src/libsyntax/feature_gate/check.rs

   1 use rustc_feature::{ACCEPTED_FEATURES, ACTIVE_FEATURES, Features, Feature, State as FeatureState};
   2 use rustc_feature::{REMOVED_FEATURES, STABLE_REMOVED_FEATURES};
   3 use rustc_feature::{AttributeGate, BUILTIN_ATTRIBUTE_MAP};
   4
   5 use crate::ast::{self, AssocTyConstraint, AssocTyConstraintKind, NodeId};
   6 use crate::ast::{GenericParam, GenericParamKind, PatKind, RangeEnd, VariantData};
   7 use crate::attr;
   8 use crate::source_map::Spanned;
   9 use crate::edition::{ALL_EDITIONS, Edition};
  10 use crate::visit::{self, FnKind, Visitor};
  11 use crate::sess::ParseSess;
  12 use crate::symbol::{Symbol, sym};
  13
  14 use errors::{Applicability, DiagnosticBuilder, Handler};
  15 use rustc_data_structures::fx::FxHashMap;
  16 use syntax_pos::{Span, DUMMY_SP, MultiSpan};
  17 use log::debug;
  18
  19 use rustc_error_codes::*;
  20
  21
  22 use std::env;
  23 use std::num::NonZeroU32;
  24
  25 macro_rules! gate_feature_fn {
  26     ($cx: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr, $level: expr) => {{
  27         let (cx, has_feature, span,
  28              name, explain, level) = (&*$cx, $has_feature, $span, $name, $explain, $level);
  29         let has_feature: bool = has_feature(&$cx.features);
  30         debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
  31         if !has_feature && !span.allows_unstable($name) {
  32             leveled_feature_err(cx.parse_sess, name, span, GateIssue::Language, explain, level)
  33                 .emit();
  34         }
  35     }}
  36 }
  37
  38 macro_rules! gate_feature {
  39     ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {
  40         gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
  41                          sym::$feature, $explain, GateStrength::Hard)
  42     };
  43     ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {
  44         gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
  45                          sym::$feature, $explain, $level)
  46     };
  47 }
  48
  49 pub fn check_attribute(attr: &ast::Attribute, parse_sess: &ParseSess, features: &Features) {
  50     PostExpansionVisitor { parse_sess, features }.visit_attribute(attr)
  51 }
  52
  53 fn find_lang_feature_issue(feature: Symbol) -> Option<NonZeroU32> {
  54     if let Some(info) = ACTIVE_FEATURES.iter().find(|t| t.name == feature) {
  55         // FIXME (#28244): enforce that active features have issue numbers
  56         // assert!(info.issue().is_some())
  57         info.issue()
  58     } else {
  59         // search in Accepted, Removed, or Stable Removed features
  60         let found = ACCEPTED_FEATURES
  61             .iter()
  62             .chain(REMOVED_FEATURES)
  63             .chain(STABLE_REMOVED_FEATURES)
  64             .find(|t| t.name == feature);
  65         match found {
  66             Some(found) => found.issue(),
  67             None => panic!("feature `{}` is not declared anywhere", feature),
  68         }
  69     }
  70 }
  71
  72 pub enum GateIssue {
  73     Language,
  74     Library(Option<NonZeroU32>)
  75 }
  76
  77 #[derive(Debug, Copy, Clone, PartialEq)]
  78 pub enum GateStrength {
  79     /// A hard error. (Most feature gates should use this.)
  80     Hard,
  81     /// Only a warning. (Use this only as backwards-compatibility demands.)
