On Fri, May 5, 2023 at 1:02 PM Junio C Hamano <gitster@xxxxxxxxx> wrote: > 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 Glad to see "THis" from v1 fixed. > 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. The above description is very clear and well stated, even to someone like me who didn't follow the discussion which culminated in this patch. > 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 s/worth/worthwhile/ > alone may be worth it. And this final part addresses the big question which v1 left dangling (specifically, "why the proposed patch doesn't eliminate NO_OUTPUT altogether). Good. > Signed-off-by: Junio C Hamano <gitster@xxxxxxxxx>
