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::{
   7     self, AssocTyConstraint, AssocTyConstraintKind, NodeId, GenericParam, GenericParamKind,
   8     PatKind, RangeEnd,
   9 };
  10 use crate::attr::{self, check_builtin_attribute};
  11 use crate::source_map::Spanned;
  12 use crate::edition::{ALL_EDITIONS, Edition};
  13 use crate::visit::{self, FnKind, Visitor};
  14 use crate::parse::{token, ParseSess};
  15 use crate::parse::parser::Parser;
  16 use crate::symbol::{Symbol, sym};
  17 use crate::tokenstream::TokenTree;
  18
  19 use errors::{Applicability, DiagnosticBuilder, Handler};
  20 use rustc_data_structures::fx::FxHashMap;
  21 use rustc_target::spec::abi::Abi;
  22 use syntax_pos::{Span, DUMMY_SP, MultiSpan};
  23 use log::debug;
  24
  25 use std::env;
  26
  27 #[derive(Copy, Clone, Debug)]
  28 pub enum Stability {
  29     Unstable,
  30     // First argument is tracking issue link; second argument is an optional
  31     // help message, which defaults to "remove this attribute"
  32     Deprecated(&'static str, Option<&'static str>),
  33 }
  34
  35 macro_rules! gate_feature_fn {
  36     ($cx: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr, $level: expr) => {{
  37         let (cx, has_feature, span,
  38              name, explain, level) = (&*$cx, $has_feature, $span, $name, $explain, $level);
  39         let has_feature: bool = has_feature(&$cx.features);
  40         debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
  41         if !has_feature && !span.allows_unstable($name) {
  42             leveled_feature_err(cx.parse_sess, name, span, GateIssue::Language, explain, level)
  43                 .emit();
  44         }
  45     }}
  46 }
  47
  48 macro_rules! gate_feature {
  49     ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {
  50         gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
  51                          sym::$feature, $explain, GateStrength::Hard)
  52     };
  53     ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {
  54         gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
  55                          sym::$feature, $explain, $level)
  56     };
  57 }
  58
  59 crate fn check_attribute(attr: &ast::Attribute, parse_sess: &ParseSess, features: &Features) {
  60     PostExpansionVisitor { parse_sess, features }.visit_attribute(attr)
  61 }
  62
  63 fn find_lang_feature_issue(feature: Symbol) -> Option<u32> {
  64     if let Some(info) = ACTIVE_FEATURES.iter().find(|t| t.name == feature) {
  65         // FIXME (#28244): enforce that active features have issue numbers
  66         // assert!(info.issue.is_some())
  67         info.issue
  68     } else {
  69         // search in Accepted, Removed, or Stable Removed features
  70         let found = ACCEPTED_FEATURES.iter().chain(REMOVED_FEATURES).chain(STABLE_REMOVED_FEATURES)
  71             .find(|t| t.name == feature);
  72         match found {
  73             Some(&Feature { issue, .. }) => issue,
  74             None => panic!("Feature `{}` is not declared anywhere", feature),
  75         }
  76     }
  77 }
  78
  79 pub enum GateIssue {
  80     Language,
  81     Library(Option<u32>)
  82 }
  83
  84 #[derive(Debug, Copy, Clone, PartialEq)]
  85 pub enum GateStrength {
  86     /// A hard error. (Most feature gates should use this.)
  87     Hard,
  88     /// Only a warning. (Use this only as backwards-compatibility demands.)
