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;
   6 use rustc_feature::{AttributeGate, BuiltinAttribute, BUILTIN_ATTRIBUTE_MAP};
   7 use rustc_feature::{Features, GateIssue};
   8 use rustc_session::parse::{feature_err, feature_err_issue};
   9 use rustc_session::Session;
  10 use rustc_span::source_map::Spanned;
  11 use rustc_span::symbol::sym;
  12 use rustc_span::Span;
  13
  14 use tracing::debug;
  15
  16 macro_rules! gate_feature_fn {
  17     ($visitor: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr, $help: expr) => {{
  18         let (visitor, has_feature, span, name, explain, help) =
  19             (&*$visitor, $has_feature, $span, $name, $explain, $help);
  20         let has_feature: bool = has_feature(visitor.features);
  21         debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
  22         if !has_feature && !span.allows_unstable($name) {
  23             feature_err_issue(&visitor.sess.parse_sess, name, span, GateIssue::Language, explain)
  24                 .help(help)
  25                 .emit();
  26         }
  27     }};
  28     ($visitor: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr) => {{
  29         let (visitor, has_feature, span, name, explain) =
  30             (&*$visitor, $has_feature, $span, $name, $explain);
  31         let has_feature: bool = has_feature(visitor.features);
  32         debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
  33         if !has_feature && !span.allows_unstable($name) {
  34             feature_err_issue(&visitor.sess.parse_sess, name, span, GateIssue::Language, explain)
  35                 .emit();
  36         }
  37     }};
  38 }
  39
  40 macro_rules! gate_feature_post {
  41     ($visitor: expr, $feature: ident, $span: expr, $explain: expr, $help: expr) => {
  42         gate_feature_fn!($visitor, |x: &Features| x.$feature, $span, sym::$feature, $explain, $help)
  43     };
  44     ($visitor: expr, $feature: ident, $span: expr, $explain: expr) => {
  45         gate_feature_fn!($visitor, |x: &Features| x.$feature, $span, sym::$feature, $explain)
  46     };
  47 }
  48
  49 pub fn check_attribute(attr: &ast::Attribute, sess: &Session, features: &Features) {
  50     PostExpansionVisitor { sess, features }.visit_attribute(attr)
  51 }
  52
  53 struct PostExpansionVisitor<'a> {
  54     sess: &'a Session,
  55
  56     // `sess` contains a `Features`, but this might not be that one.
  57     features: &'a Features,
  58 }
  59
  60 impl<'a> PostExpansionVisitor<'a> {
  61     fn check_abi(&self, abi: ast::StrLit, constness: ast::Const) {
  62         let ast::StrLit { symbol_unescaped, span, .. } = abi;
  63
  64         if let ast::Const::Yes(_) = constness {
  65             match symbol_unescaped.as_str() {
  66                 // Stable
  67                 "Rust" | "C" => {}
  68                 abi => gate_feature_post!(
  69                     &self,
  70                     const_extern_fn,
  71                     span,
  72                     &format!("`{}` as a `const fn` ABI is unstable", abi)
  73                 ),
  74             }
  75         }
  76
  77         match symbol_unescaped.as_str() {
  78             // Stable
  79             "Rust" | "C" | "cdecl" | "stdcall" | "fastcall" | "aapcs" | "win64" | "sysv64"
  80             | "system" => {}
  81             "rust-intrinsic" => {
  82                 gate_feature_post!(&self, intrinsics, span, "intrinsics are subject to change");
  83             }
  84             "platform-intrinsic" => {
  85                 gate_feature_post!(
  86                     &self,
  87                     platform_intrinsics,
  88                     span,
  89                     "platform intrinsics are experimental and possibly buggy"
  90                 );
  91             }
  92             "vectorcall" => {
  93                 gate_feature_post!(
  94                     &self,
  95                     abi_vectorcall,
  96                     span,
  97                     "vectorcall is experimental and subject to change"
  98                 );
  99             }
 100             "thiscall" => {
 101                 gate_feature_post!(
 102                     &self,
 103                     abi_thiscall,
 104                     span,
 105                     "thiscall is experimental and subject to change"
 106                 );
 107             }
 108             "rust-call" => {
 109                 gate_feature_post!(
 110                     &self,
 111                     unboxed_closures,
 112                     span,
 113                     "rust-call ABI is subject to change"
 114                 );
 115             }
 116             "ptx-kernel" => {
 117                 gate_feature_post!(
 118                     &self,
 119                     abi_ptx,
 120                     span,
