Markdown pane does not render new lines as hard line breaks, configurable with hard_line_break

[maximlt]

Sort of addresses #7535

This PR adds a new break_as_new parameter (better name welcome!) to the Markdown pane to make it easier for users to declare whether they want simple line breaks to be rendered with a new line or not. Unfortunately, I haven't been able to find a simple way to configure MyST-Parser to toggle this behavior.

Importantly, note that I am -1 on the current default in Panel which is break_as_new=True with markdown-it. Even if I understand the motivation to make it easier to render Markdown generated by LLMs, it makes it way more difficult to display in a nice way some Markdown formatted text (pn.Column(md_intro, <objs>) vs pn.Column(pn.pane.Markdown(md_intro, break_as_new=False), <objs>). @ahuang11 prefers the current default, @philippjfr I'll let you chime in with your opinion (and let's wait for Andrew to be back too).

Once this is settled for good, I'll add tests to this PR.

[ahuang11]

I'm okay with having break_as_new=False. The only thing is setting it to True in ChatMessage.

Also, I don't think break_as_new is intuitive, maybe breaks_as_newline?

[MarcSkovMadsen]

I think the name line_breaks is easier to remember and understand.

I also think this is actually a regression. Originally coming from Streamlit this was a major issue when moving to Panel that new lines in multiline """ strings got broken into new lines. I do believe it was fixed in Panel but at some stage it reverted to breaking lines which is quite annoying.

[maximlt]

Ok so I renamed it to hard_line_break that defaults to False, re-establishing the older behavior.

The only thing is setting it to True in ChatMessage.

@ahuang11 in 728b1fa I've made a change to enable it in ChatMessage. But I wanted to ask you, do you know if all strings passed to ChatMessage are turned into Markdown panes? If yes, it could skip calling panel(...) and directly call Markdown(..., hard_line_break) for values of str type, probably making things a bit faster.

[ahuang11]

But I wanted to ask you, do you know if all strings passed to ChatMessage are turned into Markdown panes

If it's a string, it should be a Markdown, but only if isinstance(message, str).

[maximlt]

But I wanted to ask you, do you know if all strings passed to ChatMessage are turned into Markdown panes

If it's a string, it should be a Markdown, but only if isinstance(message, str).

I shortly discussed this with Philipp this morning, who told me other components can be instantiated from a string (image pointing to a URL), and that one could see ChatMessage as a sort of opinionated repr for panel(). So always instantiating a Markdown pane for a string isn't appropriate in this case.

[codecov]

Codecov Report

Attention: Patch coverage is 88.46154% with 6 lines in your changes missing coverage. Please review.

Project coverage is 82.24%. Comparing base (d48c45f) to head (59ebb7b).
Report is 36 commits behind head on main.

Files with missing lines	Patch %	Lines
panel/tests/pane/test_markup.py	86.36%	6 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #7582    +/-   ##
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  Coverage   82.24%   82.24%            
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  Files         339      341     +2     
  Lines       51476    51702   +226     
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+ Hits        42334    42522   +188     
- Misses       9142     9180    +38     

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