ipn: fix formatting of ExitNodeIP in MaskedPrefs

%#v on a netaddr.IP showed the netaddr.IP innards.

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
(cherry picked from commit 751c42c097)

ipn/prefs.go

@@ -234,6 +234,20 @@ func (m *MaskedPrefs) Pretty() string {
 	mt := mv.Type()
 	mpv := reflect.ValueOf(&m.Prefs).Elem()
 	first := true
+
+	format := func(v reflect.Value) string {
+		switch v.Type().Kind() {
+		case reflect.String:
+			return "%s=%q"
+		case reflect.Slice:
+			// []string
+			if v.Type().Elem().Kind() == reflect.String {
+				return "%s=%q"
+			}
+		}
+		return "%s=%v"
+	}
+
 	for i := 1; i < mt.NumField(); i++ {
 		name := mt.Field(i).Name
 		if mv.Field(i).Bool() {
@@ -241,9 +255,10 @@ func (m *MaskedPrefs) Pretty() string {
 				sb.WriteString(" ")
 			}
 			first = false
-			fmt.Fprintf(&sb, "%s=%#v",
+			f := mpv.Field(i - 1)
+			fmt.Fprintf(&sb, format(f),
 				strings.TrimSuffix(name, "Set"),
-				mpv.Field(i-1).Interface())
+				f.Interface())
 		}
 	}
 	sb.WriteString("}")

ipn/prefs_test.go

@@ -615,12 +615,27 @@ func TestMaskedPrefsPretty(t *testing.T) {
 					OperatorUser:     "galaxybrain",
 					AllowSingleHosts: true,
 					RouteAll:         false,
+					ExitNodeID:       "foo",
+					AdvertiseTags:    []string{"tag:foo", "tag:bar"},
+					NetfilterMode:    preftype.NetfilterNoDivert,
 				},
 				RouteAllSet:      true,
 				HostnameSet:      true,
 				OperatorUserSet:  true,
+				ExitNodeIDSet:    true,
+				AdvertiseTagsSet: true,
+				NetfilterModeSet: true,
 			},
-			want: `MaskedPrefs{RouteAll=false Hostname="bar" OperatorUser="galaxybrain"}`,
+			want: `MaskedPrefs{RouteAll=false ExitNodeID="foo" AdvertiseTags=["tag:foo" "tag:bar"] Hostname="bar" NetfilterMode=nodivert OperatorUser="galaxybrain"}`,
+		},
+		{
+			m: &MaskedPrefs{
+				Prefs: Prefs{
+					ExitNodeIP: netaddr.IPv4(100, 102, 104, 105),
+				},
+				ExitNodeIPSet: true,
+			},
+			want: `MaskedPrefs{ExitNodeIP=100.102.104.105}`,
 		},
 	}
 	for i, tt := range tests {