plugins: Don't exit on duplicate plugin (#28390) (#28430)

* plugins: Don't exit on duplicate plugin

Signed-off-by: Arve Knudsen <arve.knudsen@gmail.com>

* Add missing files

Signed-off-by: Arve Knudsen <arve.knudsen@gmail.com>

* Fix test

Signed-off-by: Arve Knudsen <arve.knudsen@gmail.com>
(cherry picked from commit 4084b53f91)

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

pkg/plugins/plugins_test.go

@@ -2,6 +2,7 @@ package plugins
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"path/filepath"
 	"testing"
@@ -163,6 +164,23 @@ func TestPluginManager_Init(t *testing.T) {
 		require.Empty(t, pm.scanningErrors)
 		assert.Equal(t, []string{"gel"}, fm.registeredPlugins)
 	})
+
+	t.Run("With nested plugin duplicating parent", func(t *testing.T) {
+		origPluginsPath := setting.PluginsPath
+		t.Cleanup(func() {
+			setting.PluginsPath = origPluginsPath
+		})
+		setting.PluginsPath = "testdata/duplicate-plugins"
+
+		pm := &PluginManager{
+			Cfg: &setting.Cfg{},
+		}
+		err := pm.Init()
+		require.NoError(t, err)
+
+		assert.Len(t, pm.scanningErrors, 1)
+		assert.True(t, errors.Is(pm.scanningErrors[0], duplicatePluginError{}))
+	})
 }
 
 func TestPluginManager_IsBackendOnlyPlugin(t *testing.T) {