is applied to an `extern crate`. Returns `true` if valid.
 424     fn check_no_link(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 425         if target == Target::ExternCrate {
 426             true
 427         } else {
 428             self.tcx
 429                 .sess
 430                 .struct_span_err(attr.span, "attribute should be applied to an `extern crate` item")
 431                 .span_label(*span, "not an `extern crate` item")
 432                 .emit();
 433             false
 434         }
 435     }
 436
 437     /// Checks if `#[export_name]` is applied to a function or static. Returns `true` if valid.
 438     fn check_export_name(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 439         match target {
 440             Target::Static | Target::Fn | Target::Method(..) => true,
 441             _ => {
 442                 self.tcx
 443                     .sess
 444                     .struct_span_err(
 445                         attr.span,
 446                         "attribute should be applied to a function or static",
 447                     )
 448                     .span_label(*span, "not a function or static")
 449                     .emit();
 450                 false
 451             }
 452         }
 453     }
 454
 455     /// Checks if `#[rustc_args_required_const]` is applied to a function and has a valid argument.
 456     fn check_rustc_args_required_const(
 457         &self,
 458         attr: &Attribute,
 459         span: &Span,
 460         target: Target,
 461         item: Option<ItemLike<'_>>,
 462     ) -> bool {
 463         if let Target::Fn | Target::Method(..) | Target::ForeignFn = target {
 464             let mut invalid_args = vec![];
 465             for meta in attr.meta_item_list().expect("no meta item list") {
 466                 if let Some(LitKind::Int(val, _)) = meta.literal().map(|lit| &lit.kind) {
 467                     if let Some(ItemLike::Item(Item {
 468                         kind: ItemKind::Fn(FnSig { decl, .. }, ..),
 469                         ..
 470                     }))
 471                     | Some(ItemLike::ForeignItem(ForeignItem {
 472                         kind: ForeignItemKind::Fn(decl, ..),
 473                         ..
 474                     })) = item
 475                     {
 476                         let arg_count = decl.inputs.len() as u128;
 477                         if *val >= arg_count {
 478                             let span = meta.span();
 479                             self.tcx
 480                                 .sess
 481                                 .struct_span_err(span, "index exceeds number of arguments")
 482                                 .span_label(
 483                                     span,
 484                                     format!(
 485                                         "there {} only {} argument{}",
 486                                         if arg_count != 1 { "are" } else { "is" },
 487                                         arg_count,
 488                                         pluralize!(arg_count)
 489                                     ),
 490                                 )
 491                                 .emit();
 492                             return false;
 493                         }
 494                     } else {
 495                         bug!("should be a function item");
 496                     }
 497                 } else {
 498                     invalid_args.push(meta.span());
 499                 }
 500             }
 501             if !invalid_args.is_empty() {
 502                 self.tcx
 503                     .sess
 504                     .struct_span_err(invalid_args, "arguments should be non-negative integers")
 505                     .emit();
 506                 false
 507             } else {
 508                 true
 509             }
 510         } else {
 511             self.tcx
 512                 .sess
 513                 .struct_span_err(attr.span, "attribute should be applied to a function")
 514                 .span_label(*span, "not a function")
 515                 .emit();
 516             false
 517         }
 518     }
 519
 520     /// Checks if `#[link_section]` is applied to a function or static.
 521     fn check_link_section(&self, hir_id: HirId, attr: &Attribute, span: &Span, target: Target) {
 522         match target {
 523             Target::Static | Target::Fn | Target::Method(..) => {}
 524             _ => {
 525                 // FIXME: #[link_section] was previously allowed on non-functions/statics and some
 526                 // crates used this, so only emit a warning.
 527                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
 528                     lint.build("attribute should be applied to a function or static")
 529                         .warn(
 530                             "this was previously accepted by the compiler but is \
 531                              being phased out; it will become a hard error in \
 532                              a future release!",
 533                         )
 534                         .span_label(*span, "not a function or static")
 535                         .emit();
 536                 });
 537             }
 538         }
 539     }
 540
 541     /// Checks if `#[no_mangle]` is applied to a function or static.
