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 use self::Status::*;
  21
  22 use abi::RustIntrinsic;
  23 use ast::NodeId;
  24 use ast;
  25 use attr;
  26 use attr::AttrMetaMethods;
  27 use codemap::{CodeMap, Span};
  28 use diagnostic::SpanHandler;
  29 use visit;
  30 use visit::Visitor;
  31 use parse::token;
  32
  33 use std::slice;
  34 use std::ascii::AsciiExt;
  35
  36
  37 // if you change this list without updating src/doc/reference.md, @cmr will be sad
  38 static KNOWN_FEATURES: &'static [(&'static str, Status)] = &[
  39     ("globs", Active),
  40     ("macro_rules", Active),
  41     ("struct_variant", Accepted),
  42     ("asm", Active),
  43     ("managed_boxes", Removed),
  44     ("non_ascii_idents", Active),
  45     ("thread_local", Active),
  46     ("link_args", Active),
  47     ("phase", Active),
  48     ("plugin_registrar", Active),
  49     ("log_syntax", Active),
  50     ("trace_macros", Active),
  51     ("concat_idents", Active),
  52     ("unsafe_destructor", Active),
  53     ("intrinsics", Active),
  54     ("lang_items", Active),
  55
  56     ("simd", Active),
  57     ("default_type_params", Active),
  58     ("quote", Active),
  59     ("link_llvm_intrinsics", Active),
  60     ("linkage", Active),
  61     ("struct_inherit", Removed),
  62
  63     ("quad_precision_float", Removed),
  64
  65     ("rustc_diagnostic_macros", Active),
  66     ("unboxed_closures", Active),
  67     ("import_shadowing", Active),
  68     ("advanced_slice_patterns", Active),
  69     ("tuple_indexing", Accepted),
  70     ("associated_types", Active),
  71     ("visible_private_types", Active),
  72     ("slicing_syntax", Active),
  73
  74     ("if_let", Accepted),
  75     ("while_let", Accepted),
  76
  77     // A temporary feature gate used to enable parser extensions needed
  78     // to bootstrap fix for #5723.
  79     ("issue_5723_bootstrap", Accepted),
  80
  81     // A way to temporarily opt out of opt in copy. This will *never* be accepted.
  82     ("opt_out_copy", Deprecated),
  83
  84     // A way to temporarily opt out of the new orphan rules. This will *never* be accepted.
  85     ("old_orphan_check", Deprecated),
  86
  87     // These are used to test this portion of the compiler, they don't actually
  88     // mean anything
  89     ("test_accepted_feature", Accepted),
  90     ("test_removed_feature", Removed),
  91 ];
  92
  93 enum Status {
  94     /// Represents an active feature that is currently being implemented or
  95     /// currently being considered for addition/removal.
  96     Active,
  97
  98     /// Represents a feature gate that is temporarily enabling deprecated behavior.
  99     /// This gate will never be accepted.
 100     Deprecated,
 101
 102     /// Represents a feature which has since been removed (it was once Active)
 103     Removed,
 104
 105     /// This language feature has since been Accepted (it was once Active)
 106     Accepted,
 107 }
 108
 109 /// A set of features to be used by later passes.
 110 #[derive(Copy)]
 111 pub struct Features {
 112     pub default_type_params: bool,
 113     pub unboxed_closures: bool,
 114     pub rustc_diagnostic_macros: bool,
 115     pub import_shadowing: bool,
 116     pub visible_private_types: bool,
 117     pub quote: bool,
 118     pub opt_out_copy: bool,
 119     pub old_orphan_check: bool,
 120 }
 121
 122 impl Features {
 123     pub fn new() -> Features {
 124         Features {
 125             default_type_params: false,
 126             unboxed_closures: false,
 127             rustc_diagnostic_macros: false,
 128             import_shadowing: false,
 129             visible_private_types: false,
 130             quote: false,
 131             opt_out_copy: false,
 132             old_orphan_check: false,
 133         }
 134     }
 135 }
 136
 137 struct Context<'a> {
 138     features: Vec<&'static str>,
 139     span_handler: &'a SpanHandler,
 140     cm: &'a CodeMap,
 141 }
 142
 143 impl<'a> Context<'a> {
 144     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
 145         if !self.has_feature(feature) {
 146             self.span_handler.span_err(span, explain);
 147             self.span_handler.span_help(span, format!("add #![feature({})] to the \
 148                                                        crate attributes to enable",
 149                                                       feature)[]);
 150         }
 151     }
 152
 153     fn has_feature(&self, feature: &str) -> bool {
 154         self.features.iter().any(|&n| n == feature)
 155     }
 156 }
 157
 158 struct MacroVisitor<'a> {
 159     context: &'a Context<'a>
 160 }
 161
 162 impl<'a, 'v> Visitor<'v> for MacroVisitor<'a> {
 163     fn visit_view_item(&mut self, i: &ast::ViewItem) {
 164         match i.node {
 165             ast::ViewItemExternCrate(..) => {
 166                 for attr in i.attrs.iter() {
 167                     if attr.name().get() == "phase"{
 168                         self.context.gate_feature("phase", attr.span,
 169                                           "compile time crate loading is \
 170                                            experimental and possibly buggy");
