Fix MA0182 false positive for delegates used in new expressions

[Copilot]

MA0182 incorrectly reports internal delegate types as unused when instantiated via new DelegateType(...), commonly seen with Moq's .Callback() method.

Changes

• Register handler for OperationKind.DelegateCreation to track delegate instantiation
• Implement AnalyzeDelegateCreation to mark delegate types as used

Example

Previously flagged incorrectly:

// MA0182: Internal type 'tryAcquireLockDelegate' is apparently never used
private delegate void tryAcquireLockDelegate(string key, out string lockToken);

mockClient
    .Setup(x => x.TryAcquireLock(..., out outParam))
    .Callback(new tryAcquireLockDelegate((string key, out string lockToken) => 
    {
        lockToken = "42";
    }));

Now correctly recognized as used since new tryAcquireLockDelegate(...) creates an IDelegateCreationOperation.

Warning

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  • Triggering command: /usr/share/dotnet/dotnet /usr/share/dotnet/dotnet exec --runtimeconfig /home/REDACTED/work/Meziantou.Analyzer/Meziantou.Analyzer/tests/Meziantou.Analyzer.Test/bin/Release/net10.0/Meziantou.Analyzer.Test.runtimeconfig.json --depsfile /home/REDACTED/work/Meziantou.Analyzer/Meziantou.Analyzer/tests/Meziantou.Analyzer.Test/bin/Release/net10.0/Meziantou.Analyzer.Test.deps.json /home/REDACTED/work/Meziantou.Analyzer/Meziantou.Analyzer/tests/Meziantou.Analyzer.Test/bin/Release/net10.0/testhost.dll --port 45733 --endpoint 127.0.0.1:045733 --role client --parentprocessid 5438 --datacollectionport 40723 --telemetryoptedin false ziantou.Analyzer--ignore-submodules (dns block)

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Original prompt

---

This section details on the original issue you should resolve

<issue_title>MA0182 false positive using delegate</issue_title>
<issue_description>### Version of the Meziantou.Analyzer NuGet package

2.0.277

Rule Identifier

MA0182

Target Framework

Net 10.0

C# Language version

C# 12

Description

Reported error

Error MA0182 : Internal type 'tryAcquireLockDelegate' is apparently never used. If so, remove it from the assembly. If this type is intended to contain only static members, make it 'static'. (https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0182.md)

but tryAcquireLockDelegate in use in Mock .Callback

Reproduction Steps

Minimal code:

[TestFixture]
[TestOf(typeof(Program))]
public class ProgramTest
{
	public interface IInterface
	{
		bool TryAcquireLock(string key, string comment, TimeSpan timeout, out string lockToken);
	}

	private delegate void tryAcquireLockDelegate(string key, string comment, TimeSpan timeout, out string lockToken);

	[Test]
	public void Test()
	{
		var mockLockManagerClient = new Mock<IInterface>();

		string outParam;
		mockLockManagerClient
			.Setup(x => x.TryAcquireLock(It.IsAny<string>(), It.IsAny<string>(), It.IsAny<TimeSpan>(), out outParam))
			.Returns(true)
			.Callback(new tryAcquireLockDelegate((string key, string comment, TimeSpan timeout, out string lockToken) =>
			{
				lockToken = "42";
			}));
	}
}

Other information

No response</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes MA0182 false positive using delegate #967

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