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, VariantData,
   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::token;
  15 use crate::sess::ParseSess;
  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 syntax_pos::{Span, DUMMY_SP, MultiSpan};
  22 use log::debug;
  23
  24 use std::env;
  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<u32> {
  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.iter().chain(REMOVED_FEATURES).chain(STABLE_REMOVED_FEATURES)
  70             .find(|t| t.name == feature);
  71         match found {
  72             Some(&Feature { issue, .. }) => issue,
  73             None => panic!("Feature `{}` is not declared anywhere", feature),
  74         }
  75     }
  76 }
  77
  78 pub enum GateIssue {
  79     Language,
  80     Library(Option<u32>)
  81 }
  82
  83 #[derive(Debug, Copy, Clone, PartialEq)]
  84 pub enum GateStrength {
  85     /// A hard error. (Most feature gates should use this.)
  86     Hard,
  87     /// Only a warning. (Use this only as backwards-compatibility demands.)
  88     Soft,
  89 }
  90
  91 pub fn emit_feature_err(
  92     sess: &ParseSess,
  93     feature: Symbol,
  94     span: Span,
  95     issue: GateIssue,
  96     explain: &str,
  97 ) {
  98     feature_err(sess, feature, span, issue, explain).emit();
  99 }
 100
 101 pub fn feature_err<'a, S: Into<MultiSpan>>(
 102     sess: &'a ParseSess,
 103     feature: Symbol,
 104     span: S,
 105     issue: GateIssue,
 106     explain: &str,
 107 ) -> DiagnosticBuilder<'a> {
 108     leveled_feature_err(sess, feature, span, issue, explain, GateStrength::Hard)
 109 }
 110
 111 fn leveled_feature_err<'a, S: Into<MultiSpan>>(
 112     sess: &'a ParseSess,
 113     feature: Symbol,
 114     span: S,
 115     issue: GateIssue,
 116     explain: &str,
 117     level: GateStrength,
 118 ) -> DiagnosticBuilder<'a> {
 119     let diag = &sess.span_diagnostic;
 120
 121     let issue = match issue {
 122         GateIssue::Language => find_lang_feature_issue(feature),
 123         GateIssue::Library(lib) => lib,
 124     };
 125
 126     let mut err = match level {
 127         GateStrength::Hard => {
 128             diag.struct_span_err_with_code(span, explain, stringify_error_code!(E0658))
 129         }
 130         GateStrength::Soft => diag.struct_span_warn(span, explain),
 131     };
 132
 133     match issue {
 134         None | Some(0) => {}  // We still accept `0` as a stand-in for backwards compatibility
 135         Some(n) => {
 136             err.note(&format!(
 137                 "for more information, see https://github.com/rust-lang/rust/issues/{}",
 138                 n,
 139             ));
 140         }
 141     }
 142
 143     // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
 144     if sess.unstable_features.is_nightly_build() {
 145         err.help(&format!("add `#![feature({})]` to the crate attributes to enable", feature));
 146     }
 147
 148     // If we're on stable and only emitting a "soft" warning, add a note to
 149     // clarify that the feature isn't "on" (rather than being on but
 150     // warning-worthy).
