Added Support for Extension-less Assets (#10153)

# Objective

- Addresses **Support processing and loading files without extensions**
from #9714
- Addresses **More runtime loading configuration** from #9714
- Fixes #367
- Fixes #10703

## Solution

`AssetServer::load::<A>` and `AssetServer::load_with_settings::<A>` can
now use the `Asset` type parameter `A` to select a registered
`AssetLoader` without inspecting the provided `AssetPath`. This change
cascades onto `LoadContext::load` and `LoadContext::load_with_settings`.
This allows the loading of assets which have incorrect or ambiguous file
extensions.

```rust
// Allow the type to be inferred by context
let handle = asset_server.load("data/asset_no_extension");

// Hint the type through the handle
let handle: Handle<CustomAsset> = asset_server.load("data/asset_no_extension");

// Explicit through turbofish
let handle = asset_server.load::<CustomAsset>("data/asset_no_extension");
```

Since a single `AssetPath` no longer maps 1:1 with an `Asset`, I've also
modified how assets are loaded to permit multiple asset types to be
loaded from a single path. This allows for two different `AssetLoaders`
(which return different types of assets) to both load a single path (if
requested).

```rust
// Uses GltfLoader
let model = asset_server.load::<Gltf>("cube.gltf");

// Hypothetical Blob loader for data transmission (for example)
let blob = asset_server.load::<Blob>("cube.gltf");
```

As these changes are reflected in the `LoadContext` as well as the
`AssetServer`, custom `AssetLoaders` can also take advantage of this
behaviour to create more complex assets.

---

## Change Log

- Updated `custom_asset` example to demonstrate extension-less assets.
- Added `AssetServer::get_handles_untyped` and Added
`AssetServer::get_path_ids`

## Notes

As a part of that refactor, I chose to store `AssetLoader`s (within
`AssetLoaders`) using a `HashMap<TypeId, ...>` instead of a `Vec<...>`.
My reasoning for this was I needed to add a relationship between `Asset`
`TypeId`s and the `AssetLoader`, so instead of having a `Vec` and a
`HashMap`, I combined the two, removing the `usize` index from the
adjacent maps.

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>

assets/data/asset_no_extension

@@ -0,0 +1,3 @@
+CustomAsset (
+    value: 13
+)

crates/bevy_asset/src/io/mod.rs

@@ -267,10 +267,7 @@ impl AsyncRead for VecReader {
 /// Appends `.meta` to the given path.
 pub(crate) fn get_meta_path(path: &Path) -> PathBuf {
     let mut meta_path = path.to_path_buf();
-    let mut extension = path
-        .extension()
-        .unwrap_or_else(|| panic!("missing extension for asset path {path:?}"))
-        .to_os_string();
+    let mut extension = path.extension().unwrap_or_default().to_os_string();
     extension.push(".meta");
     meta_path.set_extension(extension);
     meta_path

crates/bevy_asset/src/loader.rs

@@ -37,8 +37,10 @@ pub trait AssetLoader: Send + Sync + 'static {
         load_context: &'a mut LoadContext,
     ) -> BoxedFuture<'a, Result<Self::Asset, Self::Error>>;
 
-    /// Returns a list of extensions supported by this asset loader, without the preceding dot.
-    fn extensions(&self) -> &[&str];
+    /// Returns a list of extensions supported by this [`AssetLoader`], without the preceding dot.
+    fn extensions(&self) -> &[&str] {
+        &[]
+    }
 }
 
 /// Provides type-erased access to an [`AssetLoader`].
@@ -396,7 +398,7 @@ impl<'a> LoadContext<'a> {
     /// See [`AssetPath`] for more on labeled assets.
     pub fn has_labeled_asset<'b>(&self, label: impl Into<CowArc<'b, str>>) -> bool {
         let path = self.asset_path.clone().with_label(label.into());
-        self.asset_server.get_handle_untyped(&path).is_some()
+        !self.asset_server.get_handles_untyped(&path).is_empty()
     }
 
