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 `#[repr(align(X))]` on enums.
555 (active, repr_align_enum, "1.34.0", Some(57996), None),
557 // Allows using C-variadics.
558 (active, c_variadic, "1.34.0", Some(44930), None),
560 // Allows the user of associated type bounds.
561 (active, associated_type_bounds, "1.34.0", Some(52662), None),
563 // -------------------------------------------------------------------------
564 // feature-group-end: actual feature gates
565 // -------------------------------------------------------------------------
568 // Some features are known to be incomplete and using them is likely to have
569 // unanticipated results, such as compiler crashes. We warn the user about these
571 const INCOMPLETE_FEATURES: &[Symbol] = &[
572 sym::impl_trait_in_bindings,
573 sym::generic_associated_types,
578 // -------------------------------------------------------------------------
579 // feature-group-start: removed features
580 // -------------------------------------------------------------------------
582 (removed, import_shadowing, "1.0.0", None, None, None),
583 (removed, managed_boxes, "1.0.0", None, None, None),
584 // Allows use of unary negate on unsigned integers, e.g., -e for e: u8
585 (removed, negate_unsigned, "1.0.0", Some(29645), None, None),
586 (removed, reflect, "1.0.0", Some(27749), None, None),
587 // A way to temporarily opt out of opt in copy. This will *never* be accepted.
588 (removed, opt_out_copy, "1.0.0", None, None, None),
589 (removed, quad_precision_float, "1.0.0", None, None, None),
590 (removed, struct_inherit, "1.0.0", None, None, None),
591 (removed, test_removed_feature, "1.0.0", None, None, None),
592 (removed, visible_private_types, "1.0.0", None, None, None),
593 (removed, unsafe_no_drop_flag, "1.0.0", None, None, None),
594 // Allows using items which are missing stability attributes
595 (removed, unmarked_api, "1.0.0", None, None, None),
596 (removed, allocator, "1.0.0", None, None, None),
597 (removed, simd, "1.0.0", Some(27731), None,
598 Some("removed in favor of `#[repr(simd)]`")),
599 (removed, advanced_slice_patterns, "1.0.0", Some(23121), None,
600 Some("merged into `#![feature(slice_patterns)]`")),
601 (removed, macro_reexport, "1.0.0", Some(29638), None,
602 Some("subsumed by `pub use`")),
603 (removed, pushpop_unsafe, "1.2.0", None, None, None),
604 (removed, needs_allocator, "1.4.0", Some(27389), None,
605 Some("subsumed by `#![feature(allocator_internals)]`")),
606 (removed, proc_macro_mod, "1.27.0", Some(54727), None,
607 Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
608 (removed, proc_macro_expr, "1.27.0", Some(54727), None,
609 Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
610 (removed, proc_macro_non_items, "1.27.0", Some(54727), None,
611 Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
612 (removed, proc_macro_gen, "1.27.0", Some(54727), None,
613 Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
614 (removed, panic_implementation, "1.28.0", Some(44489), None,
615 Some("subsumed by `#[panic_handler]`")),
616 // Allows the use of `#[derive(Anything)]` as sugar for `#[derive_Anything]`.
617 (removed, custom_derive, "1.32.0", Some(29644), None,
618 Some("subsumed by `#[proc_macro_derive]`")),
619 // Paths of the form: `extern::foo::bar`
620 (removed, extern_in_paths, "1.33.0", Some(55600), None,
621 Some("subsumed by `::foo::bar` paths")),
622 (removed, quote, "1.33.0", Some(29601), None, None),
624 // -------------------------------------------------------------------------
625 // feature-group-end: removed features
626 // -------------------------------------------------------------------------
630 (stable_removed, no_stack_check, "1.0.0", None, None),
634 // -------------------------------------------------------------------------
635 // feature-group-start: for testing purposes
636 // -------------------------------------------------------------------------
638 // A temporary feature gate used to enable parser extensions needed
639 // to bootstrap fix for #5723.
640 (accepted, issue_5723_bootstrap, "1.0.0", None, None),
641 // These are used to test this portion of the compiler,
642 // they don't actually mean anything.
643 (accepted, test_accepted_feature, "1.0.0", None, None),
645 // -------------------------------------------------------------------------
646 // feature-group-end: for testing purposes
647 // -------------------------------------------------------------------------
649 // -------------------------------------------------------------------------
650 // feature-group-start: accepted features
651 // -------------------------------------------------------------------------
653 // Allows using associated `type`s in `trait`s.
654 (accepted, associated_types, "1.0.0", None, None),
655 // Allows using assigning a default type to type parameters in algebraic data type definitions.
656 (accepted, default_type_params, "1.0.0", None, None),
657 // FIXME: explain `globs`.
658 (accepted, globs, "1.0.0", None, None),
659 // Allows `macro_rules!` items.
660 (accepted, macro_rules, "1.0.0", None, None),
661 // Allows use of `&foo[a..b]` as a slicing syntax.
662 (accepted, slicing_syntax, "1.0.0", None, None),
663 // Allows struct variants `Foo { baz: u8, .. }` in enums (RFC 418).
664 (accepted, struct_variant, "1.0.0", None, None),
665 // Allows indexing tuples.
666 (accepted, tuple_indexing, "1.0.0", None, None),
667 // Allows the use of `if let` expressions.
668 (accepted, if_let, "1.0.0", None, None),
669 // Allows the use of `while let` expressions.
670 (accepted, while_let, "1.0.0", None, None),
671 // Allows using `#![no_std]`.
672 (accepted, no_std, "1.6.0", None, None),
673 // Allows overloading augmented assignment operations like `a += b`.
674 (accepted, augmented_assignments, "1.8.0", Some(28235), None),
675 // Allows empty structs and enum variants with braces.
676 (accepted, braced_empty_structs, "1.8.0", Some(29720), None),
677 // Allows `#[deprecated]` attribute.
678 (accepted, deprecated, "1.9.0", Some(29935), None),
679 // Allows macros to appear in the type position.
680 (accepted, type_macros, "1.13.0", Some(27245), None),
681 // Allows use of the postfix `?` operator in expressions.
682 (accepted, question_mark, "1.13.0", Some(31436), None),
683 // Allows `..` in tuple (struct) patterns.
684 (accepted, dotdot_in_tuple_patterns, "1.14.0", Some(33627), None),
685 // Allows some increased flexibility in the name resolution rules,
686 // especially around globs and shadowing (RFC 1560).
687 (accepted, item_like_imports, "1.15.0", Some(35120), None),
688 // Allows using `Self` and associated types in struct expressions and patterns.
689 (accepted, more_struct_aliases, "1.16.0", Some(37544), None),
690 // Allows elision of `'static` lifetimes in `static`s and `const`s.
691 (accepted, static_in_const, "1.17.0", Some(35897), None),
692 // Allows field shorthands (`x` meaning `x: x`) in struct literal expressions.
693 (accepted, field_init_shorthand, "1.17.0", Some(37340), None),
694 // Allows the definition recursive static items.
695 (accepted, static_recursion, "1.17.0", Some(29719), None),
696 // Allows `pub(restricted)` visibilities (RFC 1422).
697 (accepted, pub_restricted, "1.18.0", Some(32409), None),
698 // Allows `#![windows_subsystem]`.
699 (accepted, windows_subsystem, "1.18.0", Some(37499), None),
700 // Allows `break {expr}` with a value inside `loop`s.
701 (accepted, loop_break_value, "1.19.0", Some(37339), None),
702 // Allows numeric fields in struct expressions and patterns.
703 (accepted, relaxed_adts, "1.19.0", Some(35626), None),
704 // Allows coercing non capturing closures to function pointers.
705 (accepted, closure_to_fn_coercion, "1.19.0", Some(39817), None),
706 // Allows attributes on struct literal fields.
707 (accepted, struct_field_attributes, "1.20.0", Some(38814), None),
708 // Allows the definition of associated constants in `trait` or `impl` blocks.
709 (accepted, associated_consts, "1.20.0", Some(29646), None),
710 // Allows usage of the `compile_error!` macro.
711 (accepted, compile_error, "1.20.0", Some(40872), None),
712 // Allows code like `let x: &'static u32 = &42` to work (RFC 1414).
713 (accepted, rvalue_static_promotion, "1.21.0", Some(38865), None),
714 // Allows `Drop` types in constants (RFC 1440).
715 (accepted, drop_types_in_const, "1.22.0", Some(33156), None),
716 // Allows the sysV64 ABI to be specified on all platforms
717 // instead of just the platforms on which it is the C ABI.
718 (accepted, abi_sysv64, "1.24.0", Some(36167), None),
719 // Allows `repr(align(16))` struct attribute (RFC 1358).
720 (accepted, repr_align, "1.25.0", Some(33626), None),
721 // Allows '|' at beginning of match arms (RFC 1925).
722 (accepted, match_beginning_vert, "1.25.0", Some(44101), None),
723 // Allows nested groups in `use` items (RFC 2128).
724 (accepted, use_nested_groups, "1.25.0", Some(44494), None),
725 // Allows indexing into constant arrays.
726 (accepted, const_indexing, "1.26.0", Some(29947), None),
727 // Allows using `a..=b` and `..=b` as inclusive range syntaxes.
728 (accepted, inclusive_range_syntax, "1.26.0", Some(28237), None),
729 // Allows `..=` in patterns (RFC 1192).
