Add backwards compatible support for fmt::Write

src/date.rs

@@ -824,6 +824,25 @@ impl Date {
         output: &mut impl io::Write,
         format: &(impl Formattable + ?Sized),
     ) -> Result<usize, error::Format> {
+        format.format_into_old(output, Some(self), None, None)
+    }
+
+    /// Format the `Date` using the provided [format description](crate::format_description).
+    ///
+    /// Exactly like [`Date::format_into`] but accepts a [`fmt::Write`] instead of an [`io::Write`]
+    /// ```rust
+    /// # use time::{format_description, macros::date};
+    /// let format = format_description::parse("[year]-[month]-[day]")?;
+    /// let mut buf = String::new();
+    /// date!(2020 - 01 - 02).format_into_fmt_writer(&mut buf, &format)?;
+    /// assert_eq!(buf, "2020-01-02");
+    /// # Ok::<_, time::Error>(())
+    /// ```
+    pub fn format_into_fmt_writer(
+        self,
+        output: &mut impl fmt::Write,
+        format: &(impl Formattable + ?Sized),
+    ) -> Result<(), error::Format> {
         format.format_into(output, Some(self), None, None)
     }
 

src/error/format.rs

@@ -21,6 +21,8 @@ pub enum Format {
     InvalidComponent(&'static str),
     /// A value of `std::io::Error` was returned internally.
     StdIo(io::Error),
+    /// A value of `std::fmt::Error` was returned internally.
+    StdFmt(fmt::Error),
 }
 
 impl fmt::Display for Format {
@@ -36,6 +38,7 @@ impl fmt::Display for Format {
                 component
             ),
             Self::StdIo(err) => err.fmt(f),
+            Self::StdFmt(err) => err.fmt(f),
         }
     }
 }
@@ -46,6 +49,12 @@ impl From<io::Error> for Format {
     }
 }
 
+impl From<fmt::Error> for Format {
+    fn from(err: fmt::Error) -> Self {
+        Self::StdFmt(err)
+    }
+}
+
 impl TryFrom<Format> for io::Error {
     type Error = error::DifferentVariant;
 
@@ -63,6 +72,7 @@ impl std::error::Error for Format {
         match *self {
             Self::InsufficientTypeInformation | Self::InvalidComponent(_) => None,
             Self::StdIo(ref err) => Some(err),
+            Self::StdFmt(ref err) => Some(err),
         }
     }
 }