 151     if !sess.unstable_features.is_nightly_build() && level == GateStrength::Soft {
 152         err.help("a nightly build of the compiler is required to enable this feature");
 153     }
 154
 155     err
 156
 157 }
 158
 159 const EXPLAIN_BOX_SYNTAX: &str =
 160     "box expression syntax is experimental; you can call `Box::new` instead";
 161
 162 pub const EXPLAIN_STMT_ATTR_SYNTAX: &str =
 163     "attributes on expressions are experimental";
 164
 165 pub const EXPLAIN_ALLOW_INTERNAL_UNSTABLE: &str =
 166     "allow_internal_unstable side-steps feature gating and stability checks";
 167 pub const EXPLAIN_ALLOW_INTERNAL_UNSAFE: &str =
 168     "allow_internal_unsafe side-steps the unsafe_code lint";
 169
 170 pub const EXPLAIN_UNSIZED_TUPLE_COERCION: &str =
 171     "unsized tuple coercion is not stable enough for use and is subject to change";
 172
 173 struct PostExpansionVisitor<'a> {
 174     parse_sess: &'a ParseSess,
 175     features: &'a Features,
 176 }
 177
 178 macro_rules! gate_feature_post {
 179     ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {{
 180         let (cx, span) = ($cx, $span);
 181         if !span.allows_unstable(sym::$feature) {
 182             gate_feature!(cx, $feature, span, $explain)
 183         }
 184     }};
 185     ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {{
 186         let (cx, span) = ($cx, $span);
 187         if !span.allows_unstable(sym::$feature) {
 188             gate_feature!(cx, $feature, span, $explain, $level)
 189         }
 190     }}
 191 }
 192
 193 impl<'a> PostExpansionVisitor<'a> {
 194     fn check_abi(&self, abi: ast::Abi) {
 195         let ast::Abi { symbol, span } = abi;
 196
 197         match &*symbol.as_str() {
 198             // Stable
 199             "Rust" |
 200             "C" |
 201             "cdecl" |
 202             "stdcall" |
 203             "fastcall" |
 204             "aapcs" |
 205             "win64" |
 206             "sysv64" |
 207             "system" => {}
 208             "rust-intrinsic" => {
 209                 gate_feature_post!(&self, intrinsics, span,
 210                                    "intrinsics are subject to change");
 211             },
 212             "platform-intrinsic" => {
 213                 gate_feature_post!(&self, platform_intrinsics, span,
 214                                    "platform intrinsics are experimental and possibly buggy");
 215             },
 216             "vectorcall" => {
 217                 gate_feature_post!(&self, abi_vectorcall, span,
 218                                    "vectorcall is experimental and subject to change");
 219             },
 220             "thiscall" => {
 221                 gate_feature_post!(&self, abi_thiscall, span,
 222                                    "thiscall is experimental and subject to change");
 223             },
 224             "rust-call" => {
 225                 gate_feature_post!(&self, unboxed_closures, span,
 226                                    "rust-call ABI is subject to change");
 227             },
 228             "ptx-kernel" => {
 229                 gate_feature_post!(&self, abi_ptx, span,
 230                                    "PTX ABIs are experimental and subject to change");
 231             },
 232             "unadjusted" => {
 233                 gate_feature_post!(&self, abi_unadjusted, span,
 234                                    "unadjusted ABI is an implementation detail and perma-unstable");
 235             },
 236             "msp430-interrupt" => {
 237                 gate_feature_post!(&self, abi_msp430_interrupt, span,
 238                                    "msp430-interrupt ABI is experimental and subject to change");
 239             },
 240             "x86-interrupt" => {
 241                 gate_feature_post!(&self, abi_x86_interrupt, span,
 242                                    "x86-interrupt ABI is experimental and subject to change");
 243             },
 244             "amdgpu-kernel" => {
 245                 gate_feature_post!(&self, abi_amdgpu_kernel, span,
 246                                    "amdgpu-kernel ABI is experimental and subject to change");
 247             },
 248             "efiapi" => {
 249                 gate_feature_post!(&self, abi_efiapi, span,
 250                                    "efiapi ABI is experimental and subject to change");
 251             },
 252             abi => {
 253                 self.parse_sess.span_diagnostic.delay_span_bug(
 254                     span,
 255                     &format!("unrecognized ABI not caught in lowering: {}", abi),
 256                 )
 257             }
 258         }
 259     }
 260
 261     fn maybe_report_invalid_custom_discriminants(&self, variants: &[ast::Variant]) {
 262         let has_fields = variants.iter().any(|variant| match variant.data {
 263             VariantData::Tuple(..) | VariantData::Struct(..) => true,
 264             VariantData::Unit(..) => false,
 265         });
 266
 267         let discriminant_spans = variants.iter().filter(|variant| match variant.data {
 268             VariantData::Tuple(..) | VariantData::Struct(..) => false,
 269             VariantData::Unit(..) => true,
 270         })
 271         .filter_map(|variant| variant.disr_expr.as_ref().map(|c| c.value.span))
 272         .collect::<Vec<_>>();
 273
 274         if !discriminant_spans.is_empty() && has_fields {
 275             let mut err = feature_err(
 276                 self.parse_sess,
 277                 sym::arbitrary_enum_discriminant,
 278                 discriminant_spans.clone(),
