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 // Allows #[link(..., cfg(..))]
296 (active, link_cfg, "1.14.0", Some(37406)),
298 (active, use_extern_macros, "1.15.0", Some(35896)),
300 // Allows `break {expr}` with a value inside `loop`s.
301 (active, loop_break_value, "1.14.0", Some(37339)),
303 // Allows #[target_feature(...)]
304 (active, target_feature, "1.15.0", None),
306 // `extern "ptx-*" fn()`
307 (active, abi_ptx, "1.15.0", None),
310 (active, i128_type, "1.16.0", Some(35118)),
312 // The `unadjusted` ABI. Perma unstable.
313 (active, abi_unadjusted, "1.16.0", None),
316 (active, proc_macro, "1.16.0", Some(38356)),
318 // Allows attributes on struct literal fields.
319 (active, struct_field_attributes, "1.16.0", Some(38814)),
321 // Allows #[link(kind="static-nobundle"...]
322 (active, static_nobundle, "1.16.0", Some(37403)),
324 // `extern "msp430-interrupt" fn()`
325 (active, abi_msp430_interrupt, "1.16.0", Some(38487)),
327 // Coerces non capturing closures to function pointers
328 (active, closure_to_fn_coercion, "1.17.0", Some(39817)),
330 // Used to identify crates that contain sanitizer runtimes
332 (active, sanitizer_runtime, "1.17.0", None),
334 // `extern "x86-interrupt" fn()`
335 (active, abi_x86_interrupt, "1.17.0", Some(40180)),
338 // Allows the `catch {...}` expression
339 (active, catch_expr, "1.17.0", Some(31436)),
341 // Allows `repr(align(u16))` struct attribute (RFC 1358)
342 (active, repr_align, "1.17.0", Some(33626)),
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 (see llvm.used)
348 (active, used, "1.18.0", Some(40289)),
350 // Allows module-level inline assembly by way of global_asm!()
351 (active, global_asm, "1.18.0", Some(35119)),
353 // Allows overlapping impls of marker traits
354 (active, overlapping_marker_traits, "1.18.0", Some(29864)),
356 // Allows use of the :vis macro fragment specifier
357 (active, macro_vis_matcher, "1.18.0", Some(41022)),
361 (removed, import_shadowing, "1.0.0", None),
362 (removed, managed_boxes, "1.0.0", None),
363 // Allows use of unary negate on unsigned integers, e.g. -e for e: u8
364 (removed, negate_unsigned, "1.0.0", Some(29645)),
365 (removed, reflect, "1.0.0", Some(27749)),
366 // A way to temporarily opt out of opt in copy. This will *never* be accepted.
367 (removed, opt_out_copy, "1.0.0", None),
368 (removed, quad_precision_float, "1.0.0", None),
369 (removed, struct_inherit, "1.0.0", None),
370 (removed, test_removed_feature, "1.0.0", None),
371 (removed, visible_private_types, "1.0.0", None),
372 (removed, unsafe_no_drop_flag, "1.0.0", None),
373 // Allows using items which are missing stability attributes
375 (removed, unmarked_api, "1.0.0", None),
376 (removed, pushpop_unsafe, "1.2.0", None),
380 (stable_removed, no_stack_check, "1.0.0", None),
384 (accepted, associated_types, "1.0.0", None),
385 // allow overloading augmented assignment operations like `a += b`
386 (accepted, augmented_assignments, "1.8.0", Some(28235)),
387 // allow empty structs and enum variants with braces
388 (accepted, braced_empty_structs, "1.8.0", Some(29720)),
389 (accepted, default_type_params, "1.0.0", None),
390 (accepted, globs, "1.0.0", None),
391 (accepted, if_let, "1.0.0", None),
392 // A temporary feature gate used to enable parser extensions needed
393 // to bootstrap fix for #5723.
394 (accepted, issue_5723_bootstrap, "1.0.0", None),
395 (accepted, macro_rules, "1.0.0", None),
396 // Allows using #![no_std]
397 (accepted, no_std, "1.6.0", None),
398 (accepted, slicing_syntax, "1.0.0", None),
399 (accepted, struct_variant, "1.0.0", None),
400 // These are used to test this portion of the compiler, they don't actually
402 (accepted, test_accepted_feature, "1.0.0", None),
403 (accepted, tuple_indexing, "1.0.0", None),
404 // Allows macros to appear in the type position.
405 (accepted, type_macros, "1.13.0", Some(27245)),
406 (accepted, while_let, "1.0.0", None),
407 // Allows `#[deprecated]` attribute
408 (accepted, deprecated, "1.9.0", Some(29935)),
410 (accepted, question_mark, "1.13.0", Some(31436)),
411 // Allows `..` in tuple (struct) patterns
412 (accepted, dotdot_in_tuple_patterns, "1.14.0", Some(33627)),
413 (accepted, item_like_imports, "1.14.0", Some(35120)),
414 // Allows using `Self` and associated types in struct expressions and patterns.
415 (accepted, more_struct_aliases, "1.16.0", Some(37544)),
416 // elide `'static` lifetimes in `static`s and `const`s
417 (accepted, static_in_const, "1.17.0", Some(35897)),
418 // Allows field shorthands (`x` meaning `x: x`) in struct literal expressions.
419 (accepted, field_init_shorthand, "1.17.0", Some(37340)),
420 // Allows the definition recursive static items.
421 (accepted, static_recursion, "1.17.0", Some(29719)),
422 // pub(restricted) visibilities (RFC 1422)
423 (accepted, pub_restricted, "1.18.0", Some(32409)),
424 // The #![windows_subsystem] attribute
425 (accepted, windows_subsystem, "1.18.0", Some(37499)),
427 // If you change this, please modify src/doc/unstable-book as well. You must
428 // move that documentation into the relevant place in the other docs, and
429 // remove the chapter on the flag.
