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
 326 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 327     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 328         let attr_info =
 329             attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name)).map(|a| **a);
 330         // Check feature gates for built-in attributes.
 331         if let Some((.., AttributeGate::Gated(_, name, descr, has_feature))) = attr_info {
 332             gate_feature_fn!(self, has_feature, attr.span, name, descr, GateStrength::Hard);
 333         }
 334         // Check unstable flavors of the `#[doc]` attribute.
 335         if attr.check_name(sym::doc) {
 336             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 337                 macro_rules! gate_doc { ($($name:ident => $feature:ident)*) => {
 338                     $(if nested_meta.check_name(sym::$name) {
 339                         let msg = concat!("`#[doc(", stringify!($name), ")]` is experimental");
 340                         gate_feature!(self, $feature, attr.span, msg);
 341                     })*
 342                 }}
 343
 344                 gate_doc!(
 345                     include => external_doc
 346                     cfg => doc_cfg
 347                     masked => doc_masked
 348                     spotlight => doc_spotlight
 349                     alias => doc_alias
 350                     keyword => doc_keyword
 351                 );
 352             }
 353         }
 354     }
 355
 356     fn visit_name(&mut self, sp: Span, name: ast::Name) {
 357         if !name.as_str().is_ascii() {
 358             gate_feature_post!(
 359                 &self,
 360                 non_ascii_idents,
 361                 self.parse_sess.source_map().def_span(sp),
 362                 "non-ascii idents are not fully supported"
 363             );
 364         }
 365     }
 366
 367     fn visit_item(&mut self, i: &'a ast::Item) {
 368         match i.kind {
 369             ast::ItemKind::ForeignMod(ref foreign_module) => {
 370                 self.check_abi(foreign_module.abi);
 371             }
 372
 373             ast::ItemKind::Fn(..) => {
 374                 if attr::contains_name(&i.attrs[..], sym::plugin_registrar) {
 375                     gate_feature_post!(&self, plugin_registrar, i.span,
 376                                        "compiler plugins are experimental and possibly buggy");
 377                 }
 378                 if attr::contains_name(&i.attrs[..], sym::start) {
 379                     gate_feature_post!(&self, start, i.span,
 380                                       "a `#[start]` function is an experimental \
 381                                        feature whose signature may change \
 382                                        over time");
 383                 }
 384                 if attr::contains_name(&i.attrs[..], sym::main) {
 385                     gate_feature_post!(&self, main, i.span,
 386                                        "declaration of a non-standard `#[main]` \
 387                                         function may change over time, for now \
 388                                         a top-level `fn main()` is required");
 389                 }
 390             }
 391
 392             ast::ItemKind::Struct(..) => {
 393                 for attr in attr::filter_by_name(&i.attrs[..], sym::repr) {
 394                     for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
 395                         if item.check_name(sym::simd) {
 396                             gate_feature_post!(&self, repr_simd, attr.span,
 397                                                "SIMD types are experimental and possibly buggy");
 398                         }
 399                     }
 400                 }
 401             }
 402
 403             ast::ItemKind::Enum(ast::EnumDef{ref variants, ..}, ..) => {
 404                 for variant in variants {
 405                     match (&variant.data, &variant.disr_expr) {
 406                         (ast::VariantData::Unit(..), _) => {},
 407                         (_, Some(disr_expr)) =>
 408                             gate_feature_post!(
 409                                 &self,
 410                                 arbitrary_enum_discriminant,
 411                                 disr_expr.value.span,
 412                                 "discriminants on non-unit variants are experimental"),
 413                         _ => {},
 414                     }
 415                 }
 416
 417                 let has_feature = self.features.arbitrary_enum_discriminant;
