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, RangeSyntax};
33 use errors::{DiagnosticBuilder, Handler, FatalError};
34 use visit::{self, FnKind, Visitor};
36 use symbol::{keywords, Symbol};
42 fn f(features: &mut Features, span: Span) {
43 features.declared_lib_features.push((Symbol::intern("proc_macro"), span));
44 features.proc_macro = true;
46 f as fn(&mut Features, Span)
49 fn f(features: &mut Features, _: Span) {
50 features.$field = true;
52 f as fn(&mut Features, Span)
56 macro_rules! declare_features {
57 ($((active, $feature: ident, $ver: expr, $issue: expr),)+) => {
58 /// Represents active features that are currently being implemented or
59 /// currently being considered for addition/removal.
60 const ACTIVE_FEATURES:
61 &'static [(&'static str, &'static str, Option<u32>, fn(&mut Features, Span))] =
62 &[$((stringify!($feature), $ver, $issue, set!($feature))),+];
64 /// A set of features to be used by later passes.
66 /// `#![feature]` attrs for stable language features, for error reporting
67 pub declared_stable_lang_features: Vec<(Symbol, Span)>,
68 /// `#![feature]` attrs for non-language (library) features
69 pub declared_lib_features: Vec<(Symbol, Span)>,
70 $(pub $feature: bool),+
74 pub fn new() -> Features {
76 declared_stable_lang_features: Vec::new(),
77 declared_lib_features: Vec::new(),
84 ($((removed, $feature: ident, $ver: expr, $issue: expr),)+) => {
85 /// Represents unstable features which have since been removed (it was once Active)
86 const REMOVED_FEATURES: &'static [(&'static str, &'static str, Option<u32>)] = &[
87 $((stringify!($feature), $ver, $issue)),+
91 ($((stable_removed, $feature: ident, $ver: expr, $issue: expr),)+) => {
92 /// Represents stable features which have since been removed (it was once Accepted)
93 const STABLE_REMOVED_FEATURES: &'static [(&'static str, &'static str, Option<u32>)] = &[
94 $((stringify!($feature), $ver, $issue)),+
98 ($((accepted, $feature: ident, $ver: expr, $issue: expr),)+) => {
99 /// Those language feature has since been Accepted (it was once Active)
100 const ACCEPTED_FEATURES: &'static [(&'static str, &'static str, Option<u32>)] = &[
101 $((stringify!($feature), $ver, $issue)),+
106 // If you change this, please modify src/doc/unstable-book as well.
108 // Don't ever remove anything from this list; set them to 'Removed'.
110 // The version numbers here correspond to the version in which the current status
111 // was set. This is most important for knowing when a particular feature became
114 // NB: tools/tidy/src/features.rs parses this information directly out of the
115 // source, so take care when modifying it.
118 (active, asm, "1.0.0", Some(29722)),
119 (active, concat_idents, "1.0.0", Some(29599)),
120 (active, link_args, "1.0.0", Some(29596)),
121 (active, log_syntax, "1.0.0", Some(29598)),
122 (active, non_ascii_idents, "1.0.0", Some(28979)),
123 (active, plugin_registrar, "1.0.0", Some(29597)),
124 (active, thread_local, "1.0.0", Some(29594)),
125 (active, trace_macros, "1.0.0", Some(29598)),
127 // rustc internal, for now:
128 (active, intrinsics, "1.0.0", None),
129 (active, lang_items, "1.0.0", None),
131 (active, link_llvm_intrinsics, "1.0.0", Some(29602)),
132 (active, linkage, "1.0.0", Some(29603)),
133 (active, quote, "1.0.0", Some(29601)),
137 (active, rustc_diagnostic_macros, "1.0.0", None),
138 (active, rustc_const_unstable, "1.0.0", None),
139 (active, advanced_slice_patterns, "1.0.0", Some(23121)),
140 (active, box_syntax, "1.0.0", Some(27779)),
141 (active, placement_in_syntax, "1.0.0", Some(27779)),
142 (active, unboxed_closures, "1.0.0", Some(29625)),
144 (active, fundamental, "1.0.0", Some(29635)),
145 (active, main, "1.0.0", Some(29634)),
146 (active, needs_allocator, "1.4.0", Some(27389)),
147 (active, on_unimplemented, "1.0.0", Some(29628)),
148 (active, plugin, "1.0.0", Some(29597)),
149 (active, simd_ffi, "1.0.0", Some(27731)),
150 (active, start, "1.0.0", Some(29633)),
151 (active, structural_match, "1.8.0", Some(31434)),
152 (active, panic_runtime, "1.10.0", Some(32837)),
153 (active, needs_panic_runtime, "1.10.0", Some(32837)),
155 // OIBIT specific features
156 (active, optin_builtin_traits, "1.0.0", Some(13231)),
158 // macro reexport needs more discussion and stabilization
159 (active, macro_reexport, "1.0.0", Some(29638)),
161 // Allows use of #[staged_api]
163 (active, staged_api, "1.0.0", None),
165 // Allows using #![no_core]
166 (active, no_core, "1.3.0", Some(29639)),
168 // Allows using `box` in patterns; RFC 469
169 (active, box_patterns, "1.0.0", Some(29641)),
171 // Allows using the unsafe_destructor_blind_to_params attribute;
173 (active, dropck_parametricity, "1.3.0", Some(28498)),
175 // Allows using the may_dangle attribute; RFC 1327
176 (active, dropck_eyepatch, "1.10.0", Some(34761)),
178 // Allows the use of custom attributes; RFC 572
179 (active, custom_attribute, "1.0.0", Some(29642)),
181 // Allows the use of #[derive(Anything)] as sugar for
182 // #[derive_Anything].
183 (active, custom_derive, "1.0.0", Some(29644)),
185 // Allows the use of rustc_* attributes; RFC 572
186 (active, rustc_attrs, "1.0.0", Some(29642)),
188 // Allows the use of non lexical lifetimes; RFC 2094
189 (active, nll, "1.0.0", Some(44928)),
191 // Allows the use of #[allow_internal_unstable]. This is an
192 // attribute on macro_rules! and can't use the attribute handling
193 // below (it has to be checked before expansion possibly makes
194 // macros disappear).
197 (active, allow_internal_unstable, "1.0.0", None),
199 // Allows the use of #[allow_internal_unsafe]. This is an
200 // attribute on macro_rules! and can't use the attribute handling
201 // below (it has to be checked before expansion possibly makes
202 // macros disappear).
205 (active, allow_internal_unsafe, "1.0.0", None),
207 // #23121. Array patterns have some hazards yet.
208 (active, slice_patterns, "1.0.0", Some(23121)),
210 // Allows the definition of `const fn` functions.
211 (active, const_fn, "1.2.0", Some(24111)),
213 // Allows indexing into constant arrays.
214 (active, const_indexing, "1.4.0", Some(29947)),
216 // Allows using #[prelude_import] on glob `use` items.
219 (active, prelude_import, "1.2.0", None),
221 // Allows default type parameters to influence type inference.
222 (active, default_type_parameter_fallback, "1.3.0", Some(27336)),
224 // Allows associated type defaults
225 (active, associated_type_defaults, "1.2.0", Some(29661)),
227 // allow `repr(simd)`, and importing the various simd intrinsics
228 (active, repr_simd, "1.4.0", Some(27731)),
230 // Allows cfg(target_feature = "...").
231 (active, cfg_target_feature, "1.4.0", Some(29717)),
233 // allow `extern "platform-intrinsic" { ... }`
234 (active, platform_intrinsics, "1.4.0", Some(27731)),
237 // rust runtime internal
238 (active, unwind_attributes, "1.4.0", None),
240 // allow the use of `#[naked]` on functions.
241 (active, naked_functions, "1.9.0", Some(32408)),
243 // allow `#[no_debug]`
244 (active, no_debug, "1.5.0", Some(29721)),
246 // allow `#[omit_gdb_pretty_printer_section]`
248 (active, omit_gdb_pretty_printer_section, "1.5.0", None),
250 // Allows cfg(target_vendor = "...").
251 (active, cfg_target_vendor, "1.5.0", Some(29718)),
253 // Allow attributes on expressions and non-item statements
254 (active, stmt_expr_attributes, "1.6.0", Some(15701)),
256 // allow using type ascription in expressions
257 (active, type_ascription, "1.6.0", Some(23416)),
259 // Allows cfg(target_thread_local)
260 (active, cfg_target_thread_local, "1.7.0", Some(29594)),
263 (active, abi_vectorcall, "1.7.0", None),
266 (active, inclusive_range_syntax, "1.7.0", Some(28237)),
269 (active, exclusive_range_pattern, "1.11.0", Some(37854)),
271 // impl specialization (RFC 1210)
272 (active, specialization, "1.7.0", Some(31844)),
274 // Allows cfg(target_has_atomic = "...").
275 (active, cfg_target_has_atomic, "1.9.0", Some(32976)),
277 // Allows `impl Trait` in function return types.
