I've got a custom detekt rule with type resolution and I'm receiving the `bindingContext` okay, but ...

# detekt

[Michael Marshall]

I've got a custom detekt rule with type resolution and I'm receiving the bindingContext okay, but getType is always null. What should I be doing to get the class of the object declaration?

override fun visitObjectDeclaration(declaration: KtObjectDeclaration) {
    super.visitObjectDeclaration(declaration)

    if (bindingContext == BindingContext.EMPTY) return

    if (bindingContext.getType(declaration) is Serializable) {
        report(
            CodeSmell(
                issue = issue,
                entity = Entity.from(declaration),
                message = "Do not use Java Serialization for Kotlin objects."
            )
        )
    }
}

[Michael Marshall]

I have also tried, from various internet sources
1.

(declaration.resolve() as? ClassDescriptor)?.defaultType

resolve() method not found
2.

(declaration as KtCallableDeclaration).createTypeBindingForReturnType(bindingContext)?.type

cast fails
3.

declaration.kotlinType(bindingContext)

always null

[gammax]

You should be good with:

declaration.superTypeListEntries.any { it.text == "Serializable" }

[gammax]

See this for more reference https://github.com/detekt/detekt/blob/main/detekt-rules-style/src/main/kotlin/io/g[…]bosch/detekt/rules/style/SerialVersionUIDInSerializableClass.kt

[Michael Marshall]

Hey thanks for that, although I need to check the whole class hierarchy for Serializable, not just if it's a direct super class

[Michael Marshall]

That's why I needed the type resolution, to perform the is Serializable check

[gammax]

I believe you should then use:

bindingContext[BindingContext.CLASS, declaration]?.defaultType

[Michael Marshall]

That works almost! It still fails the is Serializable check, I think it's a SimpleTypeImpl rather than the actual class, or something lazy?

[Michael Marshall]

Also is there any documentation for this? 😅

[gammax]

So the is Serializable check is most likely a bad approach. I believe you should reach a fully qualified type in some form and then do a string comparison with java.io.Serializable.

As for the documentation, that’s Kotlin PSI & the compiler API. Really bad documented 😞 That’s a known issue on JetBrains table.

[gammax]

Also my approach is generally to use the debugger. Like you add a breakpoint inside the rule, and then you try to evaluate expressions like the one I mentioned before. A bit of trial-n-error 🙂

[Michael Marshall]

Yeah it's been an absolute slog piecing together clues from around the internet 😂

[Michael Marshall]

If I can't use isSerializable then I'll need to recurse up the whole class hierarchy won't I?

[Michael Marshall]

In fact, if I can't get the class, I won't be able to do that either...

[gammax]

then I’ll need to recurse up the whole class hierarchy won’t I?

Mmm not really. I believe that with type resolution, you should be able to get all the implemented interfaces, also the one of your superclasses..

[Michael Marshall]

I didn't realise it could do that, thanks for the help!
Got it working with this

private val KtObjectDeclaration.isJavaSerializable
        get() = bindingContext[BindingContext.CLASS, this]
            ?.defaultType
            ?.supertypes()
            ?.any { it.fqNameOrNull()?.asString() == "java.io.Serializable" } == true

[gammax]

Awesome 🚀