730 (accepted, dotdoteq_in_patterns, "1.26.0", Some(28237), None),
731 // Allows `fn main()` with return types which implements `Termination` (RFC 1937).
732 (accepted, termination_trait, "1.26.0", Some(43301), None),
733 // Allows implementing `Clone` for closures where possible (RFC 2132).
734 (accepted, clone_closures, "1.26.0", Some(44490), None),
735 // Allows implementing `Copy` for closures where possible (RFC 2132).
736 (accepted, copy_closures, "1.26.0", Some(44490), None),
737 // Allows `impl Trait` in function arguments.
738 (accepted, universal_impl_trait, "1.26.0", Some(34511), None),
739 // Allows `impl Trait` in function return types.
740 (accepted, conservative_impl_trait, "1.26.0", Some(34511), None),
741 // Allows using the `u128` and `i128` types.
742 (accepted, i128_type, "1.26.0", Some(35118), None),
743 // Allows default match binding modes (RFC 2005).
744 (accepted, match_default_bindings, "1.26.0", Some(42640), None),
745 // Allows `'_` placeholder lifetimes.
746 (accepted, underscore_lifetimes, "1.26.0", Some(44524), None),
747 // Allows attributes on lifetime/type formal parameters in generics (RFC 1327).
748 (accepted, generic_param_attrs, "1.27.0", Some(48848), None),
749 // Allows `cfg(target_feature = "...")`.
750 (accepted, cfg_target_feature, "1.27.0", Some(29717), None),
751 // Allows `#[target_feature(...)]`.
752 (accepted, target_feature, "1.27.0", None, None),
753 // Allows using `dyn Trait` as a syntax for trait objects.
754 (accepted, dyn_trait, "1.27.0", Some(44662), None),
755 // Allows `#[must_use]` on functions, and introduces must-use operators (RFC 1940).
756 (accepted, fn_must_use, "1.27.0", Some(43302), None),
757 // Allows use of the `:lifetime` macro fragment specifier.
758 (accepted, macro_lifetime_matcher, "1.27.0", Some(34303), None),
759 // Allows `#[test]` functions where the return type implements `Termination` (RFC 1937).
760 (accepted, termination_trait_test, "1.27.0", Some(48854), None),
761 // Allows the `#[global_allocator]` attribute.
762 (accepted, global_allocator, "1.28.0", Some(27389), None),
763 // Allows `#[repr(transparent)]` attribute on newtype structs.
764 (accepted, repr_transparent, "1.28.0", Some(43036), None),
765 // Allows procedural macros in `proc-macro` crates.
766 (accepted, proc_macro, "1.29.0", Some(38356), None),
767 // Allows `foo.rs` as an alternative to `foo/mod.rs`.
768 (accepted, non_modrs_mods, "1.30.0", Some(44660), None),
769 // Allows use of the `:vis` macro fragment specifier
770 (accepted, macro_vis_matcher, "1.30.0", Some(41022), None),
771 // Allows importing and reexporting macros with `use`,
772 // enables macro modularization in general.
773 (accepted, use_extern_macros, "1.30.0", Some(35896), None),
774 // Allows keywords to be escaped for use as identifiers.
775 (accepted, raw_identifiers, "1.30.0", Some(48589), None),
776 // Allows attributes scoped to tools.
777 (accepted, tool_attributes, "1.30.0", Some(44690), None),
778 // Allows multi-segment paths in attributes and derives.
779 (accepted, proc_macro_path_invoc, "1.30.0", Some(38356), None),
780 // Allows all literals in attribute lists and values of key-value pairs.
781 (accepted, attr_literals, "1.30.0", Some(34981), None),
782 // Allows inferring outlives requirements (RFC 2093).
783 (accepted, infer_outlives_requirements, "1.30.0", Some(44493), None),
784 // Allows annotating functions conforming to `fn(&PanicInfo) -> !` with `#[panic_handler]`.
785 // This defines the behavior of panics.
786 (accepted, panic_handler, "1.30.0", Some(44489), None),
787 // Allows `#[used]` to preserve symbols (see llvm.used).
788 (accepted, used, "1.30.0", Some(40289), None),
789 // Allows `crate` in paths.
790 (accepted, crate_in_paths, "1.30.0", Some(45477), None),
791 // Allows resolving absolute paths as paths from other crates.
792 (accepted, extern_absolute_paths, "1.30.0", Some(44660), None),
793 // Allows access to crate names passed via `--extern` through prelude.
794 (accepted, extern_prelude, "1.30.0", Some(44660), None),
795 // Allows parentheses in patterns.
796 (accepted, pattern_parentheses, "1.31.0", Some(51087), None),
797 // Allows the definition of `const fn` functions.
798 (accepted, min_const_fn, "1.31.0", Some(53555), None),
799 // Allows scoped lints.
800 (accepted, tool_lints, "1.31.0", Some(44690), None),
801 // Allows lifetime elision in `impl` headers. For example:
802 // + `impl<I:Iterator> Iterator for &mut Iterator`
803 // + `impl Debug for Foo<'_>`
804 (accepted, impl_header_lifetime_elision, "1.31.0", Some(15872), None),
805 // Allows `extern crate foo as bar;`. This puts `bar` into extern prelude.
806 (accepted, extern_crate_item_prelude, "1.31.0", Some(55599), None),
807 // Allows use of the `:literal` macro fragment specifier (RFC 1576).
808 (accepted, macro_literal_matcher, "1.32.0", Some(35625), None),
809 // Allows use of `?` as the Kleene "at most one" operator in macros.
810 (accepted, macro_at_most_once_rep, "1.32.0", Some(48075), None),
811 // Allows `Self` struct constructor (RFC 2302).
812 (accepted, self_struct_ctor, "1.32.0", Some(51994), None),
813 // Allows `Self` in type definitions (RFC 2300).
814 (accepted, self_in_typedefs, "1.32.0", Some(49303), None),
815 // Allows `use x::y;` to search `x` in the current scope.
816 (accepted, uniform_paths, "1.32.0", Some(53130), None),
817 // Allows integer match exhaustiveness checking (RFC 2591).
818 (accepted, exhaustive_integer_patterns, "1.33.0", Some(50907), None),
819 // Allows `use path as _;` and `extern crate c as _;`.
820 (accepted, underscore_imports, "1.33.0", Some(48216), None),
821 // Allows `#[repr(packed(N))]` attribute on structs.
822 (accepted, repr_packed, "1.33.0", Some(33158), None),
823 // Allows irrefutable patterns in `if let` and `while let` statements (RFC 2086).
824 (accepted, irrefutable_let_patterns, "1.33.0", Some(44495), None),
825 // Allows calling `const unsafe fn` inside `unsafe` blocks in `const fn` functions.
826 (accepted, min_const_unsafe_fn, "1.33.0", Some(55607), None),
827 // Allows let bindings, assignments and destructuring in `const` functions and constants.
828 // As long as control flow is not implemented in const eval, `&&` and `||` may not be used
829 // at the same time as let bindings.
830 (accepted, const_let, "1.33.0", Some(48821), None),
831 // Allows `#[cfg_attr(predicate, multiple, attributes, here)]`.
832 (accepted, cfg_attr_multi, "1.33.0", Some(54881), None),
833 // Allows top level or-patterns (`p | q`) in `if let` and `while let`.
834 (accepted, if_while_or_patterns, "1.33.0", Some(48215), None),
835 // Allows `cfg(target_vendor = "...")`.
836 (accepted, cfg_target_vendor, "1.33.0", Some(29718), None),
837 // Allows `extern crate self as foo;`.
838 // This puts local crate root into extern prelude under name `foo`.
839 (accepted, extern_crate_self, "1.34.0", Some(56409), None),
840 // Allows arbitrary delimited token streams in non-macro attributes.
841 (accepted, unrestricted_attribute_tokens, "1.34.0", Some(55208), None),
843 // -------------------------------------------------------------------------
844 // feature-group-end: accepted features
845 // -------------------------------------------------------------------------
848 // If you change this, please modify `src/doc/unstable-book` as well. You must
849 // move that documentation into the relevant place in the other docs, and
850 // remove the chapter on the flag.
852 #[derive(Copy, Clone, PartialEq, Debug)]
853 pub enum AttributeType {
854 /// Normal, builtin attribute that is consumed
855 /// by the compiler before the unused_attribute check
858 /// Builtin attribute that may not be consumed by the compiler
859 /// before the unused_attribute check. These attributes
860 /// will be ignored by the unused_attribute lint
863 /// Builtin attribute that is only allowed at the crate level
867 pub enum AttributeGate {
868 /// Is gated by a given feature gate, reason
869 /// and function to check if enabled
870 Gated(Stability, Symbol, &'static str, fn(&Features) -> bool),
872 /// Ungated attribute, can be used on all release channels
876 /// A template that the attribute input must match.
877 /// Only top-level shape (`#[attr]` vs `#[attr(...)]` vs `#[attr = ...]`) is considered now.
878 #[derive(Clone, Copy)]
879 pub struct AttributeTemplate {
881 list: Option<&'static str>,
882 name_value_str: Option<&'static str>,
885 impl AttributeTemplate {
886 /// Checks that the given meta-item is compatible with this template.
887 fn compatible(&self, meta_item_kind: &ast::MetaItemKind) -> bool {
888 match meta_item_kind {
889 ast::MetaItemKind::Word => self.word,
890 ast::MetaItemKind::List(..) => self.list.is_some(),
891 ast::MetaItemKind::NameValue(lit) if lit.node.is_str() => self.name_value_str.is_some(),
892 ast::MetaItemKind::NameValue(..) => false,
897 /// A convenience macro for constructing attribute templates.