 418                 if !has_feature && !i.span.allows_unstable(sym::arbitrary_enum_discriminant) {
 419                     self.maybe_report_invalid_custom_discriminants(&variants);
 420                 }
 421             }
 422
 423             ast::ItemKind::Impl(_, polarity, defaultness, ..) => {
 424                 if polarity == ast::ImplPolarity::Negative {
 425                     gate_feature_post!(&self, optin_builtin_traits,
 426                                        i.span,
 427                                        "negative trait bounds are not yet fully implemented; \
 428                                         use marker types for now");
 429                 }
 430
 431                 if let ast::Defaultness::Default = defaultness {
 432                     gate_feature_post!(&self, specialization,
 433                                        i.span,
 434                                        "specialization is unstable");
 435                 }
 436             }
 437
 438             ast::ItemKind::Trait(ast::IsAuto::Yes, ..) => {
 439                 gate_feature_post!(&self, optin_builtin_traits,
 440                                    i.span,
 441                                    "auto traits are experimental and possibly buggy");
 442             }
 443
 444             ast::ItemKind::TraitAlias(..) => {
 445                 gate_feature_post!(
 446                     &self,
 447                     trait_alias,
 448                     i.span,
 449                     "trait aliases are experimental"
 450                 );
 451             }
 452
 453             ast::ItemKind::MacroDef(ast::MacroDef { legacy: false, .. }) => {
 454                 let msg = "`macro` is experimental";
 455                 gate_feature_post!(&self, decl_macro, i.span, msg);
 456             }
 457
 458             ast::ItemKind::OpaqueTy(..) => {
 459                 gate_feature_post!(
 460                     &self,
 461                     type_alias_impl_trait,
 462                     i.span,
 463                     "`impl Trait` in type aliases is unstable"
 464                 );
 465             }
 466
 467             _ => {}
 468         }
 469
 470         visit::walk_item(self, i);
 471     }
 472
 473     fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
 474         match i.kind {
 475             ast::ForeignItemKind::Fn(..) |
 476             ast::ForeignItemKind::Static(..) => {
 477                 let link_name = attr::first_attr_value_str_by_name(&i.attrs, sym::link_name);
 478                 let links_to_llvm = match link_name {
 479                     Some(val) => val.as_str().starts_with("llvm."),
 480                     _ => false
 481                 };
 482                 if links_to_llvm {
 483                     gate_feature_post!(&self, link_llvm_intrinsics, i.span,
 484                                        "linking to LLVM intrinsics is experimental");
 485                 }
 486             }
 487             ast::ForeignItemKind::Ty => {
 488                     gate_feature_post!(&self, extern_types, i.span,
 489                                        "extern types are experimental");
 490             }
 491             ast::ForeignItemKind::Macro(..) => {}
 492         }
 493
 494         visit::walk_foreign_item(self, i)
 495     }
 496
 497     fn visit_ty(&mut self, ty: &'a ast::Ty) {
 498         match ty.kind {
 499             ast::TyKind::BareFn(ref bare_fn_ty) => {
 500                 self.check_abi(bare_fn_ty.abi);
 501             }
 502             ast::TyKind::Never => {
 503                 gate_feature_post!(&self, never_type, ty.span,
 504                                    "The `!` type is experimental");
 505             }
 506             _ => {}
 507         }
 508         visit::walk_ty(self, ty)
 509     }
 510
 511     fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FunctionRetTy) {
 512         if let ast::FunctionRetTy::Ty(ref output_ty) = *ret_ty {
 513             if let ast::TyKind::Never = output_ty.kind {
 514                 // Do nothing.
 515             } else {
 516                 self.visit_ty(output_ty)
 517             }
 518         }
 519     }
 520
 521     fn visit_expr(&mut self, e: &'a ast::Expr) {
 522         match e.kind {
 523             ast::ExprKind::Box(_) => {
 524                 gate_feature_post!(&self, box_syntax, e.span, EXPLAIN_BOX_SYNTAX);
 525             }
 526             ast::ExprKind::Type(..) => {
 527                 // To avoid noise about type ascription in common syntax errors, only emit if it
 528                 // is the *only* error.
