Analyzer suggestion: unnecessary use of unsafe

[stephentoub]

Brief description:

We frequently find ourselves initially writing some method to use unsafe code / pointers, and so annotate the method as unsafe. Later, generally as Span<T> is employed more or as new framework APIs are utilized to improve the method, the method no longer uses pointers, but we sometimes forget to remove the unsafe keyword. It would be nice-to-have if there were an analyzer we could enable to flag such uses of unsafe that could be removed.

Languages applicable:

C#

Code example that the analyzer should report:

private unsafe void ToUpper(Span<char> span)
{
    for (int i = 0; i < span.Length; i++)
        span[i] = char.ToUpperInvariant(span[i]);
}

[sharwell]

I've wanted this for sure. Also have wanted the ability to move unsafe from a type declaration to a subset of members that actually need it.

[Youssef1313]

I'm interested in implementing this if it's approved in the design meeting.

[CyrusNajmabadi]

I'm willing to pre-emptively approve this. We would take this. Open question is on if it's feasible to encode the rules easily enough to put this in teh IDE. My preference would be more that this be done in the compiler with a hidden diagnostic.

[vatsalyaagrawal]

Design meeting notes: This should come from Compiler, request hidden diagnostic from the compiler.