Adding a prefix to TailwindCSS classes with VIM

Today we needed to add a TailwindCSS prefix to a small project we are building, to prevent clashes with other TailwindCSS classes on the same page. The setting in the tailwind.config.js was straightforward, we added this:

module.exports = {
  prefix: 'sf-',

... and now TailwindCSS will generate classes like .font-bold and .border-none as .sf-font-bold and .sf-border-none. Next up, we needed to replace all the classes in the project with their prefixed counterpart.

There were some plugins available to do this automagically in Webpack, but we decided we wanted to add them manually. A few of the classnames are dynamically set, and we doubted the plugins would find all those cases. Also: the plugins seemed to be old.

My co-worker started writing a regex for a search-and-replace, but soon stranded. You need to find the proper locations, and then within those locations, add the prefix. The prefix, however, is sometimes more of an infix, since there are other prefixes that are added before the prefix itself. See the class with md: for example:

<div className="bg-gray-100 px-4 md:px-0">
// Becomes:
<div className="sf-bg-gray-100 sf-px-4 md:sf-px-0">

While he worked on the regex and subsequently went to get coffee, I thought: I should be able to solve this in VIM in some way. I know I can make a visual selection and then type :! to get the selection as input into some shell command. If I pipe the lines to some script, I can then just split strings all I want.

One problem I ran into was that, if I make a visual selection within quotes (vi") and I then use the colon-exclamation to pipe it to some script (:'<,'>! php transform.php), I will receive the full line, as if I was using the line-wise V selection.

While searching the internet I thought: can I use a register here? And the internet had a solution for that. I ended up running the following command:

:vmap m "ay:call setreg('a', system('php transform.php', getreg('a')))<cr>gv"ap

This sets up a mapping for visual mode, and binds the m to do a series of things. It first selects the 'a' register and yanks ("ay). Since we are already in visual mode here, y is a direct yank of that selection. We are now in normal mode, so we continue to type out a command that calls a function to set register 'a' again with the output of a system call to php transform, taking in the current contents of register 'a'. We execute this command by pressing enter (<cr>). Register 'a' now contains the scripts output. We then re-select the last visual selection (gv in normal mode) and then paste from register 'a' ("ap). This effectively runs the script over the visually selected area.

I then just opened the alphabetically first file of the project and manually made visual selections that selected all the classnames. For this, I also temporary mapped m to vi", so I could just do mm once my cursor was in a className="..." (for which mouse mode is nice too: click + mm, very fast). Then, to get to each next file, just press ]f.

The project was small enough to do this last part so manually, but this at least saved me a lot of stops in between all the classnames, and also saved me the headache to scan for md: prefixes and pick the right spot. Even when the classnames were actually in a backtick-string it was no problem: as long as I defined a correct visual selection, m would replace things.

For completeness, here is transform.php:


$input = file_get_contents('php://stdin');

$classes = array_filter(explode(' ', $input));

$classes = array_map(function ($class) {
    $parts = explode(':', $class);
    $parts[count($parts)-1] = 'sf-'.$parts[count($parts)-1];
    return implode(':', $parts);
}, $classes);

echo implode(' ', $classes);