compiler/rustc_ast_passes/src/feature_gate.rs

   1 use rustc_ast as ast;
   2 use rustc_ast::visit::{self, AssocCtxt, FnCtxt, FnKind, Visitor};
   3 use rustc_ast::{AssocConstraint, AssocConstraintKind, NodeId};
   4 use rustc_ast::{PatKind, RangeEnd, VariantData};
   5 use rustc_errors::{struct_span_err, Applicability, StashKey};
   6 use rustc_feature::{AttributeGate, BuiltinAttribute, Features, GateIssue, BUILTIN_ATTRIBUTE_MAP};
   7 use rustc_session::parse::{feature_err, feature_err_issue, feature_warn};
   8 use rustc_session::Session;
   9 use rustc_span::source_map::Spanned;
  10 use rustc_span::symbol::sym;
  11 use rustc_span::Span;
  12 use rustc_target::spec::abi;
  13
  14 macro_rules! gate_feature_fn {
  15     ($visitor: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr, $help: expr) => {{
  16         let (visitor, has_feature, span, name, explain, help) =
  17             (&*$visitor, $has_feature, $span, $name, $explain, $help);
  18         let has_feature: bool = has_feature(visitor.features);
  19         debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
  20         if !has_feature && !span.allows_unstable($name) {
  21             feature_err(&visitor.sess.parse_sess, name, span, explain).help(help).emit();
  22         }
  23     }};
  24     ($visitor: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr) => {{
  25         let (visitor, has_feature, span, name, explain) =
  26             (&*$visitor, $has_feature, $span, $name, $explain);
  27         let has_feature: bool = has_feature(visitor.features);
  28         debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
  29         if !has_feature && !span.allows_unstable($name) {
  30             feature_err(&visitor.sess.parse_sess, name, span, explain).emit();
  31         }
  32     }};
  33     (future_incompatible; $visitor: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr) => {{
  34         let (visitor, has_feature, span, name, explain) =
  35             (&*$visitor, $has_feature, $span, $name, $explain);
  36         let has_feature: bool = has_feature(visitor.features);
  37         debug!(
  38             "gate_feature(feature = {:?}, span = {:?}); has? {} (future_incompatible)",
  39             name, span, has_feature
  40         );
  41         if !has_feature && !span.allows_unstable($name) {
  42             feature_warn(&visitor.sess.parse_sess, name, span, explain);
  43         }
  44     }};
  45 }
  46
  47 macro_rules! gate_feature_post {
  48     ($visitor: expr, $feature: ident, $span: expr, $explain: expr, $help: expr) => {
  49         gate_feature_fn!($visitor, |x: &Features| x.$feature, $span, sym::$feature, $explain, $help)
  50     };
  51     ($visitor: expr, $feature: ident, $span: expr, $explain: expr) => {
  52         gate_feature_fn!($visitor, |x: &Features| x.$feature, $span, sym::$feature, $explain)
  53     };
  54     (future_incompatible; $visitor: expr, $feature: ident, $span: expr, $explain: expr) => {
  55         gate_feature_fn!(future_incompatible; $visitor, |x: &Features| x.$feature, $span, sym::$feature, $explain)
  56     };
  57 }
  58
  59 pub fn check_attribute(attr: &ast::Attribute, sess: &Session, features: &Features) {
  60     PostExpansionVisitor { sess, features }.visit_attribute(attr)
  61 }
  62
  63 struct PostExpansionVisitor<'a> {
  64     sess: &'a Session,
  65
  66     // `sess` contains a `Features`, but this might not be that one.
