Improve "firstArgumentValue" and "argumentValue" extension functions

Using the argument value, which is of type "Any?", is more implicit and
thus difficult to read than using the ConstantValue instance and casting
it to the needed constant value implementation before taking the value

core/descriptors.jvm/src/org/jetbrains/kotlin/load/java/AnnotationTypeQualifierResolver.kt

@@ -27,7 +27,7 @@ import org.jetbrains.kotlin.resolve.constants.ArrayValue
 import org.jetbrains.kotlin.resolve.constants.ConstantValue
 import org.jetbrains.kotlin.resolve.constants.EnumValue
 import org.jetbrains.kotlin.resolve.descriptorUtil.annotationClass
-import org.jetbrains.kotlin.resolve.descriptorUtil.firstArgumentValue
+import org.jetbrains.kotlin.resolve.descriptorUtil.firstArgument
 import org.jetbrains.kotlin.resolve.descriptorUtil.fqNameSafe
 import org.jetbrains.kotlin.storage.StorageManager
 import org.jetbrains.kotlin.utils.Jsr305State
@@ -148,7 +148,7 @@ class AnnotationTypeQualifierResolver(storageManager: StorageManager, private va
     }
 
     private fun ClassDescriptor.migrationAnnotationStatus(): ReportLevel? {
-        val stateDescriptor = annotations.findAnnotation(MIGRATION_ANNOTATION_FQNAME)?.firstArgumentValue()?.safeAs<ClassDescriptor>()
+        val stateDescriptor = annotations.findAnnotation(MIGRATION_ANNOTATION_FQNAME)?.firstArgument()?.safeAs<EnumValue>()?.value
                               ?: return null
 
         jsr305State.migration?.let { return jsr305State.migration }

core/descriptors.jvm/src/org/jetbrains/kotlin/load/java/descriptors/util.kt

@@ -24,7 +24,8 @@ import org.jetbrains.kotlin.descriptors.impl.ValueParameterDescriptorImpl
 import org.jetbrains.kotlin.load.java.JvmAnnotationNames
 import org.jetbrains.kotlin.load.java.lazy.descriptors.LazyJavaStaticClassScope
 import org.jetbrains.kotlin.load.kotlin.JvmPackagePartSource
-import org.jetbrains.kotlin.resolve.descriptorUtil.firstArgumentValue
+import org.jetbrains.kotlin.resolve.constants.StringValue
+import org.jetbrains.kotlin.resolve.descriptorUtil.firstArgument
 import org.jetbrains.kotlin.resolve.descriptorUtil.getSuperClassNotAny
 import org.jetbrains.kotlin.resolve.descriptorUtil.module
 import org.jetbrains.kotlin.resolve.jvm.JvmClassName
@@ -78,7 +79,7 @@ fun DeserializedMemberDescriptor.isFromJvmPackagePart(): Boolean =
 
 fun ValueParameterDescriptor.getParameterNameAnnotation(): AnnotationDescriptor? {
     val annotation = annotations.findAnnotation(JvmAnnotationNames.PARAMETER_NAME_FQ_NAME) ?: return null
-    if (annotation.firstArgumentValue()?.safeAs<String>()?.isEmpty() != false) {
+    if (annotation.firstArgument()?.safeAs<StringValue>()?.value?.isEmpty() != false) {
         return null
     }
 
@@ -91,8 +92,8 @@ object NullDefaultValue : AnnotationDefaultValue()
 
 fun ValueParameterDescriptor.getDefaultValueFromAnnotation(): AnnotationDefaultValue? {
     annotations.findAnnotation(JvmAnnotationNames.DEFAULT_VALUE_FQ_NAME)
-            ?.firstArgumentValue()
-            ?.safeAs<String>()
+            ?.firstArgument()
+            ?.safeAs<StringValue>()?.value
             ?.let { return StringDefaultValue(it) }
 
     if (annotations.hasAnnotation(JvmAnnotationNames.DEFAULT_NULL_FQ_NAME)) {

core/descriptors.jvm/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaScope.kt