 542     fn check_no_mangle(&self, hir_id: HirId, attr: &Attribute, span: &Span, target: Target) {
 543         match target {
 544             Target::Static | Target::Fn | Target::Method(..) => {}
 545             _ => {
 546                 // FIXME: #[no_mangle] was previously allowed on non-functions/statics and some
 547                 // crates used this, so only emit a warning.
 548                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
 549                     lint.build("attribute should be applied to a function or static")
 550                         .warn(
 551                             "this was previously accepted by the compiler but is \
 552                              being phased out; it will become a hard error in \
 553                              a future release!",
 554                         )
 555                         .span_label(*span, "not a function or static")
 556                         .emit();
 557                 });
 558             }
 559         }
 560     }
 561
 562     /// Checks if the `#[repr]` attributes on `item` are valid.
 563     fn check_repr(
 564         &self,
 565         attrs: &'hir [Attribute],
 566         span: &Span,
 567         target: Target,
 568         item: Option<ItemLike<'_>>,
 569         hir_id: HirId,
 570     ) {
 571         // Extract the names of all repr hints, e.g., [foo, bar, align] for:
 572         // ```
 573         // #[repr(foo)]
 574         // #[repr(bar, align(8))]
 575         // ```
 576         let hints: Vec<_> = attrs
 577             .iter()
 578             .filter(|attr| self.tcx.sess.check_name(attr, sym::repr))
 579             .filter_map(|attr| attr.meta_item_list())
 580             .flatten()
 581             .collect();
 582
 583         let mut int_reprs = 0;
 584         let mut is_c = false;
 585         let mut is_simd = false;
 586         let mut is_transparent = false;
 587
 588         for hint in &hints {
 589             let (article, allowed_targets) = match hint.name_or_empty() {
 590                 name @ sym::C | name @ sym::align => {
 591                     is_c |= name == sym::C;
 592                     match target {
 593                         Target::Struct | Target::Union | Target::Enum => continue,
 594                         _ => ("a", "struct, enum, or union"),
 595                     }
 596                 }
 597                 sym::packed => {
 598                     if target != Target::Struct && target != Target::Union {
 599                         ("a", "struct or union")
 600                     } else {
 601                         continue;
 602                     }
 603                 }
 604                 sym::simd => {
 605                     is_simd = true;
 606                     if target != Target::Struct {
 607                         ("a", "struct")
 608                     } else {
 609                         continue;
 610                     }
 611                 }
 612                 sym::transparent => {
 613                     is_transparent = true;
 614                     match target {
 615                         Target::Struct | Target::Union | Target::Enum => continue,
 616                         _ => ("a", "struct, enum, or union"),
 617                     }
 618                 }
 619                 sym::no_niche => {
 620                     if !self.tcx.features().enabled(sym::no_niche) {
 621                         feature_err(
 622                             &self.tcx.sess.parse_sess,
 623                             sym::no_niche,
 624                             hint.span(),
 625                             "the attribute `repr(no_niche)` is currently unstable",
 626                         )
 627                         .emit();
 628                     }
 629                     match target {
 630                         Target::Struct | Target::Enum => continue,
 631                         _ => ("a", "struct or enum"),
 632                     }
 633                 }
 634                 sym::i8
 635                 | sym::u8
 636                 | sym::i16
 637                 | sym::u16
 638                 | sym::i32
 639                 | sym::u32
 640                 | sym::i64
 641                 | sym::u64
 642                 | sym::i128
 643                 | sym::u128
 644                 | sym::isize
 645                 | sym::usize => {
 646                     int_reprs += 1;
 647                     if target != Target::Enum {
 648                         ("an", "enum")
 649                     } else {
 650                         continue;
 651                     }
 652                 }
 653                 _ => continue,
 654             };
 655             self.emit_repr_error(
 656                 hint.span(),
 657                 *span,
 658                 &format!("attribute should be applied to {}", allowed_targets),
 659                 &format!("not {} {}", article, allowed_targets),
 660             )
 661         }
 662
 663         // Just point at all repr hints if there are any incompatibilities.