278 (active, conservative_impl_trait, "1.12.0", Some(34511)),
280 // Allows `impl Trait` in function arguments.
281 (active, universal_impl_trait, "1.23.0", Some(34511)),
284 (active, never_type, "1.13.0", Some(35121)),
286 // Allows all literals in attribute lists and values of key-value pairs.
287 (active, attr_literals, "1.13.0", Some(34981)),
289 // Allows untagged unions `union U { ... }`
290 (active, untagged_unions, "1.13.0", Some(32836)),
292 // Used to identify the `compiler_builtins` crate
294 (active, compiler_builtins, "1.13.0", None),
296 // Allows attributes on lifetime/type formal parameters in generics (RFC 1327)
297 (active, generic_param_attrs, "1.11.0", Some(34761)),
299 // Allows #[link(..., cfg(..))]
300 (active, link_cfg, "1.14.0", Some(37406)),
302 (active, use_extern_macros, "1.15.0", Some(35896)),
304 // Allows #[target_feature(...)]
305 (active, target_feature, "1.15.0", None),
307 // `extern "ptx-*" fn()`
308 (active, abi_ptx, "1.15.0", None),
311 (active, i128_type, "1.16.0", Some(35118)),
313 // The `repr(i128)` annotation for enums
314 (active, repr128, "1.16.0", Some(35118)),
316 // The `unadjusted` ABI. Perma unstable.
317 (active, abi_unadjusted, "1.16.0", None),
319 // Procedural macros 2.0.
320 (active, proc_macro, "1.16.0", Some(38356)),
322 // Declarative macros 2.0 (`macro`).
323 (active, decl_macro, "1.17.0", Some(39412)),
325 // Allows #[link(kind="static-nobundle"...]
326 (active, static_nobundle, "1.16.0", Some(37403)),
328 // `extern "msp430-interrupt" fn()`
329 (active, abi_msp430_interrupt, "1.16.0", Some(38487)),
331 // Used to identify crates that contain sanitizer runtimes
333 (active, sanitizer_runtime, "1.17.0", None),
335 // Used to identify crates that contain the profiler runtime
337 (active, profiler_runtime, "1.18.0", None),
339 // `extern "x86-interrupt" fn()`
340 (active, abi_x86_interrupt, "1.17.0", Some(40180)),
343 // Allows the `catch {...}` expression
344 (active, catch_expr, "1.17.0", Some(31436)),
346 // Allows `repr(align(u16))` struct attribute (RFC 1358)
347 (active, repr_align, "1.17.0", Some(33626)),
349 // Used to preserve symbols (see llvm.used)
350 (active, used, "1.18.0", Some(40289)),
352 // Allows module-level inline assembly by way of global_asm!()
353 (active, global_asm, "1.18.0", Some(35119)),
355 // Allows overlapping impls of marker traits
356 (active, overlapping_marker_traits, "1.18.0", Some(29864)),
358 // Allows use of the :vis macro fragment specifier
359 (active, macro_vis_matcher, "1.18.0", Some(41022)),
362 (active, abi_thiscall, "1.19.0", None),
364 // Allows a test to fail without failing the whole suite
365 (active, allow_fail, "1.19.0", Some(42219)),
367 // Allows unsized tuple coercion.
368 (active, unsized_tuple_coercion, "1.20.0", Some(42877)),
371 (active, generators, "1.21.0", None),
374 (active, trait_alias, "1.24.0", Some(41517)),
376 // global allocators and their internals
377 (active, global_allocator, "1.20.0", None),
378 (active, allocator_internals, "1.20.0", None),
381 (active, doc_cfg, "1.21.0", Some(43781)),
383 (active, doc_masked, "1.21.0", Some(44027)),
385 (active, doc_spotlight, "1.22.0", Some(45040)),
386 // #[doc(include="some-file")]
387 (active, external_doc, "1.22.0", Some(44732)),
389 // allow `#[must_use]` on functions and comparison operators (RFC 1940)
390 (active, fn_must_use, "1.21.0", Some(43302)),
392 // allow '|' at beginning of match arms (RFC 1925)
393 (active, match_beginning_vert, "1.21.0", Some(44101)),
395 // Future-proofing enums/structs with #[non_exhaustive] attribute (RFC 2008)
396 (active, non_exhaustive, "1.22.0", Some(44109)),
398 // Copy/Clone closures (RFC 2132)
399 (active, clone_closures, "1.22.0", Some(44490)),
400 (active, copy_closures, "1.22.0", Some(44490)),
402 // allow `'_` placeholder lifetimes
403 (active, underscore_lifetimes, "1.22.0", Some(44524)),
405 // allow `..=` in patterns (RFC 1192)
406 (active, dotdoteq_in_patterns, "1.22.0", Some(28237)),
408 // Default match binding modes (RFC 2005)
409 (active, match_default_bindings, "1.22.0", Some(42640)),
411 // Trait object syntax with `dyn` prefix
412 (active, dyn_trait, "1.22.0", Some(44662)),
414 // `crate` as visibility modifier, synonymous to `pub(crate)`
415 (active, crate_visibility_modifier, "1.23.0", Some(45388)),
418 (active, extern_types, "1.23.0", Some(43467)),
420 // Allow trait methods with arbitrary self types
421 (active, arbitrary_self_types, "1.23.0", Some(44874)),
423 // #![wasm_import_memory] attribute
424 (active, wasm_import_memory, "1.22.0", None),
427 (active, crate_in_paths, "1.23.0", Some(45477)),
429 // In-band lifetime bindings (e.g. `fn foo(x: &'a u8) -> &'a u8`)
430 (active, in_band_lifetimes, "1.23.0", Some(44524)),
432 // Nested groups in `use` (RFC 2128)
433 (active, use_nested_groups, "1.23.0", Some(44494)),
435 // generic associated types (RFC 1598)
436 (active, generic_associated_types, "1.23.0", Some(44265)),
438 // Resolve absolute paths as paths from other crates
439 (active, extern_absolute_paths, "1.24.0", Some(44660)),
441 // `foo.rs` as an alternative to `foo/mod.rs`
442 (active, non_modrs_mods, "1.24.0", Some(44660)),
444 // Nested `impl Trait`
445 (active, nested_impl_trait, "1.24.0", Some(34511)),
447 // Termination trait in main (RFC 1937)
448 (active, termination_trait, "1.24.0", Some(43301)),
450 // Allows use of the :lifetime macro fragment specifier
451 (active, macro_lifetime_matcher, "1.24.0", Some(46895)),
454 (active, extern_in_paths, "1.23.0", Some(44660)),
458 (removed, import_shadowing, "1.0.0", None),
459 (removed, managed_boxes, "1.0.0", None),
460 // Allows use of unary negate on unsigned integers, e.g. -e for e: u8
461 (removed, negate_unsigned, "1.0.0", Some(29645)),
462 (removed, reflect, "1.0.0", Some(27749)),
463 // A way to temporarily opt out of opt in copy. This will *never* be accepted.
464 (removed, opt_out_copy, "1.0.0", None),
465 (removed, quad_precision_float, "1.0.0", None),
466 (removed, struct_inherit, "1.0.0", None),
467 (removed, test_removed_feature, "1.0.0", None),
468 (removed, visible_private_types, "1.0.0", None),
469 (removed, unsafe_no_drop_flag, "1.0.0", None),
470 // Allows using items which are missing stability attributes
472 (removed, unmarked_api, "1.0.0", None),
473 (removed, pushpop_unsafe, "1.2.0", None),
474 (removed, allocator, "1.0.0", None),
475 // Allows the `#[simd]` attribute -- removed in favor of `#[repr(simd)]`
476 (removed, simd, "1.0.0", Some(27731)),
480 (stable_removed, no_stack_check, "1.0.0", None),
484 (accepted, associated_types, "1.0.0", None),
485 // allow overloading augmented assignment operations like `a += b`
486 (accepted, augmented_assignments, "1.8.0", Some(28235)),
487 // allow empty structs and enum variants with braces
488 (accepted, braced_empty_structs, "1.8.0", Some(29720)),
489 (accepted, default_type_params, "1.0.0", None),
490 (accepted, globs, "1.0.0", None),
491 (accepted, if_let, "1.0.0", None),
492 // A temporary feature gate used to enable parser extensions needed
493 // to bootstrap fix for #5723.
494 (accepted, issue_5723_bootstrap, "1.0.0", None),
495 (accepted, macro_rules, "1.0.0", None),
496 // Allows using #![no_std]
497 (accepted, no_std, "1.6.0", None),
498 (accepted, slicing_syntax, "1.0.0", None),
499 (accepted, struct_variant, "1.0.0", None),
500 // These are used to test this portion of the compiler, they don't actually
502 (accepted, test_accepted_feature, "1.0.0", None),
503 (accepted, tuple_indexing, "1.0.0", None),
504 // Allows macros to appear in the type position.
