src/libsyntax/feature_gate/check.rs

   1 use super::{active::{ACTIVE_FEATURES, Features}, Feature, State as FeatureState};
   2 use super::accepted::ACCEPTED_FEATURES;
   3 use super::removed::{REMOVED_FEATURES, STABLE_REMOVED_FEATURES};
   4 use super::builtin_attrs::{AttributeGate, BUILTIN_ATTRIBUTE_MAP};
   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
  23 use std::env;
  24 use std::num::NonZeroU32;
  25
  26 #[derive(Copy, Clone, Debug)]
  27 pub enum Stability {
  28     Unstable,
  29     // First argument is tracking issue link; second argument is an optional
  30     // help message, which defaults to "remove this attribute"
  31     Deprecated(&'static str, Option<&'static str>),
  32 }
  33
  34 macro_rules! gate_feature_fn {
  35     ($cx: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr, $level: expr) => {{
  36         let (cx, has_feature, span,
  37              name, explain, level) = (&*$cx, $has_feature, $span, $name, $explain, $level);
  38         let has_feature: bool = has_feature(&$cx.features);
  39         debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
  40         if !has_feature && !span.allows_unstable($name) {
  41             leveled_feature_err(cx.parse_sess, name, span, GateIssue::Language, explain, level)
  42                 .emit();
  43         }
  44     }}
  45 }
  46
  47 macro_rules! gate_feature {
  48     ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {
  49         gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
  50                          sym::$feature, $explain, GateStrength::Hard)
  51     };
  52     ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {
  53         gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
  54                          sym::$feature, $explain, $level)
  55     };
  56 }
  57
  58 pub fn check_attribute(attr: &ast::Attribute, parse_sess: &ParseSess, features: &Features) {
  59     PostExpansionVisitor { parse_sess, features }.visit_attribute(attr)
  60 }
  61
  62 fn find_lang_feature_issue(feature: Symbol) -> Option<NonZeroU32> {
  63     if let Some(info) = ACTIVE_FEATURES.iter().find(|t| t.name == feature) {
  64         // FIXME (#28244): enforce that active features have issue numbers
  65         // assert!(info.issue().is_some())
  66         info.issue()
  67     } else {
  68         // search in Accepted, Removed, or Stable Removed features
  69         let found = ACCEPTED_FEATURES
  70             .iter()
  71             .chain(REMOVED_FEATURES)
  72             .chain(STABLE_REMOVED_FEATURES)
  73             .find(|t| t.name == feature);
  74         match found {
  75             Some(found) => found.issue(),
  76             None => panic!("feature `{}` is not declared anywhere", feature),
  77         }
  78     }
  79 }
  80
  81 pub enum GateIssue {
  82     Language,
  83     Library(Option<NonZeroU32>)
  84 }
  85
  86 #[derive(Debug, Copy, Clone, PartialEq)]
  87 pub enum GateStrength {
  88     /// A hard error. (Most feature gates should use this.)
  89     Hard,
  90     /// Only a warning. (Use this only as backwards-compatibility demands.)
  91     Soft,
  92 }
  93
  94 pub fn emit_feature_err(
  95     sess: &ParseSess,
  96     feature: Symbol,
  97     span: Span,
  98     issue: GateIssue,
  99     explain: &str,
 100 ) {
 101     feature_err(sess, feature, span, issue, explain).emit();
 102 }
 103
 104 pub fn feature_err<'a, S: Into<MultiSpan>>(
 105     sess: &'a ParseSess,
 106     feature: Symbol,
 107     span: S,
 108     issue: GateIssue,
 109     explain: &str,
 110 ) -> DiagnosticBuilder<'a> {
 111     leveled_feature_err(sess, feature, span, issue, explain, GateStrength::Hard)
 112 }
 113
 114 fn leveled_feature_err<'a, S: Into<MultiSpan>>(
 115     sess: &'a ParseSess,
 116     feature: Symbol,
 117     span: S,
 118     issue: GateIssue,
 119     explain: &str,
 120     level: GateStrength,
 121 ) -> DiagnosticBuilder<'a> {
 122     let diag = &sess.span_diagnostic;
 123
 124     let issue = match issue {
 125         GateIssue::Language => find_lang_feature_issue(feature),
 126         GateIssue::Library(lib) => lib,
 127     };
 128
 129     let mut err = match level {
 130         GateStrength::Hard => {
 131             diag.struct_span_err_with_code(span, explain, stringify_error_code!(E0658))
 132         }
 133         GateStrength::Soft => diag.struct_span_warn(span, explain),
 134     };
 135
 136     if let Some(n) = issue {
 137         err.note(&format!(
 138             "for more information, see https://github.com/rust-lang/rust/issues/{}",
 139             n,
 140         ));
 141     }
 142
 143     // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
 144     if sess.unstable_features.is_nightly_build() {
 145         err.help(&format!("add `#![feature({})]` to the crate attributes to enable", feature));
 146     }
 147
 148     // If we're on stable and only emitting a "soft" warning, add a note to
 149     // clarify that the feature isn't "on" (rather than being on but
 150     // warning-worthy).
