Merged column headers should work within declarative Grid. (#12206)

- null check to prevent NPE from the merged column headers
- convert to internal columnIds for merge handling
- use correct cell in merge handling
- switch away from streams in merge handling for easier readability
- regression test

Fixes: #10464

2 files changed, 84 insertions, 0 deletions

diff --git a/uitest/src/main/java/com/vaadin/tests/declarative/DeclarativeGrid.java b/uitest/src/main/java/com/vaadin/tests/declarative/DeclarativeGrid.java
new file mode 100644
index 0000000000..082d99b309
--- /dev/null
+++ b/uitest/src/main/java/com/vaadin/tests/declarative/DeclarativeGrid.java
@@ -0,0 +1,65 @@
+package com.vaadin.tests.declarative;
+
+import static java.nio.charset.StandardCharsets.UTF_8;
+
+import java.io.ByteArrayInputStream;
+
+import com.vaadin.server.VaadinRequest;
+import com.vaadin.tests.components.AbstractTestUI;
+import com.vaadin.ui.declarative.Design;
+import com.vaadin.ui.declarative.DesignContext;
+
+public class DeclarativeGrid extends AbstractTestUI {
+
+    private String design = "" + //
+            "   <vaadin-grid>\n" + //
+            "    <table>\n" + //
+            "     <colgroup>\n" + //
+            "      <col column-id=\"project\" sortable=\"false\">\n" + //
+            "      <col column-id=\"status\" sortable=\"false\">\n" + //
+            "      <col column-id=\"date\" sortable=\"false\">\n" + //
+            "     </colgroup>\n" + //
+            "     <thead>\n" + //
+            "      <tr default>\n" + //
+            "       <th plain-text column-ids=\"project,status\" " + //
+            "          colspan=\"2\">Project and Status</th>\n" + //
+            "       <th plain-text column-ids=\"date\">Date</th>\n" + //
+            "      </tr>\n" + //
+            "     </thead>\n" + //
+            "     <tbody>\n" + //
+            "      <tr item=\"project1\">\n" + //
+            "       <td>Customer Project 1</td>\n" + //
+            "       <td>OK</td>\n" + //
+            "       <td>2020-12-31</td>\n" + //
+            "      </tr>\n" + //
+            "      <tr item=\"project2\">\n" + //
+            "       <td>Customer Project 2</td>\n" + //
+            "       <td>OK</td>\n" + //
+            "       <td>2020-07-02</td>\n" + //
+            "      </tr>\n" + //
+            "      <tr item=\"project3\">\n" + //
+            "       <td>Customer Project 3</td>\n" + //
+            "       <td>OK</td>\n" + //
+            "       <td>2019-10-01</td>\n" + //
+            "      </tr>\n" + //
+            "     </tbody>\n" + //
+            "    </table>\n" + //
+            "   </vaadin-grid>";
+
+    @Override
+    protected void setup(VaadinRequest request) {
+        DesignContext dc = Design
+                .read(new ByteArrayInputStream(design.getBytes(UTF_8)), null);
+        addComponent(dc.getRootComponent());
+    }
+
+    @Override
+    protected Integer getTicketNumber() {
+        return 10464;
+    }
+
+    @Override
+    protected String getTestDescription() {
+        return "Merged column header should not cause an exception.";
+    }
+}
diff --git a/uitest/src/test/java/com/vaadin/tests/declarative/DeclarativeGridTest.java b/uitest/src/test/java/com/vaadin/tests/declarative/DeclarativeGridTest.java
new file mode 100644
index 0000000000..5babbae75b
--- /dev/null
+++ b/uitest/src/test/java/com/vaadin/tests/declarative/DeclarativeGridTest.java
@@ -0,0 +1,19 @@
+package com.vaadin.tests.declarative;
+
+import org.junit.Test;
+
+import com.vaadin.testbench.By;
+import com.vaadin.testbench.elements.GridElement;
+import com.vaadin.tests.tb3.MultiBrowserTest;
+
+public class DeclarativeGridTest extends MultiBrowserTest {
+
+    @Test
+    public void testMergedHeaderCell() {
+        openTestURL();
+        waitForElementPresent(By.className("v-label"));
+        // ensure the grid gets loaded and has the merged header
+        GridElement grid = $(GridElement.class).first();
+        grid.getHeaderCellByCaption("Project and Status");
+    }
+}