work on macro support for capturing

README.md

@@ -103,10 +103,10 @@ The executable itself may use the `log` crate to log as well.
 If you enable the `kv_unstable` feature, you can associate structured data with your log records:
 
 ```rust
-use log::{info, trace, warn, as_serde, as_error};
+use log::{info, trace, warn};
 
 pub fn shave_the_yak(yak: &mut Yak) {
-    trace!(target = "yak_events", yak = as_serde!(yak); "Commencing yak shaving");
+    trace!(target = "yak_events", yak:serde = yak; "Commencing yak shaving");
 
     loop {
         match find_a_razor() {
@@ -116,7 +116,7 @@ pub fn shave_the_yak(yak: &mut Yak) {
                 break;
             }
             Err(err) => {
-                warn!(err = as_error!(err); "Unable to locate a razor, retrying");
+                warn!(err:error = err; "Unable to locate a razor, retrying");
             }
         }
     }

src/__private_api.rs

@@ -5,31 +5,28 @@ use crate::{Level, Metadata, Record};
 use std::fmt::Arguments;
 pub use std::{file, format_args, line, module_path, stringify};
 
-#[cfg(feature = "kv_unstable")]
-pub type Value<'a> = dyn crate::kv::value::ToValue + 'a;
-
 #[cfg(not(feature = "kv_unstable"))]
-pub type Value<'a> = str;
+pub type Value<'a> = &'a str;
 
 mod sealed {
     /// Types for the `kv` argument.
     pub trait KVs<'a> {
-        fn into_kvs(self) -> Option<&'a [(&'a str, &'a super::Value<'a>)]>;
+        fn into_kvs(self) -> Option<&'a [(&'a str, super::Value<'a>)]>;
     }
 }
 
 // Types for the `kv` argument.
 
-impl<'a> KVs<'a> for &'a [(&'a str, &'a Value<'a>)] {
+impl<'a> KVs<'a> for &'a [(&'a str, Value<'a>)] {
     #[inline]
-    fn into_kvs(self) -> Option<&'a [(&'a str, &'a Value<'a>)]> {
+    fn into_kvs(self) -> Option<&'a [(&'a str, Value<'a>)]> {
         Some(self)
     }
 }
 
 impl<'a> KVs<'a> for () {
     #[inline]
-    fn into_kvs(self) -> Option<&'a [(&'a str, &'a Value<'a>)]> {
+    fn into_kvs(self) -> Option<&'a [(&'a str, Value<'a>)]> {
         None
     }
 }
@@ -41,7 +38,7 @@ fn log_impl(
     level: Level,
     &(target, module_path, file): &(&str, &'static str, &'static str),
     line: u32,
-    kvs: Option<&[(&str, &Value)]>,
+    kvs: Option<&[(&str, Value)]>,
 ) {
     #[cfg(not(feature = "kv_unstable"))]
     if kvs.is_some() {
@@ -87,3 +84,42 @@ pub fn log<'a, K>(
 pub fn enabled(level: Level, target: &str) -> bool {
     crate::logger().enabled(&Metadata::builder().level(level).target(target).build())
 }
+
+#[cfg(feature = "kv_unstable")]
+mod kv_support {
+    use super::*;
+
+    use crate::kv;
+
+    pub type Value<'a> = kv::Value<'a>;
+
+    pub fn capture_to_value<'a, V: kv::value::ToValue + ?Sized>(v: &'a &'a V) -> Value<'a> {
+        v.to_value()
+    }
+
+    pub fn capture_debug<'a, V: core::fmt::Debug + ?Sized>(v: &'a &'a V) -> Value<'a> {
+        Value::from_debug(v)
+    }
+
+    pub fn capture_display<'a, V: core::fmt::Display + ?Sized>(v: &'a &'a V) -> Value<'a> {
+        Value::from_display(v)
+    }
+
+    #[cfg(feature = "kv_unstable_std")]
+    pub fn capture_error<'a>(v: &'a (dyn std::error::Error + 'static)) -> Value<'a> {
+        Value::from_dyn_error(v)
+    }
+
+    #[cfg(feature = "kv_unstable_sval")]
+    pub fn capture_sval<'a, V: sval::Value + ?Sized>(v: &'a &'a V) -> Value<'a> {
+        Value::from_sval(v)
+    }
+
+    #[cfg(feature = "kv_unstable_serde")]
+    pub fn capture_serde<'a, V: serde::Serialize + ?Sized>(v: &'a &'a V) -> Value<'a> {
+        Value::from_serde(v)
+    }
+}
+
+#[cfg(feature = "kv_unstable")]
+pub use self::kv_support::*;

src/kv/mod.rs

@@ -20,8 +20,8 @@
 //! unstructured text first.
