Fix return of negative integers with partial parser.

Previously, numbers such as `-1a` would return `Ok((1, 2))` from the
partial parser, because the wrapping, negative value wasn't handled.
This changes it to correctly return `Ok((-1, 2))`.

Closes #86.

lexical-parse-integer/src/shared.rs

@@ -86,6 +86,8 @@ macro_rules! invalid_digit_partial {
             } else {
                 into_error!(Overflow, (count - 1).min(min + 1))
             }
+        } else if <$t>::IS_SIGNED && $is_negative {
+            into_ok_partial!($value.wrapping_neg(), $iter.cursor() - 1)
         } else {
             into_ok_partial!($value, $iter.cursor() - 1)
         }

lexical-parse-integer/tests/api_tests.rs

@@ -28,6 +28,11 @@ fn i8_decimal_test() {
     assert_eq!(Err(Error::Overflow(2)), i8::from_lexical(b"255"));
     assert_eq!(Ok(-1), i8::from_lexical(b"-1"));
     assert_eq!(Err(Error::InvalidDigit(1)), i8::from_lexical(b"1a"));
+
+    assert_eq!(Ok((1, 1)), i8::from_lexical_partial(b"1"));
+    assert_eq!(Ok((1, 1)), i8::from_lexical_partial(b"1a"));
+    assert_eq!(Ok((-1, 2)), i8::from_lexical_partial(b"-1"));
+    assert_eq!(Ok((-1, 2)), i8::from_lexical_partial(b"-1a"));
 }
 
 #[test]