WEB-76271 PolySymbols/tests: fix problems with caching in KeyedExtensionCollector

- cache should not be used if extension point listener is not registered
- allow adding a new listener once an area is replaced
- always notify that area is replaced.

GitOrigin-RevId: 3d91be0598bc11a2cc193a764195a814d5be738c

platform/core-api/src/com/intellij/openapi/util/KeyedExtensionCollector.java

@@ -111,6 +111,8 @@ public class KeyedExtensionCollector<T, KeyT> implements ModificationTracker {
 
     cached = buildExtensions(stringKey, key);
 
+    if (!myEpListenerAdded.get()) return cached;
+
     synchronized (lock) {
       List<T> recent = cache.get(stringKey);
       if (recent != null) {
@@ -296,6 +298,7 @@ public class KeyedExtensionCollector<T, KeyT> implements ModificationTracker {
     public void areaReplaced(@NotNull ExtensionsArea area) {
       synchronized (lock) {
         cache = Java11Shim.INSTANCE.mapOf();
+        myEpListenerAdded.set(false);
         tracker.incModificationCount();
       }
     }

platform/extensions/src/com/intellij/openapi/extensions/Extensions.java

@@ -37,6 +37,9 @@ public final class Extensions {
   public static void setRootArea(@NotNull ExtensionsAreaImpl area, @NotNull Disposable parentDisposable) {
     ExtensionsAreaImpl oldRootArea = staticRootArea;
     staticRootArea = area;
+    if (oldRootArea != null) {
+      oldRootArea.notifyAreaReplaced(area);
+    }
     Disposer.register(parentDisposable, () -> {
       staticRootArea.notifyAreaReplaced(oldRootArea);
       staticRootArea = oldRootArea;
@@ -51,7 +54,8 @@ public final class Extensions {
   public static ExtensionsArea getRootArea() {
     if (rootSupplier != null) {
       return rootSupplier.get();
-    } else {
+    }
+    else {
       return staticRootArea;
     }
   }