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 check_extern(&self, ext: ast::Extern) {
 262         if let ast::Extern::Explicit(abi) = ext {
 263             self.check_abi(abi);
 264         }
 265     }
 266
 267     fn maybe_report_invalid_custom_discriminants(&self, variants: &[ast::Variant]) {
 268         let has_fields = variants.iter().any(|variant| match variant.data {
 269             VariantData::Tuple(..) | VariantData::Struct(..) => true,
 270             VariantData::Unit(..) => false,
 271         });
 272
 273         let discriminant_spans = variants.iter().filter(|variant| match variant.data {
 274             VariantData::Tuple(..) | VariantData::Struct(..) => false,
 275             VariantData::Unit(..) => true,
 276         })
 277         .filter_map(|variant| variant.disr_expr.as_ref().map(|c| c.value.span))
 278         .collect::<Vec<_>>();
 279
 280         if !discriminant_spans.is_empty() && has_fields {
 281             let mut err = feature_err(
 282                 self.parse_sess,
 283                 sym::arbitrary_enum_discriminant,
 284                 discriminant_spans.clone(),
 285                 crate::feature_gate::GateIssue::Language,
 286                 "custom discriminant values are not allowed in enums with tuple or struct variants",
 287             );
 288             for sp in discriminant_spans {
 289                 err.span_label(sp, "disallowed custom discriminant");
 290             }
 291             for variant in variants.iter() {
 292                 match &variant.data {
 293                     VariantData::Struct(..) => {
 294                         err.span_label(
 295                             variant.span,
 296                             "struct variant defined here",
 297                         );
 298                     }
 299                     VariantData::Tuple(..) => {
 300                         err.span_label(
 301                             variant.span,
 302                             "tuple variant defined here",
 303                         );
 304                     }
 305                     VariantData::Unit(..) => {}
 306                 }
 307             }
 308             err.emit();
 309         }
 310     }
 311
 312     fn check_gat(&self, generics: &ast::Generics, span: Span) {
 313         if !generics.params.is_empty() {
 314             gate_feature_post!(
 315                 &self,
 316                 generic_associated_types,
 317                 span,
 318                 "generic associated types are unstable"
 319             );
 320         }
 321         if !generics.where_clause.predicates.is_empty() {
 322             gate_feature_post!(
 323                 &self,
 324                 generic_associated_types,
 325                 span,
 326                 "where clauses on associated types are unstable"
 327             );
 328         }
 329     }
 330
 331     /// Feature gate `impl Trait` inside `type Alias = $type_expr;`.
 332     fn check_impl_trait(&self, ty: &ast::Ty) {
 333         struct ImplTraitVisitor<'a> {
 334             vis: &'a PostExpansionVisitor<'a>,
 335         }
 336         impl Visitor<'_> for ImplTraitVisitor<'_> {
 337             fn visit_ty(&mut self, ty: &ast::Ty) {
 338                 if let ast::TyKind::ImplTrait(..) = ty.kind {
 339                     gate_feature_post!(
 340                         &self.vis,
 341                         type_alias_impl_trait,
 342                         ty.span,
 343                         "`impl Trait` in type aliases is unstable"
 344                     );
 345                 }
 346                 visit::walk_ty(self, ty);
 347             }
 348         }
 349         ImplTraitVisitor { vis: self }.visit_ty(ty);
 350     }
 351 }
 352
 353 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 354     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 355         let attr_info =
 356             attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name)).map(|a| **a);
 357         // Check feature gates for built-in attributes.
 358         if let Some((.., AttributeGate::Gated(_, name, descr, has_feature))) = attr_info {
 359             gate_feature_fn!(self, has_feature, attr.span, name, descr, GateStrength::Hard);
 360         }
 361         // Check unstable flavors of the `#[doc]` attribute.
