cgen: fix codegen for selector with embed field option (fix #24084) (#24085)

vlib/v/gen/c/cgen.v

@@ -7579,6 +7579,12 @@ fn (mut g Gen) as_cast(node ast.AsCast) {
 				g.unwrap_option_type(node.expr.typ, '${node.expr.expr.name}.${node.expr.field_name}',
 					node.expr.expr.is_auto_heap())
 				is_optional_ident_var = true
+			} else if node.expr.expr is ast.SelectorExpr && node.expr.typ.has_flag(.option) {
+				if node.expr.expr.expr is ast.Ident {
+					g.unwrap_option_type(node.expr.typ, '${node.expr.expr.expr.name}.${node.expr.expr.field_name}.${node.expr.field_name}',
+						node.expr.expr.expr.is_auto_heap())
+					is_optional_ident_var = true
+				}
 			}
 		}
 		if !is_optional_ident_var {

vlib/v/tests/options/option_embed_field_test.v

@@ -0,0 +1,18 @@
+struct Foo {
+	optional_one ?string
+}
+
+struct Bar {
+	foo Foo
+}
+
+fn test_main() {
+	b := Bar{Foo{
+		optional_one: 'hello world'
+	}}
+	println(b.foo.optional_one)
+	x := b.foo.optional_one as string
+
+	assert x == 'hello world'
+	assert (b.foo.optional_one as string) == 'hello world'
+}