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::sync::LazyLock;
  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 to deal with `$($expr)?`.
 151 macro_rules! or_default {
 152     ($default:expr,) => {
 153         $default
 154     };
 155     ($default:expr, $next:expr) => {
 156         $next
 157     };
 158 }
 159
 160 /// A convenience macro for constructing attribute templates.
 161 /// E.g., `template!(Word, List: "description")` means that the attribute
 162 /// supports forms `#[attr]` and `#[attr(description)]`.
 163 macro_rules! template {
 164     (Word) => { template!(@ true, None, None) };
 165     (List: $descr: expr) => { template!(@ false, Some($descr), None) };
 166     (NameValueStr: $descr: expr) => { template!(@ false, None, Some($descr)) };
 167     (Word, List: $descr: expr) => { template!(@ true, Some($descr), None) };
 168     (Word, NameValueStr: $descr: expr) => { template!(@ true, None, Some($descr)) };
 169     (List: $descr1: expr, NameValueStr: $descr2: expr) => {
 170         template!(@ false, Some($descr1), Some($descr2))
 171     };
 172     (Word, List: $descr1: expr, NameValueStr: $descr2: expr) => {
 173         template!(@ true, Some($descr1), Some($descr2))
 174     };
 175     (@ $word: expr, $list: expr, $name_value_str: expr) => { AttributeTemplate {
 176         word: $word, list: $list, name_value_str: $name_value_str
 177     } };
 178 }
 179
 180 macro_rules! ungated {
 181     ($attr:ident, $typ:expr, $tpl:expr, $duplicates:expr $(, @only_local: $only_local:expr)? $(,)?) => {
 182         BuiltinAttribute {
 183             name: sym::$attr,
 184             only_local: or_default!(false, $($only_local)?),
 185             type_: $typ,
 186             template: $tpl,
 187             gate: Ungated,
 188             duplicates: $duplicates,
 189         }
 190     };
 191 }
 192
 193 macro_rules! gated {
 194     ($attr:ident, $typ:expr, $tpl:expr, $duplicates:expr $(, @only_local: $only_local:expr)?, $gate:ident, $msg:expr $(,)?) => {
 195         BuiltinAttribute {
 196             name: sym::$attr,
 197             only_local: or_default!(false, $($only_local)?),
 198             type_: $typ,
 199             template: $tpl,
 200             duplicates: $duplicates,
 201             gate: Gated(Stability::Unstable, sym::$gate, $msg, cfg_fn!($gate)),
 202         }
 203     };
 204     ($attr:ident, $typ:expr, $tpl:expr, $duplicates:expr $(, @only_local: $only_local:expr)?, $msg:expr $(,)?) => {
 205         BuiltinAttribute {
 206             name: sym::$attr,
 207             only_local: or_default!(false, $($only_local)?),
 208             type_: $typ,
 209             template: $tpl,
 210             duplicates: $duplicates,
 211             gate: Gated(Stability::Unstable, sym::$attr, $msg, cfg_fn!($attr)),
 212         }
 213     };
 214 }
 215
 216 macro_rules! rustc_attr {
 217     (TEST, $attr:ident, $typ:expr, $tpl:expr, $duplicate:expr $(, @only_local: $only_local:expr)? $(,)?) => {
 218         rustc_attr!(
 219             $attr,
 220             $typ,
 221             $tpl,
 222             $duplicate,
 223             $(@only_local: $only_local,)?
 224             concat!(
 225                 "the `#[",
 226                 stringify!($attr),
 227                 "]` attribute is just used for rustc unit tests \
 228                 and will never be stable",
 229             ),
 230         )
 231     };
 232     ($attr:ident, $typ:expr, $tpl:expr, $duplicates:expr $(, @only_local: $only_local:expr)?, $msg:expr $(,)?) => {
 233         BuiltinAttribute {
 234             name: sym::$attr,
 235             only_local: or_default!(false, $($only_local)?),
 236             type_: $typ,
 237             template: $tpl,
 238             duplicates: $duplicates,
 239             gate: Gated(Stability::Unstable, sym::rustc_attrs, $msg, cfg_fn!(rustc_attrs)),
 240         }
 241     };
 242 }
 243
 244 macro_rules! experimental {
 245     ($attr:ident) => {
 246         concat!("the `#[", stringify!($attr), "]` attribute is an experimental feature")
 247     };
 248 }
 249
 250 const IMPL_DETAIL: &str = "internal implementation detail";
 251 const INTERNAL_UNSTABLE: &str = "this is an internal attribute that will never be stable";
 252
 253 pub struct BuiltinAttribute {
 254     pub name: Symbol,
 255     /// Whether this attribute is only used in the local crate.
