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 lint;
  22
  23 use syntax::abi::RustIntrinsic;
  24 use syntax::ast::NodeId;
  25 use syntax::ast;
  26 use syntax::attr;
  27 use syntax::attr::AttrMetaMethods;
  28 use syntax::codemap::Span;
  29 use syntax::visit;
  30 use syntax::visit::Visitor;
  31 use syntax::parse::token;
  32
  33 use driver::session::Session;
  34
  35 use std::cell::Cell;
  36 use std::slice;
  37
  38 /// This is a list of all known features since the beginning of time. This list
  39 /// can never shrink, it may only be expanded (in order to prevent old programs
  40 /// from failing to compile). The status of each feature may change, however.
  41 static KNOWN_FEATURES: &'static [(&'static str, Status)] = &[
  42     ("globs", Active),
  43     ("macro_rules", Active),
  44     ("struct_variant", Active),
  45     ("once_fns", Active),
  46     ("asm", Active),
  47     ("managed_boxes", Active),
  48     ("non_ascii_idents", Active),
  49     ("thread_local", Active),
  50     ("link_args", Active),
  51     ("phase", Active),
  52     ("plugin_registrar", Active),
  53     ("log_syntax", Active),
  54     ("trace_macros", Active),
  55     ("concat_idents", Active),
  56     ("unsafe_destructor", Active),
  57     ("intrinsics", Active),
  58     ("lang_items", Active),
  59
  60     ("simd", Active),
  61     ("default_type_params", Active),
  62     ("quote", Active),
  63     ("linkage", Active),
  64     ("struct_inherit", Active),
  65     ("overloaded_calls", Active),
  66     ("unboxed_closure_sugar", Active),
  67
  68     ("quad_precision_float", Removed),
  69
  70     ("rustc_diagnostic_macros", Active),
  71     ("unboxed_closures", Active),
  72     ("import_shadowing", Active),
  73     ("advanced_slice_patterns", Active),
  74     ("tuple_indexing", Active),
  75
  76     // if you change this list without updating src/doc/rust.md, cmr will be sad
  77
  78     // A temporary feature gate used to enable parser extensions needed
  79     // to bootstrap fix for #5723.
  80     ("issue_5723_bootstrap", Accepted),
  81
  82     // These are used to test this portion of the compiler, they don't actually
  83     // mean anything
  84     ("test_accepted_feature", Accepted),
  85     ("test_removed_feature", Removed),
  86 ];
  87
  88 enum Status {
  89     /// Represents an active feature that is currently being implemented or
  90     /// currently being considered for addition/removal.
  91     Active,
  92
  93     /// Represents a feature which has since been removed (it was once Active)
  94     Removed,
  95
  96     /// This language feature has since been Accepted (it was once Active)
  97     Accepted,
  98 }
  99
 100 /// A set of features to be used by later passes.
 101 pub struct Features {
 102     pub default_type_params: Cell<bool>,
 103     pub overloaded_calls: Cell<bool>,
 104     pub rustc_diagnostic_macros: Cell<bool>,
 105     pub import_shadowing: Cell<bool>,
 106 }
 107
 108 impl Features {
 109     pub fn new() -> Features {
 110         Features {
 111             default_type_params: Cell::new(false),
 112             overloaded_calls: Cell::new(false),
 113             rustc_diagnostic_macros: Cell::new(false),
 114             import_shadowing: Cell::new(false),
 115         }
 116     }
 117 }
 118
 119 struct Context<'a> {
 120     features: Vec<&'static str>,
 121     sess: &'a Session,
 122 }
 123
 124 impl<'a> Context<'a> {
 125     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
 126         if !self.has_feature(feature) {
 127             self.sess.span_err(span, explain);
 128             self.sess.span_note(span, format!("add #![feature({})] to the \
 129                                                crate attributes to enable",
 130                                               feature).as_slice());
 131         }
 132     }
 133
 134     fn gate_box(&self, span: Span) {
 135         self.gate_feature("managed_boxes", span,
 136                           "The managed box syntax is being replaced by the \
 137                            `std::gc::Gc` and `std::rc::Rc` types. Equivalent \
 138                            functionality to managed trait objects will be \
 139                            implemented but is currently missing.");
 140     }
 141
 142     fn has_feature(&self, feature: &str) -> bool {
 143         self.features.iter().any(|n| n.as_slice() == feature)
 144     }
 145 }
 146
 147 impl<'a, 'v> Visitor<'v> for Context<'a> {
 148     fn visit_ident(&mut self, sp: Span, id: ast::Ident) {
 149         if !token::get_ident(id).get().is_ascii() {
 150             self.gate_feature("non_ascii_idents", sp,
