Add tree welcome views (#1693)

* add welcome view when there are no columns in the project

* update text in test

* add welcome view for tracked tree

Author: mattseddon

extension/package.json

@@ -1107,6 +1107,14 @@
         "contents": "The currently open folder does not contain a DVC project. You can initialize a project which will enable features powered by DVC.\n[Initialize Project](command:dvc.init)\nTo learn more about how to use DVC please read [our docs](https://dvc.org/doc).",
         "when": "dvc.commands.available && !dvc.cli.incompatible && !dvc.project.available"
       },
+      {
+        "view": "dvc.views.trackedExplorerTree",
+        "contents": "No tracked data to display."
+      },
+      {
+        "view": "dvc.views.experimentsColumnsTree",
+        "contents": "No columns to display."
+      },
       {
         "view": "dvc.views.experimentsTree",
         "contents": "No experiments to display. \n[Run Experiment](command:dvc.runExperiment)\n"

extension/src/experiments/columns/quickPick.test.ts

@@ -43,9 +43,9 @@ describe('pickFromColumns', () => {
   }
   const exampleColumns = [epochsParam, paramsYamlParam]
 
-  it('should return early if no params or metrics are provided', async () => {
+  it('should return early if no columns are provided', async () => {
     const picked = await pickFromColumns([], {
-      title: "can't pick from no params or metrics" as Title
+      title: "can't pick from no columns" as Title
     })
     expect(picked).toBeUndefined()
     expect(mockedShowError).toBeCalledTimes(1)

extension/src/experiments/columns/quickPick.ts

@@ -11,7 +11,7 @@ export const pickFromColumns = (
   quickPickOptions: QuickPickOptionsWithTitle
 ) => {
   if (!definedAndNonEmpty(columns)) {
-    return Toast.showError('There are no params or metrics to select from')
+    return Toast.showError('There are no columns to select from.')
   }
   return quickPickValue<Column>(
     columns.map(column => ({