Re: [PATCH v6] subtree: fix split processing with multiple subtrees present

[Christian Couder <christian.couder@gmail.com>]

On Fri, Dec 1, 2023 at 3:54 PM Zach FettersMoore via GitGitGadget
<gitgitgadget@gmail.com> wrote:
>
> From: Zach FettersMoore <zach.fetters@apollographql.com>
>
> When there are multiple subtrees present in a repository and they are
> all using 'git subtree split', the 'split' command can take a
> significant (and constantly growing) amount of time to run even when
> using the '--rejoin' flag. This is due to the fact that when processing
> commits to determine the last known split to start from when looking
> for changes, if there has been a split/merge done from another subtree
> there will be 2 split commits, one mainline and one subtree, for the
> second subtree that are part of the processing. The non-mainline
> subtree split commit will cause the processing to always need to search
> the entire history of the given subtree as part of its processing even
> though those commits are totally irrelevant to the current subtree
> split being run.
>
> To see this in practice you can use the open source GitHub repo
> 'apollo-ios-dev' and do the following in order:
>
> -Make a changes to a file in 'apollo-ios' and 'apollo-ios-codegen'
>  directories
> -Create a commit containing these changes
> -Do a split on apollo-ios-codegen
>    - Do a fetch on the subtree repo
>       - git fetch git@github.com:apollographql/apollo-ios-codegen.git
>    - git subtree split --prefix=apollo-ios-codegen --squash --rejoin

Now I get the following without your patch at this step:

$ git subtree split --prefix=apollo-ios-codegen --squash --rejoin
[...]/libexec/git-core/git-subtree: 318: Maximum function recursion
depth (1000) reached

Line 318 in git-subtree.sh contains the following:

missed=$(cache_miss "$@") || exit $?

With your patch it seems to work:

$ git subtree split --prefix=apollo-ios-codegen --squash --rejoin
Merge made by the 'ort' strategy.
e274aed3ba6d0659fb4cc014587cf31c1e8df7f4

>    - Depending on the current state of the 'apollo-ios-dev' repo
>      you may see the issue at this point if the last split was on
>      apollo-ios

I guess I see it, but it seems a bit different for me than what you describe.

Otherwise your patch looks good to me now.

Thanks,
Christian.