webpack: Use Webpack’s mode option rather than repurposing env.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

tools/webpack

@@ -12,9 +12,7 @@ STATIC_PATH = 'static/'
 def build_for_prod_or_puppeteer(quiet: bool) -> NoReturn:
     """Builds for production, writing the output to disk"""
 
-    webpack_args = ['node', 'node_modules/.bin/webpack-cli',
-                    '-p',
-                    '--env=production']
+    webpack_args = ['node', 'node_modules/.bin/webpack-cli', '-p']
     if quiet:
         webpack_args.append('--display=errors-only')
     os.execvp(webpack_args[0], webpack_args)

webpack.config.ts

@@ -20,8 +20,9 @@ const cacheLoader: webpack.RuleSetUseItem = {
     },
 };
 
-export default (env?: string): webpack.Configuration[] => {
-    const production: boolean = env === "production";
+export default (_env: unknown, argv: {mode?: string}): webpack.Configuration[] => {
+    const production: boolean = argv.mode === "production";
+
     const config: webpack.Configuration = {
         name: "frontend",
         mode: production ? "production" : "development",