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::ast;
  24 use syntax::attr;
  25 use syntax::attr::AttrMetaMethods;
  26 use syntax::codemap::Span;
  27 use syntax::visit;
  28 use syntax::visit::Visitor;
  29 use syntax::parse::token;
  30
  31 use driver::session::Session;
  32
  33 use std::cell::Cell;
  34
  35 /// This is a list of all known features since the beginning of time. This list
  36 /// can never shrink, it may only be expanded (in order to prevent old programs
  37 /// from failing to compile). The status of each feature may change, however.
  38 static KNOWN_FEATURES: &'static [(&'static str, Status)] = &[
  39     ("globs", Active),
  40     ("macro_rules", Active),
  41     ("struct_variant", Active),
  42     ("once_fns", Active),
  43     ("asm", Active),
  44     ("managed_boxes", Active),
  45     ("non_ascii_idents", Active),
  46     ("thread_local", Active),
  47     ("link_args", Active),
  48     ("phase", Active),
  49     ("macro_registrar", Active),
  50     ("log_syntax", Active),
  51     ("trace_macros", Active),
  52     ("simd", Active),
  53     ("default_type_params", Active),
  54     ("quote", Active),
  55     ("linkage", Active),
  56
  57     // These are used to test this portion of the compiler, they don't actually
  58     // mean anything
  59     ("test_accepted_feature", Accepted),
  60     ("test_removed_feature", Removed),
  61 ];
  62
  63 enum Status {
  64     /// Represents an active feature that is currently being implemented or
  65     /// currently being considered for addition/removal.
  66     Active,
  67
  68     /// Represents a feature which has since been removed (it was once Active)
  69     Removed,
  70
  71     /// This language feature has since been Accepted (it was once Active)
  72     Accepted,
  73 }
  74
  75 /// A set of features to be used by later passes.
  76 pub struct Features {
  77     default_type_params: Cell<bool>
  78 }
  79
  80 impl Features {
  81     pub fn new() -> Features {
  82         Features {
  83             default_type_params: Cell::new(false)
  84         }
  85     }
  86 }
  87
  88 struct Context<'a> {
  89     features: Vec<&'static str>,
  90     sess: &'a Session,
  91 }
  92
  93 impl<'a> Context<'a> {
  94     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
  95         if !self.has_feature(feature) {
  96             self.sess.span_err(span, explain);
  97             self.sess.span_note(span, format!("add \\#[feature({})] to the \
  98                                                   crate attributes to enable",
  99                                                  feature));
 100         }
 101     }
 102
 103     fn gate_box(&self, span: Span) {
 104         self.gate_feature("managed_boxes", span,
 105                           "The managed box syntax is being replaced by the \
 106                            `std::gc::Gc` and `std::rc::Rc` types. Equivalent \
 107                            functionality to managed trait objects will be \
 108                            implemented but is currently missing.");
 109     }
 110
 111     fn has_feature(&self, feature: &str) -> bool {
 112         self.features.iter().any(|n| n.as_slice() == feature)
 113     }
 114 }
 115
 116 impl<'a> Visitor<()> for Context<'a> {
 117     fn visit_ident(&mut self, sp: Span, id: ast::Ident, _: ()) {
 118         if !token::get_ident(id).get().is_ascii() {
 119             self.gate_feature("non_ascii_idents", sp,
 120                               "non-ascii idents are not fully supported.");
 121         }
 122     }
 123
 124     fn visit_view_item(&mut self, i: &ast::ViewItem, _: ()) {
 125         match i.node {
 126             ast::ViewItemUse(ref paths) => {
 127                 for path in paths.iter() {
 128                     match path.node {
 129                         ast::ViewPathGlob(..) => {
 130                             self.gate_feature("globs", path.span,
 131                                               "glob import statements are \
 132                                                experimental and possibly buggy");
 133                         }
 134                         _ => {}
 135                     }
 136                 }
 137             }
 138             ast::ViewItemExternCrate(..) => {
 139                 for attr in i.attrs.iter() {
 140                     if attr.name().get() == "phase"{
 141                         self.gate_feature("phase", attr.span,
 142                                           "compile time crate loading is \
 143                                            experimental and possibly buggy");
 144                     }
 145                 }
 146             }
 147         }
 148         visit::walk_view_item(self, i, ())
 149     }
 150
 151     fn visit_item(&mut self, i: &ast::Item, _:()) {
 152         for attr in i.attrs.iter() {
 153             if attr.name().equiv(&("thread_local")) {
 154                 self.gate_feature("thread_local", i.span,
 155                                   "`#[thread_local]` is an experimental feature, and does not \
 156                                   currently handle destructors. There is no corresponding \
 157                                   `#[task_local]` mapping to the task model");
 158             }
 159         }
 160         match i.node {
 161             ast::ItemEnum(ref def, _) => {
 162                 for variant in def.variants.iter() {
 163                     match variant.node.kind {
 164                         ast::StructVariantKind(..) => {
 165                             self.gate_feature("struct_variant", variant.span,
 166                                               "enum struct variants are \
 167                                                experimental and possibly buggy");
 168                         }
 169                         _ => {}
 170                     }
 171                 }
 172             }
 173
 174             ast::ItemForeignMod(..) => {
 175                 if attr::contains_name(i.attrs.as_slice(), "link_args") {
 176                     self.gate_feature("link_args", i.span,
 177                                       "the `link_args` attribute is not portable \
 178                                        across platforms, it is recommended to \
 179                                        use `#[link(name = \"foo\")]` instead")
 180                 }
 181             }
 182
 183             ast::ItemFn(..) => {
 184                 if attr::contains_name(i.attrs.as_slice(), "macro_registrar") {
 185                     self.gate_feature("macro_registrar", i.span,
 186                                       "cross-crate macro exports are \