505 (accepted, type_macros, "1.13.0", Some(27245)),
506 (accepted, while_let, "1.0.0", None),
507 // Allows `#[deprecated]` attribute
508 (accepted, deprecated, "1.9.0", Some(29935)),
510 (accepted, question_mark, "1.13.0", Some(31436)),
511 // Allows `..` in tuple (struct) patterns
512 (accepted, dotdot_in_tuple_patterns, "1.14.0", Some(33627)),
513 (accepted, item_like_imports, "1.15.0", Some(35120)),
514 // Allows using `Self` and associated types in struct expressions and patterns.
515 (accepted, more_struct_aliases, "1.16.0", Some(37544)),
516 // elide `'static` lifetimes in `static`s and `const`s
517 (accepted, static_in_const, "1.17.0", Some(35897)),
518 // Allows field shorthands (`x` meaning `x: x`) in struct literal expressions.
519 (accepted, field_init_shorthand, "1.17.0", Some(37340)),
520 // Allows the definition recursive static items.
521 (accepted, static_recursion, "1.17.0", Some(29719)),
522 // pub(restricted) visibilities (RFC 1422)
523 (accepted, pub_restricted, "1.18.0", Some(32409)),
524 // The #![windows_subsystem] attribute
525 (accepted, windows_subsystem, "1.18.0", Some(37499)),
526 // Allows `break {expr}` with a value inside `loop`s.
527 (accepted, loop_break_value, "1.19.0", Some(37339)),
528 // Permits numeric fields in struct expressions and patterns.
529 (accepted, relaxed_adts, "1.19.0", Some(35626)),
530 // Coerces non capturing closures to function pointers
531 (accepted, closure_to_fn_coercion, "1.19.0", Some(39817)),
532 // Allows attributes on struct literal fields.
533 (accepted, struct_field_attributes, "1.20.0", Some(38814)),
534 // Allows the definition of associated constants in `trait` or `impl`
536 (accepted, associated_consts, "1.20.0", Some(29646)),
537 // Usage of the `compile_error!` macro
538 (accepted, compile_error, "1.20.0", Some(40872)),
539 // See rust-lang/rfcs#1414. Allows code like `let x: &'static u32 = &42` to work.
540 (accepted, rvalue_static_promotion, "1.21.0", Some(38865)),
541 // Allow Drop types in constants (RFC 1440)
542 (accepted, drop_types_in_const, "1.22.0", Some(33156)),
543 // Allows the sysV64 ABI to be specified on all platforms
544 // instead of just the platforms on which it is the C ABI
545 (accepted, abi_sysv64, "1.24.0", Some(36167)),
548 // If you change this, please modify src/doc/unstable-book as well. You must
549 // move that documentation into the relevant place in the other docs, and
550 // remove the chapter on the flag.
552 #[derive(PartialEq, Copy, Clone, Debug)]
553 pub enum AttributeType {
554 /// Normal, builtin attribute that is consumed
555 /// by the compiler before the unused_attribute check
558 /// Builtin attribute that may not be consumed by the compiler
559 /// before the unused_attribute check. These attributes
560 /// will be ignored by the unused_attribute lint
563 /// Builtin attribute that is only allowed at the crate level
567 pub enum AttributeGate {
568 /// Is gated by a given feature gate, reason
569 /// and function to check if enabled
570 Gated(Stability, &'static str, &'static str, fn(&Features) -> bool),
572 /// Ungated attribute, can be used on all release channels
577 fn is_deprecated(&self) -> bool {
579 Gated(Stability::Deprecated(_), ..) => true,
585 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
588 // Argument is tracking issue link.
589 Deprecated(&'static str),
593 impl ::std::fmt::Debug for AttributeGate {
594 fn fmt(&self, fmt: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
596 Gated(ref stab, name, expl, _) =>
597 write!(fmt, "Gated({:?}, {}, {})", stab, name, expl),
598 Ungated => write!(fmt, "Ungated")
603 macro_rules! cfg_fn {
604 ($field: ident) => {{
605 fn f(features: &Features) -> bool {
608 f as fn(&Features) -> bool
612 pub fn deprecated_attributes() -> Vec<&'static (&'static str, AttributeType, AttributeGate)> {
613 BUILTIN_ATTRIBUTES.iter().filter(|a| a.2.is_deprecated()).collect()
616 pub fn is_builtin_attr(attr: &ast::Attribute) -> bool {
617 BUILTIN_ATTRIBUTES.iter().any(|&(builtin_name, _, _)| attr.check_name(builtin_name))
620 // Attributes that have a special meaning to rustc or rustdoc
621 pub const BUILTIN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeGate)] = &[
624 ("warn", Normal, Ungated),
625 ("allow", Normal, Ungated),
626 ("forbid", Normal, Ungated),
627 ("deny", Normal, Ungated),
629 ("macro_reexport", Normal, Ungated),
630 ("macro_use", Normal, Ungated),
631 ("macro_export", Normal, Ungated),
632 ("plugin_registrar", Normal, Ungated),
634 ("cfg", Normal, Ungated),
635 ("cfg_attr", Normal, Ungated),
636 ("main", Normal, Ungated),
637 ("start", Normal, Ungated),
638 ("test", Normal, Ungated),
639 ("bench", Normal, Ungated),
640 ("repr", Normal, Ungated),
641 ("path", Normal, Ungated),
642 ("abi", Normal, Ungated),
643 ("automatically_derived", Normal, Ungated),
644 ("no_mangle", Normal, Ungated),
645 ("no_link", Normal, Ungated),
646 ("derive", Normal, Ungated),
647 ("should_panic", Normal, Ungated),
648 ("ignore", Normal, Ungated),
649 ("no_implicit_prelude", Normal, Ungated),
650 ("reexport_test_harness_main", Normal, Ungated),
651 ("link_args", Normal, Gated(Stability::Unstable,
653 "the `link_args` attribute is experimental and not \
654 portable across platforms, it is recommended to \
655 use `#[link(name = \"foo\")] instead",
656 cfg_fn!(link_args))),
657 ("macro_escape", Normal, Ungated),
660 ("structural_match", Whitelisted, Gated(Stability::Unstable,
662 "the semantics of constant patterns is \
664 cfg_fn!(structural_match))),
667 ("non_exhaustive", Whitelisted, Gated(Stability::Unstable,
669 "non exhaustive is an experimental feature",
670 cfg_fn!(non_exhaustive))),
672 ("plugin", CrateLevel, Gated(Stability::Unstable,
674 "compiler plugins are experimental \
678 ("no_std", CrateLevel, Ungated),
679 ("no_core", CrateLevel, Gated(Stability::Unstable,
681 "no_core is experimental",
683 ("lang", Normal, Gated(Stability::Unstable,
685 "language items are subject to change",
686 cfg_fn!(lang_items))),
687 ("linkage", Whitelisted, Gated(Stability::Unstable,
689 "the `linkage` attribute is experimental \
690 and not portable across platforms",
692 ("thread_local", Whitelisted, Gated(Stability::Unstable,
694 "`#[thread_local]` is an experimental feature, and does \
695 not currently handle destructors. There is no \
696 corresponding `#[task_local]` mapping to the task \
698 cfg_fn!(thread_local))),
700 ("rustc_on_unimplemented", Normal, Gated(Stability::Unstable,
702 "the `#[rustc_on_unimplemented]` attribute \
703 is an experimental feature",
704 cfg_fn!(on_unimplemented))),
705 ("rustc_const_unstable", Normal, Gated(Stability::Unstable,
706 "rustc_const_unstable",
707 "the `#[rustc_const_unstable]` attribute \
708 is an internal feature",
709 cfg_fn!(rustc_const_unstable))),
710 ("global_allocator", Normal, Gated(Stability::Unstable,
712 "the `#[global_allocator]` attribute is \
713 an experimental feature",
714 cfg_fn!(global_allocator))),
715 ("default_lib_allocator", Whitelisted, Gated(Stability::Unstable,
716 "allocator_internals",
717 "the `#[default_lib_allocator]` \
