filter-branch: Add tests for submodules in tree-filter

Add tests to make sure that:

1) a submodule can be removed and its content replaced with regular files
   ('rewrite submodule with another content'). This test passes only with
   the previous patch applied.

2) it is possible to replace submodule revision by direct index
   manipulation ('replace submodule revision'). Although it would be
   better to run such a filter in --index-filter, this test shows that
   this functionality is not broken by the previous patch. This succeeds
   both with and without the previous patch.

Signed-off-by: Michal Sojka <sojkam1@fel.cvut.cz>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7003-filter-branch.sh

@@ -306,4 +306,43 @@ test_expect_success '--remap-to-ancestor with filename filters' '
 	test $orig_invariant = $(git rev-parse invariant)
 '
 
+test_expect_success 'setup submodule' '
+	rm -fr ?* .git &&
+	git init &&
+	test_commit file &&
+	mkdir submod &&
+	submodurl="$PWD/submod" &&
+	( cd submod &&
+	  git init &&
+	  test_commit file-in-submod ) &&
+	git submodule add "$submodurl" &&
+	git commit -m "added submodule" &&
+	test_commit add-file &&
+	( cd submod && test_commit add-in-submodule ) &&
+	git add submod &&
+	git commit -m "changed submodule" &&
+	git branch original HEAD
+'
+
+orig_head=`git show-ref --hash --head HEAD`
+
+test_expect_success 'rewrite submodule with another content' '
+	git filter-branch --tree-filter "test -d submod && {
+					 rm -rf submod &&
+					 git rm -rf --quiet submod &&
+					 mkdir submod &&
+					 : > submod/file
+					 } || :" HEAD &&
+	test $orig_head != `git show-ref --hash --head HEAD`
+'
+
+test_expect_success 'replace submodule revision' '
+	git reset --hard original &&
+	git filter-branch -f --tree-filter \
+	    "if git ls-files --error-unmatch -- submod > /dev/null 2>&1
+	     then git update-index --cacheinfo 160000 0123456789012345678901234567890123456789 submod
+	     fi" HEAD &&
+	test $orig_head != `git show-ref --hash --head HEAD`
+'
+
 test_done