Update error.rs

Author: bushrat011899

library/core/src/io/error.rs

@@ -214,6 +214,12 @@ pub struct Custom {
     outer_drop: unsafe fn(*mut Self),
 }
 
+// SAFETY: All members of `Custom` are `Send`
+unsafe impl Send for Custom {}
+
+// SAFETY: All members of `Custom` are `Sync`
+unsafe impl Sync for Custom {}
+
 impl fmt::Debug for Custom {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("Custom").field("kind", &self.kind).field("error", self.error_ref()).finish()
@@ -274,6 +280,12 @@ impl Custom {
 #[doc(hidden)]
 pub struct CustomOwner(crate::ptr::NonNull<Custom>);
 
+// SAFETY: Custom is `Send`
+unsafe impl Send for CustomOwner {}
+
+// SAFETY: Custom is `Sync`
+unsafe impl Sync for CustomOwner {}
+
 impl Drop for CustomOwner {
     fn drop(&mut self) {
         // SAFETY: `CustomOwner::from_raw` ensures this call is safe.