  89     Soft,
  90 }
  91
  92 pub fn emit_feature_err(
  93     sess: &ParseSess,
  94     feature: Symbol,
  95     span: Span,
  96     issue: GateIssue,
  97     explain: &str,
  98 ) {
  99     feature_err(sess, feature, span, issue, explain).emit();
 100 }
 101
 102 pub fn feature_err<'a, S: Into<MultiSpan>>(
 103     sess: &'a ParseSess,
 104     feature: Symbol,
 105     span: S,
 106     issue: GateIssue,
 107     explain: &str,
 108 ) -> DiagnosticBuilder<'a> {
 109     leveled_feature_err(sess, feature, span, issue, explain, GateStrength::Hard)
 110 }
 111
 112 fn leveled_feature_err<'a, S: Into<MultiSpan>>(
 113     sess: &'a ParseSess,
 114     feature: Symbol,
 115     span: S,
 116     issue: GateIssue,
 117     explain: &str,
 118     level: GateStrength,
 119 ) -> DiagnosticBuilder<'a> {
 120     let diag = &sess.span_diagnostic;
 121
 122     let issue = match issue {
 123         GateIssue::Language => find_lang_feature_issue(feature),
 124         GateIssue::Library(lib) => lib,
 125     };
 126
 127     let mut err = match level {
 128         GateStrength::Hard => {
 129             diag.struct_span_err_with_code(span, explain, stringify_error_code!(E0658))
 130         }
 131         GateStrength::Soft => diag.struct_span_warn(span, explain),
 132     };
 133
 134     match issue {
 135         None | Some(0) => {}  // We still accept `0` as a stand-in for backwards compatibility
 136         Some(n) => {
 137             err.note(&format!(
 138                 "for more information, see https://github.com/rust-lang/rust/issues/{}",
 139                 n,
 140             ));
 141         }
 142     }
 143
 144     // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
 145     if sess.unstable_features.is_nightly_build() {
 146         err.help(&format!("add `#![feature({})]` to the crate attributes to enable", feature));
 147     }
 148
 149     // If we're on stable and only emitting a "soft" warning, add a note to
 150     // clarify that the feature isn't "on" (rather than being on but
 151     // warning-worthy).
 152     if !sess.unstable_features.is_nightly_build() && level == GateStrength::Soft {
 153         err.help("a nightly build of the compiler is required to enable this feature");
 154     }
 155
 156     err
 157
 158 }
 159
 160 const EXPLAIN_BOX_SYNTAX: &str =
 161     "box expression syntax is experimental; you can call `Box::new` instead";
 162
 163 pub const EXPLAIN_STMT_ATTR_SYNTAX: &str =
 164     "attributes on expressions are experimental";
 165
 166 pub const EXPLAIN_ALLOW_INTERNAL_UNSTABLE: &str =
 167     "allow_internal_unstable side-steps feature gating and stability checks";
 168 pub const EXPLAIN_ALLOW_INTERNAL_UNSAFE: &str =
 169     "allow_internal_unsafe side-steps the unsafe_code lint";
 170
 171 pub const EXPLAIN_UNSIZED_TUPLE_COERCION: &str =
 172     "unsized tuple coercion is not stable enough for use and is subject to change";
 173
 174 struct PostExpansionVisitor<'a> {
 175     parse_sess: &'a ParseSess,
 176     features: &'a Features,
 177 }
 178
 179 macro_rules! gate_feature_post {
 180     ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {{
 181         let (cx, span) = ($cx, $span);
 182         if !span.allows_unstable(sym::$feature) {
 183             gate_feature!(cx, $feature, span, $explain)
 184         }
 185     }};
 186     ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {{
 187         let (cx, span) = ($cx, $span);
 188         if !span.allows_unstable(sym::$feature) {
 189             gate_feature!(cx, $feature, span, $explain, $level)
 190         }
 191     }}
 192 }
 193
 194 impl<'a> PostExpansionVisitor<'a> {
 195     fn check_abi(&self, abi: Abi, span: Span) {
 196         match abi {
 197             Abi::RustIntrinsic => {
 198                 gate_feature_post!(&self, intrinsics, span,
 199                                    "intrinsics are subject to change");
 200             },
 201             Abi::PlatformIntrinsic => {
 202                 gate_feature_post!(&self, platform_intrinsics, span,
 203                                    "platform intrinsics are experimental and possibly buggy");
 204             },
 205             Abi::Vectorcall => {
 206                 gate_feature_post!(&self, abi_vectorcall, span,
 207                                    "vectorcall is experimental and subject to change");
 208             },
 209             Abi::Thiscall => {
 210                 gate_feature_post!(&self, abi_thiscall, span,
 211                                    "thiscall is experimental and subject to change");
 212             },
 213             Abi::RustCall => {
 214                 gate_feature_post!(&self, unboxed_closures, span,
 215                                    "rust-call ABI is subject to change");
 216             },
 217             Abi::PtxKernel => {
 218                 gate_feature_post!(&self, abi_ptx, span,
 219                                    "PTX ABIs are experimental and subject to change");
 220             },
 221             Abi::Unadjusted => {
 222                 gate_feature_post!(&self, abi_unadjusted, span,
 223                                    "unadjusted ABI is an implementation detail and perma-unstable");
 224             },
