cedaei.com/_posts/2019-07-23-vim-folds.md

title	tags
Sorting VCF files with Vim folds	vim neovim

A while ago I wanted to sort my contacts which had become a mess. I wanted to use this opportunity to do something nice with Vim too. Enter Vim-folds.

Getting Started

I initiated a repository for the plugin.

cd ~/repos/
git init vcf.Vim

I use Vim-plug for package management in Vim and added that to Vim-plug

Plug '~/repos/vcf.Vim/'

Next, I exported all my contacts into a Virtual Contact File.

Filetype Detection

To get started I needed Vim to assign a filetype to VCFs. A small autocmd is enough to take care of that. By convention, filetype detection files go in ftdetect directory.

ftdetect/vcf.Vim

au BufNewFile,BufRead *.vcf set filetype=vcf

This sets the filetype of all files with filenames ending with .vcf to vcf

Folding

Plugins for specific filetypes are stored in the ftplugin directory. Vim sources the file if the filetype matches the filename without the .vim extension e.g. if the filetype is set to javascript, javascript.vim in ftplugin directory will be sourced.

Each contact in a VCF looks like this:

BEGIN:VCARD
VERSION:2.1
N:Lname;Fname;;;
FN:Fname Lname
TEL;VOICE:+911234567890
END:VCARD

I want my folds to look like

Fname Lname····································

I am going to use expr foldmethod. This can simply be done using set foldmethod=expr. What this tells vim is to run a function on every line and set the fold level based on that. To set the expression to run, we use set foldexpr=OurFunction().

Let's write a function first and set foldexpr to it. Define the function by the usual syntax.

function! VCFFold()
endfunction

set foldmethod=expr
set foldexpr=VCFFold()

When the function is run, vim sets a special variable v:num that tells us which line the function is being run on. To get the current line, we use the getline function.

let thisline = getline(v:lnum)

We want to start a new level fold at every line which starts with BEGIN. For all the other lines, we want to keep the same fold level as previous line since we don't have nested folds in VCF. Vim folds with expr work by running the function on each line and determining the fold level of that line based on the return value of that function. Some of the return values are:

• >n - This tells vim to start a new nth level fold there
• = - This tells vim that the fold level is same as previous line.
• n - This tells vim that the fold level is n

There are more return values. Check :help fold-expr

We can simply set the fold level to >1 at every BEGIN and set it to = on every other line. This way, every contact will end up in a fold starting at the BEGIN of every contact. We can simply use match function to check if the line begins with BEGIN and return >1 in that case, else we will return =.

if match(thisline, '^BEGIN') >= 0
	return ">1"
endif
return "="

Putting it all together, we get.

function! VCFFold()
	let thisline = getline(v:lnum)
	if match(thisline, '^BEGIN') >= 0
		return ">1"
	endif
	return "="
endfunction
set foldmethod=expr
set foldexpr=VCFFold()

Fold Text

To set the fold text, we have to set the foldtext to a function. Let's create a funtion named VCFFoldText for this purpose and set foldtext to it.

function! VCFFoldText()
endfunction

set foldtext=VCFFoldText()

The name is stored as a line N:Lname;Fname;;;. Two special variables set for foldtext function are v:foldstart and v:foldend which are the line numbers where the current fold starts and ends. We can iterate from v:foldstart to v:foldend using the range function. While iterating, we can simply look for a line that begins with N: and return the name from it. If we don't find any such line, we can return No Name.

function! VCFFoldText()
	for i in range(v:foldstart, v:foldend)
		let l:thisline = getline(i)
		if match(l:thisline, '^N:') >= 0
			" Return the string here
		endif
	endfor
	return "No Name"
endfunction

All we need to do is split the parts on semi-colons and join that array back depending on our preferences of whether we want first name first or last name first. In my case I want first name first.

let l:parts = split(l:thisline, ';')
return substitute(join(l:parts[1:], " ") . l:parts[0][2:], '\s\+', ' ', 'g')

split splits the string into an array with the second parameter (; in this case) as delimiter. I then join all the elements from first element (skipping the zeroth element which is the last name) and then append the zeroth element without the first two characters (since those are N:). Finally, I replace multiple spaces with one space.

Complete Program

function! VCFFold()
	let thisline = getline(v:lnum)
	if match(thisline, '^BEGIN') >= 0
		return ">1"
	endif
	return "="
endfunction
set foldmethod=expr
set foldexpr=VCFFold()

function! VCFFoldText()
	for i in range(v:foldstart, v:foldend)
		let l:thisline = getline(i)
		if match(l:thisline, '^N:') >= 0
			let l:parts = split(l:thisline, ';')
			return substitute(join(l:parts[1:], " ") . l:parts[0][2:], '\s\+', ' ', 'g')
		endif
	endfor
	return "No Name"
endfunction

set foldtext=VCFFoldText()

Installation

If you just want the above program, it is available as vcf.vim. You can install it with Vim-plug via:

Plug 'https://gitlab.com/ceda_ei/vcf.vim.git'