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 use self::Status::*;
  25
  26 use abi::RustIntrinsic;
  27 use ast::NodeId;
  28 use ast;
  29 use attr;
  30 use attr::AttrMetaMethods;
  31 use codemap::{CodeMap, Span};
  32 use diagnostic::SpanHandler;
  33 use visit;
  34 use visit::Visitor;
  35 use parse::token::{self, InternedString};
  36
  37 use std::slice;
  38 use std::ascii::AsciiExt;
  39
  40 // If you change this list without updating src/doc/reference.md, @cmr will be sad
  41 // Don't ever remove anything from this list; set them to 'Removed'.
  42 // The version numbers here correspond to the version in which the current status
  43 // was set. This is most important for knowing when a particular feature became
  44 // stable (active).
  45 // NB: The featureck.py script parses this information directly out of the source
  46 // so take care when modifying it.
  47 static KNOWN_FEATURES: &'static [(&'static str, &'static str, Status)] = &[
  48     ("globs", "1.0.0", Accepted),
  49     ("macro_rules", "1.0.0", Accepted),
  50     ("struct_variant", "1.0.0", Accepted),
  51     ("asm", "1.0.0", Active),
  52     ("managed_boxes", "1.0.0", Removed),
  53     ("non_ascii_idents", "1.0.0", Active),
  54     ("thread_local", "1.0.0", Active),
  55     ("link_args", "1.0.0", Active),
  56     ("phase", "1.0.0", Removed),
  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     ("unsafe_destructor", "1.0.0", Active),
  62     ("intrinsics", "1.0.0", Active),
  63     ("lang_items", "1.0.0", Active),
  64
  65     ("simd", "1.0.0", Active),
  66     ("default_type_params", "1.0.0", Accepted),
  67     ("quote", "1.0.0", Active),
  68     ("link_llvm_intrinsics", "1.0.0", Active),
  69     ("linkage", "1.0.0", Active),
  70     ("struct_inherit", "1.0.0", Removed),
  71
  72     ("quad_precision_float", "1.0.0", Removed),
  73
  74     ("rustc_diagnostic_macros", "1.0.0", Active),
  75     ("unboxed_closures", "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", Active),
  82     ("box_syntax", "1.0.0", Active),
  83     ("on_unimplemented", "1.0.0", Active),
  84     ("simd_ffi", "1.0.0", Active),
  85
  86     ("if_let", "1.0.0", Accepted),
  87     ("while_let", "1.0.0", Accepted),
  88
  89     ("plugin", "1.0.0", Active),
  90     ("start", "1.0.0", Active),
  91     ("main", "1.0.0", Active),
  92
  93     // A temporary feature gate used to enable parser extensions needed
  94     // to bootstrap fix for #5723.
  95     ("issue_5723_bootstrap", "1.0.0", Accepted),
  96
  97     // A way to temporarily opt out of opt in copy. This will *never* be accepted.
  98     ("opt_out_copy", "1.0.0", Removed),
  99
 100     // A way to temporarily opt out of the new orphan rules. This will *never* be accepted.
 101     ("old_orphan_check", "1.0.0", Deprecated),
 102
 103     // A way to temporarily opt out of the new impl rules. This will *never* be accepted.
 104     ("old_impl_check", "1.0.0", Deprecated),
 105
 106     // OIBIT specific features
 107     ("optin_builtin_traits", "1.0.0", Active),
 108
 109     // int and uint are now deprecated
 110     ("int_uint", "1.0.0", Active),
 111
 112     // macro reexport needs more discusion and stabilization
 113     ("macro_reexport", "1.0.0", Active),
 114
 115     // These are used to test this portion of the compiler, they don't actually
 116     // mean anything
 117     ("test_accepted_feature", "1.0.0", Accepted),
 118     ("test_removed_feature", "1.0.0", Removed),
 119
 120     // Allows use of #[staged_api]
 121     ("staged_api", "1.0.0", Active),
 122
 123     // Allows using items which are missing stability attributes
 124     ("unmarked_api", "1.0.0", Active)
 125 ];
 126
 127 enum Status {
 128     /// Represents an active feature that is currently being implemented or
 129     /// currently being considered for addition/removal.
 130     Active,
 131
 132     /// Represents a feature gate that is temporarily enabling deprecated behavior.
