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 crate::errors;
   8 use rustc_ast::{ast, AttrStyle, Attribute, Lit, LitKind, MetaItemKind, NestedMetaItem};
   9 use rustc_data_structures::fx::FxHashMap;
  10 use rustc_errors::{fluent, struct_span_err, Applicability, MultiSpan};
  11 use rustc_expand::base::resolve_path;
  12 use rustc_feature::{AttributeDuplicates, AttributeType, BuiltinAttribute, BUILTIN_ATTRIBUTE_MAP};
  13 use rustc_hir as hir;
  14 use rustc_hir::def_id::LocalDefId;
  15 use rustc_hir::intravisit::{self, Visitor};
  16 use rustc_hir::{
  17     self, FnSig, ForeignItem, HirId, Item, ItemKind, TraitItem, CRATE_HIR_ID, CRATE_OWNER_ID,
  18 };
  19 use rustc_hir::{MethodKind, Target};
  20 use rustc_middle::hir::nested_filter;
  21 use rustc_middle::middle::resolve_lifetime::ObjectLifetimeDefault;
  22 use rustc_middle::ty::query::Providers;
  23 use rustc_middle::ty::TyCtxt;
  24 use rustc_session::lint::builtin::{
  25     CONFLICTING_REPR_HINTS, INVALID_DOC_ATTRIBUTES, UNUSED_ATTRIBUTES,
  26 };
  27 use rustc_session::parse::feature_err;
  28 use rustc_span::symbol::{kw, sym, Symbol};
  29 use rustc_span::{Span, DUMMY_SP};
  30 use rustc_target::spec::abi::Abi;
  31 use std::collections::hash_map::Entry;
  32
  33 pub(crate) fn target_from_impl_item<'tcx>(
  34     tcx: TyCtxt<'tcx>,
  35     impl_item: &hir::ImplItem<'_>,
  36 ) -> Target {
  37     match impl_item.kind {
  38         hir::ImplItemKind::Const(..) => Target::AssocConst,
  39         hir::ImplItemKind::Fn(..) => {
  40             let parent_def_id = tcx.hir().get_parent_item(impl_item.hir_id()).def_id;
  41             let containing_item = tcx.hir().expect_item(parent_def_id);
  42             let containing_impl_is_for_trait = match &containing_item.kind {
  43                 hir::ItemKind::Impl(impl_) => impl_.of_trait.is_some(),
  44                 _ => bug!("parent of an ImplItem must be an Impl"),
  45             };
  46             if containing_impl_is_for_trait {
  47                 Target::Method(MethodKind::Trait { body: true })
  48             } else {
  49                 Target::Method(MethodKind::Inherent)
  50             }
  51         }
  52         hir::ImplItemKind::TyAlias(..) => Target::AssocTy,
  53     }
  54 }
  55
  56 #[derive(Clone, Copy)]
  57 enum ItemLike<'tcx> {
  58     Item(&'tcx Item<'tcx>),
  59     ForeignItem,
  60 }
  61
  62 struct CheckAttrVisitor<'tcx> {
  63     tcx: TyCtxt<'tcx>,
  64 }
  65
  66 impl CheckAttrVisitor<'_> {
  67     /// Checks any attribute.
  68     fn check_attributes(
  69         &self,
  70         hir_id: HirId,
  71         span: Span,
  72         target: Target,
  73         item: Option<ItemLike<'_>>,
  74     ) {
  75         let mut doc_aliases = FxHashMap::default();
  76         let mut is_valid = true;
  77         let mut specified_inline = None;
  78         let mut seen = FxHashMap::default();
  79         let attrs = self.tcx.hir().attrs(hir_id);
  80         for attr in attrs {
  81             let attr_is_valid = match attr.name_or_empty() {
  82                 sym::inline => self.check_inline(hir_id, attr, span, target),
  83                 sym::no_coverage => self.check_no_coverage(hir_id, attr, span, target),
  84                 sym::non_exhaustive => self.check_non_exhaustive(hir_id, attr, span, target),
  85                 sym::marker => self.check_marker(hir_id, attr, span, target),
  86                 sym::rustc_must_implement_one_of => {
  87                     self.check_rustc_must_implement_one_of(attr, span, target)
  88                 }
  89                 sym::target_feature => self.check_target_feature(hir_id, attr, span, target),
  90                 sym::thread_local => self.check_thread_local(attr, span, target),
  91                 sym::track_caller => {
  92                     self.check_track_caller(hir_id, attr.span, attrs, span, target)
  93                 }
  94                 sym::doc => self.check_doc_attrs(
  95                     attr,
  96                     hir_id,
  97                     target,
  98                     &mut specified_inline,
  99                     &mut doc_aliases,
 100                 ),
 101                 sym::no_link => self.check_no_link(hir_id, &attr, span, target),
 102                 sym::export_name => self.check_export_name(hir_id, &attr, span, target),
 103                 sym::rustc_layout_scalar_valid_range_start
 104                 | sym::rustc_layout_scalar_valid_range_end => {
 105                     self.check_rustc_layout_scalar_valid_range(&attr, span, target)
 106                 }
 107                 sym::allow_internal_unstable => {
 108                     self.check_allow_internal_unstable(hir_id, &attr, span, target, &attrs)
 109                 }
 110                 sym::debugger_visualizer => self.check_debugger_visualizer(&attr, target),
 111                 sym::rustc_allow_const_fn_unstable => {
 112                     self.check_rustc_allow_const_fn_unstable(hir_id, &attr, span, target)
 113                 }
 114                 sym::rustc_std_internal_symbol => {
 115                     self.check_rustc_std_internal_symbol(&attr, span, target)
 116                 }
 117                 sym::naked => self.check_naked(hir_id, attr, span, target),
 118                 sym::rustc_legacy_const_generics => {
 119                     self.check_rustc_legacy_const_generics(&attr, span, target, item)
 120                 }
 121                 sym::rustc_lint_query_instability => {
 122                     self.check_rustc_lint_query_instability(&attr, span, target)
 123                 }
 124                 sym::rustc_lint_diagnostics => {
 125                     self.check_rustc_lint_diagnostics(&attr, span, target)
 126                 }
 127                 sym::rustc_lint_opt_ty => self.check_rustc_lint_opt_ty(&attr, span, target),
 128                 sym::rustc_lint_opt_deny_field_access => {
 129                     self.check_rustc_lint_opt_deny_field_access(&attr, span, target)
 130                 }
 131                 sym::rustc_clean
 132                 | sym::rustc_dirty
 133                 | sym::rustc_if_this_changed
 134                 | sym::rustc_then_this_would_need => self.check_rustc_dirty_clean(&attr),
 135                 sym::cmse_nonsecure_entry => self.check_cmse_nonsecure_entry(attr, span, target),
 136                 sym::collapse_debuginfo => self.check_collapse_debuginfo(attr, span, target),
 137                 sym::const_trait => self.check_const_trait(attr, span, target),
 138                 sym::must_not_suspend => self.check_must_not_suspend(&attr, span, target),
 139                 sym::must_use => self.check_must_use(hir_id, &attr, span, target),
 140                 sym::rustc_pass_by_value => self.check_pass_by_value(&attr, span, target),
 141                 sym::rustc_allow_incoherent_impl => {
 142                     self.check_allow_incoherent_impl(&attr, span, target)
 143                 }
 144                 sym::rustc_has_incoherent_inherent_impls => {
 145                     self.check_has_incoherent_inherent_impls(&attr, span, target)
 146                 }
 147                 sym::rustc_const_unstable
 148                 | sym::rustc_const_stable
 149                 | sym::unstable
 150                 | sym::stable
 151                 | sym::rustc_allowed_through_unstable_modules
 152                 | sym::rustc_promotable => self.check_stability_promotable(&attr, span, target),
 153                 sym::link_ordinal => self.check_link_ordinal(&attr, span, target),
 154                 _ => true,
 155             };
 156             is_valid &= attr_is_valid;
 157
 158             // lint-only checks
 159             match attr.name_or_empty() {
 160                 sym::cold => self.check_cold(hir_id, attr, span, target),
 161                 sym::link => self.check_link(hir_id, attr, span, target),
 162                 sym::link_name => self.check_link_name(hir_id, attr, span, target),
 163                 sym::link_section => self.check_link_section(hir_id, attr, span, target),
 164                 sym::no_mangle => self.check_no_mangle(hir_id, attr, span, target),
 165                 sym::deprecated => self.check_deprecated(hir_id, attr, span, target),
 166                 sym::macro_use | sym::macro_escape => self.check_macro_use(hir_id, attr, target),
 167                 sym::path => self.check_generic_attr(hir_id, attr, target, &[Target::Mod]),
 168                 sym::plugin_registrar => self.check_plugin_registrar(hir_id, attr, target),
 169                 sym::macro_export => self.check_macro_export(hir_id, attr, target),
 170                 sym::ignore | sym::should_panic | sym::proc_macro_derive => {
 171                     self.check_generic_attr(hir_id, attr, target, &[Target::Fn])
 172                 }
 173                 sym::automatically_derived => {
 174                     self.check_generic_attr(hir_id, attr, target, &[Target::Impl])
 175                 }
 176                 sym::no_implicit_prelude => {
 177                     self.check_generic_attr(hir_id, attr, target, &[Target::Mod])
 178                 }
 179                 sym::rustc_object_lifetime_default => self.check_object_lifetime_default(hir_id),
 180                 _ => {}
 181             }
 182
 183             let builtin = attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name));
 184
 185             if hir_id != CRATE_HIR_ID {
 186                 if let Some(BuiltinAttribute { type_: AttributeType::CrateLevel, .. }) =
 187                     attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name))
 188                 {
 189                     match attr.style {
 190                         ast::AttrStyle::Outer => self.tcx.emit_spanned_lint(
 191                             UNUSED_ATTRIBUTES,
 192                             hir_id,
 193                             attr.span,
 194                             errors::OuterCrateLevelAttr,
 195                         ),
 196                         ast::AttrStyle::Inner => self.tcx.emit_spanned_lint(
 197                             UNUSED_ATTRIBUTES,
 198                             hir_id,
 199                             attr.span,
 200                             errors::InnerCrateLevelAttr,
 201                         ),
 202                     }
 203                 }
 204             }
 205
 206             if let Some(BuiltinAttribute { duplicates, .. }) = builtin {
 207                 check_duplicates(self.tcx, attr, hir_id, *duplicates, &mut seen);
 208             }
 209
 210             self.check_unused_attribute(hir_id, attr)
 211         }
 212
 213         if !is_valid {
 214             return;
 215         }
 216
 217         // FIXME(@lcnr): this doesn't belong here.
