1 //! The compiler code necessary to implement the `#[derive(RustcEncodable)]`
2 //! (and `RustcDecodable`, in `decodable.rs`) extension. The idea here is that
3 //! type-defining items may be tagged with
4 //! `#[derive(RustcEncodable, RustcDecodable)]`.
6 //! For example, a type like:
8 //! ```ignore (old code)
9 //! #[derive(RustcEncodable, RustcDecodable)]
10 //! struct Node { id: usize }
13 //! would generate two implementations like:
15 //! ```ignore (old code)
16 //! # struct Node { id: usize }
17 //! impl<S: Encoder<E>, E> Encodable<S, E> for Node {
18 //! fn encode(&self, s: &mut S) -> Result<(), E> {
19 //! s.emit_struct("Node", 1, |this| {
20 //! this.emit_struct_field("id", 0, |this| {
21 //! Encodable::encode(&self.id, this)
22 //! /* this.emit_usize(self.id) can also be used */
28 //! impl<D: Decoder<E>, E> Decodable<D, E> for Node {
29 //! fn decode(d: &mut D) -> Result<Node, E> {
30 //! d.read_struct("Node", 1, |this| {
31 //! match this.read_struct_field("id", 0, |this| Decodable::decode(this)) {
32 //! Ok(id) => Ok(Node { id: id }),
40 //! Other interesting scenarios are when the item has type parameters or
41 //! references other non-built-in types. A type definition like:
43 //! ```ignore (old code)
44 //! # #[derive(RustcEncodable, RustcDecodable)]
46 //! #[derive(RustcEncodable, RustcDecodable)]
47 //! struct Spanned<T> { node: T, span: Span }
50 //! would yield functions like:
52 //! ```ignore (old code)
53 //! # #[derive(RustcEncodable, RustcDecodable)]
55 //! # struct Spanned<T> { node: T, span: Span }
59 //! T: Encodable<S, E>
60 //! > Encodable<S, E> for Spanned<T> {
61 //! fn encode(&self, s: &mut S) -> Result<(), E> {
62 //! s.emit_struct("Spanned", 2, |this| {
63 //! this.emit_struct_field("node", 0, |this| self.node.encode(this))
65 //! this.emit_struct_field("span", 1, |this| self.span.encode(this))
73 //! T: Decodable<D, E>
74 //! > Decodable<D, E> for Spanned<T> {
75 //! fn decode(d: &mut D) -> Result<Spanned<T>, E> {
76 //! d.read_struct("Spanned", 2, |this| {
78 //! node: this.read_struct_field("node", 0, |this| Decodable::decode(this))
80 //! span: this.read_struct_field("span", 1, |this| Decodable::decode(this))
88 use crate::deriving::generic::ty::*;
89 use crate::deriving::generic::*;
90 use crate::deriving::pathvec_std;
92 use rustc_ast::{AttrVec, ExprKind, MetaItem, Mutability};
93 use rustc_expand::base::{Annotatable, ExtCtxt};
94 use rustc_span::symbol::{sym, Ident, Symbol};
97 pub fn expand_deriving_rustc_encodable(
102 push: &mut dyn FnMut(Annotatable),
105 let krate = sym::rustc_serialize;
106 let typaram = sym::__S;
108 let trait_def = TraitDef {
110 path: Path::new_(vec![krate, sym::Encodable], vec![], PathKind::Global),
111 skip_path_as_bound: false,
112 needs_copy_as_bound_if_packed: true,
113 additional_bounds: Vec::new(),
114 supports_unions: false,
115 methods: vec![MethodDef {
120 vec![Path::new_(vec![krate, sym::Encoder], vec![], PathKind::Global)],
125 Ref(Box::new(Path(Path::new_local(typaram))), Mutability::Mut),
128 ret_ty: Path(Path::new_(
129 pathvec_std!(result::Result),
132 Box::new(Path(Path::new_(vec![typaram, sym::Error], vec![], PathKind::Local))),
136 attributes: AttrVec::new(),
137 fieldless_variants_strategy: FieldlessVariantsStrategy::Default,
138 combine_substructure: combine_substructure(Box::new(|a, b, c| {
139 encodable_substructure(a, b, c, krate)
142 associated_types: Vec::new(),
146 trait_def.expand(cx, mitem, item, push)
149 fn encodable_substructure(
150 cx: &mut ExtCtxt<'_>,
152 substr: &Substructure<'_>,
155 let encoder = substr.nonselflike_args[0].clone();
156 // throw an underscore in front to suppress unused variable warnings
