src/libsyntax/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 use self::Status::*;
  21
  22 use abi::RustIntrinsic;
  23 use ast::NodeId;
  24 use ast;
  25 use attr;
  26 use attr::AttrMetaMethods;
  27 use codemap::{CodeMap, Span};
  28 use diagnostic::SpanHandler;
  29 use visit;
  30 use visit::Visitor;
  31 use parse::token;
  32
  33 use std::slice;
  34 use std::ascii::AsciiExt;
  35
  36
  37 // if you change this list without updating src/doc/reference.md, @cmr will be sad
  38 static KNOWN_FEATURES: &'static [(&'static str, Status)] = &[
  39     ("globs", Accepted),
  40     ("macro_rules", Accepted),
  41     ("struct_variant", Accepted),
  42     ("asm", Active),
  43     ("managed_boxes", Removed),
  44     ("non_ascii_idents", Active),
  45     ("thread_local", Active),
  46     ("link_args", Active),
  47     ("phase", Removed),
  48     ("plugin_registrar", Active),
  49     ("log_syntax", Active),
  50     ("trace_macros", Active),
  51     ("concat_idents", Active),
  52     ("unsafe_destructor", Active),
  53     ("intrinsics", Active),
  54     ("lang_items", Active),
  55
  56     ("simd", Active),
  57     ("default_type_params", Accepted),
  58     ("quote", Active),
  59     ("link_llvm_intrinsics", Active),
  60     ("linkage", Active),
  61     ("struct_inherit", Removed),
  62
  63     ("quad_precision_float", Removed),
  64
  65     ("rustc_diagnostic_macros", Active),
  66     ("unboxed_closures", Active),
  67     ("import_shadowing", Active),
  68     ("advanced_slice_patterns", Active),
  69     ("tuple_indexing", Accepted),
  70     ("associated_types", Accepted),
  71     ("visible_private_types", Active),
  72     ("slicing_syntax", Active),
  73     ("box_syntax", Active),
  74
  75     ("if_let", Accepted),
  76     ("while_let", Accepted),
  77
  78     ("plugin", Active),
  79
  80     // A temporary feature gate used to enable parser extensions needed
  81     // to bootstrap fix for #5723.
  82     ("issue_5723_bootstrap", Accepted),
  83
  84     // A way to temporarily opt out of opt in copy. This will *never* be accepted.
  85     ("opt_out_copy", Deprecated),
  86
  87     // A way to temporarily opt out of the new orphan rules. This will *never* be accepted.
  88     ("old_orphan_check", Deprecated),
  89
  90     // A way to temporarily opt out of the new impl rules. This will *never* be accepted.
  91     ("old_impl_check", Deprecated),
  92
  93     // OIBIT specific features
  94     ("optin_builtin_traits", Active),
  95
  96     // These are used to test this portion of the compiler, they don't actually
  97     // mean anything
  98     ("test_accepted_feature", Accepted),
  99     ("test_removed_feature", Removed),
 100 ];
 101
 102 enum Status {
 103     /// Represents an active feature that is currently being implemented or
 104     /// currently being considered for addition/removal.
 105     Active,
 106
 107     /// Represents a feature gate that is temporarily enabling deprecated behavior.
 108     /// This gate will never be accepted.
 109     Deprecated,
 110
 111     /// Represents a feature which has since been removed (it was once Active)
 112     Removed,
 113
 114     /// This language feature has since been Accepted (it was once Active)
 115     Accepted,
 116 }
 117
 118 /// A set of features to be used by later passes.
