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
18 use crate::ast::{self, NodeId, GenericParam, GenericParamKind, PatKind, RangeEnd};
20 use crate::early_buffered_lints::BufferedEarlyLintId;
21 use crate::source_map::Spanned;
22 use crate::edition::{ALL_EDITIONS, Edition};
23 use crate::visit::{self, FnKind, Visitor};
24 use crate::parse::{token, ParseSess};
25 use crate::symbol::Symbol;
26 use crate::tokenstream::TokenTree;
28 use errors::{DiagnosticBuilder, Handler};
29 use rustc_data_structures::fx::FxHashMap;
30 use rustc_target::spec::abi::Abi;
31 use syntax_pos::{Span, DUMMY_SP, symbols};
33 use lazy_static::lazy_static;
39 fn f(features: &mut Features, _: Span) {
40 features.$field = true;
42 f as fn(&mut Features, Span)
46 macro_rules! declare_features {
47 ($((active, $feature: ident, $ver: expr, $issue: expr, $edition: expr),)+) => {
48 /// Represents active features that are currently being implemented or
49 /// currently being considered for addition/removal.
50 const ACTIVE_FEATURES:
51 &[(&str, &str, Option<u32>, Option<Edition>, fn(&mut Features, Span))] =
52 &[$((stringify!($feature), $ver, $issue, $edition, set!($feature))),+];
54 /// A set of features to be used by later passes.
57 /// `#![feature]` attrs for language features, for error reporting
58 pub declared_lang_features: Vec<(Symbol, Span, Option<Symbol>)>,
59 /// `#![feature]` attrs for non-language (library) features
60 pub declared_lib_features: Vec<(Symbol, Span)>,
61 $(pub $feature: bool),+
65 pub fn new() -> Features {
67 declared_lang_features: Vec::new(),
68 declared_lib_features: Vec::new(),
73 pub fn walk_feature_fields<F>(&self, mut f: F)
74 where F: FnMut(&str, bool)
76 $(f(stringify!($feature), self.$feature);)+
81 ($((removed, $feature: ident, $ver: expr, $issue: expr, None, $reason: expr),)+) => {
82 /// Represents unstable features which have since been removed (it was once Active)
83 const REMOVED_FEATURES: &[(&str, &str, Option<u32>, Option<&str>)] = &[
84 $((stringify!($feature), $ver, $issue, $reason)),+
88 ($((stable_removed, $feature: ident, $ver: expr, $issue: expr, None),)+) => {
89 /// Represents stable features which have since been removed (it was once Accepted)
90 const STABLE_REMOVED_FEATURES: &[(&str, &str, Option<u32>, Option<&str>)] = &[
91 $((stringify!($feature), $ver, $issue, None)),+
95 ($((accepted, $feature: ident, $ver: expr, $issue: expr, None),)+) => {
96 /// Those language feature has since been Accepted (it was once Active)
97 const ACCEPTED_FEATURES: &[(&str, &str, Option<u32>, Option<&str>)] = &[
98 $((stringify!($feature), $ver, $issue, None)),+
103 // If you change this, please modify `src/doc/unstable-book` as well.
105 // Don't ever remove anything from this list; set them to 'Removed'.
107 // The version numbers here correspond to the version in which the current status
108 // was set. This is most important for knowing when a particular feature became
111 // Note that the features should be grouped into internal/user-facing
112 // and then sorted by version inside those groups. This is inforced with tidy.
114 // N.B., `tools/tidy/src/features.rs` parses this information directly out of the
115 // source, so take care when modifying it.
118 // -------------------------------------------------------------------------
119 // feature-group-start: internal feature gates
120 // -------------------------------------------------------------------------
122 // no tracking issue START
124 // Allows using the `rust-intrinsic`'s "ABI".
125 (active, intrinsics, "1.0.0", None, None),
127 // Allows using `#[lang = ".."]` attribute for linking items to special compiler logic.
128 (active, lang_items, "1.0.0", None, None),
130 // Allows using the `#[stable]` and `#[unstable]` attributes.
131 (active, staged_api, "1.0.0", None, None),
133 // Allows using `#[allow_internal_unstable]`. This is an
134 // attribute on `macro_rules!` and can't use the attribute handling
135 // below (it has to be checked before expansion possibly makes
136 // macros disappear).
137 (active, allow_internal_unstable, "1.0.0", None, None),
139 // Allows using `#[allow_internal_unsafe]`. This is an
140 // attribute on `macro_rules!` and can't use the attribute handling
141 // below (it has to be checked before expansion possibly makes
142 // macros disappear).
143 (active, allow_internal_unsafe, "1.0.0", None, None),
145 // Allows using the macros:
146 // + `__diagnostic_used`
147 // + `__register_diagnostic`
148 // +`__build_diagnostic_array`
149 (active, rustc_diagnostic_macros, "1.0.0", None, None),
151 // Allows using `#[rustc_const_unstable(feature = "foo", ..)]` which
152 // lets a function to be `const` when opted into with `#![feature(foo)]`.
153 (active, rustc_const_unstable, "1.0.0", None, None),
155 // no tracking issue END
157 // Allows using `#[link_name="llvm.*"]`.
158 (active, link_llvm_intrinsics, "1.0.0", Some(29602), None),
160 // Allows using `rustc_*` attributes (RFC 572).
161 (active, rustc_attrs, "1.0.0", Some(29642), None),
163 // Allows using `#[on_unimplemented(..)]` on traits.
164 (active, on_unimplemented, "1.0.0", Some(29628), None),
166 // Allows using the `box $expr` syntax.
167 (active, box_syntax, "1.0.0", Some(49733), None),
169 // Allows using `#[main]` to replace the entrypoint `#[lang = "start"]` calls.
170 (active, main, "1.0.0", Some(29634), None),
172 // Allows using `#[start]` on a function indicating that it is the program entrypoint.
173 (active, start, "1.0.0", Some(29633), None),
175 // Allows using the `#[fundamental]` attribute.
176 (active, fundamental, "1.0.0", Some(29635), None),
178 // Allows using the `rust-call` ABI.
179 (active, unboxed_closures, "1.0.0", Some(29625), None),
181 // Allows using the `#[linkage = ".."]` attribute.
182 (active, linkage, "1.0.0", Some(29603), None),
184 // Allows features specific to OIBIT (auto traits).
185 (active, optin_builtin_traits, "1.0.0", Some(13231), None),
187 // Allows using `box` in patterns (RFC 469).
188 (active, box_patterns, "1.0.0", Some(29641), None),
190 // no tracking issue START
192 // Allows using `#[prelude_import]` on glob `use` items.
193 (active, prelude_import, "1.2.0", None, None),
195 // no tracking issue END
197 // Allows using `#[unsafe_destructor_blind_to_params]` (RFC 1238).
198 (active, dropck_parametricity, "1.3.0", Some(28498), None),
200 // FIXME(Centril): Investigate whether this gate actually has any effect.
201 (active, needs_allocator, "1.4.0", Some(27389), 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 reinterpretation of the bits of a value of one type as another type during const eval.
489 (active, const_transmute, "1.29.0", Some(53605), None),
491 // Allows using `try {...}` expressions.
492 (active, try_blocks, "1.29.0", Some(31436), None),
494 // Allows defining an `#[alloc_error_handler]`.
495 (active, alloc_error_handler, "1.29.0", Some(51540), None),
497 // Allows using the `amdgpu-kernel` ABI.
498 (active, abi_amdgpu_kernel, "1.29.0", Some(51575), None),
500 // Allows panicking during const eval (producing compile-time errors).
501 (active, const_panic, "1.30.0", Some(51999), None),
503 // Allows `#[marker]` on certain traits allowing overlapping implementations.
504 (active, marker_trait_attr, "1.30.0", Some(29864), None),
506 // Allows macro invocations on modules expressions and statements and
507 // procedural macros to expand to non-items.
508 (active, proc_macro_hygiene, "1.30.0", Some(54727), None),
510 // Allows unsized rvalues at arguments and parameters.
511 (active, unsized_locals, "1.30.0", Some(48055), None),
513 // Allows custom test frameworks with `#![test_runner]` and `#[test_case]`.
514 (active, custom_test_frameworks, "1.30.0", Some(50297), None),
516 // Allows non-builtin attributes in inner attribute position.
517 (active, custom_inner_attributes, "1.30.0", Some(54726), None),
519 // Allows mixing bind-by-move in patterns and references to those identifiers in guards.
520 (active, bind_by_move_pattern_guards, "1.30.0", Some(15287), None),
522 // Allows `impl Trait` in bindings (`let`, `const`, `static`).
523 (active, impl_trait_in_bindings, "1.30.0", Some(34511), None),
525 // Allows `const _: TYPE = VALUE`.
526 (active, underscore_const_names, "1.31.0", Some(54912), None),
528 // Allows using `reason` in lint attributes and the `#[expect(lint)]` lint check.
529 (active, lint_reasons, "1.31.0", Some(54503), None),
531 // Allows paths to enum variants on type aliases.
532 (active, type_alias_enum_variants, "1.31.0", Some(49683), None),
534 // Allows exhaustive integer pattern matching on `usize` and `isize`.
535 (active, precise_pointer_size_matching, "1.32.0", Some(56354), None),
537 // Allows relaxing the coherence rules such that
538 // `impl<T> ForeignTrait<LocalType> for ForeignType<T> is permitted.
539 (active, re_rebalance_coherence, "1.32.0", Some(55437), None),
541 // Allows using `#[ffi_returns_twice]` on foreign functions.
542 (active, ffi_returns_twice, "1.34.0", Some(58314), None),
544 // Allows const generic types (e.g. `struct Foo<const N: usize>(...);`).
545 (active, const_generics, "1.34.0", Some(44580), None),
547 // Allows using `#[optimize(X)]`.
548 (active, optimize_attribute, "1.34.0", Some(54882), None),
550 // Allows using `#[repr(align(X))]` on enums.
551 (active, repr_align_enum, "1.34.0", Some(57996), None),
553 // Allows using C-variadics.
