3 //! This module implements the gating necessary for preventing certain compiler
4 //! features from being used by default. This module will crawl a pre-expanded
5 //! AST to ensure that there are no features which are used that are not
8 //! Features are enabled in programs via the crate-level attributes of
9 //! `#![feature(...)]` with a comma-separated list of features.
11 //! For the purpose of future feature-tracking, once code for detection of feature
12 //! gate usage is added, *do not remove it again* even once the feature
19 self, AssocTyConstraint, AssocTyConstraintKind, NodeId, GenericParam, GenericParamKind,
23 use crate::early_buffered_lints::BufferedEarlyLintId;
24 use crate::source_map::Spanned;
25 use crate::edition::{ALL_EDITIONS, Edition};
26 use crate::visit::{self, FnKind, Visitor};
27 use crate::parse::{token, ParseSess};
28 use crate::symbol::{Symbol, kw, sym};
29 use crate::tokenstream::TokenTree;
31 use errors::{Applicability, DiagnosticBuilder, Handler};
32 use rustc_data_structures::fx::FxHashMap;
33 use rustc_target::spec::abi::Abi;
34 use syntax_pos::{Span, DUMMY_SP};
36 use lazy_static::lazy_static;
42 fn f(features: &mut Features, _: Span) {
43 features.$field = true;
45 f as fn(&mut Features, Span)
49 macro_rules! declare_features {
50 ($((active, $feature: ident, $ver: expr, $issue: expr, $edition: expr),)+) => {
51 /// Represents active features that are currently being implemented or
52 /// currently being considered for addition/removal.
53 const ACTIVE_FEATURES:
54 &[(Symbol, &str, Option<u32>, Option<Edition>, fn(&mut Features, Span))] =
55 &[$((sym::$feature, $ver, $issue, $edition, set!($feature))),+];
57 /// A set of features to be used by later passes.
60 /// `#![feature]` attrs for language features, for error reporting
61 pub declared_lang_features: Vec<(Symbol, Span, Option<Symbol>)>,
62 /// `#![feature]` attrs for non-language (library) features
63 pub declared_lib_features: Vec<(Symbol, Span)>,
64 $(pub $feature: bool),+
68 pub fn new() -> Features {
70 declared_lang_features: Vec::new(),
71 declared_lib_features: Vec::new(),
76 pub fn walk_feature_fields<F>(&self, mut f: F)
77 where F: FnMut(&str, bool)
79 $(f(stringify!($feature), self.$feature);)+
84 ($((removed, $feature: ident, $ver: expr, $issue: expr, None, $reason: expr),)+) => {
85 /// Represents unstable features which have since been removed (it was once Active)
86 const REMOVED_FEATURES: &[(Symbol, &str, Option<u32>, Option<&str>)] = &[
87 $((sym::$feature, $ver, $issue, $reason)),+
91 ($((stable_removed, $feature: ident, $ver: expr, $issue: expr, None),)+) => {
92 /// Represents stable features which have since been removed (it was once Accepted)
93 const STABLE_REMOVED_FEATURES: &[(Symbol, &str, Option<u32>, Option<&str>)] = &[
94 $((sym::$feature, $ver, $issue, None)),+
98 ($((accepted, $feature: ident, $ver: expr, $issue: expr, None),)+) => {
99 /// Those language feature has since been Accepted (it was once Active)
100 const ACCEPTED_FEATURES: &[(Symbol, &str, Option<u32>, Option<&str>)] = &[
101 $((sym::$feature, $ver, $issue, None)),+
106 // If you change this, please modify `src/doc/unstable-book` as well.
108 // Don't ever remove anything from this list; set them to 'Removed'.
110 // The version numbers here correspond to the version in which the current status
111 // was set. This is most important for knowing when a particular feature became
114 // Note that the features are grouped into internal/user-facing and then
115 // sorted by version inside those groups. This is inforced with tidy.
117 // N.B., `tools/tidy/src/features.rs` parses this information directly out of the
118 // source, so take care when modifying it.
121 // -------------------------------------------------------------------------
122 // feature-group-start: internal feature gates
123 // -------------------------------------------------------------------------
125 // no-tracking-issue-start
127 // Allows using the `rust-intrinsic`'s "ABI".
128 (active, intrinsics, "1.0.0", None, None),
130 // Allows using `#[lang = ".."]` attribute for linking items to special compiler logic.
131 (active, lang_items, "1.0.0", None, None),
133 // Allows using the `#[stable]` and `#[unstable]` attributes.
134 (active, staged_api, "1.0.0", None, None),
136 // Allows using `#[allow_internal_unstable]`. This is an
137 // attribute on `macro_rules!` and can't use the attribute handling
138 // below (it has to be checked before expansion possibly makes
139 // macros disappear).
140 (active, allow_internal_unstable, "1.0.0", None, None),
142 // Allows using `#[allow_internal_unsafe]`. This is an
143 // attribute on `macro_rules!` and can't use the attribute handling
144 // below (it has to be checked before expansion possibly makes
145 // macros disappear).
146 (active, allow_internal_unsafe, "1.0.0", None, None),
148 // Allows using the macros:
149 // + `__diagnostic_used`
150 // + `__register_diagnostic`
151 // +`__build_diagnostic_array`
152 (active, rustc_diagnostic_macros, "1.0.0", None, None),
154 // Allows using `#[rustc_const_unstable(feature = "foo", ..)]` which
155 // lets a function to be `const` when opted into with `#![feature(foo)]`.
156 (active, rustc_const_unstable, "1.0.0", None, None),
158 // no-tracking-issue-end
160 // Allows using `#[link_name="llvm.*"]`.
161 (active, link_llvm_intrinsics, "1.0.0", Some(29602), None),
163 // Allows using `rustc_*` attributes (RFC 572).
164 (active, rustc_attrs, "1.0.0", Some(29642), None),
166 // Allows using `#[on_unimplemented(..)]` on traits.
167 (active, on_unimplemented, "1.0.0", Some(29628), None),
169 // Allows using the `box $expr` syntax.
170 (active, box_syntax, "1.0.0", Some(49733), None),
172 // Allows using `#[main]` to replace the entrypoint `#[lang = "start"]` calls.
173 (active, main, "1.0.0", Some(29634), None),
175 // Allows using `#[start]` on a function indicating that it is the program entrypoint.
176 (active, start, "1.0.0", Some(29633), None),
178 // Allows using the `#[fundamental]` attribute.
179 (active, fundamental, "1.0.0", Some(29635), None),
181 // Allows using the `rust-call` ABI.
182 (active, unboxed_closures, "1.0.0", Some(29625), None),
184 // Allows using the `#[linkage = ".."]` attribute.
185 (active, linkage, "1.0.0", Some(29603), None),
187 // Allows features specific to OIBIT (auto traits).
188 (active, optin_builtin_traits, "1.0.0", Some(13231), None),
190 // Allows using `box` in patterns (RFC 469).
191 (active, box_patterns, "1.0.0", Some(29641), None),
193 // no-tracking-issue-start
195 // Allows using `#[prelude_import]` on glob `use` items.
196 (active, prelude_import, "1.2.0", None, None),
198 // no-tracking-issue-end
200 // Allows using `#[unsafe_destructor_blind_to_params]` (RFC 1238).
201 (active, dropck_parametricity, "1.3.0", Some(28498), None),
203 // no-tracking-issue-start
205 // Allows using `#[omit_gdb_pretty_printer_section]`.
206 (active, omit_gdb_pretty_printer_section, "1.5.0", None, None),
208 // Allows using the `vectorcall` ABI.
209 (active, abi_vectorcall, "1.7.0", None, None),
211 // no-tracking-issue-end
213 // Allows using `#[structural_match]` which indicates that a type is structurally matchable.
214 (active, structural_match, "1.8.0", Some(31434), None),
216 // Allows using the `may_dangle` attribute (RFC 1327).
217 (active, dropck_eyepatch, "1.10.0", Some(34761), None),
219 // Allows using the `#![panic_runtime]` attribute.
220 (active, panic_runtime, "1.10.0", Some(32837), None),
222 // Allows declaring with `#![needs_panic_runtime]` that a panic runtime is needed.
223 (active, needs_panic_runtime, "1.10.0", Some(32837), None),
225 // no-tracking-issue-start
227 // Allows identifying the `compiler_builtins` crate.
228 (active, compiler_builtins, "1.13.0", None, None),
230 // Allows using the `unadjusted` ABI; perma-unstable.
231 (active, abi_unadjusted, "1.16.0", None, None),
233 // Allows identifying crates that contain sanitizer runtimes.
234 (active, sanitizer_runtime, "1.17.0", None, None),
236 // Used to identify crates that contain the profiler runtime.
237 (active, profiler_runtime, "1.18.0", None, None),
239 // Allows using the `thiscall` ABI.
240 (active, abi_thiscall, "1.19.0", None, None),
242 // Allows using `#![needs_allocator]`, an implementation detail of `#[global_allocator]`.
243 (active, allocator_internals, "1.20.0", None, None),
245 // Allows using the `format_args_nl` macro.
246 (active, format_args_nl, "1.29.0", None, None),
248 // no-tracking-issue-end
250 // Added for testing E0705; perma-unstable.
251 (active, test_2018_feature, "1.31.0", Some(0), Some(Edition::Edition2018)),
253 // -------------------------------------------------------------------------
254 // feature-group-end: internal feature gates
255 // -------------------------------------------------------------------------
257 // -------------------------------------------------------------------------
258 // feature-group-start: actual feature gates (target features)
259 // -------------------------------------------------------------------------
261 // FIXME: Document these and merge with the list below.
263 // Unstable `#[target_feature]` directives.
264 (active, arm_target_feature, "1.27.0", Some(44839), None),
265 (active, aarch64_target_feature, "1.27.0", Some(44839), None),
266 (active, hexagon_target_feature, "1.27.0", Some(44839), None),
267 (active, powerpc_target_feature, "1.27.0", Some(44839), None),
268 (active, mips_target_feature, "1.27.0", Some(44839), None),
269 (active, avx512_target_feature, "1.27.0", Some(44839), None),
270 (active, mmx_target_feature, "1.27.0", Some(44839), None),
271 (active, sse4a_target_feature, "1.27.0", Some(44839), None),
272 (active, tbm_target_feature, "1.27.0", Some(44839), None),
273 (active, wasm_target_feature, "1.30.0", Some(44839), None),
274 (active, adx_target_feature, "1.32.0", Some(44839), None),
275 (active, cmpxchg16b_target_feature, "1.32.0", Some(44839), None),
276 (active, movbe_target_feature, "1.34.0", Some(44839), None),
277 (active, rtm_target_feature, "1.35.0", Some(44839), None),
278 (active, f16c_target_feature, "1.36.0", Some(44839), None),
280 // -------------------------------------------------------------------------
281 // feature-group-end: actual feature gates (target features)
282 // -------------------------------------------------------------------------
284 // -------------------------------------------------------------------------
285 // feature-group-start: actual feature gates
286 // -------------------------------------------------------------------------
288 // Allows using `asm!` macro with which inline assembly can be embedded.
289 (active, asm, "1.0.0", Some(29722), None),
291 // Allows using the `concat_idents!` macro with which identifiers can be concatenated.
292 (active, concat_idents, "1.0.0", Some(29599), None),
294 // Allows using the `#[link_args]` attribute.
295 (active, link_args, "1.0.0", Some(29596), None),
297 // Allows defining identifiers beyond ASCII.
298 (active, non_ascii_idents, "1.0.0", Some(55467), None),
300 // Allows using `#[plugin_registrar]` on functions.
301 (active, plugin_registrar, "1.0.0", Some(29597), None),
303 // Allows using `#![plugin(myplugin)]`.
304 (active, plugin, "1.0.0", Some(29597), None),
306 // Allows using `#[thread_local]` on `static` items.
307 (active, thread_local, "1.0.0", Some(29594), None),
309 // Allows using the `log_syntax!` macro.
310 (active, log_syntax, "1.0.0", Some(29598), None),
312 // Allows using the `trace_macros!` macro.
313 (active, trace_macros, "1.0.0", Some(29598), None),
315 // Allows the use of SIMD types in functions declared in `extern` blocks.
316 (active, simd_ffi, "1.0.0", Some(27731), None),
318 // Allows using custom attributes (RFC 572).
