ComInterfaceGenerator warns twice on some warnings: once when generating the managed wrapper and another when making the native wrapper

[jtschuster]

Some warnings are made by the generator twice, once for each stub the generator makes (native, managed). The generator should only warn once.

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Issue Details

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Some warnings are made by the generator twice, once for each stub the generator makes (native, managed). The generator should only warn once.

Author:	jtschuster
Assignees:	jtschuster
Labels:	area-System.Runtime.InteropServices, source-generator
Milestone:	-

[jtschuster]

This is also causing some different warnings to appear, not just the same ones twice. For instance, for [In, Out] attributes, int[] param will warn as an int[] when generating a managed to unmanaged stub, but int* in the unmanaged to managed stub. This causes it to think [In] is not supported one case, and is the default behavior in another.

[jkoritzinsky]

The first part of this issue (the duplication) has been fixed. I don't think we can fix the "two different diagnostics" case as that's by design. We want to give valid diagnostics for the managed-to-unmanaged scenario as well as the other way, and sometimes the diagnostics are different because the scenarios are different.

I'm going to close this as completed as the remaining references to this issue will be removed in #88856