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.
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.
12 The compiler code necessary for #[deriving(Decodable)]. See
13 encodable.rs for more.
16 use ast::{MetaItem, Item, Expr, MutMutable, Ident};
18 use ext::base::ExtCtxt;
19 use ext::build::AstBuilder;
20 use ext::deriving::generic::*;
21 use parse::token::InternedString;
24 pub fn expand_deriving_decodable(cx: &mut ExtCtxt,
29 let trait_def = TraitDef {
32 path: Path::new_(~["serialize", "Decodable"], None,
33 ~[~Literal(Path::new_local("__D"))], true),
34 additional_bounds: ~[],
35 generics: LifetimeBounds {
37 bounds: ~[("__D", ~[Path::new(~["serialize", "Decoder"])])],
42 generics: LifetimeBounds::empty(),
44 args: ~[Ptr(~Literal(Path::new_local("__D")),
45 Borrowed(None, MutMutable))],
48 const_nonmatching: true,
49 combine_substructure: decodable_substructure,
54 trait_def.expand(cx, mitem, item, push)
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);
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()
75 let read_struct_field = cx.ident_of("read_struct_field");
77 let result = decode_static_fields(cx,
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),
87 cx.expr_method_call(trait_span,
89 cx.ident_of("read_struct"),
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)
96 StaticEnum(_, ref fields) => {
97 let variant = cx.ident_of("i");
100 let mut variants = ~[];
101 let rvariant_arg = cx.ident_of("read_enum_variant_arg");
103 for (i, &(name, v_span, ref parts)) in fields.iter().enumerate() {
104 variants.push(cx.expr_str(v_span, token::get_ident(name)));
106 let decoded = decode_static_fields(cx,
110 |cx, span, _, field| {
111 let idx = cx.expr_uint(span, field);
112 cx.expr_method_call(span, blkdecoder, rvariant_arg,
113 ~[idx, lambdadecode])
116 arms.push(cx.arm(v_span,
117 ~[cx.pat_lit(v_span, cx.expr_uint(v_span, i))],
121 arms.push(cx.arm_unreachable(trait_span));
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,
131 cx.ident_of("read_enum"),
133 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
134 cx.lambda_expr_1(trait_span, result, blkarg)
137 _ => cx.bug("expected StaticEnum or StaticStruct in deriving(Decodable)")
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,
146 outer_pat_ident: Ident,
147 fields: &StaticFields,
148 getarg: |&mut ExtCtxt, Span, InternedString, uint| -> @Expr)
151 Unnamed(ref fields) => {
152 if fields.is_empty() {
153 cx.expr_ident(trait_span, outer_pat_ident)
155 let fields = fields.iter().enumerate().map(|(i, &span)| {
157 token::intern_and_get_ident(format!("_field{}",
162 cx.expr_call_ident(trait_span, outer_pat_ident, fields)
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)
171 cx.expr_struct_ident(trait_span, outer_pat_ident, fields)