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For many of Nix's consumers it be convenient to easily convert a Nix error into a std::io::Error. That's currently not possible because of the InvalidPath, InvalidUtf8, and UnsupportedOperation types that have no equivalent in std::io::Error. However, very few of Nix's public APIs actually return those unusual errors. So a more useful API would be for Nix's standard error type to implement Into<std::io::Error>. This commit makes Error a simple NewType around Errno. For most functions it's a drop-in replacement. There are only three exceptions: * clearenv now returns a bespoke error type. It was the only Nix function whose error couldn't be cleanly mapped onto an Errno. * sys::signal::signal now returns Error(Errno::ENOTSUP) instead of Error::UnsupportedOperation when the user passes an incompatible argument to `handler`. * When a NixPath exceeds PATH_MAX, it will now return Error(Errno::ENAMETOOLONG) instead of Error::InvalidPath. In the latter two cases there is now some abiguity about whether the error code was generated by Nix or by the OS. But I think the ambiguity is worth it for the sake of being able to implement Into<io::Error>. This commit also introduces Error::Sys() as a migration aid. Previously that as an enum variant. Now it's a function, but it will work in many of the same contexts as the original. Fixes nix-rust#1155
Now that Nix's weird error types are eliminated, there's no reason not to simply use Errno as the Error type.
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The nix upgrade changes nix::Error to implement Into<std::io::Error>, which removes the need for us to do that on our own. nix-rust/nix#1446 has more details. Test: Build Change-Id: Ifed70bbe1fd45bb36bb12077c4a8a6492e6f0de6
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For many of Nix's consumers it be convenient to easily convert a Nix
error into a std::io::Error. That's currently not possible because of
the InvalidPath, InvalidUtf8, and UnsupportedOperation types that have
no equivalent in std::io::Error.
However, very few of Nix's public APIs actually return those unusual
errors. So a more useful API would be for Nix's standard error type to
implement Intostd::io::Error, and the few functions that must return
unusual errors like InvalidUtf8 should use bespoke error types.
This commit prototypes that approach by modifying just one function, for
now, to use the new error type.