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