I'm wondering how to check generic type parameters...

# ksp

[David Herman]

I'm wondering how to check generic type parameters for a specific subclass of a generic parent type. Will put an example in the 🧵

[David Herman]

(The example is made up but should get the point across)

// Case 1
abstract class Converter<I, O>
class NumericStringToNumberConverter : Converter<String, Int>

// Case 2
abstract class Converter<I, O>
abstract class ToStringConverter<I> : Converter<I, String>
abstract class DoubleToStringConverter : ToStringConverter<Double>

For case 1, when I visit a "NumericStringToNumberConverter" KSClassDeclaration, I want to know that it implements "Converter" and that its type parameters are bound to String and Int.

For case 2, when I visit a "DoubleToStringConverter", I want to know that it implements "Converter" as well, and that its type parameters are bound to Double and String.

[David Herman]

I assume what I need to do is, for each class, resolve the super types, and then keep visiting up the chain until I find a class with qualified name whatever.the.path.is.to.Converter (*) but then I'm not sure how to check what its specific type parameters are.

(*) Side note: Should I just do a string check against the fully qualified name? Or should I somehow fetch the KSType of whatever.the.path.is.to.Converter earlier and check against that?

[David Rawson]

I think you got the right idea with walking the super types.

Taking the KSClassDeclaration for`NumericStringToNumberConverter` you can find out the type arguments like this:

val converterTypeArguments = declaration.getAllSuperTypes().firstOrNull *{* it.declaration.qualifiedName.asString() == "Converter" *}*?.arguments

then:

_assert_(converterTypeArguments?.map { it.type.resolve() } == _listOf_(resolver.builtIns.stringType, resolver.builtIns.intType))

[David Herman]

Thanks! I'll give that a shot.

[David Herman]

Also, apologies if a basic question, but given a fully qualified class name, can I easily ask KSP to get a KSType for it (or null if not found)?

Or is the way to do this by doing a first round visit pass with a visitor whose purpose is to fetch the KSType, and then pass that into a second round visitor?

[David Herman]

(Or maybe I'm just overthinking it and should do a string test against it.resolve().declaration.qualifiedName.asString())

[David Rawson]

given a fully qualified class name, can I easily ask KSP to get a KSType for it (or null if not found)?

Would resolver.getClassDeclarationByName() work for that?

Once you have the KSClassDeclaration you can easily get to its KSType.

[David Herman]

Ah, I thought I searched resolver, don't know why I didn't see that. I was tired..... thanks!

[David Herman]

@David Rawson This worked perfectly, thank you!