archive: store number of changes since latest tag as well

This is different from latesttagdistance in that while latesttagdistance is
defined to be the length of the longest path to the latest tag,
changessincelatesttag is the number of changes contained in @ that aren't
contained in the latest tag. So, if 't' is the latest tag in the repository
below:

      t
      |
      v
 --o--o----o
    \       \
     ..o..o..@

then latesttagdistance is 2, but changessincelatesttag is 4.

Note that changessincelatesttag is always greater than or equal to the
latesttagdistance -- that's because changessincelatesttag counts all the
changes in the longest path since the latest tag, and possibly others. This is
an important fact that we'll take advantage of in upcoming patches.

mercurial/archival.py

@@ -276,8 +276,11 b' def archive(repo, dest, node, kind, deco'
                         'style': '', 'patch': None, 'git': None}
                 cmdutil.show_changeset(repo.ui, repo, opts).show(ctx)
                 ltags, dist = repo.ui.popbuffer().split('\n')
-                tags = ''.join('latesttag: %s\n' % t for t in ltags.split(':'))
+                ltags = ltags.split(':')
+                changessince = len(repo.revs('only(.,%s)', ltags[0]))
+                tags = ''.join('latesttag: %s\n' % t for t in ltags)
                 tags += 'latesttagdistance: %s\n' % dist
+                tags += 'changessincelatesttag: %s\n' % changessince
 
             return base + tags
 

tests/test-archive.t

@@ -250,6 +250,7 b' test .hg_archival.txt'
   branch: default
   latesttag: null
   latesttagdistance: 4
+  changessincelatesttag: 4
   $ hg tag -r 2 mytag
   $ hg tag -r 2 anothertag
   $ hg archive -r 2 ../test-lasttag
@@ -322,10 +323,10 b' old file -- date clamped to 1980'
   Archive:  ../old.zip
   \s*Length.* (re)
   *-----* (glob)
-  *147*80*00:00*old/.hg_archival.txt (glob)
+  *172*80*00:00*old/.hg_archival.txt (glob)
   *0*80*00:00*old/old (glob)
   *-----* (glob)
-  \s*147\s+2 files (re)
+  \s*172\s+2 files (re)
 
 show an error when a provided pattern matches no files