319 (active, custom_attribute, "1.0.0", Some(29642), None),
321 // Allows using non lexical lifetimes (RFC 2094).
322 (active, nll, "1.0.0", Some(43234), None),
324 // Allows using slice patterns.
325 (active, slice_patterns, "1.0.0", Some(23121), None),
327 // Allows the definition of `const` functions with some advanced features.
328 (active, const_fn, "1.2.0", Some(57563), None),
330 // Allows associated type defaults.
331 (active, associated_type_defaults, "1.2.0", Some(29661), None),
333 // Allows `#![no_core]`.
334 (active, no_core, "1.3.0", Some(29639), None),
336 // Allows default type parameters to influence type inference.
337 (active, default_type_parameter_fallback, "1.3.0", Some(27336), None),
339 // Allows `repr(simd)` and importing the various simd intrinsics.
340 (active, repr_simd, "1.4.0", Some(27731), None),
342 // Allows `extern "platform-intrinsic" { ... }`.
343 (active, platform_intrinsics, "1.4.0", Some(27731), None),
345 // Allows `#[unwind(..)]`.
347 // Permits specifying whether a function should permit unwinding or abort on unwind.
348 (active, unwind_attributes, "1.4.0", Some(58760), None),
350 // Allows `#[no_debug]`.
351 (active, no_debug, "1.5.0", Some(29721), None),
353 // Allows attributes on expressions and non-item statements.
354 (active, stmt_expr_attributes, "1.6.0", Some(15701), None),
356 // Allows the use of type ascription in expressions.
357 (active, type_ascription, "1.6.0", Some(23416), None),
359 // Allows `cfg(target_thread_local)`.
360 (active, cfg_target_thread_local, "1.7.0", Some(29594), None),
362 // Allows specialization of implementations (RFC 1210).
363 (active, specialization, "1.7.0", Some(31844), None),
365 // Allows using `#[naked]` on functions.
366 (active, naked_functions, "1.9.0", Some(32408), None),
368 // Allows `cfg(target_has_atomic = "...")`.
369 (active, cfg_target_has_atomic, "1.9.0", Some(32976), None),
371 // Allows `X..Y` patterns.
372 (active, exclusive_range_pattern, "1.11.0", Some(37854), None),
374 // Allows the `!` type. Does not imply 'exhaustive_patterns' (below) any more.
375 (active, never_type, "1.13.0", Some(35121), None),
377 // Allows exhaustive pattern matching on types that contain uninhabited types.
378 (active, exhaustive_patterns, "1.13.0", Some(51085), None),
380 // Allows untagged unions `union U { ... }`.
381 (active, untagged_unions, "1.13.0", Some(32836), None),
383 // Allows `#[link(..., cfg(..))]`.
384 (active, link_cfg, "1.14.0", Some(37406), None),
386 // Allows `extern "ptx-*" fn()`.
387 (active, abi_ptx, "1.15.0", Some(38788), None),
389 // Allows the `#[repr(i128)]` attribute for enums.
390 (active, repr128, "1.16.0", Some(35118), None),
392 // Allows `#[link(kind="static-nobundle"...)]`.
393 (active, static_nobundle, "1.16.0", Some(37403), None),
395 // Allows `extern "msp430-interrupt" fn()`.
396 (active, abi_msp430_interrupt, "1.16.0", Some(38487), None),
398 // Allows declarative macros 2.0 (`macro`).
399 (active, decl_macro, "1.17.0", Some(39412), None),
401 // Allows `extern "x86-interrupt" fn()`.
402 (active, abi_x86_interrupt, "1.17.0", Some(40180), None),
404 // Allows module-level inline assembly by way of `global_asm!()`.
405 (active, global_asm, "1.18.0", Some(35119), None),
407 // Allows overlapping impls of marker traits.
408 (active, overlapping_marker_traits, "1.18.0", Some(29864), None),
410 // Allows a test to fail without failing the whole suite.
411 (active, allow_fail, "1.19.0", Some(46488), None),
413 // Allows unsized tuple coercion.
414 (active, unsized_tuple_coercion, "1.20.0", Some(42877), None),
416 // Allows defining generators.
417 (active, generators, "1.21.0", Some(43122), None),
419 // Allows `#[doc(cfg(...))]`.
420 (active, doc_cfg, "1.21.0", Some(43781), None),
422 // Allows `#[doc(masked)]`.
423 (active, doc_masked, "1.21.0", Some(44027), None),
425 // Allows `#[doc(spotlight)]`.
426 (active, doc_spotlight, "1.22.0", Some(45040), None),
428 // Allows `#[doc(include = "some-file")]`.
429 (active, external_doc, "1.22.0", Some(44732), None),
431 // Allows future-proofing enums/structs with the `#[non_exhaustive]` attribute (RFC 2008).
432 (active, non_exhaustive, "1.22.0", Some(44109), None),
434 // Allows using `crate` as visibility modifier, synonymous with `pub(crate)`.
435 (active, crate_visibility_modifier, "1.23.0", Some(53120), None),
437 // Allows defining `extern type`s.
438 (active, extern_types, "1.23.0", Some(43467), None),
440 // Allows trait methods with arbitrary self types.
441 (active, arbitrary_self_types, "1.23.0", Some(44874), None),
443 // Allows in-band quantification of lifetime bindings (e.g., `fn foo(x: &'a u8) -> &'a u8`).
444 (active, in_band_lifetimes, "1.23.0", Some(44524), None),
446 // Allows associated types to be generic, e.g., `type Foo<T>;` (RFC 1598).
447 (active, generic_associated_types, "1.23.0", Some(44265), None),
449 // Allows defining `trait X = A + B;` alias items.
450 (active, trait_alias, "1.24.0", Some(41517), None),
452 // Allows infering `'static` outlives requirements (RFC 2093).
453 (active, infer_static_outlives_requirements, "1.26.0", Some(54185), None),
455 // Allows macro invocations in `extern {}` blocks.
456 (active, macros_in_extern, "1.27.0", Some(49476), None),
458 // Allows accessing fields of unions inside `const` functions.
459 (active, const_fn_union, "1.27.0", Some(51909), None),
461 // Allows casting raw pointers to `usize` during const eval.
462 (active, const_raw_ptr_to_usize_cast, "1.27.0", Some(51910), None),
464 // Allows dereferencing raw pointers during const eval.
465 (active, const_raw_ptr_deref, "1.27.0", Some(51911), None),
467 // Allows comparing raw pointers during const eval.
468 (active, const_compare_raw_pointers, "1.27.0", Some(53020), None),
470 // Allows `#[doc(alias = "...")]`.
471 (active, doc_alias, "1.27.0", Some(50146), None),
473 // Allows defining `existential type`s.
474 (active, existential_type, "1.28.0", Some(34511), None),
476 // Allows inconsistent bounds in where clauses.
477 (active, trivial_bounds, "1.28.0", Some(48214), None),
479 // Allows `'a: { break 'a; }`.
480 (active, label_break_value, "1.28.0", Some(48594), None),
482 // Allows using `#[doc(keyword = "...")]`.
483 (active, doc_keyword, "1.28.0", Some(51315), None),
485 // Allows async and await syntax.
486 (active, async_await, "1.28.0", Some(50547), None),
488 // Allows await! macro-like syntax.
489 // This will likely be removed prior to stabilization of async/await.
490 (active, await_macro, "1.28.0", Some(50547), None),
492 // Allows reinterpretation of the bits of a value of one type as another type during const eval.
493 (active, const_transmute, "1.29.0", Some(53605), None),
495 // Allows using `try {...}` expressions.
496 (active, try_blocks, "1.29.0", Some(31436), None),
498 // Allows defining an `#[alloc_error_handler]`.
499 (active, alloc_error_handler, "1.29.0", Some(51540), None),
501 // Allows using the `amdgpu-kernel` ABI.
502 (active, abi_amdgpu_kernel, "1.29.0", Some(51575), None),
504 // Allows panicking during const eval (producing compile-time errors).
505 (active, const_panic, "1.30.0", Some(51999), None),
507 // Allows `#[marker]` on certain traits allowing overlapping implementations.
508 (active, marker_trait_attr, "1.30.0", Some(29864), None),
510 // Allows macro invocations on modules expressions and statements and
511 // procedural macros to expand to non-items.
512 (active, proc_macro_hygiene, "1.30.0", Some(54727), None),
514 // Allows unsized rvalues at arguments and parameters.
515 (active, unsized_locals, "1.30.0", Some(48055), None),
517 // Allows custom test frameworks with `#![test_runner]` and `#[test_case]`.
518 (active, custom_test_frameworks, "1.30.0", Some(50297), None),
520 // Allows non-builtin attributes in inner attribute position.
521 (active, custom_inner_attributes, "1.30.0", Some(54726), None),
523 // Allows mixing bind-by-move in patterns and references to those identifiers in guards.
524 (active, bind_by_move_pattern_guards, "1.30.0", Some(15287), None),
526 // Allows `impl Trait` in bindings (`let`, `const`, `static`).
527 (active, impl_trait_in_bindings, "1.30.0", Some(34511), None),
529 // Allows `const _: TYPE = VALUE`.
530 (active, underscore_const_names, "1.31.0", Some(54912), None),
532 // Allows using `reason` in lint attributes and the `#[expect(lint)]` lint check.
533 (active, lint_reasons, "1.31.0", Some(54503), None),
535 // Allows paths to enum variants on type aliases.
536 (active, type_alias_enum_variants, "1.31.0", Some(49683), None),
538 // Allows exhaustive integer pattern matching on `usize` and `isize`.
539 (active, precise_pointer_size_matching, "1.32.0", Some(56354), None),
541 // Allows relaxing the coherence rules such that
542 // `impl<T> ForeignTrait<LocalType> for ForeignType<T> is permitted.
543 (active, re_rebalance_coherence, "1.32.0", Some(55437), None),
545 // Allows using `#[ffi_returns_twice]` on foreign functions.
546 (active, ffi_returns_twice, "1.34.0", Some(58314), None),
548 // Allows const generic types (e.g. `struct Foo<const N: usize>(...);`).
549 (active, const_generics, "1.34.0", Some(44580), None),
551 // Allows using `#[optimize(X)]`.
552 (active, optimize_attribute, "1.34.0", Some(54882), None),
554 // Allows using C-variadics.
555 (active, c_variadic, "1.34.0", Some(44930), None),
557 // Allows the user of associated type bounds.
558 (active, associated_type_bounds, "1.34.0", Some(52662), None),
560 // Allows calling constructor functions in `const fn`
561 // FIXME Create issue
562 (active, const_constructor, "1.37.0", Some(61456), None),
564 // #[repr(transparent)] on enums.
565 (active, transparent_enums, "1.37.0", Some(60405), None),
567 // #[repr(transparent)] on unions.
568 (active, transparent_unions, "1.37.0", Some(60405), None),
570 // -------------------------------------------------------------------------
571 // feature-group-end: actual feature gates
572 // -------------------------------------------------------------------------
575 // Some features are known to be incomplete and using them is likely to have
576 // unanticipated results, such as compiler crashes. We warn the user about these
578 const INCOMPLETE_FEATURES: &[Symbol] = &[
579 sym::impl_trait_in_bindings,
580 sym::generic_associated_types,
585 // -------------------------------------------------------------------------
586 // feature-group-start: removed features
587 // -------------------------------------------------------------------------
589 (removed, import_shadowing, "1.0.0", None, None, None),
590 (removed, managed_boxes, "1.0.0", None, None, None),
591 // Allows use of unary negate on unsigned integers, e.g., -e for e: u8
592 (removed, negate_unsigned, "1.0.0", Some(29645), None, None),
593 (removed, reflect, "1.0.0", Some(27749), None, None),
594 // A way to temporarily opt out of opt in copy. This will *never* be accepted.
