src/libsyntax/feature_gate/check.rs

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