Re: Bug: git branch -D can be used to delete branch which is currently checked out

From: Junio C Hamano <gitster@pobox.com>
Date: Mar 10, 2016, 18:23 UTC
Message-ID: <xmqqfuvydwf5.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <xmqqvb4udyf9.fsf@gitster.mtv.corp.google.com>

Junio C Hamano <gitster@pobox.com> writes:

Show 10 quoted lines

> It is a possibility to teach the files backend of refs API that some
> filesystems are case insensitive and do something special about them,
> but I think in the longer term a more productive solution would be
> to use the upcoming "pluggable ref backend" subsystem and either
>
>  - use a backend that is not the "files" backend (e.g. lmdb backend,
>    or the tree-object based backend);
>
>  - add a variant of "files" backend but encodes the refnames in a
>    way that is safe on case insensitive filesystems.

A typofix s/but encodes/that encodes/ is needed to make this sentence make any sense. Sorry for a typo.

Just to elaborate a bit more, here is what I mean:

 - Thanks to recent work by David, Ronnie and Michael, we eradicated
   most if not all code that assume that the result of checking
   "test -f .git/refs/heads/foo" tells us if a branch 'foo' exists
   [*1*].  They all go through the API designed to allow different
   backends to access refs.

 - The traditional code that implemented 'foo' branch as writing a
   file '.git/refs/heads/foo' has been moved to a "files" backend.
   When used on a platform with case insensitive filesystem, it can
   answer "it exists" when asked about a branch 'Foo' (notice the
   case difference).

 - We could add a new backend that is still based largely on the
   existing "files" backend code, but stores 'foo' branch as a file
   ".git/refs/6865616473/666f6f" while storing another branch 'Foo'
   as ".git/refs/6865616473/466f6f" (I just used byte values in hex
   in this example, but of course you can use a more efficient and
   mostly human readable representations).

That way, even on a platform with case insensitive filesystem, you do not have to worry about getting confused by the filesystem when you have 'foo' and 'Foo' branches.

[Footnote]

*1* This is not strictly true even in the pre-pluggable ref backend
    world, as your refs may appear in the packed-refs file, but this
    detail does not matter in the larger picture.