revset: deal with empty lists in formatspec

mercurial/revset.py

@@ -1068,6 +1068,8 b' def formatspec(expr, *args):'
     '(10 or 11):: and ((this()) or (that()))'
     >>> formatspec('%d:: and not %d::', 10, 20)
     '10:: and not 20::'
+    >>> formatspec('%ld or %ld', [], [1])
+    '(0-0) or (1)'
     >>> formatspec('keyword(%s)', 'foo\\xe9')
     "keyword('foo\\\\xe9')"
     >>> b = lambda: 'default'
@@ -1111,7 +1113,10 b' def formatspec(expr, *args):'
                 # a list of some type
                 pos += 1
                 d = expr[pos]
+                if args[arg]:
                 lv = ' or '.join(argtype(d, e) for e in args[arg])
+                else:
+                    lv = '0-0' # a minimal way to represent an empty set
                 ret += '(%s)' % lv
                 arg += 1
             else: