Commits on Mar 11, 2023

1. [macOS] Forward mouseDown/Up to view controller …

   This works around an AppKit bug in which mouseDown/mouseUp events are
   not correctly forwarded up the responder chain for views nested inside
   an NSPopover if (and only if) the macOS "Reduce Transparency"
   accessibility setting is enabled in the System Settings.
   
   When the above conditions are satisfied, the nested NSView receives the
   mouseDown:/mouseUp: call but if it delegates to the default
   implementation (implemented in NSResponder) mouseDown/mouseUp calls are
   triggered on containing views (in our case FlutterViewWrapper) but not
   triggered on the view controller and other responders in the responder
   chain until we an _NSPopoverWindow class is hit.
   
   A minimal AppKit-only (non-Flutter) repro shows this behaviour repros
   with even a minimal NSViewController implementation and an unmodified NSView.
   See: https://github.com/cbracken/PopoverRepro
   
   A radar has been filed with Apple and a copy posted to OpenRadar.
   See: http://www.openradar.me/FB12050037
   
   In order to work around this bug, we override mouseDown/mouseUp in the
   topmost containing view of FlutterView (in our case, FlutterViewWrapper)
   to have the behaviour documented as the default behaviour in
   NSResponder's mouseDown/mouseUp documentation. In otherwords, to simply
   forward the call to self.nextResponder.
   See: https://developer.apple.com/documentation/appkit/nsresponder/1524634-mousedown
   
   Because replicating the exact configuration of a FlutterView contained
   in an NSPopover and System Settings that have been modified to enable
   the "Reduce Transparency" setting is difficult and likely error-prone in
   infra, we instead simulate the bug by testing that even if NSResponder's
   mouseDown/mouseUp method are swizzled to no-op, these calls are
   correctly forwarded to the next responder in the chain.
   
   If, in the future Apple does fix this issue, this workaround can be
   removed once Flutter's minimum supported macOS SDK is at least the
   version that contains the fix.
   
   Issue: flutter/flutter#115015

   

   cbracken committed Mar 11, 2023
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