src/libsyntax/fold.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 //! A Folder represents an AST->AST fold; it accepts an AST piece,
  12 //! and returns a piece of the same type. So, for instance, macro
  13 //! expansion is a Folder that walks over an AST and produces another
  14 //! AST.
  15 //!
  16 //! Note: using a Folder (other than the MacroExpander Folder) on
  17 //! an AST before macro expansion is probably a bad idea. For instance,
  18 //! a folder renaming item names in a module will miss all of those
  19 //! that are created by the expansion of a macro.
  20
  21 use ast::*;
  22 use ast;
  23 use ast_util;
  24 use codemap::{respan, Span, Spanned};
  25 use owned_slice::OwnedSlice;
  26 use parse::token;
  27 use ptr::P;
  28 use std::ptr;
  29 use util::small_vector::SmallVector;
  30
  31 use std::rc::Rc;
  32
  33 // This could have a better place to live.
  34 pub trait MoveMap<T> {
  35     fn move_map<F>(self, f: F) -> Self where F: FnMut(T) -> T;
  36 }
  37
  38 impl<T> MoveMap<T> for Vec<T> {
  39     fn move_map<F>(mut self, mut f: F) -> Vec<T> where F: FnMut(T) -> T {
  40         for p in self.iter_mut() {
  41             unsafe {
  42                 // FIXME(#5016) this shouldn't need to zero to be safe.
  43                 ptr::write(p, f(ptr::read_and_zero(p)));
  44             }
  45         }
  46         self
  47     }
  48 }
  49
  50 impl<T> MoveMap<T> for OwnedSlice<T> {
  51     fn move_map<F>(self, f: F) -> OwnedSlice<T> where F: FnMut(T) -> T {
  52         OwnedSlice::from_vec(self.into_vec().move_map(f))
  53     }
  54 }
  55
  56 pub trait Folder : Sized {
  57     // Any additions to this trait should happen in form
  58     // of a call to a public `noop_*` function that only calls
  59     // out to the folder again, not other `noop_*` functions.
  60     //
  61     // This is a necessary API workaround to the problem of not
  62     // being able to call out to the super default method
  63     // in an overridden default method.
  64
  65     fn fold_crate(&mut self, c: Crate) -> Crate {
  66         noop_fold_crate(c, self)
  67     }
  68
  69     fn fold_meta_items(&mut self, meta_items: Vec<P<MetaItem>>) -> Vec<P<MetaItem>> {
  70         noop_fold_meta_items(meta_items, self)
  71     }
  72
  73     fn fold_meta_item(&mut self, meta_item: P<MetaItem>) -> P<MetaItem> {
  74         noop_fold_meta_item(meta_item, self)
  75     }
  76
  77     fn fold_view_path(&mut self, view_path: P<ViewPath>) -> P<ViewPath> {
  78         noop_fold_view_path(view_path, self)
  79     }
  80
  81     fn fold_view_item(&mut self, vi: ViewItem) -> ViewItem {
  82         noop_fold_view_item(vi, self)
  83     }
  84
  85     fn fold_foreign_item(&mut self, ni: P<ForeignItem>) -> P<ForeignItem> {
  86         noop_fold_foreign_item(ni, self)
  87     }
  88
  89     fn fold_item(&mut self, i: P<Item>) -> SmallVector<P<Item>> {
  90         noop_fold_item(i, self)
  91     }
  92
  93     fn fold_item_simple(&mut self, i: Item) -> Item {
  94         noop_fold_item_simple(i, self)
  95     }
  96
  97     fn fold_struct_field(&mut self, sf: StructField) -> StructField {
  98         noop_fold_struct_field(sf, self)
  99     }
 100
 101     fn fold_item_underscore(&mut self, i: Item_) -> Item_ {
 102         noop_fold_item_underscore(i, self)
 103     }
 104
 105     fn fold_fn_decl(&mut self, d: P<FnDecl>) -> P<FnDecl> {
 106         noop_fold_fn_decl(d, self)
 107     }
 108
 109     fn fold_type_method(&mut self, m: TypeMethod) -> TypeMethod {
 110         noop_fold_type_method(m, self)
 111     }
 112
 113     fn fold_method(&mut self, m: P<Method>) -> SmallVector<P<Method>> {
 114         noop_fold_method(m, self)
 115     }
 116
 117     fn fold_block(&mut self, b: P<Block>) -> P<Block> {
 118         noop_fold_block(b, self)
 119     }
 120
 121     fn fold_stmt(&mut self, s: P<Stmt>) -> SmallVector<P<Stmt>> {
 122         s.and_then(|s| noop_fold_stmt(s, self))
 123     }
 124
 125     fn fold_arm(&mut self, a: Arm) -> Arm {
 126         noop_fold_arm(a, self)
 127     }
 128
 129     fn fold_pat(&mut self, p: P<Pat>) -> P<Pat> {
 130         noop_fold_pat(p, self)
 131     }
 132
 133     fn fold_decl(&mut self, d: P<Decl>) -> SmallVector<P<Decl>> {
 134         noop_fold_decl(d, self)
 135     }
 136
 137     fn fold_expr(&mut self, e: P<Expr>) -> P<Expr> {
 138         e.map(|e| noop_fold_expr(e, self))
 139     }
 140
 141     fn fold_ty(&mut self, t: P<Ty>) -> P<Ty> {
 142         noop_fold_ty(t, self)
 143     }
 144
 145     fn fold_qpath(&mut self, t: P<QPath>) -> P<QPath> {
 146         noop_fold_qpath(t, self)
 147     }
 148
 149     fn fold_ty_binding(&mut self, t: P<TypeBinding>) -> P<TypeBinding> {
 150         noop_fold_ty_binding(t, self)
 151     }
 152
 153     fn fold_mod(&mut self, m: Mod) -> Mod {
 154         noop_fold_mod(m, self)
 155     }
 156
 157     fn fold_foreign_mod(&mut self, nm: ForeignMod) -> ForeignMod {
 158         noop_fold_foreign_mod(nm, self)
 159     }
 160
 161     fn fold_variant(&mut self, v: P<Variant>) -> P<Variant> {
 162         noop_fold_variant(v, self)
 163     }
 164
 165     fn fold_ident(&mut self, i: Ident) -> Ident {
 166         noop_fold_ident(i, self)
 167     }
 168
 169     fn fold_uint(&mut self, i: uint) -> uint {
 170         noop_fold_uint(i, self)
 171     }
 172
 173     fn fold_path(&mut self, p: Path) -> Path {
 174         noop_fold_path(p, self)
 175     }
 176
 177     fn fold_path_parameters(&mut self, p: PathParameters) -> PathParameters {
 178         noop_fold_path_parameters(p, self)
 179     }
 180
 181     fn fold_angle_bracketed_parameter_data(&mut self, p: AngleBracketedParameterData)
 182                                            -> AngleBracketedParameterData
 183     {
 184         noop_fold_angle_bracketed_parameter_data(p, self)
 185     }
 186
 187     fn fold_parenthesized_parameter_data(&mut self, p: ParenthesizedParameterData)
 188                                          -> ParenthesizedParameterData
 189     {
 190         noop_fold_parenthesized_parameter_data(p, self)
 191     }
 192
 193     fn fold_local(&mut self, l: P<Local>) -> P<Local> {
 194         noop_fold_local(l, self)
 195     }
 196
 197     fn fold_mac(&mut self, _mac: Mac) -> Mac {
 198         panic!("fold_mac disabled by default");
 199         // NB: see note about macros above.
