Removed anyhow (bevyengine#10003)

# Objective

- Fixes bevyengine#8140

## Solution

- Added Explicit Error Typing for `AssetLoader` and `AssetSaver`, which
were the last instances of `anyhow` in use across Bevy.

---

## Changelog

- Added an associated type `Error` to `AssetLoader` and `AssetSaver` for
use with the `load` and `save` methods respectively.
- Changed `ErasedAssetLoader` and `ErasedAssetSaver` `load` and `save`
methods to use `Box<dyn Error + Send + Sync + 'static>` to allow for
arbitrary `Error` types from the non-erased trait variants. Note the
strict requirements match the pre-existing requirements around
`anyhow::Error`.

## Migration Guide

- `anyhow` is no longer exported by `bevy_asset`; Add it to your own
project (if required).
- `AssetLoader` and `AssetSaver` have an associated type `Error`; Define
an appropriate error type (e.g., using `thiserror`), or use a pre-made
error type (e.g., `anyhow::Error`). Note that using `anyhow::Error` is a
drop-in replacement.
- `AssetLoaderError` has been removed; Define a new error type, or use
an alternative (e.g., `anyhow::Error`)
- All the first-party `AssetLoader`'s and `AssetSaver`'s now return
relevant (and narrow) error types instead of a single ambiguous type;
Match over the specific error type, or encapsulate (`Box<dyn>`,
`thiserror`, `anyhow`, etc.)

## Notes

A simpler PR to resolve this issue would simply define a Bevy `Error`
type defined as `Box<dyn std::error::Error + Send + Sync + 'static>`,
but I think this type of error handling should be discouraged when
possible. Since only 2 traits required the use of `anyhow`, it isn't a
substantive body of work to solidify these error types, and remove
`anyhow` entirely. End users are still encouraged to use `anyhow` if
that is their preferred error handling style. Arguably, adding the
`Error` associated type gives more freedom to end-users to decide
whether they want more or less explicit error handling (`anyhow` vs
`thiserror`).

As an aside, I didn't perform any testing on Android or WASM. CI passed
locally, but there may be mistakes for those platforms I missed.

Cargo.toml

@@ -252,7 +252,6 @@ bevy_dylib = { path = "crates/bevy_dylib", version = "0.12.0-dev", default-featu
 bevy_internal = { path = "crates/bevy_internal", version = "0.12.0-dev", default-features = false }
 
 [dev-dependencies]
-anyhow = "1.0.4"
 rand = "0.8.0"
 ron = "0.8.0"
 serde = { version = "1", features = ["derive"] }

crates/bevy_asset/Cargo.toml

@@ -23,7 +23,6 @@ bevy_reflect = { path = "../bevy_reflect", version = "0.12.0-dev" }
 bevy_tasks = { path = "../bevy_tasks", version = "0.12.0-dev" }
 bevy_utils = { path = "../bevy_utils", version = "0.12.0-dev" }
 
-anyhow = "1.0"
 async-broadcast = "0.5"
 async-fs = "1.5"
 async-lock = "2.8"

crates/bevy_asset/src/io/android.rs

@@ -2,7 +2,6 @@ use crate::io::{
     get_meta_path, AssetReader, AssetReaderError, AssetWatcher, EmptyPathStream, PathStream,
     Reader, VecReader,
 };
-use anyhow::Result;
 use bevy_log::error;
 use bevy_utils::BoxedFuture;
 use std::{ffi::CString, path::Path};

crates/bevy_asset/src/io/file/file_watcher.rs

@@ -1,5 +1,4 @@
 use crate::io::{AssetSourceEvent, AssetWatcher};
-use anyhow::Result;
 use bevy_log::error;
 use bevy_utils::Duration;
 use crossbeam_channel::Sender;

crates/bevy_asset/src/io/file/mod.rs

@@ -5,7 +5,6 @@ use crate::io::{
     get_meta_path, AssetReader, AssetReaderError, AssetWatcher, AssetWriter, AssetWriterError,
     PathStream, Reader, Writer,
 };
-use anyhow::Result;
 use async_fs::{read_dir, File};
 use bevy_utils::BoxedFuture;
 use futures_lite::StreamExt;

