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 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(&visitor.sess.parse_sess, name, span, explain).help(help).emit();
  24         }
  25     }};
  26     ($visitor: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr) => {{
  27         let (visitor, has_feature, span, name, explain) =
  28             (&*$visitor, $has_feature, $span, $name, $explain);
  29         let has_feature: bool = has_feature(visitor.features);
  30         debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
  31         if !has_feature && !span.allows_unstable($name) {
  32             feature_err(&visitor.sess.parse_sess, name, span, explain).emit();
  33         }
  34     }};
  35     (future_incompatible; $visitor: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr) => {{
  36         let (visitor, has_feature, span, name, explain) =
  37             (&*$visitor, $has_feature, $span, $name, $explain);
  38         let has_feature: bool = has_feature(visitor.features);
  39         debug!(
  40             "gate_feature(feature = {:?}, span = {:?}); has? {} (future_incompatible)",
  41             name, span, has_feature
  42         );
  43         if !has_feature && !span.allows_unstable($name) {
  44             feature_warn(&visitor.sess.parse_sess, name, span, explain);
  45         }
  46     }};
  47 }
  48
  49 macro_rules! gate_feature_post {
  50     ($visitor: expr, $feature: ident, $span: expr, $explain: expr, $help: expr) => {
  51         gate_feature_fn!($visitor, |x: &Features| x.$feature, $span, sym::$feature, $explain, $help)
  52     };
  53     ($visitor: expr, $feature: ident, $span: expr, $explain: expr) => {
  54         gate_feature_fn!($visitor, |x: &Features| x.$feature, $span, sym::$feature, $explain)
  55     };
  56     (future_incompatible; $visitor: expr, $feature: ident, $span: expr, $explain: expr) => {
  57         gate_feature_fn!(future_incompatible; $visitor, |x: &Features| x.$feature, $span, sym::$feature, $explain)
  58     };
  59 }
  60
  61 pub fn check_attribute(attr: &ast::Attribute, sess: &Session, features: &Features) {
  62     PostExpansionVisitor { sess, features }.visit_attribute(attr)
  63 }
  64
  65 struct PostExpansionVisitor<'a> {
  66     sess: &'a Session,
  67
  68     // `sess` contains a `Features`, but this might not be that one.
  69     features: &'a Features,
  70 }
  71
  72 impl<'a> PostExpansionVisitor<'a> {
  73     fn check_abi(&self, abi: ast::StrLit, constness: ast::Const) {
  74         let ast::StrLit { symbol_unescaped, span, .. } = abi;
  75
  76         if let ast::Const::Yes(_) = constness {
  77             match symbol_unescaped {
  78                 // Stable
  79                 sym::Rust | sym::C => {}
  80                 abi => gate_feature_post!(
  81                     &self,
  82                     const_extern_fn,
  83                     span,
  84                     &format!("`{}` as a `const fn` ABI is unstable", abi)
  85                 ),
  86             }
  87         }
  88
  89         match symbol_unescaped.as_str() {
  90             // Stable
  91             "Rust" | "C" | "cdecl" | "stdcall" | "fastcall" | "aapcs" | "win64" | "sysv64"
  92             | "system" => {}
  93             "rust-intrinsic" => {
  94                 gate_feature_post!(&self, intrinsics, span, "intrinsics are subject to change");
  95             }
  96             "platform-intrinsic" => {
  97                 gate_feature_post!(
  98                     &self,
  99                     platform_intrinsics,
 100                     span,
 101                     "platform intrinsics are experimental and possibly buggy"
 102                 );
 103             }
 104             "vectorcall" => {
 105                 gate_feature_post!(
 106                     &self,
 107                     abi_vectorcall,
 108                     span,
 109                     "vectorcall is experimental and subject to change"
 110                 );
 111             }
 112             "thiscall" => {
 113                 gate_feature_post!(
 114                     &self,
 115                     abi_thiscall,
 116                     span,
 117                     "thiscall is experimental and subject to change"
 118                 );
 119             }
 120             "rust-call" => {
 121                 gate_feature_post!(
 122                     &self,
 123                     unboxed_closures,
 124                     span,
 125                     "rust-call ABI is subject to change"
 126                 );
 127             }
 128             "rust-cold" => {
