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::Features;
   7 use rustc_feature::{AttributeGate, BuiltinAttribute, BUILTIN_ATTRIBUTE_MAP};
   8 use rustc_session::parse::{feature_err, feature_warn};
   9 use rustc_session::Session;
  10 use rustc_span::source_map::Spanned;
  11 use rustc_span::symbol::sym;
  12 use rustc_span::Span;
  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 symbol_unescaped.as_str() {
  88             // Stable
  89             "Rust" | "C" | "cdecl" | "stdcall" | "fastcall" | "aapcs" | "win64" | "sysv64"
  90             | "system" => {}
  91             "rust-intrinsic" => {
  92                 gate_feature_post!(&self, intrinsics, span, "intrinsics are subject to change");
  93             }
  94             "platform-intrinsic" => {
  95                 gate_feature_post!(
  96                     &self,
  97                     platform_intrinsics,
  98                     span,
  99                     "platform intrinsics are experimental and possibly buggy"
 100                 );
 101             }
 102             "vectorcall" => {
 103                 gate_feature_post!(
 104                     &self,
 105                     abi_vectorcall,
 106                     span,
 107                     "vectorcall is experimental and subject to change"
 108                 );
 109             }
 110             "thiscall" => {
 111                 gate_feature_post!(
 112                     &self,
 113                     abi_thiscall,
 114                     span,
 115                     "thiscall is experimental and subject to change"
 116                 );
 117             }
 118             "rust-call" => {
 119                 gate_feature_post!(
 120                     &self,
 121                     unboxed_closures,
 122                     span,
 123                     "rust-call ABI is subject to change"
 124                 );
 125             }
 126             "rust-cold" => {
 127                 gate_feature_post!(
 128                     &self,
 129                     rust_cold_cc,
 130                     span,
 131                     "rust-cold is experimental and subject to change"
 132                 );
 133             }
 134             "ptx-kernel" => {
 135                 gate_feature_post!(
 136                     &self,
 137                     abi_ptx,
 138                     span,
 139                     "PTX ABIs are experimental and subject to change"
 140                 );
 141             }
 142             "unadjusted" => {
 143                 gate_feature_post!(
 144                     &self,
 145                     abi_unadjusted,
 146                     span,
 147                     "unadjusted ABI is an implementation detail and perma-unstable"
 148                 );
 149             }
 150             "msp430-interrupt" => {
 151                 gate_feature_post!(
 152                     &self,
 153                     abi_msp430_interrupt,
 154                     span,
 155                     "msp430-interrupt ABI is experimental and subject to change"
 156                 );
 157             }
 158             "x86-interrupt" => {
 159                 gate_feature_post!(
 160                     &self,
 161                     abi_x86_interrupt,
 162                     span,
 163                     "x86-interrupt ABI is experimental and subject to change"
 164                 );
 165             }
 166             "amdgpu-kernel" => {
 167                 gate_feature_post!(
 168                     &self,
 169                     abi_amdgpu_kernel,
 170                     span,
 171                     "amdgpu-kernel ABI is experimental and subject to change"
 172                 );
 173             }
 174             "avr-interrupt" | "avr-non-blocking-interrupt" => {
 175                 gate_feature_post!(
 176                     &self,
 177                     abi_avr_interrupt,
 178                     span,
 179                     "avr-interrupt and avr-non-blocking-interrupt ABIs are experimental and subject to change"
 180                 );
 181             }
 182             "efiapi" => {
 183                 gate_feature_post!(
 184                     &self,
 185                     abi_efiapi,
 186                     span,
 187                     "efiapi ABI is experimental and subject to change"
 188                 );
 189             }
 190             "C-cmse-nonsecure-call" => {
 191                 gate_feature_post!(
 192                     &self,
 193                     abi_c_cmse_nonsecure_call,
 194                     span,
 195                     "C-cmse-nonsecure-call ABI is experimental and subject to change"
 196                 );
 197             }
 198             "C-unwind" => {
 199                 gate_feature_post!(
 200                     &self,
 201                     c_unwind,
 202                     span,
 203                     "C-unwind ABI is experimental and subject to change"
 204                 );
 205             }
 206             "stdcall-unwind" => {
 207                 gate_feature_post!(
 208                     &self,
 209                     c_unwind,
 210                     span,
 211                     "stdcall-unwind ABI is experimental and subject to change"
 212                 );
 213             }
 214             "system-unwind" => {
 215                 gate_feature_post!(
 216                     &self,
 217                     c_unwind,
 218                     span,
 219                     "system-unwind ABI is experimental and subject to change"
 220                 );
