filter-branch -d: Export GIT_DIR earlier

The improved error handling catches a bug in filter-branch when using
-d pointing to a path outside any git repository:

$ git filter-branch -d /tmp/foo master
fatal: Not a git repository (or any of the parent directories): .git

This error message comes from git for-each-ref in line 224. GIT_DIR is
set correctly by git-sh-setup (to the foo.git repository), but not
exported (yet).

Signed-off-by: Lars Noschinski <lars@public.noschinski.de>
Acked-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-filter-branch.sh

@@ -220,6 +220,12 @@ die ""
 # Remove tempdir on exit
 trap 'cd ../..; rm -rf "$tempdir"' 0
 
+ORIG_GIT_DIR="$GIT_DIR"
+ORIG_GIT_WORK_TREE="$GIT_WORK_TREE"
+ORIG_GIT_INDEX_FILE="$GIT_INDEX_FILE"
+GIT_WORK_TREE=.
+export GIT_DIR GIT_WORK_TREE
+
 # Make sure refs/original is empty
 git for-each-ref > "$tempdir"/backup-refs || exit
 while read sha1 type name
@@ -234,12 +240,6 @@ do
 	esac
 done < "$tempdir"/backup-refs
 
-ORIG_GIT_DIR="$GIT_DIR"
-ORIG_GIT_WORK_TREE="$GIT_WORK_TREE"
-ORIG_GIT_INDEX_FILE="$GIT_INDEX_FILE"
-GIT_WORK_TREE=.
-export GIT_DIR GIT_WORK_TREE
-
 # The refs should be updated if their heads were rewritten
 git rev-parse --no-flags --revs-only --symbolic-full-name \
 	--default HEAD "$@" > "$tempdir"/raw-heads || exit

t/t7003-filter-branch.sh

@@ -48,6 +48,18 @@ test_expect_success 'result is really identical' '
 	test $H = $(git rev-parse HEAD)
 '
 
+TRASHDIR=$(pwd)
+test_expect_success 'correct GIT_DIR while using -d' '
+	mkdir drepo &&
+	( cd drepo &&
+	git init &&
+	test_commit drepo &&
+	git filter-branch -d "$TRASHDIR/dfoo" \
+		--index-filter "cp \"$TRASHDIR\"/dfoo/backup-refs \"$TRASHDIR\"" \
+	) &&
+	grep drepo "$TRASHDIR/backup-refs"
+'
+
 test_expect_success 'Fail if commit filter fails' '
 	test_must_fail git filter-branch -f --commit-filter "exit 1" HEAD
 '