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::*;
29 use ast::{self, NodeId, PatKind, RangeEnd};
33 use errors::{DiagnosticBuilder, Handler, FatalError};
34 use visit::{self, FnKind, Visitor};
38 use std::ascii::AsciiExt;
43 fn f(features: &mut Features) -> &mut bool {
46 f as fn(&mut Features) -> &mut bool
50 macro_rules! declare_features {
51 ($((active, $feature: ident, $ver: expr, $issue: expr),)+) => {
52 /// Represents active features that are currently being implemented or
53 /// currently being considered for addition/removal.
54 const ACTIVE_FEATURES: &'static [(&'static str, &'static str,
55 Option<u32>, fn(&mut Features) -> &mut bool)] = &[
56 $((stringify!($feature), $ver, $issue, setter!($feature))),+
59 /// A set of features to be used by later passes.
61 /// #![feature] attrs for stable language features, for error reporting
62 pub declared_stable_lang_features: Vec<(Symbol, Span)>,
63 /// #![feature] attrs for non-language (library) features
64 pub declared_lib_features: Vec<(Symbol, Span)>,
65 $(pub $feature: bool),+
69 pub fn new() -> Features {
71 declared_stable_lang_features: Vec::new(),
72 declared_lib_features: Vec::new(),
79 ($((removed, $feature: ident, $ver: expr, $issue: expr),)+) => {
80 /// Represents unstable features which have since been removed (it was once Active)
81 const REMOVED_FEATURES: &'static [(&'static str, &'static str, Option<u32>)] = &[
82 $((stringify!($feature), $ver, $issue)),+
86 ($((stable_removed, $feature: ident, $ver: expr, $issue: expr),)+) => {
87 /// Represents stable features which have since been removed (it was once Accepted)
88 const STABLE_REMOVED_FEATURES: &'static [(&'static str, &'static str, Option<u32>)] = &[
89 $((stringify!($feature), $ver, $issue)),+
93 ($((accepted, $feature: ident, $ver: expr, $issue: expr),)+) => {
94 /// Those language feature has since been Accepted (it was once Active)
95 const ACCEPTED_FEATURES: &'static [(&'static str, &'static str, Option<u32>)] = &[
96 $((stringify!($feature), $ver, $issue)),+
101 // If you change this, please modify src/doc/unstable-book as well.
103 // Don't ever remove anything from this list; set them to 'Removed'.
105 // The version numbers here correspond to the version in which the current status
106 // was set. This is most important for knowing when a particular feature became
109 // NB: The featureck.py script parses this information directly out of the source
110 // so take care when modifying it.
113 (active, asm, "1.0.0", Some(29722)),
114 (active, concat_idents, "1.0.0", Some(29599)),
115 (active, link_args, "1.0.0", Some(29596)),
116 (active, log_syntax, "1.0.0", Some(29598)),
117 (active, non_ascii_idents, "1.0.0", Some(28979)),
118 (active, plugin_registrar, "1.0.0", Some(29597)),
119 (active, thread_local, "1.0.0", Some(29594)),
120 (active, trace_macros, "1.0.0", Some(29598)),
122 // rustc internal, for now:
123 (active, intrinsics, "1.0.0", None),
124 (active, lang_items, "1.0.0", None),
126 (active, link_llvm_intrinsics, "1.0.0", Some(29602)),
127 (active, linkage, "1.0.0", Some(29603)),
128 (active, quote, "1.0.0", Some(29601)),
129 (active, simd, "1.0.0", Some(27731)),
133 (active, rustc_diagnostic_macros, "1.0.0", None),
134 (active, advanced_slice_patterns, "1.0.0", Some(23121)),
135 (active, box_syntax, "1.0.0", Some(27779)),
136 (active, placement_in_syntax, "1.0.0", Some(27779)),
137 (active, unboxed_closures, "1.0.0", Some(29625)),
139 (active, allocator, "1.0.0", Some(27389)),
140 (active, fundamental, "1.0.0", Some(29635)),
141 (active, main, "1.0.0", Some(29634)),
142 (active, needs_allocator, "1.4.0", Some(27389)),
143 (active, on_unimplemented, "1.0.0", Some(29628)),
144 (active, plugin, "1.0.0", Some(29597)),
145 (active, simd_ffi, "1.0.0", Some(27731)),
146 (active, start, "1.0.0", Some(29633)),
147 (active, structural_match, "1.8.0", Some(31434)),
148 (active, panic_runtime, "1.10.0", Some(32837)),
149 (active, needs_panic_runtime, "1.10.0", Some(32837)),
151 // OIBIT specific features
152 (active, optin_builtin_traits, "1.0.0", Some(13231)),
154 // macro reexport needs more discussion and stabilization
155 (active, macro_reexport, "1.0.0", Some(29638)),
157 // Allows use of #[staged_api]
159 (active, staged_api, "1.0.0", None),
161 // Allows using #![no_core]
162 (active, no_core, "1.3.0", Some(29639)),
164 // Allows using `box` in patterns; RFC 469
165 (active, box_patterns, "1.0.0", Some(29641)),
167 // Allows using the unsafe_destructor_blind_to_params attribute;
169 (active, dropck_parametricity, "1.3.0", Some(28498)),
171 // Allows using the may_dangle attribute; RFC 1327
172 (active, dropck_eyepatch, "1.10.0", Some(34761)),
174 // Allows the use of custom attributes; RFC 572
175 (active, custom_attribute, "1.0.0", Some(29642)),
177 // Allows the use of #[derive(Anything)] as sugar for
178 // #[derive_Anything].
179 (active, custom_derive, "1.0.0", Some(29644)),
181 // Allows the use of rustc_* attributes; RFC 572
182 (active, rustc_attrs, "1.0.0", Some(29642)),
184 // Allows the use of #[allow_internal_unstable]. This is an
185 // attribute on macro_rules! and can't use the attribute handling
186 // below (it has to be checked before expansion possibly makes
187 // macros disappear).
190 (active, allow_internal_unstable, "1.0.0", None),
192 // #23121. Array patterns have some hazards yet.
193 (active, slice_patterns, "1.0.0", Some(23121)),
195 // Allows the definition of associated constants in `trait` or `impl`
197 (active, associated_consts, "1.0.0", Some(29646)),
199 // Allows the definition of `const fn` functions.
200 (active, const_fn, "1.2.0", Some(24111)),
202 // Allows indexing into constant arrays.
203 (active, const_indexing, "1.4.0", Some(29947)),
205 // Allows using #[prelude_import] on glob `use` items.
208 (active, prelude_import, "1.2.0", None),
210 // Allows default type parameters to influence type inference.
211 (active, default_type_parameter_fallback, "1.3.0", Some(27336)),
213 // Allows associated type defaults
214 (active, associated_type_defaults, "1.2.0", Some(29661)),
216 // allow `repr(simd)`, and importing the various simd intrinsics
217 (active, repr_simd, "1.4.0", Some(27731)),
219 // Allows cfg(target_feature = "...").
