Fix the behavior of & when the parent is compound.

2 files changed, 53 insertions, 12 deletions

diff --git a/scss/selector.py b/scss/selector.py
index 5fa16f0..25d32fe 100644
--- a/scss/selector.py
+++ b/scss/selector.py
@@ -1,3 +1,5 @@
+from __future__ import print_function
+
 import re
 
 # Super dumb little selector parser.
@@ -55,15 +57,34 @@ r'''
 TOKEN_TYPE_ORDER = {
     '#': 2,
     '.': 3,
-    '[': 4,
-    # Note that pseudo-selectors MUST come last, because pseudo-element
-    # selectors target a different element!
-    ':': 5,
-    '%': 6,
+    '[': 3,
+    ':': 3,
+    '%': 4,
 }
 TOKEN_SORT_KEY = lambda token: TOKEN_TYPE_ORDER.get(token[0], 0)
 
 
+def _is_combinator_subset_of(specific, general, is_first=True):
+    """Return whether `specific` matches a non-strict subset of what `general`
+    matches.
+    """
+    if is_first and general == ' ':
+        # First selector always has a space to mean "descendent of root", which
+        # still holds if any other selector appears above it
+        return True
+
+    if specific == general:
+        return True
+
+    if specific == '>' and general == ' ':
+        return True
+
+    if specific == '+' and general == '~':
+        return True
+
+    return False
+
+
 class SimpleSelector(object):
     """A simple selector, by CSS 2.1 terminology: a combination of element
     name, class selectors, id selectors, and other criteria that all apply to a
@@ -134,6 +155,11 @@ class SimpleSelector(object):
             set(self.tokens) <= set(other.tokens))
 
     def replace_parent(self, parent_simples):
+        """If ``&`` (or the legacy xCSS equivalent ``self``) appears in this
+        selector, replace it with the given iterable of parent selectors.
+
+        Returns a tuple of simple selectors.
+        """
         assert parent_simples
 
         ancestors = parent_simples[:-1]
@@ -148,14 +174,29 @@ class SimpleSelector(object):
             else:
                 new_tokens.append(token)
 
-        if did_replace:
-            # This simple selector was merged into the direct parent
-            merged_simple = type(self)(self.combinator, new_tokens)
-            return ancestors + (merged_simple,)
-        else:
-            # This simple selector is completely separate
+        if not did_replace:
+            # This simple selector doesn't contain a parent reference so just
+            # stick it on the end
             return parent_simples + (self,)
 
+        # This simple selector was merged into the direct parent.
+        merged_self = type(self)(parent.combinator, new_tokens)
+        selector = ancestors + (merged_self,)
+        # Our combinator goes on the first ancestor, i.e., substituting "foo
+        # bar baz" into "+ &.quux" produces "+ foo bar baz.quux".  This means a
+        # potential conflict with the first ancestor's combinator!
+        root = selector[0]
+        if not _is_combinator_subset_of(self.combinator, root.combinator):
+            raise ValueError(
+                "Can't sub parent {0!r} into {1!r}: "
+                "combinators {2!r} and {3!r} conflict!"
+                .format(
+                    parent_simples, self, self.combinator, root.combinator))
+
+        root = type(self)(self.combinator, root.tokens)
+        selector = (root,) + selector[1:]
+        return tuple(selector)
+
     # TODO just use set ops for these, once the constructor removes dupes
     def merge_with(self, other):
         new_tokens = self.tokens + tuple(token for token in other.tokens if token not in set(self.tokens))
diff --git a/scss/tests/files/original-doctests/037-test-7.css b/scss/tests/files/original-doctests/037-test-7.css
index 7ae523e..1f74b57 100644
--- a/scss/tests/files/original-doctests/037-test-7.css
+++ b/scss/tests/files/original-doctests/037-test-7.css
@@ -1,6 +1,6 @@
 a, #fake-links .link {
   color: blue;
 }
-a:hover, #fake-links .link:hover {
+a:hover, #fake-links :hover.link {
   text-decoration: underline;
 }