CA1859: Use concrete types when possible for improved performance, suggesting wrong type

[ygoe]

Analyzer

Diagnostic ID: CA2013: Do not use ReferenceEquals with value types

Analyzer source

SDK: Built-in CA analyzers in .NET 5 SDK or later

Version: SDK 5.0.100

OR

NuGet Package: Microsoft.CodeAnalysis.NetAnalyzers

Version: 8.0.0

Describe the bug

I don't know if any of the above information is relevant or correct, I don't understand it so I haven't touched it. If I'm supposed to enter anything in there, please make it clear in the template.

So, the analyzer "CA1859: Use concrete types when possible for improved performance" gives me a false suggestion. If I follow it, my code breaks immediately.

Steps To Reproduce

Code:

	private static object? Multiply(object? leftValue, object? rightValue)
	{
		if (ConvertToDoubleOrString(leftValue, out double left, out string? leftStr))
		{
			if (ConvertToDoubleOrString(rightValue, out double right, out string? rightStr))
			{
				return left * right;
			}
			return Repeat(rightStr, (int)left);
		}
		else if (ConvertToDoubleOrString(rightValue, out double right, out string? _))
		{
			return Repeat(leftStr, (int)right);
		}
		throw new FormatException("The * operator does not accept two string operands.");

		static string? Repeat(string? str, int count)
		{
			if (str == null)
				return null;
			var sb = new StringBuilder(str.Length * count);
			while (count-- > 0)
			{
				sb.Append(str);
			}
			return sb.ToString();
		}
	}

	// Defined in a base class:
	protected static bool ConvertToDoubleOrString(object? value, out double doubleValue, out string? stringValue)
	{
		doubleValue = 0;
		stringValue = null;
		if (value == null)
		{
			return false;
		}
		if (value is double d)
		{
			doubleValue = d;
			return true;
		}
		stringValue = Convert.ToString(value, CultureInfo.InvariantCulture)!;
		return double.TryParse(stringValue, CultureInfo.InvariantCulture, out doubleValue);
	}

Expected behavior

No suggestion, object? is already the best return type.

Actual behavior

Analyzer suggests to change return type of Multiply to string? for better performance.

Additional context

• .NET 9
• Visual Studio 17.12.4

[ygoe]

At the same time, the analyzer doesn't suggest anything in these methods where I'd expect it to do:

	private static object ShiftRight(object? leftValue, object? rightValue)
	{
		int left = (int)ConvertToDouble(leftValue);
		int right = (int)ConvertToDouble(rightValue);
		return (double)(left >> right);
	}

	private static object BitwiseOr(object? leftValue, object? rightValue)
	{
		int left = (int)ConvertToDouble(leftValue);
		int right = (int)ConvertToDouble(rightValue);
		return (double)(left | right);
	}