  67     features: &'a Features,
  68 }
  69
  70 impl<'a> PostExpansionVisitor<'a> {
  71     fn check_abi(&self, abi: ast::StrLit, constness: ast::Const) {
  72         let ast::StrLit { symbol_unescaped, span, .. } = abi;
  73
  74         if let ast::Const::Yes(_) = constness {
  75             match symbol_unescaped {
  76                 // Stable
  77                 sym::Rust | sym::C => {}
  78                 abi => gate_feature_post!(
  79                     &self,
  80                     const_extern_fn,
  81                     span,
  82                     &format!("`{}` as a `const fn` ABI is unstable", abi)
  83                 ),
  84             }
  85         }
  86
  87         match abi::is_enabled(&self.features, span, symbol_unescaped.as_str()) {
  88             Ok(()) => (),
  89             Err(abi::AbiDisabled::Unstable { feature, explain }) => {
  90                 feature_err_issue(
  91                     &self.sess.parse_sess,
  92                     feature,
  93                     span,
  94                     GateIssue::Language,
  95                     explain,
  96                 )
  97                 .emit();
  98             }
  99             Err(abi::AbiDisabled::Unrecognized) => {
 100                 if self.sess.opts.pretty.map_or(true, |ppm| ppm.needs_hir()) {
 101                     self.sess.parse_sess.span_diagnostic.delay_span_bug(
 102                         span,
 103                         &format!(
 104                             "unrecognized ABI not caught in lowering: {}",
 105                             symbol_unescaped.as_str()
 106                         ),
 107                     );
 108                 }
 109             }
 110         }
 111     }
 112
 113     fn check_extern(&self, ext: ast::Extern, constness: ast::Const) {
 114         if let ast::Extern::Explicit(abi, _) = ext {
 115             self.check_abi(abi, constness);
 116         }
 117     }
 118
 119     fn maybe_report_invalid_custom_discriminants(&self, variants: &[ast::Variant]) {
 120         let has_fields = variants.iter().any(|variant| match variant.data {
 121             VariantData::Tuple(..) | VariantData::Struct(..) => true,
 122             VariantData::Unit(..) => false,
 123         });
 124
 125         let discriminant_spans = variants
 126             .iter()
 127             .filter(|variant| match variant.data {
 128                 VariantData::Tuple(..) | VariantData::Struct(..) => false,
 129                 VariantData::Unit(..) => true,
 130             })
 131             .filter_map(|variant| variant.disr_expr.as_ref().map(|c| c.value.span))
 132             .collect::<Vec<_>>();
 133
 134         if !discriminant_spans.is_empty() && has_fields {
 135             let mut err = feature_err(
 136                 &self.sess.parse_sess,
 137                 sym::arbitrary_enum_discriminant,
 138                 discriminant_spans.clone(),
 139                 "custom discriminant values are not allowed in enums with tuple or struct variants",
 140             );
 141             for sp in discriminant_spans {
 142                 err.span_label(sp, "disallowed custom discriminant");
 143             }
 144             for variant in variants.iter() {
 145                 match &variant.data {
 146                     VariantData::Struct(..) => {
 147                         err.span_label(variant.span, "struct variant defined here");
 148                     }
 149                     VariantData::Tuple(..) => {
 150                         err.span_label(variant.span, "tuple variant defined here");
 151                     }
 152                     VariantData::Unit(..) => {}
 153                 }
 154             }
 155             err.emit();
 156         }
 157     }
 158
 159     /// Feature gate `impl Trait` inside `type Alias = $type_expr;`.
 160     fn check_impl_trait(&self, ty: &ast::Ty) {
 161         struct ImplTraitVisitor<'a> {
 162             vis: &'a PostExpansionVisitor<'a>,
 163         }
 164         impl Visitor<'_> for ImplTraitVisitor<'_> {
 165             fn visit_ty(&mut self, ty: &ast::Ty) {
 166                 if let ast::TyKind::ImplTrait(..) = ty.kind {
 167                     gate_feature_post!(
 168                         &self.vis,
 169                         type_alias_impl_trait,
 170                         ty.span,
 171                         "`impl Trait` in type aliases is unstable"
 172                     );
 173                 }
 174                 visit::walk_ty(self, ty);
 175             }
 176         }
 177         ImplTraitVisitor { vis: self }.visit_ty(ty);
 178     }
 179 }
 180
 181 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 182     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 183         let attr_info = attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name));
 184         // Check feature gates for built-in attributes.
