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) {
  62         let ast::StrLit { symbol_unescaped, span, .. } = abi;
  63
  64         match symbol_unescaped.as_str() {
  65             // Stable
  66             "Rust" | "C" | "cdecl" | "stdcall" | "fastcall" | "aapcs" | "win64" | "sysv64"
  67             | "system" => {}
  68             "rust-intrinsic" => {
  69                 gate_feature_post!(&self, intrinsics, span, "intrinsics are subject to change");
  70             }
  71             "platform-intrinsic" => {
  72                 gate_feature_post!(
  73                     &self,
  74                     platform_intrinsics,
  75                     span,
  76                     "platform intrinsics are experimental and possibly buggy"
  77                 );
  78             }
  79             "vectorcall" => {
  80                 gate_feature_post!(
  81                     &self,
  82                     abi_vectorcall,
  83                     span,
  84                     "vectorcall is experimental and subject to change"
  85                 );
  86             }
  87             "thiscall" => {
  88                 gate_feature_post!(
  89                     &self,
  90                     abi_thiscall,
  91                     span,
  92                     "thiscall is experimental and subject to change"
  93                 );
  94             }
  95             "rust-call" => {
  96                 gate_feature_post!(
  97                     &self,
  98                     unboxed_closures,
  99                     span,
 100                     "rust-call ABI is subject to change"
 101                 );
 102             }
 103             "ptx-kernel" => {
 104                 gate_feature_post!(
 105                     &self,
 106                     abi_ptx,
 107                     span,
 108                     "PTX ABIs are experimental and subject to change"
 109                 );
 110             }
 111             "unadjusted" => {
 112                 gate_feature_post!(
 113                     &self,
 114                     abi_unadjusted,
 115                     span,
 116                     "unadjusted ABI is an implementation detail and perma-unstable"
 117                 );
 118             }
 119             "msp430-interrupt" => {
 120                 gate_feature_post!(
 121                     &self,
 122                     abi_msp430_interrupt,
 123                     span,
 124                     "msp430-interrupt ABI is experimental and subject to change"
 125                 );
 126             }
 127             "x86-interrupt" => {
 128                 gate_feature_post!(
 129                     &self,
 130                     abi_x86_interrupt,
 131                     span,
 132                     "x86-interrupt ABI is experimental and subject to change"
 133                 );
 134             }
 135             "amdgpu-kernel" => {
 136                 gate_feature_post!(
 137                     &self,
 138                     abi_amdgpu_kernel,
 139                     span,
 140                     "amdgpu-kernel ABI is experimental and subject to change"
 141                 );
 142             }
 143             "avr-interrupt" | "avr-non-blocking-interrupt" => {
 144                 gate_feature_post!(
 145                     &self,
 146                     abi_avr_interrupt,
 147                     span,
 148                     "avr-interrupt and avr-non-blocking-interrupt ABIs are experimental and subject to change"
 149                 );
 150             }
 151             "efiapi" => {
 152                 gate_feature_post!(
 153                     &self,
 154                     abi_efiapi,
 155                     span,
 156                     "efiapi ABI is experimental and subject to change"
 157                 );
 158             }
 159             "C-cmse-nonsecure-call" => {
 160                 gate_feature_post!(
 161                     &self,
 162                     abi_c_cmse_nonsecure_call,
 163                     span,
 164                     "C-cmse-nonsecure-call ABI is experimental and subject to change"
 165                 );
 166             }
 167             "C-unwind" => {
 168                 gate_feature_post!(
 169                     &self,
 170                     c_unwind,
 171                     span,
 172                     "C-unwind ABI is experimental and subject to change"
 173                 );
 174             }
 175             "stdcall-unwind" => {
 176                 gate_feature_post!(
 177                     &self,
 178                     c_unwind,
 179                     span,
 180                     "stdcall-unwind ABI is experimental and subject to change"
 181                 );
 182             }
 183             "system-unwind" => {
 184                 gate_feature_post!(
 185                     &self,
 186                     c_unwind,
 187                     span,
 188                     "system-unwind ABI is experimental and subject to change"
 189                 );
 190             }
 191             "thiscall-unwind" => {
 192                 gate_feature_post!(
 193                     &self,
 194                     c_unwind,
 195                     span,
