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