 129                 gate_feature_post!(
 130                     &self,
 131                     rust_cold_cc,
 132                     span,
 133                     "rust-cold is experimental and subject to change"
 134                 );
 135             }
 136             "ptx-kernel" => {
 137                 gate_feature_post!(
 138                     &self,
 139                     abi_ptx,
 140                     span,
 141                     "PTX ABIs are experimental and subject to change"
 142                 );
 143             }
 144             "unadjusted" => {
 145                 gate_feature_post!(
 146                     &self,
 147                     abi_unadjusted,
 148                     span,
 149                     "unadjusted ABI is an implementation detail and perma-unstable"
 150                 );
 151             }
 152             "msp430-interrupt" => {
 153                 gate_feature_post!(
 154                     &self,
 155                     abi_msp430_interrupt,
 156                     span,
 157                     "msp430-interrupt ABI is experimental and subject to change"
 158                 );
 159             }
 160             "x86-interrupt" => {
 161                 gate_feature_post!(
 162                     &self,
 163                     abi_x86_interrupt,
 164                     span,
 165                     "x86-interrupt ABI is experimental and subject to change"
 166                 );
 167             }
 168             "amdgpu-kernel" => {
 169                 gate_feature_post!(
 170                     &self,
 171                     abi_amdgpu_kernel,
 172                     span,
 173                     "amdgpu-kernel ABI is experimental and subject to change"
 174                 );
 175             }
 176             "avr-interrupt" | "avr-non-blocking-interrupt" => {
 177                 gate_feature_post!(
 178                     &self,
 179                     abi_avr_interrupt,
 180                     span,
 181                     "avr-interrupt and avr-non-blocking-interrupt ABIs are experimental and subject to change"
 182                 );
 183             }
 184             "efiapi" => {
 185                 gate_feature_post!(
 186                     &self,
 187                     abi_efiapi,
 188                     span,
 189                     "efiapi ABI is experimental and subject to change"
 190                 );
 191             }
 192             "C-cmse-nonsecure-call" => {
 193                 gate_feature_post!(
 194                     &self,
 195                     abi_c_cmse_nonsecure_call,
 196                     span,
 197                     "C-cmse-nonsecure-call ABI is experimental and subject to change"
 198                 );
 199             }
 200             "C-unwind" => {
 201                 gate_feature_post!(
 202                     &self,
 203                     c_unwind,
 204                     span,
 205                     "C-unwind ABI is experimental and subject to change"
 206                 );
 207             }
 208             "stdcall-unwind" => {
 209                 gate_feature_post!(
 210                     &self,
 211                     c_unwind,
 212                     span,
 213                     "stdcall-unwind ABI is experimental and subject to change"
 214                 );
 215             }
 216             "system-unwind" => {
 217                 gate_feature_post!(
 218                     &self,
 219                     c_unwind,
 220                     span,
 221                     "system-unwind ABI is experimental and subject to change"
 222                 );
 223             }
 224             "thiscall-unwind" => {
 225                 gate_feature_post!(
 226                     &self,
 227                     c_unwind,
 228                     span,
 229                     "thiscall-unwind ABI is experimental and subject to change"
 230                 );
 231             }
 232             "cdecl-unwind" => {
 233                 gate_feature_post!(
 234                     &self,
 235                     c_unwind,
 236                     span,
 237                     "cdecl-unwind ABI is experimental and subject to change"
 238                 );
 239             }
 240             "fastcall-unwind" => {
 241                 gate_feature_post!(
 242                     &self,
 243                     c_unwind,
 244                     span,
 245                     "fastcall-unwind ABI is experimental and subject to change"
 246                 );
 247             }
 248             "vectorcall-unwind" => {
