Enum variant aliases don't work

[momvart]

Here is a failing example demonstrating that enum variant aliases are not taken into account. It also shows a divergence in behavior compared to using serde_json directly.

#[derive(Debug, serde::Deserialize)]
enum TestEnum {
    #[serde(alias = "f")]
    Foo,
    #[serde(alias = "b")]
    Bar,
}

#[derive(Debug, serde::Deserialize)]
struct Wrapper {
    test: TestEnum,
}

let json = r#"{"test": "f"}"#;
let w: Wrapper = serde_json::from_str(json).unwrap();
println!("{:?}", w);
let w: Wrapper = config::Config::builder()
    .add_source(config::File::from_str(json, config::FileFormat::Json))
    .build()
    .unwrap()
    .try_deserialize()
    .unwrap();
println!("{:?}", w);

Output:

Wrapper { t: Foo }
called `Result::unwrap()` on an `Err` value: enum TestEnum does not have variant constructor f

[sunmy2019]

In config-rs, the variant_seed cannot create a deserializer on enums with unrecognized values.

https://github.com/mehcode/config-rs/blob/57fb2610ad274dff1d2f2e4d43dfce05ca9c4835/src/de.rs#L279-L293

variant_deserializer only allows name with given str.

https://github.com/mehcode/config-rs/blob/57fb2610ad274dff1d2f2e4d43dfce05ca9c4835/src/de.rs#L244-L250

---

I got a straightforward fix to demostrate this, it is not the best.

diff --git a/src/de.rs b/src/de.rs
index 0e2b8de..4d014e9 100644
--- a/src/de.rs
+++ b/src/de.rs
@@ -313,8 +313,13 @@ impl<'de> de::EnumAccess<'de> for EnumAccess {
                 ValueKind::String(ref s) => self.variant_deserializer(s),
                 ValueKind::Table(ref t) => self.table_deserializer(t),
                 _ => Err(self.structural_error()),
-            }?;
-            seed.deserialize(deserializer)?
+            };
+            if let Ok(deserializer) = deserializer {
+                seed.deserialize(deserializer)?
+            } else {
+                let deserializer = self.value.clone();
+                seed.deserialize(deserializer)?
+            }
         };

         Ok((value, self))