Use TypeSystemCommonBackendContext in KotlinTypeMapper.writeGenericArguments

core/descriptors/src/org/jetbrains/kotlin/types/TypeSystemCommonBackendContext.kt

@@ -5,9 +5,23 @@
 
 package org.jetbrains.kotlin.types
 
+import org.jetbrains.kotlin.name.FqName
+import org.jetbrains.kotlin.types.model.KotlinTypeMarker
 import org.jetbrains.kotlin.types.model.TypeConstructorMarker
 import org.jetbrains.kotlin.types.model.TypeSystemContext
 
 interface TypeSystemCommonBackendContext : TypeSystemContext {
     fun TypeConstructorMarker.isFinalClassOrEnumEntryOrAnnotationClassConstructor(): Boolean
+
+    fun KotlinTypeMarker.hasAnnotation(fqName: FqName): Boolean
+
+    /**
+     * @return value of the first argument of the annotation with the given [fqName], if the annotation is present and
+     * the argument is of a primitive type or a String, or null otherwise.
+     *
+     * Note that this method returns null if no arguments are provided, even if the corresponding annotation parameter has a default value.
+     *
+     * TODO: provide a more granular & elaborate API here to reduce confusion
+     */
+    fun KotlinTypeMarker.getAnnotationFirstArgumentValue(fqName: FqName): Any?
 }

core/descriptors/src/org/jetbrains/kotlin/types/checker/ClassicTypeSystemContext.kt

@@ -10,6 +10,7 @@ import org.jetbrains.kotlin.builtins.KotlinBuiltIns.FQ_NAMES
 import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.descriptors.annotations.AnnotationDescriptor
 import org.jetbrains.kotlin.descriptors.annotations.Annotations
+import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.resolve.calls.inference.CapturedType
 import org.jetbrains.kotlin.resolve.constants.IntegerLiteralTypeConstructor
 import org.jetbrains.kotlin.resolve.descriptorUtil.hasExactAnnotation
@@ -485,6 +486,15 @@ interface ClassicTypeSystemContext : TypeSystemInferenceExtensionContext, TypeSy
         return this is NewCapturedTypeConstructor
     }
 
+    override fun KotlinTypeMarker.hasAnnotation(fqName: FqName): Boolean {
+        require(this is KotlinType, this::errorMessage)
+        return annotations.hasAnnotation(fqName)
+    }
+
+    override fun KotlinTypeMarker.getAnnotationFirstArgumentValue(fqName: FqName): Any? {
+        require(this is KotlinType, this::errorMessage)
+        return annotations.findAnnotation(fqName)?.allValueArguments?.values?.firstOrNull()?.value
+    }
 }
 
 fun TypeVariance.convertVariance(): Variance {