[tracing-subscriber]: add chrono feature

tracing-subscriber/Cargo.toml

@@ -32,6 +32,9 @@ fmt = ["registry", "std"]
 ansi = ["fmt", "nu-ansi-term"]
 registry = ["sharded-slab", "thread_local", "std"]
 json = ["tracing-serde", "serde", "serde_json"]
+# Enables support for `chrono` based time formatters.
+chrono-time = []
+
 # Enables support for local time when using the `time` crate timestamp
 # formatters.
 local-time = ["time/local-offset"]

tracing-subscriber/src/fmt/time/chrono_crate.rs

@@ -1,31 +1,34 @@
 use crate::fmt::format::Writer;
 use crate::fmt::time::FormatTime;
 
-/// Formats [local time]s and [UTC time]s with [formatter] implementations
+/// Formats [local time]s and [UTC time]s with `FormatTime` implementations
 /// that use the [`chrono` crate].
 ///
-/// [local time]: https://docs.rs/chrono/0.4.26/chrono/offset/struct.Local.html
-/// [UTC time]: https://docs.rs/chrono/0.4.26/chrono/offset/struct.Utc.html
-/// [`chrono` crate]: https://docs.rs/chrono/0.4.26/chrono/
-/// [formatter]: https://docs.rs/time/0.3/time/formatting/trait.Formattable.html
+/// [local time]: [`chrono::offset::Local`]
+/// [UTC time]: [`chrono::offset::Utc`]
+/// [`chrono` crate]: [`chrono`]
 
-/// Tag-type (indicating UTC timezone) enabling static dispatch
-/// to `chrono::Local` functions.
-#[derive(Debug)]
-pub struct LocalTime;
+/// Retrieve and print the current local time.
+#[cfg(feature = "chrono-time")]
+#[cfg_attr(docsrs, doc(cfg(feature = "chrono-time")))]
+#[derive(Debug, Clone, Copy, Eq, PartialEq, Default)]
+pub struct ChronoLocal;
 
-impl FormatTime for LocalTime {
+#[cfg(feature = "chrono-time")]
+impl FormatTime for ChronoLocal {
     fn format_time(&self, w: &mut Writer<'_>) -> alloc::fmt::Result {
         w.write_str(&chrono::Local::now().to_rfc3339())
     }
 }
 
-/// Tag-type (indicating the "local" timezone) enabling static
-/// dispatch to `chrono::Utc` functions.
-#[derive(Debug)]
-pub struct Utc;
+/// Retrieve and print the current UTC time.
+#[cfg(feature = "chrono-time")]
+#[cfg_attr(docsrs, doc(cfg(feature = "chrono")))]
+#[derive(Debug, Clone, Copy, Eq, PartialEq, Default)]
+pub struct ChronoUtc;
 
-impl FormatTime for Utc {
+#[cfg(feature = "chrono-time")]
+impl FormatTime for ChronoUtc {
     fn format_time(&self, w: &mut Writer<'_>) -> alloc::fmt::Result {
         w.write_str(&chrono::Utc::now().to_rfc3339())
     }
@@ -36,22 +39,26 @@ mod tests {
     use crate::fmt::format::Writer;
     use crate::fmt::time::FormatTime;
 
-    use super::LocalTime;
-    use super::Utc;
+    #[cfg(feature = "chrono-time")]
+    use super::ChronoLocal;
+    #[cfg(feature = "chrono-time")]
+    use super::ChronoUtc;
 
+    #[cfg(feature = "chrono-time")]
     #[test]
     fn test_chrono_format_time_utc() {
         let mut buf = String::new();
         let mut dst: Writer<'_> = Writer::new(&mut buf);
-        assert!(FormatTime::format_time(&Utc, &mut dst).is_ok());
+        assert!(FormatTime::format_time(&ChronoUtc, &mut dst).is_ok());
         // e.g. `buf` contains "2023-08-18T19:05:08.662499+00:00"
     }
 
+    #[cfg(feature = "chrono-time")]
     #[test]
     fn test_chrono_format_time_local() {
         let mut buf = String::new();
         let mut dst: Writer<'_> = Writer::new(&mut buf);
-        assert!(FormatTime::format_time(&LocalTime, &mut dst).is_ok());
+        assert!(FormatTime::format_time(&ChronoLocal, &mut dst).is_ok());
         // e.g. `buf` contains "2023-08-18T14:59:08.662499-04:00".
     }
 }

tracing-subscriber/src/fmt/time/mod.rs

@@ -15,7 +15,8 @@ pub use time_crate::UtcTime;
 #[cfg_attr(docsrs, doc(cfg(all(unsound_local_offset, feature = "local-time"))))]
 pub use time_crate::LocalTime;
 
-/// [`Chrono`]-based implementation for time.
+/// [`chrono`]-based implementation for time.
+#[cfg(feature = "chrono-time")]
 pub mod chrono_crate;
 
 /// A type that can measure and format the current time.