Feature:(issue_1090): Add unwrap for ExitCoder

errors.go

@@ -83,7 +83,7 @@ type ExitCoder interface {
 
 type exitError struct {
 	exitCode int
-	message  interface{}
+	err      error
 }
 
 // NewExitError calls Exit to create a new ExitCoder.
@@ -101,20 +101,35 @@ func NewExitError(message interface{}, exitCode int) ExitCoder {
 // by overiding the ExitErrHandler function on an App or the package-global
 // OsExiter function.
 func Exit(message interface{}, exitCode int) ExitCoder {
+	var err error
+
+	switch e := message.(type) {
+	case ErrorFormatter:
+		err = fmt.Errorf("%+v", message)
+	case error:
+		err = e
+	default:
+		err = fmt.Errorf("%+v", message)
+	}
+
 	return &exitError{
-		message:  message,
+		err:      err,
 		exitCode: exitCode,
 	}
 }
 
 func (ee *exitError) Error() string {
-	return fmt.Sprintf("%v", ee.message)
+	return ee.err.Error()
 }
 
 func (ee *exitError) ExitCode() int {
 	return ee.exitCode
 }
 
+func (ee *exitError) Unwrap() error {
+	return ee.err
+}
+
 // HandleExitCoder handles errors implementing ExitCoder by printing their
 // message and calling OsExiter with the given exit code.
 //

errors_test.go

@@ -45,6 +45,25 @@ func TestHandleExitCoder_ExitCoder(t *testing.T) {
 	expect(t, called, true)
 }
 
+func TestHandleExitCoder_ErrorExitCoder(t *testing.T) {
+	exitCode := 0
+	called := false
+
+	OsExiter = func(rc int) {
+		if !called {
+			exitCode = rc
+			called = true
+		}
+	}
+
+	defer func() { OsExiter = fakeOsExiter }()
+
+	HandleExitCoder(Exit(errors.New("galactic perimeter breach"), 9))
+
+	expect(t, exitCode, 9)
+	expect(t, called, true)
+}
+
 func TestHandleExitCoder_MultiErrorWithExitCoder(t *testing.T) {
 	exitCode := 0
 	called := false