Fix interpolation edge case in value parsing

Fixes sass#442

parser.cpp

@@ -415,7 +415,13 @@ namespace Sass {
     string name(Util::normalize_underscores(lexed));
     ParserState var_source_position = pstate;
     if (!lex< exactly<':'> >()) error("expected ':' after " + name + " in assignment statement", pstate);
-    Expression* val = parse_list();
+    Expression* val;
+    Selector_Lookahead lookahead = lookahead_for_value(position);
+    if (lookahead.has_interpolants && lookahead.found) {
+      val = parse_value_schema(lookahead.found);
+    } else {
+      val = parse_list();
+    }
     val->is_delayed(false);
     bool is_default = false;
     bool is_global = false;
@@ -1564,12 +1570,18 @@ namespace Sass {
       else if (lex< hex >()) {
         (*schema) << new (ctx.mem) Textual(pstate, Textual::HEX, unquote(lexed));
       }
+      else if (lex < exactly < '-' > >()) {
+        (*schema) << new (ctx.mem) String_Constant(pstate, lexed);
+      }
       else if (lex< quoted_string >()) {
         (*schema) << new (ctx.mem) String_Quoted(pstate, lexed);
       }
       else if (lex< variable >()) {
         (*schema) << new (ctx.mem) Variable(pstate, Util::normalize_underscores(lexed));
       }
+      else if (peek< parenthese_scope >()) {
+        (*schema) << parse_factor();
+      }
       else {
         error("error parsing interpolated value", pstate);
       }
@@ -2171,23 +2183,24 @@ namespace Sass {
            (q = peek< percentage >(p))                             ||
            (q = peek< dimension >(p))                              ||
            (q = peek< quoted_string >(p))                          ||
-           (q = peek< variable >(p))                            ||
+           (q = peek< variable >(p))                               ||
            (q = peek< exactly<'*'> >(p))                           ||
            (q = peek< exactly<'+'> >(p))                           ||
            (q = peek< exactly<'~'> >(p))                           ||
            (q = peek< exactly<'>'> >(p))                           ||
            (q = peek< exactly<','> >(p))                           ||
+           (q = peek< sequence<parenthese_scope, interpolant>>(p)) ||
            (saw_stuff && (q = peek< exactly<'-'> >(p)))            ||
            (q = peek< binomial >(p))                               ||
            (q = peek< block_comment >(p))                          ||
            (q = peek< sequence< optional<sign>,
                                 zero_plus<digit>,
                                 exactly<'n'> > >(p))               ||
            (q = peek< sequence< optional<sign>,
-                                one_plus<digit> > >(p))                     ||
+                                one_plus<digit> > >(p))            ||
            (q = peek< number >(p))                                 ||
            (q = peek< sequence< exactly<'&'>,
-                                identifier_alnums > >(p))        ||
+                                identifier_alnums > >(p))          ||
            (q = peek< exactly<'&'> >(p))                           ||
            (q = peek< exactly<'%'> >(p))                           ||
            (q = peek< sequence< exactly<'.'>, interpolant > >(p))  ||

prelexer.cpp

@@ -729,5 +729,16 @@ namespace Sass {
                        alternatives< exactly<';'>, exactly<'}'> >
                       >(src);
     }
+
+    const char* parenthese_scope(const char* src) {
+      return sequence <
+        exactly < '(' >,
+        skip_over_scopes <
+          exactly < '(' >,
+          exactly < ')' >
+        >
+      >(src);
+    }
+
   }
 }

prelexer.hpp

@@ -58,7 +58,7 @@ namespace Sass {
     // recursive skip stuff delimited by start/stop
     // first start/opener must be consumed already!
     template<prelexer start, prelexer stop>
-    const char* skip_over_scopes(const char* src, const char* end = 0) {
+    const char* skip_over_scopes(const char* src, const char* end) {
 
       size_t level = 0;
       bool in_squote = false;
@@ -105,6 +105,19 @@ namespace Sass {
       return 0;
     }
 
+    // skip to a skip delimited by parentheses
+    // uses smart `skip_over_scopes` internally
+    const char* parenthese_scope(const char* src);
+
+    // skip to delimiter (mx) inside given range
+    // this will savely skip over all quoted strings
+    // recursive skip stuff delimited by start/stop
+    // first start/opener must be consumed already!
+    template<prelexer start, prelexer stop>
+    const char* skip_over_scopes(const char* src) {
+      return skip_over_scopes<start, stop>(src, 0);
+    }
+
     // Match a sequence of characters delimited by the supplied chars.
     template <prelexer start, prelexer stop>
     const char* recursive_scopes(const char* src) {