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     self, AttrApplication, DebugVisualizerUnreadable, InvalidAttrAtCrateLevel, ObjectLifetimeErr,
   9     OnlyHasEffectOn, ProcMacroDiffArguments, ProcMacroInvalidAbi, ProcMacroMissingArguments,
  10     ProcMacroTypeError, ProcMacroUnsafe, TransparentIncompatible, UnrecognizedReprHint,
  11 };
  12 use rustc_ast::{ast, AttrStyle, Attribute, LitKind, MetaItemKind, MetaItemLit, NestedMetaItem};
  13 use rustc_data_structures::fx::FxHashMap;
  14 use rustc_errors::{fluent, Applicability, IntoDiagnosticArg, MultiSpan};
  15 use rustc_expand::base::resolve_path;
  16 use rustc_feature::{AttributeDuplicates, AttributeType, BuiltinAttribute, BUILTIN_ATTRIBUTE_MAP};
  17 use rustc_hir as hir;
  18 use rustc_hir::def_id::LocalDefId;
  19 use rustc_hir::intravisit::{self, Visitor};
  20 use rustc_hir::{
  21     self, FnSig, ForeignItem, HirId, Item, ItemKind, TraitItem, CRATE_HIR_ID, CRATE_OWNER_ID,
  22 };
  23 use rustc_hir::{MethodKind, Target, Unsafety};
  24 use rustc_middle::hir::nested_filter;
  25 use rustc_middle::middle::resolve_lifetime::ObjectLifetimeDefault;
  26 use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
  27 use rustc_middle::ty::query::Providers;
  28 use rustc_middle::ty::{ParamEnv, TyCtxt};
  29 use rustc_session::lint::builtin::{
  30     CONFLICTING_REPR_HINTS, INVALID_DOC_ATTRIBUTES, UNUSED_ATTRIBUTES,
  31 };
  32 use rustc_session::parse::feature_err;
  33 use rustc_span::symbol::{kw, sym, Symbol};
  34 use rustc_span::{Span, DUMMY_SP};
  35 use rustc_target::spec::abi::Abi;
  36 use std::cell::Cell;
  37 use std::collections::hash_map::Entry;
  38
  39 pub(crate) fn target_from_impl_item<'tcx>(
  40     tcx: TyCtxt<'tcx>,
  41     impl_item: &hir::ImplItem<'_>,
  42 ) -> Target {
  43     match impl_item.kind {
  44         hir::ImplItemKind::Const(..) => Target::AssocConst,
  45         hir::ImplItemKind::Fn(..) => {
  46             let parent_def_id = tcx.hir().get_parent_item(impl_item.hir_id()).def_id;
  47             let containing_item = tcx.hir().expect_item(parent_def_id);
  48             let containing_impl_is_for_trait = match &containing_item.kind {
  49                 hir::ItemKind::Impl(impl_) => impl_.of_trait.is_some(),
  50                 _ => bug!("parent of an ImplItem must be an Impl"),
  51             };
  52             if containing_impl_is_for_trait {
  53                 Target::Method(MethodKind::Trait { body: true })
  54             } else {
  55                 Target::Method(MethodKind::Inherent)
  56             }
  57         }
  58         hir::ImplItemKind::Type(..) => Target::AssocTy,
  59     }
  60 }
  61
  62 #[derive(Clone, Copy)]
  63 enum ItemLike<'tcx> {
  64     Item(&'tcx Item<'tcx>),
  65     ForeignItem,
  66 }
  67
  68 #[derive(Copy, Clone)]
  69 pub(crate) enum ProcMacroKind {
  70     FunctionLike,
  71     Derive,
  72     Attribute,
  73 }
  74
  75 impl IntoDiagnosticArg for ProcMacroKind {
  76     fn into_diagnostic_arg(self) -> rustc_errors::DiagnosticArgValue<'static> {
  77         match self {
  78             ProcMacroKind::Attribute => "attribute proc macro",
  79             ProcMacroKind::Derive => "derive proc macro",
  80             ProcMacroKind::FunctionLike => "function-like proc macro",
  81         }
  82         .into_diagnostic_arg()
  83     }
  84 }
  85
  86 struct CheckAttrVisitor<'tcx> {
  87     tcx: TyCtxt<'tcx>,
  88
  89     // Whether or not this visitor should abort after finding errors
  90     abort: Cell<bool>,
  91 }
  92
  93 impl CheckAttrVisitor<'_> {
  94     /// Checks any attribute.
  95     fn check_attributes(
  96         &self,
  97         hir_id: HirId,
  98         span: Span,
  99         target: Target,
 100         item: Option<ItemLike<'_>>,
 101     ) {
 102         let mut doc_aliases = FxHashMap::default();
 103         let mut is_valid = true;
 104         let mut specified_inline = None;
 105         let mut seen = FxHashMap::default();
 106         let attrs = self.tcx.hir().attrs(hir_id);
 107         for attr in attrs {
 108             let attr_is_valid = match attr.name_or_empty() {
 109                 sym::do_not_recommend => self.check_do_not_recommend(attr.span, target),
 110                 sym::inline => self.check_inline(hir_id, attr, span, target),
 111                 sym::no_coverage => self.check_no_coverage(hir_id, attr, span, target),
 112                 sym::non_exhaustive => self.check_non_exhaustive(hir_id, attr, span, target),
 113                 sym::marker => self.check_marker(hir_id, attr, span, target),
 114                 sym::rustc_must_implement_one_of => {
 115                     self.check_rustc_must_implement_one_of(attr, span, target)
 116                 }
 117                 sym::target_feature => self.check_target_feature(hir_id, attr, span, target),
 118                 sym::thread_local => self.check_thread_local(attr, span, target),
 119                 sym::track_caller => {
 120                     self.check_track_caller(hir_id, attr.span, attrs, span, target)
 121                 }
 122                 sym::doc => self.check_doc_attrs(
 123                     attr,
 124                     hir_id,
 125                     target,
 126                     &mut specified_inline,
 127                     &mut doc_aliases,
 128                 ),
 129                 sym::no_link => self.check_no_link(hir_id, &attr, span, target),
 130                 sym::export_name => self.check_export_name(hir_id, &attr, span, target),
 131                 sym::rustc_layout_scalar_valid_range_start
 132                 | sym::rustc_layout_scalar_valid_range_end => {
 133                     self.check_rustc_layout_scalar_valid_range(&attr, span, target)
 134                 }
 135                 sym::allow_internal_unstable => {
 136                     self.check_allow_internal_unstable(hir_id, &attr, span, target, &attrs)
 137                 }
 138                 sym::debugger_visualizer => self.check_debugger_visualizer(&attr, target),
 139                 sym::rustc_allow_const_fn_unstable => {
 140                     self.check_rustc_allow_const_fn_unstable(hir_id, &attr, span, target)
 141                 }
 142                 sym::rustc_std_internal_symbol => {
 143                     self.check_rustc_std_internal_symbol(&attr, span, target)
 144                 }
 145                 sym::naked => self.check_naked(hir_id, attr, span, target),
 146                 sym::rustc_legacy_const_generics => {
 147                     self.check_rustc_legacy_const_generics(hir_id, &attr, span, target, item)
 148                 }
 149                 sym::rustc_lint_query_instability => {
 150                     self.check_rustc_lint_query_instability(hir_id, &attr, span, target)
 151                 }
 152                 sym::rustc_lint_diagnostics => {
 153                     self.check_rustc_lint_diagnostics(hir_id, &attr, span, target)
 154                 }
 155                 sym::rustc_lint_opt_ty => self.check_rustc_lint_opt_ty(&attr, span, target),
 156                 sym::rustc_lint_opt_deny_field_access => {
 157                     self.check_rustc_lint_opt_deny_field_access(&attr, span, target)
 158                 }
 159                 sym::rustc_clean
 160                 | sym::rustc_dirty
 161                 | sym::rustc_if_this_changed
 162                 | sym::rustc_then_this_would_need => self.check_rustc_dirty_clean(&attr),
 163                 sym::cmse_nonsecure_entry => {
 164                     self.check_cmse_nonsecure_entry(hir_id, attr, span, target)
 165                 }
 166                 sym::collapse_debuginfo => self.check_collapse_debuginfo(attr, span, target),
 167                 sym::const_trait => self.check_const_trait(attr, span, target),
 168                 sym::must_not_suspend => self.check_must_not_suspend(&attr, span, target),
 169                 sym::must_use => self.check_must_use(hir_id, &attr, target),
 170                 sym::rustc_pass_by_value => self.check_pass_by_value(&attr, span, target),
 171                 sym::rustc_allow_incoherent_impl => {
 172                     self.check_allow_incoherent_impl(&attr, span, target)
 173                 }
 174                 sym::rustc_has_incoherent_inherent_impls => {
 175                     self.check_has_incoherent_inherent_impls(&attr, span, target)
 176                 }
 177                 sym::rustc_const_unstable
 178                 | sym::rustc_const_stable
 179                 | sym::unstable
 180                 | sym::stable
 181                 | sym::rustc_allowed_through_unstable_modules
 182                 | sym::rustc_promotable => self.check_stability_promotable(&attr, span, target),
 183                 sym::link_ordinal => self.check_link_ordinal(&attr, span, target),
 184                 _ => true,
 185             };
 186             is_valid &= attr_is_valid;
 187
 188             // lint-only checks
 189             match attr.name_or_empty() {
 190                 sym::cold => self.check_cold(hir_id, attr, span, target),
 191                 sym::link => self.check_link(hir_id, attr, span, target),
 192                 sym::link_name => self.check_link_name(hir_id, attr, span, target),
 193                 sym::link_section => self.check_link_section(hir_id, attr, span, target),
 194                 sym::no_mangle => self.check_no_mangle(hir_id, attr, span, target),
 195                 sym::deprecated => self.check_deprecated(hir_id, attr, span, target),
 196                 sym::macro_use | sym::macro_escape => self.check_macro_use(hir_id, attr, target),
 197                 sym::path => self.check_generic_attr(hir_id, attr, target, Target::Mod),
 198                 sym::plugin_registrar => self.check_plugin_registrar(hir_id, attr, target),
 199                 sym::macro_export => self.check_macro_export(hir_id, attr, target),
 200                 sym::ignore | sym::should_panic => {
 201                     self.check_generic_attr(hir_id, attr, target, Target::Fn)
 202                 }
 203                 sym::automatically_derived => {
 204                     self.check_generic_attr(hir_id, attr, target, Target::Impl)
 205                 }
 206                 sym::no_implicit_prelude => {
 207                     self.check_generic_attr(hir_id, attr, target, Target::Mod)
 208                 }
 209                 sym::rustc_object_lifetime_default => self.check_object_lifetime_default(hir_id),
 210                 sym::proc_macro => {
 211                     self.check_proc_macro(hir_id, target, ProcMacroKind::FunctionLike)
 212                 }
 213                 sym::proc_macro_attribute => {
 214                     self.check_proc_macro(hir_id, target, ProcMacroKind::Attribute);
 215                 }
 216                 sym::proc_macro_derive => {
 217                     self.check_generic_attr(hir_id, attr, target, Target::Fn);
 218                     self.check_proc_macro(hir_id, target, ProcMacroKind::Derive)
 219                 }
 220                 _ => {}
 221             }
 222
 223             let builtin = attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name));
 224
 225             if hir_id != CRATE_HIR_ID {
 226                 if let Some(BuiltinAttribute { type_: AttributeType::CrateLevel, .. }) =
 227                     attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name))
 228                 {
 229                     match attr.style {
 230                         ast::AttrStyle::Outer => self.tcx.emit_spanned_lint(
 231                             UNUSED_ATTRIBUTES,
 232                             hir_id,
 233                             attr.span,
 234                             errors::OuterCrateLevelAttr,
 235                         ),
 236                         ast::AttrStyle::Inner => self.tcx.emit_spanned_lint(
 237                             UNUSED_ATTRIBUTES,
 238                             hir_id,
 239                             attr.span,
 240                             errors::InnerCrateLevelAttr,
 241                         ),
 242                     }
 243                 }
 244             }
 245
 246             if let Some(BuiltinAttribute { duplicates, .. }) = builtin {
 247                 check_duplicates(self.tcx, attr, hir_id, *duplicates, &mut seen);
 248             }
 249
 250             self.check_unused_attribute(hir_id, attr)
 251         }
 252
 253         if !is_valid {
 254             return;
 255         }
 256
 257         self.check_repr(attrs, span, target, item, hir_id);
 258         self.check_used(attrs, target);
 259     }
 260
 261     fn inline_attr_str_error_with_macro_def(&self, hir_id: HirId, attr: &Attribute, sym: &str) {
 262         self.tcx.emit_spanned_lint(
 263             UNUSED_ATTRIBUTES,
 264             hir_id,
 265             attr.span,
 266             errors::IgnoredAttrWithMacro { sym },
 267         );
 268     }
 269
 270     fn inline_attr_str_error_without_macro_def(&self, hir_id: HirId, attr: &Attribute, sym: &str) {
 271         self.tcx.emit_spanned_lint(
 272             UNUSED_ATTRIBUTES,
 273             hir_id,
 274             attr.span,
 275             errors::IgnoredAttr { sym },
 276         );
 277     }
 278
 279     /// Checks if `#[do_not_recommend]` is applied on a trait impl.
