6e959db134
# Objective
Fixes #8965.
#### Background
For convenience and to ensure everything is setup properly, we
automatically add certain bounds to the derived types. The current
implementation does this by taking the types from all active fields and
adding them to the where-clause of the generated impls. I believe this
method was chosen because it won't add bounds to types that are
otherwise ignored.
```rust
#[derive(Reflect)]
struct Foo<T, U: SomeTrait, V> {
t: T,
u: U::Assoc,
#[reflect(ignore)]
v: [V; 2]
}
// Generates something like:
impl<T, U: SomeTrait, V> for Foo<T, U, V>
where
// Active:
T: Reflect,
U::Assoc: Reflect,
// Ignored:
[V; 2]: Send + Sync + Any
{
// ...
}
```
The self-referential type fails because it ends up using _itself_ as a
type bound due to being one of its own active fields.
```rust
#[derive(Reflect)]
struct Foo {
foo: Vec<Foo>
}
// Foo where Vec<Foo>: Reflect -> Vec<T> where T: Reflect -> Foo where Vec<Foo>: Reflect -> ...
```
## Solution
We can't simply parse all field types for the name of our type. That
would be both complex and prone to errors and false-positives. And even
if it wasn't, what would we replace the bound with?
Instead, I opted to go for a solution that only adds the bounds to what
really needs it: the type parameters. While the bounds on concrete types
make errors a bit cleaner, they aren't strictly necessary. This means we
can change our generated where-clause to only add bounds to generic type
parameters.
Doing this, though, returns us back to the problem of over-bounding
parameters that don't need to be bounded. To solve this, I added a new
container attribute (based on
[this](https://github.com/dtolnay/syn/issues/422#issuecomment-406882925)
comment and @nicopap's
[comment](https://github.com/bevyengine/bevy/pull/9046#issuecomment-1623593780))
that allows us to pass in a custom where clause to modify what bounds
are added to these type parameters.
This allows us to do stuff like:
```rust
trait Trait {
type Assoc;
}
// We don't need `T` to be reflectable since we only care about `T::Assoc`.
#[derive(Reflect)]
#[reflect(where T::Assoc: FromReflect)]
struct Foo<T: Trait>(T::Assoc);
#[derive(TypePath)]
struct Bar;
impl Trait for Bar {
type Assoc = usize;
}
#[derive(Reflect)]
struct Baz {
a: Foo<Bar>,
}
```
> **Note**
> I also
[tried](
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| docs-template | ||
| errors | ||
| examples | ||
| src | ||
| tests | ||
| tools | ||
| .gitattributes | ||
| .gitignore | ||
| Cargo.toml | ||
| CHANGELOG.md | ||
| clippy.toml | ||
| CODE_OF_CONDUCT.md | ||
| CONTRIBUTING.md | ||
| CREDITS.md | ||
| deny.toml | ||
| LICENSE-APACHE | ||
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| README.md | ||
| rustfmt.toml | ||
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.
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- The Bevy Book: Bevy's official documentation. The best place to start learning Bevy.
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- Official Examples: Bevy's dedicated, runnable examples, which are great for digging into specific concepts.
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Before contributing or participating in discussions with the community, you should familiarize yourself with our Code of Conduct.
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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 Bevy Book for a full tutorial.
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)
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