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 module 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     // A temporary feature gate used to enable parser extensions needed
  97     // to bootstrap fix for #5723.
  98     ("issue_5723_bootstrap", "1.0.0", Accepted),
  99
 100     // A way to temporarily opt out of opt in copy. This will *never* be accepted.
 101     ("opt_out_copy", "1.0.0", Removed),
 102
 103     // OIBIT specific features
 104     ("optin_builtin_traits", "1.0.0", Active),
 105
 106     // macro reexport needs more discussion and stabilization
 107     ("macro_reexport", "1.0.0", Active),
 108
 109     // These are used to test this portion of the compiler, they don't actually
 110     // mean anything
 111     ("test_accepted_feature", "1.0.0", Accepted),
 112     ("test_removed_feature", "1.0.0", Removed),
 113
 114     // Allows use of #[staged_api]
 115     ("staged_api", "1.0.0", Active),
 116
 117     // Allows using items which are missing stability attributes
 118     ("unmarked_api", "1.0.0", Active),
 119
 120     // Allows using #![no_std]
 121     ("no_std", "1.0.0", Active),
 122
 123     // Allows using `box` in patterns; RFC 469
 124     ("box_patterns", "1.0.0", Active),
 125
 126     // Allows using the unsafe_no_drop_flag attribute (unlikely to
 127     // switch to Accepted; see RFC 320)
 128     ("unsafe_no_drop_flag", "1.0.0", Active),
 129
 130     // Allows the use of custom attributes; RFC 572
 131     ("custom_attribute", "1.0.0", Active),
 132
 133     // Allows the use of #[derive(Anything)] as sugar for
 134     // #[derive_Anything].
 135     ("custom_derive", "1.0.0", Active),
 136
 137     // Allows the use of rustc_* attributes; RFC 572
 138     ("rustc_attrs", "1.0.0", Active),
 139
 140     // Allows the use of `static_assert`
 141     ("static_assert", "1.0.0", Active),
 142
 143     // Allows the use of #[allow_internal_unstable]. This is an
 144     // attribute on macro_rules! and can't use the attribute handling
 145     // below (it has to be checked before expansion possibly makes
 146     // macros disappear).
 147     ("allow_internal_unstable", "1.0.0", Active),
 148
 149     // #23121. Array patterns have some hazards yet.
 150     ("slice_patterns", "1.0.0", Active),
 151
 152     // Allows use of unary negate on unsigned integers, e.g. -e for e: u8
 153     ("negate_unsigned", "1.0.0", Active),
 154
 155     // Allows the definition of associated constants in `trait` or `impl`
 156     // blocks.
 157     ("associated_consts", "1.0.0", Active),
 158
 159     // Allows the definition of `const fn` functions.
 160     ("const_fn", "1.2.0", Active),
 161 ];
 162 // (changing above list without updating src/doc/reference.md makes @cmr sad)
 163
 164 enum Status {
 165     /// Represents an active feature that is currently being implemented or
 166     /// currently being considered for addition/removal.
