src/libsyntax/feature_gate.rs

   1 // Copyright 2013 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! Feature gating
  12 //!
  13 //! This modules implements the gating necessary for preventing certain compiler
  14 //! features from being used by default. This module will crawl a pre-expanded
  15 //! AST to ensure that there are no features which are used that are not
  16 //! enabled.
  17 //!
  18 //! Features are enabled in programs via the crate-level attributes of
  19 //! `#![feature(...)]` with a comma-separated list of features.
  20 //!
  21 //! For the purpose of future feature-tracking, once code for detection of feature
  22 //! gate usage is added, *do not remove it again* even once the feature
  23 //! becomes stable.
  24
  25 use self::Status::*;
  26 use self::AttributeType::*;
  27
  28 use abi::Abi;
  29 use ast::NodeId;
  30 use ast;
  31 use attr;
  32 use attr::AttrMetaMethods;
  33 use codemap::{CodeMap, Span};
  34 use diagnostic::SpanHandler;
  35 use visit;
  36 use visit::Visitor;
  37 use parse::token::{self, InternedString};
  38
  39 use std::ascii::AsciiExt;
  40
  41 // If you change this list without updating src/doc/reference.md, @cmr will be sad
  42 // Don't ever remove anything from this list; set them to 'Removed'.
  43 // The version numbers here correspond to the version in which the current status
  44 // was set. This is most important for knowing when a particular feature became
  45 // stable (active).
  46 // NB: The featureck.py script parses this information directly out of the source
  47 // so take care when modifying it.
  48 const KNOWN_FEATURES: &'static [(&'static str, &'static str, Status)] = &[
  49     ("globs", "1.0.0", Accepted),
  50     ("macro_rules", "1.0.0", Accepted),
  51     ("struct_variant", "1.0.0", Accepted),
  52     ("asm", "1.0.0", Active),
  53     ("managed_boxes", "1.0.0", Removed),
  54     ("non_ascii_idents", "1.0.0", Active),
  55     ("thread_local", "1.0.0", Active),
  56     ("link_args", "1.0.0", Active),
  57     ("plugin_registrar", "1.0.0", Active),
  58     ("log_syntax", "1.0.0", Active),
  59     ("trace_macros", "1.0.0", Active),
  60     ("concat_idents", "1.0.0", Active),
  61     ("intrinsics", "1.0.0", Active),
  62     ("lang_items", "1.0.0", Active),
  63
  64     ("simd", "1.0.0", Active),
  65     ("default_type_params", "1.0.0", Accepted),
  66     ("quote", "1.0.0", Active),
  67     ("link_llvm_intrinsics", "1.0.0", Active),
  68     ("linkage", "1.0.0", Active),
  69     ("struct_inherit", "1.0.0", Removed),
  70
  71     ("quad_precision_float", "1.0.0", Removed),
  72
  73     ("rustc_diagnostic_macros", "1.0.0", Active),
  74     ("unboxed_closures", "1.0.0", Active),
  75     ("reflect", "1.0.0", Active),
  76     ("import_shadowing", "1.0.0", Removed),
  77     ("advanced_slice_patterns", "1.0.0", Active),
  78     ("tuple_indexing", "1.0.0", Accepted),
  79     ("associated_types", "1.0.0", Accepted),
  80     ("visible_private_types", "1.0.0", Active),
  81     ("slicing_syntax", "1.0.0", Accepted),
  82     ("box_syntax", "1.0.0", Active),
  83     ("on_unimplemented", "1.0.0", Active),
  84     ("simd_ffi", "1.0.0", Active),
  85     ("allocator", "1.0.0", Active),
  86
  87     ("if_let", "1.0.0", Accepted),
  88     ("while_let", "1.0.0", Accepted),
  89
  90     ("plugin", "1.0.0", Active),
  91     ("start", "1.0.0", Active),
  92     ("main", "1.0.0", Active),
  93
  94     ("fundamental", "1.0.0", Active),
  95
  96     // Deprecate after snapshot
  97     // SNAP 5520801
  98     ("unsafe_destructor", "1.0.0", Active),
  99
 100     // A temporary feature gate used to enable parser extensions needed
 101     // to bootstrap fix for #5723.
