Tauri spawns multiple windows with `app.create_window()` in certain situations

[woubuc]

Describe the bug

If no window is added in the config file, but a window is created through app.create_window(), if the Javascript code in that window imports @tauri-apps/api then Tauri will incorrectly spawn a second window pointing to index.html (the default). This happens both in dev and in release builds.

To Reproduce

Steps to reproduce the behavior:

1. Create a Tauri project with API
2. Add a frontend page with a Javascript module that contains an import * as Tauri from '@tauri-apps/api';
3. Remove all windows from the config file ("windows": [],)
4. Create a window in the app setup with a label that isn't main, that loads the frontend page with the api import:

app.create_window(
    "test".into(),
    WindowUrl::App("test".into()),
    |builder, attrs| (builder, attrs)
).expect("Could not create window");

5. Run the app
6. It will spawn the created window and then quickly after it will spawn a second window pointing to the index page of the frontend app

I've reduced my test project to the minimal code that reproduces the error: woubuc/tauri-double-windows-repro.

Expected behavior

I expect that only 1 window opens after 1 call to app.create_window().

Platform and Versions (required):

Operating System - Windows, version 10.0.19042 X64
Webview2 - 91.0.864.71

Node.js environment
  Node.js - 14.16.0
  @tauri-apps/cli - 1.0.0-beta.6
  @tauri-apps/api - 1.0.0-beta.5

Global packages
  npm - 6.14.11
  yarn - 1.22.4

Rust environment
  rustc - 1.53.0
  cargo - 1.53.0

App directory structure
/.git
/.idea
/.nuxt
/assets
/components
/dist
/i18n
/layouts
/node_modules
/pages
/src-tauri
/static
/types

App
  tauri.rs - 1.0.0-beta.5
  build-type - bundle
  CSP - default-src blob: data: filesystem: ws: wss: http: https: tauri: 'unsa
fe-eval' 'unsafe-inline' 'self' img-src: 'self'
  distDir - ../dist
  devPath - http://localhost:3000
  framework - Vue.js (Nuxt)
  bundler - Webpack

[woubuc]

The import doesn't have to happen on page load. If I remove the top-level import and instead add a button with this onclick handler..

async onClick() {
    await import('@tauri-apps/api');
}

..then when clicking the button, the second window will spawn just like with a top-level import.

Once this second window has spawned, clicking the button again (either in the original or the new window) does not spawn any additional windows.

[amrbashir]

I think I know where the bug happens, will open a PR in a second.

[woubuc]

I've pulled the branch with your fix and built de API package locally, and it seems to work. No more double windows! 😄

[amrbashir]

Thanks for testing it. I guess we can merge it soon.