 196                     "thiscall-unwind ABI is experimental and subject to change"
 197                 );
 198             }
 199             "cdecl-unwind" => {
 200                 gate_feature_post!(
 201                     &self,
 202                     c_unwind,
 203                     span,
 204                     "cdecl-unwind ABI is experimental and subject to change"
 205                 );
 206             }
 207             "fastcall-unwind" => {
 208                 gate_feature_post!(
 209                     &self,
 210                     c_unwind,
 211                     span,
 212                     "fastcall-unwind ABI is experimental and subject to change"
 213                 );
 214             }
 215             "vectorcall-unwind" => {
 216                 gate_feature_post!(
 217                     &self,
 218                     c_unwind,
 219                     span,
 220                     "vectorcall-unwind ABI is experimental and subject to change"
 221                 );
 222             }
 223             "aapcs-unwind" => {
 224                 gate_feature_post!(
 225                     &self,
 226                     c_unwind,
 227                     span,
 228                     "aapcs-unwind ABI is experimental and subject to change"
 229                 );
 230             }
 231             "win64-unwind" => {
 232                 gate_feature_post!(
 233                     &self,
 234                     c_unwind,
 235                     span,
 236                     "win64-unwind ABI is experimental and subject to change"
 237                 );
 238             }
 239             "sysv64-unwind" => {
 240                 gate_feature_post!(
 241                     &self,
 242                     c_unwind,
 243                     span,
 244                     "sysv64-unwind ABI is experimental and subject to change"
 245                 );
 246             }
 247             "wasm" => {
 248                 gate_feature_post!(
 249                     &self,
 250                     wasm_abi,
 251                     span,
 252                     "wasm ABI is experimental and subject to change"
 253                 );
 254             }
 255             abi => {
 256                 self.sess.parse_sess.span_diagnostic.delay_span_bug(
 257                     span,
 258                     &format!("unrecognized ABI not caught in lowering: {}", abi),
 259                 );
 260             }
 261         }
 262     }
 263
 264     fn check_extern(&self, ext: ast::Extern) {
 265         if let ast::Extern::Explicit(abi) = ext {
 266             self.check_abi(abi);
 267         }
 268     }
 269
 270     fn maybe_report_invalid_custom_discriminants(&self, variants: &[ast::Variant]) {
 271         let has_fields = variants.iter().any(|variant| match variant.data {
 272             VariantData::Tuple(..) | VariantData::Struct(..) => true,
 273             VariantData::Unit(..) => false,
 274         });
 275
 276         let discriminant_spans = variants
 277             .iter()
 278             .filter(|variant| match variant.data {
 279                 VariantData::Tuple(..) | VariantData::Struct(..) => false,
 280                 VariantData::Unit(..) => true,
 281             })
 282             .filter_map(|variant| variant.disr_expr.as_ref().map(|c| c.value.span))
 283             .collect::<Vec<_>>();
 284
 285         if !discriminant_spans.is_empty() && has_fields {
 286             let mut err = feature_err(
 287                 &self.sess.parse_sess,
 288                 sym::arbitrary_enum_discriminant,
 289                 discriminant_spans.clone(),
 290                 "custom discriminant values are not allowed in enums with tuple or struct variants",
 291             );
 292             for sp in discriminant_spans {
 293                 err.span_label(sp, "disallowed custom discriminant");
 294             }
 295             for variant in variants.iter() {
 296                 match &variant.data {
 297                     VariantData::Struct(..) => {
 298                         err.span_label(variant.span, "struct variant defined here");
 299                     }
 300                     VariantData::Tuple(..) => {
 301                         err.span_label(variant.span, "tuple variant defined here");
 302                     }
 303                     VariantData::Unit(..) => {}
 304                 }
 305             }
 306             err.emit();
 307         }
 308     }
 309
 310     fn check_gat(&self, generics: &ast::Generics, span: Span) {
 311         if !generics.params.is_empty() {
 312             gate_feature_post!(
 313                 &self,
 314                 generic_associated_types,
 315                 span,
 316                 "generic associated types are unstable"
 317             );
 318         }
 319         if !generics.where_clause.predicates.is_empty() {
 320             gate_feature_post!(
 321                 &self,
 322                 generic_associated_types,
 323                 span,
 324                 "where clauses on associated types are unstable"
 325             );
 326         }
 327     }
 328
 329     /// Feature gate `impl Trait` inside `type Alias = $type_expr;`.
