This change brings back handling for circular imports, which was removed
because I originally thought that go/packages would handle that.
However, since we are type-checking from source, we still end up having
to deal with that.
Additionally, we propagate the errors of type-checking to the
diagnostics so that the user can actually see some of the problems.
Change-Id: I0139bcaae461f1bcaf95706532bc5026f2430101
Reviewed-on: https://go-review.googlesource.com/c/tools/+/166882
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Cottrell <iancottrell@google.com>