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)),
29 (sym::sanitize, sym::cfg_sanitize, cfg_fn!(cfg_sanitize)),
30 (sym::version, sym::cfg_version, cfg_fn!(cfg_version)),
33 /// Find a gated cfg determined by the `pred`icate which is given the cfg's name.
34 pub fn find_gated_cfg(pred: impl Fn(Symbol) -> bool) -> Option<&'static GatedCfg> {
35 GATED_CFGS.iter().find(|(cfg_sym, ..)| pred(*cfg_sym))
38 // If you change this, please modify `src/doc/unstable-book` as well. You must
39 // move that documentation into the relevant place in the other docs, and
40 // remove the chapter on the flag.
42 #[derive(Copy, Clone, PartialEq, Debug)]
43 pub enum AttributeType {
44 /// Normal, builtin attribute that is consumed
45 /// by the compiler before the unused_attribute check
48 /// Builtin attribute that may not be consumed by the compiler
49 /// before the unused_attribute check. These attributes
50 /// will be ignored by the unused_attribute lint
53 /// Builtin attribute that is only allowed at the crate level
57 #[derive(Clone, Copy)]
58 pub enum AttributeGate {
59 /// Is gated by a given feature gate, reason
60 /// and function to check if enabled
61 Gated(Stability, Symbol, &'static str, fn(&Features) -> bool),
63 /// Ungated attribute, can be used on all release channels
68 impl std::fmt::Debug for AttributeGate {
69 fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
71 Self::Gated(ref stab, name, expl, _) => {
72 write!(fmt, "Gated({:?}, {}, {})", stab, name, expl)
74 Self::Ungated => write!(fmt, "Ungated"),
80 fn is_deprecated(&self) -> bool {
82 Self::Gated(Stability::Deprecated(_, _), ..) => true,
88 /// A template that the attribute input must match.
89 /// Only top-level shape (`#[attr]` vs `#[attr(...)]` vs `#[attr = ...]`) is considered now.
90 #[derive(Clone, Copy, Default)]
91 pub struct AttributeTemplate {
93 pub list: Option<&'static str>,
94 pub name_value_str: Option<&'static str>,
97 /// A convenience macro for constructing attribute templates.
98 /// E.g., `template!(Word, List: "description")` means that the attribute
99 /// supports forms `#[attr]` and `#[attr(description)]`.
100 macro_rules! template {
101 (Word) => { template!(@ true, None, None) };
102 (List: $descr: expr) => { template!(@ false, Some($descr), None) };
103 (NameValueStr: $descr: expr) => { template!(@ false, None, Some($descr)) };
104 (Word, List: $descr: expr) => { template!(@ true, Some($descr), None) };
105 (Word, NameValueStr: $descr: expr) => { template!(@ true, None, Some($descr)) };
106 (List: $descr1: expr, NameValueStr: $descr2: expr) => {
107 template!(@ false, Some($descr1), Some($descr2))
109 (Word, List: $descr1: expr, NameValueStr: $descr2: expr) => {
110 template!(@ true, Some($descr1), Some($descr2))
112 (@ $word: expr, $list: expr, $name_value_str: expr) => { AttributeTemplate {
113 word: $word, list: $list, name_value_str: $name_value_str
117 macro_rules! ungated {
118 ($attr:ident, $typ:expr, $tpl:expr $(,)?) => {
119 (sym::$attr, $typ, $tpl, Ungated)
124 ($attr:ident, $typ:expr, $tpl:expr, $gate:ident, $msg:expr $(,)?) => {
125 (sym::$attr, $typ, $tpl, Gated(Stability::Unstable, sym::$gate, $msg, cfg_fn!($gate)))
127 ($attr:ident, $typ:expr, $tpl:expr, $msg:expr $(,)?) => {
128 (sym::$attr, $typ, $tpl, Gated(Stability::Unstable, sym::$attr, $msg, cfg_fn!($attr)))
132 macro_rules! rustc_attr {
133 (TEST, $attr:ident, $typ:expr, $tpl:expr $(,)?) => {
141 "]` attribute is just used for rustc unit tests \
142 and will never be stable",
146 ($attr:ident, $typ:expr, $tpl:expr, $msg:expr $(,)?) => {
151 Gated(Stability::Unstable, sym::rustc_attrs, $msg, cfg_fn!(rustc_attrs)),
156 macro_rules! experimental {
158 concat!("the `#[", stringify!($attr), "]` attribute is an experimental feature")
162 const IMPL_DETAIL: &str = "internal implementation detail";
163 const INTERNAL_UNSTABLE: &str = "this is an internal attribute that will never be stable";
165 pub type BuiltinAttribute = (Symbol, AttributeType, AttributeTemplate, AttributeGate);
167 /// Attributes that have a special meaning to rustc or rustdoc.
