PostProcess
Usage
Marking a resource with resources.PostProcess
delays any transformations to after the build, typically because one or more of the steps in the transformation chain depends on the result of the build (e.g. files in public
).
A prime use case for this is CSS purging with PostCSS.
There are currently two limitations to this:
-
This only works in
*.html
templates (i.e. templates that produces HTML files). -
You cannot manipulate the values returned from the resource’s methods. E.g. the
upper
in this example will not work as expected:{{ $css := resources.Get "css/main.css" }} {{ $css = $css | resources.PostCSS | minify | fingerprint | resources.PostProcess }} {{ $css.RelPermalink | upper }}
CSS purging with PostCSS
The below configuration will write a hugo_stats.json
file to the project root as part of the build. If you’re only using this for the production build, you should consider placing it below config/production.
build:
buildStats:
enable: true
[build]
[build.buildStats]
enable = true
{
"build": {
"buildStats": {
"enable": true
}
}
}
See the configure build documentation for details and options.
postcss.config.js
const purgecss = require('@fullhuman/postcss-purgecss')({
content: [ './hugo_stats.json' ],
defaultExtractor: (content) => {
let els = JSON.parse(content).htmlElements;
return els.tags.concat(els.classes, els.ids);
}
});
module.exports = {
plugins: [
...(process.env.HUGO_ENVIRONMENT === 'production' ? [ purgecss ] : [])
]
};
Note that in the example above, the “CSS purge step” will only be applied to the production build. This means that you need to do something like this in your head template to build and include your CSS:
{{ $css := resources.Get "css/main.css" }}
{{ $css = $css | resources.PostCSS }}
{{ if hugo.IsProduction }}
{{ $css = $css | minify | fingerprint | resources.PostProcess }}
{{ end }}
<link href="{{ $css.RelPermalink }}" rel="stylesheet" />
Hugo environment variables available in PostCSS
These are the environment variables Hugo passes down to PostCSS (and Babel), which allows you do do process.env.HUGO_ENVIRONMENT === 'production' ? [autoprefixer] : []
and similar:
- PWD
- The absolute path to the project working directory.
- HUGO_ENVIRONMENT
- The value e.g. set with
hugo -e production
(defaults toproduction
forhugo
anddevelopment
forhugo server
). - HUGO_PUBLISHDIR
-
The absolute path to the publish directory (the
public
directory). Note that the value will always point to a directory on disk even when runninghugo server
in memory mode. If you write to this folder from PostCSS when running the server, you could run the server with one of these flags:
hugo server --renderToDisk
hugo server --renderStaticToDisk
Also, Hugo will add environment variables for all files mounted below assets/_jsconfig
. A default mount will be set up with files in the project root matching this regexp: (babel|postcss|tailwind)\.config\.js
.
These will get environment variables named on the form HUGO_FILE_:filename:
where :filename:
is all upper case with periods replaced with underscore. This allows you to do this and similar:
let tailwindConfig = process.env.HUGO_FILE_TAILWIND_CONFIG_JS || './tailwind.config.js';