Add lsp signature help

[sudormrfbin]

Implements signature help, aka parameter hints:

TODO

• Obstructs the completion popup
• Bar cursor in insert mode can be seen through the popup if popup overlays the cursor
• Popup is not updated on backspace
• editor.lsp.signature-help config
• Keybind for manual triggering (Ctrl-S in insert mode)

Future Work

1. Show all signatures for a method (useful for overloaded methods)

[archseer]

Obstructs the completion popup

There's a TODO item in Popup or about adding a Bias::Above/Below that would specify a preference for popup placement around the cursor (This is only a preference because you still want to place it below if there's no space above)

helix/helix-term/src/ui/popup.rs

Lines 63 to 80 in 9bfb0ca

	// if there's a orientation preference, use that
	// if we're on the top part of the screen, do below
	// if we're on the bottom part, do above
	// -- make sure frame doesn't stick out of bounds
	let mut rel_x = position.col as u16;
	let mut rel_y = position.row as u16;
	if viewport.width <= rel_x + width {
	rel_x = rel_x.saturating_sub((rel_x + width).saturating_sub(viewport.width));
	}
	// TODO: be able to specify orientation preference. We want above for most popups, below
	// for menus/autocomplete.
	if viewport.height > rel_y + height {
	rel_y += 1 // position below point
	} else {
	rel_y = rel_y.saturating_sub(height) // position above point
	}

.

I'd add this as a builder method similar to margin:

helix/helix-term/src/ui/popup.rs

Lines 46 to 49 in 9bfb0ca

	pub fn margin(mut self, margin: Margin) -> Self {
	self.margin = margin;
	self
	}

Then you can specify the signature help to be displayed above, and completion below.

We also want to add a editor.lsp.signature-help config item that would allow configuring / disabling this since I can imagine some users find it distracting.

[archseer]

Config values used by lsp-mode.el https://github.com/emacs-lsp/lsp-mode/blob/ddb776037fc073473e0da9d07e63f57242b212fb/lsp-mode.el#L931-L958

[sudormrfbin]

I added Ctrl-s as a keybind for invoking signature help in insert mode just because, any other suggestions ?

[the-mikedavis]

It might be easier to remember something like CtrlShiftx but OTOH that's a lot of keystrokes. I think Ctrls is ok. Ctrlh could be another good option but we'd have to kill (haha) the readline/emacs binding that's already there.

[sudormrfbin]

ctrl-h would be a better keybind but it'll probably clash with backspace on a lot of terminal emulators. Switching to termwiz might be beneficial for it ability to distinguish between these too.

[archseer]

Switching to termwiz might be beneficial for it ability to distinguish between these too.

Even then we probably shouldn't rely on https://sw.kovidgoyal.net/kitty/keyboard-protocol/ by default since not every terminal supports it.

[David-Else]

ctrl-s is not a good shortcut as it means save in most editors. ctrl-space triggers autocomplete in VS Code, how about that?

[the-mikedavis]

That's a bad reason to avoid a key. I think it's even a weak reason to prefer a key (e.g. ctrl-w that deletes a word backwords in vim in insert mode). Helix's keymap shouldn't be bound by the keys other editors choose.

Ctrl-Space could be interesting though as long as the terminal accepts the inputs (iirc it gives a keycode of 0x00. idk if that gets confused with another key)

[the-mikedavis]

I noticed testing this that Backspace in insert mode will pop up the "Language server not active for current buffer" status message for buffers like scratch or text. Probably not a big deal but it does grab the eye a bit.

[pickfire]

I didn't look closely on this. Does this also work with double width characters like CJK? This seemed to be characters length after looking at the code (wasn't mentioned in the comment whether it is character length or terminal width length) and we don't seemed to be checking the width of required_size.

[archseer]

@sudormrfbin

[archseer]

I think it should if the intent is to use byte length, or do we need to use string.width() ?

[sudormrfbin]

(This actually turned out to be a bug, see #3154.)

---

Syntax highlighting uses char byte offsets so that is what we need as the final (start, end) value. Now, LSP sends the label offsets in utf-16 according to the configured OffsetEncoding (but we have it hardcoded to utf8) and the same is used by the LSP for ParameterLabel::LabelOffsets, so we would have to convert this to char byte offsets:

                    lsp::ParameterLabel::LabelOffsets([start, end]) => {
                        Some((*start as usize, *end as usize))
                    }

str.find() reports the byte index of the start of the pattern, so that would have to be changed too.

