[rustc.git] / src / libsyntax_ext / deriving / encodable.rs

// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! The compiler code necessary to implement the `#[derive(Encodable)]`
//! (and `Decodable`, in decodable.rs) extension.  The idea here is that
//! type-defining items may be tagged with `#[derive(Encodable, Decodable)]`.
//!
//! For example, a type like:
//!
//! ```ignore
//! #[derive(Encodable, Decodable)]
//! struct Node { id: usize }
//! ```
//!
//! would generate two implementations like:
//!
//! ```ignore
//! impl<S: Encoder<E>, E> Encodable<S, E> for Node {
//!     fn encode(&self, s: &mut S) -> Result<(), E> {
//!         s.emit_struct("Node", 1, |this| {
//!             this.emit_struct_field("id", 0, |this| {
//!                 Encodable::encode(&self.id, this)
//!                 /* this.emit_usize(self.id) can also be used */
//!             })
//!         })
//!     }
//! }
//!
//! impl<D: Decoder<E>, E> Decodable<D, E> for Node {
//!     fn decode(d: &mut D) -> Result<Node, E> {
//!         d.read_struct("Node", 1, |this| {
//!             match this.read_struct_field("id", 0, |this| Decodable::decode(this)) {
//!                 Ok(id) => Ok(Node { id: id }),
//!                 Err(e) => Err(e),
//!             }
//!         })
//!     }
//! }
//! ```
//!
//! Other interesting scenarios are when the item has type parameters or
//! references other non-built-in types.  A type definition like:
//!
//! ```ignore
//! #[derive(Encodable, Decodable)]
//! struct Spanned<T> { node: T, span: Span }
//! ```
//!
//! would yield functions like:
//!
//! ```ignore
//! impl<
//!     S: Encoder<E>,
//!     E,
//!     T: Encodable<S, E>
//! > Encodable<S, E> for Spanned<T> {
//!     fn encode(&self, s: &mut S) -> Result<(), E> {
//!         s.emit_struct("Spanned", 2, |this| {
//!             this.emit_struct_field("node", 0, |this| self.node.encode(this))
//!                 .unwrap();
//!             this.emit_struct_field("span", 1, |this| self.span.encode(this))
//!         })
//!     }
//! }
//!
//! impl<
//!     D: Decoder<E>,
//!     E,
//!     T: Decodable<D, E>
//! > Decodable<D, E> for Spanned<T> {
//!     fn decode(d: &mut D) -> Result<Spanned<T>, E> {
//!         d.read_struct("Spanned", 2, |this| {
//!             Ok(Spanned {
//!                 node: this.read_struct_field("node", 0, |this| Decodable::decode(this))
//!                     .unwrap(),
//!                 span: this.read_struct_field("span", 1, |this| Decodable::decode(this))
//!                     .unwrap(),
//!             })
//!         })
//!     }
//! }
//! ```

use deriving;
use deriving::generic::*;
use deriving::generic::ty::*;

use syntax::ast::{Expr, ExprKind, MetaItem, Mutability};
use syntax::ext::base::{Annotatable, ExtCtxt};
use syntax::ext::build::AstBuilder;
use syntax::parse::token;
use syntax::ptr::P;
use syntax_pos::Span;

pub fn expand_deriving_rustc_encodable(cx: &mut ExtCtxt,
                                       span: Span,
                                       mitem: &MetaItem,
                                       item: &Annotatable,
                                       push: &mut FnMut(Annotatable)) {
    expand_deriving_encodable_imp(cx, span, mitem, item, push, "rustc_serialize")
}

pub fn expand_deriving_encodable(cx: &mut ExtCtxt,
                                 span: Span,
                                 mitem: &MetaItem,
                                 item: &Annotatable,
                                 push: &mut FnMut(Annotatable)) {
    expand_deriving_encodable_imp(cx, span, mitem, item, push, "serialize")
}

fn expand_deriving_encodable_imp(cx: &mut ExtCtxt,
                                 span: Span,
                                 mitem: &MetaItem,
                                 item: &Annotatable,
                                 push: &mut FnMut(Annotatable),
                                 krate: &'static str) {
    if cx.crate_root != Some("std") {
        // FIXME(#21880): lift this requirement.
        cx.span_err(span,
                    "this trait cannot be derived with #![no_std] \
                           or #![no_core]");
        return;
    }

