src/libsyntax/ext/deriving/encodable.rs

   1 // Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 /*!
  12
  13 The compiler code necessary to implement the #[deriving(Encodable)]
  14 (and Decodable, in decodable.rs) extension.  The idea here is that
  15 type-defining items may be tagged with #[deriving(Encodable,
  16 Decodable)].
  17
  18 For example, a type like:
  19
  20 ```ignore
  21     #[deriving(Encodable, Decodable)]
  22     struct Node {id: uint}
  23 ```
  24
  25 would generate two implementations like:
  26
  27 impl<S:serialize::Encoder> Encodable<S> for Node {
  28     fn encode(&self, s: &S) {
  29         s.emit_struct("Node", 1, || {
  30             s.emit_field("id", 0, || s.emit_uint(self.id))
  31         })
  32     }
  33 }
  34
  35 impl<D:Decoder> Decodable for node_id {
  36     fn decode(d: &D) -> Node {
  37         d.read_struct("Node", 1, || {
  38             Node {
  39                 id: d.read_field(~"x", 0, || decode(d))
  40             }
  41         })
  42     }
  43 }
  44
  45 Other interesting scenarios are whe the item has type parameters or
  46 references other non-built-in types.  A type definition like:
  47
  48 ```ignore
  49     #[deriving(Encodable, Decodable)]
  50     struct spanned<T> {node: T, span: Span}
  51 ```
  52
  53 would yield functions like:
  54
  55 ```ignore
  56     impl<
  57         S: Encoder,
  58         T: Encodable<S>
  59     > spanned<T>: Encodable<S> {
  60         fn encode<S:Encoder>(s: &S) {
  61             s.emit_rec(|| {
  62                 s.emit_field("node", 0, || self.node.encode(s));
  63                 s.emit_field("span", 1, || self.span.encode(s));
  64             })
  65         }
  66     }
  67
  68     impl<
  69         D: Decoder,
  70         T: Decodable<D>
  71     > spanned<T>: Decodable<D> {
  72         fn decode(d: &D) -> spanned<T> {
  73             d.read_rec(|| {
  74                 {
  75                     node: d.read_field(~"node", 0, || decode(d)),
  76                     span: d.read_field(~"span", 1, || decode(d)),
  77                 }
  78             })
  79         }
  80     }
  81 ```
  82 */
  83
  84 use ast::{MetaItem, Item, Expr, MutMutable};
  85 use codemap::Span;
  86 use ext::base::ExtCtxt;
  87 use ext::build::AstBuilder;
  88 use ext::deriving::generic::*;
  89 use parse::token;
  90
  91 pub fn expand_deriving_encodable(cx: &mut ExtCtxt,
  92                                  span: Span,
  93                                  mitem: @MetaItem,
  94                                  item: @Item,
  95                                  push: |@Item|) {
  96     let trait_def = TraitDef {
  97         span: span,
  98         path: Path::new_(~["serialize", "Encodable"], None,
  99                          ~[~Literal(Path::new_local("__E"))], true),
 100         additional_bounds: ~[],
 101         generics: LifetimeBounds {
 102             lifetimes: ~[],
 103             bounds: ~[("__E", ~[Path::new(~["serialize", "Encoder"])])],
 104         },
 105         methods: ~[
 106             MethodDef {
 107                 name: "encode",
 108                 generics: LifetimeBounds::empty(),
 109                 explicit_self: borrowed_explicit_self(),
 110                 args: ~[Ptr(~Literal(Path::new_local("__E")),
 111                             Borrowed(None, MutMutable))],
 112                 ret_ty: nil_ty(),
 113                 inline: false,
 114                 const_nonmatching: true,
 115                 combine_substructure: encodable_substructure,
 116             },
 117         ]
 118     };
 119
 120     trait_def.expand(cx, mitem, item, push)
 121 }
 122
 123 fn encodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
 124                           substr: &Substructure) -> @Expr {
 125     let encoder = substr.nonself_args[0];
 126     // throw an underscore in front to suppress unused variable warnings
 127     let blkarg = cx.ident_of("_e");
 128     let blkencoder = cx.expr_ident(trait_span, blkarg);
 129     let encode = cx.ident_of("encode");
 130
 131     return match *substr.fields {
 132         Struct(ref fields) => {
 133             let emit_struct_field = cx.ident_of("emit_struct_field");
 134             let mut stmts = ~[];
 135             for (i, &FieldInfo {
 136                     name,
 137                     self_,
 138                     span,
 139                     ..
 140                 }) in fields.iter().enumerate() {
 141                 let name = match name {
 142                     Some(id) => token::get_ident(id),
 143                     None => {
 144                         token::intern_and_get_ident(format!("_field{}", i))
 145                     }
 146                 };
 147                 let enc = cx.expr_method_call(span, self_, encode, ~[blkencoder]);
 148                 let lambda = cx.lambda_expr_1(span, enc, blkarg);
 149                 let call = cx.expr_method_call(span, blkencoder,
 150                                                emit_struct_field,
 151                                                ~[cx.expr_str(span, name),
 152                                                  cx.expr_uint(span, i),
 153                                                  lambda]);
 154                 stmts.push(cx.stmt_expr(call));
 155             }
 156
 157             let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
 158             cx.expr_method_call(trait_span,
 159                                 encoder,
 160                                 cx.ident_of("emit_struct"),
 161                                 ~[
 162                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 163                 cx.expr_uint(trait_span, fields.len()),
 164                 blk
 165             ])
 166         }
 167
 168         EnumMatching(idx, variant, ref fields) => {
 169             // We're not generating an AST that the borrow checker is expecting,
 170             // so we need to generate a unique local variable to take the
 171             // mutable loan out on, otherwise we get conflicts which don't
 172             // actually exist.
 173             let me = cx.stmt_let(trait_span, false, blkarg, encoder);
 174             let encoder = cx.expr_ident(trait_span, blkarg);
 175             let emit_variant_arg = cx.ident_of("emit_enum_variant_arg");
 176             let mut stmts = ~[];
 177             for (i, &FieldInfo { self_, span, .. }) in fields.iter().enumerate() {
 178                 let enc = cx.expr_method_call(span, self_, encode, ~[blkencoder]);
 179                 let lambda = cx.lambda_expr_1(span, enc, blkarg);
 180                 let call = cx.expr_method_call(span, blkencoder,
 181                                                emit_variant_arg,
 182                                                ~[cx.expr_uint(span, i),
 183                                                  lambda]);
 184                 stmts.push(cx.stmt_expr(call));
 185             }
 186
 187             let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
 188             let name = cx.expr_str(trait_span, token::get_ident(variant.node.name));
 189             let call = cx.expr_method_call(trait_span, blkencoder,
 190                                            cx.ident_of("emit_enum_variant"),
 191                                            ~[name,
 192                                              cx.expr_uint(trait_span, idx),
 193                                              cx.expr_uint(trait_span, fields.len()),
 194                                              blk]);
 195             let blk = cx.lambda_expr_1(trait_span, call, blkarg);
 196             let ret = cx.expr_method_call(trait_span,
 197                                           encoder,
 198                                           cx.ident_of("emit_enum"),
 199                                           ~[
 200                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 201                 blk
 202             ]);
 203             cx.expr_block(cx.block(trait_span, ~[me], Some(ret)))
 204         }
 205
 206         _ => cx.bug("expected Struct or EnumMatching in deriving(Encodable)")
 207     };
 208 }