But strangely, with a naive test on a bit of CJK and non ASCII text, the parameter highlighting seems to work okay:

Details

fn main() {}

/// Documentation with doc tests:
///
/// ```
/// test
/// ```
fn func(_par老am0: char, _lö老虎wy̆: usize, _paröam1: &str) {
    return;
}

[archseer]

Found one issue: We need to check for the signature help capability before sending the request. If the language server doesn't support it then "Async job failed: Unhandled method textDocument/signatureHelp" is emitted to the statusline.

[sudormrfbin]

A lesser pain point is that with larger font (have weak eyes) it is often that full doc does not fit above, and it starts to try fit below. My suggestion would be to keep it simple and to just show function signature. Full doc also obstructs code when i would like to see the names of variables i defined above.

@Houkime I'll add a config option to control the display of docs 👍🏾

[sudormrfbin]

Escape now closes the popup and exits insert mode, similar to the completion popup. Closing the popup only can be done with ctrl-c. Also added a config option editor.lsp.display-signature-help-docs that controls the docs display.

[lazytanuki]

Hi and thanks for this feature !

Been playing with it a little bit, found something that looks like an issue: when writing a closure and hitting Backspace, the signature help shows up for the function for which the closure is an argument (may not be clear, see screenshot below). You should be able to reproduce it by editing helix-term/src/commands/lsp.rs as shown below:

Also, a keybinding suggestion: how about mapping C-u and C-d (which are already quite present in different parts of the editor) to put the signature help popup above or below current line (when it's already being displayed, not to trigger it) ? User case is when editing code in the middle of a function, signature help pops up below the current line, but you want to see what's there so you just press C-u and it makes the signature help switch to being above the current line.

[the-mikedavis]

Backspace triggers the LSP call - showing the signature for the function in that case is up to rust-analyzer. It can be a bit odd to show the signature of the outer call when you're in a closure - maybe we should open an issue in rust-analyzer?

[lazytanuki]

I am not sure about that, it is not doing it in neovim with the lsp signature plugin. When specifically asking for the signature help when inside the closure, this plugin returns "No signature help available". I'll try to see how this is handled by that plugin. Maybe a treesitter scope check ?

Edit: Welp, I am on a different setup right now and the issue seems to be gone, maybe it was a bug in RA and I'm using a different version at the moment, I'll check when I get back home.
Edit2: Yup, was just me running an old version of RA, cause this was fixed 3 months ago

[sudormrfbin]

Also, a keybinding suggestion: how about mapping C-u and C-d (which are already quite present in different parts of the editor) to put the signature help popup above or below current line (when it's already being displayed, not to trigger it)

C-u and C-d are already taken for scrolling the popup, and I think having a single keybind that toggles top and bottom orientations would be better anyway. And it would fit better as a generic keybind added to any popup rather than only the signature help, so a separate PR will be better (after this one gets merged, since position biasing is introduced here).

[pickfire]

Is there a way to manually trigger signature help if this is disabled? We can manually trigger completion with ctrl-x, maybe once we trigger that it automatically triggers signature help as well?

[sudormrfbin]

I added a keybind earlier but removed it due to a conflict. Adding a keybind is as easy as binding it to signature_help command, and we definitely need a built-in insert mode keybind too. Any suggestions?

We can manually trigger completion with ctrl-x, maybe once we trigger that it automatically triggers signature help as well?

I'd rather have a separate key that can toggle just the signature help popup since that allows exclusive control.

[pickfire]

I was trying this branch out and noticed that the editor.auto-completion = false no longer works as expected, even when I did not manually trigger the auto completion it still shows up.

[sudormrfbin]

I was trying this branch out and noticed that the editor.auto-completion = false no longer works as expected, even when I did not manually trigger the auto completion it still shows up.

I can't reproduce this; I tried both :set auto-completion false inside the editor and editor.auto-completion = false in the TOML config and neither of them show the completion popup unless manually triggered. The signature help pops up regardless of the auto completion setting, which is as expected.