diff --cached: do not borrow from a work tree when a path is marked as assume-unchanged

When the index says that the file in the work tree that corresponds to the blob object that is used for comparison is known to be unchanged, "diff" reads from the file and applies convert_to_git(), instead of inflating the object, to feed the internal diff engine with, because an earlier benchnark found that it tends to be faster to use this optimization. However, the index can lie when the path is marked as assume-unchanged. Disable the optimization for such paths. Signed-off-by: Junio C Hamano <gitster@pobox.com>

Junio C Hamano committed Mar 22, 2009 at 15:26 UTC 150115aded2e1e0a83db7366f59e4b5bf1aa8135

2 files changed +17 -1

diff.c

+9 -1

@@ -1687,7 +1687,8 @@ static int reuse_worktree_file(const char *name, const unsigned char *sha1, int

1687 struct stat st;

1688 int pos, len;

1689

1690 - /* We do not read the cache ourselves here, because the

1690 + /*

1691 + * We do not read the cache ourselves here, because the

1692 * benchmark with my previous version that always reads cache

1693 * shows that it makes things worse for diff-tree comparing

1694 * two linux-2.6 kernel trees in an already checked out work

@@ -1727,6 +1728,13 @@ static int reuse_worktree_file(const char *name, const unsigned char *sha1, int

1728 if (hashcmp(sha1, ce->sha1) || !S_ISREG(ce->ce_mode))

1729 return 0;

1730

1731 + /*

1732 + * If ce is marked as "assume unchanged", there is no

1733 + * guarantee that work tree matches what we are looking for.

1734 + */

1735 + if (ce->ce_flags & CE_VALID)

1736 + return 0;

1737 +

1738 /*

1739 * If ce matches the file in the work tree, we can reuse it.

1740 */

t/t4020-diff-external.sh

@@ -107,4 +107,12 @@ test_expect_success 'force diff with "diff"' '

107 test_cmp ../t4020/diff.NUL actual

108 '

109

110 +test_expect_success 'diff --cached' '

111 + git add file &&

112 + git update-index --assume-unchanged file &&

113 + echo second >file &&

114 + git diff --cached >actual &&

115 + test_cmp ../t4020/diff.NUL actual

116 +'

117 +

118 test_done