 249                 gate_feature_post!(
 250                     &self,
 251                     c_unwind,
 252                     span,
 253                     "vectorcall-unwind ABI is experimental and subject to change"
 254                 );
 255             }
 256             "aapcs-unwind" => {
 257                 gate_feature_post!(
 258                     &self,
 259                     c_unwind,
 260                     span,
 261                     "aapcs-unwind ABI is experimental and subject to change"
 262                 );
 263             }
 264             "win64-unwind" => {
 265                 gate_feature_post!(
 266                     &self,
 267                     c_unwind,
 268                     span,
 269                     "win64-unwind ABI is experimental and subject to change"
 270                 );
 271             }
 272             "sysv64-unwind" => {
 273                 gate_feature_post!(
 274                     &self,
 275                     c_unwind,
 276                     span,
 277                     "sysv64-unwind ABI is experimental and subject to change"
 278                 );
 279             }
 280             "wasm" => {
 281                 gate_feature_post!(
 282                     &self,
 283                     wasm_abi,
 284                     span,
 285                     "wasm ABI is experimental and subject to change"
 286                 );
 287             }
 288             abi => {
 289                 if self.sess.opts.pretty.map_or(true, |ppm| ppm.needs_hir()) {
 290                     self.sess.parse_sess.span_diagnostic.delay_span_bug(
 291                         span,
 292                         &format!("unrecognized ABI not caught in lowering: {}", abi),
 293                     );
 294                 }
 295             }
 296         }
 297     }
 298
 299     fn check_extern(&self, ext: ast::Extern, constness: ast::Const) {
 300         if let ast::Extern::Explicit(abi, _) = ext {
 301             self.check_abi(abi, constness);
 302         }
 303     }
 304
 305     fn maybe_report_invalid_custom_discriminants(&self, variants: &[ast::Variant]) {
 306         let has_fields = variants.iter().any(|variant| match variant.data {
 307             VariantData::Tuple(..) | VariantData::Struct(..) => true,
 308             VariantData::Unit(..) => false,
 309         });
 310
 311         let discriminant_spans = variants
 312             .iter()
 313             .filter(|variant| match variant.data {
 314                 VariantData::Tuple(..) | VariantData::Struct(..) => false,
 315                 VariantData::Unit(..) => true,
 316             })
 317             .filter_map(|variant| variant.disr_expr.as_ref().map(|c| c.value.span))
 318             .collect::<Vec<_>>();
 319
 320         if !discriminant_spans.is_empty() && has_fields {
 321             let mut err = feature_err(
 322                 &self.sess.parse_sess,
 323                 sym::arbitrary_enum_discriminant,
 324                 discriminant_spans.clone(),
 325                 "custom discriminant values are not allowed in enums with tuple or struct variants",
 326             );
 327             for sp in discriminant_spans {
 328                 err.span_label(sp, "disallowed custom discriminant");
 329             }
 330             for variant in variants.iter() {
 331                 match &variant.data {
 332                     VariantData::Struct(..) => {
 333                         err.span_label(variant.span, "struct variant defined here");
 334                     }
 335                     VariantData::Tuple(..) => {
 336                         err.span_label(variant.span, "tuple variant defined here");
 337                     }
 338                     VariantData::Unit(..) => {}
 339                 }
 340             }
 341             err.emit();
 342         }
 343     }
 344
 345     fn check_gat(&self, generics: &ast::Generics, span: Span) {
 346         if !generics.params.is_empty() {
 347             gate_feature_post!(
 348                 &self,
 349                 generic_associated_types,
 350                 span,
 351                 "generic associated types are unstable"
 352             );
 353         }
 354         if !generics.where_clause.predicates.is_empty() {
 355             gate_feature_post!(
 356                 &self,
 357                 generic_associated_types,
 358                 span,
 359                 "where clauses on associated types are unstable"
 360             );
 361         }
 362     }
 363
 364     /// Feature gate `impl Trait` inside `type Alias = $type_expr;`.