 279                 crate::feature_gate::GateIssue::Language,
 280                 "custom discriminant values are not allowed in enums with tuple or struct variants",
 281             );
 282             for sp in discriminant_spans {
 283                 err.span_label(sp, "disallowed custom discriminant");
 284             }
 285             for variant in variants.iter() {
 286                 match &variant.data {
 287                     VariantData::Struct(..) => {
 288                         err.span_label(
 289                             variant.span,
 290                             "struct variant defined here",
 291                         );
 292                     }
 293                     VariantData::Tuple(..) => {
 294                         err.span_label(
 295                             variant.span,
 296                             "tuple variant defined here",
 297                         );
 298                     }
 299                     VariantData::Unit(..) => {}
 300                 }
 301             }
 302             err.emit();
 303         }
 304     }
 305
 306     fn check_gat(&self, generics: &ast::Generics, span: Span) {
 307         if !generics.params.is_empty() {
 308             gate_feature_post!(
 309                 &self,
 310                 generic_associated_types,
 311                 span,
 312                 "generic associated types are unstable"
 313             );
 314         }
 315         if !generics.where_clause.predicates.is_empty() {
 316             gate_feature_post!(
 317                 &self,
 318                 generic_associated_types,
 319                 span,
 320                 "where clauses on associated types are unstable"
 321             );
 322         }
 323     }
 324 }
 325
 326 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 327     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 328         let attr_info =
 329             attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name)).map(|a| **a);
 330         // Check feature gates for built-in attributes.
 331         if let Some((.., AttributeGate::Gated(_, name, descr, has_feature))) = attr_info {
 332             gate_feature_fn!(self, has_feature, attr.span, name, descr, GateStrength::Hard);
 333         }
 334         // Check input tokens for built-in and key-value attributes.
 335         match attr_info {
 336             // `rustc_dummy` doesn't have any restrictions specific to built-in attributes.
 337             Some((name, _, template, _)) if name != sym::rustc_dummy =>
 338                 check_builtin_attribute(self.parse_sess, attr, name, template),
 339             _ => if let Some(TokenTree::Token(token)) =
 340                     attr.get_normal_item().tokens.trees().next() {
 341                 if token == token::Eq {
 342                     // All key-value attributes are restricted to meta-item syntax.
 343                     attr.parse_meta(self.parse_sess).map_err(|mut err| err.emit()).ok();
 344                 }
 345             }
 346         }
 347         // Check unstable flavors of the `#[doc]` attribute.
 348         if attr.check_name(sym::doc) {
 349             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 350                 macro_rules! gate_doc { ($($name:ident => $feature:ident)*) => {
 351                     $(if nested_meta.check_name(sym::$name) {
 352                         let msg = concat!("`#[doc(", stringify!($name), ")]` is experimental");
 353                         gate_feature!(self, $feature, attr.span, msg);
 354                     })*
 355                 }}
 356
 357                 gate_doc!(
 358                     include => external_doc
 359                     cfg => doc_cfg
 360                     masked => doc_masked
 361                     spotlight => doc_spotlight
 362                     alias => doc_alias
 363                     keyword => doc_keyword
 364                 );
 365             }
 366         }
 367     }
 368
 369     fn visit_name(&mut self, sp: Span, name: ast::Name) {
 370         if !name.as_str().is_ascii() {
 371             gate_feature_post!(
 372                 &self,
 373                 non_ascii_idents,
 374                 self.parse_sess.source_map().def_span(sp),
 375                 "non-ascii idents are not fully supported"
 376             );
 377         }
 378     }
 379
 380     fn visit_item(&mut self, i: &'a ast::Item) {
 381         match i.kind {
 382             ast::ItemKind::ForeignMod(ref foreign_module) => {
 383                 self.check_abi(foreign_module.abi);
 384             }
 385
 386             ast::ItemKind::Fn(..) => {
 387                 if attr::contains_name(&i.attrs[..], sym::plugin_registrar) {
 388                     gate_feature_post!(&self, plugin_registrar, i.span,
 389                                        "compiler plugins are experimental and possibly buggy");
 390                 }
 391                 if attr::contains_name(&i.attrs[..], sym::start) {
 392                     gate_feature_post!(&self, start, i.span,
 393                                       "a `#[start]` function is an experimental \
 394                                        feature whose signature may change \
 395                                        over time");
 396                 }
 397                 if attr::contains_name(&i.attrs[..], sym::main) {
 398                     gate_feature_post!(&self, main, i.span,
 399                                        "declaration of a non-standard `#[main]` \
 400                                         function may change over time, for now \
