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 std::env;
  21
  22 #[derive(Copy, Clone, Debug)]
  23 pub enum Stability {
  24     Unstable,
  25     // First argument is tracking issue link; second argument is an optional
  26     // help message, which defaults to "remove this attribute"
  27     Deprecated(&'static str, Option<&'static str>),
  28 }
  29
  30 macro_rules! gate_feature_fn {
  31     ($cx: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr, $level: expr) => {{
  32         let (cx, has_feature, span,
  33              name, explain, level) = (&*$cx, $has_feature, $span, $name, $explain, $level);
  34         let has_feature: bool = has_feature(&$cx.features);
  35         debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
  36         if !has_feature && !span.allows_unstable($name) {
  37             leveled_feature_err(cx.parse_sess, name, span, GateIssue::Language, explain, level)
  38                 .emit();
  39         }
  40     }}
  41 }
  42
  43 macro_rules! gate_feature {
  44     ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {
  45         gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
  46                          sym::$feature, $explain, GateStrength::Hard)
  47     };
  48     ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {
  49         gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
  50                          sym::$feature, $explain, $level)
  51     };
  52 }
  53
  54 pub fn check_attribute(attr: &ast::Attribute, parse_sess: &ParseSess, features: &Features) {
  55     PostExpansionVisitor { parse_sess, features }.visit_attribute(attr)
  56 }
  57
  58 fn find_lang_feature_issue(feature: Symbol) -> Option<u32> {
  59     if let Some(info) = ACTIVE_FEATURES.iter().find(|t| t.name == feature) {
  60         // FIXME (#28244): enforce that active features have issue numbers
  61         // assert!(info.issue.is_some())
  62         info.issue
  63     } else {
  64         // search in Accepted, Removed, or Stable Removed features
  65         let found = ACCEPTED_FEATURES.iter().chain(REMOVED_FEATURES).chain(STABLE_REMOVED_FEATURES)
  66             .find(|t| t.name == feature);
  67         match found {
  68             Some(&Feature { issue, .. }) => issue,
  69             None => panic!("Feature `{}` is not declared anywhere", feature),
  70         }
  71     }
  72 }
  73
  74 pub enum GateIssue {
  75     Language,
  76     Library(Option<u32>)
  77 }
  78
  79 #[derive(Debug, Copy, Clone, PartialEq)]
  80 pub enum GateStrength {
  81     /// A hard error. (Most feature gates should use this.)
  82     Hard,
  83     /// Only a warning. (Use this only as backwards-compatibility demands.)
  84     Soft,
  85 }
  86
  87 pub fn emit_feature_err(
  88     sess: &ParseSess,
  89     feature: Symbol,
  90     span: Span,
  91     issue: GateIssue,
  92     explain: &str,
  93 ) {
  94     feature_err(sess, feature, span, issue, explain).emit();
  95 }
  96
  97 pub fn feature_err<'a, S: Into<MultiSpan>>(
  98     sess: &'a ParseSess,
  99     feature: Symbol,
 100     span: S,
 101     issue: GateIssue,
 102     explain: &str,
 103 ) -> DiagnosticBuilder<'a> {
 104     leveled_feature_err(sess, feature, span, issue, explain, GateStrength::Hard)
 105 }
 106
 107 fn leveled_feature_err<'a, S: Into<MultiSpan>>(
 108     sess: &'a ParseSess,
 109     feature: Symbol,
 110     span: S,
 111     issue: GateIssue,
 112     explain: &str,
 113     level: GateStrength,
 114 ) -> DiagnosticBuilder<'a> {
 115     let diag = &sess.span_diagnostic;
 116
 117     let issue = match issue {
 118         GateIssue::Language => find_lang_feature_issue(feature),
 119         GateIssue::Library(lib) => lib,
 120     };
 121
 122     let mut err = match level {
 123         GateStrength::Hard => {
 124             diag.struct_span_err_with_code(span, explain, stringify_error_code!(E0658))
 125         }
 126         GateStrength::Soft => diag.struct_span_warn(span, explain),
 127     };
 128
 129     match issue {
 130         None | Some(0) => {}  // We still accept `0` as a stand-in for backwards compatibility
 131         Some(n) => {
 132             err.note(&format!(
 133                 "for more information, see https://github.com/rust-lang/rust/issues/{}",
 134                 n,
 135             ));
 136         }
 137     }
 138
 139     // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
 140     if sess.unstable_features.is_nightly_build() {
 141         err.help(&format!("add `#![feature({})]` to the crate attributes to enable", feature));
 142     }
 143
 144     // If we're on stable and only emitting a "soft" warning, add a note to
 145     // clarify that the feature isn't "on" (rather than being on but
 146     // warning-worthy).