 365     fn check_impl_trait(&self, ty: &ast::Ty) {
 366         struct ImplTraitVisitor<'a> {
 367             vis: &'a PostExpansionVisitor<'a>,
 368         }
 369         impl Visitor<'_> for ImplTraitVisitor<'_> {
 370             fn visit_ty(&mut self, ty: &ast::Ty) {
 371                 if let ast::TyKind::ImplTrait(..) = ty.kind {
 372                     gate_feature_post!(
 373                         &self.vis,
 374                         type_alias_impl_trait,
 375                         ty.span,
 376                         "`impl Trait` in type aliases is unstable"
 377                     );
 378                 }
 379                 visit::walk_ty(self, ty);
 380             }
 381         }
 382         ImplTraitVisitor { vis: self }.visit_ty(ty);
 383     }
 384 }
 385
 386 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 387     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 388         let attr_info = attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name));
 389         // Check feature gates for built-in attributes.
 390         if let Some(BuiltinAttribute {
 391             gate: AttributeGate::Gated(_, name, descr, has_feature),
 392             ..
 393         }) = attr_info
 394         {
 395             gate_feature_fn!(self, has_feature, attr.span, *name, descr);
 396         }
 397         // Check unstable flavors of the `#[doc]` attribute.
 398         if attr.has_name(sym::doc) {
 399             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 400                 macro_rules! gate_doc { ($($name:ident => $feature:ident)*) => {
 401                     $(if nested_meta.has_name(sym::$name) {
 402                         let msg = concat!("`#[doc(", stringify!($name), ")]` is experimental");
 403                         gate_feature_post!(self, $feature, attr.span, msg);
 404                     })*
 405                 }}
 406
 407                 gate_doc!(
 408                     cfg => doc_cfg
 409                     cfg_hide => doc_cfg_hide
 410                     masked => doc_masked
 411                     notable_trait => doc_notable_trait
 412                 );
 413
 414                 if nested_meta.has_name(sym::keyword) {
 415                     let msg = "`#[doc(keyword)]` is meant for internal use only";
 416                     gate_feature_post!(self, rustdoc_internals, attr.span, msg);
 417                 }
 418
 419                 if nested_meta.has_name(sym::fake_variadic) {
 420                     let msg = "`#[doc(fake_variadic)]` is meant for internal use only";
 421                     gate_feature_post!(self, rustdoc_internals, attr.span, msg);
 422                 }
 423             }
 424         }
 425
 426         // Emit errors for non-staged-api crates.
 427         if !self.features.staged_api {
 428             if attr.has_name(sym::unstable)
 429                 || attr.has_name(sym::stable)
 430                 || attr.has_name(sym::rustc_const_unstable)
 431                 || attr.has_name(sym::rustc_const_stable)
 432                 || attr.has_name(sym::rustc_default_body_unstable)
 433             {
 434                 struct_span_err!(
 435                     self.sess,
 436                     attr.span,
 437                     E0734,
 438                     "stability attributes may not be used outside of the standard library",
 439                 )
 440                 .emit();
 441             }
 442         }
 443     }
 444
 445     fn visit_item(&mut self, i: &'a ast::Item) {
 446         match i.kind {
 447             ast::ItemKind::ForeignMod(ref foreign_module) => {
 448                 if let Some(abi) = foreign_module.abi {
 449                     self.check_abi(abi, ast::Const::No);
 450                 }
 451             }
 452
 453             ast::ItemKind::Fn(..) => {
 454                 if self.sess.contains_name(&i.attrs, sym::start) {
 455                     gate_feature_post!(
 456                         &self,
 457                         start,
 458                         i.span,
 459                         "`#[start]` functions are experimental \
 460                          and their signature may change \
 461                          over time"
 462                     );
 463                 }
 464             }
 465
 466             ast::ItemKind::Struct(..) => {
 467                 for attr in self.sess.filter_by_name(&i.attrs, sym::repr) {
 468                     for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
 469                         if item.has_name(sym::simd) {
 470                             gate_feature_post!(
 471                                 &self,
 472                                 repr_simd,
 473                                 attr.span,
 474                                 "SIMD types are experimental and possibly buggy"
