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
15 use self::AttributeType::*;
16 use self::AttributeGate::*;
18 use rustc_data_structures::fx::FxHashMap;
19 use rustc_target::spec::abi::Abi;
20 use ast::{self, NodeId, PatKind, RangeEnd};
22 use early_buffered_lints::BufferedEarlyLintId;
23 use source_map::Spanned;
24 use edition::{ALL_EDITIONS, Edition};
25 use syntax_pos::{Span, DUMMY_SP};
26 use errors::{DiagnosticBuilder, Handler};
27 use visit::{self, FnKind, Visitor};
35 fn f(features: &mut Features, _: Span) {
36 features.$field = true;
38 f as fn(&mut Features, Span)
42 macro_rules! declare_features {
43 ($((active, $feature: ident, $ver: expr, $issue: expr, $edition: expr),)+) => {
44 /// Represents active features that are currently being implemented or
45 /// currently being considered for addition/removal.
46 const ACTIVE_FEATURES:
47 &[(&str, &str, Option<u32>, Option<Edition>, fn(&mut Features, Span))] =
48 &[$((stringify!($feature), $ver, $issue, $edition, set!($feature))),+];
50 /// A set of features to be used by later passes.
53 /// `#![feature]` attrs for language features, for error reporting
54 pub declared_lang_features: Vec<(Symbol, Span, Option<Symbol>)>,
55 /// `#![feature]` attrs for non-language (library) features
56 pub declared_lib_features: Vec<(Symbol, Span)>,
57 $(pub $feature: bool),+
61 pub fn new() -> Features {
63 declared_lang_features: Vec::new(),
64 declared_lib_features: Vec::new(),
69 pub fn walk_feature_fields<F>(&self, mut f: F)
70 where F: FnMut(&str, bool)
72 $(f(stringify!($feature), self.$feature);)+
77 ($((removed, $feature: ident, $ver: expr, $issue: expr, None, $reason: expr),)+) => {
78 /// Represents unstable features which have since been removed (it was once Active)
79 const REMOVED_FEATURES: &[(&str, &str, Option<u32>, Option<&str>)] = &[
80 $((stringify!($feature), $ver, $issue, $reason)),+
84 ($((stable_removed, $feature: ident, $ver: expr, $issue: expr, None),)+) => {
85 /// Represents stable features which have since been removed (it was once Accepted)
86 const STABLE_REMOVED_FEATURES: &[(&str, &str, Option<u32>, Option<&str>)] = &[
87 $((stringify!($feature), $ver, $issue, None)),+
91 ($((accepted, $feature: ident, $ver: expr, $issue: expr, None),)+) => {
92 /// Those language feature has since been Accepted (it was once Active)
93 const ACCEPTED_FEATURES: &[(&str, &str, Option<u32>, Option<&str>)] = &[
94 $((stringify!($feature), $ver, $issue, None)),+
99 // If you change this, please modify `src/doc/unstable-book` as well.
101 // Don't ever remove anything from this list; set them to 'Removed'.
103 // The version numbers here correspond to the version in which the current status
104 // was set. This is most important for knowing when a particular feature became
107 // N.B., `tools/tidy/src/features.rs` parses this information directly out of the
108 // source, so take care when modifying it.
111 (active, asm, "1.0.0", Some(29722), None),
112 (active, concat_idents, "1.0.0", Some(29599), None),
113 (active, link_args, "1.0.0", Some(29596), None),
114 (active, log_syntax, "1.0.0", Some(29598), None),
115 (active, non_ascii_idents, "1.0.0", Some(55467), None),
116 (active, plugin_registrar, "1.0.0", Some(29597), None),
117 (active, thread_local, "1.0.0", Some(29594), None),
118 (active, trace_macros, "1.0.0", Some(29598), None),
120 // rustc internal, for now
121 (active, intrinsics, "1.0.0", None, None),
122 (active, lang_items, "1.0.0", None, None),
123 (active, format_args_nl, "1.29.0", None, None),
125 (active, link_llvm_intrinsics, "1.0.0", Some(29602), None),
126 (active, linkage, "1.0.0", Some(29603), None),
129 (active, rustc_diagnostic_macros, "1.0.0", None, None),
130 (active, rustc_const_unstable, "1.0.0", None, None),
131 (active, box_syntax, "1.0.0", Some(49733), None),
132 (active, unboxed_closures, "1.0.0", Some(29625), None),
134 (active, fundamental, "1.0.0", Some(29635), None),
135 (active, main, "1.0.0", Some(29634), None),
136 (active, needs_allocator, "1.4.0", Some(27389), None),
137 (active, on_unimplemented, "1.0.0", Some(29628), None),
138 (active, plugin, "1.0.0", Some(29597), None),
139 (active, simd_ffi, "1.0.0", Some(27731), None),
140 (active, start, "1.0.0", Some(29633), None),
141 (active, structural_match, "1.8.0", Some(31434), None),
142 (active, panic_runtime, "1.10.0", Some(32837), None),
143 (active, needs_panic_runtime, "1.10.0", Some(32837), None),
145 // Features specific to OIBIT (auto traits)
146 (active, optin_builtin_traits, "1.0.0", Some(13231), None),
148 // Allows `#[staged_api]`.
151 (active, staged_api, "1.0.0", None, None),
153 // Allows `#![no_core]`.
154 (active, no_core, "1.3.0", Some(29639), None),
156 // Allows the use of `box` in patterns (RFC 469).
157 (active, box_patterns, "1.0.0", Some(29641), None),
159 // Allows the use of the `unsafe_destructor_blind_to_params` attribute (RFC 1238).
160 (active, dropck_parametricity, "1.3.0", Some(28498), None),
162 // Allows using the `may_dangle` attribute (RFC 1327).
163 (active, dropck_eyepatch, "1.10.0", Some(34761), None),
165 // Allows the use of custom attributes (RFC 572).
166 (active, custom_attribute, "1.0.0", Some(29642), None),
168 // Allows the use of `rustc_*` attributes (RFC 572).
169 (active, rustc_attrs, "1.0.0", Some(29642), None),
171 // Allows the use of non lexical lifetimes (RFC 2094).
172 (active, nll, "1.0.0", Some(43234), None),
174 // Allows the use of `#[allow_internal_unstable]`. This is an
175 // attribute on `macro_rules!` and can't use the attribute handling
176 // below (it has to be checked before expansion possibly makes
177 // macros disappear).
180 (active, allow_internal_unstable, "1.0.0", None, None),
182 // Allows the use of `#[allow_internal_unsafe]`. This is an
183 // attribute on `macro_rules!` and can't use the attribute handling
184 // below (it has to be checked before expansion possibly makes
185 // macros disappear).
188 (active, allow_internal_unsafe, "1.0.0", None, None),
190 // Allows the use of slice patterns (issue #23121).
191 (active, slice_patterns, "1.0.0", Some(23121), None),
193 // Allows the definition of `const` functions with some advanced features.
194 (active, const_fn, "1.2.0", Some(57563), None),
196 // Allows accessing fields of unions inside `const` functions.
197 (active, const_fn_union, "1.27.0", Some(51909), None),
199 // Allows casting raw pointers to `usize` during const eval.
200 (active, const_raw_ptr_to_usize_cast, "1.27.0", Some(51910), None),
202 // Allows dereferencing raw pointers during const eval.
203 (active, const_raw_ptr_deref, "1.27.0", Some(51911), None),
205 // Allows reinterpretation of the bits of a value of one type as another type during const eval.
206 (active, const_transmute, "1.29.0", Some(53605), None),
208 // Allows comparing raw pointers during const eval.
209 (active, const_compare_raw_pointers, "1.27.0", Some(53020), None),
211 // Allows panicking during const eval (producing compile-time errors).
212 (active, const_panic, "1.30.0", Some(51999), None),
214 // Allows using `#[prelude_import]` on glob `use` items.
217 (active, prelude_import, "1.2.0", None, None),
219 // Allows default type parameters to influence type inference.
220 (active, default_type_parameter_fallback, "1.3.0", Some(27336), None),
222 // Allows associated type defaults.
223 (active, associated_type_defaults, "1.2.0", Some(29661), None),
225 // Allows `repr(simd)` and importing the various simd intrinsics.
226 (active, repr_simd, "1.4.0", Some(27731), None),
228 // Allows `extern "platform-intrinsic" { ... }`.
229 (active, platform_intrinsics, "1.4.0", Some(27731), None),
231 // Allows `#[unwind(..)]`.
233 // rustc internal for rust runtime
234 (active, unwind_attributes, "1.4.0", None, None),
236 // Allows the use of `#[naked]` on functions.
237 (active, naked_functions, "1.9.0", Some(32408), None),
239 // Allows `#[no_debug]`.
240 (active, no_debug, "1.5.0", Some(29721), None),
242 // Allows `#[omit_gdb_pretty_printer_section]`.
245 (active, omit_gdb_pretty_printer_section, "1.5.0", None, None),
247 // Allows attributes on expressions and non-item statements.
248 (active, stmt_expr_attributes, "1.6.0", Some(15701), None),
250 // Allows the use of type ascription in expressions.
251 (active, type_ascription, "1.6.0", Some(23416), None),
253 // Allows `cfg(target_thread_local)`.
254 (active, cfg_target_thread_local, "1.7.0", Some(29594), None),
257 (active, abi_vectorcall, "1.7.0", None, None),
259 // Allows `X..Y` patterns.
260 (active, exclusive_range_pattern, "1.11.0", Some(37854), None),
262 // impl specialization (RFC 1210)
263 (active, specialization, "1.7.0", Some(31844), None),
265 // Allows `cfg(target_has_atomic = "...")`.
266 (active, cfg_target_has_atomic, "1.9.0", Some(32976), None),
268 // The `!` type. Does not imply 'exhaustive_patterns' (below) any more.
269 (active, never_type, "1.13.0", Some(35121), None),
271 // Allows exhaustive pattern matching on types that contain uninhabited types.
272 (active, exhaustive_patterns, "1.13.0", Some(51085), None),
274 // Allows untagged unions `union U { ... }`.
275 (active, untagged_unions, "1.13.0", Some(32836), None),
277 // Used to identify the `compiler_builtins` crate.
280 (active, compiler_builtins, "1.13.0", None, None),
282 // Allows `#[link(..., cfg(..))]`.
283 (active, link_cfg, "1.14.0", Some(37406), None),
285 // Allows `extern "ptx-*" fn()`.
286 (active, abi_ptx, "1.15.0", Some(38788), None),
288 // The `repr(i128)` annotation for enums.
289 (active, repr128, "1.16.0", Some(35118), None),
291 // The `unadjusted` ABI; perma-unstable.
