1 // Copyright 2013 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
13 //! This module implements the gating necessary for preventing certain compiler
14 //! features from being used by default. This module will crawl a pre-expanded
15 //! AST to ensure that there are no features which are used that are not
18 //! Features are enabled in programs via the crate-level attributes of
19 //! `#![feature(...)]` with a comma-separated list of features.
21 //! For the purpose of future feature-tracking, once code for detection of feature
22 //! gate usage is added, *do not remove it again* even once the feature
25 use self::AttributeType::*;
26 use self::AttributeGate::*;
28 use rustc_target::spec::abi::Abi;
29 use ast::{self, NodeId, PatKind, RangeEnd};
31 use edition::{ALL_EDITIONS, Edition};
33 use syntax_pos::{Span, DUMMY_SP};
34 use errors::{DiagnosticBuilder, Handler, FatalError};
35 use visit::{self, FnKind, Visitor};
37 use symbol::{keywords, Symbol};
43 fn f(features: &mut Features, span: Span) {
44 features.declared_lib_features.push((Symbol::intern("proc_macro"), span));
45 features.proc_macro = true;
47 f as fn(&mut Features, Span)
50 fn f(features: &mut Features, _: Span) {
51 features.$field = true;
53 f as fn(&mut Features, Span)
57 macro_rules! declare_features {
58 ($((active, $feature: ident, $ver: expr, $issue: expr, $edition: expr),)+) => {
59 /// Represents active features that are currently being implemented or
60 /// currently being considered for addition/removal.
61 const ACTIVE_FEATURES:
62 &'static [(&'static str, &'static str, Option<u32>,
63 Option<Edition>, fn(&mut Features, Span))] =
64 &[$((stringify!($feature), $ver, $issue, $edition, set!($feature))),+];
66 /// A set of features to be used by later passes.
69 /// `#![feature]` attrs for stable language features, for error reporting
70 pub declared_stable_lang_features: Vec<(Symbol, Span)>,
71 /// `#![feature]` attrs for non-language (library) features
72 pub declared_lib_features: Vec<(Symbol, Span)>,
73 $(pub $feature: bool),+
77 pub fn new() -> Features {
79 declared_stable_lang_features: Vec::new(),
80 declared_lib_features: Vec::new(),
85 pub fn walk_feature_fields<F>(&self, mut f: F)
86 where F: FnMut(&str, bool)
88 $(f(stringify!($feature), self.$feature);)+
93 ($((removed, $feature: ident, $ver: expr, $issue: expr, None, $reason: expr),)+) => {
94 /// Represents unstable features which have since been removed (it was once Active)
95 const REMOVED_FEATURES: &[(&str, &str, Option<u32>, Option<&str>)] = &[
96 $((stringify!($feature), $ver, $issue, $reason)),+
100 ($((stable_removed, $feature: ident, $ver: expr, $issue: expr, None),)+) => {
101 /// Represents stable features which have since been removed (it was once Accepted)
102 const STABLE_REMOVED_FEATURES: &[(&str, &str, Option<u32>, Option<&str>)] = &[
103 $((stringify!($feature), $ver, $issue, None)),+
107 ($((accepted, $feature: ident, $ver: expr, $issue: expr, None),)+) => {
108 /// Those language feature has since been Accepted (it was once Active)
109 const ACCEPTED_FEATURES: &[(&str, &str, Option<u32>, Option<&str>)] = &[
110 $((stringify!($feature), $ver, $issue, None)),+
115 // If you change this, please modify src/doc/unstable-book as well.
117 // Don't ever remove anything from this list; set them to 'Removed'.
119 // The version numbers here correspond to the version in which the current status
120 // was set. This is most important for knowing when a particular feature became
123 // NB: tools/tidy/src/features.rs parses this information directly out of the
124 // source, so take care when modifying it.
127 (active, asm, "1.0.0", Some(29722), None),
128 (active, concat_idents, "1.0.0", Some(29599), None),
129 (active, link_args, "1.0.0", Some(29596), None),
130 (active, log_syntax, "1.0.0", Some(29598), None),
131 (active, non_ascii_idents, "1.0.0", Some(28979), None),
132 (active, plugin_registrar, "1.0.0", Some(29597), None),
133 (active, thread_local, "1.0.0", Some(29594), None),
134 (active, trace_macros, "1.0.0", Some(29598), None),
136 // rustc internal, for now:
137 (active, intrinsics, "1.0.0", None, None),
138 (active, lang_items, "1.0.0", None, None),
140 (active, link_llvm_intrinsics, "1.0.0", Some(29602), None),
141 (active, linkage, "1.0.0", Some(29603), None),
142 (active, quote, "1.0.0", Some(29601), None),
146 (active, rustc_diagnostic_macros, "1.0.0", None, None),
147 (active, rustc_const_unstable, "1.0.0", None, None),
148 (active, box_syntax, "1.0.0", Some(27779), None),
149 (active, unboxed_closures, "1.0.0", Some(29625), None),
151 (active, fundamental, "1.0.0", Some(29635), None),
152 (active, main, "1.0.0", Some(29634), None),
153 (active, needs_allocator, "1.4.0", Some(27389), None),
154 (active, on_unimplemented, "1.0.0", Some(29628), None),
155 (active, plugin, "1.0.0", Some(29597), None),
156 (active, simd_ffi, "1.0.0", Some(27731), None),
157 (active, start, "1.0.0", Some(29633), None),
158 (active, structural_match, "1.8.0", Some(31434), None),
159 (active, panic_runtime, "1.10.0", Some(32837), None),
160 (active, needs_panic_runtime, "1.10.0", Some(32837), None),
162 // OIBIT specific features
163 (active, optin_builtin_traits, "1.0.0", Some(13231), None),
165 // Allows use of #[staged_api]
167 (active, staged_api, "1.0.0", None, None),
169 // Allows using #![no_core]
170 (active, no_core, "1.3.0", Some(29639), None),
172 // Allows using `box` in patterns; RFC 469
173 (active, box_patterns, "1.0.0", Some(29641), None),
175 // Allows using the unsafe_destructor_blind_to_params attribute;
177 (active, dropck_parametricity, "1.3.0", Some(28498), None),
179 // Allows using the may_dangle attribute; RFC 1327
180 (active, dropck_eyepatch, "1.10.0", Some(34761), None),
182 // Allows the use of custom attributes; RFC 572
183 (active, custom_attribute, "1.0.0", Some(29642), None),
185 // Allows the use of #[derive(Anything)] as sugar for
186 // #[derive_Anything].
187 (active, custom_derive, "1.0.0", Some(29644), None),
189 // Allows the use of rustc_* attributes; RFC 572
190 (active, rustc_attrs, "1.0.0", Some(29642), None),
192 // Allows the use of non lexical lifetimes; RFC 2094
193 (active, nll, "1.0.0", Some(43234), None),
195 // Allows the use of #[allow_internal_unstable]. This is an
196 // attribute on macro_rules! and can't use the attribute handling
197 // below (it has to be checked before expansion possibly makes
198 // macros disappear).
201 (active, allow_internal_unstable, "1.0.0", None, None),
203 // Allows the use of #[allow_internal_unsafe]. This is an
204 // attribute on macro_rules! and can't use the attribute handling
205 // below (it has to be checked before expansion possibly makes
206 // macros disappear).
209 (active, allow_internal_unsafe, "1.0.0", None, None),
211 // #23121. Array patterns have some hazards yet.
212 (active, slice_patterns, "1.0.0", Some(23121), None),
214 // Allows the definition of `const fn` functions.
215 (active, const_fn, "1.2.0", Some(24111), None),
217 // Allows using #[prelude_import] on glob `use` items.
220 (active, prelude_import, "1.2.0", None, None),
222 // Allows default type parameters to influence type inference.
223 (active, default_type_parameter_fallback, "1.3.0", Some(27336), None),
225 // Allows associated type defaults
226 (active, associated_type_defaults, "1.2.0", Some(29661), None),
228 // allow `repr(simd)`, and importing the various simd intrinsics
229 (active, repr_simd, "1.4.0", Some(27731), None),
231 // allow `extern "platform-intrinsic" { ... }`
232 (active, platform_intrinsics, "1.4.0", Some(27731), None),
234 // allow `#[unwind(..)]`
235 // rust runtime internal
236 (active, unwind_attributes, "1.4.0", None, None),
238 // allow the use of `#[naked]` on functions.
239 (active, naked_functions, "1.9.0", Some(32408), None),
241 // allow `#[no_debug]`
242 (active, no_debug, "1.5.0", Some(29721), None),
244 // allow `#[omit_gdb_pretty_printer_section]`
246 (active, omit_gdb_pretty_printer_section, "1.5.0", None, None),
248 // Allows cfg(target_vendor = "...").
249 (active, cfg_target_vendor, "1.5.0", Some(29718), None),
251 // Allow attributes on expressions and non-item statements
252 (active, stmt_expr_attributes, "1.6.0", Some(15701), None),
254 // allow using type ascription in expressions
255 (active, type_ascription, "1.6.0", Some(23416), None),
257 // Allows cfg(target_thread_local)
258 (active, cfg_target_thread_local, "1.7.0", Some(29594), None),
261 (active, abi_vectorcall, "1.7.0", None, None),
264 (active, exclusive_range_pattern, "1.11.0", Some(37854), None),
266 // impl specialization (RFC 1210)
267 (active, specialization, "1.7.0", Some(31844), None),
269 // Allows cfg(target_has_atomic = "...").