898 /// E.g., `template!(Word, List: "description")` means that the attribute
899 /// supports forms `#[attr]` and `#[attr(description)]`.
900 macro_rules! template {
901 (Word) => { template!(@ true, None, None) };
902 (List: $descr: expr) => { template!(@ false, Some($descr), None) };
903 (NameValueStr: $descr: expr) => { template!(@ false, None, Some($descr)) };
904 (Word, List: $descr: expr) => { template!(@ true, Some($descr), None) };
905 (Word, NameValueStr: $descr: expr) => { template!(@ true, None, Some($descr)) };
906 (List: $descr1: expr, NameValueStr: $descr2: expr) => {
907 template!(@ false, Some($descr1), Some($descr2))
909 (Word, List: $descr1: expr, NameValueStr: $descr2: expr) => {
910 template!(@ true, Some($descr1), Some($descr2))
912 (@ $word: expr, $list: expr, $name_value_str: expr) => { AttributeTemplate {
913 word: $word, list: $list, name_value_str: $name_value_str
918 fn is_deprecated(&self) -> bool {
920 Gated(Stability::Deprecated(_, _), ..) => true,
926 #[derive(Copy, Clone, Debug)]
929 // First argument is tracking issue link; second argument is an optional
930 // help message, which defaults to "remove this attribute"
931 Deprecated(&'static str, Option<&'static str>),
935 impl std::fmt::Debug for AttributeGate {
936 fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
938 Gated(ref stab, name, expl, _) =>
939 write!(fmt, "Gated({:?}, {}, {})", stab, name, expl),
940 Ungated => write!(fmt, "Ungated")
945 macro_rules! cfg_fn {
946 ($field: ident) => {{
947 fn f(features: &Features) -> bool {
950 f as fn(&Features) -> bool
954 pub fn deprecated_attributes() -> Vec<&'static (Symbol, AttributeType,
955 AttributeTemplate, AttributeGate)> {
956 BUILTIN_ATTRIBUTES.iter().filter(|(.., gate)| gate.is_deprecated()).collect()
959 pub fn is_builtin_attr_name(name: ast::Name) -> bool {
960 BUILTIN_ATTRIBUTE_MAP.get(&name).is_some()
963 pub fn is_builtin_attr(attr: &ast::Attribute) -> bool {
964 attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name)).is_some()
967 /// Attributes that have a special meaning to rustc or rustdoc
968 pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
974 template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#),
980 template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#),
986 template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#),
992 template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#),
996 (sym::macro_use, Normal, template!(Word, List: "name1, name2, ..."), Ungated),
997 (sym::macro_export, Normal, template!(Word, List: "local_inner_macros"), Ungated),
998 (sym::plugin_registrar, Normal, template!(Word), Ungated),
1000 (sym::cfg, Normal, template!(List: "predicate"), Ungated),
1001 (sym::cfg_attr, Normal, template!(List: "predicate, attr1, attr2, ..."), Ungated),
1002 (sym::main, Normal, template!(Word), Ungated),
1003 (sym::start, Normal, template!(Word), Ungated),
1004 (sym::repr, Normal, template!(List: "C, packed, ..."), Ungated),
1005 (sym::path, Normal, template!(NameValueStr: "file"), Ungated),
1006 (sym::automatically_derived, Normal, template!(Word), Ungated),
1007 (sym::no_mangle, Whitelisted, template!(Word), Ungated),
1008 (sym::no_link, Normal, template!(Word), Ungated),
1009 (sym::derive, Normal, template!(List: "Trait1, Trait2, ..."), Ungated),
1013 template!(Word, List: r#"expected = "reason"#, NameValueStr: "reason"),
1016 (sym::ignore, Normal, template!(Word, NameValueStr: "reason"), Ungated),
1017 (sym::no_implicit_prelude, Normal, template!(Word), Ungated),
1018 (sym::reexport_test_harness_main, Normal, template!(NameValueStr: "name"), Ungated),
1019 (sym::link_args, Normal, template!(NameValueStr: "args"), Gated(Stability::Unstable,
1021 "the `link_args` attribute is experimental and not \
1022 portable across platforms, it is recommended to \
1023 use `#[link(name = \"foo\")] instead",
1024 cfg_fn!(link_args))),
1025 (sym::macro_escape, Normal, template!(Word), Ungated),
1028 (sym::structural_match, Whitelisted, template!(Word), Gated(Stability::Unstable,
1029 sym::structural_match,
1030 "the semantics of constant patterns is \
1032 cfg_fn!(structural_match))),
1035 (sym::non_exhaustive, Whitelisted, template!(Word), Gated(Stability::Unstable,
1036 sym::non_exhaustive,
1037 "non exhaustive is an experimental feature",
1038 cfg_fn!(non_exhaustive))),
1041 (sym::marker, Normal, template!(Word), Gated(Stability::Unstable,
1042 sym::marker_trait_attr,
1043 "marker traits is an experimental feature",
1044 cfg_fn!(marker_trait_attr))),
1046 (sym::plugin, CrateLevel, template!(List: "name|name(args)"), Gated(Stability::Unstable,
1048 "compiler plugins are experimental \
1049 and possibly buggy",
1052 (sym::no_std, CrateLevel, template!(Word), Ungated),
1053 (sym::no_core, CrateLevel, template!(Word), Gated(Stability::Unstable,
1055 "no_core is experimental",
1057 (sym::lang, Normal, template!(NameValueStr: "name"), Gated(Stability::Unstable,
1059 "language items are subject to change",
1060 cfg_fn!(lang_items))),
1061 (sym::linkage, Whitelisted, template!(NameValueStr: "external|internal|..."),
1062 Gated(Stability::Unstable,
1064 "the `linkage` attribute is experimental \
1065 and not portable across platforms",
1067 (sym::thread_local, Whitelisted, template!(Word), Gated(Stability::Unstable,
1069 "`#[thread_local]` is an experimental feature, and does \
1070 not currently handle destructors",
1071 cfg_fn!(thread_local))),
1073 (sym::rustc_on_unimplemented, Whitelisted, template!(List:
1074 r#"/*opt*/ message = "...", /*opt*/ label = "...", /*opt*/ note = "...""#,
1075 NameValueStr: "message"),
1076 Gated(Stability::Unstable,
1077 sym::on_unimplemented,
1078 "the `#[rustc_on_unimplemented]` attribute \
1079 is an experimental feature",
1080 cfg_fn!(on_unimplemented))),
1081 (sym::rustc_const_unstable, Normal, template!(List: r#"feature = "name""#),
1082 Gated(Stability::Unstable,
1083 sym::rustc_const_unstable,
1084 "the `#[rustc_const_unstable]` attribute \
1085 is an internal feature",
1086 cfg_fn!(rustc_const_unstable))),
1087 (sym::global_allocator, Normal, template!(Word), Ungated),
1088 (sym::default_lib_allocator, Whitelisted, template!(Word), Gated(Stability::Unstable,
1089 sym::allocator_internals,
1090 "the `#[default_lib_allocator]` \
1091 attribute is an experimental feature",
1092 cfg_fn!(allocator_internals))),
1093 (sym::needs_allocator, Normal, template!(Word), Gated(Stability::Unstable,
1094 sym::allocator_internals,
1095 "the `#[needs_allocator]` \
1096 attribute is an experimental \
1098 cfg_fn!(allocator_internals))),
1099 (sym::panic_runtime, Whitelisted, template!(Word), Gated(Stability::Unstable,
1101 "the `#[panic_runtime]` attribute is \
1102 an experimental feature",
1103 cfg_fn!(panic_runtime))),
1104 (sym::needs_panic_runtime, Whitelisted, template!(Word), Gated(Stability::Unstable,
1105 sym::needs_panic_runtime,
1106 "the `#[needs_panic_runtime]` \
1107 attribute is an experimental \
1109 cfg_fn!(needs_panic_runtime))),
1110 (sym::rustc_outlives, Normal, template!(Word), Gated(Stability::Unstable,
1112 "the `#[rustc_outlives]` attribute \
1113 is just used for rustc unit tests \
1114 and will never be stable",
1115 cfg_fn!(rustc_attrs))),
1116 (sym::rustc_variance, Normal, template!(Word), Gated(Stability::Unstable,
1118 "the `#[rustc_variance]` attribute \
1119 is just used for rustc unit tests \
1120 and will never be stable",
1121 cfg_fn!(rustc_attrs))),
1122 (sym::rustc_layout, Normal, template!(List: "field1, field2, ..."),
1123 Gated(Stability::Unstable,
1125 "the `#[rustc_layout]` attribute \
1126 is just used for rustc unit tests \
1127 and will never be stable",
1128 cfg_fn!(rustc_attrs))),
1129 (sym::rustc_layout_scalar_valid_range_start, Whitelisted, template!(List: "value"),
1130 Gated(Stability::Unstable,
1132 "the `#[rustc_layout_scalar_valid_range_start]` attribute \
1133 is just used to enable niche optimizations in libcore \
