Re: RFC: Between git-subtree and git-submodules

From: Santi Béjar <santi@agolina.net>
Date: Jul 24, 2010, 08:33 UTC
Message-ID: <AANLkTinYXrWSXSX8EOsb-YH_KGcmtAKB9nWZyRzBwZw5@mail.gmail.com>
In-Reply-To: <AANLkTinyjinsGS2ddyMOW=3zDN1ThJcpF+dc4cBE6L9D@mail.gmail.com>

On Sat, Jul 24, 2010 at 2:57 AM, Avery Pennarun <apenwarr@gmail.com> wrote:

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> On Fri, Jul 23, 2010 at 8:13 PM, Santi Béjar <santi@agolina.net> wrote:
>>  First my requirements:
>>
>> 1) Everything[a] must be available from the same repository/branch (so I'm not
>>   worried about repository size)
>> 2) The history must be as clean as possible
>> 3) The directory content must be equal to the external module, at least when
>>   you add/update it[b]
>> 4) The external module should be able to switch back and forth between
>>   different versions.
>>
>> [a] Everything means all that you need to checkout all the commits in the
>> superproject not in the submodule.
>> [b] A consequence of #3 is that I lose all
>> change I've made in the subdirectory, if they are important I have to extract
>> them, apply them and add the module back.
>>
>> git-submodule is rule out because of #1 but accomplish #2, #3 and
>> #4. git-subtree is rule out because of #2 (even with --squash).
>> [It fails at] #3 and #4
>> without --squash but accomplish #1 and #4 with --squash. So I need something
>> in between or a mixture of both.
>
> I admit to having had some trouble parsing the above, so I moved some
> punctuation marks around.  Please let me know if I've made a mistake.
>
> If I understand correctly, you're claiming (indirectly) that
> git-subtree without --squash does not accomplish #1.  I don't see how
> this is the case.  Am I misreading?  I think git-subtree accomplishes
> #1 in both modes.

Yes, git-subtree accomplishes #1 in both modes. --squash only applies to #4.

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>
> I don't understand what you mean when you say (#2) git-subtree doesn't
> keep your history "as clean as possible."  What is "as clean as
> possible" and what part of git-subtree's history results don't you
> like?  (Of course it's very different with and without --squash.)

With git-subtree you always have the subtree history (even if it is squashed). So when you merge a second time the submodule you get the always the history of the subtree (even with --squash). So you basically always have at least two branches while examining the history. Compare this squashed history:

$ git log --graph --oneline
*   bb2dc25 (HEAD, master) Merge commit
'08b917ee90ecfd7b666364fe4ebb92aee5cdd2f7'
|\
| * 08b917e Squashed 'latex/' changes from ea35faf..895916a
* |   9de91f1 Merge commit 'b1b4c36bb8358582a6a20bb500bf98421428e2ca' as 'latex'
|\|
| * b1b4c36 Squashed 'latex/' content from commit ea35faf
* ea35faf Indent, whitespaces,...

with this pruned history:

$ git log --graph --oneline
* 8703aec (HEAD, master) Subtree 'latex/': 895916a Add files subcommand
* a942284 Subtree 'latex/': ea35faf Indent, whitespaces,...
* ea35faf Indent, whitespaces,...

But I understand that it can only be this way because of #3.

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>
> With #3, I can see that you want something different than I do; you
> want to silently revert your own patches out of the submodule's
> history, when you upgrade the submodule to a new version.  Personally,
> I find this concept a bit objectionable (it's like "git merge -s
> ours"), but okay, it's pretty easy to implement, and you've submitted
> a patch to git-subtree that does it.  My question is: why would you
> want this?  Isn't it clearer to 'git revert' the patches you don't
> want?

I prefer to do all the modifications in an external repository, even if at the end it is really a fork of the upstream repository. I think the proper place to modify the files in a subtree is in an external repository.

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>
> And for #4, it's true that git-subtree without --squash does not allow
> you to easily rewind to an older version of the submodule, while with
> --squash it does.
>
> It sounds to me like, if we added your patch to git-subtree, then
> git-subtree --squash would solve #1, #3, and #4.  And maybe we could
> fix #2 as well. Correct?

My patch does not change the behavior of --squash, it adds --prune.

Thanks, Santi