     /// "Finishes" this context by populating the final [`Asset`] value (and the erased [`AssetMeta`] value, if it exists).
@@ -546,7 +548,7 @@ impl<'a> LoadContext<'a> {
         let loaded_asset = {
             let (meta, loader, mut reader) = self
                 .asset_server
-                .get_meta_loader_and_reader(&path)
+                .get_meta_loader_and_reader(&path, None)
                 .await
                 .map_err(to_error)?;
             self.asset_server

crates/bevy_asset/src/server/info.rs

@@ -61,7 +61,7 @@ impl AssetInfo {
 
 #[derive(Default)]
 pub(crate) struct AssetInfos {
-    path_to_id: HashMap<AssetPath<'static>, UntypedAssetId>,
+    path_to_id: HashMap<AssetPath<'static>, HashMap<TypeId, UntypedAssetId>>,
     infos: HashMap<UntypedAssetId, AssetInfo>,
     /// If set to `true`, this informs [`AssetInfos`] to track data relevant to watching for changes (such as `load_dependants`)
     /// This should only be set at startup.
@@ -191,7 +191,20 @@ impl AssetInfos {
         loading_mode: HandleLoadingMode,
         meta_transform: Option<MetaTransform>,
     ) -> Result<(UntypedHandle, bool), GetOrCreateHandleInternalError> {
-        match self.path_to_id.entry(path.clone()) {
+        let handles = self.path_to_id.entry(path.clone()).or_default();
+
+        let type_id = type_id
+            .or_else(|| {
+                // If a TypeId is not provided, we may be able to infer it if only a single entry exists
+                if handles.len() == 1 {
+                    Some(*handles.keys().next().unwrap())
+                } else {
+                    None
+                }
+            })
+            .ok_or(GetOrCreateHandleInternalError::HandleMissingButTypeIdNotSpecified)?;
+
+        match handles.entry(type_id) {
             Entry::Occupied(entry) => {
                 let id = *entry.get();
                 // if there is a path_to_id entry, info always exists
@@ -222,9 +235,6 @@ impl AssetInfos {
                     // We must create a new strong handle for the existing id and ensure that the drop of the old
                     // strong handle doesn't remove the asset from the Assets collection
                     info.handle_drops_to_skip += 1;
-                    let type_id = type_id.ok_or(
-                        GetOrCreateHandleInternalError::HandleMissingButTypeIdNotSpecified,
-                    )?;
                     let provider = self
                         .handle_providers
                         .get(&type_id)
@@ -241,8 +251,6 @@ impl AssetInfos {
                     HandleLoadingMode::NotLoading => false,
                     HandleLoadingMode::Request | HandleLoadingMode::Force => true,
                 };
-                let type_id = type_id
-                    .ok_or(GetOrCreateHandleInternalError::HandleMissingButTypeIdNotSpecified)?;
                 let handle = Self::create_handle_internal(
                     &mut self.infos,
                     &self.handle_providers,
@@ -271,13 +279,52 @@ impl AssetInfos {
         self.infos.get_mut(&id)
     }
 
-    pub(crate) fn get_path_id(&self, path: &AssetPath) -> Option<UntypedAssetId> {
-        self.path_to_id.get(path).copied()
+    pub(crate) fn get_path_and_type_id_handle(
+        &self,
+        path: &AssetPath,
+        type_id: TypeId,
+    ) -> Option<UntypedHandle> {
+        let id = self.path_to_id.get(path)?.get(&type_id)?;
+        self.get_id_handle(*id)
     }
 
-    pub(crate) fn get_path_handle(&self, path: &AssetPath) -> Option<UntypedHandle> {
-        let id = *self.path_to_id.get(path)?;
-        self.get_id_handle(id)
+    pub(crate) fn get_path_ids<'a>(
+        &'a self,
+        path: &'a AssetPath<'a>,
+    ) -> impl Iterator<Item = UntypedAssetId> + 'a {
+        /// Concrete type to allow returning an `impl Iterator` even if `self.path_to_id.get(&path)` is `None`
+        enum HandlesByPathIterator<T> {
+            None,
+            Some(T),
+        }
+
+        impl<T> Iterator for HandlesByPathIterator<T>
+        where
+            T: Iterator<Item = UntypedAssetId>,
+        {
+            type Item = UntypedAssetId;
+
+            fn next(&mut self) -> Option<Self::Item> {
+                match self {
+                    HandlesByPathIterator::None => None,
+                    HandlesByPathIterator::Some(iter) => iter.next(),
+                }
+            }
+        }
+
+        if let Some(type_id_to_id) = self.path_to_id.get(path) {
+            HandlesByPathIterator::Some(type_id_to_id.values().copied())
+        } else {
+            HandlesByPathIterator::None
+        }
+    }
+
+    pub(crate) fn get_path_handles<'a>(
+        &'a self,
+        path: &'a AssetPath<'a>,
+    ) -> impl Iterator<Item = UntypedHandle> + 'a {
+        self.get_path_ids(path)
+            .filter_map(|id| self.get_id_handle(id))
     }
 
