go/types, types2: better error message when missing method is unexported
Change lookupMethod such that "foldCase" means "ignore case
and package" and analyze a lookup result further to determine
if a method name was not exported, and report a better error
message in that case.
Fixes #59831.
Change-Id: Ice6222e1fc00dba13caeda6c48971e8473d12da5
Reviewed-on: https://go-review.googlesource.com/c/go/+/549298
Run-TryBot: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com> Reviewed-by: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Robert Griesemer <gri@google.com>