 147     if !sess.unstable_features.is_nightly_build() && level == GateStrength::Soft {
 148         err.help("a nightly build of the compiler is required to enable this feature");
 149     }
 150
 151     err
 152
 153 }
 154
 155 const EXPLAIN_BOX_SYNTAX: &str =
 156     "box expression syntax is experimental; you can call `Box::new` instead";
 157
 158 pub const EXPLAIN_STMT_ATTR_SYNTAX: &str =
 159     "attributes on expressions are experimental";
 160
 161 pub const EXPLAIN_ALLOW_INTERNAL_UNSTABLE: &str =
 162     "allow_internal_unstable side-steps feature gating and stability checks";
 163 pub const EXPLAIN_ALLOW_INTERNAL_UNSAFE: &str =
 164     "allow_internal_unsafe side-steps the unsafe_code lint";
 165
 166 pub const EXPLAIN_UNSIZED_TUPLE_COERCION: &str =
 167     "unsized tuple coercion is not stable enough for use and is subject to change";
 168
 169 struct PostExpansionVisitor<'a> {
 170     parse_sess: &'a ParseSess,
 171     features: &'a Features,
 172 }
 173
 174 macro_rules! gate_feature_post {
 175     ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {{
 176         let (cx, span) = ($cx, $span);
 177         if !span.allows_unstable(sym::$feature) {
 178             gate_feature!(cx, $feature, span, $explain)
 179         }
 180     }};
 181     ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {{
 182         let (cx, span) = ($cx, $span);
 183         if !span.allows_unstable(sym::$feature) {
 184             gate_feature!(cx, $feature, span, $explain, $level)
 185         }
 186     }}
 187 }
 188
 189 impl<'a> PostExpansionVisitor<'a> {
 190     fn check_abi(&self, abi: ast::Abi) {
 191         let ast::Abi { symbol, span } = abi;
 192
 193         match &*symbol.as_str() {
 194             // Stable
 195             "Rust" |
 196             "C" |
 197             "cdecl" |
 198             "stdcall" |
 199             "fastcall" |
 200             "aapcs" |
 201             "win64" |
 202             "sysv64" |
 203             "system" => {}
 204             "rust-intrinsic" => {
 205                 gate_feature_post!(&self, intrinsics, span,
 206                                    "intrinsics are subject to change");
 207             },
 208             "platform-intrinsic" => {
 209                 gate_feature_post!(&self, platform_intrinsics, span,
 210                                    "platform intrinsics are experimental and possibly buggy");
 211             },
 212             "vectorcall" => {
 213                 gate_feature_post!(&self, abi_vectorcall, span,
 214                                    "vectorcall is experimental and subject to change");
 215             },
 216             "thiscall" => {
 217                 gate_feature_post!(&self, abi_thiscall, span,
 218                                    "thiscall is experimental and subject to change");
 219             },
 220             "rust-call" => {
 221                 gate_feature_post!(&self, unboxed_closures, span,
 222                                    "rust-call ABI is subject to change");
 223             },
 224             "ptx-kernel" => {
 225                 gate_feature_post!(&self, abi_ptx, span,
 226                                    "PTX ABIs are experimental and subject to change");
 227             },
 228             "unadjusted" => {
 229                 gate_feature_post!(&self, abi_unadjusted, span,
 230                                    "unadjusted ABI is an implementation detail and perma-unstable");
 231             },
 232             "msp430-interrupt" => {
 233                 gate_feature_post!(&self, abi_msp430_interrupt, span,
 234                                    "msp430-interrupt ABI is experimental and subject to change");
 235             },
 236             "x86-interrupt" => {
 237                 gate_feature_post!(&self, abi_x86_interrupt, span,
 238                                    "x86-interrupt ABI is experimental and subject to change");
 239             },
 240             "amdgpu-kernel" => {
 241                 gate_feature_post!(&self, abi_amdgpu_kernel, span,
 242                                    "amdgpu-kernel ABI is experimental and subject to change");
 243             },
 244             "efiapi" => {
 245                 gate_feature_post!(&self, abi_efiapi, span,
 246                                    "efiapi ABI is experimental and subject to change");
 247             },
 248             abi => {
 249                 self.parse_sess.span_diagnostic.delay_span_bug(
 250                     span,
 251                     &format!("unrecognized ABI not caught in lowering: {}", abi),
 252                 )
 253             }
 254         }
 255     }
 256
 257     fn maybe_report_invalid_custom_discriminants(&self, variants: &[ast::Variant]) {
 258         let has_fields = variants.iter().any(|variant| match variant.data {
 259             VariantData::Tuple(..) | VariantData::Struct(..) => true,
 260             VariantData::Unit(..) => false,
 261         });
 262
 263         let discriminant_spans = variants.iter().filter(|variant| match variant.data {
 264             VariantData::Tuple(..) | VariantData::Struct(..) => false,
 265             VariantData::Unit(..) => true,
 266         })
 267         .filter_map(|variant| variant.disr_expr.as_ref().map(|c| c.value.span))
 268         .collect::<Vec<_>>();