270 (active, cfg_target_has_atomic, "1.9.0", Some(32976), None),
272 // The `!` type. Does not imply exhaustive_patterns (below) any more.
273 (active, never_type, "1.13.0", Some(35121), None),
275 // Allows exhaustive pattern matching on types that contain uninhabited types.
276 (active, exhaustive_patterns, "1.13.0", None, None),
278 // Allows all literals in attribute lists and values of key-value pairs.
279 (active, attr_literals, "1.13.0", Some(34981), None),
281 // Allows untagged unions `union U { ... }`
282 (active, untagged_unions, "1.13.0", Some(32836), None),
284 // Used to identify the `compiler_builtins` crate
286 (active, compiler_builtins, "1.13.0", None, None),
288 // Allows #[link(..., cfg(..))]
289 (active, link_cfg, "1.14.0", Some(37406), None),
291 (active, use_extern_macros, "1.15.0", Some(35896), None),
293 // `extern "ptx-*" fn()`
294 (active, abi_ptx, "1.15.0", None, None),
296 // The `repr(i128)` annotation for enums
297 (active, repr128, "1.16.0", Some(35118), None),
299 // The `unadjusted` ABI. Perma unstable.
300 (active, abi_unadjusted, "1.16.0", None, None),
302 // Procedural macros 2.0.
303 (active, proc_macro, "1.16.0", Some(38356), Some(Edition::Edition2018)),
305 // Declarative macros 2.0 (`macro`).
306 (active, decl_macro, "1.17.0", Some(39412), None),
308 // Allows #[link(kind="static-nobundle"...]
309 (active, static_nobundle, "1.16.0", Some(37403), None),
311 // `extern "msp430-interrupt" fn()`
312 (active, abi_msp430_interrupt, "1.16.0", Some(38487), None),
314 // Used to identify crates that contain sanitizer runtimes
316 (active, sanitizer_runtime, "1.17.0", None, None),
318 // Used to identify crates that contain the profiler runtime
320 (active, profiler_runtime, "1.18.0", None, None),
322 // `extern "x86-interrupt" fn()`
323 (active, abi_x86_interrupt, "1.17.0", Some(40180), None),
326 // Allows the `catch {...}` expression
327 (active, catch_expr, "1.17.0", Some(31436), Some(Edition::Edition2018)),
329 // Used to preserve symbols (see llvm.used)
330 (active, used, "1.18.0", Some(40289), None),
332 // Allows module-level inline assembly by way of global_asm!()
333 (active, global_asm, "1.18.0", Some(35119), None),
335 // Allows overlapping impls of marker traits
336 (active, overlapping_marker_traits, "1.18.0", Some(29864), None),
338 // Allows use of the :vis macro fragment specifier
339 (active, macro_vis_matcher, "1.18.0", Some(41022), None),
342 (active, abi_thiscall, "1.19.0", None, None),
344 // Allows a test to fail without failing the whole suite
345 (active, allow_fail, "1.19.0", Some(42219), None),
347 // Allows unsized tuple coercion.
348 (active, unsized_tuple_coercion, "1.20.0", Some(42877), None),
351 (active, generators, "1.21.0", None, None),
354 (active, trait_alias, "1.24.0", Some(41517), None),
356 // global allocators and their internals
357 (active, global_allocator, "1.20.0", None, None),
358 (active, allocator_internals, "1.20.0", None, None),
361 (active, doc_cfg, "1.21.0", Some(43781), None),
363 (active, doc_masked, "1.21.0", Some(44027), None),
365 (active, doc_spotlight, "1.22.0", Some(45040), None),
366 // #[doc(include="some-file")]
367 (active, external_doc, "1.22.0", Some(44732), None),
369 // Future-proofing enums/structs with #[non_exhaustive] attribute (RFC 2008)
370 (active, non_exhaustive, "1.22.0", Some(44109), None),
372 // `crate` as visibility modifier, synonymous to `pub(crate)`
373 (active, crate_visibility_modifier, "1.23.0", Some(45388), Some(Edition::Edition2018)),
376 (active, extern_types, "1.23.0", Some(43467), None),
378 // Allow trait methods with arbitrary self types
379 (active, arbitrary_self_types, "1.23.0", Some(44874), None),
382 (active, crate_in_paths, "1.23.0", Some(45477), Some(Edition::Edition2018)),
384 // In-band lifetime bindings (e.g. `fn foo(x: &'a u8) -> &'a u8`)
385 (active, in_band_lifetimes, "1.23.0", Some(44524), Some(Edition::Edition2018)),
387 // generic associated types (RFC 1598)
388 (active, generic_associated_types, "1.23.0", Some(44265), None),
390 // Resolve absolute paths as paths from other crates
391 (active, extern_absolute_paths, "1.24.0", Some(44660), Some(Edition::Edition2018)),
393 // `foo.rs` as an alternative to `foo/mod.rs`
394 (active, non_modrs_mods, "1.24.0", Some(44660), Some(Edition::Edition2018)),
396 // Termination trait in tests (RFC 1937)
397 (active, termination_trait_test, "1.24.0", Some(48854), Some(Edition::Edition2018)),
400 (active, extern_in_paths, "1.23.0", Some(44660), None),
402 // Allows `#[repr(transparent)]` attribute on newtype structs
403 (active, repr_transparent, "1.25.0", Some(43036), None),
405 // Use `?` as the Kleene "at most one" operator
406 (active, macro_at_most_once_rep, "1.25.0", Some(48075), None),
408 // Infer outlives requirements; RFC 2093
409 (active, infer_outlives_requirements, "1.26.0", Some(44493), None),
411 // Multiple patterns with `|` in `if let` and `while let`
412 (active, if_while_or_patterns, "1.26.0", Some(48215), None),
414 // Parentheses in patterns
415 (active, pattern_parentheses, "1.26.0", None, None),
417 // Allows `#[repr(packed)]` attribute on structs
418 (active, repr_packed, "1.26.0", Some(33158), None),
420 // `use path as _;` and `extern crate c as _;`
421 (active, underscore_imports, "1.26.0", Some(48216), None),
423 // The #[wasm_custom_section] attribute
424 (active, wasm_custom_section, "1.26.0", None, None),
426 // The #![wasm_import_module] attribute
427 (active, wasm_import_module, "1.26.0", None, None),
429 // Allows keywords to be escaped for use as identifiers
430 (active, raw_identifiers, "1.26.0", Some(48589), None),
432 // Allows macro invocations in `extern {}` blocks
433 (active, macros_in_extern, "1.27.0", Some(49476), None),
435 // unstable #[target_feature] directives
436 (active, arm_target_feature, "1.27.0", None, None),
437 (active, aarch64_target_feature, "1.27.0", None, None),
438 (active, hexagon_target_feature, "1.27.0", None, None),
439 (active, powerpc_target_feature, "1.27.0", None, None),
440 (active, mips_target_feature, "1.27.0", None, None),
441 (active, avx512_target_feature, "1.27.0", None, None),
442 (active, mmx_target_feature, "1.27.0", None, None),
443 (active, sse4a_target_feature, "1.27.0", None, None),
444 (active, tbm_target_feature, "1.27.0", None, None),
446 // Allows macro invocations of the form `#[foo::bar]`
447 (active, proc_macro_path_invoc, "1.27.0", None, None),
449 // Allows macro invocations on modules expressions and statements and
450 // procedural macros to expand to non-items.
451 (active, proc_macro_mod, "1.27.0", None, None),
452 (active, proc_macro_expr, "1.27.0", None, None),
453 (active, proc_macro_non_items, "1.27.0", None, None),
455 // #[doc(alias = "...")]
456 (active, doc_alias, "1.27.0", Some(50146), None),
458 // Access to crate names passed via `--extern` through prelude
459 (active, extern_prelude, "1.27.0", Some(44660), Some(Edition::Edition2018)),
462 (active, tool_attributes, "1.25.0", Some(44690), None),
464 // Allows use of the :literal macro fragment specifier (RFC 1576)
465 (active, macro_literal_matcher, "1.27.0", Some(35625), None),
467 // inconsistent bounds in where clauses
468 (active, trivial_bounds, "1.28.0", Some(48214), None),
472 (removed, import_shadowing, "1.0.0", None, None, None),
473 (removed, managed_boxes, "1.0.0", None, None, None),
474 // Allows use of unary negate on unsigned integers, e.g. -e for e: u8
475 (removed, negate_unsigned, "1.0.0", Some(29645), None, None),
476 (removed, reflect, "1.0.0", Some(27749), None, None),
477 // A way to temporarily opt out of opt in copy. This will *never* be accepted.
