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     /// Feature gate `impl Trait` inside `type Alias = $type_expr;`.
 344     fn check_impl_trait(&self, ty: &ast::Ty) {
 345         struct ImplTraitVisitor<'a> {
 346             vis: &'a PostExpansionVisitor<'a>,
 347         }
 348         impl Visitor<'_> for ImplTraitVisitor<'_> {
 349             fn visit_ty(&mut self, ty: &ast::Ty) {
 350                 if let ast::TyKind::ImplTrait(..) = ty.kind {
 351                     gate_feature_post!(
 352                         &self.vis,
 353                         type_alias_impl_trait,
 354                         ty.span,
 355                         "`impl Trait` in type aliases is unstable"
 356                     );
 357                 }
 358                 visit::walk_ty(self, ty);
 359             }
 360         }
 361         ImplTraitVisitor { vis: self }.visit_ty(ty);
 362     }
 363 }
 364
 365 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 366     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 367         let attr_info = attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name));
 368         // Check feature gates for built-in attributes.
 369         if let Some(BuiltinAttribute {
 370             gate: AttributeGate::Gated(_, name, descr, has_feature),
 371             ..
 372         }) = attr_info
 373         {
 374             gate_feature_fn!(self, has_feature, attr.span, *name, descr);
 375         }
 376         // Check unstable flavors of the `#[doc]` attribute.
 377         if attr.has_name(sym::doc) {
 378             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 379                 macro_rules! gate_doc { ($($name:ident => $feature:ident)*) => {
 380                     $(if nested_meta.has_name(sym::$name) {
 381                         let msg = concat!("`#[doc(", stringify!($name), ")]` is experimental");
 382                         gate_feature_post!(self, $feature, attr.span, msg);
 383                     })*
 384                 }}
 385
 386                 gate_doc!(
 387                     cfg => doc_cfg
 388                     cfg_hide => doc_cfg_hide
 389                     masked => doc_masked
 390                     notable_trait => doc_notable_trait
 391                 );
 392
 393                 if nested_meta.has_name(sym::keyword) {
 394                     let msg = "`#[doc(keyword)]` is meant for internal use only";
 395                     gate_feature_post!(self, rustdoc_internals, attr.span, msg);
 396                 }
 397
 398                 if nested_meta.has_name(sym::fake_variadic) {
 399                     let msg = "`#[doc(fake_variadic)]` is meant for internal use only";
 400                     gate_feature_post!(self, rustdoc_internals, attr.span, msg);
 401                 }
 402             }
 403         }
 404
 405         // Emit errors for non-staged-api crates.
 406         if !self.features.staged_api {
 407             if attr.has_name(sym::unstable)
 408                 || attr.has_name(sym::stable)
 409                 || attr.has_name(sym::rustc_const_unstable)
 410                 || attr.has_name(sym::rustc_const_stable)
 411                 || attr.has_name(sym::rustc_default_body_unstable)
 412             {
 413                 struct_span_err!(
 414                     self.sess,
 415                     attr.span,
 416                     E0734,
 417                     "stability attributes may not be used outside of the standard library",
 418                 )
 419                 .emit();
 420             }
 421         }
 422     }
 423
 424     fn visit_item(&mut self, i: &'a ast::Item) {
 425         match i.kind {
 426             ast::ItemKind::ForeignMod(ref foreign_module) => {
 427                 if let Some(abi) = foreign_module.abi {
 428                     self.check_abi(abi, ast::Const::No);
 429                 }
 430             }
 431
 432             ast::ItemKind::Fn(..) => {
 433                 if self.sess.contains_name(&i.attrs, sym::start) {
 434                     gate_feature_post!(
 435                         &self,
 436                         start,
 437                         i.span,
 438                         "`#[start]` functions are experimental \
 439                          and their signature may change \
 440                          over time"
 441                     );
 442                 }
 443             }
 444
 445             ast::ItemKind::Struct(..) => {
 446                 for attr in self.sess.filter_by_name(&i.attrs, sym::repr) {
 447                     for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
 448                         if item.has_name(sym::simd) {
 449                             gate_feature_post!(
 450                                 &self,
 451                                 repr_simd,
 452                                 attr.span,
 453                                 "SIMD types are experimental and possibly buggy"
 454                             );
