*: use go mod to manage dependency

[disksing]

What problem does this PR solve?

Use go mod to manage dependency

What is changed and how it works?

Changes:

• update Makefile
• go mod init to generate go.mod file from dep configuration.
• remove vendor/ and recreate it with make vendor
• upgrade megacheck to new branch that supports go modules

Notes:

• All builds and tests commands use -mod=vendor flag to force use the vendored code. Thus we can make sure different go will build use the same code base.
• For now code still can't be placed out of GOPATH due to a gofail limitation: Failed to determine package path when source file is not inside GOPATH etcd-io/gofail#16
• To upgrade a dependency. Use GO111MODULE=on go get -u ... to update go.mod then make vendor to vendor source code.

Check List

Tests

• Integration test

[disksing]

/run-all-tests

[gregwebs]

Should be able to do build: export GO111MODULE=on

[gregwebs]

It could be useful to keep using a vendor/ directory with go modules, at least temporarily.
https://arslan.io/2018/08/26/using-go-modules-with-vendor-support-on-travis-ci/

[gregwebs]

How did these airbrakes end up getting added? They weren't there before and shouldn't be PD dependencies.

[disksing]

From go mod why gopkg.in/gemnasium/logrus-airbrake-hook.v2 we can see it is imported by github.com/sirupsen/logrus.test.

[gregwebs]

I did run that, but I didn't know what logrus.test is. It isn't listed in our dependencies.

It seems that go modules adds all transitive testing dependencies.

• https://www.reddit.com/r/golang/comments/98hbvk/go_modules_how_to_deal_with_test_dependencies/
• cmd/go: add 'require test' section to go.mod golang/go#26913
• cmd/go: 'go mod -sync' adds test dependencies of dependencies, while 'go build' does not golang/go#26626

This makes me prefer dep to go modules for now until they get more feedback on go modules.

[gregwebs]

I looked at the logrus repo and I don't see how it can reference airbrake (testing or not): https://github.com/sirupsen/logrus/search?q=airbrake&unscoped_q=airbrake

This actually seems like an issue with how they defined their go.mod. Perhaps you can ask them about it?

I still don't understand why go mod tidy doesn't remove this since it isn't needed.

GO111MODULE=on go mod why github.com/sirupsen/logrus.test
go: finding github.com/golang/protobuf/proto/testdata latest
go: finding github.com/golang/protobuf/proto latest
# github.com/sirupsen/logrus.test
(main module does not need package github.com/sirupsen/logrus.test)

[gregwebs]

It looks like there is actually an open issue about testing dependencies here: golang/go#26955. It is milestoned for 1.12 although not necessarily accepted.

[disksing]

It looks the best effort now is to keep the vendor/ directory, setup -mod=vendor in Makefile, and only use go mod when we need to update imports. The update procedure should include ./hack/clean-vendor to cleanup test files.
I'll take a try.

[gregwebs]

👍 but I don't think clean-vendor will end up removing exteraneous deps like airbrake. And now go mod is built-in automatically to go commands, so I don't know if it is possible to avoid it updating imports.

[disksing]

Hi @gregwebs Please take another look. I have reset the branch and go mod init && go mod vendor && ./hack/clean_test. Now everything seems just fine. No extra dependencies anymore. I must have done something wrong before.

[disksing]

/run-all-tests

[gregwebs]

Deps look good now! Looks like this is actually significantly decreasing the amount of code being dragged into vendor now.

I think keeping the vendor directory will help ease the transition go go modules now. In the long-term we may want to remove it, although I am not sure.

[disksing]

Yep, vendor/ should be removed in the long term. Go modules will definitely be better and better supported in the go ecosystem.

[disksing]

PTAL @rleungx @nolouch

[nolouch]

LGTM