git/t/t4000-diff-format.sh
Junio C Hamano 9d484b92ed diff: fix interaction between the "-s" option and other options
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>
2023-05-05 14:24:32 -07:00

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#!/bin/sh
#
# Copyright (c) 2005 Junio C Hamano
#
test_description='Test built-in diff output engine.
We happen to know that all diff plumbing and diff Porcelain share the
same command line parser, so testing one should be sufficient; pick
diff-files as a representative.
'
TEST_PASSES_SANITIZE_LEAK=true
. ./test-lib.sh
. "$TEST_DIRECTORY"/lib-diff.sh
echo >path0 'Line 1
Line 2
line 3'
cat path0 >path1
chmod +x path1
mkdir path2
>path2/path3
test_expect_success 'update-index --add two files with and without +x.' '
git update-index --add path0 path1 path2/path3
'
mv path0 path0-
sed -e 's/line/Line/' <path0- >path0
chmod +x path0
rm -f path1
test_expect_success 'git diff-files -p after editing work tree.' '
git diff-files -p >actual
'
# that's as far as it comes
if [ "$(git config --get core.filemode)" = false ]
then
say 'filemode disabled on the filesystem'
test_done
fi
cat >expected <<\EOF
diff --git a/path0 b/path0
old mode 100644
new mode 100755
--- a/path0
+++ b/path0
@@ -1,3 +1,3 @@
Line 1
Line 2
-line 3
+Line 3
diff --git a/path1 b/path1
deleted file mode 100755
--- a/path1
+++ /dev/null
@@ -1,3 +0,0 @@
-Line 1
-Line 2
-line 3
EOF
test_expect_success 'validate git diff-files -p output.' '
compare_diff_patch expected actual
'
test_expect_success 'git diff-files -s after editing work tree' '
git diff-files -s >actual 2>err &&
test_must_be_empty actual &&
test_must_be_empty err
'
test_expect_success 'git diff-files --no-patch as synonym for -s' '
git diff-files --no-patch >actual 2>err &&
test_must_be_empty actual &&
test_must_be_empty err
'
test_expect_success 'git diff-files --no-patch --patch shows the patch' '
git diff-files --no-patch --patch >actual &&
compare_diff_patch expected actual
'
test_expect_success 'git diff-files --no-patch --patch-with-raw shows the patch and raw data' '
git diff-files --no-patch --patch-with-raw >actual &&
grep -q "^:100644 100755 .* $ZERO_OID M path0\$" actual &&
tail -n +4 actual >actual-patch &&
compare_diff_patch expected actual-patch
'
test_expect_success 'git diff-files --patch --no-patch does not show the patch' '
git diff-files --patch --no-patch >actual 2>err &&
test_must_be_empty actual &&
test_must_be_empty err
'
# Smudge path2/path3 so that dirstat has something to show
date >path2/path3
for format in stat raw numstat shortstat summary \
dirstat cumulative dirstat-by-file \
patch-with-raw patch-with-stat compact-summary
do
test_expect_success "--no-patch in 'git diff-files --no-patch --$format' is a no-op" '
git diff-files --no-patch "--$format" >actual &&
git diff-files "--$format" >expect &&
test_cmp expect actual
'
test_expect_success "--no-patch clears all previous ones" '
git diff-files --$format -s -p >actual &&
git diff-files -p >expect &&
test_cmp expect actual
'
test_expect_success "--no-patch in 'git diff --no-patch --$format' is a no-op" '
git diff --no-patch "--$format" >actual &&
git diff "--$format" >expect &&
test_cmp expect actual
'
done
test_done