157 let blkarg = Ident::new(sym::_e, trait_span);
158 let blkencoder = cx.expr_ident(trait_span, blkarg);
159 let fn_path = cx.expr_path(cx.path_global(
162 Ident::new(krate, trait_span),
163 Ident::new(sym::Encodable, trait_span),
164 Ident::new(sym::encode, trait_span),
168 match substr.fields {
169 Struct(_, fields) => {
170 let fn_emit_struct_field_path =
171 cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_struct_field]);
172 let mut stmts = Vec::new();
173 for (i, &FieldInfo { name, ref self_expr, span, .. }) in fields.iter().enumerate() {
174 let name = match name {
176 None => Symbol::intern(&format!("_field{}", i)),
178 let self_ref = cx.expr_addr_of(span, self_expr.clone());
179 let enc = cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
180 let lambda = cx.lambda1(span, enc, blkarg);
181 let call = cx.expr_call_global(
183 fn_emit_struct_field_path.clone(),
186 cx.expr_str(span, name),
187 cx.expr_usize(span, i),
192 // last call doesn't need a try!
193 let last = fields.len() - 1;
194 let call = if i != last {
195 cx.expr_try(span, call)
197 cx.expr(span, ExprKind::Ret(Some(call)))
200 let stmt = cx.stmt_expr(call);
204 // unit structs have no fields and need to return Ok()
205 let blk = if stmts.is_empty() {
206 let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
207 cx.lambda1(trait_span, ok, blkarg)
209 cx.lambda_stmts_1(trait_span, stmts, blkarg)
212 let fn_emit_struct_path =
213 cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_struct]);
215 let expr = cx.expr_call_global(
220 cx.expr_str(trait_span, substr.type_ident.name),
221 cx.expr_usize(trait_span, fields.len()),
225 BlockOrExpr::new_expr(expr)
228 EnumMatching(idx, _, variant, fields) => {
229 // We're not generating an AST that the borrow checker is expecting,
230 // so we need to generate a unique local variable to take the
231 // mutable loan out on, otherwise we get conflicts which don't
233 let me = cx.stmt_let(trait_span, false, blkarg, encoder);
234 let encoder = cx.expr_ident(trait_span, blkarg);
236 let fn_emit_enum_variant_arg_path: Vec<_> =
237 cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_enum_variant_arg]);
239 let mut stmts = Vec::new();
240 if !fields.is_empty() {
241 let last = fields.len() - 1;
242 for (i, &FieldInfo { ref self_expr, span, .. }) in fields.iter().enumerate() {
243 let self_ref = cx.expr_addr_of(span, self_expr.clone());
245 cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
246 let lambda = cx.lambda1(span, enc, blkarg);
248 let call = cx.expr_call_global(
250 fn_emit_enum_variant_arg_path.clone(),
251 vec![blkencoder.clone(), cx.expr_usize(span, i), lambda],
253 let call = if i != last {
254 cx.expr_try(span, call)
256 cx.expr(span, ExprKind::Ret(Some(call)))
258 stmts.push(cx.stmt_expr(call));
261 let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
262 let ret_ok = cx.expr(trait_span, ExprKind::Ret(Some(ok)));
263 stmts.push(cx.stmt_expr(ret_ok));
266 let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
267 let name = cx.expr_str(trait_span, variant.ident.name);
269 let fn_emit_enum_variant_path: Vec<_> =
270 cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_enum_variant]);
272 let call = cx.expr_call_global(
274 fn_emit_enum_variant_path,
278 cx.expr_usize(trait_span, *idx),
279 cx.expr_usize(trait_span, fields.len()),
284 let blk = cx.lambda1(trait_span, call, blkarg);
285 let fn_emit_enum_path: Vec<_> =
286 cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_enum]);
287 let expr = cx.expr_call_global(
290 vec![encoder, cx.expr_str(trait_span, substr.type_ident.name), blk],
292 BlockOrExpr::new_mixed(vec![me], Some(expr))
295 _ => cx.bug("expected Struct or EnumMatching in derive(Encodable)"),