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