1 //! Built-in attributes and `cfg` flag gating.
6 use crate::{Features, Stability};
8 use rustc_data_structures::fx::FxHashMap;
9 use rustc_span::symbol::{sym, Symbol};
11 use std::lazy::SyncLazy;
13 type GateFn = fn(&Features) -> bool;
17 (|features| features.$field) as GateFn
21 pub type GatedCfg = (Symbol, Symbol, GateFn);
23 /// `cfg(...)`'s that are feature gated.
24 const GATED_CFGS: &[GatedCfg] = &[
25 // (name in cfg, feature, function to check if the feature is enabled)
26 (sym::target_thread_local, sym::cfg_target_thread_local, cfg_fn!(cfg_target_thread_local)),
27 (sym::target_has_atomic, sym::cfg_target_has_atomic, cfg_fn!(cfg_target_has_atomic)),
28 (sym::target_has_atomic_load_store, sym::cfg_target_has_atomic, cfg_fn!(cfg_target_has_atomic)),
30 sym::target_has_atomic_equal_alignment,
31 sym::cfg_target_has_atomic,
32 cfg_fn!(cfg_target_has_atomic),
34 (sym::sanitize, sym::cfg_sanitize, cfg_fn!(cfg_sanitize)),
35 (sym::version, sym::cfg_version, cfg_fn!(cfg_version)),
36 (sym::panic, sym::cfg_panic, cfg_fn!(cfg_panic)),
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))
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.
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
54 /// Builtin attribute that may not be consumed by the compiler
55 /// before the unused_attribute check. These attributes
56 /// will be ignored by the unused_attribute lint
59 /// Builtin attribute that is only allowed at the crate level
63 #[derive(Clone, Copy)]
64 pub enum AttributeGate {
65 /// Is gated by a given feature gate, reason
66 /// and function to check if enabled
67 Gated(Stability, Symbol, &'static str, fn(&Features) -> bool),
69 /// Ungated attribute, can be used on all release channels
74 impl std::fmt::Debug for AttributeGate {
75 fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
77 Self::Gated(ref stab, name, expl, _) => {
78 write!(fmt, "Gated({:?}, {}, {})", stab, name, expl)
80 Self::Ungated => write!(fmt, "Ungated"),
86 fn is_deprecated(&self) -> bool {
87 matches!(*self, Self::Gated(Stability::Deprecated(_, _), ..))
91 /// A template that the attribute input must match.
92 /// Only top-level shape (`#[attr]` vs `#[attr(...)]` vs `#[attr = ...]`) is considered now.
93 #[derive(Clone, Copy, Default)]
94 pub struct AttributeTemplate {
96 pub list: Option<&'static str>,
97 pub name_value_str: Option<&'static str>,
100 /// A convenience macro for constructing attribute templates.
101 /// E.g., `template!(Word, List: "description")` means that the attribute
102 /// supports forms `#[attr]` and `#[attr(description)]`.