554 (active, c_variadic, "1.34.0", Some(44930), None),
556 // -------------------------------------------------------------------------
557 // feature-group-end: actual feature gates
558 // -------------------------------------------------------------------------
561 // Some features are known to be incomplete and using them is likely to have
562 // unanticipated results, such as compiler crashes. We warn the user about these
564 const INCOMPLETE_FEATURES: &[&str] = &[
565 "generic_associated_types",
570 (removed, import_shadowing, "1.0.0", None, None, None),
571 (removed, managed_boxes, "1.0.0", None, None, None),
572 // Allows use of unary negate on unsigned integers, e.g., -e for e: u8
573 (removed, negate_unsigned, "1.0.0", Some(29645), None, None),
574 (removed, reflect, "1.0.0", Some(27749), None, None),
575 // A way to temporarily opt out of opt in copy. This will *never* be accepted.
576 (removed, opt_out_copy, "1.0.0", None, None, None),
577 (removed, quad_precision_float, "1.0.0", None, None, None),
578 (removed, struct_inherit, "1.0.0", None, None, None),
579 (removed, test_removed_feature, "1.0.0", None, None, None),
580 (removed, visible_private_types, "1.0.0", None, None, None),
581 (removed, unsafe_no_drop_flag, "1.0.0", None, None, None),
582 // Allows using items which are missing stability attributes
583 (removed, unmarked_api, "1.0.0", None, None, None),
584 (removed, pushpop_unsafe, "1.2.0", None, None, None),
585 (removed, allocator, "1.0.0", None, None, None),
586 (removed, simd, "1.0.0", Some(27731), None,
587 Some("removed in favor of `#[repr(simd)]`")),
588 (removed, advanced_slice_patterns, "1.0.0", Some(23121), None,
589 Some("merged into `#![feature(slice_patterns)]`")),
590 (removed, macro_reexport, "1.0.0", Some(29638), None,
591 Some("subsumed by `pub use`")),
592 (removed, proc_macro_mod, "1.27.0", Some(54727), None,
593 Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
594 (removed, proc_macro_expr, "1.27.0", Some(54727), None,
595 Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
596 (removed, proc_macro_non_items, "1.27.0", Some(54727), None,
597 Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
598 (removed, proc_macro_gen, "1.27.0", Some(54727), None,
599 Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
600 (removed, panic_implementation, "1.28.0", Some(44489), None,
601 Some("subsumed by `#[panic_handler]`")),
602 // Allows the use of `#[derive(Anything)]` as sugar for `#[derive_Anything]`.
603 (removed, custom_derive, "1.0.0", Some(29644), None,
604 Some("subsumed by `#[proc_macro_derive]`")),
605 // Paths of the form: `extern::foo::bar`
606 (removed, extern_in_paths, "1.33.0", Some(55600), None,
607 Some("subsumed by `::foo::bar` paths")),
608 (removed, quote, "1.0.0", Some(29601), None, None),
612 (stable_removed, no_stack_check, "1.0.0", None, None),
616 // A temporary feature gate used to enable parser extensions needed
617 // to bootstrap fix for #5723.
618 (accepted, issue_5723_bootstrap, "1.0.0", None, None),
619 // These are used to test this portion of the compiler,
620 // they don't actually mean anything.
621 (accepted, test_accepted_feature, "1.0.0", None, None),
623 // Allows using associated `type`s in `trait`s.
624 (accepted, associated_types, "1.0.0", None, None),
625 // Allows using assigning a default type to type parameters in algebraic data type definitions.
626 (accepted, default_type_params, "1.0.0", None, None),
627 // FIXME: explain `globs`.
628 (accepted, globs, "1.0.0", None, None),
629 // Allows `macro_rules!` items.
630 (accepted, macro_rules, "1.0.0", None, None),
631 // Allows use of `&foo[a..b]` as a slicing syntax.
632 (accepted, slicing_syntax, "1.0.0", None, None),
633 // Allows struct variants `Foo { baz: u8, .. }` in enums (RFC 418).
634 (accepted, struct_variant, "1.0.0", None, None),
635 // Allows indexing tuples.
636 (accepted, tuple_indexing, "1.0.0", None, None),
637 // Allows the use of `if let` expressions.
638 (accepted, if_let, "1.0.0", None, None),
639 // Allows the use of `while let` expressions.
640 (accepted, while_let, "1.0.0", None, None),
641 // Allows using `#![no_std]`.
642 (accepted, no_std, "1.6.0", None, None),
643 // Allows overloading augmented assignment operations like `a += b`.
644 (accepted, augmented_assignments, "1.8.0", Some(28235), None),
645 // Allows empty structs and enum variants with braces.
646 (accepted, braced_empty_structs, "1.8.0", Some(29720), None),
647 // Allows `#[deprecated]` attribute.
648 (accepted, deprecated, "1.9.0", Some(29935), None),
649 // Allows macros to appear in the type position.
650 (accepted, type_macros, "1.13.0", Some(27245), None),
651 // Allows use of the postfix `?` operator in expressions.
652 (accepted, question_mark, "1.13.0", Some(31436), None),
653 // Allows `..` in tuple (struct) patterns.
654 (accepted, dotdot_in_tuple_patterns, "1.14.0", Some(33627), None),
655 // Allows some increased flexibility in the name resolution rules,
656 // especially around globs and shadowing (RFC 1560).
657 (accepted, item_like_imports, "1.15.0", Some(35120), None),
658 // Allows using `Self` and associated types in struct expressions and patterns.
659 (accepted, more_struct_aliases, "1.16.0", Some(37544), None),
660 // Allows elision of `'static` lifetimes in `static`s and `const`s.
661 (accepted, static_in_const, "1.17.0", Some(35897), None),
662 // Allows field shorthands (`x` meaning `x: x`) in struct literal expressions.
663 (accepted, field_init_shorthand, "1.17.0", Some(37340), None),
664 // Allows the definition recursive static items.
665 (accepted, static_recursion, "1.17.0", Some(29719), None),
666 // Allows `pub(restricted)` visibilities (RFC 1422).
667 (accepted, pub_restricted, "1.18.0", Some(32409), None),
668 // Allows `#![windows_subsystem]`.
669 (accepted, windows_subsystem, "1.18.0", Some(37499), None),
670 // Allows `break {expr}` with a value inside `loop`s.
671 (accepted, loop_break_value, "1.19.0", Some(37339), None),
672 // Allows numeric fields in struct expressions and patterns.
673 (accepted, relaxed_adts, "1.19.0", Some(35626), None),
674 // Allows coercing non capturing closures to function pointers.
675 (accepted, closure_to_fn_coercion, "1.19.0", Some(39817), None),
676 // Allows attributes on struct literal fields.
677 (accepted, struct_field_attributes, "1.20.0", Some(38814), None),
678 // Allows the definition of associated constants in `trait` or `impl` blocks.
679 (accepted, associated_consts, "1.20.0", Some(29646), None),
680 // Allows usage of the `compile_error!` macro.
681 (accepted, compile_error, "1.20.0", Some(40872), None),
682 // Allows code like `let x: &'static u32 = &42` to work (RFC 1414).
683 (accepted, rvalue_static_promotion, "1.21.0", Some(38865), None),
684 // Allows `Drop` types in constants (RFC 1440).
685 (accepted, drop_types_in_const, "1.22.0", Some(33156), None),
686 // Allows the sysV64 ABI to be specified on all platforms
687 // instead of just the platforms on which it is the C ABI.
688 (accepted, abi_sysv64, "1.24.0", Some(36167), None),
689 // Allows `repr(align(16))` struct attribute (RFC 1358).
690 (accepted, repr_align, "1.25.0", Some(33626), None),
691 // Allows '|' at beginning of match arms (RFC 1925).
692 (accepted, match_beginning_vert, "1.25.0", Some(44101), None),
693 // Allows nested groups in `use` items (RFC 2128).
694 (accepted, use_nested_groups, "1.25.0", Some(44494), None),
695 // Allows indexing into constant arrays.
696 (accepted, const_indexing, "1.26.0", Some(29947), None),
697 // Allows using `a..=b` and `..=b` as inclusive range syntaxes.
698 (accepted, inclusive_range_syntax, "1.26.0", Some(28237), None),
699 // Allows `..=` in patterns (RFC 1192).
700 (accepted, dotdoteq_in_patterns, "1.26.0", Some(28237), None),
701 // Allows `fn main()` with return types which implements `Termination` (RFC 1937).
702 (accepted, termination_trait, "1.26.0", Some(43301), None),
703 // Allows implementing `Clone` for closures where possible (RFC 2132).
704 (accepted, clone_closures, "1.26.0", Some(44490), None),
705 // Allows implementing `Copy` for closures where possible (RFC 2132).
706 (accepted, copy_closures, "1.26.0", Some(44490), None),
707 // Allows `impl Trait` in function arguments.
708 (accepted, universal_impl_trait, "1.26.0", Some(34511), None),
709 // Allows `impl Trait` in function return types.
710 (accepted, conservative_impl_trait, "1.26.0", Some(34511), None),
711 // Allows using the `u128` and `i128` types.
712 (accepted, i128_type, "1.26.0", Some(35118), None),
713 // Allows default match binding modes (RFC 2005).
714 (accepted, match_default_bindings, "1.26.0", Some(42640), None),
715 // Allows `'_` placeholder lifetimes.
716 (accepted, underscore_lifetimes, "1.26.0", Some(44524), None),
717 // Allows attributes on lifetime/type formal parameters in generics (RFC 1327).
718 (accepted, generic_param_attrs, "1.27.0", Some(48848), None),
719 // Allows `cfg(target_feature = "...")`.
720 (accepted, cfg_target_feature, "1.27.0", Some(29717), None),
721 // Allows `#[target_feature(...)]`.
722 (accepted, target_feature, "1.27.0", None, None),
723 // Allows using `dyn Trait` as a syntax for trait objects.
724 (accepted, dyn_trait, "1.27.0", Some(44662), None),
725 // Allows `#[must_use]` on functions, and introduces must-use operators (RFC 1940).
726 (accepted, fn_must_use, "1.27.0", Some(43302), None),
727 // Allows use of the `:lifetime` macro fragment specifier.
728 (accepted, macro_lifetime_matcher, "1.27.0", Some(34303), None),
729 // Allows `#[test]` functions where the return type implements `Termination` (RFC 1937).
730 (accepted, termination_trait_test, "1.27.0", Some(48854), None),
731 // Allows the `#[global_allocator]` attribute.
