e21dfe81ce
6 Commits
| Author | SHA1 | Message | Date | |
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Carter Anderson
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cca5813472
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BevyError: Bevy's new catch-all error type (#18144)
## Objective Fixes #18092 Bevy's current error type is a simple type alias for `Box<dyn Error + Send + Sync + 'static>`. This largely works as a catch-all error, but it is missing a critical feature: the ability to capture a backtrace at the point that the error occurs. The best way to do this is `anyhow`-style error handling: a new error type that takes advantage of the fact that the `?` `From` conversion happens "inline" to capture the backtrace at the point of the error. ## Solution This PR adds a new `BevyError` type (replacing our old `std::error::Error` type alias), which uses the "from conversion backtrace capture" approach: ```rust fn oh_no() -> Result<(), BevyError> { // this fails with Rust's built in ParseIntError, which // is converted into the catch-all BevyError type let number: usize = "hi".parse()?; println!("parsed {number}"); Ok(()) } ``` This also updates our exported `Result` type alias to default to `BevyError`, meaning you can write this instead: ```rust fn oh_no() -> Result { let number: usize = "hi".parse()?; println!("parsed {number}"); Ok(()) } ``` When a BevyError is encountered in a system, it will use Bevy's default system error handler (which panics by default). BevyError does custom "backtrace filtering" by default, meaning we can cut out the _massive_ amount of "rust internals", "async executor internals", and "bevy system scheduler internals" that show up in backtraces. It also trims out the first generally-unnecssary `From` conversion backtrace lines that make it harder to locate the real error location. The result is a blissfully simple backtrace by default:  The full backtrace can be shown by setting the `BEVY_BACKTRACE=full` environment variable. Non-BevyError panics still use the default Rust backtrace behavior. One issue that prevented the truly noise-free backtrace during panics that you see above is that Rust's default panic handler will print the unfiltered (and largely unhelpful real-panic-point) backtrace by default, in _addition_ to our filtered BevyError backtrace (with the helpful backtrace origin) that we capture and print. To resolve this, I have extended Bevy's existing PanicHandlerPlugin to wrap the default panic handler. If we panic from the result of a BevyError, we will skip the default "print full backtrace" panic handler. This behavior can be enabled and disabled using the new `error_panic_hook` cargo feature in `bevy_app` (which is enabled by default). One downside to _not_ using `Box<dyn Error>` directly is that we can no longer take advantage of the built-in `Into` impl for strings to errors. To resolve this, I have added the following: ```rust // Before Err("some error")? // After Err(BevyError::message("some error"))? ``` We can discuss adding shorthand methods or macros for this (similar to anyhow's `anyhow!("some error")` macro), but I'd prefer to discuss that later. I have also added the following extension method: ```rust // Before some_option.ok_or("some error")?; // After some_option.ok_or_message("some error")?; ``` I've also moved all of our existing error infrastructure from `bevy_ecs::result` to `bevy_ecs::error`, as I think that is the better home for it ## Why not anyhow (or eyre)? The biggest reason is that `anyhow` needs to be a "generically useful error type", whereas Bevy is a much narrower scope. By using our own error, we can be significantly more opinionated. For example, anyhow doesn't do the extensive (and invasive) backtrace filtering that BevyError does because it can't operate on Bevy-specific context, and needs to be generically useful. Bevy also has a lot of operational context (ex: system info) that could be useful to attach to errors. If we have control over the error type, we can add whatever context we want to in a structured way. This could be increasingly useful as we add more visual / interactive error handling tools and editor integrations. Additionally, the core approach used is simple and requires almost no code. anyhow clocks in at ~2500 lines of code, but the impl here uses 160. We are able to boil this down to exactly what we need, and by doing so we improve our compile times and the understandability of our code. |
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Rob Parrett
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36cb64b382
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Bump typos to 1.30.0 (#18097)
# Objective Update `typos` and fix newly detected typos. [Changelog](https://github.com/crate-ci/typos/blob/master/CHANGELOG.md#1300---2025-03-01) (just a dictionary update releases) ## Solution Fix em - Describe the solution used to achieve the objective above. ## Testing CI |
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François Mockers
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cff17364b1
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Deterministic fallible_systems example (#17813)
# Objective - `fallible_systems` example is not deterministic ## Solution - Make it deterministic - Also fix required feature declaration |
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Jean Mertz
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7d8504f30e
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feat(ecs): implement fallible observer systems (#17731)
This commit builds on top of the work done in #16589 and #17051, by adding support for fallible observer systems. As with the previous work, the actual results of the observer system are suppressed for now, but the intention is to provide a way to handle errors in a global way. Until then, you can use a `PipeSystem` to manually handle results. --------- Signed-off-by: Jean Mertz <git@jeanmertz.com> |
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Jean Mertz
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fd67ca7eb0
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feat(ecs): configurable error handling for fallible systems (#17753)
