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
26 use self::AttributeType::*;
27 use self::AttributeGate::*;
33 use attr::AttrMetaMethods;
34 use codemap::{CodeMap, Span};
37 use visit::{FnKind, Visitor};
38 use parse::token::InternedString;
40 use std::ascii::AsciiExt;
43 // If you change this list without updating src/doc/reference.md, @cmr will be sad
44 // Don't ever remove anything from this list; set them to 'Removed'.
45 // The version numbers here correspond to the version in which the current status
46 // was set. This is most important for knowing when a particular feature became
48 // NB: The featureck.py script parses this information directly out of the source
49 // so take care when modifying it.
50 const KNOWN_FEATURES: &'static [(&'static str, &'static str, Option<u32>, Status)] = &[
51 ("globs", "1.0.0", None, Accepted),
52 ("macro_rules", "1.0.0", None, Accepted),
53 ("struct_variant", "1.0.0", None, Accepted),
54 ("asm", "1.0.0", Some(29722), Active),
55 ("managed_boxes", "1.0.0", None, Removed),
56 ("non_ascii_idents", "1.0.0", Some(28979), Active),
57 ("thread_local", "1.0.0", Some(29594), Active),
58 ("link_args", "1.0.0", Some(29596), Active),
59 ("plugin_registrar", "1.0.0", Some(29597), Active),
60 ("log_syntax", "1.0.0", Some(29598), Active),
61 ("trace_macros", "1.0.0", Some(29598), Active),
62 ("concat_idents", "1.0.0", Some(29599), Active),
64 // rustc internal, for now:
65 ("intrinsics", "1.0.0", None, Active),
66 ("lang_items", "1.0.0", None, Active),
68 ("simd", "1.0.0", Some(27731), Active),
69 ("default_type_params", "1.0.0", None, Accepted),
70 ("quote", "1.0.0", Some(29601), Active),
71 ("link_llvm_intrinsics", "1.0.0", Some(29602), Active),
72 ("linkage", "1.0.0", Some(29603), Active),
73 ("struct_inherit", "1.0.0", None, Removed),
75 ("quad_precision_float", "1.0.0", None, Removed),
78 ("rustc_diagnostic_macros", "1.0.0", None, Active),
79 ("unboxed_closures", "1.0.0", Some(29625), Active),
80 ("reflect", "1.0.0", Some(27749), Active),
81 ("import_shadowing", "1.0.0", None, Removed),
82 ("advanced_slice_patterns", "1.0.0", Some(23121), Active),
83 ("tuple_indexing", "1.0.0", None, Accepted),
84 ("associated_types", "1.0.0", None, Accepted),
85 ("visible_private_types", "1.0.0", None, Removed),
86 ("slicing_syntax", "1.0.0", None, Accepted),
87 ("box_syntax", "1.0.0", Some(27779), Active),
88 ("placement_in_syntax", "1.0.0", Some(27779), Active),
91 ("pushpop_unsafe", "1.2.0", None, Active),
93 ("on_unimplemented", "1.0.0", Some(29628), Active),
94 ("simd_ffi", "1.0.0", Some(27731), Active),
95 ("allocator", "1.0.0", Some(27389), Active),
96 ("needs_allocator", "1.4.0", Some(27389), Active),
97 ("linked_from", "1.3.0", Some(29629), Active),
99 ("if_let", "1.0.0", None, Accepted),
100 ("while_let", "1.0.0", None, Accepted),
102 ("plugin", "1.0.0", Some(29597), Active),
103 ("start", "1.0.0", Some(29633), Active),
104 ("main", "1.0.0", Some(29634), Active),
106 ("fundamental", "1.0.0", Some(29635), Active),
108 // A temporary feature gate used to enable parser extensions needed
109 // to bootstrap fix for #5723.
110 ("issue_5723_bootstrap", "1.0.0", None, Accepted),
112 // A way to temporarily opt out of opt in copy. This will *never* be accepted.
113 ("opt_out_copy", "1.0.0", None, Removed),
115 // OIBIT specific features
116 ("optin_builtin_traits", "1.0.0", Some(13231), Active),
118 // macro reexport needs more discussion and stabilization
119 ("macro_reexport", "1.0.0", Some(29638), Active),
121 // These are used to test this portion of the compiler, they don't actually
123 ("test_accepted_feature", "1.0.0", None, Accepted),
124 ("test_removed_feature", "1.0.0", None, Removed),
126 // Allows use of #[staged_api]
128 ("staged_api", "1.0.0", None, Active),
130 // Allows using items which are missing stability attributes
132 ("unmarked_api", "1.0.0", None, Active),
134 // Allows using #![no_std]
135 ("no_std", "1.0.0", None, Accepted),
137 // Allows using #![no_core]
138 ("no_core", "1.3.0", Some(29639), Active),
140 // Allows using `box` in patterns; RFC 469
141 ("box_patterns", "1.0.0", Some(29641), Active),
143 // Allows using the unsafe_no_drop_flag attribute (unlikely to
144 // switch to Accepted; see RFC 320)
145 ("unsafe_no_drop_flag", "1.0.0", None, Active),
147 // Allows using the unsafe_destructor_blind_to_params attribute;
149 ("dropck_parametricity", "1.3.0", Some(28498), Active),
151 // Allows the use of custom attributes; RFC 572
152 ("custom_attribute", "1.0.0", Some(29642), Active),
154 // Allows the use of #[derive(Anything)] as sugar for
155 // #[derive_Anything].