    let typaram = &*deriving::hygienic_type_parameter(item, "__S");

    let trait_def = TraitDef {
        span: span,
        attributes: Vec::new(),
        path: Path::new_(vec![krate, "Encodable"], None, vec![], true),
        additional_bounds: Vec::new(),
        generics: LifetimeBounds::empty(),
        is_unsafe: false,
        methods: vec!(
            MethodDef {
                name: "encode",
                generics: LifetimeBounds {
                    lifetimes: Vec::new(),
                    bounds: vec![(typaram,
                                  vec![Path::new_(vec![krate, "Encoder"], None, vec!(), true)])]
                },
                explicit_self: borrowed_explicit_self(),
                args: vec!(Ptr(Box::new(Literal(Path::new_local(typaram))),
                           Borrowed(None, Mutability::Mutable))),
                ret_ty: Literal(Path::new_(
                    pathvec_std!(cx, core::result::Result),
                    None,
                    vec!(Box::new(Tuple(Vec::new())), Box::new(Literal(Path::new_(
                        vec![typaram, "Error"], None, vec![], false
                    )))),
                    true
                )),
                attributes: Vec::new(),
                is_unsafe: false,
                unify_fieldless_variants: false,
                combine_substructure: combine_substructure(Box::new(|a, b, c| {
                    encodable_substructure(a, b, c, krate)
                })),
            }
        ),
        associated_types: Vec::new(),
    };

    trait_def.expand(cx, mitem, item, push)
}

fn encodable_substructure(cx: &mut ExtCtxt,
                          trait_span: Span,
                          substr: &Substructure,
                          krate: &'static str)
                          -> P<Expr> {
    let encoder = substr.nonself_args[0].clone();
    // throw an underscore in front to suppress unused variable warnings
    let blkarg = cx.ident_of("_e");
    let blkencoder = cx.expr_ident(trait_span, blkarg);
    let fn_path = cx.expr_path(cx.path_global(trait_span,
                                              vec![cx.ident_of(krate),
                                                   cx.ident_of("Encodable"),
                                                   cx.ident_of("encode")]));

    return match *substr.fields {
        Struct(_, ref fields) => {
            let emit_struct_field = cx.ident_of("emit_struct_field");
            let mut stmts = Vec::new();
            for (i, &FieldInfo { name, ref self_, span, .. }) in fields.iter().enumerate() {
                let name = match name {
                    Some(id) => id.name.as_str(),
                    None => token::intern_and_get_ident(&format!("_field{}", i)),
                };
                let self_ref = cx.expr_addr_of(span, self_.clone());
                let enc = cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
                let lambda = cx.lambda_expr_1(span, enc, blkarg);
                let call = cx.expr_method_call(span,
                                               blkencoder.clone(),
                                               emit_struct_field,
                                               vec![cx.expr_str(span, name),
                                                    cx.expr_usize(span, i),
                                                    lambda]);

                // last call doesn't need a try!
                let last = fields.len() - 1;
                let call = if i != last {
                    cx.expr_try(span, call)
                } else {
                    cx.expr(span, ExprKind::Ret(Some(call)))
                };
                stmts.push(cx.stmt_expr(call));
            }

            // unit structs have no fields and need to return Ok()
            if stmts.is_empty() {
                let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
                let ret_ok = cx.expr(trait_span, ExprKind::Ret(Some(ok)));
                stmts.push(cx.stmt_expr(ret_ok));
            }

            let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
            cx.expr_method_call(trait_span,
                                encoder,
                                cx.ident_of("emit_struct"),
                                vec![cx.expr_str(trait_span, substr.type_ident.name.as_str()),
                                     cx.expr_usize(trait_span, fields.len()),
                                     blk])
        }

