# Objective
- Fixes https://github.com/bevyengine/bevy/issues/12597
The current tracing customization option (the `update_subscriber` field)
was basically unusable because it provides a `dyn Subscriber` and most
layers require a `Subscriber` that also implements `for<'a>
LookupSpan<'a, Data=Data<'a>>`, so it was impossible to add a layer on
top of the `dyn Subscriber`.
This PR provides an alternative way of adding additional tracing layers
to the LogPlugin by instead creating an `Option<Layer>`.
This is enough for most situations because `Option<Layer>` and
`Vec<Layer>` both implement `Layer`.
## Solution
- Replace the `update_subscriber` field of `LogPlugin` with a
`custom_layer` field which is function pointer returning an
`Option<BoxedLayer>`
- Update the examples to showcase that this works:
- with multiple additional layers
- with Layers that were previously problematic, such as
`bevy::log::tracing_subscriber::fmt::layer().with_file(true)` (mentioned
in the issue)
Note that in the example this results in duplicate logs, since we have
our own layer on top of the default `fmt_layer` added in the LogPlugin;
maybe in the future we might want to provide a single one? Or to let the
user customize the default `fmt_layer` ? I still think this change is an
improvement upon the previous solution, which was basically broken.
---
## Changelog
> This section is optional. If this was a trivial fix, or has no
externally-visible impact, you can delete this section.
- The `LogPlugin`'s `update_subscriber` field has been replaced with
`custom_layer` to allow the user to flexibly add a `tracing::Layer` to
the layer stack
## Migration Guide
- The `LogPlugin`'s `update_subscriber` field has been replaced with
`custom_layer`
---------
Co-authored-by: BD103 <59022059+BD103@users.noreply.github.com>
# Objective
In my library,
[`bevy_dev_console`](https://github.com/doonv/bevy_dev_console) I need
access to `App` within `LogPlugin::update_subscriber` in order to
communicate with the `App` from my custom `Layer`.
## Solution
Give access to `App`.
---
## Changelog
- Added access to `App` within `LogPlugin::update_subscriber`
## Migration Guide
`LogPlugin::update_subscriber` now has a `&mut App` parameter. If you
don't need access to `App`, you can ignore the parameter with an
underscore (`_`).
```diff,rust
- fn update_subscriber(subscriber: BoxedSubscriber) -> BoxedSubscriber {
+ fn update_subscriber(_: &mut App, subscriber: BoxedSubscriber) -> BoxedSubscriber {
Box::new(subscriber.with(CustomLayer))
}
```
# Objective
This PR is heavily inspired by
https://github.com/bevyengine/bevy/pull/7682
It aims to solve the same problem: allowing the user to extend the
tracing subscriber with extra layers.
(in my case, I'd like to use `use
metrics_tracing_context::{MetricsLayer, TracingContextLayer};`)
## Solution
I'm proposing a different api where the user has the opportunity to take
the existing `subscriber` and apply any transformations on it.
---
## Changelog
- Added a `update_subscriber` option on the `LogPlugin` that lets the
user modify the `subscriber` (for example to extend it with more tracing
`Layers`
## Migration Guide
> This section is optional. If there are no breaking changes, you can
delete this section.
- Added a new field `update_subscriber` in the `LogPlugin`
---------
Co-authored-by: Charles Bournhonesque <cbournhonesque@snapchat.com>