 185         if let Some(BuiltinAttribute {
 186             gate: AttributeGate::Gated(_, name, descr, has_feature),
 187             ..
 188         }) = attr_info
 189         {
 190             gate_feature_fn!(self, has_feature, attr.span, *name, descr);
 191         }
 192         // Check unstable flavors of the `#[doc]` attribute.
 193         if attr.has_name(sym::doc) {
 194             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 195                 macro_rules! gate_doc { ($($name:ident => $feature:ident)*) => {
 196                     $(if nested_meta.has_name(sym::$name) {
 197                         let msg = concat!("`#[doc(", stringify!($name), ")]` is experimental");
 198                         gate_feature_post!(self, $feature, attr.span, msg);
 199                     })*
 200                 }}
 201
 202                 gate_doc!(
 203                     cfg => doc_cfg
 204                     cfg_hide => doc_cfg_hide
 205                     masked => doc_masked
 206                     notable_trait => doc_notable_trait
 207                 );
 208
 209                 if nested_meta.has_name(sym::keyword) {
 210                     let msg = "`#[doc(keyword)]` is meant for internal use only";
 211                     gate_feature_post!(self, rustdoc_internals, attr.span, msg);
 212                 }
 213
 214                 if nested_meta.has_name(sym::fake_variadic) {
 215                     let msg = "`#[doc(fake_variadic)]` is meant for internal use only";
 216                     gate_feature_post!(self, rustdoc_internals, attr.span, msg);
 217                 }
 218             }
 219         }
 220
 221         // Emit errors for non-staged-api crates.
 222         if !self.features.staged_api {
 223             if attr.has_name(sym::unstable)
 224                 || attr.has_name(sym::stable)
 225                 || attr.has_name(sym::rustc_const_unstable)
 226                 || attr.has_name(sym::rustc_const_stable)
 227                 || attr.has_name(sym::rustc_default_body_unstable)
 228             {
 229                 struct_span_err!(
 230                     self.sess,
 231                     attr.span,
 232                     E0734,
 233                     "stability attributes may not be used outside of the standard library",
 234                 )
 235                 .emit();
 236             }
 237         }
 238     }
 239
 240     fn visit_item(&mut self, i: &'a ast::Item) {
 241         match i.kind {
 242             ast::ItemKind::ForeignMod(ref foreign_module) => {
 243                 if let Some(abi) = foreign_module.abi {
 244                     self.check_abi(abi, ast::Const::No);
 245                 }
 246             }
 247
 248             ast::ItemKind::Fn(..) => {
 249                 if self.sess.contains_name(&i.attrs, sym::start) {
 250                     gate_feature_post!(
 251                         &self,
 252                         start,
 253                         i.span,
 254                         "`#[start]` functions are experimental \
 255                          and their signature may change \
 256                          over time"
 257                     );
 258                 }
 259             }
 260
 261             ast::ItemKind::Struct(..) => {
 262                 for attr in self.sess.filter_by_name(&i.attrs, sym::repr) {
 263                     for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
 264                         if item.has_name(sym::simd) {
 265                             gate_feature_post!(
 266                                 &self,
 267                                 repr_simd,
 268                                 attr.span,
 269                                 "SIMD types are experimental and possibly buggy"
 270                             );
 271                         }
 272                     }
 273                 }
 274             }
 275
 276             ast::ItemKind::Enum(ast::EnumDef { ref variants, .. }, ..) => {
 277                 for variant in variants {
 278                     match (&variant.data, &variant.disr_expr) {
 279                         (ast::VariantData::Unit(..), _) => {}
 280                         (_, Some(disr_expr)) => gate_feature_post!(
 281                             &self,
 282                             arbitrary_enum_discriminant,
 283                             disr_expr.value.span,
