SystemParam::validate_param into SystemParam::get_param (#23225)
# Objective As raised in [#23174](https://github.com/bevyengine/bevy/pull/23174#discussion_r2868030355_), we currently duplicate working when looking up our system parameters: once during validation, and then again when actually fetching the data. This is (maybe) slow, and would worsen the performance regression incurred by resources-as-components (#19731). This strategy also imposes some non-trivial complexity and maintainability costs. Because "validate" is a distinct step from "use", it's possible to skip validation! As far as I could tell, this is the case in a number of places before this PR: particularly in the unconventional "please just run my system" path. While in most cases this will simply result in a crash in a different place, it causes these paths to not handle Fixes #23179. Fixes #15505. ## Solution Fundamentally, what we're doing is rolling the `SystemParam::validate_param` behavior into `SystemParam::get_param`, by making the latter return a `Result`. However, there is a tremendous amount of splash damage required to get that to actually compile and expose the correct semantics. The most important of these are: - `SystemState::get` and friends now returns a `Result` - this leads to a fair bit of assorted unwrap spam in our tests and weird internal usages - these tests can probably be refactored to not use `SystemState` directly in the future now that we have better tools like `run_system_once`, but eh, not this PR's job - this is semantically correct, as these params could fail validation - `System::validate_param_unsafe` has been removed, and validation now occurs inside of `System::run_unsafe` - very much a net positive for both abstract robustness and current correctness - this impacts the strategy that various executors use: see the next section There are a *lot* of moving parts here: I'm sorry that I couldn't get this into a smaller, more incremental refactor. When reviewing this PR, you should begin with the migration guide to help get you oriented on the details: `validation_merging.md`. From there, the most important files to review are: 1. `system_param.rs`: trait changes and implementers 2. `function_system.rs`: primary implementer of `System` 3. `multithreaded.rs`: the parallel executor **NOTE TO REVIEWERS:** Please make comments to generate threads; this PR review might get fairly hairy. ### Performance discussion For the parallel `MultithreadedExecutor`, validation was previously done as a cheap pre-validation step, while checking run conditions. Now, tasks will be spawned for systems which would fail or are skipped during validation. In most cases, avoiding the extra overhead of looking up the required data twice should dominate. However, this change may negatively affect systems which are frequently skipped (e.g. due to `Single`). ### Paths not taken In this PR, I've decided not to: - Add another variant [RunSystemError](https://docs.rs/bevy/latest/bevy/ecs/system/enum.RunSystemError.html), distinguishing "validation failed" from "system ran but returned an error". - While reusing [RunSystemError::Failed](https://docs.rs/bevy/latest/bevy/ecs/system/enum.RunSystemError.html#variant.Failed) for both cases is messy, this PR is already a bit of a nightmare to review. - Return a result from `ParamSet::get_mut`. - Instead, we just `unwrap`. - Bubbling up the `Result` is technically more correct, but these were already panicking before if e.g. a resource is missing, and `ParamSet` is already an ergonomic abomination. ## Testing I've added a number of new tests to exercise the system param validation paths, ensuring that validation is done when systems are run. However, I would appreciate some help benchmarking the net impact on realistic-ish scenes. `breakout`, `bevy_city` and `many_animated_foxes` are probably a decent scattering, but I'd be very open to other suggestions. Having done this refactor, I think that it's a net improvement for robustness and clarity even without the perf benefits however, and that we should proceed unless this is a clear regression. --------- Co-authored-by: Chris Russell <8494645+chescock@users.noreply.github.com> Co-authored-by: Kevin Chen <chen.kevin.f@gmail.com>
clippy::doc_markdown expectation in the bevy main crate to be more accurate (#21590)
clippy::doc_markdown expectation in the bevy main crate to be more accurate (#21590)
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.
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.