 221             }
 222             "thiscall-unwind" => {
 223                 gate_feature_post!(
 224                     &self,
 225                     c_unwind,
 226                     span,
 227                     "thiscall-unwind ABI is experimental and subject to change"
 228                 );
 229             }
 230             "cdecl-unwind" => {
 231                 gate_feature_post!(
 232                     &self,
 233                     c_unwind,
 234                     span,
 235                     "cdecl-unwind ABI is experimental and subject to change"
 236                 );
 237             }
 238             "fastcall-unwind" => {
 239                 gate_feature_post!(
 240                     &self,
 241                     c_unwind,
 242                     span,
 243                     "fastcall-unwind ABI is experimental and subject to change"
 244                 );
 245             }
 246             "vectorcall-unwind" => {
 247                 gate_feature_post!(
 248                     &self,
 249                     c_unwind,
 250                     span,
 251                     "vectorcall-unwind ABI is experimental and subject to change"
 252                 );
 253             }
 254             "aapcs-unwind" => {
 255                 gate_feature_post!(
 256                     &self,
 257                     c_unwind,
 258                     span,
 259                     "aapcs-unwind ABI is experimental and subject to change"
 260                 );
 261             }
 262             "win64-unwind" => {
 263                 gate_feature_post!(
 264                     &self,
 265                     c_unwind,
 266                     span,
 267                     "win64-unwind ABI is experimental and subject to change"
 268                 );
 269             }
 270             "sysv64-unwind" => {
 271                 gate_feature_post!(
 272                     &self,
 273                     c_unwind,
 274                     span,
 275                     "sysv64-unwind ABI is experimental and subject to change"
 276                 );
 277             }
 278             "wasm" => {
 279                 gate_feature_post!(
 280                     &self,
 281                     wasm_abi,
 282                     span,
 283                     "wasm ABI is experimental and subject to change"
 284                 );
 285             }
 286             abi => {
 287                 if self.sess.opts.pretty.map_or(true, |ppm| ppm.needs_hir()) {
 288                     self.sess.parse_sess.span_diagnostic.delay_span_bug(
 289                         span,
 290                         &format!("unrecognized ABI not caught in lowering: {}", abi),
 291                     );
 292                 }
 293             }
 294         }
 295     }
 296
 297     fn check_extern(&self, ext: ast::Extern, constness: ast::Const) {
 298         if let ast::Extern::Explicit(abi, _) = ext {
 299             self.check_abi(abi, constness);
 300         }
 301     }
 302
 303     fn maybe_report_invalid_custom_discriminants(&self, variants: &[ast::Variant]) {
 304         let has_fields = variants.iter().any(|variant| match variant.data {
 305             VariantData::Tuple(..) | VariantData::Struct(..) => true,
 306             VariantData::Unit(..) => false,
 307         });
 308
 309         let discriminant_spans = variants
 310             .iter()
 311             .filter(|variant| match variant.data {
 312                 VariantData::Tuple(..) | VariantData::Struct(..) => false,
 313                 VariantData::Unit(..) => true,
 314             })
 315             .filter_map(|variant| variant.disr_expr.as_ref().map(|c| c.value.span))
 316             .collect::<Vec<_>>();
 317
 318         if !discriminant_spans.is_empty() && has_fields {
 319             let mut err = feature_err(
 320                 &self.sess.parse_sess,
 321                 sym::arbitrary_enum_discriminant,
 322                 discriminant_spans.clone(),
 323                 "custom discriminant values are not allowed in enums with tuple or struct variants",
 324             );
 325             for sp in discriminant_spans {
 326                 err.span_label(sp, "disallowed custom discriminant");
 327             }
 328             for variant in variants.iter() {
 329                 match &variant.data {
 330                     VariantData::Struct(..) => {
 331                         err.span_label(variant.span, "struct variant defined here");
 332                     }
 333                     VariantData::Tuple(..) => {
 334                         err.span_label(variant.span, "tuple variant defined here");
 335                     }
 336                     VariantData::Unit(..) => {}
 337                 }
 338             }
 339             err.emit();
 340         }
 341     }
 342
 343     fn check_gat(&self, generics: &ast::Generics, span: Span) {
 344         if !generics.params.is_empty() {
 345             gate_feature_post!(
 346                 &self,
 347                 generic_associated_types,
 348                 span,
 349                 "generic associated types are unstable"
 350             );
 351         }
 352         if !generics.where_clause.predicates.is_empty() {
 353             gate_feature_post!(
 354                 &self,
 355                 generic_associated_types,
 356                 span,
 357                 "where clauses on associated types are unstable"
 358             );
 359         }
 360     }
 361
 362     /// Feature gate `impl Trait` inside `type Alias = $type_expr;`.