431 #[derive(PartialEq, Copy, Clone, Debug)]
432 pub enum AttributeType {
433 /// Normal, builtin attribute that is consumed
434 /// by the compiler before the unused_attribute check
437 /// Builtin attribute that may not be consumed by the compiler
438 /// before the unused_attribute check. These attributes
439 /// will be ignored by the unused_attribute lint
442 /// Builtin attribute that is only allowed at the crate level
446 pub enum AttributeGate {
447 /// Is gated by a given feature gate, reason
448 /// and function to check if enabled
449 Gated(Stability, &'static str, &'static str, fn(&Features) -> bool),
451 /// Ungated attribute, can be used on all release channels
456 fn is_deprecated(&self) -> bool {
458 Gated(Stability::Deprecated(_), ..) => true,
464 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
467 // Argument is tracking issue link.
468 Deprecated(&'static str),
472 impl ::std::fmt::Debug for AttributeGate {
473 fn fmt(&self, fmt: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
475 Gated(ref stab, name, expl, _) =>
476 write!(fmt, "Gated({:?}, {}, {})", stab, name, expl),
477 Ungated => write!(fmt, "Ungated")
482 macro_rules! cfg_fn {
483 ($field: ident) => {{
484 fn f(features: &Features) -> bool {
487 f as fn(&Features) -> bool
491 pub fn deprecated_attributes() -> Vec<&'static (&'static str, AttributeType, AttributeGate)> {
492 BUILTIN_ATTRIBUTES.iter().filter(|a| a.2.is_deprecated()).collect()
495 pub fn is_builtin_attr(attr: &ast::Attribute) -> bool {
496 BUILTIN_ATTRIBUTES.iter().any(|&(builtin_name, _, _)| attr.check_name(builtin_name))
499 // Attributes that have a special meaning to rustc or rustdoc
500 pub const BUILTIN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeGate)] = &[
503 ("warn", Normal, Ungated),
504 ("allow", Normal, Ungated),
505 ("forbid", Normal, Ungated),
506 ("deny", Normal, Ungated),
508 ("macro_reexport", Normal, Ungated),
509 ("macro_use", Normal, Ungated),
510 ("macro_export", Normal, Ungated),
511 ("plugin_registrar", Normal, Ungated),
513 ("cfg", Normal, Ungated),
514 ("cfg_attr", Normal, Ungated),
515 ("main", Normal, Ungated),
516 ("start", Normal, Ungated),
517 ("test", Normal, Ungated),
518 ("bench", Normal, Ungated),
519 ("simd", Normal, Ungated),
520 ("repr", Normal, Ungated),
521 ("path", Normal, Ungated),
522 ("abi", Normal, Ungated),
523 ("automatically_derived", Normal, Ungated),
524 ("no_mangle", Normal, Ungated),
525 ("no_link", Normal, Ungated),
526 ("derive", Normal, Ungated),
527 ("should_panic", Normal, Ungated),
528 ("ignore", Normal, Ungated),
529 ("no_implicit_prelude", Normal, Ungated),
530 ("reexport_test_harness_main", Normal, Ungated),
531 ("link_args", Normal, Ungated),
532 ("macro_escape", Normal, Ungated),
535 ("structural_match", Whitelisted, Gated(Stability::Unstable,
537 "the semantics of constant patterns is \
539 cfg_fn!(structural_match))),
541 ("plugin", CrateLevel, Gated(Stability::Unstable,
543 "compiler plugins are experimental \
547 ("no_std", CrateLevel, Ungated),
548 ("no_core", CrateLevel, Gated(Stability::Unstable,
550 "no_core is experimental",
552 ("lang", Normal, Gated(Stability::Unstable,
554 "language items are subject to change",
555 cfg_fn!(lang_items))),
556 ("linkage", Whitelisted, Gated(Stability::Unstable,
558 "the `linkage` attribute is experimental \
559 and not portable across platforms",
561 ("thread_local", Whitelisted, Gated(Stability::Unstable,
563 "`#[thread_local]` is an experimental feature, and does \
564 not currently handle destructors. There is no \
565 corresponding `#[task_local]` mapping to the task \
567 cfg_fn!(thread_local))),
569 ("rustc_on_unimplemented", Normal, Gated(Stability::Unstable,
571 "the `#[rustc_on_unimplemented]` attribute \
572 is an experimental feature",
573 cfg_fn!(on_unimplemented))),
574 ("allocator", Whitelisted, Gated(Stability::Unstable,
576 "the `#[allocator]` attribute is an experimental feature",
577 cfg_fn!(allocator))),
578 ("needs_allocator", Normal, Gated(Stability::Unstable,
580 "the `#[needs_allocator]` \
581 attribute is an experimental \
583 cfg_fn!(needs_allocator))),
584 ("panic_runtime", Whitelisted, Gated(Stability::Unstable,
586 "the `#[panic_runtime]` attribute is \
587 an experimental feature",
588 cfg_fn!(panic_runtime))),
589 ("needs_panic_runtime", Whitelisted, Gated(Stability::Unstable,
590 "needs_panic_runtime",
591 "the `#[needs_panic_runtime]` \
592 attribute is an experimental \
594 cfg_fn!(needs_panic_runtime))),
595 ("rustc_variance", Normal, Gated(Stability::Unstable,
597 "the `#[rustc_variance]` attribute \
598 is just used for rustc unit tests \
599 and will never be stable",
600 cfg_fn!(rustc_attrs))),
601 ("rustc_error", Whitelisted, Gated(Stability::Unstable,
603 "the `#[rustc_error]` attribute \
604 is just used for rustc unit tests \
605 and will never be stable",
606 cfg_fn!(rustc_attrs))),
607 ("rustc_if_this_changed", Whitelisted, Gated(Stability::Unstable,
