Require goplugin build flag to enable go plugin support (#6393)

internal/goplugin/noplugin.go

@@ -0,0 +1,9 @@
+// +build !goplugin
+
+package goplugin
+
+import "errors"
+
+func LoadExternalPlugins(rootDir string) error {
+	return errors.New("go plugin support is not enabled")
+}

internal/goplugin/plugin.go

@@ -0,0 +1,42 @@
+// +build goplugin
+
+package goplugin
+
+import (
+	"fmt"
+	"os"
+	"path"
+	"path/filepath"
+	"plugin"
+	"strings"
+)
+
+// loadExternalPlugins loads external plugins from shared libraries (.so, .dll, etc.)
+// in the specified directory.
+func LoadExternalPlugins(rootDir string) error {
+	return filepath.Walk(rootDir, func(pth string, info os.FileInfo, err error) error {
+		// Stop if there was an error.
+		if err != nil {
+			return err
+		}
+
+		// Ignore directories.
+		if info.IsDir() {
+			return nil
+		}
+
+		// Ignore files that aren't shared libraries.
+		ext := strings.ToLower(path.Ext(pth))
+		if ext != ".so" && ext != ".dll" {
+			return nil
+		}
+
+		// Load plugin.
+		_, err = plugin.Open(pth)
+		if err != nil {
+			return fmt.Errorf("error loading %s: %s", pth, err)
+		}
+
+		return nil
+	})
+}