From 0ccc7378331440d5d9bb40703cacc0d377a4a771 Mon Sep 17 00:00:00 2001
From: Folyd <lyshuhow@gmail.com>
Date: Tue, 4 May 2021 00:15:24 +0800
Subject: [PATCH] core: impl `Value` for `&mut T` where `T: Value` (#1385)

Impl `Value` for `&mut T` where `T: Value`.

#1378 improve the `tracing::instrument` macro's recording behavior: all
primitive types implementing the `Value` trait will be recorded as
fields of that type instead of `fmt::Debug`. This PR is a prerequisite
for those `&mut` function arguments to achieve that.
---
 tracing-core/src/field.rs | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/tracing-core/src/field.rs b/tracing-core/src/field.rs
index f9da95c99d..e3c2f5782b 100644
--- a/tracing-core/src/field.rs
+++ b/tracing-core/src/field.rs
@@ -433,6 +433,19 @@ where
     }
 }
 
+impl<'a, T: ?Sized> crate::sealed::Sealed for &'a mut T where T: Value + crate::sealed::Sealed + 'a {}
+
+impl<'a, T: ?Sized> Value for &'a mut T
+where
+    T: Value + 'a,
+{
+    fn record(&self, key: &Field, visitor: &mut dyn Visit) {
+        // Don't use `(*self).record(key, visitor)`, otherwise would
+        // cause stack overflow due to `unconditional_recursion`.
+        T::record(self, key, visitor)
+    }
+}
+
 impl<'a> crate::sealed::Sealed for fmt::Arguments<'a> {}
 
 impl<'a> Value for fmt::Arguments<'a> {