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};
91 use syntax::ext::build::AstBuilder;
93 use syntax::symbol::Symbol;
96 pub fn expand_deriving_rustc_encodable(cx: &mut ExtCtxt<'_>,
100 push: &mut dyn FnMut(Annotatable)) {
101 expand_deriving_encodable_imp(cx, span, mitem, item, push, "rustc_serialize")
104 pub fn expand_deriving_encodable(cx: &mut ExtCtxt<'_>,
108 push: &mut dyn FnMut(Annotatable)) {
109 expand_deriving_encodable_imp(cx, span, mitem, item, push, "serialize")
112 fn expand_deriving_encodable_imp(cx: &mut ExtCtxt<'_>,
116 push: &mut dyn FnMut(Annotatable),
117 krate: &'static str) {
118 let typaram = &*deriving::hygienic_type_parameter(item, "__S");
120 let trait_def = TraitDef {
122 attributes: Vec::new(),
123 path: Path::new_(vec![krate, "Encodable"], None, vec![], PathKind::Global),
124 additional_bounds: Vec::new(),
125 generics: LifetimeBounds::empty(),
127 supports_unions: false,
131 generics: LifetimeBounds {
132 lifetimes: Vec::new(),
135 vec![Path::new_(vec![krate, "Encoder"], None, vec![], PathKind::Global)])
138 explicit_self: borrowed_explicit_self(),
139 args: vec![(Ptr(Box::new(Literal(Path::new_local(typaram))),
140 Borrowed(None, Mutability::Mutable)), "s")],
141 ret_ty: Literal(Path::new_(
142 pathvec_std!(cx, result::Result),
144 vec![Box::new(Tuple(Vec::new())), Box::new(Literal(Path::new_(
145 vec![typaram, "Error"], None, vec![], PathKind::Local
149 attributes: Vec::new(),
151 unify_fieldless_variants: false,
152 combine_substructure: combine_substructure(Box::new(|a, b, c| {
153 encodable_substructure(a, b, c, krate)
157 associated_types: Vec::new(),
160 trait_def.expand(cx, mitem, item, push)
163 fn encodable_substructure(cx: &mut ExtCtxt<'_>,
165 substr: &Substructure<'_>,
168 let encoder = substr.nonself_args[0].clone();
169 // throw an underscore in front to suppress unused variable warnings
170 let blkarg = cx.ident_of("_e");
171 let blkencoder = cx.expr_ident(trait_span, blkarg);
172 let fn_path = cx.expr_path(cx.path_global(trait_span,
173 vec![cx.ident_of(krate),
174 cx.ident_of("Encodable"),
175 cx.ident_of("encode")]));
177 return match *substr.fields {
178 Struct(_, ref fields) => {
179 let emit_struct_field = cx.ident_of("emit_struct_field");
180 let mut stmts = Vec::new();
181 for (i, &FieldInfo { name, ref self_, span, .. }) in fields.iter().enumerate() {
182 let name = match name {
184 None => Symbol::intern(&format!("_field{}", i)),
186 let self_ref = cx.expr_addr_of(span, self_.clone());
187 let enc = cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
188 let lambda = cx.lambda1(span, enc, blkarg);
189 let call = cx.expr_method_call(span,
192 vec![cx.expr_str(span, name),
193 cx.expr_usize(span, i),
196 // last call doesn't need a try!
197 let last = fields.len() - 1;
198 let call = if i != last {
199 cx.expr_try(span, call)
201 cx.expr(span, ExprKind::Ret(Some(call)))
204 let stmt = cx.stmt_expr(call);
208 // unit structs have no fields and need to return Ok()
209 let blk = if stmts.is_empty() {
210 let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
211 cx.lambda1(trait_span, ok, blkarg)
213 cx.lambda_stmts_1(trait_span, stmts, blkarg)
216 cx.expr_method_call(trait_span,
218 cx.ident_of("emit_struct"),
219 vec![cx.expr_str(trait_span, substr.type_ident.name),
220 cx.expr_usize(trait_span, fields.len()),
224 EnumMatching(idx, _, variant, ref fields) => {
225 // We're not generating an AST that the borrow checker is expecting,
226 // so we need to generate a unique local variable to take the
227 // mutable loan out on, otherwise we get conflicts which don't
229 let me = cx.stmt_let(trait_span, false, blkarg, encoder);
230 let encoder = cx.expr_ident(trait_span, blkarg);
231 let emit_variant_arg = cx.ident_of("emit_enum_variant_arg");
232 let mut stmts = Vec::new();
233 if !fields.is_empty() {
234 let last = fields.len() - 1;
235 for (i, &FieldInfo { ref self_, span, .. }) in fields.iter().enumerate() {
236 let self_ref = cx.expr_addr_of(span, self_.clone());
238 cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
239 let lambda = cx.lambda1(span, enc, blkarg);
240 let call = cx.expr_method_call(span,
243 vec![cx.expr_usize(span, i), lambda]);
244 let call = if i != last {
245 cx.expr_try(span, call)
247 cx.expr(span, ExprKind::Ret(Some(call)))
249 stmts.push(cx.stmt_expr(call));
252 let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
253 let ret_ok = cx.expr(trait_span, ExprKind::Ret(Some(ok)));
254 stmts.push(cx.stmt_expr(ret_ok));
257 let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
258 let name = cx.expr_str(trait_span, variant.node.ident.name);
259 let call = cx.expr_method_call(trait_span,
261 cx.ident_of("emit_enum_variant"),
263 cx.expr_usize(trait_span, idx),
264 cx.expr_usize(trait_span, fields.len()),
266 let blk = cx.lambda1(trait_span, call, blkarg);
267 let ret = cx.expr_method_call(trait_span,
269 cx.ident_of("emit_enum"),
270 vec![cx.expr_str(trait_span ,substr.type_ident.name),
272 cx.expr_block(cx.block(trait_span, vec![me, cx.stmt_expr(ret)]))
275 _ => cx.bug("expected Struct or EnumMatching in derive(Encodable)"),