src/librustc/front/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 lint;
  22
  23 use syntax::abi::RustIntrinsic;
  24 use syntax::ast::NodeId;
  25 use syntax::ast;
  26 use syntax::attr;
  27 use syntax::attr::AttrMetaMethods;
  28 use syntax::codemap::Span;
  29 use syntax::visit;
  30 use syntax::visit::Visitor;
  31 use syntax::parse::token;
  32
  33 use driver::session::Session;
  34
  35 use std::cell::Cell;
  36
  37 /// This is a list of all known features since the beginning of time. This list
  38 /// can never shrink, it may only be expanded (in order to prevent old programs
  39 /// from failing to compile). The status of each feature may change, however.
  40 static KNOWN_FEATURES: &'static [(&'static str, Status)] = &[
  41     ("globs", Active),
  42     ("macro_rules", Active),
  43     ("struct_variant", Active),
  44     ("once_fns", Active),
  45     ("asm", Active),
  46     ("managed_boxes", Active),
  47     ("non_ascii_idents", Active),
  48     ("thread_local", Active),
  49     ("link_args", Active),
  50     ("phase", Active),
  51     ("plugin_registrar", Active),
  52     ("log_syntax", Active),
  53     ("trace_macros", Active),
  54     ("concat_idents", Active),
  55     ("unsafe_destructor", Active),
  56     ("intrinsics", Active),
  57     ("lang_items", Active),
  58
  59     ("simd", Active),
  60     ("default_type_params", Active),
  61     ("quote", Active),
  62     ("linkage", Active),
  63     ("struct_inherit", Active),
  64     ("overloaded_calls", Active),
  65     ("unboxed_closure_sugar", Active),
  66
  67     ("quad_precision_float", Removed),
  68
  69     ("rustc_diagnostic_macros", Active),
  70     ("unboxed_closures", Active),
  71
  72     // A temporary feature gate used to enable parser extensions needed
  73     // to bootstrap fix for #5723.
  74     ("issue_5723_bootstrap", Active),
  75
  76     // These are used to test this portion of the compiler, they don't actually
  77     // mean anything
  78     ("test_accepted_feature", Accepted),
  79     ("test_removed_feature", Removed),
  80 ];
  81
  82 enum Status {
  83     /// Represents an active feature that is currently being implemented or
  84     /// currently being considered for addition/removal.
  85     Active,
  86
  87     /// Represents a feature which has since been removed (it was once Active)
  88     Removed,
  89
  90     /// This language feature has since been Accepted (it was once Active)
  91     Accepted,
  92 }
  93
  94 /// A set of features to be used by later passes.
  95 pub struct Features {
  96     pub default_type_params: Cell<bool>,
  97     pub issue_5723_bootstrap: Cell<bool>,
  98     pub overloaded_calls: Cell<bool>,
  99     pub rustc_diagnostic_macros: Cell<bool>
 100 }
 101
 102 impl Features {
 103     pub fn new() -> Features {
 104         Features {
 105             default_type_params: Cell::new(false),
 106             issue_5723_bootstrap: Cell::new(false),
 107             overloaded_calls: Cell::new(false),
 108             rustc_diagnostic_macros: Cell::new(false)
 109         }
 110     }
 111 }
 112
 113 struct Context<'a> {
 114     features: Vec<&'static str>,
 115     sess: &'a Session,
 116 }
 117
 118 impl<'a> Context<'a> {
 119     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
 120         if !self.has_feature(feature) {
 121             self.sess.span_err(span, explain);
 122             self.sess.span_note(span, format!("add #![feature({})] to the \
 123                                                crate attributes to enable",
 124                                               feature).as_slice());
 125         }
 126     }
 127
 128     fn gate_box(&self, span: Span) {
 129         self.gate_feature("managed_boxes", span,
 130                           "The managed box syntax is being replaced by the \
 131                            `std::gc::Gc` and `std::rc::Rc` types. Equivalent \
 132                            functionality to managed trait objects will be \
 133                            implemented but is currently missing.");
 134     }
 135
 136     fn has_feature(&self, feature: &str) -> bool {
 137         self.features.iter().any(|n| n.as_slice() == feature)
 138     }
 139 }
 140
 141 impl<'a> Visitor<()> for Context<'a> {
 142     fn visit_ident(&mut self, sp: Span, id: ast::Ident, _: ()) {
 143         if !token::get_ident(id).get().is_ascii() {
