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