 363     fn check_impl_trait(&self, ty: &ast::Ty) {
 364         struct ImplTraitVisitor<'a> {
 365             vis: &'a PostExpansionVisitor<'a>,
 366         }
 367         impl Visitor<'_> for ImplTraitVisitor<'_> {
 368             fn visit_ty(&mut self, ty: &ast::Ty) {
 369                 if let ast::TyKind::ImplTrait(..) = ty.kind {
 370                     gate_feature_post!(
 371                         &self.vis,
 372                         type_alias_impl_trait,
 373                         ty.span,
 374                         "`impl Trait` in type aliases is unstable"
 375                     );
 376                 }
 377                 visit::walk_ty(self, ty);
 378             }
 379         }
 380         ImplTraitVisitor { vis: self }.visit_ty(ty);
 381     }
 382 }
 383
 384 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 385     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 386         let attr_info = attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name));
 387         // Check feature gates for built-in attributes.
 388         if let Some(BuiltinAttribute {
 389             gate: AttributeGate::Gated(_, name, descr, has_feature),
 390             ..
 391         }) = attr_info
 392         {
 393             gate_feature_fn!(self, has_feature, attr.span, *name, descr);
 394         }
 395         // Check unstable flavors of the `#[doc]` attribute.
 396         if attr.has_name(sym::doc) {
 397             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 398                 macro_rules! gate_doc { ($($name:ident => $feature:ident)*) => {
 399                     $(if nested_meta.has_name(sym::$name) {
 400                         let msg = concat!("`#[doc(", stringify!($name), ")]` is experimental");
 401                         gate_feature_post!(self, $feature, attr.span, msg);
 402                     })*
 403                 }}
 404
 405                 gate_doc!(
 406                     cfg => doc_cfg
 407                     cfg_hide => doc_cfg_hide
 408                     masked => doc_masked
 409                     notable_trait => doc_notable_trait
 410                 );
 411
 412                 if nested_meta.has_name(sym::keyword) {
 413                     let msg = "`#[doc(keyword)]` is meant for internal use only";
 414                     gate_feature_post!(self, rustdoc_internals, attr.span, msg);
 415                 }
 416
 417                 if nested_meta.has_name(sym::fake_variadic) {
 418                     let msg = "`#[doc(fake_variadic)]` is meant for internal use only";
 419                     gate_feature_post!(self, rustdoc_internals, attr.span, msg);
 420                 }
 421             }
 422         }
 423
 424         // Emit errors for non-staged-api crates.
