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::RustIntrinsic;
  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 static 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     ("phase", "1.0.0", Removed),
  58     ("plugin_registrar", "1.0.0", Active),
  59     ("log_syntax", "1.0.0", Active),
  60     ("trace_macros", "1.0.0", Active),
  61     ("concat_idents", "1.0.0", Active),
  62     ("unsafe_destructor", "1.0.0", Active),
  63     ("intrinsics", "1.0.0", Active),
  64     ("lang_items", "1.0.0", Active),
  65
  66     ("simd", "1.0.0", Active),
  67     ("default_type_params", "1.0.0", Accepted),
  68     ("quote", "1.0.0", Active),
  69     ("link_llvm_intrinsics", "1.0.0", Active),
  70     ("linkage", "1.0.0", Active),
  71     ("struct_inherit", "1.0.0", Removed),
  72
  73     ("quad_precision_float", "1.0.0", Removed),
  74
  75     ("rustc_diagnostic_macros", "1.0.0", Active),
  76     ("unboxed_closures", "1.0.0", Active),
  77     ("import_shadowing", "1.0.0", Removed),
  78     ("advanced_slice_patterns", "1.0.0", Active),
  79     ("tuple_indexing", "1.0.0", Accepted),
  80     ("associated_types", "1.0.0", Accepted),
  81     ("visible_private_types", "1.0.0", Active),
  82     ("slicing_syntax", "1.0.0", Accepted),
  83     ("box_syntax", "1.0.0", Active),
  84     ("on_unimplemented", "1.0.0", Active),
  85     ("simd_ffi", "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     // A temporary feature gate used to enable parser extensions needed
  95     // to bootstrap fix for #5723.
  96     ("issue_5723_bootstrap", "1.0.0", Accepted),
  97
  98     // A way to temporarily opt out of opt in copy. This will *never* be accepted.
  99     ("opt_out_copy", "1.0.0", Removed),
 100
 101     // A way to temporarily opt out of the new orphan rules. This will *never* be accepted.
 102     ("old_orphan_check", "1.0.0", Deprecated),
 103
 104     // A way to temporarily opt out of the new impl rules. This will *never* be accepted.
 105     ("old_impl_check", "1.0.0", Deprecated),
 106
 107     // OIBIT specific features
 108     ("optin_builtin_traits", "1.0.0", Active),
 109
 110     // int and uint are now deprecated
 111     ("int_uint", "1.0.0", Active),
 112
 113     // macro reexport needs more discussion and stabilization
 114     ("macro_reexport", "1.0.0", Active),
 115
 116     // These are used to test this portion of the compiler, they don't actually
 117     // mean anything
 118     ("test_accepted_feature", "1.0.0", Accepted),
 119     ("test_removed_feature", "1.0.0", Removed),
 120
 121     // Allows use of #[staged_api]
 122     ("staged_api", "1.0.0", Active),
 123
 124     // Allows using items which are missing stability attributes
 125     ("unmarked_api", "1.0.0", Active),
 126
 127     // Allows using #![no_std]
 128     ("no_std", "1.0.0", Active),
 129
 130     // Allows using `box` in patterns; RFC 469
 131     ("box_patterns", "1.0.0", Active),
 132
 133     // Allows using the unsafe_no_drop_flag attribute (unlikely to
 134     // switch to Accepted; see RFC 320)
 135     ("unsafe_no_drop_flag", "1.0.0", Active),
 136
 137     // Allows the use of custom attributes; RFC 572
 138     ("custom_attribute", "1.0.0", Active),
 139
 140     // Allows the use of rustc_* attributes; RFC 572
 141     ("rustc_attrs", "1.0.0", Active),
 142 ];
 143 // (changing above list without updating src/doc/reference.md makes @cmr sad)
 144
 145 enum Status {
 146     /// Represents an active feature that is currently being implemented or
 147     /// currently being considered for addition/removal.
 148     Active,
 149
 150     /// Represents a feature gate that is temporarily enabling deprecated behavior.