478 (removed, opt_out_copy, "1.0.0", None, None, None),
479 (removed, quad_precision_float, "1.0.0", None, None, None),
480 (removed, struct_inherit, "1.0.0", None, None, None),
481 (removed, test_removed_feature, "1.0.0", None, None, None),
482 (removed, visible_private_types, "1.0.0", None, None, None),
483 (removed, unsafe_no_drop_flag, "1.0.0", None, None, None),
484 // Allows using items which are missing stability attributes
486 (removed, unmarked_api, "1.0.0", None, None, None),
487 (removed, pushpop_unsafe, "1.2.0", None, None, None),
488 (removed, allocator, "1.0.0", None, None, None),
489 (removed, simd, "1.0.0", Some(27731), None,
490 Some("removed in favor of `#[repr(simd)]`")),
491 (removed, advanced_slice_patterns, "1.0.0", Some(23121), None,
492 Some("merged into `#![feature(slice_patterns)]`")),
493 (removed, macro_reexport, "1.0.0", Some(29638), None,
494 Some("subsumed by `#![feature(use_extern_macros)]` and `pub use`")),
498 (stable_removed, no_stack_check, "1.0.0", None, None),
502 (accepted, associated_types, "1.0.0", None, None),
503 // allow overloading augmented assignment operations like `a += b`
504 (accepted, augmented_assignments, "1.8.0", Some(28235), None),
505 // allow empty structs and enum variants with braces
506 (accepted, braced_empty_structs, "1.8.0", Some(29720), None),
507 // Allows indexing into constant arrays.
508 (accepted, const_indexing, "1.26.0", Some(29947), None),
509 (accepted, default_type_params, "1.0.0", None, None),
510 (accepted, globs, "1.0.0", None, None),
511 (accepted, if_let, "1.0.0", None, None),
512 // A temporary feature gate used to enable parser extensions needed
513 // to bootstrap fix for #5723.
514 (accepted, issue_5723_bootstrap, "1.0.0", None, None),
515 (accepted, macro_rules, "1.0.0", None, None),
516 // Allows using #![no_std]
517 (accepted, no_std, "1.6.0", None, None),
518 (accepted, slicing_syntax, "1.0.0", None, None),
519 (accepted, struct_variant, "1.0.0", None, None),
520 // These are used to test this portion of the compiler, they don't actually
522 (accepted, test_accepted_feature, "1.0.0", None, None),
523 (accepted, tuple_indexing, "1.0.0", None, None),
524 // Allows macros to appear in the type position.
525 (accepted, type_macros, "1.13.0", Some(27245), None),
526 (accepted, while_let, "1.0.0", None, None),
527 // Allows `#[deprecated]` attribute
528 (accepted, deprecated, "1.9.0", Some(29935), None),
530 (accepted, question_mark, "1.13.0", Some(31436), None),
531 // Allows `..` in tuple (struct) patterns
532 (accepted, dotdot_in_tuple_patterns, "1.14.0", Some(33627), None),
533 (accepted, item_like_imports, "1.15.0", Some(35120), None),
534 // Allows using `Self` and associated types in struct expressions and patterns.
535 (accepted, more_struct_aliases, "1.16.0", Some(37544), None),
536 // elide `'static` lifetimes in `static`s and `const`s
537 (accepted, static_in_const, "1.17.0", Some(35897), None),
538 // Allows field shorthands (`x` meaning `x: x`) in struct literal expressions.
539 (accepted, field_init_shorthand, "1.17.0", Some(37340), None),
540 // Allows the definition recursive static items.
541 (accepted, static_recursion, "1.17.0", Some(29719), None),
542 // pub(restricted) visibilities (RFC 1422)
543 (accepted, pub_restricted, "1.18.0", Some(32409), None),
544 // The #![windows_subsystem] attribute
545 (accepted, windows_subsystem, "1.18.0", Some(37499), None),
546 // Allows `break {expr}` with a value inside `loop`s.
547 (accepted, loop_break_value, "1.19.0", Some(37339), None),
548 // Permits numeric fields in struct expressions and patterns.
549 (accepted, relaxed_adts, "1.19.0", Some(35626), None),
550 // Coerces non capturing closures to function pointers
551 (accepted, closure_to_fn_coercion, "1.19.0", Some(39817), None),
552 // Allows attributes on struct literal fields.
553 (accepted, struct_field_attributes, "1.20.0", Some(38814), None),
554 // Allows the definition of associated constants in `trait` or `impl`
556 (accepted, associated_consts, "1.20.0", Some(29646), None),
557 // Usage of the `compile_error!` macro
558 (accepted, compile_error, "1.20.0", Some(40872), None),
559 // See rust-lang/rfcs#1414. Allows code like `let x: &'static u32 = &42` to work.
560 (accepted, rvalue_static_promotion, "1.21.0", Some(38865), None),
561 // Allow Drop types in constants (RFC 1440)
562 (accepted, drop_types_in_const, "1.22.0", Some(33156), None),
563 // Allows the sysV64 ABI to be specified on all platforms
564 // instead of just the platforms on which it is the C ABI
565 (accepted, abi_sysv64, "1.24.0", Some(36167), None),
566 // Allows `repr(align(16))` struct attribute (RFC 1358)
567 (accepted, repr_align, "1.25.0", Some(33626), None),
568 // allow '|' at beginning of match arms (RFC 1925)
569 (accepted, match_beginning_vert, "1.25.0", Some(44101), None),
570 // Nested groups in `use` (RFC 2128)
571 (accepted, use_nested_groups, "1.25.0", Some(44494), None),
573 (accepted, inclusive_range_syntax, "1.26.0", Some(28237), None),
574 // allow `..=` in patterns (RFC 1192)
575 (accepted, dotdoteq_in_patterns, "1.26.0", Some(28237), None),
576 // Termination trait in main (RFC 1937)
577 (accepted, termination_trait, "1.26.0", Some(43301), None),
578 // Copy/Clone closures (RFC 2132)
579 (accepted, clone_closures, "1.26.0", Some(44490), None),
580 (accepted, copy_closures, "1.26.0", Some(44490), None),
581 // Allows `impl Trait` in function arguments.
582 (accepted, universal_impl_trait, "1.26.0", Some(34511), None),
583 // Allows `impl Trait` in function return types.
584 (accepted, conservative_impl_trait, "1.26.0", Some(34511), None),
586 (accepted, i128_type, "1.26.0", Some(35118), None),
587 // Default match binding modes (RFC 2005)
588 (accepted, match_default_bindings, "1.26.0", Some(42640), None),
589 // allow `'_` placeholder lifetimes
590 (accepted, underscore_lifetimes, "1.26.0", Some(44524), None),
591 // Allows attributes on lifetime/type formal parameters in generics (RFC 1327)
592 (accepted, generic_param_attrs, "1.26.0", Some(48848), None),
593 // Allows cfg(target_feature = "...").
594 (accepted, cfg_target_feature, "1.27.0", Some(29717), None),
595 // Allows #[target_feature(...)]
596 (accepted, target_feature, "1.27.0", None, None),
597 // Trait object syntax with `dyn` prefix
598 (accepted, dyn_trait, "1.27.0", Some(44662), None),
599 // allow `#[must_use]` on functions; and, must-use operators (RFC 1940)
600 (accepted, fn_must_use, "1.27.0", Some(43302), None),
601 // Allows use of the :lifetime macro fragment specifier
602 (accepted, macro_lifetime_matcher, "1.27.0", Some(34303), None),
605 // If you change this, please modify src/doc/unstable-book as well. You must
606 // move that documentation into the relevant place in the other docs, and
607 // remove the chapter on the flag.
609 #[derive(PartialEq, Copy, Clone, Debug)]
610 pub enum AttributeType {
611 /// Normal, builtin attribute that is consumed
612 /// by the compiler before the unused_attribute check
615 /// Builtin attribute that may not be consumed by the compiler
616 /// before the unused_attribute check. These attributes
617 /// will be ignored by the unused_attribute lint
620 /// Builtin attribute that is only allowed at the crate level
624 pub enum AttributeGate {
625 /// Is gated by a given feature gate, reason
626 /// and function to check if enabled
627 Gated(Stability, &'static str, &'static str, fn(&Features) -> bool),
629 /// Ungated attribute, can be used on all release channels
634 fn is_deprecated(&self) -> bool {
636 Gated(Stability::Deprecated(_), ..) => true,
642 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
645 // Argument is tracking issue link.