 225             Abi::Msp430Interrupt => {
 226                 gate_feature_post!(&self, abi_msp430_interrupt, span,
 227                                    "msp430-interrupt ABI is experimental and subject to change");
 228             },
 229             Abi::X86Interrupt => {
 230                 gate_feature_post!(&self, abi_x86_interrupt, span,
 231                                    "x86-interrupt ABI is experimental and subject to change");
 232             },
 233             Abi::AmdGpuKernel => {
 234                 gate_feature_post!(&self, abi_amdgpu_kernel, span,
 235                                    "amdgpu-kernel ABI is experimental and subject to change");
 236             },
 237             // Stable
 238             Abi::Cdecl |
 239             Abi::Stdcall |
 240             Abi::Fastcall |
 241             Abi::Aapcs |
 242             Abi::Win64 |
 243             Abi::SysV64 |
 244             Abi::Rust |
 245             Abi::C |
 246             Abi::System => {}
 247         }
 248     }
 249 }
 250
 251 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 252     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 253         let attr_info =
 254             attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name)).map(|a| **a);
 255         // Check feature gates for built-in attributes.
 256         if let Some((.., AttributeGate::Gated(_, name, descr, has_feature))) = attr_info {
 257             gate_feature_fn!(self, has_feature, attr.span, name, descr, GateStrength::Hard);
 258         }
 259         // Check input tokens for built-in and key-value attributes.
 260         match attr_info {
 261             // `rustc_dummy` doesn't have any restrictions specific to built-in attributes.
 262             Some((name, _, template, _)) if name != sym::rustc_dummy =>
 263                 check_builtin_attribute(self.parse_sess, attr, name, template),
 264             _ => if let Some(TokenTree::Token(token)) = attr.tokens.trees().next() {
 265                 if token == token::Eq {
 266                     // All key-value attributes are restricted to meta-item syntax.
 267                     attr.parse_meta(self.parse_sess).map_err(|mut err| err.emit()).ok();
 268                 }
 269             }
 270         }
 271         // Check unstable flavors of the `#[doc]` attribute.
 272         if attr.check_name(sym::doc) {
 273             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 274                 macro_rules! gate_doc { ($($name:ident => $feature:ident)*) => {
 275                     $(if nested_meta.check_name(sym::$name) {
 276                         let msg = concat!("`#[doc(", stringify!($name), ")]` is experimental");
 277                         gate_feature!(self, $feature, attr.span, msg);
 278                     })*
 279                 }}
 280
 281                 gate_doc!(
 282                     include => external_doc
 283                     cfg => doc_cfg
 284                     masked => doc_masked
 285                     spotlight => doc_spotlight
 286                     alias => doc_alias
 287                     keyword => doc_keyword
 288                 );
 289             }
 290         }
 291     }
 292
 293     fn visit_name(&mut self, sp: Span, name: ast::Name) {
 294         if !name.as_str().is_ascii() {
 295             gate_feature_post!(
 296                 &self,
 297                 non_ascii_idents,
 298                 self.parse_sess.source_map().def_span(sp),
 299                 "non-ascii idents are not fully supported"
 300             );
 301         }
 302     }
 303
 304     fn visit_item(&mut self, i: &'a ast::Item) {
 305         match i.kind {
 306             ast::ItemKind::ForeignMod(ref foreign_module) => {
 307                 self.check_abi(foreign_module.abi, i.span);
 308             }
 309
 310             ast::ItemKind::Fn(..) => {
 311                 if attr::contains_name(&i.attrs[..], sym::plugin_registrar) {
 312                     gate_feature_post!(&self, plugin_registrar, i.span,
 313                                        "compiler plugins are experimental and possibly buggy");
 314                 }
 315                 if attr::contains_name(&i.attrs[..], sym::start) {
 316                     gate_feature_post!(&self, start, i.span,
 317                                       "a `#[start]` function is an experimental \
 318                                        feature whose signature may change \
 319                                        over time");
 320                 }
 321                 if attr::contains_name(&i.attrs[..], sym::main) {
 322                     gate_feature_post!(&self, main, i.span,
 323                                        "declaration of a non-standard `#[main]` \
 324                                         function may change over time, for now \
 325                                         a top-level `fn main()` is required");
 326                 }
 327             }
 328
 329             ast::ItemKind::Struct(..) => {
 330                 for attr in attr::filter_by_name(&i.attrs[..], sym::repr) {
 331                     for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