 284                             "discriminants on non-unit variants are experimental"
 285                         ),
 286                         _ => {}
 287                     }
 288                 }
 289
 290                 let has_feature = self.features.arbitrary_enum_discriminant;
 291                 if !has_feature && !i.span.allows_unstable(sym::arbitrary_enum_discriminant) {
 292                     self.maybe_report_invalid_custom_discriminants(&variants);
 293                 }
 294             }
 295
 296             ast::ItemKind::Impl(box ast::Impl { polarity, defaultness, ref of_trait, .. }) => {
 297                 if let ast::ImplPolarity::Negative(span) = polarity {
 298                     gate_feature_post!(
 299                         &self,
 300                         negative_impls,
 301                         span.to(of_trait.as_ref().map_or(span, |t| t.path.span)),
 302                         "negative trait bounds are not yet fully implemented; \
 303                          use marker types for now"
 304                     );
 305                 }
 306
 307                 if let ast::Defaultness::Default(_) = defaultness {
 308                     gate_feature_post!(&self, specialization, i.span, "specialization is unstable");
 309                 }
 310             }
 311
 312             ast::ItemKind::Trait(box ast::Trait { is_auto: ast::IsAuto::Yes, .. }) => {
 313                 gate_feature_post!(
 314                     &self,
 315                     auto_traits,
 316                     i.span,
 317                     "auto traits are experimental and possibly buggy"
 318                 );
 319             }
 320
 321             ast::ItemKind::TraitAlias(..) => {
 322                 gate_feature_post!(&self, trait_alias, i.span, "trait aliases are experimental");
 323             }
 324
 325             ast::ItemKind::MacroDef(ast::MacroDef { macro_rules: false, .. }) => {
 326                 let msg = "`macro` is experimental";
 327                 gate_feature_post!(&self, decl_macro, i.span, msg);
 328             }
 329
 330             ast::ItemKind::TyAlias(box ast::TyAlias { ty: Some(ref ty), .. }) => {
 331                 self.check_impl_trait(&ty)
 332             }
 333
 334             _ => {}
 335         }
 336
 337         visit::walk_item(self, i);
 338     }
 339
 340     fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
 341         match i.kind {
 342             ast::ForeignItemKind::Fn(..) | ast::ForeignItemKind::Static(..) => {
 343                 let link_name = self.sess.first_attr_value_str_by_name(&i.attrs, sym::link_name);
 344                 let links_to_llvm =
 345                     link_name.map_or(false, |val| val.as_str().starts_with("llvm."));
 346                 if links_to_llvm {
 347                     gate_feature_post!(
 348                         &self,
 349                         link_llvm_intrinsics,
 350                         i.span,
 351                         "linking to LLVM intrinsics is experimental"
 352                     );
 353                 }
 354             }
 355             ast::ForeignItemKind::TyAlias(..) => {
 356                 gate_feature_post!(&self, extern_types, i.span, "extern types are experimental");
 357             }
 358             ast::ForeignItemKind::MacCall(..) => {}
 359         }
 360
 361         visit::walk_foreign_item(self, i)
 362     }
 363
 364     fn visit_ty(&mut self, ty: &'a ast::Ty) {
 365         match ty.kind {
 366             ast::TyKind::BareFn(ref bare_fn_ty) => {
 367                 // Function pointers cannot be `const`
 368                 self.check_extern(bare_fn_ty.ext, ast::Const::No);
 369             }
 370             ast::TyKind::Never => {
 371                 gate_feature_post!(&self, never_type, ty.span, "the `!` type is experimental");
 372             }
 373             ast::TyKind::TraitObject(_, ast::TraitObjectSyntax::DynStar, ..) => {
 374                 gate_feature_post!(&self, dyn_star, ty.span, "dyn* trait objects are unstable");
 375             }
 376             _ => {}
 377         }
 378         visit::walk_ty(self, ty)
 379     }
 380
 381     fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FnRetTy) {
 382         if let ast::FnRetTy::Ty(ref output_ty) = *ret_ty {
 383             if let ast::TyKind::Never = output_ty.kind {
 384                 // Do nothing.