 121                     "PTX ABIs are experimental and subject to change"
 122                 );
 123             }
 124             "unadjusted" => {
 125                 gate_feature_post!(
 126                     &self,
 127                     abi_unadjusted,
 128                     span,
 129                     "unadjusted ABI is an implementation detail and perma-unstable"
 130                 );
 131             }
 132             "msp430-interrupt" => {
 133                 gate_feature_post!(
 134                     &self,
 135                     abi_msp430_interrupt,
 136                     span,
 137                     "msp430-interrupt ABI is experimental and subject to change"
 138                 );
 139             }
 140             "x86-interrupt" => {
 141                 gate_feature_post!(
 142                     &self,
 143                     abi_x86_interrupt,
 144                     span,
 145                     "x86-interrupt ABI is experimental and subject to change"
 146                 );
 147             }
 148             "amdgpu-kernel" => {
 149                 gate_feature_post!(
 150                     &self,
 151                     abi_amdgpu_kernel,
 152                     span,
 153                     "amdgpu-kernel ABI is experimental and subject to change"
 154                 );
 155             }
 156             "avr-interrupt" | "avr-non-blocking-interrupt" => {
 157                 gate_feature_post!(
 158                     &self,
 159                     abi_avr_interrupt,
 160                     span,
 161                     "avr-interrupt and avr-non-blocking-interrupt ABIs are experimental and subject to change"
 162                 );
 163             }
 164             "efiapi" => {
 165                 gate_feature_post!(
 166                     &self,
 167                     abi_efiapi,
 168                     span,
 169                     "efiapi ABI is experimental and subject to change"
 170                 );
 171             }
 172             "C-cmse-nonsecure-call" => {
 173                 gate_feature_post!(
 174                     &self,
 175                     abi_c_cmse_nonsecure_call,
 176                     span,
 177                     "C-cmse-nonsecure-call ABI is experimental and subject to change"
 178                 );
 179             }
 180             "C-unwind" => {
 181                 gate_feature_post!(
 182                     &self,
 183                     c_unwind,
 184                     span,
 185                     "C-unwind ABI is experimental and subject to change"
 186                 );
 187             }
 188             "stdcall-unwind" => {
 189                 gate_feature_post!(
 190                     &self,
 191                     c_unwind,
 192                     span,
 193                     "stdcall-unwind ABI is experimental and subject to change"
 194                 );
 195             }
 196             "system-unwind" => {
 197                 gate_feature_post!(
 198                     &self,
 199                     c_unwind,
 200                     span,
 201                     "system-unwind ABI is experimental and subject to change"
 202                 );
 203             }
 204             "thiscall-unwind" => {
 205                 gate_feature_post!(
 206                     &self,
 207                     c_unwind,
 208                     span,
 209                     "thiscall-unwind ABI is experimental and subject to change"
 210                 );
 211             }
 212             "cdecl-unwind" => {
 213                 gate_feature_post!(
 214                     &self,
 215                     c_unwind,
 216                     span,
 217                     "cdecl-unwind ABI is experimental and subject to change"
 218                 );
 219             }
 220             "fastcall-unwind" => {
 221                 gate_feature_post!(
 222                     &self,
 223                     c_unwind,
 224                     span,
 225                     "fastcall-unwind ABI is experimental and subject to change"
 226                 );
 227             }
 228             "vectorcall-unwind" => {
 229                 gate_feature_post!(
 230                     &self,
 231                     c_unwind,
 232                     span,
 233                     "vectorcall-unwind ABI is experimental and subject to change"
 234                 );
 235             }
 236             "aapcs-unwind" => {
 237                 gate_feature_post!(
 238                     &self,
 239                     c_unwind,
 240                     span,
 241                     "aapcs-unwind ABI is experimental and subject to change"
 242                 );
 243             }
 244             "win64-unwind" => {
 245                 gate_feature_post!(
 246                     &self,
 247                     c_unwind,