 332                         if item.check_name(sym::simd) {
 333                             gate_feature_post!(&self, repr_simd, attr.span,
 334                                                "SIMD types are experimental and possibly buggy");
 335                         }
 336                     }
 337                 }
 338             }
 339
 340             ast::ItemKind::Enum(ast::EnumDef{ref variants, ..}, ..) => {
 341                 for variant in variants {
 342                     match (&variant.data, &variant.disr_expr) {
 343                         (ast::VariantData::Unit(..), _) => {},
 344                         (_, Some(disr_expr)) =>
 345                             gate_feature_post!(
 346                                 &self,
 347                                 arbitrary_enum_discriminant,
 348                                 disr_expr.value.span,
 349                                 "discriminants on non-unit variants are experimental"),
 350                         _ => {},
 351                     }
 352                 }
 353
 354                 let has_feature = self.features.arbitrary_enum_discriminant;
 355                 if !has_feature && !i.span.allows_unstable(sym::arbitrary_enum_discriminant) {
 356                     Parser::maybe_report_invalid_custom_discriminants(self.parse_sess, &variants);
 357                 }
 358             }
 359
 360             ast::ItemKind::Impl(_, polarity, defaultness, ..) => {
 361                 if polarity == ast::ImplPolarity::Negative {
 362                     gate_feature_post!(&self, optin_builtin_traits,
 363                                        i.span,
 364                                        "negative trait bounds are not yet fully implemented; \
 365                                         use marker types for now");
 366                 }
 367
 368                 if let ast::Defaultness::Default = defaultness {
 369                     gate_feature_post!(&self, specialization,
 370                                        i.span,
 371                                        "specialization is unstable");
 372                 }
 373             }
 374
 375             ast::ItemKind::Trait(ast::IsAuto::Yes, ..) => {
 376                 gate_feature_post!(&self, optin_builtin_traits,
 377                                    i.span,
 378                                    "auto traits are experimental and possibly buggy");
 379             }
 380
 381             ast::ItemKind::TraitAlias(..) => {
 382                 gate_feature_post!(
 383                     &self,
 384                     trait_alias,
 385                     i.span,
 386                     "trait aliases are experimental"
 387                 );
 388             }
 389
 390             ast::ItemKind::MacroDef(ast::MacroDef { legacy: false, .. }) => {
 391                 let msg = "`macro` is experimental";
 392                 gate_feature_post!(&self, decl_macro, i.span, msg);
 393             }
 394
 395             ast::ItemKind::OpaqueTy(..) => {
 396                 gate_feature_post!(
 397                     &self,
 398                     type_alias_impl_trait,
 399                     i.span,
 400                     "`impl Trait` in type aliases is unstable"
 401                 );
 402             }
 403
 404             _ => {}
 405         }
 406
 407         visit::walk_item(self, i);
 408     }
 409
 410     fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
 411         match i.node {
 412             ast::ForeignItemKind::Fn(..) |
 413             ast::ForeignItemKind::Static(..) => {
 414                 let link_name = attr::first_attr_value_str_by_name(&i.attrs, sym::link_name);
 415                 let links_to_llvm = match link_name {
 416                     Some(val) => val.as_str().starts_with("llvm."),
 417                     _ => false
 418                 };
 419                 if links_to_llvm {
 420                     gate_feature_post!(&self, link_llvm_intrinsics, i.span,
 421                                        "linking to LLVM intrinsics is experimental");
 422                 }
 423             }
 424             ast::ForeignItemKind::Ty => {
 425                     gate_feature_post!(&self, extern_types, i.span,
 426                                        "extern types are experimental");
 427             }
 428             ast::ForeignItemKind::Macro(..) => {}
 429         }
 430
 431         visit::walk_foreign_item(self, i)
 432     }
 433
 434     fn visit_ty(&mut self, ty: &'a ast::Ty) {
 435         match ty.kind {
 436             ast::TyKind::BareFn(ref bare_fn_ty) => {
 437                 self.check_abi(bare_fn_ty.abi, ty.span);
 438             }
 439             ast::TyKind::Never => {
 440                 gate_feature_post!(&self, never_type, ty.span,
 441                                    "The `!` type is experimental");
 442             }
 443             _ => {}
 444         }
 445         visit::walk_ty(self, ty)
 446     }
 447
 448     fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FunctionRetTy) {
 449         if let ast::FunctionRetTy::Ty(ref output_ty) = *ret_ty {
 450             if let ast::TyKind::Never = output_ty.kind {
 451                 // Do nothing.