 133     /// This gate will never be accepted.
 134     Deprecated,
 135
 136     /// Represents a feature which has since been removed (it was once Active)
 137     Removed,
 138
 139     /// This language feature has since been Accepted (it was once Active)
 140     Accepted,
 141 }
 142
 143 /// A set of features to be used by later passes.
 144 pub struct Features {
 145     pub unboxed_closures: bool,
 146     pub rustc_diagnostic_macros: bool,
 147     pub visible_private_types: bool,
 148     pub quote: bool,
 149     pub old_orphan_check: bool,
 150     pub simd_ffi: bool,
 151     pub unmarked_api: bool,
 152     pub lib_features: Vec<(InternedString, Span)>
 153 }
 154
 155 impl Features {
 156     pub fn new() -> Features {
 157         Features {
 158             unboxed_closures: false,
 159             rustc_diagnostic_macros: false,
 160             visible_private_types: false,
 161             quote: false,
 162             old_orphan_check: false,
 163             simd_ffi: false,
 164             unmarked_api: false,
 165             lib_features: Vec::new()
 166         }
 167     }
 168 }
 169
 170 struct Context<'a> {
 171     features: Vec<&'static str>,
 172     span_handler: &'a SpanHandler,
 173     cm: &'a CodeMap,
 174 }
 175
 176 impl<'a> Context<'a> {
 177     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
 178         if !self.has_feature(feature) {
 179             emit_feature_err(self.span_handler, feature, span, explain);
 180         }
 181     }
 182
 183     fn warn_feature(&self, feature: &str, span: Span, explain: &str) {
 184         if !self.has_feature(feature) {
 185             emit_feature_warn(self.span_handler, feature, span, explain);
 186         }
 187     }
 188     fn has_feature(&self, feature: &str) -> bool {
 189         self.features.iter().any(|&n| n == feature)
 190     }
 191 }
 192
 193 pub fn emit_feature_err(diag: &SpanHandler, feature: &str, span: Span, explain: &str) {
 194     diag.span_err(span, explain);
 195     diag.span_help(span, &format!("add #![feature({})] to the \
 196                                    crate attributes to enable",
 197                                   feature)[]);
 198 }
 199
 200 pub fn emit_feature_warn(diag: &SpanHandler, feature: &str, span: Span, explain: &str) {
 201     diag.span_warn(span, explain);
 202     if diag.handler.can_emit_warnings {
 203         diag.span_help(span, &format!("add #![feature({})] to the \
 204                                        crate attributes to silence this warning",
 205                                       feature)[]);
 206     }
 207 }
 208
 209 struct MacroVisitor<'a> {
 210     context: &'a Context<'a>
 211 }
 212
 213 impl<'a, 'v> Visitor<'v> for MacroVisitor<'a> {
 214     fn visit_mac(&mut self, mac: &ast::Mac) {
 215         let ast::MacInvocTT(ref path, _, _) = mac.node;
 216         let id = path.segments.last().unwrap().identifier;
 217
 218         if id == token::str_to_ident("asm") {
 219             self.context.gate_feature("asm", path.span, "inline assembly is not \
 220                 stable enough for use and is subject to change");
 221         }
 222
 223         else if id == token::str_to_ident("log_syntax") {
 224             self.context.gate_feature("log_syntax", path.span, "`log_syntax!` is not \
 225                 stable enough for use and is subject to change");
 226         }
 227
 228         else if id == token::str_to_ident("trace_macros") {
 229             self.context.gate_feature("trace_macros", path.span, "`trace_macros` is not \
 230                 stable enough for use and is subject to change");
 231         }
 232
 233         else if id == token::str_to_ident("concat_idents") {
 234             self.context.gate_feature("concat_idents", path.span, "`concat_idents` is not \
 235                 stable enough for use and is subject to change");
 236         }
 237     }
 238 }
 239
 240 struct PostExpansionVisitor<'a> {
 241     context: &'a Context<'a>
 242 }
 243
 244 impl<'a> PostExpansionVisitor<'a> {
 245     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
 246         if !self.context.cm.span_is_internal(span) {
 247             self.context.gate_feature(feature, span, explain)
 248         }
 249     }
 250 }
 251
 252 impl<'a, 'v> Visitor<'v> for PostExpansionVisitor<'a> {
 253     fn visit_name(&mut self, sp: Span, name: ast::Name) {
 254         if !token::get_name(name).get().is_ascii() {
 255             self.gate_feature("non_ascii_idents", sp,
 256                               "non-ascii idents are not fully supported.");
 257         }
 258     }
 259
 260     fn visit_item(&mut self, i: &ast::Item) {
 261         for attr in &i.attrs {
 262             if attr.name() == "thread_local" {
 263                 self.gate_feature("thread_local", i.span,
 264                                   "`#[thread_local]` is an experimental feature, and does not \
 265                                   currently handle destructors. There is no corresponding \