 385             } else {
 386                 self.visit_ty(output_ty)
 387             }
 388         }
 389     }
 390
 391     fn visit_stmt(&mut self, stmt: &'a ast::Stmt) {
 392         if let ast::StmtKind::Semi(expr) = &stmt.kind
 393             && let ast::ExprKind::Assign(lhs, _, _) = &expr.kind
 394             && let ast::ExprKind::Type(..) = lhs.kind
 395             && self.sess.parse_sess.span_diagnostic.err_count() == 0
 396             && !self.features.type_ascription
 397             && !lhs.span.allows_unstable(sym::type_ascription)
 398         {
 399             // When we encounter a statement of the form `foo: Ty = val;`, this will emit a type
 400             // ascription error, but the likely intention was to write a `let` statement. (#78907).
 401             feature_err(
 402                 &self.sess.parse_sess,
 403                 sym::type_ascription,
 404                 lhs.span,
 405                 "type ascription is experimental",
 406             ).span_suggestion_verbose(
 407                 lhs.span.shrink_to_lo(),
 408                 "you might have meant to introduce a new binding",
 409                 "let ".to_string(),
 410                 Applicability::MachineApplicable,
 411             ).emit();
 412         }
 413         visit::walk_stmt(self, stmt);
 414     }
 415
 416     fn visit_expr(&mut self, e: &'a ast::Expr) {
 417         match e.kind {
 418             ast::ExprKind::Box(_) => {
 419                 gate_feature_post!(
 420                     &self,
 421                     box_syntax,
 422                     e.span,
 423                     "box expression syntax is experimental; you can call `Box::new` instead"
 424                 );
 425             }
 426             ast::ExprKind::Type(..) => {
 427                 if self.sess.parse_sess.span_diagnostic.err_count() == 0 {
 428                     // To avoid noise about type ascription in common syntax errors,
 429                     // only emit if it is the *only* error.
 430                     gate_feature_post!(
 431                         &self,
 432                         type_ascription,
 433                         e.span,
 434                         "type ascription is experimental"
 435                     );
 436                 } else {
 437                     // And if it isn't, cancel the early-pass warning.
 438                     self.sess
 439                         .parse_sess
 440                         .span_diagnostic
 441                         .steal_diagnostic(e.span, StashKey::EarlySyntaxWarning)
 442                         .map(|err| err.cancel());
 443                 }
 444             }
 445             ast::ExprKind::TryBlock(_) => {
 446                 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
 447             }
 448             _ => {}
 449         }
 450         visit::walk_expr(self, e)
 451     }
 452
 453     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
 454         match &pattern.kind {
 455             PatKind::Slice(pats) => {
 456                 for pat in pats {
 457                     let inner_pat = match &pat.kind {
 458                         PatKind::Ident(.., Some(pat)) => pat,
 459                         _ => pat,
 460                     };
 461                     if let PatKind::Range(Some(_), None, Spanned { .. }) = inner_pat.kind {
 462                         gate_feature_post!(
 463                             &self,
 464                             half_open_range_patterns,
 465                             pat.span,
 466                             "`X..` patterns in slices are experimental"
 467                         );
 468                     }
 469                 }
 470             }
 471             PatKind::Box(..) => {
 472                 gate_feature_post!(
 473                     &self,
 474                     box_patterns,
 475                     pattern.span,
 476                     "box pattern syntax is experimental"
 477                 );
 478             }
 479             PatKind::Range(_, Some(_), Spanned { node: RangeEnd::Excluded, .. }) => {
 480                 gate_feature_post!(
 481                     &self,
 482                     exclusive_range_pattern,
 483                     pattern.span,
 484                     "exclusive range pattern syntax is experimental"
 485                 );
 486             }
 487             _ => {}
 488         }
 489         visit::walk_pat(self, pattern)
 490     }
 491
 492     fn visit_fn(&mut self, fn_kind: FnKind<'a>, span: Span, _: NodeId) {
 493         if let Some(header) = fn_kind.header() {
 494             // Stability of const fn methods are covered in `visit_assoc_item` below.