 269
 270         if !discriminant_spans.is_empty() && has_fields {
 271             let mut err = feature_err(
 272                 self.parse_sess,
 273                 sym::arbitrary_enum_discriminant,
 274                 discriminant_spans.clone(),
 275                 crate::feature_gate::GateIssue::Language,
 276                 "custom discriminant values are not allowed in enums with tuple or struct variants",
 277             );
 278             for sp in discriminant_spans {
 279                 err.span_label(sp, "disallowed custom discriminant");
 280             }
 281             for variant in variants.iter() {
 282                 match &variant.data {
 283                     VariantData::Struct(..) => {
 284                         err.span_label(
 285                             variant.span,
 286                             "struct variant defined here",
 287                         );
 288                     }
 289                     VariantData::Tuple(..) => {
 290                         err.span_label(
 291                             variant.span,
 292                             "tuple variant defined here",
 293                         );
 294                     }
 295                     VariantData::Unit(..) => {}
 296                 }
 297             }
 298             err.emit();
 299         }
 300     }
 301
 302     fn check_gat(&self, generics: &ast::Generics, span: Span) {
 303         if !generics.params.is_empty() {
 304             gate_feature_post!(
 305                 &self,
 306                 generic_associated_types,
 307                 span,
 308                 "generic associated types are unstable"
 309             );
 310         }
 311         if !generics.where_clause.predicates.is_empty() {
 312             gate_feature_post!(
 313                 &self,
 314                 generic_associated_types,
 315                 span,
 316                 "where clauses on associated types are unstable"
 317             );
 318         }
 319     }
 320 }
 321
 322 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 323     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 324         let attr_info =
 325             attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name)).map(|a| **a);
 326         // Check feature gates for built-in attributes.
 327         if let Some((.., AttributeGate::Gated(_, name, descr, has_feature))) = attr_info {
 328             gate_feature_fn!(self, has_feature, attr.span, name, descr, GateStrength::Hard);
 329         }
 330         // Check unstable flavors of the `#[doc]` attribute.
 331         if attr.check_name(sym::doc) {
 332             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 333                 macro_rules! gate_doc { ($($name:ident => $feature:ident)*) => {
 334                     $(if nested_meta.check_name(sym::$name) {
 335                         let msg = concat!("`#[doc(", stringify!($name), ")]` is experimental");
 336                         gate_feature!(self, $feature, attr.span, msg);
 337                     })*
 338                 }}
 339
 340                 gate_doc!(
 341                     include => external_doc
 342                     cfg => doc_cfg
 343                     masked => doc_masked
 344                     spotlight => doc_spotlight
 345                     alias => doc_alias
 346                     keyword => doc_keyword
 347                 );
 348             }
 349         }
 350     }
 351
 352     fn visit_name(&mut self, sp: Span, name: ast::Name) {
 353         if !name.as_str().is_ascii() {
 354             gate_feature_post!(
 355                 &self,
 356                 non_ascii_idents,
 357                 self.parse_sess.source_map().def_span(sp),
 358                 "non-ascii idents are not fully supported"
 359             );
 360         }
 361     }
 362
 363     fn visit_item(&mut self, i: &'a ast::Item) {
 364         match i.kind {
 365             ast::ItemKind::ForeignMod(ref foreign_module) => {
 366                 self.check_abi(foreign_module.abi);
 367             }
 368
 369             ast::ItemKind::Fn(..) => {
 370                 if attr::contains_name(&i.attrs[..], sym::plugin_registrar) {
 371                     gate_feature_post!(&self, plugin_registrar, i.span,
 372                                        "compiler plugins are experimental and possibly buggy");
 373                 }
 374                 if attr::contains_name(&i.attrs[..], sym::start) {
 375                     gate_feature_post!(&self, start, i.span,
 376                                       "a `#[start]` function is an experimental \
 377                                        feature whose signature may change \
 378                                        over time");
 379                 }
 380                 if attr::contains_name(&i.attrs[..], sym::main) {
 381                     gate_feature_post!(&self, main, i.span,
 382                                        "declaration of a non-standard `#[main]` \
 383                                         function may change over time, for now \
 384                                         a top-level `fn main()` is required");
 385                 }
 386             }
 387
 388             ast::ItemKind::Struct(..) => {
 389                 for attr in attr::filter_by_name(&i.attrs[..], sym::repr) {
