Add feature flag for ast viewer

Set `codeQL.experimentalAstViewer` to true in settings
in order for component to be enabled.

Author: aeisenberg

extensions/ql-vscode/package.json

@@ -387,7 +387,7 @@
         },
         {
           "command": "codeQLAstViewer.clear",
-          "when": "view == codeQLAstViewer",
+          "when": "view == codeQLAstViewer && config.codeQL.experimentalAstViewer == true",
           "group": "navigation"
         }
       ],
@@ -472,7 +472,7 @@
         {
           "command": "codeQL.viewAst",
           "group": "9_qlCommands",
-          "when": "resourceScheme == codeql-zip-archive"
+          "when": "resourceScheme == codeql-zip-archive && config.codeQL.experimentalAstViewer == true"
         },
         {
           "command": "codeQL.runQueries",
@@ -617,14 +617,16 @@
         },
         {
           "id": "codeQLAstViewer",
-          "name": "AST Viewer"
+          "name": "AST Viewer",
+          "when": "config.codeQL.experimentalAstViewer == true"
         }
       ]
     },
     "viewsWelcome": [
       {
         "view": "codeQLAstViewer",
-        "contents": "Run the 'CodeQL: View AST' command on an open source file from a Code QL database.\n[View AST](command:codeQL.viewAst)"
+        "contents": "Run the 'CodeQL: View AST' command on an open source file from a Code QL database.\n[View AST](command:codeQL.viewAst)",
+        "when": "config.codeQL.experimentalAstViewer == true"
       },
       {
         "view": "codeQLQueryHistory",

extensions/ql-vscode/src/config.ts

@@ -209,3 +209,15 @@ export class QueryHistoryConfigListener extends ConfigListener implements QueryH
     return QUERY_HISTORY_FORMAT_SETTING.getValue<string>();
   }
 }
+
+// Enable experimental features
+
+/**
+ * Any settings below are deliberately not in package.json so that
+ * they do not appear in the settings ui in vscode itself. If users
+ * want to enable experimental features, they can add them directly in
+ * their vscode settings json file.
+ */
+
+/* Advanced setting: used to enable the AST Viewer. */
+export const EXPERIMENTAL_AST_VIEWER = new Setting('experimentalAstViewer', ROOT_SETTING);