 151     if !sess.unstable_features.is_nightly_build() && level == GateStrength::Soft {
 152         err.help("a nightly build of the compiler is required to enable this feature");
 153     }
 154
 155     err
 156
 157 }
 158
 159 const EXPLAIN_BOX_SYNTAX: &str =
 160     "box expression syntax is experimental; you can call `Box::new` instead";
 161
 162 pub const EXPLAIN_STMT_ATTR_SYNTAX: &str =
 163     "attributes on expressions are experimental";
 164
 165 pub const EXPLAIN_ALLOW_INTERNAL_UNSTABLE: &str =
 166     "allow_internal_unstable side-steps feature gating and stability checks";
 167 pub const EXPLAIN_ALLOW_INTERNAL_UNSAFE: &str =
 168     "allow_internal_unsafe side-steps the unsafe_code lint";
 169
 170 pub const EXPLAIN_UNSIZED_TUPLE_COERCION: &str =
 171     "unsized tuple coercion is not stable enough for use and is subject to change";
 172
 173 struct PostExpansionVisitor<'a> {
 174     parse_sess: &'a ParseSess,
 175     features: &'a Features,
 176 }
 177
 178 macro_rules! gate_feature_post {
 179     ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {{
 180         let (cx, span) = ($cx, $span);
 181         if !span.allows_unstable(sym::$feature) {
 182             gate_feature!(cx, $feature, span, $explain)
 183         }
 184     }};
 185     ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {{
 186         let (cx, span) = ($cx, $span);
 187         if !span.allows_unstable(sym::$feature) {
 188             gate_feature!(cx, $feature, span, $explain, $level)
 189         }
 190     }}
 191 }
 192
 193 impl<'a> PostExpansionVisitor<'a> {
 194     fn check_abi(&self, abi: ast::Abi) {
 195         let ast::Abi { symbol, span } = abi;
 196
 197         match &*symbol.as_str() {
 198             // Stable
 199             "Rust" |
 200             "C" |
 201             "cdecl" |
 202             "stdcall" |
 203             "fastcall" |
 204             "aapcs" |
 205             "win64" |
 206             "sysv64" |
 207             "system" => {}
 208             "rust-intrinsic" => {
 209                 gate_feature_post!(&self, intrinsics, span,
 210                                    "intrinsics are subject to change");
 211             },
 212             "platform-intrinsic" => {
 213                 gate_feature_post!(&self, platform_intrinsics, span,
 214                                    "platform intrinsics are experimental and possibly buggy");
 215             },
 216             "vectorcall" => {
 217                 gate_feature_post!(&self, abi_vectorcall, span,
 218                                    "vectorcall is experimental and subject to change");
 219             },
 220             "thiscall" => {
 221                 gate_feature_post!(&self, abi_thiscall, span,
 222                                    "thiscall is experimental and subject to change");
 223             },
 224             "rust-call" => {
 225                 gate_feature_post!(&self, unboxed_closures, span,
 226                                    "rust-call ABI is subject to change");
 227             },
 228             "ptx-kernel" => {
 229                 gate_feature_post!(&self, abi_ptx, span,
 230                                    "PTX ABIs are experimental and subject to change");
 231             },
 232             "unadjusted" => {
 233                 gate_feature_post!(&self, abi_unadjusted, span,
 234                                    "unadjusted ABI is an implementation detail and perma-unstable");
 235             },
 236             "msp430-interrupt" => {
 237                 gate_feature_post!(&self, abi_msp430_interrupt, span,
 238                                    "msp430-interrupt ABI is experimental and subject to change");
 239             },
 240             "x86-interrupt" => {
 241                 gate_feature_post!(&self, abi_x86_interrupt, span,
 242                                    "x86-interrupt ABI is experimental and subject to change");
 243             },
 244             "amdgpu-kernel" => {
 245                 gate_feature_post!(&self, abi_amdgpu_kernel, span,
 246                                    "amdgpu-kernel ABI is experimental and subject to change");
 247             },
 248             "efiapi" => {
 249                 gate_feature_post!(&self, abi_efiapi, span,
 250                                    "efiapi ABI is experimental and subject to change");
 251             },