156 ("custom_derive", "1.0.0", Some(29644), Active),
158 // Allows the use of rustc_* attributes; RFC 572
159 ("rustc_attrs", "1.0.0", Some(29642), Active),
161 // Allows the use of #[allow_internal_unstable]. This is an
162 // attribute on macro_rules! and can't use the attribute handling
163 // below (it has to be checked before expansion possibly makes
164 // macros disappear).
167 ("allow_internal_unstable", "1.0.0", None, Active),
169 // #23121. Array patterns have some hazards yet.
170 ("slice_patterns", "1.0.0", Some(23121), Active),
172 // Allows use of unary negate on unsigned integers, e.g. -e for e: u8
173 ("negate_unsigned", "1.0.0", Some(29645), Active),
175 // Allows the definition of associated constants in `trait` or `impl`
177 ("associated_consts", "1.0.0", Some(29646), Active),
179 // Allows the definition of `const fn` functions.
180 ("const_fn", "1.2.0", Some(24111), Active),
182 // Allows indexing into constant arrays.
183 ("const_indexing", "1.4.0", Some(29947), Active),
185 // Allows using #[prelude_import] on glob `use` items.
188 ("prelude_import", "1.2.0", None, Active),
190 // Allows the definition recursive static items.
191 ("static_recursion", "1.3.0", Some(29719), Active),
193 // Allows default type parameters to influence type inference.
194 ("default_type_parameter_fallback", "1.3.0", Some(27336), Active),
196 // Allows associated type defaults
197 ("associated_type_defaults", "1.2.0", Some(29661), Active),
199 // Allows macros to appear in the type position.
200 ("type_macros", "1.3.0", Some(27336), Active),
202 // allow `repr(simd)`, and importing the various simd intrinsics
203 ("repr_simd", "1.4.0", Some(27731), Active),
205 // Allows cfg(target_feature = "...").
206 ("cfg_target_feature", "1.4.0", Some(29717), Active),
208 // allow `extern "platform-intrinsic" { ... }`
209 ("platform_intrinsics", "1.4.0", Some(27731), Active),
212 // rust runtime internal
213 ("unwind_attributes", "1.4.0", None, Active),
215 // allow empty structs and enum variants with braces
216 ("braced_empty_structs", "1.5.0", Some(29720), Active),
218 // allow overloading augmented assignment operations like `a += b`
219 ("augmented_assignments", "1.5.0", Some(28235), Active),
221 // allow `#[no_debug]`
222 ("no_debug", "1.5.0", Some(29721), Active),
224 // allow `#[omit_gdb_pretty_printer_section]`
226 ("omit_gdb_pretty_printer_section", "1.5.0", None, Active),
228 // Allows cfg(target_vendor = "...").
229 ("cfg_target_vendor", "1.5.0", Some(29718), Active),
231 // Allow attributes on expressions and non-item statements
232 ("stmt_expr_attributes", "1.6.0", Some(15701), Active),
234 // Allows `#[deprecated]` attribute
235 ("deprecated", "1.6.0", Some(29935), Active),
237 // allow using type ascription in expressions
238 ("type_ascription", "1.6.0", Some(23416), Active),
240 // Allows cfg(target_thread_local)
241 ("cfg_target_thread_local", "1.7.0", Some(29594), Active),
243 // (changing above list without updating src/doc/reference.md makes @cmr sad)
246 /// Represents an active feature that is currently being implemented or
247 /// currently being considered for addition/removal.
250 /// Represents a feature which has since been removed (it was once Active)
253 /// This language feature has since been Accepted (it was once Active)
257 // Attributes that have a special meaning to rustc or rustdoc
258 pub const KNOWN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeGate)] = &[
261 ("warn", Normal, Ungated),
262 ("allow", Normal, Ungated),
263 ("forbid", Normal, Ungated),
264 ("deny", Normal, Ungated),
266 ("macro_reexport", Normal, Ungated),
267 ("macro_use", Normal, Ungated),
268 ("macro_export", Normal, Ungated),
269 ("plugin_registrar", Normal, Ungated),
271 ("cfg", Normal, Ungated),
272 ("cfg_attr", Normal, Ungated),
273 ("main", Normal, Ungated),
274 ("start", Normal, Ungated),
275 ("test", Normal, Ungated),
276 ("bench", Normal, Ungated),
277 ("simd", Normal, Ungated),
278 ("repr", Normal, Ungated),
279 ("path", Normal, Ungated),
280 ("abi", Normal, Ungated),
281 ("automatically_derived", Normal, Ungated),
282 ("no_mangle", Normal, Ungated),
283 ("no_link", Normal, Ungated),
284 ("derive", Normal, Ungated),
285 ("should_panic", Normal, Ungated),
286 ("ignore", Normal, Ungated),
287 ("no_implicit_prelude", Normal, Ungated),
288 ("reexport_test_harness_main", Normal, Ungated),
289 ("link_args", Normal, Ungated),
290 ("macro_escape", Normal, Ungated),
292 // Not used any more, but we can't feature gate it
293 ("no_stack_check", Normal, Ungated),
295 ("plugin", CrateLevel, Gated("plugin",
296 "compiler plugins are experimental \
297 and possibly buggy")),
298 ("no_std", CrateLevel, Ungated),
299 ("no_core", CrateLevel, Gated("no_core",
300 "no_core is experimental")),
301 ("lang", Normal, Gated("lang_items",
