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::{AssocTyConstraint, AssocTyConstraintKind, NodeId};
   4 use rustc_ast::{PatKind, RangeEnd, VariantData};
   5 use rustc_errors::struct_span_err;
   6 use rustc_feature::{AttributeGate, BUILTIN_ATTRIBUTE_MAP};
   7 use rustc_feature::{Features, GateIssue};
   8 use rustc_session::parse::{feature_err, feature_err_issue};
   9 use rustc_session::Session;
  10 use rustc_span::source_map::Spanned;
  11 use rustc_span::symbol::{sym, Symbol};
  12 use rustc_span::Span;
  13
  14 use tracing::debug;
  15
  16 macro_rules! gate_feature_fn {
  17     ($visitor: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr, $help: expr) => {{
  18         let (visitor, has_feature, span, name, explain, help) =
  19             (&*$visitor, $has_feature, $span, $name, $explain, $help);
  20         let has_feature: bool = has_feature(visitor.features);
  21         debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
  22         if !has_feature && !span.allows_unstable($name) {
  23             feature_err_issue(&visitor.sess.parse_sess, name, span, GateIssue::Language, explain)
  24                 .help(help)
  25                 .emit();
  26         }
  27     }};
  28     ($visitor: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr) => {{
  29         let (visitor, has_feature, span, name, explain) =
  30             (&*$visitor, $has_feature, $span, $name, $explain);
  31         let has_feature: bool = has_feature(visitor.features);
  32         debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
  33         if !has_feature && !span.allows_unstable($name) {
  34             feature_err_issue(&visitor.sess.parse_sess, name, span, GateIssue::Language, explain)
  35                 .emit();
  36         }
  37     }};
  38 }
  39
  40 macro_rules! gate_feature_post {
  41     ($visitor: expr, $feature: ident, $span: expr, $explain: expr, $help: expr) => {
  42         gate_feature_fn!($visitor, |x: &Features| x.$feature, $span, sym::$feature, $explain, $help)
  43     };
  44     ($visitor: expr, $feature: ident, $span: expr, $explain: expr) => {
  45         gate_feature_fn!($visitor, |x: &Features| x.$feature, $span, sym::$feature, $explain)
  46     };
  47 }
  48
  49 pub fn check_attribute(attr: &ast::Attribute, sess: &Session, features: &Features) {
  50     PostExpansionVisitor { sess, features }.visit_attribute(attr)
  51 }
  52
  53 struct PostExpansionVisitor<'a> {
  54     sess: &'a Session,
  55
  56     // `sess` contains a `Features`, but this might not be that one.
  57     features: &'a Features,
  58 }
  59
  60 impl<'a> PostExpansionVisitor<'a> {
  61     fn check_abi(&self, abi: ast::StrLit) {
  62         let ast::StrLit { symbol_unescaped, span, .. } = abi;
  63
  64         match &*symbol_unescaped.as_str() {
  65             // Stable
  66             "Rust" | "C" | "cdecl" | "stdcall" | "fastcall" | "aapcs" | "win64" | "sysv64"
  67             | "system" => {}
  68             "rust-intrinsic" => {
  69                 gate_feature_post!(&self, intrinsics, span, "intrinsics are subject to change");
  70             }
  71             "platform-intrinsic" => {
  72                 gate_feature_post!(
  73                     &self,
  74                     platform_intrinsics,
  75                     span,
  76                     "platform intrinsics are experimental and possibly buggy"
  77                 );
  78             }
  79             "vectorcall" => {
  80                 gate_feature_post!(
  81                     &self,
  82                     abi_vectorcall,
  83                     span,
  84                     "vectorcall is experimental and subject to change"
  85                 );
  86             }
  87             "thiscall" => {
  88                 gate_feature_post!(
  89                     &self,
  90                     abi_thiscall,
  91                     span,
  92                     "thiscall is experimental and subject to change"
  93                 );
  94             }
  95             "rust-call" => {
  96                 gate_feature_post!(
  97                     &self,
  98                     unboxed_closures,
  99                     span,
 100                     "rust-call ABI is subject to change"
 101                 );
 102             }
 103             "ptx-kernel" => {
 104                 gate_feature_post!(
 105                     &self,
 106                     abi_ptx,
 107                     span,
 108                     "PTX ABIs are experimental and subject to change"
 109                 );
 110             }
 111             "unadjusted" => {
 112                 gate_feature_post!(
 113                     &self,
 114                     abi_unadjusted,