609 "the `#[rustc_if_this_changed]` attribute \
610 is just used for rustc unit tests \
611 and will never be stable",
612 cfg_fn!(rustc_attrs))),
613 ("rustc_then_this_would_need", Whitelisted, Gated(Stability::Unstable,
615 "the `#[rustc_if_this_changed]` attribute \
616 is just used for rustc unit tests \
617 and will never be stable",
618 cfg_fn!(rustc_attrs))),
619 ("rustc_dirty", Whitelisted, Gated(Stability::Unstable,
621 "the `#[rustc_dirty]` attribute \
622 is just used for rustc unit tests \
623 and will never be stable",
624 cfg_fn!(rustc_attrs))),
625 ("rustc_clean", Whitelisted, Gated(Stability::Unstable,
627 "the `#[rustc_clean]` attribute \
628 is just used for rustc unit tests \
629 and will never be stable",
630 cfg_fn!(rustc_attrs))),
631 ("rustc_metadata_dirty", Whitelisted, Gated(Stability::Unstable,
633 "the `#[rustc_metadata_dirty]` attribute \
634 is just used for rustc unit tests \
635 and will never be stable",
636 cfg_fn!(rustc_attrs))),
637 ("rustc_metadata_clean", Whitelisted, Gated(Stability::Unstable,
639 "the `#[rustc_metadata_clean]` attribute \
640 is just used for rustc unit tests \
641 and will never be stable",
642 cfg_fn!(rustc_attrs))),
643 ("rustc_partition_reused", Whitelisted, Gated(Stability::Unstable,
646 is just used for rustc unit tests \
647 and will never be stable",
648 cfg_fn!(rustc_attrs))),
649 ("rustc_partition_translated", Whitelisted, Gated(Stability::Unstable,
652 is just used for rustc unit tests \
653 and will never be stable",
654 cfg_fn!(rustc_attrs))),
655 ("rustc_symbol_name", Whitelisted, Gated(Stability::Unstable,
657 "internal rustc attributes will never be stable",
658 cfg_fn!(rustc_attrs))),
659 ("rustc_item_path", Whitelisted, Gated(Stability::Unstable,
661 "internal rustc attributes will never be stable",
662 cfg_fn!(rustc_attrs))),
663 ("rustc_move_fragments", Normal, Gated(Stability::Unstable,
665 "the `#[rustc_move_fragments]` attribute \
666 is just used for rustc unit tests \
667 and will never be stable",
668 cfg_fn!(rustc_attrs))),
669 ("rustc_mir", Whitelisted, Gated(Stability::Unstable,
671 "the `#[rustc_mir]` attribute \
672 is just used for rustc unit tests \
673 and will never be stable",
674 cfg_fn!(rustc_attrs))),
675 ("rustc_inherit_overflow_checks", Whitelisted, Gated(Stability::Unstable,
677 "the `#[rustc_inherit_overflow_checks]` \
678 attribute is just used to control \
679 overflow checking behavior of several \
680 libcore functions that are inlined \
681 across crates and will never be stable",
682 cfg_fn!(rustc_attrs))),
683 ("compiler_builtins", Whitelisted, Gated(Stability::Unstable,
685 "the `#[compiler_builtins]` attribute is used to \
686 identify the `compiler_builtins` crate which \
687 contains compiler-rt intrinsics and will never be \
689 cfg_fn!(compiler_builtins))),
690 ("sanitizer_runtime", Whitelisted, Gated(Stability::Unstable,
692 "the `#[sanitizer_runtime]` attribute is used to \
693 identify crates that contain the runtime of a \
694 sanitizer and will never be stable",
695 cfg_fn!(sanitizer_runtime))),
697 ("allow_internal_unstable", Normal, Gated(Stability::Unstable,
698 "allow_internal_unstable",
699 EXPLAIN_ALLOW_INTERNAL_UNSTABLE,
700 cfg_fn!(allow_internal_unstable))),
702 ("fundamental", Whitelisted, Gated(Stability::Unstable,
704 "the `#[fundamental]` attribute \
705 is an experimental feature",
706 cfg_fn!(fundamental))),
708 ("proc_macro_derive", Normal, Ungated),
710 ("rustc_copy_clone_marker", Whitelisted, Gated(Stability::Unstable,
712 "internal implementation detail",
713 cfg_fn!(rustc_attrs))),
715 // FIXME: #14408 whitelist docs since rustdoc looks at them
716 ("doc", Whitelisted, Ungated),
718 // FIXME: #14406 these are processed in trans, which happens after the
720 ("cold", Whitelisted, Ungated),
721 ("naked", Whitelisted, Gated(Stability::Unstable,
723 "the `#[naked]` attribute \
724 is an experimental feature",
725 cfg_fn!(naked_functions))),
726 ("target_feature", Whitelisted, Gated(
727 Stability::Unstable, "target_feature",
728 "the `#[target_feature]` attribute is an experimental feature",
729 cfg_fn!(target_feature))),
730 ("export_name", Whitelisted, Ungated),
731 ("inline", Whitelisted, Ungated),
732 ("link", Whitelisted, Ungated),
733 ("link_name", Whitelisted, Ungated),
734 ("link_section", Whitelisted, Ungated),
735 ("no_builtins", Whitelisted, Ungated),
736 ("no_mangle", Whitelisted, Ungated),
737 ("no_debug", Whitelisted, Gated(
738 Stability::Deprecated("https://github.com/rust-lang/rust/issues/29721"),
740 "the `#[no_debug]` attribute is an experimental feature",
742 ("omit_gdb_pretty_printer_section", Whitelisted, Gated(Stability::Unstable,
743 "omit_gdb_pretty_printer_section",
744 "the `#[omit_gdb_pretty_printer_section]` \
745 attribute is just used for the Rust test \
747 cfg_fn!(omit_gdb_pretty_printer_section))),
748 ("unsafe_destructor_blind_to_params",
750 Gated(Stability::Deprecated("https://github.com/rust-lang/rust/issues/34761"),