302 "language items are subject to change")),
303 ("linkage", Whitelisted, Gated("linkage",
304 "the `linkage` attribute is experimental \
305 and not portable across platforms")),
306 ("thread_local", Whitelisted, Gated("thread_local",
307 "`#[thread_local]` is an experimental feature, and does \
308 not currently handle destructors. There is no \
309 corresponding `#[task_local]` mapping to the task \
312 ("rustc_on_unimplemented", Normal, Gated("on_unimplemented",
313 "the `#[rustc_on_unimplemented]` attribute \
314 is an experimental feature")),
315 ("allocator", Whitelisted, Gated("allocator",
316 "the `#[allocator]` attribute is an experimental feature")),
317 ("needs_allocator", Normal, Gated("needs_allocator",
318 "the `#[needs_allocator]` \
319 attribute is an experimental \
321 ("rustc_variance", Normal, Gated("rustc_attrs",
322 "the `#[rustc_variance]` attribute \
323 is just used for rustc unit tests \
324 and will never be stable")),
325 ("rustc_error", Whitelisted, Gated("rustc_attrs",
326 "the `#[rustc_error]` attribute \
327 is just used for rustc unit tests \
328 and will never be stable")),
329 ("rustc_if_this_changed", Whitelisted, Gated("rustc_attrs",
330 "the `#[rustc_if_this_changed]` attribute \
331 is just used for rustc unit tests \
332 and will never be stable")),
333 ("rustc_then_this_would_need", Whitelisted, Gated("rustc_attrs",
334 "the `#[rustc_if_this_changed]` attribute \
335 is just used for rustc unit tests \
336 and will never be stable")),
337 ("rustc_move_fragments", Normal, Gated("rustc_attrs",
338 "the `#[rustc_move_fragments]` attribute \
339 is just used for rustc unit tests \
340 and will never be stable")),
341 ("rustc_mir", Normal, Gated("rustc_attrs",
342 "the `#[rustc_mir]` attribute \
343 is just used for rustc unit tests \
344 and will never be stable")),
346 ("allow_internal_unstable", Normal, Gated("allow_internal_unstable",
347 EXPLAIN_ALLOW_INTERNAL_UNSTABLE)),
349 ("fundamental", Whitelisted, Gated("fundamental",
350 "the `#[fundamental]` attribute \
351 is an experimental feature")),
353 ("linked_from", Normal, Gated("linked_from",
354 "the `#[linked_from]` attribute \
355 is an experimental feature")),
357 // FIXME: #14408 whitelist docs since rustdoc looks at them
358 ("doc", Whitelisted, Ungated),
360 // FIXME: #14406 these are processed in trans, which happens after the
362 ("cold", Whitelisted, Ungated),
363 ("export_name", Whitelisted, Ungated),
364 ("inline", Whitelisted, Ungated),
365 ("link", Whitelisted, Ungated),
366 ("link_name", Whitelisted, Ungated),
367 ("link_section", Whitelisted, Ungated),
368 ("no_builtins", Whitelisted, Ungated),
369 ("no_mangle", Whitelisted, Ungated),
370 ("no_debug", Whitelisted, Gated("no_debug",
371 "the `#[no_debug]` attribute \
372 is an experimental feature")),
373 ("omit_gdb_pretty_printer_section", Whitelisted, Gated("omit_gdb_pretty_printer_section",
374 "the `#[omit_gdb_pretty_printer_section]` \
375 attribute is just used for the Rust test \
377 ("unsafe_no_drop_flag", Whitelisted, Gated("unsafe_no_drop_flag",
378 "unsafe_no_drop_flag has unstable semantics \
379 and may be removed in the future")),
380 ("unsafe_destructor_blind_to_params",
382 Gated("dropck_parametricity",
383 "unsafe_destructor_blind_to_params has unstable semantics \
384 and may be removed in the future")),
385 ("unwind", Whitelisted, Gated("unwind_attributes", "#[unwind] is experimental")),
388 ("prelude_import", Whitelisted, Gated("prelude_import",
389 "`#[prelude_import]` is for use by rustc only")),
391 // FIXME: #14407 these are only looked at on-demand so we can't
392 // guarantee they'll have already been checked
393 ("rustc_deprecated", Whitelisted, Ungated),
394 ("must_use", Whitelisted, Ungated),
395 ("stable", Whitelisted, Ungated),
396 ("unstable", Whitelisted, Ungated),
397 ("deprecated", Normal, Gated("deprecated", "`#[deprecated]` attribute is unstable")),
399 ("rustc_paren_sugar", Normal, Gated("unboxed_closures",
400 "unboxed_closures are still evolving")),
401 ("rustc_reflect_like", Whitelisted, Gated("reflect",
402 "defining reflective traits is still evolving")),
404 // Crate level attributes
405 ("crate_name", CrateLevel, Ungated),
406 ("crate_type", CrateLevel, Ungated),
407 ("crate_id", CrateLevel, Ungated),
408 ("feature", CrateLevel, Ungated),
409 ("no_start", CrateLevel, Ungated),
410 ("no_main", CrateLevel, Ungated),
411 ("no_builtins", CrateLevel, Ungated),
412 ("recursion_limit", CrateLevel, Ungated),
415 macro_rules! cfg_fn {
416 (|$x: ident| $e: expr) => {{
417 fn f($x: &Features) -> bool {
420 f as fn(&Features) -> bool
423 // cfg(...)'s that are feature gated
424 const GATED_CFGS: &'static [(&'static str, &'static str, fn(&Features) -> bool)] = &[
