Untagged enums don't deserialize newtype variants which are enums properly

[Stumblinbear]

Consider the following implementation

// `Other` is a single-variant enum since using a newtype struct results in the name being lost entirely, which I believe is a serde issue.
#[derive(Debug, Serialize, Deserialize)]
enum Other {
    Env(String),
 }

#[derive(Debug, Serialize, Deserialize)]
#[serde(untagged)]
enum MaybeEnv {
    Value(String),
    Other(Other),
}

This is set up like this to allow using a raw String literal or a fallback which executes different behavior (in this case reading the string from the environment), but only if it's wrapped in Env.

The following works properly:

• Serializing MaybeEnv::Value("foo") outputs "foo"
• Serializing MaybeEnv::Other(Other::Env("bar")) outputs Env("bar")
• Deserializing "foo" results inMaybeEnv::Value("foo")

However, when deserializing Env("bar") it fails with "data did not match any variant of untagged enum MaybeEnv" instead of MaybeEnv::Other(Other::Env("bar")). I'm also unable to find a string which properly deserializes to this value at all.

I'm unsure if this is a serde limitation, but it's relatively surprising behavior since it serializes properly but fails to deserialize.

[juntyr]

This has been fixed in #451 - I'll add your test case to the test suite to ensure that it remains fixed.

[juntyr]

The fix should be released in v0.9, which I'm hoping to release in 1-2 weeks :)