Add hotfix for interpolation edge case

Fixes sass#1115

ast.hpp

@@ -1439,22 +1439,23 @@ namespace Sass {
   // Flat strings -- the lowest level of raw textual data.
   ////////////////////////////////////////////////////////
   class String_Constant : public String {
+    ADD_PROPERTY(bool, from_schema);
     ADD_PROPERTY(char, quote_mark);
     ADD_PROPERTY(string, value);
   protected:
     size_t hash_;
   public:
     String_Constant(ParserState pstate, string val)
-    : String(pstate), quote_mark_(0), value_(read_css_string(val)), hash_(0)
+    : String(pstate), from_schema_(false), quote_mark_(0), value_(read_css_string(val)), hash_(0)
     { }
     String_Constant(ParserState pstate, const char* beg)
-    : String(pstate), quote_mark_(0), value_(read_css_string(string(beg))), hash_(0)
+    : String(pstate), from_schema_(false), quote_mark_(0), value_(read_css_string(string(beg))), hash_(0)
     { }
     String_Constant(ParserState pstate, const char* beg, const char* end)
-    : String(pstate), quote_mark_(0), value_(read_css_string(string(beg, end-beg))), hash_(0)
+    : String(pstate), from_schema_(false), quote_mark_(0), value_(read_css_string(string(beg, end-beg))), hash_(0)
     { }
     String_Constant(ParserState pstate, const Token& tok)
-    : String(pstate), quote_mark_(0), value_(read_css_string(string(tok.begin, tok.end))), hash_(0)
+    : String(pstate), from_schema_(false), quote_mark_(0), value_(read_css_string(string(tok.begin, tok.end))), hash_(0)
     { }
     string type() { return "string"; }
     static string type_name() { return "string"; }

eval.cpp

@@ -888,6 +888,7 @@ namespace Sass {
     if (!str->quote_mark()) {
       str->value(string_unescape(str->value()));
     } else if (str->quote_mark()) {
+      str->from_schema(true);
       str->quote_mark('*');
     }
     return str;

output.cpp

@@ -378,7 +378,12 @@ namespace Sass {
   void Output::operator()(String_Quoted* s)
   {
     if (s->quote_mark()) {
-      append_token(quote(s->value(), s->quote_mark()), s);
+      if (s->from_schema()) {
+        append_token(quote(unevacuate_escapes(s->value()), s->quote_mark()), s);
+      } else {
+        append_token(quote(s->value(), s->quote_mark()), s);
+      }
+
     } else if (!in_comment) {
       append_token(string_to_output(s->value()), s);
     } else {

util.cpp

@@ -159,6 +159,61 @@ namespace Sass {
     return out;
   }
 
+  // unescape all double escape sequences
+  // needed after all interpolations are done
+  string unevacuate_escapes(const string& s)
+  {
+    string out("");
+    bool esc = false;
+
+    for (size_t i = 0, L = s.length(); i < L; ++i) {
+
+      // implement the same strange ruby sass behavior
+      // an escape sequence can also mean a unicode char
+      if (s[i] == '\\' && !esc) {
+        // remember
+        esc = true;
+
+        // escape length
+        size_t len = 1;
+
+        // parse as many sequence chars as possible
+        // ToDo: Check if ruby aborts after possible max
+        while (i + len < L && s[i + len] && isxdigit(s[i + len])) ++ len;
+
+        // hex string?
+        if (len > 1) {
+
+          // convert the extracted hex string to code point value
+          // ToDo: Maybe we could do this without creating a substring
+          uint32_t cp = strtol(s.substr (i + 1, len - 1).c_str(), nullptr, 16);
+
+          // assert invalid code points
+          if (cp >= 16) {
+
+            // use a very simple approach to convert via utf8 lib
+            // maybe there is a more elegant way; maybe we shoud
+            // convert the whole output from string to a stream!?
+            // allocate memory for utf8 char and convert to utf8
+            unsigned char u[5] = {0,0,0,0,0}; utf8::append(cp, u);
+            for(size_t m = 0; u[m] && m < 5; m++) out.push_back(u[m]);
+
+            // skip some more chars?
+            i += len - 1; esc = false;
+
+          }
+
+        }
+
+      } else {
+        if (esc) out += '\\';
+        esc = false;
+        out += s[i];
+      }
+    }
+    return out;
+  }
+
   // bell character is replaces with space
   string string_to_output(const string& str)
   {

util.hpp

@@ -15,6 +15,7 @@ namespace Sass {
   string read_css_string(const string& str);
   string evacuate_quotes(const string& str);
   string evacuate_escapes(const string& str);
+  string unevacuate_escapes(const string& str);
   string string_to_output(const string& str);
   string comment_to_string(const string& text);
   string normalize_wspace(const string& str);