fix(tracing): add new transaction source

[ys-zhifu]

In my opinion, the source value of customer should not be used directly, which will result in the user being unable to customize the value, so a new initialization value is required to distinguish whether it is modified or not.

Finally, the user can use the source of customer when he wants to modify context.name.

new Integrations.BrowserTracing({
        beforeNavigate: context => {
          context.name = 'test-transaction-name'
          context.metadata = {
            source: 'custom'
          }
          return context
        },
        routingInstrumentation: Sentry.vueRouterInstrumentation(router)
}),

[ys-zhifu]

This may be a good result, of course, if the changes are not significant.

[Lms24]

Hi @ys-zhifu and thanks for opening this PR!

I am sorry but I don't think we can merge this in because our transaction source specification (and here) is very strict and we cannot just add another source type (initialize).

Let me explain what source is to us and why we use it:

We use the transaction source to internally differentiate and describe how the name of the transaction was set. For instance, transaction source url means that the name of the transaction is a raw URL (e.g. /users/123/details, /users/456/details). If we manage to parameterize a URL, we set the source to route, meaning that we now have a proper, parameterized route as transaction name (e.g. /users/:userId/details). This is what happens in our Vue routing instrumentation without user intervention.

In case users give their transaction a custom name by using beforeNavigate or transaction.setName, we'll set the source to custom, meaning that the transaction name was changed by the user. In that case, we will no longer update it.

The reason why we introduced transaction source was because we needed a way to distinguish between these name types for trace propagation and dynamic sampling. We never intended to let users change the transaction source themselves.

I'm seeing that this is your second PR for the Vue router instrumentation. Would you mind telling me if the problem we fixed in #6060 still persists for you after our update? Our latest release (7.17.0) unfortunately is broken but we'll have a fix out soon. Then you can give it a try.

[AbhiPrasad]

We should have released the fix with 7.17.1. As such, closing this PR.