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