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 pub const EXPLAIN_STMT_ATTR_SYNTAX: &str =
 154     "attributes on expressions are experimental";
 155
 156 pub const EXPLAIN_UNSIZED_TUPLE_COERCION: &str =
 157     "unsized tuple coercion is not stable enough for use and is subject to change";
 158
 159 struct PostExpansionVisitor<'a> {
 160     parse_sess: &'a ParseSess,
 161     features: &'a Features,
 162 }
 163
 164 macro_rules! gate_feature_post {
 165     ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {{
 166         let (cx, span) = ($cx, $span);
 167         if !span.allows_unstable(sym::$feature) {
 168             gate_feature!(cx, $feature, span, $explain)
 169         }
 170     }};
 171     ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {{
 172         let (cx, span) = ($cx, $span);
 173         if !span.allows_unstable(sym::$feature) {
 174             gate_feature!(cx, $feature, span, $explain, $level)
 175         }
 176     }}
 177 }
 178
 179 impl<'a> PostExpansionVisitor<'a> {
 180     fn check_abi(&self, abi: ast::StrLit) {
 181         let ast::StrLit { symbol_unescaped, span, .. } = abi;
 182
 183         match &*symbol_unescaped.as_str() {
 184             // Stable
 185             "Rust" |
 186             "C" |
 187             "cdecl" |
 188             "stdcall" |
 189             "fastcall" |
 190             "aapcs" |
 191             "win64" |
 192             "sysv64" |
 193             "system" => {}
 194             "rust-intrinsic" => {
 195                 gate_feature_post!(&self, intrinsics, span,
 196                                    "intrinsics are subject to change");
 197             },
 198             "platform-intrinsic" => {
 199                 gate_feature_post!(&self, platform_intrinsics, span,
 200                                    "platform intrinsics are experimental and possibly buggy");
 201             },
 202             "vectorcall" => {
 203                 gate_feature_post!(&self, abi_vectorcall, span,
 204                                    "vectorcall is experimental and subject to change");
 205             },
 206             "thiscall" => {
 207                 gate_feature_post!(&self, abi_thiscall, span,
 208                                    "thiscall is experimental and subject to change");
 209             },
 210             "rust-call" => {
 211                 gate_feature_post!(&self, unboxed_closures, span,
 212                                    "rust-call ABI is subject to change");
 213             },
 214             "ptx-kernel" => {
 215                 gate_feature_post!(&self, abi_ptx, span,
 216                                    "PTX ABIs are experimental and subject to change");
 217             },
 218             "unadjusted" => {
 219                 gate_feature_post!(&self, abi_unadjusted, span,
 220                                    "unadjusted ABI is an implementation detail and perma-unstable");
 221             },
 222             "msp430-interrupt" => {
 223                 gate_feature_post!(&self, abi_msp430_interrupt, span,
 224                                    "msp430-interrupt ABI is experimental and subject to change");
 225             },
 226             "x86-interrupt" => {
 227                 gate_feature_post!(&self, abi_x86_interrupt, span,
 228                                    "x86-interrupt ABI is experimental and subject to change");
 229             },
 230             "amdgpu-kernel" => {
 231                 gate_feature_post!(&self, abi_amdgpu_kernel, span,
 232                                    "amdgpu-kernel ABI is experimental and subject to change");
 233             },
 234             "efiapi" => {
 235                 gate_feature_post!(&self, abi_efiapi, span,
 236                                    "efiapi ABI is experimental and subject to change");
 237             },
 238             abi => {
 239                 self.parse_sess.span_diagnostic.delay_span_bug(
 240                     span,
 241                     &format!("unrecognized ABI not caught in lowering: {}", abi),
 242                 )
 243             }
 244         }
 245     }
 246
 247     fn check_extern(&self, ext: ast::Extern) {
 248         if let ast::Extern::Explicit(abi) = ext {
