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::{AssocTyConstraint, AssocTyConstraintKind, NodeId};
   4 use rustc_ast::{PatKind, RangeEnd, VariantData};
   5 use rustc_errors::struct_span_err;
   6 use rustc_feature::{AttributeGate, 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             "wasm" => {
 200                 gate_feature_post!(
 201                     &self,
 202                     wasm_abi,
 203                     span,
 204                     "wasm ABI is experimental and subject to change"
 205                 );
 206             }
 207             abi => self
 208                 .sess
 209                 .parse_sess
 210                 .span_diagnostic
 211                 .delay_span_bug(span, &format!("unrecognized ABI not caught in lowering: {}", abi)),
 212         }
 213     }
 214
 215     fn check_extern(&self, ext: ast::Extern) {
 216         if let ast::Extern::Explicit(abi) = ext {
 217             self.check_abi(abi);
 218         }
 219     }
 220
 221     fn maybe_report_invalid_custom_discriminants(&self, variants: &[ast::Variant]) {
 222         let has_fields = variants.iter().any(|variant| match variant.data {
 223             VariantData::Tuple(..) | VariantData::Struct(..) => true,
 224             VariantData::Unit(..) => false,
 225         });
 226
 227         let discriminant_spans = variants
 228             .iter()
 229             .filter(|variant| match variant.data {
 230                 VariantData::Tuple(..) | VariantData::Struct(..) => false,
 231                 VariantData::Unit(..) => true,
 232             })
 233             .filter_map(|variant| variant.disr_expr.as_ref().map(|c| c.value.span))
 234             .collect::<Vec<_>>();
 235
 236         if !discriminant_spans.is_empty() && has_fields {
 237             let mut err = feature_err(
 238                 &self.sess.parse_sess,
 239                 sym::arbitrary_enum_discriminant,
 240                 discriminant_spans.clone(),
 241                 "custom discriminant values are not allowed in enums with tuple or struct variants",
 242             );
 243             for sp in discriminant_spans {
 244                 err.span_label(sp, "disallowed custom discriminant");
 245             }
 246             for variant in variants.iter() {
 247                 match &variant.data {
 248                     VariantData::Struct(..) => {
 249                         err.span_label(variant.span, "struct variant defined here");
 250                     }
 251                     VariantData::Tuple(..) => {
 252                         err.span_label(variant.span, "tuple variant defined here");
 253                     }
 254                     VariantData::Unit(..) => {}
 255                 }
 256             }
 257             err.emit();
 258         }
 259     }
 260
 261     fn check_gat(&self, generics: &ast::Generics, span: Span) {
 262         if !generics.params.is_empty() {
 263             gate_feature_post!(
 264                 &self,
 265                 generic_associated_types,
 266                 span,
 267                 "generic associated types are unstable"
 268             );
 269         }
 270         if !generics.where_clause.predicates.is_empty() {
 271             gate_feature_post!(
 272                 &self,
 273                 generic_associated_types,
 274                 span,
 275                 "where clauses on associated types are unstable"
 276             );
 277         }
 278     }
 279
 280     /// Feature gate `impl Trait` inside `type Alias = $type_expr;`.
 281     fn check_impl_trait(&self, ty: &ast::Ty) {
 282         struct ImplTraitVisitor<'a> {
 283             vis: &'a PostExpansionVisitor<'a>,
 284         }
 285         impl Visitor<'_> for ImplTraitVisitor<'_> {
 286             fn visit_ty(&mut self, ty: &ast::Ty) {
 287                 if let ast::TyKind::ImplTrait(..) = ty.kind {
 288                     gate_feature_post!(
 289                         &self.vis,
 290                         min_type_alias_impl_trait,
 291                         ty.span,
 292                         "`impl Trait` in type aliases is unstable"
 293                     );
 294                 }
 295                 visit::walk_ty(self, ty);
 296             }
 297         }
 298         ImplTraitVisitor { vis: self }.visit_ty(ty);
 299     }
 300 }
 301
 302 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 303     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 304         let attr_info =
 305             attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name)).map(|a| **a);
 306         // Check feature gates for built-in attributes.
