Implement makeNullableAsSpecified for TypeTemplate properly

This change fixes an SOE in isCastErased:
    @JvmStatic
    fun isCastErased(supertype: KotlinType, subtype: KotlinType, typeChecker: KotlinTypeChecker): Boolean {
        if (supertype.isMarkedNullable || subtype.isMarkedNullable) {
            return isCastErased(TypeUtils.makeNotNullable(supertype), TypeUtils.makeNotNullable(subtype), typeChecker)
        }

TypeUtils.makeNotNullable(TypeTemplate) should not return the same object
if isMarkedNullable returned true on the instance


 #KT-15516 Fixed

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/inference/CoroutineInferenceUtil.kt

@@ -56,11 +56,15 @@ import javax.inject.Inject
 
 class TypeTemplate(
         val typeVariable: TypeVariable,
-        val coroutineInferenceData: CoroutineInferenceData
-) : FlexibleType(typeVariable.originalTypeParameter.builtIns.nothingType, typeVariable.originalTypeParameter.builtIns.nullableAnyType) {
+        val coroutineInferenceData: CoroutineInferenceData,
+        nullable: Boolean = true
+) : FlexibleType(
+        typeVariable.originalTypeParameter.builtIns.nothingType,
+        typeVariable.originalTypeParameter.builtIns.anyType.makeNullableAsSpecified(nullable)
+) {
     override fun replaceAnnotations(newAnnotations: Annotations) = this
 
-    override fun makeNullableAsSpecified(newNullability: Boolean) = this
+    override fun makeNullableAsSpecified(newNullability: Boolean) = TypeTemplate(typeVariable, coroutineInferenceData, newNullability)
 
     override val delegate: SimpleType
         get() = upperBound

compiler/testData/diagnostics/testsWithStdLib/coroutines/inference/kt15516.kt

@@ -0,0 +1,18 @@
+// SKIP_TXT
+class StateMachine<Q> internal constructor() {
+    fun getInputStub(): Q = null as Q
+}
+
+fun <T> stateMachine(<!UNUSED_PARAMETER!>block<!>: suspend StateMachine<T>.() -> Unit): StateMachine<T> {
+    return StateMachine<T>()
+}
+
+class Problem<F>(){
+    fun getInputStub(): F = null as F
+
+    fun createStateMachine(): StateMachine<F> = stateMachine {
+        val letter = getInputStub()
+        if (letter is Any)
+            println("yes")
+    }
+}

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

@@ -853,6 +853,12 @@ public class DiagnosticsTestWithStdLibGenerated extends AbstractDiagnosticsTestW
                 doTest(fileName);
             }
 
+            @TestMetadata("kt15516.kt")
+            public void testKt15516() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/testsWithStdLib/coroutines/inference/kt15516.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("recursiveGenerators.kt")
             public void testRecursiveGenerators() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/testsWithStdLib/coroutines/inference/recursiveGenerators.kt");