Keeping track of the filename when parsing interpolants.

document.cpp

@@ -100,8 +100,8 @@ namespace Sass {
     ++context.ref_count;
   }
   
-  Document::Document(size_t line_number, Token t, Context& context)
-  : path(string()),
+  Document::Document(const string& path, size_t line_number, Token t, Context& context)
+  : path(path),
     source(const_cast<char*>(t.begin)),
     position(t.begin),
     end(t.end),

document.hpp

@@ -30,7 +30,7 @@ namespace Sass {
     Document(char* path_str, char* source_str, Context& ctx);
     Document(string path, char* source = 0);
     Document(string path, Context& context);
-    Document(size_t line_number, Token t, Context& context);
+    Document(const string& path, size_t line_number, Token t, Context& context);
     ~Document();
     
     template <prelexer mx>

document_parser.cpp

@@ -720,7 +720,7 @@ namespace Sass {
     if (lex< interpolant >())
     {
       Token insides(Token::make(lexed.begin + 2, lexed.end - 1));
-      Document interp(line_number, insides, context);
+      Document interp(path, line_number, insides, context);
       return interp.parse_list();
     }