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Description
Description of the false positive
In general, the cs/useless-assignment-to-local rule makes sense: https://lgtm.com/rules/1506093386171/
However, in some cases, the error results in a false positive, where the compiler would throw if the assignment was removed. This happens if the local is assigned within a try/finally block (say, by a method call returning an out), and then used in the finally block. If the method call throws an exception, the local could be left uninitialized.
Here's a simplified example:
private void Test()
{
ArraySegment<byte> rented = default; // necessary, otherwise compiler complains
try
{
MethodThatMightThrow(out rented);
}
finally
{
DoSomething(rented);
}
}
private void MethodThatMightThrow(out ArraySegment<Byte> rented)
{
//rented = default;
throw new InvalidOperationException();
}
private int DoSomething(ArraySegment<Byte> rented)
{
return rented.Array.Length; // null ref if rented isn't assigned.
}URL to the alert on the project page on LGTM.com