 529                 if self.parse_sess.span_diagnostic.err_count() == 0 {
 530                     gate_feature_post!(&self, type_ascription, e.span,
 531                                        "type ascription is experimental");
 532                 }
 533             }
 534             ast::ExprKind::TryBlock(_) => {
 535                 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
 536             }
 537             ast::ExprKind::Block(_, opt_label) => {
 538                 if let Some(label) = opt_label {
 539                     gate_feature_post!(&self, label_break_value, label.ident.span,
 540                                     "labels on blocks are unstable");
 541                 }
 542             }
 543             _ => {}
 544         }
 545         visit::walk_expr(self, e)
 546     }
 547
 548     fn visit_arm(&mut self, arm: &'a ast::Arm) {
 549         visit::walk_arm(self, arm)
 550     }
 551
 552     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
 553         match &pattern.kind {
 554             PatKind::Slice(pats) => {
 555                 for pat in &*pats {
 556                     let span = pat.span;
 557                     let inner_pat = match &pat.kind {
 558                         PatKind::Ident(.., Some(pat)) => pat,
 559                         _ => pat,
 560                     };
 561                     if inner_pat.is_rest() {
 562                         gate_feature_post!(
 563                             &self,
 564                             slice_patterns,
 565                             span,
 566                             "subslice patterns are unstable"
 567                         );
 568                     }
 569                 }
 570             }
 571             PatKind::Box(..) => {
 572                 gate_feature_post!(&self, box_patterns,
 573                                   pattern.span,
 574                                   "box pattern syntax is experimental");
 575             }
 576             PatKind::Range(_, _, Spanned { node: RangeEnd::Excluded, .. }) => {
 577                 gate_feature_post!(&self, exclusive_range_pattern, pattern.span,
 578                                    "exclusive range pattern syntax is experimental");
 579             }
 580             _ => {}
 581         }
 582         visit::walk_pat(self, pattern)
 583     }
 584
 585     fn visit_fn(&mut self,
 586                 fn_kind: FnKind<'a>,
 587                 fn_decl: &'a ast::FnDecl,
 588                 span: Span,
 589                 _node_id: NodeId) {
 590         if let Some(header) = fn_kind.header() {
 591             // Stability of const fn methods are covered in
 592             // `visit_trait_item` and `visit_impl_item` below; this is
 593             // because default methods don't pass through this point.
 594             self.check_abi(header.abi);
 595         }
 596
 597         if fn_decl.c_variadic() {
 598             gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
 599         }
 600
 601         visit::walk_fn(self, fn_kind, fn_decl, span)
 602     }
 603
 604     fn visit_generic_param(&mut self, param: &'a GenericParam) {
 605         match param.kind {
 606             GenericParamKind::Const { .. } =>
 607                 gate_feature_post!(&self, const_generics, param.ident.span,
 608                     "const generics are unstable"),
 609             _ => {}
 610         }
 611         visit::walk_generic_param(self, param)
 612     }
 613
 614     fn visit_assoc_ty_constraint(&mut self, constraint: &'a AssocTyConstraint) {
 615         match constraint.kind {
 616             AssocTyConstraintKind::Bound { .. } =>
 617                 gate_feature_post!(&self, associated_type_bounds, constraint.span,
 618                     "associated type bounds are unstable"),
 619             _ => {}
 620         }
 621         visit::walk_assoc_ty_constraint(self, constraint)
 622     }
 623
 624     fn visit_trait_item(&mut self, ti: &'a ast::TraitItem) {
 625         match ti.kind {
 626             ast::TraitItemKind::Method(ref sig, ref block) => {
 627                 if block.is_none() {
 628                     self.check_abi(sig.header.abi);
 629                 }
 630                 if sig.decl.c_variadic() {
 631                     gate_feature_post!(&self, c_variadic, ti.span,
 632                                        "C-variadic functions are unstable");
 633                 }
 634                 if sig.header.constness.node == ast::Constness::Const {
 635                     gate_feature_post!(&self, const_fn, ti.span, "const fn is unstable");
 636                 }
 637             }
 638             ast::TraitItemKind::Type(_, ref default) => {
 639                 // We use three if statements instead of something like match guards so that all
 640                 // of these errors can be emitted if all cases apply.
