Spectron version: 3.6.2

Intention

Working on microsoft/vscode#25291, I want to be able to pass --user-data-dir to my Electron application.

Problem Description

When instantiating Application and passing --user-data-dir as an argument to args, the argument is not passed as native Chrome argument, but as a Spectron one.

new Application({
            path: electronPath,
            args: [cwd, '--user-data-dir=C:\\test-user-dir'],
            env: env
        });

This creates a problem that running application instance contains two --user-data-dir parameters when spawned, where second one is a fake directory created by WebDriver (because --user-data-dir is not supplied and the one specified in constructor is passed with spectron-arg prefix to it):

"C:\Executable.exe" c:\cwd --user-data-dir=C:\test-user-dir --disable-background-networking --disable-client-side-phishing-detection --disable-default-apps --disable-hang-monitor --disable-infobars --disable-popup-blocking --disable-prompt-on-repost --disable-sync --disable-web-resources --enable-logging --ignore-certificate-errors --load-component-extension=C:\Users\t-mikapo\AppData\Local\Temp\scoped_dir15424_30047\internal --log-level=0 --metrics-recording-only --no-first-run --password-store=basic --remote-debugging-port=12730 --safebrowsing-disable-auto-update --test-type=webdriver --use-mock-keychain --user-data-dir=C:\Users\t-mikapo\AppData\Local\Temp\scoped_dir15424_28295 data:,

See --user-data-dir=C:\test-user-dir and --user-data-dir=C:\Users\t-mikapo\AppData\Local\Temp\scoped_dir15424_28295 above.

Verification

To verify that WebDriver does not create a fake directory I've hardcoded var args = ['--user-data-dir=C:\test-user-dir'] here:
https://github.com/electron/spectron/blob/master/lib/application.js#L137.

This resulted in Electron app running with the provided '--user-data-dir' and no fake one was created.

Proposal

Currently Application args accept arguments that are passed only to executable. Even API says See here for details on the Chrome arguments., they are not (or not fully with respect to the scenario above) taken into account.

It would be great to have a separate option on Application constructor, that allows to pass actual Chrome arguments to it. Please let me know if PR is needed.