@baronfel Is it possible for us to add some logic to detect if we did do a roll-forward and then errored.. and if so warn the user about the roll forward and tell them to use an older SDK?

This is not a bad idea. What happens with tools is that

• we eventually write a DotnetToolSettings.xml file that looks like this:

<?xml version="1.0" encoding="utf-8"?>
<DotNetCliTool Version="1">
  <Commands>
    <Command Name="fsautocomplete" EntryPoint="fsautocomplete.dll" Runner="dotnet" />
  </Commands>
</DotNetCliTool>

• the rollforward is set in the runtimeconfig.json to whatever we infer here

We probably need to set some other kind of data in the DotnetToolSettings.xml to signal that we opted the user into auto-rollforward so we could give an error here.

I don't think we need to do this (add the data to do error detection) for this PR - I think this behavior is correct and good and what we should have done all along, and a breaking change notice is enough. Virtually every tool author I've spoken to has wondered why this wasn't the default, so I don't think there's a user experience gap that we need to cover here.

If we get feedback from users post-preview5 that this was confusing, we can certainly come back to this though!

That makes sense.