tracing: monomorphize is_enabled call in macros (#787)

Resolves #783.

Author: davidbarsky

tracing/src/lib.rs

@@ -869,6 +869,14 @@ pub mod __macro_support {
     pub type Once = tracing_core::Once;
 }
 
+#[doc(hidden)]
+// resolves https://github.com/tokio-rs/tracing/issues/783 by forcing a monomorphization
+// in tracing, not downstream crates.
+#[inline]
+pub fn is_enabled(meta: &crate::Metadata<'_>) -> bool {
+    crate::dispatcher::get_default(|current| current.enabled(meta))
+}
+
 mod sealed {
     pub trait Sealed {}
 }

tracing/src/macros.rs

@@ -539,7 +539,7 @@ macro_rules! event {
 
             if $crate::level_enabled!($lvl) {
                 #[allow(unused_imports)]
-                use $crate::{callsite, dispatcher, Event, field::{Value, ValueSet}};
+                use $crate::{callsite, Event, field::{Value, ValueSet}};
                 use $crate::callsite::Callsite;
                 let callsite = callsite! {
                     name: concat!(
@@ -584,7 +584,7 @@ macro_rules! event {
             );
             if $crate::level_enabled!($lvl) {
                 #[allow(unused_imports)]
-                use $crate::{callsite, dispatcher, Event, field::{Value, ValueSet}};
+                use $crate::{callsite, Event, field::{Value, ValueSet}};
                 use $crate::callsite::Callsite;
                 let callsite = callsite! {
                     name: concat!(
@@ -1860,7 +1860,7 @@ macro_rules! is_enabled {
             true
         } else {
             let meta = $callsite.metadata();
-            $crate::dispatcher::get_default(|current| current.enabled(meta))
+            $crate::is_enabled(meta)
         }
     }};
 }