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     ("unsafe_destructor", Active),
  54
  55     ("simd", Active),
  56     ("default_type_params", Active),
  57     ("quote", Active),
  58     ("linkage", Active),
  59     ("struct_inherit", Active),
  60     ("overloaded_calls", Active),
  61     ("unboxed_closure_sugar", Active),
  62
  63     ("quad_precision_float", Active),
  64
  65     // A temporary feature gate used to enable parser extensions needed
  66     // to bootstrap fix for #5723.
  67     ("issue_5723_bootstrap", Active),
  68
  69     // These are used to test this portion of the compiler, they don't actually
  70     // mean anything
  71     ("test_accepted_feature", Accepted),
  72     ("test_removed_feature", Removed),
  73 ];
  74
  75 enum Status {
  76     /// Represents an active feature that is currently being implemented or
  77     /// currently being considered for addition/removal.
  78     Active,
  79
  80     /// Represents a feature which has since been removed (it was once Active)
  81     Removed,
  82
  83     /// This language feature has since been Accepted (it was once Active)
  84     Accepted,
  85 }
  86
  87 /// A set of features to be used by later passes.
  88 pub struct Features {
  89     pub default_type_params: Cell<bool>,
  90     pub quad_precision_float: Cell<bool>,
  91     pub issue_5723_bootstrap: Cell<bool>,
  92     pub overloaded_calls: Cell<bool>,
  93 }
  94
  95 impl Features {
  96     pub fn new() -> Features {
  97         Features {
  98             default_type_params: Cell::new(false),
  99             quad_precision_float: Cell::new(false),
 100             issue_5723_bootstrap: Cell::new(false),
 101             overloaded_calls: Cell::new(false),
 102         }
 103     }
 104 }
 105
 106 struct Context<'a> {
 107     features: Vec<&'static str>,
 108     sess: &'a Session,
 109 }
 110
 111 impl<'a> Context<'a> {
 112     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
 113         if !self.has_feature(feature) {
 114             self.sess.span_err(span, explain);
 115             self.sess.span_note(span, format!("add #![feature({})] to the \
 116                                                crate attributes to enable",
 117                                               feature).as_slice());
 118         }
 119     }
 120
 121     fn gate_box(&self, span: Span) {
 122         self.gate_feature("managed_boxes", span,
 123                           "The managed box syntax is being replaced by the \
 124                            `std::gc::Gc` and `std::rc::Rc` types. Equivalent \
 125                            functionality to managed trait objects will be \
 126                            implemented but is currently missing.");
 127     }
 128
 129     fn has_feature(&self, feature: &str) -> bool {
 130         self.features.iter().any(|n| n.as_slice() == feature)
 131     }
 132 }
 133
 134 impl<'a> Visitor<()> for Context<'a> {
 135     fn visit_ident(&mut self, sp: Span, id: ast::Ident, _: ()) {
 136         if !token::get_ident(id).get().is_ascii() {
 137             self.gate_feature("non_ascii_idents", sp,
 138                               "non-ascii idents are not fully supported.");
 139         }
 140     }
 141
 142     fn visit_view_item(&mut self, i: &ast::ViewItem, _: ()) {
 143         match i.node {
 144             ast::ViewItemUse(ref path) => {
 145                 match path.node {
 146                     ast::ViewPathGlob(..) => {
 147                         self.gate_feature("globs", path.span,
 148                                           "glob import statements are \
 149                                            experimental and possibly buggy");
 150                     }
 151                     _ => {}
 152                 }
 153             }
 154             ast::ViewItemExternCrate(..) => {
 155                 for attr in i.attrs.iter() {
 156                     if attr.name().get() == "phase"{
 157                         self.gate_feature("phase", attr.span,
 158                                           "compile time crate loading is \
 159                                            experimental and possibly buggy");
 160                     }
 161                 }
 162             }
 163         }
 164         visit::walk_view_item(self, i, ())
 165     }
 166
 167     fn visit_item(&mut self, i: &ast::Item, _:()) {
 168         for attr in i.attrs.iter() {
 169             if attr.name().equiv(&("thread_local")) {
 170                 self.gate_feature("thread_local", i.span,
 171                                   "`#[thread_local]` is an experimental feature, and does not \
 172                                   currently handle destructors. There is no corresponding \
 173                                   `#[task_local]` mapping to the task model");
 174             }
 175         }
 176         match i.node {
 177             ast::ItemEnum(ref def, _) => {