 102     ("issue_5723_bootstrap", "1.0.0", Accepted),
 103
 104     // A way to temporarily opt out of opt in copy. This will *never* be accepted.
 105     ("opt_out_copy", "1.0.0", Removed),
 106
 107     // OIBIT specific features
 108     ("optin_builtin_traits", "1.0.0", Active),
 109
 110     // macro reexport needs more discussion and stabilization
 111     ("macro_reexport", "1.0.0", Active),
 112
 113     // These are used to test this portion of the compiler, they don't actually
 114     // mean anything
 115     ("test_accepted_feature", "1.0.0", Accepted),
 116     ("test_removed_feature", "1.0.0", Removed),
 117
 118     // Allows use of #[staged_api]
 119     ("staged_api", "1.0.0", Active),
 120
 121     // Allows using items which are missing stability attributes
 122     ("unmarked_api", "1.0.0", Active),
 123
 124     // Allows using #![no_std]
 125     ("no_std", "1.0.0", Active),
 126
 127     // Allows using `box` in patterns; RFC 469
 128     ("box_patterns", "1.0.0", Active),
 129
 130     // Allows using the unsafe_no_drop_flag attribute (unlikely to
 131     // switch to Accepted; see RFC 320)
 132     ("unsafe_no_drop_flag", "1.0.0", Active),
 133
 134     // Allows the use of custom attributes; RFC 572
 135     ("custom_attribute", "1.0.0", Active),
 136
 137     // Allows the use of #[derive(Anything)] as sugar for
 138     // #[derive_Anything].
 139     ("custom_derive", "1.0.0", Active),
 140
 141     // Allows the use of rustc_* attributes; RFC 572
 142     ("rustc_attrs", "1.0.0", Active),
 143
 144     // Allows the use of `static_assert`
 145     ("static_assert", "1.0.0", Active),
 146
 147     // Allows the use of #[allow_internal_unstable]. This is an
 148     // attribute on macro_rules! and can't use the attribute handling
 149     // below (it has to be checked before expansion possibly makes
 150     // macros disappear).
 151     ("allow_internal_unstable", "1.0.0", Active),
 152
 153     // #23121. Array patterns have some hazards yet.
 154     ("slice_patterns", "1.0.0", Active),
 155 ];
 156 // (changing above list without updating src/doc/reference.md makes @cmr sad)
 157
 158 enum Status {
 159     /// Represents an active feature that is currently being implemented or
 160     /// currently being considered for addition/removal.
 161     Active,
 162
 163     /// Represents a feature which has since been removed (it was once Active)
 164     Removed,
 165
 166     /// This language feature has since been Accepted (it was once Active)
 167     Accepted,
 168 }
 169
 170 // Attributes that have a special meaning to rustc or rustdoc
 171 pub const KNOWN_ATTRIBUTES: &'static [(&'static str, AttributeType)] = &[
 172     // Normal attributes
 173
 174     ("warn", Normal),
 175     ("allow", Normal),
 176     ("forbid", Normal),
 177     ("deny", Normal),
 178
 179     ("macro_reexport", Normal),
 180     ("macro_use", Normal),
 181     ("macro_export", Normal),
 182     ("plugin_registrar", Normal),
 183
 184     ("cfg", Normal),
 185     ("cfg_attr", Normal),
 186     ("main", Normal),
 187     ("start", Normal),
 188     ("test", Normal),
 189     ("bench", Normal),
 190     ("simd", Normal),
 191     ("repr", Normal),
 192     ("path", Normal),
 193     ("abi", Normal),
 194     ("automatically_derived", Normal),
 195     ("no_mangle", Normal),
 196     ("no_link", Normal),
 197     ("derive", Normal),
 198     ("should_panic", Normal),
 199     ("ignore", Normal),
 200     ("no_implicit_prelude", Normal),
 201     ("reexport_test_harness_main", Normal),
 202     ("link_args", Normal),
 203     ("macro_escape", Normal),
 204
 205     ("unsafe_destructor", Gated("unsafe_destructor",
 206                                 "`#[unsafe_destructor]` does nothing anymore")),
 207     ("staged_api", Gated("staged_api",
 208                          "staged_api is for use by rustc only")),
 209     ("plugin", Gated("plugin",
 210                      "compiler plugins are experimental \
 211                       and possibly buggy")),
 212     ("no_std", Gated("no_std",
 213                      "no_std is experimental")),
 214     ("lang", Gated("lang_items",
 215                      "language items are subject to change")),
 216     ("linkage", Gated("linkage",
 217                       "the `linkage` attribute is experimental \