 200         // if you really want a folder that
 201         // works on macros, use this
 202         // definition in your trait impl:
 203         // fold::noop_fold_mac(_mac, self)
 204     }
 205
 206     fn fold_explicit_self(&mut self, es: ExplicitSelf) -> ExplicitSelf {
 207         noop_fold_explicit_self(es, self)
 208     }
 209
 210     fn fold_explicit_self_underscore(&mut self, es: ExplicitSelf_) -> ExplicitSelf_ {
 211         noop_fold_explicit_self_underscore(es, self)
 212     }
 213
 214     fn fold_lifetime(&mut self, l: Lifetime) -> Lifetime {
 215         noop_fold_lifetime(l, self)
 216     }
 217
 218     fn fold_lifetime_def(&mut self, l: LifetimeDef) -> LifetimeDef {
 219         noop_fold_lifetime_def(l, self)
 220     }
 221
 222     fn fold_attribute(&mut self, at: Attribute) -> Attribute {
 223         noop_fold_attribute(at, self)
 224     }
 225
 226     fn fold_arg(&mut self, a: Arg) -> Arg {
 227         noop_fold_arg(a, self)
 228     }
 229
 230     fn fold_generics(&mut self, generics: Generics) -> Generics {
 231         noop_fold_generics(generics, self)
 232     }
 233
 234     fn fold_trait_ref(&mut self, p: TraitRef) -> TraitRef {
 235         noop_fold_trait_ref(p, self)
 236     }
 237
 238     fn fold_poly_trait_ref(&mut self, p: PolyTraitRef) -> PolyTraitRef {
 239         noop_fold_poly_trait_ref(p, self)
 240     }
 241
 242     fn fold_struct_def(&mut self, struct_def: P<StructDef>) -> P<StructDef> {
 243         noop_fold_struct_def(struct_def, self)
 244     }
 245
 246     fn fold_lifetimes(&mut self, lts: Vec<Lifetime>) -> Vec<Lifetime> {
 247         noop_fold_lifetimes(lts, self)
 248     }
 249
 250     fn fold_lifetime_defs(&mut self, lts: Vec<LifetimeDef>) -> Vec<LifetimeDef> {
 251         noop_fold_lifetime_defs(lts, self)
 252     }
 253
 254     fn fold_ty_param(&mut self, tp: TyParam) -> TyParam {
 255         noop_fold_ty_param(tp, self)
 256     }
 257
 258     fn fold_ty_params(&mut self, tps: OwnedSlice<TyParam>) -> OwnedSlice<TyParam> {
 259         noop_fold_ty_params(tps, self)
 260     }
 261
 262     fn fold_tt(&mut self, tt: &TokenTree) -> TokenTree {
 263         noop_fold_tt(tt, self)
 264     }
 265
 266     fn fold_tts(&mut self, tts: &[TokenTree]) -> Vec<TokenTree> {
 267         noop_fold_tts(tts, self)
 268     }
 269
 270     fn fold_token(&mut self, t: token::Token) -> token::Token {
 271         noop_fold_token(t, self)
 272     }
 273
 274     fn fold_interpolated(&mut self, nt: token::Nonterminal) -> token::Nonterminal {
 275         noop_fold_interpolated(nt, self)
 276     }
 277
 278     fn fold_opt_lifetime(&mut self, o_lt: Option<Lifetime>) -> Option<Lifetime> {
 279         noop_fold_opt_lifetime(o_lt, self)
 280     }
 281
 282     fn fold_variant_arg(&mut self, va: VariantArg) -> VariantArg {
 283         noop_fold_variant_arg(va, self)
 284     }
 285
 286     fn fold_opt_bounds(&mut self, b: Option<OwnedSlice<TyParamBound>>)
 287                        -> Option<OwnedSlice<TyParamBound>> {
 288         noop_fold_opt_bounds(b, self)
 289     }
 290
 291     fn fold_bounds(&mut self, b: OwnedSlice<TyParamBound>)
 292                        -> OwnedSlice<TyParamBound> {
 293         noop_fold_bounds(b, self)
 294     }
 295
 296     fn fold_ty_param_bound(&mut self, tpb: TyParamBound) -> TyParamBound {
 297         noop_fold_ty_param_bound(tpb, self)
 298     }
 299
 300     fn fold_mt(&mut self, mt: MutTy) -> MutTy {
 301         noop_fold_mt(mt, self)
 302     }
 303
 304     fn fold_field(&mut self, field: Field) -> Field {
 305         noop_fold_field(field, self)
 306     }
 307
 308     fn fold_where_clause(&mut self, where_clause: WhereClause)
 309                          -> WhereClause {
 310         noop_fold_where_clause(where_clause, self)
 311     }
 312
 313     fn fold_where_predicate(&mut self, where_predicate: WherePredicate)
 314                             -> WherePredicate {
 315         noop_fold_where_predicate(where_predicate, self)
 316     }
 317
 318     fn fold_typedef(&mut self, typedef: Typedef) -> Typedef {
 319         noop_fold_typedef(typedef, self)
 320     }
 321
 322     fn fold_associated_type(&mut self, associated_type: AssociatedType)
 323                             -> AssociatedType {
 324         noop_fold_associated_type(associated_type, self)
 325     }
 326
 327     fn new_id(&mut self, i: NodeId) -> NodeId {
 328         i
 329     }
 330
 331     fn new_span(&mut self, sp: Span) -> Span {
 332         sp
 333     }
 334 }
 335
 336 pub fn noop_fold_meta_items<T: Folder>(meta_items: Vec<P<MetaItem>>, fld: &mut T)
 337                                        -> Vec<P<MetaItem>> {
 338     meta_items.move_map(|x| fld.fold_meta_item(x))
 339 }
 340
 341 pub fn noop_fold_view_path<T: Folder>(view_path: P<ViewPath>, fld: &mut T) -> P<ViewPath> {
 342     view_path.map(|Spanned {node, span}| Spanned {
 343         node: match node {
 344             ViewPathSimple(ident, path, node_id) => {
 345                 let id = fld.new_id(node_id);
 346                 ViewPathSimple(ident, fld.fold_path(path), id)
 347             }
 348             ViewPathGlob(path, node_id) => {
 349                 let id = fld.new_id(node_id);
 350                 ViewPathGlob(fld.fold_path(path), id)
 351             }
 352             ViewPathList(path, path_list_idents, node_id) => {
 353                 let id = fld.new_id(node_id);
 354                 ViewPathList(fld.fold_path(path),
 355                              path_list_idents.move_map(|path_list_ident| {
 356                                 Spanned {
 357                                     node: match path_list_ident.node {
 358                                         PathListIdent { id, name } =>
 359                                             PathListIdent {
 360                                                 id: fld.new_id(id),
 361                                                 name: name
 362                                             },
 363                                         PathListMod { id } =>
 364                                             PathListMod { id: fld.new_id(id) }
 365                                     },
 366                                     span: fld.new_span(path_list_ident.span)
 367                                 }
 368                              }),
 369                              id)
 370             }
 371         },
 372         span: fld.new_span(span)
 373     })
 374 }
 375
 376 pub fn noop_fold_arm<T: Folder>(Arm {attrs, pats, guard, body}: Arm, fld: &mut T) -> Arm {
 377     Arm {
 378         attrs: attrs.move_map(|x| fld.fold_attribute(x)),
 379         pats: pats.move_map(|x| fld.fold_pat(x)),
 380         guard: guard.map(|x| fld.fold_expr(x)),
 381         body: fld.fold_expr(body),
 382     }
 383 }
 384
 385 pub fn noop_fold_decl<T: Folder>(d: P<Decl>, fld: &mut T) -> SmallVector<P<Decl>> {
 386     d.and_then(|Spanned {node, span}| match node {
 387         DeclLocal(l) => SmallVector::one(P(Spanned {
 388             node: DeclLocal(fld.fold_local(l)),
 389             span: fld.new_span(span)
 390         })),
 391         DeclItem(it) => fld.fold_item(it).into_iter().map(|i| P(Spanned {
 392             node: DeclItem(i),
 393             span: fld.new_span(span)
 394         })).collect()
 395     })
 396 }
 397
 398 pub fn noop_fold_ty_binding<T: Folder>(b: P<TypeBinding>, fld: &mut T) -> P<TypeBinding> {
 399     b.map(|TypeBinding { id, ident, ty, span }| TypeBinding {
 400         id: fld.new_id(id),
 401         ident: ident,
 402         ty: fld.fold_ty(ty),
 403         span: fld.new_span(span),
 404     })
 405 }
 406
 407 pub fn noop_fold_ty<T: Folder>(t: P<Ty>, fld: &mut T) -> P<Ty> {
 408     t.map(|Ty {id, node, span}| Ty {
 409         id: fld.new_id(id),
 410         node: match node {
 411             TyInfer => node,
