Re: [PATCH] Add platform-independent .git "symlink"

From: Shawn O. Pearce <spearce@spearce.org>
Date: Feb 4, 2008, 01:57 UTC
Message-ID: <20080204015707.GH24004@spearce.org>
In-Reply-To: <alpine.LSU.1.00.0802021825220.7372@racer.site>

Johannes Schindelin <Johannes.Schindelin@gmx.de> wrote:

Show 14 quoted lines

> Howver, having .git a file pointing to another git directory allows you to 
> have locks there.  And they can be actually pretty sensible locks, like
> 
> 	.git/HEAD.<mangled-path>
> 
> actually containing the symbolic ref describing which branch we're on in 
> that working directory.  Likewise, .git/index.<mangled-path> needs to hold 
> the current index.
> 
> Of course, for this to work, you need to use different HEADs and indexes 
> only if .git was a file originally.
> 
> BTW <mangled-path> could be a hash of the path, and for convenience, we 
> could store the path in .git/workdir.<mangled-path>.

This I like. Because my day-job coworkers and I make very heavy use of git-new-workdir to manage our compile areas/working directories. :)

The biggest problem with new-workdir is the master repository cannot see the HEAD, index or logs/HEAD of the working directories. Consequently it is possible for prune (or repack -a -d) to remove objects that some workdir is still referring to. Its not uncommon for my HEAD reflogs to have stale commits in them. Every once in a while a user looses their HEAD entirely when it gets pruned away, as they had a workdir checked out on a detached HEAD.

The second biggest problem is checking out the same branch in two different directories at once. This becomes a problem only if you modify the branch, but still, its a problem.

I was thinking that we could add a WORKDIR_HASH to the .git file Lars was proposing. This hash would be the <mangled-path> suffix you are talking about above, and would avoid the need to compute the absolute path for the working directory every time we run a Git command.

The hash could be something simple, like the SHA-1 hash of the absolute path at the time of workdir creation. But it would be nice if we could recommend a specific value during workdir creation, so that the WORKDIR_HASH could start with a value that matches something the user would readily recognize.

-- 
Shawn.