 664         // This is not ideal, but tracking precisely which ones are at fault is a huge hassle.
 665         let hint_spans = hints.iter().map(|hint| hint.span());
 666
 667         // Error on repr(transparent, <anything else apart from no_niche>).
 668         let non_no_niche = |hint: &&NestedMetaItem| hint.name_or_empty() != sym::no_niche;
 669         let non_no_niche_count = hints.iter().filter(non_no_niche).count();
 670         if is_transparent && non_no_niche_count > 1 {
 671             let hint_spans: Vec<_> = hint_spans.clone().collect();
 672             struct_span_err!(
 673                 self.tcx.sess,
 674                 hint_spans,
 675                 E0692,
 676                 "transparent {} cannot have other repr hints",
 677                 target
 678             )
 679             .emit();
 680         }
 681         // Warn on repr(u8, u16), repr(C, simd), and c-like-enum-repr(C, u8)
 682         if (int_reprs > 1)
 683             || (is_simd && is_c)
 684             || (int_reprs == 1
 685                 && is_c
 686                 && item.map_or(false, |item| {
 687                     if let ItemLike::Item(item) = item {
 688                         return is_c_like_enum(item);
 689                     }
 690                     return false;
 691                 }))
 692         {
 693             self.tcx.struct_span_lint_hir(
 694                 CONFLICTING_REPR_HINTS,
 695                 hir_id,
 696                 hint_spans.collect::<Vec<Span>>(),
 697                 |lint| {
 698                     lint.build("conflicting representation hints")
 699                         .code(rustc_errors::error_code!(E0566))
 700                         .emit();
 701                 },
 702             );
 703         }
 704     }
 705
 706     fn emit_repr_error(
 707         &self,
 708         hint_span: Span,
 709         label_span: Span,
 710         hint_message: &str,
 711         label_message: &str,
 712     ) {
 713         struct_span_err!(self.tcx.sess, hint_span, E0517, "{}", hint_message)
 714             .span_label(label_span, label_message)
 715             .emit();
 716     }
 717
 718     fn check_stmt_attributes(&self, stmt: &hir::Stmt<'_>) {
 719         // When checking statements ignore expressions, they will be checked later
 720         if let hir::StmtKind::Local(ref l) = stmt.kind {
 721             self.check_attributes(l.hir_id, &l.attrs, &stmt.span, Target::Statement, None);
 722             for attr in l.attrs.iter() {
 723                 if self.tcx.sess.check_name(attr, sym::repr) {
 724                     self.emit_repr_error(
 725                         attr.span,
 726                         stmt.span,
 727                         "attribute should not be applied to a statement",
 728                         "not a struct, enum, or union",
 729                     );
 730                 }
 731             }
 732         }
 733     }
 734
 735     fn check_expr_attributes(&self, expr: &hir::Expr<'_>) {
 736         let target = match expr.kind {
 737             hir::ExprKind::Closure(..) => Target::Closure,
 738             _ => Target::Expression,
 739         };
 740         self.check_attributes(expr.hir_id, &expr.attrs, &expr.span, target, None);
 741         for attr in expr.attrs.iter() {
 742             if self.tcx.sess.check_name(attr, sym::repr) {
 743                 self.emit_repr_error(
 744                     attr.span,
 745                     expr.span,
 746                     "attribute should not be applied to an expression",
 747                     "not defining a struct, enum, or union",
 748                 );
 749             }
 750         }
 751         if target == Target::Closure {
 752             self.tcx.ensure().codegen_fn_attrs(self.tcx.hir().local_def_id(expr.hir_id));
 753         }
 754     }
 755
 756     fn check_used(&self, attrs: &'hir [Attribute], target: Target) {
 757         for attr in attrs {
 758             if self.tcx.sess.check_name(attr, sym::used) && target != Target::Static {
 759                 self.tcx
 760                     .sess
