add tests illustrating the problem

3 files changed, 27 insertions, 0 deletions

diff --git a/embassy-sync/tests/ui/sync_impl/lazy_lock_function.rs b/embassy-sync/tests/ui/sync_impl/lazy_lock_function.rs
new file mode 100644
index 000000000..c6e6f7e64
--- /dev/null
+++ b/embassy-sync/tests/ui/sync_impl/lazy_lock_function.rs
@@ -0,0 +1,15 @@
+use embassy_sync::lazy_lock::LazyLock;
+
+fn main() {
+    let x = 128u8;
+    let x_ptr: *const u8 = core::ptr::addr_of!(x);
+
+    let closure_capturing_non_sync_variable = || {
+        unsafe {
+            core::ptr::read(x_ptr)
+        }
+    };
+
+    // This should fail to compile because the closure captures a non-Sync variable: x_ptr.
+    let _lazy_u8: LazyLock<u8, _> = LazyLock::new(closure_capturing_non_sync_variable);
+}
diff --git a/embassy-sync/tests/ui/sync_impl/lazy_lock_type.rs b/embassy-sync/tests/ui/sync_impl/lazy_lock_type.rs
new file mode 100644
index 000000000..4e1383143
--- /dev/null
+++ b/embassy-sync/tests/ui/sync_impl/lazy_lock_type.rs
@@ -0,0 +1,6 @@
+use embassy_sync::lazy_lock::LazyLock;
+
+// *mut u8 is not Sync, so LazyLock should not implement Sync for this type. This should fail to compile.
+static GLOBAL: LazyLock<*mut u8> = LazyLock::new(|| core::ptr::null_mut());
+
+fn main() {}
diff --git a/embassy-sync/tests/ui/sync_impl/once_lock.rs b/embassy-sync/tests/ui/sync_impl/once_lock.rs
new file mode 100644
index 000000000..8f50d583b
--- /dev/null
+++ b/embassy-sync/tests/ui/sync_impl/once_lock.rs
@@ -0,0 +1,6 @@
+use embassy_sync::once_lock::OnceLock;
+
+// *mut u8 is not Sync, so OnceLock should not implement Sync for this type. This should fail to compile.
+static GLOBAL: OnceLock<*mut u8> = OnceLock::new();
+
+fn main() {}