 412             TyVec(ty) => TyVec(fld.fold_ty(ty)),
 413             TyPtr(mt) => TyPtr(fld.fold_mt(mt)),
 414             TyRptr(region, mt) => {
 415                 TyRptr(fld.fold_opt_lifetime(region), fld.fold_mt(mt))
 416             }
 417             TyBareFn(f) => {
 418                 TyBareFn(f.map(|BareFnTy {lifetimes, unsafety, abi, decl}| BareFnTy {
 419                     lifetimes: fld.fold_lifetime_defs(lifetimes),
 420                     unsafety: unsafety,
 421                     abi: abi,
 422                     decl: fld.fold_fn_decl(decl)
 423                 }))
 424             }
 425             TyTup(tys) => TyTup(tys.move_map(|ty| fld.fold_ty(ty))),
 426             TyParen(ty) => TyParen(fld.fold_ty(ty)),
 427             TyPath(path, id) => {
 428                 let id = fld.new_id(id);
 429                 TyPath(fld.fold_path(path), id)
 430             }
 431             TyObjectSum(ty, bounds) => {
 432                 TyObjectSum(fld.fold_ty(ty),
 433                             fld.fold_bounds(bounds))
 434             }
 435             TyQPath(qpath) => {
 436                 TyQPath(fld.fold_qpath(qpath))
 437             }
 438             TyFixedLengthVec(ty, e) => {
 439                 TyFixedLengthVec(fld.fold_ty(ty), fld.fold_expr(e))
 440             }
 441             TyTypeof(expr) => {
 442                 TyTypeof(fld.fold_expr(expr))
 443             }
 444             TyPolyTraitRef(bounds) => {
 445                 TyPolyTraitRef(bounds.move_map(|b| fld.fold_ty_param_bound(b)))
 446             }
 447         },
 448         span: fld.new_span(span)
 449     })
 450 }
 451
 452 pub fn noop_fold_qpath<T: Folder>(qpath: P<QPath>, fld: &mut T) -> P<QPath> {
 453     qpath.map(|qpath| {
 454         QPath {
 455             self_type: fld.fold_ty(qpath.self_type),
 456             trait_ref: qpath.trait_ref.map(|tr| fld.fold_trait_ref(tr)),
 457             item_name: fld.fold_ident(qpath.item_name),
 458         }
 459     })
 460 }
 461
 462 pub fn noop_fold_foreign_mod<T: Folder>(ForeignMod {abi, view_items, items}: ForeignMod,
 463                                         fld: &mut T) -> ForeignMod {
 464     ForeignMod {
 465         abi: abi,
 466         view_items: view_items.move_map(|x| fld.fold_view_item(x)),
 467         items: items.move_map(|x| fld.fold_foreign_item(x)),
 468     }
 469 }
 470
 471 pub fn noop_fold_variant<T: Folder>(v: P<Variant>, fld: &mut T) -> P<Variant> {
 472     v.map(|Spanned {node: Variant_ {id, name, attrs, kind, disr_expr, vis}, span}| Spanned {
 473         node: Variant_ {
 474             id: fld.new_id(id),
 475             name: name,
 476             attrs: attrs.move_map(|x| fld.fold_attribute(x)),
 477             kind: match kind {
 478                 TupleVariantKind(variant_args) => {
 479                     TupleVariantKind(variant_args.move_map(|x|
 480                         fld.fold_variant_arg(x)))
 481                 }
 482                 StructVariantKind(struct_def) => {
 483                     StructVariantKind(fld.fold_struct_def(struct_def))
 484                 }
 485             },
 486             disr_expr: disr_expr.map(|e| fld.fold_expr(e)),
 487             vis: vis,
 488         },
 489         span: fld.new_span(span),
 490     })
 491 }
 492
 493 pub fn noop_fold_ident<T: Folder>(i: Ident, _: &mut T) -> Ident {
 494     i
 495 }
 496
 497 pub fn noop_fold_uint<T: Folder>(i: uint, _: &mut T) -> uint {
 498     i
 499 }
 500
 501 pub fn noop_fold_path<T: Folder>(Path {global, segments, span}: Path, fld: &mut T) -> Path {
 502     Path {
 503         global: global,
 504         segments: segments.move_map(|PathSegment {identifier, parameters}| PathSegment {
 505             identifier: fld.fold_ident(identifier),
 506             parameters: fld.fold_path_parameters(parameters),
 507         }),
 508         span: fld.new_span(span)
 509     }
 510 }
 511
 512 pub fn noop_fold_path_parameters<T: Folder>(path_parameters: PathParameters, fld: &mut T)
 513                                             -> PathParameters
 514 {
 515     match path_parameters {
 516         AngleBracketedParameters(data) =>
 517             AngleBracketedParameters(fld.fold_angle_bracketed_parameter_data(data)),
 518         ParenthesizedParameters(data) =>
 519             ParenthesizedParameters(fld.fold_parenthesized_parameter_data(data)),
 520     }
 521 }
 522
 523 pub fn noop_fold_angle_bracketed_parameter_data<T: Folder>(data: AngleBracketedParameterData,
 524                                                            fld: &mut T)
 525                                                            -> AngleBracketedParameterData
 526 {
 527     let AngleBracketedParameterData { lifetimes, types, bindings } = data;
 528     AngleBracketedParameterData { lifetimes: fld.fold_lifetimes(lifetimes),
 529                                   types: types.move_map(|ty| fld.fold_ty(ty)),
 530                                   bindings: bindings.move_map(|b| fld.fold_ty_binding(b)) }
 531 }
 532
 533 pub fn noop_fold_parenthesized_parameter_data<T: Folder>(data: ParenthesizedParameterData,
 534                                                          fld: &mut T)
 535                                                          -> ParenthesizedParameterData
 536 {
 537     let ParenthesizedParameterData { inputs, output } = data;
 538     ParenthesizedParameterData { inputs: inputs.move_map(|ty| fld.fold_ty(ty)),
 539                                  output: output.map(|ty| fld.fold_ty(ty)) }
 540 }
 541
 542 pub fn noop_fold_local<T: Folder>(l: P<Local>, fld: &mut T) -> P<Local> {
 543     l.map(|Local {id, pat, ty, init, source, span}| Local {
 544         id: fld.new_id(id),
 545         ty: ty.map(|t| fld.fold_ty(t)),
 546         pat: fld.fold_pat(pat),
 547         init: init.map(|e| fld.fold_expr(e)),
 548         source: source,
 549         span: fld.new_span(span)
 550     })
 551 }
 552
 553 pub fn noop_fold_attribute<T: Folder>(at: Attribute, fld: &mut T) -> Attribute {
 554     let Spanned {node: Attribute_ {id, style, value, is_sugared_doc}, span} = at;
 555     Spanned {
 556         node: Attribute_ {
 557             id: id,
 558             style: style,
 559             value: fld.fold_meta_item(value),
 560             is_sugared_doc: is_sugared_doc
 561         },
 562         span: fld.new_span(span)
 563     }
 564 }
 565
 566 pub fn noop_fold_explicit_self_underscore<T: Folder>(es: ExplicitSelf_, fld: &mut T)
 567                                                      -> ExplicitSelf_ {
 568     match es {
 569         SelfStatic | SelfValue(_) => es,
 570         SelfRegion(lifetime, m, ident) => {
 571             SelfRegion(fld.fold_opt_lifetime(lifetime), m, ident)
 572         }
 573         SelfExplicit(typ, ident) => {
 574             SelfExplicit(fld.fold_ty(typ), ident)
 575         }
 576     }
 577 }
 578
 579 pub fn noop_fold_explicit_self<T: Folder>(Spanned {span, node}: ExplicitSelf, fld: &mut T)
 580                                           -> ExplicitSelf {
 581     Spanned {
 582         node: fld.fold_explicit_self_underscore(node),
 583         span: fld.new_span(span)
 584     }
 585 }
 586
 587
 588 pub fn noop_fold_mac<T: Folder>(Spanned {node, span}: Mac, fld: &mut T) -> Mac {
 589     Spanned {
 590         node: match node {
 591             MacInvocTT(p, tts, ctxt) => {
 592                 MacInvocTT(fld.fold_path(p), fld.fold_tts(tts.as_slice()), ctxt)
 593             }
 594         },
 595         span: fld.new_span(span)
 596     }
 597 }
 598
 599 pub fn noop_fold_meta_item<T: Folder>(mi: P<MetaItem>, fld: &mut T) -> P<MetaItem> {
 600     mi.map(|Spanned {node, span}| Spanned {
 601         node: match node {
 602             MetaWord(id) => MetaWord(id),
 603             MetaList(id, mis) => {
 604                 MetaList(id, mis.move_map(|e| fld.fold_meta_item(e)))
