# Objective
`Entity::PLACEHOLDER` acts as a magic number that will *probably* never
really exist, but it certainly could. And, `Entity` has a niche, so the
only reason to use `PLACEHOLDER` is as an alternative to `MaybeUninit`
that trades safety risks for logic risks.
As a result, bevy has generally advised against using `PLACEHOLDER`, but
we still use if for a lot internally. This pr starts removing internal
uses of it, starting from observers.
## Solution
Change all trigger target related types from `Entity` to
`Option<Entity>`
Small migration guide to come.
## Testing
CI
## Future Work
This turned a lot of code from
```rust
trigger.target()
```
to
```rust
trigger.target().unwrap()
```
The extra panic is no worse than before; it's just earlier than
panicking after passing the placeholder to something else.
But this is kinda annoying.
I would like to add a `TriggerMode` or something to `Event` that would
restrict what kinds of targets can be used for that event. Many events
like `Removed` etc, are always triggered with a target. We can make
those have a way to assume Some, etc. But I wanted to save that for a
future pr.
# Objective
The goal of `bevy_platform_support` is to provide a set of platform
agnostic APIs, alongside platform-specific functionality. This is a high
traffic crate (providing things like HashMap and Instant). Especially in
light of https://github.com/bevyengine/bevy/discussions/18799, it
deserves a friendlier / shorter name.
Given that it hasn't had a full release yet, getting this change in
before Bevy 0.16 makes sense.
## Solution
- Rename `bevy_platform_support` to `bevy_platform`.
# Objective
- Fixes#17506
- Fixes#16258
## Solution
- Added a new folder of examples, `no_std`, similar to the `mobile`
folder.
- Added a single example, `no_std_library`, which demonstrates how to
make a `no_std` compatible Bevy library.
- Added a new CI task, `check-compiles-no-std-examples`, which checks
that `no_std` examples compile on `no_std` targets.
- Added `bevy_platform_support::prelude` to `bevy::prelude`.
## Testing
- CI
---
## Notes
- I've structured the folders here to permit further `no_std` examples
(e.g., GameBoy Games, ESP32 firmware, etc.), but I am starting with the
simplest and least controversial example.
- I've tried to be as clear as possible with the documentation for this
example, catering to an audience who may not have even heard of `no_std`
before.
---------
Co-authored-by: Greeble <166992735+greeble-dev@users.noreply.github.com>