 119 #[derive(Copy)]
 120 pub struct Features {
 121     pub unboxed_closures: bool,
 122     pub rustc_diagnostic_macros: bool,
 123     pub import_shadowing: bool,
 124     pub visible_private_types: bool,
 125     pub quote: bool,
 126     pub opt_out_copy: bool,
 127     pub old_orphan_check: bool,
 128 }
 129
 130 impl Features {
 131     pub fn new() -> Features {
 132         Features {
 133             unboxed_closures: false,
 134             rustc_diagnostic_macros: false,
 135             import_shadowing: false,
 136             visible_private_types: false,
 137             quote: false,
 138             opt_out_copy: false,
 139             old_orphan_check: false,
 140         }
 141     }
 142 }
 143
 144 struct Context<'a> {
 145     features: Vec<&'static str>,
 146     span_handler: &'a SpanHandler,
 147     cm: &'a CodeMap,
 148 }
 149
 150 impl<'a> Context<'a> {
 151     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
 152         if !self.has_feature(feature) {
 153             self.span_handler.span_err(span, explain);
 154             self.span_handler.span_help(span, &format!("add #![feature({})] to the \
 155                                                        crate attributes to enable",
 156                                                       feature)[]);
 157         }
 158     }
 159
 160     fn has_feature(&self, feature: &str) -> bool {
 161         self.features.iter().any(|&n| n == feature)
 162     }
 163 }
 164
 165 struct MacroVisitor<'a> {
 166     context: &'a Context<'a>
 167 }
 168
 169 impl<'a, 'v> Visitor<'v> for MacroVisitor<'a> {
 170     fn visit_mac(&mut self, mac: &ast::Mac) {
 171         let ast::MacInvocTT(ref path, _, _) = mac.node;
 172         let id = path.segments.last().unwrap().identifier;
 173
 174         if id == token::str_to_ident("asm") {
 175             self.context.gate_feature("asm", path.span, "inline assembly is not \
 176                 stable enough for use and is subject to change");
 177         }
 178
 179         else if id == token::str_to_ident("log_syntax") {
 180             self.context.gate_feature("log_syntax", path.span, "`log_syntax!` is not \
 181                 stable enough for use and is subject to change");
 182         }
 183
 184         else if id == token::str_to_ident("trace_macros") {
 185             self.context.gate_feature("trace_macros", path.span, "`trace_macros` is not \
 186                 stable enough for use and is subject to change");
 187         }
 188
 189         else if id == token::str_to_ident("concat_idents") {
 190             self.context.gate_feature("concat_idents", path.span, "`concat_idents` is not \
 191                 stable enough for use and is subject to change");
 192         }
 193     }
 194 }
 195
 196 struct PostExpansionVisitor<'a> {
 197     context: &'a Context<'a>
 198 }
 199
 200 impl<'a> PostExpansionVisitor<'a> {
 201     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
 202         if !self.context.cm.span_is_internal(span) {
 203             self.context.gate_feature(feature, span, explain)
 204         }
 205     }
 206 }
 207
 208 impl<'a, 'v> Visitor<'v> for PostExpansionVisitor<'a> {
 209     fn visit_name(&mut self, sp: Span, name: ast::Name) {
 210         if !token::get_name(name).get().is_ascii() {
 211             self.gate_feature("non_ascii_idents", sp,
 212                               "non-ascii idents are not fully supported.");
 213         }
 214     }
 215
 216     fn visit_view_item(&mut self, i: &ast::ViewItem) {
 217         match i.node {
 218             ast::ViewItemUse(..) => {}
 219             ast::ViewItemExternCrate(..) => {
 220                 for attr in i.attrs.iter() {
 221                     if attr.check_name("plugin") {
 222                         self.gate_feature("plugin", attr.span,
 223                                           "compiler plugins are experimental \
 224                                            and possibly buggy");
 225                     }
 226                 }
 227             }
 228         }
 229         visit::walk_view_item(self, i)
 230     }
 231
 232     fn visit_item(&mut self, i: &ast::Item) {
 233         for attr in i.attrs.iter() {
 234             if attr.name() == "thread_local" {
 235                 self.gate_feature("thread_local", i.span,
 236                                   "`#[thread_local]` is an experimental feature, and does not \
 237                                   currently handle destructors. There is no corresponding \
 238                                   `#[task_local]` mapping to the task model");
 239             } else if attr.name() == "linkage" {
 240                 self.gate_feature("linkage", i.span,
 241                                   "the `linkage` attribute is experimental \
 242                                    and not portable across platforms")
 243             }
 244         }
 245         match i.node {
 246             ast::ItemForeignMod(ref foreign_module) => {
 247                 if attr::contains_name(&i.attrs[], "link_args") {
 248                     self.gate_feature("link_args", i.span,
 249                                       "the `link_args` attribute is not portable \
