Add automatic recalculation of Tree width on expand/collapse (#9767)

Fixes #9628

server/src/main/java/com/vaadin/ui/Tree.java

@@ -238,6 +238,7 @@ public class Tree<T> extends Composite
     private ItemCaptionGenerator<T> captionGenerator = String::valueOf;
     private IconGenerator<T> iconProvider = t -> null;
     private final TreeRenderer renderer;
+    private boolean autoRecalculateWidth = true;
 
     /**
      * Constructs a new Tree Component.
@@ -259,10 +260,18 @@ public class Tree<T> extends Composite
         treeGrid.setHeightUndefined();
         treeGrid.setHeightMode(HeightMode.UNDEFINED);
 
-        treeGrid.addExpandListener(e -> fireExpandEvent(e.getExpandedItem(),
-                e.isUserOriginated()));
-        treeGrid.addCollapseListener(e -> fireCollapseEvent(
-                e.getCollapsedItem(), e.isUserOriginated()));
+        treeGrid.addExpandListener(e -> {
+            fireExpandEvent(e.getExpandedItem(), e.isUserOriginated());
+            if (autoRecalculateWidth) {
+                treeGrid.recalculateColumnWidths();
+            }
+        });
+        treeGrid.addCollapseListener(e -> {
+            fireCollapseEvent(e.getCollapsedItem(), e.isUserOriginated());
+            if (autoRecalculateWidth) {
+                treeGrid.recalculateColumnWidths();
+            }
+        });
         treeGrid.addItemClickListener(e -> fireEvent(
                 new ItemClick<>(this, e.getItem(), e.getMouseEventDetails())));
     }
@@ -789,6 +798,35 @@ public class Tree<T> extends Composite
         renderer.getState().mode = contentMode;
     }
 
+    /**
+     * Returns the current state of automatic width recalculation.
+     * 
+     * @return {@code true} if enabled; {@code false} if disabled
+     * 
+     * @since 8.1.1
+     */
+    public boolean isAutoRecalculateWidth() {
+        return autoRecalculateWidth;
+    }
+
+    /**
+     * Sets the automatic width recalculation on or off. This feature is on by
+     * default.
+     * 
+     * @param autoRecalculateWidth
+     *            {@code true} to enable recalculation; {@code false} to turn it
+     *            off
+     * 
+     * @since 8.1.1
+     */
+    public void setAutoRecalculateWidth(boolean autoRecalculateWidth) {
+        this.autoRecalculateWidth = autoRecalculateWidth;
+
+        treeGrid.getColumns().get(0)
+                .setMinimumWidthFromContent(autoRecalculateWidth);
+        treeGrid.recalculateColumnWidths();
+    }
+
     /**
      * Adds a context click listener that gets notified when a context click
      * happens.

uitest/src/main/java/com/vaadin/tests/components/tree/TreeWideContent.java

@@ -0,0 +1,36 @@
+package com.vaadin.tests.components.tree;
+
+import com.vaadin.annotations.Widgetset;
+import com.vaadin.data.TreeData;
+import com.vaadin.server.VaadinRequest;
+import com.vaadin.tests.components.AbstractTestUI;
+import com.vaadin.ui.Button;
+import com.vaadin.ui.Tree;
+
+@Widgetset("com.vaadin.DefaultWidgetSet")
+public class TreeWideContent extends AbstractTestUI {
+
+    @Override
+    protected void setup(VaadinRequest request) {
+        Tree<String> tree = new Tree<>();
+
+        tree.setWidth("150px");
+        tree.setHeight("100px");
+
+        TreeData<String> data = new TreeData();
+        data.addItem(null, "Foo");
+        data.addItem("Foo", "Extra long text content that should be wider"
+                + " than the allocated width of the Tree.");
+        data.addItem(null, "Bar");
+        data.addItem(null, "Baz");
+        tree.setTreeData(data);
+
+        // Expand the wide one initially.
+        tree.expand("Foo");
+
+        addComponent(tree);
+        addComponent(new Button("Toggle auto recalc", e -> tree
+                .setAutoRecalculateWidth(!tree.isAutoRecalculateWidth())));
+    }
+
+}

uitest/src/test/java/com/vaadin/tests/components/tree/TreeWideContentTest.java

@@ -0,0 +1,48 @@
+package com.vaadin.tests.components.tree;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import com.vaadin.testbench.elements.ButtonElement;
+import com.vaadin.testbench.elements.TreeElement;
+import com.vaadin.testbench.elements.TreeGridElement;
+import com.vaadin.tests.tb3.SingleBrowserTest;
+
+public class TreeWideContentTest extends SingleBrowserTest {
+
+    @Test
+    public void testInitialSize() {
+        openTestURL();
+
+        TreeGridElement tree = $(TreeElement.class).first()
+                .wrap(TreeGridElement.class);
+        Assert.assertTrue("Row should be wider than tree",
+                tree.getTableWrapper().getSize().getWidth() < tree.getRow(0)
+                        .getSize().getWidth());
+    }
+
+    @Test
+    public void testSizeAfterCollapse() {
+        openTestURL();
+
+        TreeElement tree = $(TreeElement.class).first();
+        tree.collapse(0);
+        TreeGridElement treeGrid = tree.wrap(TreeGridElement.class);
+        Assert.assertTrue("Row should be as wide as tree",
+                treeGrid.getTableWrapper().getSize().getWidth() == treeGrid
+                        .getRow(0).getSize().getWidth());
+    }
+
+    @Test
+    public void testSizeWithAutoRecalcDisabled() {
+        openTestURL();
+        // Disable auto recalc
+        $(ButtonElement.class).first().click();
+
+        TreeElement tree = $(TreeElement.class).first();
+        TreeGridElement treeGrid = tree.wrap(TreeGridElement.class);
+        Assert.assertTrue("Row should be as wide as tree",
+                treeGrid.getTableWrapper().getSize().getWidth() == treeGrid
+                        .getRow(0).getSize().getWidth());
+    }
+}