 248                     span,
 249                     "win64-unwind ABI is experimental and subject to change"
 250                 );
 251             }
 252             "sysv64-unwind" => {
 253                 gate_feature_post!(
 254                     &self,
 255                     c_unwind,
 256                     span,
 257                     "sysv64-unwind ABI is experimental and subject to change"
 258                 );
 259             }
 260             "wasm" => {
 261                 gate_feature_post!(
 262                     &self,
 263                     wasm_abi,
 264                     span,
 265                     "wasm ABI is experimental and subject to change"
 266                 );
 267             }
 268             abi => {
 269                 self.sess.parse_sess.span_diagnostic.delay_span_bug(
 270                     span,
 271                     &format!("unrecognized ABI not caught in lowering: {}", abi),
 272                 );
 273             }
 274         }
 275     }
 276
 277     fn check_extern(&self, ext: ast::Extern, constness: ast::Const) {
 278         if let ast::Extern::Explicit(abi) = ext {
 279             self.check_abi(abi, constness);
 280         }
 281     }
 282
 283     fn maybe_report_invalid_custom_discriminants(&self, variants: &[ast::Variant]) {
 284         let has_fields = variants.iter().any(|variant| match variant.data {
 285             VariantData::Tuple(..) | VariantData::Struct(..) => true,
 286             VariantData::Unit(..) => false,
 287         });
 288
 289         let discriminant_spans = variants
 290             .iter()
 291             .filter(|variant| match variant.data {
 292                 VariantData::Tuple(..) | VariantData::Struct(..) => false,
 293                 VariantData::Unit(..) => true,
 294             })
 295             .filter_map(|variant| variant.disr_expr.as_ref().map(|c| c.value.span))
 296             .collect::<Vec<_>>();
 297
 298         if !discriminant_spans.is_empty() && has_fields {
 299             let mut err = feature_err(
 300                 &self.sess.parse_sess,
 301                 sym::arbitrary_enum_discriminant,
 302                 discriminant_spans.clone(),
 303                 "custom discriminant values are not allowed in enums with tuple or struct variants",
 304             );
 305             for sp in discriminant_spans {
 306                 err.span_label(sp, "disallowed custom discriminant");
 307             }
 308             for variant in variants.iter() {
 309                 match &variant.data {
 310                     VariantData::Struct(..) => {
 311                         err.span_label(variant.span, "struct variant defined here");
 312                     }
 313                     VariantData::Tuple(..) => {
 314                         err.span_label(variant.span, "tuple variant defined here");
 315                     }
 316                     VariantData::Unit(..) => {}
 317                 }
 318             }
 319             err.emit();
 320         }
 321     }
 322
 323     fn check_gat(&self, generics: &ast::Generics, span: Span) {
 324         if !generics.params.is_empty() {
 325             gate_feature_post!(
 326                 &self,
 327                 generic_associated_types,
 328                 span,
 329                 "generic associated types are unstable"
 330             );
 331         }
 332         if !generics.where_clause.predicates.is_empty() {
 333             gate_feature_post!(
 334                 &self,
 335                 generic_associated_types,
 336                 span,
 337                 "where clauses on associated types are unstable"
 338             );
 339         }
 340     }
 341
 342     /// Feature gate `impl Trait` inside `type Alias = $type_expr;`.
 343     fn check_impl_trait(&self, ty: &ast::Ty) {
 344         struct ImplTraitVisitor<'a> {
 345             vis: &'a PostExpansionVisitor<'a>,
 346         }
 347         impl Visitor<'_> for ImplTraitVisitor<'_> {
 348             fn visit_ty(&mut self, ty: &ast::Ty) {
 349                 if let ast::TyKind::ImplTrait(..) = ty.kind {
 350                     gate_feature_post!(
 351                         &self.vis,
 352                         type_alias_impl_trait,
 353                         ty.span,
 354                         "`impl Trait` in type aliases is unstable"
 355                     );
 356                 }
 357                 visit::walk_ty(self, ty);
 358             }
 359         }
 360         ImplTraitVisitor { vis: self }.visit_ty(ty);
 361     }
 362 }
 363
 364 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 365     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 366         let attr_info = attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name));
 367         // Check feature gates for built-in attributes.
