[tracing-subscriber]: add chrono crate implementations of FormatTime

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

@@ -8,29 +8,63 @@ use crate::fmt::time::FormatTime;
 /// [UTC time]: [`chrono::offset::Utc`]
 /// [`chrono` crate]: [`chrono`]
 
+/// The RFC 3339 format is used by default but a custom format string
+/// can be used. See [`chrono::format::strftime`]for details on
+/// the supported syntax.
+///
+/// [`chrono::format::strftime`]: https://docs.rs/chrono/0.4.9/chrono/format/strftime/index.html
+#[cfg(feature = "chrono")]
+#[cfg_attr(docsrs, doc(cfg(feature = "chrono")))]
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub enum ChronoFmtType {
+    /// Format according to the RFC 3339 convention.
+    Rfc3339,
+    /// Format according to a custom format string.
+    Custom(String),
+}
+
+#[cfg(feature = "chrono")]
+impl Default for ChronoFmtType {
+    fn default() -> Self {
+        ChronoFmtType::Rfc3339
+    }
+}
+
 /// Retrieve and print the current local time.
 #[cfg(feature = "chrono")]
 #[cfg_attr(docsrs, doc(cfg(feature = "chrono")))]
-#[derive(Debug, Clone, Copy, Eq, PartialEq, Default)]
-pub struct ChronoLocal;
+#[derive(Debug, Clone, Eq, PartialEq, Default)]
+pub struct ChronoLocal {
+    format: ChronoFmtType,
+}
 
 #[cfg(feature = "chrono")]
 impl FormatTime for ChronoLocal {
     fn format_time(&self, w: &mut Writer<'_>) -> alloc::fmt::Result {
-        w.write_str(&chrono::Local::now().to_rfc3339())
+        let t = chrono::Local::now();
+        match &self.format {
+            ChronoFmtType::Rfc3339 => w.write_str(&t.to_rfc3339()),
+            ChronoFmtType::Custom(fmt) => w.write_str(&format!("{}", t.format(fmt))),
+        }
     }
 }
 
 /// Retrieve and print the current UTC time.
 #[cfg(feature = "chrono")]
 #[cfg_attr(docsrs, doc(cfg(feature = "chrono")))]
-#[derive(Debug, Clone, Copy, Eq, PartialEq, Default)]
-pub struct ChronoUtc;
+#[derive(Debug, Clone, Eq, PartialEq, Default)]
+pub struct ChronoUtc {
+    format: ChronoFmtType,
+}
 
 #[cfg(feature = "chrono")]
 impl FormatTime for ChronoUtc {
     fn format_time(&self, w: &mut Writer<'_>) -> alloc::fmt::Result {
-        w.write_str(&chrono::Utc::now().to_rfc3339())
+        let t = chrono::Utc::now();
+        match &self.format {
+            ChronoFmtType::Rfc3339 => w.write_str(&t.to_rfc3339()),
+            ChronoFmtType::Custom(fmt) => w.write_str(&format!("{}", t.format(fmt))),
+        }
     }
 }
 
@@ -39,26 +73,53 @@ mod tests {
     use crate::fmt::format::Writer;
     use crate::fmt::time::FormatTime;
 
+    #[cfg(feature = "chrono")]
+    use super::ChronoFmtType;
     #[cfg(feature = "chrono")]
     use super::ChronoLocal;
     #[cfg(feature = "chrono")]
     use super::ChronoUtc;
 
     #[cfg(feature = "chrono")]
     #[test]
-    fn test_chrono_format_time_utc() {
+    fn test_chrono_format_time_utc_default() {
         let mut buf = String::new();
         let mut dst: Writer<'_> = Writer::new(&mut buf);
-        assert!(FormatTime::format_time(&ChronoUtc, &mut dst).is_ok());
+        assert!(FormatTime::format_time(&ChronoUtc::default(), &mut dst).is_ok());
         // e.g. `buf` contains "2023-08-18T19:05:08.662499+00:00"
     }
 
     #[cfg(feature = "chrono")]
     #[test]
-    fn test_chrono_format_time_local() {
+    fn test_chrono_format_time_utc_custom() {
+        let fmt = ChronoUtc {
+            format: ChronoFmtType::Custom("%a %b %e %T %Y".to_owned()),
+        };
         let mut buf = String::new();
         let mut dst: Writer<'_> = Writer::new(&mut buf);
-        assert!(FormatTime::format_time(&ChronoLocal, &mut dst).is_ok());
+        assert!(FormatTime::format_time(&fmt, &mut dst).is_ok());
+        println!("{}", buf);
+        // e.g. `buf` contains "Wed Aug 23 15:53:23 2023"
+    }
+
+    #[cfg(feature = "chrono")]
+    #[test]
+    fn test_chrono_format_time_local_default() {
+        let mut buf = String::new();
+        let mut dst: Writer<'_> = Writer::new(&mut buf);
+        assert!(FormatTime::format_time(&ChronoLocal::default(), &mut dst).is_ok());
         // e.g. `buf` contains "2023-08-18T14:59:08.662499-04:00".
     }
+
+    #[cfg(feature = "chrono")]
+    #[test]
+    fn test_chrono_format_time_local_custom() {
+        let fmt = ChronoLocal {
+            format: ChronoFmtType::Custom("%a %b %e %T %Y".to_owned()),
+        };
+        let mut buf = String::new();
+        let mut dst: Writer<'_> = Writer::new(&mut buf);
+        assert!(FormatTime::format_time(&fmt, &mut dst).is_ok());
+        // e.g. `buf` contains "Wed Aug 23 15:55:46 2023".
+    }
 }