Docs around exit error behavior, + handling MultiError in HandleExitCoder

errors.go

@@ -23,15 +23,19 @@ func (m MultiError) Error() string {
 	return strings.Join(errs, "\n")
 }
 
+// ExitCoder is the interface checked by `App` and `Command` for a custom exit
+// code
 type ExitCoder interface {
 	ExitCode() int
 }
 
+// ExitError fulfills both the builtin `error` interface and `ExitCoder`
 type ExitError struct {
 	exitCode int
 	message  string
 }
 
+// NewExitError makes a new *ExitError
 func NewExitError(message string, exitCode int) *ExitError {
 	return &ExitError{
 		exitCode: exitCode,
@@ -39,22 +43,33 @@ func NewExitError(message string, exitCode int) *ExitError {
 	}
 }
 
+// Error returns the string message, fulfilling the interface required by
+// `error`
 func (ee *ExitError) Error() string {
 	return ee.message
 }
 
-func (ee *ExitError) String() string {
-	return fmt.Sprintf("%s exitcode=%v", ee.message, ee.exitCode)
-}
-
+// ExitCode returns the exit code, fulfilling the interface required by
+// `ExitCoder`
 func (ee *ExitError) ExitCode() int {
 	return ee.exitCode
 }
 
 // HandleExitCoder checks if the error fulfills the ExitCoder interface, and if
-// so calls os.Exit with the given exit code.
+// so prints the error to stderr (if it is non-empty) and calls os.Exit with the
+// given exit code.  If the given error is a MultiError, then this func is
+// called on all members of the Errors slice.
 func HandleExitCoder(err error) {
 	if exitErr, ok := err.(ExitCoder); ok {
+		if err.Error() != "" {
+			fmt.Fprintln(os.Stderr, err)
+		}
 		os.Exit(exitErr.ExitCode())
 	}
+
+	if multiErr, ok := err.(MultiError); ok {
+		for _, merr := range multiErr.Errors {
+			HandleExitCoder(merr)
+		}
+	}
 }