 425         if !self.features.staged_api {
 426             if attr.has_name(sym::unstable)
 427                 || attr.has_name(sym::stable)
 428                 || attr.has_name(sym::rustc_const_unstable)
 429                 || attr.has_name(sym::rustc_const_stable)
 430                 || attr.has_name(sym::rustc_default_body_unstable)
 431             {
 432                 struct_span_err!(
 433                     self.sess,
 434                     attr.span,
 435                     E0734,
 436                     "stability attributes may not be used outside of the standard library",
 437                 )
 438                 .emit();
 439             }
 440         }
 441     }
 442
 443     fn visit_item(&mut self, i: &'a ast::Item) {
 444         match i.kind {
 445             ast::ItemKind::ForeignMod(ref foreign_module) => {
 446                 if let Some(abi) = foreign_module.abi {
 447                     self.check_abi(abi, ast::Const::No);
 448                 }
 449             }
 450
 451             ast::ItemKind::Fn(..) => {
 452                 if self.sess.contains_name(&i.attrs, sym::start) {
 453                     gate_feature_post!(
 454                         &self,
 455                         start,
 456                         i.span,
 457                         "`#[start]` functions are experimental \
 458                          and their signature may change \
 459                          over time"
 460                     );
 461                 }
 462             }
 463
 464             ast::ItemKind::Struct(..) => {
 465                 for attr in self.sess.filter_by_name(&i.attrs, sym::repr) {
 466                     for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
 467                         if item.has_name(sym::simd) {
 468                             gate_feature_post!(
 469                                 &self,
 470                                 repr_simd,
 471                                 attr.span,
 472                                 "SIMD types are experimental and possibly buggy"
 473                             );
 474                         }
 475                     }
 476                 }
 477             }
 478
 479             ast::ItemKind::Enum(ast::EnumDef { ref variants, .. }, ..) => {
 480                 for variant in variants {
 481                     match (&variant.data, &variant.disr_expr) {
 482                         (ast::VariantData::Unit(..), _) => {}
 483                         (_, Some(disr_expr)) => gate_feature_post!(
 484                             &self,
 485                             arbitrary_enum_discriminant,
 486                             disr_expr.value.span,
 487                             "discriminants on non-unit variants are experimental"
 488                         ),
 489                         _ => {}
 490                     }
 491                 }
 492
 493                 let has_feature = self.features.arbitrary_enum_discriminant;
 494                 if !has_feature && !i.span.allows_unstable(sym::arbitrary_enum_discriminant) {
 495                     self.maybe_report_invalid_custom_discriminants(&variants);
 496                 }
 497             }
 498
 499             ast::ItemKind::Impl(box ast::Impl { polarity, defaultness, ref of_trait, .. }) => {
 500                 if let ast::ImplPolarity::Negative(span) = polarity {
 501                     gate_feature_post!(
 502                         &self,
 503                         negative_impls,
 504                         span.to(of_trait.as_ref().map_or(span, |t| t.path.span)),
 505                         "negative trait bounds are not yet fully implemented; \
 506                          use marker types for now"
 507                     );
 508                 }
 509
 510                 if let ast::Defaultness::Default(_) = defaultness {
 511                     gate_feature_post!(&self, specialization, i.span, "specialization is unstable");
 512                 }
 513             }
 514
 515             ast::ItemKind::Trait(box ast::Trait { is_auto: ast::IsAuto::Yes, .. }) => {
 516                 gate_feature_post!(
 517                     &self,
 518                     auto_traits,
 519                     i.span,
 520                     "auto traits are experimental and possibly buggy"
 521                 );
 522             }
 523
 524             ast::ItemKind::TraitAlias(..) => {
 525                 gate_feature_post!(&self, trait_alias, i.span, "trait aliases are experimental");
 526             }
 527
 528             ast::ItemKind::MacroDef(ast::MacroDef { macro_rules: false, .. }) => {
 529                 let msg = "`macro` is experimental";
 530                 gate_feature_post!(&self, decl_macro, i.span, msg);
 531             }
 532
 533             ast::ItemKind::TyAlias(box ast::TyAlias { ty: Some(ref ty), .. }) => {
 534                 self.check_impl_trait(&ty)
 535             }
 536
 537             _ => {}
 538         }
 539
 540         visit::walk_item(self, i);
 541     }
 542
 543     fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
 544         match i.kind {
 545             ast::ForeignItemKind::Fn(..) | ast::ForeignItemKind::Static(..) => {
 546                 let link_name = self.sess.first_attr_value_str_by_name(&i.attrs, sym::link_name);
 547                 let links_to_llvm =
 548                     link_name.map_or(false, |val| val.as_str().starts_with("llvm."));
 549                 if links_to_llvm {
 550                     gate_feature_post!(
 551                         &self,
 552                         link_llvm_intrinsics,
 553                         i.span,
 554                         "linking to LLVM intrinsics is experimental"
 555                     );
 556                 }
 557             }
 558             ast::ForeignItemKind::TyAlias(..) => {
 559                 gate_feature_post!(&self, extern_types, i.span, "extern types are experimental");
 560             }
 561             ast::ForeignItemKind::MacCall(..) => {}
 562         }
 563
 564         visit::walk_foreign_item(self, i)
 565     }
 566
 567     fn visit_ty(&mut self, ty: &'a ast::Ty) {
 568         match ty.kind {
 569             ast::TyKind::BareFn(ref bare_fn_ty) => {
 570                 // Function pointers cannot be `const`
 571                 self.check_extern(bare_fn_ty.ext, ast::Const::No);
 572             }
 573             ast::TyKind::Never => {
 574                 gate_feature_post!(&self, never_type, ty.span, "the `!` type is experimental");
 575             }
 576             _ => {}
 577         }
 578         visit::walk_ty(self, ty)
 579     }
 580
 581     fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FnRetTy) {
 582         if let ast::FnRetTy::Ty(ref output_ty) = *ret_ty {
 583             if let ast::TyKind::Never = output_ty.kind {
 584                 // Do nothing.