 641                 if default.is_some() {
 642                     gate_feature_post!(&self, associated_type_defaults, ti.span,
 643                                        "associated type defaults are unstable");
 644                 }
 645                 self.check_gat(&ti.generics, ti.span);
 646             }
 647             _ => {}
 648         }
 649         visit::walk_trait_item(self, ti)
 650     }
 651
 652     fn visit_impl_item(&mut self, ii: &'a ast::ImplItem) {
 653         if ii.defaultness == ast::Defaultness::Default {
 654             gate_feature_post!(&self, specialization,
 655                               ii.span,
 656                               "specialization is unstable");
 657         }
 658
 659         match ii.kind {
 660             ast::ImplItemKind::Method(ref sig, _) => {
 661                 if sig.decl.c_variadic() {
 662                     gate_feature_post!(&self, c_variadic, ii.span,
 663                                        "C-variadic functions are unstable");
 664                 }
 665             }
 666             ast::ImplItemKind::OpaqueTy(..) => {
 667                 gate_feature_post!(
 668                     &self,
 669                     type_alias_impl_trait,
 670                     ii.span,
 671                     "`impl Trait` in type aliases is unstable"
 672                 );
 673             }
 674             ast::ImplItemKind::TyAlias(_) => {
 675                 self.check_gat(&ii.generics, ii.span);
 676             }
 677             _ => {}
 678         }
 679         visit::walk_impl_item(self, ii)
 680     }
 681
 682     fn visit_vis(&mut self, vis: &'a ast::Visibility) {
 683         if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.node {
 684             gate_feature_post!(&self, crate_visibility_modifier, vis.span,
 685                                "`crate` visibility modifier is experimental");
 686         }
 687         visit::walk_vis(self, vis)
 688     }
 689 }
 690
 691 pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
 692                     crate_edition: Edition, allow_features: &Option<Vec<String>>) -> Features {
 693     fn feature_removed(span_handler: &Handler, span: Span, reason: Option<&str>) {
 694         let mut err = struct_span_err!(span_handler, span, E0557, "feature has been removed");
 695         if let Some(reason) = reason {
 696             err.span_note(span, reason);
 697         } else {
 698             err.span_label(span, "feature has been removed");
 699         }
 700         err.emit();
 701     }
 702
 703     let mut features = Features::new();
 704     let mut edition_enabled_features = FxHashMap::default();
 705
 706     for &edition in ALL_EDITIONS {
 707         if edition <= crate_edition {
 708             // The `crate_edition` implies its respective umbrella feature-gate
 709             // (i.e., `#![feature(rust_20XX_preview)]` isn't needed on edition 20XX).
 710             edition_enabled_features.insert(edition.feature_name(), edition);
 711         }
 712     }
 713
 714     for feature in active_features_up_to(crate_edition) {
 715         feature.set(&mut features, DUMMY_SP);
 716         edition_enabled_features.insert(feature.name, crate_edition);
 717     }
 718
 719     // Process the edition umbrella feature-gates first, to ensure
 720     // `edition_enabled_features` is completed before it's queried.
