cmd/go: `go mod download -json` is a lot slower with go1.13

[hyangah]

The feature requested in #32239 was added to go1.13 (per https://golang.org/cl/183841).
That makes the go mod download -json command populates the Latest boolean field of the json output by performing an extra query to check the latest version of the module.

It turned out the overhead of this extra query is significant in some cases,
especially when the module has many incompatible versions tags. E.g. 'k8s.io/kubernetes' or 'github.com/openshift/origin'.

$ GOPATH=`mktemp -d` GOPROXY=direct GONOSUM=* time  ~/go/bin/go1.13 mod download -json github.com/openshift/origin@v1.3.0-alpha.0
go: finding github.com/openshift/origin v1.3.0-alpha.0
go: finding github.com/openshift/origin v4.1.0+incompatible
...
154.54user 9.60system 1:42.54elapsed 160%CPU (0avgtext+0avgdata 482292maxresident)k
112inputs+2314104outputs (0major+229264minor)pagefaults 0swaps

$ GOPATH=`mktemp -d` GOPROXY=direct GONOSUM=* time  ~/go/bin/go1.13beta1 mod download -json github.com/openshift/origin@v1.3.0-alpha.0
go: finding github.com/openshift/origin v1.3.0-alpha.0
...
12.01user 1.62system 0:15.11elapsed 90%CPU (0avgtext+0avgdata 130020maxresident)k
360inputs+414112outputs (0major+18928minor)pagefaults 0swaps

This is a huge regression compared to the benefit from the new functionality.
Let's consider to provide an option to disable, or disable it by default if optimizing the 'latest' query is non trivial.

@bcmills @jayconrod @katiehockman @heschik

[gopherbot]

Change https://golang.org/cl/198699 mentions this issue: Revert "cmd/go: add a Latest field to the output of 'go mod download -json'"

[bcmills]

@gopherbot, please backport to Go 1.13.2: this feature caused a significant performance regression for large repositories, and was newly introduced and fairly obscure (so is unlikely to have broad usage at this point).

The only likely users are other module proxy implementations; we're asking them explicitly if they care about this field in a golang-module-proxies thread.

[gopherbot]

Backport issue(s) opened: #34679 (for 1.13).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://golang.org/wiki/MinorReleases.

[bcmills]

No objections here or on the email thread, so we're going to go ahead and revert.

[gopherbot]

Change https://golang.org/cl/199079 mentions this issue: [release-branch.go1.13] Revert "cmd/go: add a Latest field to the output of 'go mod download -json'"