 167     Active,
 168
 169     /// Represents a feature which has since been removed (it was once Active)
 170     Removed,
 171
 172     /// This language feature has since been Accepted (it was once Active)
 173     Accepted,
 174 }
 175
 176 // Attributes that have a special meaning to rustc or rustdoc
 177 pub const KNOWN_ATTRIBUTES: &'static [(&'static str, AttributeType)] = &[
 178     // Normal attributes
 179
 180     ("warn", Normal),
 181     ("allow", Normal),
 182     ("forbid", Normal),
 183     ("deny", Normal),
 184
 185     ("macro_reexport", Normal),
 186     ("macro_use", Normal),
 187     ("macro_export", Normal),
 188     ("plugin_registrar", Normal),
 189
 190     ("cfg", Normal),
 191     ("cfg_attr", Normal),
 192     ("main", Normal),
 193     ("start", Normal),
 194     ("test", Normal),
 195     ("bench", Normal),
 196     ("simd", Normal),
 197     ("repr", Normal),
 198     ("path", Normal),
 199     ("abi", Normal),
 200     ("automatically_derived", Normal),
 201     ("no_mangle", Normal),
 202     ("no_link", Normal),
 203     ("derive", Normal),
 204     ("should_panic", Normal),
 205     ("ignore", Normal),
 206     ("no_implicit_prelude", Normal),
 207     ("reexport_test_harness_main", Normal),
 208     ("link_args", Normal),
 209     ("macro_escape", Normal),
 210
 211     ("staged_api", Gated("staged_api",
 212                          "staged_api is for use by rustc only")),
 213     ("plugin", Gated("plugin",
 214                      "compiler plugins are experimental \
 215                       and possibly buggy")),
 216     ("no_std", Gated("no_std",
 217                      "no_std is experimental")),
 218     ("lang", Gated("lang_items",
 219                      "language items are subject to change")),
 220     ("linkage", Gated("linkage",
 221                       "the `linkage` attribute is experimental \
 222                        and not portable across platforms")),
 223     ("thread_local", Gated("thread_local",
 224                             "`#[thread_local]` is an experimental feature, and does not \
 225                              currently handle destructors. There is no corresponding \
 226                              `#[task_local]` mapping to the task model")),
 227
 228     ("rustc_on_unimplemented", Gated("on_unimplemented",
 229                                      "the `#[rustc_on_unimplemented]` attribute \
 230                                       is an experimental feature")),
 231     ("allocator", Gated("allocator",
 232                         "the `#[allocator]` attribute is an experimental feature")),
 233     ("rustc_variance", Gated("rustc_attrs",
 234                              "the `#[rustc_variance]` attribute \
 235                               is an experimental feature")),
 236     ("rustc_error", Gated("rustc_attrs",
 237                           "the `#[rustc_error]` attribute \
 238                            is an experimental feature")),
 239     ("rustc_move_fragments", Gated("rustc_attrs",
 240                                    "the `#[rustc_move_fragments]` attribute \
 241                                     is an experimental feature")),
 242
 243     ("allow_internal_unstable", Gated("allow_internal_unstable",
 244                                       EXPLAIN_ALLOW_INTERNAL_UNSTABLE)),
 245
 246     ("fundamental", Gated("fundamental",
 247                           "the `#[fundamental]` attribute \
 248                            is an experimental feature")),
 249
 250     // FIXME: #14408 whitelist docs since rustdoc looks at them
 251     ("doc", Whitelisted),
 252
 253     // FIXME: #14406 these are processed in trans, which happens after the
 254     // lint pass
 255     ("cold", Whitelisted),
 256     ("export_name", Whitelisted),
 257     ("inline", Whitelisted),
 258     ("link", Whitelisted),
 259     ("link_name", Whitelisted),
 260     ("link_section", Whitelisted),
 261     ("no_builtins", Whitelisted),
 262     ("no_mangle", Whitelisted),
 263     ("no_stack_check", Whitelisted),
 264     ("static_assert", Gated("static_assert",
 265                             "`#[static_assert]` is an experimental feature, and has a poor API")),
 266     ("no_debug", Whitelisted),
 267     ("omit_gdb_pretty_printer_section", Whitelisted),
 268     ("unsafe_no_drop_flag", Gated("unsafe_no_drop_flag",
 269                                   "unsafe_no_drop_flag has unstable semantics \
 270                                    and may be removed in the future")),
 271
 272     // used in resolve
 273     ("prelude_import", Whitelisted),
 274
 275     // FIXME: #14407 these are only looked at on-demand so we can't
 276     // guarantee they'll have already been checked
 277     ("deprecated", Whitelisted),
 278     ("must_use", Whitelisted),
 279     ("stable", Whitelisted),
 280     ("unstable", Whitelisted),
 281
 282     ("rustc_paren_sugar", Gated("unboxed_closures",
 283                                 "unboxed_closures are still evolving")),
 284     ("rustc_reflect_like", Gated("reflect",
 285                                  "defining reflective traits is still evolving")),
 286
 287     // Crate level attributes
 288     ("crate_name", CrateLevel),
 289     ("crate_type", CrateLevel),
 290     ("crate_id", CrateLevel),
 291     ("feature", CrateLevel),
 292     ("no_start", CrateLevel),
 293     ("no_main", CrateLevel),
 294     ("no_builtins", CrateLevel),
 295     ("recursion_limit", CrateLevel),
 296 ];
 297
 298 #[derive(PartialEq, Copy, Clone, Debug)]
 299 pub enum AttributeType {
 300     /// Normal, builtin attribute that is consumed
 301     /// by the compiler before the unused_attribute check
 302     Normal,
 303
 304     /// Builtin attribute that may not be consumed by the compiler
 305     /// before the unused_attribute check. These attributes
 306     /// will be ignored by the unused_attribute lint
 307     Whitelisted,
 308
 309     /// Is gated by a given feature gate and reason
 310     /// These get whitelisted too
 311     Gated(&'static str, &'static str),
 312
 313     /// Builtin attribute that is only allowed at the crate level
 314     CrateLevel,
 315 }
 316
 317 /// A set of features to be used by later passes.