751 "dropck_parametricity",
752 "unsafe_destructor_blind_to_params has been replaced by \
753 may_dangle and will be removed in the future",
754 cfg_fn!(dropck_parametricity))),
757 Gated(Stability::Unstable,
759 "may_dangle has unstable semantics and may be removed in the future",
760 cfg_fn!(dropck_eyepatch))),
761 ("unwind", Whitelisted, Gated(Stability::Unstable,
763 "#[unwind] is experimental",
764 cfg_fn!(unwind_attributes))),
765 ("used", Whitelisted, Gated(
766 Stability::Unstable, "used",
767 "the `#[used]` attribute is an experimental feature",
771 ("prelude_import", Whitelisted, Gated(Stability::Unstable,
773 "`#[prelude_import]` is for use by rustc only",
774 cfg_fn!(prelude_import))),
776 // FIXME: #14407 these are only looked at on-demand so we can't
777 // guarantee they'll have already been checked
778 ("rustc_deprecated", Whitelisted, Ungated),
779 ("must_use", Whitelisted, Ungated),
780 ("stable", Whitelisted, Ungated),
781 ("unstable", Whitelisted, Ungated),
782 ("deprecated", Normal, Ungated),
784 ("rustc_paren_sugar", Normal, Gated(Stability::Unstable,
786 "unboxed_closures are still evolving",
787 cfg_fn!(unboxed_closures))),
789 ("windows_subsystem", Whitelisted, Ungated),
791 ("proc_macro_attribute", Normal, Gated(Stability::Unstable,
793 "attribute proc macros are currently unstable",
794 cfg_fn!(proc_macro))),
796 ("proc_macro", Normal, Gated(Stability::Unstable,
798 "function-like proc macros are currently unstable",
799 cfg_fn!(proc_macro))),
801 ("rustc_derive_registrar", Normal, Gated(Stability::Unstable,
802 "rustc_derive_registrar",
803 "used internally by rustc",
804 cfg_fn!(rustc_attrs))),
806 // Crate level attributes
807 ("crate_name", CrateLevel, Ungated),
808 ("crate_type", CrateLevel, Ungated),
809 ("crate_id", CrateLevel, Ungated),
810 ("feature", CrateLevel, Ungated),
811 ("no_start", CrateLevel, Ungated),
812 ("no_main", CrateLevel, Ungated),
813 ("no_builtins", CrateLevel, Ungated),
814 ("recursion_limit", CrateLevel, Ungated),
815 ("type_length_limit", CrateLevel, Ungated),
818 // cfg(...)'s that are feature gated
819 const GATED_CFGS: &[(&str, &str, fn(&Features) -> bool)] = &[
820 // (name in cfg, feature, function to check if the feature is enabled)
821 ("target_feature", "cfg_target_feature", cfg_fn!(cfg_target_feature)),
822 ("target_vendor", "cfg_target_vendor", cfg_fn!(cfg_target_vendor)),
823 ("target_thread_local", "cfg_target_thread_local", cfg_fn!(cfg_target_thread_local)),
824 ("target_has_atomic", "cfg_target_has_atomic", cfg_fn!(cfg_target_has_atomic)),
827 #[derive(Debug, Eq, PartialEq)]
828 pub struct GatedCfg {
834 pub fn gate(cfg: &ast::MetaItem) -> Option<GatedCfg> {
835 let name = cfg.name().as_str();
837 .position(|info| info.0 == name)
846 pub fn check_and_emit(&self, sess: &ParseSess, features: &Features) {
847 let (cfg, feature, has_feature) = GATED_CFGS[self.index];
848 if !has_feature(features) && !self.span.allows_unstable() {
849 let explain = format!("`cfg({})` is experimental and subject to change", cfg);
850 emit_feature_err(sess, feature, self.span, GateIssue::Language, &explain);
856 features: &'a Features,
857 parse_sess: &'a ParseSess,
858 plugin_attributes: &'a [(String, AttributeType)],
861 macro_rules! gate_feature_fn {
862 ($cx: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr) => {{
863 let (cx, has_feature, span, name, explain) = ($cx, $has_feature, $span, $name, $explain);
864 let has_feature: bool = has_feature(&$cx.features);
865 debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
866 if !has_feature && !span.allows_unstable() {
867 emit_feature_err(cx.parse_sess, name, span, GateIssue::Language, explain);
872 macro_rules! gate_feature {
873 ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {
874 gate_feature_fn!($cx, |x:&Features| x.$feature, $span, stringify!($feature), $explain)
878 impl<'a> Context<'a> {
879 fn check_attribute(&self, attr: &ast::Attribute, is_macro: bool) {
880 debug!("check_attribute(attr = {:?})", attr);
881 let name = unwrap_or!(attr.name(), return).as_str();
882 for &(n, ty, ref gateage) in BUILTIN_ATTRIBUTES {
884 if let Gated(_, name, desc, ref has_feature) = *gateage {
885 gate_feature_fn!(self, has_feature, attr.span, name, desc);
887 debug!("check_attribute: {:?} is builtin, {:?}, {:?}", attr.path, ty, gateage);
891 for &(ref n, ref ty) in self.plugin_attributes {
892 if attr.path == &**n {
893 // Plugins can't gate attributes, so we don't check for it
894 // unlike the code above; we only use this loop to
895 // short-circuit to avoid the checks below
896 debug!("check_attribute: {:?} is registered by a plugin, {:?}", attr.path, ty);
900 if name.starts_with("rustc_") {
901 gate_feature!(self, rustc_attrs, attr.span,
902 "unless otherwise specified, attributes \
903 with the prefix `rustc_` \
904 are reserved for internal compiler diagnostics");
905 } else if name.starts_with("derive_") {
