# Objective
Fixes#10291
This adds a way to easily log messages once within system which are
called every frame.
## Solution
Opted for a macro-based approach. The fact that the 'once' call is
tracked per call site makes the `log_once!()` macro very versatile and
easy-to-use. I suspect it will be very handy for all of us, but
especially beginners, to get some initial feedback from systems without
spamming up the place!
I've made the macro's return its internal `has_fired` state, for
situations in which that might be useful to know (trigger something else
alongside the log, for example).
Please let me know if I placed the macro's in the right location, and if
you would like me to do something more clever with the macro's
themselves, since its looking quite copy-pastey at the moment. I've
tried ways to replace 5 with 1 macro's, but no success yet.
One downside of this approach is: Say you wish to warn the user if a
resource is invalid. In this situation, the
`resource.is_valid()` check would still be performed every frame:
```rust
fn my_system(my_res: Res<MyResource>) {
if !my_res.is_valid() {
warn_once!("resource is invalid!");
}
}
```
If you want to prevent that, you would still need to introduce a local
boolean. I don't think this is a very big deal, as expensive checks
shouldn't be called every frame in any case.
## Changelog
Added: `trace_once!()`, `debug_once!()`, `info_once!()`, `warn_once!()`,
and `error_once!()` log macros which fire only once per call site.
18ac125997