 266                                   `#[task_local]` mapping to the task model");
 267             } else if attr.name() == "linkage" {
 268                 self.gate_feature("linkage", i.span,
 269                                   "the `linkage` attribute is experimental \
 270                                    and not portable across platforms")
 271             } else if attr.name() == "rustc_on_unimplemented" {
 272                 self.gate_feature("on_unimplemented", i.span,
 273                                   "the `#[rustc_on_unimplemented]` attribute \
 274                                   is an experimental feature")
 275             }
 276         }
 277         match i.node {
 278             ast::ItemExternCrate(_) => {
 279                 if attr::contains_name(&i.attrs[], "plugin") {
 280                     self.gate_feature("plugin", i.span,
 281                                       "compiler plugins are experimental \
 282                                        and possibly buggy");
 283                 } else if attr::contains_name(&i.attrs[], "macro_reexport") {
 284                     self.gate_feature("macro_reexport", i.span,
 285                                       "macros reexports are experimental \
 286                                        and possibly buggy");
 287                 }
 288             }
 289
 290             ast::ItemForeignMod(ref foreign_module) => {
 291                 if attr::contains_name(&i.attrs[], "link_args") {
 292                     self.gate_feature("link_args", i.span,
 293                                       "the `link_args` attribute is not portable \
 294                                        across platforms, it is recommended to \
 295                                        use `#[link(name = \"foo\")]` instead")
 296                 }
 297                 if foreign_module.abi == RustIntrinsic {
 298                     self.gate_feature("intrinsics",
 299                                       i.span,
 300                                       "intrinsics are subject to change")
 301                 }
 302             }
 303
 304             ast::ItemFn(..) => {
 305                 if attr::contains_name(&i.attrs[], "plugin_registrar") {
 306                     self.gate_feature("plugin_registrar", i.span,
 307                                       "compiler plugins are experimental and possibly buggy");
 308                 }
 309                 if attr::contains_name(&i.attrs[], "start") {
 310                     self.gate_feature("start", i.span,
 311                                       "a #[start] function is an experimental \
 312                                        feature whose signature may change \
 313                                        over time");
 314                 }
 315                 if attr::contains_name(&i.attrs[], "main") {
 316                     self.gate_feature("main", i.span,
 317                                       "declaration of a nonstandard #[main] \
 318                                        function may change over time, for now \
 319                                        a top-level `fn main()` is required");
 320                 }
 321             }
 322
 323             ast::ItemStruct(..) => {
 324                 if attr::contains_name(&i.attrs[], "simd") {
 325                     self.gate_feature("simd", i.span,
 326                                       "SIMD types are experimental and possibly buggy");
 327                 }
 328             }
 329
 330             ast::ItemImpl(_, polarity, _, _, _, _) => {
 331                 match polarity {
 332                     ast::ImplPolarity::Negative => {
 333                         self.gate_feature("optin_builtin_traits",
 334                                           i.span,
 335                                           "negative trait bounds are not yet fully implemented; \
 336                                           use marker types for now");
 337                     },
 338                     _ => {}
 339                 }
 340
 341                 if attr::contains_name(i.attrs.as_slice(),
 342                                        "unsafe_destructor") {
 343                     self.gate_feature("unsafe_destructor",
 344                                       i.span,
 345                                       "`#[unsafe_destructor]` allows too \
 346                                        many unsafe patterns and may be \
 347                                        removed in the future");
 348                 }
 349
 350                 if attr::contains_name(&i.attrs[],
 351                                        "old_orphan_check") {
 352                     self.gate_feature(
 353                         "old_orphan_check",
 354                         i.span,
 355                         "the new orphan check rules will eventually be strictly enforced");
 356                 }
 357
 358                 if attr::contains_name(&i.attrs[],
 359                                        "old_impl_check") {
