Fix global flags processing on top level

This fixes a regression introduced by #227. When looking up global flags by walking up the parent context's we need to consider the special case when we are starting at the very top and there is no parent context to start the traversal.

Fixes #252

app_test.go

@@ -627,6 +627,23 @@ func TestAppCommandNotFound(t *testing.T) {
 	expect(t, subcommandRun, false)
 }
 
+func TestGlobalFlag(t *testing.T) {
+	var globalFlag string
+	var globalFlagSet bool
+	app := cli.NewApp()
+	app.Flags = []cli.Flag{
+		cli.StringFlag{Name: "global, g", Usage: "global"},
+	}
+	app.Action = func(c *cli.Context) {
+		globalFlag = c.GlobalString("global")
+		globalFlagSet = c.GlobalIsSet("global")
+	}
+	app.Run([]string{"command", "-g", "foo"})
+	expect(t, globalFlag, "foo")
+	expect(t, globalFlagSet, true)
+
+}
+
 func TestGlobalFlagsInSubcommands(t *testing.T) {
 	subcommandRun := false
 	parentFlag := false

context.go

@@ -73,7 +73,7 @@ func (c *Context) Generic(name string) interface{} {
 
 // Looks up the value of a global int flag, returns 0 if no int flag exists
 func (c *Context) GlobalInt(name string) int {
-	if fs := lookupParentFlagSet(name, c); fs != nil {
+	if fs := lookupGlobalFlagSet(name, c); fs != nil {
 		return lookupInt(name, fs)
 	}
 	return 0
@@ -81,7 +81,7 @@ func (c *Context) GlobalInt(name string) int {
 
 // Looks up the value of a global time.Duration flag, returns 0 if no time.Duration flag exists
 func (c *Context) GlobalDuration(name string) time.Duration {
-	if fs := lookupParentFlagSet(name, c); fs != nil {
+	if fs := lookupGlobalFlagSet(name, c); fs != nil {
 		return lookupDuration(name, fs)
 	}
 	return 0
@@ -89,7 +89,7 @@ func (c *Context) GlobalDuration(name string) time.Duration {
 
 // Looks up the value of a global bool flag, returns false if no bool flag exists
 func (c *Context) GlobalBool(name string) bool {
-	if fs := lookupParentFlagSet(name, c); fs != nil {
+	if fs := lookupGlobalFlagSet(name, c); fs != nil {
 		return lookupBool(name, fs)
 	}
 	return false
@@ -97,7 +97,7 @@ func (c *Context) GlobalBool(name string) bool {
 
 // Looks up the value of a global string flag, returns "" if no string flag exists
 func (c *Context) GlobalString(name string) string {
-	if fs := lookupParentFlagSet(name, c); fs != nil {
+	if fs := lookupGlobalFlagSet(name, c); fs != nil {
 		return lookupString(name, fs)
 	}
 	return ""
@@ -105,7 +105,7 @@ func (c *Context) GlobalString(name string) string {
 
 // Looks up the value of a global string slice flag, returns nil if no string slice flag exists
 func (c *Context) GlobalStringSlice(name string) []string {
-	if fs := lookupParentFlagSet(name, c); fs != nil {
+	if fs := lookupGlobalFlagSet(name, c); fs != nil {
 		return lookupStringSlice(name, fs)
 	}
 	return nil
@@ -113,7 +113,7 @@ func (c *Context) GlobalStringSlice(name string) []string {
 
 // Looks up the value of a global int slice flag, returns nil if no int slice flag exists
 func (c *Context) GlobalIntSlice(name string) []int {
-	if fs := lookupParentFlagSet(name, c); fs != nil {
+	if fs := lookupGlobalFlagSet(name, c); fs != nil {
 		return lookupIntSlice(name, fs)
 	}
 	return nil
@@ -121,7 +121,7 @@ func (c *Context) GlobalIntSlice(name string) []int {
 
 // Looks up the value of a global generic flag, returns nil if no generic flag exists
 func (c *Context) GlobalGeneric(name string) interface{} {
-	if fs := lookupParentFlagSet(name, c); fs != nil {
+	if fs := lookupGlobalFlagSet(name, c); fs != nil {
 		return lookupGeneric(name, fs)
 	}
 	return nil
@@ -147,7 +147,11 @@ func (c *Context) IsSet(name string) bool {
 func (c *Context) GlobalIsSet(name string) bool {
 	if c.globalSetFlags == nil {
 		c.globalSetFlags = make(map[string]bool)
-		for ctx := c.parentContext; ctx != nil && c.globalSetFlags[name] == false; ctx = ctx.parentContext {
+		ctx := c
+		if ctx.parentContext != nil {
+			ctx = ctx.parentContext
+		}
+		for ; ctx != nil && c.globalSetFlags[name] == false; ctx = ctx.parentContext {
 			ctx.flagSet.Visit(func(f *flag.Flag) {
 				c.globalSetFlags[f.Name] = true
 			})
@@ -229,8 +233,11 @@ func (a Args) Swap(from, to int) error {
 	return nil
 }
 
-func lookupParentFlagSet(name string, ctx *Context) *flag.FlagSet {
-	for ctx := ctx.parentContext; ctx != nil; ctx = ctx.parentContext {
+func lookupGlobalFlagSet(name string, ctx *Context) *flag.FlagSet {
+	if ctx.parentContext != nil {
+		ctx = ctx.parentContext
+	}
+	for ; ctx != nil; ctx = ctx.parentContext {
 		if f := ctx.flagSet.Lookup(name); f != nil {
 			return ctx.flagSet
 		}