732 (accepted, global_allocator, "1.28.0", Some(27389), None),
733 // Allows `#[repr(transparent)]` attribute on newtype structs.
734 (accepted, repr_transparent, "1.28.0", Some(43036), None),
735 // Allows procedural macros in `proc-macro` crates.
736 (accepted, proc_macro, "1.29.0", Some(38356), None),
737 // Allows `foo.rs` as an alternative to `foo/mod.rs`.
738 (accepted, non_modrs_mods, "1.30.0", Some(44660), None),
739 // Allows use of the `:vis` macro fragment specifier
740 (accepted, macro_vis_matcher, "1.30.0", Some(41022), None),
741 // Allows importing and reexporting macros with `use`,
742 // enables macro modularization in general.
743 (accepted, use_extern_macros, "1.30.0", Some(35896), None),
744 // Allows keywords to be escaped for use as identifiers.
745 (accepted, raw_identifiers, "1.30.0", Some(48589), None),
746 // Allows attributes scoped to tools.
747 (accepted, tool_attributes, "1.30.0", Some(44690), None),
748 // Allows multi-segment paths in attributes and derives.
749 (accepted, proc_macro_path_invoc, "1.30.0", Some(38356), None),
750 // Allows all literals in attribute lists and values of key-value pairs.
751 (accepted, attr_literals, "1.30.0", Some(34981), None),
752 // Allows inferring outlives requirements (RFC 2093).
753 (accepted, infer_outlives_requirements, "1.30.0", Some(44493), None),
754 // Allows annotating functions conforming to `fn(&PanicInfo) -> !` with `#[panic_handler]`.
755 // This defines the behavior of panics.
756 (accepted, panic_handler, "1.30.0", Some(44489), None),
757 // Allows `#[used]` to preserve symbols (see llvm.used).
758 (accepted, used, "1.30.0", Some(40289), None),
759 // Allows `crate` in paths.
760 (accepted, crate_in_paths, "1.30.0", Some(45477), None),
761 // Allows resolving absolute paths as paths from other crates.
762 (accepted, extern_absolute_paths, "1.30.0", Some(44660), None),
763 // Allows access to crate names passed via `--extern` through prelude.
764 (accepted, extern_prelude, "1.30.0", Some(44660), None),
765 // Allows parentheses in patterns.
766 (accepted, pattern_parentheses, "1.31.0", Some(51087), None),
767 // Allows the definition of `const fn` functions.
768 (accepted, min_const_fn, "1.31.0", Some(53555), None),
769 // Allows scoped lints.
770 (accepted, tool_lints, "1.31.0", Some(44690), None),
771 // Allows lifetime elision in `impl` headers. For example:
772 // + `impl<I:Iterator> Iterator for &mut Iterator`
773 // + `impl Debug for Foo<'_>`
774 (accepted, impl_header_lifetime_elision, "1.31.0", Some(15872), None),
775 // Allows `extern crate foo as bar;`. This puts `bar` into extern prelude.
776 (accepted, extern_crate_item_prelude, "1.31.0", Some(55599), None),
777 // Allows use of the `:literal` macro fragment specifier (RFC 1576).
778 (accepted, macro_literal_matcher, "1.32.0", Some(35625), None),
779 // Allows use of `?` as the Kleene "at most one" operator in macros.
780 (accepted, macro_at_most_once_rep, "1.32.0", Some(48075), None),
781 // Allows `Self` struct constructor (RFC 2302).
782 (accepted, self_struct_ctor, "1.32.0", Some(51994), None),
783 // Allows `Self` in type definitions (RFC 2300).
784 (accepted, self_in_typedefs, "1.32.0", Some(49303), None),
785 // Allows `use x::y;` to search `x` in the current scope.
786 (accepted, uniform_paths, "1.32.0", Some(53130), None),
787 // Allows integer match exhaustiveness checking (RFC 2591).
788 (accepted, exhaustive_integer_patterns, "1.33.0", Some(50907), None),
789 // Allows `use path as _;` and `extern crate c as _;`.
790 (accepted, underscore_imports, "1.33.0", Some(48216), None),
791 // Allows `#[repr(packed(N))]` attribute on structs.
792 (accepted, repr_packed, "1.33.0", Some(33158), None),
793 // Allows irrefutable patterns in `if let` and `while let` statements (RFC 2086).
794 (accepted, irrefutable_let_patterns, "1.33.0", Some(44495), None),
795 // Allows calling `const unsafe fn` inside `unsafe` blocks in `const fn` functions.
796 (accepted, min_const_unsafe_fn, "1.33.0", Some(55607), None),
797 // Allows let bindings, assignments and destructuring in `const` functions and constants.
798 // As long as control flow is not implemented in const eval, `&&` and `||` may not be used
799 // at the same time as let bindings.
800 (accepted, const_let, "1.33.0", Some(48821), None),
801 // Allows `#[cfg_attr(predicate, multiple, attributes, here)]`.
802 (accepted, cfg_attr_multi, "1.33.0", Some(54881), None),
803 // Allows top level or-patterns (`p | q`) in `if let` and `while let`.
804 (accepted, if_while_or_patterns, "1.33.0", Some(48215), None),
805 // Allows `cfg(target_vendor = "...")`.
806 (accepted, cfg_target_vendor, "1.33.0", Some(29718), None),
807 // Allows `extern crate self as foo;`.
808 // This puts local crate root into extern prelude under name `foo`.
809 (accepted, extern_crate_self, "1.34.0", Some(56409), None),
810 // Allows arbitrary delimited token streams in non-macro attributes.
811 (accepted, unrestricted_attribute_tokens, "1.34.0", Some(55208), None),
814 // If you change this, please modify `src/doc/unstable-book` as well. You must
815 // move that documentation into the relevant place in the other docs, and
816 // remove the chapter on the flag.
818 #[derive(Copy, Clone, PartialEq, Debug)]
819 pub enum AttributeType {
820 /// Normal, builtin attribute that is consumed
821 /// by the compiler before the unused_attribute check
824 /// Builtin attribute that may not be consumed by the compiler
825 /// before the unused_attribute check. These attributes
826 /// will be ignored by the unused_attribute lint
829 /// Builtin attribute that is only allowed at the crate level
833 pub enum AttributeGate {
834 /// Is gated by a given feature gate, reason
835 /// and function to check if enabled
836 Gated(Stability, &'static str, &'static str, fn(&Features) -> bool),
838 /// Ungated attribute, can be used on all release channels
842 /// A template that the attribute input must match.
843 /// Only top-level shape (`#[attr]` vs `#[attr(...)]` vs `#[attr = ...]`) is considered now.
844 #[derive(Clone, Copy)]
845 pub struct AttributeTemplate {
847 list: Option<&'static str>,
848 name_value_str: Option<&'static str>,
851 impl AttributeTemplate {
852 /// Checks that the given meta-item is compatible with this template.
853 fn compatible(&self, meta_item_kind: &ast::MetaItemKind) -> bool {
854 match meta_item_kind {
855 ast::MetaItemKind::Word => self.word,
856 ast::MetaItemKind::List(..) => self.list.is_some(),
857 ast::MetaItemKind::NameValue(lit) if lit.node.is_str() => self.name_value_str.is_some(),
858 ast::MetaItemKind::NameValue(..) => false,
863 /// A convenience macro for constructing attribute templates.
864 /// E.g., `template!(Word, List: "description")` means that the attribute
865 /// supports forms `#[attr]` and `#[attr(description)]`.