 178                 for variant in def.variants.iter() {
 179                     match variant.node.kind {
 180                         ast::StructVariantKind(..) => {
 181                             self.gate_feature("struct_variant", variant.span,
 182                                               "enum struct variants are \
 183                                                experimental and possibly buggy");
 184                         }
 185                         _ => {}
 186                     }
 187                 }
 188             }
 189
 190             ast::ItemForeignMod(..) => {
 191                 if attr::contains_name(i.attrs.as_slice(), "link_args") {
 192                     self.gate_feature("link_args", i.span,
 193                                       "the `link_args` attribute is not portable \
 194                                        across platforms, it is recommended to \
 195                                        use `#[link(name = \"foo\")]` instead")
 196                 }
 197             }
 198
 199             ast::ItemFn(..) => {
 200                 if attr::contains_name(i.attrs.as_slice(), "plugin_registrar") {
 201                     self.gate_feature("plugin_registrar", i.span,
 202                                       "compiler plugins are experimental and possibly buggy");
 203                 }
 204             }
 205
 206             ast::ItemStruct(struct_definition, _) => {
 207                 if attr::contains_name(i.attrs.as_slice(), "simd") {
 208                     self.gate_feature("simd", i.span,
 209                                       "SIMD types are experimental and possibly buggy");
 210                 }
 211                 match struct_definition.super_struct {
 212                     Some(ref path) => self.gate_feature("struct_inherit", path.span,
 213                                                         "struct inheritance is experimental \
 214                                                          and possibly buggy"),
 215                     None => {}
 216                 }
 217                 if struct_definition.is_virtual {
 218                     self.gate_feature("struct_inherit", i.span,
 219                                       "struct inheritance (`virtual` keyword) is \
 220                                        experimental and possibly buggy");
 221                 }
 222             }
 223
 224             ast::ItemImpl(..) => {
 225                 if attr::contains_name(i.attrs.as_slice(),
 226                                        "unsafe_destructor") {
 227                     self.gate_feature("unsafe_destructor",
 228                                       i.span,
 229                                       "`#[unsafe_destructor]` allows too \
 230                                        many unsafe patterns and may be \
 231                                        removed in the future");
 232                 }
 233             }
 234
 235             _ => {}
 236         }
 237
 238         visit::walk_item(self, i, ());
 239     }
 240
 241     fn visit_mac(&mut self, macro: &ast::Mac, _: ()) {
 242         let ast::MacInvocTT(ref path, _, _) = macro.node;
 243         let id = path.segments.last().unwrap().identifier;
 244         let quotes = ["quote_tokens", "quote_expr", "quote_ty",
 245                       "quote_item", "quote_pat", "quote_stmt"];
 246         let msg = " is not stable enough for use and are subject to change";
 247
 248
 249         if id == token::str_to_ident("macro_rules") {
 250             self.gate_feature("macro_rules", path.span, "macro definitions are \
 251                 not stable enough for use and are subject to change");
 252         }
 253
 254         else if id == token::str_to_ident("asm") {
 255             self.gate_feature("asm", path.span, "inline assembly is not \
 256                 stable enough for use and is subject to change");
 257         }
 258
 259         else if id == token::str_to_ident("log_syntax") {
 260             self.gate_feature("log_syntax", path.span, "`log_syntax!` is not \
 261                 stable enough for use and is subject to change");
 262         }
 263
 264         else if id == token::str_to_ident("trace_macros") {
 265             self.gate_feature("trace_macros", path.span, "`trace_macros` is not \
 266                 stable enough for use and is subject to change");
 267         }
 268
 269         else if id == token::str_to_ident("concat_idents") {
 270             self.gate_feature("concat_idents", path.span, "`concat_idents` is not \
 271                 stable enough for use and is subject to change");
 272         }
 273
 274         else {
 275             for &quote in quotes.iter() {
 276                 if id == token::str_to_ident(quote) {
 277                   self.gate_feature("quote",
 278                                     path.span,
 279                                     format!("{}{}", quote, msg).as_slice());
 280                 }
