Fix for building on Redox

[jackpot51]

On a platform that does not set cfg(unix) or cfg(windows), the impl blocks modified in this PR are left empty, causing compilation to fail

This fixes compilation by not attempting to implement Encodable or Decodable on Path or PathBuf on platforms without the OsStr and OsString conversion functions.

[alexcrichton]

@brson posted more on internals but the tl;dr; is that this patch is a little worrying. Why doesn't std have a path module?

[jackpot51]

It absolutely does have a std::path module. What the issue is with this code is that it assumes that either cfg(unix) or cfg(windows) are set, when a non-unix non-windows OS might not set these config values (such as Redox).

A quick fix is to correctly annotate the impl's. A more complete fix would be to have a third function, #[cfg(redox)], that correctly decodes and encodes on Redox

[jackpot51]

@alexcrichton would you prefer a fix that adds #[cfg(redox)] and correctly decodes and encodes paths? If so, I can make a PR pretty quickly

[alexcrichton]

Yes if std::path exists then there should be a code path here for that

[jackpot51]

@alexcrichton In my newest commit, I implemented the #[cfg(redox)] functions. b99dac2

In Redox, OsStr and OsString are guaranteed to be UTF-8 slices. As such, to_str().unwrap() is guaranteed to succeed and OsString::from(String) is valid.

[jackpot51]

@alexcrichton Can you update the crate version so I can use 0.3 in manifests on Redox?