Fix JetType.equals(): flexible types are not equal to non-flexible ones, when we store them in a HashSet

compiler/frontend/src/org/jetbrains/jet/lang/types/expressions/BasicExpressionTypingVisitor.java

@@ -1081,7 +1081,12 @@ public class BasicExpressionTypingVisitor extends ExpressionTypingVisitor {
         JetType type = resolvedCall.getResultingDescriptor().getReturnType();
         if (type == null || rightType == null) return JetTypeInfo.create(null, dataFlowInfo);
 
-        return JetTypeInfo.create(TypeUtils.makeNullableAsSpecified(type, rightType.isNullable()), dataFlowInfo);
+        // Sometimes return type for special call for elvis operator might be nullable,
+        // but result is not nullable if the right type is not nullable
+        if (!TypeUtils.isNullableType(rightType) && TypeUtils.isNullableType(type)) {
+            type = TypeUtils.makeNotNullable(type);
+        }
+        return JetTypeInfo.create(type, dataFlowInfo);
     }
 
     @NotNull

compiler/testData/diagnostics/tests/inference/immutableArrayList.kt

@@ -0,0 +1,17 @@
+// FILE: p/J.java
+package p;
+
+public interface J {
+    public interface Super<T> {}
+    public interface Sub<T> extends Super<T> {}
+}
+
+// FILE: k.kt
+
+import p.J.*
+
+class Foo<T>: Sub<T> {
+    fun foo(): Super<T> {
+        return <!TYPE_INFERENCE_NO_INFORMATION_FOR_PARAMETER!>Foo<!>()
+    }
+}

compiler/testData/diagnostics/tests/inference/immutableArrayList.txt

@@ -0,0 +1,9 @@
+package
+
+internal final class Foo</*0*/ T> : p.J.Sub<T> {
+    public constructor Foo</*0*/ T>()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    internal final fun foo(): p.J.Super<T>
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/platformTypes/commonSupertype/typeOfElvis.kt

@@ -0,0 +1,20 @@
+// FILE: p/J.java
+
+package p;
+
+public class J {
+    public static J j() { return null; }
+}
+
+// FILE: k.kt
+
+import p.*
+
+fun foo(): J? = null
+
+fun main(args: Array<String>) {
+    val v = foo() ?: J.j()
+    if (v != null) {
+
+    }
+}

compiler/testData/diagnostics/tests/platformTypes/commonSupertype/typeOfElvis.txt

@@ -0,0 +1,4 @@
+package
+
+internal fun foo(): p.J?
+internal fun main(/*0*/ args: kotlin.Array<kotlin.String>): kotlin.Unit

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

@@ -4865,6 +4865,12 @@ public class JetDiagnosticsTestGenerated extends AbstractJetDiagnosticsTest {
                 doTest(fileName);
             }
             
+            @TestMetadata("immutableArrayList.kt")
+            public void testImmutableArrayList() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/inference/immutableArrayList.kt");
+                doTest(fileName);
+            }
+            
             @TestMetadata("inferInFunctionLiterals.kt")
             public void testInferInFunctionLiterals() throws Exception {
                 String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/inference/inferInFunctionLiterals.kt");
@@ -7799,6 +7805,12 @@ public class JetDiagnosticsTestGenerated extends AbstractJetDiagnosticsTest {
                     doTest(fileName);
                 }
                 
+                @TestMetadata("typeOfElvis.kt")
+                public void testTypeOfElvis() throws Exception {
+                    String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/platformTypes/commonSupertype/typeOfElvis.kt");
+                    doTest(fileName);
+                }
+                
             }
             
             @TestMetadata("compiler/testData/diagnostics/tests/platformTypes/methodCall")