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