Derive Error for more error types (#10240)

# Objective

Align all error-like types to implement `Error`.

Fixes  #10176

## Solution

- Derive `Error` on more types
- Refactor instances of manual implementations that could be derived

This adds thiserror as a dependency to bevy_transform, which might
increase compilation time -- but I don't know of any situation where you
might only use that but not any other crate that pulls in bevy_utils.

The `contributors` example has a `LoadContributorsError` type, but as
it's an example I have not updated it. Doing that would mean either
having a `use bevy_internal::utils::thiserror::Error;` in an example
file, or adding `thiserror` as a dev-dependency to the main `bevy`
crate.

---

## Changelog

- All `…Error` types now implement the `Error` trait

crates/bevy_app/src/app.rs

@@ -8,7 +8,7 @@ use bevy_ecs::{
         ScheduleBuildSettings, ScheduleLabel,
     },
 };
-use bevy_utils::{intern::Interned, tracing::debug, HashMap, HashSet};
+use bevy_utils::{intern::Interned, thiserror::Error, tracing::debug, HashMap, HashSet};
 use std::{
     fmt::Debug,
     panic::{catch_unwind, resume_unwind, AssertUnwindSafe},
@@ -28,7 +28,9 @@ pub use bevy_utils::label::DynEq;
 /// A shorthand for `Interned<dyn AppLabel>`.
 pub type InternedAppLabel = Interned<dyn AppLabel>;
 
+#[derive(Debug, Error)]
 pub(crate) enum AppError {
+    #[error("duplicate plugin {plugin_name:?}")]
     DuplicatePlugin { plugin_name: String },
 }
 

crates/bevy_ecs/src/query/error.rs

@@ -1,41 +1,28 @@
-use std::fmt;
+use thiserror::Error;
 
 use crate::entity::Entity;
 
 /// An error that occurs when retrieving a specific [`Entity`]'s query result from [`Query`](crate::system::Query) or [`QueryState`](crate::query::QueryState).
 // TODO: return the type_name as part of this error
-#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+#[derive(Debug, PartialEq, Eq, Clone, Copy, Error)]
 pub enum QueryEntityError {
     /// The given [`Entity`]'s components do not match the query.
     ///
     /// Either it does not have a requested component, or it has a component which the query filters out.
+    #[error("The components of entity {0:?} do not match the query")]
     QueryDoesNotMatch(Entity),
     /// The given [`Entity`] does not exist.
+    #[error("The entity {0:?} does not exist")]
     NoSuchEntity(Entity),
     /// The [`Entity`] was requested mutably more than once.
     ///
     /// See [`QueryState::get_many_mut`](crate::query::QueryState::get_many_mut) for an example.
+    #[error("The entity {0:?} was requested mutably more than once")]
     AliasedMutability(Entity),
 }
 
-impl std::error::Error for QueryEntityError {}
-
-impl fmt::Display for QueryEntityError {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            QueryEntityError::QueryDoesNotMatch(_) => {
-                write!(f, "The given entity's components do not match the query.")
-            }
-            QueryEntityError::NoSuchEntity(_) => write!(f, "The requested entity does not exist."),
-            QueryEntityError::AliasedMutability(_) => {
-                write!(f, "The entity was requested mutably more than once.")
-            }
-        }
-    }
-}
-
 /// An error that occurs when retrieving a specific [`Entity`]'s component from a [`Query`](crate::system::Query).
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Debug, PartialEq, Eq, Error)]
 pub enum QueryComponentError {
     /// The [`Query`](crate::system::Query) does not have read access to the requested component.
     ///
@@ -66,6 +53,7 @@ pub enum QueryComponentError {
     /// }
     /// # bevy_ecs::system::assert_is_system(get_missing_read_access_error);
     /// ```
+    #[error("This query does not have read access to the requested component")]
     MissingReadAccess,
     /// The [`Query`](crate::system::Query) does not have write access to the requested component.
     ///
@@ -93,59 +81,24 @@ pub enum QueryComponentError {
     /// }
     /// # bevy_ecs::system::assert_is_system(get_missing_write_access_error);
     /// ```
+    #[error("This query does not have write access to the requested component")]
     MissingWriteAccess,
     /// The given [`Entity`] does not have the requested component.
+    #[error("The given entity does not have the requested component")]
     MissingComponent,
     /// The requested [`Entity`] does not exist.
+    #[error("The requested entity does not exist")]
     NoSuchEntity,
 }
 