 218         if matches!(
 219             target,
 220             Target::Closure
 221                 | Target::Fn
 222                 | Target::Method(_)
 223                 | Target::ForeignFn
 224                 | Target::ForeignStatic
 225         ) {
 226             self.tcx.ensure().codegen_fn_attrs(self.tcx.hir().local_def_id(hir_id));
 227         }
 228
 229         self.check_repr(attrs, span, target, item, hir_id);
 230         self.check_used(attrs, target);
 231     }
 232
 233     fn inline_attr_str_error_with_macro_def(&self, hir_id: HirId, attr: &Attribute, sym: &str) {
 234         self.tcx.emit_spanned_lint(
 235             UNUSED_ATTRIBUTES,
 236             hir_id,
 237             attr.span,
 238             errors::IgnoredAttrWithMacro { sym },
 239         );
 240     }
 241
 242     fn inline_attr_str_error_without_macro_def(&self, hir_id: HirId, attr: &Attribute, sym: &str) {
 243         self.tcx.emit_spanned_lint(
 244             UNUSED_ATTRIBUTES,
 245             hir_id,
 246             attr.span,
 247             errors::IgnoredAttr { sym },
 248         );
 249     }
 250
 251     /// Checks if an `#[inline]` is applied to a function or a closure. Returns `true` if valid.
 252     fn check_inline(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) -> bool {
 253         match target {
 254             Target::Fn
 255             | Target::Closure
 256             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
 257             Target::Method(MethodKind::Trait { body: false }) | Target::ForeignFn => {
 258                 self.tcx.emit_spanned_lint(
 259                     UNUSED_ATTRIBUTES,
 260                     hir_id,
 261                     attr.span,
 262                     errors::IgnoredInlineAttrFnProto,
 263                 );
 264                 true
 265             }
 266             // FIXME(#65833): We permit associated consts to have an `#[inline]` attribute with
 267             // just a lint, because we previously erroneously allowed it and some crates used it
 268             // accidentally, to to be compatible with crates depending on them, we can't throw an
 269             // error here.
 270             Target::AssocConst => {
 271                 self.tcx.emit_spanned_lint(
 272                     UNUSED_ATTRIBUTES,
 273                     hir_id,
 274                     attr.span,
 275                     errors::IgnoredInlineAttrConstants,
 276                 );
 277                 true
 278             }
 279             // FIXME(#80564): Same for fields, arms, and macro defs
 280             Target::Field | Target::Arm | Target::MacroDef => {
 281                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "inline");
 282                 true
 283             }
 284             _ => {
 285                 self.tcx.sess.emit_err(errors::InlineNotFnOrClosure {
 286                     attr_span: attr.span,
 287                     defn_span: span,
 288                 });
 289                 false
 290             }
 291         }
 292     }
 293
 294     /// Checks if a `#[no_coverage]` is applied directly to a function
 295     fn check_no_coverage(
 296         &self,
 297         hir_id: HirId,
 298         attr: &Attribute,
 299         span: Span,
 300         target: Target,
 301     ) -> bool {
 302         match target {
 303             // no_coverage on function is fine
 304             Target::Fn
 305             | Target::Closure
 306             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
 307
 308             // function prototypes can't be covered
 309             Target::Method(MethodKind::Trait { body: false }) | Target::ForeignFn => {
 310                 self.tcx.emit_spanned_lint(
 311                     UNUSED_ATTRIBUTES,
 312                     hir_id,
 313                     attr.span,
 314                     errors::IgnoredNoCoverageFnProto,
 315                 );
 316                 true
 317             }
 318
 319             Target::Mod | Target::ForeignMod | Target::Impl | Target::Trait => {
 320                 self.tcx.emit_spanned_lint(
 321                     UNUSED_ATTRIBUTES,
 322                     hir_id,
 323                     attr.span,
 324                     errors::IgnoredNoCoveragePropagate,
 325                 );
 326                 true
 327             }
 328
 329             Target::Expression | Target::Statement | Target::Arm => {
 330                 self.tcx.emit_spanned_lint(
 331                     UNUSED_ATTRIBUTES,
 332                     hir_id,
 333                     attr.span,
 334                     errors::IgnoredNoCoverageFnDefn,
 335                 );
 336                 true
 337             }
 338
 339             _ => {
 340                 self.tcx.sess.emit_err(errors::IgnoredNoCoverageNotCoverable {
 341                     attr_span: attr.span,
 342                     defn_span: span,
 343                 });
 344                 false
 345             }
 346         }
 347     }
 348
 349     fn check_generic_attr(
 350         &self,
 351         hir_id: HirId,
 352         attr: &Attribute,
 353         target: Target,
 354         allowed_targets: &[Target],
 355     ) {
 356         if !allowed_targets.iter().any(|t| t == &target) {
 357             let name = attr.name_or_empty();
 358             let mut i = allowed_targets.iter();
 359             // Pluralize
 360             let b = i.next().map_or_else(String::new, |t| t.to_string() + "s");
 361             let supported_names = i.enumerate().fold(b, |mut b, (i, allowed_target)| {
 362                 if allowed_targets.len() > 2 && i == allowed_targets.len() - 2 {
 363                     b.push_str(", and ");
 364                 } else if allowed_targets.len() == 2 && i == allowed_targets.len() - 2 {
 365                     b.push_str(" and ");
 366                 } else {
 367                     b.push_str(", ");
 368                 }
 369                 // Pluralize
 370                 b.push_str(&(allowed_target.to_string() + "s"));
 371                 b
 372             });
 373             self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
 374                 lint.build(&format!("`#[{name}]` only has an effect on {}", supported_names))
 375                     .emit();
 376             });
 377         }
 378     }
 379
 380     /// Checks if `#[naked]` is applied to a function definition.
 381     fn check_naked(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) -> bool {
 382         match target {
 383             Target::Fn
 384             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
 385             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
 386             // `#[allow_internal_unstable]` attribute with just a lint, because we previously
 387             // erroneously allowed it and some crates used it accidentally, to to be compatible
 388             // with crates depending on them, we can't throw an error here.
 389             Target::Field | Target::Arm | Target::MacroDef => {
 390                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "naked");
 391                 true
 392             }
 393             _ => {
 394                 self.tcx.sess.emit_err(errors::AttrShouldBeAppliedToFn {
 395                     attr_span: attr.span,
 396                     defn_span: span,
 397                 });
 398                 false
 399             }
 400         }
 401     }
 402
 403     /// Checks if `#[cmse_nonsecure_entry]` is applied to a function definition.
 404     fn check_cmse_nonsecure_entry(&self, attr: &Attribute, span: Span, target: Target) -> bool {
 405         match target {
 406             Target::Fn
 407             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
 408             _ => {
 409                 self.tcx.sess.emit_err(errors::AttrShouldBeAppliedToFn {
 410                     attr_span: attr.span,
 411                     defn_span: span,
 412                 });
 413                 false
 414             }
 415         }
 416     }
 417
 418     /// Debugging aid for `object_lifetime_default` query.
 419     fn check_object_lifetime_default(&self, hir_id: HirId) {
 420         let tcx = self.tcx;
 421         if let Some(generics) = tcx.hir().get_generics(tcx.hir().local_def_id(hir_id)) {
 422             for p in generics.params {
 423                 let hir::GenericParamKind::Type { .. } = p.kind else { continue };
 424                 let param_id = tcx.hir().local_def_id(p.hir_id);
 425                 let default = tcx.object_lifetime_default(param_id);
 426                 let repr = match default {
 427                     ObjectLifetimeDefault::Empty => "BaseDefault".to_owned(),
 428                     ObjectLifetimeDefault::Static => "'static".to_owned(),
 429                     ObjectLifetimeDefault::Param(def_id) => tcx.item_name(def_id).to_string(),
 430                     ObjectLifetimeDefault::Ambiguous => "Ambiguous".to_owned(),
 431                 };
 432                 tcx.sess.span_err(p.span, &repr);
 433             }
 434         }
 435     }
 436
 437     /// Checks if `#[collapse_debuginfo]` is applied to a macro.
 438     fn check_collapse_debuginfo(&self, attr: &Attribute, span: Span, target: Target) -> bool {
 439         match target {
 440             Target::MacroDef => true,
 441             _ => {
 442                 self.tcx
 443                     .sess
 444                     .emit_err(errors::CollapseDebuginfo { attr_span: attr.span, defn_span: span });
 445                 false
 446             }
 447         }
 448     }
 449
 450     /// Checks if a `#[track_caller]` is applied to a non-naked function. Returns `true` if valid.
 451     fn check_track_caller(
 452         &self,
 453         hir_id: HirId,
 454         attr_span: Span,
 455         attrs: &[Attribute],
 456         span: Span,
 457         target: Target,
 458     ) -> bool {
 459         match target {
 460             _ if attrs.iter().any(|attr| attr.has_name(sym::naked)) => {
 461                 self.tcx.sess.emit_err(errors::NakedTrackedCaller { attr_span });
 462                 false
 463             }
 464             Target::Fn | Target::Method(..) | Target::ForeignFn | Target::Closure => true,
 465             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
 466             // `#[track_caller]` attribute with just a lint, because we previously
 467             // erroneously allowed it and some crates used it accidentally, to to be compatible
 468             // with crates depending on them, we can't throw an error here.
 469             Target::Field | Target::Arm | Target::MacroDef => {
 470                 for attr in attrs {
 471                     self.inline_attr_str_error_with_macro_def(hir_id, attr, "track_caller");
 472                 }
 473                 true
 474             }
 475             _ => {
 476                 self.tcx
 477                     .sess
 478                     .emit_err(errors::TrackedCallerWrongLocation { attr_span, defn_span: span });
 479                 false
 480             }
 481         }
 482     }
 483
 484     /// Checks if the `#[non_exhaustive]` attribute on an `item` is valid. Returns `true` if valid.
 485     fn check_non_exhaustive(
 486         &self,
 487         hir_id: HirId,
 488         attr: &Attribute,
 489         span: Span,
 490         target: Target,
 491     ) -> bool {
 492         match target {
 493             Target::Struct | Target::Enum | Target::Variant => true,
 494             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
 495             // `#[non_exhaustive]` attribute with just a lint, because we previously
 496             // erroneously allowed it and some crates used it accidentally, to to be compatible
 497             // with crates depending on them, we can't throw an error here.
 498             Target::Field | Target::Arm | Target::MacroDef => {
 499                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "non_exhaustive");
 500                 true
 501             }
 502             _ => {
 503                 self.tcx.sess.emit_err(errors::NonExhaustiveWrongLocation {
 504                     attr_span: attr.span,
 505                     defn_span: span,
 506                 });
 507                 false
 508             }
 509         }
 510     }
 511
 512     /// Checks if the `#[marker]` attribute on an `item` is valid. Returns `true` if valid.
 513     fn check_marker(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) -> bool {
 514         match target {
 515             Target::Trait => true,
 516             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
 517             // `#[marker]` attribute with just a lint, because we previously
 518             // erroneously allowed it and some crates used it accidentally, to to be compatible
 519             // with crates depending on them, we can't throw an error here.