 390                     for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
 391                         if item.check_name(sym::simd) {
 392                             gate_feature_post!(&self, repr_simd, attr.span,
 393                                                "SIMD types are experimental and possibly buggy");
 394                         }
 395                     }
 396                 }
 397             }
 398
 399             ast::ItemKind::Enum(ast::EnumDef{ref variants, ..}, ..) => {
 400                 for variant in variants {
 401                     match (&variant.data, &variant.disr_expr) {
 402                         (ast::VariantData::Unit(..), _) => {},
 403                         (_, Some(disr_expr)) =>
 404                             gate_feature_post!(
 405                                 &self,
 406                                 arbitrary_enum_discriminant,
 407                                 disr_expr.value.span,
 408                                 "discriminants on non-unit variants are experimental"),
 409                         _ => {},
 410                     }
 411                 }
 412
 413                 let has_feature = self.features.arbitrary_enum_discriminant;
 414                 if !has_feature && !i.span.allows_unstable(sym::arbitrary_enum_discriminant) {
 415                     self.maybe_report_invalid_custom_discriminants(&variants);
 416                 }
 417             }
 418
 419             ast::ItemKind::Impl(_, polarity, defaultness, ..) => {
 420                 if polarity == ast::ImplPolarity::Negative {
 421                     gate_feature_post!(&self, optin_builtin_traits,
 422                                        i.span,
 423                                        "negative trait bounds are not yet fully implemented; \
 424                                         use marker types for now");
 425                 }
 426
 427                 if let ast::Defaultness::Default = defaultness {
 428                     gate_feature_post!(&self, specialization,
 429                                        i.span,
 430                                        "specialization is unstable");
 431                 }
 432             }
 433
 434             ast::ItemKind::Trait(ast::IsAuto::Yes, ..) => {
 435                 gate_feature_post!(&self, optin_builtin_traits,
 436                                    i.span,
 437                                    "auto traits are experimental and possibly buggy");
 438             }
 439
 440             ast::ItemKind::TraitAlias(..) => {
 441                 gate_feature_post!(
 442                     &self,
 443                     trait_alias,
 444                     i.span,
 445                     "trait aliases are experimental"
 446                 );
 447             }
 448
 449             ast::ItemKind::MacroDef(ast::MacroDef { legacy: false, .. }) => {
 450                 let msg = "`macro` is experimental";
 451                 gate_feature_post!(&self, decl_macro, i.span, msg);
 452             }
 453
 454             ast::ItemKind::OpaqueTy(..) => {
 455                 gate_feature_post!(
 456                     &self,
 457                     type_alias_impl_trait,
 458                     i.span,
 459                     "`impl Trait` in type aliases is unstable"
 460                 );
 461             }
 462
 463             _ => {}
 464         }
 465
 466         visit::walk_item(self, i);
 467     }
 468
 469     fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
 470         match i.kind {
 471             ast::ForeignItemKind::Fn(..) |
 472             ast::ForeignItemKind::Static(..) => {
 473                 let link_name = attr::first_attr_value_str_by_name(&i.attrs, sym::link_name);
 474                 let links_to_llvm = match link_name {
 475                     Some(val) => val.as_str().starts_with("llvm."),
 476                     _ => false
 477                 };
 478                 if links_to_llvm {
 479                     gate_feature_post!(&self, link_llvm_intrinsics, i.span,
 480                                        "linking to LLVM intrinsics is experimental");
 481                 }
 482             }
 483             ast::ForeignItemKind::Ty => {
 484                     gate_feature_post!(&self, extern_types, i.span,
 485                                        "extern types are experimental");
 486             }
 487             ast::ForeignItemKind::Macro(..) => {}
 488         }
 489
 490         visit::walk_foreign_item(self, i)
 491     }
 492
 493     fn visit_ty(&mut self, ty: &'a ast::Ty) {
 494         match ty.kind {
 495             ast::TyKind::BareFn(ref bare_fn_ty) => {
 496                 self.check_abi(bare_fn_ty.abi);
 497             }
 498             ast::TyKind::Never => {
 499                 gate_feature_post!(&self, never_type, ty.span,
 500                                    "The `!` type is experimental");
 501             }
 502             _ => {}
 503         }
 504         visit::walk_ty(self, ty)
 505     }
 506
 507     fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FunctionRetTy) {
 508         if let ast::FunctionRetTy::Ty(ref output_ty) = *ret_ty {
 509             if let ast::TyKind::Never = output_ty.kind {
 510                 // Do nothing.