     pub(crate) fn get_id_handle(&self, id: UntypedAssetId) -> Option<UntypedHandle> {
@@ -289,12 +336,13 @@ impl AssetInfos {
     /// Returns `true` if the asset this path points to is still alive
     pub(crate) fn is_path_alive<'a>(&self, path: impl Into<AssetPath<'a>>) -> bool {
         let path = path.into();
-        if let Some(id) = self.path_to_id.get(&path) {
-            if let Some(info) = self.infos.get(id) {
-                return info.weak_handle.strong_count() > 0;
-            }
-        }
-        false
+
+        let result = self
+            .get_path_ids(&path)
+            .filter_map(|id| self.infos.get(&id))
+            .any(|info| info.weak_handle.strong_count() > 0);
+
+        result
     }
 
     /// Returns `true` if the asset at this path should be reloaded
@@ -592,7 +640,7 @@ impl AssetInfos {
 
     fn process_handle_drop_internal(
         infos: &mut HashMap<UntypedAssetId, AssetInfo>,
-        path_to_id: &mut HashMap<AssetPath<'static>, UntypedAssetId>,
+        path_to_id: &mut HashMap<AssetPath<'static>, HashMap<TypeId, UntypedAssetId>>,
         loader_dependants: &mut HashMap<AssetPath<'static>, HashSet<AssetPath<'static>>>,
         living_labeled_assets: &mut HashMap<AssetPath<'static>, HashSet<String>>,
         watching_for_changes: bool,
@@ -609,6 +657,8 @@ impl AssetInfos {
             return false;
         }
 
+        let type_id = entry.key().type_id();
+
         let info = entry.remove();
         let Some(path) = &info.path else {
             return true;
@@ -622,7 +672,15 @@ impl AssetInfos {
                 living_labeled_assets,
             );
         }
-        path_to_id.remove(path);
+
+        if let Some(map) = path_to_id.get_mut(path) {
+            map.remove(&type_id);
+
+            if map.is_empty() {
+                path_to_id.remove(path);
+            }
+        };
+
         true
     }
 

crates/bevy_asset/src/server/mod.rs

@@ -142,20 +142,22 @@ impl AssetServer {
             if let Some(index) = loaders.preregistered_loaders.remove(type_name) {
                 (index, false)
             } else {
-                (loaders.values.len(), true)
+                (TypeId::of::<L::Asset>(), true)
             };
         for extension in loader.extensions() {
             loaders
-                .extension_to_index
+                .extension_to_type_id
                 .insert(extension.to_string(), loader_index);
         }
 
         if is_new {
-            loaders.type_name_to_index.insert(type_name, loader_index);
-            loaders.values.push(MaybeAssetLoader::Ready(loader));
+            loaders.type_name_to_type_id.insert(type_name, loader_index);
+            loaders
+                .type_id_to_loader
+                .insert(loader_index, MaybeAssetLoader::Ready(loader));
         } else {
             let maybe_loader = std::mem::replace(
-                &mut loaders.values[loader_index],
+                loaders.type_id_to_loader.get_mut(&loader_index).unwrap(),
                 MaybeAssetLoader::Ready(loader.clone()),
             );
             match maybe_loader {
@@ -219,12 +221,12 @@ impl AssetServer {
     ) -> Result<Arc<dyn ErasedAssetLoader>, MissingAssetLoaderForExtensionError> {
         let loader = {
             let loaders = self.data.loaders.read();
-            let index = *loaders.extension_to_index.get(extension).ok_or_else(|| {
+            let index = *loaders.extension_to_type_id.get(extension).ok_or_else(|| {
                 MissingAssetLoaderForExtensionError {
                     extensions: vec![extension.to_string()],
                 }
             })?;
-            loaders.values[index].clone()
+            loaders.type_id_to_loader[&index].clone()
         };
 
         match loader {
@@ -240,13 +242,13 @@ impl AssetServer {
     ) -> Result<Arc<dyn ErasedAssetLoader>, MissingAssetLoaderForTypeNameError> {
         let loader = {
             let loaders = self.data.loaders.read();
-            let index = *loaders.type_name_to_index.get(type_name).ok_or_else(|| {
+            let index = *loaders.type_name_to_type_id.get(type_name).ok_or_else(|| {
                 MissingAssetLoaderForTypeNameError {
                     type_name: type_name.to_string(),
                 }
             })?;
 