294 (active, abi_unadjusted, "1.16.0", None, None),
296 // Declarative macros 2.0 (`macro`).
297 (active, decl_macro, "1.17.0", Some(39412), None),
299 // Allows `#[link(kind="static-nobundle"...)]`.
300 (active, static_nobundle, "1.16.0", Some(37403), None),
302 // Allows `extern "msp430-interrupt" fn()`.
303 (active, abi_msp430_interrupt, "1.16.0", Some(38487), None),
305 // Used to identify crates that contain sanitizer runtimes.
308 (active, sanitizer_runtime, "1.17.0", None, None),
310 // Used to identify crates that contain the profiler runtime.
313 (active, profiler_runtime, "1.18.0", None, None),
315 // Allows `extern "x86-interrupt" fn()`.
316 (active, abi_x86_interrupt, "1.17.0", Some(40180), None),
318 // Allows the `try {...}` expression.
319 (active, try_blocks, "1.29.0", Some(31436), None),
321 // Allows module-level inline assembly by way of `global_asm!()`.
322 (active, global_asm, "1.18.0", Some(35119), None),
324 // Allows overlapping impls of marker traits.
325 (active, overlapping_marker_traits, "1.18.0", Some(29864), None),
327 // Trait attribute to allow overlapping impls.
328 (active, marker_trait_attr, "1.30.0", Some(29864), None),
331 (active, abi_thiscall, "1.19.0", None, None),
333 // Allows a test to fail without failing the whole suite.
334 (active, allow_fail, "1.19.0", Some(46488), None),
336 // Allows unsized tuple coercion.
337 (active, unsized_tuple_coercion, "1.20.0", Some(42877), None),
340 (active, generators, "1.21.0", Some(43122), None),
343 (active, trait_alias, "1.24.0", Some(41517), None),
346 (active, allocator_internals, "1.20.0", None, None),
348 // `#[doc(cfg(...))]`
349 (active, doc_cfg, "1.21.0", Some(43781), None),
351 (active, doc_masked, "1.21.0", Some(44027), None),
352 // `#[doc(spotlight)]`
353 (active, doc_spotlight, "1.22.0", Some(45040), None),
354 // `#[doc(include = "some-file")]`
355 (active, external_doc, "1.22.0", Some(44732), None),
357 // Future-proofing enums/structs with `#[non_exhaustive]` attribute (RFC 2008).
358 (active, non_exhaustive, "1.22.0", Some(44109), None),
360 // Adds `crate` as visibility modifier, synonymous with `pub(crate)`.
361 (active, crate_visibility_modifier, "1.23.0", Some(53120), None),
364 (active, extern_types, "1.23.0", Some(43467), None),
366 // Allows trait methods with arbitrary self types.
367 (active, arbitrary_self_types, "1.23.0", Some(44874), None),
369 // In-band lifetime bindings (e.g., `fn foo(x: &'a u8) -> &'a u8`).
370 (active, in_band_lifetimes, "1.23.0", Some(44524), None),
372 // Generic associated types (RFC 1598)
373 (active, generic_associated_types, "1.23.0", Some(44265), None),
375 // Infer static outlives requirements (RFC 2093).
376 (active, infer_static_outlives_requirements, "1.26.0", Some(54185), None),
378 // Allows macro invocations in `extern {}` blocks.
379 (active, macros_in_extern, "1.27.0", Some(49476), None),
381 // `existential type`
382 (active, existential_type, "1.28.0", Some(34511), None),
384 // unstable `#[target_feature]` directives
385 (active, arm_target_feature, "1.27.0", Some(44839), None),
386 (active, aarch64_target_feature, "1.27.0", Some(44839), None),
387 (active, hexagon_target_feature, "1.27.0", Some(44839), None),
388 (active, powerpc_target_feature, "1.27.0", Some(44839), None),
389 (active, mips_target_feature, "1.27.0", Some(44839), None),
390 (active, avx512_target_feature, "1.27.0", Some(44839), None),
391 (active, mmx_target_feature, "1.27.0", Some(44839), None),
392 (active, sse4a_target_feature, "1.27.0", Some(44839), None),
393 (active, tbm_target_feature, "1.27.0", Some(44839), None),
394 (active, wasm_target_feature, "1.30.0", Some(44839), None),
395 (active, adx_target_feature, "1.32.0", Some(44839), None),
396 (active, cmpxchg16b_target_feature, "1.32.0", Some(44839), None),
397 (active, movbe_target_feature, "1.34.0", Some(44839), None),
399 // Allows macro invocations on modules expressions and statements and
400 // procedural macros to expand to non-items.
401 (active, proc_macro_hygiene, "1.30.0", Some(54727), None),
403 // `#[doc(alias = "...")]`
404 (active, doc_alias, "1.27.0", Some(50146), None),
406 // inconsistent bounds in where clauses
407 (active, trivial_bounds, "1.28.0", Some(48214), None),
409 // `'a: { break 'a; }`
410 (active, label_break_value, "1.28.0", Some(48594), None),
412 // Exhaustive pattern matching on `usize` and `isize`.
413 (active, precise_pointer_size_matching, "1.32.0", Some(56354), None),
415 // `#[doc(keyword = "...")]`
416 (active, doc_keyword, "1.28.0", Some(51315), None),
418 // Allows async and await syntax.
419 (active, async_await, "1.28.0", Some(50547), None),
421 // `#[alloc_error_handler]`
422 (active, alloc_error_handler, "1.29.0", Some(51540), None),
424 (active, abi_amdgpu_kernel, "1.29.0", Some(51575), None),
426 // Added for testing E0705; perma-unstable.
427 (active, test_2018_feature, "1.31.0", Some(0), Some(Edition::Edition2018)),
429 // support for arbitrary delimited token streams in non-macro attributes
430 (active, unrestricted_attribute_tokens, "1.30.0", Some(55208), None),
432 // Allows unsized rvalues at arguments and parameters.
433 (active, unsized_locals, "1.30.0", Some(48055), None),
437 (active, custom_test_frameworks, "1.30.0", Some(50297), None),
439 // non-builtin attributes in inner attribute position
440 (active, custom_inner_attributes, "1.30.0", Some(54726), None),
442 // Allow mixing of bind-by-move in patterns and references to
443 // those identifiers in guards, *if* we are using MIR-borrowck
444 // (aka NLL). Essentially this means you need to be using the
445 // 2018 edition or later.
446 (active, bind_by_move_pattern_guards, "1.30.0", Some(15287), None),
448 // Allows `impl Trait` in bindings (`let`, `const`, `static`).
449 (active, impl_trait_in_bindings, "1.30.0", Some(34511), None),
451 // Allows `const _: TYPE = VALUE`.
452 (active, underscore_const_names, "1.31.0", Some(54912), None),
454 // Adds `reason` and `expect` lint attributes.
455 (active, lint_reasons, "1.31.0", Some(54503), None),
457 // Allows paths to enum variants on type aliases.
458 (active, type_alias_enum_variants, "1.31.0", Some(49683), None),
460 // Re-Rebalance coherence
461 (active, re_rebalance_coherence, "1.32.0", Some(55437), None),
464 (active, optimize_attribute, "1.34.0", Some(54882), None),
468 (removed, import_shadowing, "1.0.0", None, None, None),
469 (removed, managed_boxes, "1.0.0", None, None, None),
470 // Allows use of unary negate on unsigned integers, e.g., -e for e: u8
471 (removed, negate_unsigned, "1.0.0", Some(29645), None, None),
472 (removed, reflect, "1.0.0", Some(27749), None, None),
473 // A way to temporarily opt out of opt in copy. This will *never* be accepted.
474 (removed, opt_out_copy, "1.0.0", None, None, None),
475 (removed, quad_precision_float, "1.0.0", None, None, None),
476 (removed, struct_inherit, "1.0.0", None, None, None),
477 (removed, test_removed_feature, "1.0.0", None, None, None),
478 (removed, visible_private_types, "1.0.0", None, None, None),
479 (removed, unsafe_no_drop_flag, "1.0.0", None, None, None),
480 // Allows using items which are missing stability attributes
482 (removed, unmarked_api, "1.0.0", None, None, None),
483 (removed, pushpop_unsafe, "1.2.0", None, None, None),
484 (removed, allocator, "1.0.0", None, None, None),
485 (removed, simd, "1.0.0", Some(27731), None,
486 Some("removed in favor of `#[repr(simd)]`")),
487 (removed, advanced_slice_patterns, "1.0.0", Some(23121), None,
488 Some("merged into `#![feature(slice_patterns)]`")),
489 (removed, macro_reexport, "1.0.0", Some(29638), None,
490 Some("subsumed by `pub use`")),
491 (removed, proc_macro_mod, "1.27.0", Some(54727), None,
492 Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
493 (removed, proc_macro_expr, "1.27.0", Some(54727), None,
494 Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
495 (removed, proc_macro_non_items, "1.27.0", Some(54727), None,
496 Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
497 (removed, proc_macro_gen, "1.27.0", Some(54727), None,
498 Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
499 (removed, panic_implementation, "1.28.0", Some(44489), None,
500 Some("subsumed by `#[panic_handler]`")),
501 // Allows the use of `#[derive(Anything)]` as sugar for `#[derive_Anything]`.
502 (removed, custom_derive, "1.0.0", Some(29644), None,
503 Some("subsumed by `#[proc_macro_derive]`")),
504 // Paths of the form: `extern::foo::bar`
505 (removed, extern_in_paths, "1.33.0", Some(55600), None,
506 Some("subsumed by `::foo::bar` paths")),
507 (removed, quote, "1.0.0", Some(29601), None, None),
511 (stable_removed, no_stack_check, "1.0.0", None, None),
515 (accepted, associated_types, "1.0.0", None, None),
516 // Allows overloading augmented assignment operations like `a += b`.
517 (accepted, augmented_assignments, "1.8.0", Some(28235), None),
518 // Allows empty structs and enum variants with braces.
519 (accepted, braced_empty_structs, "1.8.0", Some(29720), None),
520 // Allows indexing into constant arrays.
521 (accepted, const_indexing, "1.26.0", Some(29947), None),
522 (accepted, default_type_params, "1.0.0", None, None),
523 (accepted, globs, "1.0.0", None, None),
524 (accepted, if_let, "1.0.0", None, None),
525 // A temporary feature gate used to enable parser extensions needed
526 // to bootstrap fix for #5723.
527 (accepted, issue_5723_bootstrap, "1.0.0", None, None),
528 (accepted, macro_rules, "1.0.0", None, None),
529 // Allows using `#![no_std]`.
