go/types, types2: use existing case-insensitive lookup (remove TODO)

Rather than implementing a new, less complete mechanism to check
if a selector exists with different capitalization, use the
existing mechanism in lookupFieldOrMethodImpl by making it
available for internal use.

Pass foldCase parameter all the way trough to Object.sameId and
thus make it consistently available where Object.sameId is used.

From sameId, factor out samePkg functionality into stand-alone
predicate.

Do better case distinction when reporting an error for an undefined
selector expression.

Cleanup.

Change-Id: I7be3cecb4976a4dce3264c7e0c49a320c87101e9
Reviewed-on: https://go-review.googlesource.com/c/go/+/558315
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/test/fixedbugs/issue22794.go b/test/fixedbugs/issue22794.go
index 636af26e84..933c83dc5b 100644
--- a/test/fixedbugs/issue22794.go
+++ b/test/fixedbugs/issue22794.go
@@ -13,9 +13,9 @@ type it struct {
 
 func main() {
 	i1 := it{Floats: true}
-	if i1.floats { // ERROR "(type it .* field or method floats, but does have Floats)|undefined field or method"
+	if i1.floats { // ERROR "(type it .* field or method floats, but does have field Floats)|undefined field or method"
 	}
-	i2 := &it{floats: false} // ERROR "(but does have Floats)|unknown field|declared and not used"
-	_ = &it{InneR: "foo"}    // ERROR "(but does have inner)|unknown field"
+	i2 := &it{floats: false} // ERROR "(but does have field Floats)|unknown field|declared and not used"
+	_ = &it{InneR: "foo"}    // ERROR "(but does have field inner)|unknown field"
 	_ = i2
 }