 171                     }
 172                 }
 173             },
 174             _ => { }
 175         }
 176         visit::walk_view_item(self, i)
 177     }
 178
 179     fn visit_mac(&mut self, macro: &ast::Mac) {
 180         let ast::MacInvocTT(ref path, _, _) = macro.node;
 181         let id = path.segments.last().unwrap().identifier;
 182
 183         if id == token::str_to_ident("macro_rules") {
 184             self.context.gate_feature("macro_rules", path.span, "macro definitions are \
 185                 not stable enough for use and are subject to change");
 186         }
 187
 188         else if id == token::str_to_ident("asm") {
 189             self.context.gate_feature("asm", path.span, "inline assembly is not \
 190                 stable enough for use and is subject to change");
 191         }
 192
 193         else if id == token::str_to_ident("log_syntax") {
 194             self.context.gate_feature("log_syntax", path.span, "`log_syntax!` is not \
 195                 stable enough for use and is subject to change");
 196         }
 197
 198         else if id == token::str_to_ident("trace_macros") {
 199             self.context.gate_feature("trace_macros", path.span, "`trace_macros` is not \
 200                 stable enough for use and is subject to change");
 201         }
 202
 203         else if id == token::str_to_ident("concat_idents") {
 204             self.context.gate_feature("concat_idents", path.span, "`concat_idents` is not \
 205                 stable enough for use and is subject to change");
 206         }
 207     }
 208 }
 209
 210 struct PostExpansionVisitor<'a> {
 211     context: &'a Context<'a>
 212 }
 213
 214 impl<'a> PostExpansionVisitor<'a> {
 215     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
 216         if !self.context.cm.span_is_internal(span) {
 217             self.context.gate_feature(feature, span, explain)
 218         }
 219     }
 220 }
 221
 222 impl<'a, 'v> Visitor<'v> for PostExpansionVisitor<'a> {
 223     fn visit_name(&mut self, sp: Span, name: ast::Name) {
 224         if !token::get_name(name).get().is_ascii() {
 225             self.gate_feature("non_ascii_idents", sp,
 226                               "non-ascii idents are not fully supported.");
 227         }
 228     }
 229
 230     fn visit_view_item(&mut self, i: &ast::ViewItem) {
 231         match i.node {
 232             ast::ViewItemUse(ref path) => {
 233                 if let ast::ViewPathGlob(..) = path.node {
 234                     self.gate_feature("globs", path.span,
 235                                       "glob import statements are \
 236                                        experimental and possibly buggy");
 237                 }
 238             }
 239             ast::ViewItemExternCrate(..) => {
 240                 for attr in i.attrs.iter() {
 241                     if attr.name().get() == "phase"{
 242                         self.gate_feature("phase", attr.span,
 243                                           "compile time crate loading is \
 244                                            experimental and possibly buggy");
 245                     }
 246                 }
 247             }
 248         }
 249         visit::walk_view_item(self, i)
 250     }
 251
 252     fn visit_item(&mut self, i: &ast::Item) {
 253         for attr in i.attrs.iter() {
 254             if attr.name() == "thread_local" {
 255                 self.gate_feature("thread_local", i.span,
 256                                   "`#[thread_local]` is an experimental feature, and does not \
 257                                   currently handle destructors. There is no corresponding \
 258                                   `#[task_local]` mapping to the task model");
 259             } else if attr.name() == "linkage" {
 260                 self.gate_feature("linkage", i.span,
 261                                   "the `linkage` attribute is experimental \
 262                                    and not portable across platforms")
 263             }
 264         }
 265         match i.node {
 266             ast::ItemForeignMod(ref foreign_module) => {
 267                 if attr::contains_name(i.attrs[], "link_args") {
 268                     self.gate_feature("link_args", i.span,
 269                                       "the `link_args` attribute is not portable \
 270                                        across platforms, it is recommended to \
 271                                        use `#[link(name = \"foo\")]` instead")
 272                 }
 273                 if foreign_module.abi == RustIntrinsic {
 274                     self.gate_feature("intrinsics",
 275                                       i.span,
 276                                       "intrinsics are subject to change")
 277                 }
 278             }
 279
 280             ast::ItemFn(..) => {
 281                 if attr::contains_name(i.attrs[], "plugin_registrar") {
 282                     self.gate_feature("plugin_registrar", i.span,
 283                                       "compiler plugins are experimental and possibly buggy");