530 (accepted, no_std, "1.6.0", None, None),
531 (accepted, slicing_syntax, "1.0.0", None, None),
532 (accepted, struct_variant, "1.0.0", None, None),
533 // These are used to test this portion of the compiler, they don't actually
535 (accepted, test_accepted_feature, "1.0.0", None, None),
536 (accepted, tuple_indexing, "1.0.0", None, None),
537 // Allows macros to appear in the type position.
538 (accepted, type_macros, "1.13.0", Some(27245), None),
539 (accepted, while_let, "1.0.0", None, None),
540 // Allows `#[deprecated]` attribute.
541 (accepted, deprecated, "1.9.0", Some(29935), None),
543 (accepted, question_mark, "1.13.0", Some(31436), None),
544 // Allows `..` in tuple (struct) patterns.
545 (accepted, dotdot_in_tuple_patterns, "1.14.0", Some(33627), None),
546 (accepted, item_like_imports, "1.15.0", Some(35120), None),
547 // Allows using `Self` and associated types in struct expressions and patterns.
548 (accepted, more_struct_aliases, "1.16.0", Some(37544), None),
549 // elide `'static` lifetimes in `static`s and `const`s.
550 (accepted, static_in_const, "1.17.0", Some(35897), None),
551 // Allows field shorthands (`x` meaning `x: x`) in struct literal expressions.
552 (accepted, field_init_shorthand, "1.17.0", Some(37340), None),
553 // Allows the definition recursive static items.
554 (accepted, static_recursion, "1.17.0", Some(29719), None),
555 // `pub(restricted)` visibilities (RFC 1422)
556 (accepted, pub_restricted, "1.18.0", Some(32409), None),
557 // `#![windows_subsystem]`
558 (accepted, windows_subsystem, "1.18.0", Some(37499), None),
559 // Allows `break {expr}` with a value inside `loop`s.
560 (accepted, loop_break_value, "1.19.0", Some(37339), None),
561 // Permits numeric fields in struct expressions and patterns.
562 (accepted, relaxed_adts, "1.19.0", Some(35626), None),
563 // Coerces non capturing closures to function pointers.
564 (accepted, closure_to_fn_coercion, "1.19.0", Some(39817), None),
565 // Allows attributes on struct literal fields.
566 (accepted, struct_field_attributes, "1.20.0", Some(38814), None),
567 // Allows the definition of associated constants in `trait` or `impl` blocks.
568 (accepted, associated_consts, "1.20.0", Some(29646), None),
569 // Usage of the `compile_error!` macro.
570 (accepted, compile_error, "1.20.0", Some(40872), None),
571 // See rust-lang/rfcs#1414. Allows code like `let x: &'static u32 = &42` to work.
572 (accepted, rvalue_static_promotion, "1.21.0", Some(38865), None),
573 // Allows `Drop` types in constants (RFC 1440).
574 (accepted, drop_types_in_const, "1.22.0", Some(33156), None),
575 // Allows the sysV64 ABI to be specified on all platforms
576 // instead of just the platforms on which it is the C ABI.
577 (accepted, abi_sysv64, "1.24.0", Some(36167), None),
578 // Allows `repr(align(16))` struct attribute (RFC 1358).
579 (accepted, repr_align, "1.25.0", Some(33626), None),
580 // Allows '|' at beginning of match arms (RFC 1925).
581 (accepted, match_beginning_vert, "1.25.0", Some(44101), None),
582 // Nested groups in `use` (RFC 2128)
583 (accepted, use_nested_groups, "1.25.0", Some(44494), None),
584 // `a..=b` and `..=b`
585 (accepted, inclusive_range_syntax, "1.26.0", Some(28237), None),
586 // Allows `..=` in patterns (RFC 1192).
587 (accepted, dotdoteq_in_patterns, "1.26.0", Some(28237), None),
588 // Termination trait in main (RFC 1937)
589 (accepted, termination_trait, "1.26.0", Some(43301), None),
590 // `Copy`/`Clone` closures (RFC 2132).
591 (accepted, clone_closures, "1.26.0", Some(44490), None),
592 (accepted, copy_closures, "1.26.0", Some(44490), None),
593 // Allows `impl Trait` in function arguments.
594 (accepted, universal_impl_trait, "1.26.0", Some(34511), None),
595 // Allows `impl Trait` in function return types.
596 (accepted, conservative_impl_trait, "1.26.0", Some(34511), None),
598 (accepted, i128_type, "1.26.0", Some(35118), None),
599 // Default match binding modes (RFC 2005)
600 (accepted, match_default_bindings, "1.26.0", Some(42640), None),
601 // Allows `'_` placeholder lifetimes.
602 (accepted, underscore_lifetimes, "1.26.0", Some(44524), None),
603 // Allows attributes on lifetime/type formal parameters in generics (RFC 1327).
604 (accepted, generic_param_attrs, "1.27.0", Some(48848), None),
605 // Allows `cfg(target_feature = "...")`.
606 (accepted, cfg_target_feature, "1.27.0", Some(29717), None),
607 // Allows `#[target_feature(...)]`.
608 (accepted, target_feature, "1.27.0", None, None),
609 // Trait object syntax with `dyn` prefix
610 (accepted, dyn_trait, "1.27.0", Some(44662), None),
611 // Allows `#[must_use]` on functions, and introduces must-use operators (RFC 1940).
612 (accepted, fn_must_use, "1.27.0", Some(43302), None),
613 // Allows use of the `:lifetime` macro fragment specifier.
614 (accepted, macro_lifetime_matcher, "1.27.0", Some(34303), None),
615 // Termination trait in tests (RFC 1937)
616 (accepted, termination_trait_test, "1.27.0", Some(48854), None),
617 // The `#[global_allocator]` attribute
618 (accepted, global_allocator, "1.28.0", Some(27389), None),
619 // Allows `#[repr(transparent)]` attribute on newtype structs.
620 (accepted, repr_transparent, "1.28.0", Some(43036), None),
621 // Procedural macros in `proc-macro` crates
622 (accepted, proc_macro, "1.29.0", Some(38356), None),
623 // `foo.rs` as an alternative to `foo/mod.rs`
624 (accepted, non_modrs_mods, "1.30.0", Some(44660), None),
625 // Allows use of the `:vis` macro fragment specifier
626 (accepted, macro_vis_matcher, "1.30.0", Some(41022), None),
627 // Allows importing and reexporting macros with `use`,
628 // enables macro modularization in general.
629 (accepted, use_extern_macros, "1.30.0", Some(35896), None),
630 // Allows keywords to be escaped for use as identifiers.
631 (accepted, raw_identifiers, "1.30.0", Some(48589), None),
632 // Attributes scoped to tools.
633 (accepted, tool_attributes, "1.30.0", Some(44690), None),
634 // Allows multi-segment paths in attributes and derives.
635 (accepted, proc_macro_path_invoc, "1.30.0", Some(38356), None),
636 // Allows all literals in attribute lists and values of key-value pairs.
637 (accepted, attr_literals, "1.30.0", Some(34981), None),
638 // Infer outlives requirements (RFC 2093).
639 (accepted, infer_outlives_requirements, "1.30.0", Some(44493), None),
640 (accepted, panic_handler, "1.30.0", Some(44489), None),
641 // Used to preserve symbols (see llvm.used).
642 (accepted, used, "1.30.0", Some(40289), None),
644 (accepted, crate_in_paths, "1.30.0", Some(45477), None),
645 // Resolve absolute paths as paths from other crates.
646 (accepted, extern_absolute_paths, "1.30.0", Some(44660), None),
647 // Access to crate names passed via `--extern` through prelude.
648 (accepted, extern_prelude, "1.30.0", Some(44660), None),
649 // Parentheses in patterns
650 (accepted, pattern_parentheses, "1.31.0", Some(51087), None),
651 // Allows the definition of `const fn` functions.
652 (accepted, min_const_fn, "1.31.0", Some(53555), None),
654 (accepted, tool_lints, "1.31.0", Some(44690), None),
655 // `impl<I:Iterator> Iterator for &mut Iterator`
656 // `impl Debug for Foo<'_>`
657 (accepted, impl_header_lifetime_elision, "1.31.0", Some(15872), None),
658 // `extern crate foo as bar;` puts `bar` into extern prelude.
659 (accepted, extern_crate_item_prelude, "1.31.0", Some(55599), None),
660 // Allows use of the `:literal` macro fragment specifier (RFC 1576).
661 (accepted, macro_literal_matcher, "1.32.0", Some(35625), None),
662 // Use `?` as the Kleene "at most one" operator.
663 (accepted, macro_at_most_once_rep, "1.32.0", Some(48075), None),
664 // `Self` struct constructor (RFC 2302)
665 (accepted, self_struct_ctor, "1.32.0", Some(51994), None),
666 // `Self` in type definitions (RFC 2300)
667 (accepted, self_in_typedefs, "1.32.0", Some(49303), None),
668 // Allows `use x::y;` to search `x` in the current scope.
669 (accepted, uniform_paths, "1.32.0", Some(53130), None),
670 // Integer match exhaustiveness checking (RFC 2591)
671 (accepted, exhaustive_integer_patterns, "1.33.0", Some(50907), None),
672 // `use path as _;` and `extern crate c as _;`
673 (accepted, underscore_imports, "1.33.0", Some(48216), None),
674 // Allows `#[repr(packed(N))]` attribute on structs.
675 (accepted, repr_packed, "1.33.0", Some(33158), None),
676 // Allows irrefutable patterns in `if let` and `while let` statements (RFC 2086).
677 (accepted, irrefutable_let_patterns, "1.33.0", Some(44495), None),
678 // Allows calling `const unsafe fn` inside `unsafe` blocks in `const fn` functions.
679 (accepted, min_const_unsafe_fn, "1.33.0", Some(55607), None),
680 // Allows let bindings, assignments and destructuring in `const` functions and constants.
681 // As long as control flow is not implemented in const eval, `&&` and `||` may not be used
682 // at the same time as let bindings.
683 (accepted, const_let, "1.33.0", Some(48821), None),
684 // `#[cfg_attr(predicate, multiple, attributes, here)]`
685 (accepted, cfg_attr_multi, "1.33.0", Some(54881), None),
686 // Top level or-patterns (`p | q`) in `if let` and `while let`.
687 (accepted, if_while_or_patterns, "1.33.0", Some(48215), None),
688 // Allows `cfg(target_vendor = "...")`.
689 (accepted, cfg_target_vendor, "1.33.0", Some(29718), None),
690 // `extern crate self as foo;` puts local crate root into extern prelude under name `foo`.