 280     fn check_do_not_recommend(&self, attr_span: Span, target: Target) -> bool {
 281         if let Target::Impl = target {
 282             true
 283         } else {
 284             self.tcx.sess.emit_err(errors::IncorrectDoNotRecommendLocation { span: attr_span });
 285             false
 286         }
 287     }
 288
 289     /// Checks if an `#[inline]` is applied to a function or a closure. Returns `true` if valid.
 290     fn check_inline(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) -> bool {
 291         match target {
 292             Target::Fn
 293             | Target::Closure
 294             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
 295             Target::Method(MethodKind::Trait { body: false }) | Target::ForeignFn => {
 296                 self.tcx.emit_spanned_lint(
 297                     UNUSED_ATTRIBUTES,
 298                     hir_id,
 299                     attr.span,
 300                     errors::IgnoredInlineAttrFnProto,
 301                 );
 302                 true
 303             }
 304             // FIXME(#65833): We permit associated consts to have an `#[inline]` attribute with
 305             // just a lint, because we previously erroneously allowed it and some crates used it
 306             // accidentally, to be compatible with crates depending on them, we can't throw an
 307             // error here.
 308             Target::AssocConst => {
 309                 self.tcx.emit_spanned_lint(
 310                     UNUSED_ATTRIBUTES,
 311                     hir_id,
 312                     attr.span,
 313                     errors::IgnoredInlineAttrConstants,
 314                 );
 315                 true
 316             }
 317             // FIXME(#80564): Same for fields, arms, and macro defs
 318             Target::Field | Target::Arm | Target::MacroDef => {
 319                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "inline");
 320                 true
 321             }
 322             _ => {
 323                 self.tcx.sess.emit_err(errors::InlineNotFnOrClosure {
 324                     attr_span: attr.span,
 325                     defn_span: span,
 326                 });
 327                 false
 328             }
 329         }
 330     }
 331
 332     /// Checks if a `#[no_coverage]` is applied directly to a function
 333     fn check_no_coverage(
 334         &self,
 335         hir_id: HirId,
 336         attr: &Attribute,
 337         span: Span,
 338         target: Target,
 339     ) -> bool {
 340         match target {
 341             // no_coverage on function is fine
 342             Target::Fn
 343             | Target::Closure
 344             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
 345
 346             // function prototypes can't be covered
 347             Target::Method(MethodKind::Trait { body: false }) | Target::ForeignFn => {
 348                 self.tcx.emit_spanned_lint(
 349                     UNUSED_ATTRIBUTES,
 350                     hir_id,
 351                     attr.span,
 352                     errors::IgnoredNoCoverageFnProto,
 353                 );
 354                 true
 355             }
 356
 357             Target::Mod | Target::ForeignMod | Target::Impl | Target::Trait => {
 358                 self.tcx.emit_spanned_lint(
 359                     UNUSED_ATTRIBUTES,
 360                     hir_id,
 361                     attr.span,
 362                     errors::IgnoredNoCoveragePropagate,
 363                 );
 364                 true
 365             }
 366
 367             Target::Expression | Target::Statement | Target::Arm => {
 368                 self.tcx.emit_spanned_lint(
 369                     UNUSED_ATTRIBUTES,
 370                     hir_id,
 371                     attr.span,
 372                     errors::IgnoredNoCoverageFnDefn,
 373                 );
 374                 true
 375             }
 376
 377             _ => {
 378                 self.tcx.sess.emit_err(errors::IgnoredNoCoverageNotCoverable {
 379                     attr_span: attr.span,
 380                     defn_span: span,
 381                 });
 382                 false
 383             }
 384         }
 385     }
 386
 387     fn check_generic_attr(
 388         &self,
 389         hir_id: HirId,
 390         attr: &Attribute,
 391         target: Target,
 392         allowed_target: Target,
 393     ) {
 394         if target != allowed_target {
 395             self.tcx.emit_spanned_lint(
 396                 UNUSED_ATTRIBUTES,
 397                 hir_id,
 398                 attr.span,
 399                 OnlyHasEffectOn {
 400                     attr_name: attr.name_or_empty(),
 401                     target_name: allowed_target.name().replace(' ', "_"),
 402                 },
 403             );
 404         }
 405     }
 406
 407     /// Checks if `#[naked]` is applied to a function definition.
 408     fn check_naked(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) -> bool {
 409         match target {
 410             Target::Fn
 411             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
 412             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
 413             // `#[allow_internal_unstable]` attribute with just a lint, because we previously
 414             // erroneously allowed it and some crates used it accidentally, to be compatible
 415             // with crates depending on them, we can't throw an error here.
 416             Target::Field | Target::Arm | Target::MacroDef => {
 417                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "naked");
 418                 true
 419             }
 420             _ => {
 421                 self.tcx.sess.emit_err(errors::AttrShouldBeAppliedToFn {
 422                     attr_span: attr.span,
 423                     defn_span: span,
 424                     on_crate: hir_id == CRATE_HIR_ID,
 425                 });
 426                 false
 427             }
 428         }
 429     }
 430
 431     /// Checks if `#[cmse_nonsecure_entry]` is applied to a function definition.
 432     fn check_cmse_nonsecure_entry(
 433         &self,
 434         hir_id: HirId,
 435         attr: &Attribute,
 436         span: Span,
 437         target: Target,
 438     ) -> bool {
 439         match target {
 440             Target::Fn
 441             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
 442             _ => {
 443                 self.tcx.sess.emit_err(errors::AttrShouldBeAppliedToFn {
 444                     attr_span: attr.span,
 445                     defn_span: span,
 446                     on_crate: hir_id == CRATE_HIR_ID,
 447                 });
 448                 false
 449             }
 450         }
 451     }
 452
 453     /// Debugging aid for `object_lifetime_default` query.
 454     fn check_object_lifetime_default(&self, hir_id: HirId) {
 455         let tcx = self.tcx;
 456         if let Some(owner_id) = hir_id.as_owner()
 457             && let Some(generics) = tcx.hir().get_generics(owner_id.def_id)
 458         {
 459             for p in generics.params {
 460                 let hir::GenericParamKind::Type { .. } = p.kind else { continue };
 461                 let default = tcx.object_lifetime_default(p.def_id);
 462                 let repr = match default {
 463                     ObjectLifetimeDefault::Empty => "BaseDefault".to_owned(),
 464                     ObjectLifetimeDefault::Static => "'static".to_owned(),
 465                     ObjectLifetimeDefault::Param(def_id) => tcx.item_name(def_id).to_string(),
 466                     ObjectLifetimeDefault::Ambiguous => "Ambiguous".to_owned(),
 467                 };
 468                 tcx.sess.emit_err(ObjectLifetimeErr { span: p.span, repr });
 469             }
 470         }
 471     }
 472
 473     /// Checks if `#[collapse_debuginfo]` is applied to a macro.
 474     fn check_collapse_debuginfo(&self, attr: &Attribute, span: Span, target: Target) -> bool {
 475         match target {
 476             Target::MacroDef => true,
 477             _ => {
 478                 self.tcx
 479                     .sess
 480                     .emit_err(errors::CollapseDebuginfo { attr_span: attr.span, defn_span: span });
 481                 false
 482             }
 483         }
 484     }
 485
 486     /// Checks if a `#[track_caller]` is applied to a non-naked function. Returns `true` if valid.
 487     fn check_track_caller(
 488         &self,
 489         hir_id: HirId,
 490         attr_span: Span,
 491         attrs: &[Attribute],
 492         span: Span,
 493         target: Target,
 494     ) -> bool {
 495         match target {
 496             _ if attrs.iter().any(|attr| attr.has_name(sym::naked)) => {
 497                 self.tcx.sess.emit_err(errors::NakedTrackedCaller { attr_span });
 498                 false
 499             }
 500             Target::Fn | Target::Method(..) | Target::ForeignFn | Target::Closure => true,
 501             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
 502             // `#[track_caller]` attribute with just a lint, because we previously
 503             // erroneously allowed it and some crates used it accidentally, to be compatible
 504             // with crates depending on them, we can't throw an error here.
 505             Target::Field | Target::Arm | Target::MacroDef => {
 506                 for attr in attrs {
 507                     self.inline_attr_str_error_with_macro_def(hir_id, attr, "track_caller");
 508                 }
 509                 true
 510             }
 511             _ => {
 512                 self.tcx.sess.emit_err(errors::TrackedCallerWrongLocation {
 513                     attr_span,
 514                     defn_span: span,
 515                     on_crate: hir_id == CRATE_HIR_ID,
 516                 });
 517                 false
 518             }
 519         }
 520     }
 521
 522     /// Checks if the `#[non_exhaustive]` attribute on an `item` is valid. Returns `true` if valid.
 523     fn check_non_exhaustive(
 524         &self,
 525         hir_id: HirId,
 526         attr: &Attribute,
 527         span: Span,
 528         target: Target,
 529     ) -> bool {
 530         match target {
 531             Target::Struct | Target::Enum | Target::Variant => true,
 532             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
 533             // `#[non_exhaustive]` attribute with just a lint, because we previously
 534             // erroneously allowed it and some crates used it accidentally, to be compatible
 535             // with crates depending on them, we can't throw an error here.
 536             Target::Field | Target::Arm | Target::MacroDef => {
 537                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "non_exhaustive");
 538                 true
 539             }
 540             _ => {
 541                 self.tcx.sess.emit_err(errors::NonExhaustiveWrongLocation {
 542                     attr_span: attr.span,
 543                     defn_span: span,
 544                 });
 545                 false
 546             }
 547         }
 548     }
 549
 550     /// Checks if the `#[marker]` attribute on an `item` is valid. Returns `true` if valid.
 551     fn check_marker(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) -> bool {
 552         match target {
 553             Target::Trait => true,
 554             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
 555             // `#[marker]` attribute with just a lint, because we previously
 556             // erroneously allowed it and some crates used it accidentally, to be compatible
 557             // with crates depending on them, we can't throw an error here.
