Go (reflect): How to discover all package types at runtime?

As far as I'm aware (see here, and here) there is no type discovery mechanism in the reflect package, which expects that you already have an instance of the type or value you want to inspect.

Is there any other way to discover all exported types (especially the structs) in a running go package?

Here's what I wish I had (but it doesn't exist):

import "time"
import "fmt"

func main() {
    var types []reflect.Type
    types = reflect.DiscoverTypes(time)
    fmt.Println(types)
}

BTW, a registration function that identifies the types is not a valid approach for my use case.

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Whether you think it's a good idea or not, here's why I want this capability (because I know you're going to ask):

I've written a code generation utility that loads go source files and builds an AST to scan for types that embed a specified type. The output of the utility is a set of go test functions based on the discovered types. I invoke this utility using go generate to create the test functions then run go test to execute the generated test functions. Every time the tests change (or a new type is added) I must re-run go generate before re-running go test. This is why a registration function is not a valid option. I'd like to avoid the go generate step but that would require my utility to become a library that is imported by the running package. The library code would need to somehow scan the running namespace during init() for types that embed the expected library type.