 252             abi => {
 253                 self.parse_sess.span_diagnostic.delay_span_bug(
 254                     span,
 255                     &format!("unrecognized ABI not caught in lowering: {}", abi),
 256                 )
 257             }
 258         }
 259     }
 260
 261     fn maybe_report_invalid_custom_discriminants(&self, variants: &[ast::Variant]) {
 262         let has_fields = variants.iter().any(|variant| match variant.data {
 263             VariantData::Tuple(..) | VariantData::Struct(..) => true,
 264             VariantData::Unit(..) => false,
 265         });
 266
 267         let discriminant_spans = variants.iter().filter(|variant| match variant.data {
 268             VariantData::Tuple(..) | VariantData::Struct(..) => false,
 269             VariantData::Unit(..) => true,
 270         })
 271         .filter_map(|variant| variant.disr_expr.as_ref().map(|c| c.value.span))
 272         .collect::<Vec<_>>();
 273
 274         if !discriminant_spans.is_empty() && has_fields {
 275             let mut err = feature_err(
 276                 self.parse_sess,
 277                 sym::arbitrary_enum_discriminant,
 278                 discriminant_spans.clone(),
 279                 crate::feature_gate::GateIssue::Language,
 280                 "custom discriminant values are not allowed in enums with tuple or struct variants",
 281             );
 282             for sp in discriminant_spans {
 283                 err.span_label(sp, "disallowed custom discriminant");
 284             }
 285             for variant in variants.iter() {
 286                 match &variant.data {
 287                     VariantData::Struct(..) => {
 288                         err.span_label(
 289                             variant.span,
 290                             "struct variant defined here",
 291                         );
 292                     }
 293                     VariantData::Tuple(..) => {
 294                         err.span_label(
 295                             variant.span,
 296                             "tuple variant defined here",
 297                         );
 298                     }
 299                     VariantData::Unit(..) => {}
 300                 }
 301             }
 302             err.emit();
 303         }
 304     }
 305
 306     fn check_gat(&self, generics: &ast::Generics, span: Span) {
 307         if !generics.params.is_empty() {
 308             gate_feature_post!(
 309                 &self,
 310                 generic_associated_types,
 311                 span,
 312                 "generic associated types are unstable"
 313             );
 314         }
 315         if !generics.where_clause.predicates.is_empty() {
 316             gate_feature_post!(
 317                 &self,
 318                 generic_associated_types,
 319                 span,
 320                 "where clauses on associated types are unstable"
 321             );
 322         }
 323     }
 324
 325     /// Feature gate `impl Trait` inside `type Alias = $type_expr;`.
 326     fn check_impl_trait(&self, ty: &ast::Ty) {
 327         struct ImplTraitVisitor<'a> {
 328             vis: &'a PostExpansionVisitor<'a>,
 329         }
 330         impl Visitor<'_> for ImplTraitVisitor<'_> {
 331             fn visit_ty(&mut self, ty: &ast::Ty) {
 332                 if let ast::TyKind::ImplTrait(..) = ty.kind {
 333                     gate_feature_post!(
 334                         &self.vis,
 335                         type_alias_impl_trait,
 336                         ty.span,
 337                         "`impl Trait` in type aliases is unstable"
 338                     );
 339                 }
 340                 visit::walk_ty(self, ty);
 341             }
 342         }
 343         ImplTraitVisitor { vis: self }.visit_ty(ty);
 344     }
 345 }
 346
 347 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 348     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 349         let attr_info =
 350             attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name)).map(|a| **a);
 351         // Check feature gates for built-in attributes.
 352         if let Some((.., AttributeGate::Gated(_, name, descr, has_feature))) = attr_info {
 353             gate_feature_fn!(self, has_feature, attr.span, name, descr, GateStrength::Hard);
 354         }
 355         // Check unstable flavors of the `#[doc]` attribute.