 511             } else {
 512                 self.visit_ty(output_ty)
 513             }
 514         }
 515     }
 516
 517     fn visit_expr(&mut self, e: &'a ast::Expr) {
 518         match e.kind {
 519             ast::ExprKind::Box(_) => {
 520                 gate_feature_post!(&self, box_syntax, e.span, EXPLAIN_BOX_SYNTAX);
 521             }
 522             ast::ExprKind::Type(..) => {
 523                 // To avoid noise about type ascription in common syntax errors, only emit if it
 524                 // is the *only* error.
 525                 if self.parse_sess.span_diagnostic.err_count() == 0 {
 526                     gate_feature_post!(&self, type_ascription, e.span,
 527                                        "type ascription is experimental");
 528                 }
 529             }
 530             ast::ExprKind::TryBlock(_) => {
 531                 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
 532             }
 533             ast::ExprKind::Block(_, opt_label) => {
 534                 if let Some(label) = opt_label {
 535                     gate_feature_post!(&self, label_break_value, label.ident.span,
 536                                     "labels on blocks are unstable");
 537                 }
 538             }
 539             _ => {}
 540         }
 541         visit::walk_expr(self, e)
 542     }
 543
 544     fn visit_arm(&mut self, arm: &'a ast::Arm) {
 545         visit::walk_arm(self, arm)
 546     }
 547
 548     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
 549         match &pattern.kind {
 550             PatKind::Slice(pats) => {
 551                 for pat in &*pats {
 552                     let span = pat.span;
 553                     let inner_pat = match &pat.kind {
 554                         PatKind::Ident(.., Some(pat)) => pat,
 555                         _ => pat,
 556                     };
 557                     if inner_pat.is_rest() {
 558                         gate_feature_post!(
 559                             &self,
 560                             slice_patterns,
 561                             span,
 562                             "subslice patterns are unstable"
 563                         );
 564                     }
 565                 }
 566             }
 567             PatKind::Box(..) => {
 568                 gate_feature_post!(&self, box_patterns,
 569                                   pattern.span,
 570                                   "box pattern syntax is experimental");
 571             }
 572             PatKind::Range(_, _, Spanned { node: RangeEnd::Excluded, .. }) => {
 573                 gate_feature_post!(&self, exclusive_range_pattern, pattern.span,
 574                                    "exclusive range pattern syntax is experimental");
 575             }
 576             _ => {}
 577         }
 578         visit::walk_pat(self, pattern)
 579     }
 580
 581     fn visit_fn(&mut self,
 582                 fn_kind: FnKind<'a>,
 583                 fn_decl: &'a ast::FnDecl,
 584                 span: Span,
 585                 _node_id: NodeId) {
 586         if let Some(header) = fn_kind.header() {
 587             // Stability of const fn methods are covered in
 588             // `visit_trait_item` and `visit_impl_item` below; this is
 589             // because default methods don't pass through this point.
