go/types, types2: better error for generic type decl. with missing constraint
If a generic type declaration is missing a constraint, syntactically
it is an array type declaration with an undefined array length.
Mention the possibility of a missing constraint in the error message
for the undefined array length.
For #56064.
For #55961.
For #51145.
Change-Id: Ic161aeda9ea44faa8aa3bf3e9d62b3b13a95d4c5
Reviewed-on: https://go-review.googlesource.com/c/go/+/439559
Run-TryBot: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Robert Griesemer <gri@google.com> Reviewed-by: Robert Findley <rfindley@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>