691 (accepted, extern_crate_self, "1.34.0", Some(56409), None),
694 // If you change this, please modify `src/doc/unstable-book` as well. You must
695 // move that documentation into the relevant place in the other docs, and
696 // remove the chapter on the flag.
698 #[derive(Copy, Clone, PartialEq, Debug)]
699 pub enum AttributeType {
700 /// Normal, builtin attribute that is consumed
701 /// by the compiler before the unused_attribute check
704 /// Builtin attribute that may not be consumed by the compiler
705 /// before the unused_attribute check. These attributes
706 /// will be ignored by the unused_attribute lint
709 /// Builtin attribute that is only allowed at the crate level
713 pub enum AttributeGate {
714 /// Is gated by a given feature gate, reason
715 /// and function to check if enabled
716 Gated(Stability, &'static str, &'static str, fn(&Features) -> bool),
718 /// Ungated attribute, can be used on all release channels
722 /// A template that the attribute input must match.
723 /// Only top-level shape (`#[attr]` vs `#[attr(...)]` vs `#[attr = ...]`) is considered now.
724 #[derive(Clone, Copy)]
725 pub struct AttributeTemplate {
727 list: Option<&'static str>,
728 name_value_str: Option<&'static str>,
731 impl AttributeTemplate {
732 /// Check that the given meta-item is compatible with this template.
733 fn compatible(&self, meta_item_kind: &ast::MetaItemKind) -> bool {
734 match meta_item_kind {
735 ast::MetaItemKind::Word => self.word,
736 ast::MetaItemKind::List(..) => self.list.is_some(),
737 ast::MetaItemKind::NameValue(lit) if lit.node.is_str() => self.name_value_str.is_some(),
738 ast::MetaItemKind::NameValue(..) => false,
743 /// A convenience macro for constructing attribute templates.
744 /// E.g. `template!(Word, List: "description")` means that the attribute
745 /// supports forms `#[attr]` and `#[attr(description)]`.
746 macro_rules! template {
747 (Word) => { template!(@ true, None, None) };
748 (List: $descr: expr) => { template!(@ false, Some($descr), None) };
749 (NameValueStr: $descr: expr) => { template!(@ false, None, Some($descr)) };
750 (Word, List: $descr: expr) => { template!(@ true, Some($descr), None) };
751 (Word, NameValueStr: $descr: expr) => { template!(@ true, None, Some($descr)) };
752 (List: $descr1: expr, NameValueStr: $descr2: expr) => {
753 template!(@ false, Some($descr1), Some($descr2))
755 (Word, List: $descr1: expr, NameValueStr: $descr2: expr) => {
756 template!(@ true, Some($descr1), Some($descr2))
758 (@ $word: expr, $list: expr, $name_value_str: expr) => { AttributeTemplate {
759 word: $word, list: $list, name_value_str: $name_value_str
764 fn is_deprecated(&self) -> bool {
766 Gated(Stability::Deprecated(_, _), ..) => true,
772 #[derive(Copy, Clone, Debug)]
775 // First argument is tracking issue link; second argument is an optional
776 // help message, which defaults to "remove this attribute"
777 Deprecated(&'static str, Option<&'static str>),
781 impl ::std::fmt::Debug for AttributeGate {
782 fn fmt(&self, fmt: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
784 Gated(ref stab, name, expl, _) =>
785 write!(fmt, "Gated({:?}, {}, {})", stab, name, expl),
786 Ungated => write!(fmt, "Ungated")
791 macro_rules! cfg_fn {
792 ($field: ident) => {{
793 fn f(features: &Features) -> bool {
796 f as fn(&Features) -> bool
800 pub fn deprecated_attributes() -> Vec<&'static (&'static str, AttributeType,
801 AttributeTemplate, AttributeGate)> {
802 BUILTIN_ATTRIBUTES.iter().filter(|(.., gate)| gate.is_deprecated()).collect()
805 pub fn is_builtin_attr_name(name: ast::Name) -> bool {
806 BUILTIN_ATTRIBUTES.iter().any(|&(builtin_name, ..)| name == builtin_name)
809 pub fn is_builtin_attr(attr: &ast::Attribute) -> bool {
810 BUILTIN_ATTRIBUTES.iter().any(|&(builtin_name, ..)| attr.path == builtin_name)
813 // Attributes that have a special meaning to rustc or rustdoc
814 pub const BUILTIN_ATTRIBUTES: &[(&str, AttributeType, AttributeTemplate, AttributeGate)] = &[
817 ("warn", Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), Ungated),
818 ("allow", Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), Ungated),
819 ("forbid", Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), Ungated),
820 ("deny", Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), Ungated),
822 ("macro_use", Normal, template!(Word, List: "name1, name2, ..."), Ungated),
823 ("macro_export", Normal, template!(Word, List: "local_inner_macros"), Ungated),
824 ("plugin_registrar", Normal, template!(Word), Ungated),
826 ("cfg", Normal, template!(List: "predicate"), Ungated),
827 ("cfg_attr", Normal, template!(List: "predicate, attr1, attr2, ..."), Ungated),
828 ("main", Normal, template!(Word), Ungated),
829 ("start", Normal, template!(Word), Ungated),
830 ("repr", Normal, template!(List: "C, packed, ..."), Ungated),
831 ("path", Normal, template!(NameValueStr: "file"), Ungated),
832 ("automatically_derived", Normal, template!(Word), Ungated),
833 ("no_mangle", Normal, template!(Word), Ungated),
834 ("no_link", Normal, template!(Word), Ungated),
835 ("derive", Normal, template!(List: "Trait1, Trait2, ..."), Ungated),
836 ("should_panic", Normal, template!(Word, List: r#"expected = "reason"#, NameValueStr: "reason"),
838 ("ignore", Normal, template!(Word, NameValueStr: "reason"), Ungated),
839 ("no_implicit_prelude", Normal, template!(Word), Ungated),
840 ("reexport_test_harness_main", Normal, template!(NameValueStr: "name"), Ungated),
841 ("link_args", Normal, template!(NameValueStr: "args"), Gated(Stability::Unstable,
843 "the `link_args` attribute is experimental and not \
844 portable across platforms, it is recommended to \
845 use `#[link(name = \"foo\")] instead",
846 cfg_fn!(link_args))),
847 ("macro_escape", Normal, template!(Word), Ungated),
850 ("structural_match", Whitelisted, template!(Word), Gated(Stability::Unstable,
852 "the semantics of constant patterns is \
854 cfg_fn!(structural_match))),
857 ("non_exhaustive", Whitelisted, template!(Word), Gated(Stability::Unstable,
859 "non exhaustive is an experimental feature",
860 cfg_fn!(non_exhaustive))),
863 ("marker", Normal, template!(Word), Gated(Stability::Unstable,
865 "marker traits is an experimental feature",
866 cfg_fn!(marker_trait_attr))),
868 ("plugin", CrateLevel, template!(List: "name|name(args)"), Gated(Stability::Unstable,
870 "compiler plugins are experimental \
874 ("no_std", CrateLevel, template!(Word), Ungated),
875 ("no_core", CrateLevel, template!(Word), Gated(Stability::Unstable,
877 "no_core is experimental",
879 ("lang", Normal, template!(NameValueStr: "name"), Gated(Stability::Unstable,
881 "language items are subject to change",
882 cfg_fn!(lang_items))),
883 ("linkage", Whitelisted, template!(NameValueStr: "external|internal|..."),
884 Gated(Stability::Unstable,
886 "the `linkage` attribute is experimental \
887 and not portable across platforms",
889 ("thread_local", Whitelisted, template!(Word), Gated(Stability::Unstable,
891 "`#[thread_local]` is an experimental feature, and does \
892 not currently handle destructors.",
893 cfg_fn!(thread_local))),
895 ("rustc_on_unimplemented", Normal, template!(List:
896 r#"/*opt*/ message = "...", /*opt*/ label = "...", /*opt*/ note = "...""#,
897 NameValueStr: "message"),
898 Gated(Stability::Unstable,
900 "the `#[rustc_on_unimplemented]` attribute \
901 is an experimental feature",
902 cfg_fn!(on_unimplemented))),
903 ("rustc_const_unstable", Normal, template!(List: r#"feature = "name""#),
904 Gated(Stability::Unstable,
905 "rustc_const_unstable",
906 "the `#[rustc_const_unstable]` attribute \
907 is an internal feature",
908 cfg_fn!(rustc_const_unstable))),
909 ("global_allocator", Normal, template!(Word), Ungated),
910 ("default_lib_allocator", Whitelisted, template!(Word), Gated(Stability::Unstable,
911 "allocator_internals",
912 "the `#[default_lib_allocator]` \
913 attribute is an experimental feature",
914 cfg_fn!(allocator_internals))),
915 ("needs_allocator", Normal, template!(Word), Gated(Stability::Unstable,
916 "allocator_internals",
917 "the `#[needs_allocator]` \
918 attribute is an experimental \
920 cfg_fn!(allocator_internals))),
921 ("panic_runtime", Whitelisted, template!(Word), Gated(Stability::Unstable,
923 "the `#[panic_runtime]` attribute is \
924 an experimental feature",
925 cfg_fn!(panic_runtime))),
926 ("needs_panic_runtime", Whitelisted, template!(Word), Gated(Stability::Unstable,
927 "needs_panic_runtime",
928 "the `#[needs_panic_runtime]` \
929 attribute is an experimental \