 585             } else {
 586                 self.visit_ty(output_ty)
 587             }
 588         }
 589     }
 590
 591     fn visit_stmt(&mut self, stmt: &'a ast::Stmt) {
 592         if let ast::StmtKind::Semi(expr) = &stmt.kind
 593             && let ast::ExprKind::Assign(lhs, _, _) = &expr.kind
 594             && let ast::ExprKind::Type(..) = lhs.kind
 595             && self.sess.parse_sess.span_diagnostic.err_count() == 0
 596             && !self.features.type_ascription
 597             && !lhs.span.allows_unstable(sym::type_ascription)
 598         {
 599             // When we encounter a statement of the form `foo: Ty = val;`, this will emit a type
 600             // ascription error, but the likely intention was to write a `let` statement. (#78907).
 601             feature_err(
 602                 &self.sess.parse_sess,
 603                 sym::type_ascription,
 604                 lhs.span,
 605                 "type ascription is experimental",
 606             ).span_suggestion_verbose(
 607                 lhs.span.shrink_to_lo(),
 608                 "you might have meant to introduce a new binding",
 609                 "let ".to_string(),
 610                 Applicability::MachineApplicable,
 611             ).emit();
 612         }
 613         visit::walk_stmt(self, stmt);
 614     }
 615
 616     fn visit_expr(&mut self, e: &'a ast::Expr) {
 617         match e.kind {
 618             ast::ExprKind::Box(_) => {
 619                 gate_feature_post!(
 620                     &self,
 621                     box_syntax,
 622                     e.span,
 623                     "box expression syntax is experimental; you can call `Box::new` instead"
 624                 );
 625             }
 626             ast::ExprKind::Type(..) => {
 627                 if self.sess.parse_sess.span_diagnostic.err_count() == 0 {
 628                     // To avoid noise about type ascription in common syntax errors,
 629                     // only emit if it is the *only* error.
 630                     gate_feature_post!(
 631                         &self,
 632                         type_ascription,
 633                         e.span,
 634                         "type ascription is experimental"
 635                     );
 636                 } else {
 637                     // And if it isn't, cancel the early-pass warning.
 638                     self.sess
 639                         .parse_sess
 640                         .span_diagnostic
 641                         .steal_diagnostic(e.span, StashKey::EarlySyntaxWarning)
 642                         .map(|err| err.cancel());
 643                 }
 644             }
 645             ast::ExprKind::TryBlock(_) => {
 646                 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
 647             }
 648             _ => {}
 649         }
 650         visit::walk_expr(self, e)
 651     }
 652
 653     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
 654         match &pattern.kind {
 655             PatKind::Slice(pats) => {
 656                 for pat in pats {
 657                     let inner_pat = match &pat.kind {
 658                         PatKind::Ident(.., Some(pat)) => pat,
 659                         _ => pat,
 660                     };
 661                     if let PatKind::Range(Some(_), None, Spanned { .. }) = inner_pat.kind {
 662                         gate_feature_post!(
 663                             &self,
 664                             half_open_range_patterns,
 665                             pat.span,
 666                             "`X..` patterns in slices are experimental"
 667                         );
 668                     }
 669                 }
 670             }
 671             PatKind::Box(..) => {
 672                 gate_feature_post!(
 673                     &self,
 674                     box_patterns,
 675                     pattern.span,
 676                     "box pattern syntax is experimental"
 677                 );
 678             }
 679             PatKind::Range(_, Some(_), Spanned { node: RangeEnd::Excluded, .. }) => {
 680                 gate_feature_post!(
 681                     &self,
 682                     exclusive_range_pattern,
 683                     pattern.span,
 684                     "exclusive range pattern syntax is experimental"
 685                 );
 686             }
 687             _ => {}
 688         }
 689         visit::walk_pat(self, pattern)
 690     }
 691
 692     fn visit_fn(&mut self, fn_kind: FnKind<'a>, span: Span, _: NodeId) {
 693         if let Some(header) = fn_kind.header() {
 694             // Stability of const fn methods are covered in `visit_assoc_item` below.
