isl-server: tell sapling CLI to not spawn an editor

Summary:
See also D71572659. ISL wants sapling CLI commands to be non-interactive but
editors like `vim` can still block forever.

Let's explicitly set the editor to a non-blocking executable to avoid
surprises. ISL shouldn't normally use the interactive editor, but it's good to
be defensive so if we accidentally trigger the editor, it won't hang forever.

I choose `HGEDITOR` because it has the highest priority that overrides other
configs like `ui.editor` and `EDITOR`.

Reviewed By: muirdm

Differential Revision: D71653280

fbshipit-source-id: 00e8cc6aeded2d4910bf99c657212d5eb61e863e

Author: quark-zju

addons/isl-server/src/commands.ts

@@ -193,6 +193,9 @@ export function getExecParams(
   if (EXCLUDE_FROM_BLACKBOX_COMMANDS.has(commandName)) {
     args.push('--config', 'extensions.blackbox=!');
   }
+  // The command should be non-interactive, so do not even attempt to run an
+  // (interactive) editor.
+  const editor = os.platform() === 'win32' ? 'exit /b 1' : 'false';
   const newEnv = {
     ...options_?.env,
     ...env,
@@ -208,7 +211,7 @@ export function getExecParams(
     EDITOR: undefined,
     VISUAL: undefined,
     HGUSER: undefined,
-    HGEDITOR: undefined,
+    HGEDITOR: editor,
   } as unknown as NodeJS.ProcessEnv;
   let langEnv = newEnv.LANG ?? process.env.LANG;
   if (langEnv === undefined || !langEnv.toUpperCase().endsWith('UTF-8')) {