src/libsyntax/config.rs

   1 // Copyright 2012-2014 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 use attr::AttrMetaMethods;
  12 use errors::Handler;
  13 use feature_gate::GatedCfgAttr;
  14 use fold::Folder;
  15 use {ast, fold, attr};
  16 use visit;
  17 use codemap::{Spanned, respan};
  18 use ptr::P;
  19
  20 use util::small_vector::SmallVector;
  21
  22 /// A folder that strips out items that do not belong in the current
  23 /// configuration.
  24 struct Context<'a, F> where F: FnMut(&[ast::Attribute]) -> bool {
  25     in_cfg: F,
  26     diagnostic: &'a Handler,
  27 }
  28
  29 // Support conditional compilation by transforming the AST, stripping out
  30 // any items that do not belong in the current configuration
  31 pub fn strip_unconfigured_items(diagnostic: &Handler, krate: ast::Crate,
  32                                 feature_gated_cfgs: &mut Vec<GatedCfgAttr>)
  33                                 -> ast::Crate
  34 {
  35     // Need to do this check here because cfg runs before feature_gates
  36     check_for_gated_stmt_expr_attributes(&krate, feature_gated_cfgs);
  37
  38     let krate = process_cfg_attr(diagnostic, krate, feature_gated_cfgs);
  39     let config = krate.config.clone();
  40     strip_items(diagnostic,
  41                 krate,
  42                 |attrs| {
  43                     let mut diag = CfgDiagReal {
  44                         diag: diagnostic,
  45                         feature_gated_cfgs: feature_gated_cfgs,
  46                     };
  47                     in_cfg(&config, attrs, &mut diag)
  48                 })
  49 }
  50
  51 impl<'a, F> fold::Folder for Context<'a, F> where F: FnMut(&[ast::Attribute]) -> bool {
  52     fn fold_foreign_mod(&mut self, foreign_mod: ast::ForeignMod) -> ast::ForeignMod {
  53         fold_foreign_mod(self, foreign_mod)
  54     }
  55     fn fold_item_kind(&mut self, item: ast::ItemKind) -> ast::ItemKind {
  56         fold_item_kind(self, item)
  57     }
  58     fn fold_expr(&mut self, expr: P<ast::Expr>) -> P<ast::Expr> {
  59         // If an expr is valid to cfg away it will have been removed by the
  60         // outer stmt or expression folder before descending in here.
  61         // Anything else is always required, and thus has to error out
  62         // in case of a cfg attr.
  63         //
  64         // NB: This is intentionally not part of the fold_expr() function
  65         //     in order for fold_opt_expr() to be able to avoid this check
  66         if let Some(attr) = expr.attrs().iter().find(|a| is_cfg(a)) {
  67             self.diagnostic.span_err(attr.span,
  68                 "removing an expression is not supported in this position");
  69         }
  70         fold_expr(self, expr)
  71     }
  72     fn fold_opt_expr(&mut self, expr: P<ast::Expr>) -> Option<P<ast::Expr>> {
  73         fold_opt_expr(self, expr)
  74     }
  75     fn fold_stmt(&mut self, stmt: ast::Stmt) -> SmallVector<ast::Stmt> {
  76         fold_stmt(self, stmt)
  77     }
  78     fn fold_mac(&mut self, mac: ast::Mac) -> ast::Mac {
  79         fold::noop_fold_mac(mac, self)
  80     }
  81     fn fold_item(&mut self, item: P<ast::Item>) -> SmallVector<P<ast::Item>> {
  82         fold_item(self, item)
  83     }
  84 }
  85
  86 pub fn strip_items<'a, F>(diagnostic: &'a Handler,
  87                           krate: ast::Crate, in_cfg: F) -> ast::Crate where
  88     F: FnMut(&[ast::Attribute]) -> bool,
  89 {
