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", Removed),
  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     ("on_unimplemented", Active),
  75     ("simd_ffi", Active),
  76
  77     ("if_let", Accepted),
  78     ("while_let", Accepted),
  79
  80     ("plugin", Active),
  81     ("start", Active),
  82     ("main", Active),
  83
  84     // A temporary feature gate used to enable parser extensions needed
  85     // to bootstrap fix for #5723.
  86     ("issue_5723_bootstrap", Accepted),
  87
  88     // A way to temporarily opt out of opt in copy. This will *never* be accepted.
  89     ("opt_out_copy", Removed),
  90
  91     // A way to temporarily opt out of the new orphan rules. This will *never* be accepted.
  92     ("old_orphan_check", Deprecated),
  93
  94     // A way to temporarily opt out of the new impl rules. This will *never* be accepted.
  95     ("old_impl_check", Deprecated),
  96
  97     // OIBIT specific features
  98     ("optin_builtin_traits", Active),
  99
 100     // int and uint are now deprecated
 101     ("int_uint", Active),
 102
 103     // These are used to test this portion of the compiler, they don't actually
 104     // mean anything
 105     ("test_accepted_feature", Accepted),
 106     ("test_removed_feature", Removed),
 107 ];
 108
 109 enum Status {
 110     /// Represents an active feature that is currently being implemented or
 111     /// currently being considered for addition/removal.
 112     Active,
 113
 114     /// Represents a feature gate that is temporarily enabling deprecated behavior.
 115     /// This gate will never be accepted.
 116     Deprecated,
 117
 118     /// Represents a feature which has since been removed (it was once Active)
 119     Removed,
 120
 121     /// This language feature has since been Accepted (it was once Active)
 122     Accepted,
 123 }
 124
 125 /// A set of features to be used by later passes.
 126 #[derive(Copy)]
 127 pub struct Features {
 128     pub unboxed_closures: bool,
 129     pub rustc_diagnostic_macros: bool,
 130     pub visible_private_types: bool,
 131     pub quote: bool,
 132     pub old_orphan_check: bool,
 133     pub simd_ffi: bool,
 134 }
 135
 136 impl Features {
 137     pub fn new() -> Features {
 138         Features {
 139             unboxed_closures: false,
 140             rustc_diagnostic_macros: false,
 141             visible_private_types: false,
 142             quote: false,
 143             old_orphan_check: false,
 144             simd_ffi: false,
 145         }
 146     }
 147 }
 148
 149 struct Context<'a> {
 150     features: Vec<&'static str>,
 151     span_handler: &'a SpanHandler,
 152     cm: &'a CodeMap,
 153 }
 154
 155 impl<'a> Context<'a> {
 156     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
 157         if !self.has_feature(feature) {
 158             self.span_handler.span_err(span, explain);
 159             self.span_handler.span_help(span, &format!("add #![feature({})] to the \
 160                                                        crate attributes to enable",
 161                                                       feature)[]);
 162         }
 163     }
 164
 165     fn warn_feature(&self, feature: &str, span: Span, explain: &str) {
 166         if !self.has_feature(feature) {
 167             self.span_handler.span_warn(span, explain);
 168             self.span_handler.span_help(span, &format!("add #![feature({})] to the \
 169                                                        crate attributes to silence this warning",
 170                                                       feature)[]);
 171         }
 172     }
 173     fn has_feature(&self, feature: &str) -> bool {
 174         self.features.iter().any(|&n| n == feature)
 175     }
 176 }
 177
 178 struct MacroVisitor<'a> {
 179     context: &'a Context<'a>
 180 }
 181
 182 impl<'a, 'v> Visitor<'v> for MacroVisitor<'a> {
 183     fn visit_mac(&mut self, mac: &ast::Mac) {
 184         let ast::MacInvocTT(ref path, _, _) = mac.node;
 185         let id = path.segments.last().unwrap().identifier;
 186
 187         if id == token::str_to_ident("asm") {
 188             self.context.gate_feature("asm", path.span, "inline assembly is not \
 189                 stable enough for use and is subject to change");
 190         }
 191
 192         else if id == token::str_to_ident("log_syntax") {
 193             self.context.gate_feature("log_syntax", path.span, "`log_syntax!` is not \
 194                 stable enough for use and is subject to change");
 195         }
 196
 197         else if id == token::str_to_ident("trace_macros") {
 198             self.context.gate_feature("trace_macros", path.span, "`trace_macros` is not \
 199                 stable enough for use and is subject to change");
 200         }
 201
 202         else if id == token::str_to_ident("concat_idents") {
 203             self.context.gate_feature("concat_idents", path.span, "`concat_idents` is not \
 204                 stable enough for use and is subject to change");
 205         }
 206     }
 207 }
 208
 209 struct PostExpansionVisitor<'a> {
 210     context: &'a Context<'a>
 211 }
 212
 213 impl<'a> PostExpansionVisitor<'a> {