220 (active, cfg_target_feature, "1.4.0", Some(29717)),
222 // allow `extern "platform-intrinsic" { ... }`
223 (active, platform_intrinsics, "1.4.0", Some(27731)),
226 // rust runtime internal
227 (active, unwind_attributes, "1.4.0", None),
229 // allow the use of `#[naked]` on functions.
230 (active, naked_functions, "1.9.0", Some(32408)),
232 // allow `#[no_debug]`
233 (active, no_debug, "1.5.0", Some(29721)),
235 // allow `#[omit_gdb_pretty_printer_section]`
237 (active, omit_gdb_pretty_printer_section, "1.5.0", None),
239 // Allows cfg(target_vendor = "...").
240 (active, cfg_target_vendor, "1.5.0", Some(29718)),
242 // Allow attributes on expressions and non-item statements
243 (active, stmt_expr_attributes, "1.6.0", Some(15701)),
245 // allow using type ascription in expressions
246 (active, type_ascription, "1.6.0", Some(23416)),
248 // Allows cfg(target_thread_local)
249 (active, cfg_target_thread_local, "1.7.0", Some(29594)),
252 (active, abi_vectorcall, "1.7.0", None),
255 (active, inclusive_range_syntax, "1.7.0", Some(28237)),
258 (active, exclusive_range_pattern, "1.11.0", Some(37854)),
260 // impl specialization (RFC 1210)
261 (active, specialization, "1.7.0", Some(31844)),
263 // Allow Drop types in statics/const functions (RFC 1440)
264 (active, drop_types_in_const, "1.9.0", Some(33156)),
266 // Allows cfg(target_has_atomic = "...").
267 (active, cfg_target_has_atomic, "1.9.0", Some(32976)),
269 // Allows `impl Trait` in function return types.
270 (active, conservative_impl_trait, "1.12.0", Some(34511)),
272 // Permits numeric fields in struct expressions and patterns.
273 (active, relaxed_adts, "1.12.0", Some(35626)),
276 (active, never_type, "1.13.0", Some(35121)),
278 // Allows all literals in attribute lists and values of key-value pairs.
279 (active, attr_literals, "1.13.0", Some(34981)),
281 // Allows the sysV64 ABI to be specified on all platforms
282 // instead of just the platforms on which it is the C ABI
283 (active, abi_sysv64, "1.13.0", Some(36167)),
285 // Allows untagged unions `union U { ... }`
286 (active, untagged_unions, "1.13.0", Some(32836)),
288 // Used to identify the `compiler_builtins` crate
290 (active, compiler_builtins, "1.13.0", None),
292 // Allows attributes on lifetime/type formal parameters in generics (RFC 1327)
293 (active, generic_param_attrs, "1.11.0", Some(34761)),
295 // The #![windows_subsystem] attribute
296 (active, windows_subsystem, "1.14.0", Some(37499)),
298 // Allows #[link(..., cfg(..))]
299 (active, link_cfg, "1.14.0", Some(37406)),
301 (active, use_extern_macros, "1.15.0", Some(35896)),
303 // Allows `break {expr}` with a value inside `loop`s.
304 (active, loop_break_value, "1.14.0", Some(37339)),
306 // Allows #[target_feature(...)]
307 (active, target_feature, "1.15.0", None),
309 // `extern "ptx-*" fn()`
310 (active, abi_ptx, "1.15.0", None),
313 (active, i128_type, "1.16.0", Some(35118)),
315 // The `unadjusted` ABI. Perma unstable.
316 (active, abi_unadjusted, "1.16.0", None),
319 (active, proc_macro, "1.16.0", Some(38356)),
321 // Allows attributes on struct literal fields.
322 (active, struct_field_attributes, "1.16.0", Some(38814)),
324 // Allows #[link(kind="static-nobundle"...]
325 (active, static_nobundle, "1.16.0", Some(37403)),
327 // `extern "msp430-interrupt" fn()`
328 (active, abi_msp430_interrupt, "1.16.0", Some(38487)),
330 // Coerces non capturing closures to function pointers
331 (active, closure_to_fn_coercion, "1.17.0", Some(39817)),
333 // Used to identify crates that contain sanitizer runtimes
335 (active, sanitizer_runtime, "1.17.0", None),
337 // `extern "x86-interrupt" fn()`
338 (active, abi_x86_interrupt, "1.17.0", Some(40180)),
341 // Allows the `catch {...}` expression
342 (active, catch_expr, "1.17.0", Some(31436)),
344 // See rust-lang/rfcs#1414. Allows code like `let x: &'static u32 = &42` to work.
345 (active, rvalue_static_promotion, "1.15.1", Some(38865)),
347 // Used to preserve symbols
348 (active, used, "1.18.0", None),
352 (removed, import_shadowing, "1.0.0", None),
353 (removed, managed_boxes, "1.0.0", None),
354 // Allows use of unary negate on unsigned integers, e.g. -e for e: u8
355 (removed, negate_unsigned, "1.0.0", Some(29645)),
356 (removed, reflect, "1.0.0", Some(27749)),
357 // A way to temporarily opt out of opt in copy. This will *never* be accepted.
358 (removed, opt_out_copy, "1.0.0", None),
359 (removed, quad_precision_float, "1.0.0", None),
360 (removed, struct_inherit, "1.0.0", None),
361 (removed, test_removed_feature, "1.0.0", None),
362 (removed, visible_private_types, "1.0.0", None),
363 (removed, unsafe_no_drop_flag, "1.0.0", None),
364 // Allows using items which are missing stability attributes
366 (removed, unmarked_api, "1.0.0", None),
367 (removed, pushpop_unsafe, "1.2.0", None),
371 (stable_removed, no_stack_check, "1.0.0", None),
375 (accepted, associated_types, "1.0.0", None),
376 // allow overloading augmented assignment operations like `a += b`
377 (accepted, augmented_assignments, "1.8.0", Some(28235)),
378 // allow empty structs and enum variants with braces
379 (accepted, braced_empty_structs, "1.8.0", Some(29720)),
380 (accepted, default_type_params, "1.0.0", None),
381 (accepted, globs, "1.0.0", None),
382 (accepted, if_let, "1.0.0", None),
383 // A temporary feature gate used to enable parser extensions needed
384 // to bootstrap fix for #5723.
385 (accepted, issue_5723_bootstrap, "1.0.0", None),
386 (accepted, macro_rules, "1.0.0", None),
387 // Allows using #![no_std]
388 (accepted, no_std, "1.6.0", None),
389 (accepted, slicing_syntax, "1.0.0", None),
390 (accepted, struct_variant, "1.0.0", None),
391 // These are used to test this portion of the compiler, they don't actually
393 (accepted, test_accepted_feature, "1.0.0", None),
394 (accepted, tuple_indexing, "1.0.0", None),
395 // Allows macros to appear in the type position.
