Language server hangs on initialize when workspace root has no rescript.json (monorepo)

[hiovi]

Summary

When the editor workspace root is a monorepo root that does not itself contain a rescript.json, the language server never responds to the LSP initialize request — it hangs silently and produces no stderr output. Editors that spawn one server instance per workspace (Zed) are left with a dead server: every request (formatting, hover, completions, code actions) fails until the process is torn down.

Environment

• @rescript/language-server 1.74.0 (also reproduced on 1.72.0)
• macOS 26, Node v24.13.0
• Editor: Zed 1.18 (extension rescript 0.4.4), but this is reproducible standalone over stdio

Repo layout

  monorepo/                      ← workspace root, no rescript.json here
    packages/
      my-app/
        rescript.json            ← the actual ReScript project
        src/...

Reproduction

Pipe a framed initialize request to the server over stdio:

  python3 - <<'EOF'
  import subprocess, json
  msg = json.dumps({"jsonrpc":"2.0","id":1,"method":"initialize","params":{
    "rootUri":"file:///path/to/monorepo",   # no rescript.json at this level
    "capabilities":{}}})
  payload = f"Content-Length: {len(msg)}\r\n\r\n{msg}"
  p = subprocess.Popen(["node","node_modules/@rescript/language-server/out/cli.js","--stdio"],
                       stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
  try:
      out, err = p.communicate(payload.encode(), timeout=10)
      print("responded:", b'"id":1' in out)
  except subprocess.TimeoutExpired:
      p.kill(); print("HUNG: no response in 10s")
  EOF

Results

scenario	result
rootUri = directory containing rescript.json	responds immediately, documentFormattingProvider: true
rootUri = monorepo root (no rescript.json at root)	hangs indefinitely, no stderr
same, with workspaceFolders including the rescript.json dir	still hangs
same, with rootUri at root + cwd at the rescript.json dir	still hangs
both 1.72.0 and 1.74.0	identical behavior

Expected behavior

The server should respond to initialize even when the root has no rescript.json — either by locating the nearest project in the workspace, or by reporting an empty/unsupported workspace so the editor can degrade gracefully (or the user can be told to add the project folder).

Actual behavior

Silent hang. In Zed this manifests as: launch → cannot read LSP message headers → teardown → every subsequent request logs rescript-language-server failed: server shut down. Formatting-on-save, hover, and completions are all silently dead. The user sees no error explaining that the workspace root needs to be (or contain) a ReScript project.

Workarounds

• Open the directory containing rescript.json as the workspace root, or
• Bypass the LSP formatter via an external formatter (rescript format --stdin .res) — but semantic features remain dead.