Junio C Hamano [off-list ref] writes:

Junio C Hamano [off-list ref] writes:

quoted

I haven't run any tests (not just your new one, but existing ones)
but ...

And of course, not writing tests fails to even realize that the bug
has two components, "-s" failing to clear the bits previously set,
and other options not clearing the bit set by "-s".

This version may still be rough, but at least the full test suite
has been run with it, so I have a bit more confidence than the
earlier one (which may not mean much).

------- >8 ------------- >8 ------------- >8 -------------
Sergey Organov noticed and reported "--patch --no-patch --raw"
behaves differently from "--raw".  It turns out there are a few
interesting bugs in the implementation and documentation.

 * First, the documentation for "--no-patch" was unclear that it
   could be read to mean "--no-patch" countermands an earlier
   "--patch" but not other things.  The intention of "--no-patch"
   ever since it was introduced at d09cd15d (diff: allow --no-patch
   as synonym for -s, 2013-07-16) was to serve as a synonym for
   "-s", so "--raw --patch --no-patch" should have produced no
   output, but it can be (mis)read to allow showing only "--raw"
   output.

 * Then the interaction between "-s" and other format options were
   poorly implemented.  Modern versions of Git uses one bit each to
   represent formatting options like "--patch", "--stat" in a single
   output_format word, but for historical reasons, "-s" also is
   represented as another bit in the same word.  This allows two
   interesting bugs to happen, and we have both.

   (1) After setting a format bit, then setting NO_OUTPUT with "-s",
       the code to process another "--<format>" option drops the
       NO_OUTPUT bit to allow output to be shown again.  However,
       the code to handle "-s" only set NO_OUTPUT without unsetting
       format bits set earlier, so the earlier format bit got
       revealed upon seeing the second "--<format>" option.  THis is
       the problem Sergey observed.

   (2) After setting NO_OUTPUT with "-s", code to process
       "--<format>" option can forget to unset NO_OUTPUT, leaving
       the command still silent.

It is tempting to change the meaning of "--no-patch" to mean
"disable only the patch format output" and reimplement "-s" as "not
showing anything", but it would be an end-user visible change in
behaviour.  Let's fix the interactions of these bits to first make
"-s" work as intended.

The fix is conceptually very simple.

 * 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"?

Thanks,
-- Sergey Organov