False positive "nested constraint" exception when using an argument constraint of the wrong type

Original title: Weird issue with nested constraints and simple types

public interface IEmailFactory
    {
        Task<IList<MailMessage>> GetEmailMessages(long idPairGame, EmailTemplateType emailTemplateType);
    }

_emailFactory = new Fake<IEmailFactory>().FakedObject;

A.CallTo(() => _emailFactory.GetEmailMessages(A<int>._, A<EmailTemplateType>._)).Returns(mailMessages);

EmailTemplateType is an enum. When I change it to int it is still wrong, so it is not an issue.

FakeIt version 4.1.

It throws the following exception

FakeItEasy.Expressions.ExpressionArgumentConstraintFactory.ArgumentConstraintExpressionVisitor.VisitMember(MemberExpression node) at System.Linq.Expressions.MemberExpression.Accept(ExpressionVisitor visitor) at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node) at System.Linq.Expressions.ExpressionVisitor.VisitUnary(UnaryExpression node) at System.Linq.Expressions.UnaryExpression.Accept(ExpressionVisitor visitor) at FakeItEasy.Expressions.ExpressionArgumentConstraintFactory.CheckArgumentExpressionIsValid(Expression expression) at FakeItEasy.Expressions.ExpressionArgumentConstraintFactory.GetArgumentConstraintFromExpression(Expression expression, Object& value) at FakeItEasy.Expressions.ExpressionArgumentConstraintFactory.GetArgumentConstraint(ParsedArgumentExpression argument) at System.Linq.Utilities.<>c__DisplayClass2_03.<CombineSelectors>b__0(TSource x) at System.Linq.Enumerable.SelectEnumerableIterator2.ToArray() at System.Linq.Enumerable.ToArray[TSource](IEnumerable1 source) at FakeItEasy.Expressions.ExpressionCallMatcher..ctor(ParsedCallExpression parsedExpression, ExpressionArgumentConstraintFactory constraintFactory, MethodInfoManager methodInfoManager, Factory outputWriterFactory) at FakeItEasy.RootModule.<>c__DisplayClass0_0.<RegisterDependencies>b__4(ParsedCallExpression callSpecification) at FakeItEasy.Configuration.FakeConfigurationManager.CallTo[T](Expression1 callSpecification)

[thomaslevesque]

This change has been released as part of FakeItEasy 4.1.1.

Thanks for the report @progala2! Look for your name in the release notes. 🏆

[thomaslevesque]

There’s a problem in your code: it should be A<long>._, not A<int>._. Since the parameter is of type long, the A<int>._ constraint will never match; in fact, we even added a diagnostic in the latest analyzer.

I think this is what causing the error, since I can’t reproduce the problem when I change the constraint type. However, the exception is clearly incorrect, we definitely have a bug.