931 cfg_fn!(needs_panic_runtime))),
932 ("rustc_outlives", Normal, template!(Word), Gated(Stability::Unstable,
934 "the `#[rustc_outlives]` attribute \
935 is just used for rustc unit tests \
936 and will never be stable",
937 cfg_fn!(rustc_attrs))),
938 ("rustc_variance", Normal, template!(Word), Gated(Stability::Unstable,
940 "the `#[rustc_variance]` attribute \
941 is just used for rustc unit tests \
942 and will never be stable",
943 cfg_fn!(rustc_attrs))),
944 ("rustc_layout", Normal, template!(List: "field1, field2, ..."),
945 Gated(Stability::Unstable,
947 "the `#[rustc_layout]` attribute \
948 is just used for rustc unit tests \
949 and will never be stable",
950 cfg_fn!(rustc_attrs))),
951 ("rustc_regions", Normal, template!(Word), Gated(Stability::Unstable,
953 "the `#[rustc_regions]` attribute \
954 is just used for rustc unit tests \
955 and will never be stable",
956 cfg_fn!(rustc_attrs))),
957 ("rustc_error", Whitelisted, template!(Word), Gated(Stability::Unstable,
959 "the `#[rustc_error]` attribute \
960 is just used for rustc unit tests \
961 and will never be stable",
962 cfg_fn!(rustc_attrs))),
963 ("rustc_dump_user_substs", Whitelisted, template!(Word), Gated(Stability::Unstable,
966 is just used for rustc unit tests \
967 and will never be stable",
968 cfg_fn!(rustc_attrs))),
969 ("rustc_if_this_changed", Whitelisted, template!(Word, List: "DepNode"),
970 Gated(Stability::Unstable,
972 "the `#[rustc_if_this_changed]` attribute \
973 is just used for rustc unit tests \
974 and will never be stable",
975 cfg_fn!(rustc_attrs))),
976 ("rustc_then_this_would_need", Whitelisted, template!(List: "DepNode"),
977 Gated(Stability::Unstable,
979 "the `#[rustc_if_this_changed]` attribute \
980 is just used for rustc unit tests \
981 and will never be stable",
982 cfg_fn!(rustc_attrs))),
983 ("rustc_dirty", Whitelisted, template!(List: r#"cfg = "...", /*opt*/ label = "...",
984 /*opt*/ except = "...""#),
985 Gated(Stability::Unstable,
987 "the `#[rustc_dirty]` attribute \
988 is just used for rustc unit tests \
989 and will never be stable",
990 cfg_fn!(rustc_attrs))),
991 ("rustc_clean", Whitelisted, template!(List: r#"cfg = "...", /*opt*/ label = "...",
992 /*opt*/ except = "...""#),
993 Gated(Stability::Unstable,
995 "the `#[rustc_clean]` attribute \
996 is just used for rustc unit tests \
997 and will never be stable",
998 cfg_fn!(rustc_attrs))),
999 ("rustc_partition_reused", Whitelisted, template!(List: r#"cfg = "...", module = "...""#),
1000 Gated(Stability::Unstable,
1003 is just used for rustc unit tests \
1004 and will never be stable",
1005 cfg_fn!(rustc_attrs))),
1006 ("rustc_partition_codegened", Whitelisted, template!(List: r#"cfg = "...", module = "...""#),
1007 Gated(Stability::Unstable,
1010 is just used for rustc unit tests \
1011 and will never be stable",
1012 cfg_fn!(rustc_attrs))),
1013 ("rustc_expected_cgu_reuse", Whitelisted, template!(List: r#"cfg = "...", module = "...",
1015 Gated(Stability::Unstable,
1018 is just used for rustc unit tests \
1019 and will never be stable",
1020 cfg_fn!(rustc_attrs))),
1021 ("rustc_synthetic", Whitelisted, template!(Word), Gated(Stability::Unstable,
1024 is just used for rustc unit tests \
1025 and will never be stable",
1026 cfg_fn!(rustc_attrs))),
1027 ("rustc_symbol_name", Whitelisted, template!(Word), Gated(Stability::Unstable,
1029 "internal rustc attributes will never be stable",
1030 cfg_fn!(rustc_attrs))),
1031 ("rustc_item_path", Whitelisted, template!(Word), Gated(Stability::Unstable,
1033 "internal rustc attributes will never be stable",
1034 cfg_fn!(rustc_attrs))),
1035 ("rustc_mir", Whitelisted, template!(List: "arg1, arg2, ..."), Gated(Stability::Unstable,
1037 "the `#[rustc_mir]` attribute \
1038 is just used for rustc unit tests \
1039 and will never be stable",
1040 cfg_fn!(rustc_attrs))),
1041 ("rustc_inherit_overflow_checks", Whitelisted, template!(Word), Gated(Stability::Unstable,
1043 "the `#[rustc_inherit_overflow_checks]` \
1044 attribute is just used to control \
1045 overflow checking behavior of several \
1046 libcore functions that are inlined \
1047 across crates and will never be stable",
1048 cfg_fn!(rustc_attrs))),
1050 ("rustc_dump_program_clauses", Whitelisted, template!(Word), Gated(Stability::Unstable,
1052 "the `#[rustc_dump_program_clauses]` \
1053 attribute is just used for rustc unit \
1054 tests and will never be stable",
1055 cfg_fn!(rustc_attrs))),
1056 ("rustc_test_marker", Normal, template!(Word), Gated(Stability::Unstable,
1058 "the `#[rustc_test_marker]` attribute \
1059 is used internally to track tests",
1060 cfg_fn!(rustc_attrs))),
1061 ("rustc_transparent_macro", Whitelisted, template!(Word), Gated(Stability::Unstable,
1063 "used internally for testing macro hygiene",
1064 cfg_fn!(rustc_attrs))),
1065 ("compiler_builtins", Whitelisted, template!(Word), Gated(Stability::Unstable,
1066 "compiler_builtins",
1067 "the `#[compiler_builtins]` attribute is used to \
1068 identify the `compiler_builtins` crate which \
1069 contains compiler-rt intrinsics and will never be \
1071 cfg_fn!(compiler_builtins))),
1072 ("sanitizer_runtime", Whitelisted, template!(Word), Gated(Stability::Unstable,
1073 "sanitizer_runtime",
1074 "the `#[sanitizer_runtime]` attribute is used to \
1075 identify crates that contain the runtime of a \
1076 sanitizer and will never be stable",
1077 cfg_fn!(sanitizer_runtime))),
1078 ("profiler_runtime", Whitelisted, template!(Word), Gated(Stability::Unstable,
1080 "the `#[profiler_runtime]` attribute is used to \
1081 identify the `profiler_builtins` crate which \
1082 contains the profiler runtime and will never be \
1084 cfg_fn!(profiler_runtime))),
1086 ("allow_internal_unstable", Normal, template!(Word), Gated(Stability::Unstable,
1087 "allow_internal_unstable",
1088 EXPLAIN_ALLOW_INTERNAL_UNSTABLE,
1089 cfg_fn!(allow_internal_unstable))),
1091 ("allow_internal_unsafe", Normal, template!(Word), Gated(Stability::Unstable,
1092 "allow_internal_unsafe",
1093 EXPLAIN_ALLOW_INTERNAL_UNSAFE,
1094 cfg_fn!(allow_internal_unsafe))),
1096 ("fundamental", Whitelisted, template!(Word), Gated(Stability::Unstable,
1098 "the `#[fundamental]` attribute \
1099 is an experimental feature",
1100 cfg_fn!(fundamental))),
1102 ("proc_macro_derive", Normal, template!(List: "TraitName, \
1103 /*opt*/ attributes(name1, name2, ...)"),
1106 ("rustc_copy_clone_marker", Whitelisted, template!(Word), Gated(Stability::Unstable,
1108 "internal implementation detail",
1109 cfg_fn!(rustc_attrs))),
1111 // FIXME: #14408 whitelist docs since rustdoc looks at them
1112 ("doc", Whitelisted, template!(List: "hidden|inline|...", NameValueStr: "string"), Ungated),
1114 // FIXME: #14406 these are processed in codegen, which happens after the
1116 ("cold", Whitelisted, template!(Word), Ungated),
1117 ("naked", Whitelisted, template!(Word), Gated(Stability::Unstable,
1119 "the `#[naked]` attribute \
1120 is an experimental feature",
1121 cfg_fn!(naked_functions))),
1122 ("target_feature", Whitelisted, template!(List: r#"enable = "name""#), Ungated),
1123 ("export_name", Whitelisted, template!(NameValueStr: "name"), Ungated),
1124 ("inline", Whitelisted, template!(Word, List: "always|never"), Ungated),
1125 ("link", Whitelisted, template!(List: r#"name = "...", /*opt*/ kind = "dylib|static|...",
1126 /*opt*/ cfg = "...""#), Ungated),
1127 ("link_name", Whitelisted, template!(NameValueStr: "name"), Ungated),
1128 ("link_section", Whitelisted, template!(NameValueStr: "name"), Ungated),
1129 ("no_builtins", Whitelisted, template!(Word), Ungated),
1130 ("no_mangle", Whitelisted, template!(Word), Ungated),
1131 ("no_debug", Whitelisted, template!(Word), Gated(
1132 Stability::Deprecated("https://github.com/rust-lang/rust/issues/29721", None),
1134 "the `#[no_debug]` attribute was an experimental feature that has been \
1135 deprecated due to lack of demand",
1136 cfg_fn!(no_debug))),
1137 ("omit_gdb_pretty_printer_section", Whitelisted, template!(Word), Gated(Stability::Unstable,
1138 "omit_gdb_pretty_printer_section",
1139 "the `#[omit_gdb_pretty_printer_section]` \
1140 attribute is just used for the Rust test \
1142 cfg_fn!(omit_gdb_pretty_printer_section))),
1143 ("unsafe_destructor_blind_to_params",
1146 Gated(Stability::Deprecated("https://github.com/rust-lang/rust/issues/34761",
1147 Some("replace this attribute with `#[may_dangle]`")),
1148 "dropck_parametricity",
1149 "unsafe_destructor_blind_to_params has been replaced by \
1150 may_dangle and will be removed in the future",
1151 cfg_fn!(dropck_parametricity))),
