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;
  17 use ast::{MetaItem, Item, Expr, MutMutable, Ident};
  18 use codemap::Span;
  19 use ext::base::ExtCtxt;
  20 use ext::build::AstBuilder;
  21 use ext::deriving::generic::*;
  22 use ext::deriving::generic::ty::*;
  23 use parse::token::InternedString;
  24 use parse::token;
  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!(box Literal(Path::new_local("__D")),
  36                               box Literal(Path::new_local("__E"))), true),
  37         additional_bounds: Vec::new(),
  38         generics: LifetimeBounds {
  39             lifetimes: Vec::new(),
  40             bounds: vec!(("__D", ast::StaticSize, vec!(Path::new_(
  41                             vec!("serialize", "Decoder"), None,
  42                             vec!(box Literal(Path::new_local("__E"))), true))),
  43                          ("__E", ast::StaticSize, vec!()))
  44         },
  45         methods: vec!(
  46             MethodDef {
  47                 name: "decode",
  48                 generics: LifetimeBounds::empty(),
  49                 explicit_self: None,
  50                 args: vec!(Ptr(box Literal(Path::new_local("__D")),
  51                             Borrowed(None, MutMutable))),
  52                 ret_ty: Literal(Path::new_(vec!("std", "result", "Result"), None,
  53                                           vec!(box Self,
  54                                                box Literal(Path::new_local("__E"))), true)),
  55                 attributes: Vec::new(),
  56                 const_nonmatching: true,
  57                 combine_substructure: combine_substructure(|a, b, c| {
  58                     decodable_substructure(a, b, c)
  59                 }),
  60             })
  61     };
  62
  63     trait_def.expand(cx, mitem, item, push)
  64 }
  65
  66 fn decodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
  67                           substr: &Substructure) -> @Expr {
  68     let decoder = substr.nonself_args[0];
  69     let recurse = vec!(cx.ident_of("serialize"),
  70                     cx.ident_of("Decodable"),
  71                     cx.ident_of("decode"));
  72     // throw an underscore in front to suppress unused variable warnings
  73     let blkarg = cx.ident_of("_d");
  74     let blkdecoder = cx.expr_ident(trait_span, blkarg);
  75     let calldecode = cx.expr_call_global(trait_span, recurse, vec!(blkdecoder));
  76     let lambdadecode = cx.lambda_expr_1(trait_span, calldecode, blkarg);
  77
  78     return match *substr.fields {
  79         StaticStruct(_, ref summary) => {
  80             let nfields = match *summary {
  81                 Unnamed(ref fields) => fields.len(),
  82                 Named(ref fields) => fields.len()
  83             };
  84             let read_struct_field = cx.ident_of("read_struct_field");
  85
  86             let result = decode_static_fields(cx,
  87                                               trait_span,
  88                                               substr.type_ident,
  89                                               summary,
  90                                               |cx, span, name, field| {
  91                 cx.expr_try(span,
  92                     cx.expr_method_call(span, blkdecoder, read_struct_field,
  93                                         vec!(cx.expr_str(span, name),
  94                                           cx.expr_uint(span, field),
  95                                           lambdadecode)))
  96             });
  97             let result = cx.expr_ok(trait_span, result);
  98             cx.expr_method_call(trait_span,
  99                                 decoder,
 100                                 cx.ident_of("read_struct"),
 101                                 vec!(
 102                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 103                 cx.expr_uint(trait_span, nfields),
 104                 cx.lambda_expr_1(trait_span, result, blkarg)
 105             ))
 106         }
 107         StaticEnum(_, ref fields) => {
 108             let variant = cx.ident_of("i");
 109
 110             let mut arms = Vec::new();
 111             let mut variants = Vec::new();
 112             let rvariant_arg = cx.ident_of("read_enum_variant_arg");
 113
 114             for (i, &(name, v_span, ref parts)) in fields.iter().enumerate() {
 115                 variants.push(cx.expr_str(v_span, token::get_ident(name)));
 116
 117                 let decoded = decode_static_fields(cx,
 118                                                    v_span,
 119                                                    name,
 120                                                    parts,
 121                                                    |cx, span, _, field| {
 122                     let idx = cx.expr_uint(span, field);
 123                     cx.expr_try(span,
 124                         cx.expr_method_call(span, blkdecoder, rvariant_arg,
 125                                             vec!(idx, lambdadecode)))
 126                 });
 127
 128                 arms.push(cx.arm(v_span,
 129                                  vec!(cx.pat_lit(v_span, cx.expr_uint(v_span, i))),
 130                                  decoded));
 131             }
 132
 133             arms.push(cx.arm_unreachable(trait_span));
 134
 135             let result = cx.expr_ok(trait_span,
 136                                     cx.expr_match(trait_span,
 137                                                   cx.expr_ident(trait_span, variant), arms));
 138             let lambda = cx.lambda_expr(trait_span, vec!(blkarg, variant), result);
 139             let variant_vec = cx.expr_vec(trait_span, variants);
 140             let result = cx.expr_method_call(trait_span, blkdecoder,
 141                                              cx.ident_of("read_enum_variant"),
 142                                              vec!(variant_vec, lambda));
 143             cx.expr_method_call(trait_span,
 144                                 decoder,
 145                                 cx.ident_of("read_enum"),
 146                                 vec!(
 147                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 148                 cx.lambda_expr_1(trait_span, result, blkarg)
 149             ))
 150         }
 151         _ => cx.bug("expected StaticEnum or StaticStruct in deriving(Decodable)")
 152     };
 153 }
 154
 155 /// Create a decoder for a single enum variant/struct:
 156 /// - `outer_pat_ident` is the name of this enum variant/struct
 157 /// - `getarg` should retrieve the `uint`-th field with name `@str`.
 158 fn decode_static_fields(cx: &mut ExtCtxt,
 159                         trait_span: Span,
 160                         outer_pat_ident: Ident,
 161                         fields: &StaticFields,
 162                         getarg: |&mut ExtCtxt, Span, InternedString, uint| -> @Expr)
 163                         -> @Expr {
 164     match *fields {
 165         Unnamed(ref fields) => {
 166             if fields.is_empty() {
 167                 cx.expr_ident(trait_span, outer_pat_ident)
 168             } else {
 169                 let fields = fields.iter().enumerate().map(|(i, &span)| {
 170                     getarg(cx, span,
 171                            token::intern_and_get_ident(format!("_field{}",
 172                                                                i).as_slice()),
 173                            i)
 174                 }).collect();
 175
 176                 cx.expr_call_ident(trait_span, outer_pat_ident, fields)
 177             }
 178         }
 179         Named(ref fields) => {
 180             // use the field's span to get nicer error messages.
 181             let fields = fields.iter().enumerate().map(|(i, &(name, span))| {
 182                 let arg = getarg(cx, span, token::get_ident(name), i);
 183                 cx.field_imm(span, name, arg)
 184             }).collect();
 185             cx.expr_struct_ident(trait_span, outer_pat_ident, fields)
 186         }
 187     }
 188 }