 558             Target::Field | Target::Arm | Target::MacroDef => {
 559                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "marker");
 560                 true
 561             }
 562             _ => {
 563                 self.tcx.sess.emit_err(errors::AttrShouldBeAppliedToTrait {
 564                     attr_span: attr.span,
 565                     defn_span: span,
 566                 });
 567                 false
 568             }
 569         }
 570     }
 571
 572     /// Checks if the `#[rustc_must_implement_one_of]` attribute on a `target` is valid. Returns `true` if valid.
 573     fn check_rustc_must_implement_one_of(
 574         &self,
 575         attr: &Attribute,
 576         span: Span,
 577         target: Target,
 578     ) -> bool {
 579         match target {
 580             Target::Trait => true,
 581             _ => {
 582                 self.tcx.sess.emit_err(errors::AttrShouldBeAppliedToTrait {
 583                     attr_span: attr.span,
 584                     defn_span: span,
 585                 });
 586                 false
 587             }
 588         }
 589     }
 590
 591     /// Checks if the `#[target_feature]` attribute on `item` is valid. Returns `true` if valid.
 592     fn check_target_feature(
 593         &self,
 594         hir_id: HirId,
 595         attr: &Attribute,
 596         span: Span,
 597         target: Target,
 598     ) -> bool {
 599         match target {
 600             Target::Fn
 601             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
 602             // FIXME: #[target_feature] was previously erroneously allowed on statements and some
 603             // crates used this, so only emit a warning.
 604             Target::Statement => {
 605                 self.tcx.emit_spanned_lint(
 606                     UNUSED_ATTRIBUTES,
 607                     hir_id,
 608                     attr.span,
 609                     errors::TargetFeatureOnStatement,
 610                 );
 611                 true
 612             }
 613             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
 614             // `#[target_feature]` attribute with just a lint, because we previously
 615             // erroneously allowed it and some crates used it accidentally, to be compatible
 616             // with crates depending on them, we can't throw an error here.
 617             Target::Field | Target::Arm | Target::MacroDef => {
 618                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "target_feature");
 619                 true
 620             }
 621             _ => {
 622                 self.tcx.sess.emit_err(errors::AttrShouldBeAppliedToFn {
 623                     attr_span: attr.span,
 624                     defn_span: span,
 625                     on_crate: hir_id == CRATE_HIR_ID,
 626                 });
 627                 false
 628             }
 629         }
 630     }
 631
 632     /// Checks if the `#[thread_local]` attribute on `item` is valid. Returns `true` if valid.
 633     fn check_thread_local(&self, attr: &Attribute, span: Span, target: Target) -> bool {
 634         match target {
 635             Target::ForeignStatic | Target::Static => true,
 636             _ => {
 637                 self.tcx.sess.emit_err(errors::AttrShouldBeAppliedToStatic {
 638                     attr_span: attr.span,
 639                     defn_span: span,
 640                 });
 641                 false
 642             }
 643         }
 644     }
 645
 646     fn doc_attr_str_error(&self, meta: &NestedMetaItem, attr_name: &str) {
 647         self.tcx.sess.emit_err(errors::DocExpectStr { attr_span: meta.span(), attr_name });
 648     }
 649
 650     fn check_doc_alias_value(
 651         &self,
 652         meta: &NestedMetaItem,
 653         doc_alias: Symbol,
 654         hir_id: HirId,
 655         target: Target,
 656         is_list: bool,
 657         aliases: &mut FxHashMap<String, Span>,
 658     ) -> bool {
 659         let tcx = self.tcx;
 660         let span = meta.name_value_literal_span().unwrap_or_else(|| meta.span());
 661         let attr_str =
 662             &format!("`#[doc(alias{})]`", if is_list { "(\"...\")" } else { " = \"...\"" });
 663         if doc_alias == kw::Empty {
 664             tcx.sess.emit_err(errors::DocAliasEmpty { span, attr_str });
 665             return false;
 666         }
 667
 668         let doc_alias_str = doc_alias.as_str();
 669         if let Some(c) = doc_alias_str
 670             .chars()
 671             .find(|&c| c == '"' || c == '\'' || (c.is_whitespace() && c != ' '))
 672         {
 673             tcx.sess.emit_err(errors::DocAliasBadChar { span, attr_str, char_: c });
 674             return false;
 675         }
 676         if doc_alias_str.starts_with(' ') || doc_alias_str.ends_with(' ') {
 677             tcx.sess.emit_err(errors::DocAliasStartEnd { span, attr_str });
 678             return false;
 679         }
 680
 681         let span = meta.span();
 682         if let Some(location) = match target {
 683             Target::AssocTy => {
 684                 let parent_def_id = self.tcx.hir().get_parent_item(hir_id).def_id;
 685                 let containing_item = self.tcx.hir().expect_item(parent_def_id);
 686                 if Target::from_item(containing_item) == Target::Impl {
 687                     Some("type alias in implementation block")
 688                 } else {
 689                     None
 690                 }
 691             }
 692             Target::AssocConst => {
 693                 let parent_def_id = self.tcx.hir().get_parent_item(hir_id).def_id;
 694                 let containing_item = self.tcx.hir().expect_item(parent_def_id);
 695                 // We can't link to trait impl's consts.
 696                 let err = "associated constant in trait implementation block";
 697                 match containing_item.kind {
 698                     ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) => Some(err),
 699                     _ => None,
 700                 }
 701             }
 702             // we check the validity of params elsewhere
 703             Target::Param => return false,
 704             Target::Expression
 705             | Target::Statement
 706             | Target::Arm
 707             | Target::ForeignMod
 708             | Target::Closure
 709             | Target::Impl => Some(target.name()),
 710             Target::ExternCrate
 711             | Target::Use
 712             | Target::Static
 713             | Target::Const
 714             | Target::Fn
 715             | Target::Mod
 716             | Target::GlobalAsm
 717             | Target::TyAlias
 718             | Target::OpaqueTy
 719             | Target::ImplTraitPlaceholder
 720             | Target::Enum
 721             | Target::Variant
 722             | Target::Struct
 723             | Target::Field
 724             | Target::Union
 725             | Target::Trait
 726             | Target::TraitAlias
 727             | Target::Method(..)
 728             | Target::ForeignFn
 729             | Target::ForeignStatic
 730             | Target::ForeignTy
 731             | Target::GenericParam(..)
 732             | Target::MacroDef
 733             | Target::PatField
 734             | Target::ExprField => None,
 735         } {
 736             tcx.sess.emit_err(errors::DocAliasBadLocation { span, attr_str, location });
 737             return false;
 738         }
 739         let item_name = self.tcx.hir().name(hir_id);
 740         if item_name == doc_alias {
 741             tcx.sess.emit_err(errors::DocAliasNotAnAlias { span, attr_str });
 742             return false;
 743         }
 744         if let Err(entry) = aliases.try_insert(doc_alias_str.to_owned(), span) {
 745             self.tcx.emit_spanned_lint(
 746                 UNUSED_ATTRIBUTES,
 747                 hir_id,
 748                 span,
 749                 errors::DocAliasDuplicated { first_defn: *entry.entry.get() },
 750             );
 751         }
 752         true
 753     }
 754
 755     fn check_doc_alias(
 756         &self,
 757         meta: &NestedMetaItem,
 758         hir_id: HirId,
 759         target: Target,
 760         aliases: &mut FxHashMap<String, Span>,
 761     ) -> bool {
 762         if let Some(values) = meta.meta_item_list() {
 763             let mut errors = 0;
 764             for v in values {
 765                 match v.lit() {
 766                     Some(l) => match l.kind {
 767                         LitKind::Str(s, _) => {
 768                             if !self.check_doc_alias_value(v, s, hir_id, target, true, aliases) {
 769                                 errors += 1;
 770                             }
 771                         }
 772                         _ => {
 773                             self.tcx
 774                                 .sess
 775                                 .emit_err(errors::DocAliasNotStringLiteral { span: v.span() });
 776                             errors += 1;
 777                         }
 778                     },
 779                     None => {
 780                         self.tcx.sess.emit_err(errors::DocAliasNotStringLiteral { span: v.span() });
 781                         errors += 1;
 782                     }
 783                 }
 784             }
 785             errors == 0
 786         } else if let Some(doc_alias) = meta.value_str() {
 787             self.check_doc_alias_value(meta, doc_alias, hir_id, target, false, aliases)
 788         } else {
 789             self.tcx.sess.emit_err(errors::DocAliasMalformed { span: meta.span() });
 790             false
 791         }
 792     }
 793
 794     fn check_doc_keyword(&self, meta: &NestedMetaItem, hir_id: HirId) -> bool {
 795         let doc_keyword = meta.value_str().unwrap_or(kw::Empty);
 796         if doc_keyword == kw::Empty {
 797             self.doc_attr_str_error(meta, "keyword");
 798             return false;
 799         }
 800         match self.tcx.hir().find(hir_id).and_then(|node| match node {
 801             hir::Node::Item(item) => Some(&item.kind),
 802             _ => None,
 803         }) {
 804             Some(ItemKind::Mod(ref module)) => {
 805                 if !module.item_ids.is_empty() {
 806                     self.tcx.sess.emit_err(errors::DocKeywordEmptyMod { span: meta.span() });
 807                     return false;
 808                 }
 809             }
 810             _ => {
 811                 self.tcx.sess.emit_err(errors::DocKeywordNotMod { span: meta.span() });
 812                 return false;
 813             }
 814         }
 815         if !rustc_lexer::is_ident(doc_keyword.as_str()) {
 816             self.tcx.sess.emit_err(errors::DocKeywordInvalidIdent {
 817                 span: meta.name_value_literal_span().unwrap_or_else(|| meta.span()),
 818                 doc_keyword,
 819             });
 820             return false;
 821         }
 822         true
 823     }
 824
 825     fn check_doc_fake_variadic(&self, meta: &NestedMetaItem, hir_id: HirId) -> bool {
 826         match self.tcx.hir().find(hir_id).and_then(|node| match node {
 827             hir::Node::Item(item) => Some(&item.kind),
 828             _ => None,
 829         }) {
 830             Some(ItemKind::Impl(ref i)) => {
 831                 let is_valid = matches!(&i.self_ty.kind, hir::TyKind::Tup([_]))
 832                     || if let hir::TyKind::BareFn(bare_fn_ty) = &i.self_ty.kind {
 833                         bare_fn_ty.decl.inputs.len() == 1
 834                     } else {
 835                         false
 836                     };
 837                 if !is_valid {
 838                     self.tcx.sess.emit_err(errors::DocFakeVariadicNotValid { span: meta.span() });
 839                     return false;
 840                 }
 841             }
 842             _ => {
 843                 self.tcx.sess.emit_err(errors::DocKeywordOnlyImpl { span: meta.span() });
 844                 return false;
 845             }
 846         }
 847         true
 848     }
 849
 850     /// Checks `#[doc(inline)]`/`#[doc(no_inline)]` attributes. Returns `true` if valid.
 851     ///
 852     /// A doc inlining attribute is invalid if it is applied to a non-`use` item, or
 853     /// if there are conflicting attributes for one item.
 854     ///
 855     /// `specified_inline` is used to keep track of whether we have
 856     /// already seen an inlining attribute for this item.
 857     /// If so, `specified_inline` holds the value and the span of
 858     /// the first `inline`/`no_inline` attribute.