 695             self.check_extern(header.ext, header.constness);
 696         }
 697
 698         if fn_kind.ctxt() != Some(FnCtxt::Foreign) && fn_kind.decl().c_variadic() {
 699             gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
 700         }
 701
 702         visit::walk_fn(self, fn_kind, span)
 703     }
 704
 705     fn visit_assoc_constraint(&mut self, constraint: &'a AssocConstraint) {
 706         if let AssocConstraintKind::Bound { .. } = constraint.kind {
 707             gate_feature_post!(
 708                 &self,
 709                 associated_type_bounds,
 710                 constraint.span,
 711                 "associated type bounds are unstable"
 712             )
 713         }
 714         visit::walk_assoc_constraint(self, constraint)
 715     }
 716
 717     fn visit_assoc_item(&mut self, i: &'a ast::AssocItem, ctxt: AssocCtxt) {
 718         let is_fn = match i.kind {
 719             ast::AssocItemKind::Fn(_) => true,
 720             ast::AssocItemKind::TyAlias(box ast::TyAlias { ref generics, ref ty, .. }) => {
 721                 if let (Some(_), AssocCtxt::Trait) = (ty, ctxt) {
 722                     gate_feature_post!(
 723                         &self,
 724                         associated_type_defaults,
 725                         i.span,
 726                         "associated type defaults are unstable"
 727                     );
 728                 }
 729                 if let Some(ty) = ty {
 730                     self.check_impl_trait(ty);
 731                 }
 732                 self.check_gat(generics, i.span);
 733                 false
 734             }
 735             _ => false,
 736         };
 737         if let ast::Defaultness::Default(_) = i.kind.defaultness() {
 738             // Limit `min_specialization` to only specializing functions.
 739             gate_feature_fn!(
 740                 &self,
 741                 |x: &Features| x.specialization || (is_fn && x.min_specialization),
 742                 i.span,
 743                 sym::specialization,
 744                 "specialization is unstable"
 745             );
 746         }
 747         visit::walk_assoc_item(self, i, ctxt)
 748     }
 749 }
 750
 751 pub fn check_crate(krate: &ast::Crate, sess: &Session) {
 752     maybe_stage_features(sess, krate);
 753     check_incompatible_features(sess);
 754     let mut visitor = PostExpansionVisitor { sess, features: &sess.features_untracked() };
 755
 756     let spans = sess.parse_sess.gated_spans.spans.borrow();
 757     macro_rules! gate_all {
 758         ($gate:ident, $msg:literal, $help:literal) => {
 759             if let Some(spans) = spans.get(&sym::$gate) {
 760                 for span in spans {
 761                     gate_feature_post!(&visitor, $gate, *span, $msg, $help);
 762                 }
 763             }
 764         };
 765         ($gate:ident, $msg:literal) => {
 766             if let Some(spans) = spans.get(&sym::$gate) {
 767                 for span in spans {
 768                     gate_feature_post!(&visitor, $gate, *span, $msg);
 769                 }
 770             }
 771         };
 772     }
 773     gate_all!(
 774         if_let_guard,
 775         "`if let` guards are experimental",
 776         "you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`"
 777     );
 778     gate_all!(let_chains, "`let` expressions in this position are unstable");
 779     gate_all!(
 780         async_closure,
 781         "async closures are unstable",
 782         "to use an async block, remove the `||`: `async {`"
 783     );
 784     gate_all!(
 785         closure_lifetime_binder,
 786         "`for<...>` binders for closures are experimental",
 787         "consider removing `for<...>`"
 788     );
 789     gate_all!(more_qualified_paths, "usage of qualified paths in this context is experimental");
 790     gate_all!(generators, "yield syntax is experimental");
 791     gate_all!(raw_ref_op, "raw address of syntax is experimental");
 792     gate_all!(const_trait_impl, "const trait impls are experimental");
 793     gate_all!(half_open_range_patterns, "half-open range patterns are unstable");
 794     gate_all!(inline_const, "inline-const is experimental");
 795     gate_all!(inline_const_pat, "inline-const in pattern position is experimental");
 796     gate_all!(associated_const_equality, "associated const equality is incomplete");
 797     gate_all!(yeet_expr, "`do yeet` expression is experimental");
 798
 799     // All uses of `gate_all!` below this point were added in #65742,
 800     // and subsequently disabled (with the non-early gating readded).
