Add breaking change to Configurer, returns error

bonzai.go

@@ -35,13 +35,13 @@ package bonzai
 // ensure that the resulting values for edge matches can be used without
 // needing a trim.
 type Configurer interface {
-	Init() error              // must initialize a new configuration
-	Data() string             // must return full YAML
-	Print()                   // must print full YAML to os.Stdout
-	Edit() error              // must open full YAML in local editor
-	OverWrite(with any) error // safely replace all configuration
-	Query(q string) string    // yq compatible query string
-	QueryPrint(q string)      // prints result to os.Stdout
+	Init() error                    // must initialize a new configuration
+	Data() (string, error)          // must return full YAML
+	Print() error                   // must print full YAML to os.Stdout
+	Edit() error                    // must open full YAML in local editor
+	OverWrite(with any) error       // safely replace all configuration
+	Query(q string) (string, error) // yq compatible query string
+	QueryPrint(q string) error      // prints result to os.Stdout
 }
 
 // Vars specifies the package persistent variables driver interface. All

z/cmd.go

@@ -522,12 +522,11 @@ func (x *Cmd) Log(format string, a ...any) {
 }
 
 // C is a shorter version of Z.Conf.Query(x.Path()+"."+q) for
-// convenience. Logs the error and returns a blank string if Z.Conf is
-// not defined (see UseConf).
-func (x *Cmd) C(q string) string {
+// convenience. See UseConf.
+func (x *Cmd) C(q string) (string, error) {
 	if Conf == nil {
 		log.Printf("cmd %q requires a configurer (Z.Conf must be assigned)", x.Name)
-		return ""
+		return "", UsesConf{x}
 	}
 	path := x.Path()
 	if path != "." {