crates/bevy_asset/src/io/gated.rs

@@ -1,5 +1,4 @@
 use crate::io::{AssetReader, AssetReaderError, PathStream, Reader};
-use anyhow::Result;
 use bevy_utils::{BoxedFuture, HashMap};
 use crossbeam_channel::{Receiver, Sender};
 use parking_lot::RwLock;

crates/bevy_asset/src/io/memory.rs

@@ -1,5 +1,4 @@
 use crate::io::{AssetReader, AssetReaderError, PathStream, Reader};
-use anyhow::Result;
 use bevy_utils::{BoxedFuture, HashMap};
 use futures_io::AsyncRead;
 use futures_lite::{ready, Stream};

crates/bevy_asset/src/io/processor_gated.rs

@@ -3,7 +3,6 @@ use crate::{
     processor::{AssetProcessorData, ProcessStatus},
     AssetPath,
 };
-use anyhow::Result;
 use async_lock::RwLockReadGuardArc;
 use bevy_log::trace;
 use bevy_utils::BoxedFuture;

crates/bevy_asset/src/io/wasm.rs

@@ -2,7 +2,6 @@ use crate::io::{
     get_meta_path, AssetReader, AssetReaderError, AssetWatcher, EmptyPathStream, PathStream,
     Reader, VecReader,
 };
-use anyhow::Result;
 use bevy_log::error;
 use bevy_utils::BoxedFuture;
 use js_sys::{Uint8Array, JSON};

crates/bevy_asset/src/lib.rs

@@ -35,7 +35,6 @@ pub use path::*;
 pub use reflect::*;
 pub use server::*;
 
-pub use anyhow;
 pub use bevy_utils::BoxedFuture;
 
 use crate::{
@@ -428,8 +427,9 @@ mod tests {
             Reader,
         },
         loader::{AssetLoader, LoadContext},
-        Asset, AssetApp, AssetEvent, AssetId, AssetPlugin, AssetProvider, AssetProviders,
-        AssetServer, Assets, DependencyLoadState, LoadState, RecursiveDependencyLoadState,
+        Asset, AssetApp, AssetEvent, AssetId, AssetPath, AssetPlugin, AssetProvider,
+        AssetProviders, AssetServer, Assets, DependencyLoadState, LoadState,
+        RecursiveDependencyLoadState,
     };
     use bevy_app::{App, Update};
     use bevy_core::TaskPoolPlugin;
@@ -444,6 +444,7 @@ mod tests {
     use futures_lite::AsyncReadExt;
     use serde::{Deserialize, Serialize};
     use std::path::Path;
+    use thiserror::Error;
 
     #[derive(Asset, TypePath, Debug)]
     pub struct CoolText {
@@ -471,24 +472,40 @@ mod tests {
     #[derive(Default)]
     struct CoolTextLoader;
 
+    #[derive(Error, Debug)]
+    enum CoolTextLoaderError {
+        #[error("Could not load dependency: {dependency}")]
+        CannotLoadDependency { dependency: AssetPath<'static> },
+        #[error("A RON error occurred during loading")]
+        RonSpannedError(#[from] ron::error::SpannedError),
+        #[error("An IO error occurred during loading")]
+        Io(#[from] std::io::Error),
+    }
+
     impl AssetLoader for CoolTextLoader {
         type Asset = CoolText;
 
         type Settings = ();
 
+        type Error = CoolTextLoaderError;
+
         fn load<'a>(
             &'a self,
             reader: &'a mut Reader,
             _settings: &'a Self::Settings,
             load_context: &'a mut LoadContext,
-        ) -> BoxedFuture<'a, Result<Self::Asset, anyhow::Error>> {
+        ) -> BoxedFuture<'a, Result<Self::Asset, Self::Error>> {
             Box::pin(async move {
                 let mut bytes = Vec::new();
                 reader.read_to_end(&mut bytes).await?;
                 let mut ron: CoolTextRon = ron::de::from_bytes(&bytes)?;
                 let mut embedded = String::new();
                 for dep in ron.embedded_dependencies {
-                    let loaded = load_context.load_direct(&dep).await?;
+                    let loaded = load_context.load_direct(&dep).await.map_err(|_| {
+                        Self::Error::CannotLoadDependency {
+                            dependency: dep.into(),
+                        }
+                    })?;
                     let cool = loaded.get::<CoolText>().unwrap();
                     embedded.push_str(&cool.text);
                 }

