Fix derive(Decode) for enums with lifetime parameters and struct-like variants

derive/src/decode.rs

@@ -50,7 +50,7 @@ pub fn quote(
 				let index = utils::variant_index(v, i);
 
 				let create = create_instance(
-					quote! { #type_name #type_generics :: #name },
+					quote! { #type_name :: #name #type_generics },
 					&format!("{}::{}", type_name, name),
 					input,
 					&v.fields,

tests/mod.rs

@@ -12,6 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use std::borrow::Cow;
+
 use parity_scale_codec::{
 	Compact, CompactAs, Decode, DecodeWithMemTracking, Encode, EncodeAsRef, Error, HasCompact,
 	Output,
@@ -941,3 +943,29 @@ fn non_literal_variant_discriminant() {
 		B = A + 1,
 	}
 }
+
+#[test]
+fn derive_decode_for_enum_with_lifetime_param_and_struct_like_variant() {
+	// An enum that has a lifetime parameter and a struct-like variant.
+	#[derive(PartialEq, Eq, Debug, DeriveDecode, DeriveEncode)]
+	enum Enum<'a> {
+		StructLike { val: u8 },
+		// For completeness, also check a struct-like variant that actually uses the lifetime,
+		// as well as the corresponding tuple-like variants.
+		StructLikeCow { val: Cow<'a, u8> },
+		TupleLike(u8),
+		TupleLikeCow(Cow<'a, u8>),
+	}
+
+	let val = 123;
+	let objs = vec![
+		Enum::StructLike { val: 234 },
+		Enum::StructLikeCow { val: Cow::Borrowed(&val) },
+		Enum::TupleLike(234),
+		Enum::TupleLikeCow(Cow::Borrowed(&val)),
+	];
+
+	let data = objs.encode();
+	let objs_d = Vec::<Enum>::decode(&mut &data[..]).unwrap();
+	assert_eq!(objs_d, objs);
+}