Netlify issue: missing node_modules packages. (resolved, but FYI)

In your README you mention that you must install postcss with npm or yarn. I'd done this with yarn add <package-name> -D, which places things in the devDependencies hash key in package.json. This is fine. Typically running bundle exec jekyll build locally will result in everything working just fine. Great!

Here's the hiccup: In many jekyll + postcss blog posts (eg: here) there are instructions that instruct people to set the following ENV variables:

When building for production, always set JEKYLL_ENV=production and NODE_ENV=production on the command line. When these variables are set to production, unused Tailwind styles are purged and the output is processed with cssnano.

This where the problem comes in. When deploying and building on Netlify NODE_ENV=production + yarn add ______ -D seems to result in an empty ./node_modules directory.

When I moved everything from devDependencies to dependencies in packages.json then everything started working.

I don't know if this is a Netlify thing or not but, in the off-chance anyone shows up here with missing node_modules packages, this might be the answer.

TLDR: Do not install your node dependencies via yarn add .... -D or npm install <package-name> --save-dev

The report discusses README installation guidance, package.json dependency sections, and production builds using JEKYLL_ENV and NODE_ENV. Start by checking the README and package.json, then compare the local bundle exec jekyll build with the Netlify production setup. The issue is marked resolved and specifies no requested code or documentation change.