        EnumMatching(idx, variant, ref fields) => {
            // We're not generating an AST that the borrow checker is expecting,
            // so we need to generate a unique local variable to take the
            // mutable loan out on, otherwise we get conflicts which don't
            // actually exist.
            let me = cx.stmt_let(trait_span, false, blkarg, encoder);
            let encoder = cx.expr_ident(trait_span, blkarg);
            let emit_variant_arg = cx.ident_of("emit_enum_variant_arg");
            let mut stmts = Vec::new();
            if !fields.is_empty() {
                let last = fields.len() - 1;
                for (i, &FieldInfo { ref self_, span, .. }) in fields.iter().enumerate() {
                    let self_ref = cx.expr_addr_of(span, self_.clone());
                    let enc =
                        cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
                    let lambda = cx.lambda_expr_1(span, enc, blkarg);
                    let call = cx.expr_method_call(span,
                                                   blkencoder.clone(),
                                                   emit_variant_arg,
                                                   vec![cx.expr_usize(span, i), lambda]);
                    let call = if i != last {
                        cx.expr_try(span, call)
                    } else {
                        cx.expr(span, ExprKind::Ret(Some(call)))
                    };
                    stmts.push(cx.stmt_expr(call));
                }
            } else {
                let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
                let ret_ok = cx.expr(trait_span, ExprKind::Ret(Some(ok)));
                stmts.push(cx.stmt_expr(ret_ok));
            }

            let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
            let name = cx.expr_str(trait_span, variant.node.name.name.as_str());
            let call = cx.expr_method_call(trait_span,
                                           blkencoder,
                                           cx.ident_of("emit_enum_variant"),
                                           vec![name,
                                                cx.expr_usize(trait_span, idx),
                                                cx.expr_usize(trait_span, fields.len()),
                                                blk]);
            let blk = cx.lambda_expr_1(trait_span, call, blkarg);
            let ret = cx.expr_method_call(trait_span,
                                          encoder,
                                          cx.ident_of("emit_enum"),
                                          vec![cx.expr_str(trait_span,
                                                           substr.type_ident.name.as_str()),
                                               blk]);
            cx.expr_block(cx.block(trait_span, vec![me, cx.stmt_expr(ret)]))
        }