 368         if let Some(BuiltinAttribute {
 369             gate: AttributeGate::Gated(_, name, descr, has_feature),
 370             ..
 371         }) = attr_info
 372         {
 373             gate_feature_fn!(self, has_feature, attr.span, *name, descr);
 374         }
 375         // Check unstable flavors of the `#[doc]` attribute.
 376         if attr.has_name(sym::doc) {
 377             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 378                 macro_rules! gate_doc { ($($name:ident => $feature:ident)*) => {
 379                     $(if nested_meta.has_name(sym::$name) {
 380                         let msg = concat!("`#[doc(", stringify!($name), ")]` is experimental");
 381                         gate_feature_post!(self, $feature, attr.span, msg);
 382                     })*
 383                 }}
 384
 385                 gate_doc!(
 386                     cfg => doc_cfg
 387                     cfg_hide => doc_cfg_hide
 388                     masked => doc_masked
 389                     notable_trait => doc_notable_trait
 390                 );
 391
 392                 if nested_meta.has_name(sym::keyword) {
 393                     let msg = "`#[doc(keyword)]` is meant for internal use only";
 394                     gate_feature_post!(self, rustdoc_internals, attr.span, msg);
 395                 }
 396             }
 397         }
 398
 399         // Check for unstable modifiers on `#[link(..)]` attribute
 400         if attr.has_name(sym::link) {
 401             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 402                 if nested_meta.has_name(sym::modifiers) {
 403                     if let Some(modifiers) = nested_meta.value_str() {
 404                         for modifier in modifiers.as_str().split(',') {
 405                             if let Some(modifier) = modifier.strip_prefix(&['+', '-']) {
 406                                 macro_rules! gate_modifier { ($($name:literal => $feature:ident)*) => {
 407                                     $(if modifier == $name {
 408                                         let msg = concat!("`#[link(modifiers=\"", $name, "\")]` is unstable");
 409                                         gate_feature_post!(
 410                                             self,
 411                                             $feature,
 412                                             nested_meta.name_value_literal_span().unwrap(),
 413                                             msg
 414                                         );
 415                                     })*
 416                                 }}
 417
 418                                 gate_modifier!(
 419                                     "bundle" => native_link_modifiers_bundle
 420                                     "verbatim" => native_link_modifiers_verbatim
 421                                     "as-needed" => native_link_modifiers_as_needed
 422                                 );
 423                             }
 424                         }
 425                     }
 426                 }
 427             }
 428         }
 429
 430         // Emit errors for non-staged-api crates.
 431         if !self.features.staged_api {
 432             if attr.has_name(sym::rustc_deprecated)
 433                 || attr.has_name(sym::unstable)
 434                 || attr.has_name(sym::stable)
 435                 || attr.has_name(sym::rustc_const_unstable)
 436                 || attr.has_name(sym::rustc_const_stable)
 437             {
 438                 struct_span_err!(
 439                     self.sess,
 440                     attr.span,
 441                     E0734,
 442                     "stability attributes may not be used outside of the standard library",
 443                 )
 444                 .emit();
 445             }
 446         }
 447     }
 448
 449     fn visit_item(&mut self, i: &'a ast::Item) {
 450         match i.kind {
 451             ast::ItemKind::ForeignMod(ref foreign_module) => {
 452                 if let Some(abi) = foreign_module.abi {
 453                     self.check_abi(abi, ast::Const::No);
 454                 }
 455             }
 456
 457             ast::ItemKind::Fn(..) => {
 458                 if self.sess.contains_name(&i.attrs, sym::start) {
 459                     gate_feature_post!(
 460                         &self,
 461                         start,
 462                         i.span,
 463                         "`#[start]` functions are experimental \
 464                          and their signature may change \
 465                          over time"
 466                     );
 467                 }
 468             }
 469
 470             ast::ItemKind::Struct(..) => {
 471                 for attr in self.sess.filter_by_name(&i.attrs, sym::repr) {
 472                     for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
 473                         if item.has_name(sym::simd) {
 474                             gate_feature_post!(
