Avoid recursive selection changes in ast viewer

This will prevent selections jumping around when an ast entry is
selected and its child has the same source location as the current
selection.

extensions/ql-vscode/src/astViewer.ts

@@ -8,6 +8,7 @@ import {
   TreeItem,
   TreeView,
   TextEditorSelectionChangeEvent,
+  TextEditorSelectionChangeKind,
   Location,
   Range
 } from 'vscode';
@@ -33,7 +34,7 @@ export interface ChildAstItem extends AstItem {
   parent: ChildAstItem | AstItem;
 }
 
-class AstViewerDataProvider  extends DisposableObject implements TreeDataProvider<AstItem> {
+class AstViewerDataProvider extends DisposableObject implements TreeDataProvider<AstItem> {
 
   public roots: AstItem[] = [];
   public db: DatabaseItem | undefined;
@@ -47,9 +48,9 @@ class AstViewerDataProvider  extends DisposableObject implements TreeDataProvide
     super();
     this.push(
       commandRunner('codeQLAstViewer.gotoCode',
-      async (item: AstItem) => {
-        await showLocation(item.fileLocation);
-      })
+        async (item: AstItem) => {
+          await showLocation(item.fileLocation);
+        })
     );
   }
 
@@ -160,6 +161,11 @@ export class AstViewer extends DisposableObject {
       return;
     }
 
+    // Avoid recursive tree-source code updates.
+    if (e.kind === TextEditorSelectionChangeKind.Command) {
+      return;
+    }
+
     if (
       this.treeView.visible &&
       e.textEditor.document.uri.fsPath === this.currentFile &&