 859     fn check_doc_inline(
 860         &self,
 861         attr: &Attribute,
 862         meta: &NestedMetaItem,
 863         hir_id: HirId,
 864         target: Target,
 865         specified_inline: &mut Option<(bool, Span)>,
 866     ) -> bool {
 867         match target {
 868             Target::Use | Target::ExternCrate => {
 869                 let do_inline = meta.name_or_empty() == sym::inline;
 870                 if let Some((prev_inline, prev_span)) = *specified_inline {
 871                     if do_inline != prev_inline {
 872                         let mut spans = MultiSpan::from_spans(vec![prev_span, meta.span()]);
 873                         spans.push_span_label(prev_span, fluent::passes_doc_inline_conflict_first);
 874                         spans.push_span_label(
 875                             meta.span(),
 876                             fluent::passes_doc_inline_conflict_second,
 877                         );
 878                         self.tcx.sess.emit_err(errors::DocKeywordConflict { spans });
 879                         return false;
 880                     }
 881                     true
 882                 } else {
 883                     *specified_inline = Some((do_inline, meta.span()));
 884                     true
 885                 }
 886             }
 887             _ => {
 888                 self.tcx.emit_spanned_lint(
 889                     INVALID_DOC_ATTRIBUTES,
 890                     hir_id,
 891                     meta.span(),
 892                     errors::DocInlineOnlyUse {
 893                         attr_span: meta.span(),
 894                         item_span: (attr.style == AttrStyle::Outer)
 895                             .then(|| self.tcx.hir().span(hir_id)),
 896                     },
 897                 );
 898                 false
 899             }
 900         }
 901     }
 902
 903     /// Checks that an attribute is *not* used at the crate level. Returns `true` if valid.
 904     fn check_attr_not_crate_level(
 905         &self,
 906         meta: &NestedMetaItem,
 907         hir_id: HirId,
 908         attr_name: &str,
 909     ) -> bool {
 910         if CRATE_HIR_ID == hir_id {
 911             self.tcx.sess.emit_err(errors::DocAttrNotCrateLevel { span: meta.span(), attr_name });
 912             return false;
 913         }
 914         true
 915     }
 916
 917     /// Checks that an attribute is used at the crate level. Returns `true` if valid.
 918     fn check_attr_crate_level(
 919         &self,
 920         attr: &Attribute,
 921         meta: &NestedMetaItem,
 922         hir_id: HirId,
 923     ) -> bool {
 924         if hir_id != CRATE_HIR_ID {
 925             self.tcx.struct_span_lint_hir(
 926                 INVALID_DOC_ATTRIBUTES,
 927                 hir_id,
 928                 meta.span(),
 929                 fluent::passes_attr_crate_level,
 930                 |err| {
 931                     if attr.style == AttrStyle::Outer
 932                         && self.tcx.hir().get_parent_item(hir_id) == CRATE_OWNER_ID
 933                     {
 934                         if let Ok(mut src) = self.tcx.sess.source_map().span_to_snippet(attr.span) {
 935                             src.insert(1, '!');
 936                             err.span_suggestion_verbose(
 937                                 attr.span,
 938                                 fluent::suggestion,
 939                                 src,
 940                                 Applicability::MaybeIncorrect,
 941                             );
 942                         } else {
 943                             err.span_help(attr.span, fluent::help);
 944                         }
 945                     }
 946                     err.note(fluent::note);
 947                     err
 948                 },
 949             );
 950             return false;
 951         }
 952         true
 953     }
 954
 955     /// Checks that `doc(test(...))` attribute contains only valid attributes. Returns `true` if
 956     /// valid.
 957     fn check_test_attr(&self, meta: &NestedMetaItem, hir_id: HirId) -> bool {
 958         let mut is_valid = true;
 959         if let Some(metas) = meta.meta_item_list() {
 960             for i_meta in metas {
 961                 match i_meta.name_or_empty() {
 962                     sym::attr | sym::no_crate_inject => {}
 963                     _ => {
 964                         self.tcx.emit_spanned_lint(
 965                             INVALID_DOC_ATTRIBUTES,
 966                             hir_id,
 967                             i_meta.span(),
 968                             errors::DocTestUnknown {
 969                                 path: rustc_ast_pretty::pprust::path_to_string(
 970                                     &i_meta.meta_item().unwrap().path,
 971                                 ),
 972                             },
 973                         );
 974                         is_valid = false;
 975                     }
 976                 }
 977             }
 978         } else {
 979             self.tcx.emit_spanned_lint(
 980                 INVALID_DOC_ATTRIBUTES,
 981                 hir_id,
 982                 meta.span(),
 983                 errors::DocTestTakesList,
 984             );
 985             is_valid = false;
 986         }
 987         is_valid
 988     }
 989
 990     /// Check that the `#![doc(cfg_hide(...))]` attribute only contains a list of attributes.
 991     /// Returns `true` if valid.
 992     fn check_doc_cfg_hide(&self, meta: &NestedMetaItem, hir_id: HirId) -> bool {
 993         if meta.meta_item_list().is_some() {
 994             true
 995         } else {
 996             self.tcx.emit_spanned_lint(
 997                 INVALID_DOC_ATTRIBUTES,
 998                 hir_id,
 999                 meta.span(),
1000                 errors::DocCfgHideTakesList,
1001             );
1002             false
1003         }
1004     }
1005
1006     /// Runs various checks on `#[doc]` attributes. Returns `true` if valid.
1007     ///
1008     /// `specified_inline` should be initialized to `None` and kept for the scope
1009     /// of one item. Read the documentation of [`check_doc_inline`] for more information.
1010     ///
1011     /// [`check_doc_inline`]: Self::check_doc_inline
1012     fn check_doc_attrs(
1013         &self,
1014         attr: &Attribute,
1015         hir_id: HirId,
1016         target: Target,
1017         specified_inline: &mut Option<(bool, Span)>,
1018         aliases: &mut FxHashMap<String, Span>,
1019     ) -> bool {
1020         let mut is_valid = true;
1021
1022         if let Some(mi) = attr.meta() && let Some(list) = mi.meta_item_list() {
1023             for meta in list {
1024                 if let Some(i_meta) = meta.meta_item() {
1025                     match i_meta.name_or_empty() {
1026                         sym::alias
1027                             if !self.check_attr_not_crate_level(meta, hir_id, "alias")
1028                                 || !self.check_doc_alias(meta, hir_id, target, aliases) =>
1029                         {
1030                             is_valid = false
1031                         }
1032
1033                         sym::keyword
1034                             if !self.check_attr_not_crate_level(meta, hir_id, "keyword")
1035                                 || !self.check_doc_keyword(meta, hir_id) =>
1036                         {
1037                             is_valid = false
1038                         }
1039
1040                         sym::fake_variadic
1041                             if !self.check_attr_not_crate_level(meta, hir_id, "fake_variadic")
1042                                 || !self.check_doc_fake_variadic(meta, hir_id) =>
1043                         {
1044                             is_valid = false
1045                         }
1046
1047                         sym::html_favicon_url
1048                         | sym::html_logo_url
1049                         | sym::html_playground_url
1050                         | sym::issue_tracker_base_url
1051                         | sym::html_root_url
1052                         | sym::html_no_source
1053                         | sym::test
1054                             if !self.check_attr_crate_level(attr, meta, hir_id) =>
1055                         {
1056                             is_valid = false;
1057                         }
1058
1059                         sym::cfg_hide
1060                             if !self.check_attr_crate_level(attr, meta, hir_id)
1061                                 || !self.check_doc_cfg_hide(meta, hir_id) =>
1062                         {
1063                             is_valid = false;
1064                         }
1065
1066                         sym::inline | sym::no_inline
1067                             if !self.check_doc_inline(
1068                                 attr,
1069                                 meta,
1070                                 hir_id,
1071                                 target,
1072                                 specified_inline,
1073                             ) =>
1074                         {
1075                             is_valid = false;
1076                         }
1077
1078                         // no_default_passes: deprecated
1079                         // passes: deprecated
1080                         // plugins: removed, but rustdoc warns about it itself
1081                         sym::alias
1082                         | sym::cfg
1083                         | sym::cfg_hide
1084                         | sym::hidden
1085                         | sym::html_favicon_url
1086                         | sym::html_logo_url
1087                         | sym::html_no_source
1088                         | sym::html_playground_url
1089                         | sym::html_root_url
1090                         | sym::inline
1091                         | sym::issue_tracker_base_url
1092                         | sym::keyword
1093                         | sym::masked
1094                         | sym::no_default_passes
1095                         | sym::no_inline
1096                         | sym::notable_trait
1097                         | sym::passes
1098                         | sym::plugins
1099                         | sym::fake_variadic => {}
1100
1101                         sym::test => {
1102                             if !self.check_test_attr(meta, hir_id) {
1103                                 is_valid = false;
1104                             }
1105                         }
1106
1107                         sym::primitive => {
1108                             if !self.tcx.features().rustdoc_internals {
1109                                 self.tcx.emit_spanned_lint(
1110                                     INVALID_DOC_ATTRIBUTES,
1111                                     hir_id,
1112                                     i_meta.span,
1113                                     errors::DocPrimitive,
1114                                 );
1115                             }
1116                         }
1117
1118                         _ => {
1119                             let path = rustc_ast_pretty::pprust::path_to_string(&i_meta.path);
1120                             if i_meta.has_name(sym::spotlight) {
1121                                 self.tcx.emit_spanned_lint(
1122                                     INVALID_DOC_ATTRIBUTES,
1123                                     hir_id,
1124                                     i_meta.span,
1125                                     errors::DocTestUnknownSpotlight {
1126                                         path,
1127                                         span: i_meta.span
1128                                     }
1129                                 );
1130                             } else if i_meta.has_name(sym::include) &&
1131                                     let Some(value) = i_meta.value_str() {
1132                                 let applicability = if list.len() == 1 {
1133                                     Applicability::MachineApplicable
1134                                 } else {
1135                                     Applicability::MaybeIncorrect
1136                                 };
1137                                 // If there are multiple attributes, the suggestion would suggest
1138                                 // deleting all of them, which is incorrect.
