cgen: fix struct fn ptr call (#18260)

vlib/v/gen/c/fn.v

@@ -1478,8 +1478,14 @@ fn (mut g Gen) fn_call(node ast.CallExpr) {
 	mut is_interface_call := false
 	mut is_selector_call := false
 	if node.left_type != 0 {
+		mut fn_typ := ast.Type(0)
 		left_sym := g.table.sym(node.left_type)
-		if left_sym.kind == .interface_ {
+		if node.is_field {
+			if field := g.table.find_field_with_embeds(left_sym, node.name) {
+				fn_typ = field.typ
+			}
+		}
+		if left_sym.kind == .interface_ || fn_typ.is_ptr() {
 			is_interface_call = true
 			g.write('(*')
 		}

vlib/v/tests/fn_ptr_call_test.v

@@ -0,0 +1,22 @@
+struct Animal {
+mut:
+	age  fn (p int) int
+	duck Duck
+}
+
+struct Duck {
+mut:
+	age &fn (p int) int
+}
+
+fn test_main() {
+	mut animal := Animal{
+		age: fn (x int) int {
+			return 5
+		}
+	}
+	animal.duck = Duck{
+		age: &animal.age
+	}
+	assert animal.duck.age(1) == 5
+}