866 macro_rules! template {
867 (Word) => { template!(@ true, None, None) };
868 (List: $descr: expr) => { template!(@ false, Some($descr), None) };
869 (NameValueStr: $descr: expr) => { template!(@ false, None, Some($descr)) };
870 (Word, List: $descr: expr) => { template!(@ true, Some($descr), None) };
871 (Word, NameValueStr: $descr: expr) => { template!(@ true, None, Some($descr)) };
872 (List: $descr1: expr, NameValueStr: $descr2: expr) => {
873 template!(@ false, Some($descr1), Some($descr2))
875 (Word, List: $descr1: expr, NameValueStr: $descr2: expr) => {
876 template!(@ true, Some($descr1), Some($descr2))
878 (@ $word: expr, $list: expr, $name_value_str: expr) => { AttributeTemplate {
879 word: $word, list: $list, name_value_str: $name_value_str
884 fn is_deprecated(&self) -> bool {
886 Gated(Stability::Deprecated(_, _), ..) => true,
892 #[derive(Copy, Clone, Debug)]
895 // First argument is tracking issue link; second argument is an optional
896 // help message, which defaults to "remove this attribute"
897 Deprecated(&'static str, Option<&'static str>),
901 impl std::fmt::Debug for AttributeGate {
902 fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
904 Gated(ref stab, name, expl, _) =>
905 write!(fmt, "Gated({:?}, {}, {})", stab, name, expl),
906 Ungated => write!(fmt, "Ungated")
911 macro_rules! cfg_fn {
912 ($field: ident) => {{
913 fn f(features: &Features) -> bool {
916 f as fn(&Features) -> bool
920 pub fn deprecated_attributes() -> Vec<&'static (Symbol, AttributeType,
921 AttributeTemplate, AttributeGate)> {
922 BUILTIN_ATTRIBUTES.iter().filter(|(.., gate)| gate.is_deprecated()).collect()
925 pub fn is_builtin_attr_name(name: ast::Name) -> bool {
926 BUILTIN_ATTRIBUTE_MAP.get(&name).is_some()
929 pub fn is_builtin_attr(attr: &ast::Attribute) -> bool {
930 attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name)).is_some()
933 /// Attributes that have a special meaning to rustc or rustdoc
934 pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
940 template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#),
946 template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#),
952 template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#),
958 template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#),
962 (symbols::macro_use, Normal, template!(Word, List: "name1, name2, ..."), Ungated),
963 (symbols::macro_export, Normal, template!(Word, List: "local_inner_macros"), Ungated),
964 (symbols::plugin_registrar, Normal, template!(Word), Ungated),
966 (symbols::cfg, Normal, template!(List: "predicate"), Ungated),
967 (symbols::cfg_attr, Normal, template!(List: "predicate, attr1, attr2, ..."), Ungated),
968 (symbols::main, Normal, template!(Word), Ungated),
969 (symbols::start, Normal, template!(Word), Ungated),
970 (symbols::repr, Normal, template!(List: "C, packed, ..."), Ungated),
971 (symbols::path, Normal, template!(NameValueStr: "file"), Ungated),
972 (symbols::automatically_derived, Normal, template!(Word), Ungated),
973 (symbols::no_mangle, Normal, template!(Word), Ungated),
974 (symbols::no_link, Normal, template!(Word), Ungated),
975 (symbols::derive, Normal, template!(List: "Trait1, Trait2, ..."), Ungated),
977 symbols::should_panic,
979 template!(Word, List: r#"expected = "reason"#, NameValueStr: "reason"),
982 (symbols::ignore, Normal, template!(Word, NameValueStr: "reason"), Ungated),
983 (symbols::no_implicit_prelude, Normal, template!(Word), Ungated),
984 (symbols::reexport_test_harness_main, Normal, template!(NameValueStr: "name"), Ungated),
985 (symbols::link_args, Normal, template!(NameValueStr: "args"), Gated(Stability::Unstable,
987 "the `link_args` attribute is experimental and not \
988 portable across platforms, it is recommended to \
989 use `#[link(name = \"foo\")] instead",
990 cfg_fn!(link_args))),
991 (symbols::macro_escape, Normal, template!(Word), Ungated),
994 (symbols::structural_match, Whitelisted, template!(Word), Gated(Stability::Unstable,
996 "the semantics of constant patterns is \
998 cfg_fn!(structural_match))),
1001 (symbols::non_exhaustive, Whitelisted, template!(Word), Gated(Stability::Unstable,
1003 "non exhaustive is an experimental feature",
1004 cfg_fn!(non_exhaustive))),
1007 (symbols::marker, Normal, template!(Word), Gated(Stability::Unstable,
1008 "marker_trait_attr",
1009 "marker traits is an experimental feature",
1010 cfg_fn!(marker_trait_attr))),
1012 (symbols::plugin, CrateLevel, template!(List: "name|name(args)"), Gated(Stability::Unstable,
1014 "compiler plugins are experimental \
1015 and possibly buggy",
1018 (symbols::no_std, CrateLevel, template!(Word), Ungated),
1019 (symbols::no_core, CrateLevel, template!(Word), Gated(Stability::Unstable,
1021 "no_core is experimental",
1023 (symbols::lang, Normal, template!(NameValueStr: "name"), Gated(Stability::Unstable,
1025 "language items are subject to change",
1026 cfg_fn!(lang_items))),
1027 (symbols::linkage, Whitelisted, template!(NameValueStr: "external|internal|..."),
1028 Gated(Stability::Unstable,
1030 "the `linkage` attribute is experimental \
1031 and not portable across platforms",
1033 (symbols::thread_local, Whitelisted, template!(Word), Gated(Stability::Unstable,
1035 "`#[thread_local]` is an experimental feature, and does \
1036 not currently handle destructors",
1037 cfg_fn!(thread_local))),
1039 (symbols::rustc_on_unimplemented, Whitelisted, template!(List:
1040 r#"/*opt*/ message = "...", /*opt*/ label = "...", /*opt*/ note = "...""#,
1041 NameValueStr: "message"),
1042 Gated(Stability::Unstable,
1044 "the `#[rustc_on_unimplemented]` attribute \
1045 is an experimental feature",
1046 cfg_fn!(on_unimplemented))),
1047 (symbols::rustc_const_unstable, Normal, template!(List: r#"feature = "name""#),
1048 Gated(Stability::Unstable,
1049 "rustc_const_unstable",
1050 "the `#[rustc_const_unstable]` attribute \
1051 is an internal feature",
1052 cfg_fn!(rustc_const_unstable))),
1053 (symbols::global_allocator, Normal, template!(Word), Ungated),
1054 (symbols::default_lib_allocator, Whitelisted, template!(Word), Gated(Stability::Unstable,
1055 "allocator_internals",
1056 "the `#[default_lib_allocator]` \
1057 attribute is an experimental feature",
1058 cfg_fn!(allocator_internals))),
1059 (symbols::needs_allocator, Normal, template!(Word), Gated(Stability::Unstable,
1060 "allocator_internals",
1061 "the `#[needs_allocator]` \
1062 attribute is an experimental \
1064 cfg_fn!(allocator_internals))),
1065 (symbols::panic_runtime, Whitelisted, template!(Word), Gated(Stability::Unstable,
1067 "the `#[panic_runtime]` attribute is \
1068 an experimental feature",
1069 cfg_fn!(panic_runtime))),
1070 (symbols::needs_panic_runtime, Whitelisted, template!(Word), Gated(Stability::Unstable,
1071 "needs_panic_runtime",
1072 "the `#[needs_panic_runtime]` \
1073 attribute is an experimental \
1075 cfg_fn!(needs_panic_runtime))),
1076 (symbols::rustc_outlives, Normal, template!(Word), Gated(Stability::Unstable,
1078 "the `#[rustc_outlives]` attribute \
1079 is just used for rustc unit tests \
1080 and will never be stable",
1081 cfg_fn!(rustc_attrs))),
1082 (symbols::rustc_variance, Normal, template!(Word), Gated(Stability::Unstable,
1084 "the `#[rustc_variance]` attribute \
1085 is just used for rustc unit tests \
1086 and will never be stable",
1087 cfg_fn!(rustc_attrs))),
1088 (symbols::rustc_layout, Normal, template!(List: "field1, field2, ..."),
1089 Gated(Stability::Unstable,
1091 "the `#[rustc_layout]` attribute \
1092 is just used for rustc unit tests \
1093 and will never be stable",
1094 cfg_fn!(rustc_attrs))),
1095 (symbols::rustc_layout_scalar_valid_range_start, Whitelisted, template!(List: "value"),
1096 Gated(Stability::Unstable,
1098 "the `#[rustc_layout_scalar_valid_range_start]` attribute \
1099 is just used to enable niche optimizations in libcore \
1100 and will never be stable",
1101 cfg_fn!(rustc_attrs))),
1102 (symbols::rustc_layout_scalar_valid_range_end, Whitelisted, template!(List: "value"),
1103 Gated(Stability::Unstable,
1105 "the `#[rustc_layout_scalar_valid_range_end]` attribute \
1106 is just used to enable niche optimizations in libcore \
1107 and will never be stable",
1108 cfg_fn!(rustc_attrs))),
1109 (symbols::rustc_regions, Normal, template!(Word), Gated(Stability::Unstable,
1111 "the `#[rustc_regions]` attribute \
1112 is just used for rustc unit tests \
1113 and will never be stable",
1114 cfg_fn!(rustc_attrs))),
1115 (symbols::rustc_error, Whitelisted, template!(Word), Gated(Stability::Unstable,
1117 "the `#[rustc_error]` attribute \
1118 is just used for rustc unit tests \
1119 and will never be stable",
1120 cfg_fn!(rustc_attrs))),
1121 (symbols::rustc_dump_user_substs, Whitelisted, template!(Word), Gated(Stability::Unstable,
1124 is just used for rustc unit tests \
1125 and will never be stable",
1126 cfg_fn!(rustc_attrs))),
1127 (symbols::rustc_if_this_changed, Whitelisted, template!(Word, List: "DepNode"),
1128 Gated(Stability::Unstable,
1130 "the `#[rustc_if_this_changed]` attribute \
1131 is just used for rustc unit tests \
1132 and will never be stable",
1133 cfg_fn!(rustc_attrs))),
1134 (symbols::rustc_then_this_would_need, Whitelisted, template!(List: "DepNode"),
1135 Gated(Stability::Unstable,
1137 "the `#[rustc_if_this_changed]` attribute \
1138 is just used for rustc unit tests \
1139 and will never be stable",
1140 cfg_fn!(rustc_attrs))),
1141 (symbols::rustc_dirty, Whitelisted, template!(List: r#"cfg = "...", /*opt*/ label = "...",
1142 /*opt*/ except = "...""#),
1143 Gated(Stability::Unstable,
1145 "the `#[rustc_dirty]` attribute \
1146 is just used for rustc unit tests \
1147 and will never be stable",
1148 cfg_fn!(rustc_attrs))),
1149 (symbols::rustc_clean, Whitelisted, template!(List: r#"cfg = "...", /*opt*/ label = "...",
1150 /*opt*/ except = "...""#),
1151 Gated(Stability::Unstable,
1153 "the `#[rustc_clean]` attribute \
1154 is just used for rustc unit tests \
1155 and will never be stable",
1156 cfg_fn!(rustc_attrs))),
1158 symbols::rustc_partition_reused,
1160 template!(List: r#"cfg = "...", module = "...""#),
1162 Stability::Unstable,
1165 is just used for rustc unit tests \
1166 and will never be stable",
