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 {
31 attributes: Vec::new(),
32 path: Path::new_(vec!("serialize", "Decodable"), None,
33 vec!(~Literal(Path::new_local("__D"))), true),
34 additional_bounds: Vec::new(),
35 generics: LifetimeBounds {
36 lifetimes: Vec::new(),
37 bounds: vec!(("__D", vec!(Path::new(vec!("serialize", "Decoder"))))),
42 generics: LifetimeBounds::empty(),
44 args: vec!(Ptr(~Literal(Path::new_local("__D")),
45 Borrowed(None, MutMutable))),
48 const_nonmatching: true,
49 combine_substructure: decodable_substructure,
53 trait_def.expand(cx, mitem, item, push)
56 fn decodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
57 substr: &Substructure) -> @Expr {
58 let decoder = substr.nonself_args[0];
59 let recurse = vec!(cx.ident_of("serialize"),
60 cx.ident_of("Decodable"),
61 cx.ident_of("decode"));
62 // throw an underscore in front to suppress unused variable warnings
63 let blkarg = cx.ident_of("_d");
64 let blkdecoder = cx.expr_ident(trait_span, blkarg);
65 let calldecode = cx.expr_call_global(trait_span, recurse, vec!(blkdecoder));
66 let lambdadecode = cx.lambda_expr_1(trait_span, calldecode, blkarg);
68 return match *substr.fields {
69 StaticStruct(_, ref summary) => {
70 let nfields = match *summary {
71 Unnamed(ref fields) => fields.len(),
72 Named(ref fields) => fields.len()
74 let read_struct_field = cx.ident_of("read_struct_field");
76 let result = decode_static_fields(cx,
80 |cx, span, name, field| {
81 cx.expr_method_call(span, blkdecoder, read_struct_field,
82 vec!(cx.expr_str(span, name),
83 cx.expr_uint(span, field),
86 cx.expr_method_call(trait_span,
88 cx.ident_of("read_struct"),
90 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
91 cx.expr_uint(trait_span, nfields),
92 cx.lambda_expr_1(trait_span, result, blkarg)
95 StaticEnum(_, ref fields) => {
96 let variant = cx.ident_of("i");
98 let mut arms = Vec::new();
99 let mut variants = Vec::new();
100 let rvariant_arg = cx.ident_of("read_enum_variant_arg");
102 for (i, &(name, v_span, ref parts)) in fields.iter().enumerate() {
103 variants.push(cx.expr_str(v_span, token::get_ident(name)));
105 let decoded = decode_static_fields(cx,
109 |cx, span, _, field| {
110 let idx = cx.expr_uint(span, field);
111 cx.expr_method_call(span, blkdecoder, rvariant_arg,
112 vec!(idx, lambdadecode))
115 arms.push(cx.arm(v_span,
116 vec!(cx.pat_lit(v_span, cx.expr_uint(v_span, i))),
120 arms.push(cx.arm_unreachable(trait_span));
122 let result = cx.expr_match(trait_span, cx.expr_ident(trait_span, variant), arms);
123 let lambda = cx.lambda_expr(trait_span, vec!(blkarg, variant), result);
124 let variant_vec = cx.expr_vec(trait_span, variants);
125 let result = cx.expr_method_call(trait_span, blkdecoder,
126 cx.ident_of("read_enum_variant"),
127 vec!(variant_vec, lambda));
128 cx.expr_method_call(trait_span,
130 cx.ident_of("read_enum"),
132 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
133 cx.lambda_expr_1(trait_span, result, blkarg)
136 _ => cx.bug("expected StaticEnum or StaticStruct in deriving(Decodable)")
140 /// Create a decoder for a single enum variant/struct:
141 /// - `outer_pat_ident` is the name of this enum variant/struct
142 /// - `getarg` should retrieve the `uint`-th field with name `@str`.
143 fn decode_static_fields(cx: &mut ExtCtxt,
145 outer_pat_ident: Ident,
146 fields: &StaticFields,
147 getarg: |&mut ExtCtxt, Span, InternedString, uint| -> @Expr)
150 Unnamed(ref fields) => {
151 if fields.is_empty() {
152 cx.expr_ident(trait_span, outer_pat_ident)
154 let fields = fields.iter().enumerate().map(|(i, &span)| {
156 token::intern_and_get_ident(format!("_field{}",
161 cx.expr_call_ident(trait_span, outer_pat_ident, fields)
164 Named(ref fields) => {
165 // use the field's span to get nicer error messages.
166 let fields = fields.iter().enumerate().map(|(i, &(name, span))| {
167 let arg = getarg(cx, span, token::get_ident(name), i);
168 cx.field_imm(span, name, arg)
170 cx.expr_struct_ident(trait_span, outer_pat_ident, fields)