compiler/rustc_feature/src/builtin_attrs.rs

   1 //! Built-in attributes and `cfg` flag gating.
   2
   3 use AttributeDuplicates::*;
   4 use AttributeGate::*;
   5 use AttributeType::*;
   6
   7 use crate::{Features, Stability};
   8
   9 use rustc_data_structures::fx::FxHashMap;
  10 use rustc_span::symbol::{sym, Symbol};
  11
  12 use std::lazy::SyncLazy;
  13
  14 type GateFn = fn(&Features) -> bool;
  15
  16 macro_rules! cfg_fn {
  17     ($field: ident) => {
  18         (|features| features.$field) as GateFn
  19     };
  20 }
  21
  22 pub type GatedCfg = (Symbol, Symbol, GateFn);
  23
  24 /// `cfg(...)`'s that are feature gated.
  25 const GATED_CFGS: &[GatedCfg] = &[
  26     // (name in cfg, feature, function to check if the feature is enabled)
  27     (sym::target_abi, sym::cfg_target_abi, cfg_fn!(cfg_target_abi)),
  28     (sym::target_thread_local, sym::cfg_target_thread_local, cfg_fn!(cfg_target_thread_local)),
  29     (
  30         sym::target_has_atomic_equal_alignment,
  31         sym::cfg_target_has_atomic_equal_alignment,
  32         cfg_fn!(cfg_target_has_atomic_equal_alignment),
  33     ),
  34     (sym::target_has_atomic_load_store, sym::cfg_target_has_atomic, cfg_fn!(cfg_target_has_atomic)),
  35     (sym::sanitize, sym::cfg_sanitize, cfg_fn!(cfg_sanitize)),
  36     (sym::version, sym::cfg_version, cfg_fn!(cfg_version)),
  37 ];
  38
  39 /// Find a gated cfg determined by the `pred`icate which is given the cfg's name.
  40 pub fn find_gated_cfg(pred: impl Fn(Symbol) -> bool) -> Option<&'static GatedCfg> {
  41     GATED_CFGS.iter().find(|(cfg_sym, ..)| pred(*cfg_sym))
  42 }
  43
  44 // If you change this, please modify `src/doc/unstable-book` as well. You must
  45 // move that documentation into the relevant place in the other docs, and
  46 // remove the chapter on the flag.
  47
  48 #[derive(Copy, Clone, PartialEq, Debug)]
  49 pub enum AttributeType {
  50     /// Normal, builtin attribute that is consumed
  51     /// by the compiler before the unused_attribute check
  52     Normal,
  53
  54     /// Builtin attribute that is only allowed at the crate level
  55     CrateLevel,
  56 }
  57
  58 #[derive(Clone, Copy)]
  59 pub enum AttributeGate {
  60     /// Is gated by a given feature gate, reason
  61     /// and function to check if enabled
  62     Gated(Stability, Symbol, &'static str, fn(&Features) -> bool),
  63
  64     /// Ungated attribute, can be used on all release channels
  65     Ungated,
  66 }
  67
  68 // fn() is not Debug
  69 impl std::fmt::Debug for AttributeGate {
  70     fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
  71         match *self {
  72             Self::Gated(ref stab, name, expl, _) => {
  73                 write!(fmt, "Gated({:?}, {}, {})", stab, name, expl)
  74             }
  75             Self::Ungated => write!(fmt, "Ungated"),
  76         }
  77     }
  78 }
  79
  80 impl AttributeGate {
  81     fn is_deprecated(&self) -> bool {
  82         matches!(*self, Self::Gated(Stability::Deprecated(_, _), ..))
  83     }
  84 }
  85
  86 /// A template that the attribute input must match.
  87 /// Only top-level shape (`#[attr]` vs `#[attr(...)]` vs `#[attr = ...]`) is considered now.
  88 #[derive(Clone, Copy, Default)]
  89 pub struct AttributeTemplate {
  90     /// If `true`, the attribute is allowed to be a bare word like `#[test]`.
  91     pub word: bool,
  92     /// If `Some`, the attribute is allowed to take a list of items like `#[allow(..)]`.
  93     pub list: Option<&'static str>,
  94     /// If `Some`, the attribute is allowed to be a name/value pair where the
  95     /// value is a string, like `#[must_use = "reason"]`.
  96     pub name_value_str: Option<&'static str>,
  97 }
  98
  99 /// How to handle multiple duplicate attributes on the same item.
 100 #[derive(Clone, Copy, Default)]
 101 pub enum AttributeDuplicates {
 102     /// Duplicates of this attribute are allowed.
