runtime: expose Builder::rng_seed without tokio_unstable

Moves `Builder::rng_seed`, the `runtime::RngSeed` re-export, and
`RngSeed::from_bytes` out of `cfg_unstable!` so callers can seed the
scheduler RNG (and thus get deterministic `select!` branch ordering)
without `--cfg tokio_unstable`.

The underlying `seed_generator` field and all runtime plumbing were
already unconditional; only the public setter and type re-export were
gated. No behavior change for builds that already set `tokio_unstable`.

Upstream tracking issue: tokio-rs#4879 (introduced in tokio-rs#4910).

Author: antsujay

tokio/Cargo.toml

@@ -6,7 +6,7 @@ name = "tokio"
 #   - README.md
 # - Update CHANGELOG.md.
 # - Create "v1.x.y" git tag.
-version = "1.49.0+anthropic.1"
+version = "1.49.0+anthropic.2"
 edition = "2021"
 rust-version = "1.71"
 authors = ["Tokio Contributors <team@tokio.rs>"]

tokio/src/runtime/builder.rs

@@ -1412,39 +1412,39 @@ impl Builder {
             self.disable_lifo_slot = true;
             self
         }
+    }
 
-        /// Specifies the random number generation seed to use within all
-        /// threads associated with the runtime being built.
-        ///
-        /// This option is intended to make certain parts of the runtime
-        /// deterministic (e.g. the [`tokio::select!`] macro). In the case of
-        /// [`tokio::select!`] it will ensure that the order that branches are
-        /// polled is deterministic.
-        ///
-        /// In addition to the code specifying `rng_seed` and interacting with
-        /// the runtime, the internals of Tokio and the Rust compiler may affect
-        /// the sequences of random numbers. In order to ensure repeatable
-        /// results, the version of Tokio, the versions of all other
-        /// dependencies that interact with Tokio, and the Rust compiler version
-        /// should also all remain constant.
-        ///
-        /// # Examples
-        ///
-        /// ```
-        /// # use tokio::runtime::{self, RngSeed};
-        /// # pub fn main() {
-        /// let seed = RngSeed::from_bytes(b"place your seed here");
-        /// let rt = runtime::Builder::new_current_thread()
-        ///     .rng_seed(seed)
-        ///     .build();
-        /// # }
-        /// ```
-        ///
-        /// [`tokio::select!`]: crate::select
-        pub fn rng_seed(&mut self, seed: RngSeed) -> &mut Self {
-            self.seed_generator = RngSeedGenerator::new(seed);
-            self
-        }
+    /// Specifies the random number generation seed to use within all
+    /// threads associated with the runtime being built.
+    ///
+    /// This option is intended to make certain parts of the runtime
+    /// deterministic (e.g. the [`tokio::select!`] macro). In the case of
+    /// [`tokio::select!`] it will ensure that the order that branches are
+    /// polled is deterministic.
+    ///
+    /// In addition to the code specifying `rng_seed` and interacting with
+    /// the runtime, the internals of Tokio and the Rust compiler may affect
+    /// the sequences of random numbers. In order to ensure repeatable
+    /// results, the version of Tokio, the versions of all other
+    /// dependencies that interact with Tokio, and the Rust compiler version
+    /// should also all remain constant.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use tokio::runtime::{self, RngSeed};
+    /// # pub fn main() {
+    /// let seed = RngSeed::from_bytes(b"place your seed here");
+    /// let rt = runtime::Builder::new_current_thread()
+    ///     .rng_seed(seed)
+    ///     .build();
+    /// # }
+    /// ```
+    ///
+    /// [`tokio::select!`]: crate::select
+    pub fn rng_seed(&mut self, seed: RngSeed) -> &mut Self {
+        self.seed_generator = RngSeedGenerator::new(seed);
+        self
     }
 
     cfg_unstable_metrics! {

tokio/src/runtime/mod.rs

@@ -550,9 +550,9 @@ cfg_rt! {
 
     mod builder;
     pub use self::builder::Builder;
+    pub use crate::util::rand::RngSeed;
     cfg_unstable! {
         pub use self::builder::UnhandledPanic;
-        pub use crate::util::rand::RngSeed;
 
         mod local_runtime;
         pub use local_runtime::{LocalRuntime, LocalOptions};

tokio/src/util/rand.rs

@@ -2,9 +2,7 @@ cfg_rt! {
     mod rt;
     pub(crate) use rt::RngSeedGenerator;
 
-    cfg_unstable! {
-        mod rt_unstable;
-    }
+    mod rt_unstable;
 }
 
 /// A seed for random number generation.