don't report negated compile-time constants as always true/false (IDEA-118388)

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

@@ -536,6 +536,10 @@ public class DataFlowInspectionBase extends BaseJavaBatchLocalInspectionTool {
   }
 
   private static boolean isCompileConstantInIfCondition(PsiElement element) {
+    if (element instanceof PsiPrefixExpression && ((PsiPrefixExpression)element).getOperationTokenType() == JavaTokenType.EXCL) {
+      return isCompileConstantInIfCondition(((PsiPrefixExpression)element).getOperand());
+    }
+
     if (!(element instanceof PsiReferenceExpression)) return false;
     PsiElement resolved = ((PsiReferenceExpression)element).resolve();
     if (!(resolved instanceof PsiField)) return false;

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

@@ -0,0 +1,14 @@
+class Fun {
+  public static final boolean isDebug = true;
+
+  void foo() {
+    if (isDebug) {
+      System.out.println();
+    }
+  }
+  void fooNegated() {
+    if (!isDebug) {
+      System.out.println();
+    }
+  }
+}

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

@@ -184,6 +184,8 @@ public class DataFlowInspectionTest extends LightCodeInsightFixtureTestCase {
   public void testUnknownFloatMayBeNaN() { doTest(); }
   public void testFloatEquality() { doTest(); }
   public void testLastConstantConditionInAnd() { doTest(); }
+  
+  public void testCompileTimeConstant() { doTest(); }
 
   public void testTransientFinalField() { doTest(); }
   public void testRememberLocalTransientFieldState() { doTest(); }