 151     /// This gate will never be accepted.
 152     Deprecated,
 153
 154     /// Represents a feature which has since been removed (it was once Active)
 155     Removed,
 156
 157     /// This language feature has since been Accepted (it was once Active)
 158     Accepted,
 159 }
 160
 161 // Attributes that have a special meaning to rustc or rustdoc
 162 pub static KNOWN_ATTRIBUTES: &'static [(&'static str, AttributeType)] = &[
 163     // Normal attributes
 164
 165     ("warn", Normal),
 166     ("allow", Normal),
 167     ("forbid", Normal),
 168     ("deny", Normal),
 169
 170     ("macro_reexport", Normal),
 171     ("macro_use", Normal),
 172     ("macro_export", Normal),
 173     ("plugin_registrar", Normal),
 174
 175     ("cfg", Normal),
 176     ("main", Normal),
 177     ("start", Normal),
 178     ("test", Normal),
 179     ("bench", Normal),
 180     ("simd", Normal),
 181     ("repr", Normal),
 182     ("path", Normal),
 183     ("abi", Normal),
 184     ("unsafe_destructor", Normal),
 185     ("automatically_derived", Normal),
 186     ("no_mangle", Normal),
 187     ("no_link", Normal),
 188     ("derive", Normal),
 189     ("should_fail", Normal),
 190     ("ignore", Normal),
 191     ("no_implicit_prelude", Normal),
 192     ("reexport_test_harness_main", Normal),
 193     ("link_args", Normal),
 194     ("macro_escape", Normal),
 195
 196
 197     ("staged_api", Gated("staged_api",
 198                          "staged_api is for use by rustc only")),
 199     ("plugin", Gated("plugin",
 200                      "compiler plugins are experimental \
 201                       and possibly buggy")),
 202     ("no_std", Gated("no_std",
 203                      "no_std is experimental")),
 204     ("lang", Gated("lang_items",
 205                      "language items are subject to change")),
 206     ("linkage", Gated("linkage",
 207                       "the `linkage` attribute is experimental \
 208                        and not portable across platforms")),
 209     ("thread_local", Gated("thread_local",
 210                             "`#[thread_local]` is an experimental feature, and does not \
 211                              currently handle destructors. There is no corresponding \
 212                              `#[task_local]` mapping to the task model")),
 213
 214     ("rustc_on_unimplemented", Gated("on_unimplemented",
 215                                      "the `#[rustc_on_unimplemented]` attribute \
 216                                       is an experimental feature")),
 217     ("rustc_variance", Gated("rustc_attrs",
 218                              "the `#[rustc_variance]` attribute \
 219                               is an experimental feature")),
 220     ("rustc_error", Gated("rustc_attrs",
 221                           "the `#[rustc_error]` attribute \
 222                            is an experimental feature")),
 223     ("rustc_move_fragments", Gated("rustc_attrs",
 224                                    "the `#[rustc_move_fragments]` attribute \
 225                                     is an experimental feature")),
 226
 227     // FIXME: #14408 whitelist docs since rustdoc looks at them
 228     ("doc", Whitelisted),
 229
 230     // FIXME: #14406 these are processed in trans, which happens after the
 231     // lint pass
 232     ("cold", Whitelisted),
 233     ("export_name", Whitelisted),
 234     ("inline", Whitelisted),
 235     ("link", Whitelisted),
 236     ("link_name", Whitelisted),
 237     ("link_section", Whitelisted),
 238     ("no_builtins", Whitelisted),
 239     ("no_mangle", Whitelisted),
 240     ("no_split_stack", Whitelisted),
 241     ("no_stack_check", Whitelisted),
 242     ("packed", Whitelisted),
 243     ("static_assert", Whitelisted),
 244     ("no_debug", Whitelisted),
 245     ("omit_gdb_pretty_printer_section", Whitelisted),
 246     ("unsafe_no_drop_flag", Whitelisted),
 247
 248     // used in resolve
 249     ("prelude_import", Whitelisted),
 250
 251     // FIXME: #14407 these are only looked at on-demand so we can't
 252     // guarantee they'll have already been checked
 253     ("deprecated", Whitelisted),
 254     ("must_use", Whitelisted),
 255     ("stable", Whitelisted),
 256     ("unstable", Whitelisted),
 257
 258     // FIXME: #19470 this shouldn't be needed forever
 259     ("old_orphan_check", Whitelisted),