 256     ///
 257     /// If so, it is not encoded in the crate metadata.
 258     pub only_local: bool,
 259     pub type_: AttributeType,
 260     pub template: AttributeTemplate,
 261     pub duplicates: AttributeDuplicates,
 262     pub gate: AttributeGate,
 263 }
 264
 265 /// Attributes that have a special meaning to rustc or rustdoc.
 266 #[rustfmt::skip]
 267 pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
 268     // ==========================================================================
 269     // Stable attributes:
 270     // ==========================================================================
 271
 272     // Conditional compilation:
 273     ungated!(cfg, Normal, template!(List: "predicate"), DuplicatesOk),
 274     ungated!(cfg_attr, Normal, template!(List: "predicate, attr1, attr2, ..."), DuplicatesOk),
 275
 276     // Testing:
 277     ungated!(ignore, Normal, template!(Word, NameValueStr: "reason"), WarnFollowing),
 278     ungated!(
 279         should_panic, Normal,
 280         template!(Word, List: r#"expected = "reason""#, NameValueStr: "reason"), FutureWarnFollowing,
 281     ),
 282     // FIXME(Centril): This can be used on stable but shouldn't.
 283     ungated!(reexport_test_harness_main, CrateLevel, template!(NameValueStr: "name"), ErrorFollowing),
 284
 285     // Macros:
 286     ungated!(automatically_derived, Normal, template!(Word), WarnFollowing),
 287     ungated!(macro_use, Normal, template!(Word, List: "name1, name2, ..."), WarnFollowingWordOnly),
 288     ungated!(macro_escape, Normal, template!(Word), WarnFollowing), // Deprecated synonym for `macro_use`.
 289     ungated!(macro_export, Normal, template!(Word, List: "local_inner_macros"), WarnFollowing),
 290     ungated!(proc_macro, Normal, template!(Word), ErrorFollowing),
 291     ungated!(
 292         proc_macro_derive, Normal,
 293         template!(List: "TraitName, /*opt*/ attributes(name1, name2, ...)"), ErrorFollowing,
 294     ),
 295     ungated!(proc_macro_attribute, Normal, template!(Word), ErrorFollowing),
 296
 297     // Lints:
 298     ungated!(
 299         warn, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#),
 300         DuplicatesOk, @only_local: true,
 301     ),
 302     ungated!(
 303         allow, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#),
 304         DuplicatesOk, @only_local: true,
 305     ),
 306     gated!(
 307         expect, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), DuplicatesOk,
 308         lint_reasons, experimental!(expect)
 309     ),
 310     ungated!(
 311         forbid, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#),
 312         DuplicatesOk, @only_local: true,
 313     ),
 314     ungated!(
 315         deny, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#),
 316         DuplicatesOk, @only_local: true,
 317     ),
 318     ungated!(must_use, Normal, template!(Word, NameValueStr: "reason"), FutureWarnFollowing),
 319     gated!(
 320         must_not_suspend, Normal, template!(Word, NameValueStr: "reason"), WarnFollowing,
 321         experimental!(must_not_suspend)
 322     ),
 323     ungated!(
 324         deprecated, Normal,
 325         template!(
 326             Word,
 327             List: r#"/*opt*/ since = "version", /*opt*/ note = "reason""#,
 328             NameValueStr: "reason"
 329         ),
 330         ErrorFollowing
 331     ),
 332
 333     // Crate properties:
 334     ungated!(crate_name, CrateLevel, template!(NameValueStr: "name"), FutureWarnFollowing),
 335     ungated!(crate_type, CrateLevel, template!(NameValueStr: "bin|lib|..."), DuplicatesOk),
 336     // crate_id is deprecated
 337     ungated!(crate_id, CrateLevel, template!(NameValueStr: "ignored"), FutureWarnFollowing),
 338
 339     // ABI, linking, symbols, and FFI
 340     ungated!(
 341         link, Normal,
 342         template!(List: r#"name = "...", /*opt*/ kind = "dylib|static|...", /*opt*/ wasm_import_module = "...", /*opt*/ import_name_type = "decorated|noprefix|undecorated""#),
 343         DuplicatesOk,
 344     ),
 345     ungated!(link_name, Normal, template!(NameValueStr: "name"), FutureWarnPreceding),
 346     ungated!(no_link, Normal, template!(Word), WarnFollowing),
 347     ungated!(repr, Normal, template!(List: "C"), DuplicatesOk, @only_local: true),
 348     ungated!(export_name, Normal, template!(NameValueStr: "name"), FutureWarnPreceding),