 801     // We emit an early future-incompatible warning for these.
 802     // New syntax gates should go above here to get a hard error gate.
 803     macro_rules! gate_all {
 804         ($gate:ident, $msg:literal) => {
 805             for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 806                 gate_feature_post!(future_incompatible; &visitor, $gate, *span, $msg);
 807             }
 808         };
 809     }
 810
 811     gate_all!(trait_alias, "trait aliases are experimental");
 812     gate_all!(associated_type_bounds, "associated type bounds are unstable");
 813     gate_all!(decl_macro, "`macro` is experimental");
 814     gate_all!(box_patterns, "box pattern syntax is experimental");
 815     gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
 816     gate_all!(try_blocks, "`try` blocks are unstable");
 817     gate_all!(box_syntax, "box expression syntax is experimental; you can call `Box::new` instead");
 818     gate_all!(type_ascription, "type ascription is experimental");
 819
 820     visit::walk_crate(&mut visitor, krate);
 821 }
 822
 823 fn maybe_stage_features(sess: &Session, krate: &ast::Crate) {
 824     // checks if `#![feature]` has been used to enable any lang feature
 825     // does not check the same for lib features unless there's at least one
 826     // declared lang feature
 827     if !sess.opts.unstable_features.is_nightly_build() {
 828         let lang_features = &sess.features_untracked().declared_lang_features;
 829         if lang_features.len() == 0 {
 830             return;
 831         }
 832         for attr in krate.attrs.iter().filter(|attr| attr.has_name(sym::feature)) {
 833             let mut err = struct_span_err!(
 834                 sess.parse_sess.span_diagnostic,
 835                 attr.span,
 836                 E0554,
 837                 "`#![feature]` may not be used on the {} release channel",
 838                 option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)")
 839             );
 840             let mut all_stable = true;
 841             for ident in
 842                 attr.meta_item_list().into_iter().flatten().flat_map(|nested| nested.ident())
 843             {
 844                 let name = ident.name;
 845                 let stable_since = lang_features
 846                     .iter()
 847                     .flat_map(|&(feature, _, since)| if feature == name { since } else { None })
 848                     .next();
 849                 if let Some(since) = stable_since {
 850                     err.help(&format!(
 851                         "the feature `{}` has been stable since {} and no longer requires \
 852                                   an attribute to enable",
 853                         name, since
 854                     ));
 855                 } else {
 856                     all_stable = false;
 857                 }
 858             }
 859             if all_stable {
 860                 err.span_suggestion(
 861                     attr.span,
 862                     "remove the attribute",
 863                     "",
 864                     Applicability::MachineApplicable,
 865                 );
 866             }
 867             err.emit();
 868         }
 869     }
 870 }
 871
 872 fn check_incompatible_features(sess: &Session) {
 873     let features = sess.features_untracked();
 874
 875     let declared_features = features
 876         .declared_lang_features
 877         .iter()
 878         .copied()
 879         .map(|(name, span, _)| (name, span))
 880         .chain(features.declared_lib_features.iter().copied());
 881
 882     for (f1, f2) in rustc_feature::INCOMPATIBLE_FEATURES
 883         .iter()
 884         .filter(|&&(f1, f2)| features.enabled(f1) && features.enabled(f2))
 885     {
 886         if let Some((f1_name, f1_span)) = declared_features.clone().find(|(name, _)| name == f1) {
 887             if let Some((f2_name, f2_span)) = declared_features.clone().find(|(name, _)| name == f2)
 888             {
 889                 let spans = vec![f1_span, f2_span];
 890                 sess.struct_span_err(
 891                     spans.clone(),
 892                     &format!(
 893                         "features `{}` and `{}` are incompatible, using them at the same time \
 894                         is not allowed",
 895                         f1_name, f2_name
 896                     ),
 897                 )
 898                 .help("remove one of these features")
 899                 .emit();
 900             }
 901         }
 902     }
 903 }