Implement *Context.GlobalSet + relevant CHANGELOG entry

CHANGELOG.md

@@ -8,6 +8,8 @@
 - This file!
 - Support for placeholders in flag usage strings
 - `App.Metadata` map for arbitrary data/state management
+- `Set` and `GlobalSet` methods on `*cli.Context` for altering values after
+parsing.
 
 ### Changed
 - The `App.Action` and `Command.Action` now prefer a return signature of

context.go

@@ -146,6 +146,11 @@ func (c *Context) Set(name, value string) error {
 	return c.flagSet.Set(name, value)
 }
 
+// GlobalSet sets a context flag to a value on the global flagset
+func (c *Context) GlobalSet(name, value string) error {
+	return globalContext(c).flagSet.Set(name, value)
+}
+
 // Determines if the flag was actually set
 func (c *Context) IsSet(name string) bool {
 	if c.setFlags == nil {
@@ -252,6 +257,21 @@ func (a Args) Swap(from, to int) error {
 	return nil
 }
 
+func globalContext(ctx *Context) *Context {
+	if ctx == nil {
+		return nil
+	}
+
+	for {
+		if ctx.parentContext == nil {
+			return ctx
+		}
+		ctx = ctx.parentContext
+	}
+
+	return nil
+}
+
 func lookupGlobalFlagSet(name string, ctx *Context) *flag.FlagSet {
 	if ctx.parentContext != nil {
 		ctx = ctx.parentContext

context_test.go

@@ -211,3 +211,22 @@ func TestContext_Set(t *testing.T) {
 	c.Set("int", "1")
 	expect(t, c.Int("int"), 1)
 }
+
+func TestContext_GlobalSet(t *testing.T) {
+	gSet := flag.NewFlagSet("test", 0)
+	gSet.Int("int", 5, "an int")
+
+	set := flag.NewFlagSet("sub", 0)
+	set.Int("int", 3, "an int")
+
+	pc := NewContext(nil, gSet, nil)
+	c := NewContext(nil, set, pc)
+
+	c.Set("int", "1")
+	expect(t, c.Int("int"), 1)
+	expect(t, c.GlobalInt("int"), 5)
+
+	c.GlobalSet("int", "1")
+	expect(t, c.Int("int"), 1)
+	expect(t, c.GlobalInt("int"), 1)
+}