feat(zip-it-and-ship-it): feature flag ability to dynamically import funcion inside request handler (#6248)

this gives us the ability to catch any errors which may arise when importing the function's code,
and also allows us to prepare more within the bootstrapping phase before the functions code is
executed - such as populating process.env or any bootstrapping that may require information
provided by Proxy for the invocation

Author: JakeChampion

packages/zip-it-and-ship-it/src/feature_flags.ts

@@ -29,6 +29,9 @@ export const defaultFlags = {
 
   // Adds the `___netlify-telemetry.mjs` file to the function bundle.
   zisi_add_instrumentation_loader: true,
+
+  // Dynamically import the function handler.
+  zisi_dynamic_import_function_handler: false,
 } as const
 
 export type FeatureFlags = Partial<Record<keyof typeof defaultFlags, boolean>>

packages/zip-it-and-ship-it/src/runtimes/node/utils/entry_file.ts

@@ -51,6 +51,12 @@ const getEntryFileContents = (
   const importPath = `.${mainPath.startsWith('/') ? mainPath : `/${mainPath}`}`
 
   if (runtimeAPIVersion === 2) {
+    if (featureFlags.zisi_dynamic_import_function_handler) {
+      return [
+        `import * as bootstrap from './${BOOTSTRAP_FILE_NAME}'`,
+        `export const handler = bootstrap.getLambdaHandler('${importPath}')`,
+      ].join(';')
+    }
     return [
       `import * as bootstrap from './${BOOTSTRAP_FILE_NAME}'`,
       `import * as func from '${importPath}'`,