  82     Soft,
  83 }
  84
  85 pub fn emit_feature_err(
  86     sess: &ParseSess,
  87     feature: Symbol,
  88     span: Span,
  89     issue: GateIssue,
  90     explain: &str,
  91 ) {
  92     feature_err(sess, feature, span, issue, explain).emit();
  93 }
  94
  95 pub fn feature_err<'a, S: Into<MultiSpan>>(
  96     sess: &'a ParseSess,
  97     feature: Symbol,
  98     span: S,
  99     issue: GateIssue,
 100     explain: &str,
 101 ) -> DiagnosticBuilder<'a> {
 102     leveled_feature_err(sess, feature, span, issue, explain, GateStrength::Hard)
 103 }
 104
 105 fn leveled_feature_err<'a, S: Into<MultiSpan>>(
 106     sess: &'a ParseSess,
 107     feature: Symbol,
 108     span: S,
 109     issue: GateIssue,
 110     explain: &str,
 111     level: GateStrength,
 112 ) -> DiagnosticBuilder<'a> {
 113     let diag = &sess.span_diagnostic;
 114
 115     let issue = match issue {
 116         GateIssue::Language => find_lang_feature_issue(feature),
 117         GateIssue::Library(lib) => lib,
 118     };
 119
 120     let mut err = match level {
 121         GateStrength::Hard => {
 122             diag.struct_span_err_with_code(span, explain, stringify_error_code!(E0658))
 123         }
 124         GateStrength::Soft => diag.struct_span_warn(span, explain),
 125     };
 126
 127     if let Some(n) = issue {
 128         err.note(&format!(
 129             "for more information, see https://github.com/rust-lang/rust/issues/{}",
 130             n,
 131         ));
 132     }
 133
 134     // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
 135     if sess.unstable_features.is_nightly_build() {
 136         err.help(&format!("add `#![feature({})]` to the crate attributes to enable", feature));
 137     }
 138
 139     // If we're on stable and only emitting a "soft" warning, add a note to
 140     // clarify that the feature isn't "on" (rather than being on but
 141     // warning-worthy).
 142     if !sess.unstable_features.is_nightly_build() && level == GateStrength::Soft {
 143         err.help("a nightly build of the compiler is required to enable this feature");
 144     }
 145
 146     err
 147
 148 }
 149
 150 const EXPLAIN_BOX_SYNTAX: &str =
 151     "box expression syntax is experimental; you can call `Box::new` instead";
 152
 153 struct PostExpansionVisitor<'a> {
 154     parse_sess: &'a ParseSess,
 155     features: &'a Features,
 156 }
 157
 158 macro_rules! gate_feature_post {
 159     ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {{
 160         let (cx, span) = ($cx, $span);
 161         if !span.allows_unstable(sym::$feature) {
 162             gate_feature!(cx, $feature, span, $explain)
 163         }
 164     }};
 165     ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {{
 166         let (cx, span) = ($cx, $span);
 167         if !span.allows_unstable(sym::$feature) {
 168             gate_feature!(cx, $feature, span, $explain, $level)
 169         }
 170     }}
 171 }
 172
 173 impl<'a> PostExpansionVisitor<'a> {
 174     fn check_abi(&self, abi: ast::StrLit) {
 175         let ast::StrLit { symbol_unescaped, span, .. } = abi;
 176
 177         match &*symbol_unescaped.as_str() {
 178             // Stable
 179             "Rust" |
 180             "C" |
 181             "cdecl" |
 182             "stdcall" |
 183             "fastcall" |
 184             "aapcs" |
 185             "win64" |
 186             "sysv64" |
 187             "system" => {}
 188             "rust-intrinsic" => {
 189                 gate_feature_post!(&self, intrinsics, span,
 190                                    "intrinsics are subject to change");
 191             },
 192             "platform-intrinsic" => {
 193                 gate_feature_post!(&self, platform_intrinsics, span,
 194                                    "platform intrinsics are experimental and possibly buggy");
 195             },
 196             "vectorcall" => {
 197                 gate_feature_post!(&self, abi_vectorcall, span,
 198                                    "vectorcall is experimental and subject to change");
 199             },
 200             "thiscall" => {
 201                 gate_feature_post!(&self, abi_thiscall, span,
 202                                    "thiscall is experimental and subject to change");
 203             },
 204             "rust-call" => {
 205                 gate_feature_post!(&self, unboxed_closures, span,
 206                                    "rust-call ABI is subject to change");
 207             },
 208             "ptx-kernel" => {
 209                 gate_feature_post!(&self, abi_ptx, span,
 210                                    "PTX ABIs are experimental and subject to change");
 211             },
 212             "unadjusted" => {
 213                 gate_feature_post!(&self, abi_unadjusted, span,
 214                                    "unadjusted ABI is an implementation detail and perma-unstable");
 215             },
 216             "msp430-interrupt" => {
 217                 gate_feature_post!(&self, abi_msp430_interrupt, span,
 218                                    "msp430-interrupt ABI is experimental and subject to change");
 219             },
 220             "x86-interrupt" => {