646 Deprecated(&'static str),
650 impl ::std::fmt::Debug for AttributeGate {
651 fn fmt(&self, fmt: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
653 Gated(ref stab, name, expl, _) =>
654 write!(fmt, "Gated({:?}, {}, {})", stab, name, expl),
655 Ungated => write!(fmt, "Ungated")
660 macro_rules! cfg_fn {
661 ($field: ident) => {{
662 fn f(features: &Features) -> bool {
665 f as fn(&Features) -> bool
669 pub fn deprecated_attributes() -> Vec<&'static (&'static str, AttributeType, AttributeGate)> {
670 BUILTIN_ATTRIBUTES.iter().filter(|a| a.2.is_deprecated()).collect()
673 pub fn is_builtin_attr(attr: &ast::Attribute) -> bool {
674 BUILTIN_ATTRIBUTES.iter().any(|&(builtin_name, _, _)| attr.check_name(builtin_name))
677 // Attributes that have a special meaning to rustc or rustdoc
678 pub const BUILTIN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeGate)] = &[
681 ("warn", Normal, Ungated),
682 ("allow", Normal, Ungated),
683 ("forbid", Normal, Ungated),
684 ("deny", Normal, Ungated),
686 ("macro_use", Normal, Ungated),
687 ("macro_export", Normal, Ungated),
688 ("plugin_registrar", Normal, Ungated),
690 ("cfg", Normal, Ungated),
691 ("cfg_attr", Normal, Ungated),
692 ("main", Normal, Ungated),
693 ("start", Normal, Ungated),
694 ("test", Normal, Ungated),
695 ("bench", Normal, Ungated),
696 ("repr", Normal, Ungated),
697 ("path", Normal, Ungated),
698 ("abi", Normal, Ungated),
699 ("automatically_derived", Normal, Ungated),
700 ("no_mangle", Normal, Ungated),
701 ("no_link", Normal, Ungated),
702 ("derive", Normal, Ungated),
703 ("should_panic", Normal, Ungated),
704 ("ignore", Normal, Ungated),
705 ("no_implicit_prelude", Normal, Ungated),
706 ("reexport_test_harness_main", Normal, Ungated),
707 ("link_args", Normal, Gated(Stability::Unstable,
709 "the `link_args` attribute is experimental and not \
710 portable across platforms, it is recommended to \
711 use `#[link(name = \"foo\")] instead",
712 cfg_fn!(link_args))),
713 ("macro_escape", Normal, Ungated),
716 ("structural_match", Whitelisted, Gated(Stability::Unstable,
718 "the semantics of constant patterns is \
720 cfg_fn!(structural_match))),
723 ("non_exhaustive", Whitelisted, Gated(Stability::Unstable,
725 "non exhaustive is an experimental feature",
726 cfg_fn!(non_exhaustive))),
728 ("plugin", CrateLevel, Gated(Stability::Unstable,
730 "compiler plugins are experimental \
734 ("no_std", CrateLevel, Ungated),
735 ("no_core", CrateLevel, Gated(Stability::Unstable,
737 "no_core is experimental",
739 ("lang", Normal, Gated(Stability::Unstable,
741 "language items are subject to change",
742 cfg_fn!(lang_items))),
743 ("linkage", Whitelisted, Gated(Stability::Unstable,
745 "the `linkage` attribute is experimental \
746 and not portable across platforms",
748 ("thread_local", Whitelisted, Gated(Stability::Unstable,
750 "`#[thread_local]` is an experimental feature, and does \
751 not currently handle destructors.",
752 cfg_fn!(thread_local))),
754 ("rustc_on_unimplemented", Normal, Gated(Stability::Unstable,
756 "the `#[rustc_on_unimplemented]` attribute \
757 is an experimental feature",
758 cfg_fn!(on_unimplemented))),
759 ("rustc_const_unstable", Normal, Gated(Stability::Unstable,
760 "rustc_const_unstable",
761 "the `#[rustc_const_unstable]` attribute \
762 is an internal feature",
763 cfg_fn!(rustc_const_unstable))),
764 ("global_allocator", Normal, Gated(Stability::Unstable,
766 "the `#[global_allocator]` attribute is \
767 an experimental feature",
768 cfg_fn!(global_allocator))),
769 ("default_lib_allocator", Whitelisted, Gated(Stability::Unstable,
770 "allocator_internals",
771 "the `#[default_lib_allocator]` \
772 attribute is an experimental feature",
773 cfg_fn!(allocator_internals))),
774 ("needs_allocator", Normal, Gated(Stability::Unstable,
775 "allocator_internals",
776 "the `#[needs_allocator]` \
777 attribute is an experimental \
779 cfg_fn!(allocator_internals))),
780 ("panic_runtime", Whitelisted, Gated(Stability::Unstable,
782 "the `#[panic_runtime]` attribute is \
783 an experimental feature",
784 cfg_fn!(panic_runtime))),
785 ("needs_panic_runtime", Whitelisted, Gated(Stability::Unstable,
786 "needs_panic_runtime",
787 "the `#[needs_panic_runtime]` \
788 attribute is an experimental \
790 cfg_fn!(needs_panic_runtime))),
791 ("rustc_variance", Normal, Gated(Stability::Unstable,
793 "the `#[rustc_variance]` attribute \
794 is just used for rustc unit tests \
795 and will never be stable",
796 cfg_fn!(rustc_attrs))),
797 ("rustc_regions", Normal, Gated(Stability::Unstable,
799 "the `#[rustc_regions]` attribute \
800 is just used for rustc unit tests \
801 and will never be stable",
802 cfg_fn!(rustc_attrs))),
803 ("rustc_error", Whitelisted, Gated(Stability::Unstable,
805 "the `#[rustc_error]` attribute \
806 is just used for rustc unit tests \
807 and will never be stable",
808 cfg_fn!(rustc_attrs))),
809 ("rustc_if_this_changed", Whitelisted, Gated(Stability::Unstable,
811 "the `#[rustc_if_this_changed]` attribute \
812 is just used for rustc unit tests \
813 and will never be stable",
814 cfg_fn!(rustc_attrs))),
815 ("rustc_then_this_would_need", Whitelisted, Gated(Stability::Unstable,
817 "the `#[rustc_if_this_changed]` attribute \
818 is just used for rustc unit tests \
819 and will never be stable",
820 cfg_fn!(rustc_attrs))),
821 ("rustc_dirty", Whitelisted, Gated(Stability::Unstable,
823 "the `#[rustc_dirty]` attribute \
824 is just used for rustc unit tests \
825 and will never be stable",
826 cfg_fn!(rustc_attrs))),
827 ("rustc_clean", Whitelisted, Gated(Stability::Unstable,
829 "the `#[rustc_clean]` attribute \
830 is just used for rustc unit tests \
831 and will never be stable",
832 cfg_fn!(rustc_attrs))),
833 ("rustc_partition_reused", Whitelisted, Gated(Stability::Unstable,
836 is just used for rustc unit tests \
837 and will never be stable",
838 cfg_fn!(rustc_attrs))),
839 ("rustc_partition_translated", Whitelisted, Gated(Stability::Unstable,
842 is just used for rustc unit tests \
843 and will never be stable",
844 cfg_fn!(rustc_attrs))),
845 ("rustc_serialize_exclude_null", Normal, Gated(Stability::Unstable,
847 "the `#[rustc_serialize_exclude_null]` attribute \
848 is an internal-only feature",
849 cfg_fn!(rustc_attrs))),
850 ("rustc_synthetic", Whitelisted, Gated(Stability::Unstable,
853 is just used for rustc unit tests \
854 and will never be stable",
855 cfg_fn!(rustc_attrs))),
856 ("rustc_symbol_name", Whitelisted, Gated(Stability::Unstable,
858 "internal rustc attributes will never be stable",
859 cfg_fn!(rustc_attrs))),
860 ("rustc_item_path", Whitelisted, Gated(Stability::Unstable,
862 "internal rustc attributes will never be stable",
863 cfg_fn!(rustc_attrs))),
864 ("rustc_mir", Whitelisted, Gated(Stability::Unstable,
866 "the `#[rustc_mir]` attribute \
867 is just used for rustc unit tests \
868 and will never be stable",
869 cfg_fn!(rustc_attrs))),
870 ("rustc_inherit_overflow_checks", Whitelisted, Gated(Stability::Unstable,
872 "the `#[rustc_inherit_overflow_checks]` \
873 attribute is just used to control \
874 overflow checking behavior of several \
875 libcore functions that are inlined \
876 across crates and will never be stable",
877 cfg_fn!(rustc_attrs))),
879 ("rustc_dump_program_clauses", Whitelisted, Gated(Stability::Unstable,
881 "the `#[rustc_dump_program_clauses]` \
882 attribute is just used for rustc unit \
883 tests and will never be stable",
884 cfg_fn!(rustc_attrs))),
887 ("nll", Whitelisted, Gated(Stability::Unstable,
889 "Non lexical lifetimes",
891 ("compiler_builtins", Whitelisted, Gated(Stability::Unstable,
893 "the `#[compiler_builtins]` attribute is used to \
894 identify the `compiler_builtins` crate which \
895 contains compiler-rt intrinsics and will never be \
897 cfg_fn!(compiler_builtins))),
898 ("sanitizer_runtime", Whitelisted, Gated(Stability::Unstable,
900 "the `#[sanitizer_runtime]` attribute is used to \
901 identify crates that contain the runtime of a \
902 sanitizer and will never be stable",
903 cfg_fn!(sanitizer_runtime))),
904 ("profiler_runtime", Whitelisted, Gated(Stability::Unstable,
906 "the `#[profiler_runtime]` attribute is used to \
907 identify the `profiler_builtins` crate which \
908 contains the profiler runtime and will never be \
910 cfg_fn!(profiler_runtime))),
912 ("allow_internal_unstable", Normal, Gated(Stability::Unstable,
913 "allow_internal_unstable",
914 EXPLAIN_ALLOW_INTERNAL_UNSTABLE,
915 cfg_fn!(allow_internal_unstable))),
917 ("allow_internal_unsafe", Normal, Gated(Stability::Unstable,
918 "allow_internal_unsafe",
919 EXPLAIN_ALLOW_INTERNAL_UNSAFE,
920 cfg_fn!(allow_internal_unsafe))),
922 ("fundamental", Whitelisted, Gated(Stability::Unstable,
924 "the `#[fundamental]` attribute \
925 is an experimental feature",
926 cfg_fn!(fundamental))),
928 ("proc_macro_derive", Normal, Ungated),
930 ("rustc_copy_clone_marker", Whitelisted, Gated(Stability::Unstable,
932 "internal implementation detail",
933 cfg_fn!(rustc_attrs))),
935 // FIXME: #14408 whitelist docs since rustdoc looks at them
936 ("doc", Whitelisted, Ungated),
938 // FIXME: #14406 these are processed in trans, which happens after the
940 ("cold", Whitelisted, Ungated),
941 ("naked", Whitelisted, Gated(Stability::Unstable,
943 "the `#[naked]` attribute \
944 is an experimental feature",
945 cfg_fn!(naked_functions))),
946 ("target_feature", Whitelisted, Ungated),
947 ("export_name", Whitelisted, Ungated),
