Correctly detach components in merged cells (#8773)

* Correctly detach components in merged cells

This was already once fixed in 7.7 in #8142

server/src/main/java/com/vaadin/ui/components/grid/StaticSection.java

@@ -388,6 +388,13 @@ public abstract class StaticSection<ROW extends StaticSection.StaticRow<?>>
             for (CELL cell : cells.values()) {
                 cell.detach();
             }
+            for (CellState cellState : rowState.cellGroups.keySet()) {
+                if (cellState.type == GridStaticCellType.WIDGET
+                        && cellState.connector != null) {
+                    ((Component) cellState.connector).setParent(null);
+                    cellState.connector = null;
+                }
+            }
         }
 
         void checkIfAlreadyMerged(String columnId) {

server/src/test/java/com/vaadin/tests/server/component/grid/GridChildrenTest.java

@@ -63,6 +63,17 @@ public class GridChildrenTest {
         Assert.assertNull(label.getParent());
     }
 
+    @Test
+    public void removeHeaderWithComponentInMergedHeaderCell() {
+        HeaderCell merged = grid.getDefaultHeaderRow().join("foo", "bar",
+                "baz");
+        Label label = new Label();
+        merged.setComponent(label);
+        Assert.assertEquals(grid, label.getParent());
+        grid.removeHeaderRow(0);
+        Assert.assertNull(label.getParent());
+    }
+
     @Test
     public void removeComponentInMergedFooterCell() {
         FooterCell merged = grid.addFooterRowAt(0).join("foo", "bar", "baz");
@@ -73,6 +84,16 @@ public class GridChildrenTest {
         Assert.assertNull(label.getParent());
     }
 
+    @Test
+    public void removeFooterWithComponentInMergedFooterCell() {
+        FooterCell merged = grid.addFooterRowAt(0).join("foo", "bar", "baz");
+        Label label = new Label();
+        merged.setComponent(label);
+        Assert.assertEquals(grid, label.getParent());
+        grid.removeFooterRow(0);
+        Assert.assertNull(label.getParent());
+    }
+
     @Test
     public void componentsInMergedFooter() {
         FooterCell merged = grid.addFooterRowAt(0).join("foo", "bar", "baz");