add support for exec plugins

pkg/plugins/compiler.go

@@ -17,7 +17,9 @@ import (
 	"fmt"
 	"os"
 	"os/exec"
+	"path"
 	"path/filepath"
+	"runtime"
 	"time"
 
 	"sigs.k8s.io/kustomize/k8sdeps/kv/plugin"
@@ -51,6 +53,15 @@ func DefaultSrcRoot() (string, error) {
 	}
 	nope = append(nope, root)
 
+	// get the root kustomize source directory when
+	// GOPATH is not set
+	_, filename, _, _ := runtime.Caller(1)
+	root = path.Join(path.Dir(filename), "../..", plugin.PluginRoot)
+	if FileExists(root) {
+		return root, nil
+	}
+	nope = append(nope, root)
+
 	root = filepath.Join(
 		pgmconfig.ConfigRoot(), plugin.PluginRoot)
 	if FileExists(root) {