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//! The compiler code necessary for `#[derive(RustcDecodable)]`. See encodable.rs for more.
use crate::deriving::generic::ty::*;
use crate::deriving::generic::*;
use crate::deriving::pathvec_std;
use rustc_ast::ptr::P;
use rustc_ast::{self as ast, Expr, MetaItem, Mutability};
use rustc_expand::base::{Annotatable, ExtCtxt};
use rustc_span::symbol::{sym, Ident, Symbol};
use rustc_span::Span;
pub fn expand_deriving_rustc_decodable(
cx: &mut ExtCtxt<'_>,
span: Span,
mitem: &MetaItem,
item: &Annotatable,
push: &mut dyn FnMut(Annotatable),
) {
let krate = sym::rustc_serialize;
let typaram = sym::__D;
let trait_def = TraitDef {
span,
path: Path::new_(vec![krate, sym::Decodable], vec![], PathKind::Global),
skip_path_as_bound: false,
additional_bounds: Vec::new(),
generics: Bounds::empty(),
supports_unions: false,
methods: vec![MethodDef {
name: sym::decode,
generics: Bounds {
bounds: vec![(
typaram,
vec![Path::new_(vec![krate, sym::Decoder], vec![], PathKind::Global)],
)],
},
explicit_self: false,
nonself_args: vec![(
Ref(Box::new(Path(Path::new_local(typaram))), Mutability::Mut),
sym::d,
)],
ret_ty: Path(Path::new_(
pathvec_std!(result::Result),
vec![
Box::new(Self_),
Box::new(Path(Path::new_(vec![typaram, sym::Error], vec![], PathKind::Local))),
],
PathKind::Std,
)),
attributes: ast::AttrVec::new(),
unify_fieldless_variants: false,
combine_substructure: combine_substructure(Box::new(|a, b, c| {
decodable_substructure(a, b, c, krate)
})),
}],
associated_types: Vec::new(),
};
trait_def.expand(cx, mitem, item, push)
}
fn decodable_substructure(
cx: &mut ExtCtxt<'_>,
trait_span: Span,
substr: &Substructure<'_>,
krate: Symbol,
) -> BlockOrExpr {
let decoder = substr.nonselflike_args[0].clone();
let recurse = vec![
Ident::new(krate, trait_span),
Ident::new(sym::Decodable, trait_span),
Ident::new(sym::decode, trait_span),
];
let exprdecode = cx.expr_path(cx.path_global(trait_span, recurse));
// throw an underscore in front to suppress unused variable warnings
let blkarg = Ident::new(sym::_d, trait_span);
let blkdecoder = cx.expr_ident(trait_span, blkarg);
let expr = match *substr.fields {
StaticStruct(_, ref summary) => {
let nfields = match *summary {
Unnamed(ref fields, _) => fields.len(),
Named(ref fields) => fields.len(),
};
let fn_read_struct_field_path: Vec<_> =
cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_struct_field]);
let path = cx.path_ident(trait_span, substr.type_ident);
let result =
decode_static_fields(cx, trait_span, path, summary, |cx, span, name, field| {
cx.expr_try(
span,
cx.expr_call_global(
span,
fn_read_struct_field_path.clone(),
vec![
blkdecoder.clone(),
cx.expr_str(span, name),
cx.expr_usize(span, field),
exprdecode.clone(),
],
),
)
});
let result = cx.expr_ok(trait_span, result);
let fn_read_struct_path: Vec<_> =
cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_struct]);
cx.expr_call_global(
trait_span,
fn_read_struct_path,
vec![
decoder,
cx.expr_str(trait_span, substr.type_ident.name),
cx.expr_usize(trait_span, nfields),
cx.lambda1(trait_span, result, blkarg),
],
)
}
StaticEnum(_, ref fields) => {
let variant = Ident::new(sym::i, trait_span);
let mut arms = Vec::with_capacity(fields.len() + 1);
let mut variants = Vec::with_capacity(fields.len());
let fn_read_enum_variant_arg_path: Vec<_> =
cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_enum_variant_arg]);
for (i, &(ident, v_span, ref parts)) in fields.iter().enumerate() {
variants.push(cx.expr_str(v_span, ident.name));
let path = cx.path(trait_span, vec![substr.type_ident, ident]);
let decoded =
decode_static_fields(cx, v_span, path, parts, |cx, span, _, field| {
let idx = cx.expr_usize(span, field);
cx.expr_try(
span,
cx.expr_call_global(
span,
fn_read_enum_variant_arg_path.clone(),
vec![blkdecoder.clone(), idx, exprdecode.clone()],
),
)
});
arms.push(cx.arm(v_span, cx.pat_lit(v_span, cx.expr_usize(v_span, i)), decoded));
}
arms.push(cx.arm_unreachable(trait_span));
let result = cx.expr_ok(
trait_span,
cx.expr_match(trait_span, cx.expr_ident(trait_span, variant), arms),
);
let lambda = cx.lambda(trait_span, vec![blkarg, variant], result);
let variant_array_ref = cx.expr_array_ref(trait_span, variants);
let fn_read_enum_variant_path: Vec<_> =
cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_enum_variant]);
let result = cx.expr_call_global(
trait_span,
fn_read_enum_variant_path,
vec![blkdecoder, variant_array_ref, lambda],
);
let fn_read_enum_path: Vec<_> =
cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_enum]);
cx.expr_call_global(
trait_span,
fn_read_enum_path,
vec![
decoder,
cx.expr_str(trait_span, substr.type_ident.name),
cx.lambda1(trait_span, result, blkarg),
],
)
}
_ => cx.bug("expected StaticEnum or StaticStruct in derive(Decodable)"),
};
BlockOrExpr::new_expr(expr)
}
/// Creates a decoder for a single enum variant/struct:
/// - `outer_pat_path` is the path to this enum variant/struct
/// - `getarg` should retrieve the `usize`-th field with name `@str`.
fn decode_static_fields<F>(
cx: &mut ExtCtxt<'_>,
trait_span: Span,
outer_pat_path: ast::Path,
fields: &StaticFields,
mut getarg: F,
) -> P<Expr>
where
F: FnMut(&mut ExtCtxt<'_>, Span, Symbol, usize) -> P<Expr>,
{
match *fields {
Unnamed(ref fields, is_tuple) => {
let path_expr = cx.expr_path(outer_pat_path);
if !is_tuple {
path_expr
} else {
let fields = fields
.iter()
.enumerate()
.map(|(i, &span)| getarg(cx, span, Symbol::intern(&format!("_field{}", i)), i))
.collect();
cx.expr_call(trait_span, path_expr, fields)
}
}
Named(ref fields) => {
// use the field's span to get nicer error messages.
let fields = fields
.iter()
.enumerate()
.map(|(i, &(ident, span))| {
let arg = getarg(cx, span, ident.name, i);
cx.field_imm(span, ident, arg)
})
.collect();
cx.expr_struct(trait_span, outer_pat_path, fields)
}
}
}
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