 520             Target::Field | Target::Arm | Target::MacroDef => {
 521                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "marker");
 522                 true
 523             }
 524             _ => {
 525                 self.tcx.sess.emit_err(errors::AttrShouldBeAppliedToTrait {
 526                     attr_span: attr.span,
 527                     defn_span: span,
 528                 });
 529                 false
 530             }
 531         }
 532     }
 533
 534     /// Checks if the `#[rustc_must_implement_one_of]` attribute on a `target` is valid. Returns `true` if valid.
 535     fn check_rustc_must_implement_one_of(
 536         &self,
 537         attr: &Attribute,
 538         span: Span,
 539         target: Target,
 540     ) -> bool {
 541         match target {
 542             Target::Trait => true,
 543             _ => {
 544                 self.tcx.sess.emit_err(errors::AttrShouldBeAppliedToTrait {
 545                     attr_span: attr.span,
 546                     defn_span: span,
 547                 });
 548                 false
 549             }
 550         }
 551     }
 552
 553     /// Checks if the `#[target_feature]` attribute on `item` is valid. Returns `true` if valid.
 554     fn check_target_feature(
 555         &self,
 556         hir_id: HirId,
 557         attr: &Attribute,
 558         span: Span,
 559         target: Target,
 560     ) -> bool {
 561         match target {
 562             Target::Fn
 563             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
 564             // FIXME: #[target_feature] was previously erroneously allowed on statements and some
 565             // crates used this, so only emit a warning.
 566             Target::Statement => {
 567                 self.tcx.emit_spanned_lint(
 568                     UNUSED_ATTRIBUTES,
 569                     hir_id,
 570                     attr.span,
 571                     errors::TargetFeatureOnStatement,
 572                 );
 573                 true
 574             }
 575             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
 576             // `#[target_feature]` attribute with just a lint, because we previously
 577             // erroneously allowed it and some crates used it accidentally, to to be compatible
 578             // with crates depending on them, we can't throw an error here.
 579             Target::Field | Target::Arm | Target::MacroDef => {
 580                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "target_feature");
 581                 true
 582             }
 583             _ => {
 584                 self.tcx.sess.emit_err(errors::AttrShouldBeAppliedToFn {
 585                     attr_span: attr.span,
 586                     defn_span: span,
 587                 });
 588                 false
 589             }
 590         }
 591     }
 592
 593     /// Checks if the `#[thread_local]` attribute on `item` is valid. Returns `true` if valid.
 594     fn check_thread_local(&self, attr: &Attribute, span: Span, target: Target) -> bool {
 595         match target {
 596             Target::ForeignStatic | Target::Static => true,
 597             _ => {
 598                 self.tcx.sess.emit_err(errors::AttrShouldBeAppliedToStatic {
 599                     attr_span: attr.span,
 600                     defn_span: span,
 601                 });
 602                 false
 603             }
 604         }
 605     }
 606
 607     fn doc_attr_str_error(&self, meta: &NestedMetaItem, attr_name: &str) {
 608         self.tcx.sess.emit_err(errors::DocExpectStr { attr_span: meta.span(), attr_name });
 609     }
 610
 611     fn check_doc_alias_value(
 612         &self,
 613         meta: &NestedMetaItem,
 614         doc_alias: Symbol,
 615         hir_id: HirId,
 616         target: Target,
 617         is_list: bool,
 618         aliases: &mut FxHashMap<String, Span>,
 619     ) -> bool {
 620         let tcx = self.tcx;
 621         let span = meta.name_value_literal_span().unwrap_or_else(|| meta.span());
 622         let attr_str =
 623             &format!("`#[doc(alias{})]`", if is_list { "(\"...\")" } else { " = \"...\"" });
 624         if doc_alias == kw::Empty {
 625             tcx.sess.emit_err(errors::DocAliasEmpty { span, attr_str });
 626             return false;
 627         }
 628
 629         let doc_alias_str = doc_alias.as_str();
 630         if let Some(c) = doc_alias_str
 631             .chars()
 632             .find(|&c| c == '"' || c == '\'' || (c.is_whitespace() && c != ' '))
 633         {
 634             tcx.sess.emit_err(errors::DocAliasBadChar { span, attr_str, char_: c });
 635             return false;
 636         }
 637         if doc_alias_str.starts_with(' ') || doc_alias_str.ends_with(' ') {
 638             tcx.sess.emit_err(errors::DocAliasStartEnd { span, attr_str });
 639             return false;
 640         }
 641
 642         let span = meta.span();
 643         if let Some(location) = match target {
 644             Target::AssocTy => {
 645                 let parent_def_id = self.tcx.hir().get_parent_item(hir_id).def_id;
 646                 let containing_item = self.tcx.hir().expect_item(parent_def_id);
 647                 if Target::from_item(containing_item) == Target::Impl {
 648                     Some("type alias in implementation block")
 649                 } else {
 650                     None
 651                 }
 652             }
 653             Target::AssocConst => {
 654                 let parent_def_id = self.tcx.hir().get_parent_item(hir_id).def_id;
 655                 let containing_item = self.tcx.hir().expect_item(parent_def_id);
 656                 // We can't link to trait impl's consts.
 657                 let err = "associated constant in trait implementation block";
 658                 match containing_item.kind {
 659                     ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) => Some(err),
 660                     _ => None,
 661                 }
 662             }
 663             // we check the validity of params elsewhere
 664             Target::Param => return false,
 665             Target::Expression
 666             | Target::Statement
 667             | Target::Arm
 668             | Target::ForeignMod
 669             | Target::Closure
 670             | Target::Impl => Some(target.name()),
 671             Target::ExternCrate
 672             | Target::Use
 673             | Target::Static
 674             | Target::Const
 675             | Target::Fn
 676             | Target::Mod
 677             | Target::GlobalAsm
 678             | Target::TyAlias
 679             | Target::OpaqueTy
 680             | Target::ImplTraitPlaceholder
 681             | Target::Enum
 682             | Target::Variant
 683             | Target::Struct
 684             | Target::Field
 685             | Target::Union
 686             | Target::Trait
 687             | Target::TraitAlias
 688             | Target::Method(..)
 689             | Target::ForeignFn
 690             | Target::ForeignStatic
 691             | Target::ForeignTy
 692             | Target::GenericParam(..)
 693             | Target::MacroDef
 694             | Target::PatField
 695             | Target::ExprField => None,
 696         } {
 697             tcx.sess.emit_err(errors::DocAliasBadLocation { span, attr_str, location });
 698             return false;
 699         }
 700         let item_name = self.tcx.hir().name(hir_id);
 701         if item_name == doc_alias {
 702             tcx.sess.emit_err(errors::DocAliasNotAnAlias { span, attr_str });
 703             return false;
 704         }
 705         if let Err(entry) = aliases.try_insert(doc_alias_str.to_owned(), span) {
 706             self.tcx.emit_spanned_lint(
 707                 UNUSED_ATTRIBUTES,
 708                 hir_id,
 709                 span,
 710                 errors::DocAliasDuplicated { first_defn: *entry.entry.get() },
 711             );
 712         }
 713         true
 714     }
 715
 716     fn check_doc_alias(
 717         &self,
 718         meta: &NestedMetaItem,
 719         hir_id: HirId,
 720         target: Target,
 721         aliases: &mut FxHashMap<String, Span>,
 722     ) -> bool {
 723         if let Some(values) = meta.meta_item_list() {
 724             let mut errors = 0;
 725             for v in values {
 726                 match v.literal() {
 727                     Some(l) => match l.kind {
 728                         LitKind::Str(s, _) => {
 729                             if !self.check_doc_alias_value(v, s, hir_id, target, true, aliases) {
 730                                 errors += 1;
 731                             }
 732                         }
 733                         _ => {
 734                             self.tcx
 735                                 .sess
 736                                 .emit_err(errors::DocAliasNotStringLiteral { span: v.span() });
 737                             errors += 1;
 738                         }
 739                     },
 740                     None => {
 741                         self.tcx.sess.emit_err(errors::DocAliasNotStringLiteral { span: v.span() });
 742                         errors += 1;
 743                     }
 744                 }
 745             }
 746             errors == 0
 747         } else if let Some(doc_alias) = meta.value_str() {
 748             self.check_doc_alias_value(meta, doc_alias, hir_id, target, false, aliases)
 749         } else {
 750             self.tcx.sess.emit_err(errors::DocAliasMalformed { span: meta.span() });
 751             false
 752         }
 753     }
 754
 755     fn check_doc_keyword(&self, meta: &NestedMetaItem, hir_id: HirId) -> bool {
 756         let doc_keyword = meta.value_str().unwrap_or(kw::Empty);
 757         if doc_keyword == kw::Empty {
 758             self.doc_attr_str_error(meta, "keyword");
 759             return false;
 760         }
 761         match self.tcx.hir().find(hir_id).and_then(|node| match node {
 762             hir::Node::Item(item) => Some(&item.kind),
 763             _ => None,
 764         }) {
 765             Some(ItemKind::Mod(ref module)) => {
 766                 if !module.item_ids.is_empty() {
 767                     self.tcx.sess.emit_err(errors::DocKeywordEmptyMod { span: meta.span() });
 768                     return false;
 769                 }
 770             }
 771             _ => {
 772                 self.tcx.sess.emit_err(errors::DocKeywordNotMod { span: meta.span() });
 773                 return false;
 774             }
 775         }
 776         if !rustc_lexer::is_ident(doc_keyword.as_str()) {
 777             self.tcx.sess.emit_err(errors::DocKeywordInvalidIdent {
 778                 span: meta.name_value_literal_span().unwrap_or_else(|| meta.span()),
 779                 doc_keyword,
 780             });
 781             return false;
 782         }
 783         true
 784     }
 785
 786     fn check_doc_fake_variadic(&self, meta: &NestedMetaItem, hir_id: HirId) -> bool {
 787         match self.tcx.hir().find(hir_id).and_then(|node| match node {
 788             hir::Node::Item(item) => Some(&item.kind),
 789             _ => None,
 790         }) {
 791             Some(ItemKind::Impl(ref i)) => {
 792                 let is_valid = matches!(&i.self_ty.kind, hir::TyKind::Tup([_]))
 793                     || if let hir::TyKind::BareFn(bare_fn_ty) = &i.self_ty.kind {
 794                         bare_fn_ty.decl.inputs.len() == 1
 795                     } else {
 796                         false
 797                     };
 798                 if !is_valid {
 799                     self.tcx.sess.emit_err(errors::DocFakeVariadicNotValid { span: meta.span() });
 800                     return false;
 801                 }
 802             }
 803             _ => {
 804                 self.tcx.sess.emit_err(errors::DocKeywordOnlyImpl { span: meta.span() });
 805                 return false;
 806             }
 807         }
 808         true
 809     }
 810
 811     /// Checks `#[doc(inline)]`/`#[doc(no_inline)]` attributes. Returns `true` if valid.