 249             self.check_abi(abi);
 250         }
 251     }
 252
 253     fn maybe_report_invalid_custom_discriminants(&self, variants: &[ast::Variant]) {
 254         let has_fields = variants.iter().any(|variant| match variant.data {
 255             VariantData::Tuple(..) | VariantData::Struct(..) => true,
 256             VariantData::Unit(..) => false,
 257         });
 258
 259         let discriminant_spans = variants.iter().filter(|variant| match variant.data {
 260             VariantData::Tuple(..) | VariantData::Struct(..) => false,
 261             VariantData::Unit(..) => true,
 262         })
 263         .filter_map(|variant| variant.disr_expr.as_ref().map(|c| c.value.span))
 264         .collect::<Vec<_>>();
 265
 266         if !discriminant_spans.is_empty() && has_fields {
 267             let mut err = feature_err(
 268                 self.parse_sess,
 269                 sym::arbitrary_enum_discriminant,
 270                 discriminant_spans.clone(),
 271                 crate::feature_gate::GateIssue::Language,
 272                 "custom discriminant values are not allowed in enums with tuple or struct variants",
 273             );
 274             for sp in discriminant_spans {
 275                 err.span_label(sp, "disallowed custom discriminant");
 276             }
 277             for variant in variants.iter() {
 278                 match &variant.data {
 279                     VariantData::Struct(..) => {
 280                         err.span_label(
 281                             variant.span,
 282                             "struct variant defined here",
 283                         );
 284                     }
 285                     VariantData::Tuple(..) => {
 286                         err.span_label(
 287                             variant.span,
 288                             "tuple variant defined here",
 289                         );
 290                     }
 291                     VariantData::Unit(..) => {}
 292                 }
 293             }
 294             err.emit();
 295         }
 296     }
 297
 298     fn check_gat(&self, generics: &ast::Generics, span: Span) {
 299         if !generics.params.is_empty() {
 300             gate_feature_post!(
 301                 &self,
 302                 generic_associated_types,
 303                 span,
 304                 "generic associated types are unstable"
 305             );
 306         }
 307         if !generics.where_clause.predicates.is_empty() {
 308             gate_feature_post!(
 309                 &self,
 310                 generic_associated_types,
 311                 span,
 312                 "where clauses on associated types are unstable"
 313             );
 314         }
 315     }
 316
 317     /// Feature gate `impl Trait` inside `type Alias = $type_expr;`.
 318     fn check_impl_trait(&self, ty: &ast::Ty) {
 319         struct ImplTraitVisitor<'a> {
 320             vis: &'a PostExpansionVisitor<'a>,
 321         }
 322         impl Visitor<'_> for ImplTraitVisitor<'_> {
 323             fn visit_ty(&mut self, ty: &ast::Ty) {
 324                 if let ast::TyKind::ImplTrait(..) = ty.kind {
 325                     gate_feature_post!(
 326                         &self.vis,
 327                         type_alias_impl_trait,
 328                         ty.span,
 329                         "`impl Trait` in type aliases is unstable"
 330                     );
 331                 }
 332                 visit::walk_ty(self, ty);
 333             }
 334         }
 335         ImplTraitVisitor { vis: self }.visit_ty(ty);
 336     }
 337 }
 338
 339 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 340     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 341         let attr_info =
 342             attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name)).map(|a| **a);
 343         // Check feature gates for built-in attributes.
 344         if let Some((.., AttributeGate::Gated(_, name, descr, has_feature))) = attr_info {
 345             gate_feature_fn!(self, has_feature, attr.span, name, descr, GateStrength::Hard);
 346         }
 347         // Check unstable flavors of the `#[doc]` attribute.