 362         if attr.check_name(sym::doc) {
 363             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 364                 macro_rules! gate_doc { ($($name:ident => $feature:ident)*) => {
 365                     $(if nested_meta.check_name(sym::$name) {
 366                         let msg = concat!("`#[doc(", stringify!($name), ")]` is experimental");
 367                         gate_feature!(self, $feature, attr.span, msg);
 368                     })*
 369                 }}
 370
 371                 gate_doc!(
 372                     include => external_doc
 373                     cfg => doc_cfg
 374                     masked => doc_masked
 375                     spotlight => doc_spotlight
 376                     alias => doc_alias
 377                     keyword => doc_keyword
 378                 );
 379             }
 380         }
 381     }
 382
 383     fn visit_name(&mut self, sp: Span, name: ast::Name) {
 384         if !name.as_str().is_ascii() {
 385             gate_feature_post!(
 386                 &self,
 387                 non_ascii_idents,
 388                 self.parse_sess.source_map().def_span(sp),
 389                 "non-ascii idents are not fully supported"
 390             );
 391         }
 392     }
 393
 394     fn visit_item(&mut self, i: &'a ast::Item) {
 395         match i.kind {
 396             ast::ItemKind::ForeignMod(ref foreign_module) => {
 397                 if let Some(abi) = foreign_module.abi {
 398                     self.check_abi(abi);
 399                 }
 400             }
 401
 402             ast::ItemKind::Fn(..) => {
 403                 if attr::contains_name(&i.attrs[..], sym::plugin_registrar) {
 404                     gate_feature_post!(&self, plugin_registrar, i.span,
 405                                        "compiler plugins are experimental and possibly buggy");
 406                 }
 407                 if attr::contains_name(&i.attrs[..], sym::start) {
 408                     gate_feature_post!(&self, start, i.span,
 409                                       "a `#[start]` function is an experimental \
 410                                        feature whose signature may change \
 411                                        over time");
 412                 }
 413                 if attr::contains_name(&i.attrs[..], sym::main) {
 414                     gate_feature_post!(&self, main, i.span,
 415                                        "declaration of a non-standard `#[main]` \
 416                                         function may change over time, for now \
 417                                         a top-level `fn main()` is required");
 418                 }
 419             }
 420
 421             ast::ItemKind::Struct(..) => {
 422                 for attr in attr::filter_by_name(&i.attrs[..], sym::repr) {
 423                     for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
 424                         if item.check_name(sym::simd) {
 425                             gate_feature_post!(&self, repr_simd, attr.span,
 426                                                "SIMD types are experimental and possibly buggy");
 427                         }
 428                     }
 429                 }
 430             }
 431
 432             ast::ItemKind::Enum(ast::EnumDef{ref variants, ..}, ..) => {
 433                 for variant in variants {
 434                     match (&variant.data, &variant.disr_expr) {
 435                         (ast::VariantData::Unit(..), _) => {},
 436                         (_, Some(disr_expr)) =>
 437                             gate_feature_post!(
 438                                 &self,
 439                                 arbitrary_enum_discriminant,
 440                                 disr_expr.value.span,
 441                                 "discriminants on non-unit variants are experimental"),
 442                         _ => {},
 443                     }
 444                 }
 445
 446                 let has_feature = self.features.arbitrary_enum_discriminant;
 447                 if !has_feature && !i.span.allows_unstable(sym::arbitrary_enum_discriminant) {
 448                     self.maybe_report_invalid_custom_discriminants(&variants);
 449                 }
 450             }
 451
 452             ast::ItemKind::Impl(_, polarity, defaultness, ..) => {
 453                 if polarity == ast::ImplPolarity::Negative {
 454                     gate_feature_post!(&self, optin_builtin_traits,
 455                                        i.span,
 456                                        "negative trait bounds are not yet fully implemented; \
 457                                         use marker types for now");
 458                 }
 459
 460                 if let ast::Defaultness::Default = defaultness {
 461                     gate_feature_post!(&self, specialization,
 462                                        i.span,
 463                                        "specialization is unstable");
 464                 }
 465             }
 466
 467             ast::ItemKind::Trait(ast::IsAuto::Yes, ..) => {
 468                 gate_feature_post!(&self, optin_builtin_traits,
 469                                    i.span,
 470                                    "auto traits are experimental and possibly buggy");
 471             }
 472
 473             ast::ItemKind::TraitAlias(..) => {
 474                 gate_feature_post!(
 475                     &self,
 476                     trait_alias,
 477                     i.span,
 478                     "trait aliases are experimental"
 479                 );
