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
13 The compiler code necessary to implement the `#[deriving(Encodable)]`
14 (and `Decodable`, in decodable.rs) extension. The idea here is that
15 type-defining items may be tagged with `#[deriving(Encodable, Decodable)]`.
16
17 For example, a type like:
18
19 ```ignore
20 #[deriving(Encodable, Decodable)]
21 struct Node { id: uint }
22 ```
23
24 would generate two implementations like:
25
26 ```ignore
27 impl<S:serialize::Encoder> Encodable<S> for Node {
28 fn encode(&self, s: &S) {
29 s.emit_struct("Node", 1, || {
30 s.emit_field("id", 0, || s.emit_uint(self.id))
31 })
32 }
33 }
34
35 impl<D:Decoder> Decodable for node_id {
36 fn decode(d: &D) -> Node {
37 d.read_struct("Node", 1, || {
38 Node {
39 id: d.read_field("x".to_owned(), 0, || decode(d))
40 }
41 })
42 }
43 }
44 ```
45
46 Other interesting scenarios are whe the item has type parameters or
47 references other non-built-in types. A type definition like:
48
49 ```ignore
50 #[deriving(Encodable, Decodable)]
51 struct spanned<T> { node: T, span: Span }
52 ```
53
54 would yield functions like:
55
56 ```ignore
57 impl<
58 S: Encoder,
59 T: Encodable<S>
60 > spanned<T>: Encodable<S> {
61 fn encode<S:Encoder>(s: &S) {
62 s.emit_rec(|| {
63 s.emit_field("node", 0, || self.node.encode(s));
64 s.emit_field("span", 1, || self.span.encode(s));
65 })
66 }
67 }
68
69 impl<
70 D: Decoder,
71 T: Decodable<D>
72 > spanned<T>: Decodable<D> {
73 fn decode(d: &D) -> spanned<T> {
74 d.read_rec(|| {
75 {
76 node: d.read_field("node".to_owned(), 0, || decode(d)),
77 span: d.read_field("span".to_owned(), 1, || decode(d)),
78 }
79 })
80 }
81 }
82 ```
83 */
84
85 use ast;
86 use ast::{MetaItem, Item, Expr, ExprRet, MutMutable, LitNil};
87 use codemap::Span;
88 use ext::base::ExtCtxt;
89 use ext::build::AstBuilder;
90 use ext::deriving::generic::*;
91 use parse::token;
92
93 pub fn expand_deriving_encodable(cx: &mut ExtCtxt,
94 span: Span,
95 mitem: @MetaItem,
96 item: @Item,
97 push: |@Item|) {
98 let trait_def = TraitDef {
99 span: span,
100 attributes: Vec::new(),
101 path: Path::new_(vec!("serialize", "Encodable"), None,
102 vec!(box Literal(Path::new_local("__S")),
103 box Literal(Path::new_local("__E"))), true),
104 additional_bounds: Vec::new(),
105 generics: LifetimeBounds {
106 lifetimes: Vec::new(),
107 bounds: vec!(("__S", ast::StaticSize, vec!(Path::new_(
108 vec!("serialize", "Encoder"), None,
109 vec!(box Literal(Path::new_local("__E"))), true))),
110 ("__E", ast::StaticSize, vec!()))
111 },
112 methods: vec!(
113 MethodDef {
114 name: "encode",
115 generics: LifetimeBounds::empty(),
116 explicit_self: borrowed_explicit_self(),
117 args: vec!(Ptr(box Literal(Path::new_local("__S")),
118 Borrowed(None, MutMutable))),
119 ret_ty: Literal(Path::new_(vec!("std", "result", "Result"),
120 None,
121 vec!(box Tuple(Vec::new()),
122 box Literal(Path::new_local("__E"))),
123 true)),
124 attributes: Vec::new(),
125 const_nonmatching: true,
126 combine_substructure: combine_substructure(|a, b, c| {
127 encodable_substructure(a, b, c)
128 }),
129 })
130 };
131
132 trait_def.expand(cx, mitem, item, push)
133 }
134
135 fn encodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
136 substr: &Substructure) -> @Expr {
137 let encoder = substr.nonself_args[0];
138 // throw an underscore in front to suppress unused variable warnings
139 let blkarg = cx.ident_of("_e");
140 let blkencoder = cx.expr_ident(trait_span, blkarg);
141 let encode = cx.ident_of("encode");
142
143 return match *substr.fields {
144 Struct(ref fields) => {
145 let emit_struct_field = cx.ident_of("emit_struct_field");
146 let mut stmts = Vec::new();
147 let last = fields.len() - 1;
148 for (i, &FieldInfo {
149 name,
150 self_,
151 span,
152 ..
