Confusion about new default Python language server Pyrefly

[jeffkeller-einc]

The release notes for https://github.com/posit-dev/positron/releases/tag/2025.12.0-167 contains this:

We no longer bundle the Pyright extension because its functionality overlaps with Pyrefly. If you do not want to use Pyrefly, disable that extension.

What is "that extension" in this case? Pyright or Pyrefly? When I read this it sounds like Pyright is required to use Pyrefly, but if that is the case, why is Pyright no longer bundled with Positron?

My goal is to enjoy the intended default Positron experience. But I'm unsure what settings changes I need to make to an existing Positron installation here.

[juliasilge]

Ah, thanks for this question! We do literally mean if you do not want to use Pyrefly then disable Pyrefly. This would be someone who, say, really loves the ty extension and prefers to use it over Pyrefly.

If you have an existing Positron installation, there's nothing you must do to have a good experience. If you want to really clean things up, then I would say you can:

• uninstall the Pyright extension
• uninstall the "Python Environments" extension (we never purposefully installed this for you, but at some points in the past it could get installed as a dependency of other extensions and it does not work in Positron)

I would say these are optional, but it would keep your installation a bit cleaned up. 🧼 🧹

[cbowdon]

I've uninstalled Pyright and Python Environments for an existing installation, but Pyrefly does not seem to be taking effect. Is some action necessary to activate Pyrefly?

[cbowdon]

Thanks for responding @austin3dickey . I see no Pyrefly in my extensions, which I assumed was because it's bundled? Do I need to install it manually for an existing Positron installation/workspace?

Edit: Pyrefly works fine if I install it manually.

[austin3dickey]

Good to hear @cbowdon! Are you on the latest version of Positron? I'd expect Pyrefly to be bundled with Positron on version 2025.12.0-167. If it wasn't, I wonder if there was something that uninstalled it, like a setting.

which I assumed was because it's bundled

We have two strategies for bundling extensions - some are bootstrapped, which means they're simply downloaded as-is from Open VSX and shipped with Positron so you see them in the Extensions pane (and can uninstall/disable them), and some are built-in, which means their code actually lives in the Positron repo, and they're more critical and you don't see them in the list without a certain filter. But Pyrefly is the former.

[cbowdon]

@austin3dickey Yes, 2025.12.0 build 167. I've had my install a long time (loving Positron, many thanks to you and the rest of the team!) so it's certainly possible that some long-forgotten setting is interfering. That said, the only apparently relevant lines in settings.json are:

  "remote.downloadExtensionsLocally": true,
  "extensions.allowed": "*"

Is there anything you can think of that I should check?

[austin3dickey]

Oh, interesting. Are you using the remote SSH feature? If so, is there any difference in whether Pyrefly is installed between when you're logged into the server vs. not? (I realize that might have changed since you installed Pyrefly 😅)

[cbowdon]

It's all dev work on a local machine, so I guess it shouldn't be that. I have a new theory: it's profiles, and my lack of understanding thereabouts.

I just opened a new window with the Default profile, which I haven't used for a few weeks. Pyrefly is present in the extensions (and Pyright btw.) I definitely didn't install Pyrefly in this profile at any point previously, so I guess it is showing up because it has bootstrapped correctly.

The other profiles I've created have their own specific extensions. It makes some sense that Pyrefly wouldn't be injected into these - maybe these profiles have a very carefully selected set of extensions that I wouldn't want to be touched. (They don't, of course - all a huge mess of things I needed at a particular moment in time. 😆) That would explain what I'm seeing, anyway.

If this is the right explanation, then arguably Pyrefly and other bundled extensions should actually be injected into all profiles, or there should be an option in the Profiles UI that allows the user to opt in/out of bundled extensions. But equally, maybe I should just have understood profiles better before using them.