 452             } else {
 453                 self.visit_ty(output_ty)
 454             }
 455         }
 456     }
 457
 458     fn visit_expr(&mut self, e: &'a ast::Expr) {
 459         match e.kind {
 460             ast::ExprKind::Box(_) => {
 461                 gate_feature_post!(&self, box_syntax, e.span, EXPLAIN_BOX_SYNTAX);
 462             }
 463             ast::ExprKind::Type(..) => {
 464                 // To avoid noise about type ascription in common syntax errors, only emit if it
 465                 // is the *only* error.
 466                 if self.parse_sess.span_diagnostic.err_count() == 0 {
 467                     gate_feature_post!(&self, type_ascription, e.span,
 468                                        "type ascription is experimental");
 469                 }
 470             }
 471             ast::ExprKind::TryBlock(_) => {
 472                 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
 473             }
 474             ast::ExprKind::Block(_, opt_label) => {
 475                 if let Some(label) = opt_label {
 476                     gate_feature_post!(&self, label_break_value, label.ident.span,
 477                                     "labels on blocks are unstable");
 478                 }
 479             }
 480             _ => {}
 481         }
 482         visit::walk_expr(self, e)
 483     }
 484
 485     fn visit_arm(&mut self, arm: &'a ast::Arm) {
 486         visit::walk_arm(self, arm)
 487     }
 488
 489     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
 490         match &pattern.kind {
 491             PatKind::Slice(pats) => {
 492                 for pat in &*pats {
 493                     let span = pat.span;
 494                     let inner_pat = match &pat.kind {
 495                         PatKind::Ident(.., Some(pat)) => pat,
 496                         _ => pat,
 497                     };
 498                     if inner_pat.is_rest() {
 499                         gate_feature_post!(
 500                             &self,
 501                             slice_patterns,
 502                             span,
 503                             "subslice patterns are unstable"
 504                         );
 505                     }
 506                 }
 507             }
 508             PatKind::Box(..) => {
 509                 gate_feature_post!(&self, box_patterns,
 510                                   pattern.span,
 511                                   "box pattern syntax is experimental");
 512             }
 513             PatKind::Range(_, _, Spanned { node: RangeEnd::Excluded, .. }) => {
 514                 gate_feature_post!(&self, exclusive_range_pattern, pattern.span,
 515                                    "exclusive range pattern syntax is experimental");
 516             }
 517             _ => {}
 518         }
 519         visit::walk_pat(self, pattern)
 520     }
 521
 522     fn visit_fn(&mut self,
 523                 fn_kind: FnKind<'a>,
 524                 fn_decl: &'a ast::FnDecl,
 525                 span: Span,
 526                 _node_id: NodeId) {
 527         if let Some(header) = fn_kind.header() {
 528             // Stability of const fn methods are covered in
 529             // `visit_trait_item` and `visit_impl_item` below; this is
 530             // because default methods don't pass through this point.