 480             }
 481
 482             ast::ItemKind::MacroDef(ast::MacroDef { legacy: false, .. }) => {
 483                 let msg = "`macro` is experimental";
 484                 gate_feature_post!(&self, decl_macro, i.span, msg);
 485             }
 486
 487             ast::ItemKind::TyAlias(ref ty, ..) => self.check_impl_trait(&ty),
 488
 489             _ => {}
 490         }
 491
 492         visit::walk_item(self, i);
 493     }
 494
 495     fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
 496         match i.kind {
 497             ast::ForeignItemKind::Fn(..) |
 498             ast::ForeignItemKind::Static(..) => {
 499                 let link_name = attr::first_attr_value_str_by_name(&i.attrs, sym::link_name);
 500                 let links_to_llvm = match link_name {
 501                     Some(val) => val.as_str().starts_with("llvm."),
 502                     _ => false
 503                 };
 504                 if links_to_llvm {
 505                     gate_feature_post!(&self, link_llvm_intrinsics, i.span,
 506                                        "linking to LLVM intrinsics is experimental");
 507                 }
 508             }
 509             ast::ForeignItemKind::Ty => {
 510                     gate_feature_post!(&self, extern_types, i.span,
 511                                        "extern types are experimental");
 512             }
 513             ast::ForeignItemKind::Macro(..) => {}
 514         }
 515
 516         visit::walk_foreign_item(self, i)
 517     }
 518
 519     fn visit_ty(&mut self, ty: &'a ast::Ty) {
 520         match ty.kind {
 521             ast::TyKind::BareFn(ref bare_fn_ty) => {
 522                 self.check_extern(bare_fn_ty.ext);
 523             }
 524             ast::TyKind::Never => {
 525                 gate_feature_post!(&self, never_type, ty.span,
 526                                    "The `!` type is experimental");
 527             }
 528             _ => {}
 529         }
 530         visit::walk_ty(self, ty)
 531     }
 532
 533     fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FunctionRetTy) {
 534         if let ast::FunctionRetTy::Ty(ref output_ty) = *ret_ty {
 535             if let ast::TyKind::Never = output_ty.kind {
 536                 // Do nothing.
 537             } else {
 538                 self.visit_ty(output_ty)
 539             }
 540         }
 541     }
 542
 543     fn visit_expr(&mut self, e: &'a ast::Expr) {
 544         match e.kind {
 545             ast::ExprKind::Box(_) => {
 546                 gate_feature_post!(&self, box_syntax, e.span, EXPLAIN_BOX_SYNTAX);
 547             }
 548             ast::ExprKind::Type(..) => {
 549                 // To avoid noise about type ascription in common syntax errors, only emit if it
 550                 // is the *only* error.
 551                 if self.parse_sess.span_diagnostic.err_count() == 0 {
 552                     gate_feature_post!(&self, type_ascription, e.span,
 553                                        "type ascription is experimental");
 554                 }
 555             }
 556             ast::ExprKind::TryBlock(_) => {
 557                 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
 558             }
 559             ast::ExprKind::Block(_, opt_label) => {
 560                 if let Some(label) = opt_label {
 561                     gate_feature_post!(&self, label_break_value, label.ident.span,
 562                                     "labels on blocks are unstable");
 563                 }
 564             }
 565             _ => {}
 566         }
 567         visit::walk_expr(self, e)
 568     }
 569
 570     fn visit_arm(&mut self, arm: &'a ast::Arm) {
 571         visit::walk_arm(self, arm)
 572     }
 573
 574     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
 575         match &pattern.kind {
 576             PatKind::Slice(pats) => {
 577                 for pat in &*pats {
 578                     let span = pat.span;
 579                     let inner_pat = match &pat.kind {
 580                         PatKind::Ident(.., Some(pat)) => pat,
 581                         _ => pat,
 582                     };
 583                     if inner_pat.is_rest() {
 584                         gate_feature_post!(
 585                             &self,
 586                             slice_patterns,
 587                             span,
 588                             "subslice patterns are unstable"
 589                         );
 590                     }
 591                 }
 592             }
 593             PatKind::Box(..) => {
 594                 gate_feature_post!(&self, box_patterns,
 595                                   pattern.span,
 596                                   "box pattern syntax is experimental");
 597             }
 598             PatKind::Range(_, _, Spanned { node: RangeEnd::Excluded, .. }) => {
 599                 gate_feature_post!(&self, exclusive_range_pattern, pattern.span,
 600                                    "exclusive range pattern syntax is experimental");
 601             }
 602             _ => {}
 603         }
 604         visit::walk_pat(self, pattern)
 605     }
 606
 607     fn visit_fn(&mut self,
 608                 fn_kind: FnKind<'a>,
 609                 fn_decl: &'a ast::FnDecl,
 610                 span: Span,
 611                 _node_id: NodeId) {
 612         if let Some(header) = fn_kind.header() {
 613             // Stability of const fn methods are covered in
 614             // `visit_trait_item` and `visit_impl_item` below; this is
 615             // because default methods don't pass through this point.
