Remove `Sized` bound from `MutexGuard::map`

Since `MutexGuard` has `T: ?Sized`, `U` does not need to be restricted
to `Sized` types. This now allows using `map` to cast from
`MutexGuard<'_, M, ImplsTrait>` to `MutexGuard<'_, M, dyn Trait>`.

2 files changed, 3 insertions, 2 deletions

diff --git a/embassy-sync/CHANGELOG.md b/embassy-sync/CHANGELOG.md
index a53d5f5b1..242b8b7ab 100644
--- a/embassy-sync/CHANGELOG.md
+++ b/embassy-sync/CHANGELOG.md
@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 <!-- next-header -->
 ## Unreleased - ReleaseDate
 - Fix wakers getting dropped by `Signal::reset`
+- Remove `Sized` trait bound from `MutexGuard::map`
 
 ## 0.7.2 - 2025-08-26
 
diff --git a/embassy-sync/src/mutex.rs b/embassy-sync/src/mutex.rs
index 4ce6dd987..aea682899 100644
--- a/embassy-sync/src/mutex.rs
+++ b/embassy-sync/src/mutex.rs
@@ -187,7 +187,7 @@ where
     T: ?Sized,
 {
     /// Returns a locked view over a portion of the locked data.
-    pub fn map<U>(this: Self, fun: impl FnOnce(&mut T) -> &mut U) -> MappedMutexGuard<'a, M, U> {
+    pub fn map<U: ?Sized>(this: Self, fun: impl FnOnce(&mut T) -> &mut U) -> MappedMutexGuard<'a, M, U> {
         let mutex = this.mutex;
         let value = fun(unsafe { &mut *this.mutex.inner.get() });
         // Don't run the `drop` method for MutexGuard. The ownership of the underlying
@@ -279,7 +279,7 @@ where
     T: ?Sized,
 {
     /// Returns a locked view over a portion of the locked data.
-    pub fn map<U>(this: Self, fun: impl FnOnce(&mut T) -> &mut U) -> MappedMutexGuard<'a, M, U> {
+    pub fn map<U: ?Sized>(this: Self, fun: impl FnOnce(&mut T) -> &mut U) -> MappedMutexGuard<'a, M, U> {
         let state = this.state;
         let value = fun(unsafe { &mut *this.value });
         // Don't run the `drop` method for MutexGuard. The ownership of the underlying