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     ("plugin_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     ("struct_inherit", Active),
  59     ("overloaded_calls", Active),
  60     ("unboxed_closure_sugar", Active),
  61
  62     ("quad_precision_float", Active),
  63
  64     // A temporary feature gate used to enable parser extensions needed
  65     // to bootstrap fix for #5723.
  66     ("issue_5723_bootstrap", Active),
  67
  68     // These are used to test this portion of the compiler, they don't actually
  69     // mean anything
  70     ("test_accepted_feature", Accepted),
  71     ("test_removed_feature", Removed),
  72 ];
  73
  74 enum Status {
  75     /// Represents an active feature that is currently being implemented or
  76     /// currently being considered for addition/removal.
  77     Active,
  78
  79     /// Represents a feature which has since been removed (it was once Active)
  80     Removed,
  81
  82     /// This language feature has since been Accepted (it was once Active)
  83     Accepted,
  84 }
  85
  86 /// A set of features to be used by later passes.
  87 pub struct Features {
  88     pub default_type_params: Cell<bool>,
  89     pub quad_precision_float: Cell<bool>,
  90     pub issue_5723_bootstrap: Cell<bool>,
  91     pub overloaded_calls: Cell<bool>,
  92 }
  93
  94 impl Features {
  95     pub fn new() -> Features {
  96         Features {
  97             default_type_params: Cell::new(false),
  98             quad_precision_float: Cell::new(false),
  99             issue_5723_bootstrap: Cell::new(false),
 100             overloaded_calls: Cell::new(false),
 101         }
 102     }
 103 }
 104
 105 struct Context<'a> {
 106     features: Vec<&'static str>,
 107     sess: &'a Session,
 108 }
 109
 110 impl<'a> Context<'a> {
 111     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
 112         if !self.has_feature(feature) {
 113             self.sess.span_err(span, explain);
 114             self.sess.span_note(span, format!("add #![feature({})] to the \
 115                                                crate attributes to enable",
 116                                               feature).as_slice());
 117         }
 118     }
 119
 120     fn gate_box(&self, span: Span) {
 121         self.gate_feature("managed_boxes", span,
 122                           "The managed box syntax is being replaced by the \
 123                            `std::gc::Gc` and `std::rc::Rc` types. Equivalent \
 124                            functionality to managed trait objects will be \
 125                            implemented but is currently missing.");
 126     }
 127
 128     fn has_feature(&self, feature: &str) -> bool {
 129         self.features.iter().any(|n| n.as_slice() == feature)
 130     }
 131 }
 132
 133 impl<'a> Visitor<()> for Context<'a> {
 134     fn visit_ident(&mut self, sp: Span, id: ast::Ident, _: ()) {
 135         if !token::get_ident(id).get().is_ascii() {
 136             self.gate_feature("non_ascii_idents", sp,
 137                               "non-ascii idents are not fully supported.");
 138         }
 139     }
 140
 141     fn visit_view_item(&mut self, i: &ast::ViewItem, _: ()) {
 142         match i.node {
 143             ast::ViewItemUse(ref path) => {
 144                 match path.node {
 145                     ast::ViewPathGlob(..) => {
 146                         self.gate_feature("globs", path.span,
 147                                           "glob import statements are \
 148                                            experimental and possibly buggy");
 149                     }
 150                     _ => {}
 151                 }
 152             }
 153             ast::ViewItemExternCrate(..) => {
 154                 for attr in i.attrs.iter() {
 155                     if attr.name().get() == "phase"{
 156                         self.gate_feature("phase", attr.span,
 157                                           "compile time crate loading is \
 158                                            experimental and possibly buggy");
 159                     }
 160                 }
 161             }
 162         }
 163         visit::walk_view_item(self, i, ())
 164     }
 165
 166     fn visit_item(&mut self, i: &ast::Item, _:()) {
 167         for attr in i.attrs.iter() {
 168             if attr.name().equiv(&("thread_local")) {
 169                 self.gate_feature("thread_local", i.span,
 170                                   "`#[thread_local]` is an experimental feature, and does not \
 171                                   currently handle destructors. There is no corresponding \
 172                                   `#[task_local]` mapping to the task model");
 173             }