103 macro_rules! template {
104 (Word) => { template!(@ true, None, None) };
105 (List: $descr: expr) => { template!(@ false, Some($descr), None) };
106 (NameValueStr: $descr: expr) => { template!(@ false, None, Some($descr)) };
107 (Word, List: $descr: expr) => { template!(@ true, Some($descr), None) };
108 (Word, NameValueStr: $descr: expr) => { template!(@ true, None, Some($descr)) };
109 (List: $descr1: expr, NameValueStr: $descr2: expr) => {
110 template!(@ false, Some($descr1), Some($descr2))
112 (Word, List: $descr1: expr, NameValueStr: $descr2: expr) => {
113 template!(@ true, Some($descr1), Some($descr2))
115 (@ $word: expr, $list: expr, $name_value_str: expr) => { AttributeTemplate {
116 word: $word, list: $list, name_value_str: $name_value_str
120 macro_rules! ungated {
121 ($attr:ident, $typ:expr, $tpl:expr $(,)?) => {
122 (sym::$attr, $typ, $tpl, Ungated)
127 ($attr:ident, $typ:expr, $tpl:expr, $gate:ident, $msg:expr $(,)?) => {
128 (sym::$attr, $typ, $tpl, Gated(Stability::Unstable, sym::$gate, $msg, cfg_fn!($gate)))
130 ($attr:ident, $typ:expr, $tpl:expr, $msg:expr $(,)?) => {
131 (sym::$attr, $typ, $tpl, Gated(Stability::Unstable, sym::$attr, $msg, cfg_fn!($attr)))
135 macro_rules! rustc_attr {
136 (TEST, $attr:ident, $typ:expr, $tpl:expr $(,)?) => {
144 "]` attribute is just used for rustc unit tests \
145 and will never be stable",
149 ($attr:ident, $typ:expr, $tpl:expr, $msg:expr $(,)?) => {
154 Gated(Stability::Unstable, sym::rustc_attrs, $msg, cfg_fn!(rustc_attrs)),
159 macro_rules! experimental {
161 concat!("the `#[", stringify!($attr), "]` attribute is an experimental feature")
165 const IMPL_DETAIL: &str = "internal implementation detail";
166 const INTERNAL_UNSTABLE: &str = "this is an internal attribute that will never be stable";
168 pub type BuiltinAttribute = (Symbol, AttributeType, AttributeTemplate, AttributeGate);
170 /// Attributes that have a special meaning to rustc or rustdoc.
172 pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
173 // ==========================================================================
174 // Stable attributes:
175 // ==========================================================================
177 // Conditional compilation:
178 ungated!(cfg, Normal, template!(List: "predicate")),
179 ungated!(cfg_attr, Normal, template!(List: "predicate, attr1, attr2, ...")),
182 ungated!(ignore, Normal, template!(Word, NameValueStr: "reason")),
184 should_panic, Normal,
185 template!(Word, List: r#"expected = "reason"#, NameValueStr: "reason"),
187 // FIXME(Centril): This can be used on stable but shouldn't.
188 ungated!(reexport_test_harness_main, Normal, template!(NameValueStr: "name")),
191 ungated!(automatically_derived, Normal, template!(Word)),
193 ungated!(macro_use, Normal, template!(Word, List: "name1, name2, ...")),
194 ungated!(macro_escape, Normal, template!(Word)), // Deprecated synonym for `macro_use`.
195 ungated!(macro_export, Normal, template!(Word, List: "local_inner_macros")),
196 ungated!(proc_macro, Normal, template!(Word)),
198 proc_macro_derive, Normal,
199 template!(List: "TraitName, /*opt*/ attributes(name1, name2, ...)"),
201 ungated!(proc_macro_attribute, Normal, template!(Word)),
204 ungated!(warn, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#)),
205 ungated!(allow, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#)),
206 ungated!(forbid, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#)),
207 ungated!(deny, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#)),
208 ungated!(must_use, AssumedUsed, template!(Word, NameValueStr: "reason")),
214 List: r#"/*opt*/ since = "version", /*opt*/ note = "reason""#,
215 NameValueStr: "reason"
220 ungated!(crate_name, CrateLevel, template!(NameValueStr: "name")),
221 ungated!(crate_type, CrateLevel, template!(NameValueStr: "bin|lib|...")),
222 ungated!(crate_id, CrateLevel, template!(NameValueStr: "ignored")),
224 // ABI, linking, symbols, and FFI
227 template!(List: r#"name = "...", /*opt*/ kind = "dylib|static|...", /*opt*/ wasm_import_module = "...""#),
229 ungated!(link_name, AssumedUsed, template!(NameValueStr: "name")),
230 ungated!(no_link, AssumedUsed, template!(Word)),
231 ungated!(repr, AssumedUsed, template!(List: "C")),
232 ungated!(export_name, AssumedUsed, template!(NameValueStr: "name")),
233 ungated!(link_section, AssumedUsed, template!(NameValueStr: "name")),
