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