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diffcore-delta: avoid ignoring final 'line' of file

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hash_chars() would hash lines to integers, and store them in a spanhash,
but cut lines at 64 characters.  Thus, whenever it reached 64 characters
or a newline, it would create a new spanhash.  The problem is, the final
part of the file might not end 64 characters after the previous 'line'
and might not end with a newline.  This could, for example, cause an
85-byte file with 12 lines and only the first character in the file
differing to appear merely 23% similar rather than the expected 97%.
Ensure the last line is included, and add a testcase that would have
caught this problem.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Elijah Newren 2024-01-13 04:26:13 +00:00 committed by Junio C Hamano
parent ec58344906
commit 1c5bc6971e
2 changed files with 28 additions and 0 deletions
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4
diffcore-delta.c
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@ -159,6 +159,10 @@ static struct spanhash_top *hash_chars(struct repository *r,
n = 0;
accum1 = accum2 = 0;
}
if (n > 0) {
hashval = (accum1 + accum2 * 0x61) % HASHBASE;
hash = add_spanhash(hash, hashval, n);
}
QSORT(hash->data, (size_t)1ul << hash->alloc_log2, spanhash_cmp);
return hash;
}

24
t/t4001-diff-rename.sh
View File

@ -286,4 +286,28 @@ test_expect_success 'basename similarity vs best similarity' '
test_cmp expected actual
'
test_expect_success 'last line matters too' '
{
test_write_lines a 0 1 2 3 4 5 6 7 8 9 &&
printf "git ignores final up to 63 characters if not newline terminated"
} >no-final-lf &&
git add no-final-lf &&
git commit -m "original version of file with no final newline" &&
# Change ONLY the first character of the whole file
{
test_write_lines b 0 1 2 3 4 5 6 7 8 9 &&
printf "git ignores final up to 63 characters if not newline terminated"
} >no-final-lf &&
git add no-final-lf &&
git mv no-final-lf still-absent-final-lf &&
git commit -a -m "rename no-final-lf -> still-absent-final-lf" &&
git diff-tree -r -M --name-status HEAD^ HEAD >actual &&
sed -e "s/^R[0-9]* /R /" actual >actual.munged &&
cat >expected <<-\EOF &&
R no-final-lf still-absent-final-lf
EOF
test_cmp expected actual.munged
'
test_done