 221                 gate_feature_post!(&self, abi_x86_interrupt, span,
 222                                    "x86-interrupt ABI is experimental and subject to change");
 223             },
 224             "amdgpu-kernel" => {
 225                 gate_feature_post!(&self, abi_amdgpu_kernel, span,
 226                                    "amdgpu-kernel ABI is experimental and subject to change");
 227             },
 228             "efiapi" => {
 229                 gate_feature_post!(&self, abi_efiapi, span,
 230                                    "efiapi ABI is experimental and subject to change");
 231             },
 232             abi => {
 233                 self.parse_sess.span_diagnostic.delay_span_bug(
 234                     span,
 235                     &format!("unrecognized ABI not caught in lowering: {}", abi),
 236                 )
 237             }
 238         }
 239     }
 240
 241     fn check_extern(&self, ext: ast::Extern) {
 242         if let ast::Extern::Explicit(abi) = ext {
 243             self.check_abi(abi);
 244         }
 245     }
 246
 247     fn maybe_report_invalid_custom_discriminants(&self, variants: &[ast::Variant]) {
 248         let has_fields = variants.iter().any(|variant| match variant.data {
 249             VariantData::Tuple(..) | VariantData::Struct(..) => true,
 250             VariantData::Unit(..) => false,
 251         });
 252
 253         let discriminant_spans = variants.iter().filter(|variant| match variant.data {
 254             VariantData::Tuple(..) | VariantData::Struct(..) => false,
 255             VariantData::Unit(..) => true,
 256         })
 257         .filter_map(|variant| variant.disr_expr.as_ref().map(|c| c.value.span))
 258         .collect::<Vec<_>>();
 259
 260         if !discriminant_spans.is_empty() && has_fields {
 261             let mut err = feature_err(
 262                 self.parse_sess,
 263                 sym::arbitrary_enum_discriminant,
 264                 discriminant_spans.clone(),
 265                 crate::feature_gate::GateIssue::Language,
 266                 "custom discriminant values are not allowed in enums with tuple or struct variants",
 267             );
 268             for sp in discriminant_spans {
 269                 err.span_label(sp, "disallowed custom discriminant");
 270             }
 271             for variant in variants.iter() {
 272                 match &variant.data {
 273                     VariantData::Struct(..) => {
 274                         err.span_label(
 275                             variant.span,
 276                             "struct variant defined here",
 277                         );
 278                     }
 279                     VariantData::Tuple(..) => {
 280                         err.span_label(
 281                             variant.span,
 282                             "tuple variant defined here",
 283                         );
 284                     }
 285                     VariantData::Unit(..) => {}
 286                 }
 287             }
 288             err.emit();
 289         }
 290     }
 291
 292     fn check_gat(&self, generics: &ast::Generics, span: Span) {
 293         if !generics.params.is_empty() {
 294             gate_feature_post!(
 295                 &self,
 296                 generic_associated_types,
 297                 span,
 298                 "generic associated types are unstable"
 299             );
 300         }
 301         if !generics.where_clause.predicates.is_empty() {
 302             gate_feature_post!(
 303                 &self,
 304                 generic_associated_types,
 305                 span,
 306                 "where clauses on associated types are unstable"
 307             );
 308         }
 309     }
 310
 311     /// Feature gate `impl Trait` inside `type Alias = $type_expr;`.
 312     fn check_impl_trait(&self, ty: &ast::Ty) {
 313         struct ImplTraitVisitor<'a> {
 314             vis: &'a PostExpansionVisitor<'a>,
 315         }
 316         impl Visitor<'_> for ImplTraitVisitor<'_> {
 317             fn visit_ty(&mut self, ty: &ast::Ty) {
 318                 if let ast::TyKind::ImplTrait(..) = ty.kind {
 319                     gate_feature_post!(
 320                         &self.vis,
 321                         type_alias_impl_trait,
 322                         ty.span,
 323                         "`impl Trait` in type aliases is unstable"
 324                     );
 325                 }
 326                 visit::walk_ty(self, ty);
 327             }
 328         }
 329         ImplTraitVisitor { vis: self }.visit_ty(ty);
 330     }
 331 }
 332
 333 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 334     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 335         let attr_info =
 336             attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name)).map(|a| **a);
 337         // Check feature gates for built-in attributes.
 338         if let Some((.., AttributeGate::Gated(_, name, descr, has_feature))) = attr_info {
 339             gate_feature_fn!(self, has_feature, attr.span, name, descr, GateStrength::Hard);
 340         }
 341         // Check unstable flavors of the `#[doc]` attribute.