 401                                         a top-level `fn main()` is required");
 402                 }
 403             }
 404
 405             ast::ItemKind::Struct(..) => {
 406                 for attr in attr::filter_by_name(&i.attrs[..], sym::repr) {
 407                     for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
 408                         if item.check_name(sym::simd) {
 409                             gate_feature_post!(&self, repr_simd, attr.span,
 410                                                "SIMD types are experimental and possibly buggy");
 411                         }
 412                     }
 413                 }
 414             }
 415
 416             ast::ItemKind::Enum(ast::EnumDef{ref variants, ..}, ..) => {
 417                 for variant in variants {
 418                     match (&variant.data, &variant.disr_expr) {
 419                         (ast::VariantData::Unit(..), _) => {},
 420                         (_, Some(disr_expr)) =>
 421                             gate_feature_post!(
 422                                 &self,
 423                                 arbitrary_enum_discriminant,
 424                                 disr_expr.value.span,
 425                                 "discriminants on non-unit variants are experimental"),
 426                         _ => {},
 427                     }
 428                 }
 429
 430                 let has_feature = self.features.arbitrary_enum_discriminant;
 431                 if !has_feature && !i.span.allows_unstable(sym::arbitrary_enum_discriminant) {
 432                     self.maybe_report_invalid_custom_discriminants(&variants);
 433                 }
 434             }
 435
 436             ast::ItemKind::Impl(_, polarity, defaultness, ..) => {
 437                 if polarity == ast::ImplPolarity::Negative {
 438                     gate_feature_post!(&self, optin_builtin_traits,
 439                                        i.span,
 440                                        "negative trait bounds are not yet fully implemented; \
 441                                         use marker types for now");
 442                 }
 443
 444                 if let ast::Defaultness::Default = defaultness {
 445                     gate_feature_post!(&self, specialization,
 446                                        i.span,
 447                                        "specialization is unstable");
 448                 }
 449             }
 450
 451             ast::ItemKind::Trait(ast::IsAuto::Yes, ..) => {
 452                 gate_feature_post!(&self, optin_builtin_traits,
 453                                    i.span,
 454                                    "auto traits are experimental and possibly buggy");
 455             }
 456
 457             ast::ItemKind::TraitAlias(..) => {
 458                 gate_feature_post!(
 459                     &self,
 460                     trait_alias,
 461                     i.span,
 462                     "trait aliases are experimental"
 463                 );
 464             }
 465
 466             ast::ItemKind::MacroDef(ast::MacroDef { legacy: false, .. }) => {
 467                 let msg = "`macro` is experimental";
 468                 gate_feature_post!(&self, decl_macro, i.span, msg);
 469             }
 470
 471             ast::ItemKind::OpaqueTy(..) => {
 472                 gate_feature_post!(
 473                     &self,
 474                     type_alias_impl_trait,
 475                     i.span,
 476                     "`impl Trait` in type aliases is unstable"
 477                 );
 478             }
 479
 480             _ => {}
 481         }
 482
 483         visit::walk_item(self, i);
 484     }
 485
 486     fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
 487         match i.kind {
 488             ast::ForeignItemKind::Fn(..) |
 489             ast::ForeignItemKind::Static(..) => {
 490                 let link_name = attr::first_attr_value_str_by_name(&i.attrs, sym::link_name);
 491                 let links_to_llvm = match link_name {
 492                     Some(val) => val.as_str().starts_with("llvm."),
 493                     _ => false
 494                 };
 495                 if links_to_llvm {
 496                     gate_feature_post!(&self, link_llvm_intrinsics, i.span,
 497                                        "linking to LLVM intrinsics is experimental");
 498                 }
 499             }
 500             ast::ForeignItemKind::Ty => {
 501                     gate_feature_post!(&self, extern_types, i.span,
 502                                        "extern types are experimental");
 503             }
 504             ast::ForeignItemKind::Macro(..) => {}
 505         }
 506
 507         visit::walk_foreign_item(self, i)
 508     }
 509
 510     fn visit_ty(&mut self, ty: &'a ast::Ty) {
 511         match ty.kind {
 512             ast::TyKind::BareFn(ref bare_fn_ty) => {
 513                 self.check_abi(bare_fn_ty.abi);
 514             }
 515             ast::TyKind::Never => {
 516                 gate_feature_post!(&self, never_type, ty.span,
 517                                    "The `!` type is experimental");
 518             }
 519             _ => {}
 520         }
 521         visit::walk_ty(self, ty)
 522     }
 523
 524     fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FunctionRetTy) {
 525         if let ast::FunctionRetTy::Ty(ref output_ty) = *ret_ty {
 526             if let ast::TyKind::Never = output_ty.kind {
 527                 // Do nothing.