        _ => cx.bug("expected Struct or EnumMatching in derive(Encodable)"),
    };
}
Commit	Line	Data
970d7e83 LB	1	// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
	2	// file at the top-level directory of this distribution and at
	3	// http://rust-lang.org/COPYRIGHT.
	4	//
	5	// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
	6	// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
	7	// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
	8	// option. This file may not be copied, modified, or distributed
	9	// except according to those terms.
	10
1a4d82fc JJ	11	//! The compiler code necessary to implement the `#[derive(Encodable)]`
	12	//! (and `Decodable`, in decodable.rs) extension. The idea here is that
	13	//! type-defining items may be tagged with `#[derive(Encodable, Decodable)]`.
	14	//!
	15	//! For example, a type like:
	16	//!
	17	//! ```ignore
	18	//! #[derive(Encodable, Decodable)]
85aaf69f	19	//! struct Node { id: usize }
1a4d82fc JJ	20	//! ```
	21	//!
	22	//! would generate two implementations like:
	23	//!
	24	//! ```ignore
	25	//! impl<S: Encoder<E>, E> Encodable<S, E> for Node {
	26	//! fn encode(&self, s: &mut S) -> Result<(), E> {
	27	//! s.emit_struct("Node", 1, \|this\| {
	28	//! this.emit_struct_field("id", 0, \|this\| {
	29	//! Encodable::encode(&self.id, this)
85aaf69f	30	//! /* this.emit_usize(self.id) can also be used */
1a4d82fc JJ	31	//! })
	32	//! })
	33	//! }
	34	//! }
	35	//!
	36	//! impl<D: Decoder<E>, E> Decodable<D, E> for Node {
	37	//! fn decode(d: &mut D) -> Result<Node, E> {
	38	//! d.read_struct("Node", 1, \|this\| {
	39	//! match this.read_struct_field("id", 0, \|this\| Decodable::decode(this)) {
	40	//! Ok(id) => Ok(Node { id: id }),
	41	//! Err(e) => Err(e),
	42	//! }
	43	//! })
	44	//! }
	45	//! }
	46	//! ```
	47	//!
	48	//! Other interesting scenarios are when the item has type parameters or
	49	//! references other non-built-in types. A type definition like:
	50	//!
	51	//! ```ignore
	52	//! #[derive(Encodable, Decodable)]
	53	//! struct Spanned<T> { node: T, span: Span }
	54	//! ```
	55	//!
	56	//! would yield functions like:
	57	//!
	58	//! ```ignore
	59	//! impl<
	60	//! S: Encoder<E>,
	61	//! E,
	62	//! T: Encodable<S, E>
	63	//! > Encodable<S, E> for Spanned<T> {
	64	//! fn encode(&self, s: &mut S) -> Result<(), E> {
	65	//! s.emit_struct("Spanned", 2, \|this\| {
	66	//! this.emit_struct_field("node", 0, \|this\| self.node.encode(this))
c34b1796	67	//! .unwrap();
1a4d82fc JJ	68	//! this.emit_struct_field("span", 1, \|this\| self.span.encode(this))
	69	//! })
	70	//! }
	71	//! }
	72	//!
	73	//! impl<
	74	//! D: Decoder<E>,
	75	//! E,
	76	//! T: Decodable<D, E>
	77	//! > Decodable<D, E> for Spanned<T> {
	78	//! fn decode(d: &mut D) -> Result<Spanned<T>, E> {
	79	//! d.read_struct("Spanned", 2, \|this\| {
	80	//! Ok(Spanned {
	81	//! node: this.read_struct_field("node", 0, \|this\| Decodable::decode(this))
c34b1796	82	//! .unwrap(),
1a4d82fc	83	//! span: this.read_struct_field("span", 1, \|this\| Decodable::decode(this))
c34b1796	84	//! .unwrap(),
1a4d82fc JJ	85	//! })
	86	//! })
	87	//! }
	88	//! }
	89	//! ```
970d7e83	90
54a0048b	91	use deriving;
9cc50fc6 SL	92	use deriving::generic::*;
	93	use deriving::generic::ty::*;
	94
5bcae85e SL	95	use syntax::ast::{Expr, ExprKind, MetaItem, Mutability};
5bcae85e SL	96	use syntax::ext::base::{Annotatable, ExtCtxt};
9cc50fc6 SL	97	use syntax::ext::build::AstBuilder;
	98	use syntax::parse::token;
	99	use syntax::ptr::P;
3157f602	100	use syntax_pos::Span;
970d7e83	101
d9579d0f AL	102	pub fn expand_deriving_rustc_encodable(cx: &mut ExtCtxt,
	103	span: Span,
	104	mitem: &MetaItem,
62682a34	105	item: &Annotatable,