  90     let mut ctxt = Context {
  91         in_cfg: in_cfg,
  92         diagnostic: diagnostic,
  93     };
  94     ctxt.fold_crate(krate)
  95 }
  96
  97 fn filter_foreign_item<F>(cx: &mut Context<F>,
  98                           item: ast::ForeignItem)
  99                           -> Option<ast::ForeignItem> where
 100     F: FnMut(&[ast::Attribute]) -> bool
 101 {
 102     if foreign_item_in_cfg(cx, &item) {
 103         Some(item)
 104     } else {
 105         None
 106     }
 107 }
 108
 109 fn fold_foreign_mod<F>(cx: &mut Context<F>,
 110                        ast::ForeignMod {abi, items}: ast::ForeignMod)
 111                        -> ast::ForeignMod where
 112     F: FnMut(&[ast::Attribute]) -> bool
 113 {
 114     ast::ForeignMod {
 115         abi: abi,
 116         items: items.into_iter()
 117                     .filter_map(|a| filter_foreign_item(cx, a))
 118                     .collect()
 119     }
 120 }
 121
 122 fn fold_item<F>(cx: &mut Context<F>, item: P<ast::Item>) -> SmallVector<P<ast::Item>> where
 123     F: FnMut(&[ast::Attribute]) -> bool
 124 {
 125     if item_in_cfg(cx, &item) {
 126         SmallVector::one(item.map(|i| cx.fold_item_simple(i)))
 127     } else {
 128         SmallVector::zero()
 129     }
 130 }
 131
 132 fn fold_item_kind<F>(cx: &mut Context<F>, item: ast::ItemKind) -> ast::ItemKind where
 133     F: FnMut(&[ast::Attribute]) -> bool
 134 {
 135     let item = match item {
 136         ast::ItemKind::Impl(u, o, a, b, c, impl_items) => {
 137             let impl_items = impl_items.into_iter()
 138                                        .filter(|ii| (cx.in_cfg)(&ii.attrs))
 139                                        .collect();
 140             ast::ItemKind::Impl(u, o, a, b, c, impl_items)
 141         }
 142         ast::ItemKind::Trait(u, a, b, methods) => {
 143             let methods = methods.into_iter()
 144                                  .filter(|ti| (cx.in_cfg)(&ti.attrs))
 145                                  .collect();
 146             ast::ItemKind::Trait(u, a, b, methods)
 147         }
 148         ast::ItemKind::Struct(def, generics) => {
 149             ast::ItemKind::Struct(fold_struct(cx, def), generics)
 150         }
 151         ast::ItemKind::Enum(def, generics) => {
 152             let variants = def.variants.into_iter().filter_map(|v| {
 153                 if !(cx.in_cfg)(&v.node.attrs) {
 154                     None
 155                 } else {
 156                     Some(Spanned {
 157                         node: ast::Variant_ {
 158                             name: v.node.name,
 159                             attrs: v.node.attrs,
 160                             data: fold_struct(cx, v.node.data),
 161                             disr_expr: v.node.disr_expr,
 162                         },
 163                         span: v.span
 164                     })
 165                 }
 166             });
 167             ast::ItemKind::Enum(ast::EnumDef {
 168                 variants: variants.collect(),
 169             }, generics)
 170         }
 171         item => item,
 172     };
 173
 174     fold::noop_fold_item_kind(item, cx)
 175 }
 176
 177 fn fold_struct<F>(cx: &mut Context<F>, vdata: ast::VariantData) -> ast::VariantData where
 178     F: FnMut(&[ast::Attribute]) -> bool
 179 {
 180     match vdata {
 181         ast::VariantData::Struct(fields, id) => {
 182             ast::VariantData::Struct(fields.into_iter().filter(|m| {
