Support parsing negative timestamps

Author: pitdicker

src/format/parse.rs

@@ -357,7 +357,7 @@ where
                     Minute => (2, false, Parsed::set_minute),
                     Second => (2, false, Parsed::set_second),
                     Nanosecond => (9, false, Parsed::set_nanosecond),
-                    Timestamp => (usize::MAX, false, Parsed::set_timestamp),
+                    Timestamp => (usize::MAX, true, Parsed::set_timestamp),
 
                     // for the future expansion
                     Internal(ref int) => match int._dummy {},
@@ -366,8 +366,7 @@ where
                 s = s.trim_start();
                 let v = if signed {
                     if s.starts_with('-') {
-                        let v = try_consume!(scan::number(&s[1..], 1, usize::MAX));
-                        0i64.checked_sub(v).ok_or(OUT_OF_RANGE)?
+                        try_consume!(scan::negative_number(&s[1..], 1, usize::MAX))
                     } else if s.starts_with('+') {
                         try_consume!(scan::number(&s[1..], 1, usize::MAX))
                     } else {
@@ -765,6 +764,7 @@ mod tests {
         check("  +   42", &[Space("  "), num(Year)], Err(INVALID));
         check("-", &[num(Year)], Err(TOO_SHORT));
         check("+", &[num(Year)], Err(TOO_SHORT));
+        check("-9223372036854775808", &[num(Timestamp)], parsed!(timestamp: i64::MIN));
 
         // unsigned numeric
         check("345", &[num(Ordinal)], parsed!(ordinal: 345));

src/format/scan.rs

@@ -15,6 +15,16 @@ use crate::Weekday;
 /// Any number that does not fit in `i64` is an error.
 #[inline]
 pub(super) fn number(s: &str, min: usize, max: usize) -> ParseResult<(&str, i64)> {
+    let (s, n) = negative_number(s, min, max)?;
+    Ok((s, n.checked_neg().ok_or(OUT_OF_RANGE)?))
+}
+
+/// Tries to parse a negative number from `min` to `max` digits.
+///
+/// This method parses a value as a negative integer, of wich the range is one larger than the range
+/// of positive integers. This is to allows us to parse `i64::MIN`.
+#[inline]
+pub(super) fn negative_number(s: &str, min: usize, max: usize) -> ParseResult<(&str, i64)> {
     assert!(min <= max);
 
     // We are only interested in ascii numbers, so we can work with the `str` as bytes. We stop on
@@ -36,7 +46,7 @@ pub(super) fn number(s: &str, min: usize, max: usize) -> ParseResult<(&str, i64)
             }
         }
 
-        n = match n.checked_mul(10).and_then(|n| n.checked_add((c - b'0') as i64)) {
+        n = match n.checked_mul(10).and_then(|n| n.checked_sub((c - b'0') as i64)) {
             Some(n) => n,
             None => return Err(OUT_OF_RANGE),
         };