 475                             );
 476                         }
 477                     }
 478                 }
 479             }
 480
 481             ast::ItemKind::Enum(ast::EnumDef { ref variants, .. }, ..) => {
 482                 for variant in variants {
 483                     match (&variant.data, &variant.disr_expr) {
 484                         (ast::VariantData::Unit(..), _) => {}
 485                         (_, Some(disr_expr)) => gate_feature_post!(
 486                             &self,
 487                             arbitrary_enum_discriminant,
 488                             disr_expr.value.span,
 489                             "discriminants on non-unit variants are experimental"
 490                         ),
 491                         _ => {}
 492                     }
 493                 }
 494
 495                 let has_feature = self.features.arbitrary_enum_discriminant;
 496                 if !has_feature && !i.span.allows_unstable(sym::arbitrary_enum_discriminant) {
 497                     self.maybe_report_invalid_custom_discriminants(&variants);
 498                 }
 499             }
 500
 501             ast::ItemKind::Impl(box ast::Impl { polarity, defaultness, ref of_trait, .. }) => {
 502                 if let ast::ImplPolarity::Negative(span) = polarity {
 503                     gate_feature_post!(
 504                         &self,
 505                         negative_impls,
 506                         span.to(of_trait.as_ref().map_or(span, |t| t.path.span)),
 507                         "negative trait bounds are not yet fully implemented; \
 508                          use marker types for now"
 509                     );
 510                 }
 511
 512                 if let ast::Defaultness::Default(_) = defaultness {
 513                     gate_feature_post!(&self, specialization, i.span, "specialization is unstable");
 514                 }
 515             }
 516
 517             ast::ItemKind::Trait(box ast::Trait { is_auto: ast::IsAuto::Yes, .. }) => {
 518                 gate_feature_post!(
 519                     &self,
 520                     auto_traits,
 521                     i.span,
 522                     "auto traits are experimental and possibly buggy"
 523                 );
 524             }
 525
 526             ast::ItemKind::TraitAlias(..) => {
 527                 gate_feature_post!(&self, trait_alias, i.span, "trait aliases are experimental");
 528             }
 529
 530             ast::ItemKind::MacroDef(ast::MacroDef { macro_rules: false, .. }) => {
 531                 let msg = "`macro` is experimental";
 532                 gate_feature_post!(&self, decl_macro, i.span, msg);
 533             }
 534
 535             ast::ItemKind::TyAlias(box ast::TyAlias { ty: Some(ref ty), .. }) => {
 536                 self.check_impl_trait(&ty)
 537             }
 538
 539             _ => {}
 540         }
 541
 542         visit::walk_item(self, i);
 543     }
 544
 545     fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
 546         match i.kind {
 547             ast::ForeignItemKind::Fn(..) | ast::ForeignItemKind::Static(..) => {
 548                 let link_name = self.sess.first_attr_value_str_by_name(&i.attrs, sym::link_name);
 549                 let links_to_llvm =
 550                     link_name.map_or(false, |val| val.as_str().starts_with("llvm."));
 551                 if links_to_llvm {
 552                     gate_feature_post!(
 553                         &self,
 554                         link_llvm_intrinsics,
 555                         i.span,
 556                         "linking to LLVM intrinsics is experimental"
 557                     );
 558                 }
 559             }
 560             ast::ForeignItemKind::TyAlias(..) => {
 561                 gate_feature_post!(&self, extern_types, i.span, "extern types are experimental");
 562             }
 563             ast::ForeignItemKind::MacCall(..) => {}
 564         }
 565
 566         visit::walk_foreign_item(self, i)
 567     }
 568
 569     fn visit_ty(&mut self, ty: &'a ast::Ty) {
 570         match ty.kind {
 571             ast::TyKind::BareFn(ref bare_fn_ty) => {
 572                 // Function pointers cannot be `const`
 573                 self.check_extern(bare_fn_ty.ext, ast::Const::No);
 574             }
 575             ast::TyKind::Never => {
 576                 gate_feature_post!(&self, never_type, ty.span, "the `!` type is experimental");
 577             }
 578             _ => {}
 579         }
 580         visit::walk_ty(self, ty)
 581     }
 582
 583     fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FnRetTy) {
 584         if let ast::FnRetTy::Ty(ref output_ty) = *ret_ty {
 585             if let ast::TyKind::Never = output_ty.kind {
 586                 // Do nothing.