-impl std::error::Error for QueryComponentError {}
-
-impl std::fmt::Display for QueryComponentError {
-    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
-        match self {
-            QueryComponentError::MissingReadAccess => {
-                write!(
-                    f,
-                    "This query does not have read access to the requested component."
-                )
-            }
-            QueryComponentError::MissingWriteAccess => {
-                write!(
-                    f,
-                    "This query does not have write access to the requested component."
-                )
-            }
-            QueryComponentError::MissingComponent => {
-                write!(f, "The given entity does not have the requested component.")
-            }
-            QueryComponentError::NoSuchEntity => {
-                write!(f, "The requested entity does not exist.")
-            }
-        }
-    }
-}
-
 /// An error that occurs when evaluating a [`Query`](crate::system::Query) or [`QueryState`](crate::query::QueryState) as a single expected result via
 /// [`get_single`](crate::system::Query::get_single) or [`get_single_mut`](crate::system::Query::get_single_mut).
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum QuerySingleError {
     /// No entity fits the query.
+    #[error("No entities fit the query {0}")]
     NoEntities(&'static str),
     /// Multiple entities fit the query.
+    #[error("Multiple entities fit the query {0}")]
     MultipleEntities(&'static str),
 }
-
-impl std::error::Error for QuerySingleError {}
-
-impl std::fmt::Display for QuerySingleError {
-    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
-        match self {
-            QuerySingleError::NoEntities(query) => write!(f, "No entities fit the query {query}"),
-            QuerySingleError::MultipleEntities(query) => {
-                write!(f, "Multiple entities fit the query {query}!")
-            }
-        }
-    }
-}

crates/bevy_ecs/src/system/system_registry.rs

@@ -3,6 +3,7 @@ use crate::system::{BoxedSystem, Command, IntoSystem};
 use crate::world::World;
 use crate::{self as bevy_ecs};
 use bevy_ecs_macros::Component;
+use thiserror::Error;
 
 /// A small wrapper for [`BoxedSystem`] that also keeps track whether or not the system has been initialized.
 #[derive(Component)]
@@ -197,15 +198,18 @@ impl Command for RunSystem {
 }
 
 /// An operation with stored systems failed.
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum RegisteredSystemError {
     /// A system was run by id, but no system with that id was found.
     ///
     /// Did you forget to register it?
+    #[error("System {0:?} was not registered")]
     SystemIdNotRegistered(SystemId),
     /// A system tried to run itself recursively.
+    #[error("System {0:?} tried to run itself recursively")]
     Recursive(SystemId),
     /// A system tried to remove itself.
+    #[error("System {0:?} tried to remove itself")]
     SelfRemove(SystemId),
 }
 

crates/bevy_render/src/render_asset.rs

@@ -6,10 +6,12 @@ use bevy_ecs::{
     schedule::SystemConfigs,
     system::{StaticSystemParam, SystemParam, SystemParamItem},
 };
-use bevy_utils::{HashMap, HashSet};
+use bevy_utils::{thiserror::Error, HashMap, HashSet};
 use std::marker::PhantomData;
 
+#[derive(Debug, Error)]
 pub enum PrepareAssetError<E: Send + Sync + 'static> {
+    #[error("Failed to prepare asset")]
     RetryNextUpdate(E),
 }
 

crates/bevy_render/src/render_resource/bind_group.rs

@@ -7,6 +7,7 @@ use crate::{
     texture::FallbackImage,
 };
 pub use bevy_render_macros::AsBindGroup;
+use bevy_utils::thiserror::Error;
 use encase::ShaderType;
 use std::ops::Deref;
 use wgpu::{BindGroupEntry, BindGroupLayoutDescriptor, BindGroupLayoutEntry, BindingResource};
@@ -325,8 +326,10 @@ pub trait AsBindGroup {
 }
 
 /// An error that occurs during [`AsBindGroup::as_bind_group`] calls.
+#[derive(Debug, Error)]
 pub enum AsBindGroupError {
     /// The bind group could not be generated. Try again next frame.
+    #[error("The bind group could not be generated")]
     RetryNextUpdate,
 }
 

crates/bevy_transform/Cargo.toml

@@ -16,6 +16,7 @@ bevy_hierarchy = { path = "../bevy_hierarchy", version = "0.12.0-dev" }
 bevy_math = { path = "../bevy_math", version = "0.12.0-dev" }
 bevy_reflect = { path = "../bevy_reflect", version = "0.12.0-dev", features = ["bevy"] }
 serde = { version = "1", features = ["derive"], optional = true }
+thiserror = "1.0"
 