 260     ("old_impl_check", Whitelisted),
 261     ("rustc_paren_sugar", Whitelisted), // FIXME: #18101 temporary unboxed closure hack
 262
 263     // Crate level attributes
 264     ("crate_name", CrateLevel),
 265     ("crate_type", CrateLevel),
 266     ("crate_id", CrateLevel),
 267     ("feature", CrateLevel),
 268     ("no_start", CrateLevel),
 269     ("no_main", CrateLevel),
 270     ("no_builtins", CrateLevel),
 271     ("recursion_limit", CrateLevel),
 272 ];
 273
 274 #[derive(PartialEq, Copy)]
 275 pub enum AttributeType {
 276     /// Normal, builtin attribute that is consumed
 277     /// by the compiler before the unused_attribute check
 278     Normal,
 279
 280     /// Builtin attribute that may not be consumed by the compiler
 281     /// before the unused_attribute check. These attributes
 282     /// will be ignored by the unused_attribute lint
 283     Whitelisted,
 284
 285     /// Is gated by a given feature gate and reason
 286     /// These get whitelisted too
 287     Gated(&'static str, &'static str),
 288
 289     /// Builtin attribute that is only allowed at the crate level
 290     CrateLevel,
 291 }
 292
 293 /// A set of features to be used by later passes.
 294 pub struct Features {
 295     pub unboxed_closures: bool,
 296     pub rustc_diagnostic_macros: bool,
 297     pub visible_private_types: bool,
 298     pub allow_quote: bool,
 299     pub allow_asm: bool,
 300     pub allow_log_syntax: bool,
 301     pub allow_concat_idents: bool,
 302     pub allow_trace_macros: bool,
 303     pub old_orphan_check: bool,
 304     pub simd_ffi: bool,
 305     pub unmarked_api: bool,
 306     /// spans of #![feature] attrs for stable language features. for error reporting
 307     pub declared_stable_lang_features: Vec<Span>,
 308     /// #![feature] attrs for non-language (library) features
 309     pub declared_lib_features: Vec<(InternedString, Span)>
 310 }
 311
 312 impl Features {
 313     pub fn new() -> Features {
 314         Features {
 315             unboxed_closures: false,
 316             rustc_diagnostic_macros: false,
 317             visible_private_types: false,
 318             allow_quote: false,
 319             allow_asm: false,
 320             allow_log_syntax: false,
 321             allow_concat_idents: false,
 322             allow_trace_macros: false,
 323             old_orphan_check: false,
 324             simd_ffi: false,
 325             unmarked_api: false,
 326             declared_stable_lang_features: Vec::new(),
 327             declared_lib_features: Vec::new()
 328         }
 329     }
 330 }
 331
 332 struct Context<'a> {
 333     features: Vec<&'static str>,
 334     span_handler: &'a SpanHandler,
 335     cm: &'a CodeMap,
 336 }
 337
 338 impl<'a> Context<'a> {
 339     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
 340         if !self.has_feature(feature) {
 341             emit_feature_err(self.span_handler, feature, span, explain);
 342         }
 343     }
 344
 345     fn warn_feature(&self, feature: &str, span: Span, explain: &str) {
 346         if !self.has_feature(feature) {
 347             emit_feature_warn(self.span_handler, feature, span, explain);
 348         }
 349     }
 350     fn has_feature(&self, feature: &str) -> bool {
 351         self.features.iter().any(|&n| n == feature)
 352     }
 353 }
 354
 355 pub fn emit_feature_err(diag: &SpanHandler, feature: &str, span: Span, explain: &str) {
 356     diag.span_err(span, explain);
 357     diag.span_help(span, &format!("add #![feature({})] to the \
 358                                    crate attributes to enable",
 359                                   feature));
 360 }
 361
 362 pub fn emit_feature_warn(diag: &SpanHandler, feature: &str, span: Span, explain: &str) {
 363     diag.span_warn(span, explain);
 364     if diag.handler.can_emit_warnings {
 365         diag.span_help(span, &format!("add #![feature({})] to the \
 366                                        crate attributes to silence this warning",
 367                                       feature));
 368     }
 369 }
 370
 371 pub const EXPLAIN_ASM: &'static str =
 372     "inline assembly is not stable enough for use and is subject to change";
 373
 374 pub const EXPLAIN_LOG_SYNTAX: &'static str =
 375     "`log_syntax!` is not stable enough for use and is subject to change";
 376
 377 pub const EXPLAIN_CONCAT_IDENTS: &'static str =