 218                        and not portable across platforms")),
 219     ("thread_local", Gated("thread_local",
 220                             "`#[thread_local]` is an experimental feature, and does not \
 221                              currently handle destructors. There is no corresponding \
 222                              `#[task_local]` mapping to the task model")),
 223
 224     ("rustc_on_unimplemented", Gated("on_unimplemented",
 225                                      "the `#[rustc_on_unimplemented]` attribute \
 226                                       is an experimental feature")),
 227     ("allocator", Gated("allocator",
 228                         "the `#[allocator]` attribute is an experimental feature")),
 229     ("rustc_variance", Gated("rustc_attrs",
 230                              "the `#[rustc_variance]` attribute \
 231                               is an experimental feature")),
 232     ("rustc_error", Gated("rustc_attrs",
 233                           "the `#[rustc_error]` attribute \
 234                            is an experimental feature")),
 235     ("rustc_move_fragments", Gated("rustc_attrs",
 236                                    "the `#[rustc_move_fragments]` attribute \
 237                                     is an experimental feature")),
 238
 239     ("allow_internal_unstable", Gated("allow_internal_unstable",
 240                                       EXPLAIN_ALLOW_INTERNAL_UNSTABLE)),
 241
 242     ("fundamental", Gated("fundamental",
 243                           "the `#[fundamental]` attribute \
 244                            is an experimental feature")),
 245
 246     // FIXME: #14408 whitelist docs since rustdoc looks at them
 247     ("doc", Whitelisted),
 248
 249     // FIXME: #14406 these are processed in trans, which happens after the
 250     // lint pass
 251     ("cold", Whitelisted),
 252     ("export_name", Whitelisted),
 253     ("inline", Whitelisted),
 254     ("link", Whitelisted),
 255     ("link_name", Whitelisted),
 256     ("link_section", Whitelisted),
 257     ("no_builtins", Whitelisted),
 258     ("no_mangle", Whitelisted),
 259     ("no_stack_check", Whitelisted),
 260     ("packed", Whitelisted),
 261     ("static_assert", Gated("static_assert",
 262                             "`#[static_assert]` is an experimental feature, and has a poor API")),
 263     ("no_debug", Whitelisted),
 264     ("omit_gdb_pretty_printer_section", Whitelisted),
 265     ("unsafe_no_drop_flag", Gated("unsafe_no_drop_flag",
 266                                   "unsafe_no_drop_flag has unstable semantics \
 267                                    and may be removed in the future")),
 268
 269     // used in resolve
 270     ("prelude_import", Whitelisted),
 271
 272     // FIXME: #14407 these are only looked at on-demand so we can't
 273     // guarantee they'll have already been checked
 274     ("deprecated", Whitelisted),
 275     ("must_use", Whitelisted),
 276     ("stable", Whitelisted),
 277     ("unstable", Whitelisted),
 278
 279     ("rustc_paren_sugar", Gated("unboxed_closures",
 280                                 "unboxed_closures are still evolving")),
 281     ("rustc_reflect_like", Gated("reflect",
 282                                  "defining reflective traits is still evolving")),
 283
 284     // Crate level attributes
 285     ("crate_name", CrateLevel),
 286     ("crate_type", CrateLevel),
 287     ("crate_id", CrateLevel),
 288     ("feature", CrateLevel),
 289     ("no_start", CrateLevel),
 290     ("no_main", CrateLevel),
 291     ("no_builtins", CrateLevel),
 292     ("recursion_limit", CrateLevel),
 293 ];
 294
 295 #[derive(PartialEq, Copy, Debug)]
 296 pub enum AttributeType {
 297     /// Normal, builtin attribute that is consumed
 298     /// by the compiler before the unused_attribute check
 299     Normal,
 300
 301     /// Builtin attribute that may not be consumed by the compiler
 302     /// before the unused_attribute check. These attributes
 303     /// will be ignored by the unused_attribute lint
 304     Whitelisted,
 305
 306     /// Is gated by a given feature gate and reason
 307     /// These get whitelisted too
 308     Gated(&'static str, &'static str),
 309
 310     /// Builtin attribute that is only allowed at the crate level
 311     CrateLevel,
 312 }
 313
 314 /// A set of features to be used by later passes.
