Make ResultCode a TextMarshaler/TextUnmarshaler.

Author: bobg

result.go

@@ -45,6 +45,30 @@ func (r ResultCode) String() string {
 	}
 }
 
+func (r ResultCode) MarshalText() ([]byte, error) {
+	switch r {
+	case None, Patchlevel, Minor, Major:
+		return []byte(r.String()), nil
+	}
+	return nil, fmt.Errorf("unknown ResultCode value %d", r)
+}
+
+func (r *ResultCode) UnmarshalText(text []byte) error {
+	switch string(text) {
+	case "None":
+		*r = None
+	case "Patchlevel":
+		*r = Patchlevel
+	case "Minor":
+		*r = Minor
+	case "Major":
+		*r = Major
+	default:
+		return fmt.Errorf("unknown ResultCode value %q", text)
+	}
+	return nil
+}
+
 type wrapped struct {
 	r       Result
 	whyfmt  string

result_test.go

@@ -2,6 +2,8 @@ package modver
 
 import (
 	"bytes"
+	"encoding/json"
+	"fmt"
 	"testing"
 )
 
@@ -21,3 +23,52 @@ func TestPretty(t *testing.T) {
 		t.Errorf("got %s, want %s", buf, want)
 	}
 }
+
+func TestMarshalResultCode(t *testing.T) {
+	cases := []struct {
+		rc      ResultCode
+		want    string
+		wantErr bool
+	}{{
+		rc:   None,
+		want: `"None"`,
+	}, {
+		rc:   Patchlevel,
+		want: `"Patchlevel"`,
+	}, {
+		rc:   Minor,
+		want: `"Minor"`,
+	}, {
+		rc:   Major,
+		want: `"Major"`,
+	}, {
+		rc:      ResultCode(42),
+		wantErr: true,
+	}}
+
+	for i, tc := range cases {
+		t.Run(fmt.Sprintf("case_%02d", i+1), func(t *testing.T) {
+			got, err := json.Marshal(tc.rc)
+			if err != nil && tc.wantErr {
+				return
+			}
+			if err != nil {
+				t.Fatal(err)
+			}
+			if tc.wantErr {
+				t.Fatal("got no error but want one")
+			}
+			if string(got) != tc.want {
+				t.Errorf("marshaling: got %s, want %s", string(got), tc.want)
+			}
+
+			var rc ResultCode
+			if err := json.Unmarshal(got, &rc); err != nil {
+				t.Fatal(err)
+			}
+			if rc != tc.rc {
+				t.Errorf("unmarshaling: got %v, want %v", rc, tc.rc)
+			}
+		})
+	}
+}