 378     "`concat_idents` is not stable enough for use and is subject to change";
 379
 380 pub const EXPLAIN_TRACE_MACROS: &'static str =
 381     "`trace_macros` is not stable enough for use and is subject to change";
 382
 383 struct MacroVisitor<'a> {
 384     context: &'a Context<'a>
 385 }
 386
 387 impl<'a, 'v> Visitor<'v> for MacroVisitor<'a> {
 388     fn visit_mac(&mut self, mac: &ast::Mac) {
 389         let ast::MacInvocTT(ref path, _, _) = mac.node;
 390         let id = path.segments.last().unwrap().identifier;
 391
 392         // Issue 22234: If you add a new case here, make sure to also
 393         // add code to catch the macro during or after expansion.
 394         //
 395         // We still keep this MacroVisitor (rather than *solely*
 396         // relying on catching cases during or after expansion) to
 397         // catch uses of these macros within conditionally-compiled
 398         // code, e.g. `#[cfg]`-guarded functions.
 399
 400         if id == token::str_to_ident("asm") {
 401             self.context.gate_feature("asm", path.span, EXPLAIN_ASM);
 402         }
 403
 404         else if id == token::str_to_ident("log_syntax") {
 405             self.context.gate_feature("log_syntax", path.span, EXPLAIN_LOG_SYNTAX);
 406         }
 407
 408         else if id == token::str_to_ident("trace_macros") {
 409             self.context.gate_feature("trace_macros", path.span, EXPLAIN_TRACE_MACROS);
 410         }
 411
 412         else if id == token::str_to_ident("concat_idents") {
 413             self.context.gate_feature("concat_idents", path.span, EXPLAIN_CONCAT_IDENTS);
 414         }
 415     }
 416 }
 417
 418 struct PostExpansionVisitor<'a> {
 419     context: &'a Context<'a>
 420 }
 421
 422 impl<'a> PostExpansionVisitor<'a> {
 423     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
 424         if !self.context.cm.span_is_internal(span) {
 425             self.context.gate_feature(feature, span, explain)
 426         }
 427     }
 428 }
 429
 430 impl<'a, 'v> Visitor<'v> for PostExpansionVisitor<'a> {
 431     fn visit_name(&mut self, sp: Span, name: ast::Name) {
 432         if !token::get_name(name).is_ascii() {
 433             self.gate_feature("non_ascii_idents", sp,
 434                               "non-ascii idents are not fully supported.");
 435         }
 436     }
 437
 438     fn visit_item(&mut self, i: &ast::Item) {
 439         match i.node {
 440             ast::ItemExternCrate(_) => {
 441                 if attr::contains_name(&i.attrs[..], "macro_reexport") {
 442                     self.gate_feature("macro_reexport", i.span,
 443                                       "macros reexports are experimental \
 444                                        and possibly buggy");
 445                 }
 446             }
 447
 448             ast::ItemForeignMod(ref foreign_module) => {
 449                 if attr::contains_name(&i.attrs[..], "link_args") {
 450                     self.gate_feature("link_args", i.span,
 451                                       "the `link_args` attribute is not portable \
 452                                        across platforms, it is recommended to \
 453                                        use `#[link(name = \"foo\")]` instead")
 454                 }
 455                 if foreign_module.abi == RustIntrinsic {
 456                     self.gate_feature("intrinsics",
 457                                       i.span,
 458                                       "intrinsics are subject to change")
 459                 }
 460             }
 461
 462             ast::ItemFn(..) => {
 463                 if attr::contains_name(&i.attrs[..], "plugin_registrar") {
 464                     self.gate_feature("plugin_registrar", i.span,
 465                                       "compiler plugins are experimental and possibly buggy");
 466                 }
 467                 if attr::contains_name(&i.attrs[..], "start") {
 468                     self.gate_feature("start", i.span,
 469                                       "a #[start] function is an experimental \
 470                                        feature whose signature may change \
 471                                        over time");
 472                 }
 473                 if attr::contains_name(&i.attrs[..], "main") {
 474                     self.gate_feature("main", i.span,
