cgen: fix sumtype option unwrapping (fix #24746) (#24770)

Author: felipensp

vlib/v/gen/c/cgen.v

@@ -5287,8 +5287,9 @@ fn (mut g Gen) ident(node ast.Ident) {
 				obj_sym := g.table.sym(g.unwrap_generic(node.obj.typ))
 				if !prevent_sum_type_unwrapping_once {
 					nested_unwrap := node.obj.smartcasts.len > 1
-					if is_option && nested_unwrap && obj_sym.kind == .sum_type {
-						g.write('*(')
+					unwrap_sumtype := is_option && nested_unwrap && obj_sym.kind == .sum_type
+					if unwrap_sumtype {
+						g.write('(*(')
 					}
 					for i, typ in node.obj.smartcasts {
 						is_option_unwrap := i == 0 && is_option
@@ -5379,6 +5380,9 @@ fn (mut g Gen) ident(node ast.Ident) {
 									&& obj_sym.kind in [.sum_type, .interface] {
 									g.write('${dot}_${cast_sym.cname}')
 								}
+								if i != 0 && unwrap_sumtype {
+									g.write(')')
+								}
 							}
 						}
 						if i == 0 && node.obj.ct_type_var != .smartcast && node.obj.is_unwrapped {

vlib/v/tests/options/option_sumtype_unwrap_test.v

@@ -0,0 +1,40 @@
+type TxPayload = Can | u8
+
+enum Tx {
+	empty
+	data
+	can
+}
+
+fn (tx Tx) frame_bytes(payload ?TxPayload) ![]u8 {
+	match tx {
+		.empty {
+			return [u8(tx)]
+		}
+		.data {
+			if payload != none {
+				if payload is u8 {
+					return [u8(tx), payload]
+				}
+			}
+			return error('Invalid data')
+		}
+		.can {
+			if payload != none {
+				if payload is Can {
+					return [u8(tx), payload.net]
+				}
+			}
+			return error('Invalid can')
+		}
+	}
+}
+
+struct Can {
+	net u8
+}
+
+fn test_main() {
+	assert Tx.empty.frame_bytes(none)! == [u8(0)]
+	assert Tx.data.frame_bytes(u8(123))! == [u8(1), 123]
+}