 174         }
 175         match i.node {
 176             ast::ItemEnum(ref def, _) => {
 177                 for variant in def.variants.iter() {
 178                     match variant.node.kind {
 179                         ast::StructVariantKind(..) => {
 180                             self.gate_feature("struct_variant", variant.span,
 181                                               "enum struct variants are \
 182                                                experimental and possibly buggy");
 183                         }
 184                         _ => {}
 185                     }
 186                 }
 187             }
 188
 189             ast::ItemForeignMod(..) => {
 190                 if attr::contains_name(i.attrs.as_slice(), "link_args") {
 191                     self.gate_feature("link_args", i.span,
 192                                       "the `link_args` attribute is not portable \
 193                                        across platforms, it is recommended to \
 194                                        use `#[link(name = \"foo\")]` instead")
 195                 }
 196             }
 197
 198             ast::ItemFn(..) => {
 199                 if attr::contains_name(i.attrs.as_slice(), "plugin_registrar") {
 200                     self.gate_feature("plugin_registrar", i.span,
 201                                       "compiler plugins are experimental and possibly buggy");
 202                 }
 203             }
 204
 205             ast::ItemStruct(struct_definition, _) => {
 206                 if attr::contains_name(i.attrs.as_slice(), "simd") {
 207                     self.gate_feature("simd", i.span,
 208                                       "SIMD types are experimental and possibly buggy");
 209                 }
 210                 match struct_definition.super_struct {
 211                     Some(ref path) => self.gate_feature("struct_inherit", path.span,
 212                                                         "struct inheritance is experimental \
 213                                                          and possibly buggy"),
 214                     None => {}
 215                 }
 216                 if struct_definition.is_virtual {
 217                     self.gate_feature("struct_inherit", i.span,
 218                                       "struct inheritance (`virtual` keyword) is \
 219                                        experimental and possibly buggy");
 220                 }
 221             }
 222
 223             _ => {}
 224         }
 225
 226         visit::walk_item(self, i, ());
 227     }
 228
 229     fn visit_mac(&mut self, macro: &ast::Mac, _: ()) {
 230         let ast::MacInvocTT(ref path, _, _) = macro.node;
 231         let id = path.segments.last().unwrap().identifier;
 232         let quotes = ["quote_tokens", "quote_expr", "quote_ty",
 233                       "quote_item", "quote_pat", "quote_stmt"];
 234         let msg = " is not stable enough for use and are subject to change";
 235
 236
 237         if id == token::str_to_ident("macro_rules") {
 238             self.gate_feature("macro_rules", path.span, "macro definitions are \
 239                 not stable enough for use and are subject to change");
 240         }
 241
 242         else if id == token::str_to_ident("asm") {
 243             self.gate_feature("asm", path.span, "inline assembly is not \
 244                 stable enough for use and is subject to change");
 245         }
 246
 247         else if id == token::str_to_ident("log_syntax") {
 248             self.gate_feature("log_syntax", path.span, "`log_syntax!` is not \
 249                 stable enough for use and is subject to change");
 250         }
 251
 252         else if id == token::str_to_ident("trace_macros") {
 253             self.gate_feature("trace_macros", path.span, "`trace_macros` is not \
 254                 stable enough for use and is subject to change");
 255         }
 256
 257         else if id == token::str_to_ident("concat_idents") {
 258             self.gate_feature("concat_idents", path.span, "`concat_idents` is not \
 259                 stable enough for use and is subject to change");
 260         }
 261
 262         else {
 263             for &quote in quotes.iter() {
 264                 if id == token::str_to_ident(quote) {
 265                   self.gate_feature("quote",
 266                                     path.span,
 267                                     format!("{}{}", quote, msg).as_slice());
 268                 }
 269             }
 270         }
 271     }
 272
 273     fn visit_foreign_item(&mut self, i: &ast::ForeignItem, _: ()) {
 274         match i.node {
 275             ast::ForeignItemFn(..) | ast::ForeignItemStatic(..) => {
