1 //! The compiler code necessary to implement the `#[derive(Encodable)]`
2 //! (and `Decodable`, in `decodable.rs`) extension. The idea here is that
3 //! type-defining items may be tagged with `#[derive(Encodable, Decodable)]`.
5 //! For example, a type like:
8 //! #[derive(Encodable, Decodable)]
9 //! struct Node { id: usize }
12 //! would generate two implementations like:
15 //! # struct Node { id: usize }
16 //! impl<S: Encoder<E>, E> Encodable<S, E> for Node {
17 //! fn encode(&self, s: &mut S) -> Result<(), E> {
18 //! s.emit_struct("Node", 1, |this| {
19 //! this.emit_struct_field("id", 0, |this| {
20 //! Encodable::encode(&self.id, this)
21 //! /* this.emit_usize(self.id) can also be used */
27 //! impl<D: Decoder<E>, E> Decodable<D, E> for Node {
28 //! fn decode(d: &mut D) -> Result<Node, E> {
29 //! d.read_struct("Node", 1, |this| {
30 //! match this.read_struct_field("id", 0, |this| Decodable::decode(this)) {
31 //! Ok(id) => Ok(Node { id: id }),
39 //! Other interesting scenarios are when the item has type parameters or
40 //! references other non-built-in types. A type definition like:
43 //! # #[derive(Encodable, Decodable)] struct Span;
44 //! #[derive(Encodable, Decodable)]
45 //! struct Spanned<T> { node: T, span: Span }
48 //! would yield functions like:
51 //! # #[derive(Encodable, Decodable)] struct Span;
52 //! # struct Spanned<T> { node: T, span: Span }
56 //! T: Encodable<S, E>
57 //! > Encodable<S, E> for Spanned<T> {
58 //! fn encode(&self, s: &mut S) -> Result<(), E> {
59 //! s.emit_struct("Spanned", 2, |this| {
60 //! this.emit_struct_field("node", 0, |this| self.node.encode(this))
62 //! this.emit_struct_field("span", 1, |this| self.span.encode(this))
70 //! T: Decodable<D, E>
71 //! > Decodable<D, E> for Spanned<T> {
72 //! fn decode(d: &mut D) -> Result<Spanned<T>, E> {
73 //! d.read_struct("Spanned", 2, |this| {
75 //! node: this.read_struct_field("node", 0, |this| Decodable::decode(this))
77 //! span: this.read_struct_field("span", 1, |this| Decodable::decode(this))
85 use crate::deriving::{self, pathvec_std};
86 use crate::deriving::generic::*;
87 use crate::deriving::generic::ty::*;
89 use syntax::ast::{Expr, ExprKind, MetaItem, Mutability};
90 use syntax::ext::base::{Annotatable, ExtCtxt};
92 use syntax::symbol::Symbol;
95 pub fn expand_deriving_rustc_encodable(cx: &mut ExtCtxt<'_>,
99 push: &mut dyn FnMut(Annotatable)) {
100 expand_deriving_encodable_imp(cx, span, mitem, item, push, "rustc_serialize")
103 pub fn expand_deriving_encodable(cx: &mut ExtCtxt<'_>,
107 push: &mut dyn FnMut(Annotatable)) {
108 expand_deriving_encodable_imp(cx, span, mitem, item, push, "serialize")
111 fn expand_deriving_encodable_imp(cx: &mut ExtCtxt<'_>,
115 push: &mut dyn FnMut(Annotatable),
116 krate: &'static str) {
117 let typaram = &*deriving::hygienic_type_parameter(item, "__S");
119 let trait_def = TraitDef {
121 attributes: Vec::new(),
122 path: Path::new_(vec![krate, "Encodable"], None, vec![], PathKind::Global),
123 additional_bounds: Vec::new(),
124 generics: LifetimeBounds::empty(),
126 supports_unions: false,
130 generics: LifetimeBounds {
131 lifetimes: Vec::new(),
134 vec![Path::new_(vec![krate, "Encoder"], None, vec![], PathKind::Global)])
137 explicit_self: borrowed_explicit_self(),
138 args: vec![(Ptr(Box::new(Literal(Path::new_local(typaram))),
139 Borrowed(None, Mutability::Mutable)), "s")],
140 ret_ty: Literal(Path::new_(
141 pathvec_std!(cx, result::Result),
143 vec![Box::new(Tuple(Vec::new())), Box::new(Literal(Path::new_(
144 vec![typaram, "Error"], None, vec![], PathKind::Local
148 attributes: Vec::new(),
150 unify_fieldless_variants: false,