 348         if attr.check_name(sym::doc) {
 349             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 350                 macro_rules! gate_doc { ($($name:ident => $feature:ident)*) => {
 351                     $(if nested_meta.check_name(sym::$name) {
 352                         let msg = concat!("`#[doc(", stringify!($name), ")]` is experimental");
 353                         gate_feature!(self, $feature, attr.span, msg);
 354                     })*
 355                 }}
 356
 357                 gate_doc!(
 358                     include => external_doc
 359                     cfg => doc_cfg
 360                     masked => doc_masked
 361                     spotlight => doc_spotlight
 362                     alias => doc_alias
 363                     keyword => doc_keyword
 364                 );
 365             }
 366         }
 367     }
 368
 369     fn visit_name(&mut self, sp: Span, name: ast::Name) {
 370         if !name.as_str().is_ascii() {
 371             gate_feature_post!(
 372                 &self,
 373                 non_ascii_idents,
 374                 self.parse_sess.source_map().def_span(sp),
 375                 "non-ascii idents are not fully supported"
 376             );
 377         }
 378     }
 379
 380     fn visit_item(&mut self, i: &'a ast::Item) {
 381         match i.kind {
 382             ast::ItemKind::ForeignMod(ref foreign_module) => {
 383                 if let Some(abi) = foreign_module.abi {
 384                     self.check_abi(abi);
 385                 }
 386             }
 387
 388             ast::ItemKind::Fn(..) => {
 389                 if attr::contains_name(&i.attrs[..], sym::plugin_registrar) {
 390                     gate_feature_post!(&self, plugin_registrar, i.span,
 391                                        "compiler plugins are experimental and possibly buggy");
 392                 }
 393                 if attr::contains_name(&i.attrs[..], sym::start) {
 394                     gate_feature_post!(&self, start, i.span,
 395                                       "a `#[start]` function is an experimental \
 396                                        feature whose signature may change \
 397                                        over time");
 398                 }
 399                 if attr::contains_name(&i.attrs[..], sym::main) {
 400                     gate_feature_post!(&self, main, i.span,
 401                                        "declaration of a non-standard `#[main]` \
 402                                         function may change over time, for now \
 403                                         a top-level `fn main()` is required");
 404                 }
 405             }
 406
 407             ast::ItemKind::Struct(..) => {
 408                 for attr in attr::filter_by_name(&i.attrs[..], sym::repr) {
 409                     for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
 410                         if item.check_name(sym::simd) {
 411                             gate_feature_post!(&self, repr_simd, attr.span,
 412                                                "SIMD types are experimental and possibly buggy");
 413                         }
 414                     }
 415                 }
 416             }
 417
 418             ast::ItemKind::Enum(ast::EnumDef{ref variants, ..}, ..) => {
 419                 for variant in variants {
 420                     match (&variant.data, &variant.disr_expr) {
 421                         (ast::VariantData::Unit(..), _) => {},
 422                         (_, Some(disr_expr)) =>
 423                             gate_feature_post!(
 424                                 &self,
 425                                 arbitrary_enum_discriminant,
 426                                 disr_expr.value.span,
 427                                 "discriminants on non-unit variants are experimental"),
 428                         _ => {},
 429                     }
 430                 }
 431
 432                 let has_feature = self.features.arbitrary_enum_discriminant;
 433                 if !has_feature && !i.span.allows_unstable(sym::arbitrary_enum_discriminant) {
 434                     self.maybe_report_invalid_custom_discriminants(&variants);
 435                 }
 436             }
 437
 438             ast::ItemKind::Impl(_, polarity, defaultness, ..) => {
 439                 if polarity == ast::ImplPolarity::Negative {
 440                     gate_feature_post!(&self, optin_builtin_traits,
 441                                        i.span,
 442                                        "negative trait bounds are not yet fully implemented; \
 443                                         use marker types for now");
 444                 }
 445
 446                 if let ast::Defaultness::Default = defaultness {
 447                     gate_feature_post!(&self, specialization,
 448                                        i.span,
 449                                        "specialization is unstable");
 450                 }
 451             }
 452
 453             ast::ItemKind::Trait(ast::IsAuto::Yes, ..) => {
 454                 gate_feature_post!(&self, optin_builtin_traits,
 455                                    i.span,
 456                                    "auto traits are experimental and possibly buggy");