 721     for attr in krate_attrs {
 722         if !attr.check_name(sym::feature) {
 723             continue
 724         }
 725
 726         let list = match attr.meta_item_list() {
 727             Some(list) => list,
 728             None => continue,
 729         };
 730
 731         for mi in list {
 732             if !mi.is_word() {
 733                 continue;
 734             }
 735
 736             let name = mi.name_or_empty();
 737
 738             let edition = ALL_EDITIONS.iter().find(|e| name == e.feature_name()).copied();
 739             if let Some(edition) = edition {
 740                 if edition <= crate_edition {
 741                     continue;
 742                 }
 743
 744                 for feature in active_features_up_to(edition) {
 745                     // FIXME(Manishearth) there is currently no way to set
 746                     // lib features by edition
 747                     feature.set(&mut features, DUMMY_SP);
 748                     edition_enabled_features.insert(feature.name, edition);
 749                 }
 750             }
 751         }
 752     }
 753
 754     for attr in krate_attrs {
 755         if !attr.check_name(sym::feature) {
 756             continue
 757         }
 758
 759         let list = match attr.meta_item_list() {
 760             Some(list) => list,
 761             None => continue,
 762         };
 763
 764         let bad_input = |span| {
 765             struct_span_err!(span_handler, span, E0556, "malformed `feature` attribute input")
 766         };
 767
 768         for mi in list {
 769             let name = match mi.ident() {
 770                 Some(ident) if mi.is_word() => ident.name,
 771                 Some(ident) => {
 772                     bad_input(mi.span()).span_suggestion(
 773                         mi.span(),
 774                         "expected just one word",
 775                         format!("{}", ident.name),
 776                         Applicability::MaybeIncorrect,
 777                     ).emit();
 778                     continue
 779                 }
 780                 None => {
 781                     bad_input(mi.span()).span_label(mi.span(), "expected just one word").emit();
 782                     continue
 783                 }
 784             };
 785
 786             if let Some(edition) = edition_enabled_features.get(&name) {
 787                 struct_span_warn!(
 788                     span_handler,
 789                     mi.span(),
 790                     E0705,
 791                     "the feature `{}` is included in the Rust {} edition",
 792                     name,
 793                     edition,
 794                 ).emit();
 795                 continue;
 796             }
 797
 798             if ALL_EDITIONS.iter().any(|e| name == e.feature_name()) {
 799                 // Handled in the separate loop above.
 800                 continue;
 801             }
 802
 803             let removed = REMOVED_FEATURES.iter().find(|f| name == f.name);
 804             let stable_removed = STABLE_REMOVED_FEATURES.iter().find(|f| name == f.name);
 805             if let Some(Feature { state, .. }) = removed.or(stable_removed) {
 806                 if let FeatureState::Removed { reason }
 807                 | FeatureState::Stabilized { reason } = state
 808                 {
 809                     feature_removed(span_handler, mi.span(), *reason);
 810                     continue;
 811                 }
 812             }
 813
 814             if let Some(Feature { since, .. }) = ACCEPTED_FEATURES.iter().find(|f| name == f.name) {
 815                 let since = Some(Symbol::intern(since));
 816                 features.declared_lang_features.push((name, mi.span(), since));
 817                 continue;
 818             }
 819
 820             if let Some(allowed) = allow_features.as_ref() {
 821                 if allowed.iter().find(|&f| name.as_str() == *f).is_none() {
 822                     span_err!(span_handler, mi.span(), E0725,
 823                               "the feature `{}` is not in the list of allowed features",
 824                               name);
 825                     continue;
 826                 }
 827             }
 828
 829             if let Some(f) = ACTIVE_FEATURES.iter().find(|f| name == f.name) {
 830                 f.set(&mut features, mi.span());
 831                 features.declared_lang_features.push((name, mi.span(), None));
 832                 continue;
 833             }
 834
 835             features.declared_lib_features.push((name, mi.span()));
 836         }
 837     }
 838
 839     features
 840 }
 841
 842 fn active_features_up_to(edition: Edition) -> impl Iterator<Item=&'static Feature> {
 843     ACTIVE_FEATURES.iter()
 844     .filter(move |feature| {
 845         if let Some(feature_edition) = feature.edition {
 846             feature_edition <= edition
 847         } else {
 848             false
 849         }
 850     })
 851 }
 852
 853 pub fn check_crate(krate: &ast::Crate,
 854                    parse_sess: &ParseSess,
 855                    features: &Features,
 856                    unstable: UnstableFeatures) {
 857     maybe_stage_features(&parse_sess.span_diagnostic, krate, unstable);
 858     let mut visitor = PostExpansionVisitor { parse_sess, features };
 859
 860     let spans = parse_sess.gated_spans.spans.borrow();
 861     macro_rules! gate_all {
 862         ($gate:ident, $msg:literal) => {
 863             for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 864                 gate_feature!(&visitor, $gate, *span, $msg);
 865             }
 866         }
 867     }
 868     gate_all!(let_chains, "`let` expressions in this position are experimental");
 869     gate_all!(async_closure, "async closures are unstable");
 870     gate_all!(generators, "yield syntax is experimental");
 871     gate_all!(or_patterns, "or-patterns syntax is experimental");
 872     gate_all!(const_extern_fn, "`const extern fn` definitions are unstable");
 873
 874     // All uses of `gate_all!` below this point were added in #65742,
 875     // and subsequently disabled (with the non-early gating readded).