425 // (name in cfg, feature, function to check if the feature is enabled)
426 ("target_feature", "cfg_target_feature", cfg_fn!(|x| x.cfg_target_feature)),
427 ("target_vendor", "cfg_target_vendor", cfg_fn!(|x| x.cfg_target_vendor)),
428 ("target_thread_local", "cfg_target_thread_local",
429 cfg_fn!(|x| x.cfg_target_thread_local)),
432 #[derive(Debug, Eq, PartialEq)]
433 pub enum GatedCfgAttr {
438 #[derive(Debug, Eq, PartialEq)]
439 pub struct GatedCfg {
444 impl Ord for GatedCfgAttr {
445 fn cmp(&self, other: &GatedCfgAttr) -> cmp::Ordering {
446 let to_tup = |s: &GatedCfgAttr| match *s {
447 GatedCfgAttr::GatedCfg(ref gated_cfg) => {
448 (gated_cfg.span.lo.0, gated_cfg.span.hi.0, gated_cfg.index)
450 GatedCfgAttr::GatedAttr(ref span) => {
451 (span.lo.0, span.hi.0, GATED_CFGS.len())
454 to_tup(self).cmp(&to_tup(other))
458 impl PartialOrd for GatedCfgAttr {
459 fn partial_cmp(&self, other: &GatedCfgAttr) -> Option<cmp::Ordering> {
460 Some(self.cmp(other))
465 pub fn check_and_emit(&self,
466 diagnostic: &Handler,
470 GatedCfgAttr::GatedCfg(ref cfg) => {
471 cfg.check_and_emit(diagnostic, features, codemap);
473 GatedCfgAttr::GatedAttr(span) => {
474 if !features.stmt_expr_attributes {
475 emit_feature_err(diagnostic,
476 "stmt_expr_attributes",
479 EXPLAIN_STMT_ATTR_SYNTAX);
487 pub fn gate(cfg: &ast::MetaItem) -> Option<GatedCfg> {
488 let name = cfg.name();
490 .position(|info| info.0 == name)
498 fn check_and_emit(&self,
499 diagnostic: &Handler,
502 let (cfg, feature, has_feature) = GATED_CFGS[self.index];
503 if !has_feature(features) && !codemap.span_allows_unstable(self.span) {
504 let explain = format!("`cfg({})` is experimental and subject to change", cfg);
505 emit_feature_err(diagnostic, feature, self.span, GateIssue::Language, &explain);
511 #[derive(PartialEq, Copy, Clone, Debug)]
512 pub enum AttributeType {
513 /// Normal, builtin attribute that is consumed
514 /// by the compiler before the unused_attribute check
517 /// Builtin attribute that may not be consumed by the compiler
518 /// before the unused_attribute check. These attributes
519 /// will be ignored by the unused_attribute lint
522 /// Builtin attribute that is only allowed at the crate level
526 #[derive(PartialEq, Copy, Clone, Debug)]
527 pub enum AttributeGate {
528 /// Is gated by a given feature gate and reason
529 Gated(&'static str, &'static str),
531 /// Ungated attribute, can be used on all release channels
535 /// A set of features to be used by later passes.
536 pub struct Features {
537 pub unboxed_closures: bool,
538 pub rustc_diagnostic_macros: bool,
539 pub allow_quote: bool,
541 pub allow_log_syntax: bool,
542 pub allow_concat_idents: bool,
543 pub allow_trace_macros: bool,
544 pub allow_internal_unstable: bool,
545 pub allow_custom_derive: bool,
546 pub allow_placement_in: bool,
548 pub allow_pushpop_unsafe: bool,
550 pub unmarked_api: bool,
551 pub negate_unsigned: bool,
552 /// spans of #![feature] attrs for stable language features. for error reporting
553 pub declared_stable_lang_features: Vec<Span>,
554 /// #![feature] attrs for non-language (library) features
555 pub declared_lib_features: Vec<(InternedString, Span)>,
557 pub const_indexing: bool,
558 pub static_recursion: bool,
559 pub default_type_parameter_fallback: bool,
560 pub type_macros: bool,
561 pub cfg_target_feature: bool,
562 pub cfg_target_vendor: bool,
563 pub cfg_target_thread_local: bool,
564 pub augmented_assignments: bool,
565 pub braced_empty_structs: bool,
566 pub staged_api: bool,
567 pub stmt_expr_attributes: bool,
568 pub deprecated: bool,
572 pub fn new() -> Features {
574 unboxed_closures: false,
575 rustc_diagnostic_macros: false,
578 allow_log_syntax: false,
579 allow_concat_idents: false,
580 allow_trace_macros: false,
581 allow_internal_unstable: false,
582 allow_custom_derive: false,
583 allow_placement_in: false,
585 allow_pushpop_unsafe: false,
588 negate_unsigned: false,
589 declared_stable_lang_features: Vec::new(),
590 declared_lib_features: Vec::new(),
592 const_indexing: false,
593 static_recursion: false,
594 default_type_parameter_fallback: false,
596 cfg_target_feature: false,
597 cfg_target_vendor: false,
598 cfg_target_thread_local: false,
599 augmented_assignments: false,
600 braced_empty_structs: false,
602 stmt_expr_attributes: false,
608 const EXPLAIN_BOX_SYNTAX: &'static str =
609 "box expression syntax is experimental; you can call `Box::new` instead.";
611 const EXPLAIN_PLACEMENT_IN: &'static str =
612 "placement-in expression syntax is experimental and subject to change.";
614 const EXPLAIN_PUSHPOP_UNSAFE: &'static str =
615 "push/pop_unsafe macros are experimental and subject to change.";
617 const EXPLAIN_STMT_ATTR_SYNTAX: &'static str =
618 "attributes on non-item statements and expressions are experimental.";