 349     ungated!(link_section, Normal, template!(NameValueStr: "name"), FutureWarnPreceding),
 350     ungated!(no_mangle, Normal, template!(Word), WarnFollowing, @only_local: true),
 351     ungated!(used, Normal, template!(Word, List: "compiler|linker"), WarnFollowing, @only_local: true),
 352     ungated!(link_ordinal, Normal, template!(List: "ordinal"), ErrorPreceding),
 353
 354     // Limits:
 355     ungated!(recursion_limit, CrateLevel, template!(NameValueStr: "N"), FutureWarnFollowing),
 356     ungated!(type_length_limit, CrateLevel, template!(NameValueStr: "N"), FutureWarnFollowing),
 357     gated!(
 358         const_eval_limit, CrateLevel, template!(NameValueStr: "N"), ErrorFollowing,
 359         const_eval_limit, experimental!(const_eval_limit)
 360     ),
 361     gated!(
 362         move_size_limit, CrateLevel, template!(NameValueStr: "N"), ErrorFollowing,
 363         large_assignments, experimental!(move_size_limit)
 364     ),
 365
 366     // Entry point:
 367     gated!(unix_sigpipe, Normal, template!(Word, NameValueStr: "inherit|sig_ign|sig_dfl"), ErrorFollowing, experimental!(unix_sigpipe)),
 368     ungated!(start, Normal, template!(Word), WarnFollowing),
 369     ungated!(no_start, CrateLevel, template!(Word), WarnFollowing),
 370     ungated!(no_main, CrateLevel, template!(Word), WarnFollowing),
 371
 372     // Modules, prelude, and resolution:
 373     ungated!(path, Normal, template!(NameValueStr: "file"), FutureWarnFollowing),
 374     ungated!(no_std, CrateLevel, template!(Word), WarnFollowing),
 375     ungated!(no_implicit_prelude, Normal, template!(Word), WarnFollowing),
 376     ungated!(non_exhaustive, Normal, template!(Word), WarnFollowing),
 377
 378     // Runtime
 379     ungated!(
 380         windows_subsystem, CrateLevel,
 381         template!(NameValueStr: "windows|console"), FutureWarnFollowing
 382     ),
 383     ungated!(panic_handler, Normal, template!(Word), WarnFollowing), // RFC 2070
 384
 385     // Code generation:
 386     ungated!(inline, Normal, template!(Word, List: "always|never"), FutureWarnFollowing, @only_local: true),
 387     ungated!(cold, Normal, template!(Word), WarnFollowing, @only_local: true),
 388     ungated!(no_builtins, CrateLevel, template!(Word), WarnFollowing),
 389     ungated!(
 390         target_feature, Normal, template!(List: r#"enable = "name""#),
 391         DuplicatesOk, @only_local: true,
 392     ),
 393     ungated!(track_caller, Normal, template!(Word), WarnFollowing),
 394     ungated!(instruction_set, Normal, template!(List: "set"), ErrorPreceding),
 395     gated!(
 396         no_sanitize, Normal,
 397         template!(List: "address, memory, thread"), DuplicatesOk,
 398         experimental!(no_sanitize)
 399     ),
 400     gated!(no_coverage, Normal, template!(Word), WarnFollowing, experimental!(no_coverage)),
 401
 402     ungated!(
 403         doc, Normal, template!(List: "hidden|inline|...", NameValueStr: "string"), DuplicatesOk
 404     ),
 405
 406     // ==========================================================================
 407     // Unstable attributes:
 408     // ==========================================================================
 409
 410     // RFC #3191: #[debugger_visualizer] support
 411     gated!(
 412         debugger_visualizer, Normal, template!(List: r#"natvis_file = "...", gdb_script_file = "...""#),
 413         DuplicatesOk, experimental!(debugger_visualizer)
 414     ),
 415
 416     // Linking:
 417     gated!(naked, Normal, template!(Word), WarnFollowing, @only_local: true, naked_functions, experimental!(naked)),
 418
 419     // Plugins:
 420     BuiltinAttribute {
 421         name: sym::plugin,
 422         only_local: false,
 423         type_: CrateLevel,
 424         template: template!(List: "name"),
 425         duplicates: DuplicatesOk,
 426         gate: Gated(
 427             Stability::Deprecated(
 428                 "https://github.com/rust-lang/rust/pull/64675",
 429                 Some("may be removed in a future compiler version"),
 430             ),
 431             sym::plugin,
 432             "compiler plugins are deprecated",
 433             cfg_fn!(plugin)
 434         ),
 435     },
 436
 437     // Testing:
 438     gated!(
 439         test_runner, CrateLevel, template!(List: "path"), ErrorFollowing, custom_test_frameworks,
 440         "custom test frameworks are an unstable feature",
 441     ),