5bcae85e	106	push: &mut FnMut(Annotatable)) {
1a4d82fc	107	expand_deriving_encodable_imp(cx, span, mitem, item, push, "rustc_serialize")
970d7e83 LB	108	}
970d7e83 LB	109
d9579d0f AL	110	pub fn expand_deriving_encodable(cx: &mut ExtCtxt,
	111	span: Span,
	112	mitem: &MetaItem,
62682a34	113	item: &Annotatable,
5bcae85e	114	push: &mut FnMut(Annotatable)) {
1a4d82fc	115	expand_deriving_encodable_imp(cx, span, mitem, item, push, "serialize")
970d7e83 LB	116	}
970d7e83 LB	117
d9579d0f AL	118	fn expand_deriving_encodable_imp(cx: &mut ExtCtxt,
	119	span: Span,
	120	mitem: &MetaItem,
62682a34	121	item: &Annotatable,
d9579d0f	122	push: &mut FnMut(Annotatable),
5bcae85e	123	krate: &'static str) {
e9174d1e	124	if cx.crate_root != Some("std") {
85aaf69f	125	// FIXME(#21880): lift this requirement.
5bcae85e SL	126	cx.span_err(span,
5bcae85e SL	127	"this trait cannot be derived with #![no_std] \
e9174d1e	128	or #![no_core]");
85aaf69f SL	129	return;
	130	}
	131
54a0048b SL	132	let typaram = &*deriving::hygienic_type_parameter(item, "__S");
54a0048b SL	133
970d7e83	134	let trait_def = TraitDef {
1a4d82fc JJ	135	span: span,
1a4d82fc JJ	136	attributes: Vec::new(),
5bcae85e	137	path: Path::new_(vec![krate, "Encodable"], None, vec![], true),
1a4d82fc JJ	138	additional_bounds: Vec::new(),
1a4d82fc JJ	139	generics: LifetimeBounds::empty(),
e9174d1e	140	is_unsafe: false,
1a4d82fc	141	methods: vec!(
970d7e83 LB	142	MethodDef {
970d7e83 LB	143	name: "encode",
1a4d82fc JJ	144	generics: LifetimeBounds {
1a4d82fc JJ	145	lifetimes: Vec::new(),
54a0048b SL	146	bounds: vec![(typaram,
54a0048b SL	147	vec![Path::new_(vec![krate, "Encoder"], None, vec!(), true)])]
1a4d82fc JJ	148	},
1a4d82fc JJ	149	explicit_self: borrowed_explicit_self(),
54a0048b	150	args: vec!(Ptr(Box::new(Literal(Path::new_local(typaram))),
a7813a04	151	Borrowed(None, Mutability::Mutable))),
1a4d82fc	152	ret_ty: Literal(Path::new_(
85aaf69f	153	pathvec_std!(cx, core::result::Result),
1a4d82fc	154	None,
d9579d0f	155	vec!(Box::new(Tuple(Vec::new())), Box::new(Literal(Path::new_(
54a0048b	156	vec![typaram, "Error"], None, vec![], false
d9579d0f	157	)))),
1a4d82fc JJ	158	true
	159	)),
	160	attributes: Vec::new(),
62682a34	161	is_unsafe: false,
a7813a04	162	unify_fieldless_variants: false,
c34b1796	163	combine_substructure: combine_substructure(Box::new(\|a, b, c\| {
a7813a04	164	encodable_substructure(a, b, c, krate)
c34b1796	165	})),
85aaf69f SL	166	}
	167	),
	168	associated_types: Vec::new(),
970d7e83 LB	169	};
970d7e83 LB	170
62682a34	171	trait_def.expand(cx, mitem, item, push)
970d7e83 LB	172	}
970d7e83 LB	173
5bcae85e SL	174	fn encodable_substructure(cx: &mut ExtCtxt,
	175	trait_span: Span,
	176	substr: &Substructure,
	177	krate: &'static str)
	178	-> P<Expr> {
1a4d82fc	179	let encoder = substr.nonself_args[0].clone();
970d7e83 LB	180	// throw an underscore in front to suppress unused variable warnings
970d7e83 LB	181	let blkarg = cx.ident_of("_e");
1a4d82fc	182	let blkencoder = cx.expr_ident(trait_span, blkarg);
5bcae85e SL	183	let fn_path = cx.expr_path(cx.path_global(trait_span,
	184	vec![cx.ident_of(krate),
	185	cx.ident_of("Encodable"),
	186	cx.ident_of("encode")]));
970d7e83 LB	187
970d7e83 LB	188	return match *substr.fields {
7453a54e	189	Struct(_, ref fields) => {
970d7e83	190	let emit_struct_field = cx.ident_of("emit_struct_field");
1a4d82fc	191	let mut stmts = Vec::new();
5bcae85e	192	for (i, &FieldInfo { name, ref self_, span, .. }) in fields.iter().enumerate() {
1a4d82fc	193	let name = match name {
c1a9b12d	194	Some(id) => id.name.as_str(),
5bcae85e	195	None => token::intern_and_get_ident(&format!("_field{}", i)),
970d7e83	196	};
a7813a04 XL	197	let self_ref = cx.expr_addr_of(span, self_.clone());
