IDEA-209947 Handle reassigned variables when fact is preserved; see through getters as variables

GitOrigin-RevId: 547cf499bdc952fc8b88af5896abffb57c628fea

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

@@ -1,6 +1,7 @@
 // Copyright 2000-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 package com.intellij.codeInspection.dataFlow;
 
+import com.intellij.codeInspection.dataFlow.instructions.AssignInstruction;
 import com.intellij.codeInspection.dataFlow.instructions.ConditionalGotoInstruction;
 import com.intellij.codeInspection.dataFlow.instructions.ExpressionPushingInstruction;
 import com.intellij.codeInspection.dataFlow.instructions.Instruction;
@@ -331,6 +332,7 @@ public class TrackingDfaMemoryState extends DfaMemoryStateImpl {
 
     MemoryStateChange findRelation(DfaVariableValue value, @NotNull Predicate<Relation> relationPredicate, boolean startFromSelf) {
       return findChange(change -> {
+        if (change.myInstruction instanceof AssignInstruction && change.myTopOfStack == value) return true;
         Change varChange = change.myChanges.get(value);
         if (varChange != null && varChange.myAddedRelations.stream().anyMatch(relationPredicate)) return true;
         Change bridgeVarChange = change.myBridgeChanges.get(value);
@@ -346,6 +348,10 @@ public class TrackingDfaMemoryState extends DfaMemoryStateImpl {
           if (factPair != null) return factPair;
           factPair = factFromChange(type, change, change.myBridgeChanges.get(value));
           if (factPair != null) return factPair;
+          if (change.myInstruction instanceof AssignInstruction && change.myTopOfStack == value && change.myPrevious != null) {
+            FactDefinition<T> fact = change.myPrevious.findFact(value, type);
+            return new FactDefinition<>(change, fact.myFact);
+          }
         }
         return new FactDefinition<>(null, ((DfaVariableValue)value).getInherentFacts().get(type));
       }
@@ -508,5 +514,10 @@ public class TrackingDfaMemoryState extends DfaMemoryStateImpl {
     T getFact(T defaultFact) {
       return myFact == null ? defaultFact : myFact;
     }
+
+    @Override
+    public String toString() {
+      return myFact + " @ " + myChange;
+    }
   }
 }

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

@@ -800,14 +800,20 @@ public class TrackingRunner extends StandardDataFlowRunner {
       PsiMethodCallExpression call = (PsiMethodCallExpression)expression;
       PsiMethod method = call.resolveMethod();
       CauseItem causeItem = fromMemberNullability(nullability, method, "method", call.getMethodExpression().getReferenceNameElement());
-      if (causeItem != null) return causeItem;
-      switch (nullability) {
-        case NULL:
-        case NULLABLE:
-          return fromCallContract(factUse, call, ContractReturnValue.returnNull());
-        case NOT_NULL:
-          return fromCallContract(factUse, call, ContractReturnValue.returnNotNull());
-        default:
+      if (causeItem == null) {
+        switch (nullability) {
+          case NULL:
+          case NULLABLE:
+            causeItem = fromCallContract(factUse, call, ContractReturnValue.returnNull());
+            break;
+          case NOT_NULL:
+            causeItem = fromCallContract(factUse, call, ContractReturnValue.returnNotNull());
+            break;
+          default:
+        }
+      }
+      if (causeItem != null) {
+        return causeItem;
       }
     }
     if (expression instanceof PsiReferenceExpression) {

java/java-tests/testData/inspection/dataFlow/tracker/ReassignAfterCheck.java

@@ -0,0 +1,20 @@
+/*
+Value is always false (t == null; line#16)
+  't' was assigned (=; line#15)
+    The 'instanceof' check implies non-nullity (t.getNext() instanceof CharSequence; line#14)
+ */
+
+import org.jetbrains.annotations.Contract;
+
+class Test {
+  @Contract(pure=true)
+  native Test getNext();
+  
+  void find(Test t) {
+    while (t.getNext() instanceof CharSequence) {
+      t = t.getNext();
+      if (<selection>t == null</selection>) return;
+    }
+    System.out.println(t);
+  }
+}

java/java-tests/testSrc/com/intellij/java/codeInspection/DataFlowInspectionTrackerTest.java

@@ -170,4 +170,5 @@ public class DataFlowInspectionTrackerTest extends LightCodeInsightFixtureTestCa
   public void testCollectionSizeEquality() { doTest(); }
   public void testFailingCall() { doTest(); }
   public void testInstanceOfMethodReturn() { doTest(); }
+  public void testReassignAfterCheck() { doTest(); }
 }