620 pub fn check_for_box_syntax(f: Option<&Features>, diag: &Handler, span: Span) {
621 if let Some(&Features { allow_box: true, .. }) = f {
624 emit_feature_err(diag, "box_syntax", span, GateIssue::Language, EXPLAIN_BOX_SYNTAX);
627 pub fn check_for_placement_in(f: Option<&Features>, diag: &Handler, span: Span) {
628 if let Some(&Features { allow_placement_in: true, .. }) = f {
631 emit_feature_err(diag, "placement_in_syntax", span, GateIssue::Language, EXPLAIN_PLACEMENT_IN);
634 pub fn check_for_pushpop_syntax(f: Option<&Features>, diag: &Handler, span: Span) {
635 if let Some(&Features { allow_pushpop_unsafe: true, .. }) = f {
638 emit_feature_err(diag, "pushpop_unsafe", span, GateIssue::Language, EXPLAIN_PUSHPOP_UNSAFE);
642 features: Vec<&'static str>,
643 span_handler: &'a Handler,
645 plugin_attributes: &'a [(String, AttributeType)],
648 impl<'a> Context<'a> {
649 fn enable_feature(&mut self, feature: &'static str) {
650 debug!("enabling feature: {}", feature);
651 self.features.push(feature);
654 fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
655 let has_feature = self.has_feature(feature);
656 debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", feature, span, has_feature);
658 emit_feature_err(self.span_handler, feature, span, GateIssue::Language, explain);
661 fn has_feature(&self, feature: &str) -> bool {
662 self.features.iter().any(|&n| n == feature)
665 fn check_attribute(&self, attr: &ast::Attribute, is_macro: bool) {
666 debug!("check_attribute(attr = {:?})", attr);
667 let name = &*attr.name();
668 for &(n, ty, gateage) in KNOWN_ATTRIBUTES {
670 if let Gated(gate, desc) = gateage {
671 self.gate_feature(gate, attr.span, desc);
673 debug!("check_attribute: {:?} is known, {:?}, {:?}", name, ty, gateage);
677 for &(ref n, ref ty) in self.plugin_attributes {
679 // Plugins can't gate attributes, so we don't check for it
680 // unlike the code above; we only use this loop to
681 // short-circuit to avoid the checks below
682 debug!("check_attribute: {:?} is registered by a plugin, {:?}", name, ty);
686 if name.starts_with("rustc_") {
687 self.gate_feature("rustc_attrs", attr.span,
688 "unless otherwise specified, attributes \
689 with the prefix `rustc_` \
690 are reserved for internal compiler diagnostics");
691 } else if name.starts_with("derive_") {
692 self.gate_feature("custom_derive", attr.span,
693 "attributes of the form `#[derive_*]` are reserved \
696 // Only run the custom attribute lint during regular
697 // feature gate checking. Macro gating runs
698 // before the plugin attributes are registered
699 // so we skip this then
701 self.gate_feature("custom_attribute", attr.span,
702 &format!("The attribute `{}` is currently \
703 unknown to the compiler and \
705 added to it in the future",
712 fn find_lang_feature_issue(feature: &str) -> Option<u32> {
713 let info = KNOWN_FEATURES.iter()
714 .find(|t| t.0 == feature)
717 if let Active = info.3 {
718 // FIXME (#28244): enforce that active features have issue numbers
719 // assert!(issue.is_some())
729 pub fn emit_feature_err(diag: &Handler, feature: &str, span: Span, issue: GateIssue,
731 let issue = match issue {
732 GateIssue::Language => find_lang_feature_issue(feature),
733 GateIssue::Library(lib) => lib,
736 let mut err = if let Some(n) = issue {
737 diag.struct_span_err(span, &format!("{} (see issue #{})", explain, n))
739 diag.struct_span_err(span, explain)
742 // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
743 if option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some() {
747 err.fileline_help(span, &format!("add #![feature({})] to the \
748 crate attributes to enable",
753 pub const EXPLAIN_ASM: &'static str =
754 "inline assembly is not stable enough for use and is subject to change";
756 pub const EXPLAIN_LOG_SYNTAX: &'static str =
757 "`log_syntax!` is not stable enough for use and is subject to change";
759 pub const EXPLAIN_CONCAT_IDENTS: &'static str =
760 "`concat_idents` is not stable enough for use and is subject to change";
762 pub const EXPLAIN_TRACE_MACROS: &'static str =
763 "`trace_macros` is not stable enough for use and is subject to change";
764 pub const EXPLAIN_ALLOW_INTERNAL_UNSTABLE: &'static str =
765 "allow_internal_unstable side-steps feature gating and stability checks";
767 pub const EXPLAIN_CUSTOM_DERIVE: &'static str =
768 "`#[derive]` for custom traits is not stable enough for use and is subject to change";
770 struct MacroVisitor<'a> {
771 context: &'a Context<'a>
774 impl<'a, 'v> Visitor<'v> for MacroVisitor<'a> {
775 fn visit_mac(&mut self, mac: &ast::Mac) {
776 let path = &mac.node.path;
777 let name = path.segments.last().unwrap().identifier.name.as_str();
779 // Issue 22234: If you add a new case here, make sure to also
780 // add code to catch the macro during or after expansion.