 281             }
 282         }
 283     }
 284
 285     fn visit_foreign_item(&mut self, i: &ast::ForeignItem, _: ()) {
 286         match i.node {
 287             ast::ForeignItemFn(..) | ast::ForeignItemStatic(..) => {
 288                 if attr::contains_name(i.attrs.as_slice(), "linkage") {
 289                     self.gate_feature("linkage", i.span,
 290                                       "the `linkage` attribute is experimental \
 291                                        and not portable across platforms")
 292                 }
 293             }
 294         }
 295         visit::walk_foreign_item(self, i, ())
 296     }
 297
 298     fn visit_ty(&mut self, t: &ast::Ty, _: ()) {
 299         match t.node {
 300             ast::TyClosure(closure, _) if closure.onceness == ast::Once => {
 301                 self.gate_feature("once_fns", t.span,
 302                                   "once functions are \
 303                                    experimental and likely to be removed");
 304
 305             },
 306             ast::TyBox(_) => { self.gate_box(t.span); }
 307             ast::TyUnboxedFn(_) => {
 308                 self.gate_feature("unboxed_closure_sugar",
 309                                   t.span,
 310                                   "unboxed closure trait sugar is experimental");
 311             }
 312             _ => {}
 313         }
 314
 315         visit::walk_ty(self, t, ());
 316     }
 317
 318     fn visit_expr(&mut self, e: &ast::Expr, _: ()) {
 319         match e.node {
 320             ast::ExprUnary(ast::UnBox, _) => {
 321                 self.gate_box(e.span);
 322             }
 323             _ => {}
 324         }
 325         visit::walk_expr(self, e, ());
 326     }
 327
 328     fn visit_generics(&mut self, generics: &ast::Generics, _: ()) {
 329         for type_parameter in generics.ty_params.iter() {
 330             match type_parameter.default {
 331                 Some(ty) => {
 332                     self.gate_feature("default_type_params", ty.span,
 333                                       "default type parameters are \
 334                                        experimental and possibly buggy");
 335                 }
 336                 None => {}
 337             }
 338         }
 339         visit::walk_generics(self, generics, ());
 340     }
 341 }
 342
 343 pub fn check_crate(sess: &Session, krate: &ast::Crate) {
 344     let mut cx = Context {
 345         features: Vec::new(),
 346         sess: sess,
 347     };
 348
 349     for attr in krate.attrs.iter() {
 350         if !attr.check_name("feature") {
 351             continue
 352         }
 353
 354         match attr.meta_item_list() {
 355             None => {
 356                 sess.span_err(attr.span, "malformed feature attribute, \
 357                                           expected #![feature(...)]");
 358             }
 359             Some(list) => {
 360                 for &mi in list.iter() {
 361                     let name = match mi.node {
 362                         ast::MetaWord(ref word) => (*word).clone(),
 363                         _ => {
 364                             sess.span_err(mi.span,
 365                                           "malformed feature, expected just \
 366                                            one word");
 367                             continue
 368                         }
 369                     };
 370                     match KNOWN_FEATURES.iter()
 371                                         .find(|& &(n, _)| name.equiv(&n)) {
 372                         Some(&(name, Active)) => { cx.features.push(name); }
 373                         Some(&(_, Removed)) => {
 374                             sess.span_err(mi.span, "feature has been removed");
 375                         }
 376                         Some(&(_, Accepted)) => {
 377                             sess.span_warn(mi.span, "feature has added to rust, \
 378                                                      directive not necessary");
 379                         }
 380                         None => {
 381                             sess.add_lint(lint::UnknownFeatures,
 382                                           ast::CRATE_NODE_ID,
 383                                           mi.span,
 384                                           "unknown feature".to_string());
 385                         }
 386                     }
 387                 }
 388             }
 389         }
 390     }
 391
 392     visit::walk_crate(&mut cx, krate, ());
 393
 394     sess.abort_if_errors();
 395
 396     sess.features.default_type_params.set(cx.has_feature("default_type_params"));
 397     sess.features.quad_precision_float.set(cx.has_feature("quad_precision_float"));
 398     sess.features.issue_5723_bootstrap.set(cx.has_feature("issue_5723_bootstrap"));
 399     sess.features.overloaded_calls.set(cx.has_feature("overloaded_calls"));
 400 }