Implement a general purpose data flow analyser for Go (and Kotlin)

[alecthomas]

As we extend the system to support different kinds of resources, the need to be able to trace the usage of those values becomes increasingly necessary. Today we have config and secrets, whose usage we are able to detect only when the handle itself is used in a verb. eg.

var secret = ftl.Secret[string]("mySecret")

//ftl:export
func MyVerb(ctx context.Context, req Req) (Resp, error) {
  print(secret.Get()) // We can detect this usage.
  // ...
}

However if the secret value is retrieved at its global declaration point instead, we lose the ability to detect its usage:

var secret = ftl.Secret[string]("mySecret").Get()

//ftl:export
func MyVerb(ctx context.Context, req Req) (Resp, error) {
  print(secret) // We can't detect this usage currently.
  // ...
}

This will become more important when we add support for PII data, and database field tracing.