[release-branch.go1.23] cmd/compile: more informative panic when importing generic type alias
When GOEXPERIMENT=aliastypeparams is set, type aliases may have type
parameters. The compiler export data doesn't export that type parameter
information yet, which leads to an index-out-of-bounds panic when a
client package imports a package with a general type alias and then
refers to one of the missing type parameters.
This CL detects this specific case and panics with a more informative
panic message explaining the shortcoming. The change is only in effect
if the respective GOEXPERIMENT is enabled.
Manually tested. No test addded since this is just a temporary fix
(Go 1.24 will have a complete implementation), and because the existing
testing framework doesn't easily support testing that a compilation
panics.
Together with @taking and input from @rfindley.
For #68526.
Change-Id: I24737b153a7e2f9b705cd29a5b70b2b9e808dffc
Reviewed-on: https://go-review.googlesource.com/c/go/+/601035 Reviewed-by: Tim King <taking@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Robert Griesemer <gri@google.com>