 214     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
 215         if !self.context.cm.span_is_internal(span) {
 216             self.context.gate_feature(feature, span, explain)
 217         }
 218     }
 219 }
 220
 221 impl<'a, 'v> Visitor<'v> for PostExpansionVisitor<'a> {
 222     fn visit_name(&mut self, sp: Span, name: ast::Name) {
 223         if !token::get_name(name).get().is_ascii() {
 224             self.gate_feature("non_ascii_idents", sp,
 225                               "non-ascii idents are not fully supported.");
 226         }
 227     }
 228
 229     fn visit_item(&mut self, i: &ast::Item) {
 230         for attr in i.attrs.iter() {
 231             if attr.name() == "thread_local" {
 232                 self.gate_feature("thread_local", i.span,
 233                                   "`#[thread_local]` is an experimental feature, and does not \
 234                                   currently handle destructors. There is no corresponding \
 235                                   `#[task_local]` mapping to the task model");
 236             } else if attr.name() == "linkage" {
 237                 self.gate_feature("linkage", i.span,
 238                                   "the `linkage` attribute is experimental \
 239                                    and not portable across platforms")
 240             } else if attr.name() == "rustc_on_unimplemented" {
 241                 self.gate_feature("on_unimplemented", i.span,
 242                                   "the `#[rustc_on_unimplemented]` attribute \
 243                                   is an experimental feature")
 244             }
 245         }
 246         match i.node {
 247             ast::ItemExternCrate(_) => {
 248                 if attr::contains_name(&i.attrs[], "plugin") {
 249                     self.gate_feature("plugin", i.span,
 250                                       "compiler plugins are experimental \
 251                                        and possibly buggy");
 252                 }
 253             }
 254
 255             ast::ItemForeignMod(ref foreign_module) => {
 256                 if attr::contains_name(&i.attrs[], "link_args") {
 257                     self.gate_feature("link_args", i.span,
 258                                       "the `link_args` attribute is not portable \
 259                                        across platforms, it is recommended to \
 260                                        use `#[link(name = \"foo\")]` instead")
 261                 }
 262                 if foreign_module.abi == RustIntrinsic {
 263                     self.gate_feature("intrinsics",
 264                                       i.span,
 265                                       "intrinsics are subject to change")
 266                 }
 267             }
 268
 269             ast::ItemFn(..) => {
 270                 if attr::contains_name(&i.attrs[], "plugin_registrar") {
 271                     self.gate_feature("plugin_registrar", i.span,
 272                                       "compiler plugins are experimental and possibly buggy");
 273                 }
 274                 if attr::contains_name(&i.attrs[], "start") {
 275                     self.gate_feature("start", i.span,
 276                                       "a #[start] function is an experimental \
 277                                        feature whose signature may change \
 278                                        over time");
 279                 }
 280                 if attr::contains_name(&i.attrs[], "main") {
 281                     self.gate_feature("main", i.span,
 282                                       "declaration of a nonstandard #[main] \
 283                                        function may change over time, for now \
 284                                        a top-level `fn main()` is required");
 285                 }
 286             }
 287
 288             ast::ItemStruct(..) => {
 289                 if attr::contains_name(&i.attrs[], "simd") {
 290                     self.gate_feature("simd", i.span,
 291                                       "SIMD types are experimental and possibly buggy");
 292                 }
 293             }
 294
 295             ast::ItemImpl(_, polarity, _, _, _, _) => {
 296                 match polarity {
 297                     ast::ImplPolarity::Negative => {
 298                         self.gate_feature("optin_builtin_traits",
 299                                           i.span,
 300                                           "negative trait bounds are not yet fully implemented; \
 301                                           use marker types for now");
 302                     },
 303                     _ => {}
 304                 }
 305
 306                 if attr::contains_name(i.attrs.as_slice(),
 307                                        "unsafe_destructor") {
 308                     self.gate_feature("unsafe_destructor",
 309                                       i.span,
 310                                       "`#[unsafe_destructor]` allows too \
 311                                        many unsafe patterns and may be \
