hugolib: Add String() to fileInfo

See #5784

hugolib/fileInfo.go

@@ -60,6 +60,13 @@ func (fi *fileInfo) Filename() string {
 	return fi.basePather.Filename()
 }
 
+func (fi *fileInfo) String() string {
+	if fi == nil || fi.ReadableFile == nil {
+		return ""
+	}
+	return fi.Path()
+}
+
 func (fi *fileInfo) isOwner() bool {
 	return fi.bundleTp > bundleNot
 }

hugolib/fileInfo_test.go

@@ -0,0 +1,30 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package hugolib
+
+import (
+	"testing"
+
+	"github.com/spf13/cast"
+	"github.com/stretchr/testify/require"
+)
+
+func TestFileInfo(t *testing.T) {
+	t.Run("String", func(t *testing.T) {
+		assert := require.New(t)
+		fi := &fileInfo{}
+		_, err := cast.ToStringE(fi)
+		assert.NoError(err)
+	})
+}