roundtripping causes implicitly closed code block to disappear

[ChristianMurphy]

Subject of the issue

:notebook: note the tab at the end of the second line, it is significant

is stringified as:

````markdown

which changes the structure

Your environment

• OS: Ubuntu
• Packages: mdast-util-to-markdown 0.6.4
• Env: node v15.5.1, npm 7.3.0

Steps to reproduce

parse

which has the structure

```json
{
    "type": "root",
    "children": [
        {
            "type": "code"
        }
    ]
}

and stringify it:

the resulting markdown has a different structure than the original

{
    "type": "root",
    "children": []
}

:notebook: comparing how the two pieces of markdown text are being parsed with https://spec.commonmark.org/dingus it appears in both cases it is parsed as expected.

Expected behavior

structure is the same

Actual behavior

structure is different

[wooorm]

It’s not about closing, it’s about blank lines in fenced code possibly existing, but not in indented code