CdkOverlay icw FlexibleConnectedPositionStrategy breaks iOS when keyboard + scrolling

[jpzwarte]

Bug, feature request, or proposal:

So Overlay adds a div.cdk-overlay-container to the body with position:fixed that fills the entire viewport. Based on that behavior, when positioning the overlay component, FlexibleConnectedPositionStrategy._getOriginPoint returns the top value of the ClientRect. Since the overlay container is fixed, there is no need to take the scroll position into account.

So the component i'm displaying in the overlay contains a <input type="text"> (it's a dropdown component with autocomplete/filtering ability).

Enter iOS: When the overlay is shown, the text input gets the focus automatically. This causes iOS to show the keyboard. This also causes iOS to "disable" all fixed elements. position: fixed becomes position: absolute when the keyboard is visible.

So suddenly the behavior described in the first paragraph no longer works. It should now take the scroll position into account when calculating the originPoint.

What is the expected behavior?

It should position the overlay correctly when the iOS keyboard is visible.

What is the current behavior?

It fails to take the scroll position into account when the iOS keyboard is visible.

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

Latest angular/CDK, all iOS versions.

[jpzwarte]

cc @crisbeto @josephperrott

[crisbeto]

Closing as a duplicate of #6341.

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