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Fix #17711

fn main() {
	mut a := ?int(12)
	match a? {
		12 { println(a) }
		//none { println('none') }
		else { println('else') }
	}

	match a {
		none { println('none') }
		else { println('else') }
	}
	
	a = none

	match a {
		none { println('none') }
		else { println('else') }
	}

	mut b := ?string('aaa')
	match b? {
		'aaa' { println(b) }
		else { println('else') }
	}

	match b {
		none { println('none') }
		else { println('else') }
	}

	b = none
	match b {
		none { println('none') }
		else { println('else') }
	}
}

Added error when using option type without unwrap to check against value different of none:

bug.v:4:8: error: `match` expression with Option type only checks against `none`, to match its value you must unwrap it first `var?`
    2 |     mut a := ?int(12)
    3 |     match a {
    4 |         12 { println(a) }
      |              ~~~~~~~~~~
    5 |         else { println('else') }
    6 |     }

Just curious. Why match expression with Option type only checks against none? Is matching its value and checking against none at the same time a bad idea? Why?

Just curious. Why match expression with Option type only checks against none? Is matching its value and checking against none at the same time a bad idea? Why?

Because the value needs to be unwrapped first. Here:

	b = none
	match b {
		none { println('none') }
		else { println('else') }
	}

the else branch could have access to the unwrapped values of b (if it was not none). The match itself however has access only to the wrapped value of b, which can be either none or valid value of the type string.