t6020: fix incompatible parameter expansion

Ævar reported that the function `make_user_friendly_and_stable_output()`
failed on a i386 box (gcc45) in the gcc farm boxes with error:

    sed: couldn't re-allocate memory

It turns out that older versions of bash (4.3) or dash (0.5.7) cannot
evaluate expression like `${A%${A#???????}}` used to get the leading 7
characters of variable A.

Replace the incompatible parameter expansion so that t6020 works on
older version of bash or dash.

Reported-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Jiang Xin <zhiyou.jx@alibaba-inc.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t6020-bundle-misc.sh

@@ -80,30 +80,42 @@ test_commit_setvar () {
 	eval $var=$oid
 }
 
+get_abbrev_oid () {
+	oid=$1 &&
+	suffix=${oid#???????} &&
+	oid=${oid%$suffix} &&
+	if test -n "$oid"
+	then
+		echo "$oid"
+	else
+		echo "undefined-oid"
+	fi
+}
+
 # Format the output of git commands to make a user-friendly and stable
 # text.  We can easily prepare the expect text without having to worry
 # about future changes of the commit ID and spaces of the output.
 make_user_friendly_and_stable_output () {
 	sed \
-		-e "s/${A%${A#???????}}[0-9a-f]*/<COMMIT-A>/g" \
-		-e "s/${B%${B#???????}}[0-9a-f]*/<COMMIT-B>/g" \
-		-e "s/${C%${C#???????}}[0-9a-f]*/<COMMIT-C>/g" \
-		-e "s/${D%${D#???????}}[0-9a-f]*/<COMMIT-D>/g" \
-		-e "s/${E%${E#???????}}[0-9a-f]*/<COMMIT-E>/g" \
-		-e "s/${F%${F#???????}}[0-9a-f]*/<COMMIT-F>/g" \
-		-e "s/${G%${G#???????}}[0-9a-f]*/<COMMIT-G>/g" \
-		-e "s/${H%${H#???????}}[0-9a-f]*/<COMMIT-H>/g" \
-		-e "s/${I%${I#???????}}[0-9a-f]*/<COMMIT-I>/g" \
-		-e "s/${J%${J#???????}}[0-9a-f]*/<COMMIT-J>/g" \
-		-e "s/${K%${K#???????}}[0-9a-f]*/<COMMIT-K>/g" \
-		-e "s/${L%${L#???????}}[0-9a-f]*/<COMMIT-L>/g" \
-		-e "s/${M%${M#???????}}[0-9a-f]*/<COMMIT-M>/g" \
-		-e "s/${N%${N#???????}}[0-9a-f]*/<COMMIT-N>/g" \
-		-e "s/${O%${O#???????}}[0-9a-f]*/<COMMIT-O>/g" \
-		-e "s/${P%${P#???????}}[0-9a-f]*/<COMMIT-P>/g" \
-		-e "s/${TAG1%${TAG1#???????}}[0-9a-f]*/<TAG-1>/g" \
-		-e "s/${TAG2%${TAG2#???????}}[0-9a-f]*/<TAG-2>/g" \
-		-e "s/${TAG3%${TAG3#???????}}[0-9a-f]*/<TAG-3>/g" \
+		-e "s/$(get_abbrev_oid $A)[0-9a-f]*/<COMMIT-A>/g" \
+		-e "s/$(get_abbrev_oid $B)[0-9a-f]*/<COMMIT-B>/g" \
+		-e "s/$(get_abbrev_oid $C)[0-9a-f]*/<COMMIT-C>/g" \
+		-e "s/$(get_abbrev_oid $D)[0-9a-f]*/<COMMIT-D>/g" \
+		-e "s/$(get_abbrev_oid $E)[0-9a-f]*/<COMMIT-E>/g" \
+		-e "s/$(get_abbrev_oid $F)[0-9a-f]*/<COMMIT-F>/g" \
+		-e "s/$(get_abbrev_oid $G)[0-9a-f]*/<COMMIT-G>/g" \
+		-e "s/$(get_abbrev_oid $H)[0-9a-f]*/<COMMIT-H>/g" \
+		-e "s/$(get_abbrev_oid $I)[0-9a-f]*/<COMMIT-I>/g" \
+		-e "s/$(get_abbrev_oid $J)[0-9a-f]*/<COMMIT-J>/g" \
+		-e "s/$(get_abbrev_oid $K)[0-9a-f]*/<COMMIT-K>/g" \
+		-e "s/$(get_abbrev_oid $L)[0-9a-f]*/<COMMIT-L>/g" \
+		-e "s/$(get_abbrev_oid $M)[0-9a-f]*/<COMMIT-M>/g" \
+		-e "s/$(get_abbrev_oid $N)[0-9a-f]*/<COMMIT-N>/g" \
+		-e "s/$(get_abbrev_oid $O)[0-9a-f]*/<COMMIT-O>/g" \
+		-e "s/$(get_abbrev_oid $P)[0-9a-f]*/<COMMIT-P>/g" \
+		-e "s/$(get_abbrev_oid $TAG1)[0-9a-f]*/<TAG-1>/g" \
+		-e "s/$(get_abbrev_oid $TAG2)[0-9a-f]*/<TAG-2>/g" \
+		-e "s/$(get_abbrev_oid $TAG3)[0-9a-f]*/<TAG-3>/g" \
 		-e "s/ *\$//"
 }