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")),
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))),
46 generics: LifetimeBounds::empty(),
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)),
53 const_nonmatching: true,
54 combine_substructure: combine_substructure(|a, b, c| {
55 decodable_substructure(a, b, c)
60 trait_def.expand(cx, mitem, item, push)
63 fn decodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
64 substr: &Substructure) -> @Expr {
65 let decoder = substr.nonself_args[0];
66 let recurse = vec!(cx.ident_of("serialize"),
67 cx.ident_of("Decodable"),
68 cx.ident_of("decode"));
69 // throw an underscore in front to suppress unused variable warnings
70 let blkarg = cx.ident_of("_d");
71 let blkdecoder = cx.expr_ident(trait_span, blkarg);
72 let calldecode = cx.expr_call_global(trait_span, recurse, vec!(blkdecoder));
73 let lambdadecode = cx.lambda_expr_1(trait_span, calldecode, blkarg);
75 return match *substr.fields {
76 StaticStruct(_, ref summary) => {
77 let nfields = match *summary {
78 Unnamed(ref fields) => fields.len(),
79 Named(ref fields) => fields.len()
81 let read_struct_field = cx.ident_of("read_struct_field");
83 let result = decode_static_fields(cx,
87 |cx, span, name, field| {
89 cx.expr_method_call(span, blkdecoder, read_struct_field,
90 vec!(cx.expr_str(span, name),
91 cx.expr_uint(span, field),
94 let result = cx.expr_ok(trait_span, result);
95 cx.expr_method_call(trait_span,
97 cx.ident_of("read_struct"),
99 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
100 cx.expr_uint(trait_span, nfields),
101 cx.lambda_expr_1(trait_span, result, blkarg)
104 StaticEnum(_, ref fields) => {
105 let variant = cx.ident_of("i");
107 let mut arms = Vec::new();
108 let mut variants = Vec::new();
109 let rvariant_arg = cx.ident_of("read_enum_variant_arg");
111 for (i, &(name, v_span, ref parts)) in fields.iter().enumerate() {
112 variants.push(cx.expr_str(v_span, token::get_ident(name)));
114 let decoded = decode_static_fields(cx,
118 |cx, span, _, field| {
119 let idx = cx.expr_uint(span, field);
121 cx.expr_method_call(span, blkdecoder, rvariant_arg,
122 vec!(idx, lambdadecode)))
125 arms.push(cx.arm(v_span,
126 vec!(cx.pat_lit(v_span, cx.expr_uint(v_span, i))),
130 arms.push(cx.arm_unreachable(trait_span));
132 let result = cx.expr_ok(trait_span,
133 cx.expr_match(trait_span,
134 cx.expr_ident(trait_span, variant), arms));
135 let lambda = cx.lambda_expr(trait_span, vec!(blkarg, variant), result);
136 let variant_vec = cx.expr_vec(trait_span, variants);
137 let result = cx.expr_method_call(trait_span, blkdecoder,
138 cx.ident_of("read_enum_variant"),
139 vec!(variant_vec, lambda));
140 cx.expr_method_call(trait_span,
142 cx.ident_of("read_enum"),
144 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
145 cx.lambda_expr_1(trait_span, result, blkarg)
148 _ => cx.bug("expected StaticEnum or StaticStruct in deriving(Decodable)")
152 /// Create a decoder for a single enum variant/struct:
153 /// - `outer_pat_ident` is the name of this enum variant/struct
154 /// - `getarg` should retrieve the `uint`-th field with name `@str`.
155 fn decode_static_fields(cx: &mut ExtCtxt,
157 outer_pat_ident: Ident,
158 fields: &StaticFields,
159 getarg: |&mut ExtCtxt, Span, InternedString, uint| -> @Expr)
162 Unnamed(ref fields) => {
163 if fields.is_empty() {
164 cx.expr_ident(trait_span, outer_pat_ident)
166 let fields = fields.iter().enumerate().map(|(i, &span)| {
168 token::intern_and_get_ident(format!("_field{}",
173 cx.expr_call_ident(trait_span, outer_pat_ident, fields)
176 Named(ref fields) => {
177 // use the field's span to get nicer error messages.
178 let fields = fields.iter().enumerate().map(|(i, &(name, span))| {
179 let arg = getarg(cx, span, token::get_ident(name), i);
180 cx.field_imm(span, name, arg)
182 cx.expr_struct_ident(trait_span, outer_pat_ident, fields)