checker: wrong method check for array and array of options

[enghitalo]

Describe the bug

decode_array think that []?int is []int

Reproduction Steps

struct Decoder { }

pub fn decode[T](val string) !T {
	mut decoder := Decoder{}
	mut result := T{}
	decoder.decode_value(mut result)!
	return result
}

fn (mut decoder Decoder) decode_value[T](mut val T) ! {
	$if T.unaliased_typ is $array {
		// checking wrongly. `decode_array` think that `[]?int` is `[]int`
		decoder.decode_array(mut val)!
		return
	} $else $if T.unaliased_typ is $struct {
		$for field in T.fields {
			decoder.decode_value(mut val.$(field.name))!
		}
	}
}

fn (mut decoder Decoder) decode_array[T](mut val []T) ! {}

struct Foo {
	int  []int
	oint []?int
}

fn main() {
	decode[Foo]('')!
}

Expected Behavior

Not error

Current Behavior

code.v:13:27: error: cannot use `&[]?int` as `&[]int` in argument 1 to `Decoder.decode_array`
   11 |     $if T.unaliased_typ is $array {
   12 |         // checking wrongly
   13 |         decoder.decode_array(mut val)!
      |                                 ~~~
   14 |         return
   15 |     } $else $if T.unaliased_typ is $struct {

Possible Solution

No response

Additional Information/Context

No response

V version

V 0.4.10 d9afebc

Environment details (OS name and version, etc.)

Ubuntu

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[huly-for-github]

Connected to Huly®: V_0.6-22795

[jorgeluismireles]

I got similar error with this simplification even without using mut (difference is reference &):

fn decode[T](val T) ! {
	$if T is []?int {
		decode_array(val)!
	} $else {
		return error('?')
	}
}

fn decode_array[T](val []T) ! { }

fn main() {
	o := []?int { len:4 }
	decode(o)!
}

code.v:3:16: error: cannot use `[]?int` as `[]int` in argument 1 to `decode_array`
    1 | fn decode[T](val T) ! {
    2 |     $if T is []?int {
    3 |         decode_array(val)!
      |                      ~~~

Works with a simple array []int (without option).

[felipensp]

This is because the parameter is not []?T.