948 ("inline", Whitelisted, Ungated),
949 ("link", Whitelisted, Ungated),
950 ("link_name", Whitelisted, Ungated),
951 ("link_section", Whitelisted, Ungated),
952 ("no_builtins", Whitelisted, Ungated),
953 ("no_mangle", Whitelisted, Ungated),
954 ("no_debug", Whitelisted, Gated(
955 Stability::Deprecated("https://github.com/rust-lang/rust/issues/29721"),
957 "the `#[no_debug]` attribute was an experimental feature that has been \
958 deprecated due to lack of demand",
960 ("wasm_import_module", Normal, Gated(Stability::Unstable,
961 "wasm_import_module",
962 "experimental attribute",
963 cfg_fn!(wasm_import_module))),
964 ("omit_gdb_pretty_printer_section", Whitelisted, Gated(Stability::Unstable,
965 "omit_gdb_pretty_printer_section",
966 "the `#[omit_gdb_pretty_printer_section]` \
967 attribute is just used for the Rust test \
969 cfg_fn!(omit_gdb_pretty_printer_section))),
970 ("unsafe_destructor_blind_to_params",
972 Gated(Stability::Deprecated("https://github.com/rust-lang/rust/issues/34761"),
973 "dropck_parametricity",
974 "unsafe_destructor_blind_to_params has been replaced by \
975 may_dangle and will be removed in the future",
976 cfg_fn!(dropck_parametricity))),
979 Gated(Stability::Unstable,
981 "may_dangle has unstable semantics and may be removed in the future",
982 cfg_fn!(dropck_eyepatch))),
983 ("unwind", Whitelisted, Gated(Stability::Unstable,
985 "#[unwind] is experimental",
986 cfg_fn!(unwind_attributes))),
987 ("used", Whitelisted, Gated(
988 Stability::Unstable, "used",
989 "the `#[used]` attribute is an experimental feature",
993 ("prelude_import", Whitelisted, Gated(Stability::Unstable,
995 "`#[prelude_import]` is for use by rustc only",
996 cfg_fn!(prelude_import))),
998 // FIXME: #14407 these are only looked at on-demand so we can't
999 // guarantee they'll have already been checked
1000 ("rustc_deprecated", Whitelisted, Ungated),
1001 ("must_use", Whitelisted, Ungated),
1002 ("stable", Whitelisted, Ungated),
1003 ("unstable", Whitelisted, Ungated),
1004 ("deprecated", Normal, Ungated),
1006 ("rustc_paren_sugar", Normal, Gated(Stability::Unstable,
1008 "unboxed_closures are still evolving",
1009 cfg_fn!(unboxed_closures))),
1011 ("windows_subsystem", Whitelisted, Ungated),
1013 ("proc_macro_attribute", Normal, Gated(Stability::Unstable,
1015 "attribute proc macros are currently unstable",
1016 cfg_fn!(proc_macro))),
1018 ("proc_macro", Normal, Gated(Stability::Unstable,
1020 "function-like proc macros are currently unstable",
1021 cfg_fn!(proc_macro))),
1023 ("rustc_derive_registrar", Normal, Gated(Stability::Unstable,
1024 "rustc_derive_registrar",
1025 "used internally by rustc",
1026 cfg_fn!(rustc_attrs))),
1028 ("allow_fail", Normal, Gated(Stability::Unstable,
1030 "allow_fail attribute is currently unstable",
1031 cfg_fn!(allow_fail))),
1033 ("rustc_std_internal_symbol", Whitelisted, Gated(Stability::Unstable,
1035 "this is an internal attribute that will \
1037 cfg_fn!(rustc_attrs))),
1039 // whitelists "identity-like" conversion methods to suggest on type mismatch
1040 ("rustc_conversion_suggestion", Whitelisted, Gated(Stability::Unstable,
1042 "this is an internal attribute that will \
1044 cfg_fn!(rustc_attrs))),
1046 ("rustc_args_required_const", Whitelisted, Gated(Stability::Unstable,
1048 "never will be stable",
1049 cfg_fn!(rustc_attrs))),
1052 ("infer_outlives_requirements", Normal, Gated(Stability::Unstable,
1053 "infer_outlives_requirements",
1054 "infer outlives requirements is an experimental feature",
1055 cfg_fn!(infer_outlives_requirements))),
1057 ("wasm_custom_section", Whitelisted, Gated(Stability::Unstable,
1058 "wasm_custom_section",
1059 "attribute is currently unstable",
1060 cfg_fn!(wasm_custom_section))),
1062 // Crate level attributes
1063 ("crate_name", CrateLevel, Ungated),
1064 ("crate_type", CrateLevel, Ungated),
1065 ("crate_id", CrateLevel, Ungated),
1066 ("feature", CrateLevel, Ungated),
1067 ("no_start", CrateLevel, Ungated),
1068 ("no_main", CrateLevel, Ungated),
1069 ("no_builtins", CrateLevel, Ungated),
1070 ("recursion_limit", CrateLevel, Ungated),
1071 ("type_length_limit", CrateLevel, Ungated),
1074 // cfg(...)'s that are feature gated
1075 const GATED_CFGS: &[(&str, &str, fn(&Features) -> bool)] = &[
1076 // (name in cfg, feature, function to check if the feature is enabled)
1077 ("target_vendor", "cfg_target_vendor", cfg_fn!(cfg_target_vendor)),
1078 ("target_thread_local", "cfg_target_thread_local", cfg_fn!(cfg_target_thread_local)),
1079 ("target_has_atomic", "cfg_target_has_atomic", cfg_fn!(cfg_target_has_atomic)),
1082 #[derive(Debug, Eq, PartialEq)]
1083 pub struct GatedCfg {
1089 pub fn gate(cfg: &ast::MetaItem) -> Option<GatedCfg> {
1090 let name = cfg.name().as_str();
1092 .position(|info| info.0 == name)
1101 pub fn check_and_emit(&self, sess: &ParseSess, features: &Features) {
1102 let (cfg, feature, has_feature) = GATED_CFGS[self.index];
1103 if !has_feature(features) && !self.span.allows_unstable() {
1104 let explain = format!("`cfg({})` is experimental and subject to change", cfg);
1105 emit_feature_err(sess, feature, self.span, GateIssue::Language, &explain);
1110 struct Context<'a> {
1111 features: &'a Features,
1112 parse_sess: &'a ParseSess,
1113 plugin_attributes: &'a [(String, AttributeType)],
1116 macro_rules! gate_feature_fn {
1117 ($cx: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr, $level: expr) => {{
1118 let (cx, has_feature, span,
1119 name, explain, level) = ($cx, $has_feature, $span, $name, $explain, $level);
1120 let has_feature: bool = has_feature(&$cx.features);
1121 debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
1122 if !has_feature && !span.allows_unstable() {
1123 leveled_feature_err(cx.parse_sess, name, span, GateIssue::Language, explain, level)
1129 macro_rules! gate_feature {
1130 ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {
1131 gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
1132 stringify!($feature), $explain, GateStrength::Hard)
1134 ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {
1135 gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
1136 stringify!($feature), $explain, $level)
1140 impl<'a> Context<'a> {
1141 fn check_attribute(&self, attr: &ast::Attribute, is_macro: bool) {
1142 debug!("check_attribute(attr = {:?})", attr);
1143 let name = attr.name().as_str();
1144 for &(n, ty, ref gateage) in BUILTIN_ATTRIBUTES {
1146 if let Gated(_, name, desc, ref has_feature) = *gateage {
1147 gate_feature_fn!(self, has_feature, attr.span, name, desc, GateStrength::Hard);
1148 } else if name == "doc" {
1149 if let Some(content) = attr.meta_item_list() {
1150 if content.iter().any(|c| c.check_name("include")) {
1151 gate_feature!(self, external_doc, attr.span,
1152 "#[doc(include = \"...\")] is experimental"
1157 debug!("check_attribute: {:?} is builtin, {:?}, {:?}", attr.path, ty, gateage);
1161 for &(ref n, ref ty) in self.plugin_attributes {
1162 if attr.path == &**n {
1163 // Plugins can't gate attributes, so we don't check for it
1164 // unlike the code above; we only use this loop to
1165 // short-circuit to avoid the checks below
1166 debug!("check_attribute: {:?} is registered by a plugin, {:?}", attr.path, ty);
1170 if name.starts_with("rustc_") {
1171 gate_feature!(self, rustc_attrs, attr.span,
1172 "unless otherwise specified, attributes \
1173 with the prefix `rustc_` \
1174 are reserved for internal compiler diagnostics");
1175 } else if name.starts_with("derive_") {
1176 gate_feature!(self, custom_derive, attr.span, EXPLAIN_DERIVE_UNDERSCORE);
1177 } else if !attr::is_known(attr) {
1178 // Only run the custom attribute lint during regular
1179 // feature gate checking. Macro gating runs
1180 // before the plugin attributes are registered
1181 // so we skip this then
1183 if attr.is_scoped() {
1184 gate_feature!(self, tool_attributes, attr.span,
1185 &format!("scoped attribute `{}` is experimental", attr.path));
1186 if attr::is_known_tool(attr) {
1187 attr::mark_used(attr);
1190 self.parse_sess.span_diagnostic,
1193 "an unknown tool name found in scoped attribute: `{}`.",
1198 gate_feature!(self, custom_attribute, attr.span,
1199 &format!("The attribute `{}` is currently \
1200 unknown to the compiler and \
1202 added to it in the future",
1210 pub fn check_attribute(attr: &ast::Attribute, parse_sess: &ParseSess, features: &Features) {
1211 let cx = Context { features: features, parse_sess: parse_sess, plugin_attributes: &[] };
1212 cx.check_attribute(attr, true);
1215 pub fn find_lang_feature_accepted_version(feature: &str) -> Option<&'static str> {
1216 ACCEPTED_FEATURES.iter().find(|t| t.0 == feature).map(|t| t.1)
1219 fn find_lang_feature_issue(feature: &str) -> Option<u32> {
1220 if let Some(info) = ACTIVE_FEATURES.iter().find(|t| t.0 == feature) {
1222 // FIXME (#28244): enforce that active features have issue numbers
1223 // assert!(issue.is_some())
1226 // search in Accepted, Removed, or Stable Removed features
1227 let found = ACCEPTED_FEATURES.iter().chain(REMOVED_FEATURES).chain(STABLE_REMOVED_FEATURES)
1228 .find(|t| t.0 == feature);
1230 Some(&(_, _, issue, _)) => issue,
1231 None => panic!("Feature `{}` is not declared anywhere", feature),
1236 pub enum GateIssue {
1238 Library(Option<u32>)
1241 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
1242 pub enum GateStrength {
1243 /// A hard error. (Most feature gates should use this.)
