Merge pull request #1091 from rliebz/document-exit-errors

Update docs and tests around cli.Exit

app.go

@@ -76,8 +76,9 @@ type App struct {
 	Writer io.Writer
 	// ErrWriter writes error output
 	ErrWriter io.Writer
-	// Execute this function to handle ExitErrors. If not provided, HandleExitCoder is provided to
-	// function as a default, so this is optional.
+	// ExitErrHandler processes any error encountered while running an App before
+	// it is returned to the caller. If no function is provided, HandleExitCoder
+	// is used as the default behavior.
 	ExitErrHandler ExitErrHandlerFunc
 	// Other custom info
 	Metadata map[string]interface{}

errors.go

@@ -17,11 +17,10 @@ var ErrWriter io.Writer = os.Stderr
 // MultiError is an error that wraps multiple errors.
 type MultiError interface {
 	error
-	// Errors returns a copy of the errors slice
 	Errors() []error
 }
 
-// NewMultiError creates a new MultiError. Pass in one or more errors.
+// newMultiError creates a new MultiError. Pass in one or more errors.
 func newMultiError(err ...error) MultiError {
 	ret := multiError(err)
 	return &ret
@@ -65,13 +64,20 @@ type exitError struct {
 	message  interface{}
 }
 
-// NewExitError makes a new *exitError
+// NewExitError calls Exit to create a new ExitCoder.
+//
+// Deprecated: This function is a duplicate of Exit and will eventually be removed.
 func NewExitError(message interface{}, exitCode int) ExitCoder {
 	return Exit(message, exitCode)
 }
 
-// Exit wraps a message and exit code into an ExitCoder suitable for handling by
-// HandleExitCoder
+// Exit wraps a message and exit code into an error, which by default is
+// handled with a call to os.Exit during default error handling.
+//
+// This is the simplest way to trigger a non-zero exit code for an App without
+// having to call os.Exit manually. During testing, this behavior can be avoided
+// by overiding the ExitErrHandler function on an App or the package-global
+// OsExiter function.
 func Exit(message interface{}, exitCode int) ExitCoder {
 	return &exitError{
 		message:  message,
@@ -87,10 +93,14 @@ func (ee *exitError) ExitCode() int {
 	return ee.exitCode
 }
 
-// HandleExitCoder checks if the error fulfills the ExitCoder interface, and if
-// 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 and calls OsExiter with the last exit code.
+// HandleExitCoder handles errors implementing ExitCoder by printing their
+// message and calling OsExiter with the given exit code.
+//
+// If the given error instead implements MultiError, each error will be checked
+// for the ExitCoder interface, and OsExiter will be called with the last exit
+// code found, or exit code 1 if no ExitCoder is found.
+//
+// This function is the default error-handling behavior for an App.
 func HandleExitCoder(err error) {
 	if err == nil {
 		return

errors_test.go

@@ -67,6 +67,26 @@ func TestHandleExitCoder_MultiErrorWithExitCoder(t *testing.T) {
 	expect(t, called, true)
 }
 
+func TestHandleExitCoder_MultiErrorWithoutExitCoder(t *testing.T) {
+	exitCode := 0
+	called := false
+
+	OsExiter = func(rc int) {
+		if !called {
+			exitCode = rc
+			called = true
+		}
+	}
+
+	defer func() { OsExiter = fakeOsExiter }()
+
+	err := newMultiError(errors.New("wowsa"), errors.New("egad"))
+	HandleExitCoder(err)
+
+	expect(t, exitCode, 1)
+	expect(t, called, true)
+}
+
 // make a stub to not import pkg/errors
 type ErrorWithFormat struct {
 	error