1167 cfg_fn!(rustc_attrs)
1171 symbols::rustc_partition_codegened,
1173 template!(List: r#"cfg = "...", module = "...""#),
1175 Stability::Unstable,
1178 is just used for rustc unit tests \
1179 and will never be stable",
1180 cfg_fn!(rustc_attrs),
1183 (symbols::rustc_expected_cgu_reuse, Whitelisted, template!(List: r#"cfg = "...", module = "...",
1185 Gated(Stability::Unstable,
1188 is just used for rustc unit tests \
1189 and will never be stable",
1190 cfg_fn!(rustc_attrs))),
1191 (symbols::rustc_synthetic, Whitelisted, template!(Word), Gated(Stability::Unstable,
1194 is just used for rustc unit tests \
1195 and will never be stable",
1196 cfg_fn!(rustc_attrs))),
1197 (symbols::rustc_symbol_name, Whitelisted, template!(Word), Gated(Stability::Unstable,
1199 "internal rustc attributes will never be stable",
1200 cfg_fn!(rustc_attrs))),
1201 (symbols::rustc_def_path, Whitelisted, template!(Word), Gated(Stability::Unstable,
1203 "internal rustc attributes will never be stable",
1204 cfg_fn!(rustc_attrs))),
1205 (symbols::rustc_mir, Whitelisted, template!(List: "arg1, arg2, ..."), Gated(Stability::Unstable,
1207 "the `#[rustc_mir]` attribute \
1208 is just used for rustc unit tests \
1209 and will never be stable",
1210 cfg_fn!(rustc_attrs))),
1212 symbols::rustc_inherit_overflow_checks,
1216 Stability::Unstable,
1218 "the `#[rustc_inherit_overflow_checks]` \
1219 attribute is just used to control \
1220 overflow checking behavior of several \
1221 libcore functions that are inlined \
1222 across crates and will never be stable",
1223 cfg_fn!(rustc_attrs),
1227 (symbols::rustc_dump_program_clauses, Whitelisted, template!(Word), Gated(Stability::Unstable,
1229 "the `#[rustc_dump_program_clauses]` \
1230 attribute is just used for rustc unit \
1231 tests and will never be stable",
1232 cfg_fn!(rustc_attrs))),
1233 (symbols::rustc_test_marker, Normal, template!(Word), Gated(Stability::Unstable,
1235 "the `#[rustc_test_marker]` attribute \
1236 is used internally to track tests",
1237 cfg_fn!(rustc_attrs))),
1238 (symbols::rustc_transparent_macro, Whitelisted, template!(Word), Gated(Stability::Unstable,
1240 "used internally for testing macro hygiene",
1241 cfg_fn!(rustc_attrs))),
1242 (symbols::compiler_builtins, Whitelisted, template!(Word), Gated(Stability::Unstable,
1243 "compiler_builtins",
1244 "the `#[compiler_builtins]` attribute is used to \
1245 identify the `compiler_builtins` crate which \
1246 contains compiler-rt intrinsics and will never be \
1248 cfg_fn!(compiler_builtins))),
1249 (symbols::sanitizer_runtime, Whitelisted, template!(Word), Gated(Stability::Unstable,
1250 "sanitizer_runtime",
1251 "the `#[sanitizer_runtime]` attribute is used to \
1252 identify crates that contain the runtime of a \
1253 sanitizer and will never be stable",
1254 cfg_fn!(sanitizer_runtime))),
1255 (symbols::profiler_runtime, Whitelisted, template!(Word), Gated(Stability::Unstable,
1257 "the `#[profiler_runtime]` attribute is used to \
1258 identify the `profiler_builtins` crate which \
1259 contains the profiler runtime and will never be \
1261 cfg_fn!(profiler_runtime))),
1263 (symbols::allow_internal_unstable, Normal, template!(Word, List: "feat1, feat2, ..."),
1264 Gated(Stability::Unstable,
1265 "allow_internal_unstable",
1266 EXPLAIN_ALLOW_INTERNAL_UNSTABLE,
1267 cfg_fn!(allow_internal_unstable))),
1269 (symbols::allow_internal_unsafe, Normal, template!(Word), Gated(Stability::Unstable,
1270 "allow_internal_unsafe",
1271 EXPLAIN_ALLOW_INTERNAL_UNSAFE,
1272 cfg_fn!(allow_internal_unsafe))),
1274 (symbols::fundamental, Whitelisted, template!(Word), Gated(Stability::Unstable,
1276 "the `#[fundamental]` attribute \
1277 is an experimental feature",
1278 cfg_fn!(fundamental))),
1280 (symbols::proc_macro_derive, Normal, template!(List: "TraitName, \
1281 /*opt*/ attributes(name1, name2, ...)"),
1284 (symbols::rustc_copy_clone_marker, Whitelisted, template!(Word), Gated(Stability::Unstable,
1286 "internal implementation detail",
1287 cfg_fn!(rustc_attrs))),
1289 // FIXME: #14408 whitelist docs since rustdoc looks at them
1293 template!(List: "hidden|inline|...", NameValueStr: "string"),
1297 // FIXME: #14406 these are processed in codegen, which happens after the
1299 (symbols::cold, Whitelisted, template!(Word), Ungated),
1300 (symbols::naked, Whitelisted, template!(Word), Gated(Stability::Unstable,
1302 "the `#[naked]` attribute \
1303 is an experimental feature",
1304 cfg_fn!(naked_functions))),
1305 (symbols::ffi_returns_twice, Whitelisted, template!(Word), Gated(Stability::Unstable,
1306 "ffi_returns_twice",
1307 "the `#[ffi_returns_twice]` attribute \
1308 is an experimental feature",
1309 cfg_fn!(ffi_returns_twice))),
1310 (symbols::target_feature, Whitelisted, template!(List: r#"enable = "name""#), Ungated),
1311 (symbols::export_name, Whitelisted, template!(NameValueStr: "name"), Ungated),
1312 (symbols::inline, Whitelisted, template!(Word, List: "always|never"), Ungated),
1313 (symbols::link, Whitelisted, template!(List: r#"name = "...", /*opt*/ kind = "dylib|static|...",
1314 /*opt*/ cfg = "...""#), Ungated),
1315 (symbols::link_name, Whitelisted, template!(NameValueStr: "name"), Ungated),
1316 (symbols::link_section, Whitelisted, template!(NameValueStr: "name"), Ungated),
1317 (symbols::no_builtins, Whitelisted, template!(Word), Ungated),
1318 (symbols::no_debug, Whitelisted, template!(Word), Gated(
1319 Stability::Deprecated("https://github.com/rust-lang/rust/issues/29721", None),
1321 "the `#[no_debug]` attribute was an experimental feature that has been \
1322 deprecated due to lack of demand",
1323 cfg_fn!(no_debug))),
1325 symbols::omit_gdb_pretty_printer_section,
1329 Stability::Unstable,
1330 "omit_gdb_pretty_printer_section",
1331 "the `#[omit_gdb_pretty_printer_section]` \
1332 attribute is just used for the Rust test \
1334 cfg_fn!(omit_gdb_pretty_printer_section)
1337 (symbols::unsafe_destructor_blind_to_params,
1340 Gated(Stability::Deprecated("https://github.com/rust-lang/rust/issues/34761",
1341 Some("replace this attribute with `#[may_dangle]`")),
1342 "dropck_parametricity",
1343 "unsafe_destructor_blind_to_params has been replaced by \
1344 may_dangle and will be removed in the future",
1345 cfg_fn!(dropck_parametricity))),
1346 (symbols::may_dangle,
1349 Gated(Stability::Unstable,
1351 "may_dangle has unstable semantics and may be removed in the future",
1352 cfg_fn!(dropck_eyepatch))),
1353 (symbols::unwind, Whitelisted, template!(List: "allowed|aborts"), Gated(Stability::Unstable,
1354 "unwind_attributes",
1355 "#[unwind] is experimental",
1356 cfg_fn!(unwind_attributes))),
1357 (symbols::used, Whitelisted, template!(Word), Ungated),
1360 (symbols::prelude_import, Whitelisted, template!(Word), Gated(Stability::Unstable,
1362 "`#[prelude_import]` is for use by rustc only",
1363 cfg_fn!(prelude_import))),
1365 // FIXME: #14407 these are only looked at on-demand so we can't
1366 // guarantee they'll have already been checked
1368 symbols::rustc_deprecated,
1370 template!(List: r#"since = "version", reason = "...""#),
1373 (symbols::must_use, Whitelisted, template!(Word, NameValueStr: "reason"), Ungated),
1377 template!(List: r#"feature = "name", since = "version""#),
1383 template!(List: r#"feature = "name", reason = "...", issue = "N""#),
1386 (symbols::deprecated,
1390 List: r#"/*opt*/ since = "version", /*opt*/ note = "reason"#,
1391 NameValueStr: "reason"
1396 (symbols::rustc_paren_sugar, Normal, template!(Word), Gated(Stability::Unstable,
1398 "unboxed_closures are still evolving",
1399 cfg_fn!(unboxed_closures))),
1401 (symbols::windows_subsystem, Whitelisted, template!(NameValueStr: "windows|console"), Ungated),
1403 (symbols::proc_macro_attribute, Normal, template!(Word), Ungated),
1404 (symbols::proc_macro, Normal, template!(Word), Ungated),
1406 (symbols::rustc_proc_macro_decls, Normal, template!(Word), Gated(Stability::Unstable,
1408 "used internally by rustc",
1409 cfg_fn!(rustc_attrs))),
1411 (symbols::allow_fail, Normal, template!(Word), Gated(Stability::Unstable,
1413 "allow_fail attribute is currently unstable",
1414 cfg_fn!(allow_fail))),
1416 (symbols::rustc_std_internal_symbol, Whitelisted, template!(Word), Gated(Stability::Unstable,
1418 "this is an internal attribute that will \
1420 cfg_fn!(rustc_attrs))),
1422 // whitelists "identity-like" conversion methods to suggest on type mismatch
1423 (symbols::rustc_conversion_suggestion, Whitelisted, template!(Word), Gated(Stability::Unstable,
1425 "this is an internal attribute that will \
1427 cfg_fn!(rustc_attrs))),
1430 symbols::rustc_args_required_const,
1432 template!(List: "N"),
1433 Gated(Stability::Unstable, "rustc_attrs", "never will be stable", cfg_fn!(rustc_attrs))
1436 (symbols::panic_handler, Normal, template!(Word), Ungated),
1438 (symbols::alloc_error_handler, Normal, template!(Word), Gated(Stability::Unstable,
1439 "alloc_error_handler",
1440 "#[alloc_error_handler] is an unstable feature",
1441 cfg_fn!(alloc_error_handler))),
1444 (symbols::optimize, Whitelisted, template!(List: "size|speed"), Gated(Stability::Unstable,
1445 "optimize_attribute",
1446 "#[optimize] attribute is an unstable feature",
1447 cfg_fn!(optimize_attribute))),
1449 // Crate level attributes
1450 (symbols::crate_name, CrateLevel, template!(NameValueStr: "name"), Ungated),
1451 (symbols::crate_type, CrateLevel, template!(NameValueStr: "bin|lib|..."), Ungated),
1452 (symbols::crate_id, CrateLevel, template!(NameValueStr: "ignored"), Ungated),
1453 (symbols::feature, CrateLevel, template!(List: "name1, name1, ..."), Ungated),
1454 (symbols::no_start, CrateLevel, template!(Word), Ungated),
1455 (symbols::no_main, CrateLevel, template!(Word), Ungated),
1456 (symbols::recursion_limit, CrateLevel, template!(NameValueStr: "N"), Ungated),
1457 (symbols::type_length_limit, CrateLevel, template!(NameValueStr: "N"), Ungated),
1458 (symbols::test_runner, CrateLevel, template!(List: "path"), Gated(Stability::Unstable,
1459 "custom_test_frameworks",
1460 EXPLAIN_CUSTOM_TEST_FRAMEWORKS,
1461 cfg_fn!(custom_test_frameworks))),
1464 pub type BuiltinAttribute = (Symbol, AttributeType, AttributeTemplate, AttributeGate);