 318 pub struct Features {
 319     pub unboxed_closures: bool,
 320     pub rustc_diagnostic_macros: bool,
 321     pub visible_private_types: bool,
 322     pub allow_quote: bool,
 323     pub allow_asm: bool,
 324     pub allow_log_syntax: bool,
 325     pub allow_concat_idents: bool,
 326     pub allow_trace_macros: bool,
 327     pub allow_internal_unstable: bool,
 328     pub allow_custom_derive: bool,
 329     pub simd_ffi: bool,
 330     pub unmarked_api: bool,
 331     pub negate_unsigned: bool,
 332     /// spans of #![feature] attrs for stable language features. for error reporting
 333     pub declared_stable_lang_features: Vec<Span>,
 334     /// #![feature] attrs for non-language (library) features
 335     pub declared_lib_features: Vec<(InternedString, Span)>,
 336     pub const_fn: bool,
 337 }
 338
 339 impl Features {
 340     pub fn new() -> Features {
 341         Features {
 342             unboxed_closures: false,
 343             rustc_diagnostic_macros: false,
 344             visible_private_types: false,
 345             allow_quote: false,
 346             allow_asm: false,
 347             allow_log_syntax: false,
 348             allow_concat_idents: false,
 349             allow_trace_macros: false,
 350             allow_internal_unstable: false,
 351             allow_custom_derive: false,
 352             simd_ffi: false,
 353             unmarked_api: false,
 354             negate_unsigned: false,
 355             declared_stable_lang_features: Vec::new(),
 356             declared_lib_features: Vec::new(),
 357             const_fn: false,
 358         }
 359     }
 360 }
 361
 362 struct Context<'a> {
 363     features: Vec<&'static str>,
 364     span_handler: &'a SpanHandler,
 365     cm: &'a CodeMap,
 366     plugin_attributes: &'a [(String, AttributeType)],
 367 }
 368
 369 impl<'a> Context<'a> {
 370     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
 371         let has_feature = self.has_feature(feature);
 372         debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", feature, span, has_feature);
 373         if !has_feature {
 374             emit_feature_err(self.span_handler, feature, span, explain);
 375         }
 376     }
 377     fn has_feature(&self, feature: &str) -> bool {
 378         self.features.iter().any(|&n| n == feature)
 379     }
 380
 381     fn check_attribute(&self, attr: &ast::Attribute, is_macro: bool) {
 382         debug!("check_attribute(attr = {:?})", attr);
 383         let name = &*attr.name();
 384         for &(n, ty) in KNOWN_ATTRIBUTES {
 385             if n == name {
 386                 if let Gated(gate, desc) = ty {
 387                     self.gate_feature(gate, attr.span, desc);
 388                 }
 389                 debug!("check_attribute: {:?} is known, {:?}", name, ty);
 390                 return;
 391             }
 392         }
 393         for &(ref n, ref ty) in self.plugin_attributes.iter() {
 394             if &*n == name {
 395                 // Plugins can't gate attributes, so we don't check for it
 396                 // unlike the code above; we only use this loop to
 397                 // short-circuit to avoid the checks below
 398                 debug!("check_attribute: {:?} is registered by a plugin, {:?}", name, ty);
 399                 return;
 400             }
 401         }
 402         if name.starts_with("rustc_") {
 403             self.gate_feature("rustc_attrs", attr.span,
 404                               "unless otherwise specified, attributes \
 405                                with the prefix `rustc_` \
 406                                are reserved for internal compiler diagnostics");