 330     fn check_impl_trait(&self, ty: &ast::Ty) {
 331         struct ImplTraitVisitor<'a> {
 332             vis: &'a PostExpansionVisitor<'a>,
 333         }
 334         impl Visitor<'_> for ImplTraitVisitor<'_> {
 335             fn visit_ty(&mut self, ty: &ast::Ty) {
 336                 if let ast::TyKind::ImplTrait(..) = ty.kind {
 337                     gate_feature_post!(
 338                         &self.vis,
 339                         type_alias_impl_trait,
 340                         ty.span,
 341                         "`impl Trait` in type aliases is unstable"
 342                     );
 343                 }
 344                 visit::walk_ty(self, ty);
 345             }
 346         }
 347         ImplTraitVisitor { vis: self }.visit_ty(ty);
 348     }
 349 }
 350
 351 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 352     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 353         let attr_info = attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name));
 354         // Check feature gates for built-in attributes.
 355         if let Some(BuiltinAttribute {
 356             gate: AttributeGate::Gated(_, name, descr, has_feature),
 357             ..
 358         }) = attr_info
 359         {
 360             gate_feature_fn!(self, has_feature, attr.span, *name, descr);
 361         }
 362         // Check unstable flavors of the `#[doc]` attribute.
 363         if attr.has_name(sym::doc) {
 364             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 365                 macro_rules! gate_doc { ($($name:ident => $feature:ident)*) => {
 366                     $(if nested_meta.has_name(sym::$name) {
 367                         let msg = concat!("`#[doc(", stringify!($name), ")]` is experimental");
 368                         gate_feature_post!(self, $feature, attr.span, msg);
 369                     })*
 370                 }}
 371
 372                 gate_doc!(
 373                     cfg => doc_cfg
 374                     cfg_hide => doc_cfg_hide
 375                     masked => doc_masked
 376                     notable_trait => doc_notable_trait
 377                 );
 378
 379                 if nested_meta.has_name(sym::keyword) {
 380                     let msg = "`#[doc(keyword)]` is meant for internal use only";
 381                     gate_feature_post!(self, rustdoc_internals, attr.span, msg);
 382                 }
 383             }
 384         }
 385
 386         // Check for unstable modifiers on `#[link(..)]` attribute
 387         if attr.has_name(sym::link) {
 388             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 389                 if nested_meta.has_name(sym::modifiers) {
 390                     gate_feature_post!(
 391                         self,
 392                         native_link_modifiers,
 393                         nested_meta.span(),
 394                         "native link modifiers are experimental"
 395                     );
 396
 397                     if let Some(modifiers) = nested_meta.value_str() {
 398                         for modifier in modifiers.as_str().split(',') {
 399                             if let Some(modifier) = modifier.strip_prefix(&['+', '-']) {
 400                                 macro_rules! gate_modifier { ($($name:literal => $feature:ident)*) => {
 401                                     $(if modifier == $name {
 402                                         let msg = concat!("`#[link(modifiers=\"", $name, "\")]` is unstable");
 403                                         gate_feature_post!(
 404                                             self,
 405                                             $feature,
 406                                             nested_meta.name_value_literal_span().unwrap(),
 407                                             msg
 408                                         );
 409                                     })*
 410                                 }}
 411
 412                                 gate_modifier!(
 413                                     "bundle" => native_link_modifiers_bundle
 414                                     "verbatim" => native_link_modifiers_verbatim
 415                                     "whole-archive" => native_link_modifiers_whole_archive
 416                                     "as-needed" => native_link_modifiers_as_needed
 417                                 );
 418                             }
 419                         }
 420                     }
 421                 }
 422             }
 423         }
 424
 425         // Emit errors for non-staged-api crates.