1139                                 self.tcx.emit_spanned_lint(
1140                                     INVALID_DOC_ATTRIBUTES,
1141                                     hir_id,
1142                                     i_meta.span,
1143                                     errors::DocTestUnknownInclude {
1144                                         path,
1145                                         value: value.to_string(),
1146                                         inner: match attr.style { AttrStyle::Inner=>  "!" , AttrStyle::Outer => "" },
1147                                         sugg: (attr.meta().unwrap().span, applicability),
1148                                     }
1149                                 );
1150                             } else {
1151                                 self.tcx.emit_spanned_lint(
1152                                     INVALID_DOC_ATTRIBUTES,
1153                                     hir_id,
1154                                     i_meta.span,
1155                                     errors::DocTestUnknownAny { path }
1156                                 );
1157                             }
1158                             is_valid = false;
1159                         }
1160                     }
1161                 } else {
1162                     self.tcx.emit_spanned_lint(
1163                         INVALID_DOC_ATTRIBUTES,
1164                         hir_id,
1165                         meta.span(),
1166                         errors::DocInvalid,
1167                     );
1168                     is_valid = false;
1169                 }
1170             }
1171         }
1172
1173         is_valid
1174     }
1175
1176     /// Warns against some misuses of `#[pass_by_value]`
1177     fn check_pass_by_value(&self, attr: &Attribute, span: Span, target: Target) -> bool {
1178         match target {
1179             Target::Struct | Target::Enum | Target::TyAlias => true,
1180             _ => {
1181                 self.tcx.sess.emit_err(errors::PassByValue { attr_span: attr.span, span });
1182                 false
1183             }
1184         }
1185     }
1186
1187     fn check_allow_incoherent_impl(&self, attr: &Attribute, span: Span, target: Target) -> bool {
1188         match target {
1189             Target::Method(MethodKind::Inherent) => true,
1190             _ => {
1191                 self.tcx.sess.emit_err(errors::AllowIncoherentImpl { attr_span: attr.span, span });
1192                 false
1193             }
1194         }
1195     }
1196
1197     fn check_has_incoherent_inherent_impls(
1198         &self,
1199         attr: &Attribute,
1200         span: Span,
1201         target: Target,
1202     ) -> bool {
1203         match target {
1204             Target::Trait | Target::Struct | Target::Enum | Target::Union | Target::ForeignTy => {
1205                 true
1206             }
1207             _ => {
1208                 self.tcx
1209                     .sess
1210                     .emit_err(errors::HasIncoherentInherentImpl { attr_span: attr.span, span });
1211                 false
1212             }
1213         }
1214     }
1215
1216     /// Warns against some misuses of `#[must_use]`
1217     fn check_must_use(&self, hir_id: HirId, attr: &Attribute, target: Target) -> bool {
1218         if !matches!(
1219             target,
1220             Target::Fn
1221                 | Target::Enum
1222                 | Target::Struct
1223                 | Target::Union
1224                 | Target::Method(_)
1225                 | Target::ForeignFn
1226                 // `impl Trait` in return position can trip
1227                 // `unused_must_use` if `Trait` is marked as
1228                 // `#[must_use]`
1229                 | Target::Trait
1230         ) {
1231             let article = match target {
1232                 Target::ExternCrate
1233                 | Target::OpaqueTy
1234                 | Target::Enum
1235                 | Target::Impl
1236                 | Target::Expression
1237                 | Target::Arm
1238                 | Target::AssocConst
1239                 | Target::AssocTy => "an",
1240                 _ => "a",
1241             };
1242
1243             self.tcx.emit_spanned_lint(
1244                 UNUSED_ATTRIBUTES,
1245                 hir_id,
1246                 attr.span,
1247                 errors::MustUseNoEffect { article, target },
1248             );
1249         }
1250
1251         // For now, its always valid
1252         true
1253     }
1254
1255     /// Checks if `#[must_not_suspend]` is applied to a function. Returns `true` if valid.
1256     fn check_must_not_suspend(&self, attr: &Attribute, span: Span, target: Target) -> bool {
1257         match target {
1258             Target::Struct | Target::Enum | Target::Union | Target::Trait => true,
1259             _ => {
1260                 self.tcx.sess.emit_err(errors::MustNotSuspend { attr_span: attr.span, span });
1261                 false
1262             }
1263         }
1264     }
1265
1266     /// Checks if `#[cold]` is applied to a non-function. Returns `true` if valid.
1267     fn check_cold(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) {
1268         match target {
1269             Target::Fn | Target::Method(..) | Target::ForeignFn | Target::Closure => {}
1270             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
1271             // `#[cold]` attribute with just a lint, because we previously
1272             // erroneously allowed it and some crates used it accidentally, to be compatible
1273             // with crates depending on them, we can't throw an error here.
1274             Target::Field | Target::Arm | Target::MacroDef => {
1275                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "cold");
1276             }
1277             _ => {
1278                 // FIXME: #[cold] was previously allowed on non-functions and some crates used
1279                 // this, so only emit a warning.
1280                 self.tcx.emit_spanned_lint(
1281                     UNUSED_ATTRIBUTES,
1282                     hir_id,
1283                     attr.span,
1284                     errors::Cold { span, on_crate: hir_id == CRATE_HIR_ID },
1285                 );
1286             }
1287         }
1288     }
1289
1290     /// Checks if `#[link]` is applied to an item other than a foreign module.
1291     fn check_link(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) {
1292         if target == Target::ForeignMod
1293             && let hir::Node::Item(item) = self.tcx.hir().get(hir_id)
1294             && let Item { kind: ItemKind::ForeignMod { abi, .. }, .. } = item
1295             && !matches!(abi, Abi::Rust | Abi::RustIntrinsic | Abi::PlatformIntrinsic)
1296         {
1297             return;
1298         }
1299
1300         self.tcx.emit_spanned_lint(
1301             UNUSED_ATTRIBUTES,
1302             hir_id,
1303             attr.span,
1304             errors::Link { span: (target != Target::ForeignMod).then_some(span) },
1305         );
1306     }
1307
1308     /// Checks if `#[link_name]` is applied to an item other than a foreign function or static.
1309     fn check_link_name(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) {
1310         match target {
1311             Target::ForeignFn | Target::ForeignStatic => {}
1312             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
1313             // `#[link_name]` attribute with just a lint, because we previously
1314             // erroneously allowed it and some crates used it accidentally, to be compatible
1315             // with crates depending on them, we can't throw an error here.
1316             Target::Field | Target::Arm | Target::MacroDef => {
1317                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "link_name");
1318             }
1319             _ => {
1320                 // FIXME: #[cold] was previously allowed on non-functions/statics and some crates
1321                 // used this, so only emit a warning.
1322                 let attr_span = matches!(target, Target::ForeignMod).then_some(attr.span);
1323                 if let Some(s) = attr.value_str() {
1324                     self.tcx.emit_spanned_lint(
1325                         UNUSED_ATTRIBUTES,
1326                         hir_id,
1327                         attr.span,
1328                         errors::LinkName { span, attr_span, value: s.as_str() },
1329                     );
1330                 } else {
1331                     self.tcx.emit_spanned_lint(
1332                         UNUSED_ATTRIBUTES,
1333                         hir_id,
1334                         attr.span,
1335                         errors::LinkName { span, attr_span, value: "..." },
1336                     );
1337                 };
1338             }
1339         }
1340     }
1341
1342     /// Checks if `#[no_link]` is applied to an `extern crate`. Returns `true` if valid.
1343     fn check_no_link(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) -> bool {
1344         match target {
1345             Target::ExternCrate => true,
1346             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
1347             // `#[no_link]` attribute with just a lint, because we previously
1348             // erroneously allowed it and some crates used it accidentally, to be compatible
1349             // with crates depending on them, we can't throw an error here.
1350             Target::Field | Target::Arm | Target::MacroDef => {
1351                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "no_link");
1352                 true
1353             }
1354             _ => {
1355                 self.tcx.sess.emit_err(errors::NoLink { attr_span: attr.span, span });
1356                 false
1357             }
1358         }
1359     }
1360
1361     fn is_impl_item(&self, hir_id: HirId) -> bool {
1362         matches!(self.tcx.hir().get(hir_id), hir::Node::ImplItem(..))
1363     }
1364
1365     /// Checks if `#[export_name]` is applied to a function or static. Returns `true` if valid.
1366     fn check_export_name(
1367         &self,
1368         hir_id: HirId,
1369         attr: &Attribute,
1370         span: Span,
1371         target: Target,
1372     ) -> bool {
1373         match target {
1374             Target::Static | Target::Fn => true,
1375             Target::Method(..) if self.is_impl_item(hir_id) => true,
1376             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
1377             // `#[export_name]` attribute with just a lint, because we previously
1378             // erroneously allowed it and some crates used it accidentally, to be compatible
1379             // with crates depending on them, we can't throw an error here.
1380             Target::Field | Target::Arm | Target::MacroDef => {
1381                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "export_name");
1382                 true
1383             }
1384             _ => {
1385                 self.tcx.sess.emit_err(errors::ExportName { attr_span: attr.span, span });
1386                 false
1387             }
1388         }
1389     }
1390
1391     fn check_rustc_layout_scalar_valid_range(
1392         &self,
1393         attr: &Attribute,
1394         span: Span,
1395         target: Target,
1396     ) -> bool {
1397         if target != Target::Struct {
1398             self.tcx.sess.emit_err(errors::RustcLayoutScalarValidRangeNotStruct {
1399                 attr_span: attr.span,
1400                 span,
1401             });
1402             return false;
1403         }
1404
1405         let Some(list) = attr.meta_item_list() else {
1406             return false;
1407         };
1408
1409         if matches!(&list[..], &[NestedMetaItem::Lit(MetaItemLit { kind: LitKind::Int(..), .. })]) {
1410             true
1411         } else {
1412             self.tcx.sess.emit_err(errors::RustcLayoutScalarValidRangeArg { attr_span: attr.span });
1413             false
1414         }
1415     }
1416
1417     /// Checks if `#[rustc_legacy_const_generics]` is applied to a function and has a valid argument.
1418     fn check_rustc_legacy_const_generics(
1419         &self,
1420         hir_id: HirId,
1421         attr: &Attribute,
1422         span: Span,
1423         target: Target,
1424         item: Option<ItemLike<'_>>,
1425     ) -> bool {
1426         let is_function = matches!(target, Target::Fn);
1427         if !is_function {
1428             self.tcx.sess.emit_err(errors::AttrShouldBeAppliedToFn {
1429                 attr_span: attr.span,
1430                 defn_span: span,
1431                 on_crate: hir_id == CRATE_HIR_ID,
1432             });
1433             return false;
1434         }
1435
1436         let Some(list) = attr.meta_item_list() else {
1437             // The attribute form is validated on AST.
1438             return false;
1439         };
1440
1441         let Some(ItemLike::Item(Item {
1442             kind: ItemKind::Fn(FnSig { decl, .. }, generics, _),
1443             ..
1444         }))  = item else {
1445             bug!("should be a function item");
1446         };
1447
1448         for param in generics.params {
1449             match param.kind {
1450                 hir::GenericParamKind::Const { .. } => {}
1451                 _ => {
1452                     self.tcx.sess.emit_err(errors::RustcLegacyConstGenericsOnly {
1453                         attr_span: attr.span,
1454                         param_span: param.span,
1455                     });
1456                     return false;
1457                 }
1458             }
1459         }
1460
1461         if list.len() != generics.params.len() {
1462             self.tcx.sess.emit_err(errors::RustcLegacyConstGenericsIndex {
1463                 attr_span: attr.span,
1464                 generics_span: generics.span,
1465             });
1466             return false;
1467         }
1468
1469         let arg_count = decl.inputs.len() as u128 + generics.params.len() as u128;
1470         let mut invalid_args = vec![];
1471         for meta in list {
1472             if let Some(LitKind::Int(val, _)) = meta.lit().map(|lit| &lit.kind) {
1473                 if *val >= arg_count {
1474                     let span = meta.span();
1475                     self.tcx.sess.emit_err(errors::RustcLegacyConstGenericsIndexExceed {
1476                         span,
1477                         arg_count: arg_count as usize,
1478                     });
1479                     return false;
1480                 }
1481             } else {
1482                 invalid_args.push(meta.span());
1483             }
1484         }
1485
1486         if !invalid_args.is_empty() {
1487             self.tcx.sess.emit_err(errors::RustcLegacyConstGenericsIndexNegative { invalid_args });
1488             false
1489         } else {
1490             true
1491         }
1492     }
1493
1494     /// Helper function for checking that the provided attribute is only applied to a function or
1495     /// method.
1496     fn check_applied_to_fn_or_method(
1497         &self,
1498         hir_id: HirId,
1499         attr: &Attribute,
1500         span: Span,
1501         target: Target,
1502     ) -> bool {
1503         let is_function = matches!(target, Target::Fn | Target::Method(..));
1504         if !is_function {
1505             self.tcx.sess.emit_err(errors::AttrShouldBeAppliedToFn {
1506                 attr_span: attr.span,
1507                 defn_span: span,
1508                 on_crate: hir_id == CRATE_HIR_ID,
1509             });
1510             false
1511         } else {
1512             true
1513         }
1514     }
1515
1516     /// Checks that the `#[rustc_lint_query_instability]` attribute is only applied to a function
1517     /// or method.
