Keep instance lenses stable even if parsed results are unavailable

[July541]

Not function signature lenses only(#3541), instance signatures have the same issue.

This pr uses staled results to prevent flicker.

I take hls-class-plugin considered first just because I'm more familiar with this than familiar with function type lenses😉

[michaelpj]

Seems like there's a general principle: code lenses should always use useWithStale, since otherwise they flicker. Doesn't really matter for other stuff so much. It would be nice to write that down somewhere, not sure where.

[michaelpj]

and here

[michaelpj]

Interestingly, this seems like somewhere we shouldn't do it. We really want the up-to-date module to compute an edit! But because we return the edit as part of the code lens, we have to. So the thing to do in the long run would be to implment codeLens/resolve so only the resolution method would need this. Worth a comment!

Also relevant for #3536

[July541]

Should be pointing out that we have three lens behaviors now:

1. import lens
2. top-level signature lens
3. class instance lens

import lens has been using useWithStale, and I'm applying the substitution for the other two.

That means we'd have similar comments for every lens provider :(

[michaelpj]

That means we'd have similar comments for every lens provider :(

I think it's an important comment in all those places, unfortunately. Unless we want to adopt the GHC Note convention and just write a Note once and reference it from all of them.

[July541]

So the thing to do in the long run would be to implment codeLens/resolve so only the resolution method would need this. Worth a comment!

@michaelpj I'm a little confused, do you mean we compute lenses by fresh type checked result, and resolve it with the staled result?

And, what's the meaning of resolve, does it mean apply the lens or refresh the lens, or anything else?

[michaelpj]

I'm a little confused, do you mean we compute lenses by fresh type checked result, and resolve it with the staled result?

Other way around 😅 I think that's reasonable? It means that when you click on the lens it might be a bit out of date, but then you'll get the right then when its inserted.

And, what's the meaning of resolve, does it mean apply the lens or refresh the lens, or anything else?

The codeLens/resolve method lets you fill in some information in the lens result later. In particular, you can fill in the edit later! So you can quickly/inaccurately produce the initial lens results, and then when someone clicks on it fill in the full correct edit.

But this is future work anyway!