Fix: constraint T? >: Int! should transform to T >: Int

compiler/testData/diagnostics/tests/controlStructures/typeInferenceForExclExcl.kt

@@ -0,0 +1,20 @@
+// !CHECK_TYPE
+// FILE: A.java
+public class A {
+    public static String foo() {
+        return "";
+    }
+}
+
+// FILE: b.kt
+fun <T: Any> exclExcl(t: T?): T = t!!
+
+fun test11() {
+    // not 'String!'
+    exclExcl(A.foo()) checkType { it : _<String> }
+    exclExcl(A.foo()) checkType { <!TYPE_MISMATCH!>it<!> : _<String?> }
+
+    // not 'String!'
+    A.foo()!! checkType { it : _<String> }
+    A.foo()!! checkType { <!TYPE_MISMATCH!>it<!> : _<String?> }
+}

compiler/testData/diagnostics/tests/controlStructures/typeInferenceForExclExcl.txt

@@ -0,0 +1,14 @@
+package
+
+internal fun </*0*/ T : kotlin.Any> exclExcl(/*0*/ t: T?): T
+internal fun test11(): kotlin.Unit
+
+public open class A {
+    public constructor A()
+    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
+
+    // Static members
+    public open fun foo(): kotlin.String!
+}

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

@@ -2022,6 +2022,12 @@ public class JetDiagnosticsTestGenerated extends AbstractJetDiagnosticsTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("typeInferenceForExclExcl.kt")
+            public void testTypeInferenceForExclExcl() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/controlStructures/typeInferenceForExclExcl.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("valVarCatchParameter.kt")
             public void testValVarCatchParameter() throws Exception {
                 String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/controlStructures/valVarCatchParameter.kt");

core/descriptors/src/org/jetbrains/kotlin/resolve/calls/inference/ConstraintSystemImpl.kt

@@ -333,18 +333,20 @@ public class ConstraintSystemImpl : ConstraintSystem {
 
         val typeBounds = getTypeBounds(parameterType)
 
-        if (!parameterType.isMarkedNullable() || !newConstrainingType.isMarkedNullable()) {
+        if (!parameterType.isMarkedNullable() || !TypeUtils.isNullableType(newConstrainingType)) {
             typeBounds.addBound(boundKind, newConstrainingType, constraintPosition)
             return
         }
         // For parameter type T:
         // constraint T? =  Int? should transform to T >: Int and T <: Int?
-        // constraint T? >: Int? should transform to T >: Int
+        // constraint T? = Int! should transform to T >: Int and T <: Int!
+
+        // constraints T? >: Int?; T? >: Int! should transform to T >: Int
         val notNullConstrainingType = TypeUtils.makeNotNullable(newConstrainingType)
         if (boundKind == EXACT_BOUND || boundKind == LOWER_BOUND) {
             typeBounds.addBound(LOWER_BOUND, notNullConstrainingType, constraintPosition)
         }
-        // constraint T? <: Int? should transform to T <: Int?
+        // constraints T? <: Int?; T? <: Int! should transform to T <: Int?; T <: Int! correspondingly
         if (boundKind == EXACT_BOUND || boundKind == UPPER_BOUND) {
             typeBounds.addBound(UPPER_BOUND, newConstrainingType, constraintPosition)
         }