 531             self.check_abi(header.abi, span);
 532         }
 533
 534         if fn_decl.c_variadic {
 535             gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
 536         }
 537
 538         visit::walk_fn(self, fn_kind, fn_decl, span)
 539     }
 540
 541     fn visit_generic_param(&mut self, param: &'a GenericParam) {
 542         match param.kind {
 543             GenericParamKind::Const { .. } =>
 544                 gate_feature_post!(&self, const_generics, param.ident.span,
 545                     "const generics are unstable"),
 546             _ => {}
 547         }
 548         visit::walk_generic_param(self, param)
 549     }
 550
 551     fn visit_assoc_ty_constraint(&mut self, constraint: &'a AssocTyConstraint) {
 552         match constraint.kind {
 553             AssocTyConstraintKind::Bound { .. } =>
 554                 gate_feature_post!(&self, associated_type_bounds, constraint.span,
 555                     "associated type bounds are unstable"),
 556             _ => {}
 557         }
 558         visit::walk_assoc_ty_constraint(self, constraint)
 559     }
 560
 561     fn visit_trait_item(&mut self, ti: &'a ast::TraitItem) {
 562         match ti.kind {
 563             ast::TraitItemKind::Method(ref sig, ref block) => {
 564                 if block.is_none() {
 565                     self.check_abi(sig.header.abi, ti.span);
 566                 }
 567                 if sig.decl.c_variadic {
 568                     gate_feature_post!(&self, c_variadic, ti.span,
 569                                        "C-variadic functions are unstable");
 570                 }
 571                 if sig.header.constness.node == ast::Constness::Const {
 572                     gate_feature_post!(&self, const_fn, ti.span, "const fn is unstable");
 573                 }
 574             }
 575             ast::TraitItemKind::Type(_, ref default) => {
 576                 // We use three if statements instead of something like match guards so that all
 577                 // of these errors can be emitted if all cases apply.
 578                 if default.is_some() {
 579                     gate_feature_post!(&self, associated_type_defaults, ti.span,
 580                                        "associated type defaults are unstable");
 581                 }
 582                 if !ti.generics.params.is_empty() {
 583                     gate_feature_post!(&self, generic_associated_types, ti.span,
 584                                        "generic associated types are unstable");
 585                 }
 586                 if !ti.generics.where_clause.predicates.is_empty() {
 587                     gate_feature_post!(&self, generic_associated_types, ti.span,
 588                                        "where clauses on associated types are unstable");
 589                 }
 590             }
 591             _ => {}
 592         }
 593         visit::walk_trait_item(self, ti)
 594     }
 595
 596     fn visit_impl_item(&mut self, ii: &'a ast::ImplItem) {
 597         if ii.defaultness == ast::Defaultness::Default {
 598             gate_feature_post!(&self, specialization,
 599                               ii.span,
 600                               "specialization is unstable");
 601         }
 602
 603         match ii.kind {
 604             ast::ImplItemKind::Method(..) => {}
 605             ast::ImplItemKind::OpaqueTy(..) => {
 606                 gate_feature_post!(
 607                     &self,
 608                     type_alias_impl_trait,
 609                     ii.span,
 610                     "`impl Trait` in type aliases is unstable"
 611                 );
 612             }
 613             ast::ImplItemKind::TyAlias(_) => {
 614                 if !ii.generics.params.is_empty() {
 615                     gate_feature_post!(&self, generic_associated_types, ii.span,
 616                                        "generic associated types are unstable");
 617                 }
 618                 if !ii.generics.where_clause.predicates.is_empty() {
 619                     gate_feature_post!(&self, generic_associated_types, ii.span,
 620                                        "where clauses on associated types are unstable");
 621                 }
 622             }
 623             _ => {}
 624         }
 625         visit::walk_impl_item(self, ii)
 626     }
 627
 628     fn visit_vis(&mut self, vis: &'a ast::Visibility) {
 629         if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.node {
 630             gate_feature_post!(&self, crate_visibility_modifier, vis.span,
 631                                "`crate` visibility modifier is experimental");
 632         }
 633         visit::walk_vis(self, vis)
 634     }
 635 }
 636
 637 pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
 638                     crate_edition: Edition, allow_features: &Option<Vec<String>>) -> Features {
 639     fn feature_removed(span_handler: &Handler, span: Span, reason: Option<&str>) {
 640         let mut err = struct_span_err!(span_handler, span, E0557, "feature has been removed");
 641         if let Some(reason) = reason {
 642             err.span_note(span, reason);
 643         } else {
 644             err.span_label(span, "feature has been removed");
 645         }
 646         err.emit();
 647     }
 648
 649     let mut features = Features::new();
 650     let mut edition_enabled_features = FxHashMap::default();
 651
 652     for &edition in ALL_EDITIONS {
 653         if edition <= crate_edition {
 654             // The `crate_edition` implies its respective umbrella feature-gate
 655             // (i.e., `#![feature(rust_20XX_preview)]` isn't needed on edition 20XX).