 115                     span,
 116                     "unadjusted ABI is an implementation detail and perma-unstable"
 117                 );
 118             }
 119             "msp430-interrupt" => {
 120                 gate_feature_post!(
 121                     &self,
 122                     abi_msp430_interrupt,
 123                     span,
 124                     "msp430-interrupt ABI is experimental and subject to change"
 125                 );
 126             }
 127             "x86-interrupt" => {
 128                 gate_feature_post!(
 129                     &self,
 130                     abi_x86_interrupt,
 131                     span,
 132                     "x86-interrupt ABI is experimental and subject to change"
 133                 );
 134             }
 135             "amdgpu-kernel" => {
 136                 gate_feature_post!(
 137                     &self,
 138                     abi_amdgpu_kernel,
 139                     span,
 140                     "amdgpu-kernel ABI is experimental and subject to change"
 141                 );
 142             }
 143             "avr-interrupt" | "avr-non-blocking-interrupt" => {
 144                 gate_feature_post!(
 145                     &self,
 146                     abi_avr_interrupt,
 147                     span,
 148                     "avr-interrupt and avr-non-blocking-interrupt ABIs are experimental and subject to change"
 149                 );
 150             }
 151             "efiapi" => {
 152                 gate_feature_post!(
 153                     &self,
 154                     abi_efiapi,
 155                     span,
 156                     "efiapi ABI is experimental and subject to change"
 157                 );
 158             }
 159             abi => self
 160                 .sess
 161                 .parse_sess
 162                 .span_diagnostic
 163                 .delay_span_bug(span, &format!("unrecognized ABI not caught in lowering: {}", abi)),
 164         }
 165     }
 166
 167     fn check_extern(&self, ext: ast::Extern) {
 168         if let ast::Extern::Explicit(abi) = ext {
 169             self.check_abi(abi);
 170         }
 171     }
 172
 173     fn maybe_report_invalid_custom_discriminants(&self, variants: &[ast::Variant]) {
 174         let has_fields = variants.iter().any(|variant| match variant.data {
 175             VariantData::Tuple(..) | VariantData::Struct(..) => true,
 176             VariantData::Unit(..) => false,
 177         });
 178
 179         let discriminant_spans = variants
 180             .iter()
 181             .filter(|variant| match variant.data {
 182                 VariantData::Tuple(..) | VariantData::Struct(..) => false,
 183                 VariantData::Unit(..) => true,
 184             })
 185             .filter_map(|variant| variant.disr_expr.as_ref().map(|c| c.value.span))
 186             .collect::<Vec<_>>();
 187
 188         if !discriminant_spans.is_empty() && has_fields {
 189             let mut err = feature_err(
 190                 &self.sess.parse_sess,
 191                 sym::arbitrary_enum_discriminant,
 192                 discriminant_spans.clone(),
 193                 "custom discriminant values are not allowed in enums with tuple or struct variants",
 194             );
 195             for sp in discriminant_spans {
 196                 err.span_label(sp, "disallowed custom discriminant");
 197             }
 198             for variant in variants.iter() {
 199                 match &variant.data {
 200                     VariantData::Struct(..) => {
 201                         err.span_label(variant.span, "struct variant defined here");
 202                     }
 203                     VariantData::Tuple(..) => {
 204                         err.span_label(variant.span, "tuple variant defined here");
 205                     }
 206                     VariantData::Unit(..) => {}
 207                 }
 208             }
 209             err.emit();
 210         }
 211     }
 212
 213     fn check_gat(&self, generics: &ast::Generics, span: Span) {
 214         if !generics.params.is_empty() {
 215             gate_feature_post!(
 216                 &self,
 217                 generic_associated_types,
 218                 span,
 219                 "generic associated types are unstable"
 220             );
 221         }
 222         if !generics.where_clause.predicates.is_empty() {
 223             gate_feature_post!(
 224                 &self,
 225                 generic_associated_types,
 226                 span,
 227                 "where clauses on associated types are unstable"
 228             );
 229         }
 230     }
 231
 232     /// Feature gate `impl Trait` inside `type Alias = $type_expr;`.