 475                                       "declaration of a nonstandard #[main] \
 476                                        function may change over time, for now \
 477                                        a top-level `fn main()` is required");
 478                 }
 479             }
 480
 481             ast::ItemStruct(..) => {
 482                 if attr::contains_name(&i.attrs[..], "simd") {
 483                     self.gate_feature("simd", i.span,
 484                                       "SIMD types are experimental and possibly buggy");
 485                 }
 486             }
 487
 488             ast::ItemImpl(_, polarity, _, _, _, _) => {
 489                 match polarity {
 490                     ast::ImplPolarity::Negative => {
 491                         self.gate_feature("optin_builtin_traits",
 492                                           i.span,
 493                                           "negative trait bounds are not yet fully implemented; \
 494                                           use marker types for now");
 495                     },
 496                     _ => {}
 497                 }
 498
 499                 if attr::contains_name(&i.attrs,
 500                                        "unsafe_destructor") {
 501                     self.gate_feature("unsafe_destructor",
 502                                       i.span,
 503                                       "`#[unsafe_destructor]` allows too \
 504                                        many unsafe patterns and may be \
 505                                        removed in the future");
 506                 }
 507
 508                 if attr::contains_name(&i.attrs[..],
 509                                        "old_orphan_check") {
 510                     self.gate_feature(
 511                         "old_orphan_check",
 512                         i.span,
 513                         "the new orphan check rules will eventually be strictly enforced");
 514                 }
 515
 516                 if attr::contains_name(&i.attrs[..],
 517                                        "old_impl_check") {
 518                     self.gate_feature("old_impl_check",
 519                                       i.span,
 520                                       "`#[old_impl_check]` will be removed in the future");
 521                 }
 522             }
 523
 524             _ => {}
 525         }
 526
 527         visit::walk_item(self, i);
 528     }
 529
 530     fn visit_foreign_item(&mut self, i: &ast::ForeignItem) {
 531         if attr::contains_name(&i.attrs, "linkage") {
 532             self.gate_feature("linkage", i.span,
 533                               "the `linkage` attribute is experimental \
 534                                and not portable across platforms")
 535         }
 536
 537         let links_to_llvm = match attr::first_attr_value_str_by_name(&i.attrs,
 538                                                                      "link_name") {
 539             Some(val) => val.starts_with("llvm."),
 540             _ => false
 541         };
 542         if links_to_llvm {
 543             self.gate_feature("link_llvm_intrinsics", i.span,
 544                               "linking to LLVM intrinsics is experimental");
 545         }
 546
 547         visit::walk_foreign_item(self, i)
 548     }
 549
 550     fn visit_ty(&mut self, t: &ast::Ty) {
 551         match t.node {
 552             ast::TyPath(ref p, _) => {
 553                 match &*p.segments {
 554
 555                     [ast::PathSegment { identifier, .. }] => {
 556                         let name = token::get_ident(identifier);
 557                         let msg = if name == "int" {
 558                             Some("the `int` type is deprecated; \
 559                                   use `isize` or a fixed-sized integer")
 560                         } else if name == "uint" {
 561                             Some("the `uint` type is deprecated; \
 562                                   use `usize` or a fixed-sized integer")
 563                         } else {
 564                             None
 565                         };
 566
 567                         if let Some(msg) = msg {
 568                             self.context.warn_feature("int_uint", t.span, msg)
 569                         }
 570                     }