 761                     .span_err(attr.span, "attribute must be applied to a `static` variable");
 762             }
 763         }
 764     }
 765 }
 766
 767 impl Visitor<'tcx> for CheckAttrVisitor<'tcx> {
 768     type Map = Map<'tcx>;
 769
 770     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 771         NestedVisitorMap::OnlyBodies(self.tcx.hir())
 772     }
 773
 774     fn visit_item(&mut self, item: &'tcx Item<'tcx>) {
 775         let target = Target::from_item(item);
 776         self.check_attributes(
 777             item.hir_id,
 778             item.attrs,
 779             &item.span,
 780             target,
 781             Some(ItemLike::Item(item)),
 782         );
 783         intravisit::walk_item(self, item)
 784     }
 785
 786     fn visit_trait_item(&mut self, trait_item: &'tcx TraitItem<'tcx>) {
 787         let target = Target::from_trait_item(trait_item);
 788         self.check_attributes(trait_item.hir_id, &trait_item.attrs, &trait_item.span, target, None);
 789         intravisit::walk_trait_item(self, trait_item)
 790     }
 791
 792     fn visit_foreign_item(&mut self, f_item: &'tcx ForeignItem<'tcx>) {
 793         let target = Target::from_foreign_item(f_item);
 794         self.check_attributes(
 795             f_item.hir_id,
 796             &f_item.attrs,
 797             &f_item.span,
 798             target,
 799             Some(ItemLike::ForeignItem(f_item)),
 800         );
 801         intravisit::walk_foreign_item(self, f_item)
 802     }
 803
 804     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
 805         let target = target_from_impl_item(self.tcx, impl_item);
 806         self.check_attributes(impl_item.hir_id, &impl_item.attrs, &impl_item.span, target, None);
 807         intravisit::walk_impl_item(self, impl_item)
 808     }
 809
 810     fn visit_stmt(&mut self, stmt: &'tcx hir::Stmt<'tcx>) {
 811         self.check_stmt_attributes(stmt);
 812         intravisit::walk_stmt(self, stmt)
 813     }
 814
 815     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
 816         self.check_expr_attributes(expr);
 817         intravisit::walk_expr(self, expr)
 818     }
 819 }
 820
 821 fn is_c_like_enum(item: &Item<'_>) -> bool {
 822     if let ItemKind::Enum(ref def, _) = item.kind {
 823         for variant in def.variants {
 824             match variant.data {
 825                 hir::VariantData::Unit(..) => { /* continue */ }
 826                 _ => return false,
 827             }
 828         }
 829         true
 830     } else {
 831         false
 832     }
 833 }
 834
 835 fn check_invalid_crate_level_attr(tcx: TyCtxt<'_>, attrs: &[Attribute]) {
 836     const ATTRS_TO_CHECK: &[Symbol] = &[
 837         sym::macro_export,
 838         sym::repr,
 839         sym::path,
 840         sym::automatically_derived,
 841         sym::start,
 842         sym::main,
 843     ];
 844
 845     for attr in attrs {
 846         for attr_to_check in ATTRS_TO_CHECK {
 847             if tcx.sess.check_name(attr, *attr_to_check) {
 848                 tcx.sess
 849                     .struct_span_err(
 850                         attr.span,
 851                         &format!(
 852                             "`{}` attribute cannot be used at crate level",
 853                             attr_to_check.to_ident_string()
 854                         ),
 855                     )
 856                     .emit();
 857             }
 858         }
 859     }
 860 }
 861
 862 fn check_mod_attrs(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
 863     tcx.hir()
 864         .visit_item_likes_in_module(module_def_id, &mut CheckAttrVisitor { tcx }.as_deep_visitor());
 865     if module_def_id.is_top_level_module() {
 866         CheckAttrVisitor { tcx }.check_attributes(
 867             CRATE_HIR_ID,
 868             tcx.hir().krate_attrs(),
 869             &DUMMY_SP,
 870             Target::Mod,
 871             None,
 872         );
 873         check_invalid_crate_level_attr(tcx, tcx.hir().krate_attrs());
 874     }
 875 }
 876
 877 pub(crate) fn provide(providers: &mut Providers) {
 878     *providers = Providers { check_mod_attrs, ..*providers };
 879 }