 656             edition_enabled_features.insert(edition.feature_name(), edition);
 657         }
 658     }
 659
 660     for feature in active_features_up_to(crate_edition) {
 661         feature.set(&mut features, DUMMY_SP);
 662         edition_enabled_features.insert(feature.name, crate_edition);
 663     }
 664
 665     // Process the edition umbrella feature-gates first, to ensure
 666     // `edition_enabled_features` is completed before it's queried.
 667     for attr in krate_attrs {
 668         if !attr.check_name(sym::feature) {
 669             continue
 670         }
 671
 672         let list = match attr.meta_item_list() {
 673             Some(list) => list,
 674             None => continue,
 675         };
 676
 677         for mi in list {
 678             if !mi.is_word() {
 679                 continue;
 680             }
 681
 682             let name = mi.name_or_empty();
 683
 684             let edition = ALL_EDITIONS.iter().find(|e| name == e.feature_name()).copied();
 685             if let Some(edition) = edition {
 686                 if edition <= crate_edition {
 687                     continue;
 688                 }
 689
 690                 for feature in active_features_up_to(edition) {
 691                     // FIXME(Manishearth) there is currently no way to set
 692                     // lib features by edition
 693                     feature.set(&mut features, DUMMY_SP);
 694                     edition_enabled_features.insert(feature.name, edition);
 695                 }
 696             }
 697         }
 698     }
 699
 700     for attr in krate_attrs {
 701         if !attr.check_name(sym::feature) {
 702             continue
 703         }
 704
 705         let list = match attr.meta_item_list() {
 706             Some(list) => list,
 707             None => continue,
 708         };
 709
 710         let bad_input = |span| {
 711             struct_span_err!(span_handler, span, E0556, "malformed `feature` attribute input")
 712         };
 713
 714         for mi in list {
 715             let name = match mi.ident() {
 716                 Some(ident) if mi.is_word() => ident.name,
 717                 Some(ident) => {
 718                     bad_input(mi.span()).span_suggestion(
 719                         mi.span(),
 720                         "expected just one word",
 721                         format!("{}", ident.name),
 722                         Applicability::MaybeIncorrect,
 723                     ).emit();
 724                     continue
 725                 }
 726                 None => {
 727                     bad_input(mi.span()).span_label(mi.span(), "expected just one word").emit();
 728                     continue
 729                 }
 730             };
 731
 732             if let Some(edition) = edition_enabled_features.get(&name) {
 733                 struct_span_warn!(
 734                     span_handler,
 735                     mi.span(),
 736                     E0705,
 737                     "the feature `{}` is included in the Rust {} edition",
 738                     name,
 739                     edition,
 740                 ).emit();
 741                 continue;
 742             }
 743
 744             if ALL_EDITIONS.iter().any(|e| name == e.feature_name()) {
 745                 // Handled in the separate loop above.
