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

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>

diff --git a/diffcore-delta.c b/diffcore-delta.c
index 18d8f766d70108e868a5bb21ad6c45550bb8c34d..0b45f644001ed827214868ee799f3b1f0f5570d1 100644 (file)
--- a/diffcore-delta.c
+++ b/diffcore-delta.c
@@ -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;
 }

diff --git a/t/t4001-diff-rename.sh b/t/t4001-diff-rename.sh
index 3dc90470446dbb81e9c9421dbc7c21d3648d91f4..c0d88e5e0d6afc97a9c87202bd8ead31b6c50e0c 100755 (executable)
--- a/t/t4001-diff-rename.sh
+++ b/t/t4001-diff-rename.sh
@@ -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