tokio: add `rt-current-thread` optional feature

- Adds a minimum `rt-current-thread` optional feature that exports
  `tokio::runtime::current_thread`.
- Adds a `macros` optional feature to enable the `#[tokio::main]` and
  `#[tokio::test]` attributes.
- Adjusts `#[tokio::main]` macro to select a runtime "automatically" if
  a specific strategy isn't specified. Allows using the macro with only
  the rt-current-thread feature.

1 files changed, 6 insertions, 1 deletions

diff --git a/tokio/src/lib.rs b/tokio/src/lib.rs
index 30375c0a..14a7a3ab 100644
--- a/tokio/src/lib.rs
+++ b/tokio/src/lib.rs
@@ -72,7 +72,10 @@
 
 macro_rules! if_runtime {
     ($($i:item)*) => ($(
-        #[cfg(any(feature = "rt-full"))]
+        #[cfg(any(
+            feature = "rt-full",
+            feature = "rt-current-thread",
+        ))]
         $i
     )*)
 }
@@ -103,8 +106,10 @@ if_runtime! {
     pub use crate::executor::spawn;
 
     #[cfg(not(test))] // Work around for rust-lang/rust#62127
+    #[cfg(feature = "macros")]
     #[doc(inline)]
     pub use tokio_macros::main;
+    #[cfg(feature = "macros")]
     #[doc(inline)]
     pub use tokio_macros::test;
 }