 307         if let Some((.., AttributeGate::Gated(_, name, descr, has_feature))) = attr_info {
 308             gate_feature_fn!(self, has_feature, attr.span, name, descr);
 309         }
 310         // Check unstable flavors of the `#[doc]` attribute.
 311         if self.sess.check_name(attr, sym::doc) {
 312             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 313                 macro_rules! gate_doc { ($($name:ident => $feature:ident)*) => {
 314                     $(if nested_meta.has_name(sym::$name) {
 315                         let msg = concat!("`#[doc(", stringify!($name), ")]` is experimental");
 316                         gate_feature_post!(self, $feature, attr.span, msg);
 317                     })*
 318                 }}
 319
 320                 gate_doc!(
 321                     cfg => doc_cfg
 322                     masked => doc_masked
 323                     notable_trait => doc_notable_trait
 324                     keyword => doc_keyword
 325                 );
 326             }
 327         }
 328
 329         // Check for unstable modifiers on `#[link(..)]` attribute
 330         if self.sess.check_name(attr, sym::link) {
 331             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 332                 if nested_meta.has_name(sym::modifiers) {
 333                     gate_feature_post!(
 334                         self,
 335                         native_link_modifiers,
 336                         nested_meta.span(),
 337                         "native link modifiers are experimental"
 338                     );
 339
 340                     if let Some(modifiers) = nested_meta.value_str() {
 341                         for modifier in modifiers.as_str().split(',') {
 342                             if let Some(modifier) = modifier.strip_prefix(&['+', '-'][..]) {
 343                                 macro_rules! gate_modifier { ($($name:literal => $feature:ident)*) => {
 344                                     $(if modifier == $name {
 345                                         let msg = concat!("`#[link(modifiers=\"", $name, "\")]` is unstable");
 346                                         gate_feature_post!(
 347                                             self,
 348                                             $feature,
 349                                             nested_meta.name_value_literal_span().unwrap(),
 350                                             msg
 351                                         );
 352                                     })*
 353                                 }}
 354
 355                                 gate_modifier!(
 356                                     "bundle" => native_link_modifiers_bundle
 357                                     "verbatim" => native_link_modifiers_verbatim
 358                                     "whole-archive" => native_link_modifiers_whole_archive
 359                                     "as-needed" => native_link_modifiers_as_needed
 360                                 );
 361                             }
 362                         }
 363                     }
 364                 }
 365             }
 366         }
 367     }
 368
 369     fn visit_item(&mut self, i: &'a ast::Item) {
 370         match i.kind {
 371             ast::ItemKind::ForeignMod(ref foreign_module) => {
 372                 if let Some(abi) = foreign_module.abi {
 373                     self.check_abi(abi);
 374                 }
 375             }
 376
 377             ast::ItemKind::Fn(..) => {
 378                 if self.sess.contains_name(&i.attrs[..], sym::plugin_registrar) {
 379                     gate_feature_post!(
 380                         &self,
 381                         plugin_registrar,
 382                         i.span,
 383                         "compiler plugins are experimental and possibly buggy"
 384                     );
 385                 }
 386                 if self.sess.contains_name(&i.attrs[..], sym::start) {
 387                     gate_feature_post!(
 388                         &self,
 389                         start,
 390                         i.span,
 391                         "`#[start]` functions are experimental \
 392                          and their signature may change \
 393                          over time"
 394                     );
 395                 }
 396             }
 397
 398             ast::ItemKind::Struct(..) => {
 399                 for attr in self.sess.filter_by_name(&i.attrs[..], sym::repr) {
 400                     for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
 401                         if item.has_name(sym::simd) {
 402                             gate_feature_post!(
 403                                 &self,
 404                                 repr_simd,
 405                                 attr.span,
 406                                 "SIMD types are experimental and possibly buggy"
 407                             );
 408                         }
 409                     }
 410                 }
 411             }
 412
 413             ast::ItemKind::Enum(ast::EnumDef { ref variants, .. }, ..) => {
 414                 for variant in variants {
 415                     match (&variant.data, &variant.disr_expr) {
 416                         (ast::VariantData::Unit(..), _) => {}
 417                         (_, Some(disr_expr)) => gate_feature_post!(
 418                             &self,
 419                             arbitrary_enum_discriminant,
 420                             disr_expr.value.span,
 421                             "discriminants on non-unit variants are experimental"
 422                         ),
 423                         _ => {}
 424                     }
 425                 }
 426
 427                 let has_feature = self.features.arbitrary_enum_discriminant;
 428                 if !has_feature && !i.span.allows_unstable(sym::arbitrary_enum_discriminant) {
 429                     self.maybe_report_invalid_custom_discriminants(&variants);
 430                 }
 431             }
 432
 433             ast::ItemKind::Impl(box ast::ImplKind {
 434                 polarity, defaultness, ref of_trait, ..
