Disambiguate Error type in TryFrom (#29)

* disambiguate Error type in TryFrom

* add testcase for enum with error variant

Author: cmrschwarz

src/build.rs

@@ -180,7 +180,7 @@ impl Enum {
             impl #parent_impl core::convert::TryFrom<#parent_ident #parent_ty> for #child_ident #child_ty #parent_where {
                 type Error = #error;
 
-                fn try_from(parent: #parent_ident #parent_ty) -> Result<Self, Self::Error> {
+                fn try_from(parent: #parent_ident #parent_ty) -> Result<Self, <Self as core::convert::TryFrom<#parent_ident #parent_ty>>::Error> {
                     match parent {
                         #(#try_from_parent_arms),*,
                         _ => Err(#error)

tests/it.rs

@@ -72,3 +72,18 @@ enum Whew<'a: 'b, 'b, 'c, T, U> {
     #[subenum(Phew)]
     B(&'b [&'c [U; 7]]),
 }
+
+#[subenum(SubEnumWithErrorVariant)]
+#[derive(Debug, Clone, Copy, PartialEq)]
+enum EnumWithErrorVariant {
+    #[subenum(SubEnumWithErrorVariant)]
+    Error,
+}
+
+#[test]
+fn test_enum_with_error_variant() {
+    let a = EnumWithErrorVariant::Error;
+    let b = SubEnumWithErrorVariant::try_from(a).unwrap();
+
+    assert_eq!(a, b);
+}