 616             self.check_extern(header.ext);
 617         }
 618
 619         if fn_decl.c_variadic() {
 620             gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
 621         }
 622
 623         visit::walk_fn(self, fn_kind, fn_decl, span)
 624     }
 625
 626     fn visit_generic_param(&mut self, param: &'a GenericParam) {
 627         match param.kind {
 628             GenericParamKind::Const { .. } =>
 629                 gate_feature_post!(&self, const_generics, param.ident.span,
 630                     "const generics are unstable"),
 631             _ => {}
 632         }
 633         visit::walk_generic_param(self, param)
 634     }
 635
 636     fn visit_assoc_ty_constraint(&mut self, constraint: &'a AssocTyConstraint) {
 637         match constraint.kind {
 638             AssocTyConstraintKind::Bound { .. } =>
 639                 gate_feature_post!(&self, associated_type_bounds, constraint.span,
 640                     "associated type bounds are unstable"),
 641             _ => {}
 642         }
 643         visit::walk_assoc_ty_constraint(self, constraint)
 644     }
 645
 646     fn visit_trait_item(&mut self, ti: &'a ast::TraitItem) {
 647         match ti.kind {
 648             ast::TraitItemKind::Method(ref sig, ref block) => {
 649                 if block.is_none() {
 650                     self.check_extern(sig.header.ext);
 651                 }
 652                 if sig.decl.c_variadic() {
 653                     gate_feature_post!(&self, c_variadic, ti.span,
 654                                        "C-variadic functions are unstable");
 655                 }
 656                 if sig.header.constness.node == ast::Constness::Const {
 657                     gate_feature_post!(&self, const_fn, ti.span, "const fn is unstable");
 658                 }
 659             }
 660             ast::TraitItemKind::Type(_, ref default) => {
 661                 if let Some(ty) = default {
 662                     self.check_impl_trait(ty);
 663                     gate_feature_post!(&self, associated_type_defaults, ti.span,
 664                                        "associated type defaults are unstable");
 665                 }
 666                 self.check_gat(&ti.generics, ti.span);
 667             }
 668             _ => {}
 669         }
 670         visit::walk_trait_item(self, ti)
 671     }
 672
 673     fn visit_impl_item(&mut self, ii: &'a ast::ImplItem) {
 674         if ii.defaultness == ast::Defaultness::Default {
 675             gate_feature_post!(&self, specialization,
 676                               ii.span,
 677                               "specialization is unstable");
 678         }
 679
 680         match ii.kind {
 681             ast::ImplItemKind::Method(ref sig, _) => {
 682                 if sig.decl.c_variadic() {
 683                     gate_feature_post!(&self, c_variadic, ii.span,
 684                                        "C-variadic functions are unstable");
 685                 }
 686             }
 687             ast::ImplItemKind::TyAlias(ref ty) => {
 688                 self.check_impl_trait(ty);
 689                 self.check_gat(&ii.generics, ii.span);
 690             }
 691             _ => {}
 692         }
 693         visit::walk_impl_item(self, ii)
 694     }
 695
 696     fn visit_vis(&mut self, vis: &'a ast::Visibility) {
 697         if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.node {
 698             gate_feature_post!(&self, crate_visibility_modifier, vis.span,
 699                                "`crate` visibility modifier is experimental");
 700         }
 701         visit::walk_vis(self, vis)
 702     }
 703 }
 704
 705 pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
 706                     crate_edition: Edition, allow_features: &Option<Vec<String>>) -> Features {
 707     fn feature_removed(span_handler: &Handler, span: Span, reason: Option<&str>) {
 708         let mut err = struct_span_err!(span_handler, span, E0557, "feature has been removed");
 709         if let Some(reason) = reason {
 710             err.span_note(span, reason);
 711         } else {
 712             err.span_label(span, "feature has been removed");
 713         }
 714         err.emit();
 715     }
 716
 717     let mut features = Features::new();
 718     let mut edition_enabled_features = FxHashMap::default();
 719
 720     for &edition in ALL_EDITIONS {
 721         if edition <= crate_edition {
 722             // The `crate_edition` implies its respective umbrella feature-gate
 723             // (i.e., `#![feature(rust_20XX_preview)]` isn't needed on edition 20XX).
 724             edition_enabled_features.insert(edition.feature_name(), edition);
 725         }
 726     }
 727
 728     for feature in active_features_up_to(crate_edition) {
 729         feature.set(&mut features, DUMMY_SP);
 730         edition_enabled_features.insert(feature.name, crate_edition);
 731     }
 732
 733     // Process the edition umbrella feature-gates first, to ensure
 734     // `edition_enabled_features` is completed before it's queried.