234 ungated!(no_mangle, AssumedUsed, template!(Word)),
235 ungated!(used, AssumedUsed, template!(Word)),
238 ungated!(recursion_limit, CrateLevel, template!(NameValueStr: "N")),
239 ungated!(type_length_limit, CrateLevel, template!(NameValueStr: "N")),
241 const_eval_limit, CrateLevel, template!(NameValueStr: "N"), const_eval_limit,
242 experimental!(const_eval_limit)
245 move_size_limit, CrateLevel, template!(NameValueStr: "N"), large_assignments,
246 experimental!(move_size_limit)
250 ungated!(main, Normal, template!(Word)),
251 ungated!(start, Normal, template!(Word)),
252 ungated!(no_start, CrateLevel, template!(Word)),
253 ungated!(no_main, CrateLevel, template!(Word)),
255 // Modules, prelude, and resolution:
256 ungated!(path, Normal, template!(NameValueStr: "file")),
257 ungated!(no_std, CrateLevel, template!(Word)),
258 ungated!(no_implicit_prelude, Normal, template!(Word)),
259 ungated!(non_exhaustive, AssumedUsed, template!(Word)),
262 ungated!(windows_subsystem, AssumedUsed, template!(NameValueStr: "windows|console")),
263 ungated!(panic_handler, Normal, template!(Word)), // RFC 2070
266 ungated!(inline, AssumedUsed, template!(Word, List: "always|never")),
267 ungated!(cold, AssumedUsed, template!(Word)),
268 ungated!(no_builtins, AssumedUsed, template!(Word)),
269 ungated!(target_feature, AssumedUsed, template!(List: r#"enable = "name""#)),
270 ungated!(track_caller, AssumedUsed, template!(Word)),
272 no_sanitize, AssumedUsed,
273 template!(List: "address, memory, thread"),
274 experimental!(no_sanitize)
276 gated!(no_coverage, AssumedUsed, template!(Word), experimental!(no_coverage)),
278 // FIXME: #14408 assume docs are used since rustdoc looks at them.
279 ungated!(doc, AssumedUsed, template!(List: "hidden|inline|...", NameValueStr: "string")),
281 // ==========================================================================
282 // Unstable attributes:
283 // ==========================================================================
286 gated!(naked, AssumedUsed, template!(Word), naked_functions, experimental!(naked)),
288 link_ordinal, AssumedUsed, template!(List: "ordinal"), raw_dylib,
289 experimental!(link_ordinal)
294 sym::plugin_registrar, Normal, template!(Word),
296 Stability::Deprecated(
297 "https://github.com/rust-lang/rust/pull/64675",
298 Some("may be removed in a future compiler version"),
300 sym::plugin_registrar,
301 "compiler plugins are deprecated",
302 cfg_fn!(plugin_registrar)
306 sym::plugin, CrateLevel, template!(List: "name"),
308 Stability::Deprecated(
309 "https://github.com/rust-lang/rust/pull/64675",
310 Some("may be removed in a future compiler version"),
313 "compiler plugins are deprecated",
319 gated!(allow_fail, Normal, template!(Word), experimental!(allow_fail)),
321 test_runner, CrateLevel, template!(List: "path"), custom_test_frameworks,
322 "custom test frameworks are an unstable feature",
325 gated!(marker, AssumedUsed, template!(Word), marker_trait_attr, experimental!(marker)),
327 thread_local, AssumedUsed, template!(Word),
328 "`#[thread_local]` is an experimental feature, and does not currently handle destructors",
330 gated!(no_core, CrateLevel, template!(Word), experimental!(no_core)),
333 optimize, AssumedUsed, template!(List: "size|speed"), optimize_attribute,
334 experimental!(optimize),
337 gated!(instruction_set, AssumedUsed, template!(List: "set"), isa_attribute, experimental!(instruction_set)),
339 gated!(ffi_returns_twice, AssumedUsed, template!(Word), experimental!(ffi_returns_twice)),
340 gated!(ffi_pure, AssumedUsed, template!(Word), experimental!(ffi_pure)),
341 gated!(ffi_const, AssumedUsed, template!(Word), experimental!(ffi_const)),
343 register_attr, CrateLevel, template!(List: "attr1, attr2, ..."),
344 experimental!(register_attr),
347 register_tool, CrateLevel, template!(List: "tool1, tool2, ..."),
348 experimental!(register_tool),
351 gated!(cmse_nonsecure_entry, AssumedUsed, template!(Word), experimental!(cmse_nonsecure_entry)),
353 // ==========================================================================
354 // Internal attributes: Stability, deprecation, and unsafe:
355 // ==========================================================================
357 ungated!(feature, CrateLevel, template!(List: "name1, name1, ...")),
358 // FIXME(#14407) -- only looked at on-demand so we can't
359 // guarantee they'll have already been checked.