 590             self.check_abi(header.abi);
 591         }
 592
 593         if fn_decl.c_variadic() {
 594             gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
 595         }
 596
 597         visit::walk_fn(self, fn_kind, fn_decl, span)
 598     }
 599
 600     fn visit_generic_param(&mut self, param: &'a GenericParam) {
 601         match param.kind {
 602             GenericParamKind::Const { .. } =>
 603                 gate_feature_post!(&self, const_generics, param.ident.span,
 604                     "const generics are unstable"),
 605             _ => {}
 606         }
 607         visit::walk_generic_param(self, param)
 608     }
 609
 610     fn visit_assoc_ty_constraint(&mut self, constraint: &'a AssocTyConstraint) {
 611         match constraint.kind {
 612             AssocTyConstraintKind::Bound { .. } =>
 613                 gate_feature_post!(&self, associated_type_bounds, constraint.span,
 614                     "associated type bounds are unstable"),
 615             _ => {}
 616         }
 617         visit::walk_assoc_ty_constraint(self, constraint)
 618     }
 619
 620     fn visit_trait_item(&mut self, ti: &'a ast::TraitItem) {
 621         match ti.kind {
 622             ast::TraitItemKind::Method(ref sig, ref block) => {
 623                 if block.is_none() {
 624                     self.check_abi(sig.header.abi);
 625                 }
 626                 if sig.decl.c_variadic() {
 627                     gate_feature_post!(&self, c_variadic, ti.span,
 628                                        "C-variadic functions are unstable");
 629                 }
 630                 if sig.header.constness.node == ast::Constness::Const {
 631                     gate_feature_post!(&self, const_fn, ti.span, "const fn is unstable");
 632                 }
 633             }
 634             ast::TraitItemKind::Type(_, ref default) => {
 635                 // We use three if statements instead of something like match guards so that all
 636                 // of these errors can be emitted if all cases apply.
 637                 if default.is_some() {
 638                     gate_feature_post!(&self, associated_type_defaults, ti.span,
 639                                        "associated type defaults are unstable");
 640                 }
 641                 self.check_gat(&ti.generics, ti.span);
 642             }
 643             _ => {}
 644         }
 645         visit::walk_trait_item(self, ti)
 646     }
 647
 648     fn visit_impl_item(&mut self, ii: &'a ast::ImplItem) {
 649         if ii.defaultness == ast::Defaultness::Default {
 650             gate_feature_post!(&self, specialization,
 651                               ii.span,
 652                               "specialization is unstable");
 653         }
 654
 655         match ii.kind {
 656             ast::ImplItemKind::Method(ref sig, _) => {
 657                 if sig.decl.c_variadic() {
 658                     gate_feature_post!(&self, c_variadic, ii.span,
 659                                        "C-variadic functions are unstable");
 660                 }
 661             }
 662             ast::ImplItemKind::OpaqueTy(..) => {
 663                 gate_feature_post!(
 664                     &self,
 665                     type_alias_impl_trait,
 666                     ii.span,
 667                     "`impl Trait` in type aliases is unstable"
 668                 );
 669             }
 670             ast::ImplItemKind::TyAlias(_) => {
 671                 self.check_gat(&ii.generics, ii.span);
 672             }
 673             _ => {}
 674         }
 675         visit::walk_impl_item(self, ii)
 676     }
 677
 678     fn visit_vis(&mut self, vis: &'a ast::Visibility) {
 679         if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.node {
 680             gate_feature_post!(&self, crate_visibility_modifier, vis.span,
 681                                "`crate` visibility modifier is experimental");
 682         }
 683         visit::walk_vis(self, vis)
 684     }
 685 }
 686
 687 pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
 688                     crate_edition: Edition, allow_features: &Option<Vec<String>>) -> Features {
 689     fn feature_removed(span_handler: &Handler, span: Span, reason: Option<&str>) {
 690         let mut err = struct_span_err!(span_handler, span, E0557, "feature has been removed");
 691         if let Some(reason) = reason {
 692             err.span_note(span, reason);
 693         } else {
 694             err.span_label(span, "feature has been removed");
 695         }
 696         err.emit();
 697     }
 698
 699     let mut features = Features::new();
 700     let mut edition_enabled_features = FxHashMap::default();
 701
 702     for &edition in ALL_EDITIONS {
 703         if edition <= crate_edition {
 704             // The `crate_edition` implies its respective umbrella feature-gate
 705             // (i.e., `#![feature(rust_20XX_preview)]` isn't needed on edition 20XX).
 706             edition_enabled_features.insert(edition.feature_name(), edition);
 707         }
 708     }
 709
 710     for feature in active_features_up_to(crate_edition) {
 711         feature.set(&mut features, DUMMY_SP);
 712         edition_enabled_features.insert(feature.name, crate_edition);
 713     }
 714
 715     // Process the edition umbrella feature-gates first, to ensure
 716     // `edition_enabled_features` is completed before it's queried.