595 (removed, opt_out_copy, "1.0.0", None, None, None),
596 (removed, quad_precision_float, "1.0.0", None, None, None),
597 (removed, struct_inherit, "1.0.0", None, None, None),
598 (removed, test_removed_feature, "1.0.0", None, None, None),
599 (removed, visible_private_types, "1.0.0", None, None, None),
600 (removed, unsafe_no_drop_flag, "1.0.0", None, None, None),
601 // Allows using items which are missing stability attributes
602 (removed, unmarked_api, "1.0.0", None, None, None),
603 (removed, allocator, "1.0.0", None, None, None),
604 (removed, simd, "1.0.0", Some(27731), None,
605 Some("removed in favor of `#[repr(simd)]`")),
606 (removed, advanced_slice_patterns, "1.0.0", Some(23121), None,
607 Some("merged into `#![feature(slice_patterns)]`")),
608 (removed, macro_reexport, "1.0.0", Some(29638), None,
609 Some("subsumed by `pub use`")),
610 (removed, pushpop_unsafe, "1.2.0", None, None, None),
611 (removed, needs_allocator, "1.4.0", Some(27389), None,
612 Some("subsumed by `#![feature(allocator_internals)]`")),
613 (removed, proc_macro_mod, "1.27.0", Some(54727), None,
614 Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
615 (removed, proc_macro_expr, "1.27.0", Some(54727), None,
616 Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
617 (removed, proc_macro_non_items, "1.27.0", Some(54727), None,
618 Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
619 (removed, proc_macro_gen, "1.27.0", Some(54727), None,
620 Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
621 (removed, panic_implementation, "1.28.0", Some(44489), None,
622 Some("subsumed by `#[panic_handler]`")),
623 // Allows the use of `#[derive(Anything)]` as sugar for `#[derive_Anything]`.
624 (removed, custom_derive, "1.32.0", Some(29644), None,
625 Some("subsumed by `#[proc_macro_derive]`")),
626 // Paths of the form: `extern::foo::bar`
627 (removed, extern_in_paths, "1.33.0", Some(55600), None,
628 Some("subsumed by `::foo::bar` paths")),
629 (removed, quote, "1.33.0", Some(29601), None, None),
631 // -------------------------------------------------------------------------
632 // feature-group-end: removed features
633 // -------------------------------------------------------------------------
637 (stable_removed, no_stack_check, "1.0.0", None, None),
641 // -------------------------------------------------------------------------
642 // feature-group-start: for testing purposes
643 // -------------------------------------------------------------------------
645 // A temporary feature gate used to enable parser extensions needed
646 // to bootstrap fix for #5723.
647 (accepted, issue_5723_bootstrap, "1.0.0", None, None),
648 // These are used to test this portion of the compiler,
649 // they don't actually mean anything.
650 (accepted, test_accepted_feature, "1.0.0", None, None),
652 // -------------------------------------------------------------------------
653 // feature-group-end: for testing purposes
654 // -------------------------------------------------------------------------
656 // -------------------------------------------------------------------------
657 // feature-group-start: accepted features
658 // -------------------------------------------------------------------------
660 // Allows using associated `type`s in `trait`s.
661 (accepted, associated_types, "1.0.0", None, None),
662 // Allows using assigning a default type to type parameters in algebraic data type definitions.
663 (accepted, default_type_params, "1.0.0", None, None),
664 // FIXME: explain `globs`.
665 (accepted, globs, "1.0.0", None, None),
666 // Allows `macro_rules!` items.
667 (accepted, macro_rules, "1.0.0", None, None),
668 // Allows use of `&foo[a..b]` as a slicing syntax.
669 (accepted, slicing_syntax, "1.0.0", None, None),
670 // Allows struct variants `Foo { baz: u8, .. }` in enums (RFC 418).
671 (accepted, struct_variant, "1.0.0", None, None),
672 // Allows indexing tuples.
673 (accepted, tuple_indexing, "1.0.0", None, None),
674 // Allows the use of `if let` expressions.
675 (accepted, if_let, "1.0.0", None, None),
676 // Allows the use of `while let` expressions.
677 (accepted, while_let, "1.0.0", None, None),
678 // Allows using `#![no_std]`.
679 (accepted, no_std, "1.6.0", None, None),
680 // Allows overloading augmented assignment operations like `a += b`.
681 (accepted, augmented_assignments, "1.8.0", Some(28235), None),
682 // Allows empty structs and enum variants with braces.
683 (accepted, braced_empty_structs, "1.8.0", Some(29720), None),
684 // Allows `#[deprecated]` attribute.
685 (accepted, deprecated, "1.9.0", Some(29935), None),
686 // Allows macros to appear in the type position.
687 (accepted, type_macros, "1.13.0", Some(27245), None),
688 // Allows use of the postfix `?` operator in expressions.
689 (accepted, question_mark, "1.13.0", Some(31436), None),
690 // Allows `..` in tuple (struct) patterns.
691 (accepted, dotdot_in_tuple_patterns, "1.14.0", Some(33627), None),
692 // Allows some increased flexibility in the name resolution rules,
693 // especially around globs and shadowing (RFC 1560).
694 (accepted, item_like_imports, "1.15.0", Some(35120), None),
695 // Allows using `Self` and associated types in struct expressions and patterns.
696 (accepted, more_struct_aliases, "1.16.0", Some(37544), None),
697 // Allows elision of `'static` lifetimes in `static`s and `const`s.
698 (accepted, static_in_const, "1.17.0", Some(35897), None),
699 // Allows field shorthands (`x` meaning `x: x`) in struct literal expressions.
700 (accepted, field_init_shorthand, "1.17.0", Some(37340), None),
701 // Allows the definition recursive static items.
702 (accepted, static_recursion, "1.17.0", Some(29719), None),
703 // Allows `pub(restricted)` visibilities (RFC 1422).
704 (accepted, pub_restricted, "1.18.0", Some(32409), None),
705 // Allows `#![windows_subsystem]`.
706 (accepted, windows_subsystem, "1.18.0", Some(37499), None),
707 // Allows `break {expr}` with a value inside `loop`s.
708 (accepted, loop_break_value, "1.19.0", Some(37339), None),
709 // Allows numeric fields in struct expressions and patterns.
710 (accepted, relaxed_adts, "1.19.0", Some(35626), None),
711 // Allows coercing non capturing closures to function pointers.
712 (accepted, closure_to_fn_coercion, "1.19.0", Some(39817), None),
713 // Allows attributes on struct literal fields.
714 (accepted, struct_field_attributes, "1.20.0", Some(38814), None),
715 // Allows the definition of associated constants in `trait` or `impl` blocks.
716 (accepted, associated_consts, "1.20.0", Some(29646), None),
717 // Allows usage of the `compile_error!` macro.
718 (accepted, compile_error, "1.20.0", Some(40872), None),
719 // Allows code like `let x: &'static u32 = &42` to work (RFC 1414).
720 (accepted, rvalue_static_promotion, "1.21.0", Some(38865), None),
721 // Allows `Drop` types in constants (RFC 1440).
722 (accepted, drop_types_in_const, "1.22.0", Some(33156), None),
723 // Allows the sysV64 ABI to be specified on all platforms
724 // instead of just the platforms on which it is the C ABI.
725 (accepted, abi_sysv64, "1.24.0", Some(36167), None),
726 // Allows `repr(align(16))` struct attribute (RFC 1358).
727 (accepted, repr_align, "1.25.0", Some(33626), None),
728 // Allows '|' at beginning of match arms (RFC 1925).
729 (accepted, match_beginning_vert, "1.25.0", Some(44101), None),
730 // Allows nested groups in `use` items (RFC 2128).
731 (accepted, use_nested_groups, "1.25.0", Some(44494), None),
732 // Allows indexing into constant arrays.
733 (accepted, const_indexing, "1.26.0", Some(29947), None),
734 // Allows using `a..=b` and `..=b` as inclusive range syntaxes.
735 (accepted, inclusive_range_syntax, "1.26.0", Some(28237), None),
736 // Allows `..=` in patterns (RFC 1192).
737 (accepted, dotdoteq_in_patterns, "1.26.0", Some(28237), None),
738 // Allows `fn main()` with return types which implements `Termination` (RFC 1937).
739 (accepted, termination_trait, "1.26.0", Some(43301), None),
740 // Allows implementing `Clone` for closures where possible (RFC 2132).
741 (accepted, clone_closures, "1.26.0", Some(44490), None),
742 // Allows implementing `Copy` for closures where possible (RFC 2132).
743 (accepted, copy_closures, "1.26.0", Some(44490), None),
744 // Allows `impl Trait` in function arguments.
745 (accepted, universal_impl_trait, "1.26.0", Some(34511), None),
746 // Allows `impl Trait` in function return types.
747 (accepted, conservative_impl_trait, "1.26.0", Some(34511), None),
748 // Allows using the `u128` and `i128` types.
749 (accepted, i128_type, "1.26.0", Some(35118), None),
750 // Allows default match binding modes (RFC 2005).
751 (accepted, match_default_bindings, "1.26.0", Some(42640), None),
752 // Allows `'_` placeholder lifetimes.
753 (accepted, underscore_lifetimes, "1.26.0", Some(44524), None),
754 // Allows attributes on lifetime/type formal parameters in generics (RFC 1327).
755 (accepted, generic_param_attrs, "1.27.0", Some(48848), None),
756 // Allows `cfg(target_feature = "...")`.
757 (accepted, cfg_target_feature, "1.27.0", Some(29717), None),
758 // Allows `#[target_feature(...)]`.
759 (accepted, target_feature, "1.27.0", None, None),
760 // Allows using `dyn Trait` as a syntax for trait objects.
761 (accepted, dyn_trait, "1.27.0", Some(44662), None),
762 // Allows `#[must_use]` on functions, and introduces must-use operators (RFC 1940).
763 (accepted, fn_must_use, "1.27.0", Some(43302), None),
764 // Allows use of the `:lifetime` macro fragment specifier.
765 (accepted, macro_lifetime_matcher, "1.27.0", Some(34303), None),
766 // Allows `#[test]` functions where the return type implements `Termination` (RFC 1937).
767 (accepted, termination_trait_test, "1.27.0", Some(48854), None),
768 // Allows the `#[global_allocator]` attribute.
769 (accepted, global_allocator, "1.28.0", Some(27389), None),
770 // Allows `#[repr(transparent)]` attribute on newtype structs.
771 (accepted, repr_transparent, "1.28.0", Some(43036), None),
772 // Allows procedural macros in `proc-macro` crates.
773 (accepted, proc_macro, "1.29.0", Some(38356), None),
774 // Allows `foo.rs` as an alternative to `foo/mod.rs`.
775 (accepted, non_modrs_mods, "1.30.0", Some(44660), None),
776 // Allows use of the `:vis` macro fragment specifier
777 (accepted, macro_vis_matcher, "1.30.0", Some(41022), None),
778 // Allows importing and reexporting macros with `use`,
779 // enables macro modularization in general.
780 (accepted, use_extern_macros, "1.30.0", Some(35896), None),
781 // Allows keywords to be escaped for use as identifiers.
782 (accepted, raw_identifiers, "1.30.0", Some(48589), None),
783 // Allows attributes scoped to tools.
784 (accepted, tool_attributes, "1.30.0", Some(44690), None),
785 // Allows multi-segment paths in attributes and derives.
786 (accepted, proc_macro_path_invoc, "1.30.0", Some(38356), None),
787 // Allows all literals in attribute lists and values of key-value pairs.
788 (accepted, attr_literals, "1.30.0", Some(34981), None),
789 // Allows inferring outlives requirements (RFC 2093).
790 (accepted, infer_outlives_requirements, "1.30.0", Some(44493), None),
791 // Allows annotating functions conforming to `fn(&PanicInfo) -> !` with `#[panic_handler]`.
792 // This defines the behavior of panics.
793 (accepted, panic_handler, "1.30.0", Some(44489), None),
794 // Allows `#[used]` to preserve symbols (see llvm.used).
795 (accepted, used, "1.30.0", Some(40289), None),
796 // Allows `crate` in paths.
797 (accepted, crate_in_paths, "1.30.0", Some(45477), None),
798 // Allows resolving absolute paths as paths from other crates.
799 (accepted, extern_absolute_paths, "1.30.0", Some(44660), None),
800 // Allows access to crate names passed via `--extern` through prelude.
801 (accepted, extern_prelude, "1.30.0", Some(44660), None),
802 // Allows parentheses in patterns.
803 (accepted, pattern_parentheses, "1.31.0", Some(51087), None),
804 // Allows the definition of `const fn` functions.
805 (accepted, min_const_fn, "1.31.0", Some(53555), None),
806 // Allows scoped lints.
