Fix '&' multiplication

Let'S do it by example:

  .ident_a, .ident_b {
    & + & + & { color: red; }
  }

We have to generate all permutations of the parent identifier list and
the amount of ampersand child identifiers. In the above case, the
exploded identifier list has ident_count**ampersand_count entries (8).

As a bonus, we get the same identifier sort order as lessc does.

Conflicts:
	lesscpy/plib/identifier.py

lesscpy/lessc/utility.py

@@ -11,6 +11,7 @@
 from __future__ import print_function
 
 import collections
+import itertools
 import math
 import re
 import sys
@@ -276,3 +277,15 @@ def convergent_round(value, ndigits=0):
                 nearest_even = integral_part + 0.5
                 return math.ceil(nearest_even)
     return round(value, ndigits)
+
+
+def permutations_with_replacement(iterable, r=None):
+    """Return successive r length permutations of elements in the iterable.
+
+    Similar to itertools.permutation but withouth repeated values filtering.
+    """
+    pool = tuple(iterable)
+    n = len(pool)
+    r = n if r is None else r
+    for indices in itertools.product(range(n), repeat=r):
+        yield list(pool[i] for i in indices)

lesscpy/plib/identifier.py

@@ -96,36 +96,46 @@ def root(self, scope, names):
         if parent:
             parent = parent[-1]
             if parent.parsed:
-                return [self._pscn(part, n)
-                        if part and part[0] not in self._subp
-                        else n
-                        for part in parent.parsed
-                        for n in names]
+                parsed_names = []
+                for name in names:
+                    ampersand_count = name.count('&')
+                    if ampersand_count:
+                        filtered_parts = []
+                        for part in parent.parsed:
+                            if part and part[0] not in self._subp:
+                                filtered_parts.append(part)
+                        permutations = list(utility.permutations_with_replacement(filtered_parts, ampersand_count))
+                        for permutation in permutations:
+                            parsed = []
+                            for name_part in name:
+                                if name_part == "&":
+                                    parent_part = permutation.pop(0)
+                                    if parsed and parsed[-1].endswith(']'):
+                                        parsed.extend(' ')
+                                    if parent_part[-1] == ' ':
+                                        parent_part.pop()
+                                    parsed.extend(parent_part)
+                                else:
+                                    parsed.append(name_part)
+                            parsed_names.append(parsed)
+                    else:
+                        # NOTE(saschpe): Maybe this code can be expressed with permutations too?
+                        for part in parent.parsed:
+                            if part and part[0] not in self._subp:
+                                parsed = []
+                                if name[0] == "@media":
+                                    parsed.extend(name)
+                                else:
+                                    parsed.extend(part)
+                                    if part[-1] != ' ':
+                                        parsed.append(' ')
+                                    parsed.extend(name)
+                                parsed_names.append(parsed)
+                            else:
+                                parsed_names.append(name)
+                return parsed_names
         return names
 
-    def _pscn(self, parent, name):
-        """
-        """
-        parsed = []
-        if any((n for n in name if n == '&')):
-            for n in name:
-                if n == '&':
-                    if parsed[-1].endswith(']'):
-                        parsed.extend(' ')
-                    if parent[-1] == ' ':
-                        parent.pop()
-                    parsed.extend(parent)
-                else:
-                    parsed.append(n)
-        elif name[0] == "@media":
-            parsed.extend(name)
-        else:
-            parsed.extend(parent)
-            if parent[-1] != ' ':
-                parsed.append(' ')
-            parsed.extend(name)
-        return parsed
-
     def raw(self, clean=False):
         """Raw identifier.
         args:

lesscpy/test/bootstrap3/css/theme.css

@@ -9,16 +9,16 @@
 	box-shadow: inset 0 1px 0 rgba(255,255,255,.15), 0 1px 1px rgba(0,0,0,.075);
 }
 .btn-default:active,
-.btn-default.active,
 .btn-primary:active,
-.btn-primary.active,
 .btn-success:active,
-.btn-success.active,
 .btn-info:active,
-.btn-info.active,
 .btn-warning:active,
-.btn-warning.active,
 .btn-danger:active,
+.btn-default.active,
+.btn-primary.active,
+.btn-success.active,
+.btn-info.active,
+.btn-warning.active,
 .btn-danger.active {
 	-webkit-box-shadow: inset 0 3px 5px rgba(0,0,0,.125);
 	box-shadow: inset 0 3px 5px rgba(0,0,0,.125);