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: Vec::new(),
  32         path: Path::new_(vec!("serialize", "Decodable"), None,
  33                          vec!(~Literal(Path::new_local("__D")),
  34                               ~Literal(Path::new_local("__E"))), true),
  35         additional_bounds: Vec::new(),
  36         generics: LifetimeBounds {
  37             lifetimes: Vec::new(),
  38             bounds: vec!(("__D", vec!(Path::new_(
  39                             vec!("serialize", "Decoder"), None,
  40                             vec!(~Literal(Path::new_local("__E"))), true))),
  41                          ("__E", vec!()))
  42         },
  43         methods: vec!(
  44             MethodDef {
  45                 name: "decode",
  46                 generics: LifetimeBounds::empty(),
  47                 explicit_self: None,
  48                 args: vec!(Ptr(~Literal(Path::new_local("__D")),
  49                             Borrowed(None, MutMutable))),
  50                 ret_ty: Literal(Path::new_(vec!("std", "result", "Result"), None,
  51                                           vec!(~Self, ~Literal(Path::new_local("__E"))), true)),
  52                 inline: false,
  53                 const_nonmatching: true,
  54                 combine_substructure: decodable_substructure,
  55             })
  56     };
  57
  58     trait_def.expand(cx, mitem, item, push)
  59 }
  60
  61 fn decodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
  62                           substr: &Substructure) -> @Expr {
  63     let decoder = substr.nonself_args[0];
  64     let recurse = vec!(cx.ident_of("serialize"),
  65                     cx.ident_of("Decodable"),
  66                     cx.ident_of("decode"));
  67     // throw an underscore in front to suppress unused variable warnings
  68     let blkarg = cx.ident_of("_d");
  69     let blkdecoder = cx.expr_ident(trait_span, blkarg);
  70     let calldecode = cx.expr_call_global(trait_span, recurse, vec!(blkdecoder));
  71     let lambdadecode = cx.lambda_expr_1(trait_span, calldecode, blkarg);
  72
  73     return match *substr.fields {
  74         StaticStruct(_, ref summary) => {
  75             let nfields = match *summary {
  76                 Unnamed(ref fields) => fields.len(),
  77                 Named(ref fields) => fields.len()
  78             };
  79             let read_struct_field = cx.ident_of("read_struct_field");
  80
  81             let result = decode_static_fields(cx,
  82                                               trait_span,
  83                                               substr.type_ident,
  84                                               summary,
  85                                               |cx, span, name, field| {
  86                 cx.expr_try(span,
  87                     cx.expr_method_call(span, blkdecoder, read_struct_field,
  88                                         vec!(cx.expr_str(span, name),
  89                                           cx.expr_uint(span, field),
  90                                           lambdadecode)))
  91             });
  92             let result = cx.expr_ok(trait_span, result);
  93             cx.expr_method_call(trait_span,
  94                                 decoder,
  95                                 cx.ident_of("read_struct"),
  96                                 vec!(
  97                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
  98                 cx.expr_uint(trait_span, nfields),
  99                 cx.lambda_expr_1(trait_span, result, blkarg)
 100             ))
 101         }
 102         StaticEnum(_, ref fields) => {
 103             let variant = cx.ident_of("i");
 104
 105             let mut arms = Vec::new();
 106             let mut variants = Vec::new();
 107             let rvariant_arg = cx.ident_of("read_enum_variant_arg");
 108
 109             for (i, &(name, v_span, ref parts)) in fields.iter().enumerate() {
 110                 variants.push(cx.expr_str(v_span, token::get_ident(name)));
 111
 112                 let decoded = decode_static_fields(cx,
 113                                                    v_span,
 114                                                    name,
 115                                                    parts,
 116                                                    |cx, span, _, field| {
 117                     let idx = cx.expr_uint(span, field);
 118                     cx.expr_try(span,
 119                         cx.expr_method_call(span, blkdecoder, rvariant_arg,
 120                                             vec!(idx, lambdadecode)))
 121                 });
 122
 123                 arms.push(cx.arm(v_span,
 124                                  vec!(cx.pat_lit(v_span, cx.expr_uint(v_span, i))),
 125                                  decoded));
 126             }
 127
 128             arms.push(cx.arm_unreachable(trait_span));
 129
 130             let result = cx.expr_ok(trait_span,
 131                                     cx.expr_match(trait_span,
 132                                                   cx.expr_ident(trait_span, variant), arms));
 133             let lambda = cx.lambda_expr(trait_span, vec!(blkarg, variant), result);
 134             let variant_vec = cx.expr_vec(trait_span, variants);
 135             let result = cx.expr_method_call(trait_span, blkdecoder,
 136                                              cx.ident_of("read_enum_variant"),
 137                                              vec!(variant_vec, lambda));
 138             cx.expr_method_call(trait_span,
 139                                 decoder,
 140                                 cx.ident_of("read_enum"),
 141                                 vec!(
 142                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 143                 cx.lambda_expr_1(trait_span, result, blkarg)
 144             ))
 145         }
 146         _ => cx.bug("expected StaticEnum or StaticStruct in deriving(Decodable)")
 147     };
 148 }
 149
 150 /// Create a decoder for a single enum variant/struct:
 151 /// - `outer_pat_ident` is the name of this enum variant/struct
 152 /// - `getarg` should retrieve the `uint`-th field with name `@str`.
 153 fn decode_static_fields(cx: &mut ExtCtxt,
 154                         trait_span: Span,
 155                         outer_pat_ident: Ident,
 156                         fields: &StaticFields,
 157                         getarg: |&mut ExtCtxt, Span, InternedString, uint| -> @Expr)
 158                         -> @Expr {
 159     match *fields {
 160         Unnamed(ref fields) => {
 161             if fields.is_empty() {
 162                 cx.expr_ident(trait_span, outer_pat_ident)
 163             } else {
 164                 let fields = fields.iter().enumerate().map(|(i, &span)| {
 165                     getarg(cx, span,
 166                            token::intern_and_get_ident(format!("_field{}",
 167                                                                i)),
 168                            i)
 169                 }).collect();
 170
 171                 cx.expr_call_ident(trait_span, outer_pat_ident, fields)
 172             }
 173         }
 174         Named(ref fields) => {
 175             // use the field's span to get nicer error messages.
 176             let fields = fields.iter().enumerate().map(|(i, &(name, span))| {
 177                 let arg = getarg(cx, span, token::get_ident(name), i);
 178                 cx.field_imm(span, name, arg)
 179             }).collect();
 180             cx.expr_struct_ident(trait_span, outer_pat_ident, fields)
 181         }
 182     }
 183 }