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AmbiguousMatchException on System.Text.Json deserialization with FSharp.Core version 9.0.300 #18596
Description
When I deserialize FSharp class I get this exception
Repro steps
just download and run this project
MultipleCompilationMappingAttributesRepro.zip
Expected behavior
No exception
Actual behavior
System.Reflection.AmbiguousMatchException: Multiple custom attributes of the same type 'Microsoft.FSharp.Core.CompilationMappingAttribute' found.
Known workarounds
Downgrade to 9.0.202 or lower
Related information
- .NET 8, 9
Activity
T-Gro commentedon May 23, 2025
This was addressed with dotnet/runtime#114961 , duplicate of dotnet/runtime#114824
cmeeren commentedon Jun 13, 2025
As far as I can tell, a fix was published in .NET 9.0.6 (SDK 9.0.301). At least that was the milestone used here. But when running with FSharp.Core 9.0.300 on .NET 9.0.6, I still get this error. It therefore seems I have no recourse but to downgrade FSharp.Core to 9.0.202.
When can I safely upgrade to FSharp.Core 9.0.300?
T-Gro commentedon Jun 16, 2025
@cmeeren : This did not meet the
dotnet/runtime's bar for a servicing, and the change only applies to .NET 10, including preview versions of .NET 10.The combination of .NET 9 runtime and 9.0.300 FsharpCore will still have this error unfortunately.