Plugins: Update renderer plugin source (#80643)

* rework renderer plugin source

* add tests

pkg/plugins/manager/sources/source_local_disk.go

@@ -2,6 +2,10 @@ package sources
 
 import (
 	"context"
+	"errors"
+	"os"
+	"path/filepath"
+	"slices"
 
 	"github.com/grafana/grafana/pkg/plugins"
 )
@@ -36,3 +40,31 @@ func (s *LocalSource) DefaultSignature(_ context.Context) (plugins.Signature, bo
 		return plugins.Signature{}, false
 	}
 }
+
+func DirAsLocalSources(pluginsPath string, class plugins.Class) ([]*LocalSource, error) {
+	if pluginsPath == "" {
+		return []*LocalSource{}, errors.New("plugins path not configured")
+	}
+
+	// It's safe to ignore gosec warning G304 since the variable part of the file path comes from a configuration
+	// variable.
+	// nolint:gosec
+	d, err := os.ReadDir(pluginsPath)
+	if err != nil {
+		return []*LocalSource{}, errors.New("failed to open plugins path")
+	}
+
+	var pluginDirs []string
+	for _, dir := range d {
+		if dir.IsDir() || dir.Type()&os.ModeSymlink == os.ModeSymlink {
+			pluginDirs = append(pluginDirs, filepath.Join(pluginsPath, dir.Name()))
+		}
+	}
+	slices.Sort(pluginDirs)
+
+	var sources []*LocalSource
+	for _, dir := range pluginDirs {
+		sources = append(sources, NewLocalSource(class, []string{dir}))
+	}
+	return sources, nil
+}