Make Label Send + Sync (#139)

buffer/src/value.rs

@@ -1509,6 +1509,14 @@ mod alloc_support {
         use sval::Stream as _;
         use sval_derive::*;
 
+        #[test]
+        fn is_send_sync() {
+            fn assert<T: Send + Sync>() {}
+
+            assert::<ValueBuf>();
+            assert::<Value>();
+        }
+
         #[test]
         fn empty_is_complete() {
             assert!(!ValueBuf::new().is_complete());

src/data.rs

@@ -40,6 +40,11 @@ pub struct Label<'computed> {
     _marker: PhantomData<&'computed str>,
 }
 
+// SAFETY: Label doesn't mutate or synchronize: it acts just like a `&str`
+unsafe impl<'computed> Send for Label<'computed> { }
+// SAFETY: Label doesn't mutate or synchronize: it acts just like a `&str`
+unsafe impl<'computed> Sync for Label<'computed> { }
+
 #[cfg(not(feature = "alloc"))]
 impl<'computed> Clone for Label<'computed> {
     fn clone(&self) -> Self {
@@ -344,6 +349,13 @@ mod alloc_support {
 mod tests {
     use super::*;
 
+    #[test]
+    fn label_send_sync() {
+        fn assert<T: Send + Sync>() {}
+
+        assert::<Label>();
+    }
+
     #[test]
     fn label_static() {
         let label = Label::new("a");