 103     ///
 104     /// This should only be used with attributes where duplicates have semantic
 105     /// meaning, or some kind of "additive" behavior. For example, `#[warn(..)]`
 106     /// can be specified multiple times, and it combines all the entries. Or use
 107     /// this if there is validation done elsewhere.
 108     #[default]
 109     DuplicatesOk,
 110     /// Duplicates after the first attribute will be an unused_attribute warning.
 111     ///
 112     /// This is usually used for "word" attributes, where they are used as a
 113     /// boolean marker, like `#[used]`. It is not necessarily wrong that there
 114     /// are duplicates, but the others should probably be removed.
 115     WarnFollowing,
 116     /// Same as `WarnFollowing`, but only issues warnings for word-style attributes.
 117     ///
 118     /// This is only for special cases, for example multiple `#[macro_use]` can
 119     /// be warned, but multiple `#[macro_use(...)]` should not because the list
 120     /// form has different meaning from the word form.
 121     WarnFollowingWordOnly,
 122     /// Duplicates after the first attribute will be an error.
 123     ///
 124     /// This should be used where duplicates would be ignored, but carry extra
 125     /// meaning that could cause confusion. For example, `#[stable(since="1.0")]
 126     /// #[stable(since="2.0")]`, which version should be used for `stable`?
 127     ErrorFollowing,
 128     /// Duplicates preceding the last instance of the attribute will be an error.
 129     ///
 130     /// This is the same as `ErrorFollowing`, except the last attribute is the
 131     /// one that is "used". This is typically used in cases like codegen
 132     /// attributes which usually only honor the last attribute.
 133     ErrorPreceding,
 134     /// Duplicates after the first attribute will be an unused_attribute warning
 135     /// with a note that this will be an error in the future.
 136     ///
 137     /// This should be used for attributes that should be `ErrorFollowing`, but
 138     /// because older versions of rustc silently accepted (and ignored) the
 139     /// attributes, this is used to transition.
 140     FutureWarnFollowing,
 141     /// Duplicates preceding the last instance of the attribute will be a
 142     /// warning, with a note that this will be an error in the future.
 143     ///
 144     /// This is the same as `FutureWarnFollowing`, except the last attribute is
 145     /// the one that is "used". Ideally these can eventually migrate to
 146     /// `ErrorPreceding`.
 147     FutureWarnPreceding,
 148 }
 149
 150 /// A convenience macro for constructing attribute templates.
 151 /// E.g., `template!(Word, List: "description")` means that the attribute
 152 /// supports forms `#[attr]` and `#[attr(description)]`.
 153 macro_rules! template {
 154     (Word) => { template!(@ true, None, None) };
 155     (List: $descr: expr) => { template!(@ false, Some($descr), None) };
 156     (NameValueStr: $descr: expr) => { template!(@ false, None, Some($descr)) };
 157     (Word, List: $descr: expr) => { template!(@ true, Some($descr), None) };
 158     (Word, NameValueStr: $descr: expr) => { template!(@ true, None, Some($descr)) };
 159     (List: $descr1: expr, NameValueStr: $descr2: expr) => {
 160         template!(@ false, Some($descr1), Some($descr2))
 161     };
 162     (Word, List: $descr1: expr, NameValueStr: $descr2: expr) => {
 163         template!(@ true, Some($descr1), Some($descr2))
 164     };
 165     (@ $word: expr, $list: expr, $name_value_str: expr) => { AttributeTemplate {
 166         word: $word, list: $list, name_value_str: $name_value_str
 167     } };
 168 }
 169
 170 macro_rules! ungated {
 171     ($attr:ident, $typ:expr, $tpl:expr, $duplicates:expr $(,)?) => {
 172         BuiltinAttribute {
 173             name: sym::$attr,
 174             type_: $typ,
 175             template: $tpl,
 176             gate: Ungated,
 177             duplicates: $duplicates,
 178         }
 179     };
 180 }
 181
 182 macro_rules! gated {
 183     ($attr:ident, $typ:expr, $tpl:expr, $duplicates:expr, $gate:ident, $msg:expr $(,)?) => {
 184         BuiltinAttribute {
 185             name: sym::$attr,
 186             type_: $typ,
 187             template: $tpl,
 188             duplicates: $duplicates,
 189             gate: Gated(Stability::Unstable, sym::$gate, $msg, cfg_fn!($gate)),
 190         }
 191     };
 192     ($attr:ident, $typ:expr, $tpl:expr, $duplicates:expr, $msg:expr $(,)?) => {
 193         BuiltinAttribute {
 194             name: sym::$attr,
 195             type_: $typ,
