Cannot compile template with Lookup helper - signature or security transparency is not compatible

Question

I'm trying to use the following template (TestTemplate) in a console application using .NET Core 2.1 and Handlebars.Net 1.9.5

<html>
<head>
    <title>A title</title>
</head>

<body>
    {{ > (lookup TemplateName)}}
</body>
</html>

So the line with {{ > (lookup TemplateName)}} is causing me problems.

The idea is to use a partial, where the partial name will be resolved later by passing the TemplateName variable.

However, when I try to compile the template by using

var foo = Resource1.TestTemplate;
Handlebars.Compile(Encoding.UTF8.GetString(foo));

I get the following exception :

System.ArgumentException: Cannot bind to the target method because its signature or security transparency is not compatible with that of the delegate type. at System.Reflection.RuntimeMethodInfo.CreateDelegateInternal(Type delegateType, Object firstArgument, DelegateBindingFlags bindingFlags) at HandlebarsDotNet.Compiler.SubExpressionVisitor.GetHelperDelegateFromMethodCallExpression(MethodCallExpression helperCall) at HandlebarsDotNet.Compiler.SubExpressionVisitor.VisitSubExpression(SubExpressionExpression subex) at System.Linq.Expressions.ExpressionVisitor.VisitUnary(UnaryExpression node) at System.Linq.Expressions.UnaryExpression.Accept(ExpressionVisitor visitor) at System.Dynamic.Utils.ExpressionVisitorUtils.VisitArguments(ExpressionVisitor visitor, IArgumentProvider nodes) at System.Linq.Expressions.ExpressionVisitor.VisitMethodCall(MethodCallExpression node) at System.Linq.Expressions.MethodCallExpression.Accept(ExpressionVisitor visitor) at System.Linq.Expressions.ExpressionVisitor.VisitUnary(UnaryExpression node) at System.Linq.Expressions.UnaryExpression.Accept(ExpressionVisitor visitor) at System.Linq.Expressions.ExpressionVisitor.VisitConditional(ConditionalExpression node) at System.Linq.Expressions.ConditionalExpression.Accept(ExpressionVisitor visitor) at System.Dynamic.Utils.ExpressionVisitorUtils.VisitBlockExpressions(ExpressionVisitor visitor, BlockExpression block) at System.Linq.Expressions.ExpressionVisitor.VisitBlock(BlockExpression node) at System.Linq.Expressions.BlockExpression.Accept(ExpressionVisitor visitor) at HandlebarsDotNet.Compiler.FunctionBuilder.Compile(IEnumerable1 expressions, Expression parentContext, String templatePath) --- End of inner exception stack trace --- at HandlebarsDotNet.Compiler.FunctionBuilder.Compile(IEnumerable1 expressions, Expression parentContext, String templatePath) at HandlebarsDotNet.Compiler.FunctionBuilder.Compile(IEnumerable1 expressions, String templatePath) --- End of inner exception stack trace --- at HandlebarsDotNet.Compiler.FunctionBuilder.Compile(IEnumerable1 expressions, String templatePath) at HandlebarsDotNet.Handlebars.HandlebarsEnvironment.Compile(String template)

I hope someone has an idea, because I've already been searching quite some time.

bluedot · Accepted Answer · 2018-09-27 09:45:33Z

2

Ok I totally missed that I was looking at the HandleBars.js documentation.

In HandleBars.js the lookup helper is built-in, but so far, it isn't in the .net version.

So you have to declare the lookup helper yourself, which in my case goes something like this:

Handlebars.RegisterHelper("lookup", (output, context, arguments) => { output.WriteSafeString(arguments[0]); });

Hope it can help someone else.

answered Sep 27, 2018 at 9:45

bluedot

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1 Comment

Rex M Over a year ago

Thanks for adding this! Would love to see a PR submitted to add it to the core library, as well. Cheers!

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