Re: [PATCH] Documentation/git-bisect.txt: add --no-ff to merge command

From: Junio C Hamano <gitster@pobox.com>
Date: Oct 29, 2019, 02:24 UTC
Message-ID: <xmqq4kzs8f1l.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <20191028222405.GE12487@google.com>

Jonathan Nieder <jrnieder@gmail.com> writes:

Show 5 quoted lines

> As an orthogonal point, I wonder whether we can start the multi-step
> migration of making --no-commit imply --no-ff by default:
>
>  1. Act as --ff when --no-commit is passed without --ff or --no-ff
>     (the state today)

which means "--no-commit controls whether a new commit is created or not and nothing else, and because --ff is the default for merge, merging a true descendant will fast-forward".

>  5. Refuse to perform a fast-forward merge with --no-commit is passed
>     without --ff or --no-ff, just as though --no-ff were passed.

Is that a good endgame, though? It is correct that "--no-ff" means "do not allow the merge to be fast-forwarded and the way the option does so is by creating an otherwise unnecessary merge commit", and "--no-commit" means "do not allow creating any new commit", so technically they are mutually incompatible, but would it be useful?

I'd imagine that a more useful behaviour would be for "git merge X" with any other options to honor this basic trait: the working tree and the index after the operation shows the result of merging X and HEAD, if the merge can cleanly be made, and otherwise the working tree and the index would show something close to the result of such a merge with conflicts that would help recording the result of the merge manually.

For that, wouldn't it make more sense ot change the semantics of the "--no-commit" option from "no new commit gets created" to "HEAD is not moved"? "git merge --no-commit X" when X is a descendant of HEAD would then become "git read-tree -m -u HEAD X" plus perhaps storing X in .git/MERGE_HEAD file etc. to prepare for concluding "git commit" to record the result manually.

In any case, as you said,

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>>>> -if   git merge --no-commit hot-fix &&
>>>> +if   git merge --no-commit --no-ff hot-fix &&
>>>
>>> Good.
>
> This part still looks like a good change to me. :)

This looks good to me too.