feat(fmt)!: Generalize custom formatter to 'RecordFormat'

src/fmt/mod.rs

@@ -200,7 +200,18 @@ impl fmt::Debug for Formatter {
     }
 }
 
-pub(crate) trait RecordFormat {
+/// Formats a log [`Record`] to be outputted
+///
+/// This is called on each record logged and should format the
+/// log record and output it to the given [`Formatter`].
+///
+/// This is expected to output the content directly to the
+/// [`Formatter`] so that implementations can use the [`std::fmt`] macros
+/// to format and output without intermediate heap allocations.
+///
+/// When the `color` feature is enabled, styling via ANSI escape codes is supported and the
+/// output will automatically respect [`Builder::write_style`].
+pub trait RecordFormat {
     fn format(&self, formatter: &mut Formatter, record: &Record<'_>) -> io::Result<()>;
 }
 

src/logger.rs

@@ -1,4 +1,6 @@
-use std::{borrow::Cow, cell::RefCell, env, io};
+#[cfg(feature = "kv")]
+use std::io;
+use std::{borrow::Cow, cell::RefCell, env};
 
 use log::{LevelFilter, Log, Metadata, Record, SetLoggerError};
 
@@ -242,7 +244,7 @@ impl Builder {
     /// [`std::fmt`]: https://doc.rust-lang.org/std/fmt/index.html
     pub fn format<F>(&mut self, format: F) -> &mut Self
     where
-        F: Fn(&mut Formatter, &Record<'_>) -> io::Result<()> + Sync + Send + 'static,
+        F: fmt::RecordFormat + Sync + Send + 'static,
     {
         self.format.custom_format = Some(Box::new(format));
         self