Re: Branch deletion question / possible bug?

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi,

On Sat, 28 Apr 2018, Philip Oakley wrote:

> From: "Jacob Keller" <jacob.keller@gmail.com>
> > On Fri, Apr 27, 2018 at 5:29 PM, Tang (US), Pik S <Pik.S.Tang@boeing.com>
> > wrote:
> > > Hi,
> > >
> > > I discovered that I was able to delete the feature branch I was in, due
> > > to some fat fingering on my part and case insensitivity.  I never
> > > realized this could be done before.  A quick google search did not give
> > > me a whole lot to work with...
> > >
> > > Steps to reproduce:
> > > 1. Create a feature branch, "editCss"
> > > 2. git checkout master
> > > 3. git checkout editCSS
> > > 4. git checkout editCss
> > > 5. git branch -d editCSS
> > >
> >
> > Are you running on a case-insensitive file system? What version of
> > git? I thought I recalled seeing commits to help avoid creating
> > branches of the same name with separate case when we know we're on a
> > file system which is case-insensitive..
> >
> > > Normally, it should have been impossible for a user to delete the branch
> > > they're on.  And the deletion left me in a weird state that took a while
> > > to dig out of.
> > >
> > > I know this was a user error, but I was also wondering if this was a bug.
> >
> > If we have not yet done this, I think we should. Long term this would
> > be fixed by using a separate format to store refs than the filesystem,
> > which has a few projects being worked on but none have been put into a
> > release.
> 
> Yes, this is an on-going problem on Windows and other case insentive
> systems. At the moment the branch name becomes embedded as a file name, so
> when Git requests details of a branch from the filesystem, it can get a case
> insensitive equivalent. Meanwhile, internally Git is checking for equality
> in a case sensitive [Linux] way with obvious consequences such as this - The
> most obvious being when there is no "*" current branch marker in the branch
> status list.
> 
> It's a bit tricky to fix (internally the name and the path are passed down
> different call chains), and depends on how one expects the case
> insensitivity to work - the kicker is when someone does an edit of the name
> via the file system and expects Git to cope (i.e. devs knowing, or think
> they know, too much detail ;-).
> 
> The refs can also get packed, so the "bad spelling" gets baked in.
> Ultimately it probably means that GfW and other systems will need  a case
> sensitivity check when opening paths...

FWIW I outlined what I think is the best route to fix this for good:

https://github.com/git-for-windows/git/issues/1623#issuecomment-380085257

Essentially, I think we should teach Git the trick to check the spelling
before calling lstat() in refs/files-backend.c.

To check the spelling, we would need an API to get the on-disk
representation of a given path. On Windows, I know this call. On Linux,
apparently canonicalize_file_name() might do the job, but that is a GNU
libc extension, and won't help us on macOS.

Any ideas?

Ciao,
Dscho