 735     for attr in krate_attrs {
 736         if !attr.check_name(sym::feature) {
 737             continue
 738         }
 739
 740         let list = match attr.meta_item_list() {
 741             Some(list) => list,
 742             None => continue,
 743         };
 744
 745         for mi in list {
 746             if !mi.is_word() {
 747                 continue;
 748             }
 749
 750             let name = mi.name_or_empty();
 751
 752             let edition = ALL_EDITIONS.iter().find(|e| name == e.feature_name()).copied();
 753             if let Some(edition) = edition {
 754                 if edition <= crate_edition {
 755                     continue;
 756                 }
 757
 758                 for feature in active_features_up_to(edition) {
 759                     // FIXME(Manishearth) there is currently no way to set
 760                     // lib features by edition
 761                     feature.set(&mut features, DUMMY_SP);
 762                     edition_enabled_features.insert(feature.name, edition);
 763                 }
 764             }
 765         }
 766     }
 767
 768     for attr in krate_attrs {
 769         if !attr.check_name(sym::feature) {
 770             continue
 771         }
 772
 773         let list = match attr.meta_item_list() {
 774             Some(list) => list,
 775             None => continue,
 776         };
 777
 778         let bad_input = |span| {
 779             struct_span_err!(span_handler, span, E0556, "malformed `feature` attribute input")
 780         };
 781
 782         for mi in list {
 783             let name = match mi.ident() {
 784                 Some(ident) if mi.is_word() => ident.name,
 785                 Some(ident) => {
 786                     bad_input(mi.span()).span_suggestion(
 787                         mi.span(),
 788                         "expected just one word",
 789                         format!("{}", ident.name),
 790                         Applicability::MaybeIncorrect,
 791                     ).emit();
 792                     continue
 793                 }
 794                 None => {
 795                     bad_input(mi.span()).span_label(mi.span(), "expected just one word").emit();
 796                     continue
 797                 }
 798             };
 799
 800             if let Some(edition) = edition_enabled_features.get(&name) {
 801                 struct_span_warn!(
 802                     span_handler,
 803                     mi.span(),
 804                     E0705,
 805                     "the feature `{}` is included in the Rust {} edition",
 806                     name,
 807                     edition,
 808                 ).emit();
 809                 continue;
 810             }
 811
 812             if ALL_EDITIONS.iter().any(|e| name == e.feature_name()) {
 813                 // Handled in the separate loop above.
 814                 continue;
 815             }
 816
 817             let removed = REMOVED_FEATURES.iter().find(|f| name == f.name);
 818             let stable_removed = STABLE_REMOVED_FEATURES.iter().find(|f| name == f.name);
 819             if let Some(Feature { state, .. }) = removed.or(stable_removed) {
 820                 if let FeatureState::Removed { reason }
 821                 | FeatureState::Stabilized { reason } = state
 822                 {
 823                     feature_removed(span_handler, mi.span(), *reason);
 824                     continue;
 825                 }
 826             }
 827
 828             if let Some(Feature { since, .. }) = ACCEPTED_FEATURES.iter().find(|f| name == f.name) {
 829                 let since = Some(Symbol::intern(since));
 830                 features.declared_lang_features.push((name, mi.span(), since));
 831                 continue;
 832             }
 833
 834             if let Some(allowed) = allow_features.as_ref() {
 835                 if allowed.iter().find(|&f| name.as_str() == *f).is_none() {
 836                     span_err!(span_handler, mi.span(), E0725,
 837                               "the feature `{}` is not in the list of allowed features",
 838                               name);
 839                     continue;
 840                 }
 841             }
 842
 843             if let Some(f) = ACTIVE_FEATURES.iter().find(|f| name == f.name) {
 844                 f.set(&mut features, mi.span());
 845                 features.declared_lang_features.push((name, mi.span(), None));
 846                 continue;
 847             }
 848
 849             features.declared_lib_features.push((name, mi.span()));
 850         }
 851     }
 852
 853     features
 854 }
 855
 856 fn active_features_up_to(edition: Edition) -> impl Iterator<Item=&'static Feature> {
 857     ACTIVE_FEATURES.iter()
 858     .filter(move |feature| {
 859         if let Some(feature_edition) = feature.edition {
 860             feature_edition <= edition
 861         } else {
 862             false
 863         }
 864     })
 865 }
 866
 867 pub fn check_crate(krate: &ast::Crate,
 868                    parse_sess: &ParseSess,
 869                    features: &Features,
 870                    unstable: UnstableFeatures) {
 871     maybe_stage_features(&parse_sess.span_diagnostic, krate, unstable);
 872     let mut visitor = PostExpansionVisitor { parse_sess, features };
 873
 874     let spans = parse_sess.gated_spans.spans.borrow();
 875     macro_rules! gate_all {
 876         ($gate:ident, $msg:literal) => {
 877             for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 878                 gate_feature!(&visitor, $gate, *span, $msg);
 879             }
 880         }
 881     }
 882     gate_all!(let_chains, "`let` expressions in this position are experimental");
 883     gate_all!(async_closure, "async closures are unstable");
 884     gate_all!(generators, "yield syntax is experimental");
 885     gate_all!(or_patterns, "or-patterns syntax is experimental");
 886     gate_all!(const_extern_fn, "`const extern fn` definitions are unstable");
 887
 888     // All uses of `gate_all!` below this point were added in #65742,
 889     // and subsequently disabled (with the non-early gating readded).
