Allow using short type names for asset processors. (#21339)

# Objective

- Previously, asset processors needed to be **fully specified**. This
meant writing met files by hand was incredibly cumbersome.
- In addition, using `core::any::type_name` is generally undesirable
since it is only intended for debugging.

## Solution

- Require `TypePath` impl on `AssetLoader`, `AssetTransformer`,
`AssetSaver`, and `AssetProcessor`.
- Register loaders and processors by their `TypePath::type_path`. This
makes the path format stable.
- Additionally register the processors by their
`TypePath::short_type_path`, and ensure there are no other processors
with the same `short_type_path`. If a user tries to use an ambiguous
short type path, we list out all full type paths.

Note: I left doing this with asset loaders as a future PR. There's more
complexity there (since we have to deal with pre-registering asset
loaders), and this seems like the bigger "bang for our buck".

## Testing

- I ran the asset_processing example. No change.
- I changed the asset processing example to use the short type path. It
still behaved as expected.
- I created a new AssetTransformer in
`asset_processing::sneaky::CoolTextTransformer` and a new processor that
looked identical to the regular one (but using the sneaky transformer).
It printed an error, listing out the full paths of both processors!

---------

Co-authored-by: Carter Anderson <[email protected]>

Author: andriyDev

crates/bevy_animation/src/graph.rs

@@ -19,7 +19,7 @@ use bevy_ecs::{
     system::{Res, ResMut},
 };
 use bevy_platform::collections::HashMap;
-use bevy_reflect::{prelude::ReflectDefault, Reflect};
+use bevy_reflect::{prelude::ReflectDefault, Reflect, TypePath};
 use derive_more::derive::From;
 use petgraph::{
     graph::{DiGraph, NodeIndex},
@@ -238,7 +238,7 @@ pub enum AnimationNodeType {
 ///
 /// The canonical extension for [`AnimationGraph`]s is `.animgraph.ron`. Plain
 /// `.animgraph` is supported as well.
-#[derive(Default)]
+#[derive(Default, TypePath)]
 pub struct AnimationGraphAssetLoader;
 
 /// Errors that can occur when serializing animation graphs to RON.

crates/bevy_asset/src/lib.rs

@@ -769,7 +769,7 @@ mod tests {
         pub sub_texts: Vec<String>,
     }
 
-    #[derive(Default)]
+    #[derive(Default, TypePath)]
     pub struct CoolTextLoader;
 
     #[derive(Error, Debug)]
@@ -1934,6 +1934,7 @@ mod tests {
             .init_asset::<SubText>()
             .register_asset_loader(CoolTextLoader);
 
+        #[derive(TypePath)]
         struct NestedLoadOfSubassetLoader;
 
         impl AssetLoader for NestedLoadOfSubassetLoader {
@@ -1986,6 +1987,7 @@ mod tests {
         // Extension "rsp" for Recursive Self Path (RSP).
         dir.insert_asset_text(Path::new("abc.rsp"), "");
 
+        #[derive(TypePath)]
         struct ImmediateSelfLoader;
 
         impl AssetLoader for ImmediateSelfLoader {
@@ -2040,6 +2042,7 @@ mod tests {
 
         dir.insert_asset_text(Path::new("abc.rsp"), "");
 
+        #[derive(TypePath)]
         struct ImmediateSelfLoader;
 
         impl AssetLoader for ImmediateSelfLoader {
@@ -2103,6 +2106,8 @@ mod tests {
 
         #[derive(Asset, TypePath)]
         pub struct TestAsset(Handle<TestAsset>);
+
+        #[derive(TypePath)]
         struct DeferredSelfLoader;
 
         impl AssetLoader for DeferredSelfLoader {
@@ -2186,6 +2191,7 @@ mod tests {
 
         dir.insert_asset_text(Path::new("abc.rsp"), "");
 
+        #[derive(TypePath)]
         struct ReadBytesSelfLoader;
 
         impl AssetLoader for ReadBytesSelfLoader {
@@ -2270,6 +2276,8 @@ mod tests {
 
         #[derive(Asset, TypePath)]
         pub struct TestAssetUD(Handle<crate::LoadedUntypedAsset>);
+
+        #[derive(TypePath)]
         struct ImmediateSelfLoader;
 
         impl AssetLoader for ImmediateSelfLoader {
@@ -2531,6 +2539,7 @@ mod tests {
     // Note: we can't just use the GatedReader, since currently we hold the handle until after
     // we've selected the reader. The GatedReader blocks this process, so we need to wait until
     // we gate in the loader instead.
+    #[derive(TypePath)]
     struct GatedLoader {
         in_loader_sender: Sender<()>,
         gate_receiver: Receiver<()>,
@@ -2834,6 +2843,7 @@ mod tests {
         #[derive(Serialize, Deserialize, Default)]
         struct U8LoaderSettings(u8);
 