 605             }
 606             MetaNameValue(id, s) => MetaNameValue(id, s)
 607         },
 608         span: fld.new_span(span)
 609     })
 610 }
 611
 612 pub fn noop_fold_arg<T: Folder>(Arg {id, pat, ty}: Arg, fld: &mut T) -> Arg {
 613     Arg {
 614         id: fld.new_id(id),
 615         pat: fld.fold_pat(pat),
 616         ty: fld.fold_ty(ty)
 617     }
 618 }
 619
 620 pub fn noop_fold_tt<T: Folder>(tt: &TokenTree, fld: &mut T) -> TokenTree {
 621     match *tt {
 622         TtToken(span, ref tok) =>
 623             TtToken(span, fld.fold_token(tok.clone())),
 624         TtDelimited(span, ref delimed) => {
 625             TtDelimited(span, Rc::new(
 626                             Delimited {
 627                                 delim: delimed.delim,
 628                                 open_span: delimed.open_span,
 629                                 tts: fld.fold_tts(delimed.tts.as_slice()),
 630                                 close_span: delimed.close_span,
 631                             }
 632                         ))
 633         },
 634         TtSequence(span, ref seq) =>
 635             TtSequence(span,
 636                        Rc::new(SequenceRepetition {
 637                            tts: fld.fold_tts(seq.tts.as_slice()),
 638                            separator: seq.separator.clone().map(|tok| fld.fold_token(tok)),
 639                            ..**seq
 640                        })),
 641     }
 642 }
 643
 644 pub fn noop_fold_tts<T: Folder>(tts: &[TokenTree], fld: &mut T) -> Vec<TokenTree> {
 645     tts.iter().map(|tt| fld.fold_tt(tt)).collect()
 646 }
 647
 648 // apply ident folder if it's an ident, apply other folds to interpolated nodes
 649 pub fn noop_fold_token<T: Folder>(t: token::Token, fld: &mut T) -> token::Token {
 650     match t {
 651         token::Ident(id, followed_by_colons) => {
 652             token::Ident(fld.fold_ident(id), followed_by_colons)
 653         }
 654         token::Lifetime(id) => token::Lifetime(fld.fold_ident(id)),
 655         token::Interpolated(nt) => token::Interpolated(fld.fold_interpolated(nt)),
 656         token::SubstNt(ident, namep) => {
 657             token::SubstNt(fld.fold_ident(ident), namep)
 658         }
 659         token::MatchNt(name, kind, namep, kindp) => {
 660             token::MatchNt(fld.fold_ident(name), fld.fold_ident(kind), namep, kindp)
 661         }
 662         _ => t
 663     }
 664 }
 665
 666 /// apply folder to elements of interpolated nodes
 667 //
 668 // NB: this can occur only when applying a fold to partially expanded code, where
 669 // parsed pieces have gotten implanted ito *other* macro invocations. This is relevant
 670 // for macro hygiene, but possibly not elsewhere.
 671 //
 672 // One problem here occurs because the types for fold_item, fold_stmt, etc. allow the
 673 // folder to return *multiple* items; this is a problem for the nodes here, because
 674 // they insist on having exactly one piece. One solution would be to mangle the fold
 675 // trait to include one-to-many and one-to-one versions of these entry points, but that
 676 // would probably confuse a lot of people and help very few. Instead, I'm just going
 677 // to put in dynamic checks. I think the performance impact of this will be pretty much
 678 // nonexistent. The danger is that someone will apply a fold to a partially expanded
 679 // node, and will be confused by the fact that their "fold_item" or "fold_stmt" isn't
 680 // getting called on NtItem or NtStmt nodes. Hopefully they'll wind up reading this
 681 // comment, and doing something appropriate.
 682 //
 683 // BTW, design choice: I considered just changing the type of, e.g., NtItem to contain
 684 // multiple items, but decided against it when I looked at parse_item_or_view_item and
 685 // tried to figure out what I would do with multiple items there....
 686 pub fn noop_fold_interpolated<T: Folder>(nt: token::Nonterminal, fld: &mut T)
 687                                          -> token::Nonterminal {
 688     match nt {
 689         token::NtItem(item) =>
 690             token::NtItem(fld.fold_item(item)
 691                           // this is probably okay, because the only folds likely
 692                           // to peek inside interpolated nodes will be renamings/markings,
 693                           // which map single items to single items
 694                           .expect_one("expected fold to produce exactly one item")),
 695         token::NtBlock(block) => token::NtBlock(fld.fold_block(block)),
 696         token::NtStmt(stmt) =>
 697             token::NtStmt(fld.fold_stmt(stmt)
 698                           // this is probably okay, because the only folds likely
 699                           // to peek inside interpolated nodes will be renamings/markings,
 700                           // which map single items to single items
 701                           .expect_one("expected fold to produce exactly one statement")),
 702         token::NtPat(pat) => token::NtPat(fld.fold_pat(pat)),
 703         token::NtExpr(expr) => token::NtExpr(fld.fold_expr(expr)),
 704         token::NtTy(ty) => token::NtTy(fld.fold_ty(ty)),
 705         token::NtIdent(box id, is_mod_name) =>
 706             token::NtIdent(box fld.fold_ident(id), is_mod_name),
 707         token::NtMeta(meta_item) => token::NtMeta(fld.fold_meta_item(meta_item)),
 708         token::NtPath(box path) => token::NtPath(box fld.fold_path(path)),
 709         token::NtTT(tt) => token::NtTT(P(fld.fold_tt(&*tt))),
 710     }
 711 }
 712
 713 pub fn noop_fold_fn_decl<T: Folder>(decl: P<FnDecl>, fld: &mut T) -> P<FnDecl> {
 714     decl.map(|FnDecl {inputs, output, variadic}| FnDecl {
 715         inputs: inputs.move_map(|x| fld.fold_arg(x)),
 716         output: match output {
 717             Return(ty) => Return(fld.fold_ty(ty)),
 718             NoReturn(span) => NoReturn(span)
 719         },
 720         variadic: variadic
 721     })
 722 }
 723
 724 pub fn noop_fold_ty_param_bound<T>(tpb: TyParamBound, fld: &mut T)
 725                                    -> TyParamBound
 726                                    where T: Folder {
 727     match tpb {
 728         TraitTyParamBound(ty, modifier) => TraitTyParamBound(fld.fold_poly_trait_ref(ty), modifier),
 729         RegionTyParamBound(lifetime) => RegionTyParamBound(fld.fold_lifetime(lifetime)),
 730     }
 731 }
 732
 733 pub fn noop_fold_ty_param<T: Folder>(tp: TyParam, fld: &mut T) -> TyParam {
 734     let TyParam {id, ident, bounds, default, span} = tp;
 735     TyParam {
 736         id: fld.new_id(id),
 737         ident: ident,
 738         bounds: fld.fold_bounds(bounds),
 739         default: default.map(|x| fld.fold_ty(x)),
 740         span: span
 741     }
 742 }
 743
 744 pub fn noop_fold_ty_params<T: Folder>(tps: OwnedSlice<TyParam>, fld: &mut T)
 745                                       -> OwnedSlice<TyParam> {
 746     tps.move_map(|tp| fld.fold_ty_param(tp))
 747 }
 748
 749 pub fn noop_fold_lifetime<T: Folder>(l: Lifetime, fld: &mut T) -> Lifetime {
 750     Lifetime {
 751         id: fld.new_id(l.id),
 752         name: l.name,
 753         span: fld.new_span(l.span)
 754     }
 755 }
 756
 757 pub fn noop_fold_lifetime_def<T: Folder>(l: LifetimeDef, fld: &mut T)
 758                                          -> LifetimeDef {
 759     LifetimeDef {
 760         lifetime: fld.fold_lifetime(l.lifetime),
 761         bounds: fld.fold_lifetimes(l.bounds),
 762     }
 763 }
 764
 765 pub fn noop_fold_lifetimes<T: Folder>(lts: Vec<Lifetime>, fld: &mut T) -> Vec<Lifetime> {
 766     lts.move_map(|l| fld.fold_lifetime(l))
 767 }
 768
 769 pub fn noop_fold_lifetime_defs<T: Folder>(lts: Vec<LifetimeDef>, fld: &mut T)
 770                                           -> Vec<LifetimeDef> {
 771     lts.move_map(|l| fld.fold_lifetime_def(l))
 772 }
 773