 250                                        across platforms, it is recommended to \
 251                                        use `#[link(name = \"foo\")]` instead")
 252                 }
 253                 if foreign_module.abi == RustIntrinsic {
 254                     self.gate_feature("intrinsics",
 255                                       i.span,
 256                                       "intrinsics are subject to change")
 257                 }
 258             }
 259
 260             ast::ItemFn(..) => {
 261                 if attr::contains_name(&i.attrs[], "plugin_registrar") {
 262                     self.gate_feature("plugin_registrar", i.span,
 263                                       "compiler plugins are experimental and possibly buggy");
 264                 }
 265             }
 266
 267             ast::ItemStruct(..) => {
 268                 if attr::contains_name(&i.attrs[], "simd") {
 269                     self.gate_feature("simd", i.span,
 270                                       "SIMD types are experimental and possibly buggy");
 271                 }
 272             }
 273
 274             ast::ItemImpl(_, polarity, _, _, _, _) => {
 275                 match polarity {
 276                     ast::ImplPolarity::Negative => {
 277                         self.gate_feature("optin_builtin_traits",
 278                                           i.span,
 279                                           "negative trait bounds are not yet fully implemented; \
 280                                           use marker types for now");
 281                     },
 282                     _ => {}
 283                 }
 284
 285                 if attr::contains_name(i.attrs.as_slice(),
 286                                        "unsafe_destructor") {
 287                     self.gate_feature("unsafe_destructor",
 288                                       i.span,
 289                                       "`#[unsafe_destructor]` allows too \
 290                                        many unsafe patterns and may be \
 291                                        removed in the future");
 292                 }
 293
 294                 if attr::contains_name(&i.attrs[],
 295                                        "old_orphan_check") {
 296                     self.gate_feature(
 297                         "old_orphan_check",
 298                         i.span,
 299                         "the new orphan check rules will eventually be strictly enforced");
 300                 }
 301
 302                 if attr::contains_name(&i.attrs[],
 303                                        "old_impl_check") {
 304                     self.gate_feature("old_impl_check",
 305                                       i.span,
 306                                       "`#[old_impl_check]` will be removed in the future");
 307                 }
 308             }
 309
 310             _ => {}
 311         }
 312
 313         visit::walk_item(self, i);
 314     }
 315
 316     fn visit_foreign_item(&mut self, i: &ast::ForeignItem) {
 317         if attr::contains_name(&i.attrs[], "linkage") {
 318             self.gate_feature("linkage", i.span,
 319                               "the `linkage` attribute is experimental \
 320                                and not portable across platforms")
 321         }
 322
 323         let links_to_llvm = match attr::first_attr_value_str_by_name(i.attrs.as_slice(),
 324                                                                      "link_name") {
 325             Some(val) => val.get().starts_with("llvm."),
 326             _ => false
 327         };
 328         if links_to_llvm {
 329             self.gate_feature("link_llvm_intrinsics", i.span,
 330                               "linking to LLVM intrinsics is experimental");
 331         }
 332
 333         visit::walk_foreign_item(self, i)
 334     }
 335
 336     fn visit_ty(&mut self, t: &ast::Ty) {
 337         visit::walk_ty(self, t);
 338     }
 339
 340     fn visit_expr(&mut self, e: &ast::Expr) {
 341         match e.node {
 342             ast::ExprBox(..) | ast::ExprUnary(ast::UnOp::UnUniq, _) => {
 343                 self.gate_feature("box_syntax",
 344                                   e.span,
 345                                   "box expression syntax is experimental in alpha release; \
 346                                    you can call `Box::new` instead.");
 347             }
 348             _ => {}
 349         }
 350         visit::walk_expr(self, e);
 351     }
 352
 353     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 354         if attr::contains_name(slice::ref_slice(attr), "lang") {
 355             self.gate_feature("lang_items",
 356                               attr.span,
 357                               "language items are subject to change");
 358         }
 359     }
 360
 361     fn visit_pat(&mut self, pattern: &ast::Pat) {
 362         match pattern.node {
 363             ast::PatVec(_, Some(_), ref last) if !last.is_empty() => {
 364                 self.gate_feature("advanced_slice_patterns",
 365                                   pattern.span,