 442     // RFC #1268
 443     gated!(
 444         marker, Normal, template!(Word), WarnFollowing, marker_trait_attr, experimental!(marker)
 445     ),
 446     gated!(
 447         thread_local, Normal, template!(Word), WarnFollowing,
 448         "`#[thread_local]` is an experimental feature, and does not currently handle destructors",
 449     ),
 450     gated!(no_core, CrateLevel, template!(Word), WarnFollowing, experimental!(no_core)),
 451     // RFC 2412
 452     gated!(
 453         optimize, Normal, template!(List: "size|speed"), ErrorPreceding, optimize_attribute,
 454         experimental!(optimize),
 455     ),
 456
 457     gated!(
 458         ffi_returns_twice, Normal, template!(Word), WarnFollowing, experimental!(ffi_returns_twice)
 459     ),
 460     gated!(ffi_pure, Normal, template!(Word), WarnFollowing, experimental!(ffi_pure)),
 461     gated!(ffi_const, Normal, template!(Word), WarnFollowing, experimental!(ffi_const)),
 462     gated!(
 463         register_tool, CrateLevel, template!(List: "tool1, tool2, ..."), DuplicatesOk,
 464         experimental!(register_tool),
 465     ),
 466
 467     gated!(
 468         cmse_nonsecure_entry, Normal, template!(Word), WarnFollowing,
 469         experimental!(cmse_nonsecure_entry)
 470     ),
 471     // RFC 2632
 472     gated!(
 473         const_trait, Normal, template!(Word), WarnFollowing, const_trait_impl,
 474         "`const_trait` is a temporary placeholder for marking a trait that is suitable for `const` \
 475         `impls` and all default bodies as `const`, which may be removed or renamed in the \
 476         future."
 477     ),
 478     // lang-team MCP 147
 479     gated!(
 480         deprecated_safe, Normal, template!(List: r#"since = "version", note = "...""#), ErrorFollowing,
 481         experimental!(deprecated_safe),
 482     ),
 483
 484     // `#[collapse_debuginfo]`
 485     gated!(
 486         collapse_debuginfo, Normal, template!(Word), WarnFollowing,
 487         experimental!(collapse_debuginfo)
 488     ),
 489
 490     // ==========================================================================
 491     // Internal attributes: Stability, deprecation, and unsafe:
 492     // ==========================================================================
 493
 494     ungated!(
 495         feature, CrateLevel,
 496         template!(List: "name1, name2, ..."), DuplicatesOk, @only_local: true,
 497     ),
 498     // DuplicatesOk since it has its own validation
 499     ungated!(
 500         stable, Normal,
 501         template!(List: r#"feature = "name", since = "version""#), DuplicatesOk, @only_local: true,
 502     ),
 503     ungated!(
 504         unstable, Normal,
 505         template!(List: r#"feature = "name", reason = "...", issue = "N""#), DuplicatesOk,
 506     ),
 507     ungated!(rustc_const_unstable, Normal, template!(List: r#"feature = "name""#), DuplicatesOk),
 508     ungated!(
 509         rustc_const_stable, Normal,
 510         template!(List: r#"feature = "name""#), DuplicatesOk, @only_local: true,
 511     ),
 512     ungated!(
 513         rustc_default_body_unstable, Normal,
 514         template!(List: r#"feature = "name", reason = "...", issue = "N""#), DuplicatesOk
 515     ),
 516     gated!(
 517         allow_internal_unstable, Normal, template!(Word, List: "feat1, feat2, ..."), DuplicatesOk,
 518         "allow_internal_unstable side-steps feature gating and stability checks",
 519     ),
 520     gated!(
 521         rustc_allow_const_fn_unstable, Normal,
 522         template!(Word, List: "feat1, feat2, ..."), DuplicatesOk,
 523         "rustc_allow_const_fn_unstable side-steps feature gating and stability checks"
 524     ),
 525     gated!(
 526         allow_internal_unsafe, Normal, template!(Word), WarnFollowing,
 527         "allow_internal_unsafe side-steps the unsafe_code lint",
 528     ),
 529     ungated!(rustc_safe_intrinsic, Normal, template!(Word), DuplicatesOk),
 530     rustc_attr!(rustc_allowed_through_unstable_modules, Normal, template!(Word), WarnFollowing,
 531     "rustc_allowed_through_unstable_modules special cases accidental stabilizations of stable items \
 532     through unstable paths"),
 533
 534     // ==========================================================================
 535     // Internal attributes: Type system related:
 536     // ==========================================================================
