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For multibinding using * definitely makes sense.

However I'm wondering whether for regular bindings using the actual type parameter would make more sense. For example if I bind SQLDelight's ColumnAdpater, I'd probably would want the bound type for class InstantColumnAdapter : ColumnAdapter<String, Instant> to be ColumnAdapter<String, Instant>.

This was debated over and over again and there are other tickets discussing this. We didn't want to support this, because it adds inconsistency with boundType. Imagine this example:

@ContributesBinding(AppScope::class, boundType = CharSequence::class)
@ContributesMultbinding(AppScope::class)
object MyClass : List<String>, CharSequence { .. }

Which super type should be used is unclear, you'd need to use boundType similar to ContributesBinding in the sample. But boundType doesn't allow define the generic type.

You can always support your use case with a custom code generator.

For the @ContributesBinding issue, what if we just take the actual parent type instead of *? So in your example @ContributesBinding would bind into ColumnAdapter<String, Instant>. However, @ContributesMultibinding would still bind star bindings, so it would bind ColumnAdapter<*, *>.

As for theboundType issue, what if you just need to specify the type and type parameter are inferred from actual paremters? So, in your case, you would enter @ContributesMultbinding(AppScope::class, boundType = List::class) and Anvil would know that you meant List<String>, since MyClass extends it.

Added extra commits with above issues addressed.

As part of this I also had to fix a bug in isTypeParameter function, where this function would falsely return false if parent type had either out or in keywords (d7f0917).

This has come up a few times on my team and we'd really like to have this functionality. Even if it doesn't fix every issue, it would be nice to at least do something, even if it's only generic supertypes for now.

Any solution for this use case?

I can look into solving conflicts and getting this into mergeable state if I get some feedback from Anvil team that this is actually something they want to get merged. They have been pretty silent so far.