 475                                 &self,
 476                                 repr_simd,
 477                                 attr.span,
 478                                 "SIMD types are experimental and possibly buggy"
 479                             );
 480                         }
 481                     }
 482                 }
 483             }
 484
 485             ast::ItemKind::Enum(ast::EnumDef { ref variants, .. }, ..) => {
 486                 for variant in variants {
 487                     match (&variant.data, &variant.disr_expr) {
 488                         (ast::VariantData::Unit(..), _) => {}
 489                         (_, Some(disr_expr)) => gate_feature_post!(
 490                             &self,
 491                             arbitrary_enum_discriminant,
 492                             disr_expr.value.span,
 493                             "discriminants on non-unit variants are experimental"
 494                         ),
 495                         _ => {}
 496                     }
 497                 }
 498
 499                 let has_feature = self.features.arbitrary_enum_discriminant;
 500                 if !has_feature && !i.span.allows_unstable(sym::arbitrary_enum_discriminant) {
 501                     self.maybe_report_invalid_custom_discriminants(&variants);
 502                 }
 503             }
 504
 505             ast::ItemKind::Impl(box ast::Impl { polarity, defaultness, ref of_trait, .. }) => {
 506                 if let ast::ImplPolarity::Negative(span) = polarity {
 507                     gate_feature_post!(
 508                         &self,
 509                         negative_impls,
 510                         span.to(of_trait.as_ref().map_or(span, |t| t.path.span)),
 511                         "negative trait bounds are not yet fully implemented; \
 512                          use marker types for now"
 513                     );
 514                 }
 515
 516                 if let ast::Defaultness::Default(_) = defaultness {
 517                     gate_feature_post!(&self, specialization, i.span, "specialization is unstable");
 518                 }
 519             }
 520
 521             ast::ItemKind::Trait(box ast::Trait { is_auto: ast::IsAuto::Yes, .. }) => {
 522                 gate_feature_post!(
 523                     &self,
 524                     auto_traits,
 525                     i.span,
 526                     "auto traits are experimental and possibly buggy"
 527                 );
 528             }
 529
 530             ast::ItemKind::TraitAlias(..) => {
 531                 gate_feature_post!(&self, trait_alias, i.span, "trait aliases are experimental");
 532             }
 533
 534             ast::ItemKind::MacroDef(ast::MacroDef { macro_rules: false, .. }) => {
 535                 let msg = "`macro` is experimental";
 536                 gate_feature_post!(&self, decl_macro, i.span, msg);
 537             }
 538
 539             ast::ItemKind::TyAlias(box ast::TyAlias { ty: Some(ref ty), .. }) => {
 540                 self.check_impl_trait(&ty)
 541             }
 542
 543             _ => {}
 544         }
 545
 546         visit::walk_item(self, i);
 547     }
 548
 549     fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
 550         match i.kind {
 551             ast::ForeignItemKind::Fn(..) | ast::ForeignItemKind::Static(..) => {
 552                 let link_name = self.sess.first_attr_value_str_by_name(&i.attrs, sym::link_name);
 553                 let links_to_llvm =
 554                     link_name.map_or(false, |val| val.as_str().starts_with("llvm."));
 555                 if links_to_llvm {
 556                     gate_feature_post!(
 557                         &self,
 558                         link_llvm_intrinsics,
 559                         i.span,
 560                         "linking to LLVM intrinsics is experimental"
 561                     );
 562                 }
 563             }
 564             ast::ForeignItemKind::TyAlias(..) => {
 565                 gate_feature_post!(&self, extern_types, i.span, "extern types are experimental");
 566             }
 567             ast::ForeignItemKind::MacCall(..) => {}
 568         }
 569
 570         visit::walk_foreign_item(self, i)
 571     }
 572
 573     fn visit_ty(&mut self, ty: &'a ast::Ty) {
 574         match ty.kind {
 575             ast::TyKind::BareFn(ref bare_fn_ty) => {
 576                 // Function pointers cannot be `const`
 577                 self.check_extern(bare_fn_ty.ext, ast::Const::No);
 578             }
 579             ast::TyKind::Never => {
 580                 gate_feature_post!(&self, never_type, ty.span, "the `!` type is experimental");
 581             }
 582             _ => {}
 583         }
 584         visit::walk_ty(self, ty)
 585     }
 586
 587     fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FnRetTy) {
 588         if let ast::FnRetTy::Ty(ref output_ty) = *ret_ty {
 589             if let ast::TyKind::Never = output_ty.kind {
 590                 // Do nothing.