 356         if attr.check_name(sym::doc) {
 357             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 358                 macro_rules! gate_doc { ($($name:ident => $feature:ident)*) => {
 359                     $(if nested_meta.check_name(sym::$name) {
 360                         let msg = concat!("`#[doc(", stringify!($name), ")]` is experimental");
 361                         gate_feature!(self, $feature, attr.span, msg);
 362                     })*
 363                 }}
 364
 365                 gate_doc!(
 366                     include => external_doc
 367                     cfg => doc_cfg
 368                     masked => doc_masked
 369                     spotlight => doc_spotlight
 370                     alias => doc_alias
 371                     keyword => doc_keyword
 372                 );
 373             }
 374         }
 375     }
 376
 377     fn visit_name(&mut self, sp: Span, name: ast::Name) {
 378         if !name.as_str().is_ascii() {
 379             gate_feature_post!(
 380                 &self,
 381                 non_ascii_idents,
 382                 self.parse_sess.source_map().def_span(sp),
 383                 "non-ascii idents are not fully supported"
 384             );
 385         }
 386     }
 387
 388     fn visit_item(&mut self, i: &'a ast::Item) {
 389         match i.kind {
 390             ast::ItemKind::ForeignMod(ref foreign_module) => {
 391                 self.check_abi(foreign_module.abi);
 392             }
 393
 394             ast::ItemKind::Fn(..) => {
 395                 if attr::contains_name(&i.attrs[..], sym::plugin_registrar) {
 396                     gate_feature_post!(&self, plugin_registrar, i.span,
 397                                        "compiler plugins are experimental and possibly buggy");
 398                 }
 399                 if attr::contains_name(&i.attrs[..], sym::start) {
 400                     gate_feature_post!(&self, start, i.span,
 401                                       "a `#[start]` function is an experimental \
 402                                        feature whose signature may change \
 403                                        over time");
 404                 }
 405                 if attr::contains_name(&i.attrs[..], sym::main) {
 406                     gate_feature_post!(&self, main, i.span,
 407                                        "declaration of a non-standard `#[main]` \
 408                                         function may change over time, for now \
 409                                         a top-level `fn main()` is required");
 410                 }
 411             }
 412
 413             ast::ItemKind::Struct(..) => {
 414                 for attr in attr::filter_by_name(&i.attrs[..], sym::repr) {
 415                     for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
 416                         if item.check_name(sym::simd) {
 417                             gate_feature_post!(&self, repr_simd, attr.span,
 418                                                "SIMD types are experimental and possibly buggy");
 419                         }
 420                     }
 421                 }
 422             }
 423
 424             ast::ItemKind::Enum(ast::EnumDef{ref variants, ..}, ..) => {
 425                 for variant in variants {
 426                     match (&variant.data, &variant.disr_expr) {
 427                         (ast::VariantData::Unit(..), _) => {},
 428                         (_, Some(disr_expr)) =>
 429                             gate_feature_post!(
 430                                 &self,
 431                                 arbitrary_enum_discriminant,
 432                                 disr_expr.value.span,
 433                                 "discriminants on non-unit variants are experimental"),
 434                         _ => {},
 435                     }
 436                 }
 437
 438                 let has_feature = self.features.arbitrary_enum_discriminant;
 439                 if !has_feature && !i.span.allows_unstable(sym::arbitrary_enum_discriminant) {
 440                     self.maybe_report_invalid_custom_discriminants(&variants);
 441                 }
 442             }
 443
 444             ast::ItemKind::Impl(_, polarity, defaultness, ..) => {
 445                 if polarity == ast::ImplPolarity::Negative {
 446                     gate_feature_post!(&self, optin_builtin_traits,
 447                                        i.span,
 448                                        "negative trait bounds are not yet fully implemented; \
 449                                         use marker types for now");
 450                 }
 451
 452                 if let ast::Defaultness::Default = defaultness {
 453                     gate_feature_post!(&self, specialization,
 454                                        i.span,
 455                                        "specialization is unstable");
 456                 }
 457             }
 458
 459             ast::ItemKind::Trait(ast::IsAuto::Yes, ..) => {
 460                 gate_feature_post!(&self, optin_builtin_traits,
 461                                    i.span,
 462                                    "auto traits are experimental and possibly buggy");
 463             }
 464
 465             ast::ItemKind::TraitAlias(..) => {
 466                 gate_feature_post!(
 467                     &self,
 468                     trait_alias,
 469                     i.span,
 470                     "trait aliases are experimental"
 471                 );
 472             }
 473