 537
 538     gated!(fundamental, Normal, template!(Word), WarnFollowing, experimental!(fundamental)),
 539     gated!(
 540         may_dangle, Normal, template!(Word), WarnFollowing, dropck_eyepatch,
 541         "`may_dangle` has unstable semantics and may be removed in the future",
 542     ),
 543
 544     // ==========================================================================
 545     // Internal attributes: Runtime related:
 546     // ==========================================================================
 547
 548     rustc_attr!(rustc_allocator, Normal, template!(Word), WarnFollowing, IMPL_DETAIL),
 549     rustc_attr!(rustc_nounwind, Normal, template!(Word), WarnFollowing, IMPL_DETAIL),
 550     rustc_attr!(rustc_reallocator, Normal, template!(Word), WarnFollowing, IMPL_DETAIL),
 551     rustc_attr!(rustc_deallocator, Normal, template!(Word), WarnFollowing, IMPL_DETAIL),
 552     rustc_attr!(rustc_allocator_zeroed, Normal, template!(Word), WarnFollowing, IMPL_DETAIL),
 553     gated!(
 554         default_lib_allocator, Normal, template!(Word), WarnFollowing, allocator_internals,
 555         experimental!(default_lib_allocator),
 556     ),
 557     gated!(
 558         needs_allocator, Normal, template!(Word), WarnFollowing, allocator_internals,
 559         experimental!(needs_allocator),
 560     ),
 561     gated!(panic_runtime, Normal, template!(Word), WarnFollowing, experimental!(panic_runtime)),
 562     gated!(
 563         needs_panic_runtime, Normal, template!(Word), WarnFollowing,
 564         experimental!(needs_panic_runtime)
 565     ),
 566     gated!(
 567         compiler_builtins, Normal, template!(Word), WarnFollowing,
 568         "the `#[compiler_builtins]` attribute is used to identify the `compiler_builtins` crate \
 569         which contains compiler-rt intrinsics and will never be stable",
 570     ),
 571     gated!(
 572         profiler_runtime, Normal, template!(Word), WarnFollowing,
 573         "the `#[profiler_runtime]` attribute is used to identify the `profiler_builtins` crate \
 574         which contains the profiler runtime and will never be stable",
 575     ),
 576
 577     // ==========================================================================
 578     // Internal attributes, Linkage:
 579     // ==========================================================================
 580
 581     gated!(
 582         linkage, Normal, template!(NameValueStr: "external|internal|..."), ErrorPreceding, @only_local: true,
 583         "the `linkage` attribute is experimental and not portable across platforms",
 584     ),
 585     rustc_attr!(
 586         rustc_std_internal_symbol, Normal, template!(Word), WarnFollowing, @only_local: true, INTERNAL_UNSTABLE
 587     ),
 588
 589     // ==========================================================================
 590     // Internal attributes, Macro related:
 591     // ==========================================================================
 592
 593     rustc_attr!(
 594         rustc_builtin_macro, Normal,
 595         template!(Word, List: "name, /*opt*/ attributes(name1, name2, ...)"), ErrorFollowing,
 596         IMPL_DETAIL,
 597     ),
 598     rustc_attr!(rustc_proc_macro_decls, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE),
 599     rustc_attr!(
 600         rustc_macro_transparency, Normal,
 601         template!(NameValueStr: "transparent|semitransparent|opaque"), ErrorFollowing,
 602         "used internally for testing macro hygiene",
 603     ),
 604
 605     // ==========================================================================
 606     // Internal attributes, Diagnostics related:
 607     // ==========================================================================
 608
 609     rustc_attr!(
 610         rustc_on_unimplemented, Normal,
 611         template!(
 612             List: r#"/*opt*/ message = "...", /*opt*/ label = "...", /*opt*/ note = "...""#,
 613             NameValueStr: "message"
 614         ),
 615         ErrorFollowing,
 616         INTERNAL_UNSTABLE
 617     ),
 618     // Enumerates "identity-like" conversion methods to suggest on type mismatch.
 619     rustc_attr!(
 620         rustc_conversion_suggestion, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE
 621     ),
 622     // Prevents field reads in the marked trait or method to be considered
 623     // during dead code analysis.