169 pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
170 // ==========================================================================
171 // Stable attributes:
172 // ==========================================================================
174 // Conditional compilation:
175 ungated!(cfg, Normal, template!(List: "predicate")),
176 ungated!(cfg_attr, Normal, template!(List: "predicate, attr1, attr2, ...")),
179 ungated!(ignore, Normal, template!(Word, NameValueStr: "reason")),
181 should_panic, Normal,
182 template!(Word, List: r#"expected = "reason"#, NameValueStr: "reason"),
184 // FIXME(Centril): This can be used on stable but shouldn't.
185 ungated!(reexport_test_harness_main, Normal, template!(NameValueStr: "name")),
188 ungated!(derive, Normal, template!(List: "Trait1, Trait2, ...")),
189 ungated!(automatically_derived, Normal, template!(Word)),
191 ungated!(macro_use, Normal, template!(Word, List: "name1, name2, ...")),
192 ungated!(macro_escape, Normal, template!(Word)), // Deprecated synonym for `macro_use`.
193 ungated!(macro_export, Normal, template!(Word, List: "local_inner_macros")),
194 ungated!(proc_macro, Normal, template!(Word)),
196 proc_macro_derive, Normal,
197 template!(List: "TraitName, /*opt*/ attributes(name1, name2, ...)"),
199 ungated!(proc_macro_attribute, Normal, template!(Word)),
202 ungated!(warn, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#)),
203 ungated!(allow, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#)),
204 ungated!(forbid, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#)),
205 ungated!(deny, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#)),
206 ungated!(must_use, AssumedUsed, template!(Word, NameValueStr: "reason")),
212 List: r#"/*opt*/ since = "version", /*opt*/ note = "reason""#,
213 NameValueStr: "reason"
218 ungated!(crate_name, CrateLevel, template!(NameValueStr: "name")),
219 ungated!(crate_type, CrateLevel, template!(NameValueStr: "bin|lib|...")),
220 ungated!(crate_id, CrateLevel, template!(NameValueStr: "ignored")),
222 // ABI, linking, symbols, and FFI
225 template!(List: r#"name = "...", /*opt*/ kind = "dylib|static|...", /*opt*/ wasm_import_module = "...""#),
227 ungated!(link_name, AssumedUsed, template!(NameValueStr: "name")),
228 ungated!(no_link, Normal, template!(Word)),
229 ungated!(repr, Normal, template!(List: "C")),
230 ungated!(export_name, AssumedUsed, template!(NameValueStr: "name")),
231 ungated!(link_section, AssumedUsed, template!(NameValueStr: "name")),
232 ungated!(no_mangle, AssumedUsed, template!(Word)),
233 ungated!(used, AssumedUsed, template!(Word)),
236 ungated!(recursion_limit, CrateLevel, template!(NameValueStr: "N")),
237 ungated!(type_length_limit, CrateLevel, template!(NameValueStr: "N")),
239 const_eval_limit, CrateLevel, template!(NameValueStr: "N"), const_eval_limit,
240 experimental!(const_eval_limit)
244 ungated!(main, Normal, template!(Word)),
245 ungated!(start, Normal, template!(Word)),
246 ungated!(no_start, CrateLevel, template!(Word)),
247 ungated!(no_main, CrateLevel, template!(Word)),
249 // Modules, prelude, and resolution:
250 ungated!(path, Normal, template!(NameValueStr: "file")),
251 ungated!(no_std, CrateLevel, template!(Word)),
252 ungated!(no_implicit_prelude, Normal, template!(Word)),
253 ungated!(non_exhaustive, AssumedUsed, template!(Word)),
256 ungated!(windows_subsystem, AssumedUsed, template!(NameValueStr: "windows|console")),
257 ungated!(panic_handler, Normal, template!(Word)), // RFC 2070
260 ungated!(inline, AssumedUsed, template!(Word, List: "always|never")),
261 ungated!(cold, AssumedUsed, template!(Word)),
262 ungated!(no_builtins, AssumedUsed, template!(Word)),
263 ungated!(target_feature, AssumedUsed, template!(List: r#"enable = "name""#)),
264 ungated!(track_caller, AssumedUsed, template!(Word)),
266 no_sanitize, AssumedUsed,
267 template!(List: "address, memory, thread"),
268 experimental!(no_sanitize)
271 // FIXME: #14408 assume docs are used since rustdoc looks at them.
