Unable to use nested lists in DAG markdown documentation

[Richiecakes]

Apache Airflow version: 2.0.2

What happened:

Tried to use the following markdown as a doc_md string passed to a DAG

- Example
    -  Nested List

It was rendered in the web UI as a single list with no nesting or indentation.

What you expected to happen:

I expected the list to display as a nested list with visible indentation.

How to reproduce it:

Try and pass a DAG a doc_md string of the above nested list.
I think the bug will affect any markdown that relies on meaningful indentation (tabs or spaces)

[boring-cyborg]

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[Richiecakes]

#14564 I suspect this pull request may be the reason since it appears to strip spaces and tabs from every line of the markdown. A minor issue, but as a lover of nested lists, would be great to get them working again 😄

[Richiecakes]

This also affects code blocks, which is probably more important than nested lists, but it shows that markdown docstrings are quite limited.

textwrap.dedent could well be part of the solution here.

[Dr-Denzy]

I will try and reproduce this.

[uranusjr]

The cause is the same as #16138 (comment). Instead of str.lstrip() each line, the parser need to dedent the lines more smartly to preserve internal indentation.

[ashb]

textwrap.dedent would do the job here wouldn't it?

[uranusjr]

I think so (mentioned in the linked comment), but someone needs to actually try.

[uranusjr]

I tried, it works well. The linked PR fixed nested lists, but does not fix triple-tick code blocks because it’s a non-universal extension syntax. See my comments in the PR for details.