 571                     _ => {}
 572                 }
 573             }
 574             _ => {}
 575         }
 576         visit::walk_ty(self, t);
 577     }
 578
 579     fn visit_expr(&mut self, e: &ast::Expr) {
 580         match e.node {
 581             ast::ExprBox(..) | ast::ExprUnary(ast::UnOp::UnUniq, _) => {
 582                 self.gate_feature("box_syntax",
 583                                   e.span,
 584                                   "box expression syntax is experimental; \
 585                                    you can call `Box::new` instead.");
 586             }
 587             ast::ExprLit(ref lit) => {
 588                 match lit.node {
 589                     ast::LitInt(_, ty) => {
 590                         let msg = if let ast::SignedIntLit(ast::TyIs(true), _) = ty {
 591                             Some("the `i` and `is` suffixes on integers are deprecated; \
 592                                   use `isize` or one of the fixed-sized suffixes")
 593                         } else if let ast::UnsignedIntLit(ast::TyUs(true)) = ty {
 594                             Some("the `u` and `us` suffixes on integers are deprecated; \
 595                                   use `usize` or one of the fixed-sized suffixes")
 596                         } else {
 597                             None
 598                         };
 599                         if let Some(msg) = msg {
 600                             self.context.warn_feature("int_uint", e.span, msg);
 601                         }
 602                     }
 603                     _ => {}
 604                 }
 605             }
 606             _ => {}
 607         }
 608         visit::walk_expr(self, e);
 609     }
 610
 611     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 612         let name = &*attr.name();
 613         for &(n, ty) in KNOWN_ATTRIBUTES {
 614             if n == name {
 615                 if let Gated(gate, desc) = ty {
 616                     self.gate_feature(gate, attr.span, desc);
 617                 }
 618                 return;
 619             }
 620         }
 621         if name.starts_with("rustc_") {
 622             self.gate_feature("rustc_attrs", attr.span,
 623                               "unless otherwise specified, attributes \
 624                                with the prefix `rustc_` \
 625                                are reserved for internal compiler diagnostics");
 626         } else {
 627             self.gate_feature("custom_attribute", attr.span,
 628                        format!("The attribute `{}` is currently \
 629                                 unknown to the the compiler and \
 630                                 may have meaning \
 631                                 added to it in the future",
 632                                 name).as_slice());
 633         }
 634     }
 635
 636     fn visit_pat(&mut self, pattern: &ast::Pat) {
 637         match pattern.node {
 638             ast::PatVec(_, Some(_), ref last) if !last.is_empty() => {
 639                 self.gate_feature("advanced_slice_patterns",
 640                                   pattern.span,
 641                                   "multiple-element slice matches anywhere \
 642                                    but at the end of a slice (e.g. \
 643                                    `[0, ..xs, 0]` are experimental")
 644             }
 645             ast::PatBox(..) => {
 646                 self.gate_feature("box_patterns",
 647                                   pattern.span,
 648                                   "box pattern syntax is experimental");
 649             }
 650             _ => {}
 651         }
 652         visit::walk_pat(self, pattern)
 653     }
 654
 655     fn visit_fn(&mut self,
 656                 fn_kind: visit::FnKind<'v>,
 657                 fn_decl: &'v ast::FnDecl,
 658                 block: &'v ast::Block,
 659                 span: Span,
 660                 _node_id: NodeId) {
 661         match fn_kind {
 662             visit::FkItemFn(_, _, _, abi) if abi == RustIntrinsic => {
 663                 self.gate_feature("intrinsics",
 664                                   span,
 665                                   "intrinsics are subject to change")
 666             }
 667             _ => {}
 668         }
 669         visit::walk_fn(self, fn_kind, fn_decl, block, span);
