Update CONTRIBUTING.md

[merenbach]

Summary

Fix a tiny typo and ensure that errgroup is installed.

Problem

When trying to run make for the first time, the following error appears on my machine:

CGO_ENABLED=0 go run vendor/github.com/gobuffalo/packr/packr/main.go build -v -i -ldflags '-X github.com/argoproj/argo-cd.version=0.1.0 -X github.com/argoproj/argo-cd.buildDate=2018-03-12T22:29:44Z -X github.com/argoproj/argo-cd.gitCommit=1247c2264dace02a81bf474a2a7a5eea3be9962a -X github.com/argoproj/argo-cd.gitTreeState=clean -X github.com/argoproj/argo-cd/install.imageTag=latest -extldflags "-static"' -o /Users/amerenbach/go/src/github.com/argoproj/argo-cd/dist/argocd ./cmd/argocd
vendor/github.com/gobuffalo/packr/builder/builder.go:12:2: cannot find package "golang.org/x/sync/errgroup" in any of:
	/Users/amerenbach/go/src/github.com/argoproj/argo-cd/vendor/golang.org/x/sync/errgroup (vendor tree)
	/usr/local/Cellar/go/1.10/libexec/src/golang.org/x/sync/errgroup (from $GOROOT)
	/Users/amerenbach/go/src/golang.org/x/sync/errgroup (from $GOPATH)
make: *** [cli] Error 1

Solution

errgroup is required by https://github.com/gobuffalo/packr, which is installed with install/install.go. For some reason this is not recursively installed with dep ensure. Adding it to install/install.go had the effect of ensuring it would be installed with dep ensure, but then make errors out with an imported-but-not-used error since this then constitutes a direct import.

This looks like a simple missing library, so I've added errgroup to the list of prerequisites in the README. @alexmt Please let me know if I may refactor this.

[alexmt]

Nice catch @merenbach ! Looks like we forgot to add 'errgroup' dependency. Can you please add errgroup package into Gopkg.toml and Gopkg.lock instead of documenting it?

Following command should regenerate both Gopkg.toml and Gopkg.lock :

add dep ensure -add golang.org/x/sync/errgroup

[merenbach]

@alexmt Thank you for the update! When I run that command, Gopkg.lock and Gokpkg.toml update as expected. I receive the following output:

$ dep ensure -add golang.org/x/sync/errgroup
Fetching sources...

"golang.org/x/sync/errgroup" is not imported by your project, and has been temporarily added to Gopkg.lock and vendor/.
If you run "dep ensure" again before actually importing it, it will disappear from Gopkg.lock and vendor/.

I tried running dep ensure again afterward and while my changes were not reverted, I received the following output that says the import may be ignored:

Warning: the following project(s) have [[constraint]] stanzas in Gopkg.toml:

  ✗  golang.org/x/sync

However, these projects are not direct dependencies of the current project:
they are not imported in any .go files, nor are they in the 'required' list in
Gopkg.toml. Dep only applies [[constraint]] rules to direct dependencies, so
these rules will have no effect.

Either import/require packages from these projects so that they become direct
dependencies, or convert each [[constraint]] to an [[override]] to enforce rules
on these projects, if they happen to be transitive dependencies, [sic]

(The message ends with a comma, oddly.)

This comment on a tangentially related dep issue suggests adding to the required list instead might be a good way to go, so I've updated my code with that. Please let me know if I may explore any further avenues of consideration.

[alexmt]

LGTM