 151                               "non-ascii idents are not fully supported.");
 152         }
 153     }
 154
 155     fn visit_view_item(&mut self, i: &ast::ViewItem) {
 156         match i.node {
 157             ast::ViewItemUse(ref path) => {
 158                 match path.node {
 159                     ast::ViewPathGlob(..) => {
 160                         self.gate_feature("globs", path.span,
 161                                           "glob import statements are \
 162                                            experimental and possibly buggy");
 163                     }
 164                     _ => {}
 165                 }
 166             }
 167             ast::ViewItemExternCrate(..) => {
 168                 for attr in i.attrs.iter() {
 169                     if attr.name().get() == "phase"{
 170                         self.gate_feature("phase", attr.span,
 171                                           "compile time crate loading is \
 172                                            experimental and possibly buggy");
 173                     }
 174                 }
 175             }
 176         }
 177         visit::walk_view_item(self, i)
 178     }
 179
 180     fn visit_item(&mut self, i: &ast::Item) {
 181         for attr in i.attrs.iter() {
 182             if attr.name().equiv(&("thread_local")) {
 183                 self.gate_feature("thread_local", i.span,
 184                                   "`#[thread_local]` is an experimental feature, and does not \
 185                                   currently handle destructors. There is no corresponding \
 186                                   `#[task_local]` mapping to the task model");
 187             }
 188         }
 189         match i.node {
 190             ast::ItemEnum(ref def, _) => {
 191                 for variant in def.variants.iter() {
 192                     match variant.node.kind {
 193                         ast::StructVariantKind(..) => {
 194                             self.gate_feature("struct_variant", variant.span,
 195                                               "enum struct variants are \
 196                                                experimental and possibly buggy");
 197                         }
 198                         _ => {}
 199                     }
 200                 }
 201             }
 202
 203             ast::ItemForeignMod(ref foreign_module) => {
 204                 if attr::contains_name(i.attrs.as_slice(), "link_args") {
 205                     self.gate_feature("link_args", i.span,
 206                                       "the `link_args` attribute is not portable \
 207                                        across platforms, it is recommended to \
 208                                        use `#[link(name = \"foo\")]` instead")
 209                 }
 210                 if foreign_module.abi == RustIntrinsic {
 211                     self.gate_feature("intrinsics",
 212                                       i.span,
 213                                       "intrinsics are subject to change")
 214                 }
 215             }
 216
 217             ast::ItemFn(..) => {
 218                 if attr::contains_name(i.attrs.as_slice(), "plugin_registrar") {
 219                     self.gate_feature("plugin_registrar", i.span,
 220                                       "compiler plugins are experimental and possibly buggy");
 221                 }
 222             }
 223
 224             ast::ItemStruct(ref struct_definition, _) => {
 225                 if attr::contains_name(i.attrs.as_slice(), "simd") {
 226                     self.gate_feature("simd", i.span,
 227                                       "SIMD types are experimental and possibly buggy");
 228                 }
 229                 match struct_definition.super_struct {
 230                     Some(ref path) => self.gate_feature("struct_inherit", path.span,
 231                                                         "struct inheritance is experimental \
 232                                                          and possibly buggy"),
 233                     None => {}
 234                 }
 235                 if struct_definition.is_virtual {
 236                     self.gate_feature("struct_inherit", i.span,
 237                                       "struct inheritance (`virtual` keyword) is \
 238                                        experimental and possibly buggy");
 239                 }
 240             }
 241
 242             ast::ItemImpl(..) => {
 243                 if attr::contains_name(i.attrs.as_slice(),
 244                                        "unsafe_destructor") {
