Ban importing aliased domains. (#696)

* Ban importing aliased domains,

* move import test.

test/imports/banned_deps_test.go

@@ -0,0 +1,76 @@
+/*
+Copyright 2019 The Knative Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package imports
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+)
+
+type vbTuple struct {
+	banned string
+	vanity string
+}
+
+var bannedImports = []vbTuple{
+	{
+		banned: "github.com/knative",
+		vanity: "knative.dev",
+	}, {
+		banned: "github.com/kubernetes",
+		vanity: "k8s.io",
+	}, {
+		banned: "github.com/istio",
+		vanity: "istio.io",
+	},
+}
+
+// TestBannedImports run with:
+//   go test ./vendor/knative.dev/pkg/test/imports/ -run TestBannedImports
+// Or with test-infra:
+//   report_go_test ${REPO_ROOT_DIR}/vendor/knative.dev/pkg/test/imports/...
+func TestBannedImports(t *testing.T) {
+	_, filename, _, _ := runtime.Caller(0)
+	dir := filepath.Dir(filename)
+
+	if !strings.Contains(dir, "vendor") {
+		t.Skipf("knative.dev/pkg not vendored, skipping...")
+	}
+
+	parts := strings.Split(dir, "vendor")
+
+	dir = fmt.Sprintf("%s%s%s", parts[0], string(filepath.Separator), "vendor")
+
+	err := filepath.Walk(dir, func(path string, info os.FileInfo, err error) error {
+		if !info.IsDir() {
+			return nil
+		}
+		for _, vb := range bannedImports {
+			if strings.HasSuffix(path, vb.banned) {
+				return fmt.Errorf("%q is a banned import prefix, use vanity import prefix %q instead", vb.banned, vb.vanity)
+			}
+		}
+		return nil
+	})
+	if err != nil {
+		t.Errorf(err.Error())
+	}
+}