allow whitespace between mixin name and args

src/parse/mixin.rs

@@ -32,7 +32,8 @@ impl<'a> Parser<'a> {
             return Err(("Mixins may not be declared in control directives.", span).into());
         }
 
-        self.whitespace();
+        self.whitespace_or_comment();
+
         let args = match self.toks.next() {
             Some(Token { kind: '(', .. }) => self.parse_func_args()?,
             Some(Token { kind: '{', .. }) => FuncArgs::new(),

tests/mixins.rs

@@ -552,6 +552,17 @@ test!(
     }",
     "space-after-content {\n  arg1: value1;\n  arg2: value2;\n}\n"
 );
+test!(
+    space_between_mixin_and_args,
+    "@mixin foo /**/ ()  /**/ {
+        color: red;
+    }
+
+    a {
+        @include foo;
+    }",
+    "a {\n  color: red;\n}\n"
+);
 error!(
     mixin_in_function,
     "@function foo() {