Hi, i am writing a compiler plugin. I have diffic...

# compiler

[Johannes Barop]

Hi,

i am writing a compiler plugin. I have difficulties calling a method on an object (property of a class).

For example, with static methods I do it with `pluginContext.referenceFunctions(FqName("kotlin.io.println")); irCall(funPrintln) ...``. Can anyone give me a tip on how this works with functions on an instance? Thanks!

[shikasd]

You need to find a class first, then find the required function inside to get the symbol/fn instance.
To call, you just do irCall and put dispatchReceiver property to point to instance. (similar for extension functions, just use extensionReceiver there)

[shikasd]

It might be the case that you don't have to find the class btw, but I am not sure referenceFunctions works this way

[raulraja]

To add to Andrei's comments if you need to get the receiver expression, if the instance is an object you may have to get a hold of it with something like IrGetObjectValueImpl
If it's a class and you need to contruct an instance first IrConstructorCallImpl

[Johannes Barop]

Thank you. I think I am getting somewhere!

I think the last piece I am missing how to retrieve the instance.

That's my code

override fun lower(irClass: IrClass) {
  val propertyToClose: IrProperty = /* ... */

  val propertyClassSymbol: IrClassSymbol = pluginContext.findClassOf(propertyToClose)
  val propertyClass: IrClass = propertyClassSymbol.owner
  val propertyCloseFunction: IrSimpleFunction = propertyClass.functions.single { it.name == closeName }
  closeFunction.body = DeclarationIrBuilder(pluginContext, closeFunction.symbol).irBlockBody {
    +irCall(propertyCloseFunction).apply {
      dispatchReceiver = irGetField(irClass.thisReceiver /* Type mismatch: IrValueParameter vs IrExpression? */, propertyToClose.backingField!!)
  }
}

How do I get the instance of the property?

[natario1]

I think you should add irGet around irClass.thisReceiver

[Johannes Barop]

Hm. This compiles, but during code generation I'm getting a No mapping for symbol: VALUE_PARAMETER INSTANCE_RECEIVER.

This is the `dump()`of the generated IR:

CALL 'public open fun close (): kotlin.Unit declared in <root>.ExternalResource' type=kotlin.Unit origin=null
      $this: GET_FIELD 'FIELD PROPERTY_BACKING_FIELD name:firstResource type:<root>.ExternalResource visibility:private [final]' type=<root>.ExternalResource origin=null
        receiver: GET_VAR '<this>: <root>.ResourceManager declared in <root>.ResourceManager' type=<root>.ResourceManager origin=null

This is what i ant to generate:

CALL 'public open fun close (): kotlin.Unit declared in <root>.ExternalResource' type=kotlin.Unit origin=null
            $this: CALL 'private final fun <get-firstResource> (): <root>.ExternalResource declared in <root>.ResourceManager' type=<root>.ExternalResource origin=GET_PROPERTY
              $this: GET_VAR '<this>: <root>.ResourceManager declared in <root>.ResourceManager.close' type=<root>.ResourceManager origin=null

[natario1]

You can try getting ResourceManager instance from the function, like closeFunction.dispatchReceiverParameter IIRC. Assuming closeFunction is a member of the manager

[Johannes Barop]

It works now:

Instead of irGet(irClass.thisReceiver!!) it works with irGet(thisCloseFunction.dispatchReceiverParameter!!)

Full snippet:

override fun lower(irClass: IrClass) {
    /* ... */
    val propertyToClose: IrProperty = /* ... */
    val propertyClassSymbol: IrClassSymbol = pluginContext.findClassOf(propertyToClose)
    val propertyClass: IrClass = propertyClassSymbol.owner
    val propertyCloseFunction: IrSimpleFunction =
      propertyClass.functions.single { it.name == closeName }

    thisCloseFunction.body = DeclarationIrBuilder(pluginContext, thisCloseFunction.symbol).irBlockBody {
      +irCall(propertyCloseFunction).apply {
        dispatchReceiver = irCall(propertyToClose.getter!!).apply {
          dispatchReceiver = irGet(thisCloseFunction.dispatchReceiverParameter!!)
        }
      }
    }
  }

Thanks for the help and nudges in the right direction 🙂

[Johannes Barop]

BTW: My proof of concept of "imitating" RAII of C++ is finished.
Would love to get some feedback.

https://github.com/jbarop/kraii/