[MM-18121] Fix config set panic (#12083)

* Fix config set panic

* Change error message

* Add a test case

* Update error string

cmd/mattermost/commands/config.go

@@ -21,6 +21,8 @@ import (
 	"github.com/mattermost/viper"
 )
 
+const noSettingsNamed = "unable to find a setting named: %s"
+
 var ConfigCmd = &cobra.Command{
 	Use:   "config",
 	Short: "Configuration",
@@ -296,7 +298,7 @@ func updateConfigValue(configSetting string, newVal []string, oldConfig, newConf
 func UpdateMap(configMap map[string]interface{}, configSettings []string, newVal []string) error {
 	res, ok := configMap[configSettings[0]]
 	if !ok {
-		return fmt.Errorf("unable to find a setting with that name %s", configSettings[0])
+		return fmt.Errorf(noSettingsNamed, configSettings[0])
 	}
 
 	value := reflect.ValueOf(res)
@@ -308,6 +310,9 @@ func UpdateMap(configMap map[string]interface{}, configSettings []string, newVal
 		if len(configSettings) == 1 {
 			return errors.New("unable to set multiple settings at once")
 		}
+		if value.Len() == 0 {
+			return fmt.Errorf(noSettingsNamed, configSettings[1])
+		}
 		return UpdateMap(res.(map[string]interface{}), configSettings[1:], newVal)
 
 	case reflect.Int:
@@ -319,7 +324,7 @@ func UpdateMap(configMap map[string]interface{}, configSettings []string, newVal
 			configMap[configSettings[0]] = val
 			return nil
 		}
-		return fmt.Errorf("unable to find a setting with that name %s", configSettings[0])
+		return fmt.Errorf(noSettingsNamed, configSettings[0])
 
 	case reflect.Int64:
 		if len(configSettings) == 1 {
@@ -330,7 +335,7 @@ func UpdateMap(configMap map[string]interface{}, configSettings []string, newVal
 			configMap[configSettings[0]] = int64(val)
 			return nil
 		}
-		return fmt.Errorf("unable to find a setting with that name %s", configSettings[0])
+		return fmt.Errorf(noSettingsNamed, configSettings[0])
 
 	case reflect.Bool:
 		if len(configSettings) == 1 {
@@ -341,21 +346,21 @@ func UpdateMap(configMap map[string]interface{}, configSettings []string, newVal
 			configMap[configSettings[0]] = val
 			return nil
 		}
-		return fmt.Errorf("unable to find a setting with that name %s", configSettings[0])
+		return fmt.Errorf(noSettingsNamed, configSettings[0])
 
 	case reflect.String:
 		if len(configSettings) == 1 {
 			configMap[configSettings[0]] = newVal[0]
 			return nil
 		}
-		return fmt.Errorf("unable to find a setting with that name %s", configSettings[0])
+		return fmt.Errorf(noSettingsNamed, configSettings[0])
 
 	case reflect.Slice:
 		if len(configSettings) == 1 {
 			configMap[configSettings[0]] = newVal
 			return nil
 		}
-		return fmt.Errorf("unable to find a setting with that name %s", configSettings[0])
+		return fmt.Errorf(noSettingsNamed, configSettings[0])
 
 	default:
 		return errors.New("type not supported yet")

cmd/mattermost/commands/config_test.go

@@ -141,6 +141,12 @@ func TestConfigSet(t *testing.T) {
 		assert.NotContains(t, string(output), "invalid-key")
 	})
 
+	t.Run("Error when the parameter of an unknown plugin is set", func(t *testing.T) {
+		output, err := th.RunCommandWithOutput(t, "config", "set", "PluginSettings.Plugins.someplugin", "true")
+		assert.Error(t, err)
+		assert.NotContains(t, string(output), "panic")
+	})
+
 	t.Run("Error when the wrong locale is set", func(t *testing.T) {
 		th.CheckCommand(t, "config", "set", "LocalizationSettings.DefaultServerLocale", "es")
 		assert.Error(t, th.RunCommand(t, "config", "set", "LocalizationSettings.DefaultServerLocale", "invalid-key"))