906 gate_feature!(self, custom_derive, attr.span, EXPLAIN_DERIVE_UNDERSCORE);
907 } else if !attr::is_known(attr) {
908 // Only run the custom attribute lint during regular
909 // feature gate checking. Macro gating runs
910 // before the plugin attributes are registered
911 // so we skip this then
913 gate_feature!(self, custom_attribute, attr.span,
914 &format!("The attribute `{}` is currently \
915 unknown to the compiler and \
917 added to it in the future",
924 pub fn check_attribute(attr: &ast::Attribute, parse_sess: &ParseSess, features: &Features) {
925 let cx = Context { features: features, parse_sess: parse_sess, plugin_attributes: &[] };
926 cx.check_attribute(attr, true);
929 pub fn find_lang_feature_accepted_version(feature: &str) -> Option<&'static str> {
930 ACCEPTED_FEATURES.iter().find(|t| t.0 == feature).map(|t| t.1)
933 fn find_lang_feature_issue(feature: &str) -> Option<u32> {
934 if let Some(info) = ACTIVE_FEATURES.iter().find(|t| t.0 == feature) {
936 // FIXME (#28244): enforce that active features have issue numbers
937 // assert!(issue.is_some())
940 // search in Accepted, Removed, or Stable Removed features
941 let found = ACCEPTED_FEATURES.iter().chain(REMOVED_FEATURES).chain(STABLE_REMOVED_FEATURES)
942 .find(|t| t.0 == feature);
944 Some(&(_, _, issue)) => issue,
945 None => panic!("Feature `{}` is not declared anywhere", feature),
955 pub fn emit_feature_err(sess: &ParseSess, feature: &str, span: Span, issue: GateIssue,
957 feature_err(sess, feature, span, issue, explain).emit();
960 pub fn feature_err<'a>(sess: &'a ParseSess, feature: &str, span: Span, issue: GateIssue,
961 explain: &str) -> DiagnosticBuilder<'a> {
962 let diag = &sess.span_diagnostic;
964 let issue = match issue {
965 GateIssue::Language => find_lang_feature_issue(feature),
966 GateIssue::Library(lib) => lib,
969 let mut err = if let Some(n) = issue {
970 diag.struct_span_err(span, &format!("{} (see issue #{})", explain, n))
972 diag.struct_span_err(span, explain)
975 // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
976 if sess.unstable_features.is_nightly_build() {
977 err.help(&format!("add #![feature({})] to the \
978 crate attributes to enable",
985 const EXPLAIN_BOX_SYNTAX: &'static str =
986 "box expression syntax is experimental; you can call `Box::new` instead.";
988 pub const EXPLAIN_STMT_ATTR_SYNTAX: &'static str =
989 "attributes on non-item statements and expressions are experimental.";
991 pub const EXPLAIN_ASM: &'static str =
992 "inline assembly is not stable enough for use and is subject to change";
994 pub const EXPLAIN_GLOBAL_ASM: &'static str =
995 "`global_asm!` is not stable enough for use and is subject to change";
997 pub const EXPLAIN_LOG_SYNTAX: &'static str =
998 "`log_syntax!` is not stable enough for use and is subject to change";
1000 pub const EXPLAIN_CONCAT_IDENTS: &'static str =
1001 "`concat_idents` is not stable enough for use and is subject to change";
1003 pub const EXPLAIN_TRACE_MACROS: &'static str =
1004 "`trace_macros` is not stable enough for use and is subject to change";
1005 pub const EXPLAIN_ALLOW_INTERNAL_UNSTABLE: &'static str =
1006 "allow_internal_unstable side-steps feature gating and stability checks";
1008 pub const EXPLAIN_CUSTOM_DERIVE: &'static str =
1009 "`#[derive]` for custom traits is deprecated and will be removed in the future.";
1011 pub const EXPLAIN_DEPR_CUSTOM_DERIVE: &'static str =
1012 "`#[derive]` for custom traits is deprecated and will be removed in the future. \
1013 Prefer using procedural macro custom derive.";
1015 pub const EXPLAIN_DERIVE_UNDERSCORE: &'static str =
1016 "attributes of the form `#[derive_*]` are reserved for the compiler";
1018 pub const EXPLAIN_VIS_MATCHER: &'static str =
1019 ":vis fragment specifier is experimental and subject to change";
1021 pub const EXPLAIN_PLACEMENT_IN: &'static str =
1022 "placement-in expression syntax is experimental and subject to change.";
1024 pub const CLOSURE_TO_FN_COERCION: &'static str =
1025 "non-capturing closure to fn coercion is experimental";
1027 struct PostExpansionVisitor<'a> {
1028 context: &'a Context<'a>,
1031 macro_rules! gate_feature_post {
1032 ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {{
1033 let (cx, span) = ($cx, $span);
1034 if !span.allows_unstable() {
1035 gate_feature!(cx.context, $feature, span, $explain)
1040 impl<'a> PostExpansionVisitor<'a> {
1041 fn check_abi(&self, abi: Abi, span: Span) {
1043 Abi::RustIntrinsic => {
1044 gate_feature_post!(&self, intrinsics, span,
1045 "intrinsics are subject to change");
1047 Abi::PlatformIntrinsic => {
1048 gate_feature_post!(&self, platform_intrinsics, span,
1049 "platform intrinsics are experimental and possibly buggy");
1051 Abi::Vectorcall => {
1052 gate_feature_post!(&self, abi_vectorcall, span,
1053 "vectorcall is experimental and subject to change");
1056 gate_feature_post!(&self, unboxed_closures, span,
1057 "rust-call ABI is subject to change");
1060 gate_feature_post!(&self, abi_sysv64, span,
