Fix an issue where closure rewriting required class internals

Surfaced through previous sanity-checking commits, this reorders some
internal operations to...

Closes #1174

crates/cli-support/src/js/mod.rs

@@ -171,8 +171,6 @@ impl<'a> Context<'a> {
     }
 
     pub fn finalize(&mut self, module_name: &str) -> Result<(String, String), Error> {
-        self.write_classes()?;
-
         self.bind("__wbindgen_object_clone_ref", &|me| {
             me.expose_get_object();
             me.expose_add_heap_object();
@@ -429,6 +427,7 @@ impl<'a> Context<'a> {
         })?;
 
         closures::rewrite(self).with_context(|_| "failed to generate internal closure shims")?;
+        self.write_classes()?;
         self.unexport_unused_internal_exports();
 
         // Handle the `start` function, if one was specified. If we're in a

tests/wasm/closures.js

@@ -1,4 +1,5 @@
 const assert = require('assert');
+const wasm = require('wasm-bindgen-test');
 
 exports.works_call = a => {
     a();
@@ -97,3 +98,7 @@ exports.drop_during_call_save = f => {
   DROP_DURING_CALL = f;
 };
 exports.drop_during_call_call = () => DROP_DURING_CALL();
+
+exports.js_test_closure_returner = () => {
+  wasm.closure_returner().someKey();
+};

tests/wasm/closures.rs

@@ -63,6 +63,8 @@ extern "C" {
 
     fn drop_during_call_save(a: &Closure<Fn()>);
     fn drop_during_call_call();
+
+    fn js_test_closure_returner();
 }
 
 #[wasm_bindgen_test]
@@ -279,3 +281,33 @@ fn drop_during_call_ok() {
         assert!(HIT);
     }
 }
+
+#[wasm_bindgen_test]
+fn test_closure_returner() {
+    type ClosureType = FnMut() -> BadStruct;
+
+    use js_sys::{Object, Reflect};
+    use wasm_bindgen::JsCast;
+
+    js_test_closure_returner();
+
+    #[wasm_bindgen]
+    pub struct ClosureHandle(Closure<ClosureType>);
+
+    #[wasm_bindgen]
+    pub struct BadStruct {}
+
+    #[wasm_bindgen]
+    pub fn closure_returner() -> Result<Object, JsValue> {
+
+        let o = Object::new();
+
+        let some_fn = Closure::wrap(Box::new(move || BadStruct {}) as Box<ClosureType>);
+        Reflect::set(&o, &JsValue::from("someKey"), &some_fn.as_ref().unchecked_ref())
+            .unwrap();
+        Reflect::set(&o, &JsValue::from("handle"), &JsValue::from(ClosureHandle(some_fn)))
+            .unwrap();
+
+        Ok(o)
+    }
+}