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     ("concat_idents", Active),
  53
  54     ("simd", Active),
  55     ("default_type_params", Active),
  56     ("quote", Active),
  57     ("linkage", Active),
  58
  59     // These are used to test this portion of the compiler, they don't actually
  60     // mean anything
  61     ("test_accepted_feature", Accepted),
  62     ("test_removed_feature", Removed),
  63 ];
  64
  65 enum Status {
  66     /// Represents an active feature that is currently being implemented or
  67     /// currently being considered for addition/removal.
  68     Active,
  69
  70     /// Represents a feature which has since been removed (it was once Active)
  71     Removed,
  72
  73     /// This language feature has since been Accepted (it was once Active)
  74     Accepted,
  75 }
  76
  77 /// A set of features to be used by later passes.
  78 pub struct Features {
  79     pub default_type_params: Cell<bool>
  80 }
  81
  82 impl Features {
  83     pub fn new() -> Features {
  84         Features {
  85             default_type_params: Cell::new(false)
  86         }
  87     }
  88 }
  89
  90 struct Context<'a> {
  91     features: Vec<&'static str>,
  92     sess: &'a Session,
  93 }
  94
  95 impl<'a> Context<'a> {
  96     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
  97         if !self.has_feature(feature) {
  98             self.sess.span_err(span, explain);
  99             self.sess.span_note(span, format!("add \\#[feature({})] to the \
 100                                                   crate attributes to enable",
 101                                                  feature));
 102         }
 103     }
 104
 105     fn gate_box(&self, span: Span) {
 106         self.gate_feature("managed_boxes", span,
 107                           "The managed box syntax is being replaced by the \
 108                            `std::gc::Gc` and `std::rc::Rc` types. Equivalent \
 109                            functionality to managed trait objects will be \
 110                            implemented but is currently missing.");
 111     }
 112
 113     fn has_feature(&self, feature: &str) -> bool {
 114         self.features.iter().any(|n| n.as_slice() == feature)
 115     }
 116 }
 117
 118 impl<'a> Visitor<()> for Context<'a> {
 119     fn visit_ident(&mut self, sp: Span, id: ast::Ident, _: ()) {
 120         if !token::get_ident(id).get().is_ascii() {
 121             self.gate_feature("non_ascii_idents", sp,
 122                               "non-ascii idents are not fully supported.");
 123         }
 124     }
 125
 126     fn visit_view_item(&mut self, i: &ast::ViewItem, _: ()) {
 127         match i.node {
 128             ast::ViewItemUse(ref paths) => {
 129                 for path in paths.iter() {
 130                     match path.node {
 131                         ast::ViewPathGlob(..) => {
 132                             self.gate_feature("globs", path.span,
 133                                               "glob import statements are \
 134                                                experimental and possibly buggy");
 135                         }
 136                         _ => {}
 137                     }
 138                 }
 139             }
 140             ast::ViewItemExternCrate(..) => {
 141                 for attr in i.attrs.iter() {
 142                     if attr.name().get() == "phase"{
 143                         self.gate_feature("phase", attr.span,
 144                                           "compile time crate loading is \
 145                                            experimental and possibly buggy");
 146                     }
 147                 }
 148             }
 149         }
 150         visit::walk_view_item(self, i, ())
 151     }
 152
 153     fn visit_item(&mut self, i: &ast::Item, _:()) {
 154         for attr in i.attrs.iter() {
 155             if attr.name().equiv(&("thread_local")) {
 156                 self.gate_feature("thread_local", i.span,
 157                                   "`#[thread_local]` is an experimental feature, and does not \
 158                                   currently handle destructors. There is no corresponding \
 159                                   `#[task_local]` mapping to the task model");
 160             }
 161         }
 162         match i.node {
 163             ast::ItemEnum(ref def, _) => {
 164                 for variant in def.variants.iter() {
 165                     match variant.node.kind {
 166                         ast::StructVariantKind(..) => {
 167                             self.gate_feature("struct_variant", variant.span,
 168                                               "enum struct variants are \
 169                                                experimental and possibly buggy");
 170                         }
 171                         _ => {}
 172                     }
 173                 }
 174             }
 175
 176             ast::ItemForeignMod(..) => {
 177                 if attr::contains_name(i.attrs.as_slice(), "link_args") {
 178                     self.gate_feature("link_args", i.span,
 179                                       "the `link_args` attribute is not portable \
 180                                        across platforms, it is recommended to \
 181                                        use `#[link(name = \"foo\")]` instead")
 182                 }
 183             }
 184
 185             ast::ItemFn(..) => {
 186                 if attr::contains_name(i.attrs.as_slice(), "macro_registrar") {
 187                     self.gate_feature("macro_registrar", i.span,
 188                                       "cross-crate macro exports are \
 189                                        experimental and possibly buggy");
 190                 }
 191             }
 192
 193             ast::ItemStruct(..) => {
 194                 if attr::contains_name(i.attrs.as_slice(), "simd") {
 195                     self.gate_feature("simd", i.span,
 196                                       "SIMD types are experimental and possibly buggy");
 197                 }
 198             }
 199
 200             _ => {}
 201         }
 202
 203         visit::walk_item(self, i, ());
 204     }
 205