807 (accepted, tool_lints, "1.31.0", Some(44690), None),
808 // Allows lifetime elision in `impl` headers. For example:
809 // + `impl<I:Iterator> Iterator for &mut Iterator`
810 // + `impl Debug for Foo<'_>`
811 (accepted, impl_header_lifetime_elision, "1.31.0", Some(15872), None),
812 // Allows `extern crate foo as bar;`. This puts `bar` into extern prelude.
813 (accepted, extern_crate_item_prelude, "1.31.0", Some(55599), None),
814 // Allows use of the `:literal` macro fragment specifier (RFC 1576).
815 (accepted, macro_literal_matcher, "1.32.0", Some(35625), None),
816 // Allows use of `?` as the Kleene "at most one" operator in macros.
817 (accepted, macro_at_most_once_rep, "1.32.0", Some(48075), None),
818 // Allows `Self` struct constructor (RFC 2302).
819 (accepted, self_struct_ctor, "1.32.0", Some(51994), None),
820 // Allows `Self` in type definitions (RFC 2300).
821 (accepted, self_in_typedefs, "1.32.0", Some(49303), None),
822 // Allows `use x::y;` to search `x` in the current scope.
823 (accepted, uniform_paths, "1.32.0", Some(53130), None),
824 // Allows integer match exhaustiveness checking (RFC 2591).
825 (accepted, exhaustive_integer_patterns, "1.33.0", Some(50907), None),
826 // Allows `use path as _;` and `extern crate c as _;`.
827 (accepted, underscore_imports, "1.33.0", Some(48216), None),
828 // Allows `#[repr(packed(N))]` attribute on structs.
829 (accepted, repr_packed, "1.33.0", Some(33158), None),
830 // Allows irrefutable patterns in `if let` and `while let` statements (RFC 2086).
831 (accepted, irrefutable_let_patterns, "1.33.0", Some(44495), None),
832 // Allows calling `const unsafe fn` inside `unsafe` blocks in `const fn` functions.
833 (accepted, min_const_unsafe_fn, "1.33.0", Some(55607), None),
834 // Allows let bindings, assignments and destructuring in `const` functions and constants.
835 // As long as control flow is not implemented in const eval, `&&` and `||` may not be used
836 // at the same time as let bindings.
837 (accepted, const_let, "1.33.0", Some(48821), None),
838 // Allows `#[cfg_attr(predicate, multiple, attributes, here)]`.
839 (accepted, cfg_attr_multi, "1.33.0", Some(54881), None),
840 // Allows top level or-patterns (`p | q`) in `if let` and `while let`.
841 (accepted, if_while_or_patterns, "1.33.0", Some(48215), None),
842 // Allows `cfg(target_vendor = "...")`.
843 (accepted, cfg_target_vendor, "1.33.0", Some(29718), None),
844 // Allows `extern crate self as foo;`.
845 // This puts local crate root into extern prelude under name `foo`.
846 (accepted, extern_crate_self, "1.34.0", Some(56409), None),
847 // Allows arbitrary delimited token streams in non-macro attributes.
848 (accepted, unrestricted_attribute_tokens, "1.34.0", Some(55208), None),
849 // Allows using `#[repr(align(X))]` on enums with equivalent semantics
850 // to wrapping an enum in a wrapper struct with `#[repr(align(X))]`.
851 (accepted, repr_align_enum, "1.37.0", Some(57996), None),
853 // -------------------------------------------------------------------------
854 // feature-group-end: accepted features
855 // -------------------------------------------------------------------------
858 // If you change this, please modify `src/doc/unstable-book` as well. You must
859 // move that documentation into the relevant place in the other docs, and
860 // remove the chapter on the flag.
862 #[derive(Copy, Clone, PartialEq, Debug)]
863 pub enum AttributeType {
864 /// Normal, builtin attribute that is consumed
865 /// by the compiler before the unused_attribute check
868 /// Builtin attribute that may not be consumed by the compiler
869 /// before the unused_attribute check. These attributes
870 /// will be ignored by the unused_attribute lint
873 /// Builtin attribute that is only allowed at the crate level
877 pub enum AttributeGate {
878 /// Is gated by a given feature gate, reason
879 /// and function to check if enabled
880 Gated(Stability, Symbol, &'static str, fn(&Features) -> bool),
882 /// Ungated attribute, can be used on all release channels
886 /// A template that the attribute input must match.
887 /// Only top-level shape (`#[attr]` vs `#[attr(...)]` vs `#[attr = ...]`) is considered now.
888 #[derive(Clone, Copy)]
889 pub struct AttributeTemplate {
891 list: Option<&'static str>,
892 name_value_str: Option<&'static str>,
895 impl AttributeTemplate {
896 /// Checks that the given meta-item is compatible with this template.
897 fn compatible(&self, meta_item_kind: &ast::MetaItemKind) -> bool {
898 match meta_item_kind {
899 ast::MetaItemKind::Word => self.word,
900 ast::MetaItemKind::List(..) => self.list.is_some(),
901 ast::MetaItemKind::NameValue(lit) if lit.node.is_str() => self.name_value_str.is_some(),
902 ast::MetaItemKind::NameValue(..) => false,
907 /// A convenience macro for constructing attribute templates.
908 /// E.g., `template!(Word, List: "description")` means that the attribute
909 /// supports forms `#[attr]` and `#[attr(description)]`.
910 macro_rules! template {
911 (Word) => { template!(@ true, None, None) };
912 (List: $descr: expr) => { template!(@ false, Some($descr), None) };
913 (NameValueStr: $descr: expr) => { template!(@ false, None, Some($descr)) };
914 (Word, List: $descr: expr) => { template!(@ true, Some($descr), None) };
915 (Word, NameValueStr: $descr: expr) => { template!(@ true, None, Some($descr)) };
916 (List: $descr1: expr, NameValueStr: $descr2: expr) => {
917 template!(@ false, Some($descr1), Some($descr2))
919 (Word, List: $descr1: expr, NameValueStr: $descr2: expr) => {
920 template!(@ true, Some($descr1), Some($descr2))
922 (@ $word: expr, $list: expr, $name_value_str: expr) => { AttributeTemplate {
923 word: $word, list: $list, name_value_str: $name_value_str
928 fn is_deprecated(&self) -> bool {
930 Gated(Stability::Deprecated(_, _), ..) => true,
936 #[derive(Copy, Clone, Debug)]
939 // First argument is tracking issue link; second argument is an optional
940 // help message, which defaults to "remove this attribute"
941 Deprecated(&'static str, Option<&'static str>),
945 impl std::fmt::Debug for AttributeGate {
946 fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
948 Gated(ref stab, name, expl, _) =>
949 write!(fmt, "Gated({:?}, {}, {})", stab, name, expl),
950 Ungated => write!(fmt, "Ungated")
955 macro_rules! cfg_fn {
956 ($field: ident) => {{
957 fn f(features: &Features) -> bool {
960 f as fn(&Features) -> bool
964 pub fn deprecated_attributes() -> Vec<&'static (Symbol, AttributeType,
965 AttributeTemplate, AttributeGate)> {
966 BUILTIN_ATTRIBUTES.iter().filter(|(.., gate)| gate.is_deprecated()).collect()
969 pub fn is_builtin_attr_name(name: ast::Name) -> bool {
970 BUILTIN_ATTRIBUTE_MAP.get(&name).is_some()
973 pub fn is_builtin_attr(attr: &ast::Attribute) -> bool {
974 attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name)).is_some()
977 /// Attributes that have a special meaning to rustc or rustdoc
978 pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
984 template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#),
990 template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#),
996 template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#),
1002 template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#),
1006 (sym::macro_use, Normal, template!(Word, List: "name1, name2, ..."), Ungated),
1007 (sym::macro_export, Normal, template!(Word, List: "local_inner_macros"), Ungated),
1008 (sym::plugin_registrar, Normal, template!(Word), Ungated),
1010 (sym::cfg, Normal, template!(List: "predicate"), Ungated),
1011 (sym::cfg_attr, Normal, template!(List: "predicate, attr1, attr2, ..."), Ungated),
1012 (sym::main, Normal, template!(Word), Ungated),
1013 (sym::start, Normal, template!(Word), Ungated),
1014 (sym::repr, Normal, template!(List: "C, packed, ..."), Ungated),
1015 (sym::path, Normal, template!(NameValueStr: "file"), Ungated),
1016 (sym::automatically_derived, Normal, template!(Word), Ungated),
1017 (sym::no_mangle, Whitelisted, template!(Word), Ungated),
1018 (sym::no_link, Normal, template!(Word), Ungated),
1019 (sym::derive, Normal, template!(List: "Trait1, Trait2, ..."), Ungated),
1023 template!(Word, List: r#"expected = "reason"#, NameValueStr: "reason"),
1026 (sym::ignore, Normal, template!(Word, NameValueStr: "reason"), Ungated),
1027 (sym::no_implicit_prelude, Normal, template!(Word), Ungated),
1028 (sym::reexport_test_harness_main, Normal, template!(NameValueStr: "name"), Ungated),
1029 (sym::link_args, Normal, template!(NameValueStr: "args"), Gated(Stability::Unstable,
1031 "the `link_args` attribute is experimental and not \
1032 portable across platforms, it is recommended to \
1033 use `#[link(name = \"foo\")] instead",
1034 cfg_fn!(link_args))),
1035 (sym::macro_escape, Normal, template!(Word), Ungated),
1038 (sym::structural_match, Whitelisted, template!(Word), Gated(Stability::Unstable,
1039 sym::structural_match,
1040 "the semantics of constant patterns is \
1042 cfg_fn!(structural_match))),
1045 (sym::non_exhaustive, Whitelisted, template!(Word), Gated(Stability::Unstable,
1046 sym::non_exhaustive,
1047 "non exhaustive is an experimental feature",
1048 cfg_fn!(non_exhaustive))),
1051 (sym::marker, Normal, template!(Word), Gated(Stability::Unstable,
1052 sym::marker_trait_attr,
1053 "marker traits is an experimental feature",
1054 cfg_fn!(marker_trait_attr))),
1056 (sym::plugin, CrateLevel, template!(List: "name|name(args)"), Gated(Stability::Unstable,
1058 "compiler plugins are experimental \
1059 and possibly buggy",
1062 (sym::no_std, CrateLevel, template!(Word), Ungated),
1063 (sym::no_core, CrateLevel, template!(Word), Gated(Stability::Unstable,
1065 "no_core is experimental",
1067 (sym::lang, Normal, template!(NameValueStr: "name"), Gated(Stability::Unstable,
1069 "language items are subject to change",
1070 cfg_fn!(lang_items))),
1071 (sym::linkage, Whitelisted, template!(NameValueStr: "external|internal|..."),
1072 Gated(Stability::Unstable,
1074 "the `linkage` attribute is experimental \
1075 and not portable across platforms",
1077 (sym::thread_local, Whitelisted, template!(Word), Gated(Stability::Unstable,
1079 "`#[thread_local]` is an experimental feature, and does \
1080 not currently handle destructors",
1081 cfg_fn!(thread_local))),
