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