782 // We still keep this MacroVisitor (rather than *solely*
783 // relying on catching cases during or after expansion) to
784 // catch uses of these macros within conditionally-compiled
785 // code, e.g. `#[cfg]`-guarded functions.
788 self.context.gate_feature("asm", path.span, EXPLAIN_ASM);
791 else if name == "log_syntax" {
792 self.context.gate_feature("log_syntax", path.span, EXPLAIN_LOG_SYNTAX);
795 else if name == "trace_macros" {
796 self.context.gate_feature("trace_macros", path.span, EXPLAIN_TRACE_MACROS);
799 else if name == "concat_idents" {
800 self.context.gate_feature("concat_idents", path.span, EXPLAIN_CONCAT_IDENTS);
804 fn visit_attribute(&mut self, attr: &'v ast::Attribute) {
805 self.context.check_attribute(attr, true);
808 fn visit_expr(&mut self, e: &ast::Expr) {
809 // Issue 22181: overloaded-`box` and placement-`in` are
810 // implemented via a desugaring expansion, so their feature
811 // gates go into MacroVisitor since that works pre-expansion.
813 // Issue 22234: we also check during expansion as well.
814 // But we keep these checks as a pre-expansion check to catch
815 // uses in e.g. conditionalized code.
817 if let ast::ExprBox(_) = e.node {
818 self.context.gate_feature("box_syntax", e.span, EXPLAIN_BOX_SYNTAX);
821 if let ast::ExprInPlace(..) = e.node {
822 self.context.gate_feature("placement_in_syntax", e.span, EXPLAIN_PLACEMENT_IN);
825 visit::walk_expr(self, e);
829 struct PostExpansionVisitor<'a> {
830 context: &'a Context<'a>,
833 impl<'a> PostExpansionVisitor<'a> {
834 fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
835 if !self.context.cm.span_allows_unstable(span) {
836 self.context.gate_feature(feature, span, explain)
841 impl<'a, 'v> Visitor<'v> for PostExpansionVisitor<'a> {
842 fn visit_attribute(&mut self, attr: &ast::Attribute) {
843 if !self.context.cm.span_allows_unstable(attr.span) {
844 self.context.check_attribute(attr, false);
848 fn visit_name(&mut self, sp: Span, name: ast::Name) {
849 if !name.as_str().is_ascii() {
850 self.gate_feature("non_ascii_idents", sp,
851 "non-ascii idents are not fully supported.");
855 fn visit_item(&mut self, i: &ast::Item) {
857 ast::ItemExternCrate(_) => {
858 if attr::contains_name(&i.attrs[..], "macro_reexport") {
859 self.gate_feature("macro_reexport", i.span,
860 "macros reexports are experimental \
861 and possibly buggy");
865 ast::ItemForeignMod(ref foreign_module) => {
866 if attr::contains_name(&i.attrs[..], "link_args") {
867 self.gate_feature("link_args", i.span,
868 "the `link_args` attribute is not portable \
869 across platforms, it is recommended to \
870 use `#[link(name = \"foo\")]` instead")
872 let maybe_feature = match foreign_module.abi {
873 Abi::RustIntrinsic => Some(("intrinsics", "intrinsics are subject to change")),
874 Abi::PlatformIntrinsic => {
875 Some(("platform_intrinsics",
876 "platform intrinsics are experimental and possibly buggy"))
880 if let Some((feature, msg)) = maybe_feature {
881 self.gate_feature(feature, i.span, msg)
886 if attr::contains_name(&i.attrs[..], "plugin_registrar") {
887 self.gate_feature("plugin_registrar", i.span,
888 "compiler plugins are experimental and possibly buggy");
890 if attr::contains_name(&i.attrs[..], "start") {
891 self.gate_feature("start", i.span,
892 "a #[start] function is an experimental \
893 feature whose signature may change \
896 if attr::contains_name(&i.attrs[..], "main") {
897 self.gate_feature("main", i.span,
898 "declaration of a nonstandard #[main] \
899 function may change over time, for now \
900 a top-level `fn main()` is required");
904 ast::ItemStruct(..) => {
905 if attr::contains_name(&i.attrs[..], "simd") {
906 self.gate_feature("simd", i.span,
907 "SIMD types are experimental and possibly buggy");
908 self.context.span_handler.span_warn(i.span,
909 "the `#[simd]` attribute is deprecated, \
910 use `#[repr(simd)]` instead");
912 for attr in &i.attrs {
913 if attr.name() == "repr" {
914 for item in attr.meta_item_list().unwrap_or(&[]) {
915 if item.name() == "simd" {
916 self.gate_feature("repr_simd", i.span,
917 "SIMD types are experimental and possibly buggy");
925 ast::ItemDefaultImpl(..) => {
926 self.gate_feature("optin_builtin_traits",
928 "default trait implementations are experimental \
929 and possibly buggy");
932 ast::ItemImpl(_, polarity, _, _, _, _) => {
934 ast::ImplPolarity::Negative => {
935 self.gate_feature("optin_builtin_traits",
937 "negative trait bounds are not yet fully implemented; \
938 use marker types for now");
947 visit::walk_item(self, i);
950 fn visit_variant_data(&mut self, s: &'v ast::VariantData, _: ast::Ident,
951 _: &'v ast::Generics, _: ast::NodeId, span: Span) {
952 if s.fields().is_empty() {