 312                                        removed in the future");
 313                 }
 314
 315                 if attr::contains_name(&i.attrs[],
 316                                        "old_orphan_check") {
 317                     self.gate_feature(
 318                         "old_orphan_check",
 319                         i.span,
 320                         "the new orphan check rules will eventually be strictly enforced");
 321                 }
 322
 323                 if attr::contains_name(&i.attrs[],
 324                                        "old_impl_check") {
 325                     self.gate_feature("old_impl_check",
 326                                       i.span,
 327                                       "`#[old_impl_check]` will be removed in the future");
 328                 }
 329             }
 330
 331             _ => {}
 332         }
 333
 334         visit::walk_item(self, i);
 335     }
 336
 337     fn visit_foreign_item(&mut self, i: &ast::ForeignItem) {
 338         if attr::contains_name(&i.attrs[], "linkage") {
 339             self.gate_feature("linkage", i.span,
 340                               "the `linkage` attribute is experimental \
 341                                and not portable across platforms")
 342         }
 343
 344         let links_to_llvm = match attr::first_attr_value_str_by_name(i.attrs.as_slice(),
 345                                                                      "link_name") {
 346             Some(val) => val.get().starts_with("llvm."),
 347             _ => false
 348         };
 349         if links_to_llvm {
 350             self.gate_feature("link_llvm_intrinsics", i.span,
 351                               "linking to LLVM intrinsics is experimental");
 352         }
 353
 354         visit::walk_foreign_item(self, i)
 355     }
 356
 357     fn visit_ty(&mut self, t: &ast::Ty) {
 358         match t.node {
 359             ast::TyPath(ref p, _) => {
 360                 match &*p.segments {
 361
 362                     [ast::PathSegment { identifier, .. }] => {
 363                         let name = token::get_ident(identifier);
 364                         let msg = if name == "int" {
 365                             Some("the `int` type is deprecated; \
 366                                   use `isize` or a fixed-sized integer")
 367                         } else if name == "uint" {
 368                             Some("the `uint` type is deprecated; \
 369                                   use `usize` or a fixed-sized integer")
 370                         } else {
 371                             None
 372                         };
 373
 374                         if let Some(msg) = msg {
 375                             self.context.warn_feature("int_uint", t.span, msg)
 376                         }
 377                     }
 378                     _ => {}
 379                 }
 380             }
 381             _ => {}
 382         }
 383         visit::walk_ty(self, t);
 384     }
 385
 386     fn visit_expr(&mut self, e: &ast::Expr) {
 387         match e.node {
 388             ast::ExprBox(..) | ast::ExprUnary(ast::UnOp::UnUniq, _) => {
 389                 self.gate_feature("box_syntax",
 390                                   e.span,
 391                                   "box expression syntax is experimental in alpha release; \
 392                                    you can call `Box::new` instead.");
 393             }
 394             ast::ExprLit(ref lit) => {
 395                 match lit.node {
 396                     ast::LitInt(_, ty) => {
 397                         let msg = if let ast::SignedIntLit(ast::TyIs(true), _) = ty {
 398                             Some("the `i` suffix on integers is deprecated; use `is` \
 399                                   or one of the fixed-sized suffixes")
 400                         } else if let ast::UnsignedIntLit(ast::TyUs(true)) = ty {
 401                             Some("the `u` suffix on integers is deprecated; use `us` \
 402                                  or one of the fixed-sized suffixes")
 403                         } else {
 404                             None
 405                         };
 406                         if let Some(msg) = msg {
 407                             self.context.warn_feature("int_uint", e.span, msg);
 408                         }
 409                     }
 410                     _ => {}
 411                 }
 412             }
 413             _ => {}
 414         }
 415         visit::walk_expr(self, e);
 416     }
 417
 418     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 419         if attr::contains_name(slice::ref_slice(attr), "lang") {
 420             self.gate_feature("lang_items",
 421                               attr.span,
 422                               "language items are subject to change");
 423         }
 424     }
 425
 426     fn visit_pat(&mut self, pattern: &ast::Pat) {
 427         match pattern.node {
 428             ast::PatVec(_, Some(_), ref last) if !last.is_empty() => {
 429                 self.gate_feature("advanced_slice_patterns",
 430                                   pattern.span,