718 attribute is an experimental feature",
719 cfg_fn!(allocator_internals))),
720 ("needs_allocator", Normal, Gated(Stability::Unstable,
721 "allocator_internals",
722 "the `#[needs_allocator]` \
723 attribute is an experimental \
725 cfg_fn!(allocator_internals))),
726 ("panic_runtime", Whitelisted, Gated(Stability::Unstable,
728 "the `#[panic_runtime]` attribute is \
729 an experimental feature",
730 cfg_fn!(panic_runtime))),
731 ("needs_panic_runtime", Whitelisted, Gated(Stability::Unstable,
732 "needs_panic_runtime",
733 "the `#[needs_panic_runtime]` \
734 attribute is an experimental \
736 cfg_fn!(needs_panic_runtime))),
737 ("rustc_variance", Normal, Gated(Stability::Unstable,
739 "the `#[rustc_variance]` attribute \
740 is just used for rustc unit tests \
741 and will never be stable",
742 cfg_fn!(rustc_attrs))),
743 ("rustc_regions", Normal, Gated(Stability::Unstable,
745 "the `#[rustc_regions]` attribute \
746 is just used for rustc unit tests \
747 and will never be stable",
748 cfg_fn!(rustc_attrs))),
749 ("rustc_error", Whitelisted, Gated(Stability::Unstable,
751 "the `#[rustc_error]` attribute \
752 is just used for rustc unit tests \
753 and will never be stable",
754 cfg_fn!(rustc_attrs))),
755 ("rustc_if_this_changed", Whitelisted, Gated(Stability::Unstable,
757 "the `#[rustc_if_this_changed]` attribute \
758 is just used for rustc unit tests \
759 and will never be stable",
760 cfg_fn!(rustc_attrs))),
761 ("rustc_then_this_would_need", Whitelisted, Gated(Stability::Unstable,
763 "the `#[rustc_if_this_changed]` attribute \
764 is just used for rustc unit tests \
765 and will never be stable",
766 cfg_fn!(rustc_attrs))),
767 ("rustc_dirty", Whitelisted, Gated(Stability::Unstable,
769 "the `#[rustc_dirty]` attribute \
770 is just used for rustc unit tests \
771 and will never be stable",
772 cfg_fn!(rustc_attrs))),
773 ("rustc_clean", Whitelisted, Gated(Stability::Unstable,
775 "the `#[rustc_clean]` attribute \
776 is just used for rustc unit tests \
777 and will never be stable",
778 cfg_fn!(rustc_attrs))),
779 ("rustc_partition_reused", Whitelisted, Gated(Stability::Unstable,
782 is just used for rustc unit tests \
783 and will never be stable",
784 cfg_fn!(rustc_attrs))),
785 ("rustc_partition_translated", Whitelisted, Gated(Stability::Unstable,
788 is just used for rustc unit tests \
789 and will never be stable",
790 cfg_fn!(rustc_attrs))),
791 ("rustc_synthetic", Whitelisted, Gated(Stability::Unstable,
794 is just used for rustc unit tests \
795 and will never be stable",
796 cfg_fn!(rustc_attrs))),
797 ("rustc_symbol_name", Whitelisted, Gated(Stability::Unstable,
799 "internal rustc attributes will never be stable",
800 cfg_fn!(rustc_attrs))),
801 ("rustc_item_path", Whitelisted, Gated(Stability::Unstable,
803 "internal rustc attributes will never be stable",
804 cfg_fn!(rustc_attrs))),
805 ("rustc_mir", Whitelisted, Gated(Stability::Unstable,
807 "the `#[rustc_mir]` attribute \
808 is just used for rustc unit tests \
809 and will never be stable",
810 cfg_fn!(rustc_attrs))),
811 ("rustc_inherit_overflow_checks", Whitelisted, Gated(Stability::Unstable,
813 "the `#[rustc_inherit_overflow_checks]` \
814 attribute is just used to control \
815 overflow checking behavior of several \
816 libcore functions that are inlined \
817 across crates and will never be stable",
818 cfg_fn!(rustc_attrs))),
821 ("nll", Whitelisted, Gated(Stability::Unstable,
823 "Non lexical lifetimes",
825 ("compiler_builtins", Whitelisted, Gated(Stability::Unstable,
827 "the `#[compiler_builtins]` attribute is used to \
828 identify the `compiler_builtins` crate which \
829 contains compiler-rt intrinsics and will never be \
831 cfg_fn!(compiler_builtins))),
832 ("sanitizer_runtime", Whitelisted, Gated(Stability::Unstable,
834 "the `#[sanitizer_runtime]` attribute is used to \
835 identify crates that contain the runtime of a \
836 sanitizer and will never be stable",
837 cfg_fn!(sanitizer_runtime))),
838 ("profiler_runtime", Whitelisted, Gated(Stability::Unstable,
840 "the `#[profiler_runtime]` attribute is used to \
841 identify the `profiler_builtins` crate which \
842 contains the profiler runtime and will never be \
844 cfg_fn!(profiler_runtime))),
846 ("allow_internal_unstable", Normal, Gated(Stability::Unstable,
847 "allow_internal_unstable",
848 EXPLAIN_ALLOW_INTERNAL_UNSTABLE,
849 cfg_fn!(allow_internal_unstable))),
851 ("allow_internal_unsafe", Normal, Gated(Stability::Unstable,
852 "allow_internal_unsafe",
853 EXPLAIN_ALLOW_INTERNAL_UNSAFE,
854 cfg_fn!(allow_internal_unsafe))),
856 ("fundamental", Whitelisted, Gated(Stability::Unstable,
858 "the `#[fundamental]` attribute \
859 is an experimental feature",
860 cfg_fn!(fundamental))),
862 ("proc_macro_derive", Normal, Ungated),
864 ("rustc_copy_clone_marker", Whitelisted, Gated(Stability::Unstable,
866 "internal implementation detail",
867 cfg_fn!(rustc_attrs))),
869 // FIXME: #14408 whitelist docs since rustdoc looks at them
870 ("doc", Whitelisted, Ungated),
872 // FIXME: #14406 these are processed in trans, which happens after the
874 ("cold", Whitelisted, Ungated),
875 ("naked", Whitelisted, Gated(Stability::Unstable,
877 "the `#[naked]` attribute \
878 is an experimental feature",
879 cfg_fn!(naked_functions))),
880 ("target_feature", Whitelisted, Gated(
881 Stability::Unstable, "target_feature",
882 "the `#[target_feature]` attribute is an experimental feature",
883 cfg_fn!(target_feature))),
884 ("export_name", Whitelisted, Ungated),
885 ("inline", Whitelisted, Ungated),
886 ("link", Whitelisted, Ungated),
887 ("link_name", Whitelisted, Ungated),
888 ("link_section", Whitelisted, Ungated),
889 ("no_builtins", Whitelisted, Ungated),
890 ("no_mangle", Whitelisted, Ungated),
891 ("no_debug", Whitelisted, Gated(
892 Stability::Deprecated("https://github.com/rust-lang/rust/issues/29721"),
894 "the `#[no_debug]` attribute was an experimental feature that has been \
895 deprecated due to lack of demand",
897 ("omit_gdb_pretty_printer_section", Whitelisted, Gated(Stability::Unstable,
898 "omit_gdb_pretty_printer_section",
899 "the `#[omit_gdb_pretty_printer_section]` \
900 attribute is just used for the Rust test \
902 cfg_fn!(omit_gdb_pretty_printer_section))),
903 ("unsafe_destructor_blind_to_params",
905 Gated(Stability::Deprecated("https://github.com/rust-lang/rust/issues/34761"),
906 "dropck_parametricity",
907 "unsafe_destructor_blind_to_params has been replaced by \
908 may_dangle and will be removed in the future",
909 cfg_fn!(dropck_parametricity))),
912 Gated(Stability::Unstable,
914 "may_dangle has unstable semantics and may be removed in the future",
915 cfg_fn!(dropck_eyepatch))),
916 ("unwind", Whitelisted, Gated(Stability::Unstable,
918 "#[unwind] is experimental",
919 cfg_fn!(unwind_attributes))),
920 ("used", Whitelisted, Gated(
921 Stability::Unstable, "used",
922 "the `#[used]` attribute is an experimental feature",
926 ("prelude_import", Whitelisted, Gated(Stability::Unstable,
928 "`#[prelude_import]` is for use by rustc only",
929 cfg_fn!(prelude_import))),
931 // FIXME: #14407 these are only looked at on-demand so we can't