 342         if attr.check_name(sym::doc) {
 343             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 344                 macro_rules! gate_doc { ($($name:ident => $feature:ident)*) => {
 345                     $(if nested_meta.check_name(sym::$name) {
 346                         let msg = concat!("`#[doc(", stringify!($name), ")]` is experimental");
 347                         gate_feature!(self, $feature, attr.span, msg);
 348                     })*
 349                 }}
 350
 351                 gate_doc!(
 352                     include => external_doc
 353                     cfg => doc_cfg
 354                     masked => doc_masked
 355                     spotlight => doc_spotlight
 356                     alias => doc_alias
 357                     keyword => doc_keyword
 358                 );
 359             }
 360         }
 361     }
 362
 363     fn visit_name(&mut self, sp: Span, name: ast::Name) {
 364         if !name.as_str().is_ascii() {
 365             gate_feature_post!(
 366                 &self,
 367                 non_ascii_idents,
 368                 self.parse_sess.source_map().def_span(sp),
 369                 "non-ascii idents are not fully supported"
 370             );
 371         }
 372     }
 373
 374     fn visit_item(&mut self, i: &'a ast::Item) {
 375         match i.kind {
 376             ast::ItemKind::ForeignMod(ref foreign_module) => {
 377                 if let Some(abi) = foreign_module.abi {
 378                     self.check_abi(abi);
 379                 }
 380             }
 381
 382             ast::ItemKind::Fn(..) => {
 383                 if attr::contains_name(&i.attrs[..], sym::plugin_registrar) {
 384                     gate_feature_post!(&self, plugin_registrar, i.span,
 385                                        "compiler plugins are experimental and possibly buggy");
 386                 }
 387                 if attr::contains_name(&i.attrs[..], sym::start) {
 388                     gate_feature_post!(&self, start, i.span,
 389                                       "a `#[start]` function is an experimental \
 390                                        feature whose signature may change \
 391                                        over time");
 392                 }
 393                 if attr::contains_name(&i.attrs[..], sym::main) {
 394                     gate_feature_post!(&self, main, i.span,
 395                                        "declaration of a non-standard `#[main]` \
 396                                         function may change over time, for now \
 397                                         a top-level `fn main()` is required");
 398                 }
 399             }
 400
 401             ast::ItemKind::Struct(..) => {
 402                 for attr in attr::filter_by_name(&i.attrs[..], sym::repr) {
 403                     for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
 404                         if item.check_name(sym::simd) {
 405                             gate_feature_post!(&self, repr_simd, attr.span,
 406                                                "SIMD types are experimental and possibly buggy");
 407                         }
 408                     }
 409                 }
 410             }
 411
 412             ast::ItemKind::Enum(ast::EnumDef{ref variants, ..}, ..) => {
 413                 for variant in variants {
 414                     match (&variant.data, &variant.disr_expr) {
 415                         (ast::VariantData::Unit(..), _) => {},
 416                         (_, Some(disr_expr)) =>
 417                             gate_feature_post!(
 418                                 &self,
 419                                 arbitrary_enum_discriminant,
 420                                 disr_expr.value.span,
 421                                 "discriminants on non-unit variants are experimental"),
 422                         _ => {},
 423                     }
 424                 }
 425
 426                 let has_feature = self.features.arbitrary_enum_discriminant;
 427                 if !has_feature && !i.span.allows_unstable(sym::arbitrary_enum_discriminant) {
 428                     self.maybe_report_invalid_custom_discriminants(&variants);
 429                 }
 430             }
 431
 432             ast::ItemKind::Impl(_, polarity, defaultness, ..) => {
 433                 if polarity == ast::ImplPolarity::Negative {
 434                     gate_feature_post!(&self, optin_builtin_traits,
 435                                        i.span,
 436                                        "negative trait bounds are not yet fully implemented; \
 437                                         use marker types for now");
 438                 }
 439
 440                 if let ast::Defaultness::Default = defaultness {
 441                     gate_feature_post!(&self, specialization,
 442                                        i.span,
 443                                        "specialization is unstable");
 444                 }
 445             }
 446
 447             ast::ItemKind::Trait(ast::IsAuto::Yes, ..) => {
 448                 gate_feature_post!(&self, optin_builtin_traits,
 449                                    i.span,
 450                                    "auto traits are experimental and possibly buggy");
