Improve deprecation handling in unquote function

Fixes #1291

Author: mgreter

error_handling.cpp

@@ -20,6 +20,15 @@ namespace Sass {
     warn(msg, pstate);
   }
 
+  void deprecated(string msg, ParserState pstate)
+  {
+    string cwd(Sass::File::get_cwd());
+    cerr << "DEPRECATION WARNING: " << msg << endl;
+    cerr << "will be an error in future versions of Sass." << endl;
+    string rel_path(Sass::File::resolve_relative_path(pstate.path, cwd, cwd));
+    cerr << "        on line " << pstate.line+1 << " of " << rel_path << endl;
+  }
+
   void error(string msg, ParserState pstate)
   {
     throw Sass_Error(Sass_Error::syntax, pstate, msg);

error_handling.hpp

@@ -24,6 +24,9 @@ namespace Sass {
   void warn(string msg, ParserState pstate);
   void warn(string msg, ParserState pstate, Backtrace* bt);
 
+  void deprecated(string msg, ParserState pstate);
+  // void deprecated(string msg, ParserState pstate, Backtrace* bt);
+
   void error(string msg, ParserState pstate);
   void error(string msg, ParserState pstate, Backtrace* bt);
 

functions.cpp

@@ -777,8 +777,15 @@ namespace Sass {
         result->sass_fix_1291(string_quoted->quote_mark() != 0);
         return result;
       }
-      To_String to_string(&ctx);
-      return new (ctx.mem) String_Constant(pstate, unquote(string(arg->perform(&to_string))));
+      else if (dynamic_cast<String_Constant*>(arg)) {
+        return (Expression*) arg;
+      }
+      else {
+        To_String to_string(&ctx);
+        string val(arg->perform(&to_string));
+        deprecated("Passing " + val + ", a non-string value, to unquote()", pstate);
+        return (Expression*) arg;
+      }
     }
 
     Signature quote_sig = "quote($string)";