 812     ///
 813     /// A doc inlining attribute is invalid if it is applied to a non-`use` item, or
 814     /// if there are conflicting attributes for one item.
 815     ///
 816     /// `specified_inline` is used to keep track of whether we have
 817     /// already seen an inlining attribute for this item.
 818     /// If so, `specified_inline` holds the value and the span of
 819     /// the first `inline`/`no_inline` attribute.
 820     fn check_doc_inline(
 821         &self,
 822         attr: &Attribute,
 823         meta: &NestedMetaItem,
 824         hir_id: HirId,
 825         target: Target,
 826         specified_inline: &mut Option<(bool, Span)>,
 827     ) -> bool {
 828         if target == Target::Use || target == Target::ExternCrate {
 829             let do_inline = meta.name_or_empty() == sym::inline;
 830             if let Some((prev_inline, prev_span)) = *specified_inline {
 831                 if do_inline != prev_inline {
 832                     let mut spans = MultiSpan::from_spans(vec![prev_span, meta.span()]);
 833                     spans.push_span_label(prev_span, fluent::passes::doc_inline_conflict_first);
 834                     spans.push_span_label(meta.span(), fluent::passes::doc_inline_conflict_second);
 835                     self.tcx.sess.emit_err(errors::DocKeywordConflict { spans });
 836                     return false;
 837                 }
 838                 true
 839             } else {
 840                 *specified_inline = Some((do_inline, meta.span()));
 841                 true
 842             }
 843         } else {
 844             self.tcx.emit_spanned_lint(
 845                 INVALID_DOC_ATTRIBUTES,
 846                 hir_id,
 847                 meta.span(),
 848                 errors::DocInlineOnlyUse {
 849                     attr_span: meta.span(),
 850                     item_span: (attr.style == AttrStyle::Outer)
 851                         .then(|| self.tcx.hir().span(hir_id)),
 852                 },
 853             );
 854             false
 855         }
 856     }
 857
 858     /// Checks that an attribute is *not* used at the crate level. Returns `true` if valid.
 859     fn check_attr_not_crate_level(
 860         &self,
 861         meta: &NestedMetaItem,
 862         hir_id: HirId,
 863         attr_name: &str,
 864     ) -> bool {
 865         if CRATE_HIR_ID == hir_id {
 866             self.tcx.sess.emit_err(errors::DocAttrNotCrateLevel { span: meta.span(), attr_name });
 867             return false;
 868         }
 869         true
 870     }
 871
 872     /// Checks that an attribute is used at the crate level. Returns `true` if valid.
 873     fn check_attr_crate_level(
 874         &self,
 875         attr: &Attribute,
 876         meta: &NestedMetaItem,
 877         hir_id: HirId,
 878     ) -> bool {
 879         if hir_id != CRATE_HIR_ID {
 880             self.tcx.struct_span_lint_hir(INVALID_DOC_ATTRIBUTES, hir_id, meta.span(), |lint| {
 881                 let mut err = lint.build(fluent::passes::attr_crate_level);
 882                 if attr.style == AttrStyle::Outer
 883                     && self.tcx.hir().get_parent_item(hir_id) == CRATE_OWNER_ID
 884                 {
 885                     if let Ok(mut src) = self.tcx.sess.source_map().span_to_snippet(attr.span) {
 886                         src.insert(1, '!');
 887                         err.span_suggestion_verbose(
 888                             attr.span,
 889                             fluent::passes::suggestion,
 890                             src,
 891                             Applicability::MaybeIncorrect,
 892                         );
 893                     } else {
 894                         err.span_help(attr.span, fluent::passes::help);
 895                     }
 896                 }
 897                 err.note(fluent::passes::note).emit();
 898             });
 899             return false;
 900         }
 901         true
 902     }
 903
 904     /// Checks that `doc(test(...))` attribute contains only valid attributes. Returns `true` if
 905     /// valid.
 906     fn check_test_attr(&self, meta: &NestedMetaItem, hir_id: HirId) -> bool {
 907         let mut is_valid = true;
 908         if let Some(metas) = meta.meta_item_list() {
 909             for i_meta in metas {
 910                 match i_meta.name_or_empty() {
 911                     sym::attr | sym::no_crate_inject => {}
 912                     _ => {
 913                         self.tcx.emit_spanned_lint(
 914                             INVALID_DOC_ATTRIBUTES,
 915                             hir_id,
 916                             i_meta.span(),
 917                             errors::DocTestUnknown {
 918                                 path: rustc_ast_pretty::pprust::path_to_string(
 919                                     &i_meta.meta_item().unwrap().path,
 920                                 ),
 921                             },
 922                         );
 923                         is_valid = false;
 924                     }
 925                 }
 926             }
 927         } else {
 928             self.tcx.emit_spanned_lint(
 929                 INVALID_DOC_ATTRIBUTES,
 930                 hir_id,
 931                 meta.span(),
 932                 errors::DocTestTakesList,
 933             );
 934             is_valid = false;
 935         }
 936         is_valid
 937     }
 938
 939     /// Runs various checks on `#[doc]` attributes. Returns `true` if valid.
 940     ///
 941     /// `specified_inline` should be initialized to `None` and kept for the scope
 942     /// of one item. Read the documentation of [`check_doc_inline`] for more information.
 943     ///
 944     /// [`check_doc_inline`]: Self::check_doc_inline
 945     fn check_doc_attrs(
 946         &self,
 947         attr: &Attribute,
 948         hir_id: HirId,
 949         target: Target,
 950         specified_inline: &mut Option<(bool, Span)>,
 951         aliases: &mut FxHashMap<String, Span>,
 952     ) -> bool {
 953         let mut is_valid = true;
 954
 955         if let Some(mi) = attr.meta() && let Some(list) = mi.meta_item_list() {
 956             for meta in list {
 957                 if let Some(i_meta) = meta.meta_item() {
 958                     match i_meta.name_or_empty() {
 959                         sym::alias
 960                             if !self.check_attr_not_crate_level(meta, hir_id, "alias")
 961                                 || !self.check_doc_alias(meta, hir_id, target, aliases) =>
 962                         {
 963                             is_valid = false
 964                         }
 965
 966                         sym::keyword
 967                             if !self.check_attr_not_crate_level(meta, hir_id, "keyword")
 968                                 || !self.check_doc_keyword(meta, hir_id) =>
 969                         {
 970                             is_valid = false
 971                         }
 972
 973                         sym::fake_variadic
 974                             if !self.check_attr_not_crate_level(meta, hir_id, "fake_variadic")
 975                                 || !self.check_doc_fake_variadic(meta, hir_id) =>
 976                         {
 977                             is_valid = false
 978                         }
 979
 980                         sym::html_favicon_url
 981                         | sym::html_logo_url
 982                         | sym::html_playground_url
 983                         | sym::issue_tracker_base_url
 984                         | sym::html_root_url
 985                         | sym::html_no_source
 986                         | sym::test
 987                             if !self.check_attr_crate_level(attr, meta, hir_id) =>
 988                         {
 989                             is_valid = false;
 990                         }
 991
 992                         sym::inline | sym::no_inline
 993                             if !self.check_doc_inline(
 994                                 attr,
 995                                 meta,
 996                                 hir_id,
 997                                 target,
 998                                 specified_inline,
 999                             ) =>
1000                         {
1001                             is_valid = false;
1002                         }
1003
1004                         // no_default_passes: deprecated
1005                         // passes: deprecated
1006                         // plugins: removed, but rustdoc warns about it itself
1007                         sym::alias
1008                         | sym::cfg
1009                         | sym::cfg_hide
1010                         | sym::hidden
1011                         | sym::html_favicon_url
1012                         | sym::html_logo_url
1013                         | sym::html_no_source
1014                         | sym::html_playground_url
1015                         | sym::html_root_url
1016                         | sym::inline
1017                         | sym::issue_tracker_base_url
1018                         | sym::keyword
1019                         | sym::masked
1020                         | sym::no_default_passes
1021                         | sym::no_inline
1022                         | sym::notable_trait
1023                         | sym::passes
1024                         | sym::plugins
1025                         | sym::fake_variadic => {}
1026
1027                         sym::test => {
1028                             if !self.check_test_attr(meta, hir_id) {
1029                                 is_valid = false;
1030                             }
1031                         }
1032
1033                         sym::primitive => {
1034                             if !self.tcx.features().rustdoc_internals {
1035                                 self.tcx.emit_spanned_lint(
1036                                     INVALID_DOC_ATTRIBUTES,
1037                                     hir_id,
1038                                     i_meta.span,
1039                                     errors::DocPrimitive,
1040                                 );
1041                             }
1042                         }
1043
1044                         _ => {
1045                             let path = rustc_ast_pretty::pprust::path_to_string(&i_meta.path);
1046                             if i_meta.has_name(sym::spotlight) {
1047                                 self.tcx.emit_spanned_lint(
1048                                     INVALID_DOC_ATTRIBUTES,
1049                                     hir_id,
1050                                     i_meta.span,
1051                                     errors::DocTestUnknownSpotlight {
1052                                         path,
1053                                         span: i_meta.span
1054                                     }
1055                                 );
1056                             } else if i_meta.has_name(sym::include) &&
1057                                     let Some(value) = i_meta.value_str() {
1058                                 let applicability = if list.len() == 1 {
1059                                     Applicability::MachineApplicable
1060                                 } else {
1061                                     Applicability::MaybeIncorrect
1062                                 };
1063                                 // If there are multiple attributes, the suggestion would suggest
1064                                 // deleting all of them, which is incorrect.
1065                                 self.tcx.emit_spanned_lint(
1066                                     INVALID_DOC_ATTRIBUTES,
1067                                     hir_id,
1068                                     i_meta.span,
1069                                     errors::DocTestUnknownInclude {
1070                                         path,
1071                                         value: value.to_string(),
1072                                         inner: (attr.style == AttrStyle::Inner)
1073                                             .then_some("!")