 //!
 //! In `log`, user-defined attributes are part of a [`Source`] on the log record.
-//! Each attribute is a key-value; a pair of [`Key`] and [`Value`]. Keys are strings 
-//! and values are a datum of any type that can be formatted or serialized. Simple types 
+//! Each attribute is a key-value; a pair of [`Key`] and [`Value`]. Keys are strings
+//! and values are a datum of any type that can be formatted or serialized. Simple types
 //! like strings, booleans, and numbers are supported, as well as arbitrarily complex
 //! structures involving nested objects and sequences.
 //!
@@ -36,14 +36,14 @@
 //! ## Working with key-values on log records
 //!
 //! Use the [`LogRecord::key_values`] method to access key-values.
-//! 
+//!
 //! Individual values can be pulled from the source by their key:
 //!
 //! ```
 //! # fn main() -> Result<(), log::kv::Error> {
 //! use log::kv::{Source, Key, Value};
 //! # let record = log::Record::builder().key_values(&[("a", 1)]).build();
-//! 
+//!
 //! // info!("Something of interest"; a = 1);
 //! let a: Value = record.key_values().get(Key::from("a")).unwrap();
 //! # Ok(())
@@ -56,28 +56,28 @@
 //! # fn main() -> Result<(), log::kv::Error> {
 //! # let record = log::Record::builder().key_values(&[("a", 1), ("b", 2), ("c", 3)]).build();
 //! use std::collections::BTreeMap;
-//! 
+//!
 //! use log::kv::{self, Source, Key, Value, source::Visitor};
-//! 
+//!
 //! struct Collect<'kvs>(BTreeMap<Key<'kvs>, Value<'kvs>>);
-//! 
+//!
 //! impl<'kvs> Visitor<'kvs> for Collect<'kvs> {
 //!     fn visit_pair(&mut self, key: Key<'kvs>, value: Value<'kvs>) -> Result<(), kv::Error> {
 //!         self.0.insert(key, value);
-//! 
+//!
 //!         Ok(())
 //!     }
 //! }
-//! 
+//!
 //! let mut visitor = Collect(BTreeMap::new());
-//! 
+//!
 //! // info!("Something of interest"; a = 1, b = 2, c = 3);
 //! record.key_values().visit(&mut visitor)?;
-//! 
+//!
 //! let collected = visitor.0;
-//! 
+//!
 //! assert_eq!(
-//!     vec!["a", "b", "c"], 
+//!     vec!["a", "b", "c"],
 //!     collected
 //!         .keys()
 //!         .map(|k| k.as_str())
@@ -93,10 +93,10 @@
 //! # fn main() -> Result<(), log::kv::Error> {
 //! use log::kv::{Source, Key};
 //! # let record = log::Record::builder().key_values(&[("a", 1)]).build();
-//! 
+//!
 //! // info!("Something of interest"; a = 1);
 //! let a = record.key_values().get(Key::from("a")).unwrap();
-//! 
+//!
 //! assert_eq!(1, a.to_i64().unwrap());
 //! # Ok(())
 //! # }
@@ -109,9 +109,9 @@
 //! # fn main() -> Result<(), log::kv::Error> {
 //! use log::kv::{self, Source, Key, value::Visitor};
 //! # let record = log::Record::builder().key_values(&[("a", 1)]).build();
-//! 
+//!
 //! struct IsNumeric(bool);
-//! 
+//!
 //! impl<'kvs> Visitor<'kvs> for IsNumeric {
 //!     fn visit_any(&mut self, _value: kv::Value) -> Result<(), kv::Error> {
 //!         self.0 = false;
@@ -143,23 +143,23 @@
 //!         Ok(())
 //!     }
 //! }
-//! 
