sumtype smartcast: bug 1

[enghitalo]

Describe the bug

#20270

Reproduction Steps

type TestSum = int | string

struct Abc {
	s TestSum
}

fn gen[T](struc T) {
	$if T is $struct {
		$for field in T.fields {
			field_value := struc.$(field.name)
			$if field_value is $sumtype {
				$for v in field_value.variants {
					if field_value is v { // smartcast
						// works beautifully
						dump(field_value)
						// Not Works
						$if field_value is string {
							println('text') // bug
						} $else $if field_value is int {
							println('text')
						} $else {
							println('text')
						}
					}
				}
			}
		}
	}
}

fn main() {
	a := Abc{TestSum(123)}
	b := Abc{TestSum('foo')}
	gen[Abc](a)
	gen[Abc](b)
}

Expected Behavior

[discardable.v:15] field_value: 123
text
[discardable.v:15] field_value: foo
text

Current Behavior

discardable.v:19:8: cgen error: checker bug; print arg.typ is 0
   17 |                         $if field_value is string {
   18 |                             // dump(field_value)
   19 |                             println('text')
      |                             ~~~~~~~~~~~~~~~
   20 |                         } $else $if field_value is int {
   21 |                             println('text')

Possible Solution

No response

Additional Information/Context

No response

V version

V 0.4.3 4690fec

Environment details (OS name and version, etc.)

Ubuntu

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