1061 "sysv64 ABI is experimental and subject to change");
1064 gate_feature_post!(&self, abi_ptx, span,
1065 "PTX ABIs are experimental and subject to change");
1067 Abi::Unadjusted => {
1068 gate_feature_post!(&self, abi_unadjusted, span,
1069 "unadjusted ABI is an implementation detail and perma-unstable");
1071 Abi::Msp430Interrupt => {
1072 gate_feature_post!(&self, abi_msp430_interrupt, span,
1073 "msp430-interrupt ABI is experimental and subject to change");
1075 Abi::X86Interrupt => {
1076 gate_feature_post!(&self, abi_x86_interrupt, span,
1077 "x86-interrupt ABI is experimental and subject to change");
1092 fn contains_novel_literal(item: &ast::MetaItem) -> bool {
1093 use ast::MetaItemKind::*;
1094 use ast::NestedMetaItemKind::*;
1098 NameValue(ref lit) => !lit.node.is_str(),
1099 List(ref list) => list.iter().any(|li| {
1101 MetaItem(ref mi) => contains_novel_literal(mi),
1108 fn starts_with_digit(s: &str) -> bool {
1109 s.as_bytes().first().cloned().map_or(false, |b| b >= b'0' && b <= b'9')
1112 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
1113 fn visit_attribute(&mut self, attr: &ast::Attribute) {
1114 if !attr.span.allows_unstable() {
1115 // check for gated attributes
1116 self.context.check_attribute(attr, false);
1119 if self.context.features.proc_macro && attr::is_known(attr) {
1123 let meta = panictry!(attr.parse_meta(self.context.parse_sess));
1124 if contains_novel_literal(&meta) {
1125 gate_feature_post!(&self, attr_literals, attr.span,
1126 "non-string literals in attributes, or string \
1127 literals in top-level positions, are experimental");
1131 fn visit_name(&mut self, sp: Span, name: ast::Name) {
1132 if !name.as_str().is_ascii() {
1133 gate_feature_post!(&self, non_ascii_idents, sp,
1134 "non-ascii idents are not fully supported.");
1138 fn visit_item(&mut self, i: &'a ast::Item) {
1140 ast::ItemKind::ExternCrate(_) => {
1141 if attr::contains_name(&i.attrs[..], "macro_reexport") {
1142 gate_feature_post!(&self, macro_reexport, i.span,
1143 "macros reexports are experimental \
1144 and possibly buggy");
1148 ast::ItemKind::ForeignMod(ref foreign_module) => {
1149 if attr::contains_name(&i.attrs[..], "link_args") {
1150 gate_feature_post!(&self, link_args, i.span,
1151 "the `link_args` attribute is not portable \
1152 across platforms, it is recommended to \
1153 use `#[link(name = \"foo\")]` instead")
1155 self.check_abi(foreign_module.abi, i.span);
1158 ast::ItemKind::Fn(..) => {
1159 if attr::contains_name(&i.attrs[..], "plugin_registrar") {
1160 gate_feature_post!(&self, plugin_registrar, i.span,
1161 "compiler plugins are experimental and possibly buggy");
1163 if attr::contains_name(&i.attrs[..], "start") {
1164 gate_feature_post!(&self, start, i.span,
1165 "a #[start] function is an experimental \
1166 feature whose signature may change \
1169 if attr::contains_name(&i.attrs[..], "main") {
1170 gate_feature_post!(&self, main, i.span,
1171 "declaration of a nonstandard #[main] \
1172 function may change over time, for now \
1173 a top-level `fn main()` is required");
1177 ast::ItemKind::Struct(..) => {
1178 if attr::contains_name(&i.attrs[..], "simd") {
1179 gate_feature_post!(&self, simd, i.span,
1180 "SIMD types are experimental and possibly buggy");
1181 self.context.parse_sess.span_diagnostic.span_warn(i.span,
1182 "the `#[simd]` attribute \
1183 is deprecated, use \
1184 `#[repr(simd)]` instead");
1186 for attr in &i.attrs {
1187 if attr.path == "repr" {
1188 for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
1189 if item.check_name("simd") {
1190 gate_feature_post!(&self, repr_simd, i.span,
1191 "SIMD types are experimental \
1192 and possibly buggy");
1195 if item.check_name("align") {
1196 gate_feature_post!(&self, repr_align, i.span,
1197 "the struct `#[repr(align(u16))]` attribute \
1205 ast::ItemKind::Union(..) => {
1206 gate_feature_post!(&self, untagged_unions,
1208 "unions are unstable and possibly buggy");
1211 ast::ItemKind::DefaultImpl(..) => {
1212 gate_feature_post!(&self, optin_builtin_traits,
1214 "default trait implementations are experimental \
1215 and possibly buggy");
1218 ast::ItemKind::Impl(_, polarity, defaultness, _, _, _, _) => {
1219 if polarity == ast::ImplPolarity::Negative {
1220 gate_feature_post!(&self, optin_builtin_traits,
1222 "negative trait bounds are not yet fully implemented; \
1223 use marker types for now");
1226 if let ast::Defaultness::Default = defaultness {
1227 gate_feature_post!(&self, specialization,
1229 "specialization is unstable");
1236 visit::walk_item(self, i);
1239 fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
1240 let links_to_llvm = match attr::first_attr_value_str_by_name(&i.attrs, "link_name") {
1241 Some(val) => val.as_str().starts_with("llvm."),
1245 gate_feature_post!(&self, link_llvm_intrinsics, i.span,
1246 "linking to LLVM intrinsics is experimental");
1249 visit::walk_foreign_item(self, i)
1252 fn visit_ty(&mut self, ty: &'a ast::Ty) {
