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