1134 and will never be stable",
1135 cfg_fn!(rustc_attrs))),
1136 (sym::rustc_layout_scalar_valid_range_end, Whitelisted, template!(List: "value"),
1137 Gated(Stability::Unstable,
1139 "the `#[rustc_layout_scalar_valid_range_end]` attribute \
1140 is just used to enable niche optimizations in libcore \
1141 and will never be stable",
1142 cfg_fn!(rustc_attrs))),
1143 (sym::rustc_nonnull_optimization_guaranteed, Whitelisted, template!(Word),
1144 Gated(Stability::Unstable,
1146 "the `#[rustc_nonnull_optimization_guaranteed]` attribute \
1147 is just used to enable niche optimizations in libcore \
1148 and will never be stable",
1149 cfg_fn!(rustc_attrs))),
1150 (sym::rustc_regions, Normal, template!(Word), Gated(Stability::Unstable,
1152 "the `#[rustc_regions]` attribute \
1153 is just used for rustc unit tests \
1154 and will never be stable",
1155 cfg_fn!(rustc_attrs))),
1156 (sym::rustc_error, Whitelisted, template!(Word), Gated(Stability::Unstable,
1158 "the `#[rustc_error]` attribute \
1159 is just used for rustc unit tests \
1160 and will never be stable",
1161 cfg_fn!(rustc_attrs))),
1162 (sym::rustc_dump_user_substs, Whitelisted, template!(Word), Gated(Stability::Unstable,
1165 is just used for rustc unit tests \
1166 and will never be stable",
1167 cfg_fn!(rustc_attrs))),
1168 (sym::rustc_if_this_changed, Whitelisted, template!(Word, List: "DepNode"),
1169 Gated(Stability::Unstable,
1171 "the `#[rustc_if_this_changed]` attribute \
1172 is just used for rustc unit tests \
1173 and will never be stable",
1174 cfg_fn!(rustc_attrs))),
1175 (sym::rustc_then_this_would_need, Whitelisted, template!(List: "DepNode"),
1176 Gated(Stability::Unstable,
1178 "the `#[rustc_if_this_changed]` attribute \
1179 is just used for rustc unit tests \
1180 and will never be stable",
1181 cfg_fn!(rustc_attrs))),
1182 (sym::rustc_dirty, Whitelisted, template!(List: r#"cfg = "...", /*opt*/ label = "...",
1183 /*opt*/ except = "...""#),
1184 Gated(Stability::Unstable,
1186 "the `#[rustc_dirty]` attribute \
1187 is just used for rustc unit tests \
1188 and will never be stable",
1189 cfg_fn!(rustc_attrs))),
1190 (sym::rustc_clean, Whitelisted, template!(List: r#"cfg = "...", /*opt*/ label = "...",
1191 /*opt*/ except = "...""#),
1192 Gated(Stability::Unstable,
1194 "the `#[rustc_clean]` attribute \
1195 is just used for rustc unit tests \
1196 and will never be stable",
1197 cfg_fn!(rustc_attrs))),
1199 sym::rustc_partition_reused,
1201 template!(List: r#"cfg = "...", module = "...""#),
1203 Stability::Unstable,
1206 is just used for rustc unit tests \
1207 and will never be stable",
1208 cfg_fn!(rustc_attrs)
1212 sym::rustc_partition_codegened,
1214 template!(List: r#"cfg = "...", module = "...""#),
1216 Stability::Unstable,
1219 is just used for rustc unit tests \
1220 and will never be stable",
1221 cfg_fn!(rustc_attrs),
1224 (sym::rustc_expected_cgu_reuse, Whitelisted, template!(List: r#"cfg = "...", module = "...",
1226 Gated(Stability::Unstable,
1229 is just used for rustc unit tests \
1230 and will never be stable",
1231 cfg_fn!(rustc_attrs))),
1232 (sym::rustc_synthetic, Whitelisted, template!(Word), Gated(Stability::Unstable,
1235 is just used for rustc unit tests \
1236 and will never be stable",
1237 cfg_fn!(rustc_attrs))),
1238 (sym::rustc_symbol_name, Whitelisted, template!(Word), Gated(Stability::Unstable,
1240 "internal rustc attributes will never be stable",
1241 cfg_fn!(rustc_attrs))),
1242 (sym::rustc_def_path, Whitelisted, template!(Word), Gated(Stability::Unstable,
1244 "internal rustc attributes will never be stable",
1245 cfg_fn!(rustc_attrs))),
1246 (sym::rustc_mir, Whitelisted, template!(List: "arg1, arg2, ..."), Gated(Stability::Unstable,
1248 "the `#[rustc_mir]` attribute \
1249 is just used for rustc unit tests \
1250 and will never be stable",
1251 cfg_fn!(rustc_attrs))),
1253 sym::rustc_inherit_overflow_checks,
1257 Stability::Unstable,
1259 "the `#[rustc_inherit_overflow_checks]` \
1260 attribute is just used to control \
1261 overflow checking behavior of several \
1262 libcore functions that are inlined \
1263 across crates and will never be stable",
1264 cfg_fn!(rustc_attrs),
1268 (sym::rustc_dump_program_clauses, Whitelisted, template!(Word), Gated(Stability::Unstable,
1270 "the `#[rustc_dump_program_clauses]` \
1271 attribute is just used for rustc unit \
1272 tests and will never be stable",
1273 cfg_fn!(rustc_attrs))),
1274 (sym::rustc_test_marker, Normal, template!(Word), Gated(Stability::Unstable,
1276 "the `#[rustc_test_marker]` attribute \
1277 is used internally to track tests",
1278 cfg_fn!(rustc_attrs))),
1279 (sym::rustc_transparent_macro, Whitelisted, template!(Word), Gated(Stability::Unstable,
1281 "used internally for testing macro hygiene",
1282 cfg_fn!(rustc_attrs))),
1283 (sym::compiler_builtins, Whitelisted, template!(Word), Gated(Stability::Unstable,
1284 sym::compiler_builtins,
1285 "the `#[compiler_builtins]` attribute is used to \
1286 identify the `compiler_builtins` crate which \
1287 contains compiler-rt intrinsics and will never be \
1289 cfg_fn!(compiler_builtins))),
1290 (sym::sanitizer_runtime, Whitelisted, template!(Word), Gated(Stability::Unstable,
1291 sym::sanitizer_runtime,
1292 "the `#[sanitizer_runtime]` attribute is used to \
1293 identify crates that contain the runtime of a \
1294 sanitizer and will never be stable",
1295 cfg_fn!(sanitizer_runtime))),
1296 (sym::profiler_runtime, Whitelisted, template!(Word), Gated(Stability::Unstable,
1297 sym::profiler_runtime,
1298 "the `#[profiler_runtime]` attribute is used to \
1299 identify the `profiler_builtins` crate which \
1300 contains the profiler runtime and will never be \
1302 cfg_fn!(profiler_runtime))),
1304 (sym::allow_internal_unstable, Normal, template!(Word, List: "feat1, feat2, ..."),
1305 Gated(Stability::Unstable,
1306 sym::allow_internal_unstable,
1307 EXPLAIN_ALLOW_INTERNAL_UNSTABLE,
1308 cfg_fn!(allow_internal_unstable))),
1310 (sym::allow_internal_unsafe, Normal, template!(Word), Gated(Stability::Unstable,
1311 sym::allow_internal_unsafe,
1312 EXPLAIN_ALLOW_INTERNAL_UNSAFE,
1313 cfg_fn!(allow_internal_unsafe))),
1315 (sym::fundamental, Whitelisted, template!(Word), Gated(Stability::Unstable,
1317 "the `#[fundamental]` attribute \
1318 is an experimental feature",
1319 cfg_fn!(fundamental))),
1321 (sym::proc_macro_derive, Normal, template!(List: "TraitName, \
1322 /*opt*/ attributes(name1, name2, ...)"),
1325 (sym::rustc_copy_clone_marker, Whitelisted, template!(Word), Gated(Stability::Unstable,
1327 "internal implementation detail",
1328 cfg_fn!(rustc_attrs))),
1330 // FIXME: #14408 whitelist docs since rustdoc looks at them
1334 template!(List: "hidden|inline|...", NameValueStr: "string"),
1338 // FIXME: #14406 these are processed in codegen, which happens after the
1340 (sym::cold, Whitelisted, template!(Word), Ungated),
1341 (sym::naked, Whitelisted, template!(Word), Gated(Stability::Unstable,
1342 sym::naked_functions,
1343 "the `#[naked]` attribute \
1344 is an experimental feature",
1345 cfg_fn!(naked_functions))),
1346 (sym::ffi_returns_twice, Whitelisted, template!(Word), Gated(Stability::Unstable,
1347 sym::ffi_returns_twice,
1348 "the `#[ffi_returns_twice]` attribute \
1349 is an experimental feature",
1350 cfg_fn!(ffi_returns_twice))),
1351 (sym::target_feature, Whitelisted, template!(List: r#"enable = "name""#), Ungated),
1352 (sym::export_name, Whitelisted, template!(NameValueStr: "name"), Ungated),
1353 (sym::inline, Whitelisted, template!(Word, List: "always|never"), Ungated),
1354 (sym::link, Whitelisted, template!(List: r#"name = "...", /*opt*/ kind = "dylib|static|...",
1355 /*opt*/ cfg = "...""#), Ungated),
1356 (sym::link_name, Whitelisted, template!(NameValueStr: "name"), Ungated),
1357 (sym::link_section, Whitelisted, template!(NameValueStr: "name"), Ungated),
1358 (sym::no_builtins, Whitelisted, template!(Word), Ungated),