954 self.gate_feature("braced_empty_structs", span,
955 "empty structs and enum variants with braces are unstable");
956 } else if s.is_tuple() {
957 self.context.span_handler.struct_span_err(span, "empty tuple structs and enum \
958 variants are not allowed, use \
959 unit structs and enum variants \
961 .span_help(span, "remove trailing `()` to make a unit \
962 struct or unit enum variant")
966 visit::walk_struct_def(self, s)
969 fn visit_foreign_item(&mut self, i: &ast::ForeignItem) {
970 let links_to_llvm = match attr::first_attr_value_str_by_name(&i.attrs,
972 Some(val) => val.starts_with("llvm."),
976 self.gate_feature("link_llvm_intrinsics", i.span,
977 "linking to LLVM intrinsics is experimental");
980 visit::walk_foreign_item(self, i)
983 fn visit_expr(&mut self, e: &ast::Expr) {
986 self.gate_feature("box_syntax",
988 "box expression syntax is experimental; \
989 you can call `Box::new` instead.");
991 ast::ExprType(..) => {
992 self.gate_feature("type_ascription", e.span,
993 "type ascription is experimental");
997 visit::walk_expr(self, e);
1000 fn visit_pat(&mut self, pattern: &ast::Pat) {
1001 match pattern.node {
1002 ast::PatVec(_, Some(_), ref last) if !last.is_empty() => {
1003 self.gate_feature("advanced_slice_patterns",
1005 "multiple-element slice matches anywhere \
1006 but at the end of a slice (e.g. \
1007 `[0, ..xs, 0]`) are experimental")
1009 ast::PatVec(..) => {
1010 self.gate_feature("slice_patterns",
1012 "slice pattern syntax is experimental");
1014 ast::PatBox(..) => {
1015 self.gate_feature("box_patterns",
1017 "box pattern syntax is experimental");
1021 visit::walk_pat(self, pattern)
1024 fn visit_fn(&mut self,
1025 fn_kind: FnKind<'v>,
1026 fn_decl: &'v ast::FnDecl,
1027 block: &'v ast::Block,
1030 // check for const fn declarations
1032 FnKind::ItemFn(_, _, _, ast::Constness::Const, _, _) => {
1033 self.gate_feature("const_fn", span, "const fn is unstable");
1036 // stability of const fn methods are covered in
1037 // visit_trait_item and visit_impl_item below; this is
1038 // because default methods don't pass through this
1044 FnKind::ItemFn(_, _, _, _, abi, _) if abi == Abi::RustIntrinsic => {
1045 self.gate_feature("intrinsics",
1047 "intrinsics are subject to change")
1049 FnKind::ItemFn(_, _, _, _, abi, _) |
1050 FnKind::Method(_, &ast::MethodSig { abi, .. }, _) if abi == Abi::RustCall => {
1051 self.gate_feature("unboxed_closures",
1053 "rust-call ABI is subject to change")
1057 visit::walk_fn(self, fn_kind, fn_decl, block, span);
1060 fn visit_trait_item(&mut self, ti: &'v ast::TraitItem) {
1062 ast::ConstTraitItem(..) => {
1063 self.gate_feature("associated_consts",
1065 "associated constants are experimental")
1067 ast::MethodTraitItem(ref sig, _) => {
1068 if sig.constness == ast::Constness::Const {
1069 self.gate_feature("const_fn", ti.span, "const fn is unstable");
1072 ast::TypeTraitItem(_, Some(_)) => {
1073 self.gate_feature("associated_type_defaults", ti.span,
1074 "associated type defaults are unstable");
1078 visit::walk_trait_item(self, ti);
1081 fn visit_impl_item(&mut self, ii: &'v ast::ImplItem) {
1083 ast::ImplItemKind::Const(..) => {
1084 self.gate_feature("associated_consts",
1086 "associated constants are experimental")
1088 ast::ImplItemKind::Method(ref sig, _) => {
1089 if sig.constness == ast::Constness::Const {
1090 self.gate_feature("const_fn", ii.span, "const fn is unstable");
1095 visit::walk_impl_item(self, ii);
1099 fn check_crate_inner<F>(cm: &CodeMap, span_handler: &Handler,
1101 plugin_attributes: &[(String, AttributeType)],
1104 where F: FnOnce(&mut Context, &ast::Crate)
1106 let mut cx = Context {
1107 features: Vec::new(),
1108 span_handler: span_handler,
1110 plugin_attributes: plugin_attributes,
1113 let mut accepted_features = Vec::new();
1114 let mut unknown_features = Vec::new();
1116 for attr in &krate.attrs {
1117 if !attr.check_name("feature") {
1121 match attr.meta_item_list() {
1123 span_handler.span_err(attr.span, "malformed feature attribute, \
1124 expected #![feature(...)]");
1128 let name = match mi.node {
1129 ast::MetaWord(ref word) => (*word).clone(),
1131 span_handler.span_err(mi.span,
1132 "malformed feature, expected just \
1137 match KNOWN_FEATURES.iter()
1138 .find(|& &(n, _, _, _)| name == n) {
1139 Some(&(name, _, _, Active)) => {
1140 cx.enable_feature(name);
1142 Some(&(_, _, _, Removed)) => {
1143 span_handler.span_err(mi.span, "feature has been removed");
1145 Some(&(_, _, _, Accepted)) => {
1146 accepted_features.push(mi.span);
1149 unknown_features.push((name, mi.span));
1157 check(&mut cx, krate);
1159 // FIXME (pnkfelix): Before adding the 99th entry below, change it
1160 // to a single-pass (instead of N calls to `.has_feature`).