 457             }
 458
 459             ast::ItemKind::TraitAlias(..) => {
 460                 gate_feature_post!(
 461                     &self,
 462                     trait_alias,
 463                     i.span,
 464                     "trait aliases are experimental"
 465                 );
 466             }
 467
 468             ast::ItemKind::MacroDef(ast::MacroDef { legacy: false, .. }) => {
 469                 let msg = "`macro` is experimental";
 470                 gate_feature_post!(&self, decl_macro, i.span, msg);
 471             }
 472
 473             ast::ItemKind::TyAlias(ref ty, ..) => self.check_impl_trait(&ty),
 474
 475             _ => {}
 476         }
 477
 478         visit::walk_item(self, i);
 479     }
 480
 481     fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
 482         match i.kind {
 483             ast::ForeignItemKind::Fn(..) |
 484             ast::ForeignItemKind::Static(..) => {
 485                 let link_name = attr::first_attr_value_str_by_name(&i.attrs, sym::link_name);
 486                 let links_to_llvm = match link_name {
 487                     Some(val) => val.as_str().starts_with("llvm."),
 488                     _ => false
 489                 };
 490                 if links_to_llvm {
 491                     gate_feature_post!(&self, link_llvm_intrinsics, i.span,
 492                                        "linking to LLVM intrinsics is experimental");
 493                 }
 494             }
 495             ast::ForeignItemKind::Ty => {
 496                     gate_feature_post!(&self, extern_types, i.span,
 497                                        "extern types are experimental");
 498             }
 499             ast::ForeignItemKind::Macro(..) => {}
 500         }
 501
 502         visit::walk_foreign_item(self, i)
 503     }
 504
 505     fn visit_ty(&mut self, ty: &'a ast::Ty) {
 506         match ty.kind {
 507             ast::TyKind::BareFn(ref bare_fn_ty) => {
 508                 self.check_extern(bare_fn_ty.ext);
 509             }
 510             _ => {}
 511         }
 512         visit::walk_ty(self, ty)
 513     }
 514
 515     fn visit_expr(&mut self, e: &'a ast::Expr) {
 516         match e.kind {
 517             ast::ExprKind::Box(_) => {
 518                 gate_feature_post!(&self, box_syntax, e.span, EXPLAIN_BOX_SYNTAX);
 519             }
 520             ast::ExprKind::Type(..) => {
 521                 // To avoid noise about type ascription in common syntax errors, only emit if it
 522                 // is the *only* error.
 523                 if self.parse_sess.span_diagnostic.err_count() == 0 {
 524                     gate_feature_post!(&self, type_ascription, e.span,
 525                                        "type ascription is experimental");
 526                 }
 527             }
 528             ast::ExprKind::TryBlock(_) => {
 529                 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
 530             }
 531             ast::ExprKind::Block(_, opt_label) => {
 532                 if let Some(label) = opt_label {
 533                     gate_feature_post!(&self, label_break_value, label.ident.span,
 534                                     "labels on blocks are unstable");
 535                 }
 536             }
 537             _ => {}
 538         }
 539         visit::walk_expr(self, e)
 540     }
 541
 542     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
 543         match &pattern.kind {
 544             PatKind::Slice(pats) => {
 545                 for pat in &*pats {
 546                     let span = pat.span;
 547                     let inner_pat = match &pat.kind {
 548                         PatKind::Ident(.., Some(pat)) => pat,
 549                         _ => pat,
 550                     };
 551                     if inner_pat.is_rest() {
 552                         gate_feature_post!(
 553                             &self,
 554                             slice_patterns,
 555                             span,
 556                             "subslice patterns are unstable"
 557                         );
 558                     }
 559                 }
 560             }
 561             PatKind::Box(..) => {
 562                 gate_feature_post!(&self, box_patterns,
 563                                   pattern.span,
 564                                   "box pattern syntax is experimental");
 565             }
 566             PatKind::Range(_, _, Spanned { node: RangeEnd::Excluded, .. }) => {
 567                 gate_feature_post!(&self, exclusive_range_pattern, pattern.span,
 568                                    "exclusive range pattern syntax is experimental");
 569             }
 570             _ => {}
 571         }
 572         visit::walk_pat(self, pattern)
 573     }
 574
 575     fn visit_fn(&mut self,
 576                 fn_kind: FnKind<'a>,
 577                 fn_decl: &'a ast::FnDecl,
 578                 span: Span,
 579                 _node_id: NodeId) {
 580         if let Some(header) = fn_kind.header() {
 581             // Stability of const fn methods are covered in
 582             // `visit_trait_item` and `visit_impl_item` below; this is
 583             // because default methods don't pass through this point.
