[IR] Support isAssignable in builders and serialization.

compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IrFileDeserializer.kt

@@ -1010,7 +1010,7 @@ abstract class IrFileDeserializer(
                 flags.isCrossInline,
                 flags.isNoInline,
                 flags.isHidden,
-                false
+                flags.isAssignable
             ).apply {
                 if (proto.hasDefaultValue())
                     defaultValue = irFactory.createExpressionBody(deserializeExpressionBody(proto.defaultValue))

compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IrFlags.java

@@ -30,6 +30,7 @@ public class IrFlags extends Flags {
     // Parameters
 
     public static final BooleanFlagField IS_HIDDEN = FlagField.booleanAfter(IS_NOINLINE);
+    public static final BooleanFlagField IS_ASSIGNABLE = FlagField.booleanAfter(IS_HIDDEN);
 
     // Local variables
     public static final BooleanFlagField IS_LOCAL_VAR = FlagField.booleanAfter(HAS_ANNOTATIONS);
@@ -88,13 +89,15 @@ public class IrFlags extends Flags {
             boolean declaresDefaultValue,
             boolean isCrossinline,
             boolean isNoinline,
-            boolean isHidden
+            boolean isHidden,
+            boolean isAssignable
     ) {
         return HAS_ANNOTATIONS.toFlags(hasAnnotations)
                | DECLARES_DEFAULT_VALUE.toFlags(declaresDefaultValue)
                | IS_CROSSINLINE.toFlags(isCrossinline)
                | IS_NOINLINE.toFlags(isNoinline)
                | IS_HIDDEN.toFlags(isHidden)
+               | IS_ASSIGNABLE.toFlags(isAssignable)
                 ;
     }
 

compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/encodings/BinaryFlags.kt

@@ -143,11 +143,19 @@ inline class ValueParameterFlags(val flags: Long) {
     val isCrossInline: Boolean get() = IrFlags.IS_CROSSINLINE.get(flags.toInt())
     val isNoInline: Boolean get() = IrFlags.IS_NOINLINE.get(flags.toInt())
     val isHidden: Boolean get() = IrFlags.IS_HIDDEN.get(flags.toInt())
+    val isAssignable: Boolean get() = IrFlags.IS_ASSIGNABLE.get(flags.toInt())
 
     companion object {
         fun encode(param: IrValueParameter): Long {
             return param.run {
-                IrFlags.getValueParameterFlags(annotations.isNotEmpty(), defaultValue != null, isCrossinline, isNoinline, isHidden).toLong()
+                IrFlags.getValueParameterFlags(
+                    annotations.isNotEmpty(),
+                    defaultValue != null,
+                    isCrossinline,
+                    isNoinline,
+                    isHidden,
+                    isAssignable
+                ).toLong()
             }
         }