 451             }
 452
 453             ast::ItemKind::TraitAlias(..) => {
 454                 gate_feature_post!(
 455                     &self,
 456                     trait_alias,
 457                     i.span,
 458                     "trait aliases are experimental"
 459                 );
 460             }
 461
 462             ast::ItemKind::MacroDef(ast::MacroDef { legacy: false, .. }) => {
 463                 let msg = "`macro` is experimental";
 464                 gate_feature_post!(&self, decl_macro, i.span, msg);
 465             }
 466
 467             ast::ItemKind::TyAlias(ref ty, ..) => self.check_impl_trait(&ty),
 468
 469             _ => {}
 470         }
 471
 472         visit::walk_item(self, i);
 473     }
 474
 475     fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
 476         match i.kind {
 477             ast::ForeignItemKind::Fn(..) |
 478             ast::ForeignItemKind::Static(..) => {
 479                 let link_name = attr::first_attr_value_str_by_name(&i.attrs, sym::link_name);
 480                 let links_to_llvm = match link_name {
 481                     Some(val) => val.as_str().starts_with("llvm."),
 482                     _ => false
 483                 };
 484                 if links_to_llvm {
 485                     gate_feature_post!(&self, link_llvm_intrinsics, i.span,
 486                                        "linking to LLVM intrinsics is experimental");
 487                 }
 488             }
 489             ast::ForeignItemKind::Ty => {
 490                     gate_feature_post!(&self, extern_types, i.span,
 491                                        "extern types are experimental");
 492             }
 493             ast::ForeignItemKind::Macro(..) => {}
 494         }
 495
 496         visit::walk_foreign_item(self, i)
 497     }
 498
 499     fn visit_ty(&mut self, ty: &'a ast::Ty) {
 500         match ty.kind {
 501             ast::TyKind::BareFn(ref bare_fn_ty) => {
 502                 self.check_extern(bare_fn_ty.ext);
 503             }
 504             _ => {}
 505         }
 506         visit::walk_ty(self, ty)
 507     }
 508
 509     fn visit_expr(&mut self, e: &'a ast::Expr) {
 510         match e.kind {
 511             ast::ExprKind::Box(_) => {
 512                 gate_feature_post!(&self, box_syntax, e.span, EXPLAIN_BOX_SYNTAX);
 513             }
 514             ast::ExprKind::Type(..) => {
 515                 // To avoid noise about type ascription in common syntax errors, only emit if it
 516                 // is the *only* error.
 517                 if self.parse_sess.span_diagnostic.err_count() == 0 {
 518                     gate_feature_post!(&self, type_ascription, e.span,
 519                                        "type ascription is experimental");
 520                 }
 521             }
 522             ast::ExprKind::TryBlock(_) => {
 523                 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
 524             }
 525             ast::ExprKind::Block(_, opt_label) => {
 526                 if let Some(label) = opt_label {
 527                     gate_feature_post!(&self, label_break_value, label.ident.span,
 528                                     "labels on blocks are unstable");
 529                 }
 530             }
 531             _ => {}
 532         }
 533         visit::walk_expr(self, e)
 534     }
 535
 536     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
 537         match &pattern.kind {
 538             PatKind::Slice(pats) => {
 539                 for pat in &*pats {
 540                     let span = pat.span;
 541                     let inner_pat = match &pat.kind {
 542                         PatKind::Ident(.., Some(pat)) => pat,
 543                         _ => pat,
 544                     };
 545                     if inner_pat.is_rest() {
 546                         gate_feature_post!(
 547                             &self,
 548                             slice_patterns,
 549                             span,
 550                             "subslice patterns are unstable"
 551                         );
 552                     }
 553                 }
 554             }
 555             PatKind::Box(..) => {
 556                 gate_feature_post!(&self, box_patterns,
 557                                   pattern.span,
 558                                   "box pattern syntax is experimental");
 559             }
 560             PatKind::Range(_, _, Spanned { node: RangeEnd::Excluded, .. }) => {
 561                 gate_feature_post!(&self, exclusive_range_pattern, pattern.span,
 562                                    "exclusive range pattern syntax is experimental");
 563             }
 564             _ => {}
 565         }
 566         visit::walk_pat(self, pattern)
 567     }
 568
 569     fn visit_fn(&mut self,
 570                 fn_kind: FnKind<'a>,
 571                 fn_decl: &'a ast::FnDecl,
 572                 span: Span,
 573                 _node_id: NodeId) {
 574         if let Some(header) = fn_kind.header() {
 575             // Stability of const fn methods are covered in
 576             // `visit_trait_item` and `visit_impl_item` below; this is
 577             // because default methods don't pass through this point.
