preserve extra info across PeekMessage (#5838) #6014
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Addresses #5442
This is a port of a servicing fix in .NET 4.7-4.8.
Description
As part of a mitigation for an OS problem (delivering WM_CHAR messages after the related WM_KEYDOWN message has been marked "handled"), WPF reorders the thread's message queue by removing a certain private message, then re-inserting it at the end of the queue. This happens early while acting on a WM_KEYDOWN, but has the (undocumented) side-effect of overwriting the "extra info" associated with the WM_KEYDOWN.
This is fixed by preserving the "extra info" across the call that removes the private message.
Customer Impact
Extra info attached to a WM_KEYDOWN is lost.
Regression
No.
Testing
Ad-hoc around customer scenario.
Standard regression testing.
Risk
Low. Port of a .NETFx servicing fix released earlier this year.