 774 pub fn noop_fold_opt_lifetime<T: Folder>(o_lt: Option<Lifetime>, fld: &mut T)
 775                                          -> Option<Lifetime> {
 776     o_lt.map(|lt| fld.fold_lifetime(lt))
 777 }
 778
 779 pub fn noop_fold_generics<T: Folder>(Generics {ty_params, lifetimes, where_clause}: Generics,
 780                                      fld: &mut T) -> Generics {
 781     Generics {
 782         ty_params: fld.fold_ty_params(ty_params),
 783         lifetimes: fld.fold_lifetime_defs(lifetimes),
 784         where_clause: fld.fold_where_clause(where_clause),
 785     }
 786 }
 787
 788 pub fn noop_fold_where_clause<T: Folder>(
 789                               WhereClause {id, predicates}: WhereClause,
 790                               fld: &mut T)
 791                               -> WhereClause {
 792     WhereClause {
 793         id: fld.new_id(id),
 794         predicates: predicates.move_map(|predicate| {
 795             fld.fold_where_predicate(predicate)
 796         })
 797     }
 798 }
 799
 800 pub fn noop_fold_where_predicate<T: Folder>(
 801                                  pred: WherePredicate,
 802                                  fld: &mut T)
 803                                  -> WherePredicate {
 804     match pred {
 805         ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate{bounded_ty,
 806                                                                      bounds,
 807                                                                      span}) => {
 808             ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
 809                 bounded_ty: fld.fold_ty(bounded_ty),
 810                 bounds: bounds.move_map(|x| fld.fold_ty_param_bound(x)),
 811                 span: fld.new_span(span)
 812             })
 813         }
 814         ast::WherePredicate::RegionPredicate(ast::WhereRegionPredicate{lifetime,
 815                                                                        bounds,
 816                                                                        span}) => {
 817             ast::WherePredicate::RegionPredicate(ast::WhereRegionPredicate {
 818                 span: fld.new_span(span),
 819                 lifetime: fld.fold_lifetime(lifetime),
 820                 bounds: bounds.move_map(|bound| fld.fold_lifetime(bound))
 821             })
 822         }
 823         ast::WherePredicate::EqPredicate(ast::WhereEqPredicate{id,
 824                                                                path,
 825                                                                ty,
 826                                                                span}) => {
 827             ast::WherePredicate::EqPredicate(ast::WhereEqPredicate{
 828                 id: fld.new_id(id),
 829                 path: fld.fold_path(path),
 830                 ty:fld.fold_ty(ty),
 831                 span: fld.new_span(span)
 832             })
 833         }
 834     }
 835 }
 836
 837 pub fn noop_fold_typedef<T>(t: Typedef, folder: &mut T)
 838                             -> Typedef
 839                             where T: Folder {
 840     let new_id = folder.new_id(t.id);
 841     let new_span = folder.new_span(t.span);
 842     let new_attrs = t.attrs.iter().map(|attr| {
 843         folder.fold_attribute((*attr).clone())
 844     }).collect();
 845     let new_ident = folder.fold_ident(t.ident);
 846     let new_type = folder.fold_ty(t.typ);
 847     ast::Typedef {
 848         ident: new_ident,
 849         typ: new_type,
 850         id: new_id,
 851         span: new_span,
 852         vis: t.vis,
 853         attrs: new_attrs,
 854     }
 855 }
 856
 857 pub fn noop_fold_associated_type<T>(at: AssociatedType, folder: &mut T)
 858                                     -> AssociatedType
 859                                     where T: Folder
 860 {
 861     let new_attrs = at.attrs
 862                       .iter()
 863                       .map(|attr| folder.fold_attribute((*attr).clone()))
 864                       .collect();
 865     let new_param = folder.fold_ty_param(at.ty_param);
 866     ast::AssociatedType {
 867         attrs: new_attrs,
 868         ty_param: new_param,
 869     }
 870 }
 871
 872 pub fn noop_fold_struct_def<T: Folder>(struct_def: P<StructDef>, fld: &mut T) -> P<StructDef> {
 873     struct_def.map(|StructDef { fields, ctor_id }| StructDef {
 874         fields: fields.move_map(|f| fld.fold_struct_field(f)),
 875         ctor_id: ctor_id.map(|cid| fld.new_id(cid)),
 876     })
 877 }
 878
 879 pub fn noop_fold_trait_ref<T: Folder>(p: TraitRef, fld: &mut T) -> TraitRef {
 880     let id = fld.new_id(p.ref_id);
 881     let TraitRef {
 882         path,
 883         ref_id: _,
 884     } = p;
 885     ast::TraitRef {
 886         path: fld.fold_path(path),
 887         ref_id: id,
 888     }
 889 }
 890
 891 pub fn noop_fold_poly_trait_ref<T: Folder>(p: PolyTraitRef, fld: &mut T) -> PolyTraitRef {
 892     ast::PolyTraitRef {
 893         bound_lifetimes: fld.fold_lifetime_defs(p.bound_lifetimes),
 894         trait_ref: fld.fold_trait_ref(p.trait_ref)
 895     }
 896 }
 897
 898 pub fn noop_fold_struct_field<T: Folder>(f: StructField, fld: &mut T) -> StructField {
 899     let StructField {node: StructField_ {id, kind, ty, attrs}, span} = f;
 900     Spanned {
 901         node: StructField_ {
 902             id: fld.new_id(id),
 903             kind: kind,
 904             ty: fld.fold_ty(ty),
 905             attrs: attrs.move_map(|a| fld.fold_attribute(a))
 906         },
 907         span: fld.new_span(span)
 908     }
 909 }
 910
 911 pub fn noop_fold_field<T: Folder>(Field {ident, expr, span}: Field, folder: &mut T) -> Field {
 912     Field {
 913         ident: respan(ident.span, folder.fold_ident(ident.node)),
 914         expr: folder.fold_expr(expr),
 915         span: folder.new_span(span)
 916     }
 917 }
 918
 919 pub fn noop_fold_mt<T: Folder>(MutTy {ty, mutbl}: MutTy, folder: &mut T) -> MutTy {
 920     MutTy {
 921         ty: folder.fold_ty(ty),
 922         mutbl: mutbl,
 923     }
 924 }
 925
 926 pub fn noop_fold_opt_bounds<T: Folder>(b: Option<OwnedSlice<TyParamBound>>, folder: &mut T)
 927                                        -> Option<OwnedSlice<TyParamBound>> {
 928     b.map(|bounds| folder.fold_bounds(bounds))
 929 }
 930
 931 fn noop_fold_bounds<T: Folder>(bounds: TyParamBounds, folder: &mut T)
 932                           -> TyParamBounds {
 933     bounds.move_map(|bound| folder.fold_ty_param_bound(bound))
 934 }
 935
 936 fn noop_fold_variant_arg<T: Folder>(VariantArg {id, ty}: VariantArg, folder: &mut T)
 937                                     -> VariantArg {
 938     VariantArg {
 939         id: folder.new_id(id),
 940         ty: folder.fold_ty(ty)
 941     }
 942 }
 943
 944 pub fn noop_fold_view_item<T: Folder>(ViewItem {node, attrs, vis, span}: ViewItem,
 945                                       folder: &mut T) -> ViewItem {
 946     ViewItem {
 947         node: match node {
 948             ViewItemExternCrate(ident, string, node_id) => {
 949                 ViewItemExternCrate(ident, string,
 950                                     folder.new_id(node_id))
 951             }
 952             ViewItemUse(view_path) => {
 953                 ViewItemUse(folder.fold_view_path(view_path))
 954             }
 955         },
 956         attrs: attrs.move_map(|a| folder.fold_attribute(a)),
 957         vis: vis,
 958         span: folder.new_span(span)
 959     }
 960 }
 961
 962 pub fn noop_fold_block<T: Folder>(b: P<Block>, folder: &mut T) -> P<Block> {
 963     b.map(|Block {id, view_items, stmts, expr, rules, span}| Block {
 964         id: folder.new_id(id),
 965         view_items: view_items.move_map(|x| folder.fold_view_item(x)),
 966         stmts: stmts.into_iter().flat_map(|s| folder.fold_stmt(s).into_iter()).collect(),
 967         expr: expr.map(|x| folder.fold_expr(x)),
 968         rules: rules,