 233     fn check_impl_trait(&self, ty: &ast::Ty) {
 234         struct ImplTraitVisitor<'a> {
 235             vis: &'a PostExpansionVisitor<'a>,
 236         }
 237         impl Visitor<'_> for ImplTraitVisitor<'_> {
 238             fn visit_ty(&mut self, ty: &ast::Ty) {
 239                 if let ast::TyKind::ImplTrait(..) = ty.kind {
 240                     gate_feature_post!(
 241                         &self.vis,
 242                         type_alias_impl_trait,
 243                         ty.span,
 244                         "`impl Trait` in type aliases is unstable"
 245                     );
 246                 }
 247                 visit::walk_ty(self, ty);
 248             }
 249         }
 250         ImplTraitVisitor { vis: self }.visit_ty(ty);
 251     }
 252 }
 253
 254 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 255     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 256         let attr_info =
 257             attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name)).map(|a| **a);
 258         // Check feature gates for built-in attributes.
 259         if let Some((.., AttributeGate::Gated(_, name, descr, has_feature))) = attr_info {
 260             gate_feature_fn!(self, has_feature, attr.span, name, descr);
 261         }
 262         // Check unstable flavors of the `#[doc]` attribute.
 263         if self.sess.check_name(attr, sym::doc) {
 264             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 265                 macro_rules! gate_doc { ($($name:ident => $feature:ident)*) => {
 266                     $(if nested_meta.has_name(sym::$name) {
 267                         let msg = concat!("`#[doc(", stringify!($name), ")]` is experimental");
 268                         gate_feature_post!(self, $feature, attr.span, msg);
 269                     })*
 270                 }}
 271
 272                 gate_doc!(
 273                     include => external_doc
 274                     cfg => doc_cfg
 275                     masked => doc_masked
 276                     spotlight => doc_spotlight
 277                     keyword => doc_keyword
 278                 );
 279             }
 280         }
 281     }
 282
 283     fn visit_name(&mut self, sp: Span, name: Symbol) {
 284         if !name.as_str().is_ascii() {
 285             gate_feature_post!(
 286                 &self,
 287                 non_ascii_idents,
 288                 self.sess.parse_sess.source_map().guess_head_span(sp),
 289                 "non-ascii idents are not fully supported"
 290             );
 291         }
 292     }
 293
 294     fn visit_item(&mut self, i: &'a ast::Item) {
 295         match i.kind {
 296             ast::ItemKind::ForeignMod(ref foreign_module) => {
 297                 if let Some(abi) = foreign_module.abi {
 298                     self.check_abi(abi);
 299                 }
 300             }
 301
 302             ast::ItemKind::Fn(..) => {
 303                 if self.sess.contains_name(&i.attrs[..], sym::plugin_registrar) {
 304                     gate_feature_post!(
 305                         &self,
 306                         plugin_registrar,
 307                         i.span,
 308                         "compiler plugins are experimental and possibly buggy"
 309                     );
 310                 }
 311                 if self.sess.contains_name(&i.attrs[..], sym::start) {
 312                     gate_feature_post!(
 313                         &self,
 314                         start,
 315                         i.span,
 316                         "`#[start]` functions are experimental \
 317                          and their signature may change \
 318                          over time"
 319                     );
 320                 }
 321                 if self.sess.contains_name(&i.attrs[..], sym::main) {
 322                     gate_feature_post!(
 323                         &self,
 324                         main,
 325                         i.span,
 326                         "declaration of a non-standard `#[main]` \
 327                          function may change over time, for now \
 328                          a top-level `fn main()` is required"
 329                     );
 330                 }
 331             }
 332
 333             ast::ItemKind::Struct(..) => {
 334                 for attr in self.sess.filter_by_name(&i.attrs[..], sym::repr) {
 335                     for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
 336                         if item.has_name(sym::simd) {
 337                             gate_feature_post!(
 338                                 &self,
 339                                 repr_simd,
 340                                 attr.span,