 584             self.check_extern(header.ext);
 585         }
 586
 587         if fn_decl.c_variadic() {
 588             gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
 589         }
 590
 591         visit::walk_fn(self, fn_kind, fn_decl, span)
 592     }
 593
 594     fn visit_generic_param(&mut self, param: &'a GenericParam) {
 595         match param.kind {
 596             GenericParamKind::Const { .. } =>
 597                 gate_feature_post!(&self, const_generics, param.ident.span,
 598                     "const generics are unstable"),
 599             _ => {}
 600         }
 601         visit::walk_generic_param(self, param)
 602     }
 603
 604     fn visit_assoc_ty_constraint(&mut self, constraint: &'a AssocTyConstraint) {
 605         match constraint.kind {
 606             AssocTyConstraintKind::Bound { .. } =>
 607                 gate_feature_post!(&self, associated_type_bounds, constraint.span,
 608                     "associated type bounds are unstable"),
 609             _ => {}
 610         }
 611         visit::walk_assoc_ty_constraint(self, constraint)
 612     }
 613
 614     fn visit_trait_item(&mut self, ti: &'a ast::TraitItem) {
 615         match ti.kind {
 616             ast::TraitItemKind::Method(ref sig, ref block) => {
 617                 if block.is_none() {
 618                     self.check_extern(sig.header.ext);
 619                 }
 620                 if sig.decl.c_variadic() {
 621                     gate_feature_post!(&self, c_variadic, ti.span,
 622                                        "C-variadic functions are unstable");
 623                 }
 624                 if sig.header.constness.node == ast::Constness::Const {
 625                     gate_feature_post!(&self, const_fn, ti.span, "const fn is unstable");
 626                 }
 627             }
 628             ast::TraitItemKind::Type(_, ref default) => {
 629                 if let Some(ty) = default {
 630                     self.check_impl_trait(ty);
 631                     gate_feature_post!(&self, associated_type_defaults, ti.span,
 632                                        "associated type defaults are unstable");
 633                 }
 634                 self.check_gat(&ti.generics, ti.span);
 635             }
 636             _ => {}
 637         }
 638         visit::walk_trait_item(self, ti)
 639     }
 640
 641     fn visit_impl_item(&mut self, ii: &'a ast::ImplItem) {
 642         if ii.defaultness == ast::Defaultness::Default {
 643             gate_feature_post!(&self, specialization,
 644                               ii.span,
 645                               "specialization is unstable");
 646         }
 647
 648         match ii.kind {
 649             ast::ImplItemKind::Method(ref sig, _) => {
 650                 if sig.decl.c_variadic() {
 651                     gate_feature_post!(&self, c_variadic, ii.span,
 652                                        "C-variadic functions are unstable");
 653                 }
 654             }
 655             ast::ImplItemKind::TyAlias(ref ty) => {
 656                 self.check_impl_trait(ty);
 657                 self.check_gat(&ii.generics, ii.span);
 658             }
 659             _ => {}
 660         }
 661         visit::walk_impl_item(self, ii)
 662     }
 663
 664     fn visit_vis(&mut self, vis: &'a ast::Visibility) {
 665         if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.node {
 666             gate_feature_post!(&self, crate_visibility_modifier, vis.span,
 667                                "`crate` visibility modifier is experimental");
 668         }
 669         visit::walk_vis(self, vis)
 670     }
 671 }
 672
 673 pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
 674                     crate_edition: Edition, allow_features: &Option<Vec<String>>) -> Features {
 675     fn feature_removed(span_handler: &Handler, span: Span, reason: Option<&str>) {
 676         let mut err = struct_span_err!(span_handler, span, E0557, "feature has been removed");
 677         err.span_label(span, "feature has been removed");
 678         if let Some(reason) = reason {
 679             err.note(reason);
 680         }
 681         err.emit();
 682     }
 683
 684     let mut features = Features::new();
 685     let mut edition_enabled_features = FxHashMap::default();
 686
 687     for &edition in ALL_EDITIONS {
 688         if edition <= crate_edition {
 689             // The `crate_edition` implies its respective umbrella feature-gate
 690             // (i.e., `#![feature(rust_20XX_preview)]` isn't needed on edition 20XX).
 691             edition_enabled_features.insert(edition.feature_name(), edition);
 692         }
 693     }
 694
 695     for feature in active_features_up_to(crate_edition) {
 696         feature.set(&mut features, DUMMY_SP);
 697         edition_enabled_features.insert(feature.name, crate_edition);
 698     }
 699
 700     // Process the edition umbrella feature-gates first, to ensure
 701     // `edition_enabled_features` is completed before it's queried.