 624     rustc_attr!(
 625         rustc_trivial_field_reads, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE
 626     ),
 627     // Used by the `rustc::potential_query_instability` lint to warn methods which
 628     // might not be stable during incremental compilation.
 629     rustc_attr!(rustc_lint_query_instability, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE),
 630     // Used by the `rustc::untranslatable_diagnostic` and `rustc::diagnostic_outside_of_impl` lints
 631     // to assist in changes to diagnostic APIs.
 632     rustc_attr!(rustc_lint_diagnostics, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE),
 633     // Used by the `rustc::bad_opt_access` lint to identify `DebuggingOptions` and `CodegenOptions`
 634     // types (as well as any others in future).
 635     rustc_attr!(rustc_lint_opt_ty, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE),
 636     // Used by the `rustc::bad_opt_access` lint on fields
 637     // types (as well as any others in future).
 638     rustc_attr!(rustc_lint_opt_deny_field_access, Normal, template!(List: "message"), WarnFollowing, INTERNAL_UNSTABLE),
 639
 640     // ==========================================================================
 641     // Internal attributes, Const related:
 642     // ==========================================================================
 643
 644     rustc_attr!(rustc_promotable, Normal, template!(Word), WarnFollowing, IMPL_DETAIL),
 645     rustc_attr!(
 646         rustc_legacy_const_generics, Normal, template!(List: "N"), ErrorFollowing,
 647         INTERNAL_UNSTABLE
 648     ),
 649     // Do not const-check this function's body. It will always get replaced during CTFE.
 650     rustc_attr!(
 651         rustc_do_not_const_check, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE
 652     ),
 653
 654     // ==========================================================================
 655     // Internal attributes, Layout related:
 656     // ==========================================================================
 657
 658     rustc_attr!(
 659         rustc_layout_scalar_valid_range_start, Normal, template!(List: "value"), ErrorFollowing,
 660         "the `#[rustc_layout_scalar_valid_range_start]` attribute is just used to enable \
 661         niche optimizations in libcore and libstd and will never be stable",
 662     ),
 663     rustc_attr!(
 664         rustc_layout_scalar_valid_range_end, Normal, template!(List: "value"), ErrorFollowing,
 665         "the `#[rustc_layout_scalar_valid_range_end]` attribute is just used to enable \
 666         niche optimizations in libcore and libstd and will never be stable",
 667     ),
 668     rustc_attr!(
 669         rustc_nonnull_optimization_guaranteed, Normal, template!(Word), WarnFollowing,
 670         "the `#[rustc_nonnull_optimization_guaranteed]` attribute is just used to enable \
 671         niche optimizations in libcore and libstd and will never be stable",
 672     ),
 673
 674     // ==========================================================================
 675     // Internal attributes, Misc:
 676     // ==========================================================================
 677     gated!(
 678         lang, Normal, template!(NameValueStr: "name"), DuplicatesOk, @only_local: true, lang_items,
 679         "language items are subject to change",
 680     ),
 681     rustc_attr!(
 682         rustc_pass_by_value, Normal,
 683         template!(Word), ErrorFollowing,
 684         "#[rustc_pass_by_value] is used to mark types that must be passed by value instead of reference."
 685     ),
 686     rustc_attr!(
 687         rustc_coherence_is_core, AttributeType::CrateLevel, template!(Word), ErrorFollowing, @only_local: true,
 688         "#![rustc_coherence_is_core] allows inherent methods on builtin types, only intended to be used in `core`."
 689     ),
 690     rustc_attr!(
 691         rustc_allow_incoherent_impl, AttributeType::Normal, template!(Word), ErrorFollowing, @only_local: true,
 692         "#[rustc_allow_incoherent_impl] has to be added to all impl items of an incoherent inherent impl."
 693     ),
 694     rustc_attr!(
 695         rustc_deny_explicit_impl, AttributeType::Normal, template!(Word), ErrorFollowing, @only_local: false,
 696         "#[rustc_deny_explicit_impl] enforces that a trait can have no user-provided impls"
 697     ),
 698     rustc_attr!(
 699         rustc_has_incoherent_inherent_impls, AttributeType::Normal, template!(Word), ErrorFollowing,
 700         "#[rustc_has_incoherent_inherent_impls] allows the addition of incoherent inherent impls for \
 701          the given type by annotating all impl items with #[rustc_allow_incoherent_impl]."
 702     ),
 703     rustc_attr!(
 704         rustc_box, AttributeType::Normal, template!(Word), ErrorFollowing,
 705         "#[rustc_box] allows creating boxes \
 706         and it is only intended to be used in `alloc`."