 435             }) => {
 436                 if let ast::ImplPolarity::Negative(span) = polarity {
 437                     gate_feature_post!(
 438                         &self,
 439                         negative_impls,
 440                         span.to(of_trait.as_ref().map_or(span, |t| t.path.span)),
 441                         "negative trait bounds are not yet fully implemented; \
 442                          use marker types for now"
 443                     );
 444                 }
 445
 446                 if let ast::Defaultness::Default(_) = defaultness {
 447                     gate_feature_post!(&self, specialization, i.span, "specialization is unstable");
 448                 }
 449             }
 450
 451             ast::ItemKind::Trait(box ast::TraitKind(ast::IsAuto::Yes, ..)) => {
 452                 gate_feature_post!(
 453                     &self,
 454                     auto_traits,
 455                     i.span,
 456                     "auto traits are experimental and possibly buggy"
 457                 );
 458             }
 459
 460             ast::ItemKind::TraitAlias(..) => {
 461                 gate_feature_post!(&self, trait_alias, i.span, "trait aliases are experimental");
 462             }
 463
 464             ast::ItemKind::MacroDef(ast::MacroDef { macro_rules: false, .. }) => {
 465                 let msg = "`macro` is experimental";
 466                 gate_feature_post!(&self, decl_macro, i.span, msg);
 467             }
 468
 469             ast::ItemKind::TyAlias(box ast::TyAliasKind(_, _, _, Some(ref ty))) => {
 470                 self.check_impl_trait(&ty)
 471             }
 472
 473             _ => {}
 474         }
 475
 476         visit::walk_item(self, i);
 477     }
 478
 479     fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
 480         match i.kind {
 481             ast::ForeignItemKind::Fn(..) | ast::ForeignItemKind::Static(..) => {
 482                 let link_name = self.sess.first_attr_value_str_by_name(&i.attrs, sym::link_name);
 483                 let links_to_llvm =
 484                     link_name.map_or(false, |val| val.as_str().starts_with("llvm."));
 485                 if links_to_llvm {
 486                     gate_feature_post!(
 487                         &self,
 488                         link_llvm_intrinsics,
 489                         i.span,
 490                         "linking to LLVM intrinsics is experimental"
 491                     );
 492                 }
 493             }
 494             ast::ForeignItemKind::TyAlias(..) => {
 495                 gate_feature_post!(&self, extern_types, i.span, "extern types are experimental");
 496             }
 497             ast::ForeignItemKind::MacCall(..) => {}
 498         }
 499
 500         visit::walk_foreign_item(self, i)
 501     }
 502
 503     fn visit_ty(&mut self, ty: &'a ast::Ty) {
 504         match ty.kind {
 505             ast::TyKind::BareFn(ref bare_fn_ty) => {
 506                 self.check_extern(bare_fn_ty.ext);
 507             }
 508             ast::TyKind::Never => {
 509                 gate_feature_post!(&self, never_type, ty.span, "the `!` type is experimental");
 510             }
 511             _ => {}
 512         }
 513         visit::walk_ty(self, ty)
 514     }
 515
 516     fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FnRetTy) {
 517         if let ast::FnRetTy::Ty(ref output_ty) = *ret_ty {
 518             if let ast::TyKind::Never = output_ty.kind {
 519                 // Do nothing.