 717     for attr in krate_attrs {
 718         if !attr.check_name(sym::feature) {
 719             continue
 720         }
 721
 722         let list = match attr.meta_item_list() {
 723             Some(list) => list,
 724             None => continue,
 725         };
 726
 727         for mi in list {
 728             if !mi.is_word() {
 729                 continue;
 730             }
 731
 732             let name = mi.name_or_empty();
 733
 734             let edition = ALL_EDITIONS.iter().find(|e| name == e.feature_name()).copied();
 735             if let Some(edition) = edition {
 736                 if edition <= crate_edition {
 737                     continue;
 738                 }
 739
 740                 for feature in active_features_up_to(edition) {
 741                     // FIXME(Manishearth) there is currently no way to set
 742                     // lib features by edition
 743                     feature.set(&mut features, DUMMY_SP);
 744                     edition_enabled_features.insert(feature.name, edition);
 745                 }
 746             }
 747         }
 748     }
 749
 750     for attr in krate_attrs {
 751         if !attr.check_name(sym::feature) {
 752             continue
 753         }
 754
 755         let list = match attr.meta_item_list() {
 756             Some(list) => list,
 757             None => continue,
 758         };
 759
 760         let bad_input = |span| {
 761             struct_span_err!(span_handler, span, E0556, "malformed `feature` attribute input")
 762         };
 763
 764         for mi in list {
 765             let name = match mi.ident() {
 766                 Some(ident) if mi.is_word() => ident.name,
 767                 Some(ident) => {
 768                     bad_input(mi.span()).span_suggestion(
 769                         mi.span(),
 770                         "expected just one word",
 771                         format!("{}", ident.name),
 772                         Applicability::MaybeIncorrect,
 773                     ).emit();
 774                     continue
 775                 }
 776                 None => {
 777                     bad_input(mi.span()).span_label(mi.span(), "expected just one word").emit();
 778                     continue
 779                 }
 780             };
 781
 782             if let Some(edition) = edition_enabled_features.get(&name) {
 783                 struct_span_warn!(
 784                     span_handler,
 785                     mi.span(),
 786                     E0705,
 787                     "the feature `{}` is included in the Rust {} edition",
 788                     name,
 789                     edition,
 790                 ).emit();
 791                 continue;
 792             }
 793
 794             if ALL_EDITIONS.iter().any(|e| name == e.feature_name()) {
 795                 // Handled in the separate loop above.
 796                 continue;
 797             }
 798
 799             let removed = REMOVED_FEATURES.iter().find(|f| name == f.name);
 800             let stable_removed = STABLE_REMOVED_FEATURES.iter().find(|f| name == f.name);
 801             if let Some(Feature { state, .. }) = removed.or(stable_removed) {
 802                 if let FeatureState::Removed { reason }
 803                 | FeatureState::Stabilized { reason } = state
 804                 {
 805                     feature_removed(span_handler, mi.span(), *reason);
 806                     continue;
 807                 }
 808             }
 809
 810             if let Some(Feature { since, .. }) = ACCEPTED_FEATURES.iter().find(|f| name == f.name) {
 811                 let since = Some(Symbol::intern(since));
 812                 features.declared_lang_features.push((name, mi.span(), since));
 813                 continue;
 814             }
 815
 816             if let Some(allowed) = allow_features.as_ref() {
 817                 if allowed.iter().find(|&f| name.as_str() == *f).is_none() {
 818                     span_err!(span_handler, mi.span(), E0725,
 819                               "the feature `{}` is not in the list of allowed features",
 820                               name);
 821                     continue;
 822                 }
 823             }
 824
 825             if let Some(f) = ACTIVE_FEATURES.iter().find(|f| name == f.name) {
 826                 f.set(&mut features, mi.span());
 827                 features.declared_lang_features.push((name, mi.span(), None));
 828                 continue;
 829             }
 830
 831             features.declared_lib_features.push((name, mi.span()));
 832         }
 833     }
 834
 835     features
 836 }
 837
 838 fn active_features_up_to(edition: Edition) -> impl Iterator<Item=&'static Feature> {
 839     ACTIVE_FEATURES.iter()
 840     .filter(move |feature| {
 841         if let Some(feature_edition) = feature.edition {
 842             feature_edition <= edition
 843         } else {
 844             false
 845         }
 846     })
 847 }
 848
 849 pub fn check_crate(krate: &ast::Crate,
 850                    parse_sess: &ParseSess,
 851                    features: &Features,
 852                    unstable: UnstableFeatures) {
 853     maybe_stage_features(&parse_sess.span_diagnostic, krate, unstable);
 854     let mut visitor = PostExpansionVisitor { parse_sess, features };
 855
 856     let spans = parse_sess.gated_spans.spans.borrow();
 857     macro_rules! gate_all {
 858         ($gate:ident, $msg:literal) => {
 859             for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 860                 gate_feature!(&visitor, $gate, *span, $msg);
 861             }
 862         }
 863     }
 864     gate_all!(let_chains, "`let` expressions in this position are experimental");
 865     gate_all!(async_closure, "async closures are unstable");
 866     gate_all!(generators, "yield syntax is experimental");
 867     gate_all!(or_patterns, "or-patterns syntax is experimental");
 868     gate_all!(const_extern_fn, "`const extern fn` definitions are unstable");
 869
 870     // All uses of `gate_all!` below this point were added in #65742,
 871     // and subsequently disabled (with the non-early gating readded).
