Support multiline url declarations

This is a continuation of the previous work done to bring our
`url()` parsing up to scratch with Ruby Sass. With this update
we can remove the trasnitional legacy `url()` parsing logic.

Fixes sass#1096

src/parser.cpp

@@ -298,12 +298,13 @@ namespace Sass {
       else if (lex< uri_prefix >()) {
         Arguments* args = SASS_MEMORY_NEW(ctx.mem, Arguments, pstate);
         Function_Call* result = SASS_MEMORY_NEW(ctx.mem, Function_Call, pstate, "url", args);
+
         if (lex< quoted_string >()) {
           Expression* the_url = parse_string();
           *args << SASS_MEMORY_NEW(ctx.mem, Argument, the_url->pstate(), the_url);
         }
-        else if (lex < uri_value >(false)) { // don't skip comments
-          String* the_url = parse_interpolated_chunk(lexed);
+        else if (String* the_url = parse_url_function_argument()) {
+
           *args << SASS_MEMORY_NEW(ctx.mem, Argument, the_url->pstate(), the_url);
         }
         else if (peek < skip_over_scopes < exactly < '(' >, exactly < ')' > > >(position)) {
@@ -1687,29 +1688,53 @@ namespace Sass {
   }
 
   String* Parser::parse_url_function_string()
+  {
+    std::string prefix("");
+    if (lex< uri_prefix >()) {
+      prefix = std::string(lexed);
+    }
+
+    String* url_string = parse_url_function_argument();
+
+    std::string suffix("");
+    if (lex< real_uri_suffix >()) {
+      suffix = std::string(lexed);
+    }
+
+    if (String_Schema* schema = dynamic_cast<String_Schema*>(url_string)) {
+      String_Schema* res = SASS_MEMORY_NEW(ctx.mem, String_Schema, pstate);
+      (*res) << SASS_MEMORY_NEW(ctx.mem, String_Constant, pstate, prefix);
+      (*res) += schema;
+      (*res) << SASS_MEMORY_NEW(ctx.mem, String_Constant, pstate, suffix);
+      return res;
+    } else {
+      std::string res = prefix + url_string->to_string() + suffix;
+      return SASS_MEMORY_NEW(ctx.mem, String_Constant, pstate, res);
+    }
+  }
+
+  String* Parser::parse_url_function_argument()
   {
     const char* p = position;
 
-    lex< uri_prefix >();
-    std::string prefix = lexed;
+    std::string uri("");
+    if (lex< real_uri_value >(false)) {
+      uri = lexed.to_string();
+    }
 
-    lex< real_uri_value >(false);
-    std::string uri = lexed;
 
     if (peek< exactly< hash_lbrace > >()) {
       const char* pp = position;
       // TODO: error checking for unclosed interpolants
       while (peek< exactly< hash_lbrace > >(pp)) {
         pp = sequence< interpolant, real_uri_value >(pp);
       }
-      position = peek< real_uri_suffix >(pp);
+      position = pp;
       return parse_interpolated_chunk(Token(p, position));
     } else {
-      lex< real_uri_suffix >();
-      std::string res = prefix + Util::rtrim(uri) + lexed.to_string();
+      std::string res = Util::rtrim(uri);
       return SASS_MEMORY_NEW(ctx.mem, String_Constant, pstate, res);
     }
-
   }
 
   Function_Call* Parser::parse_function_call()

src/parser.hpp

@@ -253,6 +253,7 @@ namespace Sass {
     Function_Call* parse_function_call();
     Function_Call_Schema* parse_function_call_schema();
     String* parse_url_function_string();
+    String* parse_url_function_argument();
     String* parse_interpolated_chunk(Token, bool constant = false);
     String* parse_string();
     String_Constant* parse_static_expression();

src/prelexer.cpp

@@ -605,23 +605,6 @@ namespace Sass {
     const char* uri_prefix(const char* src) {
       return exactly<url_kwd>(src);
     }
-    const char* uri_value(const char* src)
-    {
-      return
-      sequence <
-        negate <
-          exactly < '$' >
-        >,
-        zero_plus <
-          alternatives <
-            alnum,
-            interpolant,
-            exactly <'/'>,
-            class_char < uri_chars >
-          >
-        >
-      >(src);
-    }
 
     // TODO: rename the following two functions
     /* no longer used - remove?

src/prelexer.hpp

@@ -296,7 +296,6 @@ namespace Sass {
     // const char* rgb_prefix(const char* src);
     // Match CSS uri specifiers.
     const char* uri_prefix(const char* src);
-    const char* uri_value(const char* src);
     // Match CSS "!important" keyword.
     const char* kwd_important(const char* src);
     // Match CSS "!optional" keyword.