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;
26 pub fn expand_deriving_decodable(cx: &mut ExtCtxt,
31 let trait_def = TraitDef {
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"))))),
44 generics: LifetimeBounds::empty(),
46 args: vec!(Ptr(~Literal(Path::new_local("__D")),
47 Borrowed(None, MutMutable))),
50 const_nonmatching: true,
51 combine_substructure: decodable_substructure,
55 trait_def.expand(cx, mitem, item, push)
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);
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()
76 let read_struct_field = cx.ident_of("read_struct_field");
78 let result = decode_static_fields(cx,
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),
88 cx.expr_method_call(trait_span,
90 cx.ident_of("read_struct"),
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)
97 StaticEnum(_, ref fields) => {
98 let variant = cx.ident_of("i");
100 let mut arms = Vec::new();
101 let mut variants = Vec::new();
102 let rvariant_arg = cx.ident_of("read_enum_variant_arg");
104 for (i, &(name, v_span, ref parts)) in fields.iter().enumerate() {
105 variants.push(cx.expr_str(v_span, token::get_ident(name)));
107 let decoded = decode_static_fields(cx,
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))
117 arms.push(cx.arm(v_span,
118 vec!(cx.pat_lit(v_span, cx.expr_uint(v_span, i))),
122 arms.push(cx.arm_unreachable(trait_span));
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,
132 cx.ident_of("read_enum"),
134 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
135 cx.lambda_expr_1(trait_span, result, blkarg)
138 _ => cx.bug("expected StaticEnum or StaticStruct in deriving(Decodable)")
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,
147 outer_pat_ident: Ident,
148 fields: &StaticFields,
149 getarg: |&mut ExtCtxt, Span, InternedString, uint| -> @Expr)
152 Unnamed(ref fields) => {
153 if fields.is_empty() {
154 cx.expr_ident(trait_span, outer_pat_ident)
156 let fields = fields.iter().enumerate().map(|(i, &span)| {
158 token::intern_and_get_ident(format!("_field{}",
163 cx.expr_call_ident(trait_span, outer_pat_ident, fields)
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)
172 cx.expr_struct_ident(trait_span, outer_pat_ident, fields)