 407         } else if name.starts_with("derive_") {
 408             self.gate_feature("custom_derive", attr.span,
 409                               "attributes of the form `#[derive_*]` are reserved \
 410                                for the compiler");
 411         } else {
 412             // Only run the custom attribute lint during regular
 413             // feature gate checking. Macro gating runs
 414             // before the plugin attributes are registered
 415             // so we skip this then
 416             if !is_macro {
 417                 self.gate_feature("custom_attribute", attr.span,
 418                            &format!("The attribute `{}` is currently \
 419                                     unknown to the compiler and \
 420                                     may have meaning \
 421                                     added to it in the future",
 422                                     name));
 423             }
 424         }
 425     }
 426 }
 427
 428 pub fn emit_feature_err(diag: &SpanHandler, feature: &str, span: Span, explain: &str) {
 429     diag.span_err(span, explain);
 430
 431     // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
 432     if option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some() { return; }
 433     diag.fileline_help(span, &format!("add #![feature({})] to the \
 434                                    crate attributes to enable",
 435                                   feature));
 436 }
 437
 438 pub fn emit_feature_warn(diag: &SpanHandler, feature: &str, span: Span, explain: &str) {
 439     diag.span_warn(span, explain);
 440
 441     // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
 442     if option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some() { return; }
 443     if diag.handler.can_emit_warnings {
 444         diag.fileline_help(span, &format!("add #![feature({})] to the \
 445                                        crate attributes to silence this warning",
 446                                       feature));
 447     }
 448 }
 449
 450 pub const EXPLAIN_ASM: &'static str =
 451     "inline assembly is not stable enough for use and is subject to change";
 452
 453 pub const EXPLAIN_LOG_SYNTAX: &'static str =
 454     "`log_syntax!` is not stable enough for use and is subject to change";
 455
 456 pub const EXPLAIN_CONCAT_IDENTS: &'static str =
 457     "`concat_idents` is not stable enough for use and is subject to change";
 458
 459 pub const EXPLAIN_TRACE_MACROS: &'static str =
 460     "`trace_macros` is not stable enough for use and is subject to change";
 461 pub const EXPLAIN_ALLOW_INTERNAL_UNSTABLE: &'static str =
 462     "allow_internal_unstable side-steps feature gating and stability checks";
 463
 464 pub const EXPLAIN_CUSTOM_DERIVE: &'static str =
 465     "`#[derive]` for custom traits is not stable enough for use and is subject to change";
 466
 467 struct MacroVisitor<'a> {
 468     context: &'a Context<'a>
 469 }
 470
 471 impl<'a, 'v> Visitor<'v> for MacroVisitor<'a> {
 472     fn visit_mac(&mut self, mac: &ast::Mac) {
 473         let ast::MacInvocTT(ref path, _, _) = mac.node;
 474         let id = path.segments.last().unwrap().identifier;
 475
 476         // Issue 22234: If you add a new case here, make sure to also
 477         // add code to catch the macro during or after expansion.
 478         //
 479         // We still keep this MacroVisitor (rather than *solely*
 480         // relying on catching cases during or after expansion) to
 481         // catch uses of these macros within conditionally-compiled
 482         // code, e.g. `#[cfg]`-guarded functions.