1467 pub static ref BUILTIN_ATTRIBUTE_MAP: FxHashMap<Symbol, &'static BuiltinAttribute> = {
1468 let mut map = FxHashMap::default();
1469 for attr in BUILTIN_ATTRIBUTES.iter() {
1470 if map.insert(attr.0, attr).is_some() {
1471 panic!("duplicate builtin attribute `{}`", attr.0);
1478 // cfg(...)'s that are feature gated
1479 const GATED_CFGS: &[(&str, &str, fn(&Features) -> bool)] = &[
1480 // (name in cfg, feature, function to check if the feature is enabled)
1481 ("target_thread_local", "cfg_target_thread_local", cfg_fn!(cfg_target_thread_local)),
1482 ("target_has_atomic", "cfg_target_has_atomic", cfg_fn!(cfg_target_has_atomic)),
1483 ("rustdoc", "doc_cfg", cfg_fn!(doc_cfg)),
1487 pub struct GatedCfg {
1493 pub fn gate(cfg: &ast::MetaItem) -> Option<GatedCfg> {
1495 .position(|info| cfg.check_name(info.0))
1504 pub fn check_and_emit(&self, sess: &ParseSess, features: &Features) {
1505 let (cfg, feature, has_feature) = GATED_CFGS[self.index];
1506 if !has_feature(features) && !self.span.allows_unstable(feature) {
1507 let explain = format!("`cfg({})` is experimental and subject to change", cfg);
1508 emit_feature_err(sess, feature, self.span, GateIssue::Language, &explain);
1513 struct Context<'a> {
1514 features: &'a Features,
1515 parse_sess: &'a ParseSess,
1516 plugin_attributes: &'a [(String, AttributeType)],
1519 macro_rules! gate_feature_fn {
1520 ($cx: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr, $level: expr) => {{
1521 let (cx, has_feature, span,
1522 name, explain, level) = ($cx, $has_feature, $span, $name, $explain, $level);
1523 let has_feature: bool = has_feature(&$cx.features);
1524 debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
1525 if !has_feature && !span.allows_unstable($name) {
1526 leveled_feature_err(cx.parse_sess, name, span, GateIssue::Language, explain, level)
1532 macro_rules! gate_feature {
1533 ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {
1534 gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
1535 stringify!($feature), $explain, GateStrength::Hard)
1537 ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {
1538 gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
1539 stringify!($feature), $explain, $level)
1543 impl<'a> Context<'a> {
1546 attr: &ast::Attribute,
1547 attr_info: Option<&BuiltinAttribute>,
1550 debug!("check_attribute(attr = {:?})", attr);
1551 if let Some(&(name, ty, _template, ref gateage)) = attr_info {
1552 if let Gated(_, name, desc, ref has_feature) = *gateage {
1553 if !attr.span.allows_unstable(name) {
1555 self, has_feature, attr.span, name, desc, GateStrength::Hard
1558 } else if name == symbols::doc {
1559 if let Some(content) = attr.meta_item_list() {
1560 if content.iter().any(|c| c.check_name(symbols::include)) {
1561 gate_feature!(self, external_doc, attr.span,
1562 "#[doc(include = \"...\")] is experimental"
1567 debug!("check_attribute: {:?} is builtin, {:?}, {:?}", attr.path, ty, gateage);
1570 for &(ref n, ref ty) in self.plugin_attributes {
1571 if attr.path == &**n {
1572 // Plugins can't gate attributes, so we don't check for it
1573 // unlike the code above; we only use this loop to
1574 // short-circuit to avoid the checks below.
1575 debug!("check_attribute: {:?} is registered by a plugin, {:?}", attr.path, ty);
1579 if !attr::is_known(attr) {
1580 if attr.name_or_empty().starts_with("rustc_") {
1581 let msg = "unless otherwise specified, attributes with the prefix `rustc_` \
1582 are reserved for internal compiler diagnostics";
1583 gate_feature!(self, rustc_attrs, attr.span, msg);
1584 } else if !is_macro {
1585 // Only run the custom attribute lint during regular feature gate
1586 // checking. Macro gating runs before the plugin attributes are
1587 // registered, so we skip this in that case.
1588 let msg = format!("The attribute `{}` is currently unknown to the compiler and \
1589 may have meaning added to it in the future", attr.path);
1590 gate_feature!(self, custom_attribute, attr.span, &msg);
1596 pub fn check_attribute(attr: &ast::Attribute, parse_sess: &ParseSess, features: &Features) {
1597 let cx = Context { features: features, parse_sess: parse_sess, plugin_attributes: &[] };
1600 attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name).map(|a| *a)),
1605 fn find_lang_feature_issue(feature: &str) -> Option<u32> {
1606 if let Some(info) = ACTIVE_FEATURES.iter().find(|t| t.0 == feature) {
1608 // FIXME (#28244): enforce that active features have issue numbers
1609 // assert!(issue.is_some())
1612 // search in Accepted, Removed, or Stable Removed features
1613 let found = ACCEPTED_FEATURES.iter().chain(REMOVED_FEATURES).chain(STABLE_REMOVED_FEATURES)
1614 .find(|t| t.0 == feature);
1616 Some(&(_, _, issue, _)) => issue,
1617 None => panic!("Feature `{}` is not declared anywhere", feature),
1622 pub enum GateIssue {
1624 Library(Option<u32>)
1627 #[derive(Debug, Copy, Clone, PartialEq)]
1628 pub enum GateStrength {
1629 /// A hard error. (Most feature gates should use this.)
1631 /// Only a warning. (Use this only as backwards-compatibility demands.)
1635 pub fn emit_feature_err(
1642 feature_err(sess, feature, span, issue, explain).emit();
1645 pub fn feature_err<'a>(
1646 sess: &'a ParseSess,
1651 ) -> DiagnosticBuilder<'a> {
1652 leveled_feature_err(sess, feature, span, issue, explain, GateStrength::Hard)
1655 fn leveled_feature_err<'a>(
1656 sess: &'a ParseSess,
1661 level: GateStrength,
1662 ) -> DiagnosticBuilder<'a> {
1663 let diag = &sess.span_diagnostic;
1665 let issue = match issue {
1666 GateIssue::Language => find_lang_feature_issue(feature),
1667 GateIssue::Library(lib) => lib,
1670 let mut err = match level {
1671 GateStrength::Hard => {
1672 diag.struct_span_err_with_code(span, explain, stringify_error_code!(E0658))
1674 GateStrength::Soft => diag.struct_span_warn(span, explain),
1678 None | Some(0) => {} // We still accept `0` as a stand-in for backwards compatibility
1681 "for more information, see https://github.com/rust-lang/rust/issues/{}",
1687 // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
1688 if sess.unstable_features.is_nightly_build() {
1689 err.help(&format!("add #![feature({})] to the crate attributes to enable", feature));
1692 // If we're on stable and only emitting a "soft" warning, add a note to
1693 // clarify that the feature isn't "on" (rather than being on but
1695 if !sess.unstable_features.is_nightly_build() && level == GateStrength::Soft {
1696 err.help("a nightly build of the compiler is required to enable this feature");
1703 const EXPLAIN_BOX_SYNTAX: &str =
1704 "box expression syntax is experimental; you can call `Box::new` instead";
1706 pub const EXPLAIN_STMT_ATTR_SYNTAX: &str =
1707 "attributes on expressions are experimental";
1709 pub const EXPLAIN_ASM: &str =
1710 "inline assembly is not stable enough for use and is subject to change";
1712 pub const EXPLAIN_GLOBAL_ASM: &str =
1713 "`global_asm!` is not stable enough for use and is subject to change";
1715 pub const EXPLAIN_CUSTOM_TEST_FRAMEWORKS: &str =
1716 "custom test frameworks are an unstable feature";
1718 pub const EXPLAIN_LOG_SYNTAX: &str =
1719 "`log_syntax!` is not stable enough for use and is subject to change";
1721 pub const EXPLAIN_CONCAT_IDENTS: &str =
1722 "`concat_idents` is not stable enough for use and is subject to change";
1724 pub const EXPLAIN_FORMAT_ARGS_NL: &str =
1725 "`format_args_nl` is only for internal language use and is subject to change";
1727 pub const EXPLAIN_TRACE_MACROS: &str =
1728 "`trace_macros` is not stable enough for use and is subject to change";
1729 pub const EXPLAIN_ALLOW_INTERNAL_UNSTABLE: &str =
1730 "allow_internal_unstable side-steps feature gating and stability checks";
1731 pub const EXPLAIN_ALLOW_INTERNAL_UNSAFE: &str =
1732 "allow_internal_unsafe side-steps the unsafe_code lint";
1734 pub const EXPLAIN_UNSIZED_TUPLE_COERCION: &str =
1735 "unsized tuple coercion is not stable enough for use and is subject to change";
1737 struct PostExpansionVisitor<'a> {
1738 context: &'a Context<'a>,
1739 builtin_attributes: &'static FxHashMap<Symbol, &'static BuiltinAttribute>,
1742 macro_rules! gate_feature_post {
1743 ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {{
1744 let (cx, span) = ($cx, $span);
1745 if !span.allows_unstable(stringify!($feature)) {
1746 gate_feature!(cx.context, $feature, span, $explain)
1749 ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {{
1750 let (cx, span) = ($cx, $span);
1751 if !span.allows_unstable(stringify!($feature)) {
1752 gate_feature!(cx.context, $feature, span, $explain, $level)
1757 impl<'a> PostExpansionVisitor<'a> {
1758 fn check_abi(&self, abi: Abi, span: Span) {
1760 Abi::RustIntrinsic => {
1761 gate_feature_post!(&self, intrinsics, span,
1762 "intrinsics are subject to change");
1764 Abi::PlatformIntrinsic => {
1765 gate_feature_post!(&self, platform_intrinsics, span,
1766 "platform intrinsics are experimental and possibly buggy");
1768 Abi::Vectorcall => {
1769 gate_feature_post!(&self, abi_vectorcall, span,
1770 "vectorcall is experimental and subject to change");
1773 gate_feature_post!(&self, abi_thiscall, span,
1774 "thiscall is experimental and subject to change");
1777 gate_feature_post!(&self, unboxed_closures, span,
1778 "rust-call ABI is subject to change");
1781 gate_feature_post!(&self, abi_ptx, span,
1782 "PTX ABIs are experimental and subject to change");
1784 Abi::Unadjusted => {
1785 gate_feature_post!(&self, abi_unadjusted, span,
1786 "unadjusted ABI is an implementation detail and perma-unstable");
1788 Abi::Msp430Interrupt => {
1789 gate_feature_post!(&self, abi_msp430_interrupt, span,
1790 "msp430-interrupt ABI is experimental and subject to change");
1792 Abi::X86Interrupt => {
1793 gate_feature_post!(&self, abi_x86_interrupt, span,
1794 "x86-interrupt ABI is experimental and subject to change");
1796 Abi::AmdGpuKernel => {
1797 gate_feature_post!(&self, abi_amdgpu_kernel, span,
1798 "amdgpu-kernel ABI is experimental and subject to change");
1813 fn check_builtin_attribute(&mut self, attr: &ast::Attribute, name: Symbol,
1814 template: AttributeTemplate) {
1815 // Some special attributes like `cfg` must be checked
1816 // before the generic check, so we skip them here.
