RBS, Ruby’s new type signature language

Cool. And glad to see this called out:

Better IDE integration: Parsing RBS files gives IDEs better understanding of the Ruby code. Method name completions run faster. On-the-fly error reporting detects more problems. Refactoring can be more reliable!

IDE support (autocomplete, refactoring and quick documentation) is the most important reason to annotate argument and return types.

I've been using typescript for a few years now and to be honest I almost never rely on the compilation errors. I just use the built in Jetbrains IDE completion, autosuggestion, and navigation to make it work.

Yep. A good IDE to a first approximation doesn't allow compilation errors to occur because you are auto-completing everything, including symbol completion based on the type at cursor, etc.

Jetbrains is a wonderful company.

Since the advent of LSP, I think the value proposition of a full featured IDE has been greatly diminished.

For example, I used to use Intellij for Scala but recently switched to Emacs+Metals and haven't really missed anything. In fact, it's probably an even better editing experience.

Intellij still has better refactoring (though I don't use it much), and the integrated debugger and database viewer are really nice. I've found myself using Emacs and only switching to Intellij for the aforementioned specialized tasks.

5 years ago you would have been crazy not using an IDE for JVM work but this is no longer the case. LSP is such a wonderful technology and has empowered the creation of new programming languages like never before. It's truly remarkable.

If I was Intellij, I would be a little worried about my future market share. They simply can't provide the same value as before, and I'm not sure how they intend to change that.