SMARTS output for [x] is wrong

[greglandrum]

Problem 1 is that [x] by itself should match an atom with at least one ring bond, instead it's matching something with exactly one ring bond (which is equivalent to "never"):

In [19]: m = Chem.MolFromSmiles('C1CC1')

In [20]: m.HasSubstructMatch(Chem.MolFromSmarts('[x]'))
Out[20]: False

Problem 2 is that the output is kind of stupid:

In [3]: Chem.MolToSmarts(Chem.MolFromSmarts('[x]'))
Out[3]: '[$(*@*)&!$(*(@*)@*)]'

This is somewhat byzantine, and can never match, but it's at least correct:

In [4]: Chem.MolToSmarts(Chem.MolFromSmarts('[x1]'))
Out[4]: '[$(*@*)&!$(*(@*)@*)]'