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-command-template.t	Mon Aug 24 23:07:00 2015 -0400
+++ b/tests/test-command-template.t	Sun Aug 23 23:44:58 2015 -0400
@@ -2690,6 +2690,19 @@
   1: t1+0
   0: null+1
 
+  $ hg log --template "{rev}: {latesttag('re:^t[13]$') % '{tag}, C: {changes}, D: {distance}'}\n"
+  10: t3, C: 8, D: 7
+  9: t3, C: 7, D: 6
+  8: t3, C: 6, D: 5
+  7: t3, C: 5, D: 4
+  6: t3, C: 4, D: 3
+  5: t3, C: 3, D: 2
+  4: t3, C: 1, D: 1
+  3: t3, C: 0, D: 0
+  2: t1, C: 1, D: 1
+  1: t1, C: 0, D: 0
+  0: null, C: 1, D: 1
+
   $ cd ..