Plugins: Update renderer plugin source (#80643)

* rework renderer plugin source

* add tests

pkg/plugins/manager/sources/source_local_disk_test.go

@@ -0,0 +1,71 @@
+package sources
+
+import (
+	"errors"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/grafana/grafana/pkg/plugins"
+)
+
+func TestDirAsLocalSources(t *testing.T) {
+	testdataDir := "../testdata"
+
+	tests := []struct {
+		name        string
+		pluginsPath string
+		expected    []*LocalSource
+		err         error
+	}{
+		{
+			name:        "Empty path returns an error",
+			pluginsPath: "",
+			expected:    []*LocalSource{},
+			err:         errors.New("plugins path not configured"),
+		},
+		{
+			name:        "Directory with subdirectories",
+			pluginsPath: filepath.Join(testdataDir, "pluginRootWithDist"),
+			expected: []*LocalSource{
+				{
+					paths: []string{filepath.Join(testdataDir, "pluginRootWithDist", "datasource")},
+					class: plugins.ClassExternal,
+				},
+				{
+					paths: []string{filepath.Join(testdataDir, "pluginRootWithDist", "dist")},
+					class: plugins.ClassExternal,
+				},
+				{
+					paths: []string{filepath.Join(testdataDir, "pluginRootWithDist", "panel")},
+					class: plugins.ClassExternal,
+				},
+			},
+		},
+		{
+			name:        "Directory with no subdirectories",
+			pluginsPath: filepath.Join(testdataDir, "pluginRootWithDist", "datasource"),
+			expected:    nil,
+		},
+		{
+			name:        "Directory with a symlink to a directory",
+			pluginsPath: filepath.Join(testdataDir, "symbolic-plugin-dirs"),
+			expected: []*LocalSource{
+				{
+					paths: []string{filepath.Join(testdataDir, "symbolic-plugin-dirs", "plugin")},
+					class: plugins.ClassExternal,
+				},
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := DirAsLocalSources(tt.pluginsPath, plugins.ClassExternal)
+			if tt.err != nil {
+				require.Errorf(t, err, tt.err.Error())
+			}
+			require.Equal(t, tt.expected, got)
+		})
+	}
+}