 702     for attr in krate_attrs {
 703         if !attr.check_name(sym::feature) {
 704             continue
 705         }
 706
 707         let list = match attr.meta_item_list() {
 708             Some(list) => list,
 709             None => continue,
 710         };
 711
 712         for mi in list {
 713             if !mi.is_word() {
 714                 continue;
 715             }
 716
 717             let name = mi.name_or_empty();
 718
 719             let edition = ALL_EDITIONS.iter().find(|e| name == e.feature_name()).copied();
 720             if let Some(edition) = edition {
 721                 if edition <= crate_edition {
 722                     continue;
 723                 }
 724
 725                 for feature in active_features_up_to(edition) {
 726                     // FIXME(Manishearth) there is currently no way to set
 727                     // lib features by edition
 728                     feature.set(&mut features, DUMMY_SP);
 729                     edition_enabled_features.insert(feature.name, edition);
 730                 }
 731             }
 732         }
 733     }
 734
 735     for attr in krate_attrs {
 736         if !attr.check_name(sym::feature) {
 737             continue
 738         }
 739
 740         let list = match attr.meta_item_list() {
 741             Some(list) => list,
 742             None => continue,
 743         };
 744
 745         let bad_input = |span| {
 746             struct_span_err!(span_handler, span, E0556, "malformed `feature` attribute input")
 747         };
 748
 749         for mi in list {
 750             let name = match mi.ident() {
 751                 Some(ident) if mi.is_word() => ident.name,
 752                 Some(ident) => {
 753                     bad_input(mi.span()).span_suggestion(
 754                         mi.span(),
 755                         "expected just one word",
 756                         format!("{}", ident.name),
 757                         Applicability::MaybeIncorrect,
 758                     ).emit();
 759                     continue
 760                 }
 761                 None => {
 762                     bad_input(mi.span()).span_label(mi.span(), "expected just one word").emit();
 763                     continue
 764                 }
 765             };
 766
 767             if let Some(edition) = edition_enabled_features.get(&name) {
 768                 struct_span_warn!(
 769                     span_handler,
 770                     mi.span(),
 771                     E0705,
 772                     "the feature `{}` is included in the Rust {} edition",
 773                     name,
 774                     edition,
 775                 ).emit();
 776                 continue;
 777             }
 778
 779             if ALL_EDITIONS.iter().any(|e| name == e.feature_name()) {
 780                 // Handled in the separate loop above.
 781                 continue;
 782             }
 783
 784             let removed = REMOVED_FEATURES.iter().find(|f| name == f.name);
 785             let stable_removed = STABLE_REMOVED_FEATURES.iter().find(|f| name == f.name);
 786             if let Some(Feature { state, .. }) = removed.or(stable_removed) {
 787                 if let FeatureState::Removed { reason }
 788                 | FeatureState::Stabilized { reason } = state
 789                 {
 790                     feature_removed(span_handler, mi.span(), *reason);
 791                     continue;
 792                 }
 793             }
 794
 795             if let Some(Feature { since, .. }) = ACCEPTED_FEATURES.iter().find(|f| name == f.name) {
 796                 let since = Some(Symbol::intern(since));
 797                 features.declared_lang_features.push((name, mi.span(), since));
 798                 continue;
 799             }
 800
 801             if let Some(allowed) = allow_features.as_ref() {
 802                 if allowed.iter().find(|&f| name.as_str() == *f).is_none() {
 803                     span_err!(span_handler, mi.span(), E0725,
 804                               "the feature `{}` is not in the list of allowed features",
 805                               name);
 806                     continue;
 807                 }
 808             }
 809
 810             if let Some(f) = ACTIVE_FEATURES.iter().find(|f| name == f.name) {
 811                 f.set(&mut features, mi.span());
 812                 features.declared_lang_features.push((name, mi.span(), None));
 813                 continue;
 814             }
 815
 816             features.declared_lib_features.push((name, mi.span()));
 817         }
 818     }
 819
 820     features
 821 }
 822
 823 fn active_features_up_to(edition: Edition) -> impl Iterator<Item=&'static Feature> {
 824     ACTIVE_FEATURES.iter()
 825     .filter(move |feature| {
 826         if let Some(feature_edition) = feature.edition {
 827             feature_edition <= edition
 828         } else {
 829             false
 830         }
 831     })
 832 }
 833
 834 pub fn check_crate(krate: &ast::Crate,
 835                    parse_sess: &ParseSess,
 836                    features: &Features,
 837                    unstable: UnstableFeatures) {
 838     maybe_stage_features(&parse_sess.span_diagnostic, krate, unstable);
 839     let mut visitor = PostExpansionVisitor { parse_sess, features };
 840
 841     let spans = parse_sess.gated_spans.spans.borrow();
 842     macro_rules! gate_all {
 843         ($gate:ident, $msg:literal) => {
 844             for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 845                 gate_feature!(&visitor, $gate, *span, $msg);
 846             }
 847         }
 848     }
 849     gate_all!(let_chains, "`let` expressions in this position are experimental");
 850     gate_all!(async_closure, "async closures are unstable");
 851     gate_all!(generators, "yield syntax is experimental");
 852     gate_all!(or_patterns, "or-patterns syntax is experimental");
 853     gate_all!(const_extern_fn, "`const extern fn` definitions are unstable");
 854     gate_all!(raw_ref_op, "raw address of syntax is experimental");
 855
 856     // All uses of `gate_all!` below this point were added in #65742,
 857     // and subsequently disabled (with the non-early gating readded).