 528             } else {
 529                 self.visit_ty(output_ty)
 530             }
 531         }
 532     }
 533
 534     fn visit_expr(&mut self, e: &'a ast::Expr) {
 535         match e.kind {
 536             ast::ExprKind::Box(_) => {
 537                 gate_feature_post!(&self, box_syntax, e.span, EXPLAIN_BOX_SYNTAX);
 538             }
 539             ast::ExprKind::Type(..) => {
 540                 // To avoid noise about type ascription in common syntax errors, only emit if it
 541                 // is the *only* error.
 542                 if self.parse_sess.span_diagnostic.err_count() == 0 {
 543                     gate_feature_post!(&self, type_ascription, e.span,
 544                                        "type ascription is experimental");
 545                 }
 546             }
 547             ast::ExprKind::TryBlock(_) => {
 548                 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
 549             }
 550             ast::ExprKind::Block(_, opt_label) => {
 551                 if let Some(label) = opt_label {
 552                     gate_feature_post!(&self, label_break_value, label.ident.span,
 553                                     "labels on blocks are unstable");
 554                 }
 555             }
 556             _ => {}
 557         }
 558         visit::walk_expr(self, e)
 559     }
 560
 561     fn visit_arm(&mut self, arm: &'a ast::Arm) {
 562         visit::walk_arm(self, arm)
 563     }
 564
 565     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
 566         match &pattern.kind {
 567             PatKind::Slice(pats) => {
 568                 for pat in &*pats {
 569                     let span = pat.span;
 570                     let inner_pat = match &pat.kind {
 571                         PatKind::Ident(.., Some(pat)) => pat,
 572                         _ => pat,
 573                     };
 574                     if inner_pat.is_rest() {
 575                         gate_feature_post!(
 576                             &self,
 577                             slice_patterns,
 578                             span,
 579                             "subslice patterns are unstable"
 580                         );
 581                     }
 582                 }
 583             }
 584             PatKind::Box(..) => {
 585                 gate_feature_post!(&self, box_patterns,
 586                                   pattern.span,
 587                                   "box pattern syntax is experimental");
 588             }
 589             PatKind::Range(_, _, Spanned { node: RangeEnd::Excluded, .. }) => {
 590                 gate_feature_post!(&self, exclusive_range_pattern, pattern.span,
 591                                    "exclusive range pattern syntax is experimental");
 592             }
 593             _ => {}
 594         }
 595         visit::walk_pat(self, pattern)
 596     }
 597
 598     fn visit_fn(&mut self,
 599                 fn_kind: FnKind<'a>,
 600                 fn_decl: &'a ast::FnDecl,
 601                 span: Span,
 602                 _node_id: NodeId) {
 603         if let Some(header) = fn_kind.header() {
 604             // Stability of const fn methods are covered in
 605             // `visit_trait_item` and `visit_impl_item` below; this is
 606             // because default methods don't pass through this point.