932 // guarantee they'll have already been checked
933 ("rustc_deprecated", Whitelisted, Ungated),
934 ("must_use", Whitelisted, Ungated),
935 ("stable", Whitelisted, Ungated),
936 ("unstable", Whitelisted, Ungated),
937 ("deprecated", Normal, Ungated),
939 ("rustc_paren_sugar", Normal, Gated(Stability::Unstable,
941 "unboxed_closures are still evolving",
942 cfg_fn!(unboxed_closures))),
944 ("windows_subsystem", Whitelisted, Ungated),
946 ("proc_macro_attribute", Normal, Gated(Stability::Unstable,
948 "attribute proc macros are currently unstable",
949 cfg_fn!(proc_macro))),
951 ("proc_macro", Normal, Gated(Stability::Unstable,
953 "function-like proc macros are currently unstable",
954 cfg_fn!(proc_macro))),
956 ("rustc_derive_registrar", Normal, Gated(Stability::Unstable,
957 "rustc_derive_registrar",
958 "used internally by rustc",
959 cfg_fn!(rustc_attrs))),
961 ("allow_fail", Normal, Gated(Stability::Unstable,
963 "allow_fail attribute is currently unstable",
964 cfg_fn!(allow_fail))),
966 ("rustc_std_internal_symbol", Whitelisted, Gated(Stability::Unstable,
968 "this is an internal attribute that will \
970 cfg_fn!(rustc_attrs))),
972 // whitelists "identity-like" conversion methods to suggest on type mismatch
973 ("rustc_conversion_suggestion", Whitelisted, Gated(Stability::Unstable,
975 "this is an internal attribute that will \
977 cfg_fn!(rustc_attrs))),
979 ("wasm_import_memory", Whitelisted, Gated(Stability::Unstable,
980 "wasm_import_memory",
981 "wasm_import_memory attribute is currently unstable",
982 cfg_fn!(wasm_import_memory))),
984 // Crate level attributes
985 ("crate_name", CrateLevel, Ungated),
986 ("crate_type", CrateLevel, Ungated),
987 ("crate_id", CrateLevel, Ungated),
988 ("feature", CrateLevel, Ungated),
989 ("no_start", CrateLevel, Ungated),
990 ("no_main", CrateLevel, Ungated),
991 ("no_builtins", CrateLevel, Ungated),
992 ("recursion_limit", CrateLevel, Ungated),
993 ("type_length_limit", CrateLevel, Ungated),
996 // cfg(...)'s that are feature gated
997 const GATED_CFGS: &[(&str, &str, fn(&Features) -> bool)] = &[
998 // (name in cfg, feature, function to check if the feature is enabled)
999 ("target_feature", "cfg_target_feature", cfg_fn!(cfg_target_feature)),
1000 ("target_vendor", "cfg_target_vendor", cfg_fn!(cfg_target_vendor)),
1001 ("target_thread_local", "cfg_target_thread_local", cfg_fn!(cfg_target_thread_local)),
1002 ("target_has_atomic", "cfg_target_has_atomic", cfg_fn!(cfg_target_has_atomic)),
1005 #[derive(Debug, Eq, PartialEq)]
1006 pub struct GatedCfg {
1012 pub fn gate(cfg: &ast::MetaItem) -> Option<GatedCfg> {
1013 let name = cfg.name().as_str();
1015 .position(|info| info.0 == name)
1024 pub fn check_and_emit(&self, sess: &ParseSess, features: &Features) {
1025 let (cfg, feature, has_feature) = GATED_CFGS[self.index];
1026 if !has_feature(features) && !self.span.allows_unstable() {
1027 let explain = format!("`cfg({})` is experimental and subject to change", cfg);
1028 emit_feature_err(sess, feature, self.span, GateIssue::Language, &explain);
1033 struct Context<'a> {
1034 features: &'a Features,
1035 parse_sess: &'a ParseSess,
1036 plugin_attributes: &'a [(String, AttributeType)],
1039 macro_rules! gate_feature_fn {
1040 ($cx: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr, $level: expr) => {{
1041 let (cx, has_feature, span,
1042 name, explain, level) = ($cx, $has_feature, $span, $name, $explain, $level);
1043 let has_feature: bool = has_feature(&$cx.features);
1044 debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
1045 if !has_feature && !span.allows_unstable() {
1046 leveled_feature_err(cx.parse_sess, name, span, GateIssue::Language, explain, level)
1052 macro_rules! gate_feature {
1053 ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {
1054 gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
1055 stringify!($feature), $explain, GateStrength::Hard)
1057 ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {
1058 gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
1059 stringify!($feature), $explain, $level)
1063 impl<'a> Context<'a> {
1064 fn check_attribute(&self, attr: &ast::Attribute, is_macro: bool) {
1065 debug!("check_attribute(attr = {:?})", attr);
1066 let name = unwrap_or!(attr.name(), return).as_str();
1067 for &(n, ty, ref gateage) in BUILTIN_ATTRIBUTES {
1069 if let Gated(_, name, desc, ref has_feature) = *gateage {
1070 gate_feature_fn!(self, has_feature, attr.span, name, desc, GateStrength::Hard);
1071 } else if name == "doc" {
1072 if let Some(content) = attr.meta_item_list() {
1073 if content.iter().any(|c| c.check_name("include")) {
1074 gate_feature!(self, external_doc, attr.span,
1075 "#[doc(include = \"...\")] is experimental"
1080 debug!("check_attribute: {:?} is builtin, {:?}, {:?}", attr.path, ty, gateage);
1084 for &(ref n, ref ty) in self.plugin_attributes {
1085 if attr.path == &**n {
1086 // Plugins can't gate attributes, so we don't check for it
1087 // unlike the code above; we only use this loop to
1088 // short-circuit to avoid the checks below
1089 debug!("check_attribute: {:?} is registered by a plugin, {:?}", attr.path, ty);
1093 if name.starts_with("rustc_") {
1094 gate_feature!(self, rustc_attrs, attr.span,
1095 "unless otherwise specified, attributes \
1096 with the prefix `rustc_` \
1097 are reserved for internal compiler diagnostics");
1098 } else if name.starts_with("derive_") {
1099 gate_feature!(self, custom_derive, attr.span, EXPLAIN_DERIVE_UNDERSCORE);
1100 } else if !attr::is_known(attr) {
1101 // Only run the custom attribute lint during regular
1102 // feature gate checking. Macro gating runs
1103 // before the plugin attributes are registered
1104 // so we skip this then
1106 gate_feature!(self, custom_attribute, attr.span,
1107 &format!("The attribute `{}` is currently \
1108 unknown to the compiler and \
1110 added to it in the future",
1117 pub fn check_attribute(attr: &ast::Attribute, parse_sess: &ParseSess, features: &Features) {
1118 let cx = Context { features: features, parse_sess: parse_sess, plugin_attributes: &[] };
1119 cx.check_attribute(attr, true);
1122 pub fn find_lang_feature_accepted_version(feature: &str) -> Option<&'static str> {
1123 ACCEPTED_FEATURES.iter().find(|t| t.0 == feature).map(|t| t.1)
1126 fn find_lang_feature_issue(feature: &str) -> Option<u32> {
1127 if let Some(info) = ACTIVE_FEATURES.iter().find(|t| t.0 == feature) {
1129 // FIXME (#28244): enforce that active features have issue numbers
1130 // assert!(issue.is_some())
1133 // search in Accepted, Removed, or Stable Removed features
1134 let found = ACCEPTED_FEATURES.iter().chain(REMOVED_FEATURES).chain(STABLE_REMOVED_FEATURES)
1135 .find(|t| t.0 == feature);
1137 Some(&(_, _, issue)) => issue,
1138 None => panic!("Feature `{}` is not declared anywhere", feature),
1143 pub enum GateIssue {
1145 Library(Option<u32>)
1148 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
1149 pub enum GateStrength {
1150 /// A hard error. (Most feature gates should use this.)
1152 /// Only a warning. (Use this only as backwards-compatibility demands.)