1254 ast::TyKind::BareFn(ref bare_fn_ty) => {
1255 self.check_abi(bare_fn_ty.abi, ty.span);
1257 ast::TyKind::ImplTrait(..) => {
1258 gate_feature_post!(&self, conservative_impl_trait, ty.span,
1259 "`impl Trait` is experimental");
1261 ast::TyKind::Never => {
1262 gate_feature_post!(&self, never_type, ty.span,
1263 "The `!` type is experimental");
1267 visit::walk_ty(self, ty)
1270 fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FunctionRetTy) {
1271 if let ast::FunctionRetTy::Ty(ref output_ty) = *ret_ty {
1272 if output_ty.node != ast::TyKind::Never {
1273 self.visit_ty(output_ty)
1278 fn visit_expr(&mut self, e: &'a ast::Expr) {
1280 ast::ExprKind::Box(_) => {
1281 gate_feature_post!(&self, box_syntax, e.span, EXPLAIN_BOX_SYNTAX);
1283 ast::ExprKind::Type(..) => {
1284 gate_feature_post!(&self, type_ascription, e.span,
1285 "type ascription is experimental");
1287 ast::ExprKind::Range(_, _, ast::RangeLimits::Closed) => {
1288 gate_feature_post!(&self, inclusive_range_syntax,
1290 "inclusive range syntax is experimental");
1292 ast::ExprKind::InPlace(..) => {
1293 gate_feature_post!(&self, placement_in_syntax, e.span, EXPLAIN_PLACEMENT_IN);
1295 ast::ExprKind::Struct(_, ref fields, _) => {
1296 for field in fields {
1297 if starts_with_digit(&field.ident.node.name.as_str()) {
1298 gate_feature_post!(&self, relaxed_adts,
1300 "numeric fields in struct expressions are unstable");
1304 ast::ExprKind::Break(_, Some(_)) => {
1305 gate_feature_post!(&self, loop_break_value, e.span,
1306 "`break` with a value is experimental");
1308 ast::ExprKind::Lit(ref lit) => {
1309 if let ast::LitKind::Int(_, ref ty) = lit.node {
1311 ast::LitIntType::Signed(ast::IntTy::I128) |
1312 ast::LitIntType::Unsigned(ast::UintTy::U128) => {
1313 gate_feature_post!(&self, i128_type, e.span,
1314 "128-bit integers are not stable");
1320 ast::ExprKind::Catch(_) => {
1321 gate_feature_post!(&self, catch_expr, e.span, "`catch` expression is experimental");
1325 visit::walk_expr(self, e);
1328 fn visit_pat(&mut self, pattern: &'a ast::Pat) {
1329 match pattern.node {
1330 PatKind::Slice(_, Some(_), ref last) if !last.is_empty() => {
1331 gate_feature_post!(&self, advanced_slice_patterns,
1333 "multiple-element slice matches anywhere \
1334 but at the end of a slice (e.g. \
1335 `[0, ..xs, 0]`) are experimental")
1337 PatKind::Slice(..) => {
1338 gate_feature_post!(&self, slice_patterns,
1340 "slice pattern syntax is experimental");
1342 PatKind::Box(..) => {
1343 gate_feature_post!(&self, box_patterns,
1345 "box pattern syntax is experimental");
1347 PatKind::Struct(_, ref fields, _) => {
1348 for field in fields {
1349 if starts_with_digit(&field.node.ident.name.as_str()) {
1350 gate_feature_post!(&self, relaxed_adts,
1352 "numeric fields in struct patterns are unstable");
1356 PatKind::Range(_, _, RangeEnd::Excluded) => {
1357 gate_feature_post!(&self, exclusive_range_pattern, pattern.span,
1358 "exclusive range pattern syntax is experimental");
1362 visit::walk_pat(self, pattern)
1365 fn visit_fn(&mut self,
1366 fn_kind: FnKind<'a>,
1367 fn_decl: &'a ast::FnDecl,
1370 // check for const fn declarations
1371 if let FnKind::ItemFn(_, _, _, Spanned { node: ast::Constness::Const, .. }, _, _, _) =
1373 gate_feature_post!(&self, const_fn, span, "const fn is unstable");
1375 // stability of const fn methods are covered in
1376 // visit_trait_item and visit_impl_item below; this is
1377 // because default methods don't pass through this
1381 FnKind::ItemFn(_, _, _, _, abi, _, _) |
1382 FnKind::Method(_, &ast::MethodSig { abi, .. }, _, _) => {
1383 self.check_abi(abi, span);
1387 visit::walk_fn(self, fn_kind, fn_decl, span);
1390 fn visit_trait_item(&mut self, ti: &'a ast::TraitItem) {
1392 ast::TraitItemKind::Const(..) => {
1393 gate_feature_post!(&self, associated_consts,
1395 "associated constants are experimental")
1397 ast::TraitItemKind::Method(ref sig, ref block) => {
1398 if block.is_none() {
1399 self.check_abi(sig.abi, ti.span);
1401 if sig.constness.node == ast::Constness::Const {
1402 gate_feature_post!(&self, const_fn, ti.span, "const fn is unstable");
1405 ast::TraitItemKind::Type(_, Some(_)) => {
1406 gate_feature_post!(&self, associated_type_defaults, ti.span,
1407 "associated type defaults are unstable");
1411 visit::walk_trait_item(self, ti);
1414 fn visit_impl_item(&mut self, ii: &'a ast::ImplItem) {
1415 if ii.defaultness == ast::Defaultness::Default {
1416 gate_feature_post!(&self, specialization,
1418 "specialization is unstable");
1422 ast::ImplItemKind::Const(..) => {
1423 gate_feature_post!(&self, associated_consts,
1425 "associated constants are experimental")
1427 ast::ImplItemKind::Method(ref sig, _) => {
1428 if sig.constness.node == ast::Constness::Const {
1429 gate_feature_post!(&self, const_fn, ii.span, "const fn is unstable");
1434 visit::walk_impl_item(self, ii);
1437 fn visit_generics(&mut self, g: &'a ast::Generics) {
1438 for t in &g.ty_params {