 196             template: $tpl,
 197             duplicates: $duplicates,
 198             gate: Gated(Stability::Unstable, sym::$attr, $msg, cfg_fn!($attr)),
 199         }
 200     };
 201 }
 202
 203 macro_rules! rustc_attr {
 204     (TEST, $attr:ident, $typ:expr, $tpl:expr, $duplicate:expr $(,)?) => {
 205         rustc_attr!(
 206             $attr,
 207             $typ,
 208             $tpl,
 209             $duplicate,
 210             concat!(
 211                 "the `#[",
 212                 stringify!($attr),
 213                 "]` attribute is just used for rustc unit tests \
 214                 and will never be stable",
 215             ),
 216         )
 217     };
 218     ($attr:ident, $typ:expr, $tpl:expr, $duplicates:expr, $msg:expr $(,)?) => {
 219         BuiltinAttribute {
 220             name: sym::$attr,
 221             type_: $typ,
 222             template: $tpl,
 223             duplicates: $duplicates,
 224             gate: Gated(Stability::Unstable, sym::rustc_attrs, $msg, cfg_fn!(rustc_attrs)),
 225         }
 226     };
 227 }
 228
 229 macro_rules! experimental {
 230     ($attr:ident) => {
 231         concat!("the `#[", stringify!($attr), "]` attribute is an experimental feature")
 232     };
 233 }
 234
 235 const IMPL_DETAIL: &str = "internal implementation detail";
 236 const INTERNAL_UNSTABLE: &str = "this is an internal attribute that will never be stable";
 237
 238 pub struct BuiltinAttribute {
 239     pub name: Symbol,
 240     pub type_: AttributeType,
 241     pub template: AttributeTemplate,
 242     pub duplicates: AttributeDuplicates,
 243     pub gate: AttributeGate,
 244 }
 245
 246 /// Attributes that have a special meaning to rustc or rustdoc.
 247 #[rustfmt::skip]
 248 pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
 249     // ==========================================================================
 250     // Stable attributes:
 251     // ==========================================================================
 252
 253     // Conditional compilation:
 254     ungated!(cfg, Normal, template!(List: "predicate"), DuplicatesOk),
 255     ungated!(cfg_attr, Normal, template!(List: "predicate, attr1, attr2, ..."), DuplicatesOk),
 256
 257     // Testing:
 258     ungated!(ignore, Normal, template!(Word, NameValueStr: "reason"), WarnFollowing),
 259     ungated!(
 260         should_panic, Normal,
 261         template!(Word, List: r#"expected = "reason"#, NameValueStr: "reason"), FutureWarnFollowing,
 262     ),
 263     // FIXME(Centril): This can be used on stable but shouldn't.
 264     ungated!(reexport_test_harness_main, CrateLevel, template!(NameValueStr: "name"), ErrorFollowing),
 265
 266     // Macros:
 267     ungated!(automatically_derived, Normal, template!(Word), WarnFollowing),
 268     ungated!(macro_use, Normal, template!(Word, List: "name1, name2, ..."), WarnFollowingWordOnly),
 269     ungated!(macro_escape, Normal, template!(Word), WarnFollowing), // Deprecated synonym for `macro_use`.
 270     ungated!(macro_export, Normal, template!(Word, List: "local_inner_macros"), WarnFollowing),
 271     ungated!(proc_macro, Normal, template!(Word), ErrorFollowing),
 272     ungated!(
 273         proc_macro_derive, Normal,
 274         template!(List: "TraitName, /*opt*/ attributes(name1, name2, ...)"), ErrorFollowing,
 275     ),
 276     ungated!(proc_macro_attribute, Normal, template!(Word), ErrorFollowing),
 277
 278     // Lints:
 279     ungated!(
 280         warn, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), DuplicatesOk
 281     ),
 282     ungated!(
 283         allow, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), DuplicatesOk
 284     ),
 285     ungated!(
 286         forbid, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), DuplicatesOk
 287     ),
 288     ungated!(
 289         deny, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), DuplicatesOk
 290     ),
 291     ungated!(must_use, Normal, template!(Word, NameValueStr: "reason"), FutureWarnFollowing),
 292     gated!(
 293         must_not_suspend, Normal, template!(Word, NameValueStr: "reason"), WarnFollowing,
 294         must_not_suspend, experimental!(must_not_suspend)
 295     ),
 296     ungated!(
 297         deprecated, Normal,
 298         template!(
 299             Word,
 300             List: r#"/*opt*/ since = "version", /*opt*/ note = "reason""#,
 301             NameValueStr: "reason"
 302         ),
 303         // This has special duplicate handling in E0550 to handle duplicates with rustc_deprecated
 304         DuplicatesOk
 305     ),
 306
 307     // Crate properties:
 308     ungated!(crate_name, CrateLevel, template!(NameValueStr: "name"), FutureWarnFollowing),
 309     ungated!(crate_type, CrateLevel, template!(NameValueStr: "bin|lib|..."), FutureWarnFollowing),
 310     // crate_id is deprecated
 311     ungated!(crate_id, CrateLevel, template!(NameValueStr: "ignored"), FutureWarnFollowing),
 312
 313     // ABI, linking, symbols, and FFI
 314     ungated!(
 315         link, Normal,
 316         template!(List: r#"name = "...", /*opt*/ kind = "dylib|static|...", /*opt*/ wasm_import_module = "...""#),
 317         DuplicatesOk,
 318     ),
 319     ungated!(link_name, Normal, template!(NameValueStr: "name"), FutureWarnPreceding),
 320     ungated!(no_link, Normal, template!(Word), WarnFollowing),
 321     ungated!(repr, Normal, template!(List: "C"), DuplicatesOk),
 322     ungated!(export_name, Normal, template!(NameValueStr: "name"), FutureWarnPreceding),
 323     ungated!(link_section, Normal, template!(NameValueStr: "name"), FutureWarnPreceding),
 324     ungated!(no_mangle, Normal, template!(Word), WarnFollowing),
 325     ungated!(used, Normal, template!(Word, List: "compiler|linker"), WarnFollowing),
 326
 327     // Limits:
 328     ungated!(recursion_limit, CrateLevel, template!(NameValueStr: "N"), FutureWarnFollowing),
 329     ungated!(type_length_limit, CrateLevel, template!(NameValueStr: "N"), FutureWarnFollowing),
 330     gated!(
 331         const_eval_limit, CrateLevel, template!(NameValueStr: "N"), ErrorFollowing,
 332         const_eval_limit, experimental!(const_eval_limit)
 333     ),
 334     gated!(
 335         move_size_limit, CrateLevel, template!(NameValueStr: "N"), ErrorFollowing,
 336         large_assignments, experimental!(move_size_limit)
 337     ),
 338
 339     // Entry point:
 340     ungated!(start, Normal, template!(Word), WarnFollowing),
 341     ungated!(no_start, CrateLevel, template!(Word), WarnFollowing),
 342     ungated!(no_main, CrateLevel, template!(Word), WarnFollowing),
 343
 344     // Modules, prelude, and resolution:
 345     ungated!(path, Normal, template!(NameValueStr: "file"), FutureWarnFollowing),
 346     ungated!(no_std, CrateLevel, template!(Word), WarnFollowing),
 347     ungated!(no_implicit_prelude, Normal, template!(Word), WarnFollowing),
 348     ungated!(non_exhaustive, Normal, template!(Word), WarnFollowing),
 349
 350     // Runtime
 351     ungated!(
 352         windows_subsystem, CrateLevel,
 353         template!(NameValueStr: "windows|console"), FutureWarnFollowing
 354     ),
 355     ungated!(panic_handler, Normal, template!(Word), WarnFollowing), // RFC 2070
 356
 357     // Code generation:
 358     ungated!(inline, Normal, template!(Word, List: "always|never"), FutureWarnFollowing),
 359     ungated!(cold, Normal, template!(Word), WarnFollowing),
 360     ungated!(no_builtins, CrateLevel, template!(Word), WarnFollowing),
 361     ungated!(target_feature, Normal, template!(List: r#"enable = "name""#), DuplicatesOk),
 362     ungated!(track_caller, Normal, template!(Word), WarnFollowing),
 363     gated!(
 364         no_sanitize, Normal,
 365         template!(List: "address, memory, thread"), DuplicatesOk,
 366         experimental!(no_sanitize)
 367     ),
 368     gated!(no_coverage, Normal, template!(Word), WarnFollowing, experimental!(no_coverage)),
 369
 370     ungated!(
 371         doc, Normal, template!(List: "hidden|inline|...", NameValueStr: "string"), DuplicatesOk
 372     ),
 373
 374     // ==========================================================================
 375     // Unstable attributes:
 376     // ==========================================================================
 377
 378     // Linking:
 379     gated!(naked, Normal, template!(Word), WarnFollowing, naked_functions, experimental!(naked)),
 380     gated!(
 381         link_ordinal, Normal, template!(List: "ordinal"), ErrorPreceding, raw_dylib,
 382         experimental!(link_ordinal)
 383     ),
 384
 385     // Plugins:
 386     BuiltinAttribute {
 387         name: sym::plugin,
 388         type_: CrateLevel,
 389         template: template!(List: "name"),
 390         duplicates: DuplicatesOk,
 391         gate: Gated(
 392             Stability::Deprecated(
 393                 "https://github.com/rust-lang/rust/pull/64675",
 394                 Some("may be removed in a future compiler version"),
 395             ),
 396             sym::plugin,
 397             "compiler plugins are deprecated",
 398             cfg_fn!(plugin)
 399         ),
 400     },
 401
 402     // Testing:
 403     gated!(