396 (accepted, type_macros, "1.13.0", Some(27245)),
397 (accepted, while_let, "1.0.0", None),
398 // Allows `#[deprecated]` attribute
399 (accepted, deprecated, "1.9.0", Some(29935)),
401 (accepted, question_mark, "1.13.0", Some(31436)),
402 // Allows `..` in tuple (struct) patterns
403 (accepted, dotdot_in_tuple_patterns, "1.14.0", Some(33627)),
404 (accepted, item_like_imports, "1.14.0", Some(35120)),
405 // Allows using `Self` and associated types in struct expressions and patterns.
406 (accepted, more_struct_aliases, "1.16.0", Some(37544)),
407 // elide `'static` lifetimes in `static`s and `const`s
408 (accepted, static_in_const, "1.17.0", Some(35897)),
409 // Allows field shorthands (`x` meaning `x: x`) in struct literal expressions.
410 (accepted, field_init_shorthand, "1.17.0", Some(37340)),
411 // Allows the definition recursive static items.
412 (accepted, static_recursion, "1.17.0", Some(29719)),
413 // pub(restricted) visibilities (RFC 1422)
414 (accepted, pub_restricted, "1.17.0", Some(32409)),
417 // If you change this, please modify src/doc/unstable-book as well. You must
418 // move that documentation into the relevant place in the other docs, and
419 // remove the chapter on the flag.
421 #[derive(PartialEq, Copy, Clone, Debug)]
422 pub enum AttributeType {
423 /// Normal, builtin attribute that is consumed
424 /// by the compiler before the unused_attribute check
427 /// Builtin attribute that may not be consumed by the compiler
428 /// before the unused_attribute check. These attributes
429 /// will be ignored by the unused_attribute lint
432 /// Builtin attribute that is only allowed at the crate level
436 pub enum AttributeGate {
437 /// Is gated by a given feature gate, reason
438 /// and function to check if enabled
439 Gated(Stability, &'static str, &'static str, fn(&Features) -> bool),
441 /// Ungated attribute, can be used on all release channels
446 fn is_deprecated(&self) -> bool {
448 Gated(Stability::Deprecated(_), ..) => true,
454 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
457 // Argument is tracking issue link.
458 Deprecated(&'static str),
462 impl ::std::fmt::Debug for AttributeGate {
463 fn fmt(&self, fmt: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
465 Gated(ref stab, ref name, ref expl, _) =>
466 write!(fmt, "Gated({:?}, {}, {})", stab, name, expl),
467 Ungated => write!(fmt, "Ungated")
472 macro_rules! cfg_fn {
473 ($field: ident) => {{
474 fn f(features: &Features) -> bool {
477 f as fn(&Features) -> bool
481 pub fn deprecated_attributes() -> Vec<&'static (&'static str, AttributeType, AttributeGate)> {
482 BUILTIN_ATTRIBUTES.iter().filter(|a| a.2.is_deprecated()).collect()
485 pub fn is_builtin_attr(attr: &ast::Attribute) -> bool {
486 BUILTIN_ATTRIBUTES.iter().any(|&(builtin_name, _, _)| attr.check_name(builtin_name))
489 // Attributes that have a special meaning to rustc or rustdoc
490 pub const BUILTIN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeGate)] = &[
493 ("warn", Normal, Ungated),
494 ("allow", Normal, Ungated),
495 ("forbid", Normal, Ungated),
496 ("deny", Normal, Ungated),
498 ("macro_reexport", Normal, Ungated),
499 ("macro_use", Normal, Ungated),
500 ("macro_export", Normal, Ungated),
501 ("plugin_registrar", Normal, Ungated),
503 ("cfg", Normal, Ungated),
504 ("cfg_attr", Normal, Ungated),
505 ("main", Normal, Ungated),
506 ("start", Normal, Ungated),
507 ("test", Normal, Ungated),
508 ("bench", Normal, Ungated),
509 ("simd", Normal, Ungated),
510 ("repr", Normal, Ungated),
511 ("path", Normal, Ungated),
512 ("abi", Normal, Ungated),
513 ("automatically_derived", Normal, Ungated),
514 ("no_mangle", Normal, Ungated),
515 ("no_link", Normal, Ungated),
516 ("derive", Normal, Ungated),
517 ("should_panic", Normal, Ungated),
518 ("ignore", Normal, Ungated),
519 ("no_implicit_prelude", Normal, Ungated),
520 ("reexport_test_harness_main", Normal, Ungated),
521 ("link_args", Normal, Ungated),
522 ("macro_escape", Normal, Ungated),
525 ("structural_match", Whitelisted, Gated(Stability::Unstable,
527 "the semantics of constant patterns is \
529 cfg_fn!(structural_match))),
531 ("plugin", CrateLevel, Gated(Stability::Unstable,
533 "compiler plugins are experimental \
537 ("no_std", CrateLevel, Ungated),
538 ("no_core", CrateLevel, Gated(Stability::Unstable,
540 "no_core is experimental",
542 ("lang", Normal, Gated(Stability::Unstable,
544 "language items are subject to change",
545 cfg_fn!(lang_items))),
546 ("linkage", Whitelisted, Gated(Stability::Unstable,
548 "the `linkage` attribute is experimental \
549 and not portable across platforms",
551 ("thread_local", Whitelisted, Gated(Stability::Unstable,
553 "`#[thread_local]` is an experimental feature, and does \
554 not currently handle destructors. There is no \
555 corresponding `#[task_local]` mapping to the task \
557 cfg_fn!(thread_local))),
559 ("rustc_on_unimplemented", Normal, Gated(Stability::Unstable,
561 "the `#[rustc_on_unimplemented]` attribute \
562 is an experimental feature",
563 cfg_fn!(on_unimplemented))),
564 ("allocator", Whitelisted, Gated(Stability::Unstable,
566 "the `#[allocator]` attribute is an experimental feature",
567 cfg_fn!(allocator))),
568 ("needs_allocator", Normal, Gated(Stability::Unstable,
570 "the `#[needs_allocator]` \
571 attribute is an experimental \
573 cfg_fn!(needs_allocator))),
574 ("panic_runtime", Whitelisted, Gated(Stability::Unstable,
576 "the `#[panic_runtime]` attribute is \
577 an experimental feature",
578 cfg_fn!(panic_runtime))),
579 ("needs_panic_runtime", Whitelisted, Gated(Stability::Unstable,
580 "needs_panic_runtime",
581 "the `#[needs_panic_runtime]` \
582 attribute is an experimental \
584 cfg_fn!(needs_panic_runtime))),
585 ("rustc_variance", Normal, Gated(Stability::Unstable,
587 "the `#[rustc_variance]` attribute \
588 is just used for rustc unit tests \
589 and will never be stable",
590 cfg_fn!(rustc_attrs))),
