FinalUtils: check that field is not accessed with invalid qualifier

Fixes IDEA-193896 "Can be final" is not true

plugins/InspectionGadgets/InspectionGadgetsAnalysis/src/com/siyeh/ig/psiutils/FinalUtils.java

@@ -19,6 +19,7 @@ import com.intellij.codeInsight.daemon.impl.HighlightInfo;
 import com.intellij.codeInsight.daemon.impl.analysis.HighlightControlFlowUtil;
 import com.intellij.psi.*;
 import com.intellij.psi.controlFlow.ControlFlowUtil;
+import com.intellij.psi.controlFlow.LocalsOrMyInstanceFieldsControlFlowPolicy;
 import com.intellij.psi.search.PsiElementProcessor;
 import com.intellij.psi.util.PsiTreeUtil;
 import com.intellij.psi.util.PsiUtil;
@@ -54,6 +55,7 @@ public class FinalUtils {
         .checkVariableInitializedBeforeUsage(ref, variable, uninitializedVarProblems, variable.getContainingFile(), true);
       if (highlightInfo != null) return false;
       if (!PsiUtil.isAccessedForWriting(ref)) return true;
+      if (!LocalsOrMyInstanceFieldsControlFlowPolicy.isLocalOrMyInstanceReference(ref)) return false;
       if (ControlFlowUtil.isVariableAssignedInLoop(ref, variable)) return false;
       if (variable instanceof PsiField) {
         if (PsiUtil.findEnclosingConstructorOrInitializer(ref) == null) return false;

plugins/InspectionGadgets/test/com/siyeh/igtest/style/field_final/FieldMayBeFinal.java

@@ -1083,4 +1083,12 @@ class T75 {
 
     private Inner() {innerField = 0;}
   }
-}
+}
+// IDEA-193896
+class T76 {
+  private T76 a;
+  T76(T76 other) {
+    a = other;
+    other.a = null;
+  }
+}