bevy/crates/bevy_ui/src
Carter Anderson dcc03724a5 Base Sets (#7466)
# Objective

NOTE: This depends on #7267 and should not be merged until #7267 is merged. If you are reviewing this before that is merged, I highly recommend viewing the Base Sets commit instead of trying to find my changes amongst those from #7267.

"Default sets" as described by the [Stageless RFC](https://github.com/bevyengine/rfcs/pull/45) have some [unfortunate consequences](https://github.com/bevyengine/bevy/discussions/7365).

## Solution

This adds "base sets" as a variant of `SystemSet`:

A set is a "base set" if `SystemSet::is_base` returns `true`. Typically this will be opted-in to using the `SystemSet` derive:

```rust
#[derive(SystemSet, Clone, Hash, Debug, PartialEq, Eq)]
#[system_set(base)]
enum MyBaseSet {
  A,
  B,
}
``` 

**Base sets are exclusive**: a system can belong to at most one "base set". Adding a system to more than one will result in an error. When possible we fail immediately during system-config-time with a nice file + line number. For the more nested graph-ey cases, this will fail at the final schedule build. 

**Base sets cannot belong to other sets**: this is where the word "base" comes from

Systems and Sets can only be added to base sets using `in_base_set`. Calling `in_set` with a base set will fail. As will calling `in_base_set` with a normal set.

```rust
app.add_system(foo.in_base_set(MyBaseSet::A))
       // X must be a normal set ... base sets cannot be added to base sets
       .configure_set(X.in_base_set(MyBaseSet::A))
```

Base sets can still be configured like normal sets:

```rust
app.add_system(MyBaseSet::B.after(MyBaseSet::Ap))
``` 

The primary use case for base sets is enabling a "default base set":

```rust
schedule.set_default_base_set(CoreSet::Update)
  // this will belong to CoreSet::Update by default
  .add_system(foo)
  // this will override the default base set with PostUpdate
  .add_system(bar.in_base_set(CoreSet::PostUpdate))
```

This allows us to build apis that work by default in the standard Bevy style. This is a rough analog to the "default stage" model, but it use the new "stageless sets" model instead, with all of the ordering flexibility (including exclusive systems) that it provides.

---

## Changelog

- Added "base sets" and ported CoreSet to use them.

## Migration Guide

TODO
2023-02-06 03:10:08 +00:00
..
flex Remove broken DoubleEndedIterator impls on event iterators (#7469) 2023-02-05 15:18:19 +00:00
render Migrate engine to Schedule v3 (#7267) 2023-02-06 02:04:50 +00:00
widget Don't ignore UI scale for text (#7510) 2023-02-05 18:15:22 +00:00
camera_config.rs Extract component derive (#7399) 2023-01-30 18:12:16 +00:00
focus.rs expose cursor position with scale (#7297) 2023-01-20 14:25:24 +00:00
geometry.rs change the default width and height of Size to Val::Auto (#7475) 2023-02-03 01:35:06 +00:00
lib.rs Base Sets (#7466) 2023-02-06 03:10:08 +00:00
node_bundles.rs Change default FocusPolicy to Pass (#7161) 2023-01-12 17:15:20 +00:00
stack.rs Migrate engine to Schedule v3 (#7267) 2023-02-06 02:04:50 +00:00
ui_node.rs Fix various typos (#7096) 2023-01-06 00:43:30 +00:00
update.rs Add z-index support with a predictable UI stack (#5877) 2022-11-02 22:06:04 +00:00