crates/bevy_asset/src/loader.rs

@@ -26,13 +26,15 @@ pub trait AssetLoader: Send + Sync + 'static {
     type Asset: crate::Asset;
     /// The settings type used by this [`AssetLoader`].
     type Settings: Settings + Default + Serialize + for<'a> Deserialize<'a>;
+    /// The type of [error](`std::error::Error`) which could be encountered by this loader.
+    type Error: std::error::Error + Send + Sync + 'static;
     /// Asynchronously loads [`AssetLoader::Asset`] (and any other labeled assets) from the bytes provided by [`Reader`].
     fn load<'a>(
         &'a self,
         reader: &'a mut Reader,
         settings: &'a Self::Settings,
         load_context: &'a mut LoadContext,
-    ) -> BoxedFuture<'a, Result<Self::Asset, anyhow::Error>>;
+    ) -> 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];
@@ -46,7 +48,10 @@ pub trait ErasedAssetLoader: Send + Sync + 'static {
         reader: &'a mut Reader,
         meta: Box<dyn AssetMetaDyn>,
         load_context: LoadContext<'a>,
-    ) -> BoxedFuture<'a, Result<ErasedLoadedAsset, AssetLoaderError>>;
+    ) -> BoxedFuture<
+        'a,
+        Result<ErasedLoadedAsset, Box<dyn std::error::Error + Send + Sync + 'static>>,
+    >;
 
     /// Returns a list of extensions supported by this asset loader, without the preceding dot.
     fn extensions(&self) -> &[&str];
@@ -64,17 +69,6 @@ pub trait ErasedAssetLoader: Send + Sync + 'static {
     fn asset_type_id(&self) -> TypeId;
 }
 
-/// An error encountered during [`AssetLoader::load`].
-#[derive(Error, Debug)]
-pub enum AssetLoaderError {
-    /// Any error that occurs during load.
-    #[error(transparent)]
-    Load(#[from] anyhow::Error),
-    /// A failure to deserialize metadata during load.
-    #[error(transparent)]
-    DeserializeMeta(#[from] DeserializeMetaError),
-}
-
 impl<L> ErasedAssetLoader for L
 where
     L: AssetLoader + Send + Sync,
@@ -85,7 +79,10 @@ where
         reader: &'a mut Reader,
         meta: Box<dyn AssetMetaDyn>,
         mut load_context: LoadContext<'a>,
-    ) -> BoxedFuture<'a, Result<ErasedLoadedAsset, AssetLoaderError>> {
+    ) -> BoxedFuture<
+        'a,
+        Result<ErasedLoadedAsset, Box<dyn std::error::Error + Send + Sync + 'static>>,
+    > {
         Box::pin(async move {
             let settings = meta
                 .loader_settings()

crates/bevy_asset/src/meta.rs

@@ -193,12 +193,13 @@ impl VisitAssetDependencies for () {
 impl AssetLoader for () {
     type Asset = ();
     type Settings = ();
+    type Error = std::io::Error;
     fn load<'a>(
         &'a self,
         _reader: &'a mut crate::io::Reader,
         _settings: &'a Self::Settings,
         _load_context: &'a mut crate::LoadContext,
-    ) -> bevy_utils::BoxedFuture<'a, Result<Self::Asset, anyhow::Error>> {
+    ) -> bevy_utils::BoxedFuture<'a, Result<Self::Asset, Self::Error>> {
         unreachable!();
     }
 

