filter-branch: deal with object name vs. pathname ambiguity in tree-filter

'git filter-branch' fails complaining about an ambiguous argument, if
a tree-filter renames a path and the new pathname happens to match an
existing object name.

After the tree-filter has been applied, 'git filter-branch' looks for
changed paths by running:

  git diff-index -r --name-only --ignore-submodules $commit

which then, because of the lack of disambiguating double-dash, can't
decide whether to treat '$commit' as revision or path and errors out.

Add that disambiguating double-dash after 'git diff-index's revision
argument to make sure that '$commit' is interpreted as a revision.

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: Jeff King <peff@peff.net>

git-filter-branch.sh

@@ -319,7 +319,7 @@ while read commit parents; do
 			die "tree filter failed: $filter_tree"
 
 		(
-			git diff-index -r --name-only --ignore-submodules $commit &&
+			git diff-index -r --name-only --ignore-submodules $commit -- &&
 			git ls-files --others
 		) > "$tempdir"/tree-state || exit
 		git update-index --add --replace --remove --stdin \

t/t7003-filter-branch.sh

@@ -418,4 +418,11 @@ test_expect_success 'filter commit message without trailing newline' '
 	test_cmp expect actual
 '
 
+test_expect_success 'tree-filter deals with object name vs pathname ambiguity' '
+	test_when_finished "git reset --hard original" &&
+	ambiguous=$(git rev-list -1 HEAD) &&
+	git filter-branch --tree-filter "mv file.t $ambiguous" HEAD^.. &&
+	git show HEAD:$ambiguous
+'
+
 test_done