 360                     self.gate_feature("old_impl_check",
 361                                       i.span,
 362                                       "`#[old_impl_check]` will be removed in the future");
 363                 }
 364             }
 365
 366             _ => {}
 367         }
 368
 369         visit::walk_item(self, i);
 370     }
 371
 372     fn visit_foreign_item(&mut self, i: &ast::ForeignItem) {
 373         if attr::contains_name(&i.attrs[], "linkage") {
 374             self.gate_feature("linkage", i.span,
 375                               "the `linkage` attribute is experimental \
 376                                and not portable across platforms")
 377         }
 378
 379         let links_to_llvm = match attr::first_attr_value_str_by_name(i.attrs.as_slice(),
 380                                                                      "link_name") {
 381             Some(val) => val.get().starts_with("llvm."),
 382             _ => false
 383         };
 384         if links_to_llvm {
 385             self.gate_feature("link_llvm_intrinsics", i.span,
 386                               "linking to LLVM intrinsics is experimental");
 387         }
 388
 389         visit::walk_foreign_item(self, i)
 390     }
 391
 392     fn visit_ty(&mut self, t: &ast::Ty) {
 393         match t.node {
 394             ast::TyPath(ref p, _) => {
 395                 match &*p.segments {
 396
 397                     [ast::PathSegment { identifier, .. }] => {
 398                         let name = token::get_ident(identifier);
 399                         let msg = if name == "int" {
 400                             Some("the `int` type is deprecated; \
 401                                   use `isize` or a fixed-sized integer")
 402                         } else if name == "uint" {
 403                             Some("the `uint` type is deprecated; \
 404                                   use `usize` or a fixed-sized integer")
 405                         } else {
 406                             None
 407                         };
 408
 409                         if let Some(msg) = msg {
 410                             self.context.warn_feature("int_uint", t.span, msg)
 411                         }
 412                     }
 413                     _ => {}
 414                 }
 415             }
 416             _ => {}
 417         }
 418         visit::walk_ty(self, t);
 419     }
 420
 421     fn visit_expr(&mut self, e: &ast::Expr) {
 422         match e.node {
 423             ast::ExprBox(..) | ast::ExprUnary(ast::UnOp::UnUniq, _) => {
 424                 self.gate_feature("box_syntax",
 425                                   e.span,
 426                                   "box expression syntax is experimental in alpha release; \
 427                                    you can call `Box::new` instead.");
 428             }
 429             ast::ExprLit(ref lit) => {
 430                 match lit.node {
 431                     ast::LitInt(_, ty) => {
 432                         let msg = if let ast::SignedIntLit(ast::TyIs(true), _) = ty {
 433                             Some("the `i` suffix on integers is deprecated; use `is` \
 434                                   or one of the fixed-sized suffixes")
 435                         } else if let ast::UnsignedIntLit(ast::TyUs(true)) = ty {
 436                             Some("the `u` suffix on integers is deprecated; use `us` \
 437                                  or one of the fixed-sized suffixes")
 438                         } else {
 439                             None
 440                         };
 441                         if let Some(msg) = msg {
 442                             self.context.warn_feature("int_uint", e.span, msg);
 443                         }
 444                     }
 445                     _ => {}
 446                 }
 447             }
 448             _ => {}
 449         }
 450         visit::walk_expr(self, e);
 451     }
 452
 453     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 454         if attr.check_name("staged_api") {
 455             self.gate_feature("staged_api", attr.span,
 456                               "staged_api is for use by rustc only");
 457         }
 458
 459         if attr::contains_name(slice::ref_slice(attr), "lang") {
 460             self.gate_feature("lang_items",
 461                               attr.span,
 462                               "language items are subject to change");
 463         }
 464     }
 465
 466     fn visit_pat(&mut self, pattern: &ast::Pat) {
 467         match pattern.node {
 468             ast::PatVec(_, Some(_), ref last) if !last.is_empty() => {
 469                 self.gate_feature("advanced_slice_patterns",
 470                                   pattern.span,
 471                                   "multiple-element slice matches anywhere \
 472                                    but at the end of a slice (e.g. \
