cca5813472
## 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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What is Bevy?
Bevy is a refreshingly simple data-driven game engine built in Rust. It is free and open-source forever!
WARNING
Bevy is still in the early stages of development. Important features are missing. Documentation is sparse. A new version of Bevy containing breaking changes to the API is released approximately once every 3 months. We provide migration guides, but we can't guarantee migrations will always be easy. Use only if you are willing to work in this environment.
MSRV: Bevy relies heavily on improvements in the Rust language and compiler. As a result, the Minimum Supported Rust Version (MSRV) is generally close to "the latest stable release" of Rust.
Design Goals
- Capable: Offer a complete 2D and 3D feature set
- Simple: Easy for newbies to pick up, but infinitely flexible for power users
- Data Focused: Data-oriented architecture using the Entity Component System paradigm
- Modular: Use only what you need. Replace what you don't like
- Fast: App logic should run quickly, and when possible, in parallel
- Productive: Changes should compile quickly ... waiting isn't fun
About
- Features: A quick overview of Bevy's features.
- News: A development blog that covers our progress, plans and shiny new features.
Docs
- Quick Start Guide: Bevy's official Quick Start Guide. The best place to start learning Bevy.
- Bevy Rust API Docs: Bevy's Rust API docs, which are automatically generated from the doc comments in this repo.
- Official Examples: Bevy's dedicated, runnable examples, which are great for digging into specific concepts.
- Community-Made Learning Resources: More tutorials, documentation, and examples made by the Bevy community.
Community
Before contributing or participating in discussions with the community, you should familiarize yourself with our Code of Conduct.
- Discord: Bevy's official discord server.
- Reddit: Bevy's official subreddit.
- GitHub Discussions: The best place for questions about Bevy, answered right here!
- Bevy Assets: A collection of awesome Bevy projects, tools, plugins and learning materials.
Contributing
If you'd like to help build Bevy, check out the Contributor's Guide. For simple problems, feel free to open an issue or PR and tackle it yourself!
For more complex architecture decisions and experimental mad science, please open an RFC (Request For Comments) so we can brainstorm together effectively!
Getting Started
We recommend checking out the Quick Start Guide for a brief introduction.
Follow the Setup guide to ensure your development environment is set up correctly. Once set up, you can quickly try out the examples by cloning this repo and running the following commands:
# Switch to the correct version (latest release, default is main development branch)
git checkout latest
# Runs the "breakout" example
cargo run --example breakout
To draw a window with standard functionality enabled, use:
use bevy::prelude::*;
fn main(){
App::new()
.add_plugins(DefaultPlugins)
.run();
}
Fast Compiles
Bevy can be built just fine using default configuration on stable Rust. However for really fast iterative compiles, you should enable the "fast compiles" setup by following the instructions here.
Bevy Cargo Features
This list outlines the different cargo features supported by Bevy. These allow you to customize the Bevy feature set for your use-case.
Thanks
Bevy is the result of the hard work of many people. A huge thanks to all Bevy contributors, the many open source projects that have come before us, the Rust gamedev ecosystem, and the many libraries we build on.
A huge thanks to Bevy's generous sponsors. Bevy will always be free and open source, but it isn't free to make. Please consider sponsoring our work if you like what we're building.
This project is tested with BrowserStack.
License
Bevy is free, open source and permissively licensed! Except where noted (below and/or in individual files), all code in this repository is dual-licensed under either:
- MIT License (LICENSE-MIT or http://opensource.org/licenses/MIT)
- Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
at your option. This means you can select the license you prefer! This dual-licensing approach is the de-facto standard in the Rust ecosystem and there are very good reasons to include both.
Some of the engine's code carries additional copyright notices and license terms due to their external origins.
These are generally BSD-like, but exact details vary by crate:
If the README of a crate contains a 'License' header (or similar), the additional copyright notices and license terms applicable to that crate will be listed.
The above licensing requirement still applies to contributions to those crates, and sections of those crates will carry those license terms.
The license field of each crate will also reflect this.
For example, bevy_mikktspace has code under the Zlib license (as well as a copyright notice when choosing the MIT license).
The assets included in this repository (for our examples) typically fall under different open licenses. These will not be included in your game (unless copied in by you), and they are not distributed in the published bevy crates. See CREDITS.md for the details of the licenses of those files.
Your contributions
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.