 206     fn visit_mac(&mut self, macro: &ast::Mac, _: ()) {
 207         let ast::MacInvocTT(ref path, _, _) = macro.node;
 208         let id = path.segments.last().unwrap().identifier;
 209         let quotes = ["quote_tokens", "quote_expr", "quote_ty",
 210                       "quote_item", "quote_pat", "quote_stmt"];
 211         let msg = " is not stable enough for use and are subject to change";
 212
 213
 214         if id == token::str_to_ident("macro_rules") {
 215             self.gate_feature("macro_rules", path.span, "macro definitions are \
 216                 not stable enough for use and are subject to change");
 217         }
 218
 219         else if id == token::str_to_ident("asm") {
 220             self.gate_feature("asm", path.span, "inline assembly is not \
 221                 stable enough for use and is subject to change");
 222         }
 223
 224         else if id == token::str_to_ident("log_syntax") {
 225             self.gate_feature("log_syntax", path.span, "`log_syntax!` is not \
 226                 stable enough for use and is subject to change");
 227         }
 228
 229         else if id == token::str_to_ident("trace_macros") {
 230             self.gate_feature("trace_macros", path.span, "`trace_macros` is not \
 231                 stable enough for use and is subject to change");
 232         }
 233
 234         else if id == token::str_to_ident("concat_idents") {
 235             self.gate_feature("concat_idents", path.span, "`concat_idents` is not \
 236                 stable enough for use and is subject to change");
 237         }
 238
 239         else {
 240             for &quote in quotes.iter() {
 241                 if id == token::str_to_ident(quote) {
 242                   self.gate_feature("quote", path.span, quote + msg);
 243                 }
 244             }
 245         }
 246     }
 247
 248     fn visit_foreign_item(&mut self, i: &ast::ForeignItem, _: ()) {
 249         match i.node {
 250             ast::ForeignItemFn(..) | ast::ForeignItemStatic(..) => {
 251                 if attr::contains_name(i.attrs.as_slice(), "linkage") {
 252                     self.gate_feature("linkage", i.span,
 253                                       "the `linkage` attribute is experimental \
 254                                        and not portable across platforms")
 255                 }
 256             }
 257         }
 258         visit::walk_foreign_item(self, i, ())
 259     }
 260
 261     fn visit_ty(&mut self, t: &ast::Ty, _: ()) {
 262         match t.node {
 263             ast::TyClosure(closure) if closure.onceness == ast::Once &&
 264                     closure.sigil != ast::OwnedSigil => {
 265                 self.gate_feature("once_fns", t.span,
 266                                   "once functions are \
 267                                    experimental and likely to be removed");
 268
 269             },
 270             ast::TyBox(_) => { self.gate_box(t.span); }
 271             _ => {}
 272         }
 273
 274         visit::walk_ty(self, t, ());
 275     }
 276
 277     fn visit_expr(&mut self, e: &ast::Expr, _: ()) {
 278         match e.node {
 279             ast::ExprUnary(ast::UnBox, _) => {
 280                 self.gate_box(e.span);
 281             }
 282             _ => {}
 283         }
 284         visit::walk_expr(self, e, ());
 285     }
 286
 287     fn visit_generics(&mut self, generics: &ast::Generics, _: ()) {
 288         for type_parameter in generics.ty_params.iter() {
 289             match type_parameter.default {
 290                 Some(ty) => {
 291                     self.gate_feature("default_type_params", ty.span,
 292                                       "default type parameters are \
 293                                        experimental and possibly buggy");
 294                 }
 295                 None => {}
 296             }
 297         }
 298         visit::walk_generics(self, generics, ());
 299     }
 300 }
 301
 302 pub fn check_crate(sess: &Session, krate: &ast::Crate) {
 303     let mut cx = Context {
 304         features: Vec::new(),
 305         sess: sess,
 306     };
 307
 308     for attr in krate.attrs.iter() {
 309         if !attr.name().equiv(&("feature")) {
 310             continue
 311         }
 312
 313         match attr.meta_item_list() {
 314             None => {
 315                 sess.span_err(attr.span, "malformed feature attribute, \
 316                                           expected #[feature(...)]");
 317             }
 318             Some(list) => {
 319                 for &mi in list.iter() {
 320                     let name = match mi.node {
 321                         ast::MetaWord(ref word) => (*word).clone(),
 322                         _ => {
 323                             sess.span_err(mi.span,
 324                                           "malformed feature, expected just \
 325                                            one word");
 326                             continue
 327                         }
 328                     };
 329                     match KNOWN_FEATURES.iter()
 330                                         .find(|& &(n, _)| name.equiv(&n)) {
 331                         Some(&(name, Active)) => { cx.features.push(name); }
 332                         Some(&(_, Removed)) => {
 333                             sess.span_err(mi.span, "feature has been removed");
 334                         }
 335                         Some(&(_, Accepted)) => {
 336                             sess.span_warn(mi.span, "feature has added to rust, \
 337                                                      directive not necessary");
 338                         }
 339                         None => {
 340                             sess.add_lint(lint::UnknownFeatures,
 341                                           ast::CRATE_NODE_ID,
 342                                           mi.span,
 343                                           ~"unknown feature");
 344                         }
 345                     }
 346                 }
 347             }
 348         }
 349     }
 350
 351     visit::walk_crate(&mut cx, krate, ());
 352
 353     sess.abort_if_errors();
 354
 355     sess.features.default_type_params.set(cx.has_feature("default_type_params"));
 356 }