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             "C-cmse-nonsecure-call" => {
 160                 gate_feature_post!(
 161                     &self,
 162                     abi_c_cmse_nonsecure_call,
 163                     span,
 164                     "C-cmse-nonsecure-call ABI is experimental and subject to change"
 165                 );
 166             }
 167             abi => self
 168                 .sess
 169                 .parse_sess
 170                 .span_diagnostic
 171                 .delay_span_bug(span, &format!("unrecognized ABI not caught in lowering: {}", abi)),
 172         }
 173     }
 174
 175     fn check_extern(&self, ext: ast::Extern) {
 176         if let ast::Extern::Explicit(abi) = ext {
 177             self.check_abi(abi);
 178         }
 179     }
 180
 181     fn maybe_report_invalid_custom_discriminants(&self, variants: &[ast::Variant]) {
 182         let has_fields = variants.iter().any(|variant| match variant.data {
 183             VariantData::Tuple(..) | VariantData::Struct(..) => true,
 184             VariantData::Unit(..) => false,
 185         });
 186
 187         let discriminant_spans = variants
 188             .iter()
 189             .filter(|variant| match variant.data {
 190                 VariantData::Tuple(..) | VariantData::Struct(..) => false,
 191                 VariantData::Unit(..) => true,
 192             })
 193             .filter_map(|variant| variant.disr_expr.as_ref().map(|c| c.value.span))
 194             .collect::<Vec<_>>();
 195
 196         if !discriminant_spans.is_empty() && has_fields {
 197             let mut err = feature_err(
 198                 &self.sess.parse_sess,
 199                 sym::arbitrary_enum_discriminant,
 200                 discriminant_spans.clone(),
 201                 "custom discriminant values are not allowed in enums with tuple or struct variants",
 202             );
 203             for sp in discriminant_spans {
 204                 err.span_label(sp, "disallowed custom discriminant");
 205             }
 206             for variant in variants.iter() {
 207                 match &variant.data {
 208                     VariantData::Struct(..) => {
 209                         err.span_label(variant.span, "struct variant defined here");
 210                     }
 211                     VariantData::Tuple(..) => {
 212                         err.span_label(variant.span, "tuple variant defined here");
 213                     }
 214                     VariantData::Unit(..) => {}
 215                 }
 216             }
 217             err.emit();
 218         }
 219     }
 220
 221     fn check_gat(&self, generics: &ast::Generics, span: Span) {
 222         if !generics.params.is_empty() {
 223             gate_feature_post!(
 224                 &self,
 225                 generic_associated_types,
 226                 span,
 227                 "generic associated types are unstable"
 228             );
 229         }
 230         if !generics.where_clause.predicates.is_empty() {
 231             gate_feature_post!(
 232                 &self,
 233                 generic_associated_types,
 234                 span,
 235                 "where clauses on associated types are unstable"
 236             );
 237         }
 238     }
 239
 240     /// Feature gate `impl Trait` inside `type Alias = $type_expr;`.
 241     fn check_impl_trait(&self, ty: &ast::Ty) {
 242         struct ImplTraitVisitor<'a> {
 243             vis: &'a PostExpansionVisitor<'a>,
 244         }
 245         impl Visitor<'_> for ImplTraitVisitor<'_> {
 246             fn visit_ty(&mut self, ty: &ast::Ty) {
 247                 if let ast::TyKind::ImplTrait(..) = ty.kind {
 248                     gate_feature_post!(
 249                         &self.vis,
 250                         type_alias_impl_trait,
 251                         ty.span,
 252                         "`impl Trait` in type aliases is unstable"
 253                     );
 254                 }
 255                 visit::walk_ty(self, ty);
 256             }
 257         }
 258         ImplTraitVisitor { vis: self }.visit_ty(ty);
 259     }
 260 }
 261
 262 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 263     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 264         let attr_info =
 265             attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name)).map(|a| **a);
 266         // Check feature gates for built-in attributes.
 267         if let Some((.., AttributeGate::Gated(_, name, descr, has_feature))) = attr_info {
 268             gate_feature_fn!(self, has_feature, attr.span, name, descr);
 269         }
 270         // Check unstable flavors of the `#[doc]` attribute.
