Pasting paragraphs sometimes adds unexpected linebreaks

[mejo-]

Describe the bug
When pasting paragraphs to a document, sometimes unexpected linebreaks are added in between the paragraph. As soon as you do one change in the paragraph, all unexpected linebreaks get deleted at once.

As an example, paste the first 3-4 paragraphs of the wikipedia article about Fairy Tales into a document.

To Reproduce
Steps to reproduce the behavior:

1. Open a document, paste the example paragraph from above.
2. See unexpected linebreaks
3. Add one character anywhere in the paragraph
4. The the unexpected linebreaks disappearing.

[juliusknorr]

This seems to come from the white-space: pre-wrap; that is added to the paragraph. Might be coming from @tiptap/vue-2/src/NodeViewContent.ts

[mejo-]

Indeed, that's the reason for this behaviour. I wonder whether we should use our own implementation of NodeViewContent without white-space: pre-wrap? @juliushaertl and @max-nextcloud do you see any reason why we would need white-space: pre-wrap in NodeViewContent?

[juliusknorr]

This seems to come from the prosemirror stylesheet recommentations ad would also warn in ProseMirror/prosemirror-view@b8b814c, but i think it the original paragraph node doesn't have it we can also drop it here.

ProseMirror/prosemirror#981 might give a bit of reasoning for what it is needed

[juliusknorr]

Worth to double check against this logic

text/src/extensions/Markdown.js

Lines 79 to 104 in b57faa0

	key: new PluginKey('pasteEventHandler'),
	props: {
	handleDOMEvents: {
	mouseup(_, event) {
	shiftKey = event.shiftKey
	return false
	},
	},
	handleKeyDown(_, event) {
	shiftKey = event.shiftKey
	return false
	},
	clipboardTextParser(str, $context, _, view) {
	const parser = DOMParser.fromSchema(view.state.schema)
	const doc = document.cloneNode(false)
	const dom = doc.createElement('div')
	if (shiftKey) {
	// Treat single newlines as linebreaks and double newlines as paragraph breaks when pasting as plaintext
	dom.innerHTML = '<p>' + str.replaceAll('\n', '<br />').replaceAll('<br /><br />', '</p><p>') + '</p>'
	} else {
	dom.innerHTML = markdownit.render(str)
	}
	return parser.parseSlice(dom, { preserveWhitespace: true, context: $context })
	},
	},

[max-nextcloud]

Experiments

replace the preserveWhitespace: full in parseHtml with true

This will fix the unexpected line breaks but at the same time also breaks the tests for preserving line breaks in markdown.

in addition to #4624 I also remove whiteSpace setting in NodeViewWrapper

Removing this broke the #4624 fix as now whiteSpace was inheriting pre-wrap again from the .Prosemirror tag.

Conclusion

We actually have some conflicting interest here:

• preserve whitespace (in md files, when pasting lists of plaintext separate by empty lines)
• get rid of unexpected linebreaks when pasting html content.

However it's hard to destinguish pasting html from the initial load as we are also inserting html there.

[max-nextcloud]

Looks like prosemirror has a transformPastedHtml option that we could use to get rid of newlines outside of pre tags:

https://github.com/ProseMirror/prosemirror-view/blob/a93d102a121585d2244c7d23ba8383e277cf4aac/src/clipboard.ts#L64