[IR] Support of @OptionalExpectation in IrActualizer

^KT-56579 Fixed

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/actualizer/ExpectActualCollector.kt

@@ -112,7 +112,7 @@ private class ClassifiersLinkCollector(
         val actualClassifier = actualClassifiers[actualTypeId]
         if (actualClassifier != null) {
             expectActualMap[expectElement.symbol] = actualClassifier
-        } else {
+        } else if (!expectElement.containsOptionalExpectation()) {
             reportMissingActual(expectElement)
         }
     }
@@ -181,7 +181,7 @@ private class CallablesLinkCollector(
                 declaration.getter?.symbol?.let { expectActualMap[it] = actualProperty.getter!!.symbol }
                 declaration.setter?.symbol?.let { expectActualMap[it] = actualProperty.setter!!.symbol }
             }
-        } else {
+        } else if (!declaration.parent.containsOptionalExpectation()) {
             reportMissingActual(declaration)
         }
     }

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/actualizer/IrActualizer.kt

@@ -14,20 +14,29 @@ object IrActualizer {
     fun actualize(mainFragment: IrModuleFragment, dependentFragments: List<IrModuleFragment>) {
         val (expectActualMap, typeAliasMap) = ExpectActualCollector(mainFragment, dependentFragments).collect()
         FunctionDefaultParametersActualizer(expectActualMap).actualize()
-        removeExpectDeclarations(dependentFragments)
+        removeExpectDeclarations(dependentFragments, expectActualMap)
         addMissingFakeOverrides(expectActualMap, dependentFragments, typeAliasMap)
         linkExpectToActual(expectActualMap, dependentFragments)
         mergeIrFragments(mainFragment, dependentFragments)
     }
 
-    private fun removeExpectDeclarations(dependentFragments: List<IrModuleFragment>) {
+    private fun removeExpectDeclarations(dependentFragments: List<IrModuleFragment>, expectActualMap: Map<IrSymbol, IrSymbol>) {
         for (fragment in dependentFragments) {
             for (file in fragment.files) {
-                file.declarations.removeAll { it.isProperExpect }
+                file.declarations.removeIf { shouldRemoveExpectDeclaration(it, expectActualMap) }
             }
         }
     }
 
+    private fun shouldRemoveExpectDeclaration(irDeclaration: IrDeclaration, expectActualMap: Map<IrSymbol, IrSymbol>): Boolean {
+        return when (irDeclaration) {
+            is IrClass -> irDeclaration.isExpect && (!irDeclaration.containsOptionalExpectation() || expectActualMap.containsKey(irDeclaration.symbol))
+            is IrProperty -> irDeclaration.isExpect
+            is IrFunction -> irDeclaration.isExpect
+            else -> false
+        }
+    }
+
     private fun addMissingFakeOverrides(
         expectActualMap: Map<IrSymbol, IrSymbol>,
         dependentFragments: List<IrModuleFragment>,

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/actualizer/IrActualizerUtils.kt

@@ -5,14 +5,20 @@
 
 package org.jetbrains.kotlin.backend.common.actualizer
 
+import org.jetbrains.kotlin.descriptors.ClassKind
 import org.jetbrains.kotlin.ir.IrElement
-import org.jetbrains.kotlin.ir.declarations.*
+import org.jetbrains.kotlin.ir.declarations.IrClass
+import org.jetbrains.kotlin.ir.declarations.IrDeclarationBase
+import org.jetbrains.kotlin.ir.declarations.IrDeclarationWithName
+import org.jetbrains.kotlin.ir.declarations.IrFunction
 import org.jetbrains.kotlin.ir.symbols.IrSymbol
 import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.types.classifierOrFail
+import org.jetbrains.kotlin.ir.util.hasAnnotation
 import org.jetbrains.kotlin.ir.util.kotlinFqName
 import org.jetbrains.kotlin.ir.util.render
 import org.jetbrains.kotlin.name.FqName
+import org.jetbrains.kotlin.resolve.multiplatform.OptionalAnnotationUtil
 
 fun generateIrElementFullName(
     declaration: IrElement,
@@ -73,4 +79,10 @@ fun reportMissingActual(irElement: IrElement) {
 fun reportManyInterfacesMembersNotImplemented(declaration: IrClass, actualMember: IrDeclarationWithName) {
     // TODO: setup diagnostics reporting
     throw AssertionError("${declaration.name} must override ${actualMember.name} because it inherits multiple interface methods of it")
+}
+
+internal fun IrElement.containsOptionalExpectation(): Boolean {
+    return this is IrClass &&
+            this.kind == ClassKind.ANNOTATION_CLASS &&
+            this.hasAnnotation(OptionalAnnotationUtil.OPTIONAL_EXPECTATION_FQ_NAME)
 }