1155 Gated(Stability::Unstable,
1157 "may_dangle has unstable semantics and may be removed in the future",
1158 cfg_fn!(dropck_eyepatch))),
1159 ("unwind", Whitelisted, template!(List: "allowed"), Gated(Stability::Unstable,
1160 "unwind_attributes",
1161 "#[unwind] is experimental",
1162 cfg_fn!(unwind_attributes))),
1163 ("used", Whitelisted, template!(Word), Ungated),
1166 ("prelude_import", Whitelisted, template!(Word), Gated(Stability::Unstable,
1168 "`#[prelude_import]` is for use by rustc only",
1169 cfg_fn!(prelude_import))),
1171 // FIXME: #14407 these are only looked at on-demand so we can't
1172 // guarantee they'll have already been checked
1173 ("rustc_deprecated", Whitelisted, template!(List: r#"since = "version", reason = "...""#),
1175 ("must_use", Whitelisted, template!(Word, NameValueStr: "reason"), Ungated),
1176 ("stable", Whitelisted, template!(List: r#"feature = "name", since = "version""#), Ungated),
1177 ("unstable", Whitelisted, template!(List: r#"feature = "name", reason = "...", issue = "N""#),
1179 ("deprecated", Normal, template!(Word, List: r#"/*opt*/ since = "version",
1180 /*opt*/ note = "reason"#,
1181 NameValueStr: "reason"), Ungated),
1183 ("rustc_paren_sugar", Normal, template!(Word), Gated(Stability::Unstable,
1185 "unboxed_closures are still evolving",
1186 cfg_fn!(unboxed_closures))),
1188 ("windows_subsystem", Whitelisted, template!(NameValueStr: "windows|console"), Ungated),
1190 ("proc_macro_attribute", Normal, template!(Word), Ungated),
1191 ("proc_macro", Normal, template!(Word), Ungated),
1193 ("rustc_proc_macro_decls", Normal, template!(Word), Gated(Stability::Unstable,
1194 "rustc_proc_macro_decls",
1195 "used internally by rustc",
1196 cfg_fn!(rustc_attrs))),
1198 ("allow_fail", Normal, template!(Word), Gated(Stability::Unstable,
1200 "allow_fail attribute is currently unstable",
1201 cfg_fn!(allow_fail))),
1203 ("rustc_std_internal_symbol", Whitelisted, template!(Word), Gated(Stability::Unstable,
1205 "this is an internal attribute that will \
1207 cfg_fn!(rustc_attrs))),
1209 // whitelists "identity-like" conversion methods to suggest on type mismatch
1210 ("rustc_conversion_suggestion", Whitelisted, template!(Word), Gated(Stability::Unstable,
1212 "this is an internal attribute that will \
1214 cfg_fn!(rustc_attrs))),
1216 ("rustc_args_required_const", Whitelisted, template!(List: "N"), Gated(Stability::Unstable,
1218 "never will be stable",
1219 cfg_fn!(rustc_attrs))),
1221 ("panic_handler", Normal, template!(Word), Ungated),
1223 ("alloc_error_handler", Normal, template!(Word), Gated(Stability::Unstable,
1224 "alloc_error_handler",
1225 "#[alloc_error_handler] is an unstable feature",
1226 cfg_fn!(alloc_error_handler))),
1229 ("optimize", Whitelisted, template!(List: "size|speed"), Gated(Stability::Unstable,
1230 "optimize_attribute",
1231 "#[optimize] attribute is an unstable feature",
1232 cfg_fn!(optimize_attribute))),
1234 // Crate level attributes
1235 ("crate_name", CrateLevel, template!(NameValueStr: "name"), Ungated),
1236 ("crate_type", CrateLevel, template!(NameValueStr: "bin|lib|..."), Ungated),
1237 ("crate_id", CrateLevel, template!(NameValueStr: "ignored"), Ungated),
1238 ("feature", CrateLevel, template!(List: "name1, name1, ..."), Ungated),
1239 ("no_start", CrateLevel, template!(Word), Ungated),
1240 ("no_main", CrateLevel, template!(Word), Ungated),
1241 ("no_builtins", CrateLevel, template!(Word), Ungated),
1242 ("recursion_limit", CrateLevel, template!(NameValueStr: "N"), Ungated),
1243 ("type_length_limit", CrateLevel, template!(NameValueStr: "N"), Ungated),
1244 ("test_runner", CrateLevel, template!(List: "path"), Gated(Stability::Unstable,
1245 "custom_test_frameworks",
1246 EXPLAIN_CUSTOM_TEST_FRAMEWORKS,
1247 cfg_fn!(custom_test_frameworks))),
1250 // cfg(...)'s that are feature gated
1251 const GATED_CFGS: &[(&str, &str, fn(&Features) -> bool)] = &[
1252 // (name in cfg, feature, function to check if the feature is enabled)
1253 ("target_thread_local", "cfg_target_thread_local", cfg_fn!(cfg_target_thread_local)),
1254 ("target_has_atomic", "cfg_target_has_atomic", cfg_fn!(cfg_target_has_atomic)),
1255 ("rustdoc", "doc_cfg", cfg_fn!(doc_cfg)),
1259 pub struct GatedCfg {
1265 pub fn gate(cfg: &ast::MetaItem) -> Option<GatedCfg> {
1266 let name = cfg.name().as_str();
1268 .position(|info| info.0 == name)
1277 pub fn check_and_emit(&self, sess: &ParseSess, features: &Features) {
1278 let (cfg, feature, has_feature) = GATED_CFGS[self.index];
1279 if !has_feature(features) && !self.span.allows_unstable() {
1280 let explain = format!("`cfg({})` is experimental and subject to change", cfg);
1281 emit_feature_err(sess, feature, self.span, GateIssue::Language, &explain);
1286 struct Context<'a> {
1287 features: &'a Features,
1288 parse_sess: &'a ParseSess,
1289 plugin_attributes: &'a [(String, AttributeType)],
1292 macro_rules! gate_feature_fn {
1293 ($cx: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr, $level: expr) => {{
1294 let (cx, has_feature, span,
1295 name, explain, level) = ($cx, $has_feature, $span, $name, $explain, $level);
1296 let has_feature: bool = has_feature(&$cx.features);
1297 debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
1298 if !has_feature && !span.allows_unstable() {
1299 leveled_feature_err(cx.parse_sess, name, span, GateIssue::Language, explain, level)
1305 macro_rules! gate_feature {
1306 ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {
1307 gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
1308 stringify!($feature), $explain, GateStrength::Hard)
1310 ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {
1311 gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
1312 stringify!($feature), $explain, $level)
1316 impl<'a> Context<'a> {
1317 fn check_attribute(&self, attr: &ast::Attribute, is_macro: bool) {
1318 debug!("check_attribute(attr = {:?})", attr);
1319 let name = attr.name().as_str();
1320 for &(n, ty, _template, ref gateage) in BUILTIN_ATTRIBUTES {
1322 if let Gated(_, name, desc, ref has_feature) = *gateage {
1323 gate_feature_fn!(self, has_feature, attr.span, name, desc, GateStrength::Hard);
1324 } else if name == "doc" {
1325 if let Some(content) = attr.meta_item_list() {
1326 if content.iter().any(|c| c.check_name("include")) {
1327 gate_feature!(self, external_doc, attr.span,
1328 "#[doc(include = \"...\")] is experimental"
1333 debug!("check_attribute: {:?} is builtin, {:?}, {:?}", attr.path, ty, gateage);
1337 for &(ref n, ref ty) in self.plugin_attributes {
1338 if attr.path == &**n {
1339 // Plugins can't gate attributes, so we don't check for it
1340 // unlike the code above; we only use this loop to
1341 // short-circuit to avoid the checks below.
1342 debug!("check_attribute: {:?} is registered by a plugin, {:?}", attr.path, ty);
1346 if !attr::is_known(attr) {
1347 if name.starts_with("rustc_") {
1348 let msg = "unless otherwise specified, attributes with the prefix `rustc_` \
1349 are reserved for internal compiler diagnostics";
1350 gate_feature!(self, rustc_attrs, attr.span, msg);
1351 } else if !is_macro {
1352 // Only run the custom attribute lint during regular feature gate
1353 // checking. Macro gating runs before the plugin attributes are
1354 // registered, so we skip this in that case.
1355 let msg = format!("The attribute `{}` is currently unknown to the compiler and \
1356 may have meaning added to it in the future", attr.path);
1357 gate_feature!(self, custom_attribute, attr.span, &msg);
1363 pub fn check_attribute(attr: &ast::Attribute, parse_sess: &ParseSess, features: &Features) {
1364 let cx = Context { features: features, parse_sess: parse_sess, plugin_attributes: &[] };
1365 cx.check_attribute(attr, true);
1368 fn find_lang_feature_issue(feature: &str) -> Option<u32> {
1369 if let Some(info) = ACTIVE_FEATURES.iter().find(|t| t.0 == feature) {
1371 // FIXME (#28244): enforce that active features have issue numbers
1372 // assert!(issue.is_some())
1375 // search in Accepted, Removed, or Stable Removed features
1376 let found = ACCEPTED_FEATURES.iter().chain(REMOVED_FEATURES).chain(STABLE_REMOVED_FEATURES)
1377 .find(|t| t.0 == feature);
1379 Some(&(_, _, issue, _)) => issue,
1380 None => panic!("Feature `{}` is not declared anywhere", feature),
1385 pub enum GateIssue {
1387 Library(Option<u32>)
1390 #[derive(Debug, Copy, Clone, PartialEq)]
1391 pub enum GateStrength {
1392 /// A hard error. (Most feature gates should use this.)
1394 /// Only a warning. (Use this only as backwards-compatibility demands.)