 284                 }
 285             }
 286
 287             ast::ItemStruct(..) => {
 288                 if attr::contains_name(i.attrs[], "simd") {
 289                     self.gate_feature("simd", i.span,
 290                                       "SIMD types are experimental and possibly buggy");
 291                 }
 292             }
 293
 294             ast::ItemImpl(_, _, _, _, ref items) => {
 295                 if attr::contains_name(i.attrs[],
 296                                        "unsafe_destructor") {
 297                     self.gate_feature("unsafe_destructor",
 298                                       i.span,
 299                                       "`#[unsafe_destructor]` allows too \
 300                                        many unsafe patterns and may be \
 301                                        removed in the future");
 302                 }
 303
 304                 if attr::contains_name(i.attrs[],
 305                                        "old_orphan_check") {
 306                     self.gate_feature(
 307                         "old_orphan_check",
 308                         i.span,
 309                         "the new orphan check rules will eventually be strictly enforced");
 310                 }
 311
 312                 for item in items.iter() {
 313                     match *item {
 314                         ast::MethodImplItem(_) => {}
 315                         ast::TypeImplItem(ref typedef) => {
 316                             self.gate_feature("associated_types",
 317                                               typedef.span,
 318                                               "associated types are \
 319                                                experimental")
 320                         }
 321                     }
 322                 }
 323             }
 324
 325             _ => {}
 326         }
 327
 328         visit::walk_item(self, i);
 329     }
 330
 331     fn visit_trait_item(&mut self, trait_item: &ast::TraitItem) {
 332         match *trait_item {
 333             ast::RequiredMethod(_) | ast::ProvidedMethod(_) => {}
 334             ast::TypeTraitItem(ref ti) => {
 335                 self.gate_feature("associated_types",
 336                                   ti.ty_param.span,
 337                                   "associated types are experimental")
 338             }
 339         }
 340     }
 341
 342     fn visit_foreign_item(&mut self, i: &ast::ForeignItem) {
 343         if attr::contains_name(i.attrs[], "linkage") {
 344             self.gate_feature("linkage", i.span,
 345                               "the `linkage` attribute is experimental \
 346                                and not portable across platforms")
 347         }
 348
 349         let links_to_llvm = match attr::first_attr_value_str_by_name(i.attrs[], "link_name") {
 350             Some(val) => val.get().starts_with("llvm."),
 351             _ => false
 352         };
 353         if links_to_llvm {
 354             self.gate_feature("link_llvm_intrinsics", i.span,
 355                               "linking to LLVM intrinsics is experimental");
 356         }
 357
 358         visit::walk_foreign_item(self, i)
 359     }
 360
 361     fn visit_ty(&mut self, t: &ast::Ty) {
 362         if let ast::TyClosure(ref closure) =  t.node {
 363             // this used to be blocked by a feature gate, but it should just
 364             // be plain impossible right now
 365             assert!(closure.onceness != ast::Once);
 366         }
 367
 368         visit::walk_ty(self, t);
 369     }
 370
 371     fn visit_expr(&mut self, e: &ast::Expr) {
 372         match e.node {
 373             ast::ExprRange(..) => {
 374                 self.gate_feature("slicing_syntax",
 375                                   e.span,
 376                                   "range syntax is experimental");
 377             }
 378             _ => {}
 379         }
 380         visit::walk_expr(self, e);
 381     }
 382
 383     fn visit_generics(&mut self, generics: &ast::Generics) {
 384         for type_parameter in generics.ty_params.iter() {
 385             match type_parameter.default {
 386                 Some(ref ty) => {
 387                     self.gate_feature("default_type_params", ty.span,
 388                                       "default type parameters are \
 389                                        experimental and possibly buggy");
 390                 }
 391                 None => {}
 392             }
 393         }
 394         visit::walk_generics(self, generics);
 395     }
 396
 397     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 398         if attr::contains_name(slice::ref_slice(attr), "lang") {
 399             self.gate_feature("lang_items",
 400                               attr.span,
 401                               "language items are subject to change");
 402         }
 403     }
 404
 405     fn visit_pat(&mut self, pattern: &ast::Pat) {
 406         match pattern.node {
 407             ast::PatVec(_, Some(_), ref last) if !last.is_empty() => {
