Rely on Command context in Run()

Was previously relying on the parent context which caused things like
`.Command` to not be available to OnUsageError().

Fixes #609

command.go

@@ -154,19 +154,20 @@ func (c Command) Run(ctx *Context) (err error) {
 	}
 
 	context := NewContext(ctx.App, set, ctx)
+	context.Command = c
 	if checkCommandCompletions(context, c.Name) {
 		return nil
 	}
 
 	if err != nil {
 		if c.OnUsageError != nil {
-			err := c.OnUsageError(ctx, err, false)
+			err := c.OnUsageError(context, err, false)
 			HandleExitCoder(err)
 			return err
 		}
-		fmt.Fprintln(ctx.App.Writer, "Incorrect Usage:", err.Error())
-		fmt.Fprintln(ctx.App.Writer)
-		ShowCommandHelp(ctx, c.Name)
+		fmt.Fprintln(context.App.Writer, "Incorrect Usage:", err.Error())
+		fmt.Fprintln(context.App.Writer)
+		ShowCommandHelp(context, c.Name)
 		return err
 	}
 
@@ -191,9 +192,9 @@ func (c Command) Run(ctx *Context) (err error) {
 	if c.Before != nil {
 		err = c.Before(context)
 		if err != nil {
-			fmt.Fprintln(ctx.App.Writer, err)
-			fmt.Fprintln(ctx.App.Writer)
-			ShowCommandHelp(ctx, c.Name)
+			fmt.Fprintln(context.App.Writer, err)
+			fmt.Fprintln(context.App.Writer)
+			ShowCommandHelp(context, c.Name)
 			HandleExitCoder(err)
 			return err
 		}
@@ -203,7 +204,6 @@ func (c Command) Run(ctx *Context) (err error) {
 		c.Action = helpSubcommand.Action
 	}
 
-	context.Command = c
 	err = HandleAction(c.Action, context)
 
 	if err != nil {

command_test.go

@@ -127,6 +127,30 @@ func TestCommand_Run_BeforeSavesMetadata(t *testing.T) {
 	}
 }
 
+func TestCommand_OnUsageError_hasCommandContext(t *testing.T) {
+	app := NewApp()
+	app.Commands = []Command{
+		{
+			Name: "bar",
+			Flags: []Flag{
+				IntFlag{Name: "flag"},
+			},
+			OnUsageError: func(c *Context, err error, _ bool) error {
+				return fmt.Errorf("intercepted in %s: %s", c.Command.Name, err.Error())
+			},
+		},
+	}
+
+	err := app.Run([]string{"foo", "bar", "--flag=wrong"})
+	if err == nil {
+		t.Fatalf("expected to receive error from Run, got none")
+	}
+
+	if !strings.HasPrefix(err.Error(), "intercepted in bar") {
+		t.Errorf("Expect an intercepted error, but got \"%v\"", err)
+	}
+}
+
 func TestCommand_OnUsageError_WithWrongFlagValue(t *testing.T) {
 	app := NewApp()
 	app.Commands = []Command{