Re: [RFC] Submodules in GIT

[Sven Verdoolaege <skimo@kotnet.org>]

On Fri, Dec 01, 2006 at 04:12:10PM -0800, Linus Torvalds wrote:
> So within the supermodule, on a "git object" level, a submodule should 
> just be named by the SHA1 that was it's HEAD when it was committed within 
> the supermodule. So in the "tree object", you'd see something like the 
> following when you go "git ls-tree HEAD" on the superproject:
> 
> 	...
> 	100644 blob 08602f522183dc43787616f37cba9b8af4e3dade	xdiff-interface.c
> 	100644 blob 1346908bea31319aabeabdfd955e2ea9aab37456	xdiff-interface.h
> 	040000 tree 959dd5d97e665998eb26c764d3a889ae7903d9c2	xdiff
> 	050000 link 0215ffb08ce99e2bb59eca114a99499a4d06e704	xyzzy
> 
> where that 050000 is the new magic type (I picked one out of my *ss: it's 
> not a valid type for a file mode, so it's a godo choice, but it could be 
> anythign that cannot conflict with a real file), which just specifies the 
> "link" part. The SHA1 is the SHA1 of the commit, and the "xyzzy" is 
> obviously just the name within the directory of the submodule.
> 
> That's all that is actually required for a lot of git commands that 
> already expect all objects to be available (ie "git checkout", "git diff" 
> etc).

But is this object (and all the objects it points to) going to be
available (in the superproject) ?
The following seems to suggest that you think they shouldn't.
How is fsck-objects then going to check that such an object is
valid ?  Is it going to call fsck-objects recursively on the
(available) submodules ?

On Fri, Dec 01, 2006 at 03:30:32PM -0800, Linus Torvalds wrote:
> The only thing that a submodule must NOT be allowed to do on its own is 
> pruning (and it's distant cousin "git repack -d").

How are you going to enforce this if the submodule isn't supposed
to know that it is being used as a submodule ?

> You must always prune 
> from the supermodule, because the submodule cannot really know on its own 
> what references point into it.

How is one of the supermodules going to know what references from other
supermodules containing the submodule point into the submodule ?