1163 unboxed_closures: cx.has_feature("unboxed_closures"),
1164 rustc_diagnostic_macros: cx.has_feature("rustc_diagnostic_macros"),
1165 allow_quote: cx.has_feature("quote"),
1166 allow_asm: cx.has_feature("asm"),
1167 allow_log_syntax: cx.has_feature("log_syntax"),
1168 allow_concat_idents: cx.has_feature("concat_idents"),
1169 allow_trace_macros: cx.has_feature("trace_macros"),
1170 allow_internal_unstable: cx.has_feature("allow_internal_unstable"),
1171 allow_custom_derive: cx.has_feature("custom_derive"),
1172 allow_placement_in: cx.has_feature("placement_in_syntax"),
1173 allow_box: cx.has_feature("box_syntax"),
1174 allow_pushpop_unsafe: cx.has_feature("pushpop_unsafe"),
1175 simd_ffi: cx.has_feature("simd_ffi"),
1176 unmarked_api: cx.has_feature("unmarked_api"),
1177 negate_unsigned: cx.has_feature("negate_unsigned"),
1178 declared_stable_lang_features: accepted_features,
1179 declared_lib_features: unknown_features,
1180 const_fn: cx.has_feature("const_fn"),
1181 const_indexing: cx.has_feature("const_indexing"),
1182 static_recursion: cx.has_feature("static_recursion"),
1183 default_type_parameter_fallback: cx.has_feature("default_type_parameter_fallback"),
1184 type_macros: cx.has_feature("type_macros"),
1185 cfg_target_feature: cx.has_feature("cfg_target_feature"),
1186 cfg_target_vendor: cx.has_feature("cfg_target_vendor"),
1187 cfg_target_thread_local: cx.has_feature("cfg_target_thread_local"),
1188 augmented_assignments: cx.has_feature("augmented_assignments"),
1189 braced_empty_structs: cx.has_feature("braced_empty_structs"),
1190 staged_api: cx.has_feature("staged_api"),
1191 stmt_expr_attributes: cx.has_feature("stmt_expr_attributes"),
1192 deprecated: cx.has_feature("deprecated"),
1196 pub fn check_crate_macros(cm: &CodeMap, span_handler: &Handler, krate: &ast::Crate)
1198 check_crate_inner(cm, span_handler, krate, &[] as &'static [_],
1199 |ctx, krate| visit::walk_crate(&mut MacroVisitor { context: ctx }, krate))
1202 pub fn check_crate(cm: &CodeMap, span_handler: &Handler, krate: &ast::Crate,
1203 plugin_attributes: &[(String, AttributeType)],
1204 unstable: UnstableFeatures) -> Features
1206 maybe_stage_features(span_handler, krate, unstable);
1208 check_crate_inner(cm, span_handler, krate, plugin_attributes,
1209 |ctx, krate| visit::walk_crate(&mut PostExpansionVisitor { context: ctx },
1213 #[derive(Clone, Copy)]
1214 pub enum UnstableFeatures {
1215 /// Hard errors for unstable features are active, as on
1216 /// beta/stable channels.
1218 /// Allow features to me activated, as on nightly.
1220 /// Errors are bypassed for bootstrapping. This is required any time
1221 /// during the build that feature-related lints are set to warn or above
1222 /// because the build turns on warnings-as-errors and uses lots of unstable
1223 /// features. As a result, this is always required for building Rust itself.
1227 fn maybe_stage_features(span_handler: &Handler, krate: &ast::Crate,
1228 unstable: UnstableFeatures) {
1229 let allow_features = match unstable {
1230 UnstableFeatures::Allow => true,
1231 UnstableFeatures::Disallow => false,
1232 UnstableFeatures::Cheat => true
1234 if !allow_features {
1235 for attr in &krate.attrs {
1236 if attr.check_name("feature") {
1237 let release_channel = option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)");
1238 let ref msg = format!("#[feature] may not be used on the {} release channel",
1240 span_handler.span_err(attr.span, msg);