1817 let should_skip = |name| name == symbols::cfg;
1818 // Some of previously accepted forms were used in practice,
1819 // report them as warnings for now.
1820 let should_warn = |name| name == symbols::doc || name == symbols::ignore ||
1821 name == symbols::inline || name == symbols::link;
1823 match attr.parse_meta(self.context.parse_sess) {
1824 Ok(meta) => if !should_skip(name) && !template.compatible(&meta.node) {
1825 let mut msg = "attribute must be of the form ".to_owned();
1826 let mut first = true;
1829 msg.push_str(&format!("`#[{}{}]`", name, ""));
1831 if let Some(descr) = template.list {
1833 msg.push_str(" or ");
1836 msg.push_str(&format!("`#[{}({})]`", name, descr));
1838 if let Some(descr) = template.name_value_str {
1840 msg.push_str(" or ");
1842 msg.push_str(&format!("`#[{} = \"{}\"]`", name, descr));
1844 if should_warn(name) {
1845 self.context.parse_sess.buffer_lint(
1846 BufferedEarlyLintId::IllFormedAttributeInput,
1852 self.context.parse_sess.span_diagnostic.span_err(meta.span, &msg);
1855 Err(mut err) => err.emit(),
1860 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
1861 fn visit_attribute(&mut self, attr: &ast::Attribute) {
1862 let attr_info = attr.ident().and_then(|ident| {
1863 self.builtin_attributes.get(&ident.name).map(|a| *a)
1866 // check for gated attributes
1867 self.context.check_attribute(attr, attr_info, false);
1869 if attr.check_name(symbols::doc) {
1870 if let Some(content) = attr.meta_item_list() {
1871 if content.len() == 1 && content[0].check_name(symbols::cfg) {
1872 gate_feature_post!(&self, doc_cfg, attr.span,
1873 "#[doc(cfg(...))] is experimental"
1875 } else if content.iter().any(|c| c.check_name(symbols::masked)) {
1876 gate_feature_post!(&self, doc_masked, attr.span,
1877 "#[doc(masked)] is experimental"
1879 } else if content.iter().any(|c| c.check_name(symbols::spotlight)) {
1880 gate_feature_post!(&self, doc_spotlight, attr.span,
1881 "#[doc(spotlight)] is experimental"
1883 } else if content.iter().any(|c| c.check_name(symbols::alias)) {
1884 gate_feature_post!(&self, doc_alias, attr.span,
1885 "#[doc(alias = \"...\")] is experimental"
1887 } else if content.iter().any(|c| c.check_name(symbols::keyword)) {
1888 gate_feature_post!(&self, doc_keyword, attr.span,
1889 "#[doc(keyword = \"...\")] is experimental"
1896 Some(&(name, _, template, _)) => self.check_builtin_attribute(
1901 None => if let Some(TokenTree::Token(_, token::Eq)) = attr.tokens.trees().next() {
1902 // All key-value attributes are restricted to meta-item syntax.
1903 attr.parse_meta(self.context.parse_sess).map_err(|mut err| err.emit()).ok();
1908 fn visit_name(&mut self, sp: Span, name: ast::Name) {
1909 if !name.as_str().is_ascii() {
1913 self.context.parse_sess.source_map().def_span(sp),
1914 "non-ascii idents are not fully supported"
1919 fn visit_item(&mut self, i: &'a ast::Item) {
1921 ast::ItemKind::Const(_,_) => {
1922 if i.ident.name == "_" {
1923 gate_feature_post!(&self, underscore_const_names, i.span,
1924 "naming constants with `_` is unstable");
1928 ast::ItemKind::ForeignMod(ref foreign_module) => {
1929 self.check_abi(foreign_module.abi, i.span);
1932 ast::ItemKind::Fn(..) => {
1933 if attr::contains_name(&i.attrs[..], "plugin_registrar") {
1934 gate_feature_post!(&self, plugin_registrar, i.span,
1935 "compiler plugins are experimental and possibly buggy");
1937 if attr::contains_name(&i.attrs[..], "start") {
1938 gate_feature_post!(&self, start, i.span,
1939 "a #[start] function is an experimental \
1940 feature whose signature may change \
1943 if attr::contains_name(&i.attrs[..], "main") {
1944 gate_feature_post!(&self, main, i.span,
1945 "declaration of a nonstandard #[main] \
1946 function may change over time, for now \
1947 a top-level `fn main()` is required");
1951 ast::ItemKind::Struct(..) => {
1952 for attr in attr::filter_by_name(&i.attrs[..], "repr") {
1953 for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
1954 if item.check_name(symbols::simd) {
1955 gate_feature_post!(&self, repr_simd, attr.span,
1956 "SIMD types are experimental and possibly buggy");
1962 ast::ItemKind::Enum(..) => {
1963 for attr in attr::filter_by_name(&i.attrs[..], "repr") {
1964 for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
1965 if item.check_name(symbols::align) {
1966 gate_feature_post!(&self, repr_align_enum, attr.span,
1967 "`#[repr(align(x))]` on enums is experimental");
1973 ast::ItemKind::Impl(_, polarity, defaultness, _, _, _, _) => {
1974 if polarity == ast::ImplPolarity::Negative {
1975 gate_feature_post!(&self, optin_builtin_traits,
1977 "negative trait bounds are not yet fully implemented; \
1978 use marker types for now");
1981 if let ast::Defaultness::Default = defaultness {
1982 gate_feature_post!(&self, specialization,
1984 "specialization is unstable");
1988 ast::ItemKind::Trait(ast::IsAuto::Yes, ..) => {
1989 gate_feature_post!(&self, optin_builtin_traits,
1991 "auto traits are experimental and possibly buggy");
1994 ast::ItemKind::TraitAlias(..) => {
1999 "trait aliases are experimental"
2003 ast::ItemKind::MacroDef(ast::MacroDef { legacy: false, .. }) => {
2004 let msg = "`macro` is experimental";
2005 gate_feature_post!(&self, decl_macro, i.span, msg);
2008 ast::ItemKind::Existential(..) => {
2013 "existential types are unstable"
2020 visit::walk_item(self, i);
2023 fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
2025 ast::ForeignItemKind::Fn(..) |
2026 ast::ForeignItemKind::Static(..) => {
2027 let link_name = attr::first_attr_value_str_by_name(&i.attrs, "link_name");
2028 let links_to_llvm = match link_name {
2029 Some(val) => val.as_str().starts_with("llvm."),
2033 gate_feature_post!(&self, link_llvm_intrinsics, i.span,
2034 "linking to LLVM intrinsics is experimental");
2037 ast::ForeignItemKind::Ty => {
2038 gate_feature_post!(&self, extern_types, i.span,
2039 "extern types are experimental");
2041 ast::ForeignItemKind::Macro(..) => {}
2044 visit::walk_foreign_item(self, i)
2047 fn visit_ty(&mut self, ty: &'a ast::Ty) {
2049 ast::TyKind::BareFn(ref bare_fn_ty) => {
2050 self.check_abi(bare_fn_ty.abi, ty.span);
2052 ast::TyKind::Never => {
2053 gate_feature_post!(&self, never_type, ty.span,
2054 "The `!` type is experimental");
2058 visit::walk_ty(self, ty)
2061 fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FunctionRetTy) {
2062 if let ast::FunctionRetTy::Ty(ref output_ty) = *ret_ty {
2063 if let ast::TyKind::Never = output_ty.node {
2066 self.visit_ty(output_ty)
2071 fn visit_expr(&mut self, e: &'a ast::Expr) {
2073 ast::ExprKind::Box(_) => {
2074 gate_feature_post!(&self, box_syntax, e.span, EXPLAIN_BOX_SYNTAX);
2076 ast::ExprKind::Type(..) => {
2077 // To avoid noise about type ascription in common syntax errors, only emit if it
2078 // is the *only* error.
2079 if self.context.parse_sess.span_diagnostic.err_count() == 0 {
2080 gate_feature_post!(&self, type_ascription, e.span,
2081 "type ascription is experimental");
2084 ast::ExprKind::ObsoleteInPlace(..) => {
2085 // these get a hard error in ast-validation
2087 ast::ExprKind::Yield(..) => {
2088 gate_feature_post!(&self, generators,
2090 "yield syntax is experimental");
2092 ast::ExprKind::TryBlock(_) => {
2093 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
2095 ast::ExprKind::Block(_, opt_label) => {
2096 if let Some(label) = opt_label {
2097 gate_feature_post!(&self, label_break_value, label.ident.span,
2098 "labels on blocks are unstable");
2101 ast::ExprKind::Closure(_, ast::IsAsync::Async { .. }, ..) => {
2102 gate_feature_post!(&self, async_await, e.span, "async closures are unstable");
2104 ast::ExprKind::Async(..) => {
2105 gate_feature_post!(&self, async_await, e.span, "async blocks are unstable");
2109 visit::walk_expr(self, e);
2112 fn visit_arm(&mut self, arm: &'a ast::Arm) {
2113 visit::walk_arm(self, arm)
2116 fn visit_pat(&mut self, pattern: &'a ast::Pat) {
2117 match pattern.node {
2118 PatKind::Slice(_, Some(ref subslice), _) => {
2119 gate_feature_post!(&self, slice_patterns,
2121 "syntax for subslices in slice patterns is not yet stabilized");
2123 PatKind::Box(..) => {
2124 gate_feature_post!(&self, box_patterns,
2126 "box pattern syntax is experimental");
2128 PatKind::Range(_, _, Spanned { node: RangeEnd::Excluded, .. }) => {
2129 gate_feature_post!(&self, exclusive_range_pattern, pattern.span,
2130 "exclusive range pattern syntax is experimental");
2134 visit::walk_pat(self, pattern)
2137 fn visit_fn(&mut self,
2138 fn_kind: FnKind<'a>,
2139 fn_decl: &'a ast::FnDecl,
2142 if let Some(header) = fn_kind.header() {
2143 // Check for const fn and async fn declarations.
