Conceal comments in Vim/Neovim

Question

I am writing a lot of latex and would like to conceal comments. There are often several lines of text that I comment but would like to keep/not delete.

Concealing comments explained: A comment is longer than a given line is spread over multiple lines. I would like to always shorten the comment at the end of the line and only show ".." or a symbol. When the cursor moves over the comment, I would like it to unfold again with all the line breaks. Conceal as soon as the cursor leaves the line.

Unconcealed (.. representing line break):

% asdffdsaaasdffdsa
  ..lbfds

Concealed:

% asdffdsaaasffd..

An advanced feature would be the concealing of several consecutive commented lines to collapse and end on ..[#collapsed_lines].

Unconcealed (.. representing line break):

% asdffdsaaasdffdsa
  ..lbfds
% asdfsdsdsss

Concealed:

% asdffdsaaasd..[2]

I am using Vimtex. Is there such a plugin or feature within Vimtex I haven't discovered or understood, allowing me to do so?

Answer 1

Vim natively supports folding lines of text. See :help folds for the whole documentation.

Here's a quick solution I hacked together using the sample code already present in :help fold-expr as a starting point. Put the lines below in a file used for LaTeX, e.g. ~/.vim/after/ftplugin/latex.vim:

set foldexpr=match(getline(v:lnum),'^\s*%')!=-1
set foldmethod=expr

It will make this text:

Some text
% this is a comment
% so is this
Some more text

look like this:

Some text
+-- 2 lines: % this is a comment---------------------------------------
Some more text

I would say that's reasonably close to your requirements.

You will have noticed that this is an answer for original Vim. You may have to translate it into neovim's syntax. I keep on hearing that neovim is much more advanced so this should be a no-brainer. I hope it's at least a pointer in the right direction.

Addendum:

I just read the question again and there seems to be another problem: you are talking about multi-line comments. AFAIK, LaTeX does not support multi-line comments so this is really just one very long line that is (visually) wrapped by Vim. No newline character is inserted. You can turn it off with :set nowrap, which will give you very long lines. See :help 'wrap'.

Answer 2

Enable folding of comments with the option g:vimtex_fold_types

Since you are already using VimTeX, have you tried to set

" .vimrc
let g:vimtex_fold_enabled = 1
let g:vimtex_fold_types = {
    \  'comments': {'enabled' : 1},
    \}

-- init.lua
vim.g.vimtex_fold_enabled = true
vim.g.vimtex_fold_types = {
  comments = { enabled = true }
}

Example with set foldtext=foldtext()

Some text
% this is a comment
% with many lines
% with many lines
% with many lines
% with many lines
% with many lines
Some more text

is shown to me as

For more info :h vimtex-fold