py: error out if a "skip" character was given with non-dict to util.dirs() stable

py: error out if a "skip" character was given with non-dict to util.dirs()

util.dirs() keeps track of the directories in its input collection. If
a "skip" character is given to it, it will assume the input is a
dirstate map and it will skip entries that are in the given "skip"
state. I think this is used only for skipping removed entries ("r") in
the dirtate. The C implementation of util.dirs() errors out if it was
given a skip character and a non-dict was passed. The pure
implementation simply ignored the request skip state. Let's make it
easier to discover bugs here by erroring out in the pure
implementation too. Let's also switch to checking for the dict-ness,
to make the C implementation (since that's clearly been sufficient for
many years). This last change makes test-issue660.t pass on py3 in
pure mode, since the old check was for existence of iteritems(), which
doesn't exist on py3.

Differential Revision: https://phab.mercurial-scm.org/D6669

--- a/mercurial/util.py	Mon Jul 22 09:55:05 2019 -0700
+++ b/mercurial/util.py	Sun Jul 21 18:04:05 2019 -0700
@@ -3173,10 +3173,13 @@
     def __init__(self, map, skip=None):
         self._dirs = {}
         addpath = self.addpath
-        if safehasattr(map, 'iteritems') and skip is not None:
+        if isinstance(map, dict) and skip is not None:
             for f, s in map.iteritems():
                 if s[0] != skip:
                     addpath(f)
+        elif skip is not None:
+            raise error.ProgrammingError("skip character is only supported "
+                                         "with a dict source")
         else:
             for f in map:
                 addpath(f)