How do you write a dynamic module that supports both sync (register) and async (registerAsync) configuration sharing the same internal providers?
Extract the core provider creation into a private static helper method so both sync and async configuration paths produce the same set of providers. This prevents duplication and keeps both paths in sync when core providers change.
Shared private helper for sync and async config paths
Benefits of the private helper pattern:
Single source of truth — adding or removing a core provider only requires changing the helper.
Both sync and async paths stay automatically synchronized.
Reduces code duplication and the risk of the two paths drifting apart over time.
This is the pattern used inside NestJS framework modules like @nestjs/throttler.