Re: Git clone and case sensitivity

[Jeff King <peff@peff.net>]

On Sun, Jul 29, 2018 at 07:26:41AM +0200, Duy Nguyen wrote:

> > strcasecmp() will only catch a subset of the cases. We really need to
> > follow the same folding rules that the filesystem would.
> 
> True. But that's how we handle case insensitivity internally. If a
> filesytem has more sophisticated folding rules then git will not work
> well on that one anyway.

Hrm. Yeah, I guess that's the best we can do for the actual in-memory
checks. Everything else depends on doing an actual filesystem operation,
and our icase stuff kicks in way before then. I was mostly thinking of
HFS+ utf8 normalization weirdness, but I guess people are accustomed to
that by now.

> > For the case of clone, I actually wonder if we could detect during the
> > checkout step that a file already exists. Since we know that the
> > directory we started with was empty, then if it does, either:
> >
> >   - there's some funny case-folding going on that means two paths in the
> >     repository map to the same name in the filesystem; or
> >
> >   - somebody else is writing to the directory at the same time as us
> 
> This is exactly what my first patch does (minus the sparse checkout
> part).

Right, sorry, I should have read that one more carefully.

> But without knowing the exact folding rules, I don't think we can
> locate this "somebody else" who wrote the first path. So if N paths
> are treated the same by this filesystem, we could only report N-1 of
> them.
> 
> If we want to report just one path when this happens though, then this
> works quite well.

Hmm. Since most such systems are case-preserving, would it be possible
to report the name of the existing file? Doing it via opendir/readdir is
hacky, and anyway puts the burden on us to find the matching name. Doing
it via fstat() on the opened file doesn't work because at that the
filesystem has resolved the name to an inode.

So yeah, perhaps strcasecmp() is the best we can do (I do agree that
being able to mention all of the conflicting names is a benefit).

I guess we should be using fspathcmp(), though, in case it later learns
to be smarter.

-Peff