cmd/go: fix listing of ambiguous paths
Passing ambiguous patterns, ending in `.go`, to `go list` results in them
being interpreted as Go files despite potentially being package references.
This can then result in errors on other package references.
The parsing logic is modified to check for a locally present file
corresponding to any pattern ending in `.go`. If no such file is present
the pattern is considered to be a package reference.
We're also adding a variety of non-regression tests that fail with the
original parsing code but passes after applying the fix.
Fixes #32483
Fixes #34653
Change-Id: I073871da0dfc5641a359643f95ac14608fdca09b
GitHub-Last-Rev:
5abc200103ffc122df05422d79cf30c3ba0ee646
GitHub-Pull-Request: golang/go#34663
Reviewed-on: https://go-review.googlesource.com/c/go/+/198459
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>