another attempt for IDEA-89059 Selected item is scrolled off the bottom of the code completion popup

platform/lang-impl/src/com/intellij/codeInsight/lookup/impl/LookupImpl.java

@@ -477,16 +477,13 @@ public class LookupImpl extends LightweightHint implements LookupEx, Disposable
       updateListHeight(listModel);
 
       myList.setSelectedIndex(toSelect);
-      if (onExplicitAction && myShown) {
-        myList.ensureIndexIsVisible(toSelect);
-      }
       return !oldModel.equals(items);
     }
 
   }
 
   private boolean isSelectionVisible() {
-    return myList.getFirstVisibleIndex() <= myList.getSelectedIndex() && myList.getSelectedIndex() <= myList.getLastVisibleIndex();
+    return ListScrollingUtil.isIndexFullyVisible(myList, myList.getSelectedIndex());
   }
 
   private boolean checkReused() {
@@ -1286,7 +1283,7 @@ public class LookupImpl extends LightweightHint implements LookupEx, Disposable
       }
       HintManagerImpl.updateLocation(this, myEditor, rectangle.getLocation());
 
-      if (reused || selectionVisible) {
+      if (reused || selectionVisible || onExplicitAction) {
         ensureSelectionVisible();
       }
     }

platform/platform-api/src/com/intellij/ui/ListScrollingUtil.java

@@ -176,6 +176,20 @@ public class ListScrollingUtil {
     }
   }
 
+  public static boolean isIndexFullyVisible(JList list, int index) {
+    int first = list.getFirstVisibleIndex();
+    int last = list.getLastVisibleIndex();
+
+    if (index < 0 || first < 0 || last < 0 || index < first || index > last) {
+      return false;
+    }
+    if (index > first && index < last) {
+      return true;
+    }
+
+    return list.getVisibleRect().contains(list.getCellBounds(index, index));
+  }
+
   private static int getVisibleRowCount(JList list) {
     return list.getLastVisibleIndex() - list.getFirstVisibleIndex() + 1;
   }