@@ -36,7 +36,8 @@ import org.jetbrains.kotlin.load.java.structure.JavaMethod
 import org.jetbrains.kotlin.load.java.structure.JavaValueParameter
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.resolve.DescriptorUtils
-import org.jetbrains.kotlin.resolve.descriptorUtil.firstArgumentValue
+import org.jetbrains.kotlin.resolve.constants.StringValue
+import org.jetbrains.kotlin.resolve.descriptorUtil.firstArgument
 import org.jetbrains.kotlin.resolve.retainMostSpecificInEachOverridableGroup
 import org.jetbrains.kotlin.resolve.scopes.DescriptorKindExclude.NonExtensions
 import org.jetbrains.kotlin.resolve.scopes.DescriptorKindFilter
@@ -174,8 +175,8 @@ abstract class LazyJavaScope(protected val c: LazyJavaResolverContext) : MemberS
             val typeUsage = TypeUsage.COMMON.toAttributes()
             val parameterName = annotations
                     .findAnnotation(JvmAnnotationNames.PARAMETER_NAME_FQ_NAME)
-                    ?.firstArgumentValue()
-                    ?.safeAs<String>()
+                    ?.firstArgument()
+                    ?.safeAs<StringValue>()?.value
 
             val (outType, varargElementType) =
                     if (javaParameter.isVararg) {

core/descriptors.jvm/src/org/jetbrains/kotlin/load/java/typeEnhancement/signatureEnhancement.kt

@@ -30,7 +30,8 @@ import org.jetbrains.kotlin.load.kotlin.SignatureBuildingComponents
 import org.jetbrains.kotlin.load.kotlin.computeJvmDescriptor
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.platform.JavaToKotlinClassMap
-import org.jetbrains.kotlin.resolve.descriptorUtil.firstArgumentValue
+import org.jetbrains.kotlin.resolve.constants.EnumValue
+import org.jetbrains.kotlin.resolve.descriptorUtil.firstArgument
 import org.jetbrains.kotlin.types.*
 import org.jetbrains.kotlin.types.checker.KotlinTypeChecker
 import org.jetbrains.kotlin.types.typeUtil.isTypeParameter
@@ -49,12 +50,10 @@ class SignatureEnhancement(
 ) {
 
     private fun AnnotationDescriptor.extractNullabilityTypeFromArgument(): NullabilityQualifierWithMigrationStatus? {
-        val enumEntryDescriptor = firstArgumentValue()
+        val enumEntryDescriptor = firstArgument().safeAs<EnumValue>()?.value
                                   // if no argument is specified, use default value: NOT_NULL
                                   ?: return NullabilityQualifierWithMigrationStatus(NullabilityQualifier.NOT_NULL)
 
-        if (enumEntryDescriptor !is ClassDescriptor) return null
-
         return when (enumEntryDescriptor.name.asString()) {
             "ALWAYS" -> NullabilityQualifierWithMigrationStatus(NullabilityQualifier.NOT_NULL)
             "MAYBE", "NEVER" -> NullabilityQualifierWithMigrationStatus(NullabilityQualifier.NULLABLE)

core/descriptors/src/org/jetbrains/kotlin/resolve/DescriptorUtils.kt

@@ -30,6 +30,7 @@ import org.jetbrains.kotlin.name.FqNameUnsafe
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.resolve.DescriptorUtils
 import org.jetbrains.kotlin.resolve.DescriptorUtils.getContainingClass
+import org.jetbrains.kotlin.resolve.constants.ConstantValue
 import org.jetbrains.kotlin.resolve.constants.EnumValue
 import org.jetbrains.kotlin.resolve.scopes.DescriptorKindFilter
 import org.jetbrains.kotlin.resolve.scopes.MemberScope
@@ -416,7 +417,7 @@ fun ClassDescriptor.isSubclassOf(superclass: ClassDescriptor): Boolean = Descrip
 val AnnotationDescriptor.annotationClass: ClassDescriptor?
     get() = type.constructor.declarationDescriptor as? ClassDescriptor
 
-fun AnnotationDescriptor.firstArgumentValue() = allValueArguments.values.firstOrNull()?.value
+fun AnnotationDescriptor.firstArgument(): ConstantValue<*>? = allValueArguments.values.firstOrNull()
 
 fun MemberDescriptor.isEffectivelyExternal(): Boolean {
     if (isExternal) return true