 607             self.check_abi(header.abi);
 608         }
 609
 610         if fn_decl.c_variadic() {
 611             gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
 612         }
 613
 614         visit::walk_fn(self, fn_kind, fn_decl, span)
 615     }
 616
 617     fn visit_generic_param(&mut self, param: &'a GenericParam) {
 618         match param.kind {
 619             GenericParamKind::Const { .. } =>
 620                 gate_feature_post!(&self, const_generics, param.ident.span,
 621                     "const generics are unstable"),
 622             _ => {}
 623         }
 624         visit::walk_generic_param(self, param)
 625     }
 626
 627     fn visit_assoc_ty_constraint(&mut self, constraint: &'a AssocTyConstraint) {
 628         match constraint.kind {
 629             AssocTyConstraintKind::Bound { .. } =>
 630                 gate_feature_post!(&self, associated_type_bounds, constraint.span,
 631                     "associated type bounds are unstable"),
 632             _ => {}
 633         }
 634         visit::walk_assoc_ty_constraint(self, constraint)
 635     }
 636
 637     fn visit_trait_item(&mut self, ti: &'a ast::TraitItem) {
 638         match ti.kind {
 639             ast::TraitItemKind::Method(ref sig, ref block) => {
 640                 if block.is_none() {
 641                     self.check_abi(sig.header.abi);
 642                 }
 643                 if sig.decl.c_variadic() {
 644                     gate_feature_post!(&self, c_variadic, ti.span,
 645                                        "C-variadic functions are unstable");
 646                 }
 647                 if sig.header.constness.node == ast::Constness::Const {
 648                     gate_feature_post!(&self, const_fn, ti.span, "const fn is unstable");
 649                 }
 650             }
 651             ast::TraitItemKind::Type(_, ref default) => {
 652                 // We use three if statements instead of something like match guards so that all
 653                 // of these errors can be emitted if all cases apply.
 654                 if default.is_some() {
 655                     gate_feature_post!(&self, associated_type_defaults, ti.span,
 656                                        "associated type defaults are unstable");
 657                 }
 658                 self.check_gat(&ti.generics, ti.span);
 659             }
 660             _ => {}
 661         }
 662         visit::walk_trait_item(self, ti)
 663     }
 664
 665     fn visit_impl_item(&mut self, ii: &'a ast::ImplItem) {
 666         if ii.defaultness == ast::Defaultness::Default {
 667             gate_feature_post!(&self, specialization,
 668                               ii.span,
 669                               "specialization is unstable");
 670         }
 671
 672         match ii.kind {
 673             ast::ImplItemKind::Method(ref sig, _) => {
 674                 if sig.decl.c_variadic() {
 675                     gate_feature_post!(&self, c_variadic, ii.span,
 676                                        "C-variadic functions are unstable");
 677                 }
 678             }
 679             ast::ImplItemKind::OpaqueTy(..) => {
 680                 gate_feature_post!(
 681                     &self,
 682                     type_alias_impl_trait,
 683                     ii.span,
 684                     "`impl Trait` in type aliases is unstable"
 685                 );
 686             }
 687             ast::ImplItemKind::TyAlias(_) => {
 688                 self.check_gat(&ii.generics, ii.span);
 689             }
 690             _ => {}
 691         }
 692         visit::walk_impl_item(self, ii)
 693     }
 694
 695     fn visit_vis(&mut self, vis: &'a ast::Visibility) {
 696         if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.node {
 697             gate_feature_post!(&self, crate_visibility_modifier, vis.span,
 698                                "`crate` visibility modifier is experimental");
 699         }
 700         visit::walk_vis(self, vis)
 701     }
 702 }
 703
 704 pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
 705                     crate_edition: Edition, allow_features: &Option<Vec<String>>) -> Features {
 706     fn feature_removed(span_handler: &Handler, span: Span, reason: Option<&str>) {
 707         let mut err = struct_span_err!(span_handler, span, E0557, "feature has been removed");
 708         if let Some(reason) = reason {
 709             err.span_note(span, reason);
 710         } else {
 711             err.span_label(span, "feature has been removed");
 712         }
 713         err.emit();
 714     }
 715
 716     let mut features = Features::new();
 717     let mut edition_enabled_features = FxHashMap::default();
 718
 719     for &edition in ALL_EDITIONS {
 720         if edition <= crate_edition {
 721             // The `crate_edition` implies its respective umbrella feature-gate
 722             // (i.e., `#![feature(rust_20XX_preview)]` isn't needed on edition 20XX).
 723             edition_enabled_features.insert(edition.feature_name(), edition);
 724         }
 725     }
 726
 727     for feature in active_features_up_to(crate_edition) {
 728         feature.set(&mut features, DUMMY_SP);
 729         edition_enabled_features.insert(feature.name, crate_edition);
 730     }
 731
 732     // Process the edition umbrella feature-gates first, to ensure
 733     // `edition_enabled_features` is completed before it's queried.
