Async formatting

[hovsater]

Whenever I save a file (:write) with LSP enabled (e.g., solargraph for Ruby or rust-analyzer for Rust) the editor halts for 1-2 seconds until finally finishing. This behaviour isn't present when LSP is disabled.

[archseer]

This is because we try to :format via the LSP before saving. I was afraid this would be an issue on a slower language server (you can also notice it before rust-analyzer fully boots up). Need to handle that better, probably by making it opt-in per language.

[hovsater]

Would it be possible to format the code asynchronously? It's kind of unexpected that it's a synchronous operation blocking the UI.

If not, I think it makes sense for you to be able to opt out. 👍

[archseer]

I think you would likely run into issues if formatting took a while to run async while you made further text edits.

I'll add a config option to enable it only for certain languages.

[hovsater]

Yeah, I guess it depends. I've seen it done both ways. If done asynchronously, one could discard the formatting if the buffer changed in between saving the file and the action actually completing.

[jneem]

I think it does make sense to discard the formatting in that case, but one annoying thing is that you want the formatting to be saved. I guess you'd need to:

1. make a clone of the document synchronously (cheap, because Ropes clone cheaply)
2. spawn a "format" task that computes the formatting changes, then spawns a "save" task and returns the formatting changes
3. the "save" task applies the formatting changes to the cloned document and then saves it
4. the main task gets the formatting changes from the format task and applies them as long as the document hasn't changed.

I could try implementing that if it sounds reasonable.

[pickfire]

Same noticeable delay when I press gd waiting for lsp. It doesn't automatically do the task even though lsp starts up. Should have sort of queuing mechanism.

[jneem]

Is there no interest in the async formatting version? I like auto-format on save, but I'd also like it not to block the editor...

[archseer]

Sorry about that, I missed the comment! I think some of this overlaps with #177 (comment)

I'd be interested in this, but the async aspects of helix-term still need some work. It's hard to keep a reference in a spawned task without blocking, you'd probably need some sort of a callback mechanism similar to how the LspCallbacks hack works (you keep a DocumentId, the callback gives you a &mut Editor that can be used to look up the doc again).

[archseer]

Same noticeable delay when I press gd waiting for lsp. It doesn't automatically do the task even though lsp starts up. Should have sort of queuing mechanism.

This is because rust-analyzer takes some time to index before it starts responding to queries. workDone events from LSP will give us a way to cancel these types of queries, at the moment we time out after 2s and then discard the data once received later.

[archseer]

#285 now solves this, thanks to @jneem for the implementation!