+## Quilt driver
+
+quilt()
+{
+ if [ -z "$_dep_is_tgish" ]; then
+ # This dep is not for rewrite
+ return
+ fi
+
+ filename="$output/$_dep.diff"
+ if [ -e "$filename" ]; then
+ # We've already seen this dep
+ return
+ fi
+
+ mkdir -p "$(dirname "$filename")"
+ tg patch "$_dep" >"$filename"
+ echo "$_dep.diff -p1" >>"$output/series"
+ echo "Exported $_dep"
+}
+
+
+## Machinery
+
+if [ "$driver" = "collapse" ]; then
+ [ -n "$output" ] ||
+ die "no target branch specified"
+ ! git rev-parse --verify "$output" >/dev/null 2>&1 ||
+ die "target branch '$output' already exists; first run: git branch -D $output"
+
+elif [ "$driver" = "quilt" ]; then
+ [ -n "$output" ] ||
+ die "no target directory specified"
+ [ ! -e "$output" ] ||
+ die "target directory already exists: $output"
+
+ mkdir -p "$output"
+fi
+
+
+driver()
+{
+ branch_needs_update >/dev/null
+ [ "$_ret" -eq 0 ] ||
+ die "cancelling export of $_dep (-> $_name): branch not up-to-date"
+
+ $driver
+}
+
+# Call driver on all the branches - this will happen
+# in topological order.
+recurse_deps driver "$name"
+(_ret=0; _dep="$name"; _name=""; _dep_is_tgish=1; driver)
+
+
+if [ "$driver" = "collapse" ]; then
+ git update-ref "refs/heads/$output" "$(cat "$playground/$name")"
+
+ depcount="$(cat "$playground/^ticker" | wc -l)"
+ echo "Exported topic branch $name (total $depcount topics) to branch $output"