 366                                   "multiple-element slice matches anywhere \
 367                                    but at the end of a slice (e.g. \
 368                                    `[0, ..xs, 0]` are experimental")
 369             }
 370             ast::PatBox(..) => {
 371                 self.gate_feature("box_syntax",
 372                                   pattern.span,
 373                                   "box pattern syntax is experimental in alpha release");
 374             }
 375             _ => {}
 376         }
 377         visit::walk_pat(self, pattern)
 378     }
 379
 380     fn visit_fn(&mut self,
 381                 fn_kind: visit::FnKind<'v>,
 382                 fn_decl: &'v ast::FnDecl,
 383                 block: &'v ast::Block,
 384                 span: Span,
 385                 _node_id: NodeId) {
 386         match fn_kind {
 387             visit::FkItemFn(_, _, _, abi) if abi == RustIntrinsic => {
 388                 self.gate_feature("intrinsics",
 389                                   span,
 390                                   "intrinsics are subject to change")
 391             }
 392             _ => {}
 393         }
 394         visit::walk_fn(self, fn_kind, fn_decl, block, span);
 395     }
 396 }
 397
 398 fn check_crate_inner<F>(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate,
 399                         check: F)
 400                        -> (Features, Vec<Span>)
 401     where F: FnOnce(&mut Context, &ast::Crate)
 402 {
 403     let mut cx = Context {
 404         features: Vec::new(),
 405         span_handler: span_handler,
 406         cm: cm,
 407     };
 408
 409     let mut unknown_features = Vec::new();
 410
 411     for attr in krate.attrs.iter() {
 412         if !attr.check_name("feature") {
 413             continue
 414         }
 415
 416         match attr.meta_item_list() {
 417             None => {
 418                 span_handler.span_err(attr.span, "malformed feature attribute, \
 419                                                   expected #![feature(...)]");
 420             }
 421             Some(list) => {
 422                 for mi in list.iter() {
 423                     let name = match mi.node {
 424                         ast::MetaWord(ref word) => (*word).clone(),
 425                         _ => {
 426                             span_handler.span_err(mi.span,
 427                                                   "malformed feature, expected just \
 428                                                    one word");
 429                             continue
 430                         }
 431                     };
 432                     match KNOWN_FEATURES.iter()
 433                                         .find(|& &(n, _)| name == n) {
 434                         Some(&(name, Active)) => {
 435                             cx.features.push(name);
 436                         }
 437                         Some(&(name, Deprecated)) => {
 438                             cx.features.push(name);
 439                             span_handler.span_warn(
 440                                 mi.span,
 441                                 "feature is deprecated and will only be available \
 442                                  for a limited time, please rewrite code that relies on it");
 443                         }
 444                         Some(&(_, Removed)) => {
 445                             span_handler.span_err(mi.span, "feature has been removed");
 446                         }
 447                         Some(&(_, Accepted)) => {
 448                             span_handler.span_warn(mi.span, "feature has been added to Rust, \
 449                                                              directive not necessary");
 450                         }
 451                         None => {
 452                             unknown_features.push(mi.span);
 453                         }
 454                     }
 455                 }
 456             }
 457         }
 458     }
 459
 460     check(&mut cx, krate);
 461
 462     (Features {
 463         unboxed_closures: cx.has_feature("unboxed_closures"),
 464         rustc_diagnostic_macros: cx.has_feature("rustc_diagnostic_macros"),
 465         import_shadowing: cx.has_feature("import_shadowing"),
 466         visible_private_types: cx.has_feature("visible_private_types"),
 467         quote: cx.has_feature("quote"),
 468         opt_out_copy: cx.has_feature("opt_out_copy"),
 469         old_orphan_check: cx.has_feature("old_orphan_check"),
 470     },
 471     unknown_features)
 472 }
 473
 474 pub fn check_crate_macros(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate)
 475 -> (Features, Vec<Span>) {
 476     check_crate_inner(cm, span_handler, krate,
 477                       |ctx, krate| visit::walk_crate(&mut MacroVisitor { context: ctx }, krate))
 478 }
 479
 480 pub fn check_crate(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate)
 481 -> (Features, Vec<Span>) {
 482     check_crate_inner(cm, span_handler, krate,
 483                       |ctx, krate| visit::walk_crate(&mut PostExpansionVisitor { context: ctx },
 484                                                      krate))
 485 }