Only return something from getPathData once discover has run at least once

extensions/ql-vscode/src/common/vscode/file-path-discovery.ts

@@ -34,6 +34,12 @@ interface PathData {
  * relevant, and what extra data to compute for each file.
  */
 export abstract class FilePathDiscovery<T extends PathData> extends Discovery {
+  /**
+   * Has `discover` been called. This allows distinguishing between
+   * "no paths found" and not having scanned yet.
+   */
+  private discoverHasCompletedOnce = false;
+
   /** The set of known paths and associated data that we are tracking */
   private pathData: T[] = [];
 
@@ -73,7 +79,10 @@ export abstract class FilePathDiscovery<T extends PathData> extends Discovery {
     this.push(this.watcher.onDidChange(this.fileChanged.bind(this)));
   }
 
-  protected getPathData(): ReadonlyArray<Readonly<T>> {
+  protected getPathData(): ReadonlyArray<Readonly<T>> | undefined {
+    if (!this.discoverHasCompletedOnce) {
+      return undefined;
+    }
     return this.pathData;
   }
 
@@ -171,6 +180,7 @@ export abstract class FilePathDiscovery<T extends PathData> extends Discovery {
       }
     }
 
+    this.discoverHasCompletedOnce = true;
     if (pathsUpdated) {
       this.onDidChangePathDataEmitter.fire();
     }

extensions/ql-vscode/src/queries-panel/query-discovery.ts

@@ -56,10 +56,15 @@ export class QueryDiscovery
    *
    * Trivial directories where there is only one child will be collapsed into a single node.
    */
-  public buildQueryTree(): Array<FileTreeNode<string>> {
+  public buildQueryTree(): Array<FileTreeNode<string>> | undefined {
+    const pathData = this.getPathData();
+    if (pathData === undefined) {
+      return undefined;
+    }
+
     const roots = [];
     for (const workspaceFolder of getOnDiskWorkspaceFoldersObjects()) {
-      const queriesInRoot = this.getPathData().filter((query) =>
+      const queriesInRoot = pathData.filter((query) =>
         containsPath(workspaceFolder.uri.fsPath, query.path),
       );
       if (queriesInRoot.length === 0) {

extensions/ql-vscode/src/queries-panel/query-pack-discovery.ts

@@ -37,7 +37,7 @@ export class QueryPackDiscovery extends FilePathDiscovery<QueryPack> {
    */
   public getLanguageForQueryFile(queryPath: string): QueryLanguage | undefined {
     // Find all packs in a higher directory than the query
-    const packs = this.getPathData().filter((queryPack) =>
+    const packs = (this.getPathData() || []).filter((queryPack) =>
       containsPath(dirname(queryPack.path), queryPath),
     );
 

extensions/ql-vscode/src/queries-panel/query-tree-data-provider.ts

@@ -4,7 +4,7 @@ import { DisposableObject } from "../common/disposable-object";
 import { FileTreeNode } from "../common/file-tree-nodes";
 
 export interface QueryDiscoverer {
-  readonly buildQueryTree: () => Array<FileTreeNode<string>>;
+  readonly buildQueryTree: () => Array<FileTreeNode<string>> | undefined;
   readonly onDidChangeQueries: Event<void>;
 }
 
@@ -34,9 +34,11 @@ export class QueryTreeDataProvider
   }
 
   private createTree(): QueryTreeViewItem[] {
-    return this.queryDiscoverer
-      .buildQueryTree()
-      .map(this.convertFileTreeNode.bind(this));
+    const queryTree = this.queryDiscoverer.buildQueryTree();
+    if (queryTree === undefined) {
+      return [];
+    }
+    return queryTree.map(this.convertFileTreeNode.bind(this));
   }
 
   private convertFileTreeNode(

extensions/ql-vscode/test/vscode-tests/minimal-workspace/common/vscode/file-path-discovery.test.ts

@@ -34,7 +34,7 @@ class TestFilePathDiscovery extends FilePathDiscovery<TestData> {
     return this.onDidChangePathData;
   }
 
-  public getPathData(): readonly TestData[] {
+  public getPathData(): readonly TestData[] | undefined {
     return super.getPathData();
   }
 
@@ -123,6 +123,10 @@ describe("FilePathDiscovery", () => {
   });
 
   describe("initialRefresh", () => {
+    it("should return undefined until initialRefresh is called", async () => {
+      expect(discovery.getPathData()).toEqual(undefined);
+    });
+
     it("should handle no files being present", async () => {
       await discovery.initialRefresh();
       expect(discovery.getPathData()).toEqual([]);

extensions/ql-vscode/test/vscode-tests/minimal-workspace/queries-panel/query-discovery.test.ts

@@ -54,6 +54,10 @@ describe("Query pack discovery", () => {
   });
 
   describe("buildQueryTree", () => {
+    it("returns undefined before initial refresh has been done", async () => {
+      expect(discovery.buildQueryTree()).toEqual(undefined);
+    });
+
     it("returns an empty tree when there are no query files", async () => {
       await discovery.initialRefresh();