 587             } else {
 588                 self.visit_ty(output_ty)
 589             }
 590         }
 591     }
 592
 593     fn visit_stmt(&mut self, stmt: &'a ast::Stmt) {
 594         if let ast::StmtKind::Semi(expr) = &stmt.kind
 595             && let ast::ExprKind::Assign(lhs, _, _) = &expr.kind
 596             && let ast::ExprKind::Type(..) = lhs.kind
 597             && self.sess.parse_sess.span_diagnostic.err_count() == 0
 598             && !self.features.type_ascription
 599             && !lhs.span.allows_unstable(sym::type_ascription)
 600         {
 601             // When we encounter a statement of the form `foo: Ty = val;`, this will emit a type
 602             // ascription error, but the likely intention was to write a `let` statement. (#78907).
 603             feature_err(
 604                 &self.sess.parse_sess,
 605                 sym::type_ascription,
 606                 lhs.span,
 607                 "type ascription is experimental",
 608             ).span_suggestion_verbose(
 609                 lhs.span.shrink_to_lo(),
 610                 "you might have meant to introduce a new binding",
 611                 "let ".to_string(),
 612                 Applicability::MachineApplicable,
 613             ).emit();
 614         }
 615         visit::walk_stmt(self, stmt);
 616     }
 617
 618     fn visit_expr(&mut self, e: &'a ast::Expr) {
 619         match e.kind {
 620             ast::ExprKind::Box(_) => {
 621                 gate_feature_post!(
 622                     &self,
 623                     box_syntax,
 624                     e.span,
 625                     "box expression syntax is experimental; you can call `Box::new` instead"
 626                 );
 627             }
 628             ast::ExprKind::Type(..) => {
 629                 if self.sess.parse_sess.span_diagnostic.err_count() == 0 {
 630                     // To avoid noise about type ascription in common syntax errors,
 631                     // only emit if it is the *only* error.
 632                     gate_feature_post!(
 633                         &self,
 634                         type_ascription,
 635                         e.span,
 636                         "type ascription is experimental"
 637                     );
 638                 } else {
 639                     // And if it isn't, cancel the early-pass warning.
 640                     self.sess
 641                         .parse_sess
 642                         .span_diagnostic
 643                         .steal_diagnostic(e.span, StashKey::EarlySyntaxWarning)
 644                         .map(|err| err.cancel());
 645                 }
 646             }
 647             ast::ExprKind::TryBlock(_) => {
 648                 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
 649             }
 650             _ => {}
 651         }
 652         visit::walk_expr(self, e)
 653     }
 654
 655     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
 656         match &pattern.kind {
 657             PatKind::Slice(pats) => {
 658                 for pat in pats {
 659                     let inner_pat = match &pat.kind {
 660                         PatKind::Ident(.., Some(pat)) => pat,
 661                         _ => pat,
 662                     };
 663                     if let PatKind::Range(Some(_), None, Spanned { .. }) = inner_pat.kind {
 664                         gate_feature_post!(
 665                             &self,
 666                             half_open_range_patterns,
 667                             pat.span,
 668                             "`X..` patterns in slices are experimental"
 669                         );
 670                     }
 671                 }
 672             }
 673             PatKind::Box(..) => {
 674                 gate_feature_post!(
 675                     &self,
 676                     box_patterns,
 677                     pattern.span,
 678                     "box pattern syntax is experimental"
 679                 );
 680             }
 681             PatKind::Range(_, Some(_), Spanned { node: RangeEnd::Excluded, .. }) => {
 682                 gate_feature_post!(
 683                     &self,
 684                     exclusive_range_pattern,
 685                     pattern.span,
 686                     "exclusive range pattern syntax is experimental"
 687                 );
 688             }
 689             _ => {}
 690         }
 691         visit::walk_pat(self, pattern)
 692     }
 693
 694     fn visit_fn(&mut self, fn_kind: FnKind<'a>, span: Span, _: NodeId) {
 695         if let Some(header) = fn_kind.header() {
 696             // Stability of const fn methods are covered in `visit_assoc_item` below.