 426         if !self.features.staged_api {
 427             if attr.has_name(sym::rustc_deprecated)
 428                 || 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             {
 433                 struct_span_err!(
 434                     self.sess,
 435                     attr.span,
 436                     E0734,
 437                     "stability attributes may not be used outside of the standard library",
 438                 )
 439                 .emit();
 440             }
 441         }
 442     }
 443
 444     fn visit_item(&mut self, i: &'a ast::Item) {
 445         match i.kind {
 446             ast::ItemKind::ForeignMod(ref foreign_module) => {
 447                 if let Some(abi) = foreign_module.abi {
 448                     self.check_abi(abi);
 449                 }
 450             }
 451
 452             ast::ItemKind::Fn(..) => {
 453                 if self.sess.contains_name(&i.attrs, sym::start) {
 454                     gate_feature_post!(
 455                         &self,
 456                         start,
 457                         i.span,
 458                         "`#[start]` functions are experimental \
 459                          and their signature may change \
 460                          over time"
 461                     );
 462                 }
 463             }
 464
 465             ast::ItemKind::Struct(..) => {
 466                 for attr in self.sess.filter_by_name(&i.attrs, sym::repr) {
 467                     for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
 468                         if item.has_name(sym::simd) {
 469                             gate_feature_post!(
 470                                 &self,
 471                                 repr_simd,
 472                                 attr.span,
 473                                 "SIMD types are experimental and possibly buggy"
 474                             );
 475                         }
 476                     }
 477                 }
 478             }
 479
 480             ast::ItemKind::Enum(ast::EnumDef { ref variants, .. }, ..) => {
 481                 for variant in variants {
 482                     match (&variant.data, &variant.disr_expr) {
 483                         (ast::VariantData::Unit(..), _) => {}
 484                         (_, Some(disr_expr)) => gate_feature_post!(
 485                             &self,
 486                             arbitrary_enum_discriminant,
 487                             disr_expr.value.span,
 488                             "discriminants on non-unit variants are experimental"
 489                         ),
 490                         _ => {}
 491                     }
 492                 }
 493
 494                 let has_feature = self.features.arbitrary_enum_discriminant;
 495                 if !has_feature && !i.span.allows_unstable(sym::arbitrary_enum_discriminant) {
 496                     self.maybe_report_invalid_custom_discriminants(&variants);
 497                 }
 498             }
 499
 500             ast::ItemKind::Impl(box ast::Impl { polarity, defaultness, ref of_trait, .. }) => {
 501                 if let ast::ImplPolarity::Negative(span) = polarity {
 502                     gate_feature_post!(
 503                         &self,
 504                         negative_impls,
 505                         span.to(of_trait.as_ref().map_or(span, |t| t.path.span)),
 506                         "negative trait bounds are not yet fully implemented; \
 507                          use marker types for now"
 508                     );
 509                 }
 510
 511                 if let ast::Defaultness::Default(_) = defaultness {
 512                     gate_feature_post!(&self, specialization, i.span, "specialization is unstable");
 513                 }
 514             }
 515
 516             ast::ItemKind::Trait(box ast::Trait { is_auto: ast::IsAuto::Yes, .. }) => {
 517                 gate_feature_post!(
 518                     &self,
 519                     auto_traits,
 520                     i.span,
 521                     "auto traits are experimental and possibly buggy"
 522                 );
 523             }
 524
 525             ast::ItemKind::TraitAlias(..) => {
 526                 gate_feature_post!(&self, trait_alias, i.span, "trait aliases are experimental");
 527             }
 528
 529             ast::ItemKind::MacroDef(ast::MacroDef { macro_rules: false, .. }) => {
 530                 let msg = "`macro` is experimental";
 531                 gate_feature_post!(&self, decl_macro, i.span, msg);
 532             }
 533
 534             ast::ItemKind::TyAlias(box ast::TyAlias { ty: Some(ref ty), .. }) => {
 535                 self.check_impl_trait(&ty)
 536             }
 537
 538             _ => {}
 539         }
 540
 541         visit::walk_item(self, i);
 542     }
 543
 544     fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
 545         match i.kind {
 546             ast::ForeignItemKind::Fn(..) | ast::ForeignItemKind::Static(..) => {
 547                 let link_name = self.sess.first_attr_value_str_by_name(&i.attrs, sym::link_name);
 548                 let links_to_llvm =
 549                     link_name.map_or(false, |val| val.as_str().starts_with("llvm."));
 550                 if links_to_llvm {
 551                     gate_feature_post!(
 552                         &self,
 553                         link_llvm_intrinsics,
 554                         i.span,
 555                         "linking to LLVM intrinsics is experimental"
 556                     );
 557                 }
 558             }
 559             ast::ForeignItemKind::TyAlias(..) => {
 560                 gate_feature_post!(&self, extern_types, i.span, "extern types are experimental");
 561             }
 562             ast::ForeignItemKind::MacCall(..) => {}
 563         }
 564
 565         visit::walk_foreign_item(self, i)
 566     }
 567
 568     fn visit_ty(&mut self, ty: &'a ast::Ty) {
 569         match ty.kind {
 570             ast::TyKind::BareFn(ref bare_fn_ty) => {
 571                 self.check_extern(bare_fn_ty.ext);
 572             }
 573             ast::TyKind::Never => {
 574                 gate_feature_post!(&self, never_type, ty.span, "the `!` type is experimental");
 575             }
 576             _ => {}
 577         }
 578         visit::walk_ty(self, ty)
 579     }
 580
 581     fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FnRetTy) {
 582         if let ast::FnRetTy::Ty(ref output_ty) = *ret_ty {
 583             if let ast::TyKind::Never = output_ty.kind {
 584                 // Do nothing.
