Re: [PATCH 2/3] revision: add "--ignore-merges" option to counteract "-m"

[Junio C Hamano <gitster@pobox.com>]

Jeff King <peff@peff.net> writes:

> On Wed, Jul 29, 2020 at 02:22:07PM -0400, Jeff King wrote:
>
>> After thinking on it more, I flipped it to:
>> 
>>   -m::
>>   --diff-merges::
>>      [existing text...]
>> 
>> and then I don't think we need to have another block for
>> --no-diff-merges.
>> 
>> I'll likewise add a statement that "-m" is implied by "--first-parent"
>> and can be counteracted with the "--no" form, which I think should spell
>> out all the implications of the series.
>
> Hmm, I take that back. I tried adding this:
>
> diff --git a/Documentation/rev-list-options.txt b/Documentation/rev-list-options.txt
> index 0785a0cfe9..41c859e63f 100644
> --- a/Documentation/rev-list-options.txt
> +++ b/Documentation/rev-list-options.txt
> @@ -1154,7 +1154,9 @@ options may be given. See linkgit:git-diff-files[1] for more options.
>  	and diff is generated. An exception is that only diff against
>  	the first parent is shown when `--first-parent` option is given;
>  	in that case, the output represents the changes the merge
> -	brought _into_ the then-current branch.
> +	brought _into_ the then-current branch. Note that
> +	`--first-parent` implies `-m` if no combined-diff option is
> +	enabled; you can use `--no-diff-merges` to override that.
>  
>  -r::
>  	Show recursive diffs.
>
> but then I'm left wondering: why would you ever want to override it? I
> added the option as an escape hatch in case anybody really needed the
> old behavior.

Old behaviour meaning "git log --first-parent -p master..next" would
mostly list commits without patches unless there is a single-parent
commit thrown in the first-parent chain?  I would imagine it would
be one way to locate and view reverts, cherry-picks and "oops I
botched the merge previously" fix-ups on 'next'.

I could add "--no-merges" to that command line but then the output
loses all the clues on when topics are merged in what order and show
only those single-parent commits, so it is not exactly the same
thing.  It loses a lot, and the current behaviour strikes a very
good balance for the use case.

So, if we make "-m" the default in some cases (like "--first-parent"),
we do need a way to toggle it off.

Thanks.