 183                 (cx.in_cfg)(&m.attrs)
 184             }).collect(), id)
 185         }
 186         ast::VariantData::Tuple(fields, id) => {
 187             ast::VariantData::Tuple(fields.into_iter().filter(|m| {
 188                 (cx.in_cfg)(&m.attrs)
 189             }).collect(), id)
 190         }
 191         ast::VariantData::Unit(id) => ast::VariantData::Unit(id)
 192     }
 193 }
 194
 195 fn fold_opt_expr<F>(cx: &mut Context<F>, expr: P<ast::Expr>) -> Option<P<ast::Expr>>
 196     where F: FnMut(&[ast::Attribute]) -> bool
 197 {
 198     if expr_in_cfg(cx, &expr) {
 199         Some(fold_expr(cx, expr))
 200     } else {
 201         None
 202     }
 203 }
 204
 205 fn fold_expr<F>(cx: &mut Context<F>, expr: P<ast::Expr>) -> P<ast::Expr> where
 206     F: FnMut(&[ast::Attribute]) -> bool
 207 {
 208     expr.map(|ast::Expr {id, span, node, attrs}| {
 209         fold::noop_fold_expr(ast::Expr {
 210             id: id,
 211             node: match node {
 212                 ast::ExprKind::Match(m, arms) => {
 213                     ast::ExprKind::Match(m, arms.into_iter()
 214                                         .filter(|a| (cx.in_cfg)(&a.attrs))
 215                                         .collect())
 216                 }
 217                 _ => node
 218             },
 219             span: span,
 220             attrs: attrs,
 221         }, cx)
 222     })
 223 }
 224
 225 fn fold_stmt<F>(cx: &mut Context<F>, stmt: ast::Stmt) -> SmallVector<ast::Stmt>
 226     where F: FnMut(&[ast::Attribute]) -> bool
 227 {
 228     if stmt_in_cfg(cx, &stmt) {
 229         fold::noop_fold_stmt(stmt, cx)
 230     } else {
 231         SmallVector::zero()
 232     }
 233 }
 234
 235 fn stmt_in_cfg<F>(cx: &mut Context<F>, stmt: &ast::Stmt) -> bool where
 236     F: FnMut(&[ast::Attribute]) -> bool
 237 {
 238     (cx.in_cfg)(stmt.node.attrs())
 239 }
 240
 241 fn expr_in_cfg<F>(cx: &mut Context<F>, expr: &ast::Expr) -> bool where
 242     F: FnMut(&[ast::Attribute]) -> bool
 243 {
 244     (cx.in_cfg)(expr.attrs())
 245 }
 246
 247 fn item_in_cfg<F>(cx: &mut Context<F>, item: &ast::Item) -> bool where
 248     F: FnMut(&[ast::Attribute]) -> bool
 249 {
 250     return (cx.in_cfg)(&item.attrs);
 251 }
 252
 253 fn foreign_item_in_cfg<F>(cx: &mut Context<F>, item: &ast::ForeignItem) -> bool where
 254     F: FnMut(&[ast::Attribute]) -> bool
 255 {
 256     return (cx.in_cfg)(&item.attrs);
 257 }
 258
 259 fn is_cfg(attr: &ast::Attribute) -> bool {
 260     attr.check_name("cfg")
 261 }
 262
 263 // Determine if an item should be translated in the current crate
 264 // configuration based on the item's attributes
 265 fn in_cfg<T: CfgDiag>(cfg: &[P<ast::MetaItem>],
 266                       attrs: &[ast::Attribute],
 267                       diag: &mut T) -> bool {
 268     attrs.iter().all(|attr| {
 269         let mis = match attr.node.value.node {
 270             ast::MetaItemKind::List(_, ref mis) if is_cfg(&attr) => mis,
 271             _ => return true
 272         };
 273
 274         if mis.len() != 1 {
 275             diag.emit_error(|diagnostic| {
 276                 diagnostic.span_err(attr.span, "expected 1 cfg-pattern");
 277             });
 278             return true;
 279         }
 280
 281         attr::cfg_matches(cfg, &mis[0], diag)
 282     })
 283 }
 284
 285 struct CfgAttrFolder<'a, T> {
 286     diag: T,
 287     config: &'a ast::CrateConfig,
 288 }
 289
 290 // Process `#[cfg_attr]`.
