Use parse_rfc3339 directly in DateTime::parse_from_rfc3339

We want this to use the strict parser directly, so we can switch the `RFC3339`
item to a relaxed parser.

src/datetime/mod.rs

@@ -16,10 +16,12 @@ use std::time::{SystemTime, UNIX_EPOCH};
 
 #[cfg(feature = "unstable-locales")]
 use crate::format::Locale;
-use crate::format::{parse, parse_and_remainder, ParseError, ParseResult, Parsed, StrftimeItems};
+use crate::format::{
+    parse, parse_and_remainder, parse_rfc3339, Fixed, Item, ParseError, ParseResult, Parsed,
+    StrftimeItems, TOO_LONG,
+};
 #[cfg(any(feature = "alloc", feature = "std"))]
 use crate::format::{write_rfc3339, DelayedFormat};
-use crate::format::{Fixed, Item};
 use crate::naive::{Days, IsoWeek, NaiveDate, NaiveDateTime, NaiveTime};
 #[cfg(feature = "clock")]
 use crate::offset::Local;
@@ -699,9 +701,11 @@ impl DateTime<FixedOffset> {
     /// also simultaneously valid RFC 3339 values, but not all RFC 3339 values are valid ISO 8601
     /// values (or the other way around).
     pub fn parse_from_rfc3339(s: &str) -> ParseResult<DateTime<FixedOffset>> {
-        const ITEMS: &[Item<'static>] = &[Item::Fixed(Fixed::RFC3339)];
         let mut parsed = Parsed::new();
-        parse(&mut parsed, s, ITEMS.iter())?;
+        let (s, _) = parse_rfc3339(&mut parsed, s)?;
+        if !s.is_empty() {
+            return Err(TOO_LONG);
+        }
         parsed.to_datetime()
     }
 

src/format/mod.rs

@@ -69,6 +69,7 @@ pub use formatting::{format_item_localized, format_localized};
 pub use locales::Locale;
 #[cfg(all(not(feature = "unstable-locales"), any(feature = "alloc", feature = "std")))]
 pub(crate) use locales::Locale;
+pub(crate) use parse::parse_rfc3339;
 pub use parse::{parse, parse_and_remainder};
 pub use parsed::Parsed;
 pub use strftime::StrftimeItems;
@@ -450,7 +451,7 @@ const IMPOSSIBLE: ParseError = ParseError(ParseErrorKind::Impossible);
 const NOT_ENOUGH: ParseError = ParseError(ParseErrorKind::NotEnough);
 const INVALID: ParseError = ParseError(ParseErrorKind::Invalid);
 const TOO_SHORT: ParseError = ParseError(ParseErrorKind::TooShort);
-const TOO_LONG: ParseError = ParseError(ParseErrorKind::TooLong);
+pub(crate) const TOO_LONG: ParseError = ParseError(ParseErrorKind::TooLong);
 const BAD_FORMAT: ParseError = ParseError(ParseErrorKind::BadFormat);
 
 // this implementation is here only because we need some private code from `scan`

src/format/parse.rs

@@ -155,7 +155,7 @@ fn parse_rfc2822<'a>(parsed: &mut Parsed, mut s: &'a str) -> ParseResult<(&'a st
     Ok((s, ()))
 }
 
-fn parse_rfc3339<'a>(parsed: &mut Parsed, mut s: &'a str) -> ParseResult<(&'a str, ())> {
+pub(crate) fn parse_rfc3339<'a>(parsed: &mut Parsed, mut s: &'a str) -> ParseResult<(&'a str, ())> {
     macro_rules! try_consume {
         ($e:expr) => {{
             let (s_, v) = $e?;
@@ -1817,15 +1817,9 @@ mod tests {
             ("2015-01-20T00:00:1-08:00", Err(INVALID)),  // missing complete S
         ];
 
-        fn rfc3339_to_datetime(date: &str) -> ParseResult<DateTime<FixedOffset>> {
-            let mut parsed = Parsed::new();
-            parse(&mut parsed, date, [Item::Fixed(Fixed::RFC3339)].iter())?;
-            parsed.to_datetime()
-        }
-
         // Test against test data above
         for &(date, checkdate) in testdates.iter() {
-            let dt = rfc3339_to_datetime(date); // parse a date
+            let dt = DateTime::<FixedOffset>::parse_from_rfc3339(date);
             if dt != checkdate {
                 // check for expected result
                 panic!(