Wow, I remember learning about F# and thinking, "too bad it's stuck on Windows, I'll never use it". Awesome to hear that .NET Core has really changed that.

How is the incremental typechecking experience, eg in vscode? (Speed, UX)

Does F# have a prettier implementation or other fast/deterministic/opinionated formatter?

We use Rider (enterprise license) to develop our F# services. Over the past year, the experience kept improving, small tweaks kept coming, and bugs were sorted out. At the moment, some of our larger shared type definition files are a slow to edit (seems Rider/.net is trying like crazy to look over all the symbols before I've even finished typing), but overall, I had a very good experience with it.

Not aware of any linters out there. Rider might have built in rules to enforce it, but that wouldn't hook into your CI/CD.

Roughly how large of a file and how slow to edit?

Although there are some aspects to performance that are Rider-specific, it uses the same underlying compiler to deliver tooling. So some issues might be solvable at a more core layer.

Disclaimer: I work on F# at Microsoft

Our setup is multiple solutions for each service, and most inherit from "Core" parts. This type def file is about 1000 lines (can't count the number of declarations in there).

What seems to happen consistently: I can delete a label in a type record, no lag. As soon as I finish adding a label (haven't added its type yet), all matter of slow hell breaks loose and there is a 5 second delay before anything shows up. This happens regardless of whether or not the type is used in a low (<20) or high (>100) number of places. The delay is the same in all records.

The issue you're describing sounds more like a compiler/core tooling issue than a Rider issue though. Would you mind filing an issue here? https://github.com/dotnet/fsharp

We collaborate with the Rider folks quite a lot and so they'll see this if it is indeed a Rider issue.