1245 /// Only a warning. (Use this only as backwards-compatibility demands.)
1249 pub fn emit_feature_err(sess: &ParseSess, feature: &str, span: Span, issue: GateIssue,
1251 feature_err(sess, feature, span, issue, explain).emit();
1254 pub fn feature_err<'a>(sess: &'a ParseSess, feature: &str, span: Span, issue: GateIssue,
1255 explain: &str) -> DiagnosticBuilder<'a> {
1256 leveled_feature_err(sess, feature, span, issue, explain, GateStrength::Hard)
1259 fn leveled_feature_err<'a>(sess: &'a ParseSess, feature: &str, span: Span, issue: GateIssue,
1260 explain: &str, level: GateStrength) -> DiagnosticBuilder<'a> {
1261 let diag = &sess.span_diagnostic;
1263 let issue = match issue {
1264 GateIssue::Language => find_lang_feature_issue(feature),
1265 GateIssue::Library(lib) => lib,
1268 let explanation = match issue {
1269 None | Some(0) => explain.to_owned(),
1270 Some(n) => format!("{} (see issue #{})", explain, n)
1273 let mut err = match level {
1274 GateStrength::Hard => {
1275 diag.struct_span_err_with_code(span, &explanation, stringify_error_code!(E0658))
1277 GateStrength::Soft => diag.struct_span_warn(span, &explanation),
1280 // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
1281 if sess.unstable_features.is_nightly_build() {
1282 err.help(&format!("add #![feature({})] to the \
1283 crate attributes to enable",
1287 // If we're on stable and only emitting a "soft" warning, add a note to
1288 // clarify that the feature isn't "on" (rather than being on but
1290 if !sess.unstable_features.is_nightly_build() && level == GateStrength::Soft {
1291 err.help("a nightly build of the compiler is required to enable this feature");
1298 const EXPLAIN_BOX_SYNTAX: &'static str =
1299 "box expression syntax is experimental; you can call `Box::new` instead.";
1301 pub const EXPLAIN_STMT_ATTR_SYNTAX: &'static str =
1302 "attributes on expressions are experimental.";
1304 pub const EXPLAIN_ASM: &'static str =
1305 "inline assembly is not stable enough for use and is subject to change";
1307 pub const EXPLAIN_GLOBAL_ASM: &'static str =
1308 "`global_asm!` is not stable enough for use and is subject to change";
1310 pub const EXPLAIN_LOG_SYNTAX: &'static str =
1311 "`log_syntax!` is not stable enough for use and is subject to change";
1313 pub const EXPLAIN_CONCAT_IDENTS: &'static str =
1314 "`concat_idents` is not stable enough for use and is subject to change";
1316 pub const EXPLAIN_TRACE_MACROS: &'static str =
1317 "`trace_macros` is not stable enough for use and is subject to change";
1318 pub const EXPLAIN_ALLOW_INTERNAL_UNSTABLE: &'static str =
1319 "allow_internal_unstable side-steps feature gating and stability checks";
1320 pub const EXPLAIN_ALLOW_INTERNAL_UNSAFE: &'static str =
1321 "allow_internal_unsafe side-steps the unsafe_code lint";
1323 pub const EXPLAIN_CUSTOM_DERIVE: &'static str =
1324 "`#[derive]` for custom traits is deprecated and will be removed in the future.";
1326 pub const EXPLAIN_DEPR_CUSTOM_DERIVE: &'static str =
1327 "`#[derive]` for custom traits is deprecated and will be removed in the future. \
1328 Prefer using procedural macro custom derive.";
1330 pub const EXPLAIN_DERIVE_UNDERSCORE: &'static str =
1331 "attributes of the form `#[derive_*]` are reserved for the compiler";
1333 pub const EXPLAIN_VIS_MATCHER: &'static str =
1334 ":vis fragment specifier is experimental and subject to change";
1336 pub const EXPLAIN_LITERAL_MATCHER: &'static str =
1337 ":literal fragment specifier is experimental and subject to change";
1339 pub const EXPLAIN_UNSIZED_TUPLE_COERCION: &'static str =
1340 "Unsized tuple coercion is not stable enough for use and is subject to change";
1342 pub const EXPLAIN_MACRO_AT_MOST_ONCE_REP: &'static str =
1343 "Using the `?` macro Kleene operator for \"at most one\" repetition is unstable";
1345 pub const EXPLAIN_MACROS_IN_EXTERN: &'static str =
1346 "Macro invocations in `extern {}` blocks are experimental.";
1348 // mention proc-macros when enabled
1349 pub const EXPLAIN_PROC_MACROS_IN_EXTERN: &'static str =
1350 "Macro and proc-macro invocations in `extern {}` blocks are experimental.";
1352 struct PostExpansionVisitor<'a> {
1353 context: &'a Context<'a>,
1356 macro_rules! gate_feature_post {
1357 ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {{
1358 let (cx, span) = ($cx, $span);
1359 if !span.allows_unstable() {
1360 gate_feature!(cx.context, $feature, span, $explain)
1363 ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {{
1364 let (cx, span) = ($cx, $span);
1365 if !span.allows_unstable() {
1366 gate_feature!(cx.context, $feature, span, $explain, $level)
1371 impl<'a> PostExpansionVisitor<'a> {
1372 fn check_abi(&self, abi: Abi, span: Span) {
1374 Abi::RustIntrinsic => {
1375 gate_feature_post!(&self, intrinsics, span,
1376 "intrinsics are subject to change");
1378 Abi::PlatformIntrinsic => {
1379 gate_feature_post!(&self, platform_intrinsics, span,
1380 "platform intrinsics are experimental and possibly buggy");
1382 Abi::Vectorcall => {
1383 gate_feature_post!(&self, abi_vectorcall, span,
1384 "vectorcall is experimental and subject to change");
1387 gate_feature_post!(&self, abi_thiscall, span,
1388 "thiscall is experimental and subject to change");
1391 gate_feature_post!(&self, unboxed_closures, span,
1392 "rust-call ABI is subject to change");
1395 gate_feature_post!(&self, abi_ptx, span,
1396 "PTX ABIs are experimental and subject to change");
1398 Abi::Unadjusted => {
1399 gate_feature_post!(&self, abi_unadjusted, span,
1400 "unadjusted ABI is an implementation detail and perma-unstable");
1402 Abi::Msp430Interrupt => {
1403 gate_feature_post!(&self, abi_msp430_interrupt, span,
1404 "msp430-interrupt ABI is experimental and subject to change");
1406 Abi::X86Interrupt => {
1407 gate_feature_post!(&self, abi_x86_interrupt, span,
1408 "x86-interrupt ABI is experimental and subject to change");
1424 fn contains_novel_literal(item: &ast::MetaItem) -> bool {
1425 use ast::MetaItemKind::*;
1426 use ast::NestedMetaItemKind::*;
1430 NameValue(ref lit) => !lit.node.is_str(),
1431 List(ref list) => list.iter().any(|li| {
1433 MetaItem(ref mi) => contains_novel_literal(mi),
1440 impl<'a> PostExpansionVisitor<'a> {
1441 fn whole_crate_feature_gates(&mut self, _krate: &ast::Crate) {
1442 for &(ident, span) in &*self.context.parse_sess.non_modrs_mods.borrow() {
1443 if !span.allows_unstable() {
1444 let cx = &self.context;
1445 let level = GateStrength::Hard;
1446 let has_feature = cx.features.non_modrs_mods;
1447 let name = "non_modrs_mods";
1448 debug!("gate_feature(feature = {:?}, span = {:?}); has? {}",
1449 name, span, has_feature);
1451 if !has_feature && !span.allows_unstable() {
1452 leveled_feature_err(
1453 cx.parse_sess, name, span, GateIssue::Language,
1454 "mod statements in non-mod.rs files are unstable", level
1456 .help(&format!("on stable builds, rename this file to {}{}mod.rs",
1457 ident, path::MAIN_SEPARATOR))
1465 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
1466 fn visit_attribute(&mut self, attr: &ast::Attribute) {
1467 if !attr.span.allows_unstable() {
1468 // check for gated attributes
1469 self.context.check_attribute(attr, false);
1472 if attr.check_name("doc") {
1473 if let Some(content) = attr.meta_item_list() {
1474 if content.len() == 1 && content[0].check_name("cfg") {
1475 gate_feature_post!(&self, doc_cfg, attr.span,
1476 "#[doc(cfg(...))] is experimental"
1478 } else if content.iter().any(|c| c.check_name("masked")) {
1479 gate_feature_post!(&self, doc_masked, attr.span,
1480 "#[doc(masked)] is experimental"
1482 } else if content.iter().any(|c| c.check_name("spotlight")) {
1483 gate_feature_post!(&self, doc_spotlight, attr.span,
1484 "#[doc(spotlight)] is experimental"
1486 } else if content.iter().any(|c| c.check_name("alias")) {
