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.
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)]`.
17 For example, a type like:
20 #[deriving(Encodable, Decodable)]
21 struct Node { id: uint }
24 would generate two implementations like:
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))
35 impl<D:Decoder> Decodable for node_id {
36 fn decode(d: &D) -> Node {
37 d.read_struct("Node", 1, || {
39 id: d.read_field(~"x", 0, || decode(d))
46 Other interesting scenarios are whe the item has type parameters or
47 references other non-built-in types. A type definition like:
50 #[deriving(Encodable, Decodable)]
51 struct spanned<T> { node: T, span: Span }
54 would yield functions like:
60 > spanned<T>: Encodable<S> {
61 fn encode<S:Encoder>(s: &S) {
63 s.emit_field("node", 0, || self.node.encode(s));
64 s.emit_field("span", 1, || self.span.encode(s));
72 > spanned<T>: Decodable<D> {
73 fn decode(d: &D) -> spanned<T> {
76 node: d.read_field(~"node", 0, || decode(d)),
77 span: d.read_field(~"span", 1, || decode(d)),
85 use ast::{MetaItem, Item, Expr, ExprRet, MutMutable, LitNil};
87 use ext::base::ExtCtxt;
88 use ext::build::AstBuilder;
89 use ext::deriving::generic::*;
92 pub fn expand_deriving_encodable(cx: &mut ExtCtxt,
97 let trait_def = TraitDef {
99 attributes: Vec::new(),
100 path: Path::new_(vec!("serialize", "Encodable"), None,
101 vec!(~Literal(Path::new_local("__S")),
102 ~Literal(Path::new_local("__E"))), true),
103 additional_bounds: Vec::new(),
104 generics: LifetimeBounds {
105 lifetimes: Vec::new(),
106 bounds: vec!(("__S", vec!(Path::new_(
107 vec!("serialize", "Encoder"), None,
108 vec!(~Literal(Path::new_local("__E"))), true))),
114 generics: LifetimeBounds::empty(),
115 explicit_self: borrowed_explicit_self(),
116 args: vec!(Ptr(~Literal(Path::new_local("__S")),
117 Borrowed(None, MutMutable))),
118 ret_ty: Literal(Path::new_(vec!("std", "result", "Result"),
120 vec!(~Tuple(Vec::new()),
121 ~Literal(Path::new_local("__E"))),
124 const_nonmatching: true,
125 combine_substructure: encodable_substructure,
129 trait_def.expand(cx, mitem, item, push)
132 fn encodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
133 substr: &Substructure) -> @Expr {
134 let encoder = substr.nonself_args[0];
135 // throw an underscore in front to suppress unused variable warnings
136 let blkarg = cx.ident_of("_e");
137 let blkencoder = cx.expr_ident(trait_span, blkarg);
138 let encode = cx.ident_of("encode");
140 return match *substr.fields {
141 Struct(ref fields) => {
142 let emit_struct_field = cx.ident_of("emit_struct_field");
143 let mut stmts = Vec::new();
144 let last = fields.len() - 1;
150 }) in fields.iter().enumerate() {
151 let name = match name {
152 Some(id) => token::get_ident(id),
154 token::intern_and_get_ident(format!("_field{}", i))
157 let enc = cx.expr_method_call(span, self_, encode, vec!(blkencoder));
158 let lambda = cx.lambda_expr_1(span, enc, blkarg);
159 let call = cx.expr_method_call(span, blkencoder,
161 vec!(cx.expr_str(span, name),
162 cx.expr_uint(span, i),
165 // last call doesn't need a try!
166 let call = if i != last {
167 cx.expr_try(span, call)
169 cx.expr(span, ExprRet(Some(call)))
171 stmts.push(cx.stmt_expr(call));
174 let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
175 cx.expr_method_call(trait_span,
177 cx.ident_of("emit_struct"),
179 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
180 cx.expr_uint(trait_span, fields.len()),
185 EnumMatching(idx, variant, ref fields) => {
186 // We're not generating an AST that the borrow checker is expecting,
187 // so we need to generate a unique local variable to take the
188 // mutable loan out on, otherwise we get conflicts which don't
190 let me = cx.stmt_let(trait_span, false, blkarg, encoder);
191 let encoder = cx.expr_ident(trait_span, blkarg);
192 let emit_variant_arg = cx.ident_of("emit_enum_variant_arg");
193 let mut stmts = Vec::new();
194 let last = fields.len() - 1;
195 for (i, &FieldInfo { self_, span, .. }) in fields.iter().enumerate() {
196 let enc = cx.expr_method_call(span, self_, encode, vec!(blkencoder));
197 let lambda = cx.lambda_expr_1(span, enc, blkarg);
198 let call = cx.expr_method_call(span, blkencoder,
200 vec!(cx.expr_uint(span, i),
202 let call = if i != last {
203 cx.expr_try(span, call)
205 cx.expr(span, ExprRet(Some(call)))
207 stmts.push(cx.stmt_expr(call));
210 // enums with no fields need to return Ok()
211 if stmts.len() == 0 {
212 let ret_ok = cx.expr(trait_span,
213 ExprRet(Some(cx.expr_ok(trait_span,
214 cx.expr_lit(trait_span, LitNil)))));
215 stmts.push(cx.stmt_expr(ret_ok));
218 let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
219 let name = cx.expr_str(trait_span, token::get_ident(variant.node.name));
220 let call = cx.expr_method_call(trait_span, blkencoder,
221 cx.ident_of("emit_enum_variant"),
223 cx.expr_uint(trait_span, idx),
224 cx.expr_uint(trait_span, fields.len()),
226 let blk = cx.lambda_expr_1(trait_span, call, blkarg);
227 let ret = cx.expr_method_call(trait_span,
229 cx.ident_of("emit_enum"),
231 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
234 cx.expr_block(cx.block(trait_span, vec!(me), Some(ret)))
237 _ => cx.bug("expected Struct or EnumMatching in deriving(Encodable)")