crates/bevy_asset/src/processor/mod.rs

@@ -13,8 +13,8 @@ use crate::{
         get_asset_hash, get_full_asset_hash, AssetAction, AssetActionMinimal, AssetHash, AssetMeta,
         AssetMetaDyn, AssetMetaMinimal, ProcessedInfo, ProcessedInfoMinimal,
     },
-    AssetLoadError, AssetLoaderError, AssetPath, AssetServer, DeserializeMetaError,
-    LoadDirectError, MissingAssetLoaderForExtensionError, CANNOT_WATCH_ERROR_MESSAGE,
+    AssetLoadError, AssetPath, AssetServer, DeserializeMetaError,
+    MissingAssetLoaderForExtensionError, CANNOT_WATCH_ERROR_MESSAGE,
 };
 use bevy_ecs::prelude::*;
 use bevy_log::{debug, error, trace, warn};
@@ -1130,20 +1130,17 @@ impl ProcessorAssetInfos {
             Err(err) => {
                 error!("Failed to process asset {:?}: {:?}", asset_path, err);
                 // if this failed because a dependency could not be loaded, make sure it is reprocessed if that dependency is reprocessed
-                if let ProcessError::AssetLoadError(AssetLoadError::AssetLoaderError {
-                    error: AssetLoaderError::Load(loader_error),
-                    ..
+                if let ProcessError::AssetLoadError(AssetLoadError::CannotLoadDependency {
+                    path: dependency,
                 }) = err
                 {
-                    if let Some(error) = loader_error.downcast_ref::<LoadDirectError>() {
-                        let info = self.get_mut(&asset_path).expect("info should exist");
-                        info.processed_info = Some(ProcessedInfo {
-                            hash: AssetHash::default(),
-                            full_hash: AssetHash::default(),
-                            process_dependencies: vec![],
-                        });
-                        self.add_dependant(&error.dependency, asset_path.to_owned());
-                    }
+                    let info = self.get_mut(&asset_path).expect("info should exist");
+                    info.processed_info = Some(ProcessedInfo {
+                        hash: AssetHash::default(),
+                        full_hash: AssetHash::default(),
+                        process_dependencies: vec![],
+                    });
+                    self.add_dependant(&dependency, asset_path.to_owned());
                 }
 
                 let info = self.get_mut(&asset_path).expect("info should exist");

crates/bevy_asset/src/processor/process.rs

@@ -91,7 +91,7 @@ pub enum ProcessError {
     #[error("The wrong meta type was passed into a processor. This is probably an internal implementation error.")]
     WrongMetaType,
     #[error("Encountered an error while saving the asset: {0}")]
-    AssetSaveError(anyhow::Error),
+    AssetSaveError(#[from] Box<dyn std::error::Error + Send + Sync + 'static>),
     #[error("Assets without extensions are not supported.")]
     ExtensionRequired,
 }
@@ -122,7 +122,7 @@ impl<Loader: AssetLoader, Saver: AssetSaver<Asset = Loader::Asset>> Process
                 .saver
                 .save(writer, saved_asset, &settings.saver_settings)
                 .await
-                .map_err(ProcessError::AssetSaveError)?;
+                .map_err(|error| ProcessError::AssetSaveError(Box::new(error)))?;
             Ok(output_settings)
         })
     }

crates/bevy_asset/src/saver.rs

@@ -7,9 +7,14 @@ use std::ops::Deref;
 /// Saves an [`Asset`] of a given [`AssetSaver::Asset`] type. [`AssetSaver::OutputLoader`] will then be used to load the saved asset
 /// in the final deployed application. The saver should produce asset bytes in a format that [`AssetSaver::OutputLoader`] can read.
 pub trait AssetSaver: Send + Sync + 'static {
+    /// The top level [`Asset`] saved by this [`AssetSaver`].
     type Asset: Asset;
+    /// The settings type used by this [`AssetSaver`].
     type Settings: Settings + Default + Serialize + for<'a> Deserialize<'a>;
+    /// The type of [`AssetLoader`] used to load this [`Asset`]
     type OutputLoader: AssetLoader;
+    /// The type of [error](`std::error::Error`) which could be encountered by this saver.
+    type Error: std::error::Error + Send + Sync + 'static;
 
     /// Saves the given runtime [`Asset`] by writing it to a byte format using `writer`. The passed in `settings` can influence how the
     /// `asset` is saved.  
@@ -18,7 +23,7 @@ pub trait AssetSaver: Send + Sync + 'static {
         writer: &'a mut Writer,
         asset: SavedAsset<'a, Self::Asset>,
         settings: &'a Self::Settings,
-    ) -> BoxedFuture<'a, Result<<Self::OutputLoader as AssetLoader>::Settings, anyhow::Error>>;
+    ) -> BoxedFuture<'a, Result<<Self::OutputLoader as AssetLoader>::Settings, Self::Error>>;
 }
 
 /// A type-erased dynamic variant of [`AssetSaver`] that allows callers to save assets without knowing the actual type of the [`AssetSaver`].
@@ -30,7 +35,7 @@ pub trait ErasedAssetSaver: Send + Sync + 'static {
         writer: &'a mut Writer,
         asset: &'a ErasedLoadedAsset,
         settings: &'a dyn Settings,
-    ) -> BoxedFuture<'a, Result<(), anyhow::Error>>;
+    ) -> BoxedFuture<'a, Result<(), Box<dyn std::error::Error + Send + Sync + 'static>>>;
 
