src/libsyntax/ext/deriving/decodable.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 The compiler code necessary for #[deriving(Decodable)]. See
  13 encodable.rs for more.
  14 */
  15
  16 use ast::{MetaItem, Item, Expr, MutMutable, Ident};
  17 use codemap::Span;
  18 use ext::base::ExtCtxt;
  19 use ext::build::AstBuilder;
  20 use ext::deriving::generic::*;
  21 use parse::token::InternedString;
  22 use parse::token;
  23
  24 pub fn expand_deriving_decodable(cx: &mut ExtCtxt,
  25                                  span: Span,
  26                                  mitem: @MetaItem,
  27                                  item: @Item,
  28                                  push: |@Item|) {
  29     let trait_def = TraitDef {
  30         span: span,
  31         attributes: ~[],
  32         path: Path::new_(~["serialize", "Decodable"], None,
  33                          ~[~Literal(Path::new_local("__D"))], true),
  34         additional_bounds: ~[],
  35         generics: LifetimeBounds {
  36             lifetimes: ~[],
  37             bounds: ~[("__D", ~[Path::new(~["serialize", "Decoder"])])],
  38         },
  39         methods: ~[
  40             MethodDef {
  41                 name: "decode",
  42                 generics: LifetimeBounds::empty(),
  43                 explicit_self: None,
  44                 args: ~[Ptr(~Literal(Path::new_local("__D")),
  45                             Borrowed(None, MutMutable))],
  46                 ret_ty: Self,
  47                 inline: false,
  48                 const_nonmatching: true,
  49                 combine_substructure: decodable_substructure,
  50             },
  51         ]
  52     };
  53
  54     trait_def.expand(cx, mitem, item, push)
  55 }
  56
  57 fn decodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
  58                           substr: &Substructure) -> @Expr {
  59     let decoder = substr.nonself_args[0];
  60     let recurse = ~[cx.ident_of("serialize"),
  61                     cx.ident_of("Decodable"),
  62                     cx.ident_of("decode")];
  63     // throw an underscore in front to suppress unused variable warnings
  64     let blkarg = cx.ident_of("_d");
  65     let blkdecoder = cx.expr_ident(trait_span, blkarg);
  66     let calldecode = cx.expr_call_global(trait_span, recurse, ~[blkdecoder]);
  67     let lambdadecode = cx.lambda_expr_1(trait_span, calldecode, blkarg);
  68
  69     return match *substr.fields {
  70         StaticStruct(_, ref summary) => {
  71             let nfields = match *summary {
  72                 Unnamed(ref fields) => fields.len(),
  73                 Named(ref fields) => fields.len()
  74             };
  75             let read_struct_field = cx.ident_of("read_struct_field");
  76
  77             let result = decode_static_fields(cx,
  78                                               trait_span,
  79                                               substr.type_ident,
  80                                               summary,
  81                                               |cx, span, name, field| {
  82                 cx.expr_method_call(span, blkdecoder, read_struct_field,
  83                                     ~[cx.expr_str(span, name),
  84                                       cx.expr_uint(span, field),
  85                                       lambdadecode])
  86             });
  87             cx.expr_method_call(trait_span,
  88                                 decoder,
  89                                 cx.ident_of("read_struct"),
  90                                 ~[
  91                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
  92                 cx.expr_uint(trait_span, nfields),
  93                 cx.lambda_expr_1(trait_span, result, blkarg)
  94             ])
  95         }
  96         StaticEnum(_, ref fields) => {
  97             let variant = cx.ident_of("i");
  98
  99             let mut arms = ~[];
 100             let mut variants = ~[];
 101             let rvariant_arg = cx.ident_of("read_enum_variant_arg");
 102
 103             for (i, &(name, v_span, ref parts)) in fields.iter().enumerate() {
 104                 variants.push(cx.expr_str(v_span, token::get_ident(name)));
 105
 106                 let decoded = decode_static_fields(cx,
 107                                                    v_span,
 108                                                    name,
 109                                                    parts,
 110                                                    |cx, span, _, field| {
 111                     let idx = cx.expr_uint(span, field);
 112                     cx.expr_method_call(span, blkdecoder, rvariant_arg,
 113                                         ~[idx, lambdadecode])
 114                 });
 115
 116                 arms.push(cx.arm(v_span,
 117                                  ~[cx.pat_lit(v_span, cx.expr_uint(v_span, i))],
 118                                  decoded));
 119             }
 120
 121             arms.push(cx.arm_unreachable(trait_span));
 122
 123             let result = cx.expr_match(trait_span, cx.expr_ident(trait_span, variant), arms);
 124             let lambda = cx.lambda_expr(trait_span, ~[blkarg, variant], result);
 125             let variant_vec = cx.expr_vec(trait_span, variants);
 126             let result = cx.expr_method_call(trait_span, blkdecoder,
 127                                              cx.ident_of("read_enum_variant"),
 128                                              ~[variant_vec, lambda]);
 129             cx.expr_method_call(trait_span,
 130                                 decoder,
 131                                 cx.ident_of("read_enum"),
 132                                 ~[
 133                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 134                 cx.lambda_expr_1(trait_span, result, blkarg)
 135             ])
 136         }
 137         _ => cx.bug("expected StaticEnum or StaticStruct in deriving(Decodable)")
 138     };
 139 }
 140
 141 /// Create a decoder for a single enum variant/struct:
 142 /// - `outer_pat_ident` is the name of this enum variant/struct
 143 /// - `getarg` should retrieve the `uint`-th field with name `@str`.
 144 fn decode_static_fields(cx: &mut ExtCtxt,
 145                         trait_span: Span,
 146                         outer_pat_ident: Ident,
 147                         fields: &StaticFields,
 148                         getarg: |&mut ExtCtxt, Span, InternedString, uint| -> @Expr)
 149                         -> @Expr {
 150     match *fields {
 151         Unnamed(ref fields) => {
 152             if fields.is_empty() {
 153                 cx.expr_ident(trait_span, outer_pat_ident)
 154             } else {
 155                 let fields = fields.iter().enumerate().map(|(i, &span)| {
 156                     getarg(cx, span,
 157                            token::intern_and_get_ident(format!("_field{}",
 158                                                                i)),
 159                            i)
 160                 }).collect();
 161
 162                 cx.expr_call_ident(trait_span, outer_pat_ident, fields)
 163             }
 164         }
 165         Named(ref fields) => {
 166             // use the field's span to get nicer error messages.
 167             let fields = fields.iter().enumerate().map(|(i, &(name, span))| {
 168                 let arg = getarg(cx, span, token::get_ident(name), i);
 169                 cx.field_imm(span, name, arg)
 170             }).collect();
 171             cx.expr_struct_ident(trait_span, outer_pat_ident, fields)
 172         }
 173     }
 174 }