 455                         }
 456                     }
 457                 }
 458             }
 459
 460             ast::ItemKind::Enum(ast::EnumDef { ref variants, .. }, ..) => {
 461                 for variant in variants {
 462                     match (&variant.data, &variant.disr_expr) {
 463                         (ast::VariantData::Unit(..), _) => {}
 464                         (_, Some(disr_expr)) => gate_feature_post!(
 465                             &self,
 466                             arbitrary_enum_discriminant,
 467                             disr_expr.value.span,
 468                             "discriminants on non-unit variants are experimental"
 469                         ),
 470                         _ => {}
 471                     }
 472                 }
 473
 474                 let has_feature = self.features.arbitrary_enum_discriminant;
 475                 if !has_feature && !i.span.allows_unstable(sym::arbitrary_enum_discriminant) {
 476                     self.maybe_report_invalid_custom_discriminants(&variants);
 477                 }
 478             }
 479
 480             ast::ItemKind::Impl(box ast::Impl { polarity, defaultness, ref of_trait, .. }) => {
 481                 if let ast::ImplPolarity::Negative(span) = polarity {
 482                     gate_feature_post!(
 483                         &self,
 484                         negative_impls,
 485                         span.to(of_trait.as_ref().map_or(span, |t| t.path.span)),
 486                         "negative trait bounds are not yet fully implemented; \
 487                          use marker types for now"
 488                     );
 489                 }
 490
 491                 if let ast::Defaultness::Default(_) = defaultness {
 492                     gate_feature_post!(&self, specialization, i.span, "specialization is unstable");
 493                 }
 494             }
 495
 496             ast::ItemKind::Trait(box ast::Trait { is_auto: ast::IsAuto::Yes, .. }) => {
 497                 gate_feature_post!(
 498                     &self,
 499                     auto_traits,
 500                     i.span,
 501                     "auto traits are experimental and possibly buggy"
 502                 );
 503             }
 504
 505             ast::ItemKind::TraitAlias(..) => {
 506                 gate_feature_post!(&self, trait_alias, i.span, "trait aliases are experimental");
 507             }
 508
 509             ast::ItemKind::MacroDef(ast::MacroDef { macro_rules: false, .. }) => {
 510                 let msg = "`macro` is experimental";
 511                 gate_feature_post!(&self, decl_macro, i.span, msg);
 512             }
 513
 514             ast::ItemKind::TyAlias(box ast::TyAlias { ty: Some(ref ty), .. }) => {
 515                 self.check_impl_trait(&ty)
 516             }
 517
 518             _ => {}
 519         }
 520
 521         visit::walk_item(self, i);
 522     }
 523
 524     fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
 525         match i.kind {
 526             ast::ForeignItemKind::Fn(..) | ast::ForeignItemKind::Static(..) => {
 527                 let link_name = self.sess.first_attr_value_str_by_name(&i.attrs, sym::link_name);
 528                 let links_to_llvm =
 529                     link_name.map_or(false, |val| val.as_str().starts_with("llvm."));
 530                 if links_to_llvm {
 531                     gate_feature_post!(
 532                         &self,
 533                         link_llvm_intrinsics,
 534                         i.span,
 535                         "linking to LLVM intrinsics is experimental"
 536                     );
 537                 }
 538             }
 539             ast::ForeignItemKind::TyAlias(..) => {
 540                 gate_feature_post!(&self, extern_types, i.span, "extern types are experimental");
 541             }
 542             ast::ForeignItemKind::MacCall(..) => {}
 543         }
 544
 545         visit::walk_foreign_item(self, i)
 546     }
 547
 548     fn visit_ty(&mut self, ty: &'a ast::Ty) {
 549         match ty.kind {
 550             ast::TyKind::BareFn(ref bare_fn_ty) => {
 551                 // Function pointers cannot be `const`
 552                 self.check_extern(bare_fn_ty.ext, ast::Const::No);
 553             }
 554             ast::TyKind::Never => {
 555                 gate_feature_post!(&self, never_type, ty.span, "the `!` type is experimental");
 556             }
 557             ast::TyKind::TraitObject(_, ast::TraitObjectSyntax::DynStar, ..) => {
 558                 gate_feature_post!(&self, dyn_star, ty.span, "dyn* trait objects are unstable");
 559             }
 560             _ => {}
 561         }
 562         visit::walk_ty(self, ty)
 563     }
 564
 565     fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FnRetTy) {
 566         if let ast::FnRetTy::Ty(ref output_ty) = *ret_ty {
 567             if let ast::TyKind::Never = output_ty.kind {
 568                 // Do nothing.