 271         if self.sess.check_name(attr, sym::doc) {
 272             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 273                 macro_rules! gate_doc { ($($name:ident => $feature:ident)*) => {
 274                     $(if nested_meta.has_name(sym::$name) {
 275                         let msg = concat!("`#[doc(", stringify!($name), ")]` is experimental");
 276                         gate_feature_post!(self, $feature, attr.span, msg);
 277                     })*
 278                 }}
 279
 280                 gate_doc!(
 281                     include => external_doc
 282                     cfg => doc_cfg
 283                     masked => doc_masked
 284                     spotlight => doc_spotlight
 285                     keyword => doc_keyword
 286                 );
 287             }
 288         }
 289     }
 290
 291     fn visit_name(&mut self, sp: Span, name: Symbol) {
 292         if !name.as_str().is_ascii() {
 293             gate_feature_post!(
 294                 &self,
 295                 non_ascii_idents,
 296                 self.sess.parse_sess.source_map().guess_head_span(sp),
 297                 "non-ascii idents are not fully supported"
 298             );
 299         }
 300     }
 301
 302     fn visit_item(&mut self, i: &'a ast::Item) {
 303         match i.kind {
 304             ast::ItemKind::ForeignMod(ref foreign_module) => {
 305                 if let Some(abi) = foreign_module.abi {
 306                     self.check_abi(abi);
 307                 }
 308             }
 309
 310             ast::ItemKind::Fn(..) => {
 311                 if self.sess.contains_name(&i.attrs[..], sym::plugin_registrar) {
 312                     gate_feature_post!(
 313                         &self,
 314                         plugin_registrar,
 315                         i.span,
 316                         "compiler plugins are experimental and possibly buggy"
 317                     );
 318                 }
 319                 if self.sess.contains_name(&i.attrs[..], sym::start) {
 320                     gate_feature_post!(
 321                         &self,
 322                         start,
 323                         i.span,
 324                         "`#[start]` functions are experimental \
 325                          and their signature may change \
 326                          over time"
 327                     );
 328                 }
 329                 if self.sess.contains_name(&i.attrs[..], sym::main) {
 330                     gate_feature_post!(
 331                         &self,
 332                         main,
 333                         i.span,
 334                         "declaration of a non-standard `#[main]` \
 335                          function may change over time, for now \
 336                          a top-level `fn main()` is required"
 337                     );
 338                 }
 339             }
 340
 341             ast::ItemKind::Struct(..) => {
 342                 for attr in self.sess.filter_by_name(&i.attrs[..], sym::repr) {
 343                     for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
 344                         if item.has_name(sym::simd) {
 345                             gate_feature_post!(
 346                                 &self,
 347                                 repr_simd,
 348                                 attr.span,
 349                                 "SIMD types are experimental and possibly buggy"
 350                             );
 351                         }
 352                     }
 353                 }
 354             }
 355
 356             ast::ItemKind::Enum(ast::EnumDef { ref variants, .. }, ..) => {
 357                 for variant in variants {
 358                     match (&variant.data, &variant.disr_expr) {
 359                         (ast::VariantData::Unit(..), _) => {}
 360                         (_, Some(disr_expr)) => gate_feature_post!(
 361                             &self,
 362                             arbitrary_enum_discriminant,
 363                             disr_expr.value.span,
 364                             "discriminants on non-unit variants are experimental"
 365                         ),
 366                         _ => {}
 367                     }
 368                 }
 369
 370                 let has_feature = self.features.arbitrary_enum_discriminant;
 371                 if !has_feature && !i.span.allows_unstable(sym::arbitrary_enum_discriminant) {
 372                     self.maybe_report_invalid_custom_discriminants(&variants);
 373                 }
 374             }
 375
 376             ast::ItemKind::Impl { polarity, defaultness, ref of_trait, .. } => {
 377                 if let ast::ImplPolarity::Negative(span) = polarity {
 378                     gate_feature_post!(
 379                         &self,
 380                         negative_impls,
 381                         span.to(of_trait.as_ref().map_or(span, |t| t.path.span)),
 382                         "negative trait bounds are not yet fully implemented; \
 383                          use marker types for now"
 384                     );
 385                 }
 386
 387                 if let ast::Defaultness::Default(_) = defaultness {
 388                     gate_feature_post!(&self, specialization, i.span, "specialization is unstable");
 389                 }
 390             }
 391
 392             ast::ItemKind::Trait(ast::IsAuto::Yes, ..) => {