1487 gate_feature_post!(&self, doc_alias, attr.span,
1488 "#[doc(alias = \"...\")] is experimental"
1494 // allow attr_literals in #[repr(align(x))] and #[repr(packed(n))]
1495 let mut allow_attr_literal = false;
1496 if attr.path == "repr" {
1497 if let Some(content) = attr.meta_item_list() {
1498 allow_attr_literal = content.iter().any(
1499 |c| c.check_name("align") || c.check_name("packed"));
1503 if self.context.features.proc_macro && attr::is_known(attr) {
1507 if !allow_attr_literal {
1508 let meta = panictry!(attr.parse_meta(self.context.parse_sess));
1509 if contains_novel_literal(&meta) {
1510 gate_feature_post!(&self, attr_literals, attr.span,
1511 "non-string literals in attributes, or string \
1512 literals in top-level positions, are experimental");
1517 fn visit_name(&mut self, sp: Span, name: ast::Name) {
1518 if !name.as_str().is_ascii() {
1519 gate_feature_post!(&self,
1521 self.context.parse_sess.codemap().def_span(sp),
1522 "non-ascii idents are not fully supported.");
1526 fn visit_use_tree(&mut self, use_tree: &'a ast::UseTree, id: NodeId, _nested: bool) {
1527 if let ast::UseTreeKind::Simple(Some(ident)) = use_tree.kind {
1528 if ident.name == "_" {
1529 gate_feature_post!(&self, underscore_imports, use_tree.span,
1530 "renaming imports with `_` is unstable");
1534 visit::walk_use_tree(self, use_tree, id);
1537 fn visit_item(&mut self, i: &'a ast::Item) {
1539 ast::ItemKind::ExternCrate(_) => {
1540 if i.ident.name == "_" {
1541 gate_feature_post!(&self, underscore_imports, i.span,
1542 "renaming extern crates with `_` is unstable");
1546 ast::ItemKind::ForeignMod(ref foreign_module) => {
1547 self.check_abi(foreign_module.abi, i.span);
1550 ast::ItemKind::Fn(..) => {
1551 if attr::contains_name(&i.attrs[..], "plugin_registrar") {
1552 gate_feature_post!(&self, plugin_registrar, i.span,
1553 "compiler plugins are experimental and possibly buggy");
1555 if attr::contains_name(&i.attrs[..], "start") {
1556 gate_feature_post!(&self, start, i.span,
1557 "a #[start] function is an experimental \
1558 feature whose signature may change \
1561 if attr::contains_name(&i.attrs[..], "main") {
1562 gate_feature_post!(&self, main, i.span,
1563 "declaration of a nonstandard #[main] \
1564 function may change over time, for now \
1565 a top-level `fn main()` is required");
1569 ast::ItemKind::Struct(..) => {
1570 if let Some(attr) = attr::find_by_name(&i.attrs[..], "repr") {
1571 for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
1572 if item.check_name("simd") {
1573 gate_feature_post!(&self, repr_simd, attr.span,
1574 "SIMD types are experimental and possibly buggy");
1576 if item.check_name("transparent") {
1577 gate_feature_post!(&self, repr_transparent, attr.span,
1578 "the `#[repr(transparent)]` attribute \
1581 if let Some((name, _)) = item.name_value_literal() {
1582 if name == "packed" {
1583 gate_feature_post!(&self, repr_packed, attr.span,
1584 "the `#[repr(packed(n))]` attribute \
1592 ast::ItemKind::TraitAlias(..) => {
1593 gate_feature_post!(&self, trait_alias,
1595 "trait aliases are not yet fully implemented");
1598 ast::ItemKind::Impl(_, polarity, defaultness, _, _, _, _) => {
1599 if polarity == ast::ImplPolarity::Negative {
1600 gate_feature_post!(&self, optin_builtin_traits,
1602 "negative trait bounds are not yet fully implemented; \
1603 use marker types for now");
1606 if let ast::Defaultness::Default = defaultness {
1607 gate_feature_post!(&self, specialization,
1609 "specialization is unstable");
1613 ast::ItemKind::Trait(ast::IsAuto::Yes, ..) => {
1614 gate_feature_post!(&self, optin_builtin_traits,
1616 "auto traits are experimental and possibly buggy");
1619 ast::ItemKind::MacroDef(ast::MacroDef { legacy: false, .. }) => {
1620 let msg = "`macro` is experimental";
1621 gate_feature_post!(&self, decl_macro, i.span, msg);
1627 visit::walk_item(self, i);
1630 fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
1632 ast::ForeignItemKind::Fn(..) |
1633 ast::ForeignItemKind::Static(..) => {
1634 let link_name = attr::first_attr_value_str_by_name(&i.attrs, "link_name");
1635 let links_to_llvm = match link_name {
1636 Some(val) => val.as_str().starts_with("llvm."),
1640 gate_feature_post!(&self, link_llvm_intrinsics, i.span,
1641 "linking to LLVM intrinsics is experimental");
1644 ast::ForeignItemKind::Ty => {
1645 gate_feature_post!(&self, extern_types, i.span,
1646 "extern types are experimental");
1648 ast::ForeignItemKind::Macro(..) => {}
1651 visit::walk_foreign_item(self, i)
1654 fn visit_ty(&mut self, ty: &'a ast::Ty) {
1656 ast::TyKind::BareFn(ref bare_fn_ty) => {
1657 self.check_abi(bare_fn_ty.abi, ty.span);
1659 ast::TyKind::Never => {
1660 gate_feature_post!(&self, never_type, ty.span,
1661 "The `!` type is experimental");
1665 visit::walk_ty(self, ty)
1668 fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FunctionRetTy) {
1669 if let ast::FunctionRetTy::Ty(ref output_ty) = *ret_ty {
1670 if output_ty.node != ast::TyKind::Never {
1671 self.visit_ty(output_ty)
1676 fn visit_expr(&mut self, e: &'a ast::Expr) {
1678 ast::ExprKind::Box(_) => {
1679 gate_feature_post!(&self, box_syntax, e.span, EXPLAIN_BOX_SYNTAX);
1681 ast::ExprKind::Type(..) => {
1682 gate_feature_post!(&self, type_ascription, e.span,
1683 "type ascription is experimental");
1685 ast::ExprKind::Yield(..) => {
1686 gate_feature_post!(&self, generators,
1688 "yield syntax is experimental");
1690 ast::ExprKind::Catch(_) => {
1691 gate_feature_post!(&self, catch_expr, e.span, "`catch` expression is experimental");
1693 ast::ExprKind::IfLet(ref pats, ..) | ast::ExprKind::WhileLet(ref pats, ..) => {
1695 gate_feature_post!(&self, if_while_or_patterns, e.span,
1696 "multiple patterns in `if let` and `while let` are unstable");
1701 visit::walk_expr(self, e);
1704 fn visit_arm(&mut self, arm: &'a ast::Arm) {
1705 visit::walk_arm(self, arm)
1708 fn visit_pat(&mut self, pattern: &'a ast::Pat) {
1709 match pattern.node {
1710 PatKind::Slice(_, Some(ref subslice), _) => {
1711 gate_feature_post!(&self, slice_patterns,
1713 "syntax for subslices in slice patterns is not yet stabilized");
1715 PatKind::Box(..) => {
1716 gate_feature_post!(&self, box_patterns,
1718 "box pattern syntax is experimental");
1720 PatKind::Range(_, _, RangeEnd::Excluded) => {
1721 gate_feature_post!(&self, exclusive_range_pattern, pattern.span,
1722 "exclusive range pattern syntax is experimental");
1724 PatKind::Paren(..) => {
1725 gate_feature_post!(&self, pattern_parentheses, pattern.span,
1726 "parentheses in patterns are unstable");
1730 visit::walk_pat(self, pattern)
1733 fn visit_fn(&mut self,
1734 fn_kind: FnKind<'a>,
1735 fn_decl: &'a ast::FnDecl,
1738 // check for const fn declarations
1739 if let FnKind::ItemFn(_, _, Spanned { node: ast::Constness::Const, .. }, _, _, _) =
1741 gate_feature_post!(&self, const_fn, span, "const fn is unstable");
1743 // stability of const fn methods are covered in
1744 // visit_trait_item and visit_impl_item below; this is
1745 // because default methods don't pass through this
1749 FnKind::ItemFn(_, _, _, abi, _, _) |
1750 FnKind::Method(_, &ast::MethodSig { abi, .. }, _, _) => {
1751 self.check_abi(abi, span);
1755 visit::walk_fn(self, fn_kind, fn_decl, span);
1758 fn visit_trait_item(&mut self, ti: &'a ast::TraitItem) {
1760 ast::TraitItemKind::Method(ref sig, ref block) => {
1761 if block.is_none() {
1762 self.check_abi(sig.abi, ti.span);
1764 if sig.constness.node == ast::Constness::Const {
1765 gate_feature_post!(&self, const_fn, ti.span, "const fn is unstable");
1768 ast::TraitItemKind::Type(_, ref default) => {
1769 // We use three if statements instead of something like match guards so that all
1770 // of these errors can be emitted if all cases apply.
