Question

Sometimes when I’m working on a project I want to play around with some data. Often times the data is on one line and is huge (>25k characters). I understand I could set nowrap and have this line just run off the screen, but I tend to like set wrap for other reasons. So, as a workaround I want to hide these long lines in a marker fold (e.g. {{{ long line }}}). This works fine but I run into a problem with synmaxcol for some reason. If the folded line exceeds synmaxcol then when I open the file, the syntax highlighting runs over. For example:

However, as soon as I open the fold the syntax corrects itself:

Having to open the fold every time is annoying though. As you can see in this example the line is not actually all that long — it just exceeds synmaxcol. Since synmaxcol is exceeded at a “string” element, the rest of the file is highlighted as a string (so nothing but a singular double quote will stop it).

Why is this happening and how can I fix it? I’ve tried this with different syntax files and filetypes and it still occurs. I’ve also tried it with no plugins, a minimal vimrc (containing only syn on) and a modeline to set fdm=marker:synmaxcol=60 and it still happens.

Answer 1

You can manually enter :syntax sync fromstart to force Vim to rescan the syntax from the beginning of the opened file.
I would suggest defining a hotkey for convenience:

noremap  <F5> <Esc>:syntax sync fromstart<CR>
inoremap <F5> <C-o>:syntax sync fromstart<CR>

Now you can press F5 to clean up most syntax highlighting problems.

Also, have a look at Vim’s fixing syntax highlighting – wiki page
Moreover reading :help :syn-sync-first might shed some more light on the issue.

UPDATE:

I was able to reproduce this behavior on my machine (I’m running Vim 7.3.429).
However, when I wrapped the fold markers {{{ and }}} in block comments, vim correctly rendered the syntax. You can create appropriately wrapped fold-markers using the zf command. See Vim tips: Folding fun.

Normally Vim picks the correct blockcomment string based on the currently active syntax. However, my Vim is pretty vanilla and didn’t recognize Ruby syntax. I could specify autocmd FileType ruby set commentstring==begin%s=end in my .vimrc file to set the proper block comment. See :fold-create-marker for more details.

Another solution is to set synmaxcol=0, which will effectively set it to infinity. This causes Vim to check the syntax of the entire line, no matter how long it is. However, I’m not sure what kind of performance penalty you’ll have to pay for that.