1359 (sym::no_debug, Whitelisted, template!(Word), Gated(
1360 Stability::Deprecated("https://github.com/rust-lang/rust/issues/29721", None),
1362 "the `#[no_debug]` attribute was an experimental feature that has been \
1363 deprecated due to lack of demand",
1364 cfg_fn!(no_debug))),
1366 sym::omit_gdb_pretty_printer_section,
1370 Stability::Unstable,
1371 sym::omit_gdb_pretty_printer_section,
1372 "the `#[omit_gdb_pretty_printer_section]` \
1373 attribute is just used for the Rust test \
1375 cfg_fn!(omit_gdb_pretty_printer_section)
1378 (sym::unsafe_destructor_blind_to_params,
1381 Gated(Stability::Deprecated("https://github.com/rust-lang/rust/issues/34761",
1382 Some("replace this attribute with `#[may_dangle]`")),
1383 sym::dropck_parametricity,
1384 "unsafe_destructor_blind_to_params has been replaced by \
1385 may_dangle and will be removed in the future",
1386 cfg_fn!(dropck_parametricity))),
1390 Gated(Stability::Unstable,
1391 sym::dropck_eyepatch,
1392 "may_dangle has unstable semantics and may be removed in the future",
1393 cfg_fn!(dropck_eyepatch))),
1394 (sym::unwind, Whitelisted, template!(List: "allowed|aborts"), Gated(Stability::Unstable,
1395 sym::unwind_attributes,
1396 "#[unwind] is experimental",
1397 cfg_fn!(unwind_attributes))),
1398 (sym::used, Whitelisted, template!(Word), Ungated),
1401 (sym::prelude_import, Whitelisted, template!(Word), Gated(Stability::Unstable,
1402 sym::prelude_import,
1403 "`#[prelude_import]` is for use by rustc only",
1404 cfg_fn!(prelude_import))),
1406 // FIXME: #14407 these are only looked at on-demand so we can't
1407 // guarantee they'll have already been checked
1409 sym::rustc_deprecated,
1411 template!(List: r#"since = "version", reason = "...""#),
1414 (sym::must_use, Whitelisted, template!(Word, NameValueStr: "reason"), Ungated),
1418 template!(List: r#"feature = "name", since = "version""#),
1424 template!(List: r#"feature = "name", reason = "...", issue = "N""#),
1431 List: r#"/*opt*/ since = "version", /*opt*/ note = "reason""#,
1432 NameValueStr: "reason"
1437 (sym::rustc_paren_sugar, Normal, template!(Word), Gated(Stability::Unstable,
1438 sym::unboxed_closures,
1439 "unboxed_closures are still evolving",
1440 cfg_fn!(unboxed_closures))),
1442 (sym::windows_subsystem, Whitelisted, template!(NameValueStr: "windows|console"), Ungated),
1444 (sym::proc_macro_attribute, Normal, template!(Word), Ungated),
1445 (sym::proc_macro, Normal, template!(Word), Ungated),
1447 (sym::rustc_proc_macro_decls, Normal, template!(Word), Gated(Stability::Unstable,
1449 "used internally by rustc",
1450 cfg_fn!(rustc_attrs))),
1452 (sym::allow_fail, Normal, template!(Word), Gated(Stability::Unstable,
1454 "allow_fail attribute is currently unstable",
1455 cfg_fn!(allow_fail))),
1457 (sym::rustc_std_internal_symbol, Whitelisted, template!(Word), Gated(Stability::Unstable,
1459 "this is an internal attribute that will \
1461 cfg_fn!(rustc_attrs))),
1463 // whitelists "identity-like" conversion methods to suggest on type mismatch
1464 (sym::rustc_conversion_suggestion, Whitelisted, template!(Word), Gated(Stability::Unstable,
1466 "this is an internal attribute that will \
1468 cfg_fn!(rustc_attrs))),
1471 sym::rustc_args_required_const,
1473 template!(List: "N"),
1474 Gated(Stability::Unstable, sym::rustc_attrs, "never will be stable",
1475 cfg_fn!(rustc_attrs))
1478 (sym::panic_handler, Normal, template!(Word), Ungated),
1480 (sym::alloc_error_handler, Normal, template!(Word), Gated(Stability::Unstable,
1481 sym::alloc_error_handler,
1482 "#[alloc_error_handler] is an unstable feature",
1483 cfg_fn!(alloc_error_handler))),
1486 (sym::optimize, Whitelisted, template!(List: "size|speed"), Gated(Stability::Unstable,
1487 sym::optimize_attribute,
1488 "#[optimize] attribute is an unstable feature",
1489 cfg_fn!(optimize_attribute))),
1491 // Crate level attributes
1492 (sym::crate_name, CrateLevel, template!(NameValueStr: "name"), Ungated),
1493 (sym::crate_type, CrateLevel, template!(NameValueStr: "bin|lib|..."), Ungated),
1494 (sym::crate_id, CrateLevel, template!(NameValueStr: "ignored"), Ungated),
1495 (sym::feature, CrateLevel, template!(List: "name1, name1, ..."), Ungated),
1496 (sym::no_start, CrateLevel, template!(Word), Ungated),
1497 (sym::no_main, CrateLevel, template!(Word), Ungated),
1498 (sym::recursion_limit, CrateLevel, template!(NameValueStr: "N"), Ungated),
1499 (sym::type_length_limit, CrateLevel, template!(NameValueStr: "N"), Ungated),
1500 (sym::test_runner, CrateLevel, template!(List: "path"), Gated(Stability::Unstable,
1501 sym::custom_test_frameworks,
1502 EXPLAIN_CUSTOM_TEST_FRAMEWORKS,
1503 cfg_fn!(custom_test_frameworks))),
1506 pub type BuiltinAttribute = (Symbol, AttributeType, AttributeTemplate, AttributeGate);
1509 pub static ref BUILTIN_ATTRIBUTE_MAP: FxHashMap<Symbol, &'static BuiltinAttribute> = {
1510 let mut map = FxHashMap::default();
1511 for attr in BUILTIN_ATTRIBUTES.iter() {
1512 if map.insert(attr.0, attr).is_some() {
1513 panic!("duplicate builtin attribute `{}`", attr.0);
1520 // cfg(...)'s that are feature gated
1521 const GATED_CFGS: &[(Symbol, Symbol, fn(&Features) -> bool)] = &[
1522 // (name in cfg, feature, function to check if the feature is enabled)
1523 (sym::target_thread_local, sym::cfg_target_thread_local, cfg_fn!(cfg_target_thread_local)),
1524 (sym::target_has_atomic, sym::cfg_target_has_atomic, cfg_fn!(cfg_target_has_atomic)),
1525 (sym::rustdoc, sym::doc_cfg, cfg_fn!(doc_cfg)),
1529 pub struct GatedCfg {
1535 pub fn gate(cfg: &ast::MetaItem) -> Option<GatedCfg> {
1537 .position(|info| cfg.check_name(info.0))
1546 pub fn check_and_emit(&self, sess: &ParseSess, features: &Features) {
1547 let (cfg, feature, has_feature) = GATED_CFGS[self.index];
1548 if !has_feature(features) && !self.span.allows_unstable(feature) {
1549 let explain = format!("`cfg({})` is experimental and subject to change", cfg);
1550 emit_feature_err(sess, feature, self.span, GateIssue::Language, &explain);
1555 struct Context<'a> {
1556 features: &'a Features,
1557 parse_sess: &'a ParseSess,
1558 plugin_attributes: &'a [(Symbol, AttributeType)],
1561 macro_rules! gate_feature_fn {
1562 ($cx: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr, $level: expr) => {{
1563 let (cx, has_feature, span,
1564 name, explain, level) = ($cx, $has_feature, $span, $name, $explain, $level);
1565 let has_feature: bool = has_feature(&$cx.features);
1566 debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
1567 if !has_feature && !span.allows_unstable($name) {
1568 leveled_feature_err(cx.parse_sess, name, span, GateIssue::Language, explain, level)
1574 macro_rules! gate_feature {
1575 ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {
1576 gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
1577 sym::$feature, $explain, GateStrength::Hard)
1579 ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {
1580 gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
1581 sym::$feature, $explain, $level)
1585 impl<'a> Context<'a> {
1588 attr: &ast::Attribute,
1589 attr_info: Option<&BuiltinAttribute>,
1592 debug!("check_attribute(attr = {:?})", attr);
1593 if let Some(&(name, ty, _template, ref gateage)) = attr_info {
1594 if let Gated(_, name, desc, ref has_feature) = *gateage {
1595 if !attr.span.allows_unstable(name) {
1597 self, has_feature, attr.span, name, desc, GateStrength::Hard
1600 } else if name == sym::doc {
1601 if let Some(content) = attr.meta_item_list() {
1602 if content.iter().any(|c| c.check_name(sym::include)) {
1603 gate_feature!(self, external_doc, attr.span,
1604 "#[doc(include = \"...\")] is experimental"
1609 debug!("check_attribute: {:?} is builtin, {:?}, {:?}", attr.path, ty, gateage);
1612 for &(n, ty) in self.plugin_attributes {
1614 // Plugins can't gate attributes, so we don't check for it
1615 // unlike the code above; we only use this loop to
1616 // short-circuit to avoid the checks below.
