Recycle wf_root output

_reformat-common.bash

@@ -41,6 +41,13 @@ function project_root() {
 # When run from a dir with would-format configured, return
 # would-format's own directory
 wf_root() {
+    set +u
+    if [[ ! -z "${WF_ROOT}" ]]; then
+        echo "$WF_ROOT"
+        return 0
+    fi
+    set -u
+
     arg=$(pwd)/bin/would-reformat.sh
 
     pr=$(project_root "$arg")