1518     fn check_rustc_lint_query_instability(
1519         &self,
1520         hir_id: HirId,
1521         attr: &Attribute,
1522         span: Span,
1523         target: Target,
1524     ) -> bool {
1525         self.check_applied_to_fn_or_method(hir_id, attr, span, target)
1526     }
1527
1528     /// Checks that the `#[rustc_lint_diagnostics]` attribute is only applied to a function or
1529     /// method.
1530     fn check_rustc_lint_diagnostics(
1531         &self,
1532         hir_id: HirId,
1533         attr: &Attribute,
1534         span: Span,
1535         target: Target,
1536     ) -> bool {
1537         self.check_applied_to_fn_or_method(hir_id, attr, span, target)
1538     }
1539
1540     /// Checks that the `#[rustc_lint_opt_ty]` attribute is only applied to a struct.
1541     fn check_rustc_lint_opt_ty(&self, attr: &Attribute, span: Span, target: Target) -> bool {
1542         match target {
1543             Target::Struct => true,
1544             _ => {
1545                 self.tcx.sess.emit_err(errors::RustcLintOptTy { attr_span: attr.span, span });
1546                 false
1547             }
1548         }
1549     }
1550
1551     /// Checks that the `#[rustc_lint_opt_deny_field_access]` attribute is only applied to a field.
1552     fn check_rustc_lint_opt_deny_field_access(
1553         &self,
1554         attr: &Attribute,
1555         span: Span,
1556         target: Target,
1557     ) -> bool {
1558         match target {
1559             Target::Field => true,
1560             _ => {
1561                 self.tcx
1562                     .sess
1563                     .emit_err(errors::RustcLintOptDenyFieldAccess { attr_span: attr.span, span });
1564                 false
1565             }
1566         }
1567     }
1568
1569     /// Checks that the dep-graph debugging attributes are only present when the query-dep-graph
1570     /// option is passed to the compiler.
1571     fn check_rustc_dirty_clean(&self, attr: &Attribute) -> bool {
1572         if self.tcx.sess.opts.unstable_opts.query_dep_graph {
1573             true
1574         } else {
1575             self.tcx.sess.emit_err(errors::RustcDirtyClean { span: attr.span });
1576             false
1577         }
1578     }
1579
1580     /// Checks if `#[link_section]` is applied to a function or static.
1581     fn check_link_section(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) {
1582         match target {
1583             Target::Static | Target::Fn | Target::Method(..) => {}
1584             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
1585             // `#[link_section]` attribute with just a lint, because we previously
1586             // erroneously allowed it and some crates used it accidentally, to be compatible
1587             // with crates depending on them, we can't throw an error here.
1588             Target::Field | Target::Arm | Target::MacroDef => {
1589                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "link_section");
1590             }
1591             _ => {
1592                 // FIXME: #[link_section] was previously allowed on non-functions/statics and some
1593                 // crates used this, so only emit a warning.
1594                 self.tcx.emit_spanned_lint(
1595                     UNUSED_ATTRIBUTES,
1596                     hir_id,
1597                     attr.span,
1598                     errors::LinkSection { span },
1599                 );
1600             }
1601         }
1602     }
1603
1604     /// Checks if `#[no_mangle]` is applied to a function or static.
1605     fn check_no_mangle(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) {
1606         match target {
1607             Target::Static | Target::Fn => {}
1608             Target::Method(..) if self.is_impl_item(hir_id) => {}
1609             // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
1610             // `#[no_mangle]` attribute with just a lint, because we previously
1611             // erroneously allowed it and some crates used it accidentally, to be compatible
1612             // with crates depending on them, we can't throw an error here.
1613             Target::Field | Target::Arm | Target::MacroDef => {
1614                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "no_mangle");
1615             }
1616             // FIXME: #[no_mangle] was previously allowed on non-functions/statics, this should be an error
1617             // The error should specify that the item that is wrong is specifically a *foreign* fn/static
1618             // otherwise the error seems odd
1619             Target::ForeignFn | Target::ForeignStatic => {
1620                 let foreign_item_kind = match target {
1621                     Target::ForeignFn => "function",
1622                     Target::ForeignStatic => "static",
1623                     _ => unreachable!(),
1624                 };
1625                 self.tcx.emit_spanned_lint(
1626                     UNUSED_ATTRIBUTES,
1627                     hir_id,
1628                     attr.span,
1629                     errors::NoMangleForeign { span, attr_span: attr.span, foreign_item_kind },
1630                 );
1631             }
1632             _ => {
1633                 // FIXME: #[no_mangle] was previously allowed on non-functions/statics and some
1634                 // crates used this, so only emit a warning.
1635                 self.tcx.emit_spanned_lint(
1636                     UNUSED_ATTRIBUTES,
1637                     hir_id,
1638                     attr.span,
1639                     errors::NoMangle { span },
1640                 );
1641             }
1642         }
1643     }
1644
1645     /// Checks if the `#[repr]` attributes on `item` are valid.
1646     fn check_repr(
1647         &self,
1648         attrs: &[Attribute],
1649         span: Span,
1650         target: Target,
1651         item: Option<ItemLike<'_>>,
1652         hir_id: HirId,
1653     ) {
1654         // Extract the names of all repr hints, e.g., [foo, bar, align] for:
1655         // ```
1656         // #[repr(foo)]
1657         // #[repr(bar, align(8))]
1658         // ```
1659         let hints: Vec<_> = attrs
1660             .iter()
1661             .filter(|attr| attr.has_name(sym::repr))
1662             .filter_map(|attr| attr.meta_item_list())
1663             .flatten()
1664             .collect();
1665
1666         let mut int_reprs = 0;
1667         let mut is_c = false;
1668         let mut is_simd = false;
1669         let mut is_transparent = false;
1670
1671         for hint in &hints {
1672             if !hint.is_meta_item() {
1673                 self.tcx.sess.emit_err(errors::ReprIdent { span: hint.span() });
1674                 continue;
1675             }
1676
1677             match hint.name_or_empty() {
1678                 sym::C => {
1679                     is_c = true;
1680                     match target {
1681                         Target::Struct | Target::Union | Target::Enum => continue,
1682                         _ => {
1683                             self.tcx.sess.emit_err(AttrApplication::StructEnumUnion {
1684                                 hint_span: hint.span(),
1685                                 span,
1686                             });
1687                         }
1688                     }
1689                 }
1690                 sym::align => {
1691                     if let (Target::Fn, false) = (target, self.tcx.features().fn_align) {
1692                         feature_err(
1693                             &self.tcx.sess.parse_sess,
1694                             sym::fn_align,
1695                             hint.span(),
1696                             "`repr(align)` attributes on functions are unstable",
1697                         )
1698                         .emit();
1699                     }
1700
1701                     match target {
1702                         Target::Struct | Target::Union | Target::Enum | Target::Fn => continue,
1703                         _ => {
1704                             self.tcx.sess.emit_err(AttrApplication::StructEnumFunctionUnion {
1705                                 hint_span: hint.span(),
1706                                 span,
1707                             });
1708                         }
1709                     }
1710                 }
1711                 sym::packed => {
1712                     if target != Target::Struct && target != Target::Union {
1713                         self.tcx.sess.emit_err(AttrApplication::StructUnion {
1714                             hint_span: hint.span(),
1715                             span,
1716                         });
1717                     } else {
1718                         continue;
1719                     }
1720                 }
1721                 sym::simd => {
1722                     is_simd = true;
1723                     if target != Target::Struct {
1724                         self.tcx
1725                             .sess
1726                             .emit_err(AttrApplication::Struct { hint_span: hint.span(), span });
1727                     } else {
1728                         continue;
1729                     }
1730                 }
1731                 sym::transparent => {
1732                     is_transparent = true;
1733                     match target {
1734                         Target::Struct | Target::Union | Target::Enum => continue,
1735                         _ => {
1736                             self.tcx.sess.emit_err(AttrApplication::StructEnumUnion {
1737                                 hint_span: hint.span(),
1738                                 span,
1739                             });
1740                         }
1741                     }
1742                 }
1743                 sym::i8
1744                 | sym::u8
1745                 | sym::i16
1746                 | sym::u16
1747                 | sym::i32
1748                 | sym::u32
1749                 | sym::i64
1750                 | sym::u64
1751                 | sym::i128
1752                 | sym::u128
1753                 | sym::isize
1754                 | sym::usize => {
1755                     int_reprs += 1;
1756                     if target != Target::Enum {
1757                         self.tcx
1758                             .sess
1759                             .emit_err(AttrApplication::Enum { hint_span: hint.span(), span });
1760                     } else {
1761                         continue;
1762                     }
1763                 }
1764                 _ => {
1765                     self.tcx.sess.emit_err(UnrecognizedReprHint { span: hint.span() });
1766                     continue;
1767                 }
1768             };
1769         }
1770
1771         // Just point at all repr hints if there are any incompatibilities.
1772         // This is not ideal, but tracking precisely which ones are at fault is a huge hassle.
1773         let hint_spans = hints.iter().map(|hint| hint.span());
1774
1775         // Error on repr(transparent, <anything else>).
1776         if is_transparent && hints.len() > 1 {
1777             let hint_spans: Vec<_> = hint_spans.clone().collect();
1778             self.tcx
1779                 .sess
1780                 .emit_err(TransparentIncompatible { hint_spans, target: target.to_string() });
1781         }
1782         // Warn on repr(u8, u16), repr(C, simd), and c-like-enum-repr(C, u8)
1783         if (int_reprs > 1)
1784             || (is_simd && is_c)
1785             || (int_reprs == 1
1786                 && is_c
1787                 && item.map_or(false, |item| {
1788                     if let ItemLike::Item(item) = item {
1789                         return is_c_like_enum(item);
1790                     }
1791                     return false;
1792                 }))
1793         {
1794             self.tcx.emit_spanned_lint(
1795                 CONFLICTING_REPR_HINTS,
1796                 hir_id,
1797                 hint_spans.collect::<Vec<Span>>(),
1798                 errors::ReprConflicting,
1799             );
1800         }
1801     }
1802
1803     fn check_used(&self, attrs: &[Attribute], target: Target) {
1804         let mut used_linker_span = None;
1805         let mut used_compiler_span = None;
1806         for attr in attrs.iter().filter(|attr| attr.has_name(sym::used)) {
1807             if target != Target::Static {
1808                 self.tcx.sess.emit_err(errors::UsedStatic { span: attr.span });
1809             }
1810             let inner = attr.meta_item_list();
1811             match inner.as_deref() {
1812                 Some([item]) if item.has_name(sym::linker) => {
1813                     if used_linker_span.is_none() {
1814                         used_linker_span = Some(attr.span);
1815                     }
1816                 }
1817                 Some([item]) if item.has_name(sym::compiler) => {
1818                     if used_compiler_span.is_none() {
1819                         used_compiler_span = Some(attr.span);
1820                     }
1821                 }
1822                 Some(_) => {
1823                     // This error case is handled in rustc_hir_analysis::collect.
1824                 }
1825                 None => {
1826                     // Default case (compiler) when arg isn't defined.
1827                     if used_compiler_span.is_none() {
1828                         used_compiler_span = Some(attr.span);
1829                     }
1830                 }
1831             }
1832         }
1833         if let (Some(linker_span), Some(compiler_span)) = (used_linker_span, used_compiler_span) {
1834             self.tcx
1835                 .sess
1836                 .emit_err(errors::UsedCompilerLinker { spans: vec![linker_span, compiler_span] });
1837         }
1838     }
1839
1840     /// Outputs an error for `#[allow_internal_unstable]` which can only be applied to macros.