 144             self.gate_feature("non_ascii_idents", sp,
 145                               "non-ascii idents are not fully supported.");
 146         }
 147     }
 148
 149     fn visit_view_item(&mut self, i: &ast::ViewItem, _: ()) {
 150         match i.node {
 151             ast::ViewItemUse(ref path) => {
 152                 match path.node {
 153                     ast::ViewPathGlob(..) => {
 154                         self.gate_feature("globs", path.span,
 155                                           "glob import statements are \
 156                                            experimental and possibly buggy");
 157                     }
 158                     _ => {}
 159                 }
 160             }
 161             ast::ViewItemExternCrate(..) => {
 162                 for attr in i.attrs.iter() {
 163                     if attr.name().get() == "phase"{
 164                         self.gate_feature("phase", attr.span,
 165                                           "compile time crate loading is \
 166                                            experimental and possibly buggy");
 167                     }
 168                 }
 169             }
 170         }
 171         visit::walk_view_item(self, i, ())
 172     }
 173
 174     fn visit_item(&mut self, i: &ast::Item, _:()) {
 175         for attr in i.attrs.iter() {
 176             if attr.name().equiv(&("thread_local")) {
 177                 self.gate_feature("thread_local", i.span,
 178                                   "`#[thread_local]` is an experimental feature, and does not \
 179                                   currently handle destructors. There is no corresponding \
 180                                   `#[task_local]` mapping to the task model");
 181             }
 182         }
 183         match i.node {
 184             ast::ItemEnum(ref def, _) => {
 185                 for variant in def.variants.iter() {
 186                     match variant.node.kind {
 187                         ast::StructVariantKind(..) => {
 188                             self.gate_feature("struct_variant", variant.span,
 189                                               "enum struct variants are \
 190                                                experimental and possibly buggy");
 191                         }
 192                         _ => {}
 193                     }
 194                 }
 195             }
 196
 197             ast::ItemForeignMod(ref foreign_module) => {
 198                 if attr::contains_name(i.attrs.as_slice(), "link_args") {
 199                     self.gate_feature("link_args", i.span,
 200                                       "the `link_args` attribute is not portable \
 201                                        across platforms, it is recommended to \
 202                                        use `#[link(name = \"foo\")]` instead")
 203                 }
 204                 if foreign_module.abi == RustIntrinsic {
 205                     self.gate_feature("intrinsics",
 206                                       i.span,
 207                                       "intrinsics are subject to change")
 208                 }
 209             }
 210
 211             ast::ItemFn(..) => {
 212                 if attr::contains_name(i.attrs.as_slice(), "plugin_registrar") {
 213                     self.gate_feature("plugin_registrar", i.span,
 214                                       "compiler plugins are experimental and possibly buggy");
 215                 }
 216             }
 217
 218             ast::ItemStruct(struct_definition, _) => {
 219                 if attr::contains_name(i.attrs.as_slice(), "simd") {
 220                     self.gate_feature("simd", i.span,
 221                                       "SIMD types are experimental and possibly buggy");
 222                 }
 223                 match struct_definition.super_struct {
 224                     Some(ref path) => self.gate_feature("struct_inherit", path.span,
 225                                                         "struct inheritance is experimental \
 226                                                          and possibly buggy"),
 227                     None => {}
 228                 }
 229                 if struct_definition.is_virtual {
 230                     self.gate_feature("struct_inherit", i.span,
 231                                       "struct inheritance (`virtual` keyword) is \
