mx-window-missing — No Window Created

Severity: warning | Blocks morph build: no

What this error means

Neither your entry file nor your project config declares a window: there is no windowConfig export in the entry file and no window values in morph.config.json:

warning : mx-window-missing : No window declared — no `windowConfig` export and no `window` section in morph.config.json
  hint: Add `"window": { "title": "App", "width": 800, "height": 600 }` to morph.config.json
  Learn more: https://morph.levizr.com/docs/errors/mx-window-missing

This is a warning: the file still lints, but a build with no window has nothing to show.

Why Morph raises it

A Morph app is a native window containing your component tree. The window settings resolve in two layers:

1. Project defaults — the window section of morph.config.json (title, width, height). morph new always scaffolds these, so most projects already have them.
2. Per-file override — export const windowConfig = {...} in the entry (or route) file, which additionally supports size limits (minWidth, maxWidth, ...) the config section does not carry.

Exporting windowConfig is not required. When the entry file has no export, Morph falls back to the config values. This warning fires only when the fallback is missing too — no export in code and no values in config — meaning the runtime would have to guess the title and size, risking an invisible or zero-sized window with no indication of why. Non-entry component files never trigger it (only the entry module renders as a window).

Example that triggers it

morph.config.json with no window section:

{
  "name": "my-app",
  "entry": "src/App.mx"
}

// ❌ No windowConfig export either — mx-window-missing
export default function App() {
  return <div>Hello</div>;
}

With a normal scaffolded config (which includes "window"), the same file produces no warning at all.

How to fix

Prefer the config fix — one place, applies to the whole app:

// ✅ morph.config.json — project-wide window defaults
{
  "name": "My App",
  "entry": "src/App.mx",
  "window": { "title": "My App", "width": 800, "height": 600 }
}

Or override per file with windowConfig (also the only way to set size limits):

// ✅ Entry-file override with size limits
export const windowConfig = {
  title: "My App",
  width: 800,
  height: 600,
  minWidth: 400,
  minHeight: 300,
};

export default function App() {
  return <div>Hello</div>;
}

Steps:

1. Check morph.config.json for a window object with title/width/ height — if present, this warning should already be gone; if you still see it, the config file is not being picked up (wrong directory).
2. If the section is missing, add it (preferred), or export windowConfig from the entry file.
3. Re-run morph check — the warning clears.

Tuning this rule

Promote it to an error if you want missing windows to fail CI:

{
  "lint": {
    "severities": { "mx-window-missing": "error" }
  }
}

See also

• mx-windowconfig-key — unknown windowConfig key
• mx-windowconfig-type — wrong windowConfig value type
• mx-route-no-export — route file without component
• Windows and Routing Guide
• How to Configure a Morph Project