Variable 'xxx' of type 'System.String' referenced from scope '', but it is not defined'

[Jodan-pz]

Hello!
After upgrading from 2.18 to 2.19 i got this weird error when evaulating an expression.
An example of the error stack:

Exception has occurred: CLR/System.InvalidOperationException
Exception thrown: 'System.InvalidOperationException' in System.Linq.Expressions.dll: 'variable 'FK_Country' of type 'System.String' referenced from scope '', but it is not defined'
at System.Linq.Expressions.Compiler.VariableBinder.Reference(ParameterExpression node, VariableStorageKind storage)
at System.Linq.Expressions.Compiler.VariableBinder.VisitParameter(ParameterExpression node)
at System.Linq.Expressions.ExpressionVisitor.VisitBinary(BinaryExpression node)
at System.Linq.Expressions.ExpressionVisitor.Visit(ReadOnlyCollection1 nodes) at System.Linq.Expressions.Compiler.VariableBinder.VisitLambda[T](Expression1 node)
at System.Linq.Expressions.LambdaExpression.Compile()

ParameterExpression[0]
[0] [ParameterExpression] ={FK_Country}
CanReduce [bool] =false
DebugView [string] ="$FK_Country"
IsByRef [bool] =false
Name [string] ="FK_Country"
NodeType [ExpressionType] =Parameter
Type [Type] ={System.String}

The expressions is just a simple Eval( "FK_Country != "France"" )
Expression debug view : {(FK_Country != "France")}

Hope it can helps!

[davideicardi]

Are you able to reproduce this error with simple code, preferably in a unit test?

[tomhreb]

Hello,

I am facing simillar issue after upgrading to 2.19.
My scenario si slightly different - I have a custom type to which the result is cast and over which I'm doing the numerical operations, e.g.

public readonly record struct MyCustomType(decimal Value);

'Error executing expression 'function_name(variable_name)': variable 'array' of type 'System.Collections.Generic.IEnumerable`1[MyCustomType]' referenced from scope '', but it is not defined'

Unfortunately it is really hard to reproduce and totally random. I saw that the version 2.19 introduced some caching etc. so probably caused it.

[metoule]

@tomhreb can you share an expression that triggers the issue, even if it doesn't occur all the time? It would help pinpoint the root cause.

[tomhreb]

It's happening in a lot of variants and is is not dependent on the exact expression.
Generally, all the use cases we test use at least one parameter. I can't say whether it failed also for expressions without a parameter.

We're using the interpreter as a singleton.

The simplified configuration of Interpreter and function registration might look like follows:

Expression = "min(x)"
Parameter = x = IEnumerable<MyCustomType> { 1, 2, 3 };

var interpreter = new Interpreter(InterpreterOptions.SystemKeywords | InterpreterOptions.CaseInsensitive)
   .EnableAssignment(AssignmentOperators.None)
   .SetDefaultNumberType(DefaultNumberType.Decimal);

var minFunction = new MinFunction();

interpreter.SetFunction("min", minFunction.Definition);

.... 

internal class MinFunction {

public Delegate Definition => Def1;

private MyCustomType Def1(IEnumerable<MyCustomType> values) => values.Min(v => v.Value);

}

Additionally, what may be worth noting is that we're using this approach for execution:

var lambda = _interpreter.Parse(expression, parameters);

...

var result = lambda.Invoke(parameters);

[Jodan-pz]

Also i found in my use case that the execution inside a parallel.foreach raise this problem.

[metoule]

I think it's the same issue as #364, which also adds a reproduction test.

[Jodan-pz]

I Think that the problem is tied with parameterrs binding when parallel is involved.
A simple reproducible example:

[Test]
public void Should_Pass_Parallel_Eval()
{
	var target = new Interpreter();
	var conds = Enumerable.Repeat("Country != \"France\"", 10);
	var parameters = new[] { new Parameter("Country", "Italy") };
	Parallel.ForEach(conds, exp =>
	{
		Assert.That(target.Eval(exp, parameters), Is.True);
	});
}

[Test]
public void Should_Fail_Parallel_Eval()
{
	var target = new Interpreter();
	var conds = Enumerable.Repeat("Country != \"France\"", 10);

	Parallel.ForEach(conds, exp =>
	{
		var parameters = new[] { new Parameter("Country", "Italy") };
		Assert.That(target.Eval(exp, parameters), Is.True);
	});
}

[metoule]

@Jodan-pz thanks again for the repro! The fix for #364 does fix this issue too :)