S2259 FP: return value of ToList() is not null

[csaba-sagi-sonarsource]

Description

S2259 raises an issue telling that the return value of the ToList() is is null on at least one execution path.

Repro steps

        public static long Test()
        {
            long sum = 0;
            long[] array = new[] { 1L, 2L, 3L };
            List<long> test = array.ToList();
            if (test?.Count == 0)
            {
                // Do something
            }

            foreach (long number in test)  // Reported Bug: 'test' is null on at least one execution path.
            {
                sum += number;
            }

            return sum;
        }

Expected behavior

S2259 should not raise an issue.

Actual behavior

S2259 raises an issue for this case.

Known workarounds

Related information

• C#/VB.NET Plugins version: 8.27

[martin-strecker-sonarsource]

@pavel-mikula-sonarsource I wouldn't solve this issue. It is a rabbit hole (there are literally millions of APIs in the runtime that never return null). The root cause here is the nonsensical test?.Count == 0 check, which implies that test can be null. If the developer thinks so once, he should not change his mind midway.

[pavel-mikula-sonarsource]

This should be low hanging to fix. And we'll have at least some support for Linq APIs also in #3290 so I'd keep it