 232                                        experimental and possibly buggy");
 233                 }
 234             }
 235
 236             ast::ItemImpl(..) => {
 237                 if attr::contains_name(i.attrs.as_slice(),
 238                                        "unsafe_destructor") {
 239                     self.gate_feature("unsafe_destructor",
 240                                       i.span,
 241                                       "`#[unsafe_destructor]` allows too \
 242                                        many unsafe patterns and may be \
 243                                        removed in the future");
 244                 }
 245             }
 246
 247             _ => {}
 248         }
 249
 250         visit::walk_item(self, i, ());
 251     }
 252
 253     fn visit_mac(&mut self, macro: &ast::Mac, _: ()) {
 254         let ast::MacInvocTT(ref path, _, _) = macro.node;
 255         let id = path.segments.last().unwrap().identifier;
 256         let quotes = ["quote_tokens", "quote_expr", "quote_ty",
 257                       "quote_item", "quote_pat", "quote_stmt"];
 258         let msg = " is not stable enough for use and are subject to change";
 259
 260
 261         if id == token::str_to_ident("macro_rules") {
 262             self.gate_feature("macro_rules", path.span, "macro definitions are \
 263                 not stable enough for use and are subject to change");
 264         }
 265
 266         else if id == token::str_to_ident("asm") {
 267             self.gate_feature("asm", path.span, "inline assembly is not \
 268                 stable enough for use and is subject to change");
 269         }
 270
 271         else if id == token::str_to_ident("log_syntax") {
 272             self.gate_feature("log_syntax", path.span, "`log_syntax!` is not \
 273                 stable enough for use and is subject to change");
 274         }
 275
 276         else if id == token::str_to_ident("trace_macros") {
 277             self.gate_feature("trace_macros", path.span, "`trace_macros` is not \
 278                 stable enough for use and is subject to change");
 279         }
 280
 281         else if id == token::str_to_ident("concat_idents") {
 282             self.gate_feature("concat_idents", path.span, "`concat_idents` is not \
 283                 stable enough for use and is subject to change");
 284         }
 285
 286         else {
 287             for &quote in quotes.iter() {
 288                 if id == token::str_to_ident(quote) {
 289                   self.gate_feature("quote",
 290                                     path.span,
 291                                     format!("{}{}", quote, msg).as_slice());
 292                 }
 293             }
 294         }
 295     }
 296
 297     fn visit_foreign_item(&mut self, i: &ast::ForeignItem, _: ()) {
 298         if attr::contains_name(i.attrs.as_slice(), "linkage") {
 299             self.gate_feature("linkage", i.span,
 300                               "the `linkage` attribute is experimental \
 301                                and not portable across platforms")
 302         }
 303         visit::walk_foreign_item(self, i, ())
 304     }
 305
 306     fn visit_ty(&mut self, t: &ast::Ty, _: ()) {
 307         match t.node {
 308             ast::TyClosure(closure, _) if closure.onceness == ast::Once => {
 309                 self.gate_feature("once_fns", t.span,
 310                                   "once functions are \
 311                                    experimental and likely to be removed");
 312
 313             },
 314             ast::TyBox(_) => { self.gate_box(t.span); }
 315             ast::TyUnboxedFn(_) => {
 316                 self.gate_feature("unboxed_closure_sugar",
 317                                   t.span,
 318                                   "unboxed closure trait sugar is experimental");
 319             }
 320             _ => {}
 321         }
 322
 323         visit::walk_ty(self, t, ());
 324     }
 325
 326     fn visit_expr(&mut self, e: &ast::Expr, _: ()) {
 327         match e.node {
 328             ast::ExprUnary(ast::UnBox, _) => {
 329                 self.gate_box(e.span);
 330             }
 331             ast::ExprUnboxedFn(..) => {
 332                 self.gate_feature("unboxed_closures",
 333                                   e.span,
 334                                   "unboxed closures are a work-in-progress \
