cmd/go: make Tidy an option in PackageOpts rather than a separate call
This eliminates some awkwardly-stateful outside calls to
modload.{Disallow,Allow,}WriteGoMod.
Perhaps more importantly, it gives the loader the opportunity to
reload packages and revise dependencies after the tidied requirements
are computed. With lazy loading, dropping an irrelevant requirement
from the main module's go.mod file may (rarely) cause other test
dependencies for packages outside the main module to become
unresolved, which may require the loader to re-resolve those
dependencies, which may in turn add new roots and increase the
selected versions of modules providing other packages.
This refactoring allows the loader to iterate between tidying the
build list and reloading packages as needed, making the exact
sequencing of loading and tidying an implementation detail of the
modload package.
For #36460
For #40775
Change-Id: Ib6da3672f32153d5bd7d653d85e3672ab96cbe36
Reviewed-on: https://go-review.googlesource.com/c/go/+/310181
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> Reviewed-by: Jay Conrod <jayconrod@google.com>