# Objective
Allow combinator and pipe systems to delay validation of the second
system, while still allowing the second system to be skipped.
Fixes#18796
Allow fallible systems to be used as one-shot systems, reporting errors
to the error handler when used through commands.
Fixes#19722
Allow fallible systems to be used as run conditions, including when used
with combinators. Alternative to #19580.
Always validate parameters when calling the safe
`run_without_applying_deferred`, `run`, and `run_readonly` methods on a
`System`.
## Solution
Have `System::run_unsafe` return a `Result`.
We want pipe systems to run the first system before validating the
second, since the first system may affect whether the second system has
valid parameters. But if the second system skips then we have no output
value to return! So, pipe systems must return a `Result` that indicates
whether the second system ran.
But if we just make pipe systems have `Out = Result<B::Out>`, then
chaining `a.pipe(b).pipe(c)` becomes difficult. `c` would need to accept
the `Result` from `a.pipe(b)`, which means it would likely need to
return `Result` itself, giving `Result<Result<Out>>`!
Instead, we make *all* systems return a `Result`! We move the handling
of fallible systems from `IntoScheduleConfigs` and `IntoObserverSystem`
to `SystemParamFunction` and `ExclusiveSystemParamFunction`, so that an
infallible system can be wrapped before being passed to a combinator.
As a side effect, this enables fallible systems to be used as run
conditions and one-shot systems.
Now that the safe `run_without_applying_deferred`, `run`, and
`run_readonly` methods return a `Result`, we can have them perform
parameter validation themselves instead of requiring each caller to
remember to call them. `run_unsafe` will continue to not validate
parameters, since it is used in the multi-threaded executor when we want
to validate and run in separate tasks.
Note that this makes type inference a little more brittle. A function
that returns `Result<T>` can be considered either a fallible system
returning `T` or an infallible system returning `Result<T>` (and this is
important to continue supporting `pipe`-based error handling)! So there
are some cases where the output type of a system can no longer be
inferred. It will work fine when directly adding to a schedule, since
then the output type is fixed to `()` (or `bool` for run conditions).
And it will work fine when `pipe`ing to a system with a typed input
parameter.
I used a dedicated `RunSystemError` for the error type instead of plain
`BevyError` so that skipping a system does not box an error or capture a
backtrace.
# Objective
Let `bevy_utils` build with no default features.
`cargo build -p bevy_utils --no-default-features` currently fails with
```
error[E0433]: failed to resolve: use of unresolved module or unlinked crate `alloc`
--> crates\bevy_utils\src\debug_info.rs:1:5
|
1 | use alloc::{borrow::Cow, fmt, string::String};
| ^^^^^ use of unresolved module or unlinked crate `alloc`
|
= help: add `extern crate alloc` to use the `alloc` crate
error[E0432]: unresolved import `alloc`
--> crates\bevy_utils\src\debug_info.rs:1:5
|
1 | use alloc::{borrow::Cow, fmt, string::String};
| ^^^^^ help: a similar path exists: `core::alloc`
```
I would have expected CI to catch this earlier, but I have not
investigated why it did not.
## Solution
Wrap the parts of `DebugName` that use `Cow` and `String` in
`cfg::alloc!`.
If the `debug` feature is enabled, then `DebugName` itself stores a
`Cow`, so make the `debug` feature require `bevy_platform/alloc`.
That is, you can use `DebugName` in no-std contexts when it's just a
ZST! (I bet it's even possible to support no-std `debug` by storing
`&'static str` instead of `Cow<'static, str>`, but that seemed like too
much complexity for now.)
# Objective
- Many strings in bevy_ecs are created but only used for debug: system
name, component name, ...
- Those strings make a significant part of the final binary and are no
use in a released game
## Solution
- Use [`strings`](https://linux.die.net/man/1/strings) to find ...
strings in a binary
- Try to find where they come from
- Many are made from `type_name::<T>()` and only used in error / debug
messages
- Add a new structure `DebugName` that holds no value if `debug` feature
is disabled
- Replace `core::any::type_name::<T>()` by `DebugName::type_name::<T>()`
## Testing
Measurements were taken without the new feature being enabled by
default, to help with commands
### File Size
I tried building the `breakout` example with `cargo run --release
--example breakout`
|`debug` enabled|`debug` disabled|
|-|-|
|81621776 B|77735728B|
|77.84MB|74.13MB|
### Compilation time
`hyperfine --min-runs 15 --prepare "cargo clean && sleep 5"
'RUSTC_WRAPPER="" cargo build --release --example breakout'
'RUSTC_WRAPPER="" cargo build --release --example breakout --features
debug'`
```
breakout' 'RUSTC_WRAPPER="" cargo build --release --example breakout --features debug'
Benchmark 1: RUSTC_WRAPPER="" cargo build --release --example breakout
Time (mean ± σ): 84.856 s ± 3.565 s [User: 1093.817 s, System: 32.547 s]
Range (min … max): 78.038 s … 89.214 s 15 runs
Benchmark 2: RUSTC_WRAPPER="" cargo build --release --example breakout --features debug
Time (mean ± σ): 92.303 s ± 2.466 s [User: 1193.443 s, System: 33.803 s]
Range (min … max): 90.619 s … 99.684 s 15 runs
Summary
RUSTC_WRAPPER="" cargo build --release --example breakout ran
1.09 ± 0.05 times faster than RUSTC_WRAPPER="" cargo build --release --example breakout --features debug
```