 483
 484         if id == token::str_to_ident("asm") {
 485             self.context.gate_feature("asm", path.span, EXPLAIN_ASM);
 486         }
 487
 488         else if id == token::str_to_ident("log_syntax") {
 489             self.context.gate_feature("log_syntax", path.span, EXPLAIN_LOG_SYNTAX);
 490         }
 491
 492         else if id == token::str_to_ident("trace_macros") {
 493             self.context.gate_feature("trace_macros", path.span, EXPLAIN_TRACE_MACROS);
 494         }
 495
 496         else if id == token::str_to_ident("concat_idents") {
 497             self.context.gate_feature("concat_idents", path.span, EXPLAIN_CONCAT_IDENTS);
 498         }
 499     }
 500
 501     fn visit_attribute(&mut self, attr: &'v ast::Attribute) {
 502         self.context.check_attribute(attr, true);
 503     }
 504 }
 505
 506 struct PostExpansionVisitor<'a> {
 507     context: &'a Context<'a>
 508 }
 509
 510 impl<'a> PostExpansionVisitor<'a> {
 511     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
 512         if !self.context.cm.span_allows_unstable(span) {
 513             self.context.gate_feature(feature, span, explain)
 514         }
 515     }
 516 }
 517
 518 impl<'a, 'v> Visitor<'v> for PostExpansionVisitor<'a> {
 519     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 520         if !self.context.cm.span_allows_unstable(attr.span) {
 521             self.context.check_attribute(attr, false);
 522         }
 523     }
 524
 525     fn visit_name(&mut self, sp: Span, name: ast::Name) {
 526         if !token::get_name(name).is_ascii() {
 527             self.gate_feature("non_ascii_idents", sp,
 528                               "non-ascii idents are not fully supported.");
 529         }
 530     }
 531
 532     fn visit_item(&mut self, i: &ast::Item) {
 533         match i.node {
 534             ast::ItemExternCrate(_) => {
 535                 if attr::contains_name(&i.attrs[..], "macro_reexport") {
 536                     self.gate_feature("macro_reexport", i.span,
 537                                       "macros reexports are experimental \
 538                                        and possibly buggy");
 539                 }
 540             }
 541
 542             ast::ItemForeignMod(ref foreign_module) => {
 543                 if attr::contains_name(&i.attrs[..], "link_args") {
 544                     self.gate_feature("link_args", i.span,
 545                                       "the `link_args` attribute is not portable \
 546                                        across platforms, it is recommended to \
 547                                        use `#[link(name = \"foo\")]` instead")
 548                 }
 549                 if foreign_module.abi == Abi::RustIntrinsic {
 550                     self.gate_feature("intrinsics",
 551                                       i.span,
 552                                       "intrinsics are subject to change")
 553                 }
 554             }
 555
 556             ast::ItemFn(..) => {
 557                 if attr::contains_name(&i.attrs[..], "plugin_registrar") {
 558                     self.gate_feature("plugin_registrar", i.span,
 559                                       "compiler plugins are experimental and possibly buggy");
 560                 }
 561                 if attr::contains_name(&i.attrs[..], "start") {
 562                     self.gate_feature("start", i.span,
 563                                       "a #[start] function is an experimental \
 564                                        feature whose signature may change \
 565                                        over time");
 566                 }
 567                 if attr::contains_name(&i.attrs[..], "main") {
 568                     self.gate_feature("main", i.span,
 569                                       "declaration of a nonstandard #[main] \
 570                                        function may change over time, for now \
 571                                        a top-level `fn main()` is required");
 572                 }
 573             }
 574
 575             ast::ItemStruct(..) => {
 576                 if attr::contains_name(&i.attrs[..], "simd") {
 577                     self.gate_feature("simd", i.span,
 578                                       "SIMD types are experimental and possibly buggy");
 579                 }
 580             }
 581
 582             ast::ItemDefaultImpl(..) => {
 583                 self.gate_feature("optin_builtin_traits",
 584                                   i.span,
 585                                   "default trait implementations are experimental \
 586                                    and possibly buggy");
 587             }
 588
 589             ast::ItemImpl(_, polarity, _, _, _, _) => {
 590                 match polarity {
 591                     ast::ImplPolarity::Negative => {
 592                         self.gate_feature("optin_builtin_traits",
 593                                           i.span,
