Strict flag lookup

[icholy]

Checklist

• [x] Are you running the latest v2 release? The list of releases is here.
• [x] Did you check the manual for your release? The v2 manual is here.
• [x] Did you perform a search about this feature? Here's the Github guide about searching.

What problem does this solve?

I've had several cases where I've made a typo when accessing a flag value via the context.

Solution description

I'd like the library to panic if I access an undefined flag.

func main() {
	app := &cli.App{
		Flags: []cli.Flag{
			&cli.StringFlag{
				Name: "foo",
			},
		},
		Action: func(c *cli.Context) error {
		
			// I want this to panic
			_ = c.String("bar")
			return nil
		},
	}
	app.Run([]string{"test"})
}

[meatballhat]

@icholy you may want to consider using the recently-added (by @toaster 🙇🏼) ability to get the value directly from a given flag

[icholy]

I'd much prefer to keep my existing code and just enable some type of "strict mode" flag.

[dearchap]

@icholy This would be nice, are you willing to submit a PR ?

[icholy]

@dearchap if you want to, go for it. Edit see the linked pr.

[dearchap]

Fixed. .