Made `Parsed` not fully destructible.

So that we can add more fields without breaking a major compatibility
(as per RFC 1105).

src/format/parse.rs

@@ -358,9 +358,11 @@ fn test_parse() {
         ($fmt:expr, $items:expr; $err:tt) => (
             assert_eq!(parse_all($fmt, &$items), Err($err))
         );
-        ($fmt:expr, $items:expr; $($k:ident: $v:expr),*) => (
-            assert_eq!(parse_all($fmt, &$items), Ok(Parsed { $($k: Some($v),)* ..Parsed::new() }))
-        );
+        ($fmt:expr, $items:expr; $($k:ident: $v:expr),*) => (#[allow(unused_mut)] {
+            let mut expected = Parsed::new();
+            $(expected.$k = Some($v);)*
+            assert_eq!(parse_all($fmt, &$items), Ok(expected))
+        });
     }
 
     // empty string

src/format/parsed.rs

@@ -108,6 +108,9 @@ pub struct Parsed {
 
     /// Offset from the local time to UTC, in seconds.
     pub offset: Option<i32>,
+
+    /// A dummy field to make this type not fully destructible (required for API stability).
+    _dummy: (),
 }
 
 /// Checks if `old` is either empty or has the same value to `new` (i.e. "consistent"),
@@ -121,14 +124,23 @@ fn set_if_consistent<T: PartialEq>(old: &mut Option<T>, new: T) -> ParseResult<(
     }
 }
 
-impl Parsed {
-    /// Returns the initial value of parsed parts.
-    pub fn new() -> Parsed {
-        Parsed { year: None, year_div_100: None, year_mod_100: None, isoyear: None,
+impl Default for Parsed {
+    fn default() -> Parsed {
+        Parsed {
+            year: None, year_div_100: None, year_mod_100: None, isoyear: None,
             isoyear_div_100: None, isoyear_mod_100: None, month: None,
             week_from_sun: None, week_from_mon: None, isoweek: None, weekday: None,
             ordinal: None, day: None, hour_div_12: None, hour_mod_12: None, minute: None,
-                 second: None, nanosecond: None, timestamp: None, offset: None }
+            second: None, nanosecond: None, timestamp: None, offset: None,
+            _dummy: (),
+        }
+    }
+}
+
+impl Parsed {
+    /// Returns the initial value of parsed parts.
+    pub fn new() -> Parsed {
+        Parsed::default()
     }
 
     /// Tries to set the [`year`](#structfield.year) field from given value.