 734     for attr in krate_attrs {
 735         if !attr.check_name(sym::feature) {
 736             continue
 737         }
 738
 739         let list = match attr.meta_item_list() {
 740             Some(list) => list,
 741             None => continue,
 742         };
 743
 744         for mi in list {
 745             if !mi.is_word() {
 746                 continue;
 747             }
 748
 749             let name = mi.name_or_empty();
 750
 751             let edition = ALL_EDITIONS.iter().find(|e| name == e.feature_name()).copied();
 752             if let Some(edition) = edition {
 753                 if edition <= crate_edition {
 754                     continue;
 755                 }
 756
 757                 for feature in active_features_up_to(edition) {
 758                     // FIXME(Manishearth) there is currently no way to set
 759                     // lib features by edition
 760                     feature.set(&mut features, DUMMY_SP);
 761                     edition_enabled_features.insert(feature.name, edition);
 762                 }
 763             }
 764         }
 765     }
 766
 767     for attr in krate_attrs {
 768         if !attr.check_name(sym::feature) {
 769             continue
 770         }
 771
 772         let list = match attr.meta_item_list() {
 773             Some(list) => list,
 774             None => continue,
 775         };
 776
 777         let bad_input = |span| {
 778             struct_span_err!(span_handler, span, E0556, "malformed `feature` attribute input")
 779         };
 780
 781         for mi in list {
 782             let name = match mi.ident() {
 783                 Some(ident) if mi.is_word() => ident.name,
 784                 Some(ident) => {
 785                     bad_input(mi.span()).span_suggestion(
 786                         mi.span(),
 787                         "expected just one word",
 788                         format!("{}", ident.name),
 789                         Applicability::MaybeIncorrect,
 790                     ).emit();
 791                     continue
 792                 }
 793                 None => {
 794                     bad_input(mi.span()).span_label(mi.span(), "expected just one word").emit();
 795                     continue
 796                 }
 797             };
 798
 799             if let Some(edition) = edition_enabled_features.get(&name) {
 800                 struct_span_warn!(
 801                     span_handler,
 802                     mi.span(),
 803                     E0705,
 804                     "the feature `{}` is included in the Rust {} edition",
 805                     name,
 806                     edition,
 807                 ).emit();
 808                 continue;
 809             }
 810
 811             if ALL_EDITIONS.iter().any(|e| name == e.feature_name()) {
 812                 // Handled in the separate loop above.
 813                 continue;
 814             }
 815
 816             let removed = REMOVED_FEATURES.iter().find(|f| name == f.name);
 817             let stable_removed = STABLE_REMOVED_FEATURES.iter().find(|f| name == f.name);
 818             if let Some(Feature { state, .. }) = removed.or(stable_removed) {
 819                 if let FeatureState::Removed { reason }
 820                 | FeatureState::Stabilized { reason } = state
 821                 {
 822                     feature_removed(span_handler, mi.span(), *reason);
 823                     continue;
 824                 }
 825             }
 826
 827             if let Some(Feature { since, .. }) = ACCEPTED_FEATURES.iter().find(|f| name == f.name) {
 828                 let since = Some(Symbol::intern(since));
 829                 features.declared_lang_features.push((name, mi.span(), since));
 830                 continue;
 831             }
 832
 833             if let Some(allowed) = allow_features.as_ref() {
 834                 if allowed.iter().find(|&f| name.as_str() == *f).is_none() {
 835                     span_err!(span_handler, mi.span(), E0725,
 836                               "the feature `{}` is not in the list of allowed features",
 837                               name);
 838                     continue;
 839                 }
 840             }
 841
 842             if let Some(f) = ACTIVE_FEATURES.iter().find(|f| name == f.name) {
 843                 f.set(&mut features, mi.span());
 844                 features.declared_lang_features.push((name, mi.span(), None));
 845                 continue;
 846             }
 847
 848             features.declared_lib_features.push((name, mi.span()));
 849         }
 850     }
 851
 852     features
 853 }
 854
 855 fn active_features_up_to(edition: Edition) -> impl Iterator<Item=&'static Feature> {
 856     ACTIVE_FEATURES.iter()
 857     .filter(move |feature| {
 858         if let Some(feature_edition) = feature.edition {
 859             feature_edition <= edition
 860         } else {
 861             false
 862         }
 863     })
 864 }
 865
 866 pub fn check_crate(krate: &ast::Crate,
 867                    parse_sess: &ParseSess,
 868                    features: &Features,
 869                    unstable: UnstableFeatures) {
 870     maybe_stage_features(&parse_sess.span_diagnostic, krate, unstable);
 871     let mut visitor = PostExpansionVisitor { parse_sess, features };
 872
 873     let spans = parse_sess.gated_spans.spans.borrow();
 874     macro_rules! gate_all {
 875         ($gate:ident, $msg:literal) => {
 876             for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 877                 gate_feature!(&visitor, $gate, *span, $msg);
 878             }
 879         }
 880     }
 881     gate_all!(let_chains, "`let` expressions in this position are experimental");
 882     gate_all!(async_closure, "async closures are unstable");
 883     gate_all!(generators, "yield syntax is experimental");
 884     gate_all!(or_patterns, "or-patterns syntax is experimental");
 885     gate_all!(const_extern_fn, "`const extern fn` definitions are unstable");
 886
 887     // All uses of `gate_all!` below this point were added in #65742,
 888     // and subsequently disabled (with the non-early gating readded).