1617 debug!("check_attribute: {:?} is registered by a plugin, {:?}", attr.path, ty);
1621 if !attr::is_known(attr) {
1622 if attr.name_or_empty().as_str().starts_with("rustc_") {
1623 let msg = "unless otherwise specified, attributes with the prefix `rustc_` \
1624 are reserved for internal compiler diagnostics";
1625 gate_feature!(self, rustc_attrs, attr.span, msg);
1626 } else if !is_macro {
1627 // Only run the custom attribute lint during regular feature gate
1628 // checking. Macro gating runs before the plugin attributes are
1629 // registered, so we skip this in that case.
1630 let msg = format!("The attribute `{}` is currently unknown to the compiler and \
1631 may have meaning added to it in the future", attr.path);
1632 gate_feature!(self, custom_attribute, attr.span, &msg);
1638 pub fn check_attribute(attr: &ast::Attribute, parse_sess: &ParseSess, features: &Features) {
1639 let cx = Context { features: features, parse_sess: parse_sess, plugin_attributes: &[] };
1642 attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name).map(|a| *a)),
1647 fn find_lang_feature_issue(feature: Symbol) -> Option<u32> {
1648 if let Some(info) = ACTIVE_FEATURES.iter().find(|t| t.0 == feature) {
1650 // FIXME (#28244): enforce that active features have issue numbers
1651 // assert!(issue.is_some())
1654 // search in Accepted, Removed, or Stable Removed features
1655 let found = ACCEPTED_FEATURES.iter().chain(REMOVED_FEATURES).chain(STABLE_REMOVED_FEATURES)
1656 .find(|t| t.0 == feature);
1658 Some(&(_, _, issue, _)) => issue,
1659 None => panic!("Feature `{}` is not declared anywhere", feature),
1664 pub enum GateIssue {
1666 Library(Option<u32>)
1669 #[derive(Debug, Copy, Clone, PartialEq)]
1670 pub enum GateStrength {
1671 /// A hard error. (Most feature gates should use this.)
1673 /// Only a warning. (Use this only as backwards-compatibility demands.)
1677 pub fn emit_feature_err(
1684 feature_err(sess, feature, span, issue, explain).emit();
1687 pub fn feature_err<'a>(
1688 sess: &'a ParseSess,
1693 ) -> DiagnosticBuilder<'a> {
1694 leveled_feature_err(sess, feature, span, issue, explain, GateStrength::Hard)
1697 fn leveled_feature_err<'a>(
1698 sess: &'a ParseSess,
1703 level: GateStrength,
1704 ) -> DiagnosticBuilder<'a> {
1705 let diag = &sess.span_diagnostic;
1707 let issue = match issue {
1708 GateIssue::Language => find_lang_feature_issue(feature),
1709 GateIssue::Library(lib) => lib,
1712 let mut err = match level {
1713 GateStrength::Hard => {
1714 diag.struct_span_err_with_code(span, explain, stringify_error_code!(E0658))
1716 GateStrength::Soft => diag.struct_span_warn(span, explain),
1720 None | Some(0) => {} // We still accept `0` as a stand-in for backwards compatibility
1723 "for more information, see https://github.com/rust-lang/rust/issues/{}",
1729 // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
1730 if sess.unstable_features.is_nightly_build() {
1731 err.help(&format!("add #![feature({})] to the crate attributes to enable", feature));
1734 // If we're on stable and only emitting a "soft" warning, add a note to
1735 // clarify that the feature isn't "on" (rather than being on but
1737 if !sess.unstable_features.is_nightly_build() && level == GateStrength::Soft {
1738 err.help("a nightly build of the compiler is required to enable this feature");
1745 const EXPLAIN_BOX_SYNTAX: &str =
1746 "box expression syntax is experimental; you can call `Box::new` instead";
1748 pub const EXPLAIN_STMT_ATTR_SYNTAX: &str =
1749 "attributes on expressions are experimental";
1751 pub const EXPLAIN_ASM: &str =
1752 "inline assembly is not stable enough for use and is subject to change";
1754 pub const EXPLAIN_GLOBAL_ASM: &str =
1755 "`global_asm!` is not stable enough for use and is subject to change";
1757 pub const EXPLAIN_CUSTOM_TEST_FRAMEWORKS: &str =
1758 "custom test frameworks are an unstable feature";
1760 pub const EXPLAIN_LOG_SYNTAX: &str =
1761 "`log_syntax!` is not stable enough for use and is subject to change";
1763 pub const EXPLAIN_CONCAT_IDENTS: &str =
1764 "`concat_idents` is not stable enough for use and is subject to change";
1766 pub const EXPLAIN_FORMAT_ARGS_NL: &str =
1767 "`format_args_nl` is only for internal language use and is subject to change";
1769 pub const EXPLAIN_TRACE_MACROS: &str =
1770 "`trace_macros` is not stable enough for use and is subject to change";
1771 pub const EXPLAIN_ALLOW_INTERNAL_UNSTABLE: &str =
1772 "allow_internal_unstable side-steps feature gating and stability checks";
1773 pub const EXPLAIN_ALLOW_INTERNAL_UNSAFE: &str =
1774 "allow_internal_unsafe side-steps the unsafe_code lint";
1776 pub const EXPLAIN_UNSIZED_TUPLE_COERCION: &str =
1777 "unsized tuple coercion is not stable enough for use and is subject to change";
1779 struct PostExpansionVisitor<'a> {
1780 context: &'a Context<'a>,
1781 builtin_attributes: &'static FxHashMap<Symbol, &'static BuiltinAttribute>,
1784 macro_rules! gate_feature_post {
1785 ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {{
1786 let (cx, span) = ($cx, $span);
1787 if !span.allows_unstable(sym::$feature) {
1788 gate_feature!(cx.context, $feature, span, $explain)
1791 ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {{
1792 let (cx, span) = ($cx, $span);
1793 if !span.allows_unstable(sym::$feature) {
1794 gate_feature!(cx.context, $feature, span, $explain, $level)
1799 impl<'a> PostExpansionVisitor<'a> {
1800 fn check_abi(&self, abi: Abi, span: Span) {
1802 Abi::RustIntrinsic => {
1803 gate_feature_post!(&self, intrinsics, span,
1804 "intrinsics are subject to change");
1806 Abi::PlatformIntrinsic => {
1807 gate_feature_post!(&self, platform_intrinsics, span,
1808 "platform intrinsics are experimental and possibly buggy");
1810 Abi::Vectorcall => {
1811 gate_feature_post!(&self, abi_vectorcall, span,
1812 "vectorcall is experimental and subject to change");
1815 gate_feature_post!(&self, abi_thiscall, span,
1816 "thiscall is experimental and subject to change");
1819 gate_feature_post!(&self, unboxed_closures, span,
1820 "rust-call ABI is subject to change");
1823 gate_feature_post!(&self, abi_ptx, span,
1824 "PTX ABIs are experimental and subject to change");
1826 Abi::Unadjusted => {
1827 gate_feature_post!(&self, abi_unadjusted, span,
1828 "unadjusted ABI is an implementation detail and perma-unstable");
1830 Abi::Msp430Interrupt => {
1831 gate_feature_post!(&self, abi_msp430_interrupt, span,
1832 "msp430-interrupt ABI is experimental and subject to change");
1834 Abi::X86Interrupt => {
1835 gate_feature_post!(&self, abi_x86_interrupt, span,
1836 "x86-interrupt ABI is experimental and subject to change");
1838 Abi::AmdGpuKernel => {
1839 gate_feature_post!(&self, abi_amdgpu_kernel, span,
1840 "amdgpu-kernel ABI is experimental and subject to change");
1855 fn check_builtin_attribute(&mut self, attr: &ast::Attribute, name: Symbol,
1856 template: AttributeTemplate) {
1857 // Some special attributes like `cfg` must be checked
1858 // before the generic check, so we skip them here.
1859 let should_skip = |name| name == sym::cfg;
1860 // Some of previously accepted forms were used in practice,
1861 // report them as warnings for now.
1862 let should_warn = |name| name == sym::doc || name == sym::ignore ||
1863 name == sym::inline || name == sym::link;
1865 match attr.parse_meta(self.context.parse_sess) {
1866 Ok(meta) => if !should_skip(name) && !template.compatible(&meta.node) {
1867 let error_msg = format!("malformed `{}` attribute input", name);
1868 let mut msg = "attribute must be of the form ".to_owned();
1869 let mut suggestions = vec![];
1870 let mut first = true;
1873 let code = format!("#[{}]", name);
1874 msg.push_str(&format!("`{}`", &code));
1875 suggestions.push(code);
1877 if let Some(descr) = template.list {
1879 msg.push_str(" or ");
1882 let code = format!("#[{}({})]", name, descr);
1883 msg.push_str(&format!("`{}`", &code));
1884 suggestions.push(code);
1886 if let Some(descr) = template.name_value_str {
1888 msg.push_str(" or ");
1890 let code = format!("#[{} = \"{}\"]", name, descr);
1891 msg.push_str(&format!("`{}`", &code));
1892 suggestions.push(code);
1894 if should_warn(name) {
1895 self.context.parse_sess.buffer_lint(
1896 BufferedEarlyLintId::IllFormedAttributeInput,
1902 self.context.parse_sess.span_diagnostic.struct_span_err(meta.span, &error_msg)
1905 if suggestions.len() == 1 {
1906 "must be of the form"
1908 "the following are the possible correct uses"
1910 suggestions.into_iter(),
1911 Applicability::HasPlaceholders,
1915 Err(mut err) => err.emit(),
1920 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
1921 fn visit_attribute(&mut self, attr: &ast::Attribute) {
1922 let attr_info = attr.ident().and_then(|ident| {
1923 self.builtin_attributes.get(&ident.name).map(|a| *a)
1926 // Check for gated attributes.
