Remove hack to accept "UTC" in timezone_offset_zulu

src/datetime/tests.rs

@@ -743,6 +743,17 @@ fn test_datetime_from_str() {
             )
             .unwrap())
     );
+    assert_eq!(
+        "2015-02-18T23:16:9.15Utc".parse::<DateTime<Utc>>(),
+        Ok(Utc
+            .from_local_datetime(
+                &NaiveDate::from_ymd_opt(2015, 2, 18)
+                    .unwrap()
+                    .and_hms_milli_opt(23, 16, 9, 150)
+                    .unwrap()
+            )
+            .unwrap())
+    );
 
     assert_eq!(
         "2015-2-18T23:16:9.15Z".parse::<DateTime<FixedOffset>>(),

src/format/parse.rs

@@ -542,7 +542,8 @@ impl str::FromStr for DateTime<FixedOffset> {
 /// Differences with RFC3339:
 /// - Values don't require padding to two digits.
 /// - Years outside the range 0...=9999 are accepted, but they must include a sign.
-/// - `UTC` is accepted as a valid timezone name/offset.
+/// - `UTC` is accepted as a valid timezone name/offset (for compatibility with the debug format of
+///   `DateTime<Utc>`.
 /// - There can be spaces between any of the components.
 /// - The colon in the offset may be missing.
 fn parse_rfc3339_relaxed<'a>(parsed: &mut Parsed, mut s: &'a str) -> ParseResult<(&'a str, ())> {
@@ -565,7 +566,6 @@ fn parse_rfc3339_relaxed<'a>(parsed: &mut Parsed, mut s: &'a str) -> ParseResult
         Item::Numeric(Numeric::Second, Pad::Zero),
         Item::Fixed(Fixed::Nanosecond),
         Item::Space(""),
-        Item::Fixed(Fixed::TimezoneOffsetZ),
     ];
 
     s = match parse_internal(parsed, s, DATE_ITEMS.iter()) {
@@ -580,11 +580,19 @@ fn parse_rfc3339_relaxed<'a>(parsed: &mut Parsed, mut s: &'a str) -> ParseResult
         None => return Err(TOO_SHORT),
     };
 
-    match parse_internal(parsed, s, TIME_ITEMS.iter()) {
-        Err((s, e)) if e.0 == ParseErrorKind::TooLong => Ok((s, ())),
-        Err((_s, e)) => Err(e),
-        Ok(s) => Ok((s, ())),
-    }
+    s = match parse_internal(parsed, s, TIME_ITEMS.iter()) {
+        Err((s, e)) if e.0 == ParseErrorKind::TooLong => s,
+        Err((_s, e)) => return Err(e),
+        Ok(_) => return Err(NOT_ENOUGH),
+    };
+    s = s.trim_start();
+    let (s, offset) = if s.len() >= 3 && "UTC".eq_ignore_ascii_case(&s[..3]) {
+        (&s[3..], 0)
+    } else {
+        scan::timezone_offset(s, scan::colon_or_space, true, false, true)?
+    };
+    parsed.set_offset(i64::from(offset))?;
+    Ok((s, ()))
 }
 
 #[cfg(test)]

src/format/scan.rs

@@ -210,21 +210,8 @@ where
     F: FnMut(&str) -> ParseResult<&str>,
 {
     if allow_zulu {
-        let bytes = s.as_bytes();
-        match bytes.first() {
-            Some(&b'z') | Some(&b'Z') => return Ok((&s[1..], 0)),
-            Some(&b'u') | Some(&b'U') => {
-                if bytes.len() >= 3 {
-                    let (b, c) = (bytes[1], bytes[2]);
-                    match (b | 32, c | 32) {
-                        (b't', b'c') => return Ok((&s[3..], 0)),
-                        _ => return Err(INVALID),
-                    }
-                } else {
-                    return Err(INVALID);
-                }
-            }
-            _ => {}
+        if let Some(&b'Z' | &b'z') = s.as_bytes().first() {
+            return Ok((&s[1..], 0));
         }
     }