Fix S1168 FP: when returning null in LINQ lambda

[Thieum]

Description

Regression of #761

Currently the rule S1168 raises an issue when returning null from within a lambda declared inside of a method returning a collection.

Repro steps

this code will demonstrate the false positive:

using System;
using System.Collections.Generic;
using System.Linq;

namespace ConsoleApp14
{
    static class Program
    {
        class ABC
        {
        }

        static void Main()
        {
            var test = Test();
            Console.WriteLine(test);
        }

        static IEnumerable<ABC> Test()
        {
            var list = new List<ABC>();

            return list.Select(o =>
            {
                if (o != null)
                {
                    return o;
                }
                return null;
            });
        }
    }
}

Expected behavior

S1168 shouldn't be raised inside the scope of the lambda, as the return of the lambda is different than the one of the encapsulating method.

There could be legitimate case where the return of a lambda is a collection, where this rule could apply.

Both positive and negative results in lambda should be tested.

Actual behavior

S1168 is raised inside the lambda considering the result of the encapsulating method instead of the result of the lambda.

Known workarounds

ignore S1168 around the lambda expression.

Related information

• SonarLint for Visual Studio 4.10.0.9867 / Sonar C# 7.14
• Visual Studio Enterprise 2019 16.1.3

[antoinebj]

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