Overview

Right now, createIsolatedProgram creates a ts.Program with minimal type info behind the scenes:

In theory, the services without a specified project path don’t need to make their own Program. That program was used for the experimental unused variables rule, to get program diagnostics such as unused var diagnostics... but this can take dozens of ms a file, and is rarely used by anybody.

Creating a standalone program that way isn't very expensive, but it would be nice to avoid. We should investigate whether we can get rid of it altogether.

The tricky thing here is parser types: some internal code expects ASTAndProgram instances from the parsing results. In this new world, there may not be the program from there.

Marking as accepting PRs with the caveat that everything still has to work as expected. Which may or may not be doable. Good luck! 😄

This issue is from a pairing I had with @bradzacher going over the parser internals.