1439 if !t.attrs.is_empty() {
1440 gate_feature_post!(&self, generic_param_attrs, t.attrs[0].span,
1441 "attributes on type parameter bindings are experimental");
1444 visit::walk_generics(self, g)
1447 fn visit_lifetime_def(&mut self, lifetime_def: &'a ast::LifetimeDef) {
1448 if !lifetime_def.attrs.is_empty() {
1449 gate_feature_post!(&self, generic_param_attrs, lifetime_def.attrs[0].span,
1450 "attributes on lifetime bindings are experimental");
1452 visit::walk_lifetime_def(self, lifetime_def)
1456 pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute]) -> Features {
1457 let mut features = Features::new();
1459 let mut feature_checker = MutexFeatureChecker::default();
1461 for attr in krate_attrs {
1462 if !attr.check_name("feature") {
1466 match attr.meta_item_list() {
1468 span_err!(span_handler, attr.span, E0555,
1469 "malformed feature attribute, expected #![feature(...)]");
1473 let name = if let Some(word) = mi.word() {
1476 span_err!(span_handler, mi.span, E0556,
1477 "malformed feature, expected just one word");
1481 if let Some(&(_, _, _, setter)) = ACTIVE_FEATURES.iter()
1482 .find(|& &(n, _, _, _)| name == n) {
1483 *(setter(&mut features)) = true;
1484 feature_checker.collect(&features, mi.span);
1486 else if let Some(&(_, _, _)) = REMOVED_FEATURES.iter()
1487 .find(|& &(n, _, _)| name == n)
1488 .or_else(|| STABLE_REMOVED_FEATURES.iter()
1489 .find(|& &(n, _, _)| name == n)) {
1490 span_err!(span_handler, mi.span, E0557, "feature has been removed");
1492 else if let Some(&(_, _, _)) = ACCEPTED_FEATURES.iter()
1493 .find(|& &(n, _, _)| name == n) {
1494 features.declared_stable_lang_features.push((name, mi.span));
1496 features.declared_lib_features.push((name, mi.span));
1503 feature_checker.check(span_handler);
1508 // A collector for mutually-exclusive features and their flag spans
1510 struct MutexFeatureChecker {
1511 proc_macro: Option<Span>,
1512 custom_attribute: Option<Span>,
1515 impl MutexFeatureChecker {
1516 // If this method turns out to be a hotspot due to branching,
1517 // the branching can be eliminated by modifying `setter!()` to set these spans
1518 // only for the features that need to be checked for mutual exclusion.
1519 fn collect(&mut self, features: &Features, span: Span) {
1520 if features.proc_macro {
1521 // If self.proc_macro is None, set to Some(span)
1522 self.proc_macro = self.proc_macro.or(Some(span));
1525 if features.custom_attribute {
1526 self.custom_attribute = self.custom_attribute.or(Some(span));
1530 fn check(self, handler: &Handler) {
1531 if let (Some(pm_span), Some(ca_span)) = (self.proc_macro, self.custom_attribute) {
1532 handler.struct_span_err(pm_span, "Cannot use `#![feature(proc_macro)]` and \
1533 `#![feature(custom_attribute)] at the same time")
1534 .span_note(ca_span, "`#![feature(custom_attribute)]` declared here")
1542 pub fn check_crate(krate: &ast::Crate,
1544 features: &Features,
1545 plugin_attributes: &[(String, AttributeType)],
1546 unstable: UnstableFeatures) {
1547 maybe_stage_features(&sess.span_diagnostic, krate, unstable);
1551 plugin_attributes: plugin_attributes,
1553 visit::walk_crate(&mut PostExpansionVisitor { context: &ctx }, krate);
1556 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
1557 pub enum UnstableFeatures {
1558 /// Hard errors for unstable features are active, as on
1559 /// beta/stable channels.
1561 /// Allow features to be activated, as on nightly.
1563 /// Errors are bypassed for bootstrapping. This is required any time
1564 /// during the build that feature-related lints are set to warn or above
1565 /// because the build turns on warnings-as-errors and uses lots of unstable
1566 /// features. As a result, this is always required for building Rust itself.
1570 impl UnstableFeatures {
1571 pub fn from_environment() -> UnstableFeatures {
1572 // Whether this is a feature-staged build, i.e. on the beta or stable channel
1573 let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
1574 // Whether we should enable unstable features for bootstrapping
1575 let bootstrap = env::var("RUSTC_BOOTSTRAP").is_ok();
1576 match (disable_unstable_features, bootstrap) {
1577 (_, true) => UnstableFeatures::Cheat,
1578 (true, _) => UnstableFeatures::Disallow,
1579 (false, _) => UnstableFeatures::Allow
1583 pub fn is_nightly_build(&self) -> bool {
1585 UnstableFeatures::Allow | UnstableFeatures::Cheat => true,
1591 fn maybe_stage_features(span_handler: &Handler, krate: &ast::Crate,
1592 unstable: UnstableFeatures) {
1593 let allow_features = match unstable {
1594 UnstableFeatures::Allow => true,
1595 UnstableFeatures::Disallow => false,
1596 UnstableFeatures::Cheat => true
1598 if !allow_features {
1599 for attr in &krate.attrs {
1600 if attr.check_name("feature") {
1601 let release_channel = option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)");
1602 span_err!(span_handler, attr.span, E0554,
1603 "#[feature] may not be used on the {} release channel",