153 }) in fields.iter().enumerate() {
154 let name = match name {
155 Some(id) => token::get_ident(id),
156 None => {
157 token::intern_and_get_ident(format!("_field{}", i))
158 }
159 };
160 let enc = cx.expr_method_call(span, self_, encode, vec!(blkencoder));
161 let lambda = cx.lambda_expr_1(span, enc, blkarg);
162 let call = cx.expr_method_call(span, blkencoder,
163 emit_struct_field,
164 vec!(cx.expr_str(span, name),
165 cx.expr_uint(span, i),
166 lambda));
167
168 // last call doesn't need a try!
169 let call = if i != last {
170 cx.expr_try(span, call)
171 } else {
172 cx.expr(span, ExprRet(Some(call)))
173 };
174 stmts.push(cx.stmt_expr(call));
175 }
176
177 let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
178 cx.expr_method_call(trait_span,
179 encoder,
180 cx.ident_of("emit_struct"),
181 vec!(
182 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
183 cx.expr_uint(trait_span, fields.len()),
184 blk
185 ))
186 }
187
188 EnumMatching(idx, variant, ref fields) => {
189 // We're not generating an AST that the borrow checker is expecting,
190 // so we need to generate a unique local variable to take the
191 // mutable loan out on, otherwise we get conflicts which don't
192 // actually exist.
193 let me = cx.stmt_let(trait_span, false, blkarg, encoder);
194 let encoder = cx.expr_ident(trait_span, blkarg);
195 let emit_variant_arg = cx.ident_of("emit_enum_variant_arg");
196 let mut stmts = Vec::new();
197 let last = fields.len() - 1;
198 for (i, &FieldInfo { self_, span, .. }) in fields.iter().enumerate() {
199 let enc = cx.expr_method_call(span, self_, encode, vec!(blkencoder));
200 let lambda = cx.lambda_expr_1(span, enc, blkarg);
201 let call = cx.expr_method_call(span, blkencoder,
202 emit_variant_arg,
203 vec!(cx.expr_uint(span, i),
204 lambda));
205 let call = if i != last {
206 cx.expr_try(span, call)
207 } else {
208 cx.expr(span, ExprRet(Some(call)))
209 };
210 stmts.push(cx.stmt_expr(call));
211 }
212
213 // enums with no fields need to return Ok()
214 if stmts.len() == 0 {
215 let ret_ok = cx.expr(trait_span,
216 ExprRet(Some(cx.expr_ok(trait_span,
217 cx.expr_lit(trait_span, LitNil)))));
218 stmts.push(cx.stmt_expr(ret_ok));
219 }
220
221 let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
222 let name = cx.expr_str(trait_span, token::get_ident(variant.node.name));
223 let call = cx.expr_method_call(trait_span, blkencoder,
224 cx.ident_of("emit_enum_variant"),
225 vec!(name,
226 cx.expr_uint(trait_span, idx),
227 cx.expr_uint(trait_span, fields.len()),
228 blk));
229 let blk = cx.lambda_expr_1(trait_span, call, blkarg);
230 let ret = cx.expr_method_call(trait_span,
231 encoder,
232 cx.ident_of("emit_enum"),
233 vec!(
234 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
235 blk
236 ));
237 cx.expr_block(cx.block(trait_span, vec!(me), Some(ret)))
238 }
239
240 _ => cx.bug("expected Struct or EnumMatching in deriving(Encodable)")
241 };
242 }