cmd/go/internal/mvs: prune spurious dependencies in Downgrade
Previously, mvs.Downgrade could introduce spurious dependencies if the
downgrade computed for one module lands on a “hidden” version (such as
a pseudo-version) due to a requirement introduced by the downgrade for
another module.
To eliminate those spurious dependencies, we can add one more call to
BuildList to recompute the “actual” downgraded versions, and then
including only those actual versions in the final call to BuildList.
For #36460
Change-Id: Icc6b54aa004907221b2bcbbae74598b0e4100776
Reviewed-on: https://go-review.googlesource.com/c/go/+/294294
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Michael Matloob <matloob@golang.org>