 404         test_runner, CrateLevel, template!(List: "path"), ErrorFollowing, custom_test_frameworks,
 405         "custom test frameworks are an unstable feature",
 406     ),
 407     // RFC #1268
 408     gated!(
 409         marker, Normal, template!(Word), WarnFollowing, marker_trait_attr, experimental!(marker)
 410     ),
 411     gated!(
 412         thread_local, Normal, template!(Word), WarnFollowing,
 413         "`#[thread_local]` is an experimental feature, and does not currently handle destructors",
 414     ),
 415     gated!(no_core, CrateLevel, template!(Word), WarnFollowing, experimental!(no_core)),
 416     // RFC 2412
 417     gated!(
 418         optimize, Normal, template!(List: "size|speed"), ErrorPreceding, optimize_attribute,
 419         experimental!(optimize),
 420     ),
 421     // RFC 2867
 422     gated!(
 423         instruction_set, Normal, template!(List: "set"), ErrorPreceding,
 424         isa_attribute, experimental!(instruction_set)
 425     ),
 426
 427     gated!(
 428         ffi_returns_twice, Normal, template!(Word), WarnFollowing, experimental!(ffi_returns_twice)
 429     ),
 430     gated!(ffi_pure, Normal, template!(Word), WarnFollowing, experimental!(ffi_pure)),
 431     gated!(ffi_const, Normal, template!(Word), WarnFollowing, experimental!(ffi_const)),
 432     gated!(
 433         register_attr, CrateLevel, template!(List: "attr1, attr2, ..."), DuplicatesOk,
 434         experimental!(register_attr),
 435     ),
 436     gated!(
 437         register_tool, CrateLevel, template!(List: "tool1, tool2, ..."), DuplicatesOk,
 438         experimental!(register_tool),
 439     ),
 440
 441     gated!(
 442         cmse_nonsecure_entry, Normal, template!(Word), WarnFollowing,
 443         experimental!(cmse_nonsecure_entry)
 444     ),
 445     // RFC 2632
 446     gated!(
 447         default_method_body_is_const, Normal, template!(Word), WarnFollowing, const_trait_impl,
 448         "`default_method_body_is_const` is a temporary placeholder for declaring default bodies \
 449         as `const`, which may be removed or renamed in the future."
 450     ),
 451
 452     // ==========================================================================
 453     // Internal attributes: Stability, deprecation, and unsafe:
 454     // ==========================================================================
 455
 456     ungated!(feature, CrateLevel, template!(List: "name1, name1, ..."), DuplicatesOk),
 457     // DuplicatesOk since it has its own validation
 458     ungated!(
 459         rustc_deprecated, Normal,
 460         template!(List: r#"since = "version", reason = "...""#), DuplicatesOk // See E0550
 461     ),
 462     // DuplicatesOk since it has its own validation
 463     ungated!(
 464         stable, Normal, template!(List: r#"feature = "name", since = "version""#), DuplicatesOk
 465     ),
 466     ungated!(
 467         unstable, Normal,
 468         template!(List: r#"feature = "name", reason = "...", issue = "N""#), DuplicatesOk,
 469     ),
 470     ungated!(rustc_const_unstable, Normal, template!(List: r#"feature = "name""#), DuplicatesOk),
 471     ungated!(rustc_const_stable, Normal, template!(List: r#"feature = "name""#), DuplicatesOk),
 472     gated!(
 473         allow_internal_unstable, Normal, template!(Word, List: "feat1, feat2, ..."), DuplicatesOk,
 474         "allow_internal_unstable side-steps feature gating and stability checks",
 475     ),
 476     gated!(
 477         rustc_allow_const_fn_unstable, Normal,
 478         template!(Word, List: "feat1, feat2, ..."), DuplicatesOk,
 479         "rustc_allow_const_fn_unstable side-steps feature gating and stability checks"
 480     ),
 481     gated!(
 482         allow_internal_unsafe, Normal, template!(Word), WarnFollowing,
 483         "allow_internal_unsafe side-steps the unsafe_code lint",
 484     ),
 485
 486     // ==========================================================================
 487     // Internal attributes: Type system related:
 488     // ==========================================================================
 489
 490     gated!(fundamental, Normal, template!(Word), WarnFollowing, experimental!(fundamental)),
 491     gated!(
 492         may_dangle, Normal, template!(Word), WarnFollowing, dropck_eyepatch,
 493         "`may_dangle` has unstable semantics and may be removed in the future",
 494     ),
 495
 496     // ==========================================================================
 497     // Internal attributes: Runtime related:
 498     // ==========================================================================
 499
