Re: [PATCH 2/6] diff-merges: move specific diff-index "-m" handling to diff-index

Junio C Hamano [off-list ref] writes:

This change is risky, as the loop below (which this patch moves to
parse_distinct_options()) has no knowledge of other options that
setup_revisions() helper is prepared to handle and that takes an
argument.  When parsing "git cmd --opt --cached A", setup_revisions()
may know that --opt takes an argument and eat both (i.e. the
"--cached" is not an option but an arg given to "--opt"), but the
new parse_distinct_options() helper does not; it will happily skip
"--opt" and leave it in, mistake "--cached" as an option and remove,
and instead make "A" the arg given to "--opt".

The above is not theoretical.  The series breaks

    $ git checkout master
    $ git diff-index -S --cached maint

IOW, what I predicted in the previous message with s/--opt/-S/
happens with this step.

Picking up the remnant _after_ setup_revisions() ate what it
understands would not have such a downside, as long as none of our
"distinct options" take any argument.

Can't we make "-m means something special for diff-index" without
butchering the command line processing in this step?  diff-index
does not care about --diff-merges, so letting setup_revisions()
remember only the fact that "-m" was given while parsing, and then
postprocess what "-m" means depending on the command (i.e. everybody
else would treat it as a short-hand for "--diff-merges=m" plus "we
need some form of diff output, while allowing "diff-index" to treat
it differently) should not be rocket science.

Thanks.