LGTM.com - false positive - cs/dereferenced-value-is-always-null when passed by ref to a method like Array.Resize

[ahsonkhan]

Description of the false positive

In general, the cs/dereferenced-value-is-always-null rule makes sense: https://lgtm.com/rules/1506094316834/

However, if a local is passed to a method by ref, it is possible that the method changes its value. In particular, if an array is null, Array.Resize will set it to not null. This applies generally to any method that accepts a parameter by ref.

https://github.com/dotnet/runtime/blob/c5805025613513ca71b905d3cdafdcba0769960d/src/libraries/System.Private.CoreLib/src/System/Array.cs#L43-L61

URL to the alert on the project page on LGTM.com

https://lgtm.com/projects/g/dotnet/corefx/snapshot/4fed824926d1c659c494bd5261fbae0236b2e9da/files/src/System.Runtime.Serialization.Formatters/src/System/Runtime/Serialization/FormatterServices.cs?sort=name&dir=ASC&mode=heatmap#x520a4bc6d0c2a055:1

[calumgrant]

Many thanks for your report, and I agree that this is definitely a false positive. We shall work on a fix for this.

[Whathecode]

This applies generally to any method that accepts a parameter by ref.

We just ran into the same issue. This rule does not take the ref keyword into account. I suggest to change the title of this bug report to make clear it impacts a broader scope.

Any update on this?