 520             } else {
 521                 self.visit_ty(output_ty)
 522             }
 523         }
 524     }
 525
 526     fn visit_expr(&mut self, e: &'a ast::Expr) {
 527         match e.kind {
 528             ast::ExprKind::Box(_) => {
 529                 gate_feature_post!(
 530                     &self,
 531                     box_syntax,
 532                     e.span,
 533                     "box expression syntax is experimental; you can call `Box::new` instead"
 534                 );
 535             }
 536             ast::ExprKind::Type(..) => {
 537                 // To avoid noise about type ascription in common syntax errors, only emit if it
 538                 // is the *only* error.
 539                 if self.sess.parse_sess.span_diagnostic.err_count() == 0 {
 540                     gate_feature_post!(
 541                         &self,
 542                         type_ascription,
 543                         e.span,
 544                         "type ascription is experimental"
 545                     );
 546                 }
 547             }
 548             ast::ExprKind::TryBlock(_) => {
 549                 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
 550             }
 551             ast::ExprKind::Block(_, opt_label) => {
 552                 if let Some(label) = opt_label {
 553                     gate_feature_post!(
 554                         &self,
 555                         label_break_value,
 556                         label.ident.span,
 557                         "labels on blocks are unstable"
 558                     );
 559                 }
 560             }
 561             _ => {}
 562         }
 563         visit::walk_expr(self, e)
 564     }
 565
 566     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
 567         match &pattern.kind {
 568             PatKind::Box(..) => {
 569                 gate_feature_post!(
 570                     &self,
 571                     box_patterns,
 572                     pattern.span,
 573                     "box pattern syntax is experimental"
 574                 );
 575             }
 576             PatKind::Range(_, _, Spanned { node: RangeEnd::Excluded, .. }) => {
 577                 gate_feature_post!(
 578                     &self,
 579                     exclusive_range_pattern,
 580                     pattern.span,
 581                     "exclusive range pattern syntax is experimental"
 582                 );
 583             }
 584             _ => {}
 585         }
 586         visit::walk_pat(self, pattern)
 587     }
 588
 589     fn visit_fn(&mut self, fn_kind: FnKind<'a>, span: Span, _: NodeId) {
 590         if let Some(header) = fn_kind.header() {
 591             // Stability of const fn methods are covered in `visit_assoc_item` below.
 592             self.check_extern(header.ext);
 593
 594             if let (ast::Const::Yes(_), ast::Extern::Implicit)
 595             | (ast::Const::Yes(_), ast::Extern::Explicit(_)) = (header.constness, header.ext)
 596             {
 597                 gate_feature_post!(
 598                     &self,
 599                     const_extern_fn,
 600                     span,
 601                     "`const extern fn` definitions are unstable"
 602                 );
 603             }
 604         }
 605
 606         if fn_kind.ctxt() != Some(FnCtxt::Foreign) && fn_kind.decl().c_variadic() {
 607             gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
 608         }
 609
 610         visit::walk_fn(self, fn_kind, span)
 611     }
 612
 613     fn visit_assoc_ty_constraint(&mut self, constraint: &'a AssocTyConstraint) {
 614         if let AssocTyConstraintKind::Bound { .. } = constraint.kind {
 615             gate_feature_post!(
 616                 &self,
 617                 associated_type_bounds,
 618                 constraint.span,
 619                 "associated type bounds are unstable"
 620             )
 621         }
 622         visit::walk_assoc_ty_constraint(self, constraint)
 623     }
 624
 625     fn visit_assoc_item(&mut self, i: &'a ast::AssocItem, ctxt: AssocCtxt) {
 626         let is_fn = match i.kind {
 627             ast::AssocItemKind::Fn(_) => true,
 628             ast::AssocItemKind::TyAlias(box ast::TyAliasKind(_, ref generics, _, ref ty)) => {
 629                 if let (Some(_), AssocCtxt::Trait) = (ty, ctxt) {
 630                     gate_feature_post!(
 631                         &self,
 632                         associated_type_defaults,
 633                         i.span,
 634                         "associated type defaults are unstable"
 635                     );
 636                 }
 637                 if let Some(ty) = ty {
 638                     self.check_impl_trait(ty);
 639                 }
 640                 self.check_gat(generics, i.span);
 641                 false
 642             }
 643             _ => false,
 644         };
 645         if let ast::Defaultness::Default(_) = i.kind.defaultness() {
 646             // Limit `min_specialization` to only specializing functions.