591 ("rustc_error", Whitelisted, Gated(Stability::Unstable,
593 "the `#[rustc_error]` attribute \
594 is just used for rustc unit tests \
595 and will never be stable",
596 cfg_fn!(rustc_attrs))),
597 ("rustc_if_this_changed", Whitelisted, Gated(Stability::Unstable,
599 "the `#[rustc_if_this_changed]` attribute \
600 is just used for rustc unit tests \
601 and will never be stable",
602 cfg_fn!(rustc_attrs))),
603 ("rustc_then_this_would_need", Whitelisted, Gated(Stability::Unstable,
605 "the `#[rustc_if_this_changed]` attribute \
606 is just used for rustc unit tests \
607 and will never be stable",
608 cfg_fn!(rustc_attrs))),
609 ("rustc_dirty", Whitelisted, Gated(Stability::Unstable,
611 "the `#[rustc_dirty]` attribute \
612 is just used for rustc unit tests \
613 and will never be stable",
614 cfg_fn!(rustc_attrs))),
615 ("rustc_clean", Whitelisted, Gated(Stability::Unstable,
617 "the `#[rustc_clean]` attribute \
618 is just used for rustc unit tests \
619 and will never be stable",
620 cfg_fn!(rustc_attrs))),
621 ("rustc_metadata_dirty", Whitelisted, Gated(Stability::Unstable,
623 "the `#[rustc_metadata_dirty]` attribute \
624 is just used for rustc unit tests \
625 and will never be stable",
626 cfg_fn!(rustc_attrs))),
627 ("rustc_metadata_clean", Whitelisted, Gated(Stability::Unstable,
629 "the `#[rustc_metadata_clean]` attribute \
630 is just used for rustc unit tests \
631 and will never be stable",
632 cfg_fn!(rustc_attrs))),
633 ("rustc_partition_reused", Whitelisted, Gated(Stability::Unstable,
636 is just used for rustc unit tests \
637 and will never be stable",
638 cfg_fn!(rustc_attrs))),
639 ("rustc_partition_translated", Whitelisted, Gated(Stability::Unstable,
642 is just used for rustc unit tests \
643 and will never be stable",
644 cfg_fn!(rustc_attrs))),
645 ("rustc_symbol_name", Whitelisted, Gated(Stability::Unstable,
647 "internal rustc attributes will never be stable",
648 cfg_fn!(rustc_attrs))),
649 ("rustc_item_path", Whitelisted, Gated(Stability::Unstable,
651 "internal rustc attributes will never be stable",
652 cfg_fn!(rustc_attrs))),
653 ("rustc_move_fragments", Normal, Gated(Stability::Unstable,
655 "the `#[rustc_move_fragments]` attribute \
656 is just used for rustc unit tests \
657 and will never be stable",
658 cfg_fn!(rustc_attrs))),
659 ("rustc_mir", Whitelisted, Gated(Stability::Unstable,
661 "the `#[rustc_mir]` attribute \
662 is just used for rustc unit tests \
663 and will never be stable",
664 cfg_fn!(rustc_attrs))),
665 ("rustc_inherit_overflow_checks", Whitelisted, Gated(Stability::Unstable,
667 "the `#[rustc_inherit_overflow_checks]` \
668 attribute is just used to control \
669 overflow checking behavior of several \
670 libcore functions that are inlined \
671 across crates and will never be stable",
672 cfg_fn!(rustc_attrs))),
673 ("compiler_builtins", Whitelisted, Gated(Stability::Unstable,
675 "the `#[compiler_builtins]` attribute is used to \
676 identify the `compiler_builtins` crate which \
677 contains compiler-rt intrinsics and will never be \
679 cfg_fn!(compiler_builtins))),
680 ("sanitizer_runtime", Whitelisted, Gated(Stability::Unstable,
682 "the `#[sanitizer_runtime]` attribute is used to \
683 identify crates that contain the runtime of a \
684 sanitizer and will never be stable",
685 cfg_fn!(sanitizer_runtime))),
687 ("allow_internal_unstable", Normal, Gated(Stability::Unstable,
688 "allow_internal_unstable",
689 EXPLAIN_ALLOW_INTERNAL_UNSTABLE,
690 cfg_fn!(allow_internal_unstable))),
692 ("fundamental", Whitelisted, Gated(Stability::Unstable,
694 "the `#[fundamental]` attribute \
695 is an experimental feature",
696 cfg_fn!(fundamental))),
698 ("proc_macro_derive", Normal, Ungated),
700 ("rustc_copy_clone_marker", Whitelisted, Gated(Stability::Unstable,
702 "internal implementation detail",
703 cfg_fn!(rustc_attrs))),
705 // FIXME: #14408 whitelist docs since rustdoc looks at them
706 ("doc", Whitelisted, Ungated),
708 // FIXME: #14406 these are processed in trans, which happens after the
710 ("cold", Whitelisted, Ungated),
711 ("naked", Whitelisted, Gated(Stability::Unstable,
713 "the `#[naked]` attribute \
714 is an experimental feature",
715 cfg_fn!(naked_functions))),
716 ("target_feature", Whitelisted, Gated(
717 Stability::Unstable, "target_feature",
718 "the `#[target_feature]` attribute is an experimental feature",
719 cfg_fn!(target_feature))),
720 ("export_name", Whitelisted, Ungated),
721 ("inline", Whitelisted, Ungated),
722 ("link", Whitelisted, Ungated),
723 ("link_name", Whitelisted, Ungated),
724 ("link_section", Whitelisted, Ungated),
725 ("no_builtins", Whitelisted, Ungated),
726 ("no_mangle", Whitelisted, Ungated),
727 ("no_debug", Whitelisted, Gated(
728 Stability::Deprecated("https://github.com/rust-lang/rust/issues/29721"),
730 "the `#[no_debug]` attribute is an experimental feature",
732 ("omit_gdb_pretty_printer_section", Whitelisted, Gated(Stability::Unstable,
733 "omit_gdb_pretty_printer_section",
734 "the `#[omit_gdb_pretty_printer_section]` \
735 attribute is just used for the Rust test \
737 cfg_fn!(omit_gdb_pretty_printer_section))),
738 ("unsafe_destructor_blind_to_params",
740 Gated(Stability::Deprecated("https://github.com/rust-lang/rust/issues/34761"),
741 "dropck_parametricity",
742 "unsafe_destructor_blind_to_params has been replaced by \
743 may_dangle and will be removed in the future",
744 cfg_fn!(dropck_parametricity))),
747 Gated(Stability::Unstable,
749 "may_dangle has unstable semantics and may be removed in the future",
750 cfg_fn!(dropck_eyepatch))),
751 ("unwind", Whitelisted, Gated(Stability::Unstable,
753 "#[unwind] is experimental",
754 cfg_fn!(unwind_attributes))),
755 ("used", Whitelisted, Gated(
756 Stability::Unstable, "used",
757 "the `#[used]` attribute is an experimental feature",
761 ("prelude_import", Whitelisted, Gated(Stability::Unstable,
763 "`#[prelude_import]` is for use by rustc only",