1156 pub fn emit_feature_err(sess: &ParseSess, feature: &str, span: Span, issue: GateIssue,
1158 feature_err(sess, feature, span, issue, explain).emit();
1161 pub fn feature_err<'a>(sess: &'a ParseSess, feature: &str, span: Span, issue: GateIssue,
1162 explain: &str) -> DiagnosticBuilder<'a> {
1163 leveled_feature_err(sess, feature, span, issue, explain, GateStrength::Hard)
1166 fn leveled_feature_err<'a>(sess: &'a ParseSess, feature: &str, span: Span, issue: GateIssue,
1167 explain: &str, level: GateStrength) -> DiagnosticBuilder<'a> {
1168 let diag = &sess.span_diagnostic;
1170 let issue = match issue {
1171 GateIssue::Language => find_lang_feature_issue(feature),
1172 GateIssue::Library(lib) => lib,
1175 let explanation = if let Some(n) = issue {
1176 format!("{} (see issue #{})", explain, n)
1181 let mut err = match level {
1182 GateStrength::Hard => diag.struct_span_err(span, &explanation),
1183 GateStrength::Soft => diag.struct_span_warn(span, &explanation),
1186 // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
1187 if sess.unstable_features.is_nightly_build() {
1188 err.help(&format!("add #![feature({})] to the \
1189 crate attributes to enable",
1193 // If we're on stable and only emitting a "soft" warning, add a note to
1194 // clarify that the feature isn't "on" (rather than being on but
1196 if !sess.unstable_features.is_nightly_build() && level == GateStrength::Soft {
1197 err.help("a nightly build of the compiler is required to enable this feature");
1204 const EXPLAIN_BOX_SYNTAX: &'static str =
1205 "box expression syntax is experimental; you can call `Box::new` instead.";
1207 pub const EXPLAIN_STMT_ATTR_SYNTAX: &'static str =
1208 "attributes on non-item statements and expressions are experimental.";
1210 pub const EXPLAIN_ASM: &'static str =
1211 "inline assembly is not stable enough for use and is subject to change";
1213 pub const EXPLAIN_GLOBAL_ASM: &'static str =
1214 "`global_asm!` is not stable enough for use and is subject to change";
1216 pub const EXPLAIN_LOG_SYNTAX: &'static str =
1217 "`log_syntax!` is not stable enough for use and is subject to change";
1219 pub const EXPLAIN_CONCAT_IDENTS: &'static str =
1220 "`concat_idents` is not stable enough for use and is subject to change";
1222 pub const EXPLAIN_TRACE_MACROS: &'static str =
1223 "`trace_macros` is not stable enough for use and is subject to change";
1224 pub const EXPLAIN_ALLOW_INTERNAL_UNSTABLE: &'static str =
1225 "allow_internal_unstable side-steps feature gating and stability checks";
1226 pub const EXPLAIN_ALLOW_INTERNAL_UNSAFE: &'static str =
1227 "allow_internal_unsafe side-steps the unsafe_code lint";
1229 pub const EXPLAIN_CUSTOM_DERIVE: &'static str =
1230 "`#[derive]` for custom traits is deprecated and will be removed in the future.";
1232 pub const EXPLAIN_DEPR_CUSTOM_DERIVE: &'static str =
1233 "`#[derive]` for custom traits is deprecated and will be removed in the future. \
1234 Prefer using procedural macro custom derive.";
1236 pub const EXPLAIN_DERIVE_UNDERSCORE: &'static str =
1237 "attributes of the form `#[derive_*]` are reserved for the compiler";
1239 pub const EXPLAIN_VIS_MATCHER: &'static str =
1240 ":vis fragment specifier is experimental and subject to change";
1242 pub const EXPLAIN_LIFETIME_MATCHER: &'static str =
1243 ":lifetime fragment specifier is experimental and subject to change";
1245 pub const EXPLAIN_PLACEMENT_IN: &'static str =
1246 "placement-in expression syntax is experimental and subject to change.";
1248 pub const EXPLAIN_UNSIZED_TUPLE_COERCION: &'static str =
1249 "Unsized tuple coercion is not stable enough for use and is subject to change";
1251 struct PostExpansionVisitor<'a> {
1252 context: &'a Context<'a>,
1255 macro_rules! gate_feature_post {
1256 ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {{
1257 let (cx, span) = ($cx, $span);
1258 if !span.allows_unstable() {
1259 gate_feature!(cx.context, $feature, span, $explain)
1262 ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {{
1263 let (cx, span) = ($cx, $span);
1264 if !span.allows_unstable() {
1265 gate_feature!(cx.context, $feature, span, $explain, $level)
1270 impl<'a> PostExpansionVisitor<'a> {
1271 fn check_abi(&self, abi: Abi, span: Span) {
1273 Abi::RustIntrinsic => {
1274 gate_feature_post!(&self, intrinsics, span,
1275 "intrinsics are subject to change");
1277 Abi::PlatformIntrinsic => {
1278 gate_feature_post!(&self, platform_intrinsics, span,
1279 "platform intrinsics are experimental and possibly buggy");
1281 Abi::Vectorcall => {
1282 gate_feature_post!(&self, abi_vectorcall, span,
1283 "vectorcall is experimental and subject to change");
1286 gate_feature_post!(&self, abi_thiscall, span,
1287 "thiscall is experimental and subject to change");
1290 gate_feature_post!(&self, unboxed_closures, span,
1291 "rust-call ABI is subject to change");
1294 gate_feature_post!(&self, abi_ptx, span,
1295 "PTX ABIs are experimental and subject to change");
1297 Abi::Unadjusted => {
1298 gate_feature_post!(&self, abi_unadjusted, span,
1299 "unadjusted ABI is an implementation detail and perma-unstable");
1301 Abi::Msp430Interrupt => {
1302 gate_feature_post!(&self, abi_msp430_interrupt, span,
1303 "msp430-interrupt ABI is experimental and subject to change");
1305 Abi::X86Interrupt => {
1306 gate_feature_post!(&self, abi_x86_interrupt, span,
1307 "x86-interrupt ABI is experimental and subject to change");
1323 fn contains_novel_literal(item: &ast::MetaItem) -> bool {
1324 use ast::MetaItemKind::*;
1325 use ast::NestedMetaItemKind::*;
1329 NameValue(ref lit) => !lit.node.is_str(),
1330 List(ref list) => list.iter().any(|li| {
1332 MetaItem(ref mi) => contains_novel_literal(mi),
1339 // Bans nested `impl Trait`, e.g. `impl Into<impl Debug>`.
1340 // Nested `impl Trait` _is_ allowed in associated type position,
1341 // e.g `impl Iterator<Item=impl Debug>`
1342 struct NestedImplTraitVisitor<'a> {
1343 context: &'a Context<'a>,
1344 is_in_impl_trait: bool,
1347 impl<'a> NestedImplTraitVisitor<'a> {
1348 fn with_impl_trait<F>(&mut self, is_in_impl_trait: bool, f: F)
1349 where F: FnOnce(&mut NestedImplTraitVisitor<'a>)
1351 let old_is_in_impl_trait = self.is_in_impl_trait;
1352 self.is_in_impl_trait = is_in_impl_trait;
1354 self.is_in_impl_trait = old_is_in_impl_trait;
1359 impl<'a> Visitor<'a> for NestedImplTraitVisitor<'a> {
1360 fn visit_ty(&mut self, t: &'a ast::Ty) {
1361 if let ast::TyKind::ImplTrait(_) = t.node {
1362 if self.is_in_impl_trait {
1363 gate_feature_post!(&self, nested_impl_trait, t.span,
1364 "nested `impl Trait` is experimental"
1367 self.with_impl_trait(true, |this| visit::walk_ty(this, t));
1369 visit::walk_ty(self, t);
1372 fn visit_path_parameters(&mut self, _: Span, path_parameters: &'a ast::PathParameters) {
1373 match *path_parameters {
1374 ast::PathParameters::AngleBracketed(ref params) => {
1375 for type_ in ¶ms.types {
1376 self.visit_ty(type_);
1378 for type_binding in ¶ms.bindings {
1379 // Type bindings such as `Item=impl Debug` in `Iterator<Item=Debug>`
1380 // are allowed to contain nested `impl Trait`.
1381 self.with_impl_trait(false, |this| visit::walk_ty(this, &type_binding.ty));
1384 ast::PathParameters::Parenthesized(ref params) => {
1385 for type_ in ¶ms.inputs {
1386 self.visit_ty(type_);
1388 if let Some(ref type_) = params.output {
1389 // `-> Foo` syntax is essentially an associated type binding,
1390 // so it is also allowed to contain nested `impl Trait`.
1391 self.with_impl_trait(false, |this| visit::walk_ty(this, type_));
1398 impl<'a> PostExpansionVisitor<'a> {
1399 fn whole_crate_feature_gates(&mut self, krate: &ast::Crate) {
1401 &mut NestedImplTraitVisitor {
1402 context: self.context,
1403 is_in_impl_trait: false,
1406 for &(ident, span) in &*self.context.parse_sess.non_modrs_mods.borrow() {
1407 if !span.allows_unstable() {
1408 let cx = &self.context;
1409 let level = GateStrength::Hard;
1410 let has_feature = cx.features.non_modrs_mods;
1411 let name = "non_modrs_mods";
1412 debug!("gate_feature(feature = {:?}, span = {:?}); has? {}",
1413 name, span, has_feature);
1415 if !has_feature && !span.allows_unstable() {
1416 leveled_feature_err(
1417 cx.parse_sess, name, span, GateIssue::Language,
1418 "mod statements in non-mod.rs files are unstable", level
1420 .help(&format!("on stable builds, rename this file to {}{}mod.rs",
1421 ident, path::MAIN_SEPARATOR))
1429 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
1430 fn visit_attribute(&mut self, attr: &ast::Attribute) {
1431 if !attr.span.allows_unstable() {
1432 // check for gated attributes
1433 self.context.check_attribute(attr, false);
1436 if attr.check_name("doc") {
1437 if let Some(content) = attr.meta_item_list() {
1438 if content.len() == 1 && content[0].check_name("cfg") {
1439 gate_feature_post!(&self, doc_cfg, attr.span,