a7813a04 XL	198	let enc = cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
970d7e83	199	let lambda = cx.lambda_expr_1(span, enc, blkarg);
5bcae85e SL	200	let call = cx.expr_method_call(span,
5bcae85e SL	201	blkencoder.clone(),
970d7e83	202	emit_struct_field,
5bcae85e SL	203	vec![cx.expr_str(span, name),
	204	cx.expr_usize(span, i),
	205	lambda]);
1a4d82fc JJ	206
1a4d82fc JJ	207	// last call doesn't need a try!
c34b1796	208	let last = fields.len() - 1;
1a4d82fc JJ	209	let call = if i != last {
	210	cx.expr_try(span, call)
	211	} else {
7453a54e	212	cx.expr(span, ExprKind::Ret(Some(call)))
1a4d82fc	213	};
970d7e83 LB	214	stmts.push(cx.stmt_expr(call));
	215	}
	216
1a4d82fc JJ	217	// unit structs have no fields and need to return Ok()
1a4d82fc JJ	218	if stmts.is_empty() {
7453a54e SL	219	let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
7453a54e SL	220	let ret_ok = cx.expr(trait_span, ExprKind::Ret(Some(ok)));
1a4d82fc JJ	221	stmts.push(cx.stmt_expr(ret_ok));
	222	}
	223
	224	let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
	225	cx.expr_method_call(trait_span,
	226	encoder,
	227	cx.ident_of("emit_struct"),
5bcae85e SL	228	vec![cx.expr_str(trait_span, substr.type_ident.name.as_str()),
	229	cx.expr_usize(trait_span, fields.len()),
	230	blk])
970d7e83 LB	231	}
	232
	233	EnumMatching(idx, variant, ref fields) => {
	234	// We're not generating an AST that the borrow checker is expecting,
	235	// so we need to generate a unique local variable to take the
	236	// mutable loan out on, otherwise we get conflicts which don't
	237	// actually exist.
1a4d82fc JJ	238	let me = cx.stmt_let(trait_span, false, blkarg, encoder);
1a4d82fc JJ	239	let encoder = cx.expr_ident(trait_span, blkarg);
970d7e83	240	let emit_variant_arg = cx.ident_of("emit_enum_variant_arg");
1a4d82fc	241	let mut stmts = Vec::new();
9346a6ac	242	if !fields.is_empty() {
c34b1796 AL	243	let last = fields.len() - 1;
c34b1796 AL	244	for (i, &FieldInfo { ref self_, span, .. }) in fields.iter().enumerate() {
5bcae85e SL	245	let self_ref = cx.expr_addr_of(span, self_.clone());
	246	let enc =
	247	cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
c34b1796	248	let lambda = cx.lambda_expr_1(span, enc, blkarg);
5bcae85e SL	249	let call = cx.expr_method_call(span,
5bcae85e SL	250	blkencoder.clone(),
c34b1796	251	emit_variant_arg,
5bcae85e	252	vec![cx.expr_usize(span, i), lambda]);
c34b1796 AL	253	let call = if i != last {
	254	cx.expr_try(span, call)
	255	} else {
7453a54e	256	cx.expr(span, ExprKind::Ret(Some(call)))
c34b1796 AL	257	};
	258	stmts.push(cx.stmt_expr(call));
	259	}
	260	} else {
7453a54e SL	261	let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
7453a54e SL	262	let ret_ok = cx.expr(trait_span, ExprKind::Ret(Some(ok)));
1a4d82fc JJ	263	stmts.push(cx.stmt_expr(ret_ok));
	264	}
	265
	266	let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
c1a9b12d	267	let name = cx.expr_str(trait_span, variant.node.name.name.as_str());
5bcae85e SL	268	let call = cx.expr_method_call(trait_span,
5bcae85e SL	269	blkencoder,
970d7e83	270	cx.ident_of("emit_enum_variant"),
5bcae85e SL	271	vec![name,
	272	cx.expr_usize(trait_span, idx),
	273	cx.expr_usize(trait_span, fields.len()),
	274	blk]);
1a4d82fc JJ	275	let blk = cx.lambda_expr_1(trait_span, call, blkarg);
	276	let ret = cx.expr_method_call(trait_span,
	277	encoder,
970d7e83	278	cx.ident_of("emit_enum"),
5bcae85e SL	279	vec![cx.expr_str(trait_span,
	280	substr.type_ident.name.as_str()),
	281	blk]);
3157f602	282	cx.expr_block(cx.block(trait_span, vec![me, cx.stmt_expr(ret)]))
970d7e83 LB	283	}
970d7e83 LB	284
5bcae85e	285	_ => cx.bug("expected Struct or EnumMatching in derive(Encodable)"),
970d7e83 LB	286	};
970d7e83 LB	287	}