 393                 gate_feature_post!(
 394                     &self,
 395                     auto_traits,
 396                     i.span,
 397                     "auto traits are experimental and possibly buggy"
 398                 );
 399             }
 400
 401             ast::ItemKind::TraitAlias(..) => {
 402                 gate_feature_post!(&self, trait_alias, i.span, "trait aliases are experimental");
 403             }
 404
 405             ast::ItemKind::MacroDef(ast::MacroDef { macro_rules: false, .. }) => {
 406                 let msg = "`macro` is experimental";
 407                 gate_feature_post!(&self, decl_macro, i.span, msg);
 408             }
 409
 410             ast::ItemKind::TyAlias(_, _, _, Some(ref ty)) => self.check_impl_trait(&ty),
 411
 412             _ => {}
 413         }
 414
 415         visit::walk_item(self, i);
 416     }
 417
 418     fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
 419         match i.kind {
 420             ast::ForeignItemKind::Fn(..) | ast::ForeignItemKind::Static(..) => {
 421                 let link_name = self.sess.first_attr_value_str_by_name(&i.attrs, sym::link_name);
 422                 let links_to_llvm =
 423                     link_name.map_or(false, |val| val.as_str().starts_with("llvm."));
 424                 if links_to_llvm {
 425                     gate_feature_post!(
 426                         &self,
 427                         link_llvm_intrinsics,
 428                         i.span,
 429                         "linking to LLVM intrinsics is experimental"
 430                     );
 431                 }
 432             }
 433             ast::ForeignItemKind::TyAlias(..) => {
 434                 gate_feature_post!(&self, extern_types, i.span, "extern types are experimental");
 435             }
 436             ast::ForeignItemKind::MacCall(..) => {}
 437         }
 438
 439         visit::walk_foreign_item(self, i)
 440     }
 441
 442     fn visit_ty(&mut self, ty: &'a ast::Ty) {
 443         match ty.kind {
 444             ast::TyKind::BareFn(ref bare_fn_ty) => {
 445                 self.check_extern(bare_fn_ty.ext);
 446             }
 447             ast::TyKind::Never => {
 448                 gate_feature_post!(&self, never_type, ty.span, "the `!` type is experimental");
 449             }
 450             _ => {}
 451         }
 452         visit::walk_ty(self, ty)
 453     }
 454
 455     fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FnRetTy) {
 456         if let ast::FnRetTy::Ty(ref output_ty) = *ret_ty {
 457             if let ast::TyKind::Never = output_ty.kind {
 458                 // Do nothing.
 459             } else {
 460                 self.visit_ty(output_ty)
 461             }
 462         }
 463     }
 464
 465     fn visit_expr(&mut self, e: &'a ast::Expr) {
 466         match e.kind {
 467             ast::ExprKind::Box(_) => {
 468                 gate_feature_post!(
 469                     &self,
 470                     box_syntax,
 471                     e.span,
 472                     "box expression syntax is experimental; you can call `Box::new` instead"
 473                 );
 474             }
 475             ast::ExprKind::Type(..) => {
 476                 // To avoid noise about type ascription in common syntax errors, only emit if it
 477                 // is the *only* error.
 478                 if self.sess.parse_sess.span_diagnostic.err_count() == 0 {
 479                     gate_feature_post!(
 480                         &self,
 481                         type_ascription,
 482                         e.span,
 483                         "type ascription is experimental"
 484                     );
 485                 }
 486             }
 487             ast::ExprKind::TryBlock(_) => {
 488                 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
 489             }
 490             ast::ExprKind::Block(_, opt_label) => {
 491                 if let Some(label) = opt_label {
 492                     gate_feature_post!(
 493                         &self,
 494                         label_break_value,
 495                         label.ident.span,
 496                         "labels on blocks are unstable"
 497                     );
 498                 }
 499             }
 500             _ => {}
 501         }
 502         visit::walk_expr(self, e)
 503     }
 504
 505     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
 506         match &pattern.kind {
 507             PatKind::Box(..) => {
 508                 gate_feature_post!(
 509                     &self,
 510                     box_patterns,
 511                     pattern.span,
 512                     "box pattern syntax is experimental"
 513                 );
 514             }
 515             PatKind::Range(_, _, Spanned { node: RangeEnd::Excluded, .. }) => {
 516                 gate_feature_post!(
 517                     &self,
 518                     exclusive_range_pattern,
 519                     pattern.span,
 520                     "exclusive range pattern syntax is experimental"
 521                 );
 522             }
 523             _ => {}
 524         }
 525         visit::walk_pat(self, pattern)
 526     }
 527
 528     fn visit_fn(&mut self, fn_kind: FnKind<'a>, span: Span, _: NodeId) {
 529         if let Some(header) = fn_kind.header() {
 530             // Stability of const fn methods are covered in `visit_assoc_item` below.
