Fix include! implementation for Rust file

Also add tests for including Rust file

integration-tests/templates/include_rust.out

@@ -0,0 +1 @@
+59

integration-tests/templates/include_rust.stpl

@@ -0,0 +1 @@
+<% let a = include!("includes/rust.rs"); %><%= a %>

integration-tests/templates/includes/rust.rs

@@ -0,0 +1 @@
+value + 1

integration-tests/tests/template_once.rs

@@ -184,6 +184,17 @@ fn test_rust_macro() {
     assert_render("rust_macro", RustMacro { value: Some(10) });
 }
 
+#[derive(TemplateOnce)]
+#[template(path = "include_rust.stpl")]
+struct IncludeRust {
+    value: usize,
+}
+
+#[test]
+fn test_include_rust() {
+    assert_render("include_rust", IncludeRust { value: 58 });
+}
+
 #[cfg(unix)]
 mod unix {
     use super::*;

sailfish-compiler/src/resolver.rs

@@ -63,7 +63,7 @@ impl<'s, 'h> VisitMut for ResolverImpl<'s, 'h> {
                 let absolute_path =
                     self.path_stack.last().unwrap().parent().unwrap().join(arg);
                 let absolute_path_str = absolute_path.to_string_lossy();
-                em.mac.tokens = quote! { include!(#absolute_path_str) };
+                *i = syn::parse2(quote! { include!(#absolute_path_str) }).unwrap();
             }
             return;
         }