templates-default: do not show description or summary if empty

changeset_printer shows description only if ctx.description().strip() is not
empty. The default template should do the same way.

mercurial/templates/map-cmdline.default

@@ -58,8 +58,8 b' bookmark = \'{label("log.bookmark",'
 user = '{label("log.user",
                "user:        {author}")}\n'
 
-summary = '{label("log.summary",
-                  "summary:     {desc|firstline}")}\n'
+summary = '{if(desc|strip, "{label('log.summary',
+                                   'summary:     {desc|firstline}')}\n")}'
 
 ldate = '{label("log.date",
                 "date:        {date|date}")}\n'
@@ -67,7 +67,7 b' ldate = \'{label("log.date",'
 extra = '{label("ui.debug log.extra",
                 "extra:       {key}={value|stringescape}")}\n'
 
-description = '{label("ui.note log.description",
-                       "description:")}
-               {label("ui.note log.description",
-                       "{desc|strip}")}\n\n'
+description = '{if(desc|strip, "{label('ui.note log.description',
+                                       'description:')}
+                                {label('ui.note log.description',
+                                       '{desc|strip}')}\n\n")}'

tests/test-command-template.t

@@ -96,6 +96,10 b' Template should precede style option'
 
 Default style is like normal output:
 
+  $ echo c >> c
+  $ hg add c
+  $ hg commit -qm ' '
+
   $ hg log > log.out
   $ hg log --style default > style.out
   $ cmp log.out style.out || diff -u log.out style.out
@@ -135,6 +139,8 b' Default style should also preserve color'
 
   $ mv $HGRCPATH-bak $HGRCPATH
 
+  $ hg --config extensions.strip= strip -q .
+
 Revision with no copies (used to print a traceback):
 
   $ hg tip -v --template '\n'