 408                 self.gate_feature("advanced_slice_patterns",
 409                                   pattern.span,
 410                                   "multiple-element slice matches anywhere \
 411                                    but at the end of a slice (e.g. \
 412                                    `[0, ..xs, 0]` are experimental")
 413             }
 414             _ => {}
 415         }
 416         visit::walk_pat(self, pattern)
 417     }
 418
 419     fn visit_fn(&mut self,
 420                 fn_kind: visit::FnKind<'v>,
 421                 fn_decl: &'v ast::FnDecl,
 422                 block: &'v ast::Block,
 423                 span: Span,
 424                 _node_id: NodeId) {
 425         match fn_kind {
 426             visit::FkItemFn(_, _, _, abi) if abi == RustIntrinsic => {
 427                 self.gate_feature("intrinsics",
 428                                   span,
 429                                   "intrinsics are subject to change")
 430             }
 431             _ => {}
 432         }
 433         visit::walk_fn(self, fn_kind, fn_decl, block, span);
 434     }
 435 }
 436
 437 fn check_crate_inner<F>(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate,
 438                         check: F)
 439                        -> (Features, Vec<Span>)
 440     where F: FnOnce(&mut Context, &ast::Crate)
 441 {
 442     let mut cx = Context {
 443         features: Vec::new(),
 444         span_handler: span_handler,
 445         cm: cm,
 446     };
 447
 448     let mut unknown_features = Vec::new();
 449
 450     for attr in krate.attrs.iter() {
 451         if !attr.check_name("feature") {
 452             continue
 453         }
 454
 455         match attr.meta_item_list() {
 456             None => {
 457                 span_handler.span_err(attr.span, "malformed feature attribute, \
 458                                                   expected #![feature(...)]");
 459             }
 460             Some(list) => {
 461                 for mi in list.iter() {
 462                     let name = match mi.node {
 463                         ast::MetaWord(ref word) => (*word).clone(),
 464                         _ => {
 465                             span_handler.span_err(mi.span,
 466                                                   "malformed feature, expected just \
 467                                                    one word");
 468                             continue
 469                         }
 470                     };
 471                     match KNOWN_FEATURES.iter()
 472                                         .find(|& &(n, _)| name == n) {
 473                         Some(&(name, Active)) => {
 474                             cx.features.push(name);
 475                         }
 476                         Some(&(name, Deprecated)) => {
 477                             cx.features.push(name);
 478                             span_handler.span_warn(
 479                                 mi.span,
 480                                 "feature is deprecated and will only be available \
 481                                  for a limited time, please rewrite code that relies on it");
 482                         }
 483                         Some(&(_, Removed)) => {
 484                             span_handler.span_err(mi.span, "feature has been removed");
 485                         }
 486                         Some(&(_, Accepted)) => {
 487                             span_handler.span_warn(mi.span, "feature has been added to Rust, \
 488                                                              directive not necessary");
 489                         }
 490                         None => {
 491                             unknown_features.push(mi.span);
 492                         }
 493                     }
 494                 }
 495             }
 496         }
 497     }
 498
 499     check(&mut cx, krate);
 500
 501     (Features {
 502         default_type_params: cx.has_feature("default_type_params"),
 503         unboxed_closures: cx.has_feature("unboxed_closures"),
 504         rustc_diagnostic_macros: cx.has_feature("rustc_diagnostic_macros"),
 505         import_shadowing: cx.has_feature("import_shadowing"),
 506         visible_private_types: cx.has_feature("visible_private_types"),
 507         quote: cx.has_feature("quote"),
 508         opt_out_copy: cx.has_feature("opt_out_copy"),
 509         old_orphan_check: cx.has_feature("old_orphan_check"),
 510     },
 511     unknown_features)
 512 }
 513
 514 pub fn check_crate_macros(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate)
 515 -> (Features, Vec<Span>) {
 516     check_crate_inner(cm, span_handler, krate,
 517                       |ctx, krate| visit::walk_crate(&mut MacroVisitor { context: ctx }, krate))
 518 }
 519
 520 pub fn check_crate(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate)
 521 -> (Features, Vec<Span>) {
 522     check_crate_inner(cm, span_handler, krate,
 523                       |ctx, krate| visit::walk_crate(&mut PostExpansionVisitor { context: ctx },
 524                                                      krate))
 525 }