Trim attribute used by compilation to generate EventSources during build

[marek-safar]

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Issue Details

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Author:	marek-safar
Assignees:	-
Labels:	linkable-framework
Milestone:	-

[eerhardt]

I think this is kind of interesting w.r.t. some of the "built-in source generator" discussions we've been having. cc @ericstj @jaredpar

Basically, the approach we are taking here is one that was proposed as a feature for source generators. Allowing the "source generator" to generate an attribute that user code can reference/use, but then the attribute gets removed by the compiler.

If we had that feature in Roslyn, we wouldn't need this change here.

[ericstj]

We could add Conditional("SOURCE_GENERATOR") (or whatever define that's never set) to avoid emitting the references to the attribute, but nothing available today that can avoid the definition of the attribute. Would just setting Conditional here make the linker do the right thing with no additional settings (trim an unused internal attribute)?

Related dotnet/roslyn#52749

[marek-safar]

I like the conditional attribute suggestion. Made alternative #51913 using it.