 872     macro_rules! gate_all {
 873         ($gate:ident, $msg:literal) => {
 874             // FIXME(eddyb) do something more useful than always
 875             // disabling these uses of early feature-gatings.
 876             if false {
 877                 for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 878                     gate_feature!(&visitor, $gate, *span, $msg);
 879                 }
 880             }
 881         }
 882     }
 883
 884     gate_all!(trait_alias, "trait aliases are experimental");
 885     gate_all!(associated_type_bounds, "associated type bounds are unstable");
 886     gate_all!(crate_visibility_modifier, "`crate` visibility modifier is experimental");
 887     gate_all!(const_generics, "const generics are unstable");
 888     gate_all!(decl_macro, "`macro` is experimental");
 889     gate_all!(box_patterns, "box pattern syntax is experimental");
 890     gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
 891     gate_all!(try_blocks, "`try` blocks are unstable");
 892     gate_all!(label_break_value, "labels on blocks are unstable");
 893     gate_all!(box_syntax, "box expression syntax is experimental; you can call `Box::new` instead");
 894     // To avoid noise about type ascription in common syntax errors,
 895     // only emit if it is the *only* error. (Also check it last.)
 896     if parse_sess.span_diagnostic.err_count() == 0 {
 897         gate_all!(type_ascription, "type ascription is experimental");
 898     }
 899
 900     visit::walk_crate(&mut visitor, krate);
 901 }
 902
 903 #[derive(Clone, Copy, Hash)]
 904 pub enum UnstableFeatures {
 905     /// Hard errors for unstable features are active, as on beta/stable channels.
 906     Disallow,
 907     /// Allow features to be activated, as on nightly.
 908     Allow,
 909     /// Errors are bypassed for bootstrapping. This is required any time
 910     /// during the build that feature-related lints are set to warn or above
 911     /// because the build turns on warnings-as-errors and uses lots of unstable
 912     /// features. As a result, this is always required for building Rust itself.
 913     Cheat
 914 }
 915
 916 impl UnstableFeatures {
 917     pub fn from_environment() -> UnstableFeatures {
 918         // `true` if this is a feature-staged build, i.e., on the beta or stable channel.
 919         let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
 920         // `true` if we should enable unstable features for bootstrapping.
 921         let bootstrap = env::var("RUSTC_BOOTSTRAP").is_ok();
 922         match (disable_unstable_features, bootstrap) {
 923             (_, true) => UnstableFeatures::Cheat,
 924             (true, _) => UnstableFeatures::Disallow,
 925             (false, _) => UnstableFeatures::Allow
 926         }
 927     }
 928
 929     pub fn is_nightly_build(&self) -> bool {
 930         match *self {
 931             UnstableFeatures::Allow | UnstableFeatures::Cheat => true,
 932             UnstableFeatures::Disallow => false,
 933         }
 934     }
 935 }
 936
 937 fn maybe_stage_features(span_handler: &Handler, krate: &ast::Crate, unstable: UnstableFeatures) {
 938     if !unstable.is_nightly_build() {
 939         for attr in krate.attrs.iter().filter(|attr| attr.check_name(sym::feature)) {
 940             span_err!(
 941                 span_handler, attr.span, E0554,
 942                 "`#![feature]` may not be used on the {} release channel",
 943                 option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)")
 944             );
 945         }
 946     }
 947 }