Rule S2259 FP: symbolic execution does not enter the for loop

[bzuu]

Description

The following code snippet seems to trigger a false positive S2259 'lastEx' is null on at least one execution path. on the last line with the throw statement:

public FileStream Blah()
{
	IOException lastEx = null;
	for (int i = 0; i < 10; i++)
	{
		try
		{
			return File.Open("somepath", FileMode.Open);
		}
		catch (IOException e)
		{
			lastEx = e;
		}
	}

	throw new InvalidOperationException(lastEx.Message);
}

When the for loop is removed S2259 is not raised on the last line.

Expected behavior

No S2259 raised on the last line as either the code has returned or the lastEx value has been set.

Actual behavior

Rule S2259 is raised both using the scanner for MSBuild as well as using SonarLint.

Related information

• SonarC# Version 6.5 (build 3766)
• Visual Studio Enterprise 2017 Version 15.4.1
• Scanner for MSBuild Version 3.0.2
• SonarLint 3.6.0.2584

[sm-g]

same for forest here after update from 6.8.2 to 7.4.0:

DisjointForest<TModel> forest = null;
try
{
	forest = DisjointForest<TModel>.Create(models);
}
catch (ArgumentException ex) when (ex.Message.Contains("sss", StringComparison.OrdinalIgnoreCase))
{
	return result;
}

foreach (var item in Filter<TItem, TModel>(items))
{
	var count = forest.Leaves.Count();
}

[andrei-epure-sonarsource]

This is because our Symbolic Execution engine thinks the code will never enter the loop.

    class TestForLoop
    {
        string Foo()
        {
            string s = null;
            for (int i = 0; i < 10; i++)
            {
                s = "";
            }
            return s.Trim(); // Noncompliant FP due to integer constraints
        }
    }

[andrei-epure-sonarsource]

related to #2528