 969         span: folder.new_span(span),
 970     })
 971 }
 972
 973 pub fn noop_fold_item_underscore<T: Folder>(i: Item_, folder: &mut T) -> Item_ {
 974     match i {
 975         ItemStatic(t, m, e) => {
 976             ItemStatic(folder.fold_ty(t), m, folder.fold_expr(e))
 977         }
 978         ItemConst(t, e) => {
 979             ItemConst(folder.fold_ty(t), folder.fold_expr(e))
 980         }
 981         ItemFn(decl, unsafety, abi, generics, body) => {
 982             ItemFn(
 983                 folder.fold_fn_decl(decl),
 984                 unsafety,
 985                 abi,
 986                 folder.fold_generics(generics),
 987                 folder.fold_block(body)
 988             )
 989         }
 990         ItemMod(m) => ItemMod(folder.fold_mod(m)),
 991         ItemForeignMod(nm) => ItemForeignMod(folder.fold_foreign_mod(nm)),
 992         ItemTy(t, generics) => {
 993             ItemTy(folder.fold_ty(t), folder.fold_generics(generics))
 994         }
 995         ItemEnum(enum_definition, generics) => {
 996             ItemEnum(
 997                 ast::EnumDef {
 998                     variants: enum_definition.variants.move_map(|x| folder.fold_variant(x)),
 999                 },
1000                 folder.fold_generics(generics))
1001         }
1002         ItemStruct(struct_def, generics) => {
1003             let struct_def = folder.fold_struct_def(struct_def);
1004             ItemStruct(struct_def, folder.fold_generics(generics))
1005         }
1006         ItemImpl(unsafety, polarity, generics, ifce, ty, impl_items) => {
1007             let mut new_impl_items = Vec::new();
1008             for impl_item in impl_items.iter() {
1009                 match *impl_item {
1010                     MethodImplItem(ref x) => {
1011                         for method in folder.fold_method((*x).clone())
1012                                             .into_iter() {
1013                             new_impl_items.push(MethodImplItem(method))
1014                         }
1015                     }
1016                     TypeImplItem(ref t) => {
1017                         new_impl_items.push(TypeImplItem(
1018                                 P(folder.fold_typedef((**t).clone()))));
1019                     }
1020                 }
1021             }
1022             let ifce = match ifce {
1023                 None => None,
1024                 Some(ref trait_ref) => {
1025                     Some(folder.fold_trait_ref((*trait_ref).clone()))
1026                 }
1027             };
1028             ItemImpl(unsafety,
1029                      polarity,
1030                      folder.fold_generics(generics),
1031                      ifce,
1032                      folder.fold_ty(ty),
1033                      new_impl_items)
1034         }
1035         ItemTrait(unsafety, generics, bounds, methods) => {
1036             let bounds = folder.fold_bounds(bounds);
1037             let methods = methods.into_iter().flat_map(|method| {
1038                 let r = match method {
1039                     RequiredMethod(m) => {
1040                             SmallVector::one(RequiredMethod(
1041                                     folder.fold_type_method(m)))
1042                                 .into_iter()
1043                     }
1044                     ProvidedMethod(method) => {
1045                         // the awkward collect/iter idiom here is because
1046                         // even though an iter and a map satisfy the same
1047                         // trait bound, they're not actually the same type, so
1048                         // the method arms don't unify.
1049                         let methods: SmallVector<ast::TraitItem> =
1050                             folder.fold_method(method).into_iter()
1051                             .map(|m| ProvidedMethod(m)).collect();
1052                         methods.into_iter()
1053                     }
1054                     TypeTraitItem(at) => {
1055                         SmallVector::one(TypeTraitItem(P(
1056                                     folder.fold_associated_type(
1057                                         (*at).clone()))))
1058                             .into_iter()
1059                     }
1060                 };
1061                 r
1062             }).collect();
1063             ItemTrait(unsafety,
1064                       folder.fold_generics(generics),
1065                       bounds,
1066                       methods)
1067         }
1068         ItemMac(m) => ItemMac(folder.fold_mac(m)),
1069     }
1070 }
1071
1072 pub fn noop_fold_type_method<T: Folder>(m: TypeMethod, fld: &mut T) -> TypeMethod {
1073     let TypeMethod {
1074         id,
1075         ident,
1076         attrs,
1077         unsafety,
1078         abi,
1079         decl,
1080         generics,
1081         explicit_self,
1082         vis,
1083         span
1084     } = m;
1085     TypeMethod {
1086         id: fld.new_id(id),
1087         ident: fld.fold_ident(ident),
1088         attrs: attrs.move_map(|a| fld.fold_attribute(a)),
1089         unsafety: unsafety,
1090         abi: abi,
1091         decl: fld.fold_fn_decl(decl),
1092         generics: fld.fold_generics(generics),
1093         explicit_self: fld.fold_explicit_self(explicit_self),
1094         vis: vis,
1095         span: fld.new_span(span)
1096     }
1097 }
1098
1099 pub fn noop_fold_mod<T: Folder>(Mod {inner, view_items, items}: Mod, folder: &mut T) -> Mod {
1100     Mod {
1101         inner: folder.new_span(inner),
1102         view_items: view_items.move_map(|x| folder.fold_view_item(x)),
1103         items: items.into_iter().flat_map(|x| folder.fold_item(x).into_iter()).collect(),
1104     }
1105 }
1106
1107 pub fn noop_fold_crate<T: Folder>(Crate {module, attrs, config, mut exported_macros, span}: Crate,
1108                                   folder: &mut T) -> Crate {
1109     let config = folder.fold_meta_items(config);
1110
1111     let mut items = folder.fold_item(P(ast::Item {
1112         ident: token::special_idents::invalid,
1113         attrs: attrs,
1114         id: ast::DUMMY_NODE_ID,
1115         vis: ast::Public,
1116         span: span,
1117         node: ast::ItemMod(module),
1118     })).into_iter();
1119
1120     let (module, attrs, span) = match items.next() {
1121         Some(item) => {
1122             assert!(items.next().is_none(),
1123                     "a crate cannot expand to more than one item");
1124             item.and_then(|ast::Item { attrs, span, node, .. }| {
1125                 match node {
1126                     ast::ItemMod(m) => (m, attrs, span),
1127                     _ => panic!("fold converted a module to not a module"),
1128                 }
1129             })
1130         }
1131         None => (ast::Mod {
1132             inner: span,
1133             view_items: Vec::new(),
1134             items: Vec::new(),
1135         }, Vec::new(), span)
1136     };
1137
1138     for def in exported_macros.iter_mut() {
1139         def.id = folder.new_id(def.id);
1140     }
1141
1142     Crate {
1143         module: module,
1144         attrs: attrs,
1145         config: config,
1146         exported_macros: exported_macros,
1147         span: span,
1148     }
1149 }
1150
1151 // fold one item into possibly many items
1152 pub fn noop_fold_item<T: Folder>(i: P<Item>, folder: &mut T) -> SmallVector<P<Item>> {
1153     SmallVector::one(i.map(|i| folder.fold_item_simple(i)))
1154 }
1155
1156 // fold one item into exactly one item
1157 pub fn noop_fold_item_simple<T: Folder>(Item {id, ident, attrs, node, vis, span}: Item,
1158                                         folder: &mut T) -> Item {
1159     let id = folder.new_id(id);
1160     let node = folder.fold_item_underscore(node);
1161     let ident = match node {
1162         // The node may have changed, recompute the "pretty" impl name.