 341                                 "SIMD types are experimental and possibly buggy"
 342                             );
 343                         }
 344                     }
 345                 }
 346             }
 347
 348             ast::ItemKind::Enum(ast::EnumDef { ref variants, .. }, ..) => {
 349                 for variant in variants {
 350                     match (&variant.data, &variant.disr_expr) {
 351                         (ast::VariantData::Unit(..), _) => {}
 352                         (_, Some(disr_expr)) => gate_feature_post!(
 353                             &self,
 354                             arbitrary_enum_discriminant,
 355                             disr_expr.value.span,
 356                             "discriminants on non-unit variants are experimental"
 357                         ),
 358                         _ => {}
 359                     }
 360                 }
 361
 362                 let has_feature = self.features.arbitrary_enum_discriminant;
 363                 if !has_feature && !i.span.allows_unstable(sym::arbitrary_enum_discriminant) {
 364                     self.maybe_report_invalid_custom_discriminants(&variants);
 365                 }
 366             }
 367
 368             ast::ItemKind::Impl { polarity, defaultness, ref of_trait, .. } => {
 369                 if let ast::ImplPolarity::Negative(span) = polarity {
 370                     gate_feature_post!(
 371                         &self,
 372                         negative_impls,
 373                         span.to(of_trait.as_ref().map_or(span, |t| t.path.span)),
 374                         "negative trait bounds are not yet fully implemented; \
 375                          use marker types for now"
 376                     );
 377                 }
 378
 379                 if let ast::Defaultness::Default(_) = defaultness {
 380                     gate_feature_post!(&self, specialization, i.span, "specialization is unstable");
 381                 }
 382             }
 383
 384             ast::ItemKind::Trait(ast::IsAuto::Yes, ..) => {
 385                 gate_feature_post!(
 386                     &self,
 387                     auto_traits,
 388                     i.span,
 389                     "auto traits are experimental and possibly buggy"
 390                 );
 391             }
 392
 393             ast::ItemKind::TraitAlias(..) => {
 394                 gate_feature_post!(&self, trait_alias, i.span, "trait aliases are experimental");
 395             }
 396
 397             ast::ItemKind::MacroDef(ast::MacroDef { macro_rules: false, .. }) => {
 398                 let msg = "`macro` is experimental";
 399                 gate_feature_post!(&self, decl_macro, i.span, msg);
 400             }
 401
 402             ast::ItemKind::TyAlias(_, _, _, Some(ref ty)) => self.check_impl_trait(&ty),
 403
 404             _ => {}
 405         }
 406
 407         visit::walk_item(self, i);
 408     }
 409
 410     fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
 411         match i.kind {
 412             ast::ForeignItemKind::Fn(..) | ast::ForeignItemKind::Static(..) => {
 413                 let link_name = self.sess.first_attr_value_str_by_name(&i.attrs, sym::link_name);
 414                 let links_to_llvm =
 415                     link_name.map_or(false, |val| val.as_str().starts_with("llvm."));
 416                 if links_to_llvm {
 417                     gate_feature_post!(
 418                         &self,
 419                         link_llvm_intrinsics,
 420                         i.span,
 421                         "linking to LLVM intrinsics is experimental"
 422                     );
 423                 }
 424             }
 425             ast::ForeignItemKind::TyAlias(..) => {
 426                 gate_feature_post!(&self, extern_types, i.span, "extern types are experimental");
 427             }
 428             ast::ForeignItemKind::MacCall(..) => {}
 429         }
 430
 431         visit::walk_foreign_item(self, i)
 432     }
 433
 434     fn visit_ty(&mut self, ty: &'a ast::Ty) {
 435         match ty.kind {
 436             ast::TyKind::BareFn(ref bare_fn_ty) => {
 437                 self.check_extern(bare_fn_ty.ext);
 438             }
 439             ast::TyKind::Never => {
 440                 gate_feature_post!(&self, never_type, ty.span, "the `!` type is experimental");
 441             }
 442             _ => {}
 443         }
 444         visit::walk_ty(self, ty)
 445     }
 446
 447     fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FnRetTy) {
 448         if let ast::FnRetTy::Ty(ref output_ty) = *ret_ty {
 449             if let ast::TyKind::Never = output_ty.kind {
 450                 // Do nothing.