 594                                           "negative trait bounds are not yet fully implemented; \
 595                                           use marker types for now");
 596                     },
 597                     _ => {}
 598                 }
 599             }
 600
 601             _ => {}
 602         }
 603
 604         visit::walk_item(self, i);
 605     }
 606
 607     fn visit_foreign_item(&mut self, i: &ast::ForeignItem) {
 608         let links_to_llvm = match attr::first_attr_value_str_by_name(&i.attrs,
 609                                                                      "link_name") {
 610             Some(val) => val.starts_with("llvm."),
 611             _ => false
 612         };
 613         if links_to_llvm {
 614             self.gate_feature("link_llvm_intrinsics", i.span,
 615                               "linking to LLVM intrinsics is experimental");
 616         }
 617
 618         visit::walk_foreign_item(self, i)
 619     }
 620
 621     fn visit_expr(&mut self, e: &ast::Expr) {
 622         match e.node {
 623             ast::ExprBox(..) | ast::ExprUnary(ast::UnOp::UnUniq, _) => {
 624                 self.gate_feature("box_syntax",
 625                                   e.span,
 626                                   "box expression syntax is experimental; \
 627                                    you can call `Box::new` instead.");
 628             }
 629             _ => {}
 630         }
 631         visit::walk_expr(self, e);
 632     }
 633
 634     fn visit_pat(&mut self, pattern: &ast::Pat) {
 635         match pattern.node {
 636             ast::PatVec(_, Some(_), ref last) if !last.is_empty() => {
 637                 self.gate_feature("advanced_slice_patterns",
 638                                   pattern.span,
 639                                   "multiple-element slice matches anywhere \
 640                                    but at the end of a slice (e.g. \
 641                                    `[0, ..xs, 0]`) are experimental")
 642             }
 643             ast::PatVec(..) => {
 644                 self.gate_feature("slice_patterns",
 645                                   pattern.span,
 646                                   "slice pattern syntax is experimental");
 647             }
 648             ast::PatBox(..) => {
 649                 self.gate_feature("box_patterns",
 650                                   pattern.span,
 651                                   "box pattern syntax is experimental");
 652             }
 653             _ => {}
 654         }
 655         visit::walk_pat(self, pattern)
 656     }
 657
 658     fn visit_fn(&mut self,
 659                 fn_kind: visit::FnKind<'v>,
 660                 fn_decl: &'v ast::FnDecl,
 661                 block: &'v ast::Block,
 662                 span: Span,
 663                 _node_id: NodeId) {
 664         // check for const fn declarations
 665         match fn_kind {
 666             visit::FkItemFn(_, _, _, ast::Constness::Const, _, _) => {
 667                 self.gate_feature("const_fn", span, "const fn is unstable");
 668             }
 669             _ => {
 670                 // stability of const fn methods are covered in
 671                 // visit_trait_item and visit_impl_item below; this is
 672                 // because default methods don't pass through this
 673                 // point.
 674             }
 675         }
 676
 677         match fn_kind {
 678             visit::FkItemFn(_, _, _, _, abi, _) if abi == Abi::RustIntrinsic => {
 679                 self.gate_feature("intrinsics",
 680                                   span,
 681                                   "intrinsics are subject to change")
 682             }
 683             visit::FkItemFn(_, _, _, _, abi, _) |
 684             visit::FkMethod(_, &ast::MethodSig { abi, .. }, _) if abi == Abi::RustCall => {
 685                 self.gate_feature("unboxed_closures",
 686                                   span,
 687                                   "rust-call ABI is subject to change")
 688             }
 689             _ => {}
 690         }
 691         visit::walk_fn(self, fn_kind, fn_decl, block, span);
 692     }
 693
 694     fn visit_trait_item(&mut self, ti: &'v ast::TraitItem) {
 695         match ti.node {
 696             ast::ConstTraitItem(..) => {
 697                 self.gate_feature("associated_consts",
 698                                   ti.span,
 699                                   "associated constants are experimental")
 700             }
 701             ast::MethodTraitItem(ref sig, _) => {
 702                 if sig.constness == ast::Constness::Const {
 703                     self.gate_feature("const_fn", ti.span, "const fn is unstable");
 704                 }
 705             }
 706             _ => {}
 707         }
 708         visit::walk_trait_item(self, ti);
 709     }
 710
 711     fn visit_impl_item(&mut self, ii: &'v ast::ImplItem) {
