add API proxy module template

Author: lobsterkatie

packages/nextjs/src/config/templates/apiProxyLoaderTemplate.ts

@@ -0,0 +1,43 @@
+/**
+ * This file is a template for the code which will be substituted when our webpack loader handles API files in the
+ * `pages/` directory.
+ *
+ * We use `__RESOURCE_PATH__` as a placeholder for the path to the file being wrapped. Because it's not a real package,
+ * this causes both TS and ESLint to complain, hence the pragma comments below.
+ */
+
+// @ts-ignore See above
+// eslint-disable-next-line import/no-unresolved
+import * as origModule from '__RESOURCE_PATH__';
+import * as Sentry from '@sentry/nextjs';
+import type { PageConfig } from 'next';
+
+// We import this from `withSentry` rather than directly from `next` because our version can work simultaneously with
+// multiple versions of next. See note in `withSentry` for more.
+import type { NextApiHandler } from '../../utils/withSentry';
+
+type NextApiModule = {
+  default: NextApiHandler;
+  config?: PageConfig;
+};
+
+const userApiModule = origModule as NextApiModule;
+
+const maybeWrappedHandler = userApiModule.default;
+const origConfig = userApiModule.config || {};
+
+export const config = {
+  ...origConfig,
+  api: {
+    ...origConfig.api,
+    externalResolver: true,
+  },
+};
+
+export default Sentry.withSentryAPI(maybeWrappedHandler, '__ROUTE__');
+
+// Re-export anything exported by the page module we're wrapping. When processing this code, Rollup is smart enough to
+// not include anything whose name matchs something we've explicitly exported above.
+// @ts-ignore See above
+// eslint-disable-next-line import/no-unresolved
+export * from '__RESOURCE_PATH__';