windows: error cannot lock ref ... unable to create lock

>
> I've set up a demo problematic repository on github:
> https://github.com/asottile-archive/git-windows-branch-test
>
> The minimal reproduction is:
>
> rm -rf x
> git init x
> cd x
> git remote add origin https://github.com/asottile-archive/git-windows-branch-te>
> git fetch origin --tags
>
> Here's the output:
>
> + git init x
> Initialized empty Git repository in C:/Users/IEUser/x/x/.git/
> + cd x
> + git remote add origin
> https://github.com/asottile-archive/git-windows-branch-test
> + git fetch origin --tags
> remote: Enumerating objects: 10, done.
> remote: Counting objects: 100% (10/10), done.
> remote: Compressing objects: 100% (4/4), done.
> remote: Total 10 (delta 0), reused 0 (delta 0), pack-reused 0
> Unpacking objects: 100% (10/10), done.
> From https://github.com/asottile-archive/git-windows-branch-test
>  * [new branch]      master     -> origin/master
> error: cannot lock ref 'refs/remotes/origin/pr/aux': Unable to create
> 'C:/Users/IEUser/x/x/.git/refs/remotes/origin/pr/aux.lock': No such
> file or directory
>  ! [new branch]      pr/aux     -> origin/pr/aux  (unable to update local ref)
>
>
> real-world issue: https://github.com/pre-commit/pre-commit/issues/1058
>
> Thanks
>
> Anthony

> + git fetch origin --tags
> Unpacking objects: 100% (10/10), done.
> From https://github.com/asottile-archive/git-windows-branch-test
>  * [new branch]      master     -> origin/master
> error: cannot lock ref 'refs/remotes/origin/pr/aux': Unable to create
> 'C:/Users/IEUser/x/x/.git/refs/remotes/origin/pr/aux.lock': No such
> file or directory
>  ! [new branch]      pr/aux     -> origin/pr/aux  (unable to update local ref)

>
> On Tue, Jun 18, 2019 at 12:39 PM Anthony Sottile <asottile@umich.edu> wrote:
> > + git fetch origin --tags
> > Unpacking objects: 100% (10/10), done.
> > From https://github.com/asottile-archive/git-windows-branch-test
> >  * [new branch]      master     -> origin/master
> > error: cannot lock ref 'refs/remotes/origin/pr/aux': Unable to create
> > 'C:/Users/IEUser/x/x/.git/refs/remotes/origin/pr/aux.lock': No such
> > file or directory
> >  ! [new branch]      pr/aux     -> origin/pr/aux  (unable to update local ref)
>
> AUX is a reserved[1] filename on Windows. Quoting from that source:
>
>     Do not use the following reserved names for the name of a file:
>     CON, PRN, AUX, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7,
>     COM8, COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and
>     LPT9. Also avoid these names followed immediately by an
>     extension...
>
> The default Git "ref store" is filesystem-based, so a branch named
> "aux" is problematic. Other ref store implementations would not be
> subject to this limitation (though I'm not sure what the state of the
> others is -- someone with more knowledge can probably answer that).
>
> [1]: https://docs.microsoft.com/en-us/windows/desktop/FileIO/naming-a-file#naming-conventions

> On Tue, Jun 18, 2019 at 12:39 PM Anthony Sottile <asottile@umich.edu> wrote:
>> + git fetch origin --tags
>> Unpacking objects: 100% (10/10), done.
>>  From https://github.com/asottile-archive/git-windows-branch-test
>>   * [new branch]      master     -> origin/master
>> error: cannot lock ref 'refs/remotes/origin/pr/aux': Unable to create
>> 'C:/Users/IEUser/x/x/.git/refs/remotes/origin/pr/aux.lock': No such
>> file or directory
>>   ! [new branch]      pr/aux     -> origin/pr/aux  (unable to update local ref)
> AUX is a reserved[1] filename on Windows. Quoting from that source:
>
>      Do not use the following reserved names for the name of a file:
>      CON, PRN, AUX, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7,
>      COM8, COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and
>      LPT9. Also avoid these names followed immediately by an
>      extension...
>
> The default Git "ref store" is filesystem-based, so a branch named
> "aux" is problematic. Other ref store implementations would not be
> subject to this limitation (though I'm not sure what the state of the
> others is -- someone with more knowledge can probably answer that).
>
> [1]: https://docs.microsoft.com/en-us/windows/desktop/FileIO/naming-a-file#naming-conventions

> On 18/06/2019 18:01, Eric Sunshine wrote:
> > On Tue, Jun 18, 2019 at 12:39 PM Anthony Sottile <asottile@umich.edu> wrote:
> > > + git fetch origin --tags
> > > Unpacking objects: 100% (10/10), done.
> > >  From https://github.com/asottile-archive/git-windows-branch-test
> > >   * [new branch]      master     -> origin/master
> > > error: cannot lock ref 'refs/remotes/origin/pr/aux': Unable to create
> > > 'C:/Users/IEUser/x/x/.git/refs/remotes/origin/pr/aux.lock': No such
> > > file or directory
> > >   ! [new branch]      pr/aux     -> origin/pr/aux  (unable to update local
> > >   ref)
> > AUX is a reserved[1] filename on Windows. Quoting from that source:
> >
> >      Do not use the following reserved names for the name of a file:
> >      CON, PRN, AUX, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7,
> >      COM8, COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and
> >      LPT9. Also avoid these names followed immediately by an
> >      extension...
> >
> > The default Git "ref store" is filesystem-based, so a branch named
> > "aux" is problematic. Other ref store implementations would not be
> > subject to this limitation (though I'm not sure what the state of the
> > others is -- someone with more knowledge can probably answer that).
> >
> > [1]:
> > https://docs.microsoft.com/en-us/windows/desktop/FileIO/naming-a-file#naming-conventions
> This sounds interesting. I thought (but I'm not certain) that Git for Windows
> avoided creating files in the working tree with such problematic names, so
> that a clone of a repo that contained a file "AUX" (any case, any extension
> IIRC), would be bypassed with possibly a warning message.
>
> However this looks to be a slightly different case where a _branch_ called
> "AUX" (lower cased) has been created within the clone, and it's a problem not
> trapped. Maybe worth creating a proper issue on the Git-for-Windows repo. Also
> cc'ing Dscho who may remember better than I.