 712         match ii.node {
 713             ast::ConstImplItem(..) => {
 714                 self.gate_feature("associated_consts",
 715                                   ii.span,
 716                                   "associated constants are experimental")
 717             }
 718             ast::MethodImplItem(ref sig, _) => {
 719                 if sig.constness == ast::Constness::Const {
 720                     self.gate_feature("const_fn", ii.span, "const fn is unstable");
 721                 }
 722             }
 723             _ => {}
 724         }
 725         visit::walk_impl_item(self, ii);
 726     }
 727 }
 728
 729 fn check_crate_inner<F>(cm: &CodeMap, span_handler: &SpanHandler,
 730                         krate: &ast::Crate,
 731                         plugin_attributes: &[(String, AttributeType)],
 732                         check: F)
 733                        -> Features
 734     where F: FnOnce(&mut Context, &ast::Crate)
 735 {
 736     let mut cx = Context {
 737         features: Vec::new(),
 738         span_handler: span_handler,
 739         cm: cm,
 740         plugin_attributes: plugin_attributes,
 741     };
 742
 743     let mut accepted_features = Vec::new();
 744     let mut unknown_features = Vec::new();
 745
 746     for attr in &krate.attrs {
 747         if !attr.check_name("feature") {
 748             continue
 749         }
 750
 751         match attr.meta_item_list() {
 752             None => {
 753                 span_handler.span_err(attr.span, "malformed feature attribute, \
 754                                                   expected #![feature(...)]");
 755             }
 756             Some(list) => {
 757                 for mi in list {
 758                     let name = match mi.node {
 759                         ast::MetaWord(ref word) => (*word).clone(),
 760                         _ => {
 761                             span_handler.span_err(mi.span,
 762                                                   "malformed feature, expected just \
 763                                                    one word");
 764                             continue
 765                         }
 766                     };
 767                     match KNOWN_FEATURES.iter()
 768                                         .find(|& &(n, _, _)| name == n) {
 769                         Some(&(name, _, Active)) => {
 770                             cx.features.push(name);
 771                         }
 772                         Some(&(_, _, Removed)) => {
 773                             span_handler.span_err(mi.span, "feature has been removed");
 774                         }
 775                         Some(&(_, _, Accepted)) => {
 776                             accepted_features.push(mi.span);
 777                         }
 778                         None => {
 779                             unknown_features.push((name, mi.span));
 780                         }
 781                     }
 782                 }
 783             }
 784         }
 785     }
 786
 787     check(&mut cx, krate);
 788
 789     // FIXME (pnkfelix): Before adding the 99th entry below, change it
 790     // to a single-pass (instead of N calls to `.has_feature`).
 791
 792     Features {
 793         unboxed_closures: cx.has_feature("unboxed_closures"),
 794         rustc_diagnostic_macros: cx.has_feature("rustc_diagnostic_macros"),
 795         visible_private_types: cx.has_feature("visible_private_types"),
 796         allow_quote: cx.has_feature("quote"),
 797         allow_asm: cx.has_feature("asm"),
 798         allow_log_syntax: cx.has_feature("log_syntax"),
 799         allow_concat_idents: cx.has_feature("concat_idents"),
 800         allow_trace_macros: cx.has_feature("trace_macros"),
 801         allow_internal_unstable: cx.has_feature("allow_internal_unstable"),
 802         allow_custom_derive: cx.has_feature("custom_derive"),
 803         simd_ffi: cx.has_feature("simd_ffi"),
 804         unmarked_api: cx.has_feature("unmarked_api"),
 805         negate_unsigned: cx.has_feature("negate_unsigned"),
 806         declared_stable_lang_features: accepted_features,
 807         declared_lib_features: unknown_features,
 808         const_fn: cx.has_feature("const_fn"),
 809     }
 810 }
 811
 812 pub fn check_crate_macros(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate)
 813 -> Features {
 814     check_crate_inner(cm, span_handler, krate, &[] as &'static [_],
 815                       |ctx, krate| visit::walk_crate(&mut MacroVisitor { context: ctx }, krate))
 816 }
 817
 818 pub fn check_crate(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate,
 819                    plugin_attributes: &[(String, AttributeType)]) -> Features
 820 {
 821     check_crate_inner(cm, span_handler, krate, plugin_attributes,
 822                       |ctx, krate| visit::walk_crate(&mut PostExpansionVisitor { context: ctx },
 823                                                      krate))
 824 }