ConstantCheck.cs

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using System.Dynamic.Utils;
 
namespace System.Linq.Expressions;
 
internal static class ConstantCheck
{
    internal static bool IsNull(Expression e)
    {
        return e.NodeType switch
        {
            ExpressionType.Constant => ((ConstantExpression)e).Value == null, 
            ExpressionType.Default => e.Type.IsNullableOrReferenceType(), 
            _ => false, 
        };
    }
 
    internal static AnalyzeTypeIsResult AnalyzeTypeIs(TypeBinaryExpression typeIs)
    {
        return AnalyzeTypeIs(typeIs.Expression, typeIs.TypeOperand);
    }
 
    private static AnalyzeTypeIsResult AnalyzeTypeIs(Expression operand, Type testType)
    {
        Type type = operand.Type;
        if (type == typeof(void))
        {
            if (!(testType == typeof(void)))
            {
                return AnalyzeTypeIsResult.KnownFalse;
            }
            return AnalyzeTypeIsResult.KnownTrue;
        }
        if (testType == typeof(void) || testType.IsPointer)
        {
            return AnalyzeTypeIsResult.KnownFalse;
        }
        Type nonNullableType = type.GetNonNullableType();
        Type nonNullableType2 = testType.GetNonNullableType();
        if (nonNullableType2.IsAssignableFrom(nonNullableType))
        {
            if (type.IsValueType && !type.IsNullableType())
            {
                return AnalyzeTypeIsResult.KnownTrue;
            }
            return AnalyzeTypeIsResult.KnownAssignable;
        }
        return AnalyzeTypeIsResult.Unknown;
    }
}