1074                                             .unwrap_or(""),
1075                                         sugg: (attr.meta().unwrap().span, applicability),
1076                                     }
1077                                 );
1078                             } else {
1079                                 self.tcx.emit_spanned_lint(
1080                                     INVALID_DOC_ATTRIBUTES,
1081                                     hir_id,
1082                                     i_meta.span,
1083                                     errors::DocTestUnknownAny { path }
1084                                 );
1085                             }
1086                             is_valid = false;
1087                         }
1088                     }
1089                 } else {
1090                     self.tcx.emit_spanned_lint(
1091                         INVALID_DOC_ATTRIBUTES,
1092                         hir_id,
1093                         meta.span(),
1094                         errors::DocInvalid,
1095                     );
1096                     is_valid = false;
1097                 }
1098             }
1099         }
1100
1101         is_valid
1102     }
1103
1104     /// Warns against some misuses of `#[pass_by_value]`
1105     fn check_pass_by_value(&self, attr: &Attribute, span: Span, target: Target) -> bool {
1106         match target {
1107             Target::Struct | Target::Enum | Target::TyAlias => true,
1108             _ => {
1109                 self.tcx.sess.emit_err(errors::PassByValue { attr_span: attr.span, span });
1110                 false
1111             }
1112         }
1113     }
1114
1115     fn check_allow_incoherent_impl(&self, attr: &Attribute, span: Span, target: Target) -> bool {
1116         match target {
1117             Target::Method(MethodKind::Inherent) => true,
1118             _ => {
1119                 self.tcx.sess.emit_err(errors::AllowIncoherentImpl { attr_span: attr.span, span });
1120                 false
1121             }
1122         }
1123     }
1124
1125     fn check_has_incoherent_inherent_impls(
1126         &self,
1127         attr: &Attribute,
1128         span: Span,
1129         target: Target,
1130     ) -> bool {
1131         match target {
1132             Target::Trait | Target::Struct | Target::Enum | Target::Union | Target::ForeignTy => {
1133                 true
1134             }
1135             _ => {
1136                 self.tcx
1137                     .sess
1138                     .emit_err(errors::HasIncoherentInherentImpl { attr_span: attr.span, span });
1139                 false
1140             }
1141         }
1142     }
1143
1144     /// Warns against some misuses of `#[must_use]`
1145     fn check_must_use(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) -> bool {
1146         let node = self.tcx.hir().get(hir_id);
1147         if let Some(kind) = node.fn_kind() && let rustc_hir::IsAsync::Async = kind.asyncness() {
1148             self.tcx.emit_spanned_lint(
1149                 UNUSED_ATTRIBUTES,
1150                 hir_id,
1151                 attr.span,
1152                 errors::MustUseAsync { span }
1153             );
1154         }
1155
1156         if !matches!(
1157             target,
1158             Target::Fn
1159                 | Target::Enum
1160                 | Target::Struct
1161                 | Target::Union
1162                 | Target::Method(_)
1163                 | Target::ForeignFn
1164                 // `impl Trait` in return position can trip
1165                 // `unused_must_use` if `Trait` is marked as
1166                 // `#[must_use]`
1167                 | Target::Trait
1168         ) {
1169             let article = match target {
1170                 Target::ExternCrate
1171                 | Target::OpaqueTy
1172                 | Target::Enum
1173                 | Target::Impl
1174                 | Target::Expression
1175                 | Target::Arm
1176                 | Target::AssocConst
1177                 | Target::AssocTy => "an",
1178                 _ => "a",
1179             };
1180
1181             self.tcx.emit_spanned_lint(
1182                 UNUSED_ATTRIBUTES,
1183                 hir_id,
1184                 attr.span,
1185                 errors::MustUseNoEffect { article, target },
1186             );
1187         }
1188
1189         // For now, its always valid
1190         true
1191     }
1192
1193     /// Checks if `#[must_not_suspend]` is applied to a function. Returns `true` if valid.
1194     fn check_must_not_suspend(&self, attr: &Attribute, span: Span, target: Target) -> bool {
1195         match target {
1196             Target::Struct | Target::Enum | Target::Union | Target::Trait => true,
1197             _ => {
1198                 self.tcx.sess.emit_err(errors::MustNotSuspend { attr_span: attr.span, span });
1199                 false
1200             }
1201         }
1202     }
1203
1204     /// Checks if `#[cold]` is applied to a non-function. Returns `true` if valid.
1205     fn check_cold(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) {
1206         match target {
1207             Target::Fn | Target::Method(..) | Target::ForeignFn | Target::Closure => {}
1208             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
1209             // `#[cold]` attribute with just a lint, because we previously
1210             // erroneously allowed it and some crates used it accidentally, to to be compatible
1211             // with crates depending on them, we can't throw an error here.
1212             Target::Field | Target::Arm | Target::MacroDef => {
1213                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "cold");
1214             }
1215             _ => {
1216                 // FIXME: #[cold] was previously allowed on non-functions and some crates used
1217                 // this, so only emit a warning.
1218                 self.tcx.emit_spanned_lint(
1219                     UNUSED_ATTRIBUTES,
1220                     hir_id,
1221                     attr.span,
1222                     errors::Cold { span },
1223                 );
1224             }
1225         }
1226     }
1227
1228     /// Checks if `#[link]` is applied to an item other than a foreign module.
1229     fn check_link(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) {
1230         if target == Target::ForeignMod
1231             && let hir::Node::Item(item) = self.tcx.hir().get(hir_id)
1232             && let Item { kind: ItemKind::ForeignMod { abi, .. }, .. } = item
1233             && !matches!(abi, Abi::Rust | Abi::RustIntrinsic | Abi::PlatformIntrinsic)
1234         {
1235             return;
1236         }
1237
1238         self.tcx.emit_spanned_lint(
1239             UNUSED_ATTRIBUTES,
1240             hir_id,
1241             attr.span,
1242             errors::Link { span: (target != Target::ForeignMod).then_some(span) },
1243         );
1244     }
1245
1246     /// Checks if `#[link_name]` is applied to an item other than a foreign function or static.
1247     fn check_link_name(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) {
1248         match target {
1249             Target::ForeignFn | Target::ForeignStatic => {}
1250             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
1251             // `#[link_name]` attribute with just a lint, because we previously
1252             // erroneously allowed it and some crates used it accidentally, to to be compatible
1253             // with crates depending on them, we can't throw an error here.
1254             Target::Field | Target::Arm | Target::MacroDef => {
1255                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "link_name");
1256             }
1257             _ => {
1258                 // FIXME: #[cold] was previously allowed on non-functions/statics and some crates
1259                 // used this, so only emit a warning.
1260                 let attr_span = matches!(target, Target::ForeignMod).then_some(attr.span);
1261                 if let Some(s) = attr.value_str() {
1262                     self.tcx.emit_spanned_lint(
1263                         UNUSED_ATTRIBUTES,
1264                         hir_id,
1265                         attr.span,
1266                         errors::LinkName { span, attr_span, value: s.as_str() },
1267                     );
1268                 } else {
1269                     self.tcx.emit_spanned_lint(
1270                         UNUSED_ATTRIBUTES,
1271                         hir_id,
1272                         attr.span,
1273                         errors::LinkName { span, attr_span, value: "..." },
1274                     );
1275                 };
1276             }
1277         }
1278     }
1279
1280     /// Checks if `#[no_link]` is applied to an `extern crate`. Returns `true` if valid.
1281     fn check_no_link(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) -> bool {
1282         match target {
1283             Target::ExternCrate => true,
1284             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
1285             // `#[no_link]` attribute with just a lint, because we previously
1286             // erroneously allowed it and some crates used it accidentally, to to be compatible
1287             // with crates depending on them, we can't throw an error here.
1288             Target::Field | Target::Arm | Target::MacroDef => {
1289                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "no_link");
1290                 true
1291             }
1292             _ => {
1293                 self.tcx.sess.emit_err(errors::NoLink { attr_span: attr.span, span });
1294                 false
1295             }
1296         }
1297     }
1298
1299     fn is_impl_item(&self, hir_id: HirId) -> bool {
1300         matches!(self.tcx.hir().get(hir_id), hir::Node::ImplItem(..))
1301     }
1302
1303     /// Checks if `#[export_name]` is applied to a function or static. Returns `true` if valid.
1304     fn check_export_name(
1305         &self,
1306         hir_id: HirId,
1307         attr: &Attribute,
1308         span: Span,
1309         target: Target,
1310     ) -> bool {
1311         match target {
1312             Target::Static | Target::Fn => true,
1313             Target::Method(..) if self.is_impl_item(hir_id) => true,
1314             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
1315             // `#[export_name]` attribute with just a lint, because we previously
1316             // erroneously allowed it and some crates used it accidentally, to to be compatible
1317             // with crates depending on them, we can't throw an error here.
1318             Target::Field | Target::Arm | Target::MacroDef => {
1319                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "export_name");
1320                 true
1321             }
1322             _ => {
1323                 self.tcx.sess.emit_err(errors::ExportName { attr_span: attr.span, span });
1324                 false
1325             }
1326         }
1327     }
1328
1329     fn check_rustc_layout_scalar_valid_range(
1330         &self,
1331         attr: &Attribute,
1332         span: Span,
1333         target: Target,
1334     ) -> bool {
1335         if target != Target::Struct {
1336             self.tcx.sess.emit_err(errors::RustcLayoutScalarValidRangeNotStruct {
1337                 attr_span: attr.span,
1338                 span,
1339             });
1340             return false;
1341         }
1342
1343         let Some(list) = attr.meta_item_list() else {
1344             return false;
1345         };
1346
1347         if matches!(&list[..], &[NestedMetaItem::Literal(Lit { kind: LitKind::Int(..), .. })]) {
1348             true
1349         } else {
1350             self.tcx.sess.emit_err(errors::RustcLayoutScalarValidRangeArg { attr_span: attr.span });
1351             false
1352         }
1353     }
1354
1355     /// Checks if `#[rustc_legacy_const_generics]` is applied to a function and has a valid argument.
1356     fn check_rustc_legacy_const_generics(
1357         &self,
1358         attr: &Attribute,
1359         span: Span,
1360         target: Target,
1361         item: Option<ItemLike<'_>>,
1362     ) -> bool {
1363         let is_function = matches!(target, Target::Fn);
1364         if !is_function {
1365             self.tcx.sess.emit_err(errors::AttrShouldBeAppliedToFn {
1366                 attr_span: attr.span,
1367                 defn_span: span,
1368             });
1369             return false;
1370         }
1371
1372         let Some(list) = attr.meta_item_list() else {
1373             // The attribute form is validated on AST.
1374             return false;
1375         };
1376
1377         let Some(ItemLike::Item(Item {
1378             kind: ItemKind::Fn(FnSig { decl, .. }, generics, _),
1379             ..
1380         }))  = item else {
1381             bug!("should be a function item");
1382         };
1383
1384         for param in generics.params {
1385             match param.kind {
1386                 hir::GenericParamKind::Const { .. } => {}
1387                 _ => {
1388                     self.tcx.sess.emit_err(errors::RustcLegacyConstGenericsOnly {
1389                         attr_span: attr.span,
1390                         param_span: param.span,
1391                     });
1392                     return false;
1393                 }
1394             }
1395         }
1396
1397         if list.len() != generics.params.len() {
1398             self.tcx.sess.emit_err(errors::RustcLegacyConstGenericsIndex {
1399                 attr_span: attr.span,
1400                 generics_span: generics.span,
1401             });
1402             return false;
1403         }
1404
1405         let arg_count = decl.inputs.len() as u128 + generics.params.len() as u128;
1406         let mut invalid_args = vec![];
1407         for meta in list {
1408             if let Some(LitKind::Int(val, _)) = meta.literal().map(|lit| &lit.kind) {
1409                 if *val >= arg_count {
1410                     let span = meta.span();
1411                     self.tcx.sess.emit_err(errors::RustcLegacyConstGenericsIndexExceed {
1412                         span,
1413                         arg_count: arg_count as usize,
1414                     });
1415                     return false;
1416                 }
1417             } else {
1418                 invalid_args.push(meta.span());
1419             }
1420         }
1421
1422         if !invalid_args.is_empty() {
1423             self.tcx.sess.emit_err(errors::RustcLegacyConstGenericsIndexNegative { invalid_args });
1424             false
1425         } else {
1426             true
1427         }
1428     }
1429
1430     /// Helper function for checking that the provided attribute is only applied to a function or
1431     /// method.
