feat(macros): add async mutable resource injection for `#[chain]`

Support `&mut T` resource parameters in async chain functions by using
an extract-store pattern that avoids holding mutable borrows across
await
points. Remove the previous compile-time rejection of this combination.

1 files changed, 38 insertions, 0 deletions

diff --git a/mingling_core/src/asset/global_resource.rs b/mingling_core/src/asset/global_resource.rs
index 83a779d..651655a 100644
--- a/mingling_core/src/asset/global_resource.rs
+++ b/mingling_core/src/asset/global_resource.rs
@@ -74,6 +74,44 @@ where
         }
     }
 
+    /// Internal syntax for the `&mut MyResource` syntax of async #[chain], do not use directly.
+    ///
+    /// Extracts a mutable resource from the global store (clone-out), returning an
+    /// owned value. The caller must call [`__store_res`] to write back modifications.
+    #[doc(hidden)]
+    #[must_use]
+    pub fn __extract_res_mut<Res: 'static + Default + ResourceMarker + Send + Sync>(
+        &self,
+    ) -> Res {
+        let Ok(mut guard) = self.resources.lock() else {
+            return Res::res_default();
+        };
+        if let Some(arc_res) = guard
+            .get_mut(&TypeId::of::<Res>())
+            .and_then(|a| a.downcast_mut::<Arc<Res>>())
+        {
+            match Arc::try_unwrap(std::mem::take(arc_res)) {
+                Ok(val) => val,
+                Err(arc) => (*arc).res_clone(),
+            }
+        } else {
+            Res::res_default()
+        }
+    }
+
+    /// Internal syntax for the `&mut MyResource` syntax of async #[chain], do not use directly.
+    ///
+    /// Stores a modified resource value back into the global store.
+    #[doc(hidden)]
+    pub fn __store_res<Res: 'static + Send + Sync + ResourceMarker>(
+        &self,
+        val: Res,
+    ) {
+        if let Ok(mut guard) = self.resources.lock() {
+            guard.insert(TypeId::of::<Res>(), Box::new(Arc::new(val)));
+        }
+    }
+
     /// Get an resources by type, returning `Res` if present
     #[must_use]
     pub fn res<Res: 'static + Send + Sync>(&self) -> Option<GlobalResource<Res>> {