     /// The type name of the [`AssetSaver`].
     fn type_name(&self) -> &'static str;
@@ -42,7 +47,7 @@ impl<S: AssetSaver> ErasedAssetSaver for S {
         writer: &'a mut Writer,
         asset: &'a ErasedLoadedAsset,
         settings: &'a dyn Settings,
-    ) -> BoxedFuture<'a, Result<(), anyhow::Error>> {
+    ) -> BoxedFuture<'a, Result<(), Box<dyn std::error::Error + Send + Sync + 'static>>> {
         Box::pin(async move {
             let settings = settings
                 .downcast_ref::<S::Settings>()

crates/bevy_asset/src/server/mod.rs

@@ -3,7 +3,7 @@ mod info;
 use crate::{
     folder::LoadedFolder,
     io::{AssetReader, AssetReaderError, AssetSourceEvent, AssetWatcher, Reader},
-    loader::{AssetLoader, AssetLoaderError, ErasedAssetLoader, LoadContext, LoadedAsset},
+    loader::{AssetLoader, ErasedAssetLoader, LoadContext, LoadedAsset},
     meta::{
         loader_settings_meta_transform, AssetActionMinimal, AssetMetaDyn, AssetMetaMinimal,
         MetaTransform, Settings,
@@ -666,11 +666,9 @@ impl AssetServer {
                     }
                 };
                 let loader = self.get_asset_loader_with_type_name(&loader_name).await?;
-                let meta = loader.deserialize_meta(&meta_bytes).map_err(|e| {
-                    AssetLoadError::AssetLoaderError {
+                let meta = loader.deserialize_meta(&meta_bytes).map_err(|_| {
+                    AssetLoadError::CannotLoadDependency {
                         path: asset_path.clone().into_owned(),
-                        loader: loader.type_name(),
-                        error: AssetLoaderError::DeserializeMeta(e),
                     }
                 })?;
 
@@ -698,13 +696,10 @@ impl AssetServer {
         let asset_path = asset_path.clone().into_owned();
         let load_context =
             LoadContext::new(self, asset_path.clone(), load_dependencies, populate_hashes);
-        loader.load(reader, meta, load_context).await.map_err(|e| {
-            AssetLoadError::AssetLoaderError {
-                loader: loader.type_name(),
-                path: asset_path,
-                error: e,
-            }
-        })
+        loader
+            .load(reader, meta, load_context)
+            .await
+            .map_err(|_| AssetLoadError::CannotLoadDependency { path: asset_path })
     }
 }
 
@@ -861,12 +856,8 @@ pub enum AssetLoadError {
     CannotLoadProcessedAsset { path: AssetPath<'static> },
     #[error("Asset '{path}' is configured to be ignored. It cannot be loaded.")]
     CannotLoadIgnoredAsset { path: AssetPath<'static> },
-    #[error("Asset '{path}' encountered an error in {loader}: {error}")]
-    AssetLoaderError {
-        path: AssetPath<'static>,
-        loader: &'static str,
-        error: AssetLoaderError,
-    },
+    #[error("Asset '{path}' is a dependency. It cannot be loaded directly.")]
+    CannotLoadDependency { path: AssetPath<'static> },
 }
 
 /// An error that occurs when an [`AssetLoader`] is not registered for a given extension.

crates/bevy_audio/src/audio_source.rs

@@ -1,5 +1,4 @@
 use bevy_asset::{
-    anyhow::Error,
     io::{AsyncReadExt, Reader},
     Asset, AssetLoader, LoadContext,
 };
@@ -42,13 +41,14 @@ pub struct AudioLoader;
 impl AssetLoader for AudioLoader {
     type Asset = AudioSource;
     type Settings = ();
+    type Error = std::io::Error;
 
     fn load<'a>(
         &'a self,
         reader: &'a mut Reader,
         _settings: &'a Self::Settings,
         _load_context: &'a mut LoadContext,
-    ) -> BoxedFuture<'a, Result<AudioSource, Error>> {
+    ) -> BoxedFuture<'a, Result<AudioSource, Self::Error>> {
         Box::pin(async move {
             let mut bytes = Vec::new();
             reader.read_to_end(&mut bytes).await?;