361 rustc_deprecated, AssumedUsed,
362 template!(List: r#"since = "version", reason = "...""#)
365 ungated!(stable, AssumedUsed, template!(List: r#"feature = "name", since = "version""#)),
368 unstable, AssumedUsed,
369 template!(List: r#"feature = "name", reason = "...", issue = "N""#),
372 ungated!(rustc_const_unstable, AssumedUsed, template!(List: r#"feature = "name""#)),
374 ungated!(rustc_const_stable, AssumedUsed, template!(List: r#"feature = "name""#)),
376 allow_internal_unstable, AssumedUsed, template!(Word, List: "feat1, feat2, ..."),
377 "allow_internal_unstable side-steps feature gating and stability checks",
380 rustc_allow_const_fn_unstable, AssumedUsed, template!(Word, List: "feat1, feat2, ..."),
381 "rustc_allow_const_fn_unstable side-steps feature gating and stability checks"
384 allow_internal_unsafe, Normal, template!(Word),
385 "allow_internal_unsafe side-steps the unsafe_code lint",
388 // ==========================================================================
389 // Internal attributes: Type system related:
390 // ==========================================================================
392 gated!(fundamental, AssumedUsed, template!(Word), experimental!(fundamental)),
394 may_dangle, Normal, template!(Word), dropck_eyepatch,
395 "`may_dangle` has unstable semantics and may be removed in the future",
398 // ==========================================================================
399 // Internal attributes: Runtime related:
400 // ==========================================================================
402 rustc_attr!(rustc_allocator, AssumedUsed, template!(Word), IMPL_DETAIL),
403 rustc_attr!(rustc_allocator_nounwind, AssumedUsed, template!(Word), IMPL_DETAIL),
404 gated!(alloc_error_handler, Normal, template!(Word), experimental!(alloc_error_handler)),
406 default_lib_allocator, AssumedUsed, template!(Word), allocator_internals,
407 experimental!(default_lib_allocator),
410 needs_allocator, Normal, template!(Word), allocator_internals,
411 experimental!(needs_allocator),
413 gated!(panic_runtime, AssumedUsed, template!(Word), experimental!(panic_runtime)),
414 gated!(needs_panic_runtime, AssumedUsed, template!(Word), experimental!(needs_panic_runtime)),
416 unwind, AssumedUsed, template!(List: "allowed|aborts"), unwind_attributes,
417 experimental!(unwind),
420 compiler_builtins, AssumedUsed, template!(Word),
421 "the `#[compiler_builtins]` attribute is used to identify the `compiler_builtins` crate \
422 which contains compiler-rt intrinsics and will never be stable",
425 profiler_runtime, AssumedUsed, template!(Word),
426 "the `#[profiler_runtime]` attribute is used to identify the `profiler_builtins` crate \
427 which contains the profiler runtime and will never be stable",
430 // ==========================================================================
431 // Internal attributes, Linkage:
432 // ==========================================================================
435 linkage, AssumedUsed, template!(NameValueStr: "external|internal|..."),
436 "the `linkage` attribute is experimental and not portable across platforms",
438 rustc_attr!(rustc_std_internal_symbol, AssumedUsed, template!(Word), INTERNAL_UNSTABLE),
440 // ==========================================================================
441 // Internal attributes, Macro related:
442 // ==========================================================================
444 rustc_attr!(rustc_builtin_macro, AssumedUsed, template!(Word, NameValueStr: "name"), IMPL_DETAIL),
445 rustc_attr!(rustc_proc_macro_decls, Normal, template!(Word), INTERNAL_UNSTABLE),
447 rustc_macro_transparency, AssumedUsed,
448 template!(NameValueStr: "transparent|semitransparent|opaque"),
449 "used internally for testing macro hygiene",
452 // ==========================================================================
453 // Internal attributes, Diagnostics related:
454 // ==========================================================================
457 rustc_on_unimplemented, AssumedUsed,
459 List: r#"/*opt*/ message = "...", /*opt*/ label = "...", /*opt*/ note = "...""#,
460 NameValueStr: "message"
464 // Enumerates "identity-like" conversion methods to suggest on type mismatch.
