What version of Go are you using (go version)?

1.9

Does this issue reproduce with the latest release?

Yes.

Consider a chain of functions that call each other:

func f1(x X) { ... f2(y) ... }
func f2(y Y) { ... f3(z) ... }
and so on.

Assume also that their arguments and returns values are static Go types (no interfaces).

Generally, such a chain of statically-typed invocations will fall within the domain of the SSA optimizer and will be rewritten (theoretically) optimally.

The issue arises when the invocation chain is recursive, e.g.

func f1(x X) { ... f2(y) ... }
func f2(y Y) { ... f3(z) ... }
func f3(z Z) { ... f1(x) ... }

and the user desires to implement f1 and f3 in different packages.

This is not possible due to the design of the packaging system
(because the packages of f1 and f3 would have to import each other).

Consequently, large amounts of recursive code cannot be spread across packages.

This situation has arisen in practice, so I wonder what the language designers would advise.

Thank you.