 291 fn process_cfg_attr(diagnostic: &Handler, krate: ast::Crate,
 292                     feature_gated_cfgs: &mut Vec<GatedCfgAttr>) -> ast::Crate {
 293     let mut fld = CfgAttrFolder {
 294         diag: CfgDiagReal {
 295             diag: diagnostic,
 296             feature_gated_cfgs: feature_gated_cfgs,
 297         },
 298         config: &krate.config.clone(),
 299     };
 300     fld.fold_crate(krate)
 301 }
 302
 303 impl<'a, T: CfgDiag> fold::Folder for CfgAttrFolder<'a, T> {
 304     fn fold_attribute(&mut self, attr: ast::Attribute) -> Option<ast::Attribute> {
 305         if !attr.check_name("cfg_attr") {
 306             return fold::noop_fold_attribute(attr, self);
 307         }
 308
 309         let attr_list = match attr.meta_item_list() {
 310             Some(attr_list) => attr_list,
 311             None => {
 312                 self.diag.emit_error(|diag| {
 313                     diag.span_err(attr.span,
 314                         "expected `#[cfg_attr(<cfg pattern>, <attr>)]`");
 315                 });
 316                 return None;
 317             }
 318         };
 319         let (cfg, mi) = match (attr_list.len(), attr_list.get(0), attr_list.get(1)) {
 320             (2, Some(cfg), Some(mi)) => (cfg, mi),
 321             _ => {
 322                 self.diag.emit_error(|diag| {
 323                     diag.span_err(attr.span,
 324                         "expected `#[cfg_attr(<cfg pattern>, <attr>)]`");
 325                 });
 326                 return None;
 327             }
 328         };
 329
 330         if attr::cfg_matches(&self.config[..], &cfg, &mut self.diag) {
 331             Some(respan(mi.span, ast::Attribute_ {
 332                 id: attr::mk_attr_id(),
 333                 style: attr.node.style,
 334                 value: mi.clone(),
 335                 is_sugared_doc: false,
 336             }))
 337         } else {
 338             None
 339         }
 340     }
 341
 342     // Need the ability to run pre-expansion.
 343     fn fold_mac(&mut self, mac: ast::Mac) -> ast::Mac {
 344         fold::noop_fold_mac(mac, self)
 345     }
 346 }
 347
 348 fn check_for_gated_stmt_expr_attributes(krate: &ast::Crate,
 349                                         discovered: &mut Vec<GatedCfgAttr>) {
 350     let mut v = StmtExprAttrFeatureVisitor {
 351         config: &krate.config,
 352         discovered: discovered,
 353     };
 354     visit::walk_crate(&mut v, krate);
 355 }
 356
 357 /// To cover this feature, we need to discover all attributes
 358 /// so we need to run before cfg.
 359 struct StmtExprAttrFeatureVisitor<'a, 'b> {
 360     config: &'a ast::CrateConfig,
 361     discovered: &'b mut Vec<GatedCfgAttr>,
 362 }
 363
 364 // Runs the cfg_attr and cfg folders locally in "silent" mode
 365 // to discover attribute use on stmts or expressions ahead of time
 366 impl<'v, 'a, 'b> visit::Visitor<'v> for StmtExprAttrFeatureVisitor<'a, 'b> {
 367     fn visit_stmt(&mut self, s: &'v ast::Stmt) {
 368         // check if there even are any attributes on this node
 369         let stmt_attrs = s.node.attrs();
 370         if stmt_attrs.len() > 0 {
 371             // attributes on items are fine
 372             if let ast::StmtKind::Decl(ref decl, _) = s.node {
 373                 if let ast::DeclKind::Item(_) = decl.node {
 374                     visit::walk_stmt(self, s);
 375                     return;
 376                 }
 377             }
 378
 379             // flag the offending attributes
 380             for attr in stmt_attrs {
 381                 self.discovered.push(GatedCfgAttr::GatedAttr(attr.span));
 382             }
 383
 384             // if the node does not end up being cfg-d away, walk down
 385             if node_survives_cfg(stmt_attrs, self.config) {
 386                 visit::walk_stmt(self, s);
 387             }
 388         } else {
 389             visit::walk_stmt(self, s);
 390         }
 391     }
 392
 393     fn visit_expr(&mut self, ex: &'v ast::Expr) {
 394         // check if there even are any attributes on this node
 395         let expr_attrs = ex.attrs();