 473                                    `[0, ..xs, 0]` are experimental")
 474             }
 475             ast::PatBox(..) => {
 476                 self.gate_feature("box_syntax",
 477                                   pattern.span,
 478                                   "box pattern syntax is experimental in alpha release");
 479             }
 480             _ => {}
 481         }
 482         visit::walk_pat(self, pattern)
 483     }
 484
 485     fn visit_fn(&mut self,
 486                 fn_kind: visit::FnKind<'v>,
 487                 fn_decl: &'v ast::FnDecl,
 488                 block: &'v ast::Block,
 489                 span: Span,
 490                 _node_id: NodeId) {
 491         match fn_kind {
 492             visit::FkItemFn(_, _, _, abi) if abi == RustIntrinsic => {
 493                 self.gate_feature("intrinsics",
 494                                   span,
 495                                   "intrinsics are subject to change")
 496             }
 497             _ => {}
 498         }
 499         visit::walk_fn(self, fn_kind, fn_decl, block, span);
 500     }
 501 }
 502
 503 fn check_crate_inner<F>(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate,
 504                         check: F)
 505                        -> Features
 506     where F: FnOnce(&mut Context, &ast::Crate)
 507 {
 508     let mut cx = Context {
 509         features: Vec::new(),
 510         span_handler: span_handler,
 511         cm: cm,
 512     };
 513
 514     let mut unknown_features = Vec::new();
 515
 516     for attr in &krate.attrs {
 517         if !attr.check_name("feature") {
 518             continue
 519         }
 520
 521         match attr.meta_item_list() {
 522             None => {
 523                 span_handler.span_err(attr.span, "malformed feature attribute, \
 524                                                   expected #![feature(...)]");
 525             }
 526             Some(list) => {
 527                 for mi in list {
 528                     let name = match mi.node {
 529                         ast::MetaWord(ref word) => (*word).clone(),
 530                         _ => {
 531                             span_handler.span_err(mi.span,
 532                                                   "malformed feature, expected just \
 533                                                    one word");
 534                             continue
 535                         }
 536                     };
 537                     match KNOWN_FEATURES.iter()
 538                                         .find(|& &(n, _, _)| name == n) {
 539                         Some(&(name, _, Active)) => {
 540                             cx.features.push(name);
 541                         }
 542                         Some(&(name, _, Deprecated)) => {
 543                             cx.features.push(name);
 544                             span_handler.span_warn(
 545                                 mi.span,
 546                                 "feature is deprecated and will only be available \
 547                                  for a limited time, please rewrite code that relies on it");
 548                         }
 549                         Some(&(_, _, Removed)) => {
 550                             span_handler.span_err(mi.span, "feature has been removed");
 551                         }
 552                         Some(&(_, _, Accepted)) => {
 553                             span_handler.span_warn(mi.span, "feature has been added to Rust, \
 554                                                              directive not necessary");
 555                         }
 556                         None => {
 557                             unknown_features.push((name, mi.span));
 558                         }
 559                     }
 560                 }
 561             }
 562         }
 563     }
 564
 565     check(&mut cx, krate);
 566
 567     Features {
 568         unboxed_closures: cx.has_feature("unboxed_closures"),
 569         rustc_diagnostic_macros: cx.has_feature("rustc_diagnostic_macros"),
 570         visible_private_types: cx.has_feature("visible_private_types"),
 571         quote: cx.has_feature("quote"),
 572         old_orphan_check: cx.has_feature("old_orphan_check"),
 573         simd_ffi: cx.has_feature("simd_ffi"),
 574         unmarked_api: cx.has_feature("unmarked_api"),
 575         lib_features: unknown_features
 576     }
 577 }
 578
 579 pub fn check_crate_macros(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate)
 580 -> Features {
 581     check_crate_inner(cm, span_handler, krate,
 582                       |ctx, krate| visit::walk_crate(&mut MacroVisitor { context: ctx }, krate))
 583 }
 584
 585 pub fn check_crate(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate)
 586 -> Features {
 587     check_crate_inner(cm, span_handler, krate,
 588                       |ctx, krate| visit::walk_crate(&mut PostExpansionVisitor { context: ctx },
 589                                                      krate))
 590 }
 591