 474             ast::ItemKind::MacroDef(ast::MacroDef { legacy: false, .. }) => {
 475                 let msg = "`macro` is experimental";
 476                 gate_feature_post!(&self, decl_macro, i.span, msg);
 477             }
 478
 479             ast::ItemKind::TyAlias(ref ty, ..) => self.check_impl_trait(&ty),
 480
 481             _ => {}
 482         }
 483
 484         visit::walk_item(self, i);
 485     }
 486
 487     fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
 488         match i.kind {
 489             ast::ForeignItemKind::Fn(..) |
 490             ast::ForeignItemKind::Static(..) => {
 491                 let link_name = attr::first_attr_value_str_by_name(&i.attrs, sym::link_name);
 492                 let links_to_llvm = match link_name {
 493                     Some(val) => val.as_str().starts_with("llvm."),
 494                     _ => false
 495                 };
 496                 if links_to_llvm {
 497                     gate_feature_post!(&self, link_llvm_intrinsics, i.span,
 498                                        "linking to LLVM intrinsics is experimental");
 499                 }
 500             }
 501             ast::ForeignItemKind::Ty => {
 502                     gate_feature_post!(&self, extern_types, i.span,
 503                                        "extern types are experimental");
 504             }
 505             ast::ForeignItemKind::Macro(..) => {}
 506         }
 507
 508         visit::walk_foreign_item(self, i)
 509     }
 510
 511     fn visit_ty(&mut self, ty: &'a ast::Ty) {
 512         match ty.kind {
 513             ast::TyKind::BareFn(ref bare_fn_ty) => {
 514                 self.check_abi(bare_fn_ty.abi);
 515             }
 516             ast::TyKind::Never => {
 517                 gate_feature_post!(&self, never_type, ty.span,
 518                                    "The `!` type is experimental");
 519             }
 520             _ => {}
 521         }
 522         visit::walk_ty(self, ty)
 523     }
 524
 525     fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FunctionRetTy) {
 526         if let ast::FunctionRetTy::Ty(ref output_ty) = *ret_ty {
 527             if let ast::TyKind::Never = output_ty.kind {
 528                 // Do nothing.
 529             } else {
 530                 self.visit_ty(output_ty)
 531             }
 532         }
 533     }
 534
 535     fn visit_expr(&mut self, e: &'a ast::Expr) {
 536         match e.kind {
 537             ast::ExprKind::Box(_) => {
 538                 gate_feature_post!(&self, box_syntax, e.span, EXPLAIN_BOX_SYNTAX);
 539             }
 540             ast::ExprKind::Type(..) => {
 541                 // To avoid noise about type ascription in common syntax errors, only emit if it
 542                 // is the *only* error.
 543                 if self.parse_sess.span_diagnostic.err_count() == 0 {
 544                     gate_feature_post!(&self, type_ascription, e.span,
 545                                        "type ascription is experimental");
 546                 }
 547             }
 548             ast::ExprKind::TryBlock(_) => {
 549                 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
 550             }
 551             ast::ExprKind::Block(_, opt_label) => {
 552                 if let Some(label) = opt_label {
 553                     gate_feature_post!(&self, label_break_value, label.ident.span,
 554                                     "labels on blocks are unstable");
 555                 }
 556             }
 557             _ => {}
 558         }
 559         visit::walk_expr(self, e)
 560     }
 561
 562     fn visit_arm(&mut self, arm: &'a ast::Arm) {
 563         visit::walk_arm(self, arm)
 564     }
 565
 566     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
 567         match &pattern.kind {
 568             PatKind::Slice(pats) => {
 569                 for pat in &*pats {
 570                     let span = pat.span;
 571                     let inner_pat = match &pat.kind {
 572                         PatKind::Ident(.., Some(pat)) => pat,
 573                         _ => pat,
 574                     };
 575                     if inner_pat.is_rest() {
 576                         gate_feature_post!(
 577                             &self,
 578                             slice_patterns,
 579                             span,
 580                             "subslice patterns are unstable"
 581                         );
 582                     }
 583                 }
 584             }
 585             PatKind::Box(..) => {
 586                 gate_feature_post!(&self, box_patterns,
 587                                   pattern.span,
 588                                   "box pattern syntax is experimental");
 589             }
 590             PatKind::Range(_, _, Spanned { node: RangeEnd::Excluded, .. }) => {
 591                 gate_feature_post!(&self, exclusive_range_pattern, pattern.span,
 592                                    "exclusive range pattern syntax is experimental");
 593             }
 594             _ => {}
 595         }
 596         visit::walk_pat(self, pattern)
 597     }
 598
 599     fn visit_fn(&mut self,
 600                 fn_kind: FnKind<'a>,
 601                 fn_decl: &'a ast::FnDecl,
 602                 span: Span,
 603                 _node_id: NodeId) {
 604         if let Some(header) = fn_kind.header() {
 605             // Stability of const fn methods are covered in
 606             // `visit_trait_item` and `visit_impl_item` below; this is
 607             // because default methods don't pass through this point.