+        #[derive(TypePath)]
         struct U8Loader;
 
         impl AssetLoader for U8Loader {
@@ -2912,6 +2922,7 @@ mod tests {
         let (mut app, dir) = create_app();
         dir.insert_asset(Path::new("test.txt"), &[]);
 
+        #[derive(TypePath)]
         struct TwoSubassetLoader;
 
         impl AssetLoader for TwoSubassetLoader {
@@ -2952,6 +2963,7 @@ mod tests {
     }
 
     /// A loader that immediately returns a [`TestAsset`].
+    #[derive(TypePath)]
     struct TrivialLoader;
 
     impl AssetLoader for TrivialLoader {
@@ -3030,6 +3042,7 @@ mod tests {
         #[derive(Asset, TypePath)]
         struct DeferredNested(Handle<TestAsset>);
 
+        #[derive(TypePath)]
         struct DeferredNestedLoader;
 
         impl AssetLoader for DeferredNestedLoader {
@@ -3057,6 +3070,7 @@ mod tests {
         #[derive(Asset, TypePath)]
         struct ImmediateNested(Handle<TestAsset>);
 
+        #[derive(TypePath)]
         struct ImmediateNestedLoader;
 
         impl AssetLoader for ImmediateNestedLoader {

crates/bevy_asset/src/loader.rs

@@ -14,6 +14,7 @@ use alloc::{
 use atomicow::CowArc;
 use bevy_ecs::{error::BevyError, world::World};
 use bevy_platform::collections::{HashMap, HashSet};
+use bevy_reflect::TypePath;
 use bevy_tasks::{BoxedFuture, ConditionalSendFuture};
 use core::any::{Any, TypeId};
 use downcast_rs::{impl_downcast, Downcast};
@@ -28,7 +29,7 @@ use thiserror::Error;
 /// This trait is generally used in concert with [`AssetReader`](crate::io::AssetReader) to load assets from a byte source.
 ///
 /// For a complementary version of this trait that can save assets, see [`AssetSaver`](crate::saver::AssetSaver).
-pub trait AssetLoader: Send + Sync + 'static {
+pub trait AssetLoader: TypePath + Send + Sync + 'static {
     /// The top level [`Asset`] loaded by this [`AssetLoader`].
     type Asset: Asset;
     /// The settings type used by this [`AssetLoader`].
@@ -66,8 +67,8 @@ pub trait ErasedAssetLoader: Send + Sync + 'static {
     fn deserialize_meta(&self, meta: &[u8]) -> Result<Box<dyn AssetMetaDyn>, DeserializeMetaError>;
     /// Returns the default meta value for the [`AssetLoader`] (erased as [`Box<dyn AssetMetaDyn>`]).
     fn default_meta(&self) -> Box<dyn AssetMetaDyn>;
-    /// Returns the type name of the [`AssetLoader`].
-    fn type_name(&self) -> &'static str;
+    /// Returns the type path of the [`AssetLoader`].
+    fn type_path(&self) -> &'static str;
     /// Returns the [`TypeId`] of the [`AssetLoader`].
     fn type_id(&self) -> TypeId;
     /// Returns the type name of the top-level [`Asset`] loaded by the [`AssetLoader`].
@@ -111,13 +112,13 @@ where
 
     fn default_meta(&self) -> Box<dyn AssetMetaDyn> {
         Box::new(AssetMeta::<L, ()>::new(crate::meta::AssetAction::Load {
-            loader: self.type_name().to_string(),
+            loader: self.type_path().to_string(),
             settings: L::Settings::default(),
         }))
     }
 
-    fn type_name(&self) -> &'static str {
-        core::any::type_name::<L>()
+    fn type_path(&self) -> &'static str {
+        L::type_path()
     }
 
     fn type_id(&self) -> TypeId {

crates/bevy_asset/src/loader_builders.rs

@@ -503,7 +503,7 @@ impl NestedLoader<'_, '_, StaticTyped, Immediate<'_, '_>> {
                             path,
                             requested: TypeId::of::<A>(),
                             actual_asset_name: loader.asset_type_name(),
-                            loader_name: loader.type_name(),
+                            loader_name: loader.type_path(),
                         },
                     })
             })