[Webkit-unassigned] [Bug 168403] New: sync-layer-positions-after-scroll fails if run after non-stable-viewport-scroll due to extraneous layouts

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=168403

            Bug ID: 168403
           Summary: sync-layer-positions-after-scroll fails if run after
                    non-stable-viewport-scroll due to extraneous layouts
    Classification: Unclassified
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Tools / Tests
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: thorton at apple.com
                CC: lforschler at apple.com

Created attachment 301685
  --> https://bugs.webkit.org/attachment.cgi?id=301685&action=review
logging

If you remove the viewport meta tag added to sync-layer-positions-after-scroll in https://bugs.webkit.org/show_bug.cgi?id=168376, and then:

run-webkit-tests -v --ios-simulator --no-retry-failures scrollingcoordinator/ios

You will see sync-layer-positions-after-scroll fail. If you run it by itself, it does not.

The attached logging is from a debugging session with smfr. For some reason, we get into a state where we are calling setViewportConstrainedObjectsNeedLayout repeatedly during scrolling with a fixedpos element, which breaks various assumptions of the test (causing the layer position to get set, and clearing the approximatePosition).

It seems like this is related to changing scale or useFlexibleViewport, or something, and smfr says he's seen it before.

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