 495             self.check_extern(header.ext, header.constness);
 496         }
 497
 498         if fn_kind.ctxt() != Some(FnCtxt::Foreign) && fn_kind.decl().c_variadic() {
 499             gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
 500         }
 501
 502         visit::walk_fn(self, fn_kind)
 503     }
 504
 505     fn visit_assoc_constraint(&mut self, constraint: &'a AssocConstraint) {
 506         if let AssocConstraintKind::Bound { .. } = constraint.kind {
 507             gate_feature_post!(
 508                 &self,
 509                 associated_type_bounds,
 510                 constraint.span,
 511                 "associated type bounds are unstable"
 512             )
 513         }
 514         visit::walk_assoc_constraint(self, constraint)
 515     }
 516
 517     fn visit_assoc_item(&mut self, i: &'a ast::AssocItem, ctxt: AssocCtxt) {
 518         let is_fn = match i.kind {
 519             ast::AssocItemKind::Fn(_) => true,
 520             ast::AssocItemKind::TyAlias(box ast::TyAlias { ref ty, .. }) => {
 521                 if let (Some(_), AssocCtxt::Trait) = (ty, ctxt) {
 522                     gate_feature_post!(
 523                         &self,
 524                         associated_type_defaults,
 525                         i.span,
 526                         "associated type defaults are unstable"
 527                     );
 528                 }
 529                 if let Some(ty) = ty {
 530                     self.check_impl_trait(ty);
 531                 }
 532                 false
 533             }
 534             _ => false,
 535         };
 536         if let ast::Defaultness::Default(_) = i.kind.defaultness() {
 537             // Limit `min_specialization` to only specializing functions.
 538             gate_feature_fn!(
 539                 &self,
 540                 |x: &Features| x.specialization || (is_fn && x.min_specialization),
 541                 i.span,
 542                 sym::specialization,
 543                 "specialization is unstable"
 544             );
 545         }
 546         visit::walk_assoc_item(self, i, ctxt)
 547     }
 548 }
 549
 550 pub fn check_crate(krate: &ast::Crate, sess: &Session) {
 551     maybe_stage_features(sess, krate);
 552     check_incompatible_features(sess);
 553     let mut visitor = PostExpansionVisitor { sess, features: &sess.features_untracked() };
 554
 555     let spans = sess.parse_sess.gated_spans.spans.borrow();
 556     macro_rules! gate_all {
 557         ($gate:ident, $msg:literal, $help:literal) => {
 558             if let Some(spans) = spans.get(&sym::$gate) {
 559                 for span in spans {
 560                     gate_feature_post!(&visitor, $gate, *span, $msg, $help);
 561                 }
 562             }
 563         };
 564         ($gate:ident, $msg:literal) => {
 565             if let Some(spans) = spans.get(&sym::$gate) {
 566                 for span in spans {
 567                     gate_feature_post!(&visitor, $gate, *span, $msg);
 568                 }
 569             }
 570         };
 571     }
 572     gate_all!(
 573         if_let_guard,
 574         "`if let` guards are experimental",
 575         "you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`"
 576     );
 577     gate_all!(let_chains, "`let` expressions in this position are unstable");
 578     gate_all!(
 579         async_closure,
 580         "async closures are unstable",
 581         "to use an async block, remove the `||`: `async {`"
 582     );
 583     gate_all!(
 584         closure_lifetime_binder,
 585         "`for<...>` binders for closures are experimental",
 586         "consider removing `for<...>`"
 587     );
 588     gate_all!(more_qualified_paths, "usage of qualified paths in this context is experimental");
 589     gate_all!(generators, "yield syntax is experimental");
 590     gate_all!(raw_ref_op, "raw address of syntax is experimental");
 591     gate_all!(const_trait_impl, "const trait impls are experimental");
 592     gate_all!(half_open_range_patterns, "half-open range patterns are unstable");
 593     gate_all!(inline_const, "inline-const is experimental");
 594     gate_all!(inline_const_pat, "inline-const in pattern position is experimental");
 595     gate_all!(associated_const_equality, "associated const equality is incomplete");
 596     gate_all!(yeet_expr, "`do yeet` expression is experimental");
 597
 598     // All uses of `gate_all!` below this point were added in #65742,
 599     // and subsequently disabled (with the non-early gating readded).