 585             } else {
 586                 self.visit_ty(output_ty)
 587             }
 588         }
 589     }
 590
 591     fn visit_expr(&mut self, e: &'a ast::Expr) {
 592         match e.kind {
 593             ast::ExprKind::Box(_) => {
 594                 gate_feature_post!(
 595                     &self,
 596                     box_syntax,
 597                     e.span,
 598                     "box expression syntax is experimental; you can call `Box::new` instead"
 599                 );
 600             }
 601             ast::ExprKind::Type(..) => {
 602                 // To avoid noise about type ascription in common syntax errors, only emit if it
 603                 // is the *only* error.
 604                 if self.sess.parse_sess.span_diagnostic.err_count() == 0 {
 605                     gate_feature_post!(
 606                         &self,
 607                         type_ascription,
 608                         e.span,
 609                         "type ascription is experimental"
 610                     );
 611                 }
 612             }
 613             ast::ExprKind::TryBlock(_) => {
 614                 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
 615             }
 616             ast::ExprKind::Block(_, Some(label)) => {
 617                 gate_feature_post!(
 618                     &self,
 619                     label_break_value,
 620                     label.ident.span,
 621                     "labels on blocks are unstable"
 622                 );
 623             }
 624             _ => {}
 625         }
 626         visit::walk_expr(self, e)
 627     }
 628
 629     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
 630         match &pattern.kind {
 631             PatKind::Slice(pats) => {
 632                 for pat in pats {
 633                     let inner_pat = match &pat.kind {
 634                         PatKind::Ident(.., Some(pat)) => pat,
 635                         _ => pat,
 636                     };
 637                     if let PatKind::Range(Some(_), None, Spanned { .. }) = inner_pat.kind {
 638                         gate_feature_post!(
 639                             &self,
 640                             half_open_range_patterns,
 641                             pat.span,
 642                             "`X..` patterns in slices are experimental"
 643                         );
 644                     }
 645                 }
 646             }
 647             PatKind::Box(..) => {
 648                 gate_feature_post!(
 649                     &self,
 650                     box_patterns,
 651                     pattern.span,
 652                     "box pattern syntax is experimental"
 653                 );
 654             }
 655             PatKind::Range(_, Some(_), Spanned { node: RangeEnd::Excluded, .. }) => {
 656                 gate_feature_post!(
 657                     &self,
 658                     exclusive_range_pattern,
 659                     pattern.span,
 660                     "exclusive range pattern syntax is experimental"
 661                 );
 662             }
 663             _ => {}
 664         }
 665         visit::walk_pat(self, pattern)
 666     }
 667
 668     fn visit_fn(&mut self, fn_kind: FnKind<'a>, span: Span, _: NodeId) {
 669         if let Some(header) = fn_kind.header() {
 670             // Stability of const fn methods are covered in `visit_assoc_item` below.
