Fix nullable union types

Author: afdw

crates/webidl/src/idl_type.rs

@@ -549,7 +549,12 @@ impl<'a> IdlType<'a> {
             },
             IdlType::Enum(name) => Some(ident_ty(rust_ident(camel_case_ident(name).as_str()))),
 
-            IdlType::Nullable(idl_type) => Some(option_ty(idl_type.to_syn_type(pos)?)),
+            IdlType::Nullable(idl_type) => {
+                match **idl_type {
+                    IdlType::Union(..) => idl_type.to_syn_type(pos),
+                    _ => Some(option_ty(idl_type.to_syn_type(pos)?))
+                }
+            },
             IdlType::FrozenArray(_idl_type) => None,
             IdlType::Sequence(_idl_type) => None,
             IdlType::Promise(_idl_type) => {
@@ -563,10 +568,10 @@ impl<'a> IdlType<'a> {
             }
             IdlType::Record(_idl_type_from, _idl_type_to) => None,
             IdlType::Union(_idl_types) => {
-                // Handles union types in all places except operation argument types
+                // Handles union types in all places except operation argument types.
+                // Currently treats them as any type.
                 // TODO: add better support for union types here?
-                let path = vec![rust_ident("wasm_bindgen"), rust_ident("JsValue")];
-                Some(leading_colon_path_ty(path))
+                IdlType::Any.to_syn_type(pos)
             },
 
             IdlType::Any => {