You can now configure error handlers for fallible systems. These can be configured on several levels: - Globally via `App::set_systems_error_handler` - Per-schedule via `Schedule::set_error_handler` - Per-system via a piped system (this is existing functionality) The default handler of panicking on error keeps the same behavior as before this commit. The "fallible_systems" example demonstrates the new functionality. This builds on top of #17731, #16589, #17051. --------- Signed-off-by: Jean Mertz <git@jeanmertz.com> |
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Miles Silberling-Cook
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0070514f54
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Fallible systems (#16589)
# Objective Error handling in bevy is hard. See for reference https://github.com/bevyengine/bevy/issues/11562, https://github.com/bevyengine/bevy/issues/10874 and https://github.com/bevyengine/bevy/issues/12660. The goal of this PR is to make it better, by allowing users to optionally return `Result` from systems as outlined by Cart in <https://github.com/bevyengine/bevy/issues/14275#issuecomment-2223708314>. ## Solution This PR introduces a new `ScheuleSystem` type to represent systems that can be added to schedules. Instances of this type contain either an infallible `BoxedSystem<(), ()>` or a fallible `BoxedSystem<(), Result>`. `ScheuleSystem` implements `System<In = (), Out = Result>` and replaces all uses of `BoxedSystem` in schedules. The async executor now receives a result after executing a system, which for infallible systems is always `Ok(())`. Currently it ignores this result, but more useful error handling could also be implemented. Aliases for `Error` and `Result` have been added to the `bevy_ecs` prelude, as well as const `OK` which new users may find more friendly than `Ok(())`. ## Testing - Currently there are not actual semantics changes that really require new tests, but I added a basic one just to make sure we don't break stuff in the future. - The behavior of existing systems is totally unchanged, including logging. - All of the existing systems tests pass, and I have not noticed anything strange while playing with the examples ## Showcase The following minimal example prints "hello world" once, then completes. ```rust use bevy::prelude::*; fn main() { App::new().add_systems(Update, hello_world_system).run(); } fn hello_world_system() -> Result { println!("hello world"); Err("string")?; println!("goodbye world"); OK } ``` ## Migration Guide This change should be pretty much non-breaking, except for users who have implemented their own custom executors. Those users should use `ScheduleSystem` in place of `BoxedSystem<(), ()>` and import the `System` trait where needed. They can choose to do whatever they wish with the result. ## Current Work + [x] Fix tests & doc comments + [x] Write more tests + [x] Add examples + [X] Draft release notes ## Draft Release Notes As of this release, systems can now return results. First a bit of background: Bevy has hisotrically expected systems to return the empty type `()`. While this makes sense in the context of the ecs, it's at odds with how error handling is typically done in rust: returning `Result::Error` to indicate failure, and using the short-circuiting `?` operator to propagate that error up the call stack to where it can be properly handled. Users of functional languages will tell you this is called "monadic error handling". Not being able to return `Results` from systems left bevy users with a quandry. They could add custom error handling logic to every system, or manually pipe every system into an error handler, or perhaps sidestep the issue with some combination of fallible assignents, logging, macros, and early returns. Often, users would just litter their systems with unwraps and possible panics. While any one of these approaches might be fine for a particular user, each of them has their own drawbacks, and none makes good use of the language. Serious issues could also arrise when two different crates used by the same project made different choices about error handling. Now, by returning results, systems can defer error handling to the application itself. It looks like this: ```rust // Previous, handling internally app.add_systems(my_system) fn my_system(window: Query<&Window>) { let Ok(window) = query.get_single() else { return; }; // ... do something to the window here } // Previous, handling externally app.add_systems(my_system.pipe(my_error_handler)) fn my_system(window: Query<&Window>) -> Result<(), impl Error> { let window = query.get_single()?; // ... do something to the window here Ok(()) } // Previous, panicking app.add_systems(my_system) fn my_system(window: Query<&Window>) { let window = query.single(); // ... do something to the window here } // Now app.add_systems(my_system) fn my_system(window: Query<&Window>) -> Result { let window = query.get_single()?; // ... do something to the window here Ok(()) } ``` There are currently some limitations. Systems must either return `()` or `Result<(), Box<dyn Error + Send + Sync + 'static>>`, with no in-between. Results are also ignored by default, and though implementing a custom handler is possible, it involves writing your own custom ecs executor (which is *not* recomended). Systems should return errors when they cannot perform their normal behavior. In turn, errors returned to the executor while running the schedule will (eventually) be treated as unexpected. Users and library authors should prefer to return errors for anything that disrupts the normal expected behavior of a system, and should only handle expected cases internally. We have big plans for improving error handling further: + Allowing users to change the error handling logic of the default executors. + Adding source tracking and optional backtraces to errors. + Possibly adding tracing-levels (Error/Warn/Info/Debug/Trace) to errors. + Generally making the default error logging more helpful and inteligent. + Adding monadic system combininators for fallible systems. + Possibly removing all panicking variants from our api. --------- Co-authored-by: Zachary Harrold <zac@harrold.com.au> |