don't increment psi mod counts on file writability change

java/java-impl/src/com/intellij/psi/impl/JavaCodeBlockModificationListener.java

@@ -57,7 +57,9 @@ public class JavaCodeBlockModificationListener implements PsiTreeChangePreproces
 
       case CHILD_MOVED:
       case PROPERTY_CHANGED:
-        myModificationTracker.incCounter();
+        if (PsiModificationTrackerImpl.canAffectPsi(event)) {
+          myModificationTracker.incCounter();
+        }
         break;
 
       default:

java/java-tests/testSrc/com/intellij/psi/PsiModificationTrackerTest.java

@@ -418,4 +418,20 @@ public class PsiModificationTrackerTest extends CodeInsightTestCase {
       return null;
     });
   }
+
+  public void testNoIncrementOnReadOnlyStatusChange() throws IOException {
+    VirtualFile file = addFileToProject("Foo.java", "class Foo {}").getVirtualFile();
+
+    PsiModificationTracker tracker = PsiManager.getInstance(getProject()).getModificationTracker();
+    long mc = tracker.getModificationCount();
+
+    WriteAction.run(() -> file.setWritable(false));
+    assertEquals(mc, tracker.getModificationCount());
+
+    PlatformTestUtil.tryGcSoftlyReachableObjects();
+    assertNull(PsiManagerEx.getInstanceEx(myProject).getFileManager().getCachedPsiFile(file));
+
+    WriteAction.run(() -> file.setWritable(true));
+    assertEquals(mc, tracker.getModificationCount());
+  }
 }

platform/core-impl/src/com/intellij/psi/impl/PsiModificationTrackerImpl.java

@@ -22,6 +22,7 @@ import com.intellij.openapi.project.DumbService;
 import com.intellij.openapi.project.Project;
 import com.intellij.openapi.util.ModificationTracker;
 import com.intellij.psi.PsiDirectory;
+import com.intellij.psi.PsiTreeChangeEvent;
 import com.intellij.psi.util.PsiModificationTracker;
 import com.intellij.util.messages.MessageBus;
 import org.jetbrains.annotations.NotNull;
@@ -83,6 +84,10 @@ public class PsiModificationTrackerImpl implements PsiModificationTracker, PsiTr
 
   @Override
   public void treeChanged(@NotNull PsiTreeChangeEventImpl event) {
+    if (!canAffectPsi(event)) {
+      return;
+    }
+
     myModificationCount.getAndIncrement();
     if (event.getParent() instanceof PsiDirectory 
         || event.getOldParent() instanceof PsiDirectory /* move events */) {
@@ -92,6 +97,10 @@ public class PsiModificationTrackerImpl implements PsiModificationTracker, PsiTr
     fireEvent();
   }
 
+  public static boolean canAffectPsi(@NotNull PsiTreeChangeEventImpl event) {
+    return !PsiTreeChangeEvent.PROP_WRITABLE.equals(event.getPropertyName());
+  }
+
   @Override
   public long getModificationCount() {
     return myModificationCount.get();