 889     macro_rules! gate_all {
 890         ($gate:ident, $msg:literal) => {
 891             // FIXME(eddyb) do something more useful than always
 892             // disabling these uses of early feature-gatings.
 893             if false {
 894                 for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 895                     gate_feature!(&visitor, $gate, *span, $msg);
 896                 }
 897             }
 898         }
 899     }
 900
 901     gate_all!(trait_alias, "trait aliases are experimental");
 902     gate_all!(associated_type_bounds, "associated type bounds are unstable");
 903     gate_all!(crate_visibility_modifier, "`crate` visibility modifier is experimental");
 904     gate_all!(const_generics, "const generics are unstable");
 905     gate_all!(decl_macro, "`macro` is experimental");
 906     gate_all!(box_patterns, "box pattern syntax is experimental");
 907     gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
 908     gate_all!(try_blocks, "`try` blocks are unstable");
 909     gate_all!(label_break_value, "labels on blocks are unstable");
 910     gate_all!(box_syntax, "box expression syntax is experimental; you can call `Box::new` instead");
 911     // To avoid noise about type ascription in common syntax errors,
 912     // only emit if it is the *only* error. (Also check it last.)
 913     if parse_sess.span_diagnostic.err_count() == 0 {
 914         gate_all!(type_ascription, "type ascription is experimental");
 915     }
 916
 917     visit::walk_crate(&mut visitor, krate);
 918 }
 919
 920 #[derive(Clone, Copy, Hash)]
 921 pub enum UnstableFeatures {
 922     /// Hard errors for unstable features are active, as on beta/stable channels.
 923     Disallow,
 924     /// Allow features to be activated, as on nightly.
 925     Allow,
 926     /// Errors are bypassed for bootstrapping. This is required any time
 927     /// during the build that feature-related lints are set to warn or above
 928     /// because the build turns on warnings-as-errors and uses lots of unstable
 929     /// features. As a result, this is always required for building Rust itself.
 930     Cheat
 931 }
 932
 933 impl UnstableFeatures {
 934     pub fn from_environment() -> UnstableFeatures {
 935         // `true` if this is a feature-staged build, i.e., on the beta or stable channel.
 936         let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
 937         // `true` if we should enable unstable features for bootstrapping.
 938         let bootstrap = env::var("RUSTC_BOOTSTRAP").is_ok();
 939         match (disable_unstable_features, bootstrap) {
 940             (_, true) => UnstableFeatures::Cheat,
 941             (true, _) => UnstableFeatures::Disallow,
 942             (false, _) => UnstableFeatures::Allow
 943         }
 944     }
 945
 946     pub fn is_nightly_build(&self) -> bool {
 947         match *self {
 948             UnstableFeatures::Allow | UnstableFeatures::Cheat => true,
 949             UnstableFeatures::Disallow => false,
 950         }
 951     }
 952 }
 953
 954 fn maybe_stage_features(span_handler: &Handler, krate: &ast::Crate, unstable: UnstableFeatures) {
 955     if !unstable.is_nightly_build() {
 956         for attr in krate.attrs.iter().filter(|attr| attr.check_name(sym::feature)) {
 957             span_err!(
 958                 span_handler, attr.span, E0554,
 959                 "`#![feature]` may not be used on the {} release channel",
 960                 option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)")
 961             );
 962         }
 963     }
 964 }