1841     /// (Allows proc_macro functions)
1842     fn check_allow_internal_unstable(
1843         &self,
1844         hir_id: HirId,
1845         attr: &Attribute,
1846         span: Span,
1847         target: Target,
1848         attrs: &[Attribute],
1849     ) -> bool {
1850         debug!("Checking target: {:?}", target);
1851         match target {
1852             Target::Fn => {
1853                 for attr in attrs {
1854                     if self.tcx.sess.is_proc_macro_attr(attr) {
1855                         debug!("Is proc macro attr");
1856                         return true;
1857                     }
1858                 }
1859                 debug!("Is not proc macro attr");
1860                 false
1861             }
1862             Target::MacroDef => true,
1863             // FIXME(#80564): We permit struct fields and match arms to have an
1864             // `#[allow_internal_unstable]` attribute with just a lint, because we previously
1865             // erroneously allowed it and some crates used it accidentally, to be compatible
1866             // with crates depending on them, we can't throw an error here.
1867             Target::Field | Target::Arm => {
1868                 self.inline_attr_str_error_without_macro_def(
1869                     hir_id,
1870                     attr,
1871                     "allow_internal_unstable",
1872                 );
1873                 true
1874             }
1875             _ => {
1876                 self.tcx
1877                     .sess
1878                     .emit_err(errors::AllowInternalUnstable { attr_span: attr.span, span });
1879                 false
1880             }
1881         }
1882     }
1883
1884     /// Checks if the items on the `#[debugger_visualizer]` attribute are valid.
1885     fn check_debugger_visualizer(&self, attr: &Attribute, target: Target) -> bool {
1886         match target {
1887             Target::Mod => {}
1888             _ => {
1889                 self.tcx.sess.emit_err(errors::DebugVisualizerPlacement { span: attr.span });
1890                 return false;
1891             }
1892         }
1893
1894         let Some(hints) = attr.meta_item_list() else {
1895             self.tcx.sess.emit_err(errors::DebugVisualizerInvalid { span: attr.span });
1896             return false;
1897         };
1898
1899         let hint = match hints.len() {
1900             1 => &hints[0],
1901             _ => {
1902                 self.tcx.sess.emit_err(errors::DebugVisualizerInvalid { span: attr.span });
1903                 return false;
1904             }
1905         };
1906
1907         let Some(meta_item) = hint.meta_item() else {
1908             self.tcx.sess.emit_err(errors::DebugVisualizerInvalid { span: attr.span });
1909             return false;
1910         };
1911
1912         let visualizer_path = match (meta_item.name_or_empty(), meta_item.value_str()) {
1913             (sym::natvis_file, Some(value)) => value,
1914             (sym::gdb_script_file, Some(value)) => value,
1915             (_, _) => {
1916                 self.tcx.sess.emit_err(errors::DebugVisualizerInvalid { span: meta_item.span });
1917                 return false;
1918             }
1919         };
1920
1921         let file =
1922             match resolve_path(&self.tcx.sess.parse_sess, visualizer_path.as_str(), attr.span) {
1923                 Ok(file) => file,
1924                 Err(mut err) => {
1925                     err.emit();
1926                     return false;
1927                 }
1928             };
1929
1930         match std::fs::File::open(&file) {
1931             Ok(_) => true,
1932             Err(error) => {
1933                 self.tcx.sess.emit_err(DebugVisualizerUnreadable {
1934                     span: meta_item.span,
1935                     file: &file,
1936                     error,
1937                 });
1938                 false
1939             }
1940         }
1941     }
1942
1943     /// Outputs an error for `#[allow_internal_unstable]` which can only be applied to macros.
1944     /// (Allows proc_macro functions)
1945     fn check_rustc_allow_const_fn_unstable(
1946         &self,
1947         hir_id: HirId,
1948         attr: &Attribute,
1949         span: Span,
1950         target: Target,
1951     ) -> bool {
1952         match target {
1953             Target::Fn | Target::Method(_)
1954                 if self.tcx.is_const_fn_raw(hir_id.expect_owner().to_def_id()) =>
1955             {
1956                 true
1957             }
1958             // FIXME(#80564): We permit struct fields and match arms to have an
1959             // `#[allow_internal_unstable]` attribute with just a lint, because we previously
1960             // erroneously allowed it and some crates used it accidentally, to be compatible
1961             // with crates depending on them, we can't throw an error here.
1962             Target::Field | Target::Arm | Target::MacroDef => {
1963                 self.inline_attr_str_error_with_macro_def(hir_id, attr, "allow_internal_unstable");
1964                 true
1965             }
1966             _ => {
1967                 self.tcx
1968                     .sess
1969                     .emit_err(errors::RustcAllowConstFnUnstable { attr_span: attr.span, span });
1970                 false
1971             }
1972         }
1973     }
1974
1975     fn check_rustc_std_internal_symbol(
1976         &self,
1977         attr: &Attribute,
1978         span: Span,
1979         target: Target,
1980     ) -> bool {
1981         match target {
1982             Target::Fn | Target::Static => true,
1983             _ => {
1984                 self.tcx
1985                     .sess
1986                     .emit_err(errors::RustcStdInternalSymbol { attr_span: attr.span, span });
1987                 false
1988             }
1989         }
1990     }
1991
1992     /// `#[const_trait]` only applies to traits.
1993     fn check_const_trait(&self, attr: &Attribute, _span: Span, target: Target) -> bool {
1994         match target {
1995             Target::Trait => true,
1996             _ => {
1997                 self.tcx.sess.emit_err(errors::ConstTrait { attr_span: attr.span });
1998                 false
1999             }
2000         }
2001     }
2002
2003     fn check_stability_promotable(&self, attr: &Attribute, _span: Span, target: Target) -> bool {
2004         match target {
2005             Target::Expression => {
2006                 self.tcx.sess.emit_err(errors::StabilityPromotable { attr_span: attr.span });
2007                 false
2008             }
2009             _ => true,
2010         }
2011     }
2012
2013     fn check_link_ordinal(&self, attr: &Attribute, _span: Span, target: Target) -> bool {
2014         match target {
2015             Target::ForeignFn | Target::ForeignStatic => true,
2016             _ => {
2017                 self.tcx.sess.emit_err(errors::LinkOrdinal { attr_span: attr.span });
2018                 false
2019             }
2020         }
2021     }
2022
2023     fn check_deprecated(&self, hir_id: HirId, attr: &Attribute, _span: Span, target: Target) {
2024         match target {
2025             Target::Closure | Target::Expression | Target::Statement | Target::Arm => {
2026                 self.tcx.emit_spanned_lint(
2027                     UNUSED_ATTRIBUTES,
2028                     hir_id,
2029                     attr.span,
2030                     errors::Deprecated,
2031                 );
2032             }
2033             _ => {}
2034         }
2035     }
2036
2037     fn check_macro_use(&self, hir_id: HirId, attr: &Attribute, target: Target) {
2038         let name = attr.name_or_empty();
2039         match target {
2040             Target::ExternCrate | Target::Mod => {}
2041             _ => {
2042                 self.tcx.emit_spanned_lint(
2043                     UNUSED_ATTRIBUTES,
2044                     hir_id,
2045                     attr.span,
2046                     errors::MacroUse { name },
2047                 );
2048             }
2049         }
2050     }
2051
2052     fn check_macro_export(&self, hir_id: HirId, attr: &Attribute, target: Target) {
2053         if target != Target::MacroDef {
2054             self.tcx.emit_spanned_lint(UNUSED_ATTRIBUTES, hir_id, attr.span, errors::MacroExport);
2055         }
2056     }
2057
2058     fn check_plugin_registrar(&self, hir_id: HirId, attr: &Attribute, target: Target) {
2059         if target != Target::Fn {
2060             self.tcx.emit_spanned_lint(
2061                 UNUSED_ATTRIBUTES,
2062                 hir_id,
2063                 attr.span,
2064                 errors::PluginRegistrar,
2065             );
2066         }
2067     }
2068
2069     fn check_unused_attribute(&self, hir_id: HirId, attr: &Attribute) {
2070         // Warn on useless empty attributes.
2071         let note = if matches!(
2072             attr.name_or_empty(),
2073             sym::macro_use
2074                 | sym::allow
2075                 | sym::expect
2076                 | sym::warn
2077                 | sym::deny
2078                 | sym::forbid
2079                 | sym::feature
2080                 | sym::repr
2081                 | sym::target_feature
2082         ) && attr.meta_item_list().map_or(false, |list| list.is_empty())
2083         {
2084             errors::UnusedNote::EmptyList { name: attr.name_or_empty() }
2085         } else if matches!(
2086                 attr.name_or_empty(),
2087                 sym::allow | sym::warn | sym::deny | sym::forbid | sym::expect
2088             ) && let Some(meta) = attr.meta_item_list()
2089             && meta.len() == 1
2090             && let Some(item) = meta[0].meta_item()
2091             && let MetaItemKind::NameValue(_) = &item.kind
2092             && item.path == sym::reason
2093         {
2094             errors::UnusedNote::NoLints { name: attr.name_or_empty() }
2095         } else if attr.name_or_empty() == sym::default_method_body_is_const {
2096             errors::UnusedNote::DefaultMethodBodyConst
2097         } else {
2098             return;
2099         };
2100
2101         self.tcx.emit_spanned_lint(
2102             UNUSED_ATTRIBUTES,
2103             hir_id,
2104             attr.span,
2105             errors::Unused { attr_span: attr.span, note },
2106         );
2107     }
2108
2109     /// A best effort attempt to create an error for a mismatching proc macro signature.
2110     ///
2111     /// If this best effort goes wrong, it will just emit a worse error later (see #102923)
2112     fn check_proc_macro(&self, hir_id: HirId, target: Target, kind: ProcMacroKind) {
2113         let expected_input_count = match kind {
2114             ProcMacroKind::Attribute => 2,
2115             ProcMacroKind::Derive | ProcMacroKind::FunctionLike => 1,
2116         };
2117
2118         let expected_signature = match kind {
2119             ProcMacroKind::Attribute => "fn(TokenStream, TokenStream) -> TokenStream",
2120             ProcMacroKind::Derive | ProcMacroKind::FunctionLike => "fn(TokenStream) -> TokenStream",
2121         };
2122
2123         let tcx = self.tcx;
2124         if target == Target::Fn {
2125             let Some(tokenstream) = tcx.get_diagnostic_item(sym::TokenStream) else {return};
2126             let tokenstream = tcx.type_of(tokenstream);
2127
2128             let id = hir_id.expect_owner();
2129             let hir_sig = tcx.hir().fn_sig_by_hir_id(hir_id).unwrap();
2130
2131             let sig =
2132                 tcx.liberate_late_bound_regions(id.to_def_id(), tcx.fn_sig(id).subst_identity());
2133             let sig = tcx.normalize_erasing_regions(ParamEnv::empty(), sig);
2134
2135             // We don't currently require that the function signature is equal to
2136             // `fn(TokenStream) -> TokenStream`, but instead monomorphizes to
2137             // `fn(TokenStream) -> TokenStream` after some substitution of generic arguments.
2138             //
2139             // Properly checking this means pulling in additional `rustc` crates, so we don't.
