navigator: handle empty multi-root workspace

When a multi-root workspace is opened, the navigator will try to draw
the file tree because `model.root` is a `WorkspaceNode` with no
children.

This commit handles this case by adding a bit of ui to help the user add
folders to his workspace, instead of displaying a blank view.

Signed-off-by: Paul Maréchal <paul.marechal@ericsson.com>

packages/navigator/src/browser/navigator-tree.ts

@@ -59,17 +59,24 @@ export class FileNavigatorTree extends FileTree {
     }
 }
 
+/**
+ * File tree root node for multi-root workspaces.
+ */
 export interface WorkspaceNode extends CompositeTreeNode, SelectableTreeNode {
     children: WorkspaceRootNode[];
 }
 export namespace WorkspaceNode {
+
     export const id = 'WorkspaceNodeId';
     export const name = 'WorkspaceNode';
 
     export function is(node: TreeNode | undefined): node is WorkspaceNode {
         return CompositeTreeNode.is(node) && node.id === WorkspaceNode.id;
     }
 
+    /**
+     * Create a `WorkspaceNode` that can be used as a `Tree` root.
+     */
     export function createRoot(multiRootName?: string): WorkspaceNode {
         return {
             id: WorkspaceNode.id,
@@ -82,10 +89,14 @@ export namespace WorkspaceNode {
     }
 }
 
+/**
+ * A node representing a folder from a multi-root workspace.
+ */
 export interface WorkspaceRootNode extends DirNode {
     parent: WorkspaceNode;
 }
 export namespace WorkspaceRootNode {
+
     export function is(node: Object | undefined): node is WorkspaceRootNode {
         return DirNode.is(node) && WorkspaceNode.is(node.parent);
     }

packages/navigator/src/browser/navigator-widget.tsx

@@ -133,7 +133,11 @@ export class FileNavigatorWidget extends FileTreeWidget {
     }
 
     protected renderTree(model: TreeModel): React.ReactNode {
-        return super.renderTree(model) || this.renderOpenWorkspaceDiv();
+        return this.model.root === undefined
+            ? this.renderOpenWorkspaceDiv()
+            : this.isEmptyMultiRootWorkspace(model)
+                ? this.renderEmptyMultiRootWorkspace()
+                : super.renderTree(model);
     }
 
     protected onAfterAttach(msg: Message): void {
@@ -181,11 +185,17 @@ export class FileNavigatorWidget extends FileTreeWidget {
         this.commandService.executeCommand(WorkspaceCommands.OPEN_FOLDER.id);
     }
 
+    protected readonly addFolder = () => this.doAddFolder();
+    protected doAddFolder(): void {
+        this.commandService.executeCommand(WorkspaceCommands.ADD_FOLDER.id);
+    }
+
     protected readonly keyUpHandler = (e: React.KeyboardEvent) => {
         if (Key.ENTER.keyCode === e.keyCode) {
             (e.target as HTMLElement).click();
         }
     };
+
     /**
      * Instead of rendering the file resources from the workspace, we render a placeholder
      * button when the workspace root is not yet set.
@@ -199,7 +209,8 @@ export class FileNavigatorWidget extends FileTreeWidget {
                 Open Workspace
             </button>;
         } else {
-            openButton = <button className='theia-button open-workspace-button' title='Select a folder as your workspace root' onClick={this.openFolder}
+            openButton = <button className='theia-button open-workspace-button' title='Select a folder as your workspace root'
+                onClick={this.openFolder}
                 onKeyUp={this.keyUpHandler}>
                 Open Folder
             </button>;
@@ -213,6 +224,27 @@ export class FileNavigatorWidget extends FileTreeWidget {
         </div>;
     }
 
+    /**
+     * When a multi-root workspace is opened, a user can remove all the folders from it.
+     * Instead of displaying an empty navigator tree, this will show a button to add more folders.
+     */
+    protected renderEmptyMultiRootWorkspace(): React.ReactNode {
+        return <div className='theia-navigator-container'>
+            <div className='center'>You have not yet added a folder to the workspace.</div>
+            <div className='open-workspace-button-container'>
+                <button className='theia-button open-workspace-button' title='Add a folder to your workspace'
+                    onClick={this.addFolder}
+                    onKeyUp={this.keyUpHandler}>
+                    Add Folder
+                </button>
+            </div>
+        </div>;
+    }
+
+    protected isEmptyMultiRootWorkspace(model: TreeModel): boolean {
+        return WorkspaceNode.is(model.root) && model.root.children.length === 0;
+    }
+
     protected handleClickEvent(node: TreeNode | undefined, event: React.MouseEvent<HTMLElement>): void {
         const modifierKeyCombined: boolean = isOSX ? (event.shiftKey || event.metaKey) : (event.shiftKey || event.ctrlKey);
         if (!modifierKeyCombined && node && this.corePreferences['workbench.list.openMode'] === 'singleClick') {