 531             self.check_extern(header.ext);
 532
 533             if let (ast::Const::Yes(_), ast::Extern::Implicit)
 534             | (ast::Const::Yes(_), ast::Extern::Explicit(_)) = (header.constness, header.ext)
 535             {
 536                 gate_feature_post!(
 537                     &self,
 538                     const_extern_fn,
 539                     span,
 540                     "`const extern fn` definitions are unstable"
 541                 );
 542             }
 543         }
 544
 545         if fn_kind.ctxt() != Some(FnCtxt::Foreign) && fn_kind.decl().c_variadic() {
 546             gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
 547         }
 548
 549         visit::walk_fn(self, fn_kind, span)
 550     }
 551
 552     fn visit_assoc_ty_constraint(&mut self, constraint: &'a AssocTyConstraint) {
 553         if let AssocTyConstraintKind::Bound { .. } = constraint.kind {
 554             gate_feature_post!(
 555                 &self,
 556                 associated_type_bounds,
 557                 constraint.span,
 558                 "associated type bounds are unstable"
 559             )
 560         }
 561         visit::walk_assoc_ty_constraint(self, constraint)
 562     }
 563
 564     fn visit_assoc_item(&mut self, i: &'a ast::AssocItem, ctxt: AssocCtxt) {
 565         let is_fn = match i.kind {
 566             ast::AssocItemKind::Fn(_, ref sig, _, _) => {
 567                 if let (ast::Const::Yes(_), AssocCtxt::Trait) = (sig.header.constness, ctxt) {
 568                     gate_feature_post!(&self, const_fn, i.span, "const fn is unstable");
 569                 }
 570                 true
 571             }
 572             ast::AssocItemKind::TyAlias(_, ref generics, _, ref ty) => {
 573                 if let (Some(_), AssocCtxt::Trait) = (ty, ctxt) {
 574                     gate_feature_post!(
 575                         &self,
 576                         associated_type_defaults,
 577                         i.span,
 578                         "associated type defaults are unstable"
 579                     );
 580                 }
 581                 if let Some(ty) = ty {
 582                     self.check_impl_trait(ty);
 583                 }
 584                 self.check_gat(generics, i.span);
 585                 false
 586             }
 587             _ => false,
 588         };
 589         if let ast::Defaultness::Default(_) = i.kind.defaultness() {
 590             // Limit `min_specialization` to only specializing functions.
 591             gate_feature_fn!(
 592                 &self,
 593                 |x: &Features| x.specialization || (is_fn && x.min_specialization),
 594                 i.span,
 595                 sym::specialization,
 596                 "specialization is unstable"
 597             );
 598         }
 599         visit::walk_assoc_item(self, i, ctxt)
 600     }
 601
 602     fn visit_vis(&mut self, vis: &'a ast::Visibility) {
 603         if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.kind {
 604             gate_feature_post!(
 605                 &self,
 606                 crate_visibility_modifier,
 607                 vis.span,
 608                 "`crate` visibility modifier is experimental"
 609             );
 610         }
 611         visit::walk_vis(self, vis)
 612     }
 613 }
 614
 615 pub fn check_crate(krate: &ast::Crate, sess: &Session) {
 616     maybe_stage_features(sess, krate);
 617     check_incompatible_features(sess);
 618     let mut visitor = PostExpansionVisitor { sess, features: &sess.features_untracked() };
 619
 620     let spans = sess.parse_sess.gated_spans.spans.borrow();
 621     macro_rules! gate_all {
 622         ($gate:ident, $msg:literal, $help:literal) => {
 623             if let Some(spans) = spans.get(&sym::$gate) {
 624                 for span in spans {
 625                     gate_feature_post!(&visitor, $gate, *span, $msg, $help);
 626                 }
 627             }
 628         };
 629         ($gate:ident, $msg:literal) => {
 630             if let Some(spans) = spans.get(&sym::$gate) {
 631                 for span in spans {
 632                     gate_feature_post!(&visitor, $gate, *span, $msg);
 633                 }
 634             }
 635         };
 636     }
 637     gate_all!(if_let_guard, "`if let` guards are experimental");
 638     gate_all!(let_chains, "`let` expressions in this position are experimental");
 639     gate_all!(
 640         async_closure,
 641         "async closures are unstable",
 642         "to use an async block, remove the `||`: `async {`"
 643     );
 644     gate_all!(generators, "yield syntax is experimental");
 645     gate_all!(or_patterns, "or-patterns syntax is experimental");
 646     gate_all!(raw_ref_op, "raw address of syntax is experimental");
 647     gate_all!(const_trait_bound_opt_out, "`?const` on trait bounds is experimental");
 648     gate_all!(const_trait_impl, "const trait impls are experimental");
 649     gate_all!(half_open_range_patterns, "half-open range patterns are unstable");
 650     gate_all!(inline_const, "inline-const is experimental");
 651     gate_all!(
 652         extended_key_value_attributes,
 653         "arbitrary expressions in key-value attributes are unstable"
 654     );
 655     gate_all!(
 656         const_generics_defaults,
 657         "default values for const generic parameters are experimental"
 658     );
 659     if sess.parse_sess.span_diagnostic.err_count() == 0 {
 660         // Errors for `destructuring_assignment` can get quite noisy, especially where `_` is
 661         // involved, so we only emit errors where there are no other parsing errors.