1083 (sym::rustc_on_unimplemented, Whitelisted, template!(List:
1084 r#"/*opt*/ message = "...", /*opt*/ label = "...", /*opt*/ note = "...""#,
1085 NameValueStr: "message"),
1086 Gated(Stability::Unstable,
1087 sym::on_unimplemented,
1088 "the `#[rustc_on_unimplemented]` attribute \
1089 is an experimental feature",
1090 cfg_fn!(on_unimplemented))),
1091 (sym::rustc_const_unstable, Normal, template!(List: r#"feature = "name""#),
1092 Gated(Stability::Unstable,
1093 sym::rustc_const_unstable,
1094 "the `#[rustc_const_unstable]` attribute \
1095 is an internal feature",
1096 cfg_fn!(rustc_const_unstable))),
1097 (sym::global_allocator, Normal, template!(Word), Ungated),
1098 (sym::default_lib_allocator, Whitelisted, template!(Word), Gated(Stability::Unstable,
1099 sym::allocator_internals,
1100 "the `#[default_lib_allocator]` \
1101 attribute is an experimental feature",
1102 cfg_fn!(allocator_internals))),
1103 (sym::needs_allocator, Normal, template!(Word), Gated(Stability::Unstable,
1104 sym::allocator_internals,
1105 "the `#[needs_allocator]` \
1106 attribute is an experimental \
1108 cfg_fn!(allocator_internals))),
1109 (sym::panic_runtime, Whitelisted, template!(Word), Gated(Stability::Unstable,
1111 "the `#[panic_runtime]` attribute is \
1112 an experimental feature",
1113 cfg_fn!(panic_runtime))),
1114 (sym::needs_panic_runtime, Whitelisted, template!(Word), Gated(Stability::Unstable,
1115 sym::needs_panic_runtime,
1116 "the `#[needs_panic_runtime]` \
1117 attribute is an experimental \
1119 cfg_fn!(needs_panic_runtime))),
1120 (sym::rustc_outlives, Normal, template!(Word), Gated(Stability::Unstable,
1122 "the `#[rustc_outlives]` attribute \
1123 is just used for rustc unit tests \
1124 and will never be stable",
1125 cfg_fn!(rustc_attrs))),
1126 (sym::rustc_variance, Normal, template!(Word), Gated(Stability::Unstable,
1128 "the `#[rustc_variance]` attribute \
1129 is just used for rustc unit tests \
1130 and will never be stable",
1131 cfg_fn!(rustc_attrs))),
1132 (sym::rustc_layout, Normal, template!(List: "field1, field2, ..."),
1133 Gated(Stability::Unstable,
1135 "the `#[rustc_layout]` attribute \
1136 is just used for rustc unit tests \
1137 and will never be stable",
1138 cfg_fn!(rustc_attrs))),
1139 (sym::rustc_layout_scalar_valid_range_start, Whitelisted, template!(List: "value"),
1140 Gated(Stability::Unstable,
1142 "the `#[rustc_layout_scalar_valid_range_start]` attribute \
1143 is just used to enable niche optimizations in libcore \
1144 and will never be stable",
1145 cfg_fn!(rustc_attrs))),
1146 (sym::rustc_layout_scalar_valid_range_end, Whitelisted, template!(List: "value"),
1147 Gated(Stability::Unstable,
1149 "the `#[rustc_layout_scalar_valid_range_end]` attribute \
1150 is just used to enable niche optimizations in libcore \
1151 and will never be stable",
1152 cfg_fn!(rustc_attrs))),
1153 (sym::rustc_nonnull_optimization_guaranteed, Whitelisted, template!(Word),
1154 Gated(Stability::Unstable,
1156 "the `#[rustc_nonnull_optimization_guaranteed]` attribute \
1157 is just used to enable niche optimizations in libcore \
1158 and will never be stable",
1159 cfg_fn!(rustc_attrs))),
1160 (sym::rustc_regions, Normal, template!(Word), Gated(Stability::Unstable,
1162 "the `#[rustc_regions]` attribute \
1163 is just used for rustc unit tests \
1164 and will never be stable",
1165 cfg_fn!(rustc_attrs))),
1166 (sym::rustc_error, Whitelisted, template!(Word), Gated(Stability::Unstable,
1168 "the `#[rustc_error]` attribute \
1169 is just used for rustc unit tests \
1170 and will never be stable",
1171 cfg_fn!(rustc_attrs))),
1172 (sym::rustc_dump_user_substs, Whitelisted, template!(Word), Gated(Stability::Unstable,
1175 is just used for rustc unit tests \
1176 and will never be stable",
1177 cfg_fn!(rustc_attrs))),
1178 (sym::rustc_if_this_changed, Whitelisted, template!(Word, List: "DepNode"),
1179 Gated(Stability::Unstable,
1181 "the `#[rustc_if_this_changed]` attribute \
1182 is just used for rustc unit tests \
1183 and will never be stable",
1184 cfg_fn!(rustc_attrs))),
1185 (sym::rustc_then_this_would_need, Whitelisted, template!(List: "DepNode"),
1186 Gated(Stability::Unstable,
1188 "the `#[rustc_if_this_changed]` attribute \
1189 is just used for rustc unit tests \
1190 and will never be stable",
1191 cfg_fn!(rustc_attrs))),
1192 (sym::rustc_dirty, Whitelisted, template!(List: r#"cfg = "...", /*opt*/ label = "...",
1193 /*opt*/ except = "...""#),
1194 Gated(Stability::Unstable,
1196 "the `#[rustc_dirty]` attribute \
1197 is just used for rustc unit tests \
1198 and will never be stable",
1199 cfg_fn!(rustc_attrs))),
1200 (sym::rustc_clean, Whitelisted, template!(List: r#"cfg = "...", /*opt*/ label = "...",
1201 /*opt*/ except = "...""#),
1202 Gated(Stability::Unstable,
1204 "the `#[rustc_clean]` attribute \
1205 is just used for rustc unit tests \
1206 and will never be stable",
1207 cfg_fn!(rustc_attrs))),
1209 sym::rustc_partition_reused,
1211 template!(List: r#"cfg = "...", module = "...""#),
1213 Stability::Unstable,
1216 is just used for rustc unit tests \
1217 and will never be stable",
1218 cfg_fn!(rustc_attrs)
1222 sym::rustc_partition_codegened,
1224 template!(List: r#"cfg = "...", module = "...""#),
1226 Stability::Unstable,
1229 is just used for rustc unit tests \
1230 and will never be stable",
1231 cfg_fn!(rustc_attrs),
1234 (sym::rustc_expected_cgu_reuse, Whitelisted, template!(List: r#"cfg = "...", module = "...",
1236 Gated(Stability::Unstable,
1239 is just used for rustc unit tests \
1240 and will never be stable",
1241 cfg_fn!(rustc_attrs))),
1242 (sym::rustc_synthetic, Whitelisted, template!(Word), Gated(Stability::Unstable,
1245 is just used for rustc unit tests \
1246 and will never be stable",
1247 cfg_fn!(rustc_attrs))),
1248 (sym::rustc_symbol_name, Whitelisted, template!(Word), Gated(Stability::Unstable,
1250 "internal rustc attributes will never be stable",
1251 cfg_fn!(rustc_attrs))),
1252 (sym::rustc_def_path, Whitelisted, template!(Word), Gated(Stability::Unstable,
1254 "internal rustc attributes will never be stable",
1255 cfg_fn!(rustc_attrs))),
1256 (sym::rustc_mir, Whitelisted, template!(List: "arg1, arg2, ..."), Gated(Stability::Unstable,
1258 "the `#[rustc_mir]` attribute \
1259 is just used for rustc unit tests \
1260 and will never be stable",
1261 cfg_fn!(rustc_attrs))),
1263 sym::rustc_inherit_overflow_checks,
1267 Stability::Unstable,
1269 "the `#[rustc_inherit_overflow_checks]` \
1270 attribute is just used to control \
1271 overflow checking behavior of several \
1272 libcore functions that are inlined \
1273 across crates and will never be stable",
1274 cfg_fn!(rustc_attrs),
1278 (sym::rustc_dump_program_clauses, Whitelisted, template!(Word), Gated(Stability::Unstable,
1280 "the `#[rustc_dump_program_clauses]` \
1281 attribute is just used for rustc unit \
1282 tests and will never be stable",
1283 cfg_fn!(rustc_attrs))),
1284 (sym::rustc_test_marker, Normal, template!(Word), Gated(Stability::Unstable,
1286 "the `#[rustc_test_marker]` attribute \
1287 is used internally to track tests",
1288 cfg_fn!(rustc_attrs))),
1289 (sym::rustc_transparent_macro, Whitelisted, template!(Word), Gated(Stability::Unstable,
1291 "used internally for testing macro hygiene",
1292 cfg_fn!(rustc_attrs))),
1293 (sym::compiler_builtins, Whitelisted, template!(Word), Gated(Stability::Unstable,
1294 sym::compiler_builtins,
1295 "the `#[compiler_builtins]` attribute is used to \
1296 identify the `compiler_builtins` crate which \
1297 contains compiler-rt intrinsics and will never be \
1299 cfg_fn!(compiler_builtins))),
1300 (sym::sanitizer_runtime, Whitelisted, template!(Word), Gated(Stability::Unstable,
1301 sym::sanitizer_runtime,
1302 "the `#[sanitizer_runtime]` attribute is used to \
1303 identify crates that contain the runtime of a \
1304 sanitizer and will never be stable",
1305 cfg_fn!(sanitizer_runtime))),
1306 (sym::profiler_runtime, Whitelisted, template!(Word), Gated(Stability::Unstable,
1307 sym::profiler_runtime,
1308 "the `#[profiler_runtime]` attribute is used to \
1309 identify the `profiler_builtins` crate which \
1310 contains the profiler runtime and will never be \
1312 cfg_fn!(profiler_runtime))),
1314 (sym::allow_internal_unstable, Normal, template!(Word, List: "feat1, feat2, ..."),
1315 Gated(Stability::Unstable,
1316 sym::allow_internal_unstable,
1317 EXPLAIN_ALLOW_INTERNAL_UNSTABLE,
1318 cfg_fn!(allow_internal_unstable))),
1320 (sym::allow_internal_unsafe, Normal, template!(Word), Gated(Stability::Unstable,
1321 sym::allow_internal_unsafe,
1322 EXPLAIN_ALLOW_INTERNAL_UNSAFE,
1323 cfg_fn!(allow_internal_unsafe))),
1325 (sym::fundamental, Whitelisted, template!(Word), Gated(Stability::Unstable,
1327 "the `#[fundamental]` attribute \
1328 is an experimental feature",
1329 cfg_fn!(fundamental))),
1331 (sym::proc_macro_derive, Normal, template!(List: "TraitName, \
1332 /*opt*/ attributes(name1, name2, ...)"),
1335 (sym::rustc_copy_clone_marker, Whitelisted, template!(Word), Gated(Stability::Unstable,
1337 "internal implementation detail",
1338 cfg_fn!(rustc_attrs))),
1340 (sym::rustc_allocator, Whitelisted, template!(Word), Gated(Stability::Unstable,
1342 "internal implementation detail",
1343 cfg_fn!(rustc_attrs))),
1345 (sym::rustc_dummy, Normal, template!(Word /* doesn't matter*/), Gated(Stability::Unstable,
1347 "used by the test suite",
1348 cfg_fn!(rustc_attrs))),
1350 // FIXME: #14408 whitelist docs since rustdoc looks at them
1354 template!(List: "hidden|inline|...", NameValueStr: "string"),
1358 // FIXME: #14406 these are processed in codegen, which happens after the
1360 (sym::cold, Whitelisted, template!(Word), Ungated),
1361 (sym::naked, Whitelisted, template!(Word), Gated(Stability::Unstable,
1362 sym::naked_functions,
1363 "the `#[naked]` attribute \
1364 is an experimental feature",
1365 cfg_fn!(naked_functions))),
1366 (sym::ffi_returns_twice, Whitelisted, template!(Word), Gated(Stability::Unstable,
1367 sym::ffi_returns_twice,
1368 "the `#[ffi_returns_twice]` attribute \
1369 is an experimental feature",
1370 cfg_fn!(ffi_returns_twice))),
1371 (sym::target_feature, Whitelisted, template!(List: r#"enable = "name""#), Ungated),
1372 (sym::export_name, Whitelisted, template!(NameValueStr: "name"), Ungated),