 187                                        experimental and possibly buggy");
 188                 }
 189             }
 190
 191             ast::ItemStruct(..) => {
 192                 if attr::contains_name(i.attrs.as_slice(), "simd") {
 193                     self.gate_feature("simd", i.span,
 194                                       "SIMD types are experimental and possibly buggy");
 195                 }
 196             }
 197
 198             _ => {}
 199         }
 200
 201         visit::walk_item(self, i, ());
 202     }
 203
 204     fn visit_mac(&mut self, macro: &ast::Mac, _: ()) {
 205         let ast::MacInvocTT(ref path, _, _) = macro.node;
 206         let id = path.segments.last().unwrap().identifier;
 207         let quotes = ["quote_tokens", "quote_expr", "quote_ty",
 208                       "quote_item", "quote_pat", "quote_stmt"];
 209         let msg = " is not stable enough for use and are subject to change";
 210
 211
 212         if id == token::str_to_ident("macro_rules") {
 213             self.gate_feature("macro_rules", path.span, "macro definitions are \
 214                 not stable enough for use and are subject to change");
 215         }
 216
 217         else if id == token::str_to_ident("asm") {
 218             self.gate_feature("asm", path.span, "inline assembly is not \
 219                 stable enough for use and is subject to change");
 220         }
 221
 222         else if id == token::str_to_ident("log_syntax") {
 223             self.gate_feature("log_syntax", path.span, "`log_syntax!` is not \
 224                 stable enough for use and is subject to change");
 225         }
 226
 227         else if id == token::str_to_ident("trace_macros") {
 228             self.gate_feature("trace_macros", path.span, "`trace_macros` is not \
 229                 stable enough for use and is subject to change");
 230         }
 231
 232         else {
 233             for &quote in quotes.iter() {
 234                 if id == token::str_to_ident(quote) {
 235                   self.gate_feature("quote", path.span, quote + msg);
 236                 }
 237             }
 238         }
 239     }
 240
 241     fn visit_foreign_item(&mut self, i: &ast::ForeignItem, _: ()) {
 242         match i.node {
 243             ast::ForeignItemFn(..) | ast::ForeignItemStatic(..) => {
 244                 if attr::contains_name(i.attrs.as_slice(), "linkage") {
 245                     self.gate_feature("linkage", i.span,
 246                                       "the `linkage` attribute is experimental \
 247                                        and not portable across platforms")
 248                 }
 249             }
 250         }
 251         visit::walk_foreign_item(self, i, ())
 252     }
 253
 254     fn visit_ty(&mut self, t: &ast::Ty, _: ()) {
 255         match t.node {
 256             ast::TyClosure(closure) if closure.onceness == ast::Once &&
 257                     closure.sigil != ast::OwnedSigil => {
 258                 self.gate_feature("once_fns", t.span,
 259                                   "once functions are \
 260                                    experimental and likely to be removed");
 261
 262             },
 263             ast::TyBox(_) => { self.gate_box(t.span); }
 264             _ => {}
 265         }
 266
 267         visit::walk_ty(self, t, ());
 268     }
 269
 270     fn visit_expr(&mut self, e: &ast::Expr, _: ()) {
 271         match e.node {
 272             ast::ExprUnary(ast::UnBox, _) => {
 273                 self.gate_box(e.span);
 274             }
 275             _ => {}
 276         }
 277         visit::walk_expr(self, e, ());
 278     }
 279
 280     fn visit_generics(&mut self, generics: &ast::Generics, _: ()) {
 281         for type_parameter in generics.ty_params.iter() {
 282             match type_parameter.default {
 283                 Some(ty) => {
 284                     self.gate_feature("default_type_params", ty.span,
 285                                       "default type parameters are \
 286                                        experimental and possibly buggy");
 287                 }
 288                 None => {}
 289             }
 290         }
 291         visit::walk_generics(self, generics, ());
 292     }
 293 }
 294
 295 pub fn check_crate(sess: &Session, krate: &ast::Crate) {
 296     let mut cx = Context {
 297         features: Vec::new(),
 298         sess: sess,
 299     };
 300
 301     for attr in krate.attrs.iter() {
 302         if !attr.name().equiv(&("feature")) {
 303             continue
 304         }
 305
 306         match attr.meta_item_list() {
 307             None => {
 308                 sess.span_err(attr.span, "malformed feature attribute, \
 309                                           expected #[feature(...)]");
 310             }
 311             Some(list) => {
 312                 for &mi in list.iter() {
 313                     let name = match mi.node {
 314                         ast::MetaWord(ref word) => (*word).clone(),
 315                         _ => {
 316                             sess.span_err(mi.span,
 317                                           "malformed feature, expected just \
 318                                            one word");
 319                             continue
 320                         }
 321                     };
 322                     match KNOWN_FEATURES.iter()
 323                                         .find(|& &(n, _)| name.equiv(&n)) {
 324                         Some(&(name, Active)) => { cx.features.push(name); }
 325                         Some(&(_, Removed)) => {
 326                             sess.span_err(mi.span, "feature has been removed");
 327                         }
 328                         Some(&(_, Accepted)) => {
 329                             sess.span_warn(mi.span, "feature has added to rust, \
 330                                                      directive not necessary");
 331                         }
 332                         None => {
 333                             sess.add_lint(lint::UnknownFeatures,
 334                                           ast::CRATE_NODE_ID,
 335                                           mi.span,
 336                                           ~"unknown feature");
 337                         }
 338                     }
 339                 }
 340             }
 341         }
 342     }
 343
 344     visit::walk_crate(&mut cx, krate, ());
 345
 346     sess.abort_if_errors();
 347
 348     sess.features.default_type_params.set(cx.has_feature("default_type_params"));
 349 }