Shared: normalizeDate should reject illegal years.

We only allow years between 1601 and 9999, inclusive. The ISO 8601
actually says that years are supposed to start with 1583, but MS Word
only allows 1601-9999. This should stop corrupted word files if the date
is out of that range, or is parsed incorrectly.

src/Text/Pandoc/Shared.hs

@@ -324,17 +324,22 @@ tabFilter tabStop =
 -- Date/time
 --
 
--- | Parse a date and convert (if possible) to "YYYY-MM-DD" format.
+-- | Parse a date and convert (if possible) to "YYYY-MM-DD" format. We
+-- limit years to the range 1601-9999 (ISO 8601 accepts greater than
+-- or equal to 1583, but MS Word only accepts dates starting 1601.
 normalizeDate :: String -> Maybe String
-normalizeDate s = fmap (formatTime defaultTimeLocale "%F")
-  (msum $ map (\fs -> parsetimeWith fs s) formats :: Maybe Day)
-   where parsetimeWith =
+normalizeDate s = case toGregorian <$> day of
+  Just (y, _, _) | y >= 1601 && y <= 9999 ->
+                     fmap (formatTime defaultTimeLocale "%F") day
+  _ -> Nothing
+  where day = (msum $ map (\fs -> parsetimeWith fs s) formats :: Maybe Day)
+        parsetimeWith =
 #if MIN_VERSION_time(1,5,0)
              parseTimeM True defaultTimeLocale
 #else
              parseTime defaultTimeLocale
 #endif
-         formats = ["%x","%m/%d/%Y", "%D","%F", "%d %b %Y",
+        formats = ["%x","%m/%d/%Y", "%D","%F", "%d %b %Y",
                     "%d %B %Y", "%b. %d, %Y", "%B %d, %Y",
                     "%Y%m%d", "%Y%m", "%Y"]