 245                     self.gate_feature("unsafe_destructor",
 246                                       i.span,
 247                                       "`#[unsafe_destructor]` allows too \
 248                                        many unsafe patterns and may be \
 249                                        removed in the future");
 250                 }
 251             }
 252
 253             _ => {}
 254         }
 255
 256         visit::walk_item(self, i);
 257     }
 258
 259     fn visit_mac(&mut self, macro: &ast::Mac) {
 260         let ast::MacInvocTT(ref path, _, _) = macro.node;
 261         let id = path.segments.last().unwrap().identifier;
 262         let quotes = ["quote_tokens", "quote_expr", "quote_ty",
 263                       "quote_item", "quote_pat", "quote_stmt"];
 264         let msg = " is not stable enough for use and are subject to change";
 265
 266
 267         if id == token::str_to_ident("macro_rules") {
 268             self.gate_feature("macro_rules", path.span, "macro definitions are \
 269                 not stable enough for use and are subject to change");
 270         }
 271
 272         else if id == token::str_to_ident("asm") {
 273             self.gate_feature("asm", path.span, "inline assembly is not \
 274                 stable enough for use and is subject to change");
 275         }
 276
 277         else if id == token::str_to_ident("log_syntax") {
 278             self.gate_feature("log_syntax", path.span, "`log_syntax!` is not \
 279                 stable enough for use and is subject to change");
 280         }
 281
 282         else if id == token::str_to_ident("trace_macros") {
 283             self.gate_feature("trace_macros", path.span, "`trace_macros` is not \
 284                 stable enough for use and is subject to change");
 285         }
 286
 287         else if id == token::str_to_ident("concat_idents") {
 288             self.gate_feature("concat_idents", path.span, "`concat_idents` is not \
 289                 stable enough for use and is subject to change");
 290         }
 291
 292         else {
 293             for &quote in quotes.iter() {
 294                 if id == token::str_to_ident(quote) {
 295                   self.gate_feature("quote",
 296                                     path.span,
 297                                     format!("{}{}", quote, msg).as_slice());
 298                 }
 299             }
 300         }
 301     }
 302
 303     fn visit_foreign_item(&mut self, i: &ast::ForeignItem) {
 304         if attr::contains_name(i.attrs.as_slice(), "linkage") {
 305             self.gate_feature("linkage", i.span,
 306                               "the `linkage` attribute is experimental \
 307                                and not portable across platforms")
 308         }
 309         visit::walk_foreign_item(self, i)
 310     }
 311
 312     fn visit_ty(&mut self, t: &ast::Ty) {
 313         match t.node {
 314             ast::TyClosure(ref closure) if closure.onceness == ast::Once => {
 315                 self.gate_feature("once_fns", t.span,
 316                                   "once functions are \
 317                                    experimental and likely to be removed");
 318
 319             },
 320             ast::TyBox(_) => { self.gate_box(t.span); }
 321             ast::TyUnboxedFn(..) => {
 322                 self.gate_feature("unboxed_closure_sugar",
 323                                   t.span,
 324                                   "unboxed closure trait sugar is experimental");
 325             }
 326             _ => {}
 327         }
 328
 329         visit::walk_ty(self, t);
 330     }
 331
 332     fn visit_expr(&mut self, e: &ast::Expr) {
 333         match e.node {
 334             ast::ExprUnary(ast::UnBox, _) => {
 335                 self.gate_box(e.span);
 336             }
 337             ast::ExprUnboxedFn(..) => {
 338                 self.gate_feature("unboxed_closures",
 339                                   e.span,
 340                                   "unboxed closures are a work-in-progress \
 341                                    feature with known bugs");
 342             }
 343             ast::ExprTupField(..) => {
 344                 self.gate_feature("tuple_indexing",
 345                                   e.span,
 346                                   "tuple indexing is experimental");
 347             }
 348             _ => {}
 349         }
 350         visit::walk_expr(self, e);
 351     }
 352
 353     fn visit_generics(&mut self, generics: &ast::Generics) {
 354         for type_parameter in generics.ty_params.iter() {
 355             match type_parameter.default {
