Platform code cannot differentiate between a new line placeholder and an user provided single space node

[aringenbach]

Currently we use <p>&nbsp;</p> as a way to have a placeholder for new lines in several situations. The issue is that we also convert trailing space to  , hence if a user enters a single space in a paragraph, the Rust code would output the exact same than what it outputs as a placeholder.

This replacement in Rust occurs here:

matrix-rich-text-editor/crates/wysiwyg/src/dom/nodes/text_node.rs

Lines 224 to 247 in 860222e

	let mut escaped = html_escape::encode_text(&string).to_string();
	// Replace all pairs of spaces with non-breaking ones. Transforms
	// `a b` to `a\u{A0}\u{A0}\u{A0}\u{A0} b`, which will render
	// exactly as five spaces like in the input.
	if !state.is_inside_code_block {
	escaped = escaped.replace(" ", "\u{A0}\u{A0}");
	if state.is_last_node_in_parent
	&& escaped.chars().next_back().map_or(false, |c| c == ' ')
	{
	// If this is the last node and it ends in a space, replace that
	// space with a non-breaking one.
	escaped.replace_range(escaped.len() - 1.., "\u{A0}");
	}
	if state.is_first_node_in_parent
	&& escaped.chars().next().map_or(false, |c| c == ' ')
	{
	// If this is the first node and it starts with a space, replace that
	// space with a non-breaking one.
	escaped.replace_range(..1, "\u{A0}");
	}
	}
	buf.push(escaped.as_str());

The placeholder thing is used by the parser on iOS here:

matrix-rich-text-editor/platforms/ios/lib/WysiwygComposer/Sources/HTMLParser/Extensions/DTCoreText/DTHTMLElement.swift

Lines 35 to 43 in 860222e

	if child.text() == .nbsp {
	// Removing NBSP character from e.g. <p>&nbsp;</p> since it is only used to
	// make DTCoreText able to easily parse new lines.
	removeAllChildNodes()
	let newChild = PlaceholderTextHTMLElement(from: child)
	addChildNode(newChild)
	newChild.inheritAttributes(from: self)
	newChild.interpretAttributes()
	} else {

Known issues related to this on iOS:

• If a user enters just a single space, the composer will still be considered empty, reported here: Move send button out of composer's text field element-hq/element-x-ios#1588 (review)
• If a user enters e.g. "Text" + return + space + return + "more text", the line with only a space is eventually eaten out by the composer

Not using the HTML and build the attributed string directly from the model would definitely fix that though.