1 files changed, 44 insertions, 0 deletions
diff --git a/packages/lsp/src/root.ts b/packages/lsp/src/root.ts
new file mode 100644
index 0000000..fc7814e
--- /dev/null
+++ b/packages/lsp/src/root.ts
@@ -0,0 +1,44 @@
+/**
+ * Root finder — nearest ancestor containing a marker file, bounded at cwd.
+ */
+
+export async function findRoot(
+	startDir: string,
+	cwd: string,
+	markers: readonly string[],
+	exists: (path: string) => Promise<boolean>,
+): Promise<string> {
+	const normalizedStart = normalizePath(startDir);
+	const normalizedCwd = normalizePath(cwd);
+
+	let current = normalizedStart;
+	while (true) {
+		for (const marker of markers) {
+			const markerPath = current === "/" ? `/${marker}` : `${current}/${marker}`;
+			if (await exists(markerPath)) {
+				return current;
+			}
+		}
+		if (current === normalizedCwd || current === "/") {
+			return normalizedCwd;
+		}
+		const parent = getParent(current);
+		if (parent === current) return normalizedCwd;
+		current = parent;
+	}
+}
+
+function normalizePath(p: string): string {
+	let normalized = p.replace(/\\/g, "/");
+	if (normalized.length > 1 && normalized.endsWith("/")) {
+		normalized = normalized.slice(0, -1);
+	}
+	return normalized || "/";
+}
+
+function getParent(p: string): string {
+	if (p === "/") return "/";
+	const lastSlash = p.lastIndexOf("/");
+	if (lastSlash <= 0) return "/";
+	return p.slice(0, lastSlash) || "/";
+}