272 ungated!(doc, AssumedUsed, template!(List: "hidden|inline|...", NameValueStr: "string")),
274 // ==========================================================================
275 // Unstable attributes:
276 // ==========================================================================
279 gated!(naked, AssumedUsed, template!(Word), naked_functions, experimental!(naked)),
281 link_args, Normal, template!(NameValueStr: "args"),
282 "the `link_args` attribute is experimental and not portable across platforms, \
283 it is recommended to use `#[link(name = \"foo\")] instead",
286 link_ordinal, AssumedUsed, template!(List: "ordinal"), raw_dylib,
287 experimental!(link_ordinal)
292 sym::plugin_registrar, Normal, template!(Word),
294 Stability::Deprecated(
295 "https://github.com/rust-lang/rust/pull/64675",
296 Some("may be removed in a future compiler version"),
298 sym::plugin_registrar,
299 "compiler plugins are deprecated",
300 cfg_fn!(plugin_registrar)
304 sym::plugin, CrateLevel, template!(List: "name"),
306 Stability::Deprecated(
307 "https://github.com/rust-lang/rust/pull/64675",
308 Some("may be removed in a future compiler version"),
311 "compiler plugins are deprecated",
317 gated!(allow_fail, Normal, template!(Word), experimental!(allow_fail)),
319 test_runner, CrateLevel, template!(List: "path"), custom_test_frameworks,
320 "custom test frameworks are an unstable feature",
323 gated!(marker, Normal, template!(Word), marker_trait_attr, experimental!(marker)),
325 thread_local, AssumedUsed, template!(Word),
326 "`#[thread_local]` is an experimental feature, and does not currently handle destructors",
328 gated!(no_core, CrateLevel, template!(Word), experimental!(no_core)),
331 optimize, AssumedUsed, template!(List: "size|speed"), optimize_attribute,
332 experimental!(optimize),
335 gated!(ffi_returns_twice, AssumedUsed, template!(Word), experimental!(ffi_returns_twice)),
336 gated!(ffi_pure, AssumedUsed, template!(Word), experimental!(ffi_pure)),
337 gated!(ffi_const, AssumedUsed, template!(Word), experimental!(ffi_const)),
339 register_attr, CrateLevel, template!(List: "attr1, attr2, ..."),
340 experimental!(register_attr),
343 register_tool, CrateLevel, template!(List: "tool1, tool2, ..."),
344 experimental!(register_tool),
347 // ==========================================================================
348 // Internal attributes: Stability, deprecation, and unsafe:
349 // ==========================================================================
351 ungated!(feature, CrateLevel, template!(List: "name1, name1, ...")),
352 // FIXME(#14407) -- only looked at on-demand so we can't
353 // guarantee they'll have already been checked.
355 rustc_deprecated, AssumedUsed,
356 template!(List: r#"since = "version", reason = "...""#)
359 ungated!(stable, AssumedUsed, template!(List: r#"feature = "name", since = "version""#)),
362 unstable, AssumedUsed,
363 template!(List: r#"feature = "name", reason = "...", issue = "N""#),
366 ungated!(rustc_const_unstable, AssumedUsed, template!(List: r#"feature = "name""#)),
368 ungated!(rustc_const_stable, AssumedUsed, template!(List: r#"feature = "name""#)),
370 allow_internal_unstable, AssumedUsed, template!(Word, List: "feat1, feat2, ..."),
371 "allow_internal_unstable side-steps feature gating and stability checks",
374 allow_internal_unsafe, Normal, template!(Word),
375 "allow_internal_unsafe side-steps the unsafe_code lint",
378 // ==========================================================================
379 // Internal attributes: Type system related:
380 // ==========================================================================
382 gated!(fundamental, AssumedUsed, template!(Word), experimental!(fundamental)),
384 may_dangle, Normal, template!(Word), dropck_eyepatch,
385 "`may_dangle` has unstable semantics and may be removed in the future",
388 // ==========================================================================
389 // Internal attributes: Runtime related:
390 // ==========================================================================
392 rustc_attr!(rustc_allocator, AssumedUsed, template!(Word), IMPL_DETAIL),
