RE: Branch deletion question / possible bug?

["Tang (US), Pik S" <Pik.S.Tang@boeing.com>]

Hello,

Thank you for all your replies.  I am on a case insensitive system (Windows 10) running git version 2.14.1.windows.1.  

While I can't comment on what the fix would be, it has been enlightening to learn a bit more about what's under the cover of git.  

TIL :)
Pik

-----Original Message-----
From: Johannes Schindelin [mailto:Johannes.Schindelin@gmx.de] 
Sent: Saturday, April 28, 2018 5:44 AM
To: Philip Oakley <philipoakley@iee.org>
Cc: Jacob Keller <jacob.keller@gmail.com>; Tang (US), Pik S <Pik.S.Tang@boeing.com>; Git List <git@vger.kernel.org>
Subject: Re: Branch deletion question / possible bug?

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