1373 (sym::inline, Whitelisted, template!(Word, List: "always|never"), Ungated),
1374 (sym::link, Whitelisted, template!(List: r#"name = "...", /*opt*/ kind = "dylib|static|...",
1375 /*opt*/ cfg = "...""#), Ungated),
1376 (sym::link_name, Whitelisted, template!(NameValueStr: "name"), Ungated),
1377 (sym::link_section, Whitelisted, template!(NameValueStr: "name"), Ungated),
1378 (sym::no_builtins, Whitelisted, template!(Word), Ungated),
1379 (sym::no_debug, Whitelisted, template!(Word), Gated(
1380 Stability::Deprecated("https://github.com/rust-lang/rust/issues/29721", None),
1382 "the `#[no_debug]` attribute was an experimental feature that has been \
1383 deprecated due to lack of demand",
1384 cfg_fn!(no_debug))),
1386 sym::omit_gdb_pretty_printer_section,
1390 Stability::Unstable,
1391 sym::omit_gdb_pretty_printer_section,
1392 "the `#[omit_gdb_pretty_printer_section]` \
1393 attribute is just used for the Rust test \
1395 cfg_fn!(omit_gdb_pretty_printer_section)
1398 (sym::unsafe_destructor_blind_to_params,
1401 Gated(Stability::Deprecated("https://github.com/rust-lang/rust/issues/34761",
1402 Some("replace this attribute with `#[may_dangle]`")),
1403 sym::dropck_parametricity,
1404 "unsafe_destructor_blind_to_params has been replaced by \
1405 may_dangle and will be removed in the future",
1406 cfg_fn!(dropck_parametricity))),
1410 Gated(Stability::Unstable,
1411 sym::dropck_eyepatch,
1412 "may_dangle has unstable semantics and may be removed in the future",
1413 cfg_fn!(dropck_eyepatch))),
1414 (sym::unwind, Whitelisted, template!(List: "allowed|aborts"), Gated(Stability::Unstable,
1415 sym::unwind_attributes,
1416 "#[unwind] is experimental",
1417 cfg_fn!(unwind_attributes))),
1418 (sym::used, Whitelisted, template!(Word), Ungated),
1421 (sym::prelude_import, Whitelisted, template!(Word), Gated(Stability::Unstable,
1422 sym::prelude_import,
1423 "`#[prelude_import]` is for use by rustc only",
1424 cfg_fn!(prelude_import))),
1426 // FIXME: #14407 these are only looked at on-demand so we can't
1427 // guarantee they'll have already been checked
1429 sym::rustc_deprecated,
1431 template!(List: r#"since = "version", reason = "...""#),
1434 (sym::must_use, Whitelisted, template!(Word, NameValueStr: "reason"), Ungated),
1438 template!(List: r#"feature = "name", since = "version""#),
1444 template!(List: r#"feature = "name", reason = "...", issue = "N""#),
1451 List: r#"/*opt*/ since = "version", /*opt*/ note = "reason""#,
1452 NameValueStr: "reason"
1457 (sym::rustc_paren_sugar, Normal, template!(Word), Gated(Stability::Unstable,
1458 sym::unboxed_closures,
1459 "unboxed_closures are still evolving",
1460 cfg_fn!(unboxed_closures))),
1462 (sym::windows_subsystem, Whitelisted, template!(NameValueStr: "windows|console"), Ungated),
1464 (sym::proc_macro_attribute, Normal, template!(Word), Ungated),
1465 (sym::proc_macro, Normal, template!(Word), Ungated),
1467 (sym::rustc_proc_macro_decls, Normal, template!(Word), Gated(Stability::Unstable,
1469 "used internally by rustc",
1470 cfg_fn!(rustc_attrs))),
1472 (sym::allow_fail, Normal, template!(Word), Gated(Stability::Unstable,
1474 "allow_fail attribute is currently unstable",
1475 cfg_fn!(allow_fail))),
1477 (sym::rustc_std_internal_symbol, Whitelisted, template!(Word), Gated(Stability::Unstable,
1479 "this is an internal attribute that will \
1481 cfg_fn!(rustc_attrs))),
1483 // whitelists "identity-like" conversion methods to suggest on type mismatch
1484 (sym::rustc_conversion_suggestion, Whitelisted, template!(Word), Gated(Stability::Unstable,
1486 "this is an internal attribute that will \
1488 cfg_fn!(rustc_attrs))),
1491 sym::rustc_args_required_const,
1493 template!(List: "N"),
1494 Gated(Stability::Unstable, sym::rustc_attrs, "never will be stable",
1495 cfg_fn!(rustc_attrs))
1498 (sym::panic_handler, Normal, template!(Word), Ungated),
1500 (sym::alloc_error_handler, Normal, template!(Word), Gated(Stability::Unstable,
1501 sym::alloc_error_handler,
1502 "#[alloc_error_handler] is an unstable feature",
1503 cfg_fn!(alloc_error_handler))),
1506 (sym::optimize, Whitelisted, template!(List: "size|speed"), Gated(Stability::Unstable,
1507 sym::optimize_attribute,
1508 "#[optimize] attribute is an unstable feature",
1509 cfg_fn!(optimize_attribute))),
1511 // Crate level attributes
1512 (sym::crate_name, CrateLevel, template!(NameValueStr: "name"), Ungated),
1513 (sym::crate_type, CrateLevel, template!(NameValueStr: "bin|lib|..."), Ungated),
1514 (sym::crate_id, CrateLevel, template!(NameValueStr: "ignored"), Ungated),
1515 (sym::feature, CrateLevel, template!(List: "name1, name1, ..."), Ungated),
1516 (sym::no_start, CrateLevel, template!(Word), Ungated),
1517 (sym::no_main, CrateLevel, template!(Word), Ungated),
1518 (sym::recursion_limit, CrateLevel, template!(NameValueStr: "N"), Ungated),
1519 (sym::type_length_limit, CrateLevel, template!(NameValueStr: "N"), Ungated),
1520 (sym::test_runner, CrateLevel, template!(List: "path"), Gated(Stability::Unstable,
1521 sym::custom_test_frameworks,
1522 EXPLAIN_CUSTOM_TEST_FRAMEWORKS,
1523 cfg_fn!(custom_test_frameworks))),
1526 pub type BuiltinAttribute = (Symbol, AttributeType, AttributeTemplate, AttributeGate);
1529 pub static ref BUILTIN_ATTRIBUTE_MAP: FxHashMap<Symbol, &'static BuiltinAttribute> = {
1530 let mut map = FxHashMap::default();
1531 for attr in BUILTIN_ATTRIBUTES.iter() {
1532 if map.insert(attr.0, attr).is_some() {
1533 panic!("duplicate builtin attribute `{}`", attr.0);
1540 // cfg(...)'s that are feature gated
1541 const GATED_CFGS: &[(Symbol, Symbol, fn(&Features) -> bool)] = &[
1542 // (name in cfg, feature, function to check if the feature is enabled)
1543 (sym::target_thread_local, sym::cfg_target_thread_local, cfg_fn!(cfg_target_thread_local)),
1544 (sym::target_has_atomic, sym::cfg_target_has_atomic, cfg_fn!(cfg_target_has_atomic)),
1545 (sym::rustdoc, sym::doc_cfg, cfg_fn!(doc_cfg)),
1549 pub struct GatedCfg {
1555 pub fn gate(cfg: &ast::MetaItem) -> Option<GatedCfg> {
1557 .position(|info| cfg.check_name(info.0))
1566 pub fn check_and_emit(&self, sess: &ParseSess, features: &Features) {
1567 let (cfg, feature, has_feature) = GATED_CFGS[self.index];
1568 if !has_feature(features) && !self.span.allows_unstable(feature) {
1569 let explain = format!("`cfg({})` is experimental and subject to change", cfg);
1570 emit_feature_err(sess, feature, self.span, GateIssue::Language, &explain);
1575 struct Context<'a> {
1576 features: &'a Features,
1577 parse_sess: &'a ParseSess,
1578 plugin_attributes: &'a [(Symbol, AttributeType)],
1581 macro_rules! gate_feature_fn {
1582 ($cx: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr, $level: expr) => {{
1583 let (cx, has_feature, span,
1584 name, explain, level) = ($cx, $has_feature, $span, $name, $explain, $level);
1585 let has_feature: bool = has_feature(&$cx.features);
1586 debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
1587 if !has_feature && !span.allows_unstable($name) {
1588 leveled_feature_err(cx.parse_sess, name, span, GateIssue::Language, explain, level)
1594 macro_rules! gate_feature {
1595 ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {
1596 gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
1597 sym::$feature, $explain, GateStrength::Hard)
1599 ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {
1600 gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
1601 sym::$feature, $explain, $level)
1605 impl<'a> Context<'a> {
1608 attr: &ast::Attribute,
1609 attr_info: Option<&BuiltinAttribute>,
1612 debug!("check_attribute(attr = {:?})", attr);
1613 if let Some(&(name, ty, _template, ref gateage)) = attr_info {
1614 if let Gated(_, name, desc, ref has_feature) = *gateage {
1615 if !attr.span.allows_unstable(name) {
1617 self, has_feature, attr.span, name, desc, GateStrength::Hard
1620 } else if name == sym::doc {
1621 if let Some(content) = attr.meta_item_list() {
1622 if content.iter().any(|c| c.check_name(sym::include)) {
1623 gate_feature!(self, external_doc, attr.span,
1624 "#[doc(include = \"...\")] is experimental"
1629 debug!("check_attribute: {:?} is builtin, {:?}, {:?}", attr.path, ty, gateage);
1632 for &(n, ty) in self.plugin_attributes {
1634 // Plugins can't gate attributes, so we don't check for it
1635 // unlike the code above; we only use this loop to
1636 // short-circuit to avoid the checks below.
1637 debug!("check_attribute: {:?} is registered by a plugin, {:?}", attr.path, ty);
1641 if !attr::is_known(attr) {
1642 if attr.name_or_empty().as_str().starts_with("rustc_") {
1643 let msg = "unless otherwise specified, attributes with the prefix `rustc_` \
1644 are reserved for internal compiler diagnostics";
1645 gate_feature!(self, rustc_attrs, attr.span, msg);
1646 } else if !is_macro {
1647 // Only run the custom attribute lint during regular feature gate
1648 // checking. Macro gating runs before the plugin attributes are
1649 // registered, so we skip this in that case.
1650 let msg = format!("The attribute `{}` is currently unknown to the compiler and \
1651 may have meaning added to it in the future", attr.path);
1652 gate_feature!(self, custom_attribute, attr.span, &msg);
1658 pub fn check_attribute(attr: &ast::Attribute, parse_sess: &ParseSess, features: &Features) {
1659 let cx = Context { features: features, parse_sess: parse_sess, plugin_attributes: &[] };
1662 attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name).map(|a| *a)),
1667 fn find_lang_feature_issue(feature: Symbol) -> Option<u32> {
1668 if let Some(info) = ACTIVE_FEATURES.iter().find(|t| t.0 == feature) {
1670 // FIXME (#28244): enforce that active features have issue numbers
1671 // assert!(issue.is_some())
1674 // search in Accepted, Removed, or Stable Removed features
1675 let found = ACCEPTED_FEATURES.iter().chain(REMOVED_FEATURES).chain(STABLE_REMOVED_FEATURES)
1676 .find(|t| t.0 == feature);
1678 Some(&(_, _, issue, _)) => issue,
1679 None => panic!("Feature `{}` is not declared anywhere", feature),
1684 pub enum GateIssue {
1686 Library(Option<u32>)
1689 #[derive(Debug, Copy, Clone, PartialEq)]
1690 pub enum GateStrength {
1691 /// A hard error. (Most feature gates should use this.)
1693 /// Only a warning. (Use this only as backwards-compatibility demands.)
