Markdown: nested bold+italic (***text***) loses inner formatting

[tiborgats]

Bug Description

When rendering markdown with combined bold and italic formatting (***bold and italic***), only the outermost mark is applied — the inner formatting is lost. Bold (**text**) and italic (*text*) work correctly on their own, but not when nested.

Root Cause

In crates/ui/src/text/format/markdown.rs, the parse_paragraph function handles Node::Strong and Node::Emphasis by:

1. Creating a child_paragraph
2. Recursively calling parse_paragraph on children (which pushes marked InlineNodes into child_paragraph)
3. Discarding child_paragraph and creating a new InlineNode from only the returned text string, applying just the current mark

For ***bold and italic***, the markdown AST produces:

Strong
  └── Emphasis
        └── Text("bold and italic")

When Strong processes its children, Emphasis pushes an italic-marked node into child_paragraph — but Strong ignores that and creates a new node with only bold(). The italic mark is lost.

Relevant code (lines ~76-92):

Node::Emphasis(val) => {
    let mut child_paragraph = Paragraph::default();
    for child in val.children.iter() {
        text.push_str(&parse_paragraph(&mut child_paragraph, &child, cx));
    }
    paragraph.push(
        InlineNode::new(&text).marks(vec![(0..text.len(), TextMark::default().italic())]),
    );
}
Node::Strong(val) => {
    let mut child_paragraph = Paragraph::default();
    for child in val.children.iter() {
        text.push_str(&parse_paragraph(&mut child_paragraph, &child, cx));
    }
    paragraph.push(
        InlineNode::new(&text).marks(vec![(0..text.len(), TextMark::default().bold())]),
    );
}

Suggested Fix

When the children produce InlineNodes with marks (in child_paragraph), merge those marks with the current formatting mark rather than discarding them. For example, when Strong finds that its child Emphasis already produced italic-marked nodes, the result should carry both bold and italic.

Reproduction

**bold** works
*italic* works
***bold and italic*** — only shows bold (or italic), not both

Environment

• gpui-component version: 0.5.1

Impact

Low — workaround is to avoid ***text*** syntax. But it's standard markdown that users expect to work.

[Moulberry]

#2119 applies to the html parser, but the same could could be applied to the markdown parser