Add NamedFileContentFlag.

mapper.go

@@ -721,6 +721,33 @@ func JoinEscaped(s []string, sep rune) string {
 	return strings.Join(escaped, string(sep))
 }
 
+// NamedFileContentFlag is a flag value that loads a file's contents and filename into its value.
+type NamedFileContentFlag struct {
+	Filename string
+	Contents []byte
+}
+
+func (f *NamedFileContentFlag) Decode(ctx *DecodeContext) error { // nolint: golint
+	var filename string
+	err := ctx.Scan.PopValueInto("filename", &filename)
+	if err != nil {
+		return err
+	}
+	// This allows unsetting of file content flags.
+	if filename == "" {
+		*f = NamedFileContentFlag{}
+		return nil
+	}
+	filename = ExpandPath(filename)
+	data, err := ioutil.ReadFile(filename) // nolint: gosec
+	if err != nil {
+		return errors.Errorf("failed to open %q: %s", filename, err)
+	}
+	f.Contents = data
+	f.Filename = filename
+	return nil
+}
+
 // FileContentFlag is a flag value that loads a file's contents into its value.
 type FileContentFlag []byte
 

mapper_test.go

@@ -240,6 +240,20 @@ func TestFileContentFlag(t *testing.T) {
 	require.Equal(t, []byte("hello world"), []byte(cli.File))
 }
 
+func TestNamedFileContentFlag(t *testing.T) {
+	var cli struct {
+		File kong.NamedFileContentFlag
+	}
+	f, err := ioutil.TempFile("", "")
+	require.NoError(t, err)
+	defer os.Remove(f.Name())
+	fmt.Fprint(f, "hello world")
+	f.Close()
+	_, err = mustNew(t, &cli).Parse([]string{"--file", f.Name()})
+	require.NoError(t, err)
+	require.Equal(t, []byte("hello world"), cli.File.Contents)
+}
+
 func TestNamedSliceTypesDontHaveEllipsis(t *testing.T) {
 	var cli struct {
 		File kong.FileContentFlag