1697 pub fn emit_feature_err(
1704 feature_err(sess, feature, span, issue, explain).emit();
1707 pub fn feature_err<'a>(
1708 sess: &'a ParseSess,
1713 ) -> DiagnosticBuilder<'a> {
1714 leveled_feature_err(sess, feature, span, issue, explain, GateStrength::Hard)
1717 fn leveled_feature_err<'a>(
1718 sess: &'a ParseSess,
1723 level: GateStrength,
1724 ) -> DiagnosticBuilder<'a> {
1725 let diag = &sess.span_diagnostic;
1727 let issue = match issue {
1728 GateIssue::Language => find_lang_feature_issue(feature),
1729 GateIssue::Library(lib) => lib,
1732 let mut err = match level {
1733 GateStrength::Hard => {
1734 diag.struct_span_err_with_code(span, explain, stringify_error_code!(E0658))
1736 GateStrength::Soft => diag.struct_span_warn(span, explain),
1740 None | Some(0) => {} // We still accept `0` as a stand-in for backwards compatibility
1743 "for more information, see https://github.com/rust-lang/rust/issues/{}",
1749 // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
1750 if sess.unstable_features.is_nightly_build() {
1751 err.help(&format!("add #![feature({})] to the crate attributes to enable", feature));
1754 // If we're on stable and only emitting a "soft" warning, add a note to
1755 // clarify that the feature isn't "on" (rather than being on but
1757 if !sess.unstable_features.is_nightly_build() && level == GateStrength::Soft {
1758 err.help("a nightly build of the compiler is required to enable this feature");
1765 const EXPLAIN_BOX_SYNTAX: &str =
1766 "box expression syntax is experimental; you can call `Box::new` instead";
1768 pub const EXPLAIN_STMT_ATTR_SYNTAX: &str =
1769 "attributes on expressions are experimental";
1771 pub const EXPLAIN_ASM: &str =
1772 "inline assembly is not stable enough for use and is subject to change";
1774 pub const EXPLAIN_GLOBAL_ASM: &str =
1775 "`global_asm!` is not stable enough for use and is subject to change";
1777 pub const EXPLAIN_CUSTOM_TEST_FRAMEWORKS: &str =
1778 "custom test frameworks are an unstable feature";
1780 pub const EXPLAIN_LOG_SYNTAX: &str =
1781 "`log_syntax!` is not stable enough for use and is subject to change";
1783 pub const EXPLAIN_CONCAT_IDENTS: &str =
1784 "`concat_idents` is not stable enough for use and is subject to change";
1786 pub const EXPLAIN_FORMAT_ARGS_NL: &str =
1787 "`format_args_nl` is only for internal language use and is subject to change";
1789 pub const EXPLAIN_TRACE_MACROS: &str =
1790 "`trace_macros` is not stable enough for use and is subject to change";
1791 pub const EXPLAIN_ALLOW_INTERNAL_UNSTABLE: &str =
1792 "allow_internal_unstable side-steps feature gating and stability checks";
1793 pub const EXPLAIN_ALLOW_INTERNAL_UNSAFE: &str =
1794 "allow_internal_unsafe side-steps the unsafe_code lint";
1796 pub const EXPLAIN_UNSIZED_TUPLE_COERCION: &str =
1797 "unsized tuple coercion is not stable enough for use and is subject to change";
1799 struct PostExpansionVisitor<'a> {
1800 context: &'a Context<'a>,
1801 builtin_attributes: &'static FxHashMap<Symbol, &'static BuiltinAttribute>,
1804 macro_rules! gate_feature_post {
1805 ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {{
1806 let (cx, span) = ($cx, $span);
1807 if !span.allows_unstable(sym::$feature) {
1808 gate_feature!(cx.context, $feature, span, $explain)
1811 ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {{
1812 let (cx, span) = ($cx, $span);
1813 if !span.allows_unstable(sym::$feature) {
1814 gate_feature!(cx.context, $feature, span, $explain, $level)
1819 impl<'a> PostExpansionVisitor<'a> {
1820 fn check_abi(&self, abi: Abi, span: Span) {
1822 Abi::RustIntrinsic => {
1823 gate_feature_post!(&self, intrinsics, span,
1824 "intrinsics are subject to change");
1826 Abi::PlatformIntrinsic => {
1827 gate_feature_post!(&self, platform_intrinsics, span,
1828 "platform intrinsics are experimental and possibly buggy");
1830 Abi::Vectorcall => {
1831 gate_feature_post!(&self, abi_vectorcall, span,
1832 "vectorcall is experimental and subject to change");
1835 gate_feature_post!(&self, abi_thiscall, span,
1836 "thiscall is experimental and subject to change");
1839 gate_feature_post!(&self, unboxed_closures, span,
1840 "rust-call ABI is subject to change");
1843 gate_feature_post!(&self, abi_ptx, span,
1844 "PTX ABIs are experimental and subject to change");
1846 Abi::Unadjusted => {
1847 gate_feature_post!(&self, abi_unadjusted, span,
1848 "unadjusted ABI is an implementation detail and perma-unstable");
1850 Abi::Msp430Interrupt => {
1851 gate_feature_post!(&self, abi_msp430_interrupt, span,
1852 "msp430-interrupt ABI is experimental and subject to change");
1854 Abi::X86Interrupt => {
1855 gate_feature_post!(&self, abi_x86_interrupt, span,
1856 "x86-interrupt ABI is experimental and subject to change");
1858 Abi::AmdGpuKernel => {
1859 gate_feature_post!(&self, abi_amdgpu_kernel, span,
1860 "amdgpu-kernel ABI is experimental and subject to change");
1875 fn check_builtin_attribute(&mut self, attr: &ast::Attribute, name: Symbol,
1876 template: AttributeTemplate) {
1877 // Some special attributes like `cfg` must be checked
1878 // before the generic check, so we skip them here.
1879 let should_skip = |name| name == sym::cfg;
1880 // Some of previously accepted forms were used in practice,
1881 // report them as warnings for now.
1882 let should_warn = |name| name == sym::doc || name == sym::ignore ||
1883 name == sym::inline || name == sym::link;
1885 match attr.parse_meta(self.context.parse_sess) {
1886 Ok(meta) => if !should_skip(name) && !template.compatible(&meta.node) {
1887 let error_msg = format!("malformed `{}` attribute input", name);
1888 let mut msg = "attribute must be of the form ".to_owned();
1889 let mut suggestions = vec![];
1890 let mut first = true;
1893 let code = format!("#[{}]", name);
1894 msg.push_str(&format!("`{}`", &code));
1895 suggestions.push(code);
1897 if let Some(descr) = template.list {
1899 msg.push_str(" or ");
1902 let code = format!("#[{}({})]", name, descr);
1903 msg.push_str(&format!("`{}`", &code));
1904 suggestions.push(code);
1906 if let Some(descr) = template.name_value_str {
1908 msg.push_str(" or ");
1910 let code = format!("#[{} = \"{}\"]", name, descr);
1911 msg.push_str(&format!("`{}`", &code));
1912 suggestions.push(code);
1914 if should_warn(name) {
1915 self.context.parse_sess.buffer_lint(
1916 BufferedEarlyLintId::IllFormedAttributeInput,
1922 self.context.parse_sess.span_diagnostic.struct_span_err(meta.span, &error_msg)
1925 if suggestions.len() == 1 {
1926 "must be of the form"
1928 "the following are the possible correct uses"
1930 suggestions.into_iter(),
1931 Applicability::HasPlaceholders,
1935 Err(mut err) => err.emit(),
1940 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
1941 fn visit_attribute(&mut self, attr: &ast::Attribute) {
1942 let attr_info = attr.ident().and_then(|ident| {
1943 self.builtin_attributes.get(&ident.name).map(|a| *a)
1946 // Check for gated attributes.
1947 self.context.check_attribute(attr, attr_info, false);
1949 if attr.check_name(sym::doc) {
1950 if let Some(content) = attr.meta_item_list() {
1951 if content.len() == 1 && content[0].check_name(sym::cfg) {
1952 gate_feature_post!(&self, doc_cfg, attr.span,
1953 "#[doc(cfg(...))] is experimental"
1955 } else if content.iter().any(|c| c.check_name(sym::masked)) {
1956 gate_feature_post!(&self, doc_masked, attr.span,
1957 "#[doc(masked)] is experimental"
1959 } else if content.iter().any(|c| c.check_name(sym::spotlight)) {
1960 gate_feature_post!(&self, doc_spotlight, attr.span,
1961 "#[doc(spotlight)] is experimental"
1963 } else if content.iter().any(|c| c.check_name(sym::alias)) {
1964 gate_feature_post!(&self, doc_alias, attr.span,
1965 "#[doc(alias = \"...\")] is experimental"
1967 } else if content.iter().any(|c| c.check_name(sym::keyword)) {
1968 gate_feature_post!(&self, doc_keyword, attr.span,
1969 "#[doc(keyword = \"...\")] is experimental"
1976 // `rustc_dummy` doesn't have any restrictions specific to built-in attributes.
1977 Some(&(name, _, template, _)) if name != sym::rustc_dummy =>
1978 self.check_builtin_attribute(attr, name, template),
1979 _ => if let Some(TokenTree::Token(token)) = attr.tokens.trees().next() {
1980 if token == token::Eq {
1981 // All key-value attributes are restricted to meta-item syntax.
1982 attr.parse_meta(self.context.parse_sess).map_err(|mut err| err.emit()).ok();
1988 fn visit_name(&mut self, sp: Span, name: ast::Name) {
1989 if !name.as_str().is_ascii() {
1993 self.context.parse_sess.source_map().def_span(sp),
1994 "non-ascii idents are not fully supported"
1999 fn visit_item(&mut self, i: &'a ast::Item) {
2001 ast::ItemKind::Const(_,_) => {
2002 if i.ident.name == kw::Underscore {
2003 gate_feature_post!(&self, underscore_const_names, i.span,
2004 "naming constants with `_` is unstable");
2008 ast::ItemKind::ForeignMod(ref foreign_module) => {
2009 self.check_abi(foreign_module.abi, i.span);
2012 ast::ItemKind::Fn(..) => {
2013 if attr::contains_name(&i.attrs[..], sym::plugin_registrar) {
2014 gate_feature_post!(&self, plugin_registrar, i.span,
2015 "compiler plugins are experimental and possibly buggy");
2017 if attr::contains_name(&i.attrs[..], sym::start) {
2018 gate_feature_post!(&self, start, i.span,
2019 "a #[start] function is an experimental \
2020 feature whose signature may change \
2023 if attr::contains_name(&i.attrs[..], sym::main) {
2024 gate_feature_post!(&self, main, i.span,
2025 "declaration of a nonstandard #[main] \
2026 function may change over time, for now \
2027 a top-level `fn main()` is required");
2031 ast::ItemKind::Struct(..) => {
2032 for attr in attr::filter_by_name(&i.attrs[..], sym::repr) {
2033 for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
2034 if item.check_name(sym::simd) {
2035 gate_feature_post!(&self, repr_simd, attr.span,
2036 "SIMD types are experimental and possibly buggy");
2042 ast::ItemKind::Impl(_, polarity, defaultness, _, _, _, _) => {
2043 if polarity == ast::ImplPolarity::Negative {
2044 gate_feature_post!(&self, optin_builtin_traits,
2046 "negative trait bounds are not yet fully implemented; \
2047 use marker types for now");
2050 if let ast::Defaultness::Default = defaultness {
2051 gate_feature_post!(&self, specialization,
2053 "specialization is unstable");
2057 ast::ItemKind::Trait(ast::IsAuto::Yes, ..) => {
2058 gate_feature_post!(&self, optin_builtin_traits,
2060 "auto traits are experimental and possibly buggy");
2063 ast::ItemKind::TraitAlias(..) => {
2068 "trait aliases are experimental"
2072 ast::ItemKind::MacroDef(ast::MacroDef { legacy: false, .. }) => {
2073 let msg = "`macro` is experimental";
2074 gate_feature_post!(&self, decl_macro, i.span, msg);
2077 ast::ItemKind::Existential(..) => {
2082 "existential types are unstable"
2089 visit::walk_item(self, i);
2092 fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
2094 ast::ForeignItemKind::Fn(..) |
2095 ast::ForeignItemKind::Static(..) => {
2096 let link_name = attr::first_attr_value_str_by_name(&i.attrs, sym::link_name);
2097 let links_to_llvm = match link_name {
2098 Some(val) => val.as_str().starts_with("llvm."),
2102 gate_feature_post!(&self, link_llvm_intrinsics, i.span,
2103 "linking to LLVM intrinsics is experimental");
2106 ast::ForeignItemKind::Ty => {
2107 gate_feature_post!(&self, extern_types, i.span,
2108 "extern types are experimental");
2110 ast::ForeignItemKind::Macro(..) => {}
2113 visit::walk_foreign_item(self, i)
2116 fn visit_ty(&mut self, ty: &'a ast::Ty) {
2118 ast::TyKind::BareFn(ref bare_fn_ty) => {
2119 self.check_abi(bare_fn_ty.abi, ty.span);
2121 ast::TyKind::Never => {
2122 gate_feature_post!(&self, never_type, ty.span,
2123 "The `!` type is experimental");
2127 visit::walk_ty(self, ty)
2130 fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FunctionRetTy) {
2131 if let ast::FunctionRetTy::Ty(ref output_ty) = *ret_ty {
2132 if let ast::TyKind::Never = output_ty.node {
2135 self.visit_ty(output_ty)
2140 fn visit_expr(&mut self, e: &'a ast::Expr) {
2142 ast::ExprKind::Box(_) => {
2143 gate_feature_post!(&self, box_syntax, e.span, EXPLAIN_BOX_SYNTAX);
2145 ast::ExprKind::Type(..) => {
2146 // To avoid noise about type ascription in common syntax errors, only emit if it
2147 // is the *only* error.