 500     rustc_attr!(rustc_allocator, Normal, template!(Word), WarnFollowing, IMPL_DETAIL),
 501     rustc_attr!(rustc_allocator_nounwind, Normal, template!(Word), WarnFollowing, IMPL_DETAIL),
 502     gated!(
 503         alloc_error_handler, Normal, template!(Word), WarnFollowing,
 504         experimental!(alloc_error_handler)
 505     ),
 506     gated!(
 507         default_lib_allocator, Normal, template!(Word), WarnFollowing, allocator_internals,
 508         experimental!(default_lib_allocator),
 509     ),
 510     gated!(
 511         needs_allocator, Normal, template!(Word), WarnFollowing, allocator_internals,
 512         experimental!(needs_allocator),
 513     ),
 514     gated!(panic_runtime, Normal, template!(Word), WarnFollowing, experimental!(panic_runtime)),
 515     gated!(
 516         needs_panic_runtime, Normal, template!(Word), WarnFollowing,
 517         experimental!(needs_panic_runtime)
 518     ),
 519     gated!(
 520         compiler_builtins, Normal, template!(Word), WarnFollowing,
 521         "the `#[compiler_builtins]` attribute is used to identify the `compiler_builtins` crate \
 522         which contains compiler-rt intrinsics and will never be stable",
 523     ),
 524     gated!(
 525         profiler_runtime, Normal, template!(Word), WarnFollowing,
 526         "the `#[profiler_runtime]` attribute is used to identify the `profiler_builtins` crate \
 527         which contains the profiler runtime and will never be stable",
 528     ),
 529
 530     // ==========================================================================
 531     // Internal attributes, Linkage:
 532     // ==========================================================================
 533
 534     gated!(
 535         linkage, Normal, template!(NameValueStr: "external|internal|..."), ErrorPreceding,
 536         "the `linkage` attribute is experimental and not portable across platforms",
 537     ),
 538     rustc_attr!(
 539         rustc_std_internal_symbol, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE
 540     ),
 541
 542     // ==========================================================================
 543     // Internal attributes, Macro related:
 544     // ==========================================================================
 545
 546     rustc_attr!(
 547         rustc_builtin_macro, Normal,
 548         template!(Word, List: "name, /*opt*/ attributes(name1, name2, ...)"), ErrorFollowing,
 549         IMPL_DETAIL,
 550     ),
 551     rustc_attr!(rustc_proc_macro_decls, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE),
 552     rustc_attr!(
 553         rustc_macro_transparency, Normal,
 554         template!(NameValueStr: "transparent|semitransparent|opaque"), ErrorFollowing,
 555         "used internally for testing macro hygiene",
 556     ),
 557
 558     // ==========================================================================
 559     // Internal attributes, Diagnostics related:
 560     // ==========================================================================
 561
 562     rustc_attr!(
 563         rustc_on_unimplemented, Normal,
 564         template!(
 565             List: r#"/*opt*/ message = "...", /*opt*/ label = "...", /*opt*/ note = "...""#,
 566             NameValueStr: "message"
 567         ),
 568         ErrorFollowing,
 569         INTERNAL_UNSTABLE
 570     ),
 571     // Enumerates "identity-like" conversion methods to suggest on type mismatch.
 572     rustc_attr!(
 573         rustc_conversion_suggestion, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE
 574     ),
 575     // Prevents field reads in the marked trait or method to be considered
 576     // during dead code analysis.
 577     rustc_attr!(
 578         rustc_trivial_field_reads, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE
 579     ),
 580     // Used by the `rustc::potential_query_instability` lint to warn methods which
 581     // might not be stable during incremental compilation.
 582     rustc_attr!(rustc_lint_query_instability, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE),
 583
 584     // ==========================================================================
 585     // Internal attributes, Const related:
 586     // ==========================================================================
 587
 588     rustc_attr!(rustc_promotable, Normal, template!(Word), WarnFollowing, IMPL_DETAIL),
 589     rustc_attr!(
 590         rustc_legacy_const_generics, Normal, template!(List: "N"), ErrorFollowing,
 591         INTERNAL_UNSTABLE
 592     ),
 593     // Do not const-check this function's body. It will always get replaced during CTFE.
