TW-1500: Dates formatted as ".age", ".remaining", or ".countdown" often give blank results

- The 'age' column regained the ability to show negative durations.
- The 'countdown' and 'remaining' continue to show only positive values, by
  design.
- Thanks to Jeremy John Reeder.

ChangeLog

@@ -8,6 +8,8 @@
           (thanks to James Dietrich).
 - TW-1446 Difference in how relative dates are specified in report filters since 2.3.0
           (thanks to atomicules).
+- TW-1500 Dates formatted as ".age", ".remaining", or ".countdown" often give
+          blank results (thanks to Jeremy John Reeder).
 - TW-1582 Wrong urgency for first report after reviving task with
           "mod status:pending"
 - TW-1698 tests: 'make test' should exit non-zero if tests failed

src/columns/ColTypeDate.cpp

@@ -92,7 +92,8 @@ void ColumnTypeDate::measure (Task& task, unsigned int& minimum, unsigned int& m
     else if (_style == "countdown")
     {
       ISO8601d now;
-      minimum = maximum = ISO8601p (now - date).formatVague ().length ();
+      if (now > date)
+        minimum = maximum = ISO8601p (now - date).formatVague ().length ();
     }
     else if (_style == "julian")
     {
@@ -109,7 +110,10 @@ void ColumnTypeDate::measure (Task& task, unsigned int& minimum, unsigned int& m
     else if (_style == "age")
     {
       ISO8601d now;
-      minimum = maximum = ISO8601p (now - date).formatVague ().length ();
+      if (now > date)
+        minimum = maximum = ISO8601p (now - date).formatVague ().length ();
+      else
+        minimum = maximum = ISO8601p (date - now).formatVague ().length () + 1;
     }
     else if (_style == "remaining")
     {
@@ -153,7 +157,8 @@ void ColumnTypeDate::render (
     else if (_style == "countdown")
     {
       ISO8601d now;
-      renderStringRight (lines, width, color, ISO8601p (now - date).formatVague ());
+      if (now > date)
+        renderStringRight (lines, width, color, ISO8601p (now - date).formatVague ());
     }
     else if (_style == "julian")
       renderStringRight (lines, width, color, format (date.toJulian (), 13, 12));
@@ -167,7 +172,10 @@ void ColumnTypeDate::render (
     else if (_style == "age")
     {
       ISO8601d now;
-      renderStringLeft (lines, width, color, ISO8601p (now - date).formatVague ());
+      if (now > date)
+        renderStringLeft (lines, width, color, ISO8601p (now - date).formatVague ());
+      else
+        renderStringLeft (lines, width, color, "-" + ISO8601p (date - now).formatVague ());
     }
 
     else if (_style == "remaining")

test/columns.t

@@ -373,7 +373,7 @@ class TestDateFormats(TestCase):
         """Verify due.age formatting"""
         code, out, err = self.t("xxx rc.report.xxx.columns:id,due.age")
         self.assertRegexpMatches(out, r'1\s+1d')
-        self.assertRegexpMatches(out, r'2$')
+        self.assertRegexpMatches(out, r'2\s+-16h')
 
     def test_date_format_remaining(self):
         """Verify due.remaining formatting"""