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 use std::vec::Vec;
  25
  26 pub fn expand_deriving_decodable(cx: &mut ExtCtxt,
  27                                  span: Span,
  28                                  mitem: @MetaItem,
  29                                  item: @Item,
  30                                  push: |@Item|) {
  31     let trait_def = TraitDef {
  32         span: span,
  33         attributes: Vec::new(),
  34         path: Path::new_(vec!("serialize", "Decodable"), None,
  35                          vec!(~Literal(Path::new_local("__D"))), true),
  36         additional_bounds: Vec::new(),
  37         generics: LifetimeBounds {
  38             lifetimes: Vec::new(),
  39             bounds: vec!(("__D", vec!(Path::new(vec!("serialize", "Decoder"))))),
  40         },
  41         methods: vec!(
  42             MethodDef {
  43                 name: "decode",
  44                 generics: LifetimeBounds::empty(),
  45                 explicit_self: None,
  46                 args: vec!(Ptr(~Literal(Path::new_local("__D")),
  47                             Borrowed(None, MutMutable))),
  48                 ret_ty: Self,
  49                 inline: false,
  50                 const_nonmatching: true,
  51                 combine_substructure: decodable_substructure,
  52             })
  53     };
  54
  55     trait_def.expand(cx, mitem, item, push)
  56 }
  57
  58 fn decodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
  59                           substr: &Substructure) -> @Expr {
  60     let decoder = substr.nonself_args[0];
  61     let recurse = vec!(cx.ident_of("serialize"),
  62                     cx.ident_of("Decodable"),
  63                     cx.ident_of("decode"));
  64     // throw an underscore in front to suppress unused variable warnings
  65     let blkarg = cx.ident_of("_d");
  66     let blkdecoder = cx.expr_ident(trait_span, blkarg);
  67     let calldecode = cx.expr_call_global(trait_span, recurse, vec!(blkdecoder));
  68     let lambdadecode = cx.lambda_expr_1(trait_span, calldecode, blkarg);
  69
  70     return match *substr.fields {
  71         StaticStruct(_, ref summary) => {
  72             let nfields = match *summary {
  73                 Unnamed(ref fields) => fields.len(),
  74                 Named(ref fields) => fields.len()
  75             };
  76             let read_struct_field = cx.ident_of("read_struct_field");
  77
  78             let result = decode_static_fields(cx,
  79                                               trait_span,
  80                                               substr.type_ident,
  81                                               summary,
  82                                               |cx, span, name, field| {
  83                 cx.expr_method_call(span, blkdecoder, read_struct_field,
  84                                     vec!(cx.expr_str(span, name),
  85                                       cx.expr_uint(span, field),
  86                                       lambdadecode))
  87             });
  88             cx.expr_method_call(trait_span,
  89                                 decoder,
  90                                 cx.ident_of("read_struct"),
  91                                 vec!(
  92                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
  93                 cx.expr_uint(trait_span, nfields),
  94                 cx.lambda_expr_1(trait_span, result, blkarg)
  95             ))
  96         }
  97         StaticEnum(_, ref fields) => {
  98             let variant = cx.ident_of("i");
  99
 100             let mut arms = Vec::new();
 101             let mut variants = Vec::new();
 102             let rvariant_arg = cx.ident_of("read_enum_variant_arg");
 103
 104             for (i, &(name, v_span, ref parts)) in fields.iter().enumerate() {
 105                 variants.push(cx.expr_str(v_span, token::get_ident(name)));
 106
 107                 let decoded = decode_static_fields(cx,
 108                                                    v_span,
 109                                                    name,
 110                                                    parts,
 111                                                    |cx, span, _, field| {
 112                     let idx = cx.expr_uint(span, field);
 113                     cx.expr_method_call(span, blkdecoder, rvariant_arg,
 114                                         vec!(idx, lambdadecode))
 115                 });
 116
 117                 arms.push(cx.arm(v_span,
 118                                  vec!(cx.pat_lit(v_span, cx.expr_uint(v_span, i))),
 119                                  decoded));
 120             }
 121
 122             arms.push(cx.arm_unreachable(trait_span));
 123
 124             let result = cx.expr_match(trait_span, cx.expr_ident(trait_span, variant), arms);
 125             let lambda = cx.lambda_expr(trait_span, vec!(blkarg, variant), result);
 126             let variant_vec = cx.expr_vec(trait_span, variants);
 127             let result = cx.expr_method_call(trait_span, blkdecoder,
 128                                              cx.ident_of("read_enum_variant"),
 129                                              vec!(variant_vec, lambda));
 130             cx.expr_method_call(trait_span,
 131                                 decoder,
 132                                 cx.ident_of("read_enum"),
 133                                 vec!(
 134                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 135                 cx.lambda_expr_1(trait_span, result, blkarg)
 136             ))
 137         }
 138         _ => cx.bug("expected StaticEnum or StaticStruct in deriving(Decodable)")
 139     };
 140 }
 141
 142 /// Create a decoder for a single enum variant/struct:
 143 /// - `outer_pat_ident` is the name of this enum variant/struct
 144 /// - `getarg` should retrieve the `uint`-th field with name `@str`.
 145 fn decode_static_fields(cx: &mut ExtCtxt,
 146                         trait_span: Span,
 147                         outer_pat_ident: Ident,
 148                         fields: &StaticFields,
 149                         getarg: |&mut ExtCtxt, Span, InternedString, uint| -> @Expr)
 150                         -> @Expr {
 151     match *fields {
 152         Unnamed(ref fields) => {
 153             if fields.is_empty() {
 154                 cx.expr_ident(trait_span, outer_pat_ident)
 155             } else {
 156                 let fields = fields.iter().enumerate().map(|(i, &span)| {
 157                     getarg(cx, span,
 158                            token::intern_and_get_ident(format!("_field{}",
 159                                                                i)),
 160                            i)
 161                 }).collect();
 162
 163                 cx.expr_call_ident(trait_span, outer_pat_ident, fields)
 164             }
 165         }
 166         Named(ref fields) => {
 167             // use the field's span to get nicer error messages.
 168             let fields = fields.iter().enumerate().map(|(i, &(name, span))| {
 169                 let arg = getarg(cx, span, token::get_ident(name), i);
 170                 cx.field_imm(span, name, arg)
 171             }).collect();
 172             cx.expr_struct_ident(trait_span, outer_pat_ident, fields)
 173         }
 174     }
 175 }