 608             self.check_abi(header.abi);
 609         }
 610
 611         if fn_decl.c_variadic() {
 612             gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
 613         }
 614
 615         visit::walk_fn(self, fn_kind, fn_decl, span)
 616     }
 617
 618     fn visit_generic_param(&mut self, param: &'a GenericParam) {
 619         match param.kind {
 620             GenericParamKind::Const { .. } =>
 621                 gate_feature_post!(&self, const_generics, param.ident.span,
 622                     "const generics are unstable"),
 623             _ => {}
 624         }
 625         visit::walk_generic_param(self, param)
 626     }
 627
 628     fn visit_assoc_ty_constraint(&mut self, constraint: &'a AssocTyConstraint) {
 629         match constraint.kind {
 630             AssocTyConstraintKind::Bound { .. } =>
 631                 gate_feature_post!(&self, associated_type_bounds, constraint.span,
 632                     "associated type bounds are unstable"),
 633             _ => {}
 634         }
 635         visit::walk_assoc_ty_constraint(self, constraint)
 636     }
 637
 638     fn visit_trait_item(&mut self, ti: &'a ast::TraitItem) {
 639         match ti.kind {
 640             ast::TraitItemKind::Method(ref sig, ref block) => {
 641                 if block.is_none() {
 642                     self.check_abi(sig.header.abi);
 643                 }
 644                 if sig.decl.c_variadic() {
 645                     gate_feature_post!(&self, c_variadic, ti.span,
 646                                        "C-variadic functions are unstable");
 647                 }
 648                 if sig.header.constness.node == ast::Constness::Const {
 649                     gate_feature_post!(&self, const_fn, ti.span, "const fn is unstable");
 650                 }
 651             }
 652             ast::TraitItemKind::Type(_, ref default) => {
 653                 if let Some(ty) = default {
 654                     self.check_impl_trait(ty);
 655                     gate_feature_post!(&self, associated_type_defaults, ti.span,
 656                                        "associated type defaults are unstable");
 657                 }
 658                 self.check_gat(&ti.generics, ti.span);
 659             }
 660             _ => {}
 661         }
 662         visit::walk_trait_item(self, ti)
 663     }
 664
 665     fn visit_impl_item(&mut self, ii: &'a ast::ImplItem) {
 666         if ii.defaultness == ast::Defaultness::Default {
 667             gate_feature_post!(&self, specialization,
 668                               ii.span,
 669                               "specialization is unstable");
 670         }
 671
 672         match ii.kind {
 673             ast::ImplItemKind::Method(ref sig, _) => {
 674                 if sig.decl.c_variadic() {
 675                     gate_feature_post!(&self, c_variadic, ii.span,
 676                                        "C-variadic functions are unstable");
 677                 }
 678             }
 679             ast::ImplItemKind::TyAlias(ref ty) => {
 680                 self.check_impl_trait(ty);
 681                 self.check_gat(&ii.generics, ii.span);
 682             }
 683             _ => {}
 684         }
 685         visit::walk_impl_item(self, ii)
 686     }
 687
 688     fn visit_vis(&mut self, vis: &'a ast::Visibility) {
 689         if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.node {
 690             gate_feature_post!(&self, crate_visibility_modifier, vis.span,
 691                                "`crate` visibility modifier is experimental");
 692         }
 693         visit::walk_vis(self, vis)
 694     }
 695 }
 696
 697 pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
 698                     crate_edition: Edition, allow_features: &Option<Vec<String>>) -> Features {
 699     fn feature_removed(span_handler: &Handler, span: Span, reason: Option<&str>) {
 700         let mut err = struct_span_err!(span_handler, span, E0557, "feature has been removed");
 701         if let Some(reason) = reason {
 702             err.span_note(span, reason);
 703         } else {
 704             err.span_label(span, "feature has been removed");
 705         }
 706         err.emit();
 707     }
 708
 709     let mut features = Features::new();
 710     let mut edition_enabled_features = FxHashMap::default();
 711
 712     for &edition in ALL_EDITIONS {
 713         if edition <= crate_edition {
 714             // The `crate_edition` implies its respective umbrella feature-gate
 715             // (i.e., `#![feature(rust_20XX_preview)]` isn't needed on edition 20XX).
