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Re: [PATCH] range-diff: add a --no-patch option to show a summary

On Tue, Nov 06 2018, Eric Sunshine wrote:

> On Mon, Nov 5, 2018 at 11:17 PM Junio C Hamano <gitster@xxxxxxxxx> wrote:
>> Ævar Arnfjörð Bjarmason  <avarab@xxxxxxxxx> writes:
>> > This change doesn't update git-format-patch with a --no-patch
>> > option. That can be added later similar to how format-patch first
>> > learned --range-diff, and then --creation-factor in
>> > 8631bf1cdd ("format-patch: add --creation-factor tweak for
>> > --range-diff", 2018-07-22). I don't see why anyone would want this for
>> > format-patch, it pretty much defeats the point of range-diff.
>> Does it defeats the point of range-diff to omit the patch part in
>> the context of the cover letter?  How?
>> I think the output with this option is a good addition to the cover
>> letter as an abbreviated form (as opposed to the full range-diff,
>> whose support was added earlier) that gives an overview.
> I had the same response when reading the commit message but didn't
> vocalize it. I could see people wanting to suppress the 'patch' part
> of the embedded range-diff in a cover letter (though probably not as
> commentary in a single-patch).
>> Calling this --[no-]patch might make it harder to integrate it to
>> format-patch later, though.  I suspect that people would expect
>> "format-patch --no-patch ..." to omit both the patch part of the
>> range-diff output *AND* the patch that should be applied to the
>> codebase (it of course would defeat the point of format-patch, so
>> today's format-patch would not pay attention to --no-patch, of
>> course).  We need to be careful not to break that when it happens.
> Same concern on my side, which is why I was thinking of other, less
> confusing, names, such as --summarize or such, though even that is too
> general against the full set of git-format-patch options. It could,
> perhaps be a separate option, say, "git format-patch
> --range-changes=<prev>" or something, which would embed the equivalent
> of "git range-diff --no-patch <prev>...<current>" in the cover letter.

Maybe this was discussed more when this range-diff format-patch
integration was submitted, I wasn't following that closely:

Looking at this more carefully it seems like quite a design limitation
that we're conflating the options for format-patch itself and for the
range-diff invocation it makes.

Wouldn't it be better to make all these options
e.g. --range-diff-creation-factor=*, --range-diff-no-patch,
--range-diff-U1 etc. Now there's no way to say supply a different
-U<ctx> for the range-diff & the patches themselves which seems like a
semi-common use-case.

Doing that seems to be a matter of teaching setup_revisions() to
accumulate unknown options, then parsing those into their own diffopts
with the "range-diff-" prefix stripped and handing that data off to the
range-diff machinery, not the parsed options for range-diff itself as
happens now.