2140             let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsInfer };
2141
2142             if sig.abi != Abi::Rust {
2143                 tcx.sess.emit_err(ProcMacroInvalidAbi { span: hir_sig.span, abi: sig.abi.name() });
2144                 self.abort.set(true);
2145             }
2146
2147             if sig.unsafety == Unsafety::Unsafe {
2148                 tcx.sess.emit_err(ProcMacroUnsafe { span: hir_sig.span });
2149                 self.abort.set(true);
2150             }
2151
2152             let output = sig.output();
2153
2154             // Typecheck the output
2155             if !drcx.types_may_unify(output, tokenstream) {
2156                 tcx.sess.emit_err(ProcMacroTypeError {
2157                     span: hir_sig.decl.output.span(),
2158                     found: output,
2159                     kind,
2160                     expected_signature,
2161                 });
2162                 self.abort.set(true);
2163             }
2164
2165             if sig.inputs().len() < expected_input_count {
2166                 tcx.sess.emit_err(ProcMacroMissingArguments {
2167                     expected_input_count,
2168                     span: hir_sig.span,
2169                     kind,
2170                     expected_signature,
2171                 });
2172                 self.abort.set(true);
2173             }
2174
2175             // Check that the inputs are correct, if there are enough.
2176             if sig.inputs().len() >= expected_input_count {
2177                 for (arg, input) in
2178                     sig.inputs().iter().zip(hir_sig.decl.inputs).take(expected_input_count)
2179                 {
2180                     if !drcx.types_may_unify(*arg, tokenstream) {
2181                         tcx.sess.emit_err(ProcMacroTypeError {
2182                             span: input.span,
2183                             found: *arg,
2184                             kind,
2185                             expected_signature,
2186                         });
2187                         self.abort.set(true);
2188                     }
2189                 }
2190             }
2191
2192             // Check that there are not too many arguments
2193             let body_id = tcx.hir().body_owned_by(id.def_id);
2194             let excess = tcx.hir().body(body_id).params.get(expected_input_count..);
2195             if let Some(excess @ [begin @ end] | excess @ [begin, .., end]) = excess {
2196                 tcx.sess.emit_err(ProcMacroDiffArguments {
2197                     span: begin.span.to(end.span),
2198                     count: excess.len(),
2199                     kind,
2200                     expected_signature,
2201                 });
2202                 self.abort.set(true);
2203             }
2204         }
2205     }
2206 }
2207
2208 impl<'tcx> Visitor<'tcx> for CheckAttrVisitor<'tcx> {
2209     type NestedFilter = nested_filter::OnlyBodies;
2210
2211     fn nested_visit_map(&mut self) -> Self::Map {
2212         self.tcx.hir()
2213     }
2214
2215     fn visit_item(&mut self, item: &'tcx Item<'tcx>) {
2216         // Historically we've run more checks on non-exported than exported macros,
2217         // so this lets us continue to run them while maintaining backwards compatibility.
2218         // In the long run, the checks should be harmonized.
2219         if let ItemKind::Macro(ref macro_def, _) = item.kind {
2220             let def_id = item.owner_id.to_def_id();
2221             if macro_def.macro_rules && !self.tcx.has_attr(def_id, sym::macro_export) {
2222                 check_non_exported_macro_for_invalid_attrs(self.tcx, item);
2223             }
2224         }
2225
2226         let target = Target::from_item(item);
2227         self.check_attributes(item.hir_id(), item.span, target, Some(ItemLike::Item(item)));
2228         intravisit::walk_item(self, item)
2229     }
2230
2231     fn visit_generic_param(&mut self, generic_param: &'tcx hir::GenericParam<'tcx>) {
2232         let target = Target::from_generic_param(generic_param);
2233         self.check_attributes(generic_param.hir_id, generic_param.span, target, None);
2234         intravisit::walk_generic_param(self, generic_param)
2235     }
2236
2237     fn visit_trait_item(&mut self, trait_item: &'tcx TraitItem<'tcx>) {
2238         let target = Target::from_trait_item(trait_item);
2239         self.check_attributes(trait_item.hir_id(), trait_item.span, target, None);
2240         intravisit::walk_trait_item(self, trait_item)
2241     }
2242
2243     fn visit_field_def(&mut self, struct_field: &'tcx hir::FieldDef<'tcx>) {
2244         self.check_attributes(struct_field.hir_id, struct_field.span, Target::Field, None);
2245         intravisit::walk_field_def(self, struct_field);
2246     }
2247
2248     fn visit_arm(&mut self, arm: &'tcx hir::Arm<'tcx>) {
2249         self.check_attributes(arm.hir_id, arm.span, Target::Arm, None);
2250         intravisit::walk_arm(self, arm);
2251     }
2252
2253     fn visit_foreign_item(&mut self, f_item: &'tcx ForeignItem<'tcx>) {
2254         let target = Target::from_foreign_item(f_item);
2255         self.check_attributes(f_item.hir_id(), f_item.span, target, Some(ItemLike::ForeignItem));
2256         intravisit::walk_foreign_item(self, f_item)
2257     }
2258
2259     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
2260         let target = target_from_impl_item(self.tcx, impl_item);
2261         self.check_attributes(impl_item.hir_id(), impl_item.span, target, None);
2262         intravisit::walk_impl_item(self, impl_item)
2263     }
2264
2265     fn visit_stmt(&mut self, stmt: &'tcx hir::Stmt<'tcx>) {
2266         // When checking statements ignore expressions, they will be checked later.
2267         if let hir::StmtKind::Local(ref l) = stmt.kind {
2268             self.check_attributes(l.hir_id, stmt.span, Target::Statement, None);
2269         }
2270         intravisit::walk_stmt(self, stmt)
2271     }
2272
2273     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
2274         let target = match expr.kind {
2275             hir::ExprKind::Closure { .. } => Target::Closure,
2276             _ => Target::Expression,
2277         };
2278
2279         self.check_attributes(expr.hir_id, expr.span, target, None);
2280         intravisit::walk_expr(self, expr)
2281     }
2282
2283     fn visit_expr_field(&mut self, field: &'tcx hir::ExprField<'tcx>) {
2284         self.check_attributes(field.hir_id, field.span, Target::ExprField, None);
2285         intravisit::walk_expr_field(self, field)
2286     }
2287
2288     fn visit_variant(&mut self, variant: &'tcx hir::Variant<'tcx>) {
2289         self.check_attributes(variant.hir_id, variant.span, Target::Variant, None);
2290         intravisit::walk_variant(self, variant)
2291     }
2292
2293     fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) {
2294         self.check_attributes(param.hir_id, param.span, Target::Param, None);
2295
2296         intravisit::walk_param(self, param);
2297     }
2298
2299     fn visit_pat_field(&mut self, field: &'tcx hir::PatField<'tcx>) {
2300         self.check_attributes(field.hir_id, field.span, Target::PatField, None);
2301         intravisit::walk_pat_field(self, field);
2302     }
2303 }
2304
2305 fn is_c_like_enum(item: &Item<'_>) -> bool {
2306     if let ItemKind::Enum(ref def, _) = item.kind {
2307         for variant in def.variants {
2308             match variant.data {
2309                 hir::VariantData::Unit(..) => { /* continue */ }
2310                 _ => return false,
2311             }
2312         }
2313         true
2314     } else {
2315         false
2316     }
2317 }
2318
2319 // FIXME: Fix "Cannot determine resolution" error and remove built-in macros
2320 // from this check.
2321 fn check_invalid_crate_level_attr(tcx: TyCtxt<'_>, attrs: &[Attribute]) {
2322     // Check for builtin attributes at the crate level
2323     // which were unsuccessfully resolved due to cannot determine
2324     // resolution for the attribute macro error.
2325     const ATTRS_TO_CHECK: &[Symbol] = &[
2326         sym::macro_export,
2327         sym::repr,
2328         sym::path,
2329         sym::automatically_derived,
2330         sym::start,
2331         sym::rustc_main,
2332         sym::unix_sigpipe,
2333         sym::derive,
2334         sym::test,
2335         sym::test_case,
2336         sym::global_allocator,
2337         sym::bench,
2338     ];
2339
2340     for attr in attrs {
2341         // This function should only be called with crate attributes
2342         // which are inner attributes always but lets check to make sure
2343         if attr.style == AttrStyle::Inner {
2344             for attr_to_check in ATTRS_TO_CHECK {
2345                 if attr.has_name(*attr_to_check) {
2346                     tcx.sess.emit_err(InvalidAttrAtCrateLevel {
2347                         span: attr.span,
2348                         snippet: tcx.sess.source_map().span_to_snippet(attr.span).ok(),
2349                         name: *attr_to_check,
2350                     });
2351                 }
2352             }
2353         }
2354     }
2355 }
2356
2357 fn check_non_exported_macro_for_invalid_attrs(tcx: TyCtxt<'_>, item: &Item<'_>) {
2358     let attrs = tcx.hir().attrs(item.hir_id());
2359
2360     for attr in attrs {
2361         if attr.has_name(sym::inline) {
2362             tcx.sess.emit_err(errors::NonExportedMacroInvalidAttrs { attr_span: attr.span });
2363         }
2364     }
2365 }
2366
2367 fn check_mod_attrs(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
2368     let check_attr_visitor = &mut CheckAttrVisitor { tcx, abort: Cell::new(false) };
2369     tcx.hir().visit_item_likes_in_module(module_def_id, check_attr_visitor);
2370     if module_def_id.is_top_level_module() {
2371         check_attr_visitor.check_attributes(CRATE_HIR_ID, DUMMY_SP, Target::Mod, None);
2372         check_invalid_crate_level_attr(tcx, tcx.hir().krate_attrs());
2373     }
2374     if check_attr_visitor.abort.get() {
2375         tcx.sess.abort_if_errors()
2376     }
2377 }
2378
2379 pub(crate) fn provide(providers: &mut Providers) {
2380     *providers = Providers { check_mod_attrs, ..*providers };
2381 }
2382
2383 fn check_duplicates(
2384     tcx: TyCtxt<'_>,
2385     attr: &Attribute,
2386     hir_id: HirId,
2387     duplicates: AttributeDuplicates,
2388     seen: &mut FxHashMap<Symbol, Span>,
2389 ) {
2390     use AttributeDuplicates::*;
2391     if matches!(duplicates, WarnFollowingWordOnly) && !attr.is_word() {
2392         return;
2393     }
2394     match duplicates {
2395         DuplicatesOk => {}
2396         WarnFollowing | FutureWarnFollowing | WarnFollowingWordOnly | FutureWarnPreceding => {
2397             match seen.entry(attr.name_or_empty()) {
2398                 Entry::Occupied(mut entry) => {
2399                     let (this, other) = if matches!(duplicates, FutureWarnPreceding) {
2400                         let to_remove = entry.insert(attr.span);
2401                         (to_remove, attr.span)
2402                     } else {
2403                         (attr.span, *entry.get())
2404                     };
2405                     tcx.emit_spanned_lint(
2406                         UNUSED_ATTRIBUTES,
2407                         hir_id,
2408                         this,
2409                         errors::UnusedDuplicate {
2410                             this,
2411                             other,
2412                             warning: matches!(
2413                                 duplicates,
2414                                 FutureWarnFollowing | FutureWarnPreceding
2415                             )
2416                             .then_some(()),
2417                         },
2418                     );
2419                 }
2420                 Entry::Vacant(entry) => {
2421                     entry.insert(attr.span);
2422                 }
2423             }
2424         }
2425         ErrorFollowing | ErrorPreceding => match seen.entry(attr.name_or_empty()) {
2426             Entry::Occupied(mut entry) => {
2427                 let (this, other) = if matches!(duplicates, ErrorPreceding) {
2428                     let to_remove = entry.insert(attr.span);
2429                     (to_remove, attr.span)
2430                 } else {
2431                     (attr.span, *entry.get())
2432                 };
2433                 tcx.sess.emit_err(errors::UnusedMultiple {
2434                     this,
2435                     other,
2436                     name: attr.name_or_empty(),
2437                 });
2438             }
2439             Entry::Vacant(entry) => {
2440                 entry.insert(attr.span);
2441             }
2442         },
2443     }
2444 }