764 cfg_fn!(prelude_import))),
766 // FIXME: #14407 these are only looked at on-demand so we can't
767 // guarantee they'll have already been checked
768 ("rustc_deprecated", Whitelisted, Ungated),
769 ("must_use", Whitelisted, Ungated),
770 ("stable", Whitelisted, Ungated),
771 ("unstable", Whitelisted, Ungated),
772 ("deprecated", Normal, Ungated),
774 ("rustc_paren_sugar", Normal, Gated(Stability::Unstable,
776 "unboxed_closures are still evolving",
777 cfg_fn!(unboxed_closures))),
779 ("windows_subsystem", Whitelisted, Gated(Stability::Unstable,
781 "the windows subsystem attribute \
782 is currently unstable",
783 cfg_fn!(windows_subsystem))),
785 ("proc_macro_attribute", Normal, Gated(Stability::Unstable,
787 "attribute proc macros are currently unstable",
788 cfg_fn!(proc_macro))),
790 ("proc_macro", Normal, Gated(Stability::Unstable,
792 "function-like proc macros are currently unstable",
793 cfg_fn!(proc_macro))),
795 ("rustc_derive_registrar", Normal, Gated(Stability::Unstable,
796 "rustc_derive_registrar",
797 "used internally by rustc",
798 cfg_fn!(rustc_attrs))),
800 // Crate level attributes
801 ("crate_name", CrateLevel, Ungated),
802 ("crate_type", CrateLevel, Ungated),
803 ("crate_id", CrateLevel, Ungated),
804 ("feature", CrateLevel, Ungated),
805 ("no_start", CrateLevel, Ungated),
806 ("no_main", CrateLevel, Ungated),
807 ("no_builtins", CrateLevel, Ungated),
808 ("recursion_limit", CrateLevel, Ungated),
809 ("type_length_limit", CrateLevel, Ungated),
812 // cfg(...)'s that are feature gated
813 const GATED_CFGS: &'static [(&'static str, &'static str, fn(&Features) -> bool)] = &[
814 // (name in cfg, feature, function to check if the feature is enabled)
815 ("target_feature", "cfg_target_feature", cfg_fn!(cfg_target_feature)),
816 ("target_vendor", "cfg_target_vendor", cfg_fn!(cfg_target_vendor)),
817 ("target_thread_local", "cfg_target_thread_local", cfg_fn!(cfg_target_thread_local)),
818 ("target_has_atomic", "cfg_target_has_atomic", cfg_fn!(cfg_target_has_atomic)),
821 #[derive(Debug, Eq, PartialEq)]
822 pub struct GatedCfg {
828 pub fn gate(cfg: &ast::MetaItem) -> Option<GatedCfg> {
829 let name = cfg.name().as_str();
831 .position(|info| info.0 == name)
840 pub fn check_and_emit(&self, sess: &ParseSess, features: &Features) {
841 let (cfg, feature, has_feature) = GATED_CFGS[self.index];
842 if !has_feature(features) && !self.span.allows_unstable() {
843 let explain = format!("`cfg({})` is experimental and subject to change", cfg);
844 emit_feature_err(sess, feature, self.span, GateIssue::Language, &explain);
850 features: &'a Features,
851 parse_sess: &'a ParseSess,
852 plugin_attributes: &'a [(String, AttributeType)],
855 macro_rules! gate_feature_fn {
856 ($cx: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr) => {{
857 let (cx, has_feature, span, name, explain) = ($cx, $has_feature, $span, $name, $explain);
858 let has_feature: bool = has_feature(&$cx.features);
859 debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
860 if !has_feature && !span.allows_unstable() {
861 emit_feature_err(cx.parse_sess, name, span, GateIssue::Language, explain);
866 macro_rules! gate_feature {
867 ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {
868 gate_feature_fn!($cx, |x:&Features| x.$feature, $span, stringify!($feature), $explain)
872 impl<'a> Context<'a> {
873 fn check_attribute(&self, attr: &ast::Attribute, is_macro: bool) {
874 debug!("check_attribute(attr = {:?})", attr);
875 let name = unwrap_or!(attr.name(), return).as_str();
876 for &(n, ty, ref gateage) in BUILTIN_ATTRIBUTES {
878 if let &Gated(_, ref name, ref desc, ref has_feature) = gateage {
879 gate_feature_fn!(self, has_feature, attr.span, name, desc);
881 debug!("check_attribute: {:?} is builtin, {:?}, {:?}", attr.path, ty, gateage);
885 for &(ref n, ref ty) in self.plugin_attributes {
886 if attr.path == &**n {
887 // Plugins can't gate attributes, so we don't check for it
888 // unlike the code above; we only use this loop to
889 // short-circuit to avoid the checks below
890 debug!("check_attribute: {:?} is registered by a plugin, {:?}", attr.path, ty);
894 if name.starts_with("rustc_") {
895 gate_feature!(self, rustc_attrs, attr.span,
896 "unless otherwise specified, attributes \
897 with the prefix `rustc_` \
898 are reserved for internal compiler diagnostics");
899 } else if name.starts_with("derive_") {
900 gate_feature!(self, custom_derive, attr.span, EXPLAIN_DERIVE_UNDERSCORE);
901 } else if !attr::is_known(attr) {
902 // Only run the custom attribute lint during regular
903 // feature gate checking. Macro gating runs
904 // before the plugin attributes are registered
905 // so we skip this then
907 gate_feature!(self, custom_attribute, attr.span,
908 &format!("The attribute `{}` is currently \
909 unknown to the compiler and \
911 added to it in the future",
918 pub fn check_attribute(attr: &ast::Attribute, parse_sess: &ParseSess, features: &Features) {
919 let cx = Context { features: features, parse_sess: parse_sess, plugin_attributes: &[] };
920 cx.check_attribute(attr, true);
923 pub fn find_lang_feature_accepted_version(feature: &str) -> Option<&'static str> {
924 ACCEPTED_FEATURES.iter().find(|t| t.0 == feature).map(|t| t.1)
927 fn find_lang_feature_issue(feature: &str) -> Option<u32> {
928 if let Some(info) = ACTIVE_FEATURES.iter().find(|t| t.0 == feature) {
930 // FIXME (#28244): enforce that active features have issue numbers
931 // assert!(issue.is_some())
934 // search in Accepted, Removed, or Stable Removed features
935 let found = ACCEPTED_FEATURES.iter().chain(REMOVED_FEATURES).chain(STABLE_REMOVED_FEATURES)
936 .find(|t| t.0 == feature);
938 Some(&(_, _, issue)) => issue,
939 None => panic!("Feature `{}` is not declared anywhere", feature),
949 pub fn emit_feature_err(sess: &ParseSess, feature: &str, span: Span, issue: GateIssue,
951 feature_err(sess, feature, span, issue, explain).emit();
