Sergey Organov [off-list ref] writes:

quoted

 * Whenever we set DIFF_FORMAT_FOO becasuse we saw the "--foo"
   option (e.g. DIFF_FORMAT_RAW is set when the "--raw" option is
   given), we make sure we drop DIFF_FORMAT_NO_OUTPUT.  We forgot to
   do so in some of the options and caused (2) above.

 * When processing "-s" option, we should not just set
   DIFF_FORMAT_NO_OUTPUT bit, but clear other DIFF_FORMAT_* bits.
   We didn't do so and retained format bits set by options
   previously seen, causing (1) above.

Sounds good to me. Doesn't this makes DIFF_FORMAT_NO_OUTPUT obsolete as
well, I wonder, as absence of any output bits effectively means "no
output"?

Not quite.  The latter is not "set 0 to output_format word", but
"set 0 to output_format word and then flip only NO_OUTPUT bit on".
I've written a bit more on it in a follow-up message to the patch.

Thanks.