2144 if header.asyncness.node.is_async() {
2145 gate_feature_post!(&self, async_await, span, "async fn is unstable");
2148 // Stability of const fn methods are covered in
2149 // `visit_trait_item` and `visit_impl_item` below; this is
2150 // because default methods don't pass through this point.
2151 self.check_abi(header.abi, span);
2154 if fn_decl.c_variadic {
2155 gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
2158 visit::walk_fn(self, fn_kind, fn_decl, span);
2161 fn visit_generic_param(&mut self, param: &'a GenericParam) {
2162 if let GenericParamKind::Const { .. } = param.kind {
2163 gate_feature_post!(&self, const_generics, param.ident.span,
2164 "const generics are unstable");
2166 visit::walk_generic_param(self, param);
2169 fn visit_trait_item(&mut self, ti: &'a ast::TraitItem) {
2171 ast::TraitItemKind::Method(ref sig, ref block) => {
2172 if block.is_none() {
2173 self.check_abi(sig.header.abi, ti.span);
2175 if sig.header.asyncness.node.is_async() {
2176 gate_feature_post!(&self, async_await, ti.span, "async fn is unstable");
2178 if sig.decl.c_variadic {
2179 gate_feature_post!(&self, c_variadic, ti.span,
2180 "C-variadic functions are unstable");
2182 if sig.header.constness.node == ast::Constness::Const {
2183 gate_feature_post!(&self, const_fn, ti.span, "const fn is unstable");
2186 ast::TraitItemKind::Type(_, ref default) => {
2187 // We use three if statements instead of something like match guards so that all
2188 // of these errors can be emitted if all cases apply.
2189 if default.is_some() {
2190 gate_feature_post!(&self, associated_type_defaults, ti.span,
2191 "associated type defaults are unstable");
2193 if !ti.generics.params.is_empty() {
2194 gate_feature_post!(&self, generic_associated_types, ti.span,
2195 "generic associated types are unstable");
2197 if !ti.generics.where_clause.predicates.is_empty() {
2198 gate_feature_post!(&self, generic_associated_types, ti.span,
2199 "where clauses on associated types are unstable");
2204 visit::walk_trait_item(self, ti);
2207 fn visit_impl_item(&mut self, ii: &'a ast::ImplItem) {
2208 if ii.defaultness == ast::Defaultness::Default {
2209 gate_feature_post!(&self, specialization,
2211 "specialization is unstable");
2215 ast::ImplItemKind::Method(..) => {}
2216 ast::ImplItemKind::Existential(..) => {
2221 "existential types are unstable"
2224 ast::ImplItemKind::Type(_) => {
2225 if !ii.generics.params.is_empty() {
2226 gate_feature_post!(&self, generic_associated_types, ii.span,
2227 "generic associated types are unstable");
2229 if !ii.generics.where_clause.predicates.is_empty() {
2230 gate_feature_post!(&self, generic_associated_types, ii.span,
2231 "where clauses on associated types are unstable");
2236 visit::walk_impl_item(self, ii);
2239 fn visit_vis(&mut self, vis: &'a ast::Visibility) {
2240 if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.node {
2241 gate_feature_post!(&self, crate_visibility_modifier, vis.span,
2242 "`crate` visibility modifier is experimental");
2244 visit::walk_vis(self, vis);
2248 pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
2249 crate_edition: Edition, allow_features: &Option<Vec<String>>) -> Features {
2250 fn feature_removed(span_handler: &Handler, span: Span, reason: Option<&str>) {
2251 let mut err = struct_span_err!(span_handler, span, E0557, "feature has been removed");
2252 if let Some(reason) = reason {
2253 err.span_note(span, reason);
2258 let mut features = Features::new();
2259 let mut edition_enabled_features = FxHashMap::default();
2261 for &edition in ALL_EDITIONS {
2262 if edition <= crate_edition {
2263 // The `crate_edition` implies its respective umbrella feature-gate
2264 // (i.e., `#![feature(rust_20XX_preview)]` isn't needed on edition 20XX).
2265 edition_enabled_features.insert(Symbol::intern(edition.feature_name()), edition);
2269 for &(name, .., f_edition, set) in ACTIVE_FEATURES {
2270 if let Some(f_edition) = f_edition {
2271 if f_edition <= crate_edition {
2272 set(&mut features, DUMMY_SP);
2273 edition_enabled_features.insert(Symbol::intern(name), crate_edition);
2278 // Process the edition umbrella feature-gates first, to ensure
2279 // `edition_enabled_features` is completed before it's queried.
2280 for attr in krate_attrs {
2281 if !attr.check_name(symbols::feature) {
2285 let list = match attr.meta_item_list() {
2295 let name = mi.name_or_empty();
2296 if INCOMPLETE_FEATURES.iter().any(|f| name == *f) {
2297 span_handler.struct_span_warn(
2300 "the feature `{}` is incomplete and may cause the compiler to crash",
2306 if let Some(edition) = ALL_EDITIONS.iter().find(|e| name == e.feature_name()) {
2307 if *edition <= crate_edition {
2311 for &(name, .., f_edition, set) in ACTIVE_FEATURES {
2312 if let Some(f_edition) = f_edition {
2313 if f_edition <= *edition {
2314 // FIXME(Manishearth) there is currently no way to set
2315 // lib features by edition
2316 set(&mut features, DUMMY_SP);
2317 edition_enabled_features.insert(Symbol::intern(name), *edition);
2325 for attr in krate_attrs {
2326 if !attr.check_name(symbols::feature) {
2330 let list = match attr.meta_item_list() {
2336 let name = match mi.ident() {
2337 Some(ident) if mi.is_word() => ident.name,
2339 span_err!(span_handler, mi.span(), E0556,
2340 "malformed feature, expected just one word");
2345 if let Some(edition) = edition_enabled_features.get(&name) {
2350 "the feature `{}` is included in the Rust {} edition",
2357 if ALL_EDITIONS.iter().any(|e| name == e.feature_name()) {
2358 // Handled in the separate loop above.
2362 let removed = REMOVED_FEATURES.iter().find(|f| name == f.0);
2363 let stable_removed = STABLE_REMOVED_FEATURES.iter().find(|f| name == f.0);
2364 if let Some((.., reason)) = removed.or(stable_removed) {
2365 feature_removed(span_handler, mi.span(), *reason);
2369 if let Some((_, since, ..)) = ACCEPTED_FEATURES.iter().find(|f| name == f.0) {
2370 let since = Some(Symbol::intern(since));
2371 features.declared_lang_features.push((name, mi.span(), since));
2375 if let Some(allowed) = allow_features.as_ref() {
2376 if allowed.iter().find(|f| *f == name.as_str()).is_none() {
2377 span_err!(span_handler, mi.span(), E0725,
2378 "the feature `{}` is not in the list of allowed features",
2384 if let Some((.., set)) = ACTIVE_FEATURES.iter().find(|f| name == f.0) {
2385 set(&mut features, mi.span());
2386 features.declared_lang_features.push((name, mi.span(), None));
2390 features.declared_lib_features.push((name, mi.span()));
2397 pub fn check_crate(krate: &ast::Crate,
2399 features: &Features,
2400 plugin_attributes: &[(String, AttributeType)],
2401 unstable: UnstableFeatures) {
2402 maybe_stage_features(&sess.span_diagnostic, krate, unstable);
2408 let visitor = &mut PostExpansionVisitor {
2410 builtin_attributes: &*BUILTIN_ATTRIBUTE_MAP,
2412 visit::walk_crate(visitor, krate);
2415 #[derive(Clone, Copy, Hash)]
2416 pub enum UnstableFeatures {
2417 /// Hard errors for unstable features are active, as on beta/stable channels.
2419 /// Allow features to be activated, as on nightly.
2421 /// Errors are bypassed for bootstrapping. This is required any time
2422 /// during the build that feature-related lints are set to warn or above
2423 /// because the build turns on warnings-as-errors and uses lots of unstable
2424 /// features. As a result, this is always required for building Rust itself.
2428 impl UnstableFeatures {
2429 pub fn from_environment() -> UnstableFeatures {
2430 // Whether this is a feature-staged build, i.e., on the beta or stable channel
2431 let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
2432 // Whether we should enable unstable features for bootstrapping
2433 let bootstrap = env::var("RUSTC_BOOTSTRAP").is_ok();
2434 match (disable_unstable_features, bootstrap) {
2435 (_, true) => UnstableFeatures::Cheat,
2436 (true, _) => UnstableFeatures::Disallow,
2437 (false, _) => UnstableFeatures::Allow
2441 pub fn is_nightly_build(&self) -> bool {
2443 UnstableFeatures::Allow | UnstableFeatures::Cheat => true,
2449 fn maybe_stage_features(span_handler: &Handler, krate: &ast::Crate,
2450 unstable: UnstableFeatures) {
2451 let allow_features = match unstable {
2452 UnstableFeatures::Allow => true,
2453 UnstableFeatures::Disallow => false,
2454 UnstableFeatures::Cheat => true
2456 if !allow_features {
2457 for attr in &krate.attrs {
2458 if attr.check_name(symbols::feature) {
2459 let release_channel = option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)");
2460 span_err!(span_handler, attr.span, E0554,
2461 "#![feature] may not be used on the {} release channel",