 451             } else {
 452                 self.visit_ty(output_ty)
 453             }
 454         }
 455     }
 456
 457     fn visit_expr(&mut self, e: &'a ast::Expr) {
 458         match e.kind {
 459             ast::ExprKind::Box(_) => {
 460                 gate_feature_post!(
 461                     &self,
 462                     box_syntax,
 463                     e.span,
 464                     "box expression syntax is experimental; you can call `Box::new` instead"
 465                 );
 466             }
 467             ast::ExprKind::Type(..) => {
 468                 // To avoid noise about type ascription in common syntax errors, only emit if it
 469                 // is the *only* error.
 470                 if self.sess.parse_sess.span_diagnostic.err_count() == 0 {
 471                     gate_feature_post!(
 472                         &self,
 473                         type_ascription,
 474                         e.span,
 475                         "type ascription is experimental"
 476                     );
 477                 }
 478             }
 479             ast::ExprKind::TryBlock(_) => {
 480                 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
 481             }
 482             ast::ExprKind::Block(_, opt_label) => {
 483                 if let Some(label) = opt_label {
 484                     gate_feature_post!(
 485                         &self,
 486                         label_break_value,
 487                         label.ident.span,
 488                         "labels on blocks are unstable"
 489                     );
 490                 }
 491             }
 492             _ => {}
 493         }
 494         visit::walk_expr(self, e)
 495     }
 496
 497     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
 498         match &pattern.kind {
 499             PatKind::Box(..) => {
 500                 gate_feature_post!(
 501                     &self,
 502                     box_patterns,
 503                     pattern.span,
 504                     "box pattern syntax is experimental"
 505                 );
 506             }
 507             PatKind::Range(_, _, Spanned { node: RangeEnd::Excluded, .. }) => {
 508                 gate_feature_post!(
 509                     &self,
 510                     exclusive_range_pattern,
 511                     pattern.span,
 512                     "exclusive range pattern syntax is experimental"
 513                 );
 514             }
 515             _ => {}
 516         }
 517         visit::walk_pat(self, pattern)
 518     }
 519
 520     fn visit_fn(&mut self, fn_kind: FnKind<'a>, span: Span, _: NodeId) {
 521         if let Some(header) = fn_kind.header() {
 522             // Stability of const fn methods are covered in `visit_assoc_item` below.
