Don't require alloc feature for Formatter

src/format/formatting.rs

@@ -8,19 +8,14 @@ extern crate alloc;
 
 #[cfg(feature = "alloc")]
 use alloc::string::{String, ToString};
-#[cfg(any(feature = "alloc", feature = "std"))]
 use core::borrow::Borrow;
 use core::fmt::{self, Display, Write};
 
-#[cfg(any(feature = "alloc", feature = "std"))]
 use crate::naive::{NaiveDate, NaiveDateTime, NaiveTime};
-#[cfg(any(feature = "alloc", feature = "std"))]
 use crate::offset::{FixedOffset, Offset};
-#[cfg(any(feature = "alloc", feature = "std"))]
 use crate::{Datelike, Timelike, Weekday};
 
 use super::locales;
-#[cfg(any(feature = "alloc", feature = "std"))]
 use super::{
     Colons, Fixed, InternalFixed, InternalInternal, Item, Locale, Numeric, OffsetFormat,
     OffsetPrecision, Pad,
@@ -29,7 +24,6 @@ use locales::*;
 
 /// A *temporary* object which can be used as an argument to `format!` or others.
 /// This is normally constructed via `format` methods of each date and time type.
-#[cfg(any(feature = "alloc", feature = "std"))]
 #[derive(Debug)]
 pub struct Formatter<I, Off> {
     /// The date view, if any.
@@ -45,7 +39,6 @@ pub struct Formatter<I, Off> {
     locale: Locale,
 }
 
-#[cfg(any(feature = "alloc", feature = "std"))]
 impl<'a, I, B, Off> Formatter<I, Off>
 where
     I: Iterator<Item = B> + Clone,
@@ -82,6 +75,7 @@ where
         for item in self.items.clone() {
             match *item.borrow() {
                 Item::Literal(s) | Item::Space(s) => w.write_str(s),
+                #[cfg(any(feature = "alloc", feature = "std"))]
                 Item::OwnedLiteral(ref s) | Item::OwnedSpace(ref s) => w.write_str(s),
                 Item::Numeric(ref spec, ref pad) => self.format_numeric(w, spec, pad),
                 Item::Fixed(ref spec) => self.format_fixed(w, spec),
@@ -245,17 +239,24 @@ where
     }
 }
 
-#[cfg(any(feature = "alloc", feature = "std"))]
 impl<'a, I, B, Off> Display for Formatter<I, Off>
 where
     I: Iterator<Item = B> + Clone,
     B: Borrow<Item<'a>>,
     Off: Offset + Display,
 {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        let mut result = String::new();
-        self.format(&mut result)?;
-        f.pad(&result)
+        #[cfg(any(feature = "alloc", feature = "std", test))]
+        if f.width().is_some() {
+            // Justify/pad/truncate the formatted result by rendering it to a temporary `String`
+            // first.
+            // We skip this step if there are no 'external' formatting specifiers.
+            // This is the only formatting functionality that is missing without `alloc`.
+            let mut result = String::new();
+            self.format(&mut result)?;
+            return f.pad(&result);
+        }
+        self.format(f)
     }
 }
 
@@ -425,7 +426,6 @@ pub fn format_item_localized(
         .fmt(w)
 }
 
-#[cfg(any(feature = "alloc", feature = "std"))]
 impl OffsetFormat {
     /// Writes an offset from UTC with the format defined by `self`.
     fn format(&self, w: &mut impl Write, off: FixedOffset) -> fmt::Result {
@@ -506,7 +506,6 @@ impl OffsetFormat {
 }
 
 /// Writes the date, time and offset to the string. same as `%Y-%m-%dT%H:%M:%S%.f%:z`
-#[cfg(any(feature = "alloc", feature = "std"))]
 pub(crate) fn write_rfc3339(
     w: &mut impl Write,
     dt: NaiveDateTime,
@@ -534,7 +533,6 @@ pub(crate) fn write_rfc2822(
     write_rfc2822_inner(w, dt.date(), dt.time(), off, default_locale())
 }
 
-#[cfg(any(feature = "alloc", feature = "std"))]
 /// write datetimes like `Tue, 1 Jul 2003 10:52:37 +0200`, same as `%a, %d %b %Y %H:%M:%S %z`
 fn write_rfc2822_inner(
     w: &mut impl Write,

src/format/mod.rs

@@ -54,9 +54,10 @@ pub mod strftime;
 pub(crate) mod locales;
 
 pub(crate) use formatting::write_hundreds;
+pub use formatting::Formatter;
 #[allow(deprecated)]
 #[cfg(any(feature = "alloc", feature = "std"))]
-pub use formatting::{format, format_item, DelayedFormat, Formatter};
+pub use formatting::{format, format_item, DelayedFormat};
 #[allow(deprecated)]
 #[cfg(feature = "unstable-locales")]
 pub use formatting::{format_item_localized, format_localized};