393 rustc_attr!(rustc_allocator_nounwind, AssumedUsed, template!(Word), IMPL_DETAIL),
394 gated!(alloc_error_handler, Normal, template!(Word), experimental!(alloc_error_handler)),
396 default_lib_allocator, AssumedUsed, template!(Word), allocator_internals,
397 experimental!(default_lib_allocator),
400 needs_allocator, Normal, template!(Word), allocator_internals,
401 experimental!(needs_allocator),
403 gated!(panic_runtime, AssumedUsed, template!(Word), experimental!(panic_runtime)),
404 gated!(needs_panic_runtime, AssumedUsed, template!(Word), experimental!(needs_panic_runtime)),
406 unwind, AssumedUsed, template!(List: "allowed|aborts"), unwind_attributes,
407 experimental!(unwind),
410 compiler_builtins, AssumedUsed, template!(Word),
411 "the `#[compiler_builtins]` attribute is used to identify the `compiler_builtins` crate \
412 which contains compiler-rt intrinsics and will never be stable",
415 profiler_runtime, AssumedUsed, template!(Word),
416 "the `#[profiler_runtime]` attribute is used to identify the `profiler_builtins` crate \
417 which contains the profiler runtime and will never be stable",
420 // ==========================================================================
421 // Internal attributes, Linkage:
422 // ==========================================================================
425 linkage, AssumedUsed, template!(NameValueStr: "external|internal|..."),
426 "the `linkage` attribute is experimental and not portable across platforms",
428 rustc_attr!(rustc_std_internal_symbol, AssumedUsed, template!(Word), INTERNAL_UNSTABLE),
430 // ==========================================================================
431 // Internal attributes, Macro related:
432 // ==========================================================================
434 rustc_attr!(rustc_builtin_macro, AssumedUsed, template!(Word), IMPL_DETAIL),
435 rustc_attr!(rustc_proc_macro_decls, Normal, template!(Word), INTERNAL_UNSTABLE),
437 rustc_macro_transparency, AssumedUsed,
438 template!(NameValueStr: "transparent|semitransparent|opaque"),
439 "used internally for testing macro hygiene",
442 // ==========================================================================
443 // Internal attributes, Diagnostics related:
444 // ==========================================================================
447 rustc_on_unimplemented, AssumedUsed,
449 List: r#"/*opt*/ message = "...", /*opt*/ label = "...", /*opt*/ note = "...""#,
450 NameValueStr: "message"
454 // Enumerates "identity-like" conversion methods to suggest on type mismatch.
455 rustc_attr!(rustc_conversion_suggestion, AssumedUsed, template!(Word), INTERNAL_UNSTABLE),
457 // ==========================================================================
458 // Internal attributes, Const related:
459 // ==========================================================================
461 rustc_attr!(rustc_promotable, AssumedUsed, template!(Word), IMPL_DETAIL),
462 rustc_attr!(rustc_allow_const_fn_ptr, AssumedUsed, template!(Word), IMPL_DETAIL),
463 rustc_attr!(rustc_args_required_const, AssumedUsed, template!(List: "N"), INTERNAL_UNSTABLE),
465 // ==========================================================================
466 // Internal attributes, Layout related:
467 // ==========================================================================
470 rustc_layout_scalar_valid_range_start, AssumedUsed, template!(List: "value"),
471 "the `#[rustc_layout_scalar_valid_range_start]` attribute is just used to enable \
472 niche optimizations in libcore and will never be stable",
475 rustc_layout_scalar_valid_range_end, AssumedUsed, template!(List: "value"),
476 "the `#[rustc_layout_scalar_valid_range_end]` attribute is just used to enable \
477 niche optimizations in libcore and will never be stable",
480 rustc_nonnull_optimization_guaranteed, AssumedUsed, template!(Word),
481 "the `#[rustc_nonnull_optimization_guaranteed]` attribute is just used to enable \
482 niche optimizations in libcore and will never be stable",
485 // ==========================================================================
486 // Internal attributes, Misc:
487 // ==========================================================================