 356                 Some(ref ty) => {
 357                     self.gate_feature("default_type_params", ty.span,
 358                                       "default type parameters are \
 359                                        experimental and possibly buggy");
 360                 }
 361                 None => {}
 362             }
 363         }
 364         visit::walk_generics(self, generics);
 365     }
 366
 367     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 368         if attr::contains_name(slice::ref_slice(attr), "lang") {
 369             self.gate_feature("lang_items",
 370                               attr.span,
 371                               "language items are subject to change");
 372         }
 373     }
 374
 375     fn visit_pat(&mut self, pattern: &ast::Pat) {
 376         match pattern.node {
 377             ast::PatVec(_, Some(_), ref last) if !last.is_empty() => {
 378                 self.gate_feature("advanced_slice_patterns",
 379                                   pattern.span,
 380                                   "multiple-element slice matches anywhere \
 381                                    but at the end of a slice (e.g. \
 382                                    `[0, ..xs, 0]` are experimental")
 383             }
 384             _ => {}
 385         }
 386         visit::walk_pat(self, pattern)
 387     }
 388
 389     fn visit_fn(&mut self,
 390                 fn_kind: visit::FnKind<'v>,
 391                 fn_decl: &'v ast::FnDecl,
 392                 block: &'v ast::Block,
 393                 span: Span,
 394                 _: NodeId) {
 395         match fn_kind {
 396             visit::FkItemFn(_, _, _, abi) if abi == RustIntrinsic => {
 397                 self.gate_feature("intrinsics",
 398                                   span,
 399                                   "intrinsics are subject to change")
 400             }
 401             _ => {}
 402         }
 403         visit::walk_fn(self, fn_kind, fn_decl, block, span);
 404     }
 405 }
 406
 407 pub fn check_crate(sess: &Session, krate: &ast::Crate) {
 408     let mut cx = Context {
 409         features: Vec::new(),
 410         sess: sess,
 411     };
 412
 413     for attr in krate.attrs.iter() {
 414         if !attr.check_name("feature") {
 415             continue
 416         }
 417
 418         match attr.meta_item_list() {
 419             None => {
 420                 sess.span_err(attr.span, "malformed feature attribute, \
 421                                           expected #![feature(...)]");
 422             }
 423             Some(list) => {
 424                 for mi in list.iter() {
 425                     let name = match mi.node {
 426                         ast::MetaWord(ref word) => (*word).clone(),
 427                         _ => {
 428                             sess.span_err(mi.span,
 429                                           "malformed feature, expected just \
 430                                            one word");
 431                             continue
 432                         }
 433                     };
 434                     match KNOWN_FEATURES.iter()
 435                                         .find(|& &(n, _)| name.equiv(&n)) {
 436                         Some(&(name, Active)) => { cx.features.push(name); }
 437                         Some(&(_, Removed)) => {
 438                             sess.span_err(mi.span, "feature has been removed");
 439                         }
 440                         Some(&(_, Accepted)) => {
 441                             sess.span_warn(mi.span, "feature has been added to Rust, \
 442                                                      directive not necessary");
 443                         }
 444                         None => {
 445                             sess.add_lint(lint::builtin::UNKNOWN_FEATURES,
 446                                           ast::CRATE_NODE_ID,
 447                                           mi.span,
 448                                           "unknown feature".to_string());
 449                         }
 450                     }
 451                 }
 452             }
 453         }
 454     }
 455
 456     visit::walk_crate(&mut cx, krate);
 457
 458     sess.abort_if_errors();
 459
 460     sess.features.default_type_params.set(cx.has_feature("default_type_params"));
 461     sess.features.overloaded_calls.set(cx.has_feature("overloaded_calls"));
 462     sess.features.rustc_diagnostic_macros.set(cx.has_feature("rustc_diagnostic_macros"));
 463     sess.features.import_shadowing.set(cx.has_feature("import_shadowing"));
 464 }
 465