 594     rustc_attr!(
 595         rustc_do_not_const_check, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE
 596     ),
 597
 598     // ==========================================================================
 599     // Internal attributes, Layout related:
 600     // ==========================================================================
 601
 602     rustc_attr!(
 603         rustc_layout_scalar_valid_range_start, Normal, template!(List: "value"), ErrorFollowing,
 604         "the `#[rustc_layout_scalar_valid_range_start]` attribute is just used to enable \
 605         niche optimizations in libcore and will never be stable",
 606     ),
 607     rustc_attr!(
 608         rustc_layout_scalar_valid_range_end, Normal, template!(List: "value"), ErrorFollowing,
 609         "the `#[rustc_layout_scalar_valid_range_end]` attribute is just used to enable \
 610         niche optimizations in libcore and will never be stable",
 611     ),
 612     rustc_attr!(
 613         rustc_nonnull_optimization_guaranteed, Normal, template!(Word), WarnFollowing,
 614         "the `#[rustc_nonnull_optimization_guaranteed]` attribute is just used to enable \
 615         niche optimizations in libcore and will never be stable",
 616     ),
 617
 618     // ==========================================================================
 619     // Internal attributes, Misc:
 620     // ==========================================================================
 621     gated!(
 622         lang, Normal, template!(NameValueStr: "name"), DuplicatesOk, lang_items,
 623         "language items are subject to change",
 624     ),
 625     rustc_attr!(
 626         rustc_pass_by_value, Normal,
 627         template!(Word), ErrorFollowing,
 628         "#[rustc_pass_by_value] is used to mark types that must be passed by value instead of reference."
 629     ),
 630     BuiltinAttribute {
 631         name: sym::rustc_diagnostic_item,
 632         type_: Normal,
 633         template: template!(NameValueStr: "name"),
 634         duplicates: ErrorFollowing,
 635         gate: Gated(
 636             Stability::Unstable,
 637             sym::rustc_attrs,
 638             "diagnostic items compiler internal support for linting",
 639             cfg_fn!(rustc_attrs),
 640         ),
 641     },
 642     gated!(
 643         // Used in resolve:
 644         prelude_import, Normal, template!(Word), WarnFollowing,
 645         "`#[prelude_import]` is for use by rustc only",
 646     ),
 647     gated!(
 648         rustc_paren_sugar, Normal, template!(Word), WarnFollowing, unboxed_closures,
 649         "unboxed_closures are still evolving",
 650     ),
 651     rustc_attr!(
 652         rustc_inherit_overflow_checks, Normal, template!(Word), WarnFollowing,
 653         "the `#[rustc_inherit_overflow_checks]` attribute is just used to control \
 654         overflow checking behavior of several libcore functions that are inlined \
 655         across crates and will never be stable",
 656     ),
 657     rustc_attr!(
 658         rustc_reservation_impl, Normal,
 659         template!(NameValueStr: "reservation message"), ErrorFollowing,
 660         "the `#[rustc_reservation_impl]` attribute is internally used \
 661          for reserving for `for<T> From<!> for T` impl"
 662     ),
 663     rustc_attr!(
 664         rustc_test_marker, Normal, template!(Word), WarnFollowing,
 665         "the `#[rustc_test_marker]` attribute is used internally to track tests",
 666     ),
 667     rustc_attr!(
 668         rustc_unsafe_specialization_marker, Normal, template!(Word), WarnFollowing,
 669         "the `#[rustc_unsafe_specialization_marker]` attribute is used to check specializations"
 670     ),
 671     rustc_attr!(
 672         rustc_specialization_trait, Normal, template!(Word), WarnFollowing,
 673         "the `#[rustc_specialization_trait]` attribute is used to check specializations"
 674     ),
 675     rustc_attr!(
 676         rustc_main, Normal, template!(Word), WarnFollowing,
 677         "the `#[rustc_main]` attribute is used internally to specify test entry point function",
 678     ),
 679     rustc_attr!(
 680         rustc_skip_array_during_method_dispatch, Normal, template!(Word), WarnFollowing,
 681         "the `#[rustc_skip_array_during_method_dispatch]` attribute is used to exclude a trait \
 682         from method dispatch when the receiver is an array, for compatibility in editions < 2021."