 890     macro_rules! gate_all {
 891         ($gate:ident, $msg:literal) => {
 892             // FIXME(eddyb) do something more useful than always
 893             // disabling these uses of early feature-gatings.
 894             if false {
 895                 for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 896                     gate_feature!(&visitor, $gate, *span, $msg);
 897                 }
 898             }
 899         }
 900     }
 901
 902     gate_all!(trait_alias, "trait aliases are experimental");
 903     gate_all!(associated_type_bounds, "associated type bounds are unstable");
 904     gate_all!(crate_visibility_modifier, "`crate` visibility modifier is experimental");
 905     gate_all!(const_generics, "const generics are unstable");
 906     gate_all!(decl_macro, "`macro` is experimental");
 907     gate_all!(box_patterns, "box pattern syntax is experimental");
 908     gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
 909     gate_all!(try_blocks, "`try` blocks are unstable");
 910     gate_all!(label_break_value, "labels on blocks are unstable");
 911     gate_all!(box_syntax, "box expression syntax is experimental; you can call `Box::new` instead");
 912     // To avoid noise about type ascription in common syntax errors,
 913     // only emit if it is the *only* error. (Also check it last.)
 914     if parse_sess.span_diagnostic.err_count() == 0 {
 915         gate_all!(type_ascription, "type ascription is experimental");
 916     }
 917
 918     visit::walk_crate(&mut visitor, krate);
 919 }
 920
 921 #[derive(Clone, Copy, Hash)]
 922 pub enum UnstableFeatures {
 923     /// Hard errors for unstable features are active, as on beta/stable channels.
 924     Disallow,
 925     /// Allow features to be activated, as on nightly.
 926     Allow,
 927     /// Errors are bypassed for bootstrapping. This is required any time
 928     /// during the build that feature-related lints are set to warn or above
 929     /// because the build turns on warnings-as-errors and uses lots of unstable
 930     /// features. As a result, this is always required for building Rust itself.
 931     Cheat
 932 }
 933
 934 impl UnstableFeatures {
 935     pub fn from_environment() -> UnstableFeatures {
 936         // `true` if this is a feature-staged build, i.e., on the beta or stable channel.
 937         let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
 938         // `true` if we should enable unstable features for bootstrapping.
 939         let bootstrap = env::var("RUSTC_BOOTSTRAP").is_ok();
 940         match (disable_unstable_features, bootstrap) {
 941             (_, true) => UnstableFeatures::Cheat,
 942             (true, _) => UnstableFeatures::Disallow,
 943             (false, _) => UnstableFeatures::Allow
 944         }
 945     }
 946
 947     pub fn is_nightly_build(&self) -> bool {
 948         match *self {
 949             UnstableFeatures::Allow | UnstableFeatures::Cheat => true,
 950             UnstableFeatures::Disallow => false,
 951         }
 952     }
 953 }
 954
 955 fn maybe_stage_features(span_handler: &Handler, krate: &ast::Crate, unstable: UnstableFeatures) {
 956     if !unstable.is_nightly_build() {
 957         for attr in krate.attrs.iter().filter(|attr| attr.check_name(sym::feature)) {
 958             span_err!(
 959                 span_handler, attr.span, E0554,
 960                 "`#![feature]` may not be used on the {} release channel",
 961                 option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)")
 962             );
 963         }
 964     }
 965 }