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subscriber: remove Layer impls for Arcs (#1649)

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Implementing `Layer` for `Arc`s, which are immutable, breaks the
ability to implement `Layer::on_layer` with a mutable reference.
This is necessary for per-layer filtering. See
https://github.com/tokio-rs/tracing/pull/1576#discussion_r711609810 for
details. Therefore, the `Layer` impls for `Arc`s should not be used.

In 0.3, we have the opportunity to remove these APIs. Therefore, this PR
removes them.
This commit is contained in:
Eliza Weisman 2021-10-19 10:26:29 -07:00
parent c8b91caa05
commit b420ae7f4c
1 changed files with 5 additions and 41 deletions
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46
tracing-subscriber/src/layer/mod.rs
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@ -1175,6 +1175,11 @@ where
macro_rules! layer_impl_body {
() => {
#[inline]
fn on_layer(&mut self, subscriber: &mut S) {
self.deref_mut().on_layer(subscriber);
}
#[inline]
fn new_span(&self, attrs: &span::Attributes<'_>, id: &span::Id, ctx: Context<'_, S>) {
self.deref().new_span(attrs, id, ctx)
@ -1238,48 +1243,11 @@ macro_rules! layer_impl_body {
};
}
impl<L, S> Layer<S> for Arc<L>
where
L: Layer<S>,
S: Subscriber,
{
fn on_layer(&mut self, subscriber: &mut S) {
if let Some(inner) = Arc::get_mut(self) {
// XXX(eliza): this may behave weird if another `Arc` clone of this
// layer is layered onto a _different_ subscriber...but there's no
// good solution for that...
inner.on_layer(subscriber);
}
}
layer_impl_body! {}
}
impl<S> Layer<S> for Arc<dyn Layer<S> + Send + Sync>
where
S: Subscriber,
{
fn on_layer(&mut self, subscriber: &mut S) {
if let Some(inner) = Arc::get_mut(self) {
// XXX(eliza): this may behave weird if another `Arc` clone of this
// layer is layered onto a _different_ subscriber...but there's no
// good solution for that...
inner.on_layer(subscriber);
}
}
layer_impl_body! {}
}
impl<L, S> Layer<S> for Box<L>
where
L: Layer<S>,
S: Subscriber,
{
fn on_layer(&mut self, subscriber: &mut S) {
self.deref_mut().on_layer(subscriber);
}
layer_impl_body! {}
}
@ -1287,10 +1255,6 @@ impl<S> Layer<S> for Box<dyn Layer<S> + Send + Sync>
where
S: Subscriber,
{
fn on_layer(&mut self, subscriber: &mut S) {
self.deref_mut().on_layer(subscriber);
}
layer_impl_body! {}
}