Improve rendering of `<code>` tags in documentation

[A-Walrus]

Describe your feature request

Documentation, at least for rust, can contain <code> tags, for example the documentation for into() from the standard library. The tags themselves should not be shown, and the text within should be shown the same as text within "`":

The <code> and </code> tags should not be shown and the text within them should be styled the same as the U::from(self) from above.

[the-mikedavis]

Markdown rendering for things like doc popups is handled here:

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

Lines 181 to 299 in 8deaebd

	for event in parser {
	match event {
	Event::Start(Tag::List(list)) => {
	// if the list stack is not empty this is a sub list, in that
	// case we need to push the current line before proceeding
	if !list_stack.is_empty() {
	push_line(&mut spans, &mut lines);
	}
	list_stack.push(list);
	}
	Event::End(Tag::List(_)) => {
	list_stack.pop();
	// whenever top-level list closes, empty line
	if list_stack.is_empty() {
	lines.push(Spans::default());
	}
	}
	Event::Start(Tag::Item) => {
	if list_stack.is_empty() {
	log::warn!("markdown parsing error, list item without list");
	}
	tags.push(Tag::Item);
	// get the appropriate bullet for the current list
	let bullet = list_stack
	.last()
	.unwrap_or(&None) // use the '- ' bullet in case the list stack would be empty
	.map_or(String::from("- "), |number| format!("{}. ", number));
	// increment the current list number if there is one
	if let Some(v) = list_stack.last_mut().unwrap_or(&mut None).as_mut() {
	*v += 1;
	}
	let prefix = get_indent(list_stack.len()) + bullet.as_str();
	spans.push(Span::from(prefix));
	}
	Event::Start(tag) => {
	tags.push(tag);
	if spans.is_empty() && !list_stack.is_empty() {
	// TODO: could push indent + 2 or 3 spaces to align with
	// the rest of the list.
	spans.push(Span::from(get_indent(list_stack.len())));
	}
	}
	Event::End(tag) => {
	tags.pop();
	match tag {
	Tag::Heading(_, _, _)
	| Tag::Paragraph
	| Tag::CodeBlock(CodeBlockKind::Fenced(_))
	| Tag::Item => {
	push_line(&mut spans, &mut lines);
	}
	_ => (),
	}
	// whenever heading, code block or paragraph closes, empty line
	match tag {
	Tag::Heading(_, _, _)
	| Tag::Paragraph
	| Tag::CodeBlock(CodeBlockKind::Fenced(_)) => {
	lines.push(Spans::default());
	}
	_ => (),
	}
	}
	Event::Text(text) => {
	// TODO: temp workaround
	if let Some(Tag::CodeBlock(CodeBlockKind::Fenced(language))) = tags.last() {
	let tui_text = highlighted_code_block(
	text.to_string(),
	language,
	theme,
	Arc::clone(&self.config_loader),
	None,
	);
	lines.extend(tui_text.lines.into_iter());
	} else {
	let style = if let Some(Tag::Heading(level, ..)) = tags.last() {
	match level {
	HeadingLevel::H1 => heading_styles[0],
	HeadingLevel::H2 => heading_styles[1],
	HeadingLevel::H3 => heading_styles[2],
	HeadingLevel::H4 => heading_styles[3],
	HeadingLevel::H5 => heading_styles[4],
	HeadingLevel::H6 => heading_styles[5],
	}
	} else {
	text_style
	};
	spans.push(Span::styled(text, style));
	}
	}
	Event::Code(text) | Event::Html(text) => {
	spans.push(Span::styled(text, code_style));
	}
	Event::SoftBreak | Event::HardBreak => {
	push_line(&mut spans, &mut lines);
	if !list_stack.is_empty() {
	// TODO: could push indent + 2 or 3 spaces to align with
	// the rest of the list.
	spans.push(Span::from(get_indent(list_stack.len())));
	}
	}
	Event::Rule => {
	lines.push(Spans::from(Span::styled("---", code_style)));
	lines.push(Spans::default());
	}
	// TaskListMarker(bool) true if checked
	_ => {
	log::warn!("unhandled markdown event {:?}", event);
	}
	}
	// build up a vec of Paragraph tui widgets
	}

For this snippet, the events in that loop look like

Start(CodeBlock(Fenced(Borrowed("rust"))))
Text(Borrowed("core::convert\n"))
End(CodeBlock(Fenced(Borrowed("rust"))))
Start(CodeBlock(Fenced(Borrowed("rust"))))
Text(Borrowed("fn into(self) -> U\n"))
End(CodeBlock(Fenced(Borrowed("rust"))))
Rule
Start(Paragraph)
Text(Borrowed("Calls "))
Code(Borrowed("U::from(self)"))
Text(Borrowed("."))
End(Paragraph)
Start(Paragraph)
Text(Borrowed("That is, this conversion is whatever the implementation of"))
SoftBreak
Html(Borrowed("<code>"))
SoftBreak
Start(Link(Inline, Borrowed("https://doc.rust-lang.org/nightly/core/convert/trait.From.html"), Borrowed("")))
Text(Borrowed("From"))
End(Link(Inline, Borrowed("https://doc.rust-lang.org/nightly/core/convert/trait.From.html"), Borrowed("")))
Text(Borrowed("<T"))
Text(Borrowed("> for U"))
Html(Borrowed("</code>"))
Text(Borrowed(" chooses to do."))
End(Paragraph)