 746                 continue;
 747             }
 748
 749             let removed = REMOVED_FEATURES.iter().find(|f| name == f.name);
 750             let stable_removed = STABLE_REMOVED_FEATURES.iter().find(|f| name == f.name);
 751             if let Some(Feature { state, .. }) = removed.or(stable_removed) {
 752                 if let FeatureState::Removed { reason }
 753                 | FeatureState::Stabilized { reason } = state
 754                 {
 755                     feature_removed(span_handler, mi.span(), *reason);
 756                     continue;
 757                 }
 758             }
 759
 760             if let Some(Feature { since, .. }) = ACCEPTED_FEATURES.iter().find(|f| name == f.name) {
 761                 let since = Some(Symbol::intern(since));
 762                 features.declared_lang_features.push((name, mi.span(), since));
 763                 continue;
 764             }
 765
 766             if let Some(allowed) = allow_features.as_ref() {
 767                 if allowed.iter().find(|f| *f == name.as_str()).is_none() {
 768                     span_err!(span_handler, mi.span(), E0725,
 769                               "the feature `{}` is not in the list of allowed features",
 770                               name);
 771                     continue;
 772                 }
 773             }
 774
 775             if let Some(f) = ACTIVE_FEATURES.iter().find(|f| name == f.name) {
 776                 f.set(&mut features, mi.span());
 777                 features.declared_lang_features.push((name, mi.span(), None));
 778                 continue;
 779             }
 780
 781             features.declared_lib_features.push((name, mi.span()));
 782         }
 783     }
 784
 785     features
 786 }
 787
 788 fn active_features_up_to(edition: Edition) -> impl Iterator<Item=&'static Feature> {
 789     ACTIVE_FEATURES.iter()
 790     .filter(move |feature| {
 791         if let Some(feature_edition) = feature.edition {
 792             feature_edition <= edition
 793         } else {
 794             false
 795         }
 796     })
 797 }
 798
 799 pub fn check_crate(krate: &ast::Crate,
 800                    parse_sess: &ParseSess,
 801                    features: &Features,
 802                    unstable: UnstableFeatures) {
 803     maybe_stage_features(&parse_sess.span_diagnostic, krate, unstable);
 804     let mut visitor = PostExpansionVisitor { parse_sess, features };
 805
 806     macro_rules! gate_all {
 807         ($gate:ident, $msg:literal) => { gate_all!($gate, $gate, $msg); };
 808         ($spans:ident, $gate:ident, $msg:literal) => {
 809             for span in &*parse_sess.gated_spans.$spans.borrow() {
 810                 gate_feature!(&visitor, $gate, *span, $msg);
 811             }
 812         }
 813     }
 814
 815     gate_all!(let_chains, "`let` expressions in this position are experimental");
 816     gate_all!(async_closure, "async closures are unstable");
 817     gate_all!(yields, generators, "yield syntax is experimental");
 818     gate_all!(or_patterns, "or-patterns syntax is experimental");
 819
 820     visit::walk_crate(&mut visitor, krate);
 821 }
 822
 823 #[derive(Clone, Copy, Hash)]
 824 pub enum UnstableFeatures {
 825     /// Hard errors for unstable features are active, as on beta/stable channels.
 826     Disallow,
 827     /// Allow features to be activated, as on nightly.
 828     Allow,
 829     /// Errors are bypassed for bootstrapping. This is required any time
 830     /// during the build that feature-related lints are set to warn or above
 831     /// because the build turns on warnings-as-errors and uses lots of unstable
 832     /// features. As a result, this is always required for building Rust itself.
 833     Cheat
 834 }
 835
 836 impl UnstableFeatures {
 837     pub fn from_environment() -> UnstableFeatures {
 838         // `true` if this is a feature-staged build, i.e., on the beta or stable channel.
 839         let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
 840         // `true` if we should enable unstable features for bootstrapping.
 841         let bootstrap = env::var("RUSTC_BOOTSTRAP").is_ok();
 842         match (disable_unstable_features, bootstrap) {
 843             (_, true) => UnstableFeatures::Cheat,
 844             (true, _) => UnstableFeatures::Disallow,
 845             (false, _) => UnstableFeatures::Allow
 846         }
 847     }
 848
 849     pub fn is_nightly_build(&self) -> bool {
 850         match *self {
 851             UnstableFeatures::Allow | UnstableFeatures::Cheat => true,
 852             _ => false,
 853         }
 854     }
 855 }
 856
 857 fn maybe_stage_features(span_handler: &Handler, krate: &ast::Crate, unstable: UnstableFeatures) {
 858     let allow_features = match unstable {
 859         UnstableFeatures::Allow => true,
 860         UnstableFeatures::Disallow => false,
 861         UnstableFeatures::Cheat => true
 862     };
 863     if !allow_features {
 864         for attr in &krate.attrs {
 865             if attr.check_name(sym::feature) {
 866                 let release_channel = option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)");
 867                 span_err!(span_handler, attr.span, E0554,
 868                           "`#![feature]` may not be used on the {} release channel",
 869                           release_channel);
 870             }
 871         }
 872     }
 873 }