Ensure HandleAction/HandleExitCoder work correctly with *ExitError

Closes #376

app.go

@@ -168,9 +168,7 @@ func (a *App) Run(arguments []string) (err error) {
 	if err != nil {
 		if a.OnUsageError != nil {
 			err := a.OnUsageError(context, err, false)
-			if err != nil {
+			HandleExitCoder(err)
-				HandleExitCoder(err)
-			}
 			return err
 		} else {
 			fmt.Fprintf(a.Writer, "%s\n\n", "Incorrect Usage.")
@@ -224,9 +222,7 @@ func (a *App) Run(arguments []string) (err error) {
 	// Run default Action
 	err = HandleAction(a.Action, context)
 
-	if err != nil {
+	HandleExitCoder(err)
-		HandleExitCoder(err)
-	}
 	return err
 }
 
@@ -237,7 +233,7 @@ func (a *App) RunAndExitOnError() {
 		contactSysadmin, runAndExitOnErrorDeprecationURL)
 	if err := a.Run(os.Args); err != nil {
 		fmt.Fprintln(os.Stderr, err)
-		os.Exit(1)
+		OsExiter(1)
 	}
 }
 
@@ -346,9 +342,7 @@ func (a *App) RunAsSubcommand(ctx *Context) (err error) {
 	// Run default Action
 	err = HandleAction(a.Action, context)
 
-	if err != nil {
+	HandleExitCoder(err)
-		HandleExitCoder(err)
-	}
 	return err
 }
 
@@ -438,7 +432,7 @@ func HandleAction(action interface{}, context *Context) (err error) {
 		return errInvalidActionSignature
 	}
 
-	if retErr, ok := reflect.ValueOf(vals[0].Interface()).Interface().(error); ok {
+	if retErr, ok := vals[0].Interface().(error); vals[0].IsValid() && ok {
 		return retErr
 	}
 

errors.go

@@ -6,6 +6,8 @@ import (
 	"strings"
 )
 
+var OsExiter = os.Exit
+
 type MultiError struct {
 	Errors []error
 }
@@ -26,6 +28,7 @@ func (m MultiError) Error() string {
 // ExitCoder is the interface checked by `App` and `Command` for a custom exit
 // code
 type ExitCoder interface {
+	error
 	ExitCode() int
 }
 
@@ -56,15 +59,20 @@ func (ee *ExitError) ExitCode() int {
 }
 
 // HandleExitCoder checks if the error fulfills the ExitCoder interface, and if
-// so prints the error to stderr (if it is non-empty) and calls os.Exit with the
+// so prints the error to stderr (if it is non-empty) and calls OsExiter 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 err == nil {
+		return
+	}
+
 	if exitErr, ok := err.(ExitCoder); ok {
 		if err.Error() != "" {
 			fmt.Fprintln(os.Stderr, err)
 		}
-		os.Exit(exitErr.ExitCode())
+		OsExiter(exitErr.ExitCode())
+		return
 	}
 
 	if multiErr, ok := err.(MultiError); ok {

errors_test.go

@@ -0,0 +1,60 @@
+package cli
+
+import (
+	"errors"
+	"os"
+	"testing"
+)
+
+func TestHandleExitCoder_nil(t *testing.T) {
+	exitCode := 0
+	called := false
+
+	OsExiter = func(rc int) {
+		exitCode = rc
+		called = true
+	}
+
+	defer func() { OsExiter = os.Exit }()
+
+	HandleExitCoder(nil)
+
+	expect(t, exitCode, 0)
+	expect(t, called, false)
+}
+
+func TestHandleExitCoder_ExitCoder(t *testing.T) {
+	exitCode := 0
+	called := false
+
+	OsExiter = func(rc int) {
+		exitCode = rc
+		called = true
+	}
+
+	defer func() { OsExiter = os.Exit }()
+
+	HandleExitCoder(NewExitError("galactic perimiter breach", 9))
+
+	expect(t, exitCode, 9)
+	expect(t, called, true)
+}
+
+func TestHandleExitCoder_MultiErrorWithExitCoder(t *testing.T) {
+	exitCode := 0
+	called := false
+
+	OsExiter = func(rc int) {
+		exitCode = rc
+		called = true
+	}
+
+	defer func() { OsExiter = os.Exit }()
+
+	exitErr := NewExitError("galactic perimiter breach", 9)
+	err := NewMultiError(errors.New("wowsa"), errors.New("egad"), exitErr)
+	HandleExitCoder(err)
+
+	expect(t, exitCode, 9)
+	expect(t, called, true)
+}