1398 pub fn emit_feature_err(sess: &ParseSess, feature: &str, span: Span, issue: GateIssue,
1400 feature_err(sess, feature, span, issue, explain).emit();
1403 pub fn feature_err<'a>(sess: &'a ParseSess, feature: &str, span: Span, issue: GateIssue,
1404 explain: &str) -> DiagnosticBuilder<'a> {
1405 leveled_feature_err(sess, feature, span, issue, explain, GateStrength::Hard)
1408 fn leveled_feature_err<'a>(sess: &'a ParseSess, feature: &str, span: Span, issue: GateIssue,
1409 explain: &str, level: GateStrength) -> DiagnosticBuilder<'a> {
1410 let diag = &sess.span_diagnostic;
1412 let issue = match issue {
1413 GateIssue::Language => find_lang_feature_issue(feature),
1414 GateIssue::Library(lib) => lib,
1417 let explanation = match issue {
1418 None | Some(0) => explain.to_owned(),
1419 Some(n) => format!("{} (see issue #{})", explain, n)
1422 let mut err = match level {
1423 GateStrength::Hard => {
1424 diag.struct_span_err_with_code(span, &explanation, stringify_error_code!(E0658))
1426 GateStrength::Soft => diag.struct_span_warn(span, &explanation),
1429 // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
1430 if sess.unstable_features.is_nightly_build() {
1431 err.help(&format!("add #![feature({})] to the \
1432 crate attributes to enable",
1436 // If we're on stable and only emitting a "soft" warning, add a note to
1437 // clarify that the feature isn't "on" (rather than being on but
1439 if !sess.unstable_features.is_nightly_build() && level == GateStrength::Soft {
1440 err.help("a nightly build of the compiler is required to enable this feature");
1447 const EXPLAIN_BOX_SYNTAX: &str =
1448 "box expression syntax is experimental; you can call `Box::new` instead.";
1450 pub const EXPLAIN_STMT_ATTR_SYNTAX: &str =
1451 "attributes on expressions are experimental.";
1453 pub const EXPLAIN_ASM: &str =
1454 "inline assembly is not stable enough for use and is subject to change";
1456 pub const EXPLAIN_GLOBAL_ASM: &str =
1457 "`global_asm!` is not stable enough for use and is subject to change";
1459 pub const EXPLAIN_CUSTOM_TEST_FRAMEWORKS: &str =
1460 "custom test frameworks are an unstable feature";
1462 pub const EXPLAIN_LOG_SYNTAX: &str =
1463 "`log_syntax!` is not stable enough for use and is subject to change";
1465 pub const EXPLAIN_CONCAT_IDENTS: &str =
1466 "`concat_idents` is not stable enough for use and is subject to change";
1468 pub const EXPLAIN_FORMAT_ARGS_NL: &str =
1469 "`format_args_nl` is only for internal language use and is subject to change";
1471 pub const EXPLAIN_TRACE_MACROS: &str =
1472 "`trace_macros` is not stable enough for use and is subject to change";
1473 pub const EXPLAIN_ALLOW_INTERNAL_UNSTABLE: &str =
1474 "allow_internal_unstable side-steps feature gating and stability checks";
1475 pub const EXPLAIN_ALLOW_INTERNAL_UNSAFE: &str =
1476 "allow_internal_unsafe side-steps the unsafe_code lint";
1478 pub const EXPLAIN_UNSIZED_TUPLE_COERCION: &str =
1479 "unsized tuple coercion is not stable enough for use and is subject to change";
1481 struct PostExpansionVisitor<'a> {
1482 context: &'a Context<'a>,
1485 macro_rules! gate_feature_post {
1486 ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {{
1487 let (cx, span) = ($cx, $span);
1488 if !span.allows_unstable() {
1489 gate_feature!(cx.context, $feature, span, $explain)
1492 ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {{
1493 let (cx, span) = ($cx, $span);
1494 if !span.allows_unstable() {
1495 gate_feature!(cx.context, $feature, span, $explain, $level)
1500 impl<'a> PostExpansionVisitor<'a> {
1501 fn check_abi(&self, abi: Abi, span: Span) {
1503 Abi::RustIntrinsic => {
1504 gate_feature_post!(&self, intrinsics, span,
1505 "intrinsics are subject to change");
1507 Abi::PlatformIntrinsic => {
1508 gate_feature_post!(&self, platform_intrinsics, span,
1509 "platform intrinsics are experimental and possibly buggy");
1511 Abi::Vectorcall => {
1512 gate_feature_post!(&self, abi_vectorcall, span,
1513 "vectorcall is experimental and subject to change");
1516 gate_feature_post!(&self, abi_thiscall, span,
1517 "thiscall is experimental and subject to change");
1520 gate_feature_post!(&self, unboxed_closures, span,
1521 "rust-call ABI is subject to change");
1524 gate_feature_post!(&self, abi_ptx, span,
1525 "PTX ABIs are experimental and subject to change");
1527 Abi::Unadjusted => {
1528 gate_feature_post!(&self, abi_unadjusted, span,
1529 "unadjusted ABI is an implementation detail and perma-unstable");
1531 Abi::Msp430Interrupt => {
1532 gate_feature_post!(&self, abi_msp430_interrupt, span,
1533 "msp430-interrupt ABI is experimental and subject to change");
1535 Abi::X86Interrupt => {
1536 gate_feature_post!(&self, abi_x86_interrupt, span,
1537 "x86-interrupt ABI is experimental and subject to change");
1539 Abi::AmdGpuKernel => {
1540 gate_feature_post!(&self, abi_amdgpu_kernel, span,
1541 "amdgpu-kernel ABI is experimental and subject to change");
1556 fn check_builtin_attribute(&mut self, attr: &ast::Attribute, name: &str,
1557 template: AttributeTemplate) {
1558 // Some special attributes like `cfg` must be checked
1559 // before the generic check, so we skip them here.
1560 let should_skip = |name| name == "cfg";
1561 // Some of previously accepted forms were used in practice,
1562 // report them as warnings for now.
1563 let should_warn = |name| name == "doc" || name == "ignore" ||
1564 name == "inline" || name == "link";
1566 match attr.parse_meta(self.context.parse_sess) {
1567 Ok(meta) => if !should_skip(name) && !template.compatible(&meta.node) {
1568 let mut msg = "attribute must be of the form ".to_owned();
1569 let mut first = true;
1572 msg.push_str(&format!("`#[{}{}]`", name, ""));
1574 if let Some(descr) = template.list {
1576 msg.push_str(" or ");
1579 msg.push_str(&format!("`#[{}({})]`", name, descr));
1581 if let Some(descr) = template.name_value_str {
1583 msg.push_str(" or ");
1585 msg.push_str(&format!("`#[{} = \"{}\"]`", name, descr));
1587 if should_warn(name) {
1588 self.context.parse_sess.buffer_lint(
1589 BufferedEarlyLintId::IllFormedAttributeInput,
1595 self.context.parse_sess.span_diagnostic.span_err(meta.span, &msg);
1598 Err(mut err) => err.emit(),
1603 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
1604 fn visit_attribute(&mut self, attr: &ast::Attribute) {
1605 if !attr.span.allows_unstable() {
1606 // check for gated attributes
1607 self.context.check_attribute(attr, false);
1610 if attr.check_name("doc") {
1611 if let Some(content) = attr.meta_item_list() {
1612 if content.len() == 1 && content[0].check_name("cfg") {
1613 gate_feature_post!(&self, doc_cfg, attr.span,
1614 "#[doc(cfg(...))] is experimental"
1616 } else if content.iter().any(|c| c.check_name("masked")) {
1617 gate_feature_post!(&self, doc_masked, attr.span,
1618 "#[doc(masked)] is experimental"
1620 } else if content.iter().any(|c| c.check_name("spotlight")) {
1621 gate_feature_post!(&self, doc_spotlight, attr.span,
1622 "#[doc(spotlight)] is experimental"
1624 } else if content.iter().any(|c| c.check_name("alias")) {
1625 gate_feature_post!(&self, doc_alias, attr.span,
1626 "#[doc(alias = \"...\")] is experimental"
1628 } else if content.iter().any(|c| c.check_name("keyword")) {
1629 gate_feature_post!(&self, doc_keyword, attr.span,
1630 "#[doc(keyword = \"...\")] is experimental"
1636 match BUILTIN_ATTRIBUTES.iter().find(|(name, ..)| attr.path == name) {
1637 Some(&(name, _, template, _)) => self.check_builtin_attribute(attr, name, template),
1638 None => if !self.context.features.unrestricted_attribute_tokens {
1639 // Unfortunately, `parse_meta` cannot be called speculatively
1640 // because it can report errors by itself, so we have to call it
1641 // only if the feature is disabled.
1642 if let Err(mut err) = attr.parse_meta(self.context.parse_sess) {
1643 err.help("try enabling `#![feature(unrestricted_attribute_tokens)]`").emit()
1649 fn visit_name(&mut self, sp: Span, name: ast::Name) {
1650 if !name.as_str().is_ascii() {
1651 gate_feature_post!(&self,
1653 self.context.parse_sess.source_map().def_span(sp),
1654 "non-ascii idents are not fully supported.");
1658 fn visit_item(&mut self, i: &'a ast::Item) {
1660 ast::ItemKind::Const(_,_) => {
1661 if i.ident.name == "_" {
1662 gate_feature_post!(&self, underscore_const_names, i.span,
1663 "naming constants with `_` is unstable");
1667 ast::ItemKind::ForeignMod(ref foreign_module) => {
1668 self.check_abi(foreign_module.abi, i.span);
1671 ast::ItemKind::Fn(..) => {
1672 if attr::contains_name(&i.attrs[..], "plugin_registrar") {
1673 gate_feature_post!(&self, plugin_registrar, i.span,
1674 "compiler plugins are experimental and possibly buggy");
1676 if attr::contains_name(&i.attrs[..], "start") {
1677 gate_feature_post!(&self, start, i.span,
1678 "a #[start] function is an experimental \
1679 feature whose signature may change \
1682 if attr::contains_name(&i.attrs[..], "main") {
1683 gate_feature_post!(&self, main, i.span,
1684 "declaration of a nonstandard #[main] \
1685 function may change over time, for now \
1686 a top-level `fn main()` is required");
1690 ast::ItemKind::Struct(..) => {
1691 for attr in attr::filter_by_name(&i.attrs[..], "repr") {
1692 for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
1693 if item.check_name("simd") {
1694 gate_feature_post!(&self, repr_simd, attr.span,
1695 "SIMD types are experimental and possibly buggy");
1701 ast::ItemKind::Impl(_, polarity, defaultness, _, _, _, _) => {
1702 if polarity == ast::ImplPolarity::Negative {
1703 gate_feature_post!(&self, optin_builtin_traits,
1705 "negative trait bounds are not yet fully implemented; \
1706 use marker types for now");
1709 if let ast::Defaultness::Default = defaultness {
1710 gate_feature_post!(&self, specialization,
1712 "specialization is unstable");
1716 ast::ItemKind::Trait(ast::IsAuto::Yes, ..) => {
1717 gate_feature_post!(&self, optin_builtin_traits,
1719 "auto traits are experimental and possibly buggy");
1722 ast::ItemKind::TraitAlias(..) => {
1727 "trait aliases are experimental"
1731 ast::ItemKind::MacroDef(ast::MacroDef { legacy: false, .. }) => {
1732 let msg = "`macro` is experimental";
1733 gate_feature_post!(&self, decl_macro, i.span, msg);
1736 ast::ItemKind::Existential(..) => {
1741 "existential types are unstable"
1748 visit::walk_item(self, i);
1751 fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
1753 ast::ForeignItemKind::Fn(..) |
1754 ast::ForeignItemKind::Static(..) => {
1755 let link_name = attr::first_attr_value_str_by_name(&i.attrs, "link_name");
1756 let links_to_llvm = match link_name {
1757 Some(val) => val.as_str().starts_with("llvm."),
1761 gate_feature_post!(&self, link_llvm_intrinsics, i.span,
1762 "linking to LLVM intrinsics is experimental");
1765 ast::ForeignItemKind::Ty => {
1766 gate_feature_post!(&self, extern_types, i.span,
1767 "extern types are experimental");
1769 ast::ForeignItemKind::Macro(..) => {}
1772 visit::walk_foreign_item(self, i)
1775 fn visit_ty(&mut self, ty: &'a ast::Ty) {
1777 ast::TyKind::BareFn(ref bare_fn_ty) => {
1778 self.check_abi(bare_fn_ty.abi, ty.span);
1780 ast::TyKind::Never => {
1781 gate_feature_post!(&self, never_type, ty.span,
1782 "The `!` type is experimental");
1786 visit::walk_ty(self, ty)
1789 fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FunctionRetTy) {
1790 if let ast::FunctionRetTy::Ty(ref output_ty) = *ret_ty {
1791 if let ast::TyKind::Never = output_ty.node {
1794 self.visit_ty(output_ty)
1799 fn visit_expr(&mut self, e: &'a ast::Expr) {
1801 ast::ExprKind::Box(_) => {
1802 gate_feature_post!(&self, box_syntax, e.span, EXPLAIN_BOX_SYNTAX);
1804 ast::ExprKind::Type(..) => {
1805 gate_feature_post!(&self, type_ascription, e.span,
1806 "type ascription is experimental");
1808 ast::ExprKind::ObsoleteInPlace(..) => {
1809 // these get a hard error in ast-validation
1811 ast::ExprKind::Yield(..) => {
1812 gate_feature_post!(&self, generators,
1814 "yield syntax is experimental");
1816 ast::ExprKind::TryBlock(_) => {
1817 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
1819 ast::ExprKind::Block(_, opt_label) => {
1820 if let Some(label) = opt_label {
1821 gate_feature_post!(&self, label_break_value, label.ident.span,
1822 "labels on blocks are unstable");
1825 ast::ExprKind::Closure(_, ast::IsAsync::Async { .. }, ..) => {
1826 gate_feature_post!(&self, async_await, e.span, "async closures are unstable");
1828 ast::ExprKind::Async(..) => {
1829 gate_feature_post!(&self, async_await, e.span, "async blocks are unstable");
1833 visit::walk_expr(self, e);
1836 fn visit_arm(&mut self, arm: &'a ast::Arm) {
1837 visit::walk_arm(self, arm)
1840 fn visit_pat(&mut self, pattern: &'a ast::Pat) {
1841 match pattern.node {
1842 PatKind::Slice(_, Some(ref subslice), _) => {
1843 gate_feature_post!(&self, slice_patterns,
1845 "syntax for subslices in slice patterns is not yet stabilized");
1847 PatKind::Box(..) => {
1848 gate_feature_post!(&self, box_patterns,
1850 "box pattern syntax is experimental");
1852 PatKind::Range(_, _, Spanned { node: RangeEnd::Excluded, .. }) => {
1853 gate_feature_post!(&self, exclusive_range_pattern, pattern.span,
1854 "exclusive range pattern syntax is experimental");
1858 visit::walk_pat(self, pattern)
1861 fn visit_fn(&mut self,
1862 fn_kind: FnKind<'a>,
1863 fn_decl: &'a ast::FnDecl,
1867 FnKind::ItemFn(_, header, _, _) => {
1868 // Check for const fn and async fn declarations.