 569             } else {
 570                 self.visit_ty(output_ty)
 571             }
 572         }
 573     }
 574
 575     fn visit_stmt(&mut self, stmt: &'a ast::Stmt) {
 576         if let ast::StmtKind::Semi(expr) = &stmt.kind
 577             && let ast::ExprKind::Assign(lhs, _, _) = &expr.kind
 578             && let ast::ExprKind::Type(..) = lhs.kind
 579             && self.sess.parse_sess.span_diagnostic.err_count() == 0
 580             && !self.features.type_ascription
 581             && !lhs.span.allows_unstable(sym::type_ascription)
 582         {
 583             // When we encounter a statement of the form `foo: Ty = val;`, this will emit a type
 584             // ascription error, but the likely intention was to write a `let` statement. (#78907).
 585             feature_err(
 586                 &self.sess.parse_sess,
 587                 sym::type_ascription,
 588                 lhs.span,
 589                 "type ascription is experimental",
 590             ).span_suggestion_verbose(
 591                 lhs.span.shrink_to_lo(),
 592                 "you might have meant to introduce a new binding",
 593                 "let ".to_string(),
 594                 Applicability::MachineApplicable,
 595             ).emit();
 596         }
 597         visit::walk_stmt(self, stmt);
 598     }
 599
 600     fn visit_expr(&mut self, e: &'a ast::Expr) {
 601         match e.kind {
 602             ast::ExprKind::Box(_) => {
 603                 gate_feature_post!(
 604                     &self,
 605                     box_syntax,
 606                     e.span,
 607                     "box expression syntax is experimental; you can call `Box::new` instead"
 608                 );
 609             }
 610             ast::ExprKind::Type(..) => {
 611                 if self.sess.parse_sess.span_diagnostic.err_count() == 0 {
 612                     // To avoid noise about type ascription in common syntax errors,
 613                     // only emit if it is the *only* error.
 614                     gate_feature_post!(
 615                         &self,
 616                         type_ascription,
 617                         e.span,
 618                         "type ascription is experimental"
 619                     );
 620                 } else {
 621                     // And if it isn't, cancel the early-pass warning.
 622                     self.sess
 623                         .parse_sess
 624                         .span_diagnostic
 625                         .steal_diagnostic(e.span, StashKey::EarlySyntaxWarning)
 626                         .map(|err| err.cancel());
 627                 }
 628             }
 629             ast::ExprKind::TryBlock(_) => {
 630                 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
 631             }
 632             _ => {}
 633         }
 634         visit::walk_expr(self, e)
 635     }
 636
 637     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
 638         match &pattern.kind {
 639             PatKind::Slice(pats) => {
 640                 for pat in pats {
 641                     let inner_pat = match &pat.kind {
 642                         PatKind::Ident(.., Some(pat)) => pat,
 643                         _ => pat,
 644                     };
 645                     if let PatKind::Range(Some(_), None, Spanned { .. }) = inner_pat.kind {
 646                         gate_feature_post!(
 647                             &self,
 648                             half_open_range_patterns,
 649                             pat.span,
 650                             "`X..` patterns in slices are experimental"
 651                         );
 652                     }
 653                 }
 654             }
 655             PatKind::Box(..) => {
 656                 gate_feature_post!(
 657                     &self,
 658                     box_patterns,
 659                     pattern.span,
 660                     "box pattern syntax is experimental"
 661                 );
 662             }
 663             PatKind::Range(_, Some(_), Spanned { node: RangeEnd::Excluded, .. }) => {
 664                 gate_feature_post!(
 665                     &self,
 666                     exclusive_range_pattern,
 667                     pattern.span,
 668                     "exclusive range pattern syntax is experimental"
 669                 );
 670             }
 671             _ => {}
 672         }
 673         visit::walk_pat(self, pattern)
 674     }
 675
 676     fn visit_fn(&mut self, fn_kind: FnKind<'a>, span: Span, _: NodeId) {
 677         if let Some(header) = fn_kind.header() {
 678             // Stability of const fn methods are covered in `visit_assoc_item` below.