 396         if expr_attrs.len() > 0 {
 397
 398             // flag the offending attributes
 399             for attr in expr_attrs {
 400                 self.discovered.push(GatedCfgAttr::GatedAttr(attr.span));
 401             }
 402
 403             // if the node does not end up being cfg-d away, walk down
 404             if node_survives_cfg(expr_attrs, self.config) {
 405                 visit::walk_expr(self, ex);
 406             }
 407         } else {
 408             visit::walk_expr(self, ex);
 409         }
 410     }
 411
 412     fn visit_foreign_item(&mut self, i: &'v ast::ForeignItem) {
 413         if node_survives_cfg(&i.attrs, self.config) {
 414             visit::walk_foreign_item(self, i);
 415         }
 416     }
 417
 418     fn visit_item(&mut self, i: &'v ast::Item) {
 419         if node_survives_cfg(&i.attrs, self.config) {
 420             visit::walk_item(self, i);
 421         }
 422     }
 423
 424     fn visit_impl_item(&mut self, ii: &'v ast::ImplItem) {
 425         if node_survives_cfg(&ii.attrs, self.config) {
 426             visit::walk_impl_item(self, ii);
 427         }
 428     }
 429
 430     fn visit_trait_item(&mut self, ti: &'v ast::TraitItem) {
 431         if node_survives_cfg(&ti.attrs, self.config) {
 432             visit::walk_trait_item(self, ti);
 433         }
 434     }
 435
 436     fn visit_struct_field(&mut self, s: &'v ast::StructField) {
 437         if node_survives_cfg(&s.attrs, self.config) {
 438             visit::walk_struct_field(self, s);
 439         }
 440     }
 441
 442     fn visit_variant(&mut self, v: &'v ast::Variant,
 443                      g: &'v ast::Generics, item_id: ast::NodeId) {
 444         if node_survives_cfg(&v.node.attrs, self.config) {
 445             visit::walk_variant(self, v, g, item_id);
 446         }
 447     }
 448
 449     fn visit_arm(&mut self, a: &'v ast::Arm) {
 450         if node_survives_cfg(&a.attrs, self.config) {
 451             visit::walk_arm(self, a);
 452         }
 453     }
 454
 455     // This visitor runs pre expansion, so we need to prevent
 456     // the default panic here
 457     fn visit_mac(&mut self, mac: &'v ast::Mac) {
 458         visit::walk_mac(self, mac)
 459     }
 460 }
 461
 462 pub trait CfgDiag {
 463     fn emit_error<F>(&mut self, f: F) where F: FnMut(&Handler);
 464     fn flag_gated<F>(&mut self, f: F) where F: FnMut(&mut Vec<GatedCfgAttr>);
 465 }
 466
 467 pub struct CfgDiagReal<'a, 'b> {
 468     pub diag: &'a Handler,
 469     pub feature_gated_cfgs: &'b mut Vec<GatedCfgAttr>,
 470 }
 471
 472 impl<'a, 'b> CfgDiag for CfgDiagReal<'a, 'b> {
 473     fn emit_error<F>(&mut self, mut f: F) where F: FnMut(&Handler) {
 474         f(self.diag)
 475     }
 476     fn flag_gated<F>(&mut self, mut f: F) where F: FnMut(&mut Vec<GatedCfgAttr>) {
 477         f(self.feature_gated_cfgs)
 478     }
 479 }
 480
 481 struct CfgDiagSilent {
 482     error: bool,
 483 }
 484
 485 impl CfgDiag for CfgDiagSilent {
 486     fn emit_error<F>(&mut self, _: F) where F: FnMut(&Handler) {
 487         self.error = true;
 488     }
 489     fn flag_gated<F>(&mut self, _: F) where F: FnMut(&mut Vec<GatedCfgAttr>) {}
 490 }
 491
 492 fn node_survives_cfg(attrs: &[ast::Attribute],
 493                      config: &ast::CrateConfig) -> bool {
 494     let mut survives_cfg = true;
 495
 496     for attr in attrs {
 497         let mut fld = CfgAttrFolder {
 498             diag: CfgDiagSilent { error: false },
 499             config: config,
 500         };
 501         let attr = fld.fold_attribute(attr.clone());
 502
 503         // In case of error we can just return true,
 504         // since the actual cfg folders will end compilation anyway.
 505
 506         if fld.diag.error { return true; }
 507
 508         survives_cfg &= attr.map(|attr| {
 509             let mut diag = CfgDiagSilent { error: false };
 510             let r = in_cfg(config, &[attr], &mut diag);
 511             if diag.error { return true; }
 512             r
 513         }).unwrap_or(true)
 514     }
 515
 516     survives_cfg
 517 }