1869 if header.asyncness.is_async() {
1870 gate_feature_post!(&self, async_await, span, "async fn is unstable");
1872 // Stability of const fn methods are covered in
1873 // `visit_trait_item` and `visit_impl_item` below; this is
1874 // because default methods don't pass through this point.
1876 self.check_abi(header.abi, span);
1878 FnKind::Method(_, sig, _, _) => {
1879 self.check_abi(sig.header.abi, span);
1883 visit::walk_fn(self, fn_kind, fn_decl, span);
1886 fn visit_trait_item(&mut self, ti: &'a ast::TraitItem) {
1888 ast::TraitItemKind::Method(ref sig, ref block) => {
1889 if block.is_none() {
1890 self.check_abi(sig.header.abi, ti.span);
1892 if sig.header.constness.node == ast::Constness::Const {
1893 gate_feature_post!(&self, const_fn, ti.span, "const fn is unstable");
1896 ast::TraitItemKind::Type(_, ref default) => {
1897 // We use three if statements instead of something like match guards so that all
1898 // of these errors can be emitted if all cases apply.
1899 if default.is_some() {
1900 gate_feature_post!(&self, associated_type_defaults, ti.span,
1901 "associated type defaults are unstable");
1903 if !ti.generics.params.is_empty() {
1904 gate_feature_post!(&self, generic_associated_types, ti.span,
1905 "generic associated types are unstable");
1907 if !ti.generics.where_clause.predicates.is_empty() {
1908 gate_feature_post!(&self, generic_associated_types, ti.span,
1909 "where clauses on associated types are unstable");
1914 visit::walk_trait_item(self, ti);
1917 fn visit_impl_item(&mut self, ii: &'a ast::ImplItem) {
1918 if ii.defaultness == ast::Defaultness::Default {
1919 gate_feature_post!(&self, specialization,
1921 "specialization is unstable");
1925 ast::ImplItemKind::Method(..) => {}
1926 ast::ImplItemKind::Existential(..) => {
1931 "existential types are unstable"
1934 ast::ImplItemKind::Type(_) => {
1935 if !ii.generics.params.is_empty() {
1936 gate_feature_post!(&self, generic_associated_types, ii.span,
1937 "generic associated types are unstable");
1939 if !ii.generics.where_clause.predicates.is_empty() {
1940 gate_feature_post!(&self, generic_associated_types, ii.span,
1941 "where clauses on associated types are unstable");
1946 visit::walk_impl_item(self, ii);
1949 fn visit_vis(&mut self, vis: &'a ast::Visibility) {
1950 if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.node {
1951 gate_feature_post!(&self, crate_visibility_modifier, vis.span,
1952 "`crate` visibility modifier is experimental");
1954 visit::walk_vis(self, vis);
1958 pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
1959 crate_edition: Edition) -> Features {
1960 fn feature_removed(span_handler: &Handler, span: Span, reason: Option<&str>) {
1961 let mut err = struct_span_err!(span_handler, span, E0557, "feature has been removed");
1962 if let Some(reason) = reason {
1963 err.span_note(span, reason);
1968 // Some features are known to be incomplete and using them is likely to have
1969 // unanticipated results, such as compiler crashes. We warn the user about these
1971 let incomplete_features = ["generic_associated_types"];
1973 let mut features = Features::new();
1974 let mut edition_enabled_features = FxHashMap::default();
1976 for &edition in ALL_EDITIONS {
1977 if edition <= crate_edition {
1978 // The `crate_edition` implies its respective umbrella feature-gate
1979 // (i.e., `#![feature(rust_20XX_preview)]` isn't needed on edition 20XX).
1980 edition_enabled_features.insert(Symbol::intern(edition.feature_name()), edition);
1984 for &(name, .., f_edition, set) in ACTIVE_FEATURES {
1985 if let Some(f_edition) = f_edition {
1986 if f_edition <= crate_edition {
1987 set(&mut features, DUMMY_SP);
1988 edition_enabled_features.insert(Symbol::intern(name), crate_edition);
1993 // Process the edition umbrella feature-gates first, to ensure
1994 // `edition_enabled_features` is completed before it's queried.
1995 for attr in krate_attrs {
1996 if !attr.check_name("feature") {
2000 let list = match attr.meta_item_list() {
2006 let name = if let Some(word) = mi.word() {
2012 if incomplete_features.iter().any(|f| *f == name.as_str()) {
2013 span_handler.struct_span_warn(
2016 "the feature `{}` is incomplete and may cause the compiler to crash",
2022 if let Some(edition) = ALL_EDITIONS.iter().find(|e| name == e.feature_name()) {
2023 if *edition <= crate_edition {
2027 for &(name, .., f_edition, set) in ACTIVE_FEATURES {
2028 if let Some(f_edition) = f_edition {
2029 if f_edition <= *edition {
2030 // FIXME(Manishearth) there is currently no way to set
2031 // lib features by edition
2032 set(&mut features, DUMMY_SP);
2033 edition_enabled_features.insert(Symbol::intern(name), *edition);
2041 for attr in krate_attrs {
2042 if !attr.check_name("feature") {
2046 let list = match attr.meta_item_list() {
2052 let name = if let Some(word) = mi.word() {
2055 span_err!(span_handler, mi.span, E0556,
2056 "malformed feature, expected just one word");
2060 if let Some(edition) = edition_enabled_features.get(&name) {
2065 "the feature `{}` is included in the Rust {} edition",
2072 if ALL_EDITIONS.iter().any(|e| name == e.feature_name()) {
2073 // Handled in the separate loop above.
2077 if let Some((.., set)) = ACTIVE_FEATURES.iter().find(|f| name == f.0) {
2078 set(&mut features, mi.span);
2079 features.declared_lang_features.push((name, mi.span, None));
2083 let removed = REMOVED_FEATURES.iter().find(|f| name == f.0);
2084 let stable_removed = STABLE_REMOVED_FEATURES.iter().find(|f| name == f.0);
2085 if let Some((.., reason)) = removed.or(stable_removed) {
2086 feature_removed(span_handler, mi.span, *reason);
2090 if let Some((_, since, ..)) = ACCEPTED_FEATURES.iter().find(|f| name == f.0) {
2091 let since = Some(Symbol::intern(since));
2092 features.declared_lang_features.push((name, mi.span, since));
2096 features.declared_lib_features.push((name, mi.span));
2103 pub fn check_crate(krate: &ast::Crate,
2105 features: &Features,
2106 plugin_attributes: &[(String, AttributeType)],
2107 unstable: UnstableFeatures) {
2108 maybe_stage_features(&sess.span_diagnostic, krate, unstable);
2115 let visitor = &mut PostExpansionVisitor { context: &ctx };
2116 visit::walk_crate(visitor, krate);
2119 #[derive(Clone, Copy, Hash)]
2120 pub enum UnstableFeatures {
2121 /// Hard errors for unstable features are active, as on
2122 /// beta/stable channels.
2124 /// Allow features to be activated, as on nightly.
2126 /// Errors are bypassed for bootstrapping. This is required any time
2127 /// during the build that feature-related lints are set to warn or above
2128 /// because the build turns on warnings-as-errors and uses lots of unstable
2129 /// features. As a result, this is always required for building Rust itself.
2133 impl UnstableFeatures {
2134 pub fn from_environment() -> UnstableFeatures {
2135 // Whether this is a feature-staged build, i.e., on the beta or stable channel
2136 let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
2137 // Whether we should enable unstable features for bootstrapping
2138 let bootstrap = env::var("RUSTC_BOOTSTRAP").is_ok();
2139 match (disable_unstable_features, bootstrap) {
2140 (_, true) => UnstableFeatures::Cheat,
2141 (true, _) => UnstableFeatures::Disallow,
2142 (false, _) => UnstableFeatures::Allow
2146 pub fn is_nightly_build(&self) -> bool {
2148 UnstableFeatures::Allow | UnstableFeatures::Cheat => true,
2154 fn maybe_stage_features(span_handler: &Handler, krate: &ast::Crate,
2155 unstable: UnstableFeatures) {
2156 let allow_features = match unstable {
2157 UnstableFeatures::Allow => true,
2158 UnstableFeatures::Disallow => false,
2159 UnstableFeatures::Cheat => true
2161 if !allow_features {
2162 for attr in &krate.attrs {
2163 if attr.check_name("feature") {
2164 let release_channel = option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)");
2165 span_err!(span_handler, attr.span, E0554,
2166 "#![feature] may not be used on the {} release channel",