 647             gate_feature_fn!(
 648                 &self,
 649                 |x: &Features| x.specialization || (is_fn && x.min_specialization),
 650                 i.span,
 651                 sym::specialization,
 652                 "specialization is unstable"
 653             );
 654         }
 655         visit::walk_assoc_item(self, i, ctxt)
 656     }
 657
 658     fn visit_vis(&mut self, vis: &'a ast::Visibility) {
 659         if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.kind {
 660             gate_feature_post!(
 661                 &self,
 662                 crate_visibility_modifier,
 663                 vis.span,
 664                 "`crate` visibility modifier is experimental"
 665             );
 666         }
 667         visit::walk_vis(self, vis)
 668     }
 669 }
 670
 671 pub fn check_crate(krate: &ast::Crate, sess: &Session) {
 672     maybe_stage_features(sess, krate);
 673     check_incompatible_features(sess);
 674     let mut visitor = PostExpansionVisitor { sess, features: &sess.features_untracked() };
 675
 676     let spans = sess.parse_sess.gated_spans.spans.borrow();
 677     macro_rules! gate_all {
 678         ($gate:ident, $msg:literal, $help:literal) => {
 679             if let Some(spans) = spans.get(&sym::$gate) {
 680                 for span in spans {
 681                     gate_feature_post!(&visitor, $gate, *span, $msg, $help);
 682                 }
 683             }
 684         };
 685         ($gate:ident, $msg:literal) => {
 686             if let Some(spans) = spans.get(&sym::$gate) {
 687                 for span in spans {
 688                     gate_feature_post!(&visitor, $gate, *span, $msg);
 689                 }
 690             }
 691         };
 692     }
 693     gate_all!(
 694         if_let_guard,
 695         "`if let` guards are experimental",
 696         "you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`"
 697     );
 698     gate_all!(
 699         let_chains,
 700         "`let` expressions in this position are experimental",
 701         "you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`"
 702     );
 703     gate_all!(
 704         async_closure,
 705         "async closures are unstable",
 706         "to use an async block, remove the `||`: `async {`"
 707     );
 708     gate_all!(more_qualified_paths, "usage of qualified paths in this context is experimental");
 709     gate_all!(generators, "yield syntax is experimental");
 710     gate_all!(raw_ref_op, "raw address of syntax is experimental");
 711     gate_all!(const_trait_bound_opt_out, "`?const` on trait bounds is experimental");
 712     gate_all!(const_trait_impl, "const trait impls are experimental");
 713     gate_all!(half_open_range_patterns, "half-open range patterns are unstable");
 714     gate_all!(inline_const, "inline-const is experimental");
 715     gate_all!(
 716         const_generics_defaults,
 717         "default values for const generic parameters are experimental"
 718     );
 719     if sess.parse_sess.span_diagnostic.err_count() == 0 {
 720         // Errors for `destructuring_assignment` can get quite noisy, especially where `_` is
 721         // involved, so we only emit errors where there are no other parsing errors.
 722         gate_all!(destructuring_assignment, "destructuring assignments are unstable");
 723     }
 724     gate_all!(unnamed_fields, "unnamed fields are not yet fully implemented");
 725
 726     // All uses of `gate_all!` below this point were added in #65742,
 727     // and subsequently disabled (with the non-early gating readded).
 728     macro_rules! gate_all {
 729         ($gate:ident, $msg:literal) => {
 730             // FIXME(eddyb) do something more useful than always
 731             // disabling these uses of early feature-gatings.