-            loaders.values[index].clone()
+            loaders.type_id_to_loader[&index].clone()
         };
         match loader {
             MaybeAssetLoader::Ready(loader) => Ok(loader),
@@ -279,6 +281,34 @@ impl AssetServer {
         Err(MissingAssetLoaderForExtensionError { extensions })
     }
 
+    /// Retrieves the default [`AssetLoader`] for the given [`Asset`] [`TypeId`], if one can be found.
+    pub async fn get_asset_loader_with_asset_type_id<'a>(
+        &self,
+        type_id: TypeId,
+    ) -> Result<Arc<dyn ErasedAssetLoader>, MissingAssetLoaderForTypeIdError> {
+        let loader = {
+            let loaders = self.data.loaders.read();
+            loaders
+                .type_id_to_loader
+                .get(&type_id)
+                .ok_or(MissingAssetLoaderForTypeIdError { type_id })?
+                .clone()
+        };
+
+        match loader {
+            MaybeAssetLoader::Ready(loader) => Ok(loader),
+            MaybeAssetLoader::Pending { mut receiver, .. } => Ok(receiver.recv().await.unwrap()),
+        }
+    }
+
+    /// Retrieves the default [`AssetLoader`] for the given [`Asset`] type, if one can be found.
+    pub async fn get_asset_loader_with_asset_type<'a, A: Asset>(
+        &self,
+    ) -> Result<Arc<dyn ErasedAssetLoader>, MissingAssetLoaderForTypeIdError> {
+        self.get_asset_loader_with_asset_type_id(TypeId::of::<A>())
+            .await
+    }
+
     /// Begins loading an [`Asset`] of type `A` stored at `path`. This will not block on the asset load. Instead,
     /// it returns a "strong" [`Handle`]. When the [`Asset`] is loaded (and enters [`LoadState::Loaded`]), it will be added to the
     /// associated [`Assets`] resource.
@@ -427,10 +457,12 @@ impl AssetServer {
         force: bool,
         meta_transform: Option<MetaTransform>,
     ) -> Result<UntypedHandle, AssetLoadError> {
+        let asset_type_id = input_handle.as_ref().map(|handle| handle.type_id());
+
         let path = path.into_owned();
         let path_clone = path.clone();
         let (mut meta, loader, mut reader) = self
-            .get_meta_loader_and_reader(&path_clone)
+            .get_meta_loader_and_reader(&path_clone, asset_type_id)
             .await
             .map_err(|e| {
                 // if there was an input handle, a "load" operation has already started, so we must produce a "failure" event, if
@@ -477,6 +509,11 @@ impl AssetServer {
 
         let handle = if let Some((handle, should_load)) = handle_result {
             if path.label().is_none() && handle.type_id() != loader.asset_type_id() {
+                error!(
+                    "Expected {:?}, got {:?}",
+                    handle.type_id(),
+                    loader.asset_type_id()
+                );
                 return Err(AssetLoadError::RequestedHandleTypeMismatch {
                     path: path.into_owned(),
                     requested: handle.type_id(),
@@ -569,7 +606,24 @@ impl AssetServer {
         let path = path.into().into_owned();
         IoTaskPool::get()
             .spawn(async move {
-                if server.data.infos.read().should_reload(&path) {
+                let mut reloaded = false;
+
+                let requests = server
+                    .data
+                    .infos
+                    .read()
+                    .get_path_handles(&path)
+                    .map(|handle| server.load_internal(Some(handle), path.clone(), true, None))
+                    .collect::<Vec<_>>();
+
+                for result in requests {
+                    match result.await {
+                        Ok(_) => reloaded = true,
+                        Err(err) => error!("{}", err),
+                    }
+                }
+
+                if !reloaded && server.data.infos.read().should_reload(&path) {
                     if let Err(err) = server.load_internal(None, path, true, None).await {
                         error!("{}", err);
                     }
@@ -792,7 +846,7 @@ impl AssetServer {
     /// Returns an active handle for the given path, if the asset at the given path has already started loading,
     /// or is still "alive".
     pub fn get_handle<'a, A: Asset>(&self, path: impl Into<AssetPath<'a>>) -> Option<Handle<A>> {
-        self.get_handle_untyped(path)
+        self.get_path_and_type_id_handle(&path.into(), TypeId::of::<A>())
             .map(|h| h.typed_debug_checked())
     }
 
