1 files changed, 30 insertions, 0 deletions
diff --git a/cli/js/util.ts b/cli/js/util.ts
index 013dc7ee1..77dc7db5b 100644
--- a/cli/js/util.ts
+++ b/cli/js/util.ts
@@ -223,3 +223,33 @@ export function splitNumberToParts(n: number): number[] {
   const higher = (n - lower) / 0x100000000;
   return [lower, higher];
 }
+
+/** Return the common path shared by the `paths`.
+ *
+ * @param paths The set of paths to compare.
+ * @param sep An optional separator to use. Defaults to `/`.
+ * @internal
+ */
+export function commonPath(paths: string[], sep = "/"): string {
+  const [first = "", ...remaining] = paths;
+  if (first === "" || remaining.length === 0) {
+    return "";
+  }
+  const parts = first.split(sep);
+
+  let endOfPrefix = parts.length;
+  for (const path of remaining) {
+    const compare = path.split(sep);
+    for (let i = 0; i < endOfPrefix; i++) {
+      if (compare[i] !== parts[i]) {
+        endOfPrefix = i;
+      }
+    }
+
+    if (endOfPrefix === 0) {
+      return "";
+    }
+  }
+  const prefix = parts.slice(0, endOfPrefix).join(sep);
+  return prefix.endsWith(sep) ? prefix : `${prefix}${sep}`;
+}