templater: introduce {latesttag()} function to match a pattern (issue4184) This allows the latest class of tag to be found, such as a release candidate or final build, instead of just the absolute latest. It doesn't appear that the existing keyword can be given an optional argument. There is a keyword, function and filter for 'date', so it doesn't seem harmful to introduce a new function with the same name as an existing keyword. Most functions are pretty Mercurial agnostic, but there is {revset()} as precedent. Even though templatekw.getlatesttags() returns a single tuple, one entry of which is a list, it is simplest to present this as a list of tags instead of a single item, with each tag having a distance and change count attribute. It is also closer to how {latesttag} returns a list of tags, and how this function works when not given a '%' operator.

--- a/tests/test-tag.t	Mon Aug 24 23:07:00 2015 -0400
+++ b/tests/test-tag.t	Sun Aug 23 23:44:58 2015 -0400
@@ -461,6 +461,13 @@
   $ hg log -r '.' -T "{latesttag % '{latesttag}\n'}"
   t4
   t6
+  $ hg log -r '.' -T "{latesttag('t4') % 'T: {tag}, C: {changes}, D: {distance}\n'}"
+  T: t4, C: 2, D: 2
+  $ hg log -r '.' -T "{latesttag('re:\d') % 'T: {tag}, C: {changes}, D: {distance}\n'}"
+  T: t4, C: 2, D: 2
+  T: t6, C: 2, D: 2
+  $ hg log -r . -T '{join(latesttag(), "*")}\n'
+  t4*t6
   $ hg ci -A -m4
   adding f4
   $ hg log -r 'wdir()' -T "{changessincelatesttag} changes since {latesttag}\n"