I Need A Reason!

This is a feature request for reasoning to be given when functions fail to inline. It would probably require a little bit of hacking to base, but something like the vectorization summaries that llvm provides about "This function didn't inline and why" would be really helpful. For example, "this function hit the recursion limiter," "this function has an unassigned type parameter", or "this function contains an error" would all be great things to know about why a function didn't inline, so that I can go and fix it.