1432     fn check_applied_to_fn_or_method(&self, attr: &Attribute, span: Span, target: Target) -> bool {
1433         let is_function = matches!(target, Target::Fn | Target::Method(..));
1434         if !is_function {
1435             self.tcx.sess.emit_err(errors::AttrShouldBeAppliedToFn {
1436                 attr_span: attr.span,
1437                 defn_span: span,
1438             });
1439             false
1440         } else {
1441             true
1442         }
1443     }
1444
1445     /// Checks that the `#[rustc_lint_query_instability]` attribute is only applied to a function
1446     /// or method.
1447     fn check_rustc_lint_query_instability(
1448         &self,
1449         attr: &Attribute,
1450         span: Span,
1451         target: Target,
1452     ) -> bool {
1453         self.check_applied_to_fn_or_method(attr, span, target)
1454     }
1455
1456     /// Checks that the `#[rustc_lint_diagnostics]` attribute is only applied to a function or
1457     /// method.
1458     fn check_rustc_lint_diagnostics(&self, attr: &Attribute, span: Span, target: Target) -> bool {
1459         self.check_applied_to_fn_or_method(attr, span, target)
1460     }
1461
1462     /// Checks that the `#[rustc_lint_opt_ty]` attribute is only applied to a struct.
1463     fn check_rustc_lint_opt_ty(&self, attr: &Attribute, span: Span, target: Target) -> bool {
1464         match target {
1465             Target::Struct => true,
1466             _ => {
1467                 self.tcx.sess.emit_err(errors::RustcLintOptTy { attr_span: attr.span, span });
1468                 false
1469             }
1470         }
1471     }
1472
1473     /// Checks that the `#[rustc_lint_opt_deny_field_access]` attribute is only applied to a field.
1474     fn check_rustc_lint_opt_deny_field_access(
1475         &self,
1476         attr: &Attribute,
1477         span: Span,
1478         target: Target,
1479     ) -> bool {
1480         match target {
1481             Target::Field => true,
1482             _ => {
1483                 self.tcx
1484                     .sess
1485                     .emit_err(errors::RustcLintOptDenyFieldAccess { attr_span: attr.span, span });
1486                 false
1487             }
1488         }
1489     }
1490
1491     /// Checks that the dep-graph debugging attributes are only present when the query-dep-graph
1492     /// option is passed to the compiler.
1493     fn check_rustc_dirty_clean(&self, attr: &Attribute) -> bool {
1494         if self.tcx.sess.opts.unstable_opts.query_dep_graph {
1495             true
1496         } else {
1497             self.tcx.sess.emit_err(errors::RustcDirtyClean { span: attr.span });
1498             false
1499         }
1500     }
1501
1502     /// Checks if `#[link_section]` is applied to a function or static.
1503     fn check_link_section(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) {
1504         match target {
1505             Target::Static | Target::Fn | Target::Method(..) => {}
1506             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
1507             // `#[link_section]` attribute with just a lint, because we previously
1508             // erroneously allowed it and some crates used it accidentally, to to be compatible
1509             // with crates depending on them, we can't throw an error here.
1510             Target::Field | Target::Arm | Target::MacroDef => {
1511                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "link_section");
1512             }
1513             _ => {
1514                 // FIXME: #[link_section] was previously allowed on non-functions/statics and some
1515                 // crates used this, so only emit a warning.
1516                 self.tcx.emit_spanned_lint(
1517                     UNUSED_ATTRIBUTES,
1518                     hir_id,
1519                     attr.span,
1520                     errors::LinkSection { span },
1521                 );
1522             }
1523         }
1524     }
1525
1526     /// Checks if `#[no_mangle]` is applied to a function or static.
1527     fn check_no_mangle(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) {
1528         match target {
1529             Target::Static | Target::Fn => {}
1530             Target::Method(..) if self.is_impl_item(hir_id) => {}
1531             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
1532             // `#[no_mangle]` attribute with just a lint, because we previously
1533             // erroneously allowed it and some crates used it accidentally, to to be compatible
1534             // with crates depending on them, we can't throw an error here.
1535             Target::Field | Target::Arm | Target::MacroDef => {
1536                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "no_mangle");
1537             }
1538             // FIXME: #[no_mangle] was previously allowed on non-functions/statics, this should be an error
1539             // The error should specify that the item that is wrong is specifically a *foreign* fn/static
1540             // otherwise the error seems odd
1541             Target::ForeignFn | Target::ForeignStatic => {
1542                 let foreign_item_kind = match target {
1543                     Target::ForeignFn => "function",
1544                     Target::ForeignStatic => "static",
1545                     _ => unreachable!(),
1546                 };
1547                 self.tcx.emit_spanned_lint(
1548                     UNUSED_ATTRIBUTES,
1549                     hir_id,
1550                     attr.span,
1551                     errors::NoMangleForeign { span, attr_span: attr.span, foreign_item_kind },
1552                 );
1553             }
1554             _ => {
1555                 // FIXME: #[no_mangle] was previously allowed on non-functions/statics and some
1556                 // crates used this, so only emit a warning.
1557                 self.tcx.emit_spanned_lint(
1558                     UNUSED_ATTRIBUTES,
1559                     hir_id,
1560                     attr.span,
1561                     errors::NoMangle { span },
1562                 );
1563             }
1564         }
1565     }
1566
1567     /// Checks if the `#[repr]` attributes on `item` are valid.
1568     fn check_repr(
1569         &self,
1570         attrs: &[Attribute],
1571         span: Span,
1572         target: Target,
1573         item: Option<ItemLike<'_>>,
1574         hir_id: HirId,
1575     ) {
1576         // Extract the names of all repr hints, e.g., [foo, bar, align] for:
1577         // ```
1578         // #[repr(foo)]
1579         // #[repr(bar, align(8))]
1580         // ```
1581         let hints: Vec<_> = attrs
1582             .iter()
1583             .filter(|attr| attr.has_name(sym::repr))
1584             .filter_map(|attr| attr.meta_item_list())
1585             .flatten()
1586             .collect();
1587
1588         let mut int_reprs = 0;
1589         let mut is_c = false;
1590         let mut is_simd = false;
1591         let mut is_transparent = false;
1592
1593         for hint in &hints {
1594             if !hint.is_meta_item() {
1595                 self.tcx.sess.emit_err(errors::ReprIdent { span: hint.span() });
1596                 continue;
1597             }
1598
1599             let (article, allowed_targets) = match hint.name_or_empty() {
1600                 sym::C => {
1601                     is_c = true;
1602                     match target {
1603                         Target::Struct | Target::Union | Target::Enum => continue,
1604                         _ => ("a", "struct, enum, or union"),
1605                     }
1606                 }
1607                 sym::align => {
1608                     if let (Target::Fn, false) = (target, self.tcx.features().fn_align) {
1609                         feature_err(
1610                             &self.tcx.sess.parse_sess,
1611                             sym::fn_align,
1612                             hint.span(),
1613                             "`repr(align)` attributes on functions are unstable",
1614                         )
1615                         .emit();
1616                     }
1617
1618                     match target {
1619                         Target::Struct | Target::Union | Target::Enum | Target::Fn => continue,
1620                         _ => ("a", "struct, enum, function, or union"),
1621                     }
1622                 }
1623                 sym::packed => {
1624                     if target != Target::Struct && target != Target::Union {
1625                         ("a", "struct or union")
1626                     } else {
1627                         continue;
1628                     }
1629                 }
1630                 sym::simd => {
1631                     is_simd = true;
1632                     if target != Target::Struct {
1633                         ("a", "struct")
1634                     } else {
1635                         continue;
1636                     }
1637                 }
1638                 sym::transparent => {
1639                     is_transparent = true;
1640                     match target {
1641                         Target::Struct | Target::Union | Target::Enum => continue,
1642                         _ => ("a", "struct, enum, or union"),
1643                     }
1644                 }
1645                 sym::i8
1646                 | sym::u8
1647                 | sym::i16
1648                 | sym::u16
1649                 | sym::i32
1650                 | sym::u32
1651                 | sym::i64
1652                 | sym::u64
1653                 | sym::i128
1654                 | sym::u128
1655                 | sym::isize
1656                 | sym::usize => {
1657                     int_reprs += 1;
1658                     if target != Target::Enum {
1659                         ("an", "enum")
1660                     } else {
1661                         continue;
1662                     }
1663                 }
1664                 _ => {
1665                     struct_span_err!(
1666                         self.tcx.sess,
1667                         hint.span(),
1668                         E0552,
1669                         "unrecognized representation hint"
1670                     )
1671                     .help("valid reprs are `C`, `align`, `packed`, `transparent`, `simd`, `i8`, `u8`, \
1672                           `i16`, `u16`, `i32`, `u32`, `i64`, `u64`, `i128`, `u128`, `isize`, `usize`")
1673                     .emit();
1674
1675                     continue;
1676                 }
1677             };
1678
1679             struct_span_err!(
1680                 self.tcx.sess,
1681                 hint.span(),
1682                 E0517,
1683                 "{}",
1684                 &format!("attribute should be applied to {article} {allowed_targets}")
1685             )
1686             .span_label(span, &format!("not {article} {allowed_targets}"))
1687             .emit();
1688         }
1689
1690         // Just point at all repr hints if there are any incompatibilities.
1691         // This is not ideal, but tracking precisely which ones are at fault is a huge hassle.
1692         let hint_spans = hints.iter().map(|hint| hint.span());
1693
1694         // Error on repr(transparent, <anything else>).
