This PR removes the warning for multiple browserTracingIntegrations being setup.
We realised this warning was actually just a symptom of us running a bunch of the integration code in the function itself, not int setup(). This lead to stuff running twice when users passed in a custom integration in addition to a default one, because the logic is basically:

const defaultIntergations = [browserTracingIntegration()];
const usedDefinedIntegrations = [browserTracingIntegration()];
// at this point, the function was already executed twice, leading to side effects even without calling `init`!

Now, we move all the logic to setup/setupAfterAll, so this should be safe. This means that the integration will be deduped anyhow (I added a test to make sure this is the case), and we no longer need the warning.

fixes #16369

size-limit report 📦

Path	Size	% Change	Change
@sentry/browser	23.95 kB	-	-
@sentry/browser - with treeshaking flags	23.72 kB	-	-
@sentry/browser (incl. Tracing)	38.24 kB	-0.08%	-29 B 🔽
@sentry/browser (incl. Tracing, Replay)	76.37 kB	-0.03%	-19 B 🔽
@sentry/browser (incl. Tracing, Replay) - with treeshaking flags	69.48 kB	-0.04%	-22 B 🔽
@sentry/browser (incl. Tracing, Replay with Canvas)	81.14 kB	-0.04%	-30 B 🔽
@sentry/browser (incl. Tracing, Replay, Feedback)	93.22 kB	-0.05%	-38 B 🔽
@sentry/browser (incl. Feedback)	40.72 kB	-	-
@sentry/browser (incl. sendFeedback)	28.68 kB	-	-
@sentry/browser (incl. FeedbackAsync)	33.57 kB	-	-
@sentry/react	25.73 kB	-	-
@sentry/react (incl. Tracing)	40.21 kB	-0.11%	-41 B 🔽
@sentry/vue	28.35 kB	-	-
@sentry/vue (incl. Tracing)	40.05 kB	-0.12%	-47 B 🔽
@sentry/svelte	23.98 kB	-	-
CDN Bundle	25.25 kB	-	-
CDN Bundle (incl. Tracing)	38.38 kB	-0.01%	-3 B 🔽
CDN Bundle (incl. Tracing, Replay)	74.24 kB	-0.03%	-16 B 🔽
CDN Bundle (incl. Tracing, Replay, Feedback)	79.66 kB	-0.02%	-12 B 🔽
CDN Bundle - uncompressed	73.67 kB	-	-
CDN Bundle (incl. Tracing) - uncompressed	113.59 kB	-0.1%	-104 B 🔽
CDN Bundle (incl. Tracing, Replay) - uncompressed	227.56 kB	-0.05%	-104 B 🔽
CDN Bundle (incl. Tracing, Replay, Feedback) - uncompressed	240.38 kB	-0.05%	-104 B 🔽
@sentry/nextjs (client)	41.87 kB	-0.1%	-40 B 🔽
@sentry/sveltekit (client)	38.71 kB	-0.11%	-39 B 🔽
@sentry/node	149.42 kB	-	-
@sentry/node - without tracing	98.09 kB	-	-
@sentry/aws-serverless	123.43 kB	-	-

View base workflow run

Thanks a lot for making this change! Agree that it's better to have instrumentation setup in setup.

[Lms24]

ah nice, I think this is good behaviour and probably better than taking first one. Just in case users have some kind of dynamic behaviour that builds the integrations array.

[mydea]

jup, totally, that was what we had already anyhow 👍 the test just shows that!