JVM IR: erase parameter default value when copying it to bridge

#KT-48391 Fixed

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/BridgeLowering.kt

@@ -563,11 +563,15 @@ internal class BridgeLowering(val context: JvmBackendContext) : FileLoweringPass
         substitutedType: IrType? = null
     ): IrValueParameter = copyTo(
         target, IrDeclarationOrigin.BRIDGE,
+        startOffset = target.startOffset,
+        endOffset = target.endOffset,
         type = (substitutedType?.eraseToScope(visibleTypeParameters) ?: type.eraseTypeParameters()),
         // Currently there are no special bridge methods with vararg parameters, so we don't track substituted vararg element types.
         varargElementType = varargElementType?.eraseToScope(visibleTypeParameters),
-        startOffset = target.startOffset,
-        endOffset = target.endOffset,
+        // If the parameter has a default value, replace it with a stub, as if this function is coming from an external dependency.
+        // Otherwise it can lead to all sorts of problems, for example this default value can reference private functions from another
+        // file, which would rightfully make SyntheticAccessorLowering fail.
+        defaultValue = if (defaultValue != null) createStubDefaultValue() else null,
     )
 
     private fun IrBuilderWithScope.delegatingCall(

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/DeclarationStubGenerator.kt

@@ -23,7 +23,6 @@ import org.jetbrains.kotlin.ir.UNDEFINED_OFFSET
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.declarations.lazy.*
 import org.jetbrains.kotlin.ir.IrBuiltIns
-import org.jetbrains.kotlin.ir.expressions.impl.IrErrorExpressionImpl
 import org.jetbrains.kotlin.ir.linkage.IrProvider
 import org.jetbrains.kotlin.ir.symbols.IrFieldSymbol
 import org.jetbrains.kotlin.ir.symbols.IrSymbol
@@ -241,13 +240,7 @@ abstract class DeclarationStubGenerator(
             varargElementType?.toIrType(), isCrossinline, isNoinline, isHidden = false, isAssignable = false
         ).also { irValueParameter ->
             if (descriptor.declaresDefaultValue()) {
-                irValueParameter.defaultValue =
-                    irValueParameter.factory.createExpressionBody(
-                        IrErrorExpressionImpl(
-                            UNDEFINED_OFFSET, UNDEFINED_OFFSET, descriptor.type.toIrType(),
-                            "Stub expression for default value of ${descriptor.name}"
-                        )
-                    )
+                irValueParameter.defaultValue = irValueParameter.createStubDefaultValue()
             }
         }
     }

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/IrUtils.kt

@@ -6,10 +6,7 @@
 package org.jetbrains.kotlin.ir.util
 
 import org.jetbrains.kotlin.descriptors.*
-import org.jetbrains.kotlin.ir.IrBuiltIns
-import org.jetbrains.kotlin.ir.IrElement
-import org.jetbrains.kotlin.ir.IrStatement
-import org.jetbrains.kotlin.ir.ObsoleteDescriptorBasedAPI
+import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.expressions.*
 import org.jetbrains.kotlin.ir.expressions.impl.*
@@ -174,6 +171,11 @@ fun IrExpression.coerceToUnitIfNeeded(valueType: IrType, irBuiltIns: IrBuiltIns,
 fun IrFunctionAccessExpression.usesDefaultArguments(): Boolean =
     symbol.owner.valueParameters.any { this.getValueArgument(it.index) == null }
 
+fun IrValueParameter.createStubDefaultValue(): IrExpressionBody =
+    factory.createExpressionBody(
+        IrErrorExpressionImpl(UNDEFINED_OFFSET, UNDEFINED_OFFSET, type, "Stub expression for default value of $name")
+    )
+
 val IrClass.functions: Sequence<IrSimpleFunction>
     get() = declarations.asSequence().filterIsInstance<IrSimpleFunction>()