Return components in merged header/footer cells only once (#17904)

Change-Id: Icff97b27455f3df4b07faeca3d338e7f3ba5656f

server/src/com/vaadin/ui/Grid.java

@@ -4571,7 +4571,9 @@ public class Grid extends AbstractComponent implements SelectionNotifier,
 
     @Override
     public Iterator<Component> iterator() {
-        List<Component> componentList = new ArrayList<Component>();
+        // This is a hash set to avoid adding header/footer components inside
+        // merged cells multiple times
+        LinkedHashSet<Component> componentList = new LinkedHashSet<Component>();
 
         Header header = getHeader();
         for (int i = 0; i < header.getRowCount(); ++i) {

server/tests/src/com/vaadin/tests/server/component/grid/GridChildren.java

@@ -0,0 +1,59 @@
+/*
+ * Copyright 2000-2014 Vaadin Ltd.
+ * 
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ * 
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package com.vaadin.tests.server.component.grid;
+
+import java.util.Iterator;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import com.vaadin.ui.Component;
+import com.vaadin.ui.Grid;
+import com.vaadin.ui.Grid.FooterCell;
+import com.vaadin.ui.Grid.HeaderCell;
+import com.vaadin.ui.Label;
+
+public class GridChildren {
+
+    @Test
+    public void componentsInMergedHeader() {
+        Grid grid = new Grid();
+        grid.addColumn("foo");
+        grid.addColumn("bar");
+        grid.addColumn("baz");
+        HeaderCell merged = grid.getDefaultHeaderRow()
+                .join("foo", "bar", "baz");
+        Label label = new Label();
+        merged.setComponent(label);
+        Iterator<Component> i = grid.iterator();
+        Assert.assertEquals(label, i.next());
+        Assert.assertFalse(i.hasNext());
+    }
+
+    @Test
+    public void componentsInMergedFooter() {
+        Grid grid = new Grid();
+        grid.addColumn("foo");
+        grid.addColumn("bar");
+        grid.addColumn("baz");
+        FooterCell merged = grid.addFooterRowAt(0).join("foo", "bar", "baz");
+        Label label = new Label();
+        merged.setComponent(label);
+        Iterator<Component> i = grid.iterator();
+        Assert.assertEquals(label, i.next());
+        Assert.assertFalse(i.hasNext());
+    }
+}