Improve behavior of null values in lists.

5 files changed, 39 insertions, 5 deletions

diff --git a/scss/__init__.py b/scss/__init__.py
index 3eeaaed..7d8c3b0 100644
--- a/scss/__init__.py
+++ b/scss/__init__.py
@@ -1568,12 +1568,17 @@ class Scss(object):
         result = ''
         last_prop_index = len(properties) - 1
         for i, (name, value) in enumerate(properties):
-            if value is not None:
+            if value is None:
+                prop = name
+            elif value:
                 if nl:
                     value = (nl + tb + tb).join(self._textwrap(value))
                 prop = name + ':' + sp + value
             else:
-                prop = name
+                # Empty string means there's supposed to be a value but it
+                # evaluated to nothing; skip this
+                # TODO interacts poorly with last_prop_index
+                continue
 
             if i == last_prop_index:
                 if sc:
diff --git a/scss/expression.py b/scss/expression.py
index 1c38100..8b42e7d 100644
--- a/scss/expression.py
+++ b/scss/expression.py
@@ -378,7 +378,8 @@ class ListLiteral(Expression):
 
     def evaluate(self, calculator, divide=False):
         items = [item.evaluate(calculator, divide=divide) for item in self.items]
-        return List(items, separator="," if self.comma else "")
+        # TODO sort of overloading "divide" here...  rename i think
+        return List(items, use_comma=self.comma, is_literal=not divide)
 
 
 class MapLiteral(Expression):
diff --git a/scss/tests/files/general/null-values.css b/scss/tests/files/general/null-values.css
new file mode 100644
index 0000000..16deaae
--- /dev/null
+++ b/scss/tests/files/general/null-values.css
@@ -0,0 +1,5 @@
+div {
+  a: 1, 2, 3;
+  b: 1, null, 2, null, 3;
+  c: 1  2;
+}
diff --git a/scss/tests/files/general/null-values.scss b/scss/tests/files/general/null-values.scss
new file mode 100644
index 0000000..d657ab2
--- /dev/null
+++ b/scss/tests/files/general/null-values.scss
@@ -0,0 +1,11 @@
+div {
+    // nulls should be omitted from evaluated lists
+    a: (1, null, 2, null, 3);
+    // but not from literal untouched lists
+    b: 1, null, 2, null, 3;
+
+    // entirely null lists become nothing
+    c: 1 (null, null) 2;
+    // empty properties aren't printed
+    d: (null, null);
+}
diff --git a/scss/types.py b/scss/types.py
index d0079d3..4a027d7 100644
--- a/scss/types.py
+++ b/scss/types.py
@@ -549,7 +549,7 @@ class List(Value):
 
     sass_type_name = u'list'
 
-    def __init__(self, iterable, separator=None, use_comma=None):
+    def __init__(self, iterable, separator=None, use_comma=None, is_literal=False):
         if isinstance(iterable, List):
             iterable = iterable.value
 
@@ -568,6 +568,8 @@ class List(Value):
         else:
             self.use_comma = use_comma
 
+        self.is_literal = is_literal
+
     @classmethod
     def maybe_new(cls, values, use_comma=True):
         """If `values` contains only one item, return that item.  Otherwise,
@@ -662,9 +664,19 @@ class List(Value):
 
         delim = self.delimiter(compress)
 
+        if self.is_literal:
+            value = self.value
+        else:
+            # Non-literal lists have nulls stripped
+            value = [item for item in self.value if not item.is_null]
+            # Non-empty lists containing only nulls become nothing, just like
+            # single nulls
+            if not value:
+                return ''
+
         return delim.join(
             item.render(compress=compress)
-            for item in self.value
+            for item in value
         )
 
     # DEVIATION: binary ops on lists and scalars act element-wise