Commits on May 14, 2021

1. [CoreGraphics] Adjust CGPDFOperatorTable to not use a generic Action … …

   …delegate.
   
   * CoreCLR doesn't support generic Action delegates in reverse (P/Invokes), so
     we need to find a different solution.
   * The native CGPDFOperatorTable callback API is not very friendly to us,
     because we can't pass it callback-specific data, which means that the
     managed caller must conform to the FullAOT requirement of the managed
     callback (must be a static function; must have a MonoPInvokeCallback
     attribute).
   * We can leverage the new function pointer syntax in C# 9 to make these
     requirements enforced by the C# compiler (unmanaged function pointer +
     UnmanagedCallersOnly attribute). The resulting API is still clunky to use,
     but I don't see any way around that.
   
   Fixes this monotouch-test failure with CoreCLR:
   
       [FAIL] Tamarin : System.Runtime.InteropServices.MarshalDirectiveException : Cannot marshal 'parameter #3': Non-blittable generic types cannot be marshaled.
                  at CoreGraphics.CGPDFOperatorTable.CGPDFOperatorTableSetCallback(IntPtr table, String name, Action`2 callback)
                  at CoreGraphics.CGPDFOperatorTable.SetCallback(String name, Action`2 callback)
                  at MonoTouchFixtures.CoreGraphics.PDFScannerTest.Tamarin() in xamarin-macios/tests/monotouch-test/CoreGraphics/PDFScannerTest.cs:line 102
   
   Ref: dotnet/runtime#32963

   

   rolfbjarne committed May 14, 2021
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