Implement Display and Debug for CStr

[mbartlett21]

This only prints ASCII characters and escapes the rest for Display and Debug.

(Fixes part of #534)

[ojeda]

Thanks a lot for contributing!

A few comments:

• Please squash the commits and sign them (in the Signed-off-by: sense) to show you agree with the Developer's Certificate of Origin (see Documentation/process/submitting-patches.rst).
• I love what you did here (it is a great example of how to use pattern matching), but I don't think we need to parse UTF-8 in the kernel (at least for the usual logging). Printing ASCII printable characters and escaping the rest should be enough. Note that eventually we might get to remove all Unicode-related facilities.
• As it is right now, it prints characters such as 0 as-it-is, rather than escaping them.

[mbartlett21]

@ojeda

I have squashed and signed the commits.

With the utf8 parsing, I think I might instead see if I can get it in the standard library (it already has utf16 parsing)

[ojeda]

I have squashed and signed the commits.

Thanks! It looks good to me (both the code and the commit). Could you please add a doc with an example (which would double as test)?

With the utf8 parsing, I think I might instead see if I can get it in the standard library (it already has utf16 parsing)

That would be great, yeah! Please let me know if you open the issue upstream, I would like to follow it.

[mbartlett21]

That would be great, yeah! Please let me know if you open the issue upstream, I would like to follow it.

@ojeda
It seems that Rust already had a way to decode utf8 to chars, but it was deprecated and removed in favour of utilising core::str::from_utf8 and its error type.

Previous tracking issue: rust-lang/rust#33906
Example use of core::str::from_utf8: https://doc.rust-lang.org/std/str/struct.Utf8Error.html#examples

[ojeda]

Thanks!