 876     macro_rules! gate_all {
 877         ($gate:ident, $msg:literal) => {
 878             // FIXME(eddyb) do something more useful than always
 879             // disabling these uses of early feature-gatings.
 880             if false {
 881                 for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 882                     gate_feature!(&visitor, $gate, *span, $msg);
 883                 }
 884             }
 885         }
 886     }
 887
 888     gate_all!(trait_alias, "trait aliases are experimental");
 889     gate_all!(associated_type_bounds, "associated type bounds are unstable");
 890     gate_all!(crate_visibility_modifier, "`crate` visibility modifier is experimental");
 891     gate_all!(const_generics, "const generics are unstable");
 892     gate_all!(decl_macro, "`macro` is experimental");
 893     gate_all!(box_patterns, "box pattern syntax is experimental");
 894     gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
 895     gate_all!(try_blocks, "`try` blocks are unstable");
 896     gate_all!(label_break_value, "labels on blocks are unstable");
 897     gate_all!(box_syntax, "box expression syntax is experimental; you can call `Box::new` instead");
 898     // To avoid noise about type ascription in common syntax errors,
 899     // only emit if it is the *only* error. (Also check it last.)
 900     if parse_sess.span_diagnostic.err_count() == 0 {
 901         gate_all!(type_ascription, "type ascription is experimental");
 902     }
 903
 904     visit::walk_crate(&mut visitor, krate);
 905 }
 906
 907 #[derive(Clone, Copy, Hash)]
 908 pub enum UnstableFeatures {
 909     /// Hard errors for unstable features are active, as on beta/stable channels.
 910     Disallow,
 911     /// Allow features to be activated, as on nightly.
 912     Allow,
 913     /// Errors are bypassed for bootstrapping. This is required any time
 914     /// during the build that feature-related lints are set to warn or above
 915     /// because the build turns on warnings-as-errors and uses lots of unstable
 916     /// features. As a result, this is always required for building Rust itself.
 917     Cheat
 918 }
 919
 920 impl UnstableFeatures {
 921     pub fn from_environment() -> UnstableFeatures {
 922         // `true` if this is a feature-staged build, i.e., on the beta or stable channel.
 923         let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
 924         // `true` if we should enable unstable features for bootstrapping.
 925         let bootstrap = env::var("RUSTC_BOOTSTRAP").is_ok();
 926         match (disable_unstable_features, bootstrap) {
 927             (_, true) => UnstableFeatures::Cheat,
 928             (true, _) => UnstableFeatures::Disallow,
 929             (false, _) => UnstableFeatures::Allow
 930         }
 931     }
 932
 933     pub fn is_nightly_build(&self) -> bool {
 934         match *self {
 935             UnstableFeatures::Allow | UnstableFeatures::Cheat => true,
 936             UnstableFeatures::Disallow => false,
 937         }
 938     }
 939 }
 940
 941 fn maybe_stage_features(span_handler: &Handler, krate: &ast::Crate, unstable: UnstableFeatures) {
 942     if !unstable.is_nightly_build() {
 943         for attr in krate.attrs.iter().filter(|attr| attr.check_name(sym::feature)) {
 944             span_err!(
 945                 span_handler, attr.span, E0554,
 946                 "`#![feature]` may not be used on the {} release channel",
 947                 option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)")
 948             );
 949         }
 950     }
 951 }