 679             self.check_extern(header.ext, header.constness);
 680         }
 681
 682         if fn_kind.ctxt() != Some(FnCtxt::Foreign) && fn_kind.decl().c_variadic() {
 683             gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
 684         }
 685
 686         visit::walk_fn(self, fn_kind)
 687     }
 688
 689     fn visit_assoc_constraint(&mut self, constraint: &'a AssocConstraint) {
 690         if let AssocConstraintKind::Bound { .. } = constraint.kind {
 691             gate_feature_post!(
 692                 &self,
 693                 associated_type_bounds,
 694                 constraint.span,
 695                 "associated type bounds are unstable"
 696             )
 697         }
 698         visit::walk_assoc_constraint(self, constraint)
 699     }
 700
 701     fn visit_assoc_item(&mut self, i: &'a ast::AssocItem, ctxt: AssocCtxt) {
 702         let is_fn = match i.kind {
 703             ast::AssocItemKind::Fn(_) => true,
 704             ast::AssocItemKind::TyAlias(box ast::TyAlias { ref ty, .. }) => {
 705                 if let (Some(_), AssocCtxt::Trait) = (ty, ctxt) {
 706                     gate_feature_post!(
 707                         &self,
 708                         associated_type_defaults,
 709                         i.span,
 710                         "associated type defaults are unstable"
 711                     );
 712                 }
 713                 if let Some(ty) = ty {
 714                     self.check_impl_trait(ty);
 715                 }
 716                 false
 717             }
 718             _ => false,
 719         };
 720         if let ast::Defaultness::Default(_) = i.kind.defaultness() {
 721             // Limit `min_specialization` to only specializing functions.
 722             gate_feature_fn!(
 723                 &self,
 724                 |x: &Features| x.specialization || (is_fn && x.min_specialization),
 725                 i.span,
 726                 sym::specialization,
 727                 "specialization is unstable"
 728             );
 729         }
 730         visit::walk_assoc_item(self, i, ctxt)
 731     }
 732 }
 733
 734 pub fn check_crate(krate: &ast::Crate, sess: &Session) {
 735     maybe_stage_features(sess, krate);
 736     check_incompatible_features(sess);
 737     let mut visitor = PostExpansionVisitor { sess, features: &sess.features_untracked() };
 738
 739     let spans = sess.parse_sess.gated_spans.spans.borrow();
 740     macro_rules! gate_all {
 741         ($gate:ident, $msg:literal, $help:literal) => {
 742             if let Some(spans) = spans.get(&sym::$gate) {
 743                 for span in spans {
 744                     gate_feature_post!(&visitor, $gate, *span, $msg, $help);
 745                 }
 746             }
 747         };
 748         ($gate:ident, $msg:literal) => {
 749             if let Some(spans) = spans.get(&sym::$gate) {
 750                 for span in spans {
 751                     gate_feature_post!(&visitor, $gate, *span, $msg);
 752                 }
 753             }
 754         };
 755     }
 756     gate_all!(
 757         if_let_guard,
 758         "`if let` guards are experimental",
 759         "you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`"
 760     );
 761     gate_all!(let_chains, "`let` expressions in this position are unstable");
 762     gate_all!(
 763         async_closure,
 764         "async closures are unstable",
 765         "to use an async block, remove the `||`: `async {`"
 766     );
 767     gate_all!(
 768         closure_lifetime_binder,
 769         "`for<...>` binders for closures are experimental",
 770         "consider removing `for<...>`"
 771     );
 772     gate_all!(more_qualified_paths, "usage of qualified paths in this context is experimental");
 773     gate_all!(generators, "yield syntax is experimental");
 774     gate_all!(raw_ref_op, "raw address of syntax is experimental");
 775     gate_all!(const_trait_impl, "const trait impls are experimental");
 776     gate_all!(half_open_range_patterns, "half-open range patterns are unstable");
 777     gate_all!(inline_const, "inline-const is experimental");
 778     gate_all!(inline_const_pat, "inline-const in pattern position is experimental");
 779     gate_all!(associated_const_equality, "associated const equality is incomplete");
 780     gate_all!(yeet_expr, "`do yeet` expression is experimental");
 781
 782     // All uses of `gate_all!` below this point were added in #65742,
 783     // and subsequently disabled (with the non-early gating readded).
