An assert is fired when params parameter of inferred anonymous delegate has type parameter as its type

[AlekseyTs]

        [Fact]
        public void DelegateNaturalType_07()
        {
            var src = @"
class Helper<T> 
    where T : System.Collections.Generic.List<long>, new()
{
    static public void Test3(params T a) { System.Console.WriteLine("" {0}"", a is not null); }
}

class Program
{
    static void Main()
    {
        DoTest3<System.Collections.Generic.List<long>>();
    }
    static void DoTest3<T>()
        where T : System.Collections.Generic.List<long>, new()
    {
        var a3 = Helper<T>.Test3;
        M(a3)();
    }

    static T M<T>(T t) { System.Console.WriteLine(typeof(T)); return t; }
}
";
            var comp = CreateCompilation(src, options: TestOptions.ReleaseExe);

            var verifier = CompileAndVerify(
                comp,
                symbolValidator: (m) =>
                {
                    var delegateType = m.ContainingAssembly.GetTypeByMetadataName("<>f__AnonymousDelegate0`1");
                    MethodSymbol delegateInvokeMethod = delegateType.DelegateInvokeMethod;
                    AssertEx.Equal("void <>f__AnonymousDelegate0<T1>.Invoke(params T1 arg)", delegateInvokeMethod.ToTestDisplayString());

                    // Strictly speaking it is a violation of language rules to decorate this parameter with ParamCollectionAttribute
                    // because it lacks constraints that would make it a valid 'params' type
                    // However, going through the trouble of porting constraints and differentiating/merging anonymous delegates based on them
                    // is probably not worth the trouble for this edge scenario.
                    // The types involved might be inaccessible on assembly level, etc.
                    VerifyParamsAndAttribute(delegateInvokeMethod.Parameters[0], isParamArray: false, isParamCollection: true);
                    Assert.False(delegateType.TypeParameters[0].HasConstructorConstraint);
                    Assert.Empty(delegateType.TypeParameters[0].ConstraintTypesNoUseSiteDiagnostics);
                },
                expectedOutput: ExpectedOutput(@"
<>f__AnonymousDelegate0`1[System.Collections.Generic.List`1[System.Int64]]
 True
")).VerifyDiagnostics();
        }

Observed:

Microsoft.CodeAnalysis.CSharp.UnitTests.Semantics.ParamsCollectionTests.DelegateNaturalType_07 [FAIL]
  System.InvalidOperationException : Assertion failed
  Stack Trace:
    at Microsoft.CodeAnalysis.ThrowingTraceListener.Fail(String message, String detailMessage)
       at System.Diagnostics.TraceInternal.Fail(String message, String detailMessage)
       at System.Diagnostics.Debug.Fail(String message, String detailMessage)
    src\Compilers\CSharp\Portable\Symbols\AnonymousTypes\AnonymousTypeField.cs(46,0): at Microsoft.CodeAnalysis.CSharp.Symbols.AnonymousTypeField..ctor(String name, Location location, TypeWithAnnotations typeWithAnnotations, RefKind refKind, ScopedKind scope, ConstantValue defaultValue, Boolean isParams, Boolean hasUnscopedRefAttribute)

            Debug.Assert(!isParams || !typeWithAnnotations.Type.IsTypeParameter());

The assert is ignorable, i.e. no other changes are necessary apart from removing it in order to get the test passing.

[AlekseyTs]

My recommendation is "Won't fix"