TypeConstraint#union: smarter merge of supertypes

union("is X, Y; not SubX", "is SubX, Y") now produces "is X, Y"; before it was "is Y".
Fixes IDEA-184153 Smart-cast completion fails

java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/TypeConstraint.java

@@ -169,18 +169,8 @@ public final class TypeConstraint {
     Set<DfaPsiType> leftNotTypes = new HashSet<>(this.myNotInstanceofValues);
     Set<DfaPsiType> rightTypes = new HashSet<>(other.myInstanceofValues);
     Set<DfaPsiType> rightNotTypes = new HashSet<>(other.myNotInstanceofValues);
-    for (Iterator<DfaPsiType> iterator = leftTypes.iterator(); iterator.hasNext(); ) {
-      DfaPsiType type = iterator.next();
-      if(rightNotTypes.remove(type)) {
-        iterator.remove();
-      }
-    }
-    for (Iterator<DfaPsiType> iterator = rightTypes.iterator(); iterator.hasNext(); ) {
-      DfaPsiType type = iterator.next();
-      if(leftNotTypes.remove(type)) {
-        iterator.remove();
-      }
-    }
+    filter(leftTypes, rightTypes, rightNotTypes);
+    filter(rightTypes, leftTypes, leftNotTypes);
     TypeConstraint left = create(leftTypes, leftNotTypes);
     TypeConstraint right = create(rightTypes, rightNotTypes);
     if(left.isSuperStateOf(right)) return left;
@@ -188,6 +178,18 @@ public final class TypeConstraint {
     return null;
   }
 
+  private static void filter(Set<DfaPsiType> leftTypes, Set<DfaPsiType> rightTypes, Set<DfaPsiType> rightNotTypes) {
+    Set<DfaPsiType> addTypes = new HashSet<>();
+    for (Iterator<DfaPsiType> iterator = leftTypes.iterator(); iterator.hasNext(); ) {
+      DfaPsiType type = iterator.next();
+      if(rightNotTypes.remove(type)) {
+        iterator.remove();
+        StreamEx.of(rightTypes).filter(t -> t.isAssignableFrom(type)).into(addTypes);
+      }
+    }
+    leftTypes.addAll(addTypes);
+  }
+
   @NotNull
   public Set<DfaPsiType> getInstanceofValues() {
     return Collections.unmodifiableSet(myInstanceofValues);

java/java-tests/testData/codeInsight/completion/normal/ComplexInstanceOfDfa.java

@@ -0,0 +1,25 @@
+import java.math.BigInteger;
+import java.util.function.Function;
+
+class Test {
+    interface X {
+        void methodFromX();
+        void methodFromX2();
+    }
+
+    interface Y {
+        void methodFromY();
+        void methodFromY2();
+    }
+
+    interface Z extends X {}
+
+    void test(Object obj) {
+        if(obj instanceof Z && Math.random() > 0.5) {
+            return;
+        }
+        if(obj instanceof X && obj instanceof Y) {
+            obj.method<caret>
+        }
+    }
+}

java/java-tests/testSrc/com/intellij/java/codeInsight/completion/NormalCompletionDfaTest.groovy

@@ -55,6 +55,10 @@ class NormalCompletionDfaTest extends NormalCompletionTestCase {
   void testNoUnnecessaryCastDfa() { doTest() }
   void testNoUnnecessaryCastRawDfa() { doTest() }
   void testInstanceOfAfterFunction() { doTest() }
+  void testComplexInstanceOfDfa() {
+    configureByTestName()
+    myFixture.assertPreferredCompletionItems 0, 'methodFromX', 'methodFromX2', 'methodFromY', 'methodFromY2'
+  }
 
   void testCastTwice() {
     configureByTestName()