private DirectiveTriviaSyntax ParseIfDirective(SyntaxToken hash, SyntaxToken keyword, bool isActive)
{
var expr = this.ParseExpression();
var eod = this.ParseEndOfDirective(ignoreErrors: false);
var isTrue = this.EvaluateBool(expr);
var branchTaken = isActive && isTrue;
return SyntaxFactory.IfDirectiveTrivia(hash, keyword, expr, eod, isActive, branchTaken, isTrue);
}