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.
11 //! The compiler code necessary to implement the `#[derive(Encodable)]`
12 //! (and `Decodable`, in decodable.rs) extension. The idea here is that
13 //! type-defining items may be tagged with `#[derive(Encodable, Decodable)]`.
15 //! For example, a type like:
18 //! #[derive(Encodable, Decodable)]
19 //! struct Node { id: usize }
22 //! would generate two implementations like:
25 //! impl<S: Encoder<E>, E> Encodable<S, E> for Node {
26 //! fn encode(&self, s: &mut S) -> Result<(), E> {
27 //! s.emit_struct("Node", 1, |this| {
28 //! this.emit_struct_field("id", 0, |this| {
29 //! Encodable::encode(&self.id, this)
30 //! /* this.emit_usize(self.id) can also be used */
36 //! impl<D: Decoder<E>, E> Decodable<D, E> for Node {
37 //! fn decode(d: &mut D) -> Result<Node, E> {
38 //! d.read_struct("Node", 1, |this| {
39 //! match this.read_struct_field("id", 0, |this| Decodable::decode(this)) {
40 //! Ok(id) => Ok(Node { id: id }),
48 //! Other interesting scenarios are when the item has type parameters or
49 //! references other non-built-in types. A type definition like:
52 //! #[derive(Encodable, Decodable)]
53 //! struct Spanned<T> { node: T, span: Span }
56 //! would yield functions like:
62 //! T: Encodable<S, E>
63 //! > Encodable<S, E> for Spanned<T> {
64 //! fn encode(&self, s: &mut S) -> Result<(), E> {
65 //! s.emit_struct("Spanned", 2, |this| {
66 //! this.emit_struct_field("node", 0, |this| self.node.encode(this))
68 //! this.emit_struct_field("span", 1, |this| self.span.encode(this))
76 //! T: Decodable<D, E>
77 //! > Decodable<D, E> for Spanned<T> {
78 //! fn decode(d: &mut D) -> Result<Spanned<T>, E> {
79 //! d.read_struct("Spanned", 2, |this| {
81 //! node: this.read_struct_field("node", 0, |this| Decodable::decode(this))
83 //! span: this.read_struct_field("span", 1, |this| Decodable::decode(this))
91 use ast::{MetaItem, Expr, ExprRet, MutMutable};
93 use ext::base::{ExtCtxt,Annotatable};
94 use ext::build::AstBuilder;
95 use ext::deriving::generic::*;
96 use ext::deriving::generic::ty::*;
100 pub fn expand_deriving_rustc_encodable(cx: &mut ExtCtxt,
104 push: &mut FnMut(Annotatable))
106 expand_deriving_encodable_imp(cx, span, mitem, item, push, "rustc_serialize")
109 pub fn expand_deriving_encodable(cx: &mut ExtCtxt,
113 push: &mut FnMut(Annotatable))
115 expand_deriving_encodable_imp(cx, span, mitem, item, push, "serialize")
118 fn expand_deriving_encodable_imp(cx: &mut ExtCtxt,
122 push: &mut FnMut(Annotatable),
126 // FIXME(#21880): lift this requirement.
