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diff: teach diff to read algorithm from diff driver

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It can be useful to specify diff algorithms per file type. For example,
one may want to use the minimal diff algorithm for .json files, another
for .c files, etc.

The diff machinery already checks attributes for a diff driver. Teach
the diff driver parser a new type "algorithm" to look for in the
config, which will be used if a driver has been specified through the
attributes.

Enforce precedence of the diff algorithm by favoring the command line
option, then looking at the driver attributes & config combination, then
finally the diff.algorithm config.

To enforce precedence order, use a new `ignore_driver_algorithm` member
during options parsing to indicate the diff algorithm was set via command
line args.

Signed-off-by: John Cai <johncai86@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
John Cai
2023-02-20 21:04:42 +00:00
committed by Junio C Hamano
parent 11e95e16e8
commit a4cf900ee7
6 changed files with 97 additions and 11 deletions
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38
t/lib-diff-alternative.sh
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@ -105,10 +105,46 @@ index $file1..$file2 100644
}
EOF
cat >expect_diffstat <<EOF
file1 => file2 | 21 ++++++++++-----------
1 file changed, 10 insertions(+), 11 deletions(-)
EOF
STRATEGY=$1
test_expect_success "$STRATEGY diff from attributes" '
echo "file* diff=driver" >.gitattributes &&
git config diff.driver.algorithm "$STRATEGY" &&
test_must_fail git diff --no-index file1 file2 > output &&
cat expect &&
cat output &&
test_cmp expect output
'
test_expect_success "$STRATEGY diff from attributes has valid diffstat" '
echo "file* diff=driver" >.gitattributes &&
git config diff.driver.algorithm "$STRATEGY" &&
test_must_fail git diff --stat --no-index file1 file2 > output &&
test_cmp expect_diffstat output
'
test_expect_success "$STRATEGY diff" '
test_must_fail git diff --no-index "--$STRATEGY" file1 file2 > output &&
test_must_fail git diff --no-index "--diff-algorithm=$STRATEGY" file1 file2 > output &&
test_cmp expect output
'
test_expect_success "$STRATEGY diff command line precedence before attributes" '
echo "file* diff=driver" >.gitattributes &&
git config diff.driver.algorithm myers &&
test_must_fail git diff --no-index "--diff-algorithm=$STRATEGY" file1 file2 > output &&
test_cmp expect output
'
test_expect_success "$STRATEGY diff attributes precedence before config" '
git config diff.algorithm default &&
echo "file* diff=driver" >.gitattributes &&
git config diff.driver.algorithm "$STRATEGY" &&
test_must_fail git diff --no-index file1 file2 > output &&
test_cmp expect output
'