Use gometalinter and enforcing go fmt/lint/vet (#1108)

* Use gometalinter and enforcing go fmt/lint/vet

Before this PR go fmt is enabled, go lint is suggest only.
From time to time we have to manually check for go lint and go vet
for any issues.

This fix uses gometalinter and enforcing go fmt/lint/vet.
Several reasons:
- gometalinter could handle multiple linters concurrently
- gometalinter supports suppression with `// nolint[: <linter>]`

Previously one reason we didn't enable go lint was due to the
```
warning: context.Context should be the first parameter of a function (golint)
```
this is now possible with gometalinter and `// nolint: golint` (See changes).

This fix also discovered several go vet issues and fixes it.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Fix several issues reported by gometalinter (go vet)

This commit fixes several issues reported by gometalinter (go vet).
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Increase deadline
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

Makefile

@@ -11,7 +11,7 @@ coredns: check godeps
 	CGO_ENABLED=0 $(SYSTEM) go build -v -ldflags="-s -w -X github.com/coredns/coredns/coremain.gitCommit=$(GITCOMMIT)" -o $(BINARY)
 
 .PHONY: check
-check: fmt core/zplugin.go core/dnsserver/zdirectives.go godeps
+check: linter core/zplugin.go core/dnsserver/zdirectives.go godeps
 
 .PHONY: test
 test: check
@@ -62,17 +62,11 @@ core/zplugin.go core/dnsserver/zdirectives.go: plugin.cfg
 gen:
 	go generate coredns.go
 
-.PHONY: fmt
-fmt:
-	## run go fmt
-	@test -z "$$(find . -type d | grep -vE '(/vendor|^\.$$|/.git|/.travis)' | xargs gofmt -s -l  | tee /dev/stderr)" || \
-		(echo "please format Go code with 'gofmt -s -w'" && false)
-
-.PHONY: lint
-lint:
-	go get -u github.com/golang/lint/golint
-	@test -z "$$(find . -type d | grep -vE '(/vendor|^\.$$|/.git|/.travis)' | grep -vE '(^\./pb)' | xargs golint \
-		| grep -vE "context\.Context should be the first parameter of a function" | tee /dev/stderr)"
+.PHONY: linter
+linter:
+	go get -u github.com/alecthomas/gometalinter
+	gometalinter --install golint
+	gometalinter --deadline=1m --disable-all --enable=gofmt --enable=golint --enable=vet --exclude=^vendor/ --exclude=^pb/ ./...
 
 .PHONY: clean
 clean:

plugin/plugin.go

@@ -69,7 +69,7 @@ func Error(name string, err error) error { return fmt.Errorf("%s/%s: %s", "plugi
 
 // NextOrFailure calls next.ServeDNS when next is not nill, otherwise it will return, a ServerFailure
 // and a nil error.
-func NextOrFailure(name string, next Handler, ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+func NextOrFailure(name string, next Handler, ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) { // nolint: golint
 	if next != nil {
 		if span := ot.SpanFromContext(ctx); span != nil {
 			child := span.Tracer().StartSpan(next.Name(), ot.ChildOf(span.Context()))

test/etcd_cache_test.go

@@ -68,7 +68,7 @@ func checkResponse(t *testing.T, resp *dns.Msg) {
 		t.Errorf("Expected RR to A, got: %d", resp.Answer[0].Header().Rrtype)
 	}
 	if resp.Answer[0].(*dns.A).A.String() != "127.0.0.1" {
-		t.Errorf("Expected 127.0.0.1, got: %d", resp.Answer[0].(*dns.A).A.String())
+		t.Errorf("Expected 127.0.0.1, got: %s", resp.Answer[0].(*dns.A).A.String())
 	}
 }
 

test/reload_test.go

@@ -49,6 +49,6 @@ func send(t *testing.T, server string) {
 		t.Fatalf("Expected successful reply, got %s", dns.RcodeToString[r.Rcode])
 	}
 	if len(r.Extra) != 2 {
-		t.Fatalf("Expected 2 RRs in additional, got %s", len(r.Extra))
+		t.Fatalf("Expected 2 RRs in additional, got %d", len(r.Extra))
 	}
 }