@@ -812,18 +866,58 @@ impl AssetServer {
 
     /// Returns an active untyped asset id for the given path, if the asset at the given path has already started loading,
     /// or is still "alive".
+    /// Returns the first ID in the event of multiple assets being registered against a single path.
+    ///
+    /// # See also
+    /// [`get_path_ids`][Self::get_path_ids] for all handles.
     pub fn get_path_id<'a>(&self, path: impl Into<AssetPath<'a>>) -> Option<UntypedAssetId> {
         let infos = self.data.infos.read();
         let path = path.into();
-        infos.get_path_id(&path)
+        let mut ids = infos.get_path_ids(&path);
+        ids.next()
+    }
+
+    /// Returns all active untyped asset IDs for the given path, if the assets at the given path have already started loading,
+    /// or are still "alive".
+    /// Multiple IDs will be returned in the event that a single path is used by multiple [`AssetLoader`]'s.
+    pub fn get_path_ids<'a>(&self, path: impl Into<AssetPath<'a>>) -> Vec<UntypedAssetId> {
+        let infos = self.data.infos.read();
+        let path = path.into();
+        infos.get_path_ids(&path).collect()
     }
 
     /// Returns an active untyped handle for the given path, if the asset at the given path has already started loading,
     /// or is still "alive".
+    /// Returns the first handle in the event of multiple assets being registered against a single path.
+    ///
+    /// # See also
+    /// [`get_handles_untyped`][Self::get_handles_untyped] for all handles.
     pub fn get_handle_untyped<'a>(&self, path: impl Into<AssetPath<'a>>) -> Option<UntypedHandle> {
         let infos = self.data.infos.read();
         let path = path.into();
-        infos.get_path_handle(&path)
+        let mut handles = infos.get_path_handles(&path);
+        handles.next()
+    }
+
+    /// Returns all active untyped handles for the given path, if the assets at the given path have already started loading,
+    /// or are still "alive".
+    /// Multiple handles will be returned in the event that a single path is used by multiple [`AssetLoader`]'s.
+    pub fn get_handles_untyped<'a>(&self, path: impl Into<AssetPath<'a>>) -> Vec<UntypedHandle> {
+        let infos = self.data.infos.read();
+        let path = path.into();
+        infos.get_path_handles(&path).collect()
+    }
+
+    /// Returns an active untyped handle for the given path and [`TypeId`], if the asset at the given path has already started loading,
+    /// or is still "alive".
+    pub fn get_path_and_type_id_handle(
+        &self,
+        path: &AssetPath,
+        type_id: TypeId,
+    ) -> Option<UntypedHandle> {
+        let infos = self.data.infos.read();
+        let path = path.into();
+        infos.get_path_and_type_id_handle(&path, type_id)
     }
 
     /// Returns the path for the given `id`, if it has one.
@@ -844,15 +938,15 @@ impl AssetServer {
     /// real loader is added.
     pub fn preregister_loader<L: AssetLoader>(&self, extensions: &[&str]) {
         let mut loaders = self.data.loaders.write();
-        let loader_index = loaders.values.len();
+        let loader_index = TypeId::of::<L::Asset>();
         let type_name = std::any::type_name::<L>();
         loaders
             .preregistered_loaders
             .insert(type_name, loader_index);
-        loaders.type_name_to_index.insert(type_name, loader_index);
+        loaders.type_name_to_type_id.insert(type_name, loader_index);
         for extension in extensions {
             if loaders
-                .extension_to_index
+                .extension_to_type_id
                 .insert(extension.to_string(), loader_index)
                 .is_some()
             {
@@ -862,8 +956,8 @@ impl AssetServer {
         let (mut sender, receiver) = async_broadcast::broadcast(1);
         sender.set_overflow(true);
         loaders
-            .values
-            .push(MaybeAssetLoader::Pending { sender, receiver });
+            .type_id_to_loader
+            .insert(loader_index, MaybeAssetLoader::Pending { sender, receiver });
     }
 
