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Sergey Organov noticed and reported "--patch --no-patch --raw"
behaves differently from just "--raw". It turns out that 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 X-<.
(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
behavior. 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 because 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.
It is even more tempting to lose NO_OUTPUT bit and instead take
output_format word being 0 as its replacement, but that would break
the mechanism "git show" uses to default to "--patch" output, where
the distinction between telling the command to be silent with "-s"
and having no output format specified on the command line matters,
and an explicit output format given on the command line should not
be "combined" with the default "--patch" format.
So, while we cannot lose the NO_OUTPUT bit, as a follow-up work, we
may want to replace it with OPTION_GIVEN bit, and
* make "--patch", "--raw", etc. set DIFF_FORMAT_$format bit and
DIFF_FORMAT_OPTION_GIVEN bit on for each format. "--no-raw",
etc. will set off DIFF_FORMAT_$format bit but still record the
fact that we saw an option from the command line by setting
DIFF_FORMAT_OPTION_GIVEN bit.
* make "-s" (and its synonym "--no-patch") clear all other bits
and set only the DIFF_FORMAT_OPTION_GIVEN bit on.
which I suspect would make the code much cleaner without breaking
any end-user expectations.
Once that is in place, transitioning "--no-patch" to mean the
counterpart of "--patch", just like "--no-raw" only defeats an
earlier "--raw", would be quite simple at the code level. The
social cost of migrating the end-user expectations might be too
great for it to be worth, but at least the "GIVEN" bit clean-up
alone may be worth it.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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