add test reproducing #2587, #2436, and #2411

tracing-core/tests/local_dispatch_before_init.rs

@@ -0,0 +1,40 @@
+mod common;
+
+use common::*;
+use tracing_core::{subscriber::NoSubscriber, dispatcher::{Dispatch, self}};
+
+/// This test reproduces the following issues:
+/// - https://github.com/tokio-rs/tracing/issues/2587
+/// - https://github.com/tokio-rs/tracing/issues/2411
+/// - https://github.com/tokio-rs/tracing/issues/2436
+#[test]
+fn local_dispatch_before_init() {
+    dispatcher::get_default(|current| assert!(dbg!(current).is::<NoSubscriber>()));
+
+    // Temporarily override the default dispatcher with a scoped dispatcher.
+    // Using a scoped dispatcher makes the thread local state attempt to cache
+    // the scoped default.
+    #[cfg(feature = "std")] {
+        dispatcher::with_default(&Dispatch::new(TestSubscriberB), || {
+            dispatcher::get_default(|current| {
+                assert!(
+                    dbg!(current).is::<TestSubscriberB>(),
+                    "overriden subscriber not set",
+                );
+            })
+        })
+    }
+
+    dispatcher::get_default(|current| assert!(current.is::<NoSubscriber>()));
+
+    dispatcher::set_global_default(Dispatch::new(TestSubscriberA))
+        .expect("set global dispatch failed");
+
+    dispatcher::get_default(|current| {
+        assert!(
+            dbg!(current).is::<TestSubscriberA>(),
+            "default subscriber not set"
+        );
+    });
+
+}