 335                                    feature with known bugs");
 336             }
 337             _ => {}
 338         }
 339         visit::walk_expr(self, e, ());
 340     }
 341
 342     fn visit_generics(&mut self, generics: &ast::Generics, _: ()) {
 343         for type_parameter in generics.ty_params.iter() {
 344             match type_parameter.default {
 345                 Some(ty) => {
 346                     self.gate_feature("default_type_params", ty.span,
 347                                       "default type parameters are \
 348                                        experimental and possibly buggy");
 349                 }
 350                 None => {}
 351             }
 352         }
 353         visit::walk_generics(self, generics, ());
 354     }
 355
 356     fn visit_attribute(&mut self, attr: &ast::Attribute, _: ()) {
 357         if attr::contains_name([*attr], "lang") {
 358             self.gate_feature("lang_items",
 359                               attr.span,
 360                               "language items are subject to change");
 361         }
 362     }
 363
 364     fn visit_fn(&mut self,
 365                 fn_kind: &visit::FnKind,
 366                 fn_decl: &ast::FnDecl,
 367                 block: &ast::Block,
 368                 span: Span,
 369                 _: NodeId,
 370                 (): ()) {
 371         match *fn_kind {
 372             visit::FkItemFn(_, _, _, ref abi) if *abi == RustIntrinsic => {
 373                 self.gate_feature("intrinsics",
 374                                   span,
 375                                   "intrinsics are subject to change")
 376             }
 377             _ => {}
 378         }
 379         visit::walk_fn(self, fn_kind, fn_decl, block, span, ());
 380     }
 381 }
 382
 383 pub fn check_crate(sess: &Session, krate: &ast::Crate) {
 384     let mut cx = Context {
 385         features: Vec::new(),
 386         sess: sess,
 387     };
 388
 389     for attr in krate.attrs.iter() {
 390         if !attr.check_name("feature") {
 391             continue
 392         }
 393
 394         match attr.meta_item_list() {
 395             None => {
 396                 sess.span_err(attr.span, "malformed feature attribute, \
 397                                           expected #![feature(...)]");
 398             }
 399             Some(list) => {
 400                 for &mi in list.iter() {
 401                     let name = match mi.node {
 402                         ast::MetaWord(ref word) => (*word).clone(),
 403                         _ => {
 404                             sess.span_err(mi.span,
 405                                           "malformed feature, expected just \
 406                                            one word");
 407                             continue
 408                         }
 409                     };
 410                     match KNOWN_FEATURES.iter()
 411                                         .find(|& &(n, _)| name.equiv(&n)) {
 412                         Some(&(name, Active)) => { cx.features.push(name); }
 413                         Some(&(_, Removed)) => {
 414                             sess.span_err(mi.span, "feature has been removed");
 415                         }
 416                         Some(&(_, Accepted)) => {
 417                             sess.span_warn(mi.span, "feature has added to rust, \
 418                                                      directive not necessary");
 419                         }
 420                         None => {
 421                             sess.add_lint(lint::builtin::UNKNOWN_FEATURES,
 422                                           ast::CRATE_NODE_ID,
 423                                           mi.span,
 424                                           "unknown feature".to_string());
 425                         }
 426                     }
 427                 }
 428             }
 429         }
 430     }
 431
 432     visit::walk_crate(&mut cx, krate, ());
 433
 434     sess.abort_if_errors();
 435
 436     sess.features.default_type_params.set(cx.has_feature("default_type_params"));
 437     sess.features.issue_5723_bootstrap.set(cx.has_feature("issue_5723_bootstrap"));
 438     sess.features.overloaded_calls.set(cx.has_feature("overloaded_calls"));
 439     sess.features.rustc_diagnostic_macros.set(cx.has_feature("rustc_diagnostic_macros"));
 440 }