1927 self.context.check_attribute(attr, attr_info, false);
1929 if attr.check_name(sym::doc) {
1930 if let Some(content) = attr.meta_item_list() {
1931 if content.len() == 1 && content[0].check_name(sym::cfg) {
1932 gate_feature_post!(&self, doc_cfg, attr.span,
1933 "#[doc(cfg(...))] is experimental"
1935 } else if content.iter().any(|c| c.check_name(sym::masked)) {
1936 gate_feature_post!(&self, doc_masked, attr.span,
1937 "#[doc(masked)] is experimental"
1939 } else if content.iter().any(|c| c.check_name(sym::spotlight)) {
1940 gate_feature_post!(&self, doc_spotlight, attr.span,
1941 "#[doc(spotlight)] is experimental"
1943 } else if content.iter().any(|c| c.check_name(sym::alias)) {
1944 gate_feature_post!(&self, doc_alias, attr.span,
1945 "#[doc(alias = \"...\")] is experimental"
1947 } else if content.iter().any(|c| c.check_name(sym::keyword)) {
1948 gate_feature_post!(&self, doc_keyword, attr.span,
1949 "#[doc(keyword = \"...\")] is experimental"
1956 Some(&(name, _, template, _)) => self.check_builtin_attribute(
1961 None => if let Some(TokenTree::Token(token)) = attr.tokens.trees().next() {
1962 if token == token::Eq {
1963 // All key-value attributes are restricted to meta-item syntax.
1964 attr.parse_meta(self.context.parse_sess).map_err(|mut err| err.emit()).ok();
1970 fn visit_name(&mut self, sp: Span, name: ast::Name) {
1971 if !name.as_str().is_ascii() {
1975 self.context.parse_sess.source_map().def_span(sp),
1976 "non-ascii idents are not fully supported"
1981 fn visit_item(&mut self, i: &'a ast::Item) {
1983 ast::ItemKind::Const(_,_) => {
1984 if i.ident.name == kw::Underscore {
1985 gate_feature_post!(&self, underscore_const_names, i.span,
1986 "naming constants with `_` is unstable");
1990 ast::ItemKind::ForeignMod(ref foreign_module) => {
1991 self.check_abi(foreign_module.abi, i.span);
1994 ast::ItemKind::Fn(..) => {
1995 if attr::contains_name(&i.attrs[..], sym::plugin_registrar) {
1996 gate_feature_post!(&self, plugin_registrar, i.span,
1997 "compiler plugins are experimental and possibly buggy");
1999 if attr::contains_name(&i.attrs[..], sym::start) {
2000 gate_feature_post!(&self, start, i.span,
2001 "a #[start] function is an experimental \
2002 feature whose signature may change \
2005 if attr::contains_name(&i.attrs[..], sym::main) {
2006 gate_feature_post!(&self, main, i.span,
2007 "declaration of a nonstandard #[main] \
2008 function may change over time, for now \
2009 a top-level `fn main()` is required");
2013 ast::ItemKind::Struct(..) => {
2014 for attr in attr::filter_by_name(&i.attrs[..], sym::repr) {
2015 for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
2016 if item.check_name(sym::simd) {
2017 gate_feature_post!(&self, repr_simd, attr.span,
2018 "SIMD types are experimental and possibly buggy");
2024 ast::ItemKind::Enum(..) => {
2025 for attr in attr::filter_by_name(&i.attrs[..], sym::repr) {
2026 for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
2027 if item.check_name(sym::align) {
2028 gate_feature_post!(&self, repr_align_enum, attr.span,
2029 "`#[repr(align(x))]` on enums is experimental");
2035 ast::ItemKind::Impl(_, polarity, defaultness, _, _, _, _) => {
2036 if polarity == ast::ImplPolarity::Negative {
2037 gate_feature_post!(&self, optin_builtin_traits,
2039 "negative trait bounds are not yet fully implemented; \
2040 use marker types for now");
2043 if let ast::Defaultness::Default = defaultness {
2044 gate_feature_post!(&self, specialization,
2046 "specialization is unstable");
2050 ast::ItemKind::Trait(ast::IsAuto::Yes, ..) => {
2051 gate_feature_post!(&self, optin_builtin_traits,
2053 "auto traits are experimental and possibly buggy");
2056 ast::ItemKind::TraitAlias(..) => {
2061 "trait aliases are experimental"
2065 ast::ItemKind::MacroDef(ast::MacroDef { legacy: false, .. }) => {
2066 let msg = "`macro` is experimental";
2067 gate_feature_post!(&self, decl_macro, i.span, msg);
2070 ast::ItemKind::Existential(..) => {
2075 "existential types are unstable"
2082 visit::walk_item(self, i);
2085 fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
2087 ast::ForeignItemKind::Fn(..) |
2088 ast::ForeignItemKind::Static(..) => {
2089 let link_name = attr::first_attr_value_str_by_name(&i.attrs, sym::link_name);
2090 let links_to_llvm = match link_name {
2091 Some(val) => val.as_str().starts_with("llvm."),
2095 gate_feature_post!(&self, link_llvm_intrinsics, i.span,
2096 "linking to LLVM intrinsics is experimental");
2099 ast::ForeignItemKind::Ty => {
2100 gate_feature_post!(&self, extern_types, i.span,
2101 "extern types are experimental");
2103 ast::ForeignItemKind::Macro(..) => {}
2106 visit::walk_foreign_item(self, i)
2109 fn visit_ty(&mut self, ty: &'a ast::Ty) {
2111 ast::TyKind::BareFn(ref bare_fn_ty) => {
2112 self.check_abi(bare_fn_ty.abi, ty.span);
2114 ast::TyKind::Never => {
2115 gate_feature_post!(&self, never_type, ty.span,
2116 "The `!` type is experimental");
2120 visit::walk_ty(self, ty)
2123 fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FunctionRetTy) {
2124 if let ast::FunctionRetTy::Ty(ref output_ty) = *ret_ty {
2125 if let ast::TyKind::Never = output_ty.node {
2128 self.visit_ty(output_ty)
2133 fn visit_expr(&mut self, e: &'a ast::Expr) {
2135 ast::ExprKind::Box(_) => {
2136 gate_feature_post!(&self, box_syntax, e.span, EXPLAIN_BOX_SYNTAX);
2138 ast::ExprKind::Type(..) => {
2139 // To avoid noise about type ascription in common syntax errors, only emit if it
2140 // is the *only* error.
2141 if self.context.parse_sess.span_diagnostic.err_count() == 0 {
2142 gate_feature_post!(&self, type_ascription, e.span,
2143 "type ascription is experimental");
2146 ast::ExprKind::Yield(..) => {
2147 gate_feature_post!(&self, generators,
2149 "yield syntax is experimental");
2151 ast::ExprKind::TryBlock(_) => {
2152 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
2154 ast::ExprKind::Block(_, opt_label) => {
2155 if let Some(label) = opt_label {
2156 gate_feature_post!(&self, label_break_value, label.ident.span,
2157 "labels on blocks are unstable");
2160 ast::ExprKind::Closure(_, ast::IsAsync::Async { .. }, ..) => {
2161 gate_feature_post!(&self, async_await, e.span, "async closures are unstable");
2163 ast::ExprKind::Async(..) => {
2164 gate_feature_post!(&self, async_await, e.span, "async blocks are unstable");
2166 ast::ExprKind::Await(origin, _) => {
2168 ast::AwaitOrigin::FieldLike =>
2169 gate_feature_post!(&self, async_await, e.span, "async/await is unstable"),
2170 ast::AwaitOrigin::MacroLike =>
2175 "`await!(<expr>)` macro syntax is unstable, and will soon be removed \
2176 in favor of `<expr>.await` syntax."
2182 visit::walk_expr(self, e)
2185 fn visit_arm(&mut self, arm: &'a ast::Arm) {
2186 visit::walk_arm(self, arm)
2189 fn visit_pat(&mut self, pattern: &'a ast::Pat) {
2190 match pattern.node {
2191 PatKind::Slice(_, Some(ref subslice), _) => {
2192 gate_feature_post!(&self, slice_patterns,
2194 "syntax for subslices in slice patterns is not yet stabilized");
2196 PatKind::Box(..) => {
2197 gate_feature_post!(&self, box_patterns,
2199 "box pattern syntax is experimental");
2201 PatKind::Range(_, _, Spanned { node: RangeEnd::Excluded, .. }) => {
2202 gate_feature_post!(&self, exclusive_range_pattern, pattern.span,
2203 "exclusive range pattern syntax is experimental");
2207 visit::walk_pat(self, pattern)
2210 fn visit_fn(&mut self,
2211 fn_kind: FnKind<'a>,
2212 fn_decl: &'a ast::FnDecl,
2215 if let Some(header) = fn_kind.header() {
2216 // Check for const fn and async fn declarations.
2217 if header.asyncness.node.is_async() {
2218 gate_feature_post!(&self, async_await, span, "async fn is unstable");
2221 // Stability of const fn methods are covered in
2222 // `visit_trait_item` and `visit_impl_item` below; this is
2223 // because default methods don't pass through this point.
