go/types, types2: replace setDefType with pending type check
Given a type definition of the form:
type T RHS
The setDefType function would set T.fromRHS as soon as we knew its
top-level type. For instance, in:
type S struct { ... }
S.fromRHS is set to a struct type before type-checking anything inside
the struct.
This permit access to the (incomplete) RHS type in a cyclic type
declaration. Accessing this information is fraught (as it's incomplete),
but was used for reporting certain types of cycles.
This CL replaces setDefType with a check that ensures no value of type
T is used before its RHS is set up.
This CL is strictly more complete than what setDefType achieved. For
instance, it enables correct reporting for the below cycles:
type A [unsafe.Sizeof(A{})]int
var v any = 42
type B [v.(B)]int
func f() C {
return C{}
}
type C [unsafe.Sizeof(f())]int
Fixes #76383
Fixes #76384
Change-Id: I9dfab5b708013b418fa66e43362bb4d8483fedec
Reviewed-on: https://go-review.googlesource.com/c/go/+/724140
Auto-Submit: Mark Freeman <markfreeman@google.com> Reviewed-by: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>