feat(lsp): add options.sync for code actions

[laher]

Addresses #24168

This feature helps to synchronously run code actions before writing a file - for example during a BufWritePre autocmd - so that they don't suffer from race conditions.

This PR adds a 'sync' option to vim.lsp.code_action() (aswell as a timeout_ms). This is similar to vim.lsp.format({ async = false, timeout_ms = 1000 }), but given that the exsiting behaviour is async, I used sync in this case - people would expect the default to be sync=false. I added some vim.notify notifications which seemed appropriate.

An implementation question-mark: vim.lsp.code_action() does not return the results/error of the code action, because there is nothing to return when it's run asynchronously. Would it be better to introduce a second variant vim.lsp.code_action_sync() and return results from that variant? It would be a bigger change, but I'm happy to do it, if that's preferred.

[mfussenegger]

This still wouldn't be fully sync because there might be another asynchronous resolve step.

Besides that, I'd rather go into the direction outlined in #22598 (comment)

[laher]

OK, fair enough. Thanks for the fast response. Is there something I could do to make this more amenable? even just adding a callback mechanism?

I'd be happy to try introducing a coroutine along the lines you described in #19624

... but it sounds a bit hasty to just throw it in there. Maybe it could be introduced with 'experimental' in the docs?

[icholy]

nit: The vim.lsp.buf.format(...) param is called async. It would be nice to keep the two consistent.

[laher]

You're right, but I'm leaning towards implementing this as a separate method instead, because:

• the defaults are different - .code_action() is async by default, but .format() is sync by default. I think it would still feel inconsistent.
• if it's a separate method, it can return a result, err.

... but it sounds like this is likely not going to be accepted either way. If I (or someone) doesn't think of a way to do this which satisfies the direction described by @mfussenegger , I'm probably going to close this PR.

[laher]

I have explored a couple of alternatives with callbacks & coroutines (I'm pretty new to lua's coroutines), and I haven't come up with something workable so far ... As soon as I hit an 'Attempt to yield across C-call boundary' I realised I need to learn a lot more about libuv and [lua]jit.

If I do try again, the solution would be completely different to what's here, so I may as well close this.

Thanks for the feedback and all the good work on neovim.