`markdown-fill-paragraph` could perhaps benefit from rearchitecting

[glyph]

There are a bunch of issues affecting paragraph-filling, so it might be good to consider a new approach rather than fixing these whack-a-mole. I am linking them all here so that if anyone were to pick up such an issue they will get visibility into the others:

• markdown-mode-fill-paragraph mangles inline attributes by treating them as text #862
• Comments do not fill properly #833
• Inline styles fail to syntax-highlight when broken by newlines #568
• Indented tables get wrapped by fill functions #315
• lines beginning with pipe | in math mode are not wrapped with fill-paragraph #314
• fill-paragraph is a no-op in YAML frontmatter #297

(Please feel free to close if this is not a helpful organization tool.)

[shipmints]

Another issue (not recorded anywhere): allow filling just before a code block.

This is despite markdown-mode-fill-paragraph's misleading docstring "If the point is in a code block, or just before one, do not fill." It's misleading because once paragraph-start is corrected, it works before a code block. I think the intent was a code block that contained an embedded "-" by syntax-class?

I've added this to my markdown-mode hook

(setq-local paragraph-start (concat "```\\|" paragraph-start))

Example: fill-paragraph refuses to fill paragraphs as below without this simple change.

• long line to fill long line to fill long line to fill long line to fill long line to fill long line to fill long line to fill (no whitespace between this line and the code block)

# sample code