1695         if is_transparent && hints.len() > 1 {
1696             let hint_spans: Vec<_> = hint_spans.clone().collect();
1697             struct_span_err!(
1698                 self.tcx.sess,
1699                 hint_spans,
1700                 E0692,
1701                 "transparent {} cannot have other repr hints",
1702                 target
1703             )
1704             .emit();
1705         }
1706         // Warn on repr(u8, u16), repr(C, simd), and c-like-enum-repr(C, u8)
1707         if (int_reprs > 1)
1708             || (is_simd && is_c)
1709             || (int_reprs == 1
1710                 && is_c
1711                 && item.map_or(false, |item| {
1712                     if let ItemLike::Item(item) = item {
1713                         return is_c_like_enum(item);
1714                     }
1715                     return false;
1716                 }))
1717         {
1718             self.tcx.emit_spanned_lint(
1719                 CONFLICTING_REPR_HINTS,
1720                 hir_id,
1721                 hint_spans.collect::<Vec<Span>>(),
1722                 errors::ReprConflicting,
1723             );
1724         }
1725     }
1726
1727     fn check_used(&self, attrs: &[Attribute], target: Target) {
1728         let mut used_linker_span = None;
1729         let mut used_compiler_span = None;
1730         for attr in attrs.iter().filter(|attr| attr.has_name(sym::used)) {
1731             if target != Target::Static {
1732                 self.tcx.sess.emit_err(errors::UsedStatic { span: attr.span });
1733             }
1734             let inner = attr.meta_item_list();
1735             match inner.as_deref() {
1736                 Some([item]) if item.has_name(sym::linker) => {
1737                     if used_linker_span.is_none() {
1738                         used_linker_span = Some(attr.span);
1739                     }
1740                 }
1741                 Some([item]) if item.has_name(sym::compiler) => {
1742                     if used_compiler_span.is_none() {
1743                         used_compiler_span = Some(attr.span);
1744                     }
1745                 }
1746                 Some(_) => {
1747                     // This error case is handled in rustc_typeck::collect.
1748                 }
1749                 None => {
1750                     // Default case (compiler) when arg isn't defined.
1751                     if used_compiler_span.is_none() {
1752                         used_compiler_span = Some(attr.span);
1753                     }
1754                 }
1755             }
1756         }
1757         if let (Some(linker_span), Some(compiler_span)) = (used_linker_span, used_compiler_span) {
1758             self.tcx
1759                 .sess
1760                 .emit_err(errors::UsedCompilerLinker { spans: vec![linker_span, compiler_span] });
1761         }
1762     }
1763
1764     /// Outputs an error for `#[allow_internal_unstable]` which can only be applied to macros.
1765     /// (Allows proc_macro functions)
1766     fn check_allow_internal_unstable(
1767         &self,
1768         hir_id: HirId,
1769         attr: &Attribute,
1770         span: Span,
1771         target: Target,
1772         attrs: &[Attribute],
1773     ) -> bool {
1774         debug!("Checking target: {:?}", target);
1775         match target {
1776             Target::Fn => {
1777                 for attr in attrs {
1778                     if self.tcx.sess.is_proc_macro_attr(attr) {
1779                         debug!("Is proc macro attr");
1780                         return true;
1781                     }
1782                 }
1783                 debug!("Is not proc macro attr");
1784                 false
1785             }
1786             Target::MacroDef => true,
1787             // FIXME(#80564): We permit struct fields and match arms to have an
1788             // `#[allow_internal_unstable]` attribute with just a lint, because we previously
1789             // erroneously allowed it and some crates used it accidentally, to to be compatible
1790             // with crates depending on them, we can't throw an error here.
1791             Target::Field | Target::Arm => {
1792                 self.inline_attr_str_error_without_macro_def(
1793                     hir_id,
1794                     attr,
1795                     "allow_internal_unstable",
1796                 );
1797                 true
1798             }
1799             _ => {
1800                 self.tcx
1801                     .sess
1802                     .emit_err(errors::AllowInternalUnstable { attr_span: attr.span, span });
1803                 false
1804             }
1805         }
1806     }
1807
1808     /// Checks if the items on the `#[debugger_visualizer]` attribute are valid.
1809     fn check_debugger_visualizer(&self, attr: &Attribute, target: Target) -> bool {
1810         match target {
1811             Target::Mod => {}
1812             _ => {
1813                 self.tcx.sess.emit_err(errors::DebugVisualizerPlacement { span: attr.span });
1814                 return false;
1815             }
1816         }
1817
1818         let Some(hints) = attr.meta_item_list() else {
1819             self.tcx.sess.emit_err(errors::DebugVisualizerInvalid { span: attr.span });
1820             return false;
1821         };
1822
1823         let hint = match hints.len() {
1824             1 => &hints[0],
1825             _ => {
1826                 self.tcx.sess.emit_err(errors::DebugVisualizerInvalid { span: attr.span });
1827                 return false;
1828             }
1829         };
1830
1831         let Some(meta_item) = hint.meta_item() else {
1832             self.tcx.sess.emit_err(errors::DebugVisualizerInvalid { span: attr.span });
1833             return false;
1834         };
1835
1836         let visualizer_path = match (meta_item.name_or_empty(), meta_item.value_str()) {
1837             (sym::natvis_file, Some(value)) => value,
1838             (sym::gdb_script_file, Some(value)) => value,
1839             (_, _) => {
1840                 self.tcx.sess.emit_err(errors::DebugVisualizerInvalid { span: meta_item.span });
1841                 return false;
1842             }
1843         };
1844
1845         let file =
1846             match resolve_path(&self.tcx.sess.parse_sess, visualizer_path.as_str(), attr.span) {
1847                 Ok(file) => file,
1848                 Err(mut err) => {
1849                     err.emit();
1850                     return false;
1851                 }
1852             };
1853
1854         match std::fs::File::open(&file) {
1855             Ok(_) => true,
1856             Err(err) => {
1857                 self.tcx
1858                     .sess
1859                     .struct_span_err(
1860                         meta_item.span,
1861                         &format!("couldn't read {}: {}", file.display(), err),
1862                     )
1863                     .emit();
1864                 false
1865             }
1866         }
1867     }
1868
1869     /// Outputs an error for `#[allow_internal_unstable]` which can only be applied to macros.
1870     /// (Allows proc_macro functions)
1871     fn check_rustc_allow_const_fn_unstable(
1872         &self,
1873         hir_id: HirId,
1874         attr: &Attribute,
1875         span: Span,
1876         target: Target,
1877     ) -> bool {
1878         match target {
1879             Target::Fn | Target::Method(_)
1880                 if self.tcx.is_const_fn_raw(self.tcx.hir().local_def_id(hir_id).to_def_id()) =>
1881             {
1882                 true
1883             }
1884             // FIXME(#80564): We permit struct fields and match arms to have an
1885             // `#[allow_internal_unstable]` attribute with just a lint, because we previously
1886             // erroneously allowed it and some crates used it accidentally, to to be compatible
1887             // with crates depending on them, we can't throw an error here.
1888             Target::Field | Target::Arm | Target::MacroDef => {
1889                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "allow_internal_unstable");
1890                 true
1891             }
1892             _ => {
1893                 self.tcx
1894                     .sess
1895                     .emit_err(errors::RustcAllowConstFnUnstable { attr_span: attr.span, span });
1896                 false
1897             }
1898         }
1899     }
1900
1901     fn check_rustc_std_internal_symbol(
1902         &self,
1903         attr: &Attribute,
1904         span: Span,
1905         target: Target,
1906     ) -> bool {
1907         match target {
1908             Target::Fn | Target::Static => true,
1909             _ => {
1910                 self.tcx
1911                     .sess
1912                     .emit_err(errors::RustcStdInternalSymbol { attr_span: attr.span, span });
1913                 false
1914             }
1915         }
1916     }
1917
1918     /// `#[const_trait]` only applies to traits.
1919     fn check_const_trait(&self, attr: &Attribute, _span: Span, target: Target) -> bool {
1920         match target {
1921             Target::Trait => true,
1922             _ => {
1923                 self.tcx.sess.emit_err(errors::ConstTrait { attr_span: attr.span });
1924                 false
1925             }
1926         }
1927     }
1928
1929     fn check_stability_promotable(&self, attr: &Attribute, _span: Span, target: Target) -> bool {
1930         match target {
1931             Target::Expression => {
1932                 self.tcx.sess.emit_err(errors::StabilityPromotable { attr_span: attr.span });
1933                 false
1934             }
1935             _ => true,
1936         }
1937     }
1938
1939     fn check_link_ordinal(&self, attr: &Attribute, _span: Span, target: Target) -> bool {
1940         match target {
1941             Target::ForeignFn | Target::ForeignStatic => true,
1942             _ => {
1943                 self.tcx.sess.emit_err(errors::LinkOrdinal { attr_span: attr.span });
1944                 false
1945             }
1946         }
1947     }
1948
1949     fn check_deprecated(&self, hir_id: HirId, attr: &Attribute, _span: Span, target: Target) {
1950         match target {
1951             Target::Closure | Target::Expression | Target::Statement | Target::Arm => {
1952                 self.tcx.emit_spanned_lint(
1953                     UNUSED_ATTRIBUTES,
1954                     hir_id,
1955                     attr.span,
1956                     errors::Deprecated,
1957                 );
1958             }
1959             _ => {}
1960         }
1961     }
1962
1963     fn check_macro_use(&self, hir_id: HirId, attr: &Attribute, target: Target) {
1964         let name = attr.name_or_empty();
1965         match target {
1966             Target::ExternCrate | Target::Mod => {}
1967             _ => {
1968                 self.tcx.emit_spanned_lint(
1969                     UNUSED_ATTRIBUTES,
1970                     hir_id,
1971                     attr.span,
1972                     errors::MacroUse { name },
1973                 );
1974             }
1975         }
1976     }
1977
1978     fn check_macro_export(&self, hir_id: HirId, attr: &Attribute, target: Target) {
1979         if target != Target::MacroDef {
1980             self.tcx.emit_spanned_lint(UNUSED_ATTRIBUTES, hir_id, attr.span, errors::MacroExport);
1981         }
1982     }
1983
1984     fn check_plugin_registrar(&self, hir_id: HirId, attr: &Attribute, target: Target) {
1985         if target != Target::Fn {
1986             self.tcx.emit_spanned_lint(
1987                 UNUSED_ATTRIBUTES,
1988                 hir_id,
1989                 attr.span,
1990                 errors::PluginRegistrar,
1991             );
1992         }
1993     }
1994
1995     fn check_unused_attribute(&self, hir_id: HirId, attr: &Attribute) {
1996         // Warn on useless empty attributes.
