Add optional defmt support

Author: DBLouis

Cargo.toml

@@ -20,6 +20,7 @@ name = "chrono"
 # Don't forget to adjust `ALL_NON_EXCLUSIVE_FEATURES` in CI scripts when adding a feature or an optional dependency.
 default = ["clock", "std", "oldtime", "wasmbind"]
 alloc = []
+defmt = ["dep:defmt"]
 libc = []
 winapi = ["windows-targets"]
 std = ["alloc"]
@@ -43,6 +44,7 @@ serde = { version = "1.0.99", default-features = false, optional = true }
 pure-rust-locales = { version = "0.8", optional = true }
 rkyv = { version = "0.7.43", optional = true, default-features = false }
 arbitrary = { version = "1.0.0", features = ["derive"], optional = true }
+defmt = { version = "0.3", optional = true }
 
 [target.'cfg(all(target_arch = "wasm32", not(any(target_os = "emscripten", target_os = "wasi"))))'.dependencies]
 wasm-bindgen = { version = "0.2", optional = true }

src/date.rs

@@ -551,6 +551,16 @@ where
     }
 }
 
+#[cfg(feature = "defmt")]
+impl<Tz: TimeZone> defmt::Format for Date<Tz>
+where
+    Tz::Offset: defmt::Format,
+{
+    fn format(&self, fmt: defmt::Formatter) {
+        defmt::write!(fmt, "{}{}", self.naive_local(), self.offset);
+    }
+}
+
 // Note that implementation of Arbitrary cannot be automatically derived for Date<Tz>, due to
 // the nontrivial bound <Tz as TimeZone>::Offset: Arbitrary.
 #[cfg(all(feature = "arbitrary", feature = "std"))]

src/datetime/mod.rs

@@ -1761,6 +1761,16 @@ impl<Tz: TimeZone> fmt::Debug for DateTime<Tz> {
     }
 }
 
+#[cfg(feature = "defmt")]
+impl<Tz: TimeZone> defmt::Format for DateTime<Tz>
+where
+    Tz::Offset: defmt::Format,
+{
+    fn format(&self, fmt: defmt::Formatter) {
+        defmt::write!(fmt, "{}{}", self.overflowing_naive_local(), self.offset);
+    }
+}
+
 // `fmt::Debug` is hand implemented for the `rkyv::Archive` variant of `DateTime` because
 // deriving a trait recursively does not propagate trait defined associated types with their own
 // constraints:

src/lib.rs

@@ -636,6 +636,17 @@ pub mod serde {
             }
         }
     }
+
+    #[cfg(feature = "defmt")]
+    impl<T: defmt::Format> defmt::Format for SerdeError<T> {
+        fn format(&self, fmt: defmt::Formatter) {
+            match self {
+                SerdeError::InvalidTimestamp(ts) => {
+                    defmt::write!(fmt, "value is not a legal timestamp: {}", ts)
+                }
+            }
+        }
+    }
 }
 
 /// Zero-copy serialization/deserialization with rkyv.
@@ -684,6 +695,13 @@ impl fmt::Debug for OutOfRange {
     }
 }
 
+#[cfg(feature = "defmt")]
+impl defmt::Format for OutOfRange {
+    fn format(&self, fmt: defmt::Formatter) {
+        defmt::write!(fmt, "out of range");
+    }
+}
+
 #[cfg(feature = "std")]
 impl std::error::Error for OutOfRange {}
 

src/month.rs

@@ -284,6 +284,13 @@ impl fmt::Debug for ParseMonthError {
     }
 }
 
+#[cfg(feature = "defmt")]
+impl defmt::Format for ParseMonthError {
+    fn format(&self, fmt: defmt::Formatter) {
+        defmt::write!(fmt, "ParseMonthError {{ .. }}")
+    }
+}
+
 #[cfg(feature = "serde")]
 mod month_serde {
     use super::Month;

src/naive/date/mod.rs

@@ -2128,6 +2128,7 @@ impl From<NaiveDateTime> for NaiveDate {
 
 /// Iterator over `NaiveDate` with a step size of one day.
 #[derive(Debug, Copy, Clone, Hash, PartialEq, PartialOrd, Eq, Ord)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
 pub struct NaiveDateDaysIterator {
     value: NaiveDate,
 }
@@ -2164,6 +2165,7 @@ impl FusedIterator for NaiveDateDaysIterator {}
 
 /// Iterator over `NaiveDate` with a step size of one week.
 #[derive(Debug, Copy, Clone, Hash, PartialEq, PartialOrd, Eq, Ord)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
 pub struct NaiveDateWeeksIterator {
     value: NaiveDate,
 }
@@ -2238,6 +2240,13 @@ impl fmt::Debug for NaiveDate {
     }
 }
 
+#[cfg(feature = "defmt")]
+impl defmt::Format for NaiveDate {
+    fn format(&self, _: defmt::Formatter) {
+        defmt::todo!()
+    }
+}
+
 /// The `Display` output of the naive date `d` is the same as
 /// [`d.format("%Y-%m-%d")`](crate::format::strftime).
 ///

src/naive/datetime/mod.rs

@@ -2053,6 +2053,13 @@ impl fmt::Debug for NaiveDateTime {
     }
 }
 
+#[cfg(feature = "defmt")]
+impl defmt::Format for NaiveDateTime {
+    fn format(&self, fmt: defmt::Formatter) {
+        defmt::write!(fmt, "{}T{}", self.date, self.time);
+    }
+}
+
 /// The `Display` output of the naive date and time `dt` is the same as
 /// [`dt.format("%Y-%m-%d %H:%M:%S%.f")`](crate::format::strftime).
 ///

src/naive/isoweek.rs

@@ -160,6 +160,13 @@ impl fmt::Debug for IsoWeek {
     }
 }
 
+#[cfg(feature = "defmt")]
+impl defmt::Format for IsoWeek {
+    fn format(&self, _: defmt::Formatter) {
+        defmt::todo!()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     #[cfg(feature = "rkyv-validation")]

src/naive/time/mod.rs

@@ -1529,6 +1529,13 @@ impl fmt::Debug for NaiveTime {
     }
 }
 
+#[cfg(feature = "defmt")]
+impl defmt::Format for NaiveTime {
+    fn format(&self, _: defmt::Formatter) {
+        defmt::todo!()
+    }
+}
+
 /// The `Display` output of the naive time `t` is the same as
 /// [`t.format("%H:%M:%S%.f")`](crate::format::strftime).
 ///

src/offset/fixed.rs

@@ -9,6 +9,9 @@ use core::str::FromStr;
 #[cfg(any(feature = "rkyv", feature = "rkyv-16", feature = "rkyv-32", feature = "rkyv-64"))]
 use rkyv::{Archive, Deserialize, Serialize};
 
+#[cfg(feature = "defmt")]
+use defmt::Format;
+
 use super::{MappedLocalTime, Offset, TimeZone};
 use crate::format::{scan, ParseError, OUT_OF_RANGE};
 use crate::naive::{NaiveDate, NaiveDateTime};
@@ -27,6 +30,7 @@ use crate::naive::{NaiveDate, NaiveDateTime};
     archive_attr(derive(Clone, Copy, PartialEq, Eq, Hash, Debug))
 )]
 #[cfg_attr(feature = "rkyv-validation", archive(check_bytes))]
+#[cfg_attr(feature = "defmt", derive(Format))]
 pub struct FixedOffset {
     local_minus_utc: i32,
 }