I have an “organically” grown setup for my pipes on one of my sites
I am using yarn to install what would have gone with npm to node_modