rust: move async helper functions to the util crate

So the bitbox02 crate can also use it. It will be needed to be able to
use block_on() in the tests there.

Author: benma

src/rust/bitbox02-rust/Cargo.toml

@@ -101,7 +101,8 @@ app-cardano = [
 ]
 
 testing = [
-  "bitbox02/testing"
+  "bitbox02/testing",
+  "util/testing"
 ]
 
 c-unit-testing = []

src/rust/bitbox02-rust/src/bb02_async.rs

@@ -12,37 +12,11 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use alloc::boxed::Box;
 use core::cell::RefCell;
-use core::pin::Pin;
-use core::task::{Context, Poll};
 
-/// Task is the top-level future which can be polled by an executor.
-/// Note that other futures awaited inside do not have to be pinned.
-/// The 'a lifetime allows to spin a boxed/pinned future that is not
-/// 'static, or a future with non-'static input param references.
-pub type Task<'a, O> = Pin<Box<dyn core::future::Future<Output = O> + 'a>>;
-
-/// A primitive poll invocation for a task, with no waking functionality.
-pub fn spin<O>(task: &mut Task<O>) -> Poll<O> {
-    // TODO: statically allocate the context.
-    let waker = crate::waker_fn::waker_fn(|| {});
-    let context = &mut Context::from_waker(&waker);
-    task.as_mut().poll(context)
-}
-
-/// Implements the Option future, see `option()`.
-pub struct AsyncOption<'a, O>(&'a RefCell<Option<O>>);
-
-impl<O> core::future::Future for AsyncOption<'_, O> {
-    type Output = O;
-    fn poll(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Self::Output> {
-        match self.0.borrow_mut().take() {
-            None => Poll::Pending,
-            Some(output) => Poll::Ready(output),
-        }
-    }
-}
+#[cfg(feature = "testing")]
+pub use util::bb02_async::block_on;
+pub use util::bb02_async::{Task, option, spin};
 
 /// Disables the screensaver while waiting for an option to contain a value. Afterwards, it returns that value
 pub async fn option_no_screensaver<O>(opt: &RefCell<Option<O>>) -> O {
@@ -51,20 +25,3 @@ pub async fn option_no_screensaver<O>(opt: &RefCell<Option<O>>) -> O {
     bitbox02::screen_saver::screen_saver_enable();
     result
 }
-
-/// Waits for an option to contain a value and returns that value, leaving `None` in its place.
-/// E.g. `assert_eq!(option(&Some(42)).await, 42)`.
-pub fn option<O>(option: &RefCell<Option<O>>) -> AsyncOption<'_, O> {
-    AsyncOption(option)
-}
-
-/// Polls a future until the result is available.
-#[cfg(feature = "testing")]
-pub fn block_on<O>(task: impl core::future::Future<Output = O>) -> O {
-    let mut task: crate::bb02_async::Task<O> = alloc::boxed::Box::pin(task);
-    loop {
-        if let Poll::Ready(result) = spin(&mut task) {
-            return result;
-        }
-    }
-}

src/rust/bitbox02-rust/src/lib.rs

@@ -40,7 +40,6 @@ pub mod secp256k1;
 #[cfg(feature = "app-u2f")]
 mod u2f;
 mod version;
-mod waker_fn;
 pub mod workflow;
 #[cfg(any(feature = "app-bitcoin", feature = "app-litecoin"))]
 mod xpubcache;

src/rust/bitbox02/Cargo.toml

@@ -36,7 +36,7 @@ bitbox02-rust = { path = "../bitbox02-rust" }
 
 [features]
 # Only to be enabled in unit tests and simulators
-testing = []
+testing = ["util/testing"]
 # Enables UI stubs for rust unit tests
 unit-testing = []
 # Active when the Rust code is compiled to be linked into the C unit tests and simulator.

src/rust/util/Cargo.toml

@@ -31,5 +31,6 @@ bitcoin = {workspace = true}
 
 [features]
 rtt = ["dep:rtt-target", "dep:cortex-m"]
+testing = []
 c-unit-testing = []
 firmware = []

src/rust/util/src/bb02_async.rs

@@ -0,0 +1,62 @@
+// Copyright 2025 Shift Crypto AG
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use alloc::boxed::Box;
+use core::cell::RefCell;
+use core::pin::Pin;
+use core::task::{Context, Poll};
+
+/// Task is the top-level future which can be polled by an executor.
+/// Note that other futures awaited inside do not have to be pinned.
+/// The 'a lifetime allows to spin a boxed/pinned future that is not
+/// 'static, or a future with non-'static input param references.
+pub type Task<'a, O> = Pin<Box<dyn core::future::Future<Output = O> + 'a>>;
+
+/// A primitive poll invocation for a task, with no waking functionality.
+pub fn spin<O>(task: &mut Task<O>) -> Poll<O> {
+    // TODO: statically allocate the context.
+    let waker = crate::waker_fn::waker_fn(|| {});
+    let context = &mut Context::from_waker(&waker);
+    task.as_mut().poll(context)
+}
+
+/// Implements the Option future, see `option()`.
+pub struct AsyncOption<'a, O>(&'a RefCell<Option<O>>);
+
+impl<O> core::future::Future for AsyncOption<'_, O> {
+    type Output = O;
+    fn poll(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match self.0.borrow_mut().take() {
+            None => Poll::Pending,
+            Some(output) => Poll::Ready(output),
+        }
+    }
+}
+
+/// Waits for an option to contain a value and returns that value, leaving `None` in its place.
+/// E.g. `assert_eq!(option(&Some(42)).await, 42)`.
+pub fn option<O>(option: &RefCell<Option<O>>) -> AsyncOption<'_, O> {
+    AsyncOption(option)
+}
+
+/// Polls a future until the result is available.
+#[cfg(feature = "testing")]
+pub fn block_on<O>(task: impl core::future::Future<Output = O>) -> O {
+    let mut task: crate::bb02_async::Task<O> = alloc::boxed::Box::pin(task);
+    loop {
+        if let Poll::Ready(result) = spin(&mut task) {
+            return result;
+        }
+    }
+}

src/rust/util/src/lib.rs

@@ -14,12 +14,14 @@
 
 #![cfg_attr(not(test), no_std)]
 pub mod ascii;
+pub mod bb02_async;
 pub mod bip32;
 pub mod bytes;
 pub mod cell;
 pub mod decimal;
 pub mod log;
 pub mod name;
+mod waker_fn;
 
 mod base58;
 #[cfg(feature = "p256")]