psi2ir: handle 'this' as reference to a super companion object

In super class constructor arguments, 'this' can be resolved
as a reference to a companion object of a superclass.
This breaks an assumption in psi2ir that 'this' can only refer to some
receiver from the current scope.

If 'this' refers to an 'object' (including 'companion obejct'),
and we are not inside the corresponding class scope,
then 'this' represents a reference to a singleton instance "by name"
(represented as IrGetObjectValue).

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/ArgumentsGenerationUtils.kt

@@ -134,14 +134,10 @@ private fun StatementGenerator.shouldGenerateReceiverAsSingletonReference(receiv
 }
 
 private fun StatementGenerator.generateThisOrSuperReceiver(receiver: ReceiverValue, classDescriptor: ClassDescriptor): IrExpression {
-    val expressionReceiver =
-        receiver as? ExpressionReceiver ?: throw AssertionError("'this' or 'super' receiver should be an expression receiver")
+    val expressionReceiver = receiver as? ExpressionReceiver
+        ?: throw AssertionError("'this' or 'super' receiver should be an expression receiver")
     val ktReceiver = expressionReceiver.expression
-    return IrGetValueImpl(
-        ktReceiver.startOffsetSkippingComments, ktReceiver.endOffset,
-        expressionReceiver.type.toIrType(),
-        context.symbolTable.referenceValueParameter(classDescriptor.thisAsReceiverParameter)
-    )
+    return generateThisReceiver(ktReceiver.startOffsetSkippingComments, ktReceiver.endOffset, expressionReceiver.type, classDescriptor)
 }
 
 fun StatementGenerator.generateBackingFieldReceiver(

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/StatementGenerator.kt

@@ -38,6 +38,7 @@ import org.jetbrains.kotlin.psi2ir.intermediate.createTemporaryVariableInBlock
 import org.jetbrains.kotlin.psi2ir.intermediate.setExplicitReceiverValue
 import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlin.resolve.BindingContextUtils
+import org.jetbrains.kotlin.resolve.DescriptorUtils
 import org.jetbrains.kotlin.resolve.calls.model.ResolvedCall
 import org.jetbrains.kotlin.resolve.calls.model.VariableAsFunctionResolvedCall
 import org.jetbrains.kotlin.resolve.constants.CompileTimeConstant
@@ -364,28 +365,52 @@ class StatementGenerator(
     override fun visitSafeQualifiedExpression(expression: KtSafeQualifiedExpression, data: Nothing?): IrStatement =
         expression.selectorExpression!!.accept(this, data)
 
+    private fun isInsideClass(classDescriptor: ClassDescriptor): Boolean {
+        var scopeDescriptor: DeclarationDescriptor? = scopeOwner
+        while (scopeDescriptor != null) {
+            if (scopeDescriptor == classDescriptor) return true
+            scopeDescriptor = scopeDescriptor.containingDeclaration
+        }
+        return false
+    }
+
+    fun generateThisReceiver(startOffset: Int, endOffset: Int, kotlinType: KotlinType, classDescriptor: ClassDescriptor): IrExpression {
+        val thisAsReceiverParameter = classDescriptor.thisAsReceiverParameter
+        val thisType = kotlinType.toIrType()
+
+        return if (DescriptorUtils.isObject(classDescriptor) && !isInsideClass(classDescriptor)) {
+            IrGetObjectValueImpl(
+                startOffset, endOffset,
+                thisType,
+                context.symbolTable.referenceClass(classDescriptor)
+            )
+        } else {
+            IrGetValueImpl(
+                startOffset, endOffset,
+                thisType,
+                context.symbolTable.referenceValueParameter(thisAsReceiverParameter)
+            )
+        }
+    }
+
     override fun visitThisExpression(expression: KtThisExpression, data: Nothing?): IrExpression {
         val referenceTarget = getOrFail(BindingContext.REFERENCE_TARGET, expression.instanceReference) { "No reference target for this" }
+        val startOffset = expression.startOffsetSkippingComments
+        val endOffset = expression.endOffset
         return when (referenceTarget) {
-            is ClassDescriptor -> {
-                val thisAsReceiverParameter = referenceTarget.thisAsReceiverParameter
-                val thisType = thisAsReceiverParameter.type.toIrType()
-                IrGetValueImpl(
-                    expression.startOffsetSkippingComments, expression.endOffset,
-                    thisType,
-                    context.symbolTable.referenceValueParameter(thisAsReceiverParameter)
-                )
-            }
+            is ClassDescriptor ->
+                generateThisReceiver(startOffset, endOffset, referenceTarget.thisAsReceiverParameter.type, referenceTarget)
 
             is CallableDescriptor -> {
                 val extensionReceiver = referenceTarget.extensionReceiverParameter ?: TODO("No extension receiver: $referenceTarget")
                 val extensionReceiverType = extensionReceiver.type.toIrType()
                 IrGetValueImpl(
-                    expression.startOffsetSkippingComments, expression.endOffset,
+                    startOffset, endOffset,
                     extensionReceiverType,
                     context.symbolTable.referenceValueParameter(extensionReceiver)
                 )
             }
+
             else ->
                 error("Expected this or receiver: $referenceTarget")
         }