954 pub fn feature_err<'a>(sess: &'a ParseSess, feature: &str, span: Span, issue: GateIssue,
955 explain: &str) -> DiagnosticBuilder<'a> {
956 let diag = &sess.span_diagnostic;
958 let issue = match issue {
959 GateIssue::Language => find_lang_feature_issue(feature),
960 GateIssue::Library(lib) => lib,
963 let mut err = if let Some(n) = issue {
964 diag.struct_span_err(span, &format!("{} (see issue #{})", explain, n))
966 diag.struct_span_err(span, explain)
969 // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
970 if sess.unstable_features.is_nightly_build() {
971 err.help(&format!("add #![feature({})] to the \
972 crate attributes to enable",
979 const EXPLAIN_BOX_SYNTAX: &'static str =
980 "box expression syntax is experimental; you can call `Box::new` instead.";
982 pub const EXPLAIN_STMT_ATTR_SYNTAX: &'static str =
983 "attributes on non-item statements and expressions are experimental.";
985 pub const EXPLAIN_ASM: &'static str =
986 "inline assembly is not stable enough for use and is subject to change";
988 pub const EXPLAIN_LOG_SYNTAX: &'static str =
989 "`log_syntax!` is not stable enough for use and is subject to change";
991 pub const EXPLAIN_CONCAT_IDENTS: &'static str =
992 "`concat_idents` is not stable enough for use and is subject to change";
994 pub const EXPLAIN_TRACE_MACROS: &'static str =
995 "`trace_macros` is not stable enough for use and is subject to change";
996 pub const EXPLAIN_ALLOW_INTERNAL_UNSTABLE: &'static str =
997 "allow_internal_unstable side-steps feature gating and stability checks";
999 pub const EXPLAIN_CUSTOM_DERIVE: &'static str =
1000 "`#[derive]` for custom traits is deprecated and will be removed in the future.";
1002 pub const EXPLAIN_DEPR_CUSTOM_DERIVE: &'static str =
1003 "`#[derive]` for custom traits is deprecated and will be removed in the future. \
1004 Prefer using procedural macro custom derive.";
1006 pub const EXPLAIN_DERIVE_UNDERSCORE: &'static str =
1007 "attributes of the form `#[derive_*]` are reserved for the compiler";
1009 pub const EXPLAIN_PLACEMENT_IN: &'static str =
1010 "placement-in expression syntax is experimental and subject to change.";
1012 pub const CLOSURE_TO_FN_COERCION: &'static str =
1013 "non-capturing closure to fn coercion is experimental";
1015 struct PostExpansionVisitor<'a> {
1016 context: &'a Context<'a>,
1019 macro_rules! gate_feature_post {
1020 ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {{
1021 let (cx, span) = ($cx, $span);
1022 if !span.allows_unstable() {
1023 gate_feature!(cx.context, $feature, span, $explain)
1028 impl<'a> PostExpansionVisitor<'a> {
1029 fn check_abi(&self, abi: Abi, span: Span) {
1031 Abi::RustIntrinsic => {
1032 gate_feature_post!(&self, intrinsics, span,
1033 "intrinsics are subject to change");
1035 Abi::PlatformIntrinsic => {
1036 gate_feature_post!(&self, platform_intrinsics, span,
1037 "platform intrinsics are experimental and possibly buggy");
1039 Abi::Vectorcall => {
1040 gate_feature_post!(&self, abi_vectorcall, span,
1041 "vectorcall is experimental and subject to change");
1044 gate_feature_post!(&self, unboxed_closures, span,
1045 "rust-call ABI is subject to change");
1048 gate_feature_post!(&self, abi_sysv64, span,
1049 "sysv64 ABI is experimental and subject to change");
1052 gate_feature_post!(&self, abi_ptx, span,
1053 "PTX ABIs are experimental and subject to change");
1055 Abi::Unadjusted => {
1056 gate_feature_post!(&self, abi_unadjusted, span,
1057 "unadjusted ABI is an implementation detail and perma-unstable");
1059 Abi::Msp430Interrupt => {
1060 gate_feature_post!(&self, abi_msp430_interrupt, span,
1061 "msp430-interrupt ABI is experimental and subject to change");
1063 Abi::X86Interrupt => {
1064 gate_feature_post!(&self, abi_x86_interrupt, span,
1065 "x86-interrupt ABI is experimental and subject to change");
1080 fn contains_novel_literal(item: &ast::MetaItem) -> bool {
1081 use ast::MetaItemKind::*;
1082 use ast::NestedMetaItemKind::*;
1086 NameValue(ref lit) => !lit.node.is_str(),
1087 List(ref list) => list.iter().any(|li| {
1089 MetaItem(ref mi) => contains_novel_literal(&mi),
1096 fn starts_with_digit(s: &str) -> bool {
1097 s.as_bytes().first().cloned().map_or(false, |b| b >= b'0' && b <= b'9')
1100 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
1101 fn visit_attribute(&mut self, attr: &ast::Attribute) {
1102 if !attr.span.allows_unstable() {
1103 // check for gated attributes
1104 self.context.check_attribute(attr, false);
1107 if self.context.features.proc_macro && attr::is_known(attr) {
1111 let meta = panictry!(attr.parse_meta(&self.context.parse_sess));
1112 if contains_novel_literal(&meta) {
1113 gate_feature_post!(&self, attr_literals, attr.span,
1114 "non-string literals in attributes, or string \
1115 literals in top-level positions, are experimental");
1119 fn visit_name(&mut self, sp: Span, name: ast::Name) {
1120 if !name.as_str().is_ascii() {
1121 gate_feature_post!(&self, non_ascii_idents, sp,
1122 "non-ascii idents are not fully supported.");
1126 fn visit_item(&mut self, i: &'a ast::Item) {
1128 ast::ItemKind::ExternCrate(_) => {
1129 if attr::contains_name(&i.attrs[..], "macro_reexport") {
1130 gate_feature_post!(&self, macro_reexport, i.span,
1131 "macros reexports are experimental \
1132 and possibly buggy");
1136 ast::ItemKind::ForeignMod(ref foreign_module) => {
1137 if attr::contains_name(&i.attrs[..], "link_args") {
1138 gate_feature_post!(&self, link_args, i.span,
1139 "the `link_args` attribute is not portable \
1140 across platforms, it is recommended to \
1141 use `#[link(name = \"foo\")]` instead")
1143 self.check_abi(foreign_module.abi, i.span);
1146 ast::ItemKind::Fn(..) => {
1147 if attr::contains_name(&i.attrs[..], "plugin_registrar") {
1148 gate_feature_post!(&self, plugin_registrar, i.span,
1149 "compiler plugins are experimental and possibly buggy");
1151 if attr::contains_name(&i.attrs[..], "start") {