     /// Retrieve a handle for the given path. This will create a handle (and [`AssetInfo`]) if it does not exist
@@ -885,6 +979,7 @@ impl AssetServer {
     pub(crate) async fn get_meta_loader_and_reader<'a>(
         &'a self,
         asset_path: &'a AssetPath<'_>,
+        asset_type_id: Option<TypeId>,
     ) -> Result<
         (
             Box<dyn AssetMetaDyn>,
@@ -944,19 +1039,58 @@ impl AssetServer {
                     Ok((meta, loader, reader))
                 }
                 Err(AssetReaderError::NotFound(_)) => {
-                    let loader = self.get_path_asset_loader(asset_path).await?;
+                    let loader = self.resolve_loader(asset_path, asset_type_id).await?;
+
                     let meta = loader.default_meta();
                     Ok((meta, loader, reader))
                 }
                 Err(err) => Err(err.into()),
             }
         } else {
-            let loader = self.get_path_asset_loader(asset_path).await?;
+            let loader = self.resolve_loader(asset_path, asset_type_id).await?;
+
             let meta = loader.default_meta();
             Ok((meta, loader, reader))
         }
     }
 
+    /// Selects an [`AssetLoader`] for the provided path and (optional) [`Asset`] [`TypeId`].
+    /// Prefers [`TypeId`], and falls back to reading the file extension in the provided [`AssetPath`] otherwise.
+    async fn resolve_loader<'a>(
+        &'a self,
+        asset_path: &'a AssetPath<'_>,
+        asset_type_id: Option<TypeId>,
+    ) -> Result<Arc<dyn ErasedAssetLoader>, MissingAssetLoaderForExtensionError> {
+        let loader = 'type_resolution: {
+            let Some(type_id) = asset_type_id else {
+                // If not provided an asset_type_id, type inference is broken
+                break 'type_resolution None;
+            };
+
+            let None = asset_path.label() else {
+                // Labelled sub-assets could be any type, not just the one registered for the loader
+                break 'type_resolution None;
+            };
+
+            let Ok(loader) = self.get_asset_loader_with_asset_type_id(type_id).await else {
+                bevy_log::warn!(
+                    "Could not load asset via type_id: no asset loader registered for {:?}",
+                    type_id
+                );
+                break 'type_resolution None;
+            };
+
+            Some(loader)
+        };
+
+        let loader = match loader {
+            Some(loader) => loader,
+            None => self.get_path_asset_loader(asset_path).await?,
+        };
+
+        Ok(loader)
+    }
+
     pub(crate) async fn load_with_meta_loader_and_reader(
         &self,
         asset_path: &AssetPath<'_>,
@@ -1045,9 +1179,9 @@ pub fn handle_internal_asset_events(world: &mut World) {
                 current_folder = parent.to_path_buf();
                 let parent_asset_path =
                     AssetPath::from(current_folder.clone()).with_source(source.clone());
-                if let Some(folder_handle) = infos.get_path_handle(&parent_asset_path) {
+                for folder_handle in infos.get_path_handles(&parent_asset_path) {
                     info!("Reloading folder {parent_asset_path} because the content has changed");
-                    server.load_folder_internal(folder_handle.id(), parent_asset_path);
+                    server.load_folder_internal(folder_handle.id(), parent_asset_path.clone());
                 }
             }
         };
@@ -1104,10 +1238,10 @@ pub fn handle_internal_asset_events(world: &mut World) {
 
 #[derive(Default)]
 pub(crate) struct AssetLoaders {
-    values: Vec<MaybeAssetLoader>,
-    extension_to_index: HashMap<String, usize>,
-    type_name_to_index: HashMap<&'static str, usize>,
-    preregistered_loaders: HashMap<&'static str, usize>,
+    type_id_to_loader: HashMap<TypeId, MaybeAssetLoader>,
+    extension_to_type_id: HashMap<String, TypeId>,
+    type_name_to_type_id: HashMap<&'static str, TypeId>,
+    preregistered_loaders: HashMap<&'static str, TypeId>,
 }
 
 #[derive(Clone)]
@@ -1190,6 +1324,8 @@ pub enum AssetLoadError {
     #[error(transparent)]
     MissingAssetLoaderForTypeName(#[from] MissingAssetLoaderForTypeNameError),
     #[error(transparent)]
+    MissingAssetLoaderForTypeIdError(#[from] MissingAssetLoaderForTypeIdError),
+    #[error(transparent)]
     AssetReaderError(#[from] AssetReaderError),
     #[error(transparent)]
     MissingAssetSourceError(#[from] MissingAssetSourceError),
@@ -1238,6 +1374,13 @@ pub struct MissingAssetLoaderForTypeNameError {
     type_name: String,
 }
 
