bookmarks: factor method _printer out of for loop in printbookmarks

bookmarks: factor method _printer out of for loop in printbookmarks

This allows even further customization via extensions for printing
bookmarks. For example, in hg-git this would allow printing remote refs
by just modifying the 'bmarks' parameter instead of reimplementing the
old commands.bookmarks method.

Furthermore, there is another benefit: now multiple extensions can
chain their custom data to bookmark printing. Previously, an extension
could have conflicting bookmark output due to which loaded first and
overrode commands.bookmarks. Now they can all play nicely together.

--- a/mercurial/bookmarks.py	Tue Jun 20 16:36:25 2017 -0700
+++ b/mercurial/bookmarks.py	Tue Jun 20 17:18:20 2017 -0700
@@ -765,16 +765,35 @@
         deactivate(repo)
     marks.recordchange(tr)
 
+def _printbookmarks(ui, repo, bmarks, **opts):
+    """private method to print bookmarks
+
+    Provides a way for extensions to control how bookmarks are printed (e.g.
+    prepend or postpend names)
+    """
+    fm = ui.formatter('bookmarks', opts)
+    hexfn = fm.hexfunc
+    if len(bmarks) == 0 and fm.isplain():
+        ui.status(_("no bookmarks set\n"))
+    for bmark, (n, prefix, label) in sorted(bmarks.iteritems()):
+        fm.startitem()
+        if not ui.quiet:
+            fm.plain(' %s ' % prefix, label=label)
+        fm.write('bookmark', '%s', bmark, label=label)
+        pad = " " * (25 - encoding.colwidth(bmark))
+        fm.condwrite(not ui.quiet, 'rev node', pad + ' %d:%s',
+                     repo.changelog.rev(n), hexfn(n), label=label)
+        fm.data(active=(activebookmarklabel in label))
+        fm.plain('\n')
+    fm.end()
+
 def printbookmarks(ui, repo, **opts):
     """print bookmarks to a formatter
 
     Provides a way for extensions to control how bookmarks are printed.
     """
-    fm = ui.formatter('bookmarks', opts)
-    hexfn = fm.hexfunc
     marks = repo._bookmarks
-    if len(marks) == 0 and fm.isplain():
-        ui.status(_("no bookmarks set\n"))
+    bmarks = {}
     for bmark, n in sorted(marks.iteritems()):
         active = repo._activebookmark
         if bmark == active:
@@ -782,13 +801,5 @@
         else:
             prefix, label = ' ', ''
 
-        fm.startitem()
-        if not ui.quiet:
-            fm.plain(' %s ' % prefix, label=label)
-        fm.write('bookmark', '%s', bmark, label=label)
-        pad = " " * (25 - encoding.colwidth(bmark))
-        fm.condwrite(not ui.quiet, 'rev node', pad + ' %d:%s',
-                     repo.changelog.rev(n), hexfn(n), label=label)
-        fm.data(active=(bmark == active))
-        fm.plain('\n')
-    fm.end()
+        bmarks[bmark] = (n, prefix, label)
+    _printbookmarks(ui, repo, bmarks, **opts)