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.

config-rs/src/de.rs

Lines 279 to 293 in 57fb261

	fn variant_seed<V>(self, seed: V) -> Result<(V::Value, Self::Variant)>
	where
	V: de::DeserializeSeed<'de>,
	{
	let value = {
	let deserializer = match self.value.kind {
	ValueKind::String(ref s) => self.variant_deserializer(s),
	ValueKind::Table(ref t) => self.table_deserializer(&t),
	_ => Err(self.structural_error()),
	}?;
	seed.deserialize(deserializer)?
	};
	Ok((value, self))
	}

variant_deserializer only allows name with given str.

config-rs/src/de.rs

Lines 244 to 250 in 57fb261

	fn variant_deserializer(&self, name: &str) -> Result<StrDeserializer> {
	self.variants
	.iter()
	.find(|&&s| s == name)
	.map(|&s| StrDeserializer(s))
	.ok_or_else(|| self.no_constructor_error(name))
	}

---

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))