 578             self.check_extern(header.ext);
 579         }
 580
 581         if fn_decl.c_variadic() {
 582             gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
 583         }
 584
 585         visit::walk_fn(self, fn_kind, fn_decl, span)
 586     }
 587
 588     fn visit_generic_param(&mut self, param: &'a GenericParam) {
 589         match param.kind {
 590             GenericParamKind::Const { .. } =>
 591                 gate_feature_post!(&self, const_generics, param.ident.span,
 592                     "const generics are unstable"),
 593             _ => {}
 594         }
 595         visit::walk_generic_param(self, param)
 596     }
 597
 598     fn visit_assoc_ty_constraint(&mut self, constraint: &'a AssocTyConstraint) {
 599         match constraint.kind {
 600             AssocTyConstraintKind::Bound { .. } =>
 601                 gate_feature_post!(&self, associated_type_bounds, constraint.span,
 602                     "associated type bounds are unstable"),
 603             _ => {}
 604         }
 605         visit::walk_assoc_ty_constraint(self, constraint)
 606     }
 607
 608     fn visit_trait_item(&mut self, ti: &'a ast::TraitItem) {
 609         match ti.kind {
 610             ast::TraitItemKind::Method(ref sig, ref block) => {
 611                 if block.is_none() {
 612                     self.check_extern(sig.header.ext);
 613                 }
 614                 if sig.decl.c_variadic() {
 615                     gate_feature_post!(&self, c_variadic, ti.span,
 616                                        "C-variadic functions are unstable");
 617                 }
 618                 if sig.header.constness.node == ast::Constness::Const {
 619                     gate_feature_post!(&self, const_fn, ti.span, "const fn is unstable");
 620                 }
 621             }
 622             ast::TraitItemKind::Type(_, ref default) => {
 623                 if let Some(ty) = default {
 624                     self.check_impl_trait(ty);
 625                     gate_feature_post!(&self, associated_type_defaults, ti.span,
 626                                        "associated type defaults are unstable");
 627                 }
 628                 self.check_gat(&ti.generics, ti.span);
 629             }
 630             _ => {}
 631         }
 632         visit::walk_trait_item(self, ti)
 633     }
 634
 635     fn visit_impl_item(&mut self, ii: &'a ast::ImplItem) {
 636         if ii.defaultness == ast::Defaultness::Default {
 637             gate_feature_post!(&self, specialization,
 638                               ii.span,
 639                               "specialization is unstable");
 640         }
 641
 642         match ii.kind {
 643             ast::ImplItemKind::Method(ref sig, _) => {
 644                 if sig.decl.c_variadic() {
 645                     gate_feature_post!(&self, c_variadic, ii.span,
 646                                        "C-variadic functions are unstable");
 647                 }
 648             }
 649             ast::ImplItemKind::TyAlias(ref ty) => {
 650                 self.check_impl_trait(ty);
 651                 self.check_gat(&ii.generics, ii.span);
 652             }
 653             _ => {}
 654         }
 655         visit::walk_impl_item(self, ii)
 656     }
 657
 658     fn visit_vis(&mut self, vis: &'a ast::Visibility) {
 659         if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.node {
 660             gate_feature_post!(&self, crate_visibility_modifier, vis.span,
 661                                "`crate` visibility modifier is experimental");
 662         }
 663         visit::walk_vis(self, vis)
 664     }
 665 }
 666
 667 pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
 668                     crate_edition: Edition, allow_features: &Option<Vec<String>>) -> Features {
 669     fn feature_removed(span_handler: &Handler, span: Span, reason: Option<&str>) {
 670         let mut err = struct_span_err!(span_handler, span, E0557, "feature has been removed");
 671         err.span_label(span, "feature has been removed");
 672         if let Some(reason) = reason {
 673             err.note(reason);
 674         }
 675         err.emit();
 676     }
 677
 678     let mut features = Features::new();
 679     let mut edition_enabled_features = FxHashMap::default();
 680
 681     for &edition in ALL_EDITIONS {
 682         if edition <= crate_edition {
 683             // The `crate_edition` implies its respective umbrella feature-gate
 684             // (i.e., `#![feature(rust_20XX_preview)]` isn't needed on edition 20XX).
 685             edition_enabled_features.insert(edition.feature_name(), edition);
 686         }
 687     }
 688
 689     for feature in active_features_up_to(crate_edition) {
 690         feature.set(&mut features, DUMMY_SP);
 691         edition_enabled_features.insert(feature.name, crate_edition);
 692     }
 693
 694     // Process the edition umbrella feature-gates first, to ensure
 695     // `edition_enabled_features` is completed before it's queried.
