CA2249 False positive

[winscripter]

Version Used: Visual Studio 2026 Insiders [11201.2]

Steps to Reproduce:

1. Paste this code:

string thing = "A bird was seen hopping.";
int indexOfSpace = thing.IndexOf(' ');

CA2249 is reported - three dots under the thing.IndexOf( line, suggesting to change that line into a thing.Contains(.

Diagnostic Id: CA2249

Expected Behavior:
The CA2249 warning - "replace IndexOf with string.Contains to improve readability", shouldn't be reported.

Actual Behavior:
It is reported, which doesn't make sense because we're trying to just get an index of a whitespace character in the string, not checking if it exists. Checking if it were to exist would've made sense if this was thing.IndexOf(' ') != 0, but it isn't, and the variable is of type int, so it's clear that we're just getting the index of a character than checking if the character exists.

[winscripter]

In addition, when this happens, there is no code fix for this warning either. Looking into the source code, I assume a code fix is expected to appear. I assume it's because the variable is int, not bool.

[Youssef1313]

Are you referencing the variable indexOfSpace anywhere in code and the analyzer is still reporting a diagnostic? If so, can you post the complete code?

We have already this test:

sdk/src/Microsoft.CodeAnalysis.NetAnalyzers/tests/Microsoft.CodeAnalysis.NetAnalyzers.UnitTests/Microsoft.NetCore.Analyzers/Runtime/PreferStringContainsOverIndexOfTests.cs

Lines 930 to 955 in 2b9fc02

	[Fact]
	public async Task TestRightOperandIsVariableAsync()
	{
	string csInput = @"
	namespace TestNamespace
	{
	class TestClass
	{
	private void TestMethod()
	{
	string str = ""This is a string"";
	int compare = 5;
	int index = str.IndexOf(""This"");
	if (index == compare)
	{
	}
	}
	}
	}";
	var testOrdinal = new VerifyCS.Test
	{
	TestState = { Sources = { csInput } },
	ReferenceAssemblies = ReferenceAssemblies.Net.Net50,
	};
	await testOrdinal.RunAsync();
	}

The above test asserts that no diagnostic is reported, and I suppose because the variable is used in a meaningful way that is not "contains" check.

[winscripter]

You can paste the code into a C# Console App with top-level statements enabled.

You should see the following.

After creating this issue post, I've actually realized that the CA2249 warning does disappear the moment I use the indexOfSpace variable (like in a Console.WriteLine call). However, I believe this is still a problem because, for developers like me who prefer to fix all warnings and IDE/CAxxxx suggestions to ensure that code is clean, it can cause confusion. For instance, if I'm actively writing code, and I write that indexOfSpace line or something similar (before writing a line of code that references the indexOfSpace variable), I will see the CA2249 warning, but I would be puzzled (furthermore, there's not a code fix in this context either) and would result in perhaps slowed development time as I'm trying to figure out what am I doing wrong.