1997         let note = if matches!(
1998             attr.name_or_empty(),
1999             sym::macro_use
2000                 | sym::allow
2001                 | sym::expect
2002                 | sym::warn
2003                 | sym::deny
2004                 | sym::forbid
2005                 | sym::feature
2006                 | sym::repr
2007                 | sym::target_feature
2008         ) && attr.meta_item_list().map_or(false, |list| list.is_empty())
2009         {
2010             errors::UnusedNote::EmptyList { name: attr.name_or_empty() }
2011         } else if matches!(
2012                 attr.name_or_empty(),
2013                 sym::allow | sym::warn | sym::deny | sym::forbid | sym::expect
2014             ) && let Some(meta) = attr.meta_item_list()
2015             && meta.len() == 1
2016             && let Some(item) = meta[0].meta_item()
2017             && let MetaItemKind::NameValue(_) = &item.kind
2018             && item.path == sym::reason
2019         {
2020             errors::UnusedNote::NoLints { name: attr.name_or_empty() }
2021         } else if attr.name_or_empty() == sym::default_method_body_is_const {
2022             errors::UnusedNote::DefaultMethodBodyConst
2023         } else {
2024             return;
2025         };
2026
2027         self.tcx.emit_spanned_lint(
2028             UNUSED_ATTRIBUTES,
2029             hir_id,
2030             attr.span,
2031             errors::Unused { attr_span: attr.span, note },
2032         );
2033     }
2034 }
2035
2036 impl<'tcx> Visitor<'tcx> for CheckAttrVisitor<'tcx> {
2037     type NestedFilter = nested_filter::OnlyBodies;
2038
2039     fn nested_visit_map(&mut self) -> Self::Map {
2040         self.tcx.hir()
2041     }
2042
2043     fn visit_item(&mut self, item: &'tcx Item<'tcx>) {
2044         // Historically we've run more checks on non-exported than exported macros,
2045         // so this lets us continue to run them while maintaining backwards compatibility.
2046         // In the long run, the checks should be harmonized.
2047         if let ItemKind::Macro(ref macro_def, _) = item.kind {
2048             let def_id = item.def_id.to_def_id();
2049             if macro_def.macro_rules && !self.tcx.has_attr(def_id, sym::macro_export) {
2050                 check_non_exported_macro_for_invalid_attrs(self.tcx, item);
2051             }
2052         }
2053
2054         let target = Target::from_item(item);
2055         self.check_attributes(item.hir_id(), item.span, target, Some(ItemLike::Item(item)));
2056         intravisit::walk_item(self, item)
2057     }
2058
2059     fn visit_generic_param(&mut self, generic_param: &'tcx hir::GenericParam<'tcx>) {
2060         let target = Target::from_generic_param(generic_param);
2061         self.check_attributes(generic_param.hir_id, generic_param.span, target, None);
2062         intravisit::walk_generic_param(self, generic_param)
2063     }
2064
2065     fn visit_trait_item(&mut self, trait_item: &'tcx TraitItem<'tcx>) {
2066         let target = Target::from_trait_item(trait_item);
2067         self.check_attributes(trait_item.hir_id(), trait_item.span, target, None);
2068         intravisit::walk_trait_item(self, trait_item)
2069     }
2070
2071     fn visit_field_def(&mut self, struct_field: &'tcx hir::FieldDef<'tcx>) {
2072         self.check_attributes(struct_field.hir_id, struct_field.span, Target::Field, None);
2073         intravisit::walk_field_def(self, struct_field);
2074     }
2075
2076     fn visit_arm(&mut self, arm: &'tcx hir::Arm<'tcx>) {
2077         self.check_attributes(arm.hir_id, arm.span, Target::Arm, None);
2078         intravisit::walk_arm(self, arm);
2079     }
2080
2081     fn visit_foreign_item(&mut self, f_item: &'tcx ForeignItem<'tcx>) {
2082         let target = Target::from_foreign_item(f_item);
2083         self.check_attributes(f_item.hir_id(), f_item.span, target, Some(ItemLike::ForeignItem));
2084         intravisit::walk_foreign_item(self, f_item)
2085     }
2086
2087     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
2088         let target = target_from_impl_item(self.tcx, impl_item);
2089         self.check_attributes(impl_item.hir_id(), impl_item.span, target, None);
2090         intravisit::walk_impl_item(self, impl_item)
2091     }
2092
2093     fn visit_stmt(&mut self, stmt: &'tcx hir::Stmt<'tcx>) {
2094         // When checking statements ignore expressions, they will be checked later.
2095         if let hir::StmtKind::Local(ref l) = stmt.kind {
2096             self.check_attributes(l.hir_id, stmt.span, Target::Statement, None);
2097         }
2098         intravisit::walk_stmt(self, stmt)
2099     }
2100
2101     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
2102         let target = match expr.kind {
2103             hir::ExprKind::Closure { .. } => Target::Closure,
2104             _ => Target::Expression,
2105         };
2106
2107         self.check_attributes(expr.hir_id, expr.span, target, None);
2108         intravisit::walk_expr(self, expr)
2109     }
2110
2111     fn visit_expr_field(&mut self, field: &'tcx hir::ExprField<'tcx>) {
2112         self.check_attributes(field.hir_id, field.span, Target::ExprField, None);
2113         intravisit::walk_expr_field(self, field)
2114     }
2115
2116     fn visit_variant(&mut self, variant: &'tcx hir::Variant<'tcx>) {
2117         self.check_attributes(variant.id, variant.span, Target::Variant, None);
2118         intravisit::walk_variant(self, variant)
2119     }
2120
2121     fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) {
2122         self.check_attributes(param.hir_id, param.span, Target::Param, None);
2123
2124         intravisit::walk_param(self, param);
2125     }
2126
2127     fn visit_pat_field(&mut self, field: &'tcx hir::PatField<'tcx>) {
2128         self.check_attributes(field.hir_id, field.span, Target::PatField, None);
2129         intravisit::walk_pat_field(self, field);
2130     }
2131 }
2132
2133 fn is_c_like_enum(item: &Item<'_>) -> bool {
2134     if let ItemKind::Enum(ref def, _) = item.kind {
2135         for variant in def.variants {
2136             match variant.data {
2137                 hir::VariantData::Unit(..) => { /* continue */ }
2138                 _ => return false,
2139             }
2140         }
2141         true
2142     } else {
2143         false
2144     }
2145 }
2146
2147 // FIXME: Fix "Cannot determine resolution" error and remove built-in macros
2148 // from this check.
2149 fn check_invalid_crate_level_attr(tcx: TyCtxt<'_>, attrs: &[Attribute]) {
2150     // Check for builtin attributes at the crate level
2151     // which were unsuccessfully resolved due to cannot determine
2152     // resolution for the attribute macro error.
2153     const ATTRS_TO_CHECK: &[Symbol] = &[
2154         sym::macro_export,
2155         sym::repr,
2156         sym::path,
2157         sym::automatically_derived,
2158         sym::start,
2159         sym::rustc_main,
2160         sym::unix_sigpipe,
2161         sym::derive,
2162         sym::test,
2163         sym::test_case,
2164         sym::global_allocator,
2165         sym::bench,
2166     ];
2167
2168     for attr in attrs {
2169         // This function should only be called with crate attributes
2170         // which are inner attributes always but lets check to make sure
2171         if attr.style == AttrStyle::Inner {
2172             for attr_to_check in ATTRS_TO_CHECK {
2173                 if attr.has_name(*attr_to_check) {
2174                     let mut err = tcx.sess.struct_span_err(
2175                         attr.span,
2176                         &format!(
2177                             "`{}` attribute cannot be used at crate level",
2178                             attr_to_check.to_ident_string()
2179                         ),
2180                     );
2181                     // Only emit an error with a suggestion if we can create a
2182                     // string out of the attribute span
2183                     if let Ok(src) = tcx.sess.source_map().span_to_snippet(attr.span) {
2184                         let replacement = src.replace("#!", "#");
2185                         err.span_suggestion_verbose(
2186                             attr.span,
2187                             "perhaps you meant to use an outer attribute",
2188                             replacement,
2189                             rustc_errors::Applicability::MachineApplicable,
2190                         );
2191                     }
2192                     err.emit();
2193                 }
2194             }
2195         }
2196     }
2197 }
2198
2199 fn check_non_exported_macro_for_invalid_attrs(tcx: TyCtxt<'_>, item: &Item<'_>) {
2200     let attrs = tcx.hir().attrs(item.hir_id());
2201
2202     for attr in attrs {
2203         if attr.has_name(sym::inline) {
2204             tcx.sess.emit_err(errors::NonExportedMacroInvalidAttrs { attr_span: attr.span });
2205         }
2206     }
2207 }
2208
2209 fn check_mod_attrs(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
2210     let check_attr_visitor = &mut CheckAttrVisitor { tcx };
2211     tcx.hir().visit_item_likes_in_module(module_def_id, check_attr_visitor);
2212     if module_def_id.is_top_level_module() {
2213         check_attr_visitor.check_attributes(CRATE_HIR_ID, DUMMY_SP, Target::Mod, None);
2214         check_invalid_crate_level_attr(tcx, tcx.hir().krate_attrs());
2215     }
2216 }
2217
2218 pub(crate) fn provide(providers: &mut Providers) {
2219     *providers = Providers { check_mod_attrs, ..*providers };
2220 }
2221
2222 fn check_duplicates(
2223     tcx: TyCtxt<'_>,
2224     attr: &Attribute,
2225     hir_id: HirId,
2226     duplicates: AttributeDuplicates,
2227     seen: &mut FxHashMap<Symbol, Span>,
2228 ) {
2229     use AttributeDuplicates::*;
2230     if matches!(duplicates, WarnFollowingWordOnly) && !attr.is_word() {
2231         return;
2232     }
2233     match duplicates {
2234         DuplicatesOk => {}
2235         WarnFollowing | FutureWarnFollowing | WarnFollowingWordOnly | FutureWarnPreceding => {
2236             match seen.entry(attr.name_or_empty()) {
2237                 Entry::Occupied(mut entry) => {
2238                     let (this, other) = if matches!(duplicates, FutureWarnPreceding) {
2239                         let to_remove = entry.insert(attr.span);
2240                         (to_remove, attr.span)
2241                     } else {
2242                         (attr.span, *entry.get())
2243                     };
2244                     tcx.emit_spanned_lint(
2245                         UNUSED_ATTRIBUTES,
2246                         hir_id,
2247                         this,
2248                         errors::UnusedDuplicate {
2249                             this,
2250                             other,
2251                             warning: matches!(
2252                                 duplicates,
2253                                 FutureWarnFollowing | FutureWarnPreceding
2254                             )
2255                             .then_some(()),
2256                         },
2257                     );
2258                 }
2259                 Entry::Vacant(entry) => {
2260                     entry.insert(attr.span);
2261                 }
2262             }
2263         }
2264         ErrorFollowing | ErrorPreceding => match seen.entry(attr.name_or_empty()) {
2265             Entry::Occupied(mut entry) => {
2266                 let (this, other) = if matches!(duplicates, ErrorPreceding) {
2267                     let to_remove = entry.insert(attr.span);
2268                     (to_remove, attr.span)
2269                 } else {
2270                     (attr.span, *entry.get())
2271                 };
2272                 tcx.sess.emit_err(errors::UnusedMultiple {
2273                     this,
2274                     other,
2275                     name: attr.name_or_empty(),
2276                 });
2277             }
2278             Entry::Vacant(entry) => {
2279                 entry.insert(attr.span);
2280             }
2281         },
2282     }
2283 }