 697             self.check_extern(header.ext, header.constness);
 698         }
 699
 700         if fn_kind.ctxt() != Some(FnCtxt::Foreign) && fn_kind.decl().c_variadic() {
 701             gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
 702         }
 703
 704         visit::walk_fn(self, fn_kind, span)
 705     }
 706
 707     fn visit_assoc_constraint(&mut self, constraint: &'a AssocConstraint) {
 708         if let AssocConstraintKind::Bound { .. } = constraint.kind {
 709             gate_feature_post!(
 710                 &self,
 711                 associated_type_bounds,
 712                 constraint.span,
 713                 "associated type bounds are unstable"
 714             )
 715         }
 716         visit::walk_assoc_constraint(self, constraint)
 717     }
 718
 719     fn visit_assoc_item(&mut self, i: &'a ast::AssocItem, ctxt: AssocCtxt) {
 720         let is_fn = match i.kind {
 721             ast::AssocItemKind::Fn(_) => true,
 722             ast::AssocItemKind::TyAlias(box ast::TyAlias { ref generics, ref ty, .. }) => {
 723                 if let (Some(_), AssocCtxt::Trait) = (ty, ctxt) {
 724                     gate_feature_post!(
 725                         &self,
 726                         associated_type_defaults,
 727                         i.span,
 728                         "associated type defaults are unstable"
 729                     );
 730                 }
 731                 if let Some(ty) = ty {
 732                     self.check_impl_trait(ty);
 733                 }
 734                 self.check_gat(generics, i.span);
 735                 false
 736             }
 737             _ => false,
 738         };
 739         if let ast::Defaultness::Default(_) = i.kind.defaultness() {
 740             // Limit `min_specialization` to only specializing functions.
 741             gate_feature_fn!(
 742                 &self,
 743                 |x: &Features| x.specialization || (is_fn && x.min_specialization),
 744                 i.span,
 745                 sym::specialization,
 746                 "specialization is unstable"
 747             );
 748         }
 749         visit::walk_assoc_item(self, i, ctxt)
 750     }
 751 }
 752
 753 pub fn check_crate(krate: &ast::Crate, sess: &Session) {
 754     maybe_stage_features(sess, krate);
 755     check_incompatible_features(sess);
 756     let mut visitor = PostExpansionVisitor { sess, features: &sess.features_untracked() };
 757
 758     let spans = sess.parse_sess.gated_spans.spans.borrow();
 759     macro_rules! gate_all {
 760         ($gate:ident, $msg:literal, $help:literal) => {
 761             if let Some(spans) = spans.get(&sym::$gate) {
 762                 for span in spans {
 763                     gate_feature_post!(&visitor, $gate, *span, $msg, $help);
 764                 }
 765             }
 766         };
 767         ($gate:ident, $msg:literal) => {
 768             if let Some(spans) = spans.get(&sym::$gate) {
 769                 for span in spans {
 770                     gate_feature_post!(&visitor, $gate, *span, $msg);
 771                 }
 772             }
 773         };
 774     }
 775     gate_all!(
 776         if_let_guard,
 777         "`if let` guards are experimental",
 778         "you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`"
 779     );
 780     gate_all!(let_chains, "`let` expressions in this position are unstable");
 781     gate_all!(
 782         async_closure,
 783         "async closures are unstable",
 784         "to use an async block, remove the `||`: `async {`"
 785     );
 786     gate_all!(
 787         closure_lifetime_binder,
 788         "`for<...>` binders for closures are experimental",
 789         "consider removing `for<...>`"
 790     );
 791     gate_all!(more_qualified_paths, "usage of qualified paths in this context is experimental");
 792     gate_all!(generators, "yield syntax is experimental");
 793     gate_all!(raw_ref_op, "raw address of syntax is experimental");
 794     gate_all!(const_trait_impl, "const trait impls are experimental");
 795     gate_all!(half_open_range_patterns, "half-open range patterns are unstable");
 796     gate_all!(inline_const, "inline-const is experimental");
 797     gate_all!(inline_const_pat, "inline-const in pattern position is experimental");
 798     gate_all!(associated_const_equality, "associated const equality is incomplete");
 799     gate_all!(yeet_expr, "`do yeet` expression is experimental");
 800
 801     // All uses of `gate_all!` below this point were added in #65742,
 802     // and subsequently disabled (with the non-early gating readded).