2148 if self.context.parse_sess.span_diagnostic.err_count() == 0 {
2149 gate_feature_post!(&self, type_ascription, e.span,
2150 "type ascription is experimental");
2153 ast::ExprKind::Yield(..) => {
2154 gate_feature_post!(&self, generators,
2156 "yield syntax is experimental");
2158 ast::ExprKind::TryBlock(_) => {
2159 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
2161 ast::ExprKind::Block(_, opt_label) => {
2162 if let Some(label) = opt_label {
2163 gate_feature_post!(&self, label_break_value, label.ident.span,
2164 "labels on blocks are unstable");
2167 ast::ExprKind::Closure(_, ast::IsAsync::Async { .. }, ..) => {
2168 gate_feature_post!(&self, async_await, e.span, "async closures are unstable");
2170 ast::ExprKind::Async(..) => {
2171 gate_feature_post!(&self, async_await, e.span, "async blocks are unstable");
2173 ast::ExprKind::Await(origin, _) => {
2175 ast::AwaitOrigin::FieldLike =>
2176 gate_feature_post!(&self, async_await, e.span, "async/await is unstable"),
2177 ast::AwaitOrigin::MacroLike =>
2182 "`await!(<expr>)` macro syntax is unstable, and will soon be removed \
2183 in favor of `<expr>.await` syntax."
2189 visit::walk_expr(self, e)
2192 fn visit_arm(&mut self, arm: &'a ast::Arm) {
2193 visit::walk_arm(self, arm)
2196 fn visit_pat(&mut self, pattern: &'a ast::Pat) {
2197 match pattern.node {
2198 PatKind::Slice(_, Some(ref subslice), _) => {
2199 gate_feature_post!(&self, slice_patterns,
2201 "syntax for subslices in slice patterns is not yet stabilized");
2203 PatKind::Box(..) => {
2204 gate_feature_post!(&self, box_patterns,
2206 "box pattern syntax is experimental");
2208 PatKind::Range(_, _, Spanned { node: RangeEnd::Excluded, .. }) => {
2209 gate_feature_post!(&self, exclusive_range_pattern, pattern.span,
2210 "exclusive range pattern syntax is experimental");
2214 visit::walk_pat(self, pattern)
2217 fn visit_fn(&mut self,
2218 fn_kind: FnKind<'a>,
2219 fn_decl: &'a ast::FnDecl,
2222 if let Some(header) = fn_kind.header() {
2223 // Check for const fn and async fn declarations.
2224 if header.asyncness.node.is_async() {
2225 gate_feature_post!(&self, async_await, span, "async fn is unstable");
2228 // Stability of const fn methods are covered in
2229 // `visit_trait_item` and `visit_impl_item` below; this is
2230 // because default methods don't pass through this point.
2231 self.check_abi(header.abi, span);
2234 if fn_decl.c_variadic {
2235 gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
2238 visit::walk_fn(self, fn_kind, fn_decl, span)
2241 fn visit_generic_param(&mut self, param: &'a GenericParam) {
2243 GenericParamKind::Const { .. } =>
2244 gate_feature_post!(&self, const_generics, param.ident.span,
2245 "const generics are unstable"),
2248 visit::walk_generic_param(self, param)
2251 fn visit_assoc_ty_constraint(&mut self, constraint: &'a AssocTyConstraint) {
2252 match constraint.kind {
2253 AssocTyConstraintKind::Bound { .. } =>
2254 gate_feature_post!(&self, associated_type_bounds, constraint.span,
2255 "associated type bounds are unstable"),
2258 visit::walk_assoc_ty_constraint(self, constraint)
2261 fn visit_trait_item(&mut self, ti: &'a ast::TraitItem) {
2263 ast::TraitItemKind::Method(ref sig, ref block) => {
2264 if block.is_none() {
2265 self.check_abi(sig.header.abi, ti.span);
2267 if sig.header.asyncness.node.is_async() {
2268 gate_feature_post!(&self, async_await, ti.span, "async fn is unstable");
2270 if sig.decl.c_variadic {
2271 gate_feature_post!(&self, c_variadic, ti.span,
2272 "C-variadic functions are unstable");
2274 if sig.header.constness.node == ast::Constness::Const {
2275 gate_feature_post!(&self, const_fn, ti.span, "const fn is unstable");
2278 ast::TraitItemKind::Type(_, ref default) => {
2279 // We use three if statements instead of something like match guards so that all
2280 // of these errors can be emitted if all cases apply.
2281 if default.is_some() {
2282 gate_feature_post!(&self, associated_type_defaults, ti.span,
2283 "associated type defaults are unstable");
2285 if !ti.generics.params.is_empty() {
2286 gate_feature_post!(&self, generic_associated_types, ti.span,
2287 "generic associated types are unstable");
2289 if !ti.generics.where_clause.predicates.is_empty() {
2290 gate_feature_post!(&self, generic_associated_types, ti.span,
2291 "where clauses on associated types are unstable");
2296 visit::walk_trait_item(self, ti)
2299 fn visit_impl_item(&mut self, ii: &'a ast::ImplItem) {
2300 if ii.defaultness == ast::Defaultness::Default {
2301 gate_feature_post!(&self, specialization,
2303 "specialization is unstable");
2307 ast::ImplItemKind::Method(..) => {}
2308 ast::ImplItemKind::Existential(..) => {
2313 "existential types are unstable"
2316 ast::ImplItemKind::Type(_) => {
2317 if !ii.generics.params.is_empty() {
2318 gate_feature_post!(&self, generic_associated_types, ii.span,
2319 "generic associated types are unstable");
2321 if !ii.generics.where_clause.predicates.is_empty() {
2322 gate_feature_post!(&self, generic_associated_types, ii.span,
2323 "where clauses on associated types are unstable");
2328 visit::walk_impl_item(self, ii)
2331 fn visit_vis(&mut self, vis: &'a ast::Visibility) {
2332 if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.node {
2333 gate_feature_post!(&self, crate_visibility_modifier, vis.span,
2334 "`crate` visibility modifier is experimental");
2336 visit::walk_vis(self, vis)
2340 pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
2341 crate_edition: Edition, allow_features: &Option<Vec<String>>) -> Features {
2342 fn feature_removed(span_handler: &Handler, span: Span, reason: Option<&str>) {
2343 let mut err = struct_span_err!(span_handler, span, E0557, "feature has been removed");
2344 if let Some(reason) = reason {
2345 err.span_note(span, reason);
2347 err.span_label(span, "feature has been removed");
2352 let mut features = Features::new();
2353 let mut edition_enabled_features = FxHashMap::default();
2355 for &edition in ALL_EDITIONS {
2356 if edition <= crate_edition {
2357 // The `crate_edition` implies its respective umbrella feature-gate
2358 // (i.e., `#![feature(rust_20XX_preview)]` isn't needed on edition 20XX).
2359 edition_enabled_features.insert(edition.feature_name(), edition);
2363 for &(name, .., f_edition, set) in ACTIVE_FEATURES {
2364 if let Some(f_edition) = f_edition {
2365 if f_edition <= crate_edition {
2366 set(&mut features, DUMMY_SP);
2367 edition_enabled_features.insert(name, crate_edition);
2372 // Process the edition umbrella feature-gates first, to ensure
2373 // `edition_enabled_features` is completed before it's queried.
2374 for attr in krate_attrs {
2375 if !attr.check_name(sym::feature) {
2379 let list = match attr.meta_item_list() {
2389 let name = mi.name_or_empty();
2390 if INCOMPLETE_FEATURES.iter().any(|f| name == *f) {
2391 span_handler.struct_span_warn(
2394 "the feature `{}` is incomplete and may cause the compiler to crash",
2400 if let Some(edition) = ALL_EDITIONS.iter().find(|e| name == e.feature_name()) {
2401 if *edition <= crate_edition {
2405 for &(name, .., f_edition, set) in ACTIVE_FEATURES {
2406 if let Some(f_edition) = f_edition {
2407 if f_edition <= *edition {
2408 // FIXME(Manishearth) there is currently no way to set
2409 // lib features by edition
2410 set(&mut features, DUMMY_SP);
2411 edition_enabled_features.insert(name, *edition);
2419 for attr in krate_attrs {
2420 if !attr.check_name(sym::feature) {
2424 let list = match attr.meta_item_list() {
2429 let bad_input = |span| {
2430 struct_span_err!(span_handler, span, E0556, "malformed `feature` attribute input")
2434 let name = match mi.ident() {
2435 Some(ident) if mi.is_word() => ident.name,
2437 bad_input(mi.span()).span_suggestion(
2439 "expected just one word",
2440 format!("{}", ident.name),
2441 Applicability::MaybeIncorrect,
2446 bad_input(mi.span()).span_label(mi.span(), "expected just one word").emit();
2451 if let Some(edition) = edition_enabled_features.get(&name) {
2456 "the feature `{}` is included in the Rust {} edition",
2463 if ALL_EDITIONS.iter().any(|e| name == e.feature_name()) {
2464 // Handled in the separate loop above.
2468 let removed = REMOVED_FEATURES.iter().find(|f| name == f.0);
2469 let stable_removed = STABLE_REMOVED_FEATURES.iter().find(|f| name == f.0);
2470 if let Some((.., reason)) = removed.or(stable_removed) {
2471 feature_removed(span_handler, mi.span(), *reason);
2475 if let Some((_, since, ..)) = ACCEPTED_FEATURES.iter().find(|f| name == f.0) {
2476 let since = Some(Symbol::intern(since));
2477 features.declared_lang_features.push((name, mi.span(), since));
2481 if let Some(allowed) = allow_features.as_ref() {
2482 if allowed.iter().find(|f| *f == name.as_str()).is_none() {
2483 span_err!(span_handler, mi.span(), E0725,
2484 "the feature `{}` is not in the list of allowed features",
2490 if let Some((.., set)) = ACTIVE_FEATURES.iter().find(|f| name == f.0) {
2491 set(&mut features, mi.span());
2492 features.declared_lang_features.push((name, mi.span(), None));
2496 features.declared_lib_features.push((name, mi.span()));
2503 pub fn check_crate(krate: &ast::Crate,
2505 features: &Features,
2506 plugin_attributes: &[(Symbol, AttributeType)],
2507 unstable: UnstableFeatures) {
2508 maybe_stage_features(&sess.span_diagnostic, krate, unstable);
2514 let visitor = &mut PostExpansionVisitor {
2516 builtin_attributes: &*BUILTIN_ATTRIBUTE_MAP,
2518 visit::walk_crate(visitor, krate);
2521 #[derive(Clone, Copy, Hash)]
2522 pub enum UnstableFeatures {
2523 /// Hard errors for unstable features are active, as on beta/stable channels.
2525 /// Allow features to be activated, as on nightly.
2527 /// Errors are bypassed for bootstrapping. This is required any time
2528 /// during the build that feature-related lints are set to warn or above
2529 /// because the build turns on warnings-as-errors and uses lots of unstable
2530 /// features. As a result, this is always required for building Rust itself.
2534 impl UnstableFeatures {
2535 pub fn from_environment() -> UnstableFeatures {
2536 // Whether this is a feature-staged build, i.e., on the beta or stable channel
2537 let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
2538 // Whether we should enable unstable features for bootstrapping
2539 let bootstrap = env::var("RUSTC_BOOTSTRAP").is_ok();
2540 match (disable_unstable_features, bootstrap) {
2541 (_, true) => UnstableFeatures::Cheat,
2542 (true, _) => UnstableFeatures::Disallow,
2543 (false, _) => UnstableFeatures::Allow
2547 pub fn is_nightly_build(&self) -> bool {
2549 UnstableFeatures::Allow | UnstableFeatures::Cheat => true,
2555 fn maybe_stage_features(span_handler: &Handler, krate: &ast::Crate,
2556 unstable: UnstableFeatures) {
2557 let allow_features = match unstable {
2558 UnstableFeatures::Allow => true,
2559 UnstableFeatures::Disallow => false,
2560 UnstableFeatures::Cheat => true
2562 if !allow_features {
2563 for attr in &krate.attrs {
2564 if attr.check_name(sym::feature) {
2565 let release_channel = option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)");
2566 span_err!(span_handler, attr.span, E0554,
2567 "#![feature] may not be used on the {} release channel",