 671             self.check_extern(header.ext);
 672
 673             if let (ast::Const::Yes(_), ast::Extern::Implicit)
 674             | (ast::Const::Yes(_), ast::Extern::Explicit(_)) = (header.constness, header.ext)
 675             {
 676                 gate_feature_post!(
 677                     &self,
 678                     const_extern_fn,
 679                     span,
 680                     "`const extern fn` definitions are unstable"
 681                 );
 682             }
 683         }
 684
 685         if fn_kind.ctxt() != Some(FnCtxt::Foreign) && fn_kind.decl().c_variadic() {
 686             gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
 687         }
 688
 689         visit::walk_fn(self, fn_kind, span)
 690     }
 691
 692     fn visit_assoc_constraint(&mut self, constraint: &'a AssocConstraint) {
 693         if let AssocConstraintKind::Bound { .. } = constraint.kind {
 694             gate_feature_post!(
 695                 &self,
 696                 associated_type_bounds,
 697                 constraint.span,
 698                 "associated type bounds are unstable"
 699             )
 700         }
 701         visit::walk_assoc_constraint(self, constraint)
 702     }
 703
 704     fn visit_assoc_item(&mut self, i: &'a ast::AssocItem, ctxt: AssocCtxt) {
 705         let is_fn = match i.kind {
 706             ast::AssocItemKind::Fn(_) => true,
 707             ast::AssocItemKind::TyAlias(box ast::TyAlias { ref generics, ref ty, .. }) => {
 708                 if let (Some(_), AssocCtxt::Trait) = (ty, ctxt) {
 709                     gate_feature_post!(
 710                         &self,
 711                         associated_type_defaults,
 712                         i.span,
 713                         "associated type defaults are unstable"
 714                     );
 715                 }
 716                 if let Some(ty) = ty {
 717                     self.check_impl_trait(ty);
 718                 }
 719                 self.check_gat(generics, i.span);
 720                 false
 721             }
 722             _ => false,
 723         };
 724         if let ast::Defaultness::Default(_) = i.kind.defaultness() {
 725             // Limit `min_specialization` to only specializing functions.
 726             gate_feature_fn!(
 727                 &self,
 728                 |x: &Features| x.specialization || (is_fn && x.min_specialization),
 729                 i.span,
 730                 sym::specialization,
 731                 "specialization is unstable"
 732             );
 733         }
 734         visit::walk_assoc_item(self, i, ctxt)
 735     }
 736
 737     fn visit_vis(&mut self, vis: &'a ast::Visibility) {
 738         if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.kind {
 739             gate_feature_post!(
 740                 &self,
 741                 crate_visibility_modifier,
 742                 vis.span,
 743                 "`crate` visibility modifier is experimental"
 744             );
 745         }
 746         visit::walk_vis(self, vis)
 747     }
 748 }
 749
 750 pub fn check_crate(krate: &ast::Crate, sess: &Session) {
 751     maybe_stage_features(sess, krate);
 752     check_incompatible_features(sess);
 753     let mut visitor = PostExpansionVisitor { sess, features: &sess.features_untracked() };
 754
 755     let spans = sess.parse_sess.gated_spans.spans.borrow();
 756     macro_rules! gate_all {
 757         ($gate:ident, $msg:literal, $help:literal) => {
 758             if let Some(spans) = spans.get(&sym::$gate) {
 759                 for span in spans {
 760                     gate_feature_post!(&visitor, $gate, *span, $msg, $help);
 761                 }
 762             }
 763         };
 764         ($gate:ident, $msg:literal) => {
 765             if let Some(spans) = spans.get(&sym::$gate) {
 766                 for span in spans {
 767                     gate_feature_post!(&visitor, $gate, *span, $msg);
 768                 }
 769             }
 770         };
 771     }
 772     gate_all!(
 773         if_let_guard,
 774         "`if let` guards are experimental",
 775         "you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`"
 776     );
 777     gate_all!(let_chains, "`let` expressions in this position are unstable");
 778     gate_all!(
 779         async_closure,
 780         "async closures are unstable",
 781         "to use an async block, remove the `||`: `async {`"
 782     );
 783     gate_all!(more_qualified_paths, "usage of qualified paths in this context is experimental");
 784     gate_all!(generators, "yield syntax is experimental");
 785     gate_all!(raw_ref_op, "raw address of syntax is experimental");
 786     gate_all!(const_trait_impl, "const trait impls are experimental");
 787     gate_all!(half_open_range_patterns, "half-open range patterns are unstable");
 788     gate_all!(inline_const, "inline-const is experimental");
 789     gate_all!(inline_const_pat, "inline-const in pattern position is experimental");
 790     gate_all!(associated_const_equality, "associated const equality is incomplete");
 791
 792     // All uses of `gate_all!` below this point were added in #65742,
 793     // and subsequently disabled (with the non-early gating readded).