 276                 if attr::contains_name(i.attrs.as_slice(), "linkage") {
 277                     self.gate_feature("linkage", i.span,
 278                                       "the `linkage` attribute is experimental \
 279                                        and not portable across platforms")
 280                 }
 281             }
 282         }
 283         visit::walk_foreign_item(self, i, ())
 284     }
 285
 286     fn visit_ty(&mut self, t: &ast::Ty, _: ()) {
 287         match t.node {
 288             ast::TyClosure(closure, _) if closure.onceness == ast::Once => {
 289                 self.gate_feature("once_fns", t.span,
 290                                   "once functions are \
 291                                    experimental and likely to be removed");
 292
 293             },
 294             ast::TyBox(_) => { self.gate_box(t.span); }
 295             ast::TyUnboxedFn(_) => {
 296                 self.gate_feature("unboxed_closure_sugar",
 297                                   t.span,
 298                                   "unboxed closure trait sugar is experimental");
 299             }
 300             _ => {}
 301         }
 302
 303         visit::walk_ty(self, t, ());
 304     }
 305
 306     fn visit_expr(&mut self, e: &ast::Expr, _: ()) {
 307         match e.node {
 308             ast::ExprUnary(ast::UnBox, _) => {
 309                 self.gate_box(e.span);
 310             }
 311             _ => {}
 312         }
 313         visit::walk_expr(self, e, ());
 314     }
 315
 316     fn visit_generics(&mut self, generics: &ast::Generics, _: ()) {
 317         for type_parameter in generics.ty_params.iter() {
 318             match type_parameter.default {
 319                 Some(ty) => {
 320                     self.gate_feature("default_type_params", ty.span,
 321                                       "default type parameters are \
 322                                        experimental and possibly buggy");
 323                 }
 324                 None => {}
 325             }
 326         }
 327         visit::walk_generics(self, generics, ());
 328     }
 329 }
 330
 331 pub fn check_crate(sess: &Session, krate: &ast::Crate) {
 332     let mut cx = Context {
 333         features: Vec::new(),
 334         sess: sess,
 335     };
 336
 337     for attr in krate.attrs.iter() {
 338         if !attr.check_name("feature") {
 339             continue
 340         }
 341
 342         match attr.meta_item_list() {
 343             None => {
 344                 sess.span_err(attr.span, "malformed feature attribute, \
 345                                           expected #![feature(...)]");
 346             }
 347             Some(list) => {
 348                 for &mi in list.iter() {
 349                     let name = match mi.node {
 350                         ast::MetaWord(ref word) => (*word).clone(),
 351                         _ => {
 352                             sess.span_err(mi.span,
 353                                           "malformed feature, expected just \
 354                                            one word");
 355                             continue
 356                         }
 357                     };
 358                     match KNOWN_FEATURES.iter()
 359                                         .find(|& &(n, _)| name.equiv(&n)) {
 360                         Some(&(name, Active)) => { cx.features.push(name); }
 361                         Some(&(_, Removed)) => {
 362                             sess.span_err(mi.span, "feature has been removed");
 363                         }
 364                         Some(&(_, Accepted)) => {
 365                             sess.span_warn(mi.span, "feature has added to rust, \
 366                                                      directive not necessary");
 367                         }
 368                         None => {
 369                             sess.add_lint(lint::UnknownFeatures,
 370                                           ast::CRATE_NODE_ID,
 371                                           mi.span,
 372                                           "unknown feature".to_string());
 373                         }
 374                     }
 375                 }
 376             }
 377         }
 378     }
 379
 380     visit::walk_crate(&mut cx, krate, ());
 381
 382     sess.abort_if_errors();
 383
 384     sess.features.default_type_params.set(cx.has_feature("default_type_params"));
 385     sess.features.quad_precision_float.set(cx.has_feature("quad_precision_float"));
 386     sess.features.issue_5723_bootstrap.set(cx.has_feature("issue_5723_bootstrap"));
 387     sess.features.overloaded_calls.set(cx.has_feature("overloaded_calls"));
 388 }