 696     for attr in krate_attrs {
 697         if !attr.check_name(sym::feature) {
 698             continue
 699         }
 700
 701         let list = match attr.meta_item_list() {
 702             Some(list) => list,
 703             None => continue,
 704         };
 705
 706         for mi in list {
 707             if !mi.is_word() {
 708                 continue;
 709             }
 710
 711             let name = mi.name_or_empty();
 712
 713             let edition = ALL_EDITIONS.iter().find(|e| name == e.feature_name()).copied();
 714             if let Some(edition) = edition {
 715                 if edition <= crate_edition {
 716                     continue;
 717                 }
 718
 719                 for feature in active_features_up_to(edition) {
 720                     // FIXME(Manishearth) there is currently no way to set
 721                     // lib features by edition
 722                     feature.set(&mut features, DUMMY_SP);
 723                     edition_enabled_features.insert(feature.name, edition);
 724                 }
 725             }
 726         }
 727     }
 728
 729     for attr in krate_attrs {
 730         if !attr.check_name(sym::feature) {
 731             continue
 732         }
 733
 734         let list = match attr.meta_item_list() {
 735             Some(list) => list,
 736             None => continue,
 737         };
 738
 739         let bad_input = |span| {
 740             struct_span_err!(span_handler, span, E0556, "malformed `feature` attribute input")
 741         };
 742
 743         for mi in list {
 744             let name = match mi.ident() {
 745                 Some(ident) if mi.is_word() => ident.name,
 746                 Some(ident) => {
 747                     bad_input(mi.span()).span_suggestion(
 748                         mi.span(),
 749                         "expected just one word",
 750                         format!("{}", ident.name),
 751                         Applicability::MaybeIncorrect,
 752                     ).emit();
 753                     continue
 754                 }
 755                 None => {
 756                     bad_input(mi.span()).span_label(mi.span(), "expected just one word").emit();
 757                     continue
 758                 }
 759             };
 760
 761             if let Some(edition) = edition_enabled_features.get(&name) {
 762                 struct_span_warn!(
 763                     span_handler,
 764                     mi.span(),
 765                     E0705,
 766                     "the feature `{}` is included in the Rust {} edition",
 767                     name,
 768                     edition,
 769                 ).emit();
 770                 continue;
 771             }
 772
 773             if ALL_EDITIONS.iter().any(|e| name == e.feature_name()) {
 774                 // Handled in the separate loop above.
 775                 continue;
 776             }
 777
 778             let removed = REMOVED_FEATURES.iter().find(|f| name == f.name);
 779             let stable_removed = STABLE_REMOVED_FEATURES.iter().find(|f| name == f.name);
 780             if let Some(Feature { state, .. }) = removed.or(stable_removed) {
 781                 if let FeatureState::Removed { reason }
 782                 | FeatureState::Stabilized { reason } = state
 783                 {
 784                     feature_removed(span_handler, mi.span(), *reason);
 785                     continue;
 786                 }
 787             }
 788
 789             if let Some(Feature { since, .. }) = ACCEPTED_FEATURES.iter().find(|f| name == f.name) {
 790                 let since = Some(Symbol::intern(since));
 791                 features.declared_lang_features.push((name, mi.span(), since));
 792                 continue;
 793             }
 794
 795             if let Some(allowed) = allow_features.as_ref() {
 796                 if allowed.iter().find(|&f| name.as_str() == *f).is_none() {
 797                     span_err!(span_handler, mi.span(), E0725,
 798                               "the feature `{}` is not in the list of allowed features",
 799                               name);
 800                     continue;
 801                 }
 802             }
 803
 804             if let Some(f) = ACTIVE_FEATURES.iter().find(|f| name == f.name) {
 805                 f.set(&mut features, mi.span());
 806                 features.declared_lang_features.push((name, mi.span(), None));
 807                 continue;
 808             }
 809
 810             features.declared_lib_features.push((name, mi.span()));
 811         }
 812     }
 813
 814     features
 815 }
 816
 817 fn active_features_up_to(edition: Edition) -> impl Iterator<Item=&'static Feature> {
 818     ACTIVE_FEATURES.iter()
 819     .filter(move |feature| {
 820         if let Some(feature_edition) = feature.edition {
 821             feature_edition <= edition
 822         } else {
 823             false
 824         }
 825     })
 826 }
 827
 828 pub fn check_crate(krate: &ast::Crate,
 829                    parse_sess: &ParseSess,
 830                    features: &Features,
 831                    unstable: UnstableFeatures) {
 832     maybe_stage_features(&parse_sess.span_diagnostic, krate, unstable);
 833     let mut visitor = PostExpansionVisitor { parse_sess, features };
 834
 835     let spans = parse_sess.gated_spans.spans.borrow();
 836     macro_rules! gate_all {
 837         ($gate:ident, $msg:literal) => {
 838             for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 839                 gate_feature!(&visitor, $gate, *span, $msg);
 840             }
 841         }
 842     }
 843     gate_all!(let_chains, "`let` expressions in this position are experimental");
 844     gate_all!(async_closure, "async closures are unstable");
 845     gate_all!(generators, "yield syntax is experimental");
 846     gate_all!(or_patterns, "or-patterns syntax is experimental");
 847     gate_all!(const_extern_fn, "`const extern fn` definitions are unstable");
 848     gate_all!(raw_ref_op, "raw address of syntax is experimental");
 849
 850     // All uses of `gate_all!` below this point were added in #65742,
 851     // and subsequently disabled (with the non-early gating readded).