 600     // We emit an early future-incompatible warning for these.
 601     // New syntax gates should go above here to get a hard error gate.
 602     macro_rules! gate_all {
 603         ($gate:ident, $msg:literal) => {
 604             for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 605                 gate_feature_post!(future_incompatible; &visitor, $gate, *span, $msg);
 606             }
 607         };
 608     }
 609
 610     gate_all!(trait_alias, "trait aliases are experimental");
 611     gate_all!(associated_type_bounds, "associated type bounds are unstable");
 612     gate_all!(decl_macro, "`macro` is experimental");
 613     gate_all!(box_patterns, "box pattern syntax is experimental");
 614     gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
 615     gate_all!(try_blocks, "`try` blocks are unstable");
 616     gate_all!(box_syntax, "box expression syntax is experimental; you can call `Box::new` instead");
 617     gate_all!(type_ascription, "type ascription is experimental");
 618
 619     visit::walk_crate(&mut visitor, krate);
 620 }
 621
 622 fn maybe_stage_features(sess: &Session, krate: &ast::Crate) {
 623     // checks if `#![feature]` has been used to enable any lang feature
 624     // does not check the same for lib features unless there's at least one
 625     // declared lang feature
 626     if !sess.opts.unstable_features.is_nightly_build() {
 627         let lang_features = &sess.features_untracked().declared_lang_features;
 628         if lang_features.len() == 0 {
 629             return;
 630         }
 631         for attr in krate.attrs.iter().filter(|attr| attr.has_name(sym::feature)) {
 632             let mut err = struct_span_err!(
 633                 sess.parse_sess.span_diagnostic,
 634                 attr.span,
 635                 E0554,
 636                 "`#![feature]` may not be used on the {} release channel",
 637                 option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)")
 638             );
 639             let mut all_stable = true;
 640             for ident in
 641                 attr.meta_item_list().into_iter().flatten().flat_map(|nested| nested.ident())
 642             {
 643                 let name = ident.name;
 644                 let stable_since = lang_features
 645                     .iter()
 646                     .flat_map(|&(feature, _, since)| if feature == name { since } else { None })
 647                     .next();
 648                 if let Some(since) = stable_since {
 649                     err.help(&format!(
 650                         "the feature `{}` has been stable since {} and no longer requires \
 651                                   an attribute to enable",
 652                         name, since
 653                     ));
 654                 } else {
 655                     all_stable = false;
 656                 }
 657             }
 658             if all_stable {
 659                 err.span_suggestion(
 660                     attr.span,
 661                     "remove the attribute",
 662                     "",
 663                     Applicability::MachineApplicable,
 664                 );
 665             }
 666             err.emit();
 667         }
 668     }
 669 }
 670
 671 fn check_incompatible_features(sess: &Session) {
 672     let features = sess.features_untracked();
 673
 674     let declared_features = features
 675         .declared_lang_features
 676         .iter()
 677         .copied()
 678         .map(|(name, span, _)| (name, span))
 679         .chain(features.declared_lib_features.iter().copied());
 680
 681     for (f1, f2) in rustc_feature::INCOMPATIBLE_FEATURES
 682         .iter()
 683         .filter(|&&(f1, f2)| features.enabled(f1) && features.enabled(f2))
 684     {
 685         if let Some((f1_name, f1_span)) = declared_features.clone().find(|(name, _)| name == f1) {
 686             if let Some((f2_name, f2_span)) = declared_features.clone().find(|(name, _)| name == f2)
 687             {
 688                 let spans = vec![f1_span, f2_span];
 689                 sess.struct_span_err(
 690                     spans.clone(),
 691                     &format!(
 692                         "features `{}` and `{}` are incompatible, using them at the same time \
 693                         is not allowed",
 694                         f1_name, f2_name
 695                     ),
 696                 )
 697                 .help("remove one of these features")
 698                 .emit();
 699             }
 700         }
 701     }
 702 }