identify: only query remote bookmarks if needed

Instead of all the time when operating on a remote repo. This
perf regression was introduced in 15a79ac823e8, in 4.3.

This datahint method returns nothing for -Tjson, -Tpickle, -Tdebug
--config ui.formatdebug=true and --config ui.formatjson, so the
bookmarks won't show up. I don't know what these formatters are for.
plainformatter and templateformatter work properly, and the few other
uses of datahint should have the same kind of problem.

There is further weirdness where "--template '{node}'" is not enough
to avoid querying the bookmarks, you also need to pass --id or -q.

Differential Revision: https://phab.mercurial-scm.org/D4819

mercurial/commands.py

@@ -3023,6 +3023,7 def identify(ui, repo, source=None, rev=
             output = [hexrev]
         fm.data(id=hexrev)
 
+        @util.cachefunc
         def getbms():
             bms = []
 
@@ -3033,17 +3034,17 def identify(ui, repo, source=None, rev=
 
             return sorted(bms)
 
-        bms = getbms()
         if bookmarks:
-            output.extend(bms)
+            output.extend(getbms())
         elif default and not ui.quiet:
             # multiple bookmarks for a single parent separated by '/'
-            bm = '/'.join(bms)
+            bm = '/'.join(getbms())
             if bm:
                 output.append(bm)
 
         fm.data(node=hex(remoterev))
-        fm.data(bookmarks=fm.formatlist(bms, name='bookmark'))
+        if 'bookmarks' in fm.datahint():
+            fm.data(bookmarks=fm.formatlist(getbms(), name='bookmark'))
     else:
         if rev:
             repo = scmutil.unhidehashlikerevs(repo, [rev], 'nowarn')