1163         ItemImpl(_, _, _, ref maybe_trait, ref ty, _) => {
1164             ast_util::impl_pretty_name(maybe_trait, &**ty)
1165         }
1166         _ => ident
1167     };
1168
1169     Item {
1170         id: id,
1171         ident: folder.fold_ident(ident),
1172         attrs: attrs.move_map(|e| folder.fold_attribute(e)),
1173         node: node,
1174         vis: vis,
1175         span: folder.new_span(span)
1176     }
1177 }
1178
1179 pub fn noop_fold_foreign_item<T: Folder>(ni: P<ForeignItem>, folder: &mut T) -> P<ForeignItem> {
1180     ni.map(|ForeignItem {id, ident, attrs, node, span, vis}| ForeignItem {
1181         id: folder.new_id(id),
1182         ident: folder.fold_ident(ident),
1183         attrs: attrs.move_map(|x| folder.fold_attribute(x)),
1184         node: match node {
1185             ForeignItemFn(fdec, generics) => {
1186                 ForeignItemFn(fdec.map(|FnDecl {inputs, output, variadic}| FnDecl {
1187                     inputs: inputs.move_map(|a| folder.fold_arg(a)),
1188                     output: match output {
1189                         Return(ty) => Return(folder.fold_ty(ty)),
1190                         NoReturn(span) => NoReturn(span)
1191                     },
1192                     variadic: variadic
1193                 }), folder.fold_generics(generics))
1194             }
1195             ForeignItemStatic(t, m) => {
1196                 ForeignItemStatic(folder.fold_ty(t), m)
1197             }
1198         },
1199         vis: vis,
1200         span: folder.new_span(span)
1201     })
1202 }
1203
1204 // Default fold over a method.
1205 // Invariant: produces exactly one method.
1206 pub fn noop_fold_method<T: Folder>(m: P<Method>, folder: &mut T) -> SmallVector<P<Method>> {
1207     SmallVector::one(m.map(|Method {id, attrs, node, span}| Method {
1208         id: folder.new_id(id),
1209         attrs: attrs.move_map(|a| folder.fold_attribute(a)),
1210         node: match node {
1211             MethDecl(ident,
1212                      generics,
1213                      abi,
1214                      explicit_self,
1215                      unsafety,
1216                      decl,
1217                      body,
1218                      vis) => {
1219                 MethDecl(folder.fold_ident(ident),
1220                          folder.fold_generics(generics),
1221                          abi,
1222                          folder.fold_explicit_self(explicit_self),
1223                          unsafety,
1224                          folder.fold_fn_decl(decl),
1225                          folder.fold_block(body),
1226                          vis)
1227             },
1228             MethMac(mac) => MethMac(folder.fold_mac(mac)),
1229         },
1230         span: folder.new_span(span)
1231     }))
1232 }
1233
1234 pub fn noop_fold_pat<T: Folder>(p: P<Pat>, folder: &mut T) -> P<Pat> {
1235     p.map(|Pat {id, node, span}| Pat {
1236         id: folder.new_id(id),
1237         node: match node {
1238             PatWild(k) => PatWild(k),
1239             PatIdent(binding_mode, pth1, sub) => {
1240                 PatIdent(binding_mode,
1241                         Spanned{span: folder.new_span(pth1.span),
1242                                 node: folder.fold_ident(pth1.node)},
1243                         sub.map(|x| folder.fold_pat(x)))
1244             }
1245             PatLit(e) => PatLit(folder.fold_expr(e)),
1246             PatEnum(pth, pats) => {
1247                 PatEnum(folder.fold_path(pth),
1248                         pats.map(|pats| pats.move_map(|x| folder.fold_pat(x))))
1249             }
1250             PatStruct(pth, fields, etc) => {
1251                 let pth = folder.fold_path(pth);
1252                 let fs = fields.move_map(|f| {
1253                     Spanned { span: folder.new_span(f.span),
1254                               node: ast::FieldPat {
1255                                   ident: f.node.ident,
1256                                   pat: folder.fold_pat(f.node.pat),
1257                                   is_shorthand: f.node.is_shorthand,
1258                               }}
1259                 });
1260                 PatStruct(pth, fs, etc)
1261             }
1262             PatTup(elts) => PatTup(elts.move_map(|x| folder.fold_pat(x))),
1263             PatBox(inner) => PatBox(folder.fold_pat(inner)),
1264             PatRegion(inner, mutbl) => PatRegion(folder.fold_pat(inner), mutbl),
1265             PatRange(e1, e2) => {
1266                 PatRange(folder.fold_expr(e1), folder.fold_expr(e2))
1267             },
1268             PatVec(before, slice, after) => {
1269                 PatVec(before.move_map(|x| folder.fold_pat(x)),
1270                        slice.map(|x| folder.fold_pat(x)),
1271                        after.move_map(|x| folder.fold_pat(x)))
1272             }
1273             PatMac(mac) => PatMac(folder.fold_mac(mac))
1274         },
1275         span: folder.new_span(span)
1276     })
1277 }
1278
1279 pub fn noop_fold_expr<T: Folder>(Expr {id, node, span}: Expr, folder: &mut T) -> Expr {
1280     Expr {
1281         id: folder.new_id(id),
1282         node: match node {
1283             ExprBox(p, e) => {
1284                 ExprBox(p.map(|e|folder.fold_expr(e)), folder.fold_expr(e))
1285             }
1286             ExprVec(exprs) => {
1287                 ExprVec(exprs.move_map(|x| folder.fold_expr(x)))
1288             }
1289             ExprRepeat(expr, count) => {
1290                 ExprRepeat(folder.fold_expr(expr), folder.fold_expr(count))
1291             }
1292             ExprTup(elts) => ExprTup(elts.move_map(|x| folder.fold_expr(x))),
1293             ExprCall(f, args) => {
1294                 ExprCall(folder.fold_expr(f),
1295                          args.move_map(|x| folder.fold_expr(x)))
1296             }
1297             ExprMethodCall(i, tps, args) => {
1298                 ExprMethodCall(
1299                     respan(i.span, folder.fold_ident(i.node)),
1300                     tps.move_map(|x| folder.fold_ty(x)),
1301                     args.move_map(|x| folder.fold_expr(x)))
1302             }
1303             ExprBinary(binop, lhs, rhs) => {
1304                 ExprBinary(binop,
1305                         folder.fold_expr(lhs),
1306                         folder.fold_expr(rhs))
1307             }
1308             ExprUnary(binop, ohs) => {
1309                 ExprUnary(binop, folder.fold_expr(ohs))
1310             }
1311             ExprLit(l) => ExprLit(l),
1312             ExprCast(expr, ty) => {
1313                 ExprCast(folder.fold_expr(expr), folder.fold_ty(ty))
1314             }
1315             ExprAddrOf(m, ohs) => ExprAddrOf(m, folder.fold_expr(ohs)),
1316             ExprIf(cond, tr, fl) => {
1317                 ExprIf(folder.fold_expr(cond),
1318                        folder.fold_block(tr),
1319                        fl.map(|x| folder.fold_expr(x)))
1320             }
1321             ExprIfLet(pat, expr, tr, fl) => {
1322                 ExprIfLet(folder.fold_pat(pat),
1323                           folder.fold_expr(expr),
1324                           folder.fold_block(tr),
1325                           fl.map(|x| folder.fold_expr(x)))
1326             }
1327             ExprWhile(cond, body, opt_ident) => {
1328                 ExprWhile(folder.fold_expr(cond),
1329                           folder.fold_block(body),
1330                           opt_ident.map(|i| folder.fold_ident(i)))
1331             }
1332             ExprWhileLet(pat, expr, body, opt_ident) => {
1333                 ExprWhileLet(folder.fold_pat(pat),
1334                              folder.fold_expr(expr),
1335                              folder.fold_block(body),
1336                              opt_ident.map(|i| folder.fold_ident(i)))
1337             }