 670     }
 671 }
 672
 673 fn check_crate_inner<F>(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate,
 674                         check: F)
 675                        -> Features
 676     where F: FnOnce(&mut Context, &ast::Crate)
 677 {
 678     let mut cx = Context {
 679         features: Vec::new(),
 680         span_handler: span_handler,
 681         cm: cm,
 682     };
 683
 684     let mut accepted_features = Vec::new();
 685     let mut unknown_features = Vec::new();
 686
 687     for attr in &krate.attrs {
 688         if !attr.check_name("feature") {
 689             continue
 690         }
 691
 692         match attr.meta_item_list() {
 693             None => {
 694                 span_handler.span_err(attr.span, "malformed feature attribute, \
 695                                                   expected #![feature(...)]");
 696             }
 697             Some(list) => {
 698                 for mi in list {
 699                     let name = match mi.node {
 700                         ast::MetaWord(ref word) => (*word).clone(),
 701                         _ => {
 702                             span_handler.span_err(mi.span,
 703                                                   "malformed feature, expected just \
 704                                                    one word");
 705                             continue
 706                         }
 707                     };
 708                     match KNOWN_FEATURES.iter()
 709                                         .find(|& &(n, _, _)| name == n) {
 710                         Some(&(name, _, Active)) => {
 711                             cx.features.push(name);
 712                         }
 713                         Some(&(name, _, Deprecated)) => {
 714                             cx.features.push(name);
 715                             span_handler.span_warn(
 716                                 mi.span,
 717                                 "feature is deprecated and will only be available \
 718                                  for a limited time, please rewrite code that relies on it");
 719                         }
 720                         Some(&(_, _, Removed)) => {
 721                             span_handler.span_err(mi.span, "feature has been removed");
 722                         }
 723                         Some(&(_, _, Accepted)) => {
 724                             accepted_features.push(mi.span);
 725                         }
 726                         None => {
 727                             unknown_features.push((name, mi.span));
 728                         }
 729                     }
 730                 }
 731             }
 732         }
 733     }
 734
 735     check(&mut cx, krate);
 736
 737     // FIXME (pnkfelix): Before adding the 99th entry below, change it
 738     // to a single-pass (instead of N calls to `.has_feature`).
 739
 740     Features {
 741         unboxed_closures: cx.has_feature("unboxed_closures"),
 742         rustc_diagnostic_macros: cx.has_feature("rustc_diagnostic_macros"),
 743         visible_private_types: cx.has_feature("visible_private_types"),
 744         allow_quote: cx.has_feature("quote"),
 745         allow_asm: cx.has_feature("asm"),
 746         allow_log_syntax: cx.has_feature("log_syntax"),
 747         allow_concat_idents: cx.has_feature("concat_idents"),
 748         allow_trace_macros: cx.has_feature("trace_macros"),
 749         old_orphan_check: cx.has_feature("old_orphan_check"),
 750         simd_ffi: cx.has_feature("simd_ffi"),
 751         unmarked_api: cx.has_feature("unmarked_api"),
 752         declared_stable_lang_features: accepted_features,
 753         declared_lib_features: unknown_features
 754     }
 755 }
 756
 757 pub fn check_crate_macros(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate)
 758 -> Features {
 759     check_crate_inner(cm, span_handler, krate,
 760                       |ctx, krate| visit::walk_crate(&mut MacroVisitor { context: ctx }, krate))
 761 }
 762
 763 pub fn check_crate(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate)
 764 -> Features {
 765     check_crate_inner(cm, span_handler, krate,
 766                       |ctx, krate| visit::walk_crate(&mut PostExpansionVisitor { context: ctx },
 767                                                      krate))
 768 }
 769