 732             if false {
 733                 for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 734                     gate_feature_post!(&visitor, $gate, *span, $msg);
 735                 }
 736             }
 737         };
 738     }
 739
 740     gate_all!(trait_alias, "trait aliases are experimental");
 741     gate_all!(associated_type_bounds, "associated type bounds are unstable");
 742     gate_all!(crate_visibility_modifier, "`crate` visibility modifier is experimental");
 743     gate_all!(const_generics, "const generics are unstable");
 744     gate_all!(decl_macro, "`macro` is experimental");
 745     gate_all!(box_patterns, "box pattern syntax is experimental");
 746     gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
 747     gate_all!(try_blocks, "`try` blocks are unstable");
 748     gate_all!(label_break_value, "labels on blocks are unstable");
 749     gate_all!(box_syntax, "box expression syntax is experimental; you can call `Box::new` instead");
 750     // To avoid noise about type ascription in common syntax errors,
 751     // only emit if it is the *only* error. (Also check it last.)
 752     if sess.parse_sess.span_diagnostic.err_count() == 0 {
 753         gate_all!(type_ascription, "type ascription is experimental");
 754     }
 755
 756     visit::walk_crate(&mut visitor, krate);
 757 }
 758
 759 fn maybe_stage_features(sess: &Session, krate: &ast::Crate) {
 760     use rustc_errors::Applicability;
 761
 762     if !sess.opts.unstable_features.is_nightly_build() {
 763         let lang_features = &sess.features_untracked().declared_lang_features;
 764         for attr in krate.attrs.iter().filter(|attr| sess.check_name(attr, sym::feature)) {
 765             let mut err = struct_span_err!(
 766                 sess.parse_sess.span_diagnostic,
 767                 attr.span,
 768                 E0554,
 769                 "`#![feature]` may not be used on the {} release channel",
 770                 option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)")
 771             );
 772             let mut all_stable = true;
 773             for ident in
 774                 attr.meta_item_list().into_iter().flatten().map(|nested| nested.ident()).flatten()
 775             {
 776                 let name = ident.name;
 777                 let stable_since = lang_features
 778                     .iter()
 779                     .flat_map(|&(feature, _, since)| if feature == name { since } else { None })
 780                     .next();
 781                 if let Some(since) = stable_since {
 782                     err.help(&format!(
 783                         "the feature `{}` has been stable since {} and no longer requires \
 784                                   an attribute to enable",
 785                         name, since
 786                     ));
 787                 } else {
 788                     all_stable = false;
 789                 }
 790             }
 791             if all_stable {
 792                 err.span_suggestion(
 793                     attr.span,
 794                     "remove the attribute",
 795                     String::new(),
 796                     Applicability::MachineApplicable,
 797                 );
 798             }
 799             err.emit();
 800         }
 801     }
 802 }
 803
 804 fn check_incompatible_features(sess: &Session) {
 805     let features = sess.features_untracked();
 806
 807     let declared_features = features
 808         .declared_lang_features
 809         .iter()
 810         .copied()
 811         .map(|(name, span, _)| (name, span))
 812         .chain(features.declared_lib_features.iter().copied());
 813
 814     for (f1, f2) in rustc_feature::INCOMPATIBLE_FEATURES
 815         .iter()
 816         .filter(|&&(f1, f2)| features.enabled(f1) && features.enabled(f2))
 817     {
 818         if let Some((f1_name, f1_span)) = declared_features.clone().find(|(name, _)| name == f1) {
 819             if let Some((f2_name, f2_span)) = declared_features.clone().find(|(name, _)| name == f2)
 820             {
 821                 let spans = vec![f1_span, f2_span];
 822                 sess.struct_span_err(
 823                     spans.clone(),
 824                     &format!(
 825                         "features `{}` and `{}` are incompatible, using them at the same time \
 826                         is not allowed",
 827                         f1_name, f2_name
 828                     ),
 829                 )
 830                 .help("remove one of these features")
 831                 .emit();
 832             }
 833         }
 834     }
 835 }