 431                                   "multiple-element slice matches anywhere \
 432                                    but at the end of a slice (e.g. \
 433                                    `[0, ..xs, 0]` are experimental")
 434             }
 435             ast::PatBox(..) => {
 436                 self.gate_feature("box_syntax",
 437                                   pattern.span,
 438                                   "box pattern syntax is experimental in alpha release");
 439             }
 440             _ => {}
 441         }
 442         visit::walk_pat(self, pattern)
 443     }
 444
 445     fn visit_fn(&mut self,
 446                 fn_kind: visit::FnKind<'v>,
 447                 fn_decl: &'v ast::FnDecl,
 448                 block: &'v ast::Block,
 449                 span: Span,
 450                 _node_id: NodeId) {
 451         match fn_kind {
 452             visit::FkItemFn(_, _, _, abi) if abi == RustIntrinsic => {
 453                 self.gate_feature("intrinsics",
 454                                   span,
 455                                   "intrinsics are subject to change")
 456             }
 457             _ => {}
 458         }
 459         visit::walk_fn(self, fn_kind, fn_decl, block, span);
 460     }
 461 }
 462
 463 fn check_crate_inner<F>(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate,
 464                         check: F)
 465                        -> (Features, Vec<Span>)
 466     where F: FnOnce(&mut Context, &ast::Crate)
 467 {
 468     let mut cx = Context {
 469         features: Vec::new(),
 470         span_handler: span_handler,
 471         cm: cm,
 472     };
 473
 474     let mut unknown_features = Vec::new();
 475
 476     for attr in krate.attrs.iter() {
 477         if !attr.check_name("feature") {
 478             continue
 479         }
 480
 481         match attr.meta_item_list() {
 482             None => {
 483                 span_handler.span_err(attr.span, "malformed feature attribute, \
 484                                                   expected #![feature(...)]");
 485             }
 486             Some(list) => {
 487                 for mi in list.iter() {
 488                     let name = match mi.node {
 489                         ast::MetaWord(ref word) => (*word).clone(),
 490                         _ => {
 491                             span_handler.span_err(mi.span,
 492                                                   "malformed feature, expected just \
 493                                                    one word");
 494                             continue
 495                         }
 496                     };
 497                     match KNOWN_FEATURES.iter()
 498                                         .find(|& &(n, _)| name == n) {
 499                         Some(&(name, Active)) => {
 500                             cx.features.push(name);
 501                         }
 502                         Some(&(name, Deprecated)) => {
 503                             cx.features.push(name);
 504                             span_handler.span_warn(
 505                                 mi.span,
 506                                 "feature is deprecated and will only be available \
 507                                  for a limited time, please rewrite code that relies on it");
 508                         }
 509                         Some(&(_, Removed)) => {
 510                             span_handler.span_err(mi.span, "feature has been removed");
 511                         }
 512                         Some(&(_, Accepted)) => {
 513                             span_handler.span_warn(mi.span, "feature has been added to Rust, \
 514                                                              directive not necessary");
 515                         }
 516                         None => {
 517                             unknown_features.push(mi.span);
 518                         }
 519                     }
 520                 }
 521             }
 522         }
 523     }
 524
 525     check(&mut cx, krate);
 526
 527     (Features {
 528         unboxed_closures: cx.has_feature("unboxed_closures"),
 529         rustc_diagnostic_macros: cx.has_feature("rustc_diagnostic_macros"),
 530         visible_private_types: cx.has_feature("visible_private_types"),
 531         quote: cx.has_feature("quote"),
 532         old_orphan_check: cx.has_feature("old_orphan_check"),
 533         simd_ffi: cx.has_feature("simd_ffi"),
 534     },
 535     unknown_features)
 536 }
 537
 538 pub fn check_crate_macros(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate)
 539 -> (Features, Vec<Span>) {
 540     check_crate_inner(cm, span_handler, krate,
 541                       |ctx, krate| visit::walk_crate(&mut MacroVisitor { context: ctx }, krate))
 542 }
 543
 544 pub fn check_crate(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate)
 545 -> (Features, Vec<Span>) {
 546     check_crate_inner(cm, span_handler, krate,
 547                       |ctx, krate| visit::walk_crate(&mut PostExpansionVisitor { context: ctx },
 548                                                      krate))
 549 }