make shell autocomplete more robust

app.go

@@ -145,10 +145,6 @@ func (a *App) Setup() {
 		}
 	}
 
-	if a.EnableBashCompletion {
-		a.appendFlag(BashCompletionFlag)
-	}
-
 	if !a.HideVersion {
 		a.appendFlag(VersionFlag)
 	}
@@ -173,6 +169,14 @@ func (a *App) Setup() {
 func (a *App) Run(arguments []string) (err error) {
 	a.Setup()
 
+	// handle the completion flag separately from the flagset since
+	// completion could be attempted after a flag, but before its value was put
+	// on the command line. this causes the flagset to interpret the completion
+	// flag name as the value of the flag before it which is undesirable
+	// note that we can only do this because the shell autocomplete function
+	// always appends the completion flag at the end of the command
+	complete, arguments := checkCompleteFlag(a, arguments)
+
 	// parse flags
 	set := flagSet(a.Name, a.Flags)
 	set.SetOutput(ioutil.Discard)
@@ -184,6 +188,7 @@ func (a *App) Run(arguments []string) (err error) {
 		ShowAppHelp(context)
 		return nerr
 	}
+	context.complete = complete
 
 	if checkCompletions(context) {
 		return nil
@@ -283,11 +288,6 @@ func (a *App) RunAsSubcommand(ctx *Context) (err error) {
 	}
 	a.Commands = newCmds
 
-	// append flags
-	if a.EnableBashCompletion {
-		a.appendFlag(BashCompletionFlag)
-	}
-
 	// parse flags
 	set := flagSet(a.Name, a.Flags)
 	set.SetOutput(ioutil.Discard)