127 cx.span_err(span, "this trait cannot be derived with #![no_std]");
131 let trait_def = TraitDef {
133 attributes: Vec::new(),
134 path: Path::new_(vec!(krate, "Encodable"), None, vec!(), true),
135 additional_bounds: Vec::new(),
136 generics: LifetimeBounds::empty(),
140 generics: LifetimeBounds {
141 lifetimes: Vec::new(),
142 bounds: vec!(("__S", vec!(Path::new_(
143 vec!(krate, "Encoder"), None,
146 explicit_self: borrowed_explicit_self(),
147 args: vec!(Ptr(Box::new(Literal(Path::new_local("__S"))),
148 Borrowed(None, MutMutable))),
149 ret_ty: Literal(Path::new_(
150 pathvec_std!(cx, core::result::Result),
152 vec!(Box::new(Tuple(Vec::new())), Box::new(Literal(Path::new_(
153 vec!["__S", "Error"], None, vec![], false
157 attributes: Vec::new(),
159 combine_substructure: combine_substructure(Box::new(|a, b, c| {
160 encodable_substructure(a, b, c)
164 associated_types: Vec::new(),
167 trait_def.expand(cx, mitem, item, push)
170 fn encodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
171 substr: &Substructure) -> P<Expr> {
172 let encoder = substr.nonself_args[0].clone();
173 // throw an underscore in front to suppress unused variable warnings
174 let blkarg = cx.ident_of("_e");
175 let blkencoder = cx.expr_ident(trait_span, blkarg);
176 let encode = cx.ident_of("encode");
178 return match *substr.fields {
179 Struct(ref fields) => {
180 let emit_struct_field = cx.ident_of("emit_struct_field");
181 let mut stmts = Vec::new();
187 }) in fields.iter().enumerate() {
188 let name = match name {
189 Some(id) => id.name.as_str(),
191 token::intern_and_get_ident(&format!("_field{}", i))
194 let enc = cx.expr_method_call(span, self_.clone(),
195 encode, vec!(blkencoder.clone()));
196 let lambda = cx.lambda_expr_1(span, enc, blkarg);
197 let call = cx.expr_method_call(span, blkencoder.clone(),
199 vec!(cx.expr_str(span, name),
200 cx.expr_usize(span, i),
203 // last call doesn't need a try!
204 let last = fields.len() - 1;
205 let call = if i != last {
206 cx.expr_try(span, call)
208 cx.expr(span, ExprRet(Some(call)))
210 stmts.push(cx.stmt_expr(call));
213 // unit structs have no fields and need to return Ok()
214 if stmts.is_empty() {
215 let ret_ok = cx.expr(trait_span,
216 ExprRet(Some(cx.expr_ok(trait_span,
217 cx.expr_tuple(trait_span, vec![])))));
218 stmts.push(cx.stmt_expr(ret_ok));
221 let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
222 cx.expr_method_call(trait_span,
224 cx.ident_of("emit_struct"),
226 cx.expr_str(trait_span, substr.type_ident.name.as_str()),
227 cx.expr_usize(trait_span, fields.len()),
232 EnumMatching(idx, variant, ref fields) => {
233 // We're not generating an AST that the borrow checker is expecting,
234 // so we need to generate a unique local variable to take the
235 // mutable loan out on, otherwise we get conflicts which don't
237 let me = cx.stmt_let(trait_span, false, blkarg, encoder);
238 let encoder = cx.expr_ident(trait_span, blkarg);
239 let emit_variant_arg = cx.ident_of("emit_enum_variant_arg");
240 let mut stmts = Vec::new();
241 if !fields.is_empty() {
242 let last = fields.len() - 1;
243 for (i, &FieldInfo { ref self_, span, .. }) in fields.iter().enumerate() {
244 let enc = cx.expr_method_call(span, self_.clone(),
245 encode, vec!(blkencoder.clone()));
246 let lambda = cx.lambda_expr_1(span, enc, blkarg);
247 let call = cx.expr_method_call(span, blkencoder.clone(),
249 vec!(cx.expr_usize(span, i),
251 let call = if i != last {
252 cx.expr_try(span, call)
254 cx.expr(span, ExprRet(Some(call)))
256 stmts.push(cx.stmt_expr(call));
259 let ret_ok = cx.expr(trait_span,
260 ExprRet(Some(cx.expr_ok(trait_span,
261 cx.expr_tuple(trait_span, vec![])))));
262 stmts.push(cx.stmt_expr(ret_ok));
265 let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
266 let name = cx.expr_str(trait_span, variant.node.name.name.as_str());
267 let call = cx.expr_method_call(trait_span, blkencoder,
268 cx.ident_of("emit_enum_variant"),
270 cx.expr_usize(trait_span, idx),
271 cx.expr_usize(trait_span, fields.len()),
273 let blk = cx.lambda_expr_1(trait_span, call, blkarg);
274 let ret = cx.expr_method_call(trait_span,
276 cx.ident_of("emit_enum"),
278 cx.expr_str(trait_span, substr.type_ident.name.as_str()),
281 cx.expr_block(cx.block(trait_span, vec!(me), Some(ret)))
284 _ => cx.bug("expected Struct or EnumMatching in derive(Encodable)")