Signature help

[archseer]

Discussed in #1329

^{Originally posted by matoous December 22, 2021}
Another nice functionality that can be built on top of LSPs is signature help. Vim equivalent: https://github.com/ray-x/lsp_signature.nvim. While helpful it also clutters the UI quite a bit, especially when combined with autocomplete. Something worth considering?

[archseer]

I started working on this in June:

Command

helix/helix-term/src/commands.rs

Lines 4125 to 4163 in 34766e2

	fn signature_help(cx: &mut Context) {
	let (view, doc) = current!(cx.editor);
	let language_server = match doc.language_server() {
	Some(language_server) => language_server,
	None => return,
	};
	let pos = pos_to_lsp_pos(
	doc.text(),
	doc.selection(view.id)
	.primary()
	.cursor(doc.text().slice(..)),
	language_server.offset_encoding(),
	);
	let future = language_server.text_document_signature_help(doc.identifier(), pos, None);
	cx.callback(
	future,
	move |_editor: &mut Editor,
	_compositor: &mut Compositor,
	response: Option<lsp::SignatureHelp>| {
	if let Some(signature_help) = response {
	log::info!("{:?}", signature_help);
	// signatures
	// active_signature
	// active_parameter
	// render as:
	// signature
	// ----------
	// doc
	// with active param highlighted
	}
	},
	);
	}

Hook

helix/helix-term/src/commands.rs

Lines 4213 to 4255 in 34766e2

	fn signature_help(cx: &mut Context, ch: char) {
	// if ch matches signature_help char, trigger
	let doc = doc_mut!(cx.editor);
	let language_server = match doc.language_server() {
	Some(language_server) => language_server,
	None => return,
	};
	let capabilities = language_server.capabilities();
	if let lsp::ServerCapabilities {
	signature_help_provider:
	Some(lsp::SignatureHelpOptions {
	trigger_characters: Some(triggers),
	// TODO: retrigger_characters
	..
	}),
	..
	} = capabilities
	{
	// TODO: what if trigger is multiple chars long
	let is_trigger = triggers.iter().any(|trigger| trigger.contains(ch));
	if is_trigger {
	super::signature_help(cx);
	}
	}
	// SignatureHelp {
	// signatures: [
	// SignatureInformation {
	// label: "fn open(&mut self, path: PathBuf, action: Action) -> Result<DocumentId, Error>",
	// documentation: None,
	// parameters: Some(
	// [ParameterInformation { label: Simple("path: PathBuf"), documentation: None },
	// ParameterInformation { label: Simple("action: Action"), documentation: None }]
	// ),
	// active_parameter: Some(0)
	// }
	// ],
	// active_signature: None, active_parameter: Some(0)
	// }
	}

(That TODO should be a NOTE, since the code is implementing post-insert hooks)

helix/helix-term/src/commands.rs

Lines 4287 to 4290 in 34766e2

	// TODO: need a post insert hook too for certain triggers (autocomplete, signature help, etc)
	// this could also generically look at Transaction, but it's a bit annoying to look at
	// Operation instead of Change.
	for hook in &[language_server_completion, signature_help] {

It's now possible to get a Change iterator:

helix/helix-core/src/transaction.rs

Lines 523 to 525 in 34766e2

	pub fn changes_iter(&self) -> ChangeIterator {
	self.changes.changes_iter()
	}

Some work would need to be done to have a stateful component similar to completion so we could update it when it gets re-triggered (i.e. ( opens it, then , re-triggers with next parameter's data)