go/types, types2: better errors for non-existing fields or methods
This CL improves the error messages reported when a field or method
name is used that doesn't exist. It brings the error messges on par
(or better) with the respective errors reported before Go 1.18 (i.e.
before switching to the new type checker):
Make case distinctions based on whether a field/method is exported
and how it is spelled. Factor out that logic into a new function
(lookupError) in a new file (errsupport.go), which is generated for
go/types. Use lookupError when reporting selector lookup errors
and missing struct field keys.
Add a comprehensive set of tests (lookup2.go) and spot tests for
the two cases brought up by the issue at hand.
Adjusted existing tests as needed.
Fixes #49736.
Change-Id: I2f439948dcd12f9bd1a258367862d8ff96e32305
Reviewed-on: https://go-review.googlesource.com/c/go/+/560055
Run-TryBot: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Robert Findley <rfindley@google.com> Reviewed-by: Robert Griesemer <gri@google.com>