Further tweaks to ComboBox popup positioning. (#11910)

* Further tweaks to ComboBox popup positioning.

- Updated a comment and renamed a private method for better clarity.
- Blocked unnecessary position updates.
- Added a test for #11866 / #11894.

client/src/main/java/com/vaadin/client/ui/VComboBox.java

@@ -902,11 +902,16 @@ public class VComboBox extends Composite implements Field, KeyDownHandler,
 
             int comboBoxLeft = VComboBox.this.getAbsoluteLeft();
             int comboBoxWidth = VComboBox.this.getOffsetWidth();
-            if (hasParentWithUnadjustedPositioning()) {
-                // ComboBox itself may be incorrectly positioned, don't adjust
-                // popup position yet. Width calculations must be performed
-                // anyway to avoid flickering.
-                setPopupPosition(left, top);
+            if (hasParentWithUnadjustedHorizontalPositioning()) {
+                // ComboBox itself may be incorrectly positioned, don't try to
+                // adjust horizontal popup position yet. Earlier width
+                // calculations must be performed anyway to avoid flickering.
+                if (top != topPosition) {
+                    // Variable 'left' still contains the original popupLeft,
+                    // 'top' has been updated, thus vertical position needs
+                    // adjusting.
+                    setPopupPosition(left, top);
+                }
                 return;
             }
             if (left > comboBoxLeft
@@ -929,7 +934,10 @@ public class VComboBox extends Composite implements Field, KeyDownHandler,
                 menu.setWidth(Window.getClientWidth() + "px");
             }
 
-            setPopupPosition(left, top);
+            // Only update the position if it has changed.
+            if (top != topPosition || left != getPopupLeft()) {
+                setPopupPosition(left, top);
+            }
             menu.scrollSelectionIntoView();
         }
 
@@ -941,7 +949,7 @@ public class VComboBox extends Composite implements Field, KeyDownHandler,
          * @return {@code true} if unadjusted parents found, {@code false}
          *         otherwise
          */
-        private boolean hasParentWithUnadjustedPositioning() {
+        private boolean hasParentWithUnadjustedHorizontalPositioning() {
             /*
              * If there are any VHorizontalLayouts among this VComboBox's
              * parents, any spacing or expand ratio may cause incorrect

uitest/src/main/java/com/vaadin/tests/components/combobox/ComboBoxAtBottomEdgeWithinHorizontalLayout.java

@@ -0,0 +1,38 @@
+package com.vaadin.tests.components.combobox;
+
+import java.util.Arrays;
+
+import com.vaadin.server.VaadinRequest;
+import com.vaadin.tests.components.AbstractTestUI;
+import com.vaadin.ui.Alignment;
+import com.vaadin.ui.ComboBox;
+import com.vaadin.ui.HorizontalLayout;
+
+public class ComboBoxAtBottomEdgeWithinHorizontalLayout extends AbstractTestUI {
+
+    @Override
+    protected void setup(VaadinRequest request) {
+        ComboBox<Integer> comboBox = new ComboBox<>();
+        comboBox.setItems(Arrays.asList(100, 200, 300, 400, 500));
+
+        HorizontalLayout horizontalLayout = new HorizontalLayout();
+        horizontalLayout.addComponent(comboBox);
+
+        getLayout().addComponent(horizontalLayout);
+        getLayout().setComponentAlignment(horizontalLayout,
+                Alignment.BOTTOM_RIGHT);
+        getLayout().setSizeFull();
+        getLayout().getParent().setSizeFull();
+    }
+
+    @Override
+    protected Integer getTicketNumber() {
+        return 11866;
+    }
+
+    @Override
+    protected String getTestDescription() {
+        return "ComboBox at bottom edge should open popup above "
+                + "even when within HorizontalLayout.";
+    }
+}

uitest/src/test/java/com/vaadin/tests/components/combobox/ComboBoxAtBottomEdgeWithinHorizontalLayoutTest.java

@@ -0,0 +1,29 @@
+package com.vaadin.tests.components.combobox;
+
+import org.junit.Test;
+import org.openqa.selenium.WebElement;
+
+import com.vaadin.testbench.elements.ComboBoxElement;
+import com.vaadin.tests.tb3.MultiBrowserTest;
+
+public class ComboBoxAtBottomEdgeWithinHorizontalLayoutTest
+        extends MultiBrowserTest {
+
+    @Test
+    public void ensurePopupInView() {
+        openTestURL();
+
+        ComboBoxElement cb = $(ComboBoxElement.class).first();
+        cb.openPopup();
+        WebElement popup = cb.getSuggestionPopup();
+
+        int cbBottom = cb.getLocation().getY() + cb.getSize().getHeight();
+        int popupBottom = popup.getLocation().getY()
+                + popup.getSize().getHeight();
+        assertGreaterOrEqual(String.format(
+                "Popup should not open below the ComboBox at the "
+                        + "bottom edge of the viewport. ComboBox: %s, Popup: %s",
+                cbBottom, popupBottom), cbBottom, popupBottom);
+    }
+
+}