+/// An error that occurs when an [`AssetLoader`] is not registered for a given [`Asset`] [`TypeId`].
+#[derive(Error, Debug, Clone)]
+#[error("no `AssetLoader` found with the ID '{type_id:?}'")]
+pub struct MissingAssetLoaderForTypeIdError {
+    pub type_id: TypeId,
+}
+
 fn format_missing_asset_ext(exts: &[String]) -> String {
     if !exts.is_empty() {
         format!(

examples/asset/custom_asset.rs

@@ -53,12 +53,52 @@ impl AssetLoader for CustomAssetLoader {
     }
 }
 
+#[derive(Asset, TypePath, Debug)]
+pub struct Blob {
+    pub bytes: Vec<u8>,
+}
+
+#[derive(Default)]
+pub struct BlobAssetLoader;
+
+/// Possible errors that can be produced by [`CustomAssetLoader`]
+#[non_exhaustive]
+#[derive(Debug, Error)]
+pub enum BlobAssetLoaderError {
+    /// An [IO](std::io) Error
+    #[error("Could not load file: {0}")]
+    Io(#[from] std::io::Error),
+}
+
+impl AssetLoader for BlobAssetLoader {
+    type Asset = Blob;
+    type Settings = ();
+    type Error = BlobAssetLoaderError;
+
+    fn load<'a>(
+        &'a self,
+        reader: &'a mut Reader,
+        _settings: &'a (),
+        _load_context: &'a mut LoadContext,
+    ) -> BoxedFuture<'a, Result<Self::Asset, Self::Error>> {
+        Box::pin(async move {
+            info!("Loading Blob...");
+            let mut bytes = Vec::new();
+            reader.read_to_end(&mut bytes).await?;
+
+            Ok(Blob { bytes })
+        })
+    }
+}
+
 fn main() {
     App::new()
         .add_plugins(DefaultPlugins)
         .init_resource::<State>()
         .init_asset::<CustomAsset>()
+        .init_asset::<Blob>()
         .init_asset_loader::<CustomAssetLoader>()
+        .init_asset_loader::<BlobAssetLoader>()
         .add_systems(Startup, setup)
         .add_systems(Update, print_on_load)
         .run();
@@ -67,19 +107,55 @@ fn main() {
 #[derive(Resource, Default)]
 struct State {
     handle: Handle<CustomAsset>,
+    other_handle: Handle<CustomAsset>,
+    blob: Handle<Blob>,
     printed: bool,
 }
 
 fn setup(mut state: ResMut<State>, asset_server: Res<AssetServer>) {
+    // Recommended way to load an asset
     state.handle = asset_server.load("data/asset.custom");
+
+    // File extensions are optional, but are recommended for project management and last-resort inference
+    state.other_handle = asset_server.load("data/asset_no_extension");
+
+    // Will use BlobAssetLoader instead of CustomAssetLoader thanks to type inference
+    state.blob = asset_server.load("data/asset.custom");
 }
 
-fn print_on_load(mut state: ResMut<State>, custom_assets: Res<Assets<CustomAsset>>) {
+fn print_on_load(
+    mut state: ResMut<State>,
+    custom_assets: Res<Assets<CustomAsset>>,
+    blob_assets: Res<Assets<Blob>>,
+) {
     let custom_asset = custom_assets.get(&state.handle);
-    if state.printed || custom_asset.is_none() {
+    let other_custom_asset = custom_assets.get(&state.other_handle);
+    let blob = blob_assets.get(&state.blob);
+
+    // Can't print results if the assets aren't ready
+    if state.printed {
+        return;
+    }
+
+    if custom_asset.is_none() {
+        info!("Custom Asset Not Ready");
+        return;
+    }
+
+    if other_custom_asset.is_none() {
+        info!("Other Custom Asset Not Ready");
+        return;
+    }
+
+    if blob.is_none() {
+        info!("Blob Not Ready");
         return;
     }
 
     info!("Custom asset loaded: {:?}", custom_asset.unwrap());
+    info!("Custom asset loaded: {:?}", other_custom_asset.unwrap());
+    info!("Blob Size: {:?} Bytes", blob.unwrap().bytes.len());
+
+    // Once printed, we won't print again
     state.printed = true;
 }