1440 "#[doc(cfg(...))] is experimental"
1442 } else if content.iter().any(|c| c.check_name("masked")) {
1443 gate_feature_post!(&self, doc_masked, attr.span,
1444 "#[doc(masked)] is experimental"
1446 } else if content.iter().any(|c| c.check_name("spotlight")) {
1447 gate_feature_post!(&self, doc_spotlight, attr.span,
1448 "#[doc(spotlight)] is experimental"
1454 if self.context.features.proc_macro && attr::is_known(attr) {
1458 let meta = panictry!(attr.parse_meta(self.context.parse_sess));
1459 if contains_novel_literal(&meta) {
1460 gate_feature_post!(&self, attr_literals, attr.span,
1461 "non-string literals in attributes, or string \
1462 literals in top-level positions, are experimental");
1466 fn visit_name(&mut self, sp: Span, name: ast::Name) {
1467 if !name.as_str().is_ascii() {
1468 gate_feature_post!(&self,
1470 self.context.parse_sess.codemap().def_span(sp),
1471 "non-ascii idents are not fully supported.");
1475 fn visit_item(&mut self, i: &'a ast::Item) {
1477 ast::ItemKind::ExternCrate(_) => {
1478 if let Some(attr) = attr::find_by_name(&i.attrs[..], "macro_reexport") {
1479 gate_feature_post!(&self, macro_reexport, attr.span,
1480 "macros reexports are experimental \
1481 and possibly buggy");
1485 ast::ItemKind::ForeignMod(ref foreign_module) => {
1486 self.check_abi(foreign_module.abi, i.span);
1489 ast::ItemKind::Fn(..) => {
1490 if attr::contains_name(&i.attrs[..], "plugin_registrar") {
1491 gate_feature_post!(&self, plugin_registrar, i.span,
1492 "compiler plugins are experimental and possibly buggy");
1494 if attr::contains_name(&i.attrs[..], "start") {
1495 gate_feature_post!(&self, start, i.span,
1496 "a #[start] function is an experimental \
1497 feature whose signature may change \
1500 if attr::contains_name(&i.attrs[..], "main") {
1501 gate_feature_post!(&self, main, i.span,
1502 "declaration of a nonstandard #[main] \
1503 function may change over time, for now \
1504 a top-level `fn main()` is required");
1506 if let Some(attr) = attr::find_by_name(&i.attrs[..], "must_use") {
1507 gate_feature_post!(&self, fn_must_use, attr.span,
1508 "`#[must_use]` on functions is experimental",
1509 GateStrength::Soft);
1513 ast::ItemKind::Struct(..) => {
1514 if let Some(attr) = attr::find_by_name(&i.attrs[..], "repr") {
1515 for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
1516 if item.check_name("simd") {
1517 gate_feature_post!(&self, repr_simd, attr.span,
1518 "SIMD types are experimental and possibly buggy");
1520 if item.check_name("align") {
1521 gate_feature_post!(&self, repr_align, attr.span,
1522 "the struct `#[repr(align(u16))]` attribute \
1529 ast::ItemKind::TraitAlias(..) => {
1530 gate_feature_post!(&self, trait_alias,
1532 "trait aliases are not yet fully implemented");
1535 ast::ItemKind::AutoImpl(..) => {
1536 gate_feature_post!(&self, optin_builtin_traits,
1538 "auto trait implementations are experimental \
1539 and possibly buggy");
1542 ast::ItemKind::Impl(_, polarity, defaultness, _, _, _, ref impl_items) => {
1543 if polarity == ast::ImplPolarity::Negative {
1544 gate_feature_post!(&self, optin_builtin_traits,
1546 "negative trait bounds are not yet fully implemented; \
1547 use marker types for now");
1550 if let ast::Defaultness::Default = defaultness {
1551 gate_feature_post!(&self, specialization,
1553 "specialization is unstable");
1556 for impl_item in impl_items {
1557 if let ast::ImplItemKind::Method(..) = impl_item.node {
1558 if let Some(attr) = attr::find_by_name(&impl_item.attrs[..], "must_use") {
1559 gate_feature_post!(&self, fn_must_use, attr.span,
1560 "`#[must_use]` on methods is experimental",
1561 GateStrength::Soft);
1567 ast::ItemKind::Trait(ast::IsAuto::Yes, ..) => {
1568 gate_feature_post!(&self, optin_builtin_traits,
1570 "auto traits are experimental and possibly buggy");
1573 ast::ItemKind::MacroDef(ast::MacroDef { legacy: false, .. }) => {
1574 let msg = "`macro` is experimental";
1575 gate_feature_post!(&self, decl_macro, i.span, msg);
1581 visit::walk_item(self, i);
1584 fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
1586 ast::ForeignItemKind::Fn(..) |
1587 ast::ForeignItemKind::Static(..) => {
1588 let link_name = attr::first_attr_value_str_by_name(&i.attrs, "link_name");
1589 let links_to_llvm = match link_name {
1590 Some(val) => val.as_str().starts_with("llvm."),
1594 gate_feature_post!(&self, link_llvm_intrinsics, i.span,
1595 "linking to LLVM intrinsics is experimental");
1598 ast::ForeignItemKind::Ty => {
1599 gate_feature_post!(&self, extern_types, i.span,
1600 "extern types are experimental");
1604 visit::walk_foreign_item(self, i)
1607 fn visit_ty(&mut self, ty: &'a ast::Ty) {
1609 ast::TyKind::BareFn(ref bare_fn_ty) => {
1610 self.check_abi(bare_fn_ty.abi, ty.span);
1612 ast::TyKind::Never => {
1613 gate_feature_post!(&self, never_type, ty.span,
1614 "The `!` type is experimental");
1616 ast::TyKind::TraitObject(_, ast::TraitObjectSyntax::Dyn) => {
1617 gate_feature_post!(&self, dyn_trait, ty.span,
1618 "`dyn Trait` syntax is unstable");
1622 visit::walk_ty(self, ty)
1625 fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FunctionRetTy) {
1626 if let ast::FunctionRetTy::Ty(ref output_ty) = *ret_ty {
1627 if output_ty.node != ast::TyKind::Never {
1628 self.visit_ty(output_ty)
1633 fn visit_expr(&mut self, e: &'a ast::Expr) {
1635 ast::ExprKind::Box(_) => {
1636 gate_feature_post!(&self, box_syntax, e.span, EXPLAIN_BOX_SYNTAX);
1638 ast::ExprKind::Type(..) => {
1639 gate_feature_post!(&self, type_ascription, e.span,
1640 "type ascription is experimental");
1642 ast::ExprKind::Range(_, _, ast::RangeLimits::Closed) => {
1643 gate_feature_post!(&self, inclusive_range_syntax,
1645 "inclusive range syntax is experimental");
1647 ast::ExprKind::InPlace(..) => {
1648 gate_feature_post!(&self, placement_in_syntax, e.span, EXPLAIN_PLACEMENT_IN);
1650 ast::ExprKind::Yield(..) => {
1651 gate_feature_post!(&self, generators,
1653 "yield syntax is experimental");
1655 ast::ExprKind::Lit(ref lit) => {
1656 if let ast::LitKind::Int(_, ref ty) = lit.node {
1658 ast::LitIntType::Signed(ast::IntTy::I128) |
1659 ast::LitIntType::Unsigned(ast::UintTy::U128) => {
1660 gate_feature_post!(&self, i128_type, e.span,
1661 "128-bit integers are not stable");
1667 ast::ExprKind::Catch(_) => {
1668 gate_feature_post!(&self, catch_expr, e.span, "`catch` expression is experimental");
1672 visit::walk_expr(self, e);
1675 fn visit_arm(&mut self, arm: &'a ast::Arm) {
1676 if let Some(span) = arm.beginning_vert {
1677 gate_feature_post!(&self, match_beginning_vert,
1679 "Use of a '|' at the beginning of a match arm is experimental")
1681 visit::walk_arm(self, arm)
1684 fn visit_pat(&mut self, pattern: &'a ast::Pat) {
1685 match pattern.node {
1686 PatKind::Slice(_, Some(_), ref last) if !last.is_empty() => {
1687 gate_feature_post!(&self, advanced_slice_patterns,
1689 "multiple-element slice matches anywhere \
1690 but at the end of a slice (e.g. \
1691 `[0, ..xs, 0]`) are experimental")
1693 PatKind::Slice(..) => {
1694 gate_feature_post!(&self, slice_patterns,
1696 "slice pattern syntax is experimental");
1698 PatKind::Box(..) => {
1699 gate_feature_post!(&self, box_patterns,
1701 "box pattern syntax is experimental");
1703 PatKind::Range(_, _, RangeEnd::Excluded) => {
1704 gate_feature_post!(&self, exclusive_range_pattern, pattern.span,
1705 "exclusive range pattern syntax is experimental");
1707 PatKind::Range(_, _, RangeEnd::Included(RangeSyntax::DotDotEq)) => {
1708 gate_feature_post!(&self, dotdoteq_in_patterns, pattern.span,
1709 "`..=` syntax in patterns is experimental");
1713 visit::walk_pat(self, pattern)
1716 fn visit_fn(&mut self,
1717 fn_kind: FnKind<'a>,
1718 fn_decl: &'a ast::FnDecl,
1721 // check for const fn declarations
1722 if let FnKind::ItemFn(_, _, Spanned { node: ast::Constness::Const, .. }, _, _, _) =
1724 gate_feature_post!(&self, const_fn, span, "const fn is unstable");
1726 // stability of const fn methods are covered in
1727 // visit_trait_item and visit_impl_item below; this is
1728 // because default methods don't pass through this
1732 FnKind::ItemFn(_, _, _, abi, _, _) |
1733 FnKind::Method(_, &ast::MethodSig { abi, .. }, _, _) => {
1734 self.check_abi(abi, span);
1738 visit::walk_fn(self, fn_kind, fn_decl, span);
1741 fn visit_trait_item(&mut self, ti: &'a ast::TraitItem) {
1743 ast::TraitItemKind::Method(ref sig, ref block) => {
1744 if block.is_none() {
1745 self.check_abi(sig.abi, ti.span);
1747 if sig.constness.node == ast::Constness::Const {
1748 gate_feature_post!(&self, const_fn, ti.span, "const fn is unstable");
1751 ast::TraitItemKind::Type(_, ref default) => {
1752 // We use two if statements instead of something like match guards so that both
1753 // of these errors can be emitted if both cases apply.
