Re: [PATCH v2 0/3] contrib/subtree: reduce recursion during split

From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Apr 16, 2026, 13:25 UTC
Message-ID: <27104.58166.993109.63505@chiark.greenend.org.uk>
In-Reply-To: <20260305-cs-subtree-split-recursion-v2-0-7266be870ba9@howdoi.land>

Colin Stagner writes ("[PATCH v2 0/3] contrib/subtree: reduce recursion during split"):

> On Debian's POSIX sh, shell recursion is artificially limited
> to 1000 calls. You can check if your sh has limited recursion
> with:

FTR Debian supports multiple options for /bin/sh. The shell in question, with the limit that's troubling us, is dash.

> Depending on the history graph, subtree split can recurse deeply
> enough to encounter this limit. Rewrite the rejoin-deepening
> algorithm to reduce recursive calls.

Hi. I'm a git-subtree user and indeed I was the one who reported the bug Colin is trying to fix. I would be happy to do a code review of these changes.

However, before I get stuck into that, which seems like it will involve some serious staring at shell code, I'd like to ask what seems like a logically prior question:

Why not run the script under bash in non-POSIX mode instead? I think that would sidestep the problem. If you don't want this program to always depend on bash, you could have a little snippet at the top to re-exec with bash if (1) it's available (2) we don't seem to be running under bash already. (Presumably the Debian package of git would need to Recommend bash then.)

TBH I was quite surprised, when I reported this bug some time ago, to find that git-subtree was written in shell. If it had been me I would probably have used Rust and libgit2.

Ian.

-- 
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