Fix lateinit isInitialized check in multi-file case

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/BackendContext.kt

@@ -20,6 +20,7 @@ import org.jetbrains.kotlin.backend.common.ir.DeclarationFactory
 import org.jetbrains.kotlin.backend.common.ir.Ir
 import org.jetbrains.kotlin.backend.common.ir.SharedVariablesManager
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
+import org.jetbrains.kotlin.ir.declarations.IrField
 import org.jetbrains.kotlin.ir.descriptors.IrBuiltIns
 import org.jetbrains.kotlin.ir.symbols.IrFunctionSymbol
 import org.jetbrains.kotlin.ir.symbols.IrSimpleFunctionSymbol
@@ -33,4 +34,5 @@ interface BackendContext {
     val declarationFactory: DeclarationFactory
     val internalPackageFqn: FqName
     val transformedFunction: MutableMap<IrFunctionSymbol, IrSimpleFunctionSymbol>
+    val lateinitNullableFields: MutableMap<IrField, IrField>
 }

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/LateinitLowering.kt

@@ -29,6 +29,7 @@ import org.jetbrains.kotlin.ir.declarations.impl.IrVariableImpl
 import org.jetbrains.kotlin.ir.expressions.*
 import org.jetbrains.kotlin.ir.expressions.impl.*
 import org.jetbrains.kotlin.ir.symbols.impl.IrVariableSymbolImpl
+import org.jetbrains.kotlin.ir.types.isMarkedNullable
 import org.jetbrains.kotlin.ir.types.isPrimitiveType
 import org.jetbrains.kotlin.ir.types.makeNullable
 import org.jetbrains.kotlin.ir.util.resolveFakeOverride
@@ -36,8 +37,24 @@ import org.jetbrains.kotlin.ir.visitors.IrElementTransformerVoid
 import org.jetbrains.kotlin.ir.visitors.transformChildrenVoid
 
 class LateinitLowering(val context: CommonBackendContext) : FileLoweringPass {
+
+    private val nullableFields = context.lateinitNullableFields
+    private fun buildOrGetNullableField(originalField: IrField): IrField {
+        if (originalField.type.isMarkedNullable()) return originalField
+        return nullableFields.getOrPut(originalField) {
+            buildField {
+                updateFrom(originalField)
+                type = originalField.type.makeNullable()
+                name = originalField.name
+            }.apply {
+                parent = originalField.parent
+                correspondingPropertySymbol = originalField.correspondingPropertySymbol
+            }
+        }
+    }
+
     override fun lower(irFile: IrFile) {
-        val nullableFields = mutableMapOf<IrField, IrField>()
+
         val nullableVariables = mutableMapOf<IrVariable, IrVariable>()
 
         // Transform declarations
@@ -46,17 +63,9 @@ class LateinitLowering(val context: CommonBackendContext) : FileLoweringPass {
                 declaration.transformChildrenVoid(this)
                 if (declaration.isLateinit && declaration.origin != IrDeclarationOrigin.FAKE_OVERRIDE) {
                     val oldField = declaration.backingField!!
-                    val newField = buildField {
-                        updateFrom(oldField)
-                        type = oldField.type.makeNullable()
-                        name = oldField.name
-                    }.also { newField ->
-                        newField.parent = oldField.parent
-                        newField.correspondingPropertySymbol = declaration.symbol
-                        declaration.backingField = newField
-                    }
+                    val newField = buildOrGetNullableField(oldField)
 
-                    nullableFields[oldField] = newField
+                    declaration.backingField = newField
 
                     transformGetter(newField, declaration.getter!!)
                 }
@@ -166,8 +175,11 @@ class LateinitLowering(val context: CommonBackendContext) : FileLoweringPass {
 
                 val property = receiver.getter?.owner?.resolveFakeOverride()?.correspondingProperty!!.also { assert(it.isLateinit) }
 
+                val nullableField =
+                    buildOrGetNullableField(property.backingField ?: error("Lateinit property is supposed to have backing field"))
+
                 return expression.run { context.createIrBuilder(symbol, startOffset, endOffset) }.run {
-                    irNotEquals(irGetField(receiver.dispatchReceiver, property.backingField!!), irNull())
+                    irNotEquals(irGetField(receiver.dispatchReceiver, nullableField), irNull())
                 }
             }
         })

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsIrBackendContext.kt

@@ -48,6 +48,7 @@ class JsIrBackendContext(
     override val scriptMode: Boolean = false
 ) : CommonBackendContext {
     override val transformedFunction = mutableMapOf<IrFunctionSymbol, IrSimpleFunctionSymbol>()
+    override val lateinitNullableFields = mutableMapOf<IrField, IrField>()
 
     override val builtIns = module.builtIns
 

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmBackendContext.kt

@@ -53,6 +53,7 @@ class JvmBackendContext(
     override val transformedFunction: MutableMap<IrFunctionSymbol, IrSimpleFunctionSymbol>
         get() = TODO("not implemented")
     override val scriptMode: Boolean = false
+    override val lateinitNullableFields = mutableMapOf<IrField, IrField>()
 
     override val builtIns = state.module.builtIns
     val typeMapper = IrTypeMapper(this)

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/WasmBackendContext.kt

@@ -38,6 +38,7 @@ class WasmBackendContext(
     override var inVerbosePhase: Boolean = false
     override val scriptMode = false
     override val transformedFunction = mutableMapOf<IrFunctionSymbol, IrSimpleFunctionSymbol>()
+    override val lateinitNullableFields = mutableMapOf<IrField, IrField>()
 
     // Place to store declarations excluded from code generation
     val excludedDeclarations: IrPackageFragment by lazy {