1152 gate_feature_post!(&self, start, i.span,
1153 "a #[start] function is an experimental \
1154 feature whose signature may change \
1157 if attr::contains_name(&i.attrs[..], "main") {
1158 gate_feature_post!(&self, main, i.span,
1159 "declaration of a nonstandard #[main] \
1160 function may change over time, for now \
1161 a top-level `fn main()` is required");
1165 ast::ItemKind::Struct(..) => {
1166 if attr::contains_name(&i.attrs[..], "simd") {
1167 gate_feature_post!(&self, simd, i.span,
1168 "SIMD types are experimental and possibly buggy");
1169 self.context.parse_sess.span_diagnostic.span_warn(i.span,
1170 "the `#[simd]` attribute \
1171 is deprecated, use \
1172 `#[repr(simd)]` instead");
1174 for attr in &i.attrs {
1175 if attr.path == "repr" {
1176 for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
1177 if item.check_name("simd") {
1178 gate_feature_post!(&self, repr_simd, i.span,
1179 "SIMD types are experimental \
1180 and possibly buggy");
1188 ast::ItemKind::Union(..) => {
1189 gate_feature_post!(&self, untagged_unions,
1191 "unions are unstable and possibly buggy");
1194 ast::ItemKind::DefaultImpl(..) => {
1195 gate_feature_post!(&self, optin_builtin_traits,
1197 "default trait implementations are experimental \
1198 and possibly buggy");
1201 ast::ItemKind::Impl(_, polarity, _, _, _, _) => {
1203 ast::ImplPolarity::Negative => {
1204 gate_feature_post!(&self, optin_builtin_traits,
1206 "negative trait bounds are not yet fully implemented; \
1207 use marker types for now");
1216 visit::walk_item(self, i);
1219 fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
1220 let links_to_llvm = match attr::first_attr_value_str_by_name(&i.attrs, "link_name") {
1221 Some(val) => val.as_str().starts_with("llvm."),
1225 gate_feature_post!(&self, link_llvm_intrinsics, i.span,
1226 "linking to LLVM intrinsics is experimental");
1229 visit::walk_foreign_item(self, i)
1232 fn visit_ty(&mut self, ty: &'a ast::Ty) {
1234 ast::TyKind::BareFn(ref bare_fn_ty) => {
1235 self.check_abi(bare_fn_ty.abi, ty.span);
1237 ast::TyKind::ImplTrait(..) => {
1238 gate_feature_post!(&self, conservative_impl_trait, ty.span,
1239 "`impl Trait` is experimental");
1241 ast::TyKind::Never => {
1242 gate_feature_post!(&self, never_type, ty.span,
1243 "The `!` type is experimental");
1247 visit::walk_ty(self, ty)
1250 fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FunctionRetTy) {
1251 if let ast::FunctionRetTy::Ty(ref output_ty) = *ret_ty {
1252 match output_ty.node {
1253 ast::TyKind::Never => return,
1256 self.visit_ty(output_ty)
1260 fn visit_expr(&mut self, e: &'a ast::Expr) {
1262 ast::ExprKind::Box(_) => {
1263 gate_feature_post!(&self, box_syntax, e.span, EXPLAIN_BOX_SYNTAX);
1265 ast::ExprKind::Type(..) => {
1266 gate_feature_post!(&self, type_ascription, e.span,
1267 "type ascription is experimental");
1269 ast::ExprKind::Range(_, _, ast::RangeLimits::Closed) => {
1270 gate_feature_post!(&self, inclusive_range_syntax,
1272 "inclusive range syntax is experimental");
1274 ast::ExprKind::InPlace(..) => {
1275 gate_feature_post!(&self, placement_in_syntax, e.span, EXPLAIN_PLACEMENT_IN);
1277 ast::ExprKind::Struct(_, ref fields, _) => {
1278 for field in fields {
1279 if starts_with_digit(&field.ident.node.name.as_str()) {
1280 gate_feature_post!(&self, relaxed_adts,
1282 "numeric fields in struct expressions are unstable");
1286 ast::ExprKind::Break(_, Some(_)) => {
1287 gate_feature_post!(&self, loop_break_value, e.span,
1288 "`break` with a value is experimental");
1290 ast::ExprKind::Lit(ref lit) => {
1291 if let ast::LitKind::Int(_, ref ty) = lit.node {
1293 ast::LitIntType::Signed(ast::IntTy::I128) |
1294 ast::LitIntType::Unsigned(ast::UintTy::U128) => {
1295 gate_feature_post!(&self, i128_type, e.span,
1296 "128-bit integers are not stable");
1302 ast::ExprKind::Catch(_) => {
1303 gate_feature_post!(&self, catch_expr, e.span, "`catch` expression is experimental");
1307 visit::walk_expr(self, e);
1310 fn visit_pat(&mut self, pattern: &'a ast::Pat) {
1311 match pattern.node {
1312 PatKind::Slice(_, Some(_), ref last) if !last.is_empty() => {
1313 gate_feature_post!(&self, advanced_slice_patterns,
1315 "multiple-element slice matches anywhere \
1316 but at the end of a slice (e.g. \
1317 `[0, ..xs, 0]`) are experimental")
1319 PatKind::Slice(..) => {
1320 gate_feature_post!(&self, slice_patterns,
1322 "slice pattern syntax is experimental");
1324 PatKind::Box(..) => {
1325 gate_feature_post!(&self, box_patterns,
1327 "box pattern syntax is experimental");
1329 PatKind::Struct(_, ref fields, _) => {
1330 for field in fields {
1331 if starts_with_digit(&field.node.ident.name.as_str()) {
1332 gate_feature_post!(&self, relaxed_adts,
1334 "numeric fields in struct patterns are unstable");
1338 PatKind::Range(_, _, RangeEnd::Excluded) => {
1339 gate_feature_post!(&self, exclusive_range_pattern, pattern.span,
1340 "exclusive range pattern syntax is experimental");
1344 visit::walk_pat(self, pattern)
1347 fn visit_fn(&mut self,
1348 fn_kind: FnKind<'a>,
1349 fn_decl: &'a ast::FnDecl,
1352 // check for const fn declarations
1354 FnKind::ItemFn(_, _, _, Spanned { node: ast::Constness::Const, .. }, _, _, _) => {
1355 gate_feature_post!(&self, const_fn, span, "const fn is unstable");
1358 // stability of const fn methods are covered in
1359 // visit_trait_item and visit_impl_item below; this is
1360 // because default methods don't pass through this
1366 FnKind::ItemFn(_, _, _, _, abi, _, _) |
1367 FnKind::Method(_, &ast::MethodSig { abi, .. }, _, _) => {
1368 self.check_abi(abi, span);
1372 visit::walk_fn(self, fn_kind, fn_decl, span);
1375 fn visit_trait_item(&mut self, ti: &'a ast::TraitItem) {
1377 ast::TraitItemKind::Const(..) => {
1378 gate_feature_post!(&self, associated_consts,
1380 "associated constants are experimental")
1382 ast::TraitItemKind::Method(ref sig, ref block) => {
1383 if block.is_none() {
1384 self.check_abi(sig.abi, ti.span);
