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