 315 pub struct Features {
 316     pub unboxed_closures: bool,
 317     pub rustc_diagnostic_macros: bool,
 318     pub visible_private_types: bool,
 319     pub allow_quote: bool,
 320     pub allow_asm: bool,
 321     pub allow_log_syntax: bool,
 322     pub allow_concat_idents: bool,
 323     pub allow_trace_macros: bool,
 324     pub allow_internal_unstable: bool,
 325     pub allow_custom_derive: bool,
 326     pub simd_ffi: bool,
 327     pub unmarked_api: bool,
 328     /// spans of #![feature] attrs for stable language features. for error reporting
 329     pub declared_stable_lang_features: Vec<Span>,
 330     /// #![feature] attrs for non-language (library) features
 331     pub declared_lib_features: Vec<(InternedString, Span)>
 332 }
 333
 334 impl Features {
 335     pub fn new() -> Features {
 336         Features {
 337             unboxed_closures: false,
 338             rustc_diagnostic_macros: false,
 339             visible_private_types: false,
 340             allow_quote: false,
 341             allow_asm: false,
 342             allow_log_syntax: false,
 343             allow_concat_idents: false,
 344             allow_trace_macros: false,
 345             allow_internal_unstable: false,
 346             allow_custom_derive: false,
 347             simd_ffi: false,
 348             unmarked_api: false,
 349             declared_stable_lang_features: Vec::new(),
 350             declared_lib_features: Vec::new()
 351         }
 352     }
 353 }
 354
 355 struct Context<'a> {
 356     features: Vec<&'static str>,
 357     span_handler: &'a SpanHandler,
 358     cm: &'a CodeMap,
 359 }
 360
 361 impl<'a> Context<'a> {
 362     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
 363         let has_feature = self.has_feature(feature);
 364         debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", feature, span, has_feature);
 365         if !has_feature {
 366             emit_feature_err(self.span_handler, feature, span, explain);
 367         }
 368     }
 369     fn has_feature(&self, feature: &str) -> bool {
 370         self.features.iter().any(|&n| n == feature)
 371     }
 372
 373     fn check_attribute(&self, attr: &ast::Attribute) {
 374         debug!("check_attribute(attr = {:?})", attr);
 375         let name = &*attr.name();
 376         for &(n, ty) in KNOWN_ATTRIBUTES {
 377             if n == name {
 378                 if let Gated(gate, desc) = ty {
 379                     self.gate_feature(gate, attr.span, desc);
 380                 }
 381                 debug!("check_attribute: {:?} is known, {:?}", name, ty);
 382                 return;
 383             }
 384         }
 385         if name.starts_with("rustc_") {
 386             self.gate_feature("rustc_attrs", attr.span,
 387                               "unless otherwise specified, attributes \
 388                                with the prefix `rustc_` \
 389                                are reserved for internal compiler diagnostics");
 390         } else if name.starts_with("derive_") {
 391             self.gate_feature("custom_derive", attr.span,
 392                               "attributes of the form `#[derive_*]` are reserved
 393                                for the compiler");
 394         } else {
 395             self.gate_feature("custom_attribute", attr.span,
 396                        &format!("The attribute `{}` is currently \
 397                                 unknown to the the compiler and \
 398                                 may have meaning \
 399                                 added to it in the future",
 400                                 name));
 401         }
 402     }
 403 }
 404
 405 pub fn emit_feature_err(diag: &SpanHandler, feature: &str, span: Span, explain: &str) {
 406     diag.span_err(span, explain);
 407     diag.fileline_help(span, &format!("add #![feature({})] to the \
 408                                    crate attributes to enable",
 409                                   feature));
 410 }
 411
 412 pub fn emit_feature_warn(diag: &SpanHandler, feature: &str, span: Span, explain: &str) {
 413     diag.span_warn(span, explain);
 414     if diag.handler.can_emit_warnings {
 415         diag.fileline_help(span, &format!("add #![feature({})] to the \
 416                                        crate attributes to silence this warning",
 417                                       feature));
 418     }
 419 }
 420
 421 pub const EXPLAIN_ASM: &'static str =
 422     "inline assembly is not stable enough for use and is subject to change";
 423
 424 pub const EXPLAIN_LOG_SYNTAX: &'static str =
 425     "`log_syntax!` is not stable enough for use and is subject to change";