 852     macro_rules! gate_all {
 853         ($gate:ident, $msg:literal) => {
 854             // FIXME(eddyb) do something more useful than always
 855             // disabling these uses of early feature-gatings.
 856             if false {
 857                 for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 858                     gate_feature!(&visitor, $gate, *span, $msg);
 859                 }
 860             }
 861         }
 862     }
 863
 864     gate_all!(trait_alias, "trait aliases are experimental");
 865     gate_all!(associated_type_bounds, "associated type bounds are unstable");
 866     gate_all!(crate_visibility_modifier, "`crate` visibility modifier is experimental");
 867     gate_all!(const_generics, "const generics are unstable");
 868     gate_all!(decl_macro, "`macro` is experimental");
 869     gate_all!(box_patterns, "box pattern syntax is experimental");
 870     gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
 871     gate_all!(try_blocks, "`try` blocks are unstable");
 872     gate_all!(label_break_value, "labels on blocks are unstable");
 873     gate_all!(box_syntax, "box expression syntax is experimental; you can call `Box::new` instead");
 874     // To avoid noise about type ascription in common syntax errors,
 875     // only emit if it is the *only* error. (Also check it last.)
 876     if parse_sess.span_diagnostic.err_count() == 0 {
 877         gate_all!(type_ascription, "type ascription is experimental");
 878     }
 879
 880     visit::walk_crate(&mut visitor, krate);
 881 }
 882
 883 #[derive(Clone, Copy, Hash)]
 884 pub enum UnstableFeatures {
 885     /// Hard errors for unstable features are active, as on beta/stable channels.
 886     Disallow,
 887     /// Allow features to be activated, as on nightly.
 888     Allow,
 889     /// Errors are bypassed for bootstrapping. This is required any time
 890     /// during the build that feature-related lints are set to warn or above
 891     /// because the build turns on warnings-as-errors and uses lots of unstable
 892     /// features. As a result, this is always required for building Rust itself.
 893     Cheat
 894 }
 895
 896 impl UnstableFeatures {
 897     pub fn from_environment() -> UnstableFeatures {
 898         // `true` if this is a feature-staged build, i.e., on the beta or stable channel.
 899         let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
 900         // `true` if we should enable unstable features for bootstrapping.
 901         let bootstrap = env::var("RUSTC_BOOTSTRAP").is_ok();
 902         match (disable_unstable_features, bootstrap) {
 903             (_, true) => UnstableFeatures::Cheat,
 904             (true, _) => UnstableFeatures::Disallow,
 905             (false, _) => UnstableFeatures::Allow
 906         }
 907     }
 908
 909     pub fn is_nightly_build(&self) -> bool {
 910         match *self {
 911             UnstableFeatures::Allow | UnstableFeatures::Cheat => true,
 912             UnstableFeatures::Disallow => false,
 913         }
 914     }
 915 }
 916
 917 fn maybe_stage_features(span_handler: &Handler, krate: &ast::Crate, unstable: UnstableFeatures) {
 918     if !unstable.is_nightly_build() {
 919         for attr in krate.attrs.iter().filter(|attr| attr.check_name(sym::feature)) {
 920             span_err!(
 921                 span_handler, attr.span, E0554,
 922                 "`#![feature]` may not be used on the {} release channel",
 923                 option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)")
 924             );
 925         }
 926     }
 927 }