A new rule to warn against nesting Path.Combine.

[brian-reichle]

I encountered a couple of places where someone nested Path.Combine and thought we should probably have a rule that guides people to inline them.

so:

var path = Path.Combine(Path.Combine(rootPath, "Foo"), "Bar");

becomes:

var path = Path.Combine(rootPath, "Foo", "Bar");

[yaakov-h]

Looking over the docs for this I noticed that we now also have Path.Join in modern .NET. Is there any scenarios where we should be suggesting that instead, perhaps as a separate rule?

[brian-reichle]

If the values you are joining are all strings, then I don't think it matters. But if you are getting one or more of the elements from a substring (or one of the Path.GetXXX() methods that have span overloads), then Path.Join would be preferable.
eg.

var path = Path.Combine(Path.GetDirectoryName(related), "Foo.xml");

becomes

var path = Path.Join(Path.GetDirectoryName(related.AsSpan()), "Foo.xml".AsSpan());

Might be hard to actually detect this though.