 591             } else {
 592                 self.visit_ty(output_ty)
 593             }
 594         }
 595     }
 596
 597     fn visit_expr(&mut self, e: &'a ast::Expr) {
 598         match e.kind {
 599             ast::ExprKind::Box(_) => {
 600                 gate_feature_post!(
 601                     &self,
 602                     box_syntax,
 603                     e.span,
 604                     "box expression syntax is experimental; you can call `Box::new` instead"
 605                 );
 606             }
 607             ast::ExprKind::Type(..) => {
 608                 // To avoid noise about type ascription in common syntax errors, only emit if it
 609                 // is the *only* error.
 610                 if self.sess.parse_sess.span_diagnostic.err_count() == 0 {
 611                     gate_feature_post!(
 612                         &self,
 613                         type_ascription,
 614                         e.span,
 615                         "type ascription is experimental"
 616                     );
 617                 }
 618             }
 619             ast::ExprKind::TryBlock(_) => {
 620                 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
 621             }
 622             ast::ExprKind::Block(_, Some(label)) => {
 623                 gate_feature_post!(
 624                     &self,
 625                     label_break_value,
 626                     label.ident.span,
 627                     "labels on blocks are unstable"
 628                 );
 629             }
 630             _ => {}
 631         }
 632         visit::walk_expr(self, e)
 633     }
 634
 635     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
 636         match &pattern.kind {
 637             PatKind::Slice(pats) => {
 638                 for pat in pats {
 639                     let inner_pat = match &pat.kind {
 640                         PatKind::Ident(.., Some(pat)) => pat,
 641                         _ => pat,
 642                     };
 643                     if let PatKind::Range(Some(_), None, Spanned { .. }) = inner_pat.kind {
 644                         gate_feature_post!(
 645                             &self,
 646                             half_open_range_patterns,
 647                             pat.span,
 648                             "`X..` patterns in slices are experimental"
 649                         );
 650                     }
 651                 }
 652             }
 653             PatKind::Box(..) => {
 654                 gate_feature_post!(
 655                     &self,
 656                     box_patterns,
 657                     pattern.span,
 658                     "box pattern syntax is experimental"
 659                 );
 660             }
 661             PatKind::Range(_, Some(_), Spanned { node: RangeEnd::Excluded, .. }) => {
 662                 gate_feature_post!(
 663                     &self,
 664                     exclusive_range_pattern,
 665                     pattern.span,
 666                     "exclusive range pattern syntax is experimental"
 667                 );
 668             }
 669             _ => {}
 670         }
 671         visit::walk_pat(self, pattern)
 672     }
 673
 674     fn visit_fn(&mut self, fn_kind: FnKind<'a>, span: Span, _: NodeId) {
 675         if let Some(header) = fn_kind.header() {
 676             // Stability of const fn methods are covered in `visit_assoc_item` below.