 707     ),
 708
 709     BuiltinAttribute {
 710         name: sym::rustc_diagnostic_item,
 711         // FIXME: This can be `true` once we always use `tcx.is_diagnostic_item`.
 712         only_local: false,
 713         type_: Normal,
 714         template: template!(NameValueStr: "name"),
 715         duplicates: ErrorFollowing,
 716         gate: Gated(
 717             Stability::Unstable,
 718             sym::rustc_attrs,
 719             "diagnostic items compiler internal support for linting",
 720             cfg_fn!(rustc_attrs),
 721         ),
 722     },
 723     gated!(
 724         // Used in resolve:
 725         prelude_import, Normal, template!(Word), WarnFollowing,
 726         "`#[prelude_import]` is for use by rustc only",
 727     ),
 728     gated!(
 729         rustc_paren_sugar, Normal, template!(Word), WarnFollowing, unboxed_closures,
 730         "unboxed_closures are still evolving",
 731     ),
 732     rustc_attr!(
 733         rustc_inherit_overflow_checks, Normal, template!(Word), WarnFollowing, @only_local: true,
 734         "the `#[rustc_inherit_overflow_checks]` attribute is just used to control \
 735         overflow checking behavior of several libcore functions that are inlined \
 736         across crates and will never be stable",
 737     ),
 738     rustc_attr!(
 739         rustc_reservation_impl, Normal,
 740         template!(NameValueStr: "reservation message"), ErrorFollowing,
 741         "the `#[rustc_reservation_impl]` attribute is internally used \
 742          for reserving for `for<T> From<!> for T` impl"
 743     ),
 744     rustc_attr!(
 745         rustc_test_marker, Normal, template!(NameValueStr: "name"), WarnFollowing,
 746         "the `#[rustc_test_marker]` attribute is used internally to track tests",
 747     ),
 748     rustc_attr!(
 749         rustc_unsafe_specialization_marker, Normal, template!(Word), WarnFollowing,
 750         "the `#[rustc_unsafe_specialization_marker]` attribute is used to check specializations"
 751     ),
 752     rustc_attr!(
 753         rustc_specialization_trait, Normal, template!(Word), WarnFollowing,
 754         "the `#[rustc_specialization_trait]` attribute is used to check specializations"
 755     ),
 756     rustc_attr!(
 757         rustc_main, Normal, template!(Word), WarnFollowing,
 758         "the `#[rustc_main]` attribute is used internally to specify test entry point function",
 759     ),
 760     rustc_attr!(
 761         rustc_skip_array_during_method_dispatch, Normal, template!(Word), WarnFollowing,
 762         "the `#[rustc_skip_array_during_method_dispatch]` attribute is used to exclude a trait \
 763         from method dispatch when the receiver is an array, for compatibility in editions < 2021."
 764     ),
 765     rustc_attr!(
 766         rustc_must_implement_one_of, Normal, template!(List: "function1, function2, ..."), ErrorFollowing,
 767         "the `#[rustc_must_implement_one_of]` attribute is used to change minimal complete \
 768         definition of a trait, it's currently in experimental form and should be changed before \
 769         being exposed outside of the std"
 770     ),
 771
 772     // ==========================================================================
 773     // Internal attributes, Testing:
 774     // ==========================================================================
 775
 776     rustc_attr!(TEST, rustc_effective_visibility, Normal, template!(Word), WarnFollowing),
 777     rustc_attr!(TEST, rustc_outlives, Normal, template!(Word), WarnFollowing),
 778     rustc_attr!(TEST, rustc_capture_analysis, Normal, template!(Word), WarnFollowing),
 779     rustc_attr!(TEST, rustc_insignificant_dtor, Normal, template!(Word), WarnFollowing),
 780     rustc_attr!(TEST, rustc_strict_coherence, Normal, template!(Word), WarnFollowing),
 781     rustc_attr!(TEST, rustc_variance, Normal, template!(Word), WarnFollowing),
 782     rustc_attr!(TEST, rustc_layout, Normal, template!(List: "field1, field2, ..."), WarnFollowing),
