Missing trailingBreaks when Widget decorations are used

[MathiasFavro]

I believe trailingBreaks are no longer added to all expected locations when a transaction that modifies widget decorations is dispatched. I bisected down the changed behaviour to prosemirror-view version 1.31.0 and the commits do mention decorations. Debugging the in the client also lead to updateChildren but that is how far I got.

My simplified repro is a widget decoration to show placeholder text and a transaction to replace the content of a document:

new Plugin({
	props: {
		decorations: function(state: ProseMirror.EditorState): ProseMirror.DecorationSet {
			let onlyEmptyParagraphs = true;

			state.doc.forEach(function(node: ProseMirror.ProsemirrorNode): void {
				if (node.type != schema.nodes.paragraph || node.content.size > 0)
					onlyEmptyParagraphs = false;
			});

			if (!onlyEmptyParagraphs)
				return DecorationSet.empty;

			let widget = Decoration.widget(0, function(): Element {
				let element = document.createElement("div");
				element.innerHTML = "Start writing your ideas here...";
				return element;
			});

			return DecorationSet.create(state.doc, [widget]);
		},
	},
});

To trigger the bug dispatch a transaction to replace the doc content with two nodes:

state.tr.replaceWith(0, state.doc.content.size, [
	schema.nodes.code_block.create(),
	schema.nodes.paragraph.create(),
]);

Testing in Chrome:

Document with a single empty paragraph, before transaction:

After transaction with prosemirror-view 1.30.2: Both blocks have trailing break

After transaction with prosemirror-view 1.31.0: Paragraph has no trailing break, leaving it collapsed.

The bug is not reproduced if the plugin is removed or modified to not branch, ie always return either the DecorationSet or empty, or if the transaction inserts two paragraphs. It also works as expected when the editor is loaded with the resulting document, so it appears limited to updating.

Thank you and have a good day.

[marijnh]

Thanks for the reproduction! Attached patch should help.