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