[PATCH] Make --follow support --find-copies-harder.

[Bo Yang <struggleyb.nku@gmail.com>]

'git diff --follow <commit1> <commit2> <path>' give users
the content difference of <path> between the two commits.
It will detect file copies/moves of <path> if there is any.
But with '--find-copies-harder', it does not take the
unmodified files as copy/move source. And this patch fix
this bug.

Signed-off-by: Bo Yang <struggleyb.nku@gmail.com>
---
 t/t4042-find-copies-harder.sh |   45 +++++++++++++++++++++++++++++++++++++++++
 tree-diff.c                   |    2 +
 2 files changed, 47 insertions(+), 0 deletions(-)
 create mode 100755 t/t4042-find-copies-harder.sh

diff --git a/t/t4042-find-copies-harder.sh b/t/t4042-find-copies-harder.sh
new file mode 100755
index 0000000..40d2122
--- /dev/null
+++ b/t/t4042-find-copies-harder.sh
@@ -0,0 +1,45 @@
+#!/bin/sh
+#
+# Copyright (c) 2010 Bo Yang
+#
+
+test_description='Test copy detection with --find-copies-harder in diff engine.
+
+'
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/diff-lib.sh
+
+echo >path0 'Line 1
+Line 2
+Line 3
+Line 4
+Line 5
+Line 6
+'
+
+test_expect_success \
+    'add a file path0 and commit.' \
+    'git add path0 &&
+     git commit -m "Add path0"'
+
+cat <path0 >path1
+test_expect_success \
+    'copy path0 to path1.' \
+    'git add path1 &&
+     git commit -m "Copy path1 from path0"'
+
+test_expect_success \
+    'find the copy path0 -> path1 harder' \
+    'git diff --follow --find-copies-harder HEAD^ HEAD path1 > current'
+cat >expected <<\EOF
+diff --git a/path0 b/path1
+similarity index 100%
+copy from path0
+copy to path1
+EOF
+
+test_expect_success \
+    'validate the output.' \
+    'compare_diff_patch current expected'
+
+test_done
diff --git a/tree-diff.c b/tree-diff.c
index fe9f52c..0dea53e 100644
--- a/tree-diff.c
+++ b/tree-diff.c
@@ -346,6 +346,8 @@ static void try_to_follow_renames(struct tree_desc *t1, struct tree_desc *t2, co
 
 	diff_setup(&diff_opts);
 	DIFF_OPT_SET(&diff_opts, RECURSIVE);
+	if (DIFF_OPT_TST(opt, FIND_COPIES_HARDER))
+		DIFF_OPT_SET(&diff_opts, FIND_COPIES_HARDER);
 	diff_opts.detect_rename = DIFF_DETECT_RENAME;
 	diff_opts.output_format = DIFF_FORMAT_NO_OUTPUT;
 	diff_opts.single_follow = opt->paths[0];
-- 
1.7.0.2.273.gc2413.dirty