 716             edition_enabled_features.insert(edition.feature_name(), edition);
 717         }
 718     }
 719
 720     for feature in active_features_up_to(crate_edition) {
 721         feature.set(&mut features, DUMMY_SP);
 722         edition_enabled_features.insert(feature.name, crate_edition);
 723     }
 724
 725     // Process the edition umbrella feature-gates first, to ensure
 726     // `edition_enabled_features` is completed before it's queried.
 727     for attr in krate_attrs {
 728         if !attr.check_name(sym::feature) {
 729             continue
 730         }
 731
 732         let list = match attr.meta_item_list() {
 733             Some(list) => list,
 734             None => continue,
 735         };
 736
 737         for mi in list {
 738             if !mi.is_word() {
 739                 continue;
 740             }
 741
 742             let name = mi.name_or_empty();
 743
 744             let edition = ALL_EDITIONS.iter().find(|e| name == e.feature_name()).copied();
 745             if let Some(edition) = edition {
 746                 if edition <= crate_edition {
 747                     continue;
 748                 }
 749
 750                 for feature in active_features_up_to(edition) {
 751                     // FIXME(Manishearth) there is currently no way to set
 752                     // lib features by edition
 753                     feature.set(&mut features, DUMMY_SP);
 754                     edition_enabled_features.insert(feature.name, edition);
 755                 }
 756             }
 757         }
 758     }
 759
 760     for attr in krate_attrs {
 761         if !attr.check_name(sym::feature) {
 762             continue
 763         }
 764
 765         let list = match attr.meta_item_list() {
 766             Some(list) => list,
 767             None => continue,
 768         };
 769
 770         let bad_input = |span| {
 771             struct_span_err!(span_handler, span, E0556, "malformed `feature` attribute input")
 772         };
 773
 774         for mi in list {
 775             let name = match mi.ident() {
 776                 Some(ident) if mi.is_word() => ident.name,
 777                 Some(ident) => {
 778                     bad_input(mi.span()).span_suggestion(
 779                         mi.span(),
 780                         "expected just one word",
 781                         format!("{}", ident.name),
 782                         Applicability::MaybeIncorrect,
 783                     ).emit();
 784                     continue
 785                 }
 786                 None => {
 787                     bad_input(mi.span()).span_label(mi.span(), "expected just one word").emit();
 788                     continue
 789                 }
 790             };
 791
 792             if let Some(edition) = edition_enabled_features.get(&name) {
 793                 struct_span_warn!(
 794                     span_handler,
 795                     mi.span(),
 796                     E0705,
 797                     "the feature `{}` is included in the Rust {} edition",
 798                     name,
 799                     edition,
 800                 ).emit();
 801                 continue;
 802             }
 803
 804             if ALL_EDITIONS.iter().any(|e| name == e.feature_name()) {
 805                 // Handled in the separate loop above.
 806                 continue;
 807             }
 808
 809             let removed = REMOVED_FEATURES.iter().find(|f| name == f.name);
 810             let stable_removed = STABLE_REMOVED_FEATURES.iter().find(|f| name == f.name);
 811             if let Some(Feature { state, .. }) = removed.or(stable_removed) {
 812                 if let FeatureState::Removed { reason }
 813                 | FeatureState::Stabilized { reason } = state
 814                 {
 815                     feature_removed(span_handler, mi.span(), *reason);
 816                     continue;
 817                 }
 818             }
 819
 820             if let Some(Feature { since, .. }) = ACCEPTED_FEATURES.iter().find(|f| name == f.name) {
 821                 let since = Some(Symbol::intern(since));
 822                 features.declared_lang_features.push((name, mi.span(), since));
 823                 continue;
 824             }
 825
 826             if let Some(allowed) = allow_features.as_ref() {
 827                 if allowed.iter().find(|&f| name.as_str() == *f).is_none() {
 828                     span_err!(span_handler, mi.span(), E0725,
 829                               "the feature `{}` is not in the list of allowed features",
 830                               name);
 831                     continue;
 832                 }
 833             }
 834
 835             if let Some(f) = ACTIVE_FEATURES.iter().find(|f| name == f.name) {
 836                 f.set(&mut features, mi.span());
 837                 features.declared_lang_features.push((name, mi.span(), None));
 838                 continue;
 839             }
 840
 841             features.declared_lib_features.push((name, mi.span()));
 842         }
 843     }
 844
 845     features
 846 }
 847
 848 fn active_features_up_to(edition: Edition) -> impl Iterator<Item=&'static Feature> {
 849     ACTIVE_FEATURES.iter()
 850     .filter(move |feature| {
 851         if let Some(feature_edition) = feature.edition {
 852             feature_edition <= edition
 853         } else {
 854             false
 855         }
 856     })
 857 }
 858
 859 pub fn check_crate(krate: &ast::Crate,
 860                    parse_sess: &ParseSess,
 861                    features: &Features,
 862                    unstable: UnstableFeatures) {
 863     maybe_stage_features(&parse_sess.span_diagnostic, krate, unstable);
 864     let mut visitor = PostExpansionVisitor { parse_sess, features };
 865
 866     let spans = parse_sess.gated_spans.spans.borrow();
 867     macro_rules! gate_all {
 868         ($gate:ident, $msg:literal) => {
 869             for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 870                 gate_feature!(&visitor, $gate, *span, $msg);
 871             }
 872         }
 873     }
 874     gate_all!(let_chains, "`let` expressions in this position are experimental");
 875     gate_all!(async_closure, "async closures are unstable");
 876     gate_all!(generators, "yield syntax is experimental");
 877     gate_all!(or_patterns, "or-patterns syntax is experimental");
 878     gate_all!(const_extern_fn, "`const extern fn` definitions are unstable");
 879
 880     // All uses of `gate_all!` below this point were added in #65742,
 881     // and subsequently disabled (with the non-early gating readded).