 784     // We emit an early future-incompatible warning for these.
 785     // New syntax gates should go above here to get a hard error gate.
 786     macro_rules! gate_all {
 787         ($gate:ident, $msg:literal) => {
 788             for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 789                 gate_feature_post!(future_incompatible; &visitor, $gate, *span, $msg);
 790             }
 791         };
 792     }
 793
 794     gate_all!(trait_alias, "trait aliases are experimental");
 795     gate_all!(associated_type_bounds, "associated type bounds are unstable");
 796     gate_all!(decl_macro, "`macro` is experimental");
 797     gate_all!(box_patterns, "box pattern syntax is experimental");
 798     gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
 799     gate_all!(try_blocks, "`try` blocks are unstable");
 800     gate_all!(box_syntax, "box expression syntax is experimental; you can call `Box::new` instead");
 801     gate_all!(type_ascription, "type ascription is experimental");
 802
 803     visit::walk_crate(&mut visitor, krate);
 804 }
 805
 806 fn maybe_stage_features(sess: &Session, krate: &ast::Crate) {
 807     // checks if `#![feature]` has been used to enable any lang feature
 808     // does not check the same for lib features unless there's at least one
 809     // declared lang feature
 810     if !sess.opts.unstable_features.is_nightly_build() {
 811         let lang_features = &sess.features_untracked().declared_lang_features;
 812         if lang_features.len() == 0 {
 813             return;
 814         }
 815         for attr in krate.attrs.iter().filter(|attr| attr.has_name(sym::feature)) {
 816             let mut err = struct_span_err!(
 817                 sess.parse_sess.span_diagnostic,
 818                 attr.span,
 819                 E0554,
 820                 "`#![feature]` may not be used on the {} release channel",
 821                 option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)")
 822             );
 823             let mut all_stable = true;
 824             for ident in
 825                 attr.meta_item_list().into_iter().flatten().flat_map(|nested| nested.ident())
 826             {
 827                 let name = ident.name;
 828                 let stable_since = lang_features
 829                     .iter()
 830                     .flat_map(|&(feature, _, since)| if feature == name { since } else { None })
 831                     .next();
 832                 if let Some(since) = stable_since {
 833                     err.help(&format!(
 834                         "the feature `{}` has been stable since {} and no longer requires \
 835                                   an attribute to enable",
 836                         name, since
 837                     ));
 838                 } else {
 839                     all_stable = false;
 840                 }
 841             }
 842             if all_stable {
 843                 err.span_suggestion(
 844                     attr.span,
 845                     "remove the attribute",
 846                     "",
 847                     Applicability::MachineApplicable,
 848                 );
 849             }
 850             err.emit();
 851         }
 852     }
 853 }
 854
 855 fn check_incompatible_features(sess: &Session) {
 856     let features = sess.features_untracked();
 857
 858     let declared_features = features
 859         .declared_lang_features
 860         .iter()
 861         .copied()
 862         .map(|(name, span, _)| (name, span))
 863         .chain(features.declared_lib_features.iter().copied());
 864
 865     for (f1, f2) in rustc_feature::INCOMPATIBLE_FEATURES
 866         .iter()
 867         .filter(|&&(f1, f2)| features.enabled(f1) && features.enabled(f2))
 868     {
 869         if let Some((f1_name, f1_span)) = declared_features.clone().find(|(name, _)| name == f1) {
 870             if let Some((f2_name, f2_span)) = declared_features.clone().find(|(name, _)| name == f2)
 871             {
 872                 let spans = vec![f1_span, f2_span];
 873                 sess.struct_span_err(
 874                     spans.clone(),
 875                     &format!(
 876                         "features `{}` and `{}` are incompatible, using them at the same time \
 877                         is not allowed",
 878                         f1_name, f2_name
 879                     ),
 880                 )
 881                 .help("remove one of these features")
 882                 .emit();
 883             }
 884         }
 885     }
 886 }