Taking the approach that this is just another symptom that cleaning up all the crud that thas accumulated in my vim environment over the years is long overdue... I decided to look into this further and found the culprit: I ended up looking at an ~8-year-old mediawiki.vim (!) file in my ~/.vim/ftdetect.
The lines that cause the problem: setlocal foldexpr=getline(v:lnum)=~'^\\(=\\+\\)[^=]\\+\\1\\(\\s*<!--.*-->\\)\\=\\s*$'?\">\".(len(matchstr(getline(v:lnum),'^=\\+'))-1):\"=\" setlocal fdm=expr I imagine someone familiar with foldexpr's would see at a glance what's wrong with the fold expression when the number of lines in the file runs in the thousands... A bit odd that this should take effect on markdown *.md files or *.txt files that have nothing to do with *.mw, *.wiki, or *.mediawiki... Anyway, after commenting out those two lines I'm no longer able to recreate the problem... and more importantly stuff that I had initially suspected has now been proven innocent. I looked at the current version of the mediawiki stuff on github and it turns out that the foldexr/foldmethod logic was moved to ftplugin/mediawiki.vim... When I have time I should probably take a look at the current version... see if this issue (at least in my context) has been addressed. Thanks, CJ -- -- You received this message from the "vim_use" maillist. Do not top-post! Type your reply below the text you are replying to. For more information, visit http://www.vim.org/maillist.php --- You received this message because you are subscribed to the Google Groups "vim_use" group. To unsubscribe from this group and stop receiving emails from it, send an email to vim_use+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/vim_use/20200608172324.GA12522%40turki.local.