 [dev-dependencies]
 bevy_tasks = { path = "../bevy_tasks", version = "0.12.0-dev" }

crates/bevy_transform/src/helper.rs

@@ -6,6 +6,7 @@ use bevy_ecs::{
     system::{Query, SystemParam},
 };
 use bevy_hierarchy::{HierarchyQueryExt, Parent};
+use thiserror::Error;
 
 use crate::components::{GlobalTransform, Transform};
 
@@ -63,14 +64,17 @@ fn map_error(err: QueryEntityError, ancestor: bool) -> ComputeGlobalTransformErr
 }
 
 /// Error returned by [`TransformHelper::compute_global_transform`].
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum ComputeGlobalTransformError {
     /// The entity or one of its ancestors is missing the [`Transform`] component.
+    #[error("The entity {0:?} or one of its ancestors is missing the `Transform` component")]
     MissingTransform(Entity),
     /// The entity does not exist.
+    #[error("The entity {0:?} does not exist")]
     NoSuchEntity(Entity),
     /// An ancestor is missing.
     /// This probably means that your hierarchy has been improperly maintained.
+    #[error("The ancestor {0:?} is missing")]
     MalformedHierarchy(Entity),
 }
 

crates/bevy_ui/src/layout/mod.rs

@@ -19,6 +19,7 @@ use bevy_utils::{default, HashMap};
 use bevy_window::{PrimaryWindow, Window, WindowResolution, WindowScaleFactorChanged};
 use std::fmt;
 use taffy::Taffy;
+use thiserror::Error;
 
 pub struct LayoutContext {
     pub scale_factor: f64,
@@ -228,10 +229,12 @@ with UI components as a child of an entity without UI components, results may be
     }
 }
 
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum LayoutError {
+    #[error("Invalid hierarchy")]
     InvalidHierarchy,
-    TaffyError(taffy::error::TaffyError),
+    #[error("Taffy error: {0}")]
+    TaffyError(#[from] taffy::error::TaffyError),
 }
 
 /// Updates the UI's layout tree, computes the new layout geometry and then updates the sizes and transforms of all the UI nodes.

examples/games/contributors.rs

@@ -1,6 +1,9 @@
 //! This example displays each contributor to the bevy source code as a bouncing bevy-ball.
 
-use bevy::{prelude::*, utils::HashSet};
+use bevy::{
+    prelude::*,
+    utils::{thiserror, HashSet},
+};
 use rand::{prelude::SliceRandom, Rng};
 use std::{
     env::VarError,
@@ -309,9 +312,13 @@ fn move_system(time: Res<Time>, mut query: Query<(&Velocity, &mut Transform)>) {
     }
 }
 
+#[derive(Debug, thiserror::Error)]
 enum LoadContributorsError {
-    IO(io::Error),
-    Var(VarError),
+    #[error("An IO error occurred while reading the git log.")]
+    Io(#[from] io::Error),
+    #[error("The CARGO_MANIFEST_DIR environment variable was not set.")]
+    Var(#[from] VarError),
+    #[error("The git process did not return a stdout handle.")]
     Stdout,
 }
 
@@ -321,14 +328,13 @@ enum LoadContributorsError {
 /// This function only works if `git` is installed and
 /// the program is run through `cargo`.
 fn contributors() -> Result<Contributors, LoadContributorsError> {
-    let manifest_dir = std::env::var("CARGO_MANIFEST_DIR").map_err(LoadContributorsError::Var)?;
+    let manifest_dir = std::env::var("CARGO_MANIFEST_DIR")?;
 
     let mut cmd = std::process::Command::new("git")
         .args(["--no-pager", "log", "--pretty=format:%an"])
         .current_dir(manifest_dir)
         .stdout(Stdio::piped())
-        .spawn()
-        .map_err(LoadContributorsError::IO)?;
+        .spawn()?;
 
     let stdout = cmd.stdout.take().ok_or(LoadContributorsError::Stdout)?;