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),
104 let krate = sym::rustc_serialize;
105 let typaram = sym::__S;
107 let trait_def = TraitDef {
109 path: Path::new_(vec![krate, sym::Encodable], vec![], PathKind::Global),
110 skip_path_as_bound: false,
111 additional_bounds: Vec::new(),
112 generics: Bounds::empty(),
113 supports_unions: false,
114 methods: vec![MethodDef {
119 vec![Path::new_(vec![krate, sym::Encoder], vec![], PathKind::Global)],
124 Ref(Box::new(Path(Path::new_local(typaram))), Mutability::Mut),
127 ret_ty: Path(Path::new_(
128 pathvec_std!(result::Result),
131 Box::new(Path(Path::new_(vec![typaram, sym::Error], vec![], PathKind::Local))),
135 attributes: AttrVec::new(),
136 unify_fieldless_variants: false,
137 combine_substructure: combine_substructure(Box::new(|a, b, c| {
138 encodable_substructure(a, b, c, krate)
141 associated_types: Vec::new(),
144 trait_def.expand(cx, mitem, item, push)
147 fn encodable_substructure(
148 cx: &mut ExtCtxt<'_>,
150 substr: &Substructure<'_>,
153 let encoder = substr.nonselflike_args[0].clone();
154 // throw an underscore in front to suppress unused variable warnings
155 let blkarg = Ident::new(sym::_e, trait_span);
156 let blkencoder = cx.expr_ident(trait_span, blkarg);
157 let fn_path = cx.expr_path(cx.path_global(
160 Ident::new(krate, trait_span),
161 Ident::new(sym::Encodable, trait_span),
162 Ident::new(sym::encode, trait_span),
166 match *substr.fields {
167 Struct(_, ref fields) => {
168 let fn_emit_struct_field_path =
169 cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_struct_field]);
170 let mut stmts = Vec::new();
171 for (i, &FieldInfo { name, ref self_expr, span, .. }) in fields.iter().enumerate() {
172 let name = match name {
174 None => Symbol::intern(&format!("_field{}", i)),
176 let self_ref = cx.expr_addr_of(span, self_expr.clone());
177 let enc = cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
178 let lambda = cx.lambda1(span, enc, blkarg);
179 let call = cx.expr_call_global(
181 fn_emit_struct_field_path.clone(),
184 cx.expr_str(span, name),
185 cx.expr_usize(span, i),
190 // last call doesn't need a try!
191 let last = fields.len() - 1;
192 let call = if i != last {
193 cx.expr_try(span, call)
195 cx.expr(span, ExprKind::Ret(Some(call)))
198 let stmt = cx.stmt_expr(call);
202 // unit structs have no fields and need to return Ok()
203 let blk = if stmts.is_empty() {
204 let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
205 cx.lambda1(trait_span, ok, blkarg)
207 cx.lambda_stmts_1(trait_span, stmts, blkarg)
210 let fn_emit_struct_path =
211 cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_struct]);
213 let expr = cx.expr_call_global(
218 cx.expr_str(trait_span, substr.type_ident.name),
219 cx.expr_usize(trait_span, fields.len()),
223 BlockOrExpr::new_expr(expr)
226 EnumMatching(idx, _, variant, ref fields) => {
227 // We're not generating an AST that the borrow checker is expecting,
228 // so we need to generate a unique local variable to take the
229 // mutable loan out on, otherwise we get conflicts which don't
231 let me = cx.stmt_let(trait_span, false, blkarg, encoder);
232 let encoder = cx.expr_ident(trait_span, blkarg);
234 let fn_emit_enum_variant_arg_path: Vec<_> =
235 cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_enum_variant_arg]);
237 let mut stmts = Vec::new();
238 if !fields.is_empty() {
239 let last = fields.len() - 1;
240 for (i, &FieldInfo { ref self_expr, span, .. }) in fields.iter().enumerate() {
241 let self_ref = cx.expr_addr_of(span, self_expr.clone());
243 cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
244 let lambda = cx.lambda1(span, enc, blkarg);
246 let call = cx.expr_call_global(
248 fn_emit_enum_variant_arg_path.clone(),
249 vec![blkencoder.clone(), cx.expr_usize(span, i), lambda],
251 let call = if i != last {
252 cx.expr_try(span, call)
254 cx.expr(span, ExprKind::Ret(Some(call)))
256 stmts.push(cx.stmt_expr(call));
259 let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
260 let ret_ok = cx.expr(trait_span, ExprKind::Ret(Some(ok)));
261 stmts.push(cx.stmt_expr(ret_ok));
264 let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
265 let name = cx.expr_str(trait_span, variant.ident.name);
267 let fn_emit_enum_variant_path: Vec<_> =
268 cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_enum_variant]);
270 let call = cx.expr_call_global(
272 fn_emit_enum_variant_path,
276 cx.expr_usize(trait_span, idx),
277 cx.expr_usize(trait_span, fields.len()),
282 let blk = cx.lambda1(trait_span, call, blkarg);
283 let fn_emit_enum_path: Vec<_> =
284 cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_enum]);
285 let expr = cx.expr_call_global(
288 vec![encoder, cx.expr_str(trait_span, substr.type_ident.name), blk],
290 BlockOrExpr::new_mixed(vec![me], Some(expr))
293 _ => cx.bug("expected Struct or EnumMatching in derive(Encodable)"),