1386 if sig.constness.node == ast::Constness::Const {
1387 gate_feature_post!(&self, const_fn, ti.span, "const fn is unstable");
1390 ast::TraitItemKind::Type(_, Some(_)) => {
1391 gate_feature_post!(&self, associated_type_defaults, ti.span,
1392 "associated type defaults are unstable");
1396 visit::walk_trait_item(self, ti);
1399 fn visit_impl_item(&mut self, ii: &'a ast::ImplItem) {
1400 if ii.defaultness == ast::Defaultness::Default {
1401 gate_feature_post!(&self, specialization,
1403 "specialization is unstable");
1407 ast::ImplItemKind::Const(..) => {
1408 gate_feature_post!(&self, associated_consts,
1410 "associated constants are experimental")
1412 ast::ImplItemKind::Method(ref sig, _) => {
1413 if sig.constness.node == ast::Constness::Const {
1414 gate_feature_post!(&self, const_fn, ii.span, "const fn is unstable");
1419 visit::walk_impl_item(self, ii);
1422 fn visit_generics(&mut self, g: &'a ast::Generics) {
1423 for t in &g.ty_params {
1424 if !t.attrs.is_empty() {
1425 gate_feature_post!(&self, generic_param_attrs, t.attrs[0].span,
1426 "attributes on type parameter bindings are experimental");
1429 visit::walk_generics(self, g)
1432 fn visit_lifetime_def(&mut self, lifetime_def: &'a ast::LifetimeDef) {
1433 if !lifetime_def.attrs.is_empty() {
1434 gate_feature_post!(&self, generic_param_attrs, lifetime_def.attrs[0].span,
1435 "attributes on lifetime bindings are experimental");
1437 visit::walk_lifetime_def(self, lifetime_def)
1441 pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute]) -> Features {
1442 let mut features = Features::new();
1444 let mut feature_checker = MutexFeatureChecker::default();
1446 for attr in krate_attrs {
1447 if !attr.check_name("feature") {
1451 match attr.meta_item_list() {
1453 span_err!(span_handler, attr.span, E0555,
1454 "malformed feature attribute, expected #![feature(...)]");
1458 let name = if let Some(word) = mi.word() {
1461 span_err!(span_handler, mi.span, E0556,
1462 "malformed feature, expected just one word");
1466 if let Some(&(_, _, _, setter)) = ACTIVE_FEATURES.iter()
1467 .find(|& &(n, _, _, _)| name == n) {
1468 *(setter(&mut features)) = true;
1469 feature_checker.collect(&features, mi.span);
1471 else if let Some(&(_, _, _)) = REMOVED_FEATURES.iter()
1472 .find(|& &(n, _, _)| name == n)
1473 .or_else(|| STABLE_REMOVED_FEATURES.iter()
1474 .find(|& &(n, _, _)| name == n)) {
1475 span_err!(span_handler, mi.span, E0557, "feature has been removed");
1477 else if let Some(&(_, _, _)) = ACCEPTED_FEATURES.iter()
1478 .find(|& &(n, _, _)| name == n) {
1479 features.declared_stable_lang_features.push((name, mi.span));
1481 features.declared_lib_features.push((name, mi.span));
1488 feature_checker.check(span_handler);
1493 // A collector for mutually-exclusive features and their flag spans
1495 struct MutexFeatureChecker {
1496 proc_macro: Option<Span>,
1497 custom_attribute: Option<Span>,
1500 impl MutexFeatureChecker {
1501 // If this method turns out to be a hotspot due to branching,
1502 // the branching can be eliminated by modifying `setter!()` to set these spans
1503 // only for the features that need to be checked for mutual exclusion.
1504 fn collect(&mut self, features: &Features, span: Span) {
1505 if features.proc_macro {
1506 // If self.proc_macro is None, set to Some(span)
1507 self.proc_macro = self.proc_macro.or(Some(span));
1510 if features.custom_attribute {
1511 self.custom_attribute = self.custom_attribute.or(Some(span));
1515 fn check(self, handler: &Handler) {
1516 if let (Some(pm_span), Some(ca_span)) = (self.proc_macro, self.custom_attribute) {
1517 handler.struct_span_err(pm_span, "Cannot use `#![feature(proc_macro)]` and \
1518 `#![feature(custom_attribute)] at the same time")
1519 .span_note(ca_span, "`#![feature(custom_attribute)]` declared here")
1527 pub fn check_crate(krate: &ast::Crate,
1529 features: &Features,
1530 plugin_attributes: &[(String, AttributeType)],
1531 unstable: UnstableFeatures) {
1532 maybe_stage_features(&sess.span_diagnostic, krate, unstable);
1536 plugin_attributes: plugin_attributes,
1538 visit::walk_crate(&mut PostExpansionVisitor { context: &ctx }, krate);
1541 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
1542 pub enum UnstableFeatures {
1543 /// Hard errors for unstable features are active, as on
1544 /// beta/stable channels.
1546 /// Allow features to be activated, as on nightly.
1548 /// Errors are bypassed for bootstrapping. This is required any time
1549 /// during the build that feature-related lints are set to warn or above
1550 /// because the build turns on warnings-as-errors and uses lots of unstable
1551 /// features. As a result, this is always required for building Rust itself.
1555 impl UnstableFeatures {
1556 pub fn from_environment() -> UnstableFeatures {
1557 // Whether this is a feature-staged build, i.e. on the beta or stable channel
1558 let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
1559 // Whether we should enable unstable features for bootstrapping
1560 let bootstrap = env::var("RUSTC_BOOTSTRAP").is_ok();
1561 match (disable_unstable_features, bootstrap) {
1562 (_, true) => UnstableFeatures::Cheat,
1563 (true, _) => UnstableFeatures::Disallow,
1564 (false, _) => UnstableFeatures::Allow
1568 pub fn is_nightly_build(&self) -> bool {
1570 UnstableFeatures::Allow | UnstableFeatures::Cheat => true,
1576 fn maybe_stage_features(span_handler: &Handler, krate: &ast::Crate,
1577 unstable: UnstableFeatures) {
1578 let allow_features = match unstable {
1579 UnstableFeatures::Allow => true,
1580 UnstableFeatures::Disallow => false,
1581 UnstableFeatures::Cheat => true
1583 if !allow_features {
1584 for attr in &krate.attrs {
1585 if attr.check_name("feature") {
1586 let release_channel = option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)");
1587 span_err!(span_handler, attr.span, E0554,
1588 "#[feature] may not be used on the {} release channel",