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 let krate = "rustc_serialize";
101 let typaram = &*deriving::hygienic_type_parameter(item, "__S");
103 let trait_def = TraitDef {
105 attributes: Vec::new(),
106 path: Path::new_(vec![krate, "Encodable"], None, vec![], PathKind::Global),
107 additional_bounds: Vec::new(),
108 generics: LifetimeBounds::empty(),
110 supports_unions: false,
114 generics: LifetimeBounds {
115 lifetimes: Vec::new(),
118 vec![Path::new_(vec![krate, "Encoder"], None, vec![], PathKind::Global)])
121 explicit_self: borrowed_explicit_self(),
122 args: vec![(Ptr(Box::new(Literal(Path::new_local(typaram))),
123 Borrowed(None, Mutability::Mutable)), "s")],
124 ret_ty: Literal(Path::new_(
125 pathvec_std!(cx, result::Result),
127 vec![Box::new(Tuple(Vec::new())), Box::new(Literal(Path::new_(
128 vec![typaram, "Error"], None, vec![], PathKind::Local
132 attributes: Vec::new(),
134 unify_fieldless_variants: false,
135 combine_substructure: combine_substructure(Box::new(|a, b, c| {
136 encodable_substructure(a, b, c, krate)
140 associated_types: Vec::new(),
143 trait_def.expand(cx, mitem, item, push)
146 fn encodable_substructure(cx: &mut ExtCtxt<'_>,
148 substr: &Substructure<'_>,
151 let encoder = substr.nonself_args[0].clone();
152 // throw an underscore in front to suppress unused variable warnings
153 let blkarg = cx.ident_of("_e");
154 let blkencoder = cx.expr_ident(trait_span, blkarg);
155 let fn_path = cx.expr_path(cx.path_global(trait_span,
156 vec![cx.ident_of(krate),
157 cx.ident_of("Encodable"),
158 cx.ident_of("encode")]));
160 return match *substr.fields {
161 Struct(_, ref fields) => {
162 let emit_struct_field = cx.ident_of("emit_struct_field");
163 let mut stmts = Vec::new();
164 for (i, &FieldInfo { name, ref self_, span, .. }) in fields.iter().enumerate() {
165 let name = match name {
167 None => Symbol::intern(&format!("_field{}", i)),
169 let self_ref = cx.expr_addr_of(span, self_.clone());
170 let enc = cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
171 let lambda = cx.lambda1(span, enc, blkarg);
172 let call = cx.expr_method_call(span,
175 vec![cx.expr_str(span, name),
176 cx.expr_usize(span, i),
179 // last call doesn't need a try!
180 let last = fields.len() - 1;
181 let call = if i != last {
182 cx.expr_try(span, call)
184 cx.expr(span, ExprKind::Ret(Some(call)))
187 let stmt = cx.stmt_expr(call);
191 // unit structs have no fields and need to return Ok()
192 let blk = if stmts.is_empty() {
193 let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
194 cx.lambda1(trait_span, ok, blkarg)
196 cx.lambda_stmts_1(trait_span, stmts, blkarg)
199 cx.expr_method_call(trait_span,
201 cx.ident_of("emit_struct"),
202 vec![cx.expr_str(trait_span, substr.type_ident.name),
203 cx.expr_usize(trait_span, fields.len()),
207 EnumMatching(idx, _, variant, ref fields) => {
208 // We're not generating an AST that the borrow checker is expecting,
209 // so we need to generate a unique local variable to take the
210 // mutable loan out on, otherwise we get conflicts which don't
212 let me = cx.stmt_let(trait_span, false, blkarg, encoder);
213 let encoder = cx.expr_ident(trait_span, blkarg);
214 let emit_variant_arg = cx.ident_of("emit_enum_variant_arg");
215 let mut stmts = Vec::new();
216 if !fields.is_empty() {
217 let last = fields.len() - 1;
218 for (i, &FieldInfo { ref self_, span, .. }) in fields.iter().enumerate() {
219 let self_ref = cx.expr_addr_of(span, self_.clone());
221 cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
222 let lambda = cx.lambda1(span, enc, blkarg);
223 let call = cx.expr_method_call(span,
226 vec![cx.expr_usize(span, i), lambda]);
227 let call = if i != last {
228 cx.expr_try(span, call)
230 cx.expr(span, ExprKind::Ret(Some(call)))
232 stmts.push(cx.stmt_expr(call));
235 let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
236 let ret_ok = cx.expr(trait_span, ExprKind::Ret(Some(ok)));
237 stmts.push(cx.stmt_expr(ret_ok));
240 let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
241 let name = cx.expr_str(trait_span, variant.ident.name);
242 let call = cx.expr_method_call(trait_span,
244 cx.ident_of("emit_enum_variant"),
246 cx.expr_usize(trait_span, idx),
247 cx.expr_usize(trait_span, fields.len()),
249 let blk = cx.lambda1(trait_span, call, blkarg);
250 let ret = cx.expr_method_call(trait_span,
252 cx.ident_of("emit_enum"),
253 vec![cx.expr_str(trait_span ,substr.type_ident.name),
255 cx.expr_block(cx.block(trait_span, vec![me, cx.stmt_expr(ret)]))
258 _ => cx.bug("expected Struct or EnumMatching in derive(Encodable)"),