 794     macro_rules! gate_all {
 795         ($gate:ident, $msg:literal) => {
 796             // FIXME(eddyb) do something more useful than always
 797             // disabling these uses of early feature-gatings.
 798             if false {
 799                 for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 800                     gate_feature_post!(&visitor, $gate, *span, $msg);
 801                 }
 802             }
 803         };
 804     }
 805
 806     gate_all!(trait_alias, "trait aliases are experimental");
 807     gate_all!(associated_type_bounds, "associated type bounds are unstable");
 808     gate_all!(crate_visibility_modifier, "`crate` visibility modifier is experimental");
 809     gate_all!(decl_macro, "`macro` is experimental");
 810     gate_all!(box_patterns, "box pattern syntax is experimental");
 811     gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
 812     gate_all!(try_blocks, "`try` blocks are unstable");
 813     gate_all!(label_break_value, "labels on blocks are unstable");
 814     gate_all!(box_syntax, "box expression syntax is experimental; you can call `Box::new` instead");
 815     // To avoid noise about type ascription in common syntax errors,
 816     // only emit if it is the *only* error. (Also check it last.)
 817     if sess.parse_sess.span_diagnostic.err_count() == 0 {
 818         gate_all!(type_ascription, "type ascription is experimental");
 819     }
 820
 821     visit::walk_crate(&mut visitor, krate);
 822 }
 823
 824 fn maybe_stage_features(sess: &Session, krate: &ast::Crate) {
 825     // checks if `#![feature]` has been used to enable any lang feature
 826     // does not check the same for lib features unless there's at least one
 827     // declared lang feature
 828     use rustc_errors::Applicability;
 829
 830     if !sess.opts.unstable_features.is_nightly_build() {
 831         let lang_features = &sess.features_untracked().declared_lang_features;
 832         if lang_features.len() == 0 {
 833             return;
 834         }
 835         for attr in krate.attrs.iter().filter(|attr| attr.has_name(sym::feature)) {
 836             let mut err = struct_span_err!(
 837                 sess.parse_sess.span_diagnostic,
 838                 attr.span,
 839                 E0554,
 840                 "`#![feature]` may not be used on the {} release channel",
 841                 option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)")
 842             );
 843             let mut all_stable = true;
 844             for ident in
 845                 attr.meta_item_list().into_iter().flatten().flat_map(|nested| nested.ident())
 846             {
 847                 let name = ident.name;
 848                 let stable_since = lang_features
 849                     .iter()
 850                     .flat_map(|&(feature, _, since)| if feature == name { since } else { None })
 851                     .next();
 852                 if let Some(since) = stable_since {
 853                     err.help(&format!(
 854                         "the feature `{}` has been stable since {} and no longer requires \
 855                                   an attribute to enable",
 856                         name, since
 857                     ));
 858                 } else {
 859                     all_stable = false;
 860                 }
 861             }
 862             if all_stable {
 863                 err.span_suggestion(
 864                     attr.span,
 865                     "remove the attribute",
 866                     String::new(),
 867                     Applicability::MachineApplicable,
 868                 );
 869             }
 870             err.emit();
 871         }
 872     }
 873 }
 874
 875 fn check_incompatible_features(sess: &Session) {
 876     let features = sess.features_untracked();
 877
 878     let declared_features = features
 879         .declared_lang_features
 880         .iter()
 881         .copied()
 882         .map(|(name, span, _)| (name, span))
 883         .chain(features.declared_lib_features.iter().copied());
 884
 885     for (f1, f2) in rustc_feature::INCOMPATIBLE_FEATURES
 886         .iter()
 887         .filter(|&&(f1, f2)| features.enabled(f1) && features.enabled(f2))
 888     {
 889         if let Some((f1_name, f1_span)) = declared_features.clone().find(|(name, _)| name == f1) {
 890             if let Some((f2_name, f2_span)) = declared_features.clone().find(|(name, _)| name == f2)
 891             {
 892                 let spans = vec![f1_span, f2_span];
 893                 sess.struct_span_err(
 894                     spans.clone(),
 895                     &format!(
 896                         "features `{}` and `{}` are incompatible, using them at the same time \
 897                         is not allowed",
 898                         f1_name, f2_name
 899                     ),
 900                 )
 901                 .help("remove one of these features")
 902                 .emit();
 903             }
 904         }
 905     }
 906 }