 677             self.check_extern(header.ext, header.constness);
 678         }
 679
 680         if fn_kind.ctxt() != Some(FnCtxt::Foreign) && fn_kind.decl().c_variadic() {
 681             gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
 682         }
 683
 684         visit::walk_fn(self, fn_kind, span)
 685     }
 686
 687     fn visit_assoc_constraint(&mut self, constraint: &'a AssocConstraint) {
 688         if let AssocConstraintKind::Bound { .. } = constraint.kind {
 689             gate_feature_post!(
 690                 &self,
 691                 associated_type_bounds,
 692                 constraint.span,
 693                 "associated type bounds are unstable"
 694             )
 695         }
 696         visit::walk_assoc_constraint(self, constraint)
 697     }
 698
 699     fn visit_assoc_item(&mut self, i: &'a ast::AssocItem, ctxt: AssocCtxt) {
 700         let is_fn = match i.kind {
 701             ast::AssocItemKind::Fn(_) => true,
 702             ast::AssocItemKind::TyAlias(box ast::TyAlias { ref generics, ref ty, .. }) => {
 703                 if let (Some(_), AssocCtxt::Trait) = (ty, ctxt) {
 704                     gate_feature_post!(
 705                         &self,
 706                         associated_type_defaults,
 707                         i.span,
 708                         "associated type defaults are unstable"
 709                     );
 710                 }
 711                 if let Some(ty) = ty {
 712                     self.check_impl_trait(ty);
 713                 }
 714                 self.check_gat(generics, i.span);
 715                 false
 716             }
 717             _ => false,
 718         };
 719         if let ast::Defaultness::Default(_) = i.kind.defaultness() {
 720             // Limit `min_specialization` to only specializing functions.
 721             gate_feature_fn!(
 722                 &self,
 723                 |x: &Features| x.specialization || (is_fn && x.min_specialization),
 724                 i.span,
 725                 sym::specialization,
 726                 "specialization is unstable"
 727             );
 728         }
 729         visit::walk_assoc_item(self, i, ctxt)
 730     }
 731
 732     fn visit_vis(&mut self, vis: &'a ast::Visibility) {
 733         if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.kind {
 734             gate_feature_post!(
 735                 &self,
 736                 crate_visibility_modifier,
 737                 vis.span,
 738                 "`crate` visibility modifier is experimental"
 739             );
 740         }
 741         visit::walk_vis(self, vis)
 742     }
 743 }
 744
 745 pub fn check_crate(krate: &ast::Crate, sess: &Session) {
 746     maybe_stage_features(sess, krate);
 747     check_incompatible_features(sess);
 748     let mut visitor = PostExpansionVisitor { sess, features: &sess.features_untracked() };
 749
 750     let spans = sess.parse_sess.gated_spans.spans.borrow();
 751     macro_rules! gate_all {
 752         ($gate:ident, $msg:literal, $help:literal) => {
 753             if let Some(spans) = spans.get(&sym::$gate) {
 754                 for span in spans {
 755                     gate_feature_post!(&visitor, $gate, *span, $msg, $help);
 756                 }
 757             }
 758         };
 759         ($gate:ident, $msg:literal) => {
 760             if let Some(spans) = spans.get(&sym::$gate) {
 761                 for span in spans {
 762                     gate_feature_post!(&visitor, $gate, *span, $msg);
 763                 }
 764             }
 765         };
 766     }
 767     gate_all!(
 768         if_let_guard,
 769         "`if let` guards are experimental",
 770         "you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`"
 771     );
 772     gate_all!(let_chains, "`let` expressions in this position are unstable");
 773     gate_all!(
 774         async_closure,
 775         "async closures are unstable",
 776         "to use an async block, remove the `||`: `async {`"
 777     );
 778     gate_all!(more_qualified_paths, "usage of qualified paths in this context is experimental");
 779     gate_all!(generators, "yield syntax is experimental");
 780     gate_all!(raw_ref_op, "raw address of syntax is experimental");
 781     gate_all!(const_trait_impl, "const trait impls are experimental");
 782     gate_all!(half_open_range_patterns, "half-open range patterns are unstable");
 783     gate_all!(inline_const, "inline-const is experimental");
 784     gate_all!(inline_const_pat, "inline-const in pattern position is experimental");
 785     gate_all!(associated_const_equality, "associated const equality is incomplete");
 786     gate_all!(yeet_expr, "`do yeet` expression is experimental");
 787
 788     // All uses of `gate_all!` below this point were added in #65742,
 789     // and subsequently disabled (with the non-early gating readded).
 790     macro_rules! gate_all {
 791         ($gate:ident, $msg:literal) => {
 792             // FIXME(eddyb) do something more useful than always
 793             // disabling these uses of early feature-gatings.
