From d6fb4a9ff39c9ca9059dfc70b5dbca8148f500c1 Mon Sep 17 00:00:00 2001
From: Marcus Pettersen Irgens <m@mrcus.dev>
Date: Wed, 3 Apr 2024 17:54:04 +0200
Subject: [PATCH] tracing: add record! macro

Add a macro that provides a more consise way of recording a new value
for a field.

Example usage:

```rust
fn my_function() {
    let my_new_value = my_other_function();

    // Using the current API:
    tracing::Span::current().record("example", tracing::field::debug(my_new_value));

    // Using this proposal:
    tracing::record!("example", ?my_new_value);
}
```
---
 examples/examples/record.rs | 29 +++++++++++++++++++++++++++++
 tracing/src/macros.rs       | 16 ++++++++++++++++
 2 files changed, 45 insertions(+)
 create mode 100644 examples/examples/record.rs

diff --git a/examples/examples/record.rs b/examples/examples/record.rs
new file mode 100644
index 000000000..c6bc85a35
--- /dev/null
+++ b/examples/examples/record.rs
@@ -0,0 +1,29 @@
+//! An example of using the [`record`][crate::record] macro to add a field to a span.
+#![deny(rust_2018_idioms)]
+#![allow(clippy::try_err)]
+
+use rand::{seq::SliceRandom, thread_rng};
+use tracing::{instrument, record};
+
+fn main() {
+    tracing_subscriber::fmt()
+        // enable everything
+        .with_max_level(tracing::Level::TRACE)
+        // sets this to be the default, global collector for this application.
+        .init();
+
+    do_something();
+}
+
+#[instrument(fields(important_number = tracing::field::Empty))]
+fn do_something() {
+    let important_number = get_important_number();
+    record!("important_number", %important_number);
+
+    tracing::info!("log entry with important number");
+}
+
+fn get_important_number() -> u8 {
+    let numbers = [42, 13];
+    *numbers.choose(&mut thread_rng()).unwrap()
+}
diff --git a/tracing/src/macros.rs b/tracing/src/macros.rs
index 5de45cb75..d6cf4fb73 100644
--- a/tracing/src/macros.rs
+++ b/tracing/src/macros.rs
@@ -3160,3 +3160,19 @@ macro_rules! if_log_enabled {
         }
     };
 }
+
+#[doc(hidden)]
+#[macro_export]
+macro_rules! record {
+    ($field:expr, %$value:expr) => {
+        $crate::record!($field, ::tracing::field::display(&$value))
+    };
+    ($field:expr, ?$value:expr) => {
+        $crate::record!($field, ::tracing::field::debug(&$value))
+    };
+    ($field:expr, $value:expr) => {{
+        #[allow(unused)]
+        use ::tracing::field::{debug, display};
+        ::tracing::Span::current().record($field, $value);
+    }};
+}