Type parameter is considered capable of taking any value for the purpose of cast possibility check #KT-6611 Fixed

compiler/frontend/src/org/jetbrains/kotlin/types/CastDiagnosticsUtil.kt

@@ -40,6 +40,11 @@ object CastDiagnosticsUtil {
         // This is an oversimplification (which does not render the method incomplete):
         // we consider any type parameter capable of taking any value, which may be made more precise if we considered bounds
         if (TypeUtils.isTypeParameter(lhsType) || TypeUtils.isTypeParameter(rhsType)) return true
+        if (lhsType.constructor == rhsType.constructor) {
+            if (lhsType.arguments.all { TypeUtils.isTypeParameter(it.type) }) return true
+            if (rhsType.arguments.all { TypeUtils.isTypeParameter(it.type) }) return true
+        }
+
         if (isFinal(lhsType) || isFinal(rhsType)) return false
         if (isTrait(lhsType) || isTrait(rhsType)) return true
         return false

compiler/testData/diagnostics/tests/cast/AsWithOtherParameter.kt

@@ -0,0 +1,14 @@
+// See also: KT-6611 (cast can never succeed: Class<T> -> Class<Any>)
+
+class Class<T>(val name: String, val instance: T)
+
+fun <T> test(clazz: Class<T>) {
+    println((<!UNCHECKED_CAST!>clazz as Class<Any><!>).name)
+}
+
+fun use() {
+    test(Class("String", ""))
+}
+
+fun println(s: String) = s
+

compiler/testData/diagnostics/tests/cast/AsWithOtherParameter.txt

@@ -0,0 +1,14 @@
+package
+
+public fun println(/*0*/ s: kotlin.String): kotlin.String
+public fun </*0*/ T> test(/*0*/ clazz: Class<T>): kotlin.Unit
+public fun use(): kotlin.Unit
+
+public final class Class</*0*/ T> {
+    public constructor Class</*0*/ T>(/*0*/ name: kotlin.String, /*1*/ instance: T)
+    public final val instance: T
+    public final val name: kotlin.String
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/sourceCompatibility/noBoundCallableReferences/qualifiedJavaClassLiteralInKClassExtension.kt

@@ -1,5 +1,5 @@
 // !LANGUAGE: -BoundCallableReferences
-// !DIAGNOSTICS: -CAST_NEVER_SUCCEEDS
+// !DIAGNOSTICS: -UNCHECKED_CAST
 
 import kotlin.reflect.KClass
 

compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestGenerated.java

@@ -2328,6 +2328,12 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("AsWithOtherParameter.kt")
+            public void testAsWithOtherParameter() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/cast/AsWithOtherParameter.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("constants.kt")
             public void testConstants() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/cast/constants.kt");