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 use std::vec_ng::Vec;
  35
  36 /// This is a list of all known features since the beginning of time. This list
  37 /// can never shrink, it may only be expanded (in order to prevent old programs
  38 /// from failing to compile). The status of each feature may change, however.
  39 static KNOWN_FEATURES: &'static [(&'static str, Status)] = &[
  40     ("globs", Active),
  41     ("macro_rules", Active),
  42     ("struct_variant", Active),
  43     ("once_fns", Active),
  44     ("asm", Active),
  45     ("managed_boxes", Active),
  46     ("non_ascii_idents", Active),
  47     ("thread_local", Active),
  48     ("link_args", Active),
  49     ("phase", Active),
  50     ("macro_registrar", Active),
  51     ("log_syntax", Active),
  52     ("trace_macros", Active),
  53     ("simd", Active),
  54     ("default_type_params", Active),
  55     ("quote", Active),
  56     ("linkage", Active),
  57
  58     // These are used to test this portion of the compiler, they don't actually
  59     // mean anything
  60     ("test_accepted_feature", Accepted),
  61     ("test_removed_feature", Removed),
  62 ];
  63
  64 enum Status {
  65     /// Represents an active feature that is currently being implemented or
  66     /// currently being considered for addition/removal.
  67     Active,
  68
  69     /// Represents a feature which has since been removed (it was once Active)
  70     Removed,
  71
  72     /// This language feature has since been Accepted (it was once Active)
  73     Accepted,
  74 }
  75
  76 /// A set of features to be used by later passes.
  77 pub struct Features {
  78     default_type_params: Cell<bool>
  79 }
  80
  81 impl Features {
  82     pub fn new() -> Features {
  83         Features {
  84             default_type_params: Cell::new(false)
  85         }
  86     }
  87 }
  88
  89 struct Context {
  90     features: Vec<&'static str> ,
  91     sess: Session,
  92 }
  93
  94 impl Context {
  95     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
  96         if !self.has_feature(feature) {
  97             self.sess.span_err(span, explain);
  98             self.sess.span_note(span, format!("add \\#[feature({})] to the \
  99                                                   crate attributes to enable",
 100                                                  feature));
 101         }
 102     }
 103
 104     fn gate_box(&self, span: Span) {
 105         self.gate_feature("managed_boxes", span,
 106                           "The managed box syntax is being replaced by the \
 107                            `std::gc::Gc` and `std::rc::Rc` types. Equivalent \
 108                            functionality to managed trait objects will be \
 109                            implemented but is currently missing.");
 110     }
 111
 112     fn has_feature(&self, feature: &str) -> bool {
 113         self.features.iter().any(|n| n.as_slice() == feature)
 114     }
 115 }
 116
 117 impl Visitor<()> for Context {
 118     fn visit_ident(&mut self, sp: Span, id: ast::Ident, _: ()) {
 119         if !token::get_ident(id).get().is_ascii() {
 120             self.gate_feature("non_ascii_idents", sp,
 121                               "non-ascii idents are not fully supported.");
 122         }
 123     }
 124
 125     fn visit_view_item(&mut self, i: &ast::ViewItem, _: ()) {
 126         match i.node {
 127             ast::ViewItemUse(ref paths) => {
 128                 for path in paths.iter() {
 129                     match path.node {
 130                         ast::ViewPathGlob(..) => {
 131                             self.gate_feature("globs", path.span,
 132                                               "glob import statements are \
 133                                                experimental and possibly buggy");
 134                         }
 135                         _ => {}
 136                     }
 137                 }
 138             }
 139             ast::ViewItemExternCrate(..) => {
 140                 for attr in i.attrs.iter() {
 141                     if attr.name().get() == "phase"{
 142                         self.gate_feature("phase", attr.span,
 143                                           "compile time crate loading is \
 144                                            experimental and possibly buggy");
 145                     }
 146                 }
 147             }
 148         }
 149         visit::walk_view_item(self, i, ())
 150     }
 151
 152     fn visit_item(&mut self, i: &ast::Item, _:()) {
 153         for attr in i.attrs.iter() {
 154             if attr.name().equiv(&("thread_local")) {
 155                 self.gate_feature("thread_local", i.span,
 156                                   "`#[thread_local]` is an experimental feature, and does not \
 157                                   currently handle destructors. There is no corresponding \
 158                                   `#[task_local]` mapping to the task model");
 159             }
 160         }
 161         match i.node {
 162             ast::ItemEnum(ref def, _) => {
 163                 for variant in def.variants.iter() {
 164                     match variant.node.kind {
 165                         ast::StructVariantKind(..) => {
 166                             self.gate_feature("struct_variant", variant.span,
 167                                               "enum struct variants are \
 168                                                experimental and possibly buggy");
 169                         }
 170                         _ => {}
 171                     }
 172                 }
 173             }
 174
 175             ast::ItemForeignMod(..) => {
 176                 if attr::contains_name(i.attrs.as_slice(), "link_args") {
 177                     self.gate_feature("link_args", i.span,
 178                                       "the `link_args` attribute is not portable \
 179                                        across platforms, it is recommended to \
 180                                        use `#[link(name = \"foo\")]` instead")
 181                 }
 182             }
 183
 184             ast::ItemFn(..) => {
 185                 if attr::contains_name(i.attrs.as_slice(), "macro_registrar") {
 186                     self.gate_feature("macro_registrar", i.span,
 187                                       "cross-crate macro exports are \
 188                                        experimental and possibly buggy");
 189                 }