+//!
 //! // info!("Something of interest"; a = 1);
 //! let a = record.key_values().get(Key::from("a")).unwrap();
-//! 
+//!
 //! let mut visitor = IsNumeric(false);
-//! 
+//!
 //! a.visit(&mut visitor)?;
-//! 
+//!
 //! let is_numeric = visitor.0;
-//! 
+//!
 //! assert!(is_numeric);
 //! # Ok(())
 //! # }
 //! ```
 //!
 //! To serialize a value to a format like JSON, you can also use either `serde` or `sval`:
-//! 
+//!
 //! ```
 //! # fn main() -> Result<(), Box<dyn std::error::Error>> {
 //! # #[cfg(feature = "serde")]
@@ -169,16 +169,16 @@
 //! let data = Data { a: 1, b: true, c: "Some data" };
 //! # let source = [("a", log::kv::Value::from_serde(&data))];
 //! # let record = log::Record::builder().key_values(&source).build();
-//! 
+//!
 //! // info!("Something of interest"; a = data);
 //! let a = record.key_values().get(Key::from("a")).unwrap();
-//! 
+//!
 //! assert_eq!("{\"a\":1,\"b\":true,\"c\":\"Some data\"}", serde_json::to_string(&a)?);
 //! # }
 //! # Ok(())
 //! # }
 //! ```
-//! 
+//!
 //! The choice of serialization framework depends on the needs of the consumer.
 //! If you're in a no-std environment, you can use `sval`. In other cases, you can use `serde`.
 //! Log producers and log consumers don't need to agree on the serialization framework.
@@ -187,17 +187,17 @@
 //!
 //! Values can also always be formatted using the standard `Debug` and `Display`
 //! traits:
-//! 
+//!
 //! ```
 //! # use log::kv::Key;
 //! # #[derive(Debug)] struct Data { a: i32, b: bool, c: &'static str }
 //! let data = Data { a: 1, b: true, c: "Some data" };
 //! # let source = [("a", log::kv::Value::from_debug(&data))];
 //! # let record = log::Record::builder().key_values(&source).build();
-//! 
+//!
 //! // info!("Something of interest"; a = data);
 //! let a = record.key_values().get(Key::from("a")).unwrap();
-//! 
+//!
 //! assert_eq!("Data { a: 1, b: true, c: \"Some data\" }", format!("{a:?}"));
 //! ```
 

src/kv/source.rs

@@ -1,5 +1,5 @@
 //! Sources for key-values.
-//! 
+//!
 //! This module defines the [`Source`] type and supporting APIs for
 //! working with collections of key-values.
 
@@ -11,7 +11,7 @@ use std::fmt;
 /// The source may be a single pair, a set of pairs, or a filter over a set of pairs.
 /// Use the [`Visitor`](trait.Visitor.html) trait to inspect the structured data
 /// in a source.
-/// 
+///
 /// A source is like an iterator over its key-values, except with a push-based API
 /// instead of a pull-based one.
 ///
@@ -22,27 +22,27 @@ use std::fmt;
 /// ```
 /// # fn main() -> Result<(), log::kv::Error> {
 /// use log::kv::{self, Source, Key, Value, source::Visitor};
-/// 
+///
 /// // A `Visitor` that prints all key-values
 /// // Visitors are fed the key-value pairs of each key-values
 /// struct Printer;
-/// 
+///
 /// impl<'kvs> Visitor<'kvs> for Printer {
 ///     fn visit_pair(&mut self, key: Key<'kvs>, value: Value<'kvs>) -> Result<(), kv::Error> {
 ///         println!("{key}: {value}");
-/// 
+///
 ///         Ok(())
 ///     }
 /// }
-/// 
+///
 /// // A source with 3 key-values
 /// // Common collection types implement the `Source` trait
 /// let source = &[
 ///     ("a", 1),
 ///     ("b", 2),
 ///     ("c", 3),
 /// ];
-/// 
+///
 /// // Pass an instance of the `Visitor` to a `Source` to visit it
 /// source.visit(&mut Printer)?;
 /// # Ok(())