1754 if default.is_some() {
1755 gate_feature_post!(&self, associated_type_defaults, ti.span,
1756 "associated type defaults are unstable");
1758 if ti.generics.is_parameterized() {
1759 gate_feature_post!(&self, generic_associated_types, ti.span,
1760 "generic associated types are unstable");
1765 visit::walk_trait_item(self, ti);
1768 fn visit_impl_item(&mut self, ii: &'a ast::ImplItem) {
1769 if ii.defaultness == ast::Defaultness::Default {
1770 gate_feature_post!(&self, specialization,
1772 "specialization is unstable");
1776 ast::ImplItemKind::Method(ref sig, _) => {
1777 if sig.constness.node == ast::Constness::Const {
1778 gate_feature_post!(&self, const_fn, ii.span, "const fn is unstable");
1781 ast::ImplItemKind::Type(_) if ii.generics.is_parameterized() => {
1782 gate_feature_post!(&self, generic_associated_types, ii.span,
1783 "generic associated types are unstable");
1787 visit::walk_impl_item(self, ii);
1790 fn visit_path(&mut self, path: &'a ast::Path, _id: NodeId) {
1791 for segment in &path.segments {
1792 if segment.identifier.name == keywords::Crate.name() {
1793 gate_feature_post!(&self, crate_in_paths, segment.span,
1794 "`crate` in paths is experimental");
1795 } else if segment.identifier.name == keywords::Extern.name() {
1796 gate_feature_post!(&self, extern_in_paths, segment.span,
1797 "`extern` in paths is experimental");
1801 visit::walk_path(self, path);
1804 fn visit_use_tree(&mut self, use_tree: &'a ast::UseTree, id: NodeId, nested: bool) {
1806 match use_tree.kind {
1807 ast::UseTreeKind::Simple(_) => {
1808 if use_tree.prefix.segments.len() != 1 {
1809 gate_feature_post!(&self, use_nested_groups, use_tree.span,
1810 "paths in `use` groups are experimental");
1813 ast::UseTreeKind::Glob => {
1814 gate_feature_post!(&self, use_nested_groups, use_tree.span,
1815 "glob imports in `use` groups are experimental");
1817 ast::UseTreeKind::Nested(_) => {
1818 gate_feature_post!(&self, use_nested_groups, use_tree.span,
1819 "nested groups in `use` are experimental");
1824 visit::walk_use_tree(self, use_tree, id);
1827 fn visit_vis(&mut self, vis: &'a ast::Visibility) {
1828 if let ast::Visibility::Crate(span, ast::CrateSugar::JustCrate) = *vis {
1829 gate_feature_post!(&self, crate_visibility_modifier, span,
1830 "`crate` visibility modifier is experimental");
1832 visit::walk_vis(self, vis);
1835 fn visit_generic_param(&mut self, param: &'a ast::GenericParam) {
1836 let (attrs, explain) = match *param {
1837 ast::GenericParam::Lifetime(ref ld) =>
1838 (&ld.attrs, "attributes on lifetime bindings are experimental"),
1839 ast::GenericParam::Type(ref t) =>
1840 (&t.attrs, "attributes on type parameter bindings are experimental"),
1843 if !attrs.is_empty() {
1844 gate_feature_post!(&self, generic_param_attrs, attrs[0].span, explain);
1847 visit::walk_generic_param(self, param)
1850 fn visit_lifetime(&mut self, lt: &'a ast::Lifetime) {
1851 if lt.ident.name == "'_" {
1852 gate_feature_post!(&self, underscore_lifetimes, lt.span,
1853 "underscore lifetimes are unstable");
1855 visit::walk_lifetime(self, lt)
1859 pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute]) -> Features {
1860 let mut features = Features::new();
1862 let mut feature_checker = FeatureChecker::default();
1864 for attr in krate_attrs {
1865 if !attr.check_name("feature") {
1869 match attr.meta_item_list() {
1871 span_err!(span_handler, attr.span, E0555,
1872 "malformed feature attribute, expected #![feature(...)]");
1876 let name = if let Some(word) = mi.word() {
1879 span_err!(span_handler, mi.span, E0556,
1880 "malformed feature, expected just one word");
1884 if let Some(&(_, _, _, set)) = ACTIVE_FEATURES.iter()
1885 .find(|& &(n, _, _, _)| name == n) {
1886 set(&mut features, mi.span);
1887 feature_checker.collect(&features, mi.span);
1889 else if let Some(&(_, _, _)) = REMOVED_FEATURES.iter()
1890 .find(|& &(n, _, _)| name == n)
1891 .or_else(|| STABLE_REMOVED_FEATURES.iter()
1892 .find(|& &(n, _, _)| name == n)) {
1893 span_err!(span_handler, mi.span, E0557, "feature has been removed");
1895 else if let Some(&(_, _, _)) = ACCEPTED_FEATURES.iter()
1896 .find(|& &(n, _, _)| name == n) {
1897 features.declared_stable_lang_features.push((name, mi.span));
1899 features.declared_lib_features.push((name, mi.span));
1906 feature_checker.check(span_handler);
1911 /// A collector for mutually exclusive and interdependent features and their flag spans.
1913 struct FeatureChecker {
1914 proc_macro: Option<Span>,
1915 custom_attribute: Option<Span>,
1916 copy_closures: Option<Span>,
1917 clone_closures: Option<Span>,
1920 impl FeatureChecker {
1921 // If this method turns out to be a hotspot due to branching,
1922 // the branching can be eliminated by modifying `set!()` to set these spans
1923 // only for the features that need to be checked for mutual exclusion.
1924 fn collect(&mut self, features: &Features, span: Span) {
1925 if features.proc_macro {
1926 // If self.proc_macro is None, set to Some(span)
1927 self.proc_macro = self.proc_macro.or(Some(span));
1930 if features.custom_attribute {
1931 self.custom_attribute = self.custom_attribute.or(Some(span));
1934 if features.copy_closures {
1935 self.copy_closures = self.copy_closures.or(Some(span));
1938 if features.clone_closures {
1939 self.clone_closures = self.clone_closures.or(Some(span));
1943 fn check(self, handler: &Handler) {
1944 if let (Some(pm_span), Some(ca_span)) = (self.proc_macro, self.custom_attribute) {
1945 handler.struct_span_err(pm_span, "Cannot use `#![feature(proc_macro)]` and \
1946 `#![feature(custom_attribute)] at the same time")
1947 .span_note(ca_span, "`#![feature(custom_attribute)]` declared here")
1953 if let (Some(span), None) = (self.copy_closures, self.clone_closures) {
1954 handler.struct_span_err(span, "`#![feature(copy_closures)]` can only be used with \
1955 `#![feature(clone_closures)]`")
1956 .span_note(span, "`#![feature(copy_closures)]` declared here")
1964 pub fn check_crate(krate: &ast::Crate,
1966 features: &Features,
1967 plugin_attributes: &[(String, AttributeType)],
1968 unstable: UnstableFeatures) {
1969 maybe_stage_features(&sess.span_diagnostic, krate, unstable);
1975 let visitor = &mut PostExpansionVisitor { context: &ctx };
1976 visitor.whole_crate_feature_gates(krate);
1977 visit::walk_crate(visitor, krate);
1980 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
1981 pub enum UnstableFeatures {
1982 /// Hard errors for unstable features are active, as on
1983 /// beta/stable channels.
1985 /// Allow features to be activated, as on nightly.
1987 /// Errors are bypassed for bootstrapping. This is required any time
1988 /// during the build that feature-related lints are set to warn or above
1989 /// because the build turns on warnings-as-errors and uses lots of unstable
1990 /// features. As a result, this is always required for building Rust itself.
1994 impl UnstableFeatures {
1995 pub fn from_environment() -> UnstableFeatures {
1996 // Whether this is a feature-staged build, i.e. on the beta or stable channel
1997 let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
1998 // Whether we should enable unstable features for bootstrapping
1999 let bootstrap = env::var("RUSTC_BOOTSTRAP").is_ok();
2000 match (disable_unstable_features, bootstrap) {
2001 (_, true) => UnstableFeatures::Cheat,
2002 (true, _) => UnstableFeatures::Disallow,
2003 (false, _) => UnstableFeatures::Allow
2007 pub fn is_nightly_build(&self) -> bool {
2009 UnstableFeatures::Allow | UnstableFeatures::Cheat => true,
2015 fn maybe_stage_features(span_handler: &Handler, krate: &ast::Crate,
2016 unstable: UnstableFeatures) {
2017 let allow_features = match unstable {
2018 UnstableFeatures::Allow => true,
2019 UnstableFeatures::Disallow => false,
2020 UnstableFeatures::Cheat => true
2022 if !allow_features {
2023 for attr in &krate.attrs {
2024 if attr.check_name("feature") {
2025 let release_channel = option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)");
2026 span_err!(span_handler, attr.span, E0554,
2027 "#![feature] may not be used on the {} release channel",