 683     ),
 684     rustc_attr!(
 685         rustc_must_implement_one_of, Normal, template!(List: "function1, function2, ..."), ErrorFollowing,
 686         "the `#[rustc_must_implement_one_of]` attribute is used to change minimal complete \
 687         definition of a trait, it's currently in experimental form and should be changed before \
 688         being exposed outside of the std"
 689     ),
 690
 691     // ==========================================================================
 692     // Internal attributes, Testing:
 693     // ==========================================================================
 694
 695     rustc_attr!(TEST, rustc_outlives, Normal, template!(Word), WarnFollowing),
 696     rustc_attr!(TEST, rustc_capture_analysis, Normal, template!(Word), WarnFollowing),
 697     rustc_attr!(TEST, rustc_insignificant_dtor, Normal, template!(Word), WarnFollowing),
 698     rustc_attr!(TEST, rustc_strict_coherence, Normal, template!(Word), WarnFollowing),
 699     rustc_attr!(TEST, rustc_variance, Normal, template!(Word), WarnFollowing),
 700     rustc_attr!(TEST, rustc_layout, Normal, template!(List: "field1, field2, ..."), WarnFollowing),
 701     rustc_attr!(TEST, rustc_regions, Normal, template!(Word), WarnFollowing),
 702     rustc_attr!(
 703         TEST, rustc_error, Normal,
 704         template!(Word, List: "delay_span_bug_from_inside_query"), WarnFollowingWordOnly
 705     ),
 706     rustc_attr!(TEST, rustc_dump_user_substs, Normal, template!(Word), WarnFollowing),
 707     rustc_attr!(TEST, rustc_evaluate_where_clauses, Normal, template!(Word), WarnFollowing),
 708     rustc_attr!(
 709         TEST, rustc_if_this_changed, Normal, template!(Word, List: "DepNode"), DuplicatesOk
 710     ),
 711     rustc_attr!(
 712         TEST, rustc_then_this_would_need, Normal, template!(List: "DepNode"), DuplicatesOk
 713     ),
 714     rustc_attr!(
 715         TEST, rustc_clean, Normal,
 716         template!(List: r#"cfg = "...", /*opt*/ label = "...", /*opt*/ except = "...""#),
 717         DuplicatesOk,
 718     ),
 719     rustc_attr!(
 720         TEST, rustc_partition_reused, Normal,
 721         template!(List: r#"cfg = "...", module = "...""#), DuplicatesOk,
 722     ),
 723     rustc_attr!(
 724         TEST, rustc_partition_codegened, Normal,
 725         template!(List: r#"cfg = "...", module = "...""#), DuplicatesOk,
 726     ),
 727     rustc_attr!(
 728         TEST, rustc_expected_cgu_reuse, Normal,
 729         template!(List: r#"cfg = "...", module = "...", kind = "...""#), DuplicatesOk,
 730     ),
 731     rustc_attr!(TEST, rustc_symbol_name, Normal, template!(Word), WarnFollowing),
 732     rustc_attr!(TEST, rustc_polymorphize_error, Normal, template!(Word), WarnFollowing),
 733     rustc_attr!(TEST, rustc_def_path, Normal, template!(Word), WarnFollowing),
 734     rustc_attr!(TEST, rustc_mir, Normal, template!(List: "arg1, arg2, ..."), DuplicatesOk),
 735     rustc_attr!(TEST, rustc_dump_program_clauses, Normal, template!(Word), WarnFollowing),
 736     rustc_attr!(TEST, rustc_dump_env_program_clauses, Normal, template!(Word), WarnFollowing),
 737     rustc_attr!(TEST, rustc_object_lifetime_default, Normal, template!(Word), WarnFollowing),
 738     rustc_attr!(TEST, rustc_dump_vtable, Normal, template!(Word), WarnFollowing),
 739     rustc_attr!(TEST, rustc_dummy, Normal, template!(Word /* doesn't matter*/), DuplicatesOk),
 740     gated!(
 741         omit_gdb_pretty_printer_section, Normal, template!(Word), WarnFollowing,
 742         "the `#[omit_gdb_pretty_printer_section]` attribute is just used for the Rust test suite",
 743     ),
 744 ];
 745
 746 pub fn deprecated_attributes() -> Vec<&'static BuiltinAttribute> {
 747     BUILTIN_ATTRIBUTES.iter().filter(|attr| attr.gate.is_deprecated()).collect()
 748 }
 749
 750 pub fn is_builtin_attr_name(name: Symbol) -> bool {
 751     BUILTIN_ATTRIBUTE_MAP.get(&name).is_some()
 752 }
 753
 754 pub static BUILTIN_ATTRIBUTE_MAP: SyncLazy<FxHashMap<Symbol, &BuiltinAttribute>> =
 755     SyncLazy::new(|| {
 756         let mut map = FxHashMap::default();
 757         for attr in BUILTIN_ATTRIBUTES.iter() {
 758             if map.insert(attr.name, attr).is_some() {
 759                 panic!("duplicate builtin attribute `{}`", attr.name);
 760             }
 761         }
 762         map
 763     });