489 lang, Normal, template!(NameValueStr: "name"), lang_items,
490 "language items are subject to change",
493 sym::rustc_diagnostic_item,
495 template!(NameValueStr: "name"),
499 "diagnostic items compiler internal support for linting",
500 cfg_fn!(rustc_attrs),
505 prelude_import, AssumedUsed, template!(Word),
506 "`#[prelude_import]` is for use by rustc only",
509 rustc_paren_sugar, Normal, template!(Word), unboxed_closures,
510 "unboxed_closures are still evolving",
513 rustc_inherit_overflow_checks, AssumedUsed, template!(Word),
514 "the `#[rustc_inherit_overflow_checks]` attribute is just used to control \
515 overflow checking behavior of several libcore functions that are inlined \
516 across crates and will never be stable",
518 rustc_attr!(rustc_reservation_impl, Normal, template!(NameValueStr: "reservation message"),
519 "the `#[rustc_reservation_impl]` attribute is internally used \
520 for reserving for `for<T> From<!> for T` impl"
523 rustc_test_marker, Normal, template!(Word),
524 "the `#[rustc_test_marker]` attribute is used internally to track tests",
527 rustc_unsafe_specialization_marker, Normal, template!(Word),
528 "the `#[rustc_unsafe_specialization_marker]` attribute is used to check specializations"
531 rustc_specialization_trait, Normal, template!(Word),
532 "the `#[rustc_specialization_trait]` attribute is used to check specializations"
535 // ==========================================================================
536 // Internal attributes, Testing:
537 // ==========================================================================
539 rustc_attr!(TEST, rustc_outlives, Normal, template!(Word)),
540 rustc_attr!(TEST, rustc_variance, Normal, template!(Word)),
541 rustc_attr!(TEST, rustc_layout, Normal, template!(List: "field1, field2, ...")),
542 rustc_attr!(TEST, rustc_regions, Normal, template!(Word)),
544 TEST, rustc_error, AssumedUsed,
545 template!(Word, List: "delay_span_bug_from_inside_query")
547 rustc_attr!(TEST, rustc_dump_user_substs, AssumedUsed, template!(Word)),
548 rustc_attr!(TEST, rustc_if_this_changed, AssumedUsed, template!(Word, List: "DepNode")),
549 rustc_attr!(TEST, rustc_then_this_would_need, AssumedUsed, template!(List: "DepNode")),
551 TEST, rustc_dirty, AssumedUsed,
552 template!(List: r#"cfg = "...", /*opt*/ label = "...", /*opt*/ except = "...""#),
555 TEST, rustc_clean, AssumedUsed,
556 template!(List: r#"cfg = "...", /*opt*/ label = "...", /*opt*/ except = "...""#),
559 TEST, rustc_partition_reused, AssumedUsed,
560 template!(List: r#"cfg = "...", module = "...""#),
563 TEST, rustc_partition_codegened, AssumedUsed,
564 template!(List: r#"cfg = "...", module = "...""#),
567 TEST, rustc_expected_cgu_reuse, AssumedUsed,
568 template!(List: r#"cfg = "...", module = "...", kind = "...""#),
570 rustc_attr!(TEST, rustc_synthetic, AssumedUsed, template!(Word)),
571 rustc_attr!(TEST, rustc_symbol_name, AssumedUsed, template!(Word)),
572 rustc_attr!(TEST, rustc_polymorphize_error, AssumedUsed, template!(Word)),
573 rustc_attr!(TEST, rustc_def_path, AssumedUsed, template!(Word)),
574 rustc_attr!(TEST, rustc_mir, AssumedUsed, template!(List: "arg1, arg2, ...")),
575 rustc_attr!(TEST, rustc_dump_program_clauses, AssumedUsed, template!(Word)),
576 rustc_attr!(TEST, rustc_dump_env_program_clauses, AssumedUsed, template!(Word)),
577 rustc_attr!(TEST, rustc_object_lifetime_default, AssumedUsed, template!(Word)),
578 rustc_attr!(TEST, rustc_dummy, Normal, template!(Word /* doesn't matter*/)),
580 omit_gdb_pretty_printer_section, AssumedUsed, template!(Word),
581 "the `#[omit_gdb_pretty_printer_section]` attribute is just used for the Rust test suite",
585 pub fn deprecated_attributes() -> Vec<&'static BuiltinAttribute> {
586 BUILTIN_ATTRIBUTES.iter().filter(|(.., gate)| gate.is_deprecated()).collect()
589 pub fn is_builtin_attr_name(name: Symbol) -> bool {
590 BUILTIN_ATTRIBUTE_MAP.get(&name).is_some()
593 pub static BUILTIN_ATTRIBUTE_MAP: SyncLazy<FxHashMap<Symbol, &'static BuiltinAttribute>> =
595 let mut map = FxHashMap::default();
596 for attr in BUILTIN_ATTRIBUTES.iter() {
597 if map.insert(attr.0, attr).is_some() {
598 panic!("duplicate builtin attribute `{}`", attr.0);