Re: [PATCH] Try URI quoting for embedded TAB and LF in pathnames

Linus Torvalds [off-list ref] writes:

Personally, I'd like the normal C quoting the best.

That would be fine with me too.  How about if we use the equivalent of
--quoting-style="c" for file names that contain funny bytes, and no
quoting for other file names?  So, for example, something like this:

    diff --git "space tab\tnewline\nquote\"backslash\\" b/dee/pqr
    similarity index 72%
    rename from "space tab\tnewline\nquote\"backslash\\"
    rename to dee/pqr
    index 9ee055c..243fbbc 100644
    --- "space tab\tnewline\nquote\"backslash\\"
    +++ b/dee/pqr
    @@ -1 +1,3 @@
     Fri Oct  7 23:19:04 PDT 2005
    +foo
    +foo

The surrounding double-quotes are an extra indication to the human
reader that there is something weird about the quoted file name.

Use filenames as if they are just binary blobs of data, 
that's the only thing that has a high chance of success.

Thanks for thinking those things through.  I agree mostly, but there's
still a technical problem, in that we have to decide what a "funny
byte" is if we are using C-style quoting.  For example, the simplest
approach is to say a byte is funny if it is space, backslash, quote,
an ASCII control character, or is non-ASCII.  But this will cause
perfectly-reasonable UTF-8 file names to be presented in git format
using unreadable strings like "a\293\203\257b" or whatever.

Perhaps it would be better to say that a byte is "funny" if it is
space, backslash, quote, an ASCII control character, or a byte that is
not part of a valid UTF-8 encoding.  This will let UTF-8 file names
through unscathed, while still warning the reader when funny business
is going on.  File names with other encodings (e.g., Shift-JIS) will
contain lots of backslashes, but that's OK: we don't mind making
nonstandard encodings hard-to-read, so long as we preserve the bytes
correctly.

We could implement in other GNU applications by having a new quoting
style that supports this quoting behavior.  I can arrange for that.

If somebody wants to use names with tabs and newlines, is he really
going to work with diffs? Or is it just a driver error?

The current-supported scheme with 'diff' and 'patch' should work for
everything but newlines.  I like the idea of getting it to work even
with newlines, and I am willing to sacrifice old patches with file
names starting with '"' (extremely rare, if any) to get newlines to
work.  Among other things I worry about people submitting
purposely-malformed patches in non-git environments.