 190             }
 191
 192             ast::ItemStruct(..) => {
 193                 if attr::contains_name(i.attrs.as_slice(), "simd") {
 194                     self.gate_feature("simd", i.span,
 195                                       "SIMD types are experimental and possibly buggy");
 196                 }
 197             }
 198
 199             _ => {}
 200         }
 201
 202         visit::walk_item(self, i, ());
 203     }
 204
 205     fn visit_mac(&mut self, macro: &ast::Mac, _: ()) {
 206         let ast::MacInvocTT(ref path, _, _) = macro.node;
 207         let id = path.segments.last().unwrap().identifier;
 208         let quotes = ["quote_tokens", "quote_expr", "quote_ty",
 209                       "quote_item", "quote_pat", "quote_stmt"];
 210         let msg = " is not stable enough for use and are subject to change";
 211
 212
 213         if id == token::str_to_ident("macro_rules") {
 214             self.gate_feature("macro_rules", path.span, "macro definitions are \
 215                 not stable enough for use and are subject to change");
 216         }
 217
 218         else if id == token::str_to_ident("asm") {
 219             self.gate_feature("asm", path.span, "inline assembly is not \
 220                 stable enough for use and is subject to change");
 221         }
 222
 223         else if id == token::str_to_ident("log_syntax") {
 224             self.gate_feature("log_syntax", path.span, "`log_syntax!` is not \
 225                 stable enough for use and is subject to change");
 226         }
 227
 228         else if id == token::str_to_ident("trace_macros") {
 229             self.gate_feature("trace_macros", path.span, "`trace_macros` is not \
 230                 stable enough for use and is subject to change");
 231         }
 232
 233         else {
 234             for &quote in quotes.iter() {
 235                 if id == token::str_to_ident(quote) {
 236                   self.gate_feature("quote", path.span, quote + msg);
 237                 }
 238             }
 239         }
 240     }
 241
 242     fn visit_foreign_item(&mut self, i: &ast::ForeignItem, _: ()) {
 243         match i.node {
 244             ast::ForeignItemFn(..) | ast::ForeignItemStatic(..) => {
 245                 if attr::contains_name(i.attrs.as_slice(), "linkage") {
 246                     self.gate_feature("linkage", i.span,
 247                                       "the `linkage` attribute is experimental \
 248                                        and not portable across platforms")
 249                 }
 250             }
 251         }
 252         visit::walk_foreign_item(self, i, ())
 253     }
 254
 255     fn visit_ty(&mut self, t: &ast::Ty, _: ()) {
 256         match t.node {
 257             ast::TyClosure(closure) if closure.onceness == ast::Once &&
 258                     closure.sigil != ast::OwnedSigil => {
 259                 self.gate_feature("once_fns", t.span,
 260                                   "once functions are \
 261                                    experimental and likely to be removed");
 262
 263             },
 264             ast::TyBox(_) => { self.gate_box(t.span); }
 265             _ => {}
 266         }
 267
 268         visit::walk_ty(self, t, ());
 269     }
 270
 271     fn visit_expr(&mut self, e: &ast::Expr, _: ()) {
 272         match e.node {
 273             ast::ExprUnary(ast::UnBox, _) => {
 274                 self.gate_box(e.span);
 275             }
 276             _ => {}
 277         }
 278         visit::walk_expr(self, e, ());
 279     }
 280
 281     fn visit_generics(&mut self, generics: &ast::Generics, _: ()) {
 282         for type_parameter in generics.ty_params.iter() {
 283             match type_parameter.default {
 284                 Some(ty) => {
 285                     self.gate_feature("default_type_params", ty.span,
 286                                       "default type parameters are \
 287                                        experimental and possibly buggy");
 288                 }
 289                 None => {}
 290             }
 291         }
 292         visit::walk_generics(self, generics, ());
 293     }
 294 }
 295
 296 pub fn check_crate(sess: Session, krate: &ast::Crate) {
 297     let mut cx = Context {
 298         features: Vec::new(),
 299         sess: sess,
 300     };
 301
 302     for attr in krate.attrs.iter() {
 303         if !attr.name().equiv(&("feature")) {
 304             continue
 305         }
 306
 307         match attr.meta_item_list() {
 308             None => {
 309                 sess.span_err(attr.span, "malformed feature attribute, \
 310                                           expected #[feature(...)]");
 311             }
 312             Some(list) => {
 313                 for &mi in list.iter() {
 314                     let name = match mi.node {
 315                         ast::MetaWord(ref word) => (*word).clone(),
 316                         _ => {
 317                             sess.span_err(mi.span,
 318                                           "malformed feature, expected just \
 319                                            one word");
 320                             continue
 321                         }
 322                     };
 323                     match KNOWN_FEATURES.iter()
 324                                         .find(|& &(n, _)| name.equiv(&n)) {
 325                         Some(&(name, Active)) => { cx.features.push(name); }
 326                         Some(&(_, Removed)) => {
 327                             sess.span_err(mi.span, "feature has been removed");
 328                         }
 329                         Some(&(_, Accepted)) => {
 330                             sess.span_warn(mi.span, "feature has added to rust, \
 331                                                      directive not necessary");
 332                         }
 333                         None => {
 334                             sess.add_lint(lint::UnknownFeatures,
 335                                           ast::CRATE_NODE_ID,
 336                                           mi.span,
 337                                           ~"unknown feature");
 338                         }
 339                     }
 340                 }
 341             }
 342         }
 343     }
 344
 345     visit::walk_crate(&mut cx, krate, ());
 346
 347     sess.abort_if_errors();
 348
 349     sess.features.default_type_params.set(cx.has_feature("default_type_params"));
 350 }