 523             self.check_extern(header.ext);
 524
 525             if let (ast::Const::Yes(_), ast::Extern::Implicit)
 526             | (ast::Const::Yes(_), ast::Extern::Explicit(_)) = (header.constness, header.ext)
 527             {
 528                 gate_feature_post!(
 529                     &self,
 530                     const_extern_fn,
 531                     span,
 532                     "`const extern fn` definitions are unstable"
 533                 );
 534             }
 535         }
 536
 537         if fn_kind.ctxt() != Some(FnCtxt::Foreign) && fn_kind.decl().c_variadic() {
 538             gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
 539         }
 540
 541         visit::walk_fn(self, fn_kind, span)
 542     }
 543
 544     fn visit_assoc_ty_constraint(&mut self, constraint: &'a AssocTyConstraint) {
 545         if let AssocTyConstraintKind::Bound { .. } = constraint.kind {
 546             gate_feature_post!(
 547                 &self,
 548                 associated_type_bounds,
 549                 constraint.span,
 550                 "associated type bounds are unstable"
 551             )
 552         }
 553         visit::walk_assoc_ty_constraint(self, constraint)
 554     }
 555
 556     fn visit_assoc_item(&mut self, i: &'a ast::AssocItem, ctxt: AssocCtxt) {
 557         let is_fn = match i.kind {
 558             ast::AssocItemKind::Fn(_, ref sig, _, _) => {
 559                 if let (ast::Const::Yes(_), AssocCtxt::Trait) = (sig.header.constness, ctxt) {
 560                     gate_feature_post!(&self, const_fn, i.span, "const fn is unstable");
 561                 }
 562                 true
 563             }
 564             ast::AssocItemKind::TyAlias(_, ref generics, _, ref ty) => {
 565                 if let (Some(_), AssocCtxt::Trait) = (ty, ctxt) {
 566                     gate_feature_post!(
 567                         &self,
 568                         associated_type_defaults,
 569                         i.span,
 570                         "associated type defaults are unstable"
 571                     );
 572                 }
 573                 if let Some(ty) = ty {
 574                     self.check_impl_trait(ty);
 575                 }
 576                 self.check_gat(generics, i.span);
 577                 false
 578             }
 579             _ => false,
 580         };
 581         if let ast::Defaultness::Default(_) = i.kind.defaultness() {
 582             // Limit `min_specialization` to only specializing functions.
 583             gate_feature_fn!(
 584                 &self,
 585                 |x: &Features| x.specialization || (is_fn && x.min_specialization),
 586                 i.span,
 587                 sym::specialization,
 588                 "specialization is unstable"
 589             );
 590         }
 591         visit::walk_assoc_item(self, i, ctxt)
 592     }
 593
 594     fn visit_vis(&mut self, vis: &'a ast::Visibility) {
 595         if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.kind {
 596             gate_feature_post!(
 597                 &self,
 598                 crate_visibility_modifier,
 599                 vis.span,
 600                 "`crate` visibility modifier is experimental"
 601             );
 602         }
 603         visit::walk_vis(self, vis)
 604     }
 605 }
 606
 607 pub fn check_crate(krate: &ast::Crate, sess: &Session) {
 608     maybe_stage_features(sess, krate);
 609     check_incompatible_features(sess);
 610     let mut visitor = PostExpansionVisitor { sess, features: &sess.features_untracked() };
 611
 612     let spans = sess.parse_sess.gated_spans.spans.borrow();
 613     macro_rules! gate_all {
 614         ($gate:ident, $msg:literal, $help:literal) => {
 615             if let Some(spans) = spans.get(&sym::$gate) {
 616                 for span in spans {
 617                     gate_feature_post!(&visitor, $gate, *span, $msg, $help);
 618                 }
 619             }
 620         };
 621         ($gate:ident, $msg:literal) => {
 622             if let Some(spans) = spans.get(&sym::$gate) {
 623                 for span in spans {
 624                     gate_feature_post!(&visitor, $gate, *span, $msg);
 625                 }
 626             }
 627         };
 628     }
 629     gate_all!(if_let_guard, "`if let` guards are experimental");
 630     gate_all!(let_chains, "`let` expressions in this position are experimental");
 631     gate_all!(
 632         async_closure,
 633         "async closures are unstable",
 634         "to use an async block, remove the `||`: `async {`"
 635     );
 636     gate_all!(generators, "yield syntax is experimental");
 637     gate_all!(or_patterns, "or-patterns syntax is experimental");
 638     gate_all!(raw_ref_op, "raw address of syntax is experimental");
 639     gate_all!(const_trait_bound_opt_out, "`?const` on trait bounds is experimental");
 640     gate_all!(const_trait_impl, "const trait impls are experimental");
 641     gate_all!(half_open_range_patterns, "half-open range patterns are unstable");
 642     gate_all!(inline_const, "inline-const is experimental");
 643     gate_all!(
 644         extended_key_value_attributes,
 645         "arbitrary expressions in key-value attributes are unstable"
 646     );
 647     gate_all!(
 648         const_generics_defaults,
 649         "default values for const generic parameters are experimental"
 650     );
 651     if sess.parse_sess.span_diagnostic.err_count() == 0 {
 652         // Errors for `destructuring_assignment` can get quite noisy, especially where `_` is
 653         // involved, so we only emit errors where there are no other parsing errors.
