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//! The compiler code necessary to implement the `#[derive(RustcEncodable)]`
//! (and `RustcDecodable`, in `decodable.rs`) extension. The idea here is that
//! type-defining items may be tagged with
//! `#[derive(RustcEncodable, RustcDecodable)]`.
//!
//! For example, a type like:
//!
//! ```ignore (old code)
//! #[derive(RustcEncodable, RustcDecodable)]
//! struct Node { id: usize }
//! ```
//!
//! would generate two implementations like:
//!
//! ```ignore (old code)
//! # struct Node { id: usize }
//! 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 (old code)
//! # #[derive(RustcEncodable, RustcDecodable)]
//! # struct Span;
//! #[derive(RustcEncodable, RustcDecodable)]
//! struct Spanned<T> { node: T, span: Span }
//! ```
//!
//! would yield functions like:
//!
//! ```ignore (old code)
//! # #[derive(RustcEncodable, RustcDecodable)]
//! # struct Span;
//! # struct Spanned<T> { node: T, span: Span }
//! 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 crate::deriving::generic::ty::*;
use crate::deriving::generic::*;
use crate::deriving::pathvec_std;
use rustc_ast::{AttrVec, ExprKind, MetaItem, Mutability};
use rustc_expand::base::{Annotatable, ExtCtxt};
use rustc_span::symbol::{sym, Ident, Symbol};
use rustc_span::Span;
use thin_vec::{thin_vec, ThinVec};
pub fn expand_deriving_rustc_encodable(
cx: &mut ExtCtxt<'_>,
span: Span,
mitem: &MetaItem,
item: &Annotatable,
push: &mut dyn FnMut(Annotatable),
is_const: bool,
) {
let krate = sym::rustc_serialize;
let typaram = sym::__S;
let trait_def = TraitDef {
span,
path: Path::new_(vec![krate, sym::Encodable], vec![], PathKind::Global),
skip_path_as_bound: false,
needs_copy_as_bound_if_packed: true,
additional_bounds: Vec::new(),
supports_unions: false,
methods: vec![MethodDef {
name: sym::encode,
generics: Bounds {
bounds: vec![(
typaram,
vec![Path::new_(vec![krate, sym::Encoder], vec![], PathKind::Global)],
)],
},
explicit_self: true,
nonself_args: vec![(
Ref(Box::new(Path(Path::new_local(typaram))), Mutability::Mut),
sym::s,
)],
ret_ty: Path(Path::new_(
pathvec_std!(result::Result),
vec![
Box::new(Unit),
Box::new(Path(Path::new_(vec![typaram, sym::Error], vec![], PathKind::Local))),
],
PathKind::Std,
)),
attributes: AttrVec::new(),
fieldless_variants_strategy: FieldlessVariantsStrategy::Default,
combine_substructure: combine_substructure(Box::new(|a, b, c| {
encodable_substructure(a, b, c, krate)
})),
}],
associated_types: Vec::new(),
is_const,
};
trait_def.expand(cx, mitem, item, push)
}
fn encodable_substructure(
cx: &mut ExtCtxt<'_>,
trait_span: Span,
substr: &Substructure<'_>,
krate: Symbol,
) -> BlockOrExpr {
let encoder = substr.nonselflike_args[0].clone();
// throw an underscore in front to suppress unused variable warnings
let blkarg = Ident::new(sym::_e, trait_span);
let blkencoder = cx.expr_ident(trait_span, blkarg);
let fn_path = cx.expr_path(cx.path_global(
trait_span,
vec![
Ident::new(krate, trait_span),
Ident::new(sym::Encodable, trait_span),
Ident::new(sym::encode, trait_span),
],
));
match substr.fields {
Struct(_, fields) => {
let fn_emit_struct_field_path =
cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_struct_field]);
let mut stmts = ThinVec::new();
for (i, &FieldInfo { name, ref self_expr, span, .. }) in fields.iter().enumerate() {
let name = match name {
Some(id) => id.name,
None => Symbol::intern(&format!("_field{i}")),
};
let self_ref = cx.expr_addr_of(span, self_expr.clone());
let enc =
cx.expr_call(span, fn_path.clone(), thin_vec![self_ref, blkencoder.clone()]);
let lambda = cx.lambda1(span, enc, blkarg);
let call = cx.expr_call_global(
span,
fn_emit_struct_field_path.clone(),
thin_vec![
blkencoder.clone(),
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)))
};
let stmt = cx.stmt_expr(call);
stmts.push(stmt);
}
// unit structs have no fields and need to return Ok()
let blk = if stmts.is_empty() {
let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, ThinVec::new()));
cx.lambda1(trait_span, ok, blkarg)
} else {
cx.lambda_stmts_1(trait_span, stmts, blkarg)
};
let fn_emit_struct_path =
cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_struct]);
let expr = cx.expr_call_global(
trait_span,
fn_emit_struct_path,
thin_vec![
encoder,
cx.expr_str(trait_span, substr.type_ident.name),
cx.expr_usize(trait_span, fields.len()),
blk,
],
);
BlockOrExpr::new_expr(expr)
}
EnumMatching(idx, _, variant, 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 fn_emit_enum_variant_arg_path: Vec<_> =
cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_enum_variant_arg]);
let mut stmts = ThinVec::new();
if !fields.is_empty() {
let last = fields.len() - 1;
for (i, &FieldInfo { ref self_expr, span, .. }) in fields.iter().enumerate() {
let self_ref = cx.expr_addr_of(span, self_expr.clone());
let enc = cx.expr_call(
span,
fn_path.clone(),
thin_vec![self_ref, blkencoder.clone()],
);
let lambda = cx.lambda1(span, enc, blkarg);
let call = cx.expr_call_global(
span,
fn_emit_enum_variant_arg_path.clone(),
thin_vec![blkencoder.clone(), 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, ThinVec::new()));
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.ident.name);
let fn_emit_enum_variant_path: Vec<_> =
cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_enum_variant]);
let call = cx.expr_call_global(
trait_span,
fn_emit_enum_variant_path,
thin_vec![
blkencoder,
name,
cx.expr_usize(trait_span, *idx),
cx.expr_usize(trait_span, fields.len()),
blk,
],
);
let blk = cx.lambda1(trait_span, call, blkarg);
let fn_emit_enum_path: Vec<_> =
cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_enum]);
let expr = cx.expr_call_global(
trait_span,
fn_emit_enum_path,
thin_vec![encoder, cx.expr_str(trait_span, substr.type_ident.name), blk],
);
BlockOrExpr::new_mixed(thin_vec![me], Some(expr))
}
_ => cx.bug("expected Struct or EnumMatching in derive(Encodable)"),
}
}