2224 self.check_abi(header.abi, span);
2227 if fn_decl.c_variadic {
2228 gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
2231 visit::walk_fn(self, fn_kind, fn_decl, span)
2234 fn visit_generic_param(&mut self, param: &'a GenericParam) {
2236 GenericParamKind::Const { .. } =>
2237 gate_feature_post!(&self, const_generics, param.ident.span,
2238 "const generics are unstable"),
2241 visit::walk_generic_param(self, param)
2244 fn visit_assoc_ty_constraint(&mut self, constraint: &'a AssocTyConstraint) {
2245 match constraint.kind {
2246 AssocTyConstraintKind::Bound { .. } =>
2247 gate_feature_post!(&self, associated_type_bounds, constraint.span,
2248 "associated type bounds are unstable"),
2251 visit::walk_assoc_ty_constraint(self, constraint)
2254 fn visit_trait_item(&mut self, ti: &'a ast::TraitItem) {
2256 ast::TraitItemKind::Method(ref sig, ref block) => {
2257 if block.is_none() {
2258 self.check_abi(sig.header.abi, ti.span);
2260 if sig.header.asyncness.node.is_async() {
2261 gate_feature_post!(&self, async_await, ti.span, "async fn is unstable");
2263 if sig.decl.c_variadic {
2264 gate_feature_post!(&self, c_variadic, ti.span,
2265 "C-variadic functions are unstable");
2267 if sig.header.constness.node == ast::Constness::Const {
2268 gate_feature_post!(&self, const_fn, ti.span, "const fn is unstable");
2271 ast::TraitItemKind::Type(_, ref default) => {
2272 // We use three if statements instead of something like match guards so that all
2273 // of these errors can be emitted if all cases apply.
2274 if default.is_some() {
2275 gate_feature_post!(&self, associated_type_defaults, ti.span,
2276 "associated type defaults are unstable");
2278 if !ti.generics.params.is_empty() {
2279 gate_feature_post!(&self, generic_associated_types, ti.span,
2280 "generic associated types are unstable");
2282 if !ti.generics.where_clause.predicates.is_empty() {
2283 gate_feature_post!(&self, generic_associated_types, ti.span,
2284 "where clauses on associated types are unstable");
2289 visit::walk_trait_item(self, ti)
2292 fn visit_impl_item(&mut self, ii: &'a ast::ImplItem) {
2293 if ii.defaultness == ast::Defaultness::Default {
2294 gate_feature_post!(&self, specialization,
2296 "specialization is unstable");
2300 ast::ImplItemKind::Method(..) => {}
2301 ast::ImplItemKind::Existential(..) => {
2306 "existential types are unstable"
2309 ast::ImplItemKind::Type(_) => {
2310 if !ii.generics.params.is_empty() {
2311 gate_feature_post!(&self, generic_associated_types, ii.span,
2312 "generic associated types are unstable");
2314 if !ii.generics.where_clause.predicates.is_empty() {
2315 gate_feature_post!(&self, generic_associated_types, ii.span,
2316 "where clauses on associated types are unstable");
2321 visit::walk_impl_item(self, ii)
2324 fn visit_vis(&mut self, vis: &'a ast::Visibility) {
2325 if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.node {
2326 gate_feature_post!(&self, crate_visibility_modifier, vis.span,
2327 "`crate` visibility modifier is experimental");
2329 visit::walk_vis(self, vis)
2333 pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
2334 crate_edition: Edition, allow_features: &Option<Vec<String>>) -> Features {
2335 fn feature_removed(span_handler: &Handler, span: Span, reason: Option<&str>) {
2336 let mut err = struct_span_err!(span_handler, span, E0557, "feature has been removed");
2337 if let Some(reason) = reason {
2338 err.span_note(span, reason);
2340 err.span_label(span, "feature has been removed");
2345 let mut features = Features::new();
2346 let mut edition_enabled_features = FxHashMap::default();
2348 for &edition in ALL_EDITIONS {
2349 if edition <= crate_edition {
2350 // The `crate_edition` implies its respective umbrella feature-gate
2351 // (i.e., `#![feature(rust_20XX_preview)]` isn't needed on edition 20XX).
2352 edition_enabled_features.insert(edition.feature_name(), edition);
2356 for &(name, .., f_edition, set) in ACTIVE_FEATURES {
2357 if let Some(f_edition) = f_edition {
2358 if f_edition <= crate_edition {
2359 set(&mut features, DUMMY_SP);
2360 edition_enabled_features.insert(name, crate_edition);
2365 // Process the edition umbrella feature-gates first, to ensure
2366 // `edition_enabled_features` is completed before it's queried.
2367 for attr in krate_attrs {
2368 if !attr.check_name(sym::feature) {
2372 let list = match attr.meta_item_list() {
2382 let name = mi.name_or_empty();
2383 if INCOMPLETE_FEATURES.iter().any(|f| name == *f) {
2384 span_handler.struct_span_warn(
2387 "the feature `{}` is incomplete and may cause the compiler to crash",
2393 if let Some(edition) = ALL_EDITIONS.iter().find(|e| name == e.feature_name()) {
2394 if *edition <= crate_edition {
2398 for &(name, .., f_edition, set) in ACTIVE_FEATURES {
2399 if let Some(f_edition) = f_edition {
2400 if f_edition <= *edition {
2401 // FIXME(Manishearth) there is currently no way to set
2402 // lib features by edition
2403 set(&mut features, DUMMY_SP);
2404 edition_enabled_features.insert(name, *edition);
2412 for attr in krate_attrs {
2413 if !attr.check_name(sym::feature) {
2417 let list = match attr.meta_item_list() {
2422 let bad_input = |span| {
2423 struct_span_err!(span_handler, span, E0556, "malformed `feature` attribute input")
2427 let name = match mi.ident() {
2428 Some(ident) if mi.is_word() => ident.name,
2430 bad_input(mi.span()).span_suggestion(
2432 "expected just one word",
2433 format!("{}", ident.name),
2434 Applicability::MaybeIncorrect,
2439 bad_input(mi.span()).span_label(mi.span(), "expected just one word").emit();
2444 if let Some(edition) = edition_enabled_features.get(&name) {
2449 "the feature `{}` is included in the Rust {} edition",
2456 if ALL_EDITIONS.iter().any(|e| name == e.feature_name()) {
2457 // Handled in the separate loop above.
2461 let removed = REMOVED_FEATURES.iter().find(|f| name == f.0);
2462 let stable_removed = STABLE_REMOVED_FEATURES.iter().find(|f| name == f.0);
2463 if let Some((.., reason)) = removed.or(stable_removed) {
2464 feature_removed(span_handler, mi.span(), *reason);
2468 if let Some((_, since, ..)) = ACCEPTED_FEATURES.iter().find(|f| name == f.0) {
2469 let since = Some(Symbol::intern(since));
2470 features.declared_lang_features.push((name, mi.span(), since));
2474 if let Some(allowed) = allow_features.as_ref() {
2475 if allowed.iter().find(|f| *f == name.as_str()).is_none() {
2476 span_err!(span_handler, mi.span(), E0725,
2477 "the feature `{}` is not in the list of allowed features",
2483 if let Some((.., set)) = ACTIVE_FEATURES.iter().find(|f| name == f.0) {
2484 set(&mut features, mi.span());
2485 features.declared_lang_features.push((name, mi.span(), None));
2489 features.declared_lib_features.push((name, mi.span()));
2496 pub fn check_crate(krate: &ast::Crate,
2498 features: &Features,
2499 plugin_attributes: &[(Symbol, AttributeType)],
2500 unstable: UnstableFeatures) {
2501 maybe_stage_features(&sess.span_diagnostic, krate, unstable);
2507 let visitor = &mut PostExpansionVisitor {
2509 builtin_attributes: &*BUILTIN_ATTRIBUTE_MAP,
2511 visit::walk_crate(visitor, krate);
2514 #[derive(Clone, Copy, Hash)]
2515 pub enum UnstableFeatures {
2516 /// Hard errors for unstable features are active, as on beta/stable channels.
2518 /// Allow features to be activated, as on nightly.
2520 /// Errors are bypassed for bootstrapping. This is required any time
2521 /// during the build that feature-related lints are set to warn or above
2522 /// because the build turns on warnings-as-errors and uses lots of unstable
2523 /// features. As a result, this is always required for building Rust itself.
2527 impl UnstableFeatures {
2528 pub fn from_environment() -> UnstableFeatures {
2529 // Whether this is a feature-staged build, i.e., on the beta or stable channel
2530 let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
2531 // Whether we should enable unstable features for bootstrapping
2532 let bootstrap = env::var("RUSTC_BOOTSTRAP").is_ok();
2533 match (disable_unstable_features, bootstrap) {
2534 (_, true) => UnstableFeatures::Cheat,
2535 (true, _) => UnstableFeatures::Disallow,
2536 (false, _) => UnstableFeatures::Allow
2540 pub fn is_nightly_build(&self) -> bool {
2542 UnstableFeatures::Allow | UnstableFeatures::Cheat => true,
2548 fn maybe_stage_features(span_handler: &Handler, krate: &ast::Crate,
2549 unstable: UnstableFeatures) {
2550 let allow_features = match unstable {
2551 UnstableFeatures::Allow => true,
2552 UnstableFeatures::Disallow => false,
2553 UnstableFeatures::Cheat => true
2555 if !allow_features {
2556 for attr in &krate.attrs {
2557 if attr.check_name(sym::feature) {
2558 let release_channel = option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)");
2559 span_err!(span_handler, attr.span, E0554,
2560 "#![feature] may not be used on the {} release channel",