fix dfa when a notnull parameter is assigned to null

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

@@ -268,9 +268,8 @@ public class DfaMemoryStateImpl implements DfaMemoryState {
       return;
     }
 
-    setVariableState(var, getVariableState(var).withValue(value));
+    setVariableState(var, withValueNullability(value, getVariableState(var).withValue(value)));
     if (value instanceof DfaTypeValue) {
-      setVariableState(var, getVariableState(var).withNullability(((DfaTypeValue)value).getNullness()));
       DfaRelationValue dfaInstanceof = myFactory.getRelationFactory().createRelation(var, value, JavaTokenType.INSTANCEOF_KEYWORD, false);
       if (((DfaTypeValue)value).isNotNull()) {
         applyCondition(dfaInstanceof);
@@ -293,6 +292,12 @@ public class DfaMemoryStateImpl implements DfaMemoryState {
     }
   }
 
+  private DfaVariableState withValueNullability(DfaValue value, DfaVariableState state) {
+    if (value instanceof DfaTypeValue) return state.withNullability(((DfaTypeValue)value).getNullness());
+    if (isNull(value)) return state.withNullability(Nullness.NULLABLE);
+    return state;
+  }
+
   private DfaValue handleFlush(DfaVariableValue flushed, DfaValue value) {
     if (value instanceof DfaVariableValue && (value == flushed || myFactory.getVarFactory().getAllQualifiedBy(flushed).contains(value))) {
       Nullness nullability = isNotNull(value) ? Nullness.NOT_NULL : ((DfaVariableValue)value).getInherentNullability();

java/java-tests/testData/inspection/dataFlow/fixture/MethodParametersCanChangeNullability.java

@@ -2,6 +2,7 @@ import org.jetbrains.annotations.*;
 
 class Test {
 
+  /*
   @Nullable
   String findMessage(@NotNull Element element) {
     while (element != null) {
@@ -23,6 +24,16 @@ class Test {
     }
     return null;
   }
+  */
+
+  void foo(@NotNull String param) {
+    if (equals(3)) {
+      param = null;
+    }
+    if (param != null) {
+      System.out.println();
+    }
+  }
 
 }