bug: Public and secret keys should not be required at build time

[Stadly]

Describe the bug

The public key and secret key are required when building the application with Vite. I think they should only be required at runtime, so the build system does not need to know the keys used when running the application.

To reproduce

https://stackblitz.com/edit/sveltejs-kit-template-default-qeurfm?file=src%2Froutes%2F%2Bpage.server.js

Run npm run build in the terminal. You'll get the error

publicKey is required, but was not provided. It can be provided as an argument or as an environment variable LANGFUSE_PUBLIC_KEY.

Additional information

I'm using the JS/TS SDK.

[marcklingen]

Thanks for reporting, I think the best way forward here is to just disable langfuse tracing if no secrets are configured instead of throwing exceptions. This'd be helpful to only run instrumentation in certain environments and not in tests.

[Stadly]

I'm concerned that silently disabling Langfuse will trip up people when setting up the project. I guess there should be a way to require an env var during runtime but not during build time? Sounds like a common problem to encounter.

[marcklingen]

I'd suggest logging a single warning ("langfuse environment variables not set, tracing disabled"). I think I have seen this behavior with Sentry, Betterstack, Posthog, …

[Stadly]

Yes, that sounds reasonable 👍

[marcklingen]

Moved this to #1910 as there was another user requesting this