 783     rustc_attr!(TEST, rustc_regions, Normal, template!(Word), WarnFollowing),
 784     rustc_attr!(
 785         TEST, rustc_error, Normal,
 786         template!(Word, List: "delay_span_bug_from_inside_query"), WarnFollowingWordOnly
 787     ),
 788     rustc_attr!(TEST, rustc_dump_user_substs, Normal, template!(Word), WarnFollowing),
 789     rustc_attr!(TEST, rustc_evaluate_where_clauses, Normal, template!(Word), WarnFollowing),
 790     rustc_attr!(
 791         TEST, rustc_if_this_changed, Normal, template!(Word, List: "DepNode"), DuplicatesOk
 792     ),
 793     rustc_attr!(
 794         TEST, rustc_then_this_would_need, Normal, template!(List: "DepNode"), DuplicatesOk
 795     ),
 796     rustc_attr!(
 797         TEST, rustc_clean, Normal,
 798         template!(List: r#"cfg = "...", /*opt*/ label = "...", /*opt*/ except = "...""#),
 799         DuplicatesOk,
 800     ),
 801     rustc_attr!(
 802         TEST, rustc_partition_reused, Normal,
 803         template!(List: r#"cfg = "...", module = "...""#), DuplicatesOk,
 804     ),
 805     rustc_attr!(
 806         TEST, rustc_partition_codegened, Normal,
 807         template!(List: r#"cfg = "...", module = "...""#), DuplicatesOk,
 808     ),
 809     rustc_attr!(
 810         TEST, rustc_expected_cgu_reuse, Normal,
 811         template!(List: r#"cfg = "...", module = "...", kind = "...""#), DuplicatesOk,
 812     ),
 813     rustc_attr!(TEST, rustc_symbol_name, Normal, template!(Word), WarnFollowing),
 814     rustc_attr!(TEST, rustc_polymorphize_error, Normal, template!(Word), WarnFollowing),
 815     rustc_attr!(TEST, rustc_def_path, Normal, template!(Word), WarnFollowing),
 816     rustc_attr!(TEST, rustc_mir, Normal, template!(List: "arg1, arg2, ..."), DuplicatesOk),
 817     gated!(
 818         custom_mir, Normal, template!(List: r#"dialect = "...", phase = "...""#),
 819         ErrorFollowing, "the `#[custom_mir]` attribute is just used for the Rust test suite",
 820     ),
 821     rustc_attr!(TEST, rustc_dump_program_clauses, Normal, template!(Word), WarnFollowing),
 822     rustc_attr!(TEST, rustc_dump_env_program_clauses, Normal, template!(Word), WarnFollowing),
 823     rustc_attr!(TEST, rustc_object_lifetime_default, Normal, template!(Word), WarnFollowing),
 824     rustc_attr!(TEST, rustc_dump_vtable, Normal, template!(Word), WarnFollowing),
 825     rustc_attr!(TEST, rustc_dummy, Normal, template!(Word /* doesn't matter*/), DuplicatesOk),
 826     gated!(
 827         omit_gdb_pretty_printer_section, Normal, template!(Word), WarnFollowing,
 828         "the `#[omit_gdb_pretty_printer_section]` attribute is just used for the Rust test suite",
 829     ),
 830 ];
 831
 832 pub fn deprecated_attributes() -> Vec<&'static BuiltinAttribute> {
 833     BUILTIN_ATTRIBUTES.iter().filter(|attr| attr.gate.is_deprecated()).collect()
 834 }
 835
 836 pub fn is_builtin_attr_name(name: Symbol) -> bool {
 837     BUILTIN_ATTRIBUTE_MAP.get(&name).is_some()
 838 }
 839
 840 /// Whether this builtin attribute is only used in the local crate.
 841 /// If so, it is not encoded in the crate metadata.
 842 pub fn is_builtin_only_local(name: Symbol) -> bool {
 843     BUILTIN_ATTRIBUTE_MAP.get(&name).map_or(false, |attr| attr.only_local)
 844 }
 845
 846 pub fn is_valid_for_get_attr(name: Symbol) -> bool {
 847     BUILTIN_ATTRIBUTE_MAP.get(&name).map_or(false, |attr| match attr.duplicates {
 848         WarnFollowing | ErrorFollowing | ErrorPreceding | FutureWarnFollowing
 849         | FutureWarnPreceding => true,
 850         DuplicatesOk | WarnFollowingWordOnly => false,
 851     })
 852 }
 853
 854 pub static BUILTIN_ATTRIBUTE_MAP: LazyLock<FxHashMap<Symbol, &BuiltinAttribute>> =
 855     LazyLock::new(|| {
 856         let mut map = FxHashMap::default();
 857         for attr in BUILTIN_ATTRIBUTES.iter() {
 858             if map.insert(attr.name, attr).is_some() {
 859                 panic!("duplicate builtin attribute `{}`", attr.name);
 860             }
 861         }
 862         map
 863     });