 803     // We emit an early future-incompatible warning for these.
 804     // New syntax gates should go above here to get a hard error gate.
 805     macro_rules! gate_all {
 806         ($gate:ident, $msg:literal) => {
 807             for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 808                 gate_feature_post!(future_incompatible; &visitor, $gate, *span, $msg);
 809             }
 810         };
 811     }
 812
 813     gate_all!(trait_alias, "trait aliases are experimental");
 814     gate_all!(associated_type_bounds, "associated type bounds are unstable");
 815     gate_all!(decl_macro, "`macro` is experimental");
 816     gate_all!(box_patterns, "box pattern syntax is experimental");
 817     gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
 818     gate_all!(try_blocks, "`try` blocks are unstable");
 819     gate_all!(box_syntax, "box expression syntax is experimental; you can call `Box::new` instead");
 820     gate_all!(type_ascription, "type ascription is experimental");
 821
 822     visit::walk_crate(&mut visitor, krate);
 823 }
 824
 825 fn maybe_stage_features(sess: &Session, krate: &ast::Crate) {
 826     // checks if `#![feature]` has been used to enable any lang feature
 827     // does not check the same for lib features unless there's at least one
 828     // declared lang feature
 829     if !sess.opts.unstable_features.is_nightly_build() {
 830         let lang_features = &sess.features_untracked().declared_lang_features;
 831         if lang_features.len() == 0 {
 832             return;
 833         }
 834         for attr in krate.attrs.iter().filter(|attr| attr.has_name(sym::feature)) {
 835             let mut err = struct_span_err!(
 836                 sess.parse_sess.span_diagnostic,
 837                 attr.span,
 838                 E0554,
 839                 "`#![feature]` may not be used on the {} release channel",
 840                 option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)")
 841             );
 842             let mut all_stable = true;
 843             for ident in
 844                 attr.meta_item_list().into_iter().flatten().flat_map(|nested| nested.ident())
 845             {
 846                 let name = ident.name;
 847                 let stable_since = lang_features
 848                     .iter()
 849                     .flat_map(|&(feature, _, since)| if feature == name { since } else { None })
 850                     .next();
 851                 if let Some(since) = stable_since {
 852                     err.help(&format!(
 853                         "the feature `{}` has been stable since {} and no longer requires \
 854                                   an attribute to enable",
 855                         name, since
 856                     ));
 857                 } else {
 858                     all_stable = false;
 859                 }
 860             }
 861             if all_stable {
 862                 err.span_suggestion(
 863                     attr.span,
 864                     "remove the attribute",
 865                     "",
 866                     Applicability::MachineApplicable,
 867                 );
 868             }
 869             err.emit();
 870         }
 871     }
 872 }
 873
 874 fn check_incompatible_features(sess: &Session) {
 875     let features = sess.features_untracked();
 876
 877     let declared_features = features
 878         .declared_lang_features
 879         .iter()
 880         .copied()
 881         .map(|(name, span, _)| (name, span))
 882         .chain(features.declared_lib_features.iter().copied());
 883
 884     for (f1, f2) in rustc_feature::INCOMPATIBLE_FEATURES
 885         .iter()
 886         .filter(|&&(f1, f2)| features.enabled(f1) && features.enabled(f2))
 887     {
 888         if let Some((f1_name, f1_span)) = declared_features.clone().find(|(name, _)| name == f1) {
 889             if let Some((f2_name, f2_span)) = declared_features.clone().find(|(name, _)| name == f2)
 890             {
 891                 let spans = vec![f1_span, f2_span];
 892                 sess.struct_span_err(
 893                     spans.clone(),
 894                     &format!(
 895                         "features `{}` and `{}` are incompatible, using them at the same time \
 896                         is not allowed",
 897                         f1_name, f2_name
 898                     ),
 899                 )
 900                 .help("remove one of these features")
 901                 .emit();
 902             }
 903         }
 904     }
 905 }