465 rustc_attr!(rustc_conversion_suggestion, AssumedUsed, template!(Word), INTERNAL_UNSTABLE),
467 // ==========================================================================
468 // Internal attributes, Const related:
469 // ==========================================================================
471 rustc_attr!(rustc_promotable, AssumedUsed, template!(Word), IMPL_DETAIL),
472 rustc_attr!(rustc_legacy_const_generics, AssumedUsed, template!(List: "N"), INTERNAL_UNSTABLE),
474 // ==========================================================================
475 // Internal attributes, Layout related:
476 // ==========================================================================
479 rustc_layout_scalar_valid_range_start, AssumedUsed, template!(List: "value"),
480 "the `#[rustc_layout_scalar_valid_range_start]` attribute is just used to enable \
481 niche optimizations in libcore and will never be stable",
484 rustc_layout_scalar_valid_range_end, AssumedUsed, template!(List: "value"),
485 "the `#[rustc_layout_scalar_valid_range_end]` attribute is just used to enable \
486 niche optimizations in libcore and will never be stable",
489 rustc_nonnull_optimization_guaranteed, AssumedUsed, template!(Word),
490 "the `#[rustc_nonnull_optimization_guaranteed]` attribute is just used to enable \
491 niche optimizations in libcore and will never be stable",
494 // ==========================================================================
495 // Internal attributes, Misc:
496 // ==========================================================================
498 lang, Normal, template!(NameValueStr: "name"), lang_items,
499 "language items are subject to change",
502 sym::rustc_diagnostic_item,
504 template!(NameValueStr: "name"),
508 "diagnostic items compiler internal support for linting",
509 cfg_fn!(rustc_attrs),
514 prelude_import, AssumedUsed, template!(Word),
515 "`#[prelude_import]` is for use by rustc only",
518 rustc_paren_sugar, Normal, template!(Word), unboxed_closures,
519 "unboxed_closures are still evolving",
522 rustc_inherit_overflow_checks, AssumedUsed, template!(Word),
523 "the `#[rustc_inherit_overflow_checks]` attribute is just used to control \
524 overflow checking behavior of several libcore functions that are inlined \
525 across crates and will never be stable",
527 rustc_attr!(rustc_reservation_impl, Normal, template!(NameValueStr: "reservation message"),
528 "the `#[rustc_reservation_impl]` attribute is internally used \
529 for reserving for `for<T> From<!> for T` impl"
532 rustc_test_marker, Normal, template!(Word),
533 "the `#[rustc_test_marker]` attribute is used internally to track tests",
536 rustc_unsafe_specialization_marker, Normal, template!(Word),
537 "the `#[rustc_unsafe_specialization_marker]` attribute is used to check specializations"
540 rustc_specialization_trait, Normal, template!(Word),
541 "the `#[rustc_specialization_trait]` attribute is used to check specializations"
544 rustc_main, Normal, template!(Word),
545 "the `#[rustc_main]` attribute is used internally to specify test entry point function",
548 rustc_skip_array_during_method_dispatch, Normal, template!(Word),
549 "the `#[rustc_skip_array_during_method_dispatch]` attribute is used to exclude a trait \
550 from method dispatch when the receiver is an array, for compatibility in editions < 2021."
