tracing(-futures): add Instrumented::span_and_inner_pin_mut

This is useful for implementing poll-type functions on foreign traits.

Closes #2804.

Author: sepointon

tracing-futures/src/lib.rs

@@ -449,6 +449,14 @@ where
 }
 
 impl<T> Instrumented<T> {
+    /// Get both a mutable reference to the `Span` that this type is
+    /// instrumented by and a pinned mutable reference to the inner value.
+    ///
+    /// This is useful for implementing poll-type functions on foreign traits.
+    pub fn span_and_inner_pin_mut(self: Pin<&mut Self>) -> (&mut Span, Pin<&mut T>) {
+        self.project().span_and_inner_pin_mut()
+    }
+
     /// Borrows the `Span` that this type is instrumented by.
     pub fn span(&self) -> &Span {
         &self.span

tracing/src/instrument.rs

@@ -325,6 +325,14 @@ impl<T: Future> Future for Instrumented<T> {
 impl<T: Sized> Instrument for T {}
 
 impl<T> Instrumented<T> {
+    /// Get both a mutable reference to the `Span` that this type is
+    /// instrumented by and a pinned mutable reference to the inner value.
+    ///
+    /// This is useful for implementing poll-type functions on foreign traits.
+    pub fn span_and_inner_pin_mut(self: Pin<&mut Self>) -> (&mut Span, Pin<&mut T>) {
+        self.project().span_and_inner_pin_mut()
+    }
+
     /// Borrows the `Span` that this type is instrumented by.
     pub fn span(&self) -> &Span {
         &self.span