Fix escaping of chars in Debug for Wtf8 backed OsStr

[diaphore]

I had to modify some tests : since wtf8buf_show and wtf8_show were doing the exact same thing, I repurposed wtf8_show to wtf8buf_show_str which ensures Wtf8Buf Debug-formats the same as str.

write_str_escaped might also be shared amongst other fmt but I just left it there within Wtf8::fmt for review.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @brson (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. The way Github handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[bluss]

I think we want this to just be try!(f.write_char(c)), it saves some indirections.

[diaphore]

That bit is verbatim from core::fmt. I tried write_char but it didn't work (was missing Write in scope) so I didn't touch the code. Fixing now.

[bluss]

Testcompiling some code suggests that using write_char results in some real code size improvements, i.e. the write version results in irremovable overhead. So the other instances of using write!(f, "{}", c) should probably be fixed.

#![crate_type="lib"]
use std::fmt::{self, Write};

pub fn test_write(c: char, f: &mut fmt::Formatter) -> fmt::Result {
    write!(f, "{}", c)
}

pub fn test_write_char(c: char, f: &mut fmt::Formatter) -> fmt::Result {
    f.write_char(c)
}

[alexcrichton]

Looks like there are some errors with make tidy, but otherwise looks good to me, thanks!

[diaphore]

I've got 2 instances of write! fixed in core::fmt, shall I include them in this PR ?

[alexcrichton]

What do you mean by "fixed"? Also, could you squash the commits down?

[diaphore]

@alexcrichton Changed 2 instances of write!(f, "{}", c) to f.write_char(c) : in impl Debug for str and impl Debug for str.

I'll try squashing ... it might all blow up.

[alexcrichton]

Ah ok, that's fine to throw in as well

[diaphore]

Looks like it. Thanks for your patience !

[alexcrichton]

@bors: r+ aa89504

[bors]

⌛ Testing commit aa89504 with merge 4c371bb...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt

[bluss]

Thanks @diaphore!