 426
 427 pub const EXPLAIN_CONCAT_IDENTS: &'static str =
 428     "`concat_idents` is not stable enough for use and is subject to change";
 429
 430 pub const EXPLAIN_TRACE_MACROS: &'static str =
 431     "`trace_macros` is not stable enough for use and is subject to change";
 432 pub const EXPLAIN_ALLOW_INTERNAL_UNSTABLE: &'static str =
 433     "allow_internal_unstable side-steps feature gating and stability checks";
 434
 435 pub const EXPLAIN_CUSTOM_DERIVE: &'static str =
 436     "`#[derive]` for custom traits is not stable enough for use and is subject to change";
 437
 438 struct MacroVisitor<'a> {
 439     context: &'a Context<'a>
 440 }
 441
 442 impl<'a, 'v> Visitor<'v> for MacroVisitor<'a> {
 443     fn visit_mac(&mut self, mac: &ast::Mac) {
 444         let ast::MacInvocTT(ref path, _, _) = mac.node;
 445         let id = path.segments.last().unwrap().identifier;
 446
 447         // Issue 22234: If you add a new case here, make sure to also
 448         // add code to catch the macro during or after expansion.
 449         //
 450         // We still keep this MacroVisitor (rather than *solely*
 451         // relying on catching cases during or after expansion) to
 452         // catch uses of these macros within conditionally-compiled
 453         // code, e.g. `#[cfg]`-guarded functions.
 454
 455         if id == token::str_to_ident("asm") {
 456             self.context.gate_feature("asm", path.span, EXPLAIN_ASM);
 457         }
 458
 459         else if id == token::str_to_ident("log_syntax") {
 460             self.context.gate_feature("log_syntax", path.span, EXPLAIN_LOG_SYNTAX);
 461         }
 462
 463         else if id == token::str_to_ident("trace_macros") {
 464             self.context.gate_feature("trace_macros", path.span, EXPLAIN_TRACE_MACROS);
 465         }
 466
 467         else if id == token::str_to_ident("concat_idents") {
 468             self.context.gate_feature("concat_idents", path.span, EXPLAIN_CONCAT_IDENTS);
 469         }
 470     }
 471
 472     fn visit_attribute(&mut self, attr: &'v ast::Attribute) {
 473         self.context.check_attribute(attr);
 474     }
 475 }
 476
 477 struct PostExpansionVisitor<'a> {
 478     context: &'a Context<'a>
 479 }
 480
 481 impl<'a> PostExpansionVisitor<'a> {
 482     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
 483         if !self.context.cm.span_allows_unstable(span) {
 484             self.context.gate_feature(feature, span, explain)
 485         }
 486     }
 487 }
 488
 489 impl<'a, 'v> Visitor<'v> for PostExpansionVisitor<'a> {
 490     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 491         if !self.context.cm.span_allows_unstable(attr.span) {
 492             self.context.check_attribute(attr);
 493         }
 494     }
 495
 496     fn visit_name(&mut self, sp: Span, name: ast::Name) {
 497         if !token::get_name(name).is_ascii() {
 498             self.gate_feature("non_ascii_idents", sp,
 499                               "non-ascii idents are not fully supported.");
 500         }
 501     }
 502
 503     fn visit_item(&mut self, i: &ast::Item) {
 504         match i.node {
 505             ast::ItemExternCrate(_) => {
 506                 if attr::contains_name(&i.attrs[..], "macro_reexport") {
 507                     self.gate_feature("macro_reexport", i.span,
 508                                       "macros reexports are experimental \
 509                                        and possibly buggy");
 510                 }
 511             }
 512
 513             ast::ItemForeignMod(ref foreign_module) => {
 514                 if attr::contains_name(&i.attrs[..], "link_args") {
 515                     self.gate_feature("link_args", i.span,
 516                                       "the `link_args` attribute is not portable \
 517                                        across platforms, it is recommended to \
 518                                        use `#[link(name = \"foo\")]` instead")
 519                 }
 520                 if foreign_module.abi == Abi::RustIntrinsic {
 521                     self.gate_feature("intrinsics",
 522                                       i.span,
 523                                       "intrinsics are subject to change")
 524                 }
 525             }
 526
 527             ast::ItemFn(..) => {
 528                 if attr::contains_name(&i.attrs[..], "plugin_registrar") {
 529                     self.gate_feature("plugin_registrar", i.span,
 530                                       "compiler plugins are experimental and possibly buggy");
 531                 }
 532                 if attr::contains_name(&i.attrs[..], "start") {