151 combine_substructure: combine_substructure(Box::new(|a, b, c| {
152 encodable_substructure(a, b, c, krate)
156 associated_types: Vec::new(),
159 trait_def.expand(cx, mitem, item, push)
162 fn encodable_substructure(cx: &mut ExtCtxt<'_>,
164 substr: &Substructure<'_>,
167 let encoder = substr.nonself_args[0].clone();
168 // throw an underscore in front to suppress unused variable warnings
169 let blkarg = cx.ident_of("_e");
170 let blkencoder = cx.expr_ident(trait_span, blkarg);
171 let fn_path = cx.expr_path(cx.path_global(trait_span,
172 vec![cx.ident_of(krate),
173 cx.ident_of("Encodable"),
174 cx.ident_of("encode")]));
176 return match *substr.fields {
177 Struct(_, ref fields) => {
178 let emit_struct_field = cx.ident_of("emit_struct_field");
179 let mut stmts = Vec::new();
180 for (i, &FieldInfo { name, ref self_, span, .. }) in fields.iter().enumerate() {
181 let name = match name {
183 None => Symbol::intern(&format!("_field{}", i)),
185 let self_ref = cx.expr_addr_of(span, self_.clone());
186 let enc = cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
187 let lambda = cx.lambda1(span, enc, blkarg);
188 let call = cx.expr_method_call(span,
191 vec![cx.expr_str(span, name),
192 cx.expr_usize(span, i),
195 // last call doesn't need a try!
196 let last = fields.len() - 1;
197 let call = if i != last {
198 cx.expr_try(span, call)
200 cx.expr(span, ExprKind::Ret(Some(call)))
203 let stmt = cx.stmt_expr(call);
207 // unit structs have no fields and need to return Ok()
208 let blk = if stmts.is_empty() {
209 let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
210 cx.lambda1(trait_span, ok, blkarg)
212 cx.lambda_stmts_1(trait_span, stmts, blkarg)
215 cx.expr_method_call(trait_span,
217 cx.ident_of("emit_struct"),
218 vec![cx.expr_str(trait_span, substr.type_ident.name),
219 cx.expr_usize(trait_span, fields.len()),
223 EnumMatching(idx, _, variant, ref fields) => {
224 // We're not generating an AST that the borrow checker is expecting,
225 // so we need to generate a unique local variable to take the
226 // mutable loan out on, otherwise we get conflicts which don't
228 let me = cx.stmt_let(trait_span, false, blkarg, encoder);
229 let encoder = cx.expr_ident(trait_span, blkarg);
230 let emit_variant_arg = cx.ident_of("emit_enum_variant_arg");
231 let mut stmts = Vec::new();
232 if !fields.is_empty() {
233 let last = fields.len() - 1;
234 for (i, &FieldInfo { ref self_, span, .. }) in fields.iter().enumerate() {
235 let self_ref = cx.expr_addr_of(span, self_.clone());
237 cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
238 let lambda = cx.lambda1(span, enc, blkarg);
239 let call = cx.expr_method_call(span,
242 vec![cx.expr_usize(span, i), lambda]);
243 let call = if i != last {
244 cx.expr_try(span, call)
246 cx.expr(span, ExprKind::Ret(Some(call)))
248 stmts.push(cx.stmt_expr(call));
251 let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
252 let ret_ok = cx.expr(trait_span, ExprKind::Ret(Some(ok)));
253 stmts.push(cx.stmt_expr(ret_ok));
256 let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
257 let name = cx.expr_str(trait_span, variant.node.ident.name);
258 let call = cx.expr_method_call(trait_span,
260 cx.ident_of("emit_enum_variant"),
262 cx.expr_usize(trait_span, idx),
263 cx.expr_usize(trait_span, fields.len()),
265 let blk = cx.lambda1(trait_span, call, blkarg);
266 let ret = cx.expr_method_call(trait_span,
268 cx.ident_of("emit_enum"),
269 vec![cx.expr_str(trait_span ,substr.type_ident.name),
271 cx.expr_block(cx.block(trait_span, vec![me, cx.stmt_expr(ret)]))
274 _ => cx.bug("expected Struct or EnumMatching in derive(Encodable)"),