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