 533                     self.gate_feature("start", i.span,
 534                                       "a #[start] function is an experimental \
 535                                        feature whose signature may change \
 536                                        over time");
 537                 }
 538                 if attr::contains_name(&i.attrs[..], "main") {
 539                     self.gate_feature("main", i.span,
 540                                       "declaration of a nonstandard #[main] \
 541                                        function may change over time, for now \
 542                                        a top-level `fn main()` is required");
 543                 }
 544             }
 545
 546             ast::ItemStruct(..) => {
 547                 if attr::contains_name(&i.attrs[..], "simd") {
 548                     self.gate_feature("simd", i.span,
 549                                       "SIMD types are experimental and possibly buggy");
 550                 }
 551             }
 552
 553             ast::ItemDefaultImpl(..) => {
 554                 self.gate_feature("optin_builtin_traits",
 555                                   i.span,
 556                                   "default trait implementations are experimental \
 557                                    and possibly buggy");
 558             }
 559
 560             ast::ItemImpl(_, polarity, _, _, _, _) => {
 561                 match polarity {
 562                     ast::ImplPolarity::Negative => {
 563                         self.gate_feature("optin_builtin_traits",
 564                                           i.span,
 565                                           "negative trait bounds are not yet fully implemented; \
 566                                           use marker types for now");
 567                     },
 568                     _ => {}
 569                 }
 570             }
 571
 572             _ => {}
 573         }
 574
 575         visit::walk_item(self, i);
 576     }
 577
 578     fn visit_foreign_item(&mut self, i: &ast::ForeignItem) {
 579         let links_to_llvm = match attr::first_attr_value_str_by_name(&i.attrs,
 580                                                                      "link_name") {
 581             Some(val) => val.starts_with("llvm."),
 582             _ => false
 583         };
 584         if links_to_llvm {
 585             self.gate_feature("link_llvm_intrinsics", i.span,
 586                               "linking to LLVM intrinsics is experimental");
 587         }
 588
 589         visit::walk_foreign_item(self, i)
 590     }
 591
 592     fn visit_expr(&mut self, e: &ast::Expr) {
 593         match e.node {
 594             ast::ExprBox(..) | ast::ExprUnary(ast::UnOp::UnUniq, _) => {
 595                 self.gate_feature("box_syntax",
 596                                   e.span,
 597                                   "box expression syntax is experimental; \
 598                                    you can call `Box::new` instead.");
 599             }
 600             _ => {}
 601         }
 602         visit::walk_expr(self, e);
 603     }
 604
 605     fn visit_pat(&mut self, pattern: &ast::Pat) {
 606         match pattern.node {
 607             ast::PatVec(_, Some(_), ref last) if !last.is_empty() => {
 608                 self.gate_feature("advanced_slice_patterns",
 609                                   pattern.span,
 610                                   "multiple-element slice matches anywhere \
 611                                    but at the end of a slice (e.g. \
 612                                    `[0, ..xs, 0]` are experimental")
 613             }
 614             ast::PatVec(..) => {
 615                 self.gate_feature("slice_patterns",
 616                                   pattern.span,
 617                                   "slice pattern syntax is experimental");
 618             }
 619             ast::PatBox(..) => {
 620                 self.gate_feature("box_patterns",
 621                                   pattern.span,
 622                                   "box pattern syntax is experimental");
 623             }
 624             _ => {}
 625         }
 626         visit::walk_pat(self, pattern)
 627     }
 628
 629     fn visit_fn(&mut self,
 630                 fn_kind: visit::FnKind<'v>,
 631                 fn_decl: &'v ast::FnDecl,
 632                 block: &'v ast::Block,
 633                 span: Span,
 634                 _node_id: NodeId) {
 635         match fn_kind {
 636             visit::FkItemFn(_, _, _, abi) if abi == Abi::RustIntrinsic => {