 882     macro_rules! gate_all {
 883         ($gate:ident, $msg:literal) => {
 884             // FIXME(eddyb) do something more useful than always
 885             // disabling these uses of early feature-gatings.
 886             if false {
 887                 for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 888                     gate_feature!(&visitor, $gate, *span, $msg);
 889                 }
 890             }
 891         }
 892     }
 893
 894     gate_all!(trait_alias, "trait aliases are experimental");
 895     gate_all!(associated_type_bounds, "associated type bounds are unstable");
 896     gate_all!(crate_visibility_modifier, "`crate` visibility modifier is experimental");
 897     gate_all!(const_generics, "const generics are unstable");
 898     gate_all!(decl_macro, "`macro` is experimental");
 899     gate_all!(box_patterns, "box pattern syntax is experimental");
 900     gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
 901     gate_all!(try_blocks, "`try` blocks are unstable");
 902     gate_all!(label_break_value, "labels on blocks are unstable");
 903     gate_all!(box_syntax, "box expression syntax is experimental; you can call `Box::new` instead");
 904     // To avoid noise about type ascription in common syntax errors,
 905     // only emit if it is the *only* error. (Also check it last.)
 906     if parse_sess.span_diagnostic.err_count() == 0 {
 907         gate_all!(type_ascription, "type ascription is experimental");
 908     }
 909
 910     visit::walk_crate(&mut visitor, krate);
 911 }
 912
 913 #[derive(Clone, Copy, Hash)]
 914 pub enum UnstableFeatures {
 915     /// Hard errors for unstable features are active, as on beta/stable channels.
 916     Disallow,
 917     /// Allow features to be activated, as on nightly.
 918     Allow,
 919     /// Errors are bypassed for bootstrapping. This is required any time
 920     /// during the build that feature-related lints are set to warn or above
 921     /// because the build turns on warnings-as-errors and uses lots of unstable
 922     /// features. As a result, this is always required for building Rust itself.
 923     Cheat
 924 }
 925
 926 impl UnstableFeatures {
 927     pub fn from_environment() -> UnstableFeatures {
 928         // `true` if this is a feature-staged build, i.e., on the beta or stable channel.
 929         let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
 930         // `true` if we should enable unstable features for bootstrapping.
 931         let bootstrap = env::var("RUSTC_BOOTSTRAP").is_ok();
 932         match (disable_unstable_features, bootstrap) {
 933             (_, true) => UnstableFeatures::Cheat,
 934             (true, _) => UnstableFeatures::Disallow,
 935             (false, _) => UnstableFeatures::Allow
 936         }
 937     }
 938
 939     pub fn is_nightly_build(&self) -> bool {
 940         match *self {
 941             UnstableFeatures::Allow | UnstableFeatures::Cheat => true,
 942             UnstableFeatures::Disallow => false,
 943         }
 944     }
 945 }
 946
 947 fn maybe_stage_features(span_handler: &Handler, krate: &ast::Crate, unstable: UnstableFeatures) {
 948     if !unstable.is_nightly_build() {
 949         for attr in krate.attrs.iter().filter(|attr| attr.check_name(sym::feature)) {
 950             span_err!(
 951                 span_handler, attr.span, E0554,
 952                 "`#![feature]` may not be used on the {} release channel",
 953                 option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)")
 954             );
 955         }
 956     }
 957 }