 654         gate_all!(destructuring_assignment, "destructuring assignments are unstable");
 655     }
 656
 657     // All uses of `gate_all!` below this point were added in #65742,
 658     // and subsequently disabled (with the non-early gating readded).
 659     macro_rules! gate_all {
 660         ($gate:ident, $msg:literal) => {
 661             // FIXME(eddyb) do something more useful than always
 662             // disabling these uses of early feature-gatings.
 663             if false {
 664                 for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 665                     gate_feature_post!(&visitor, $gate, *span, $msg);
 666                 }
 667             }
 668         };
 669     }
 670
 671     gate_all!(trait_alias, "trait aliases are experimental");
 672     gate_all!(associated_type_bounds, "associated type bounds are unstable");
 673     gate_all!(crate_visibility_modifier, "`crate` visibility modifier is experimental");
 674     gate_all!(const_generics, "const generics are unstable");
 675     gate_all!(decl_macro, "`macro` is experimental");
 676     gate_all!(box_patterns, "box pattern syntax is experimental");
 677     gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
 678     gate_all!(try_blocks, "`try` blocks are unstable");
 679     gate_all!(label_break_value, "labels on blocks are unstable");
 680     gate_all!(box_syntax, "box expression syntax is experimental; you can call `Box::new` instead");
 681     // To avoid noise about type ascription in common syntax errors,
 682     // only emit if it is the *only* error. (Also check it last.)
 683     if sess.parse_sess.span_diagnostic.err_count() == 0 {
 684         gate_all!(type_ascription, "type ascription is experimental");
 685     }
 686
 687     visit::walk_crate(&mut visitor, krate);
 688 }
 689
 690 fn maybe_stage_features(sess: &Session, krate: &ast::Crate) {
 691     if !sess.opts.unstable_features.is_nightly_build() {
 692         for attr in krate.attrs.iter().filter(|attr| sess.check_name(attr, sym::feature)) {
 693             struct_span_err!(
 694                 sess.parse_sess.span_diagnostic,
 695                 attr.span,
 696                 E0554,
 697                 "`#![feature]` may not be used on the {} release channel",
 698                 option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)")
 699             )
 700             .emit();
 701         }
 702     }
 703 }
 704
 705 fn check_incompatible_features(sess: &Session) {
 706     let features = sess.features_untracked();
 707
 708     let declared_features = features
 709         .declared_lang_features
 710         .iter()
 711         .copied()
 712         .map(|(name, span, _)| (name, span))
 713         .chain(features.declared_lib_features.iter().copied());
 714
 715     for (f1, f2) in rustc_feature::INCOMPATIBLE_FEATURES
 716         .iter()
 717         .filter(|&&(f1, f2)| features.enabled(f1) && features.enabled(f2))
 718     {
 719         if let Some((f1_name, f1_span)) = declared_features.clone().find(|(name, _)| name == f1) {
 720             if let Some((f2_name, f2_span)) = declared_features.clone().find(|(name, _)| name == f2)
 721             {
 722                 let spans = vec![f1_span, f2_span];
 723                 sess.struct_span_err(
 724                     spans.clone(),
 725                     &format!(
 726                         "features `{}` and `{}` are incompatible, using them at the same time \
 727                         is not allowed",
 728                         f1_name, f2_name
 729                     ),
 730                 )
 731                 .help("remove one of these features")
 732                 .emit();
 733             }
 734         }
 735     }
 736 }