 662         gate_all!(destructuring_assignment, "destructuring assignments are unstable");
 663     }
 664
 665     // All uses of `gate_all!` below this point were added in #65742,
 666     // and subsequently disabled (with the non-early gating readded).
 667     macro_rules! gate_all {
 668         ($gate:ident, $msg:literal) => {
 669             // FIXME(eddyb) do something more useful than always
 670             // disabling these uses of early feature-gatings.
 671             if false {
 672                 for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 673                     gate_feature_post!(&visitor, $gate, *span, $msg);
 674                 }
 675             }
 676         };
 677     }
 678
 679     gate_all!(trait_alias, "trait aliases are experimental");
 680     gate_all!(associated_type_bounds, "associated type bounds are unstable");
 681     gate_all!(crate_visibility_modifier, "`crate` visibility modifier is experimental");
 682     gate_all!(const_generics, "const generics are unstable");
 683     gate_all!(decl_macro, "`macro` is experimental");
 684     gate_all!(box_patterns, "box pattern syntax is experimental");
 685     gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
 686     gate_all!(try_blocks, "`try` blocks are unstable");
 687     gate_all!(label_break_value, "labels on blocks are unstable");
 688     gate_all!(box_syntax, "box expression syntax is experimental; you can call `Box::new` instead");
 689     // To avoid noise about type ascription in common syntax errors,
 690     // only emit if it is the *only* error. (Also check it last.)
 691     if sess.parse_sess.span_diagnostic.err_count() == 0 {
 692         gate_all!(type_ascription, "type ascription is experimental");
 693     }
 694
 695     visit::walk_crate(&mut visitor, krate);
 696 }
 697
 698 fn maybe_stage_features(sess: &Session, krate: &ast::Crate) {
 699     if !sess.opts.unstable_features.is_nightly_build() {
 700         for attr in krate.attrs.iter().filter(|attr| sess.check_name(attr, sym::feature)) {
 701             struct_span_err!(
 702                 sess.parse_sess.span_diagnostic,
 703                 attr.span,
 704                 E0554,
 705                 "`#![feature]` may not be used on the {} release channel",
 706                 option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)")
 707             )
 708             .emit();
 709         }
 710     }
 711 }
 712
 713 fn check_incompatible_features(sess: &Session) {
 714     let features = sess.features_untracked();
 715
 716     let declared_features = features
 717         .declared_lang_features
 718         .iter()
 719         .copied()
 720         .map(|(name, span, _)| (name, span))
 721         .chain(features.declared_lib_features.iter().copied());
 722
 723     for (f1, f2) in rustc_feature::INCOMPATIBLE_FEATURES
 724         .iter()
 725         .filter(|&&(f1, f2)| features.enabled(f1) && features.enabled(f2))
 726     {
 727         if let Some((f1_name, f1_span)) = declared_features.clone().find(|(name, _)| name == f1) {
 728             if let Some((f2_name, f2_span)) = declared_features.clone().find(|(name, _)| name == f2)
 729             {
 730                 let spans = vec![f1_span, f2_span];
 731                 sess.struct_span_err(
 732                     spans.clone(),
 733                     &format!(
 734                         "features `{}` and `{}` are incompatible, using them at the same time \
 735                         is not allowed",
 736                         f1_name, f2_name
 737                     ),
 738                 )
 739                 .help("remove one of these features")
 740                 .emit();
 741             }
 742         }
 743     }
 744 }