diff.c: output correct index lines for a split diff

A patch that changes the filetype (e.g. regular file to symlink) of a path
must be split into a deletion event followed by a creation event, which
means that we need to have two independent metainfo lines for each.
However, the code reused the single set of metainfo lines.

As the blob object names recorded on the index lines are usually not used
nor validated on the receiving end, this is not an issue with normal use
of the resulting patch.  However, when accepting a binary patch to delete
a blob, git-apply verified that the postimage blob object name on the
index line is 0{40}, hence a patch that deletes a regular file blob that
records binary contents to create a blob with different filetype (e.g. a
symbolic link) failed to apply.  "git am -3" also uses the blob object
names recorded on the index line, so it would also misbehave when
synthesizing a preimage tree.

This moves the code to generate metainfo lines around, so that two
independent sets of metainfo lines are used for the split halves.

Additional tests by Jeff King.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/t/t4114-apply-typechange.sh b/t/t4114-apply-typechange.sh
index 55334927ab..0f185caa44 100755
--- a/t/t4114-apply-typechange.sh
+++ b/t/t4114-apply-typechange.sh
@@ -25,6 +25,10 @@ test_expect_success 'setup repository and commits' '
 	git update-index foo &&
 	git commit -m "foo back to file" &&
 	git branch foo-back-to-file &&
+	printf "\0" > foo &&
+	git update-index foo &&
+	git commit -m "foo becomes binary" &&
+	git branch foo-becomes-binary &&
 	rm -f foo &&
 	git update-index --remove foo &&
 	mkdir foo &&
@@ -85,6 +89,20 @@ test_expect_success 'symlink becomes file' '
 	'
 test_debug 'cat patch'
 
+test_expect_success 'binary file becomes symlink' '
+	git checkout -f foo-becomes-binary &&
+	git diff-tree -p --binary HEAD foo-symlinked-to-bar > patch &&
+	git apply --index < patch
+	'
+test_debug 'cat patch'
+
+test_expect_success 'symlink becomes binary file' '
+	git checkout -f foo-symlinked-to-bar &&
+	git diff-tree -p --binary HEAD foo-becomes-binary > patch &&
+	git apply --index < patch
+	'
+test_debug 'cat patch'
+
 
 test_expect_success 'symlink becomes directory' '
 	git checkout -f foo-symlinked-to-bar &&