1771 if default.is_some() {
1772 gate_feature_post!(&self, associated_type_defaults, ti.span,
1773 "associated type defaults are unstable");
1775 if ti.generics.is_parameterized() {
1776 gate_feature_post!(&self, generic_associated_types, ti.span,
1777 "generic associated types are unstable");
1779 if !ti.generics.where_clause.predicates.is_empty() {
1780 gate_feature_post!(&self, generic_associated_types, ti.span,
1781 "where clauses on associated types are unstable");
1786 visit::walk_trait_item(self, ti);
1789 fn visit_impl_item(&mut self, ii: &'a ast::ImplItem) {
1790 if ii.defaultness == ast::Defaultness::Default {
1791 gate_feature_post!(&self, specialization,
1793 "specialization is unstable");
1797 ast::ImplItemKind::Method(ref sig, _) => {
1798 if sig.constness.node == ast::Constness::Const {
1799 gate_feature_post!(&self, const_fn, ii.span, "const fn is unstable");
1802 ast::ImplItemKind::Type(_) if ii.generics.is_parameterized() => {
1803 gate_feature_post!(&self, generic_associated_types, ii.span,
1804 "generic associated types are unstable");
1808 visit::walk_impl_item(self, ii);
1811 fn visit_path(&mut self, path: &'a ast::Path, _id: NodeId) {
1812 for segment in &path.segments {
1813 // Identifiers we are going to check could come from a legacy macro (e.g. `#[test]`).
1814 // For such macros identifiers must have empty context, because this context is
1815 // used during name resolution and produced names must be unhygienic for compatibility.
1816 // On the other hand, we need the actual non-empty context for feature gate checking
1817 // because it's hygienic even for legacy macros. As previously stated, such context
1818 // cannot be kept in identifiers, so it's kept in paths instead and we take it from
1819 // there while keeping location info from the ident span.
1820 let span = segment.ident.span.with_ctxt(path.span.ctxt());
1821 if segment.ident.name == keywords::Crate.name() {
1822 gate_feature_post!(&self, crate_in_paths, span,
1823 "`crate` in paths is experimental");
1824 } else if segment.ident.name == keywords::Extern.name() {
1825 gate_feature_post!(&self, extern_in_paths, span,
1826 "`extern` in paths is experimental");
1830 visit::walk_path(self, path);
1833 fn visit_vis(&mut self, vis: &'a ast::Visibility) {
1834 if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.node {
1835 gate_feature_post!(&self, crate_visibility_modifier, vis.span,
1836 "`crate` visibility modifier is experimental");
1838 visit::walk_vis(self, vis);
1842 pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
1843 crate_edition: Edition) -> Features {
1844 fn feature_removed(span_handler: &Handler, span: Span, reason: Option<&str>) {
1845 let mut err = struct_span_err!(span_handler, span, E0557, "feature has been removed");
1846 if let Some(reason) = reason {
1847 err.span_note(span, reason);
1852 let mut features = Features::new();
1854 let mut feature_checker = FeatureChecker::default();
1856 for &(.., f_edition, set) in ACTIVE_FEATURES.iter() {
1857 if let Some(f_edition) = f_edition {
1858 if f_edition <= crate_edition {
1859 set(&mut features, DUMMY_SP);
1864 for attr in krate_attrs {
1865 if !attr.check_name("feature") {
1869 let list = match attr.meta_item_list() {
1872 span_err!(span_handler, attr.span, E0555,
1873 "malformed feature attribute, expected #![feature(...)]");
1879 let name = if let Some(word) = mi.word() {
1882 span_err!(span_handler, mi.span, E0556,
1883 "malformed feature, expected just one word");
1887 if let Some((.., set)) = ACTIVE_FEATURES.iter().find(|f| name == f.0) {
1888 set(&mut features, mi.span);
1889 feature_checker.collect(&features, mi.span);
1893 let removed = REMOVED_FEATURES.iter().find(|f| name == f.0);
1894 let stable_removed = STABLE_REMOVED_FEATURES.iter().find(|f| name == f.0);
1895 if let Some((.., reason)) = removed.or(stable_removed) {
1896 feature_removed(span_handler, mi.span, *reason);
1900 if ACCEPTED_FEATURES.iter().any(|f| name == f.0) {
1901 features.declared_stable_lang_features.push((name, mi.span));
1905 if let Some(edition) = ALL_EDITIONS.iter().find(|e| name == e.feature_name()) {
1906 if *edition <= crate_edition {
1910 for &(.., f_edition, set) in ACTIVE_FEATURES.iter() {
1911 if let Some(f_edition) = f_edition {
1912 if *edition >= f_edition {
1913 // FIXME(Manishearth) there is currently no way to set
1914 // lib features by edition
1915 set(&mut features, DUMMY_SP);
1923 features.declared_lib_features.push((name, mi.span));
1927 feature_checker.check(span_handler);
1932 /// A collector for mutually exclusive and interdependent features and their flag spans.
1934 struct FeatureChecker {
1935 proc_macro: Option<Span>,
1936 custom_attribute: Option<Span>,
1939 impl FeatureChecker {
1940 // If this method turns out to be a hotspot due to branching,
1941 // the branching can be eliminated by modifying `set!()` to set these spans
1942 // only for the features that need to be checked for mutual exclusion.
1943 fn collect(&mut self, features: &Features, span: Span) {
1944 if features.proc_macro {
1945 // If self.proc_macro is None, set to Some(span)
1946 self.proc_macro = self.proc_macro.or(Some(span));
1949 if features.custom_attribute {
1950 self.custom_attribute = self.custom_attribute.or(Some(span));
1954 fn check(self, handler: &Handler) {
1955 if let (Some(pm_span), Some(ca_span)) = (self.proc_macro, self.custom_attribute) {
1956 handler.struct_span_err(pm_span, "Cannot use `#![feature(proc_macro)]` and \
1957 `#![feature(custom_attribute)] at the same time")
1958 .span_note(ca_span, "`#![feature(custom_attribute)]` declared here")
1966 pub fn check_crate(krate: &ast::Crate,
1968 features: &Features,
1969 plugin_attributes: &[(String, AttributeType)],
1970 unstable: UnstableFeatures) {
1971 maybe_stage_features(&sess.span_diagnostic, krate, unstable);
1978 if !features.raw_identifiers {
1979 for &span in sess.raw_identifier_spans.borrow().iter() {
1980 if !span.allows_unstable() {
1981 gate_feature!(&ctx, raw_identifiers, span,
1982 "raw identifiers are experimental and subject to change"
1988 let visitor = &mut PostExpansionVisitor { context: &ctx };
1989 visitor.whole_crate_feature_gates(krate);
1990 visit::walk_crate(visitor, krate);
1993 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
1994 pub enum UnstableFeatures {
1995 /// Hard errors for unstable features are active, as on
1996 /// beta/stable channels.
1998 /// Allow features to be activated, as on nightly.
2000 /// Errors are bypassed for bootstrapping. This is required any time
2001 /// during the build that feature-related lints are set to warn or above
2002 /// because the build turns on warnings-as-errors and uses lots of unstable
2003 /// features. As a result, this is always required for building Rust itself.
2007 impl UnstableFeatures {
2008 pub fn from_environment() -> UnstableFeatures {
2009 // Whether this is a feature-staged build, i.e. on the beta or stable channel
2010 let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
2011 // Whether we should enable unstable features for bootstrapping
2012 let bootstrap = env::var("RUSTC_BOOTSTRAP").is_ok();
2013 match (disable_unstable_features, bootstrap) {
2014 (_, true) => UnstableFeatures::Cheat,
2015 (true, _) => UnstableFeatures::Disallow,
2016 (false, _) => UnstableFeatures::Allow
2020 pub fn is_nightly_build(&self) -> bool {
2022 UnstableFeatures::Allow | UnstableFeatures::Cheat => true,
2028 fn maybe_stage_features(span_handler: &Handler, krate: &ast::Crate,
2029 unstable: UnstableFeatures) {
2030 let allow_features = match unstable {
2031 UnstableFeatures::Allow => true,
2032 UnstableFeatures::Disallow => false,
2033 UnstableFeatures::Cheat => true
2035 if !allow_features {
2036 for attr in &krate.attrs {
2037 if attr.check_name("feature") {
2038 let release_channel = option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)");
2039 span_err!(span_handler, attr.span, E0554,
2040 "#![feature] may not be used on the {} release channel",