`Delegate.Method` doesn't work with open instance delegates over methods on a generic type in CoreCLR

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
csharp
Domain
backend

Research direction

Start with the linked Godbolt C# reproduction and compare the expected output with the stack trace. Trace Delegate.GetMethodImpl through DiagnosticMethodInfo.Create, focusing on the incompatible generic open-instance delegate handles. Done means the reproduction completes and reports the declaring type and method name without throwing.

Written by the indexing model from the issue text.

Description

area-System.Reflection bug

Reproduction: godbolt.

Expected behavior: things work.
Actual behavior:

Unhandled exception. System.ArgumentException: Type handle 'Program+OpenInstanceDelStruct`1[System.Int32]&' and method handle with declaring type 'Program+OpenInstanceDelStruct`1[System.Int32]' are incompatible. Get RuntimeMethodHandle and declaring RuntimeTypeHandle off the same MethodBase.
   at System.RuntimeType.GetMethodBase(RuntimeType reflectedType, RuntimeMethodHandleInternal methodHandle)
   at System.Delegate.GetMethodImpl()
   at System.Diagnostics.DiagnosticMethodInfo.Create(Delegate delegate)
   at Program.Main() in /app/example.cs:line 11
Dominant language
C#
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