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//! The compiler code necessary for `#[derive(RustcDecodable)]`. See encodable.rs for more.
use crate::deriving::pathvec_std;
use crate::deriving::generic::*;
use crate::deriving::generic::ty::*;
use syntax::ast;
use syntax::ast::{Expr, MetaItem, Mutability};
use syntax::ext::base::{Annotatable, ExtCtxt};
use syntax::ptr::P;
use syntax::symbol::Symbol;
use syntax_pos::Span;
pub fn expand_deriving_rustc_decodable(cx: &mut ExtCtxt<'_>,
span: Span,
mitem: &MetaItem,
item: &Annotatable,
push: &mut dyn FnMut(Annotatable)) {
let krate = "rustc_serialize";
let typaram = "__D";
let trait_def = TraitDef {
span,
attributes: Vec::new(),
path: Path::new_(vec![krate, "Decodable"], None, vec![], PathKind::Global),
additional_bounds: Vec::new(),
generics: LifetimeBounds::empty(),
is_unsafe: false,
supports_unions: false,
methods: vec![MethodDef {
name: "decode",
generics: LifetimeBounds {
lifetimes: Vec::new(),
bounds: vec![(typaram,
vec![Path::new_(vec![krate, "Decoder"],
None,
vec![],
PathKind::Global)])],
},
explicit_self: None,
args: vec![(Ptr(Box::new(Literal(Path::new_local(typaram))),
Borrowed(None, Mutability::Mutable)), "d")],
ret_ty:
Literal(Path::new_(pathvec_std!(cx, result::Result),
None,
vec![Box::new(Self_), Box::new(Literal(Path::new_(
vec![typaram, "Error"], None, vec![], PathKind::Local
)))],
PathKind::Std)),
attributes: Vec::new(),
is_unsafe: false,
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: &str)
-> P<Expr> {
let decoder = substr.nonself_args[0].clone();
let recurse = vec![
cx.ident_of(krate, trait_span),
cx.ident_of("Decodable", trait_span),
cx.ident_of("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 = cx.ident_of("_d", trait_span);
let blkdecoder = cx.expr_ident(trait_span, blkarg);
return match *substr.fields {
StaticStruct(_, ref summary) => {
let nfields = match *summary {
Unnamed(ref fields, _) => fields.len(),
Named(ref fields) => fields.len(),
};
let read_struct_field = cx.ident_of("read_struct_field", trait_span);
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_method_call(span,
blkdecoder.clone(),
read_struct_field,
vec![cx.expr_str(span, name),
cx.expr_usize(span, field),
exprdecode.clone()]))
});
let result = cx.expr_ok(trait_span, result);
cx.expr_method_call(trait_span,
decoder,
cx.ident_of("read_struct", trait_span),
vec![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 = cx.ident_of("i", trait_span);
let mut arms = Vec::with_capacity(fields.len() + 1);
let mut variants = Vec::with_capacity(fields.len());
let rvariant_arg = cx.ident_of("read_enum_variant_arg", trait_span);
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_method_call(span,
blkdecoder.clone(),
rvariant_arg,
vec![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_vec = cx.expr_vec(trait_span, variants);
let variant_vec = cx.expr_addr_of(trait_span, variant_vec);
let result = cx.expr_method_call(trait_span,
blkdecoder,
cx.ident_of("read_enum_variant", trait_span),
vec![variant_vec, lambda]);
cx.expr_method_call(trait_span,
decoder,
cx.ident_of("read_enum", trait_span),
vec![cx.expr_str(trait_span, substr.type_ident.name),
cx.lambda1(trait_span, result, blkarg)])
}
_ => cx.bug("expected StaticEnum or StaticStruct in derive(Decodable)"),
};
}
/// 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)
}
}
}