1338             ExprForLoop(pat, iter, body, opt_ident) => {
1339                 ExprForLoop(folder.fold_pat(pat),
1340                             folder.fold_expr(iter),
1341                             folder.fold_block(body),
1342                             opt_ident.map(|i| folder.fold_ident(i)))
1343             }
1344             ExprLoop(body, opt_ident) => {
1345                 ExprLoop(folder.fold_block(body),
1346                         opt_ident.map(|i| folder.fold_ident(i)))
1347             }
1348             ExprMatch(expr, arms, source) => {
1349                 ExprMatch(folder.fold_expr(expr),
1350                         arms.move_map(|x| folder.fold_arm(x)),
1351                         source)
1352             }
1353             ExprClosure(capture_clause, opt_kind, decl, body) => {
1354                 ExprClosure(capture_clause,
1355                             opt_kind,
1356                             folder.fold_fn_decl(decl),
1357                             folder.fold_block(body))
1358             }
1359             ExprBlock(blk) => ExprBlock(folder.fold_block(blk)),
1360             ExprAssign(el, er) => {
1361                 ExprAssign(folder.fold_expr(el), folder.fold_expr(er))
1362             }
1363             ExprAssignOp(op, el, er) => {
1364                 ExprAssignOp(op,
1365                             folder.fold_expr(el),
1366                             folder.fold_expr(er))
1367             }
1368             ExprField(el, ident) => {
1369                 ExprField(folder.fold_expr(el),
1370                           respan(ident.span, folder.fold_ident(ident.node)))
1371             }
1372             ExprTupField(el, ident) => {
1373                 ExprTupField(folder.fold_expr(el),
1374                              respan(ident.span, folder.fold_uint(ident.node)))
1375             }
1376             ExprIndex(el, er) => {
1377                 ExprIndex(folder.fold_expr(el), folder.fold_expr(er))
1378             }
1379             ExprRange(e1, e2) => {
1380                 ExprRange(e1.map(|x| folder.fold_expr(x)),
1381                           e2.map(|x| folder.fold_expr(x)))
1382             }
1383             ExprPath(pth) => ExprPath(folder.fold_path(pth)),
1384             ExprBreak(opt_ident) => ExprBreak(opt_ident.map(|x| folder.fold_ident(x))),
1385             ExprAgain(opt_ident) => ExprAgain(opt_ident.map(|x| folder.fold_ident(x))),
1386             ExprRet(e) => ExprRet(e.map(|x| folder.fold_expr(x))),
1387             ExprInlineAsm(InlineAsm {
1388                 inputs,
1389                 outputs,
1390                 asm,
1391                 asm_str_style,
1392                 clobbers,
1393                 volatile,
1394                 alignstack,
1395                 dialect,
1396                 expn_id,
1397             }) => ExprInlineAsm(InlineAsm {
1398                 inputs: inputs.move_map(|(c, input)| {
1399                     (c, folder.fold_expr(input))
1400                 }),
1401                 outputs: outputs.move_map(|(c, out, is_rw)| {
1402                     (c, folder.fold_expr(out), is_rw)
1403                 }),
1404                 asm: asm,
1405                 asm_str_style: asm_str_style,
1406                 clobbers: clobbers,
1407                 volatile: volatile,
1408                 alignstack: alignstack,
1409                 dialect: dialect,
1410                 expn_id: expn_id,
1411             }),
1412             ExprMac(mac) => ExprMac(folder.fold_mac(mac)),
1413             ExprStruct(path, fields, maybe_expr) => {
1414                 ExprStruct(folder.fold_path(path),
1415                         fields.move_map(|x| folder.fold_field(x)),
1416                         maybe_expr.map(|x| folder.fold_expr(x)))
1417             },
1418             ExprParen(ex) => ExprParen(folder.fold_expr(ex))
1419         },
1420         span: folder.new_span(span)
1421     }
1422 }
1423
1424 pub fn noop_fold_stmt<T: Folder>(Spanned {node, span}: Stmt, folder: &mut T)
1425                                  -> SmallVector<P<Stmt>> {
1426     let span = folder.new_span(span);
1427     match node {
1428         StmtDecl(d, id) => {
1429             let id = folder.new_id(id);
1430             folder.fold_decl(d).into_iter().map(|d| P(Spanned {
1431                 node: StmtDecl(d, id),
1432                 span: span
1433             })).collect()
1434         }
1435         StmtExpr(e, id) => {
1436             let id = folder.new_id(id);
1437             SmallVector::one(P(Spanned {
1438                 node: StmtExpr(folder.fold_expr(e), id),
1439                 span: span
1440             }))
1441         }
1442         StmtSemi(e, id) => {
1443             let id = folder.new_id(id);
1444             SmallVector::one(P(Spanned {
1445                 node: StmtSemi(folder.fold_expr(e), id),
1446                 span: span
1447             }))
1448         }
1449         StmtMac(mac, semi) => SmallVector::one(P(Spanned {
1450             node: StmtMac(mac.map(|m| folder.fold_mac(m)), semi),
1451             span: span
1452         }))
1453     }
1454 }
1455
1456 #[cfg(test)]
1457 mod test {
1458     use std::io;
1459     use ast;
1460     use util::parser_testing::{string_to_crate, matches_codepattern};
1461     use parse::token;
1462     use print::pprust;
1463     use fold;
1464     use super::*;
1465
1466     // this version doesn't care about getting comments or docstrings in.
1467     fn fake_print_crate(s: &mut pprust::State,
1468                         krate: &ast::Crate) -> io::IoResult<()> {
1469         s.print_mod(&krate.module, krate.attrs.as_slice())
1470     }
1471
1472     // change every identifier to "zz"
1473     struct ToZzIdentFolder;
1474
1475     impl Folder for ToZzIdentFolder {
1476         fn fold_ident(&mut self, _: ast::Ident) -> ast::Ident {
1477             token::str_to_ident("zz")
1478         }
1479         fn fold_mac(&mut self, mac: ast::Mac) -> ast::Mac {
1480             fold::noop_fold_mac(mac, self)
1481         }
1482     }
1483
1484     // maybe add to expand.rs...
1485     macro_rules! assert_pred {
1486         ($pred:expr, $predname:expr, $a:expr , $b:expr) => (
1487             {
1488                 let pred_val = $pred;
1489                 let a_val = $a;
1490                 let b_val = $b;
1491                 if !(pred_val(a_val.as_slice(),b_val.as_slice())) {
1492                     panic!("expected args satisfying {}, got {} and {}",
1493                           $predname, a_val, b_val);
1494                 }
1495             }
1496         )
1497     }
1498
1499     // make sure idents get transformed everywhere
1500     #[test] fn ident_transformation () {
1501         let mut zz_fold = ToZzIdentFolder;
1502         let ast = string_to_crate(
1503             "#[a] mod b {fn c (d : e, f : g) {h!(i,j,k);l;m}}".to_string());
1504         let folded_crate = zz_fold.fold_crate(ast);
1505         assert_pred!(
1506             matches_codepattern,
1507             "matches_codepattern",
1508             pprust::to_string(|s| fake_print_crate(s, &folded_crate)),
1509             "#[a]mod zz{fn zz(zz:zz,zz:zz){zz!(zz,zz,zz);zz;zz}}".to_string());
1510     }
1511
1512     // even inside macro defs....
1513     #[test] fn ident_transformation_in_defs () {
1514         let mut zz_fold = ToZzIdentFolder;
1515         let ast = string_to_crate(
1516             "macro_rules! a {(b $c:expr $(d $e:token)f+ => \
1517              (g $(d $d $e)+))} ".to_string());
1518         let folded_crate = zz_fold.fold_crate(ast);
1519         assert_pred!(
1520             matches_codepattern,
1521             "matches_codepattern",
1522             pprust::to_string(|s| fake_print_crate(s, &folded_crate)),
1523             "zz!zz((zz$zz:zz$(zz $zz:zz)zz+=>(zz$(zz$zz$zz)+)));".to_string());
1524     }
1525 }