dfa: mark ephemeral states even when there's no way of checking contract condition (IDEA-137604)

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

@@ -262,13 +262,18 @@ public class StandardInstructionVisitor extends InstructionVisitor {
       MethodContract.ValueConstraint constraint = contract.arguments[i];
       DfaConstValue expectedValue = constraint.getComparisonValue(factory);
       if (expectedValue == null) continue;
-      
+
+      boolean nullContract = expectedValue == constFactory.getNull();
       boolean invertCondition = constraint.shouldUseNonEqComparison();
       DfaValue condition = factory.getRelationFactory().createRelation(argValue, expectedValue, EQEQ, invertCondition);
       if (condition == null) {
         if (!(argValue instanceof DfaConstValue)) {
           for (DfaMemoryState state : states) {
-            falseStates.add(state.createCopy());
+            DfaMemoryState falseCopy = state.createCopy();
+            if (nullContract) {
+              (invertCondition ? falseCopy : state).markEphemeral();
+            }
+            falseStates.add(falseCopy);
           }
           continue;
         }
@@ -277,7 +282,7 @@ public class StandardInstructionVisitor extends InstructionVisitor {
 
       LinkedHashSet<DfaMemoryState> nextStates = ContainerUtil.newLinkedHashSet();
       for (DfaMemoryState state : states) {
-        boolean unknownVsNull = expectedValue == constFactory.getNull() &&
+        boolean unknownVsNull = nullContract &&
                                 argValue instanceof DfaVariableValue &&
                                 ((DfaMemoryStateImpl)state).getVariableState((DfaVariableValue)argValue).getNullability() == Nullness.UNKNOWN;
         DfaMemoryState falseCopy = state.createCopy();

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

@@ -0,0 +1,22 @@
+import org.jetbrains.annotations.Contract;
+import org.jetbrains.annotations.Nullable;
+
+class TestCase {
+
+  private void countWordsWarning() {
+    // no warnings should be here
+    String s = normalizeSpace(unknown()).trim();
+    String s3 = normalizeSpaceInverted(unknown()).trim();
+
+    String s4 = <warning descr="Method invocation 'normalizeSpace(null).trim()' may produce 'java.lang.NullPointerException'">normalizeSpace(null).trim()</warning>;
+  }
+
+  public static native String unknown();
+
+  @Contract("null->null")
+  public static native String normalizeSpace(@Nullable String str);
+
+  @Contract("!null->!null; _->null")
+  public static native String normalizeSpaceInverted(String str);
+
+}

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

@@ -222,6 +222,7 @@ public class DataFlowInspectionTest extends LightCodeInsightFixtureTestCase {
   public void testContractWithNullable() { doTest(); }
   public void testContractWithNotNull() { doTest(); }
   public void testContractPreservesUnknownNullability() { doTest(); }
+  public void testContractPreservesUnknownMethodNullability() { doTest(); }
   public void testContractSeveralClauses() { doTest(); }
   public void testContractVarargs() { doTest(); }