 794             if false {
 795                 for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 796                     gate_feature_post!(&visitor, $gate, *span, $msg);
 797                 }
 798             }
 799         };
 800     }
 801
 802     gate_all!(trait_alias, "trait aliases are experimental");
 803     gate_all!(associated_type_bounds, "associated type bounds are unstable");
 804     gate_all!(crate_visibility_modifier, "`crate` visibility modifier is experimental");
 805     gate_all!(decl_macro, "`macro` is experimental");
 806     gate_all!(box_patterns, "box pattern syntax is experimental");
 807     gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
 808     gate_all!(try_blocks, "`try` blocks are unstable");
 809     gate_all!(label_break_value, "labels on blocks are unstable");
 810     gate_all!(box_syntax, "box expression syntax is experimental; you can call `Box::new` instead");
 811     // To avoid noise about type ascription in common syntax errors,
 812     // only emit if it is the *only* error. (Also check it last.)
 813     if sess.parse_sess.span_diagnostic.err_count() == 0 {
 814         gate_all!(type_ascription, "type ascription is experimental");
 815     }
 816
 817     visit::walk_crate(&mut visitor, krate);
 818 }
 819
 820 fn maybe_stage_features(sess: &Session, krate: &ast::Crate) {
 821     // checks if `#![feature]` has been used to enable any lang feature
 822     // does not check the same for lib features unless there's at least one
 823     // declared lang feature
 824     use rustc_errors::Applicability;
 825
 826     if !sess.opts.unstable_features.is_nightly_build() {
 827         let lang_features = &sess.features_untracked().declared_lang_features;
 828         if lang_features.len() == 0 {
 829             return;
 830         }
 831         for attr in krate.attrs.iter().filter(|attr| attr.has_name(sym::feature)) {
 832             let mut err = struct_span_err!(
 833                 sess.parse_sess.span_diagnostic,
 834                 attr.span,
 835                 E0554,
 836                 "`#![feature]` may not be used on the {} release channel",
 837                 option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)")
 838             );
 839             let mut all_stable = true;
 840             for ident in
 841                 attr.meta_item_list().into_iter().flatten().flat_map(|nested| nested.ident())
 842             {
 843                 let name = ident.name;
 844                 let stable_since = lang_features
 845                     .iter()
 846                     .flat_map(|&(feature, _, since)| if feature == name { since } else { None })
 847                     .next();
 848                 if let Some(since) = stable_since {
 849                     err.help(&format!(
 850                         "the feature `{}` has been stable since {} and no longer requires \
 851                                   an attribute to enable",
 852                         name, since
 853                     ));
 854                 } else {
 855                     all_stable = false;
 856                 }
 857             }
 858             if all_stable {
 859                 err.span_suggestion(
 860                     attr.span,
 861                     "remove the attribute",
 862                     String::new(),
 863                     Applicability::MachineApplicable,
 864                 );
 865             }
 866             err.emit();
 867         }
 868     }
 869 }
 870
 871 fn check_incompatible_features(sess: &Session) {
 872     let features = sess.features_untracked();
 873
 874     let declared_features = features
 875         .declared_lang_features
 876         .iter()
 877         .copied()
 878         .map(|(name, span, _)| (name, span))
 879         .chain(features.declared_lib_features.iter().copied());
 880
 881     for (f1, f2) in rustc_feature::INCOMPATIBLE_FEATURES
 882         .iter()
 883         .filter(|&&(f1, f2)| features.enabled(f1) && features.enabled(f2))
 884     {
 885         if let Some((f1_name, f1_span)) = declared_features.clone().find(|(name, _)| name == f1) {
 886             if let Some((f2_name, f2_span)) = declared_features.clone().find(|(name, _)| name == f2)
 887             {
 888                 let spans = vec![f1_span, f2_span];
 889                 sess.struct_span_err(
 890                     spans.clone(),
 891                     &format!(
 892                         "features `{}` and `{}` are incompatible, using them at the same time \
 893                         is not allowed",
 894                         f1_name, f2_name
 895                     ),
 896                 )
 897                 .help("remove one of these features")
 898                 .emit();
 899             }
 900         }
 901     }
 902 }