Live feedback in prompt

[A-Walrus]

Describe your feature request

When using a commands, such as select:, search:, :theme, :set-option, etc... some inputs are invalid (invalid regex, theme/option that doesn't exist).
It would be nice to have visual feedback while typing that indicates that what you are typing is invalid, for example marking your typed text or the prompt in the error color.

Kakoune for example makes the select: text red on invalid regex while you are still typing, which can be more useful than feedback only after you submit the command.

I feel like many commands could benefit from this sort of live feedback, but mostly the regex ones.

[the-mikedavis]

#7738 improved on this a little: we show tree-sitter-regex error highlighting in the prompt. We could improve this further by validating the regex with the regex-syntax crate which we already depend on transitively: we can merge highlight ranges for syntax error spans into the prompt line's highlighting. Maybe we could also show the syntax error message in the doc popup too.

[kirawi]

This can be done in

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

Lines 75 to 171 in e18b772

	pub fn raw_regex_prompt(
	cx: &mut crate::commands::Context,
	prompt: std::borrow::Cow<'static, str>,
	history_register: Option<char>,
	completion_fn: impl FnMut(&Editor, &str) -> Vec<prompt::Completion> + 'static,
	fun: impl Fn(&mut crate::compositor::Context, rope::Regex, &str, PromptEvent) + 'static,
	) {
	let (view, doc) = current!(cx.editor);
	let doc_id = view.doc;
	let snapshot = doc.selection(view.id).clone();
	let offset_snapshot = view.offset;
	let config = cx.editor.config();
	let mut prompt = Prompt::new(
	prompt,
	history_register,
	completion_fn,
	move |cx: &mut crate::compositor::Context, input: &str, event: PromptEvent| {
	match event {
	PromptEvent::Abort => {
	let (view, doc) = current!(cx.editor);
	doc.set_selection(view.id, snapshot.clone());
	view.offset = offset_snapshot;
	}
	PromptEvent::Update | PromptEvent::Validate => {
	// skip empty input
	if input.is_empty() {
	return;
	}
	let case_insensitive = if config.search.smart_case {
	!input.chars().any(char::is_uppercase)
	} else {
	false
	};
	match rope::RegexBuilder::new()
	.syntax(
	rope::Config::new()
	.case_insensitive(case_insensitive)
	.multi_line(true),
	)
	.build(input)
	{
	Ok(regex) => {
	let (view, doc) = current!(cx.editor);
	// revert state to what it was before the last update
	doc.set_selection(view.id, snapshot.clone());
	if event == PromptEvent::Validate {
	// Equivalent to push_jump to store selection just before jump
	view.jumps.push((doc_id, snapshot.clone()));
	}
	fun(cx, regex, input, event);
	let (view, doc) = current!(cx.editor);
	view.ensure_cursor_in_view(doc, config.scrolloff);
	}
	Err(err) => {
	let (view, doc) = current!(cx.editor);
	doc.set_selection(view.id, snapshot.clone());
	view.offset = offset_snapshot;
	if event == PromptEvent::Validate {
	let callback = async move {
	let call: job::Callback = Callback::EditorCompositor(Box::new(
	move |_editor: &mut Editor, compositor: &mut Compositor| {
	let contents = Text::new(format!("{}", err));
	let size = compositor.size();
	let popup = Popup::new("invalid-regex", contents)
	.position(Some(helix_core::Position::new(
	size.height as usize - 2, // 2 = statusline + commandline
	0,
	)))
	.auto_close(true);
	compositor.replace_or_push("invalid-regex", popup);
	},
	));
	Ok(call)
	};
	cx.jobs.callback(callback);
	}
	}
	}
	}
	}
	},
	)
	.with_language("regex", std::sync::Arc::clone(&cx.editor.syn_loader));
	// Calculate initial completion
	prompt.recalculate_completion(cx.editor);
	// prompt
	cx.push_layer(Box::new(prompt));
	}