553 // ==========================================================================
554 // Internal attributes, Testing:
555 // ==========================================================================
557 rustc_attr!(TEST, rustc_outlives, Normal, template!(Word)),
558 rustc_attr!(TEST, rustc_capture_analysis, Normal, template!(Word)),
559 rustc_attr!(TEST, rustc_insignificant_dtor, Normal, template!(Word)),
560 rustc_attr!(TEST, rustc_variance, Normal, template!(Word)),
561 rustc_attr!(TEST, rustc_layout, Normal, template!(List: "field1, field2, ...")),
562 rustc_attr!(TEST, rustc_regions, Normal, template!(Word)),
564 TEST, rustc_error, AssumedUsed,
565 template!(Word, List: "delay_span_bug_from_inside_query")
567 rustc_attr!(TEST, rustc_dump_user_substs, AssumedUsed, template!(Word)),
568 rustc_attr!(TEST, rustc_evaluate_where_clauses, AssumedUsed, template!(Word)),
569 rustc_attr!(TEST, rustc_if_this_changed, AssumedUsed, template!(Word, List: "DepNode")),
570 rustc_attr!(TEST, rustc_then_this_would_need, AssumedUsed, template!(List: "DepNode")),
572 TEST, rustc_dirty, AssumedUsed,
573 template!(List: r#"cfg = "...", /*opt*/ label = "...", /*opt*/ except = "...""#),
576 TEST, rustc_clean, AssumedUsed,
577 template!(List: r#"cfg = "...", /*opt*/ label = "...", /*opt*/ except = "...""#),
580 TEST, rustc_partition_reused, AssumedUsed,
581 template!(List: r#"cfg = "...", module = "...""#),
584 TEST, rustc_partition_codegened, AssumedUsed,
585 template!(List: r#"cfg = "...", module = "...""#),
588 TEST, rustc_expected_cgu_reuse, AssumedUsed,
589 template!(List: r#"cfg = "...", module = "...", kind = "...""#),
591 rustc_attr!(TEST, rustc_synthetic, AssumedUsed, template!(Word)),
592 rustc_attr!(TEST, rustc_symbol_name, AssumedUsed, template!(Word)),
593 rustc_attr!(TEST, rustc_polymorphize_error, AssumedUsed, template!(Word)),
594 rustc_attr!(TEST, rustc_def_path, AssumedUsed, template!(Word)),
595 rustc_attr!(TEST, rustc_mir, AssumedUsed, template!(List: "arg1, arg2, ...")),
596 rustc_attr!(TEST, rustc_dump_program_clauses, AssumedUsed, template!(Word)),
597 rustc_attr!(TEST, rustc_dump_env_program_clauses, AssumedUsed, template!(Word)),
598 rustc_attr!(TEST, rustc_object_lifetime_default, AssumedUsed, template!(Word)),
599 rustc_attr!(TEST, rustc_dummy, Normal, template!(Word /* doesn't matter*/)),
601 omit_gdb_pretty_printer_section, AssumedUsed, template!(Word),
602 "the `#[omit_gdb_pretty_printer_section]` attribute is just used for the Rust test suite",
606 pub fn deprecated_attributes() -> Vec<&'static BuiltinAttribute> {
607 BUILTIN_ATTRIBUTES.iter().filter(|(.., gate)| gate.is_deprecated()).collect()
610 pub fn is_builtin_attr_name(name: Symbol) -> bool {
611 BUILTIN_ATTRIBUTE_MAP.get(&name).is_some()
614 pub static BUILTIN_ATTRIBUTE_MAP: SyncLazy<FxHashMap<Symbol, &BuiltinAttribute>> =
616 let mut map = FxHashMap::default();
617 for attr in BUILTIN_ATTRIBUTES.iter() {
618 if map.insert(attr.0, attr).is_some() {
619 panic!("duplicate builtin attribute `{}`", attr.0);