 637                 self.gate_feature("intrinsics",
 638                                   span,
 639                                   "intrinsics are subject to change")
 640             }
 641             visit::FkItemFn(_, _, _, abi) |
 642             visit::FkMethod(_, &ast::MethodSig { abi, .. }) if abi == Abi::RustCall => {
 643                 self.gate_feature("unboxed_closures",
 644                                   span,
 645                                   "rust-call ABI is subject to change")
 646             }
 647             _ => {}
 648         }
 649         visit::walk_fn(self, fn_kind, fn_decl, block, span);
 650     }
 651 }
 652
 653 fn check_crate_inner<F>(cm: &CodeMap, span_handler: &SpanHandler,
 654                         krate: &ast::Crate,
 655                         check: F)
 656                        -> Features
 657     where F: FnOnce(&mut Context, &ast::Crate)
 658 {
 659     let mut cx = Context {
 660         features: Vec::new(),
 661         span_handler: span_handler,
 662         cm: cm,
 663     };
 664
 665     let mut accepted_features = Vec::new();
 666     let mut unknown_features = Vec::new();
 667
 668     for attr in &krate.attrs {
 669         if !attr.check_name("feature") {
 670             continue
 671         }
 672
 673         match attr.meta_item_list() {
 674             None => {
 675                 span_handler.span_err(attr.span, "malformed feature attribute, \
 676                                                   expected #![feature(...)]");
 677             }
 678             Some(list) => {
 679                 for mi in list {
 680                     let name = match mi.node {
 681                         ast::MetaWord(ref word) => (*word).clone(),
 682                         _ => {
 683                             span_handler.span_err(mi.span,
 684                                                   "malformed feature, expected just \
 685                                                    one word");
 686                             continue
 687                         }
 688                     };
 689                     match KNOWN_FEATURES.iter()
 690                                         .find(|& &(n, _, _)| name == n) {
 691                         Some(&(name, _, Active)) => {
 692                             cx.features.push(name);
 693                         }
 694                         Some(&(_, _, Removed)) => {
 695                             span_handler.span_err(mi.span, "feature has been removed");
 696                         }
 697                         Some(&(_, _, Accepted)) => {
 698                             accepted_features.push(mi.span);
 699                         }
 700                         None => {
 701                             unknown_features.push((name, mi.span));
 702                         }
 703                     }
 704                 }
 705             }
 706         }
 707     }
 708
 709     check(&mut cx, krate);
 710
 711     // FIXME (pnkfelix): Before adding the 99th entry below, change it
 712     // to a single-pass (instead of N calls to `.has_feature`).
 713
 714     Features {
 715         unboxed_closures: cx.has_feature("unboxed_closures"),
 716         rustc_diagnostic_macros: cx.has_feature("rustc_diagnostic_macros"),
 717         visible_private_types: cx.has_feature("visible_private_types"),
 718         allow_quote: cx.has_feature("quote"),
 719         allow_asm: cx.has_feature("asm"),
 720         allow_log_syntax: cx.has_feature("log_syntax"),
 721         allow_concat_idents: cx.has_feature("concat_idents"),
 722         allow_trace_macros: cx.has_feature("trace_macros"),
 723         allow_internal_unstable: cx.has_feature("allow_internal_unstable"),
 724         allow_custom_derive: cx.has_feature("custom_derive"),
 725         simd_ffi: cx.has_feature("simd_ffi"),
 726         unmarked_api: cx.has_feature("unmarked_api"),
 727         declared_stable_lang_features: accepted_features,
 728         declared_lib_features: unknown_features
 729     }
 730 }
 731
 732 pub fn check_crate_macros(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate)
 733 -> Features {
 734     check_crate_inner(cm, span_handler, krate,
 735                       |ctx, krate| visit::walk_crate(&mut MacroVisitor { context: ctx }, krate))
 736 }
 737
 738 pub fn check_crate(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate)
 739                    -> Features
 740 {
 741     check_crate_inner(cm, span_handler, krate,
 742                       |ctx, krate| visit::walk_crate(&mut PostExpansionVisitor { context: ctx },
 743                                                      krate))
 744 }