 858     macro_rules! gate_all {
 859         ($gate:ident, $msg:literal) => {
 860             // FIXME(eddyb) do something more useful than always
 861             // disabling these uses of early feature-gatings.
 862             if false {
 863                 for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 864                     gate_feature!(&visitor, $gate, *span, $msg);
 865                 }
 866             }
 867         }
 868     }
 869
 870     gate_all!(trait_alias, "trait aliases are experimental");
 871     gate_all!(associated_type_bounds, "associated type bounds are unstable");
 872     gate_all!(crate_visibility_modifier, "`crate` visibility modifier is experimental");
 873     gate_all!(const_generics, "const generics are unstable");
 874     gate_all!(decl_macro, "`macro` is experimental");
 875     gate_all!(box_patterns, "box pattern syntax is experimental");
 876     gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
 877     gate_all!(try_blocks, "`try` blocks are unstable");
 878     gate_all!(label_break_value, "labels on blocks are unstable");
 879     gate_all!(box_syntax, "box expression syntax is experimental; you can call `Box::new` instead");
 880     // To avoid noise about type ascription in common syntax errors,
 881     // only emit if it is the *only* error. (Also check it last.)
 882     if parse_sess.span_diagnostic.err_count() == 0 {
 883         gate_all!(type_ascription, "type ascription is experimental");
 884     }
 885
 886     visit::walk_crate(&mut visitor, krate);
 887 }
 888
 889 #[derive(Clone, Copy, Hash)]
 890 pub enum UnstableFeatures {
 891     /// Hard errors for unstable features are active, as on beta/stable channels.
 892     Disallow,
 893     /// Allow features to be activated, as on nightly.
 894     Allow,
 895     /// Errors are bypassed for bootstrapping. This is required any time
 896     /// during the build that feature-related lints are set to warn or above
 897     /// because the build turns on warnings-as-errors and uses lots of unstable
 898     /// features. As a result, this is always required for building Rust itself.
 899     Cheat
 900 }
 901
 902 impl UnstableFeatures {
 903     pub fn from_environment() -> UnstableFeatures {
 904         // `true` if this is a feature-staged build, i.e., on the beta or stable channel.
 905         let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
 906         // `true` if we should enable unstable features for bootstrapping.
 907         let bootstrap = env::var("RUSTC_BOOTSTRAP").is_ok();
 908         match (disable_unstable_features, bootstrap) {
 909             (_, true) => UnstableFeatures::Cheat,
 910             (true, _) => UnstableFeatures::Disallow,
 911             (false, _) => UnstableFeatures::Allow
 912         }
 913     }
 914
 915     pub fn is_nightly_build(&self) -> bool {
 916         match *self {
 917             UnstableFeatures::Allow | UnstableFeatures::Cheat => true,
 918             UnstableFeatures::Disallow => false,
 919         }
 920     }
 921 }
 922
 923 fn maybe_stage_features(span_handler: &Handler, krate: &ast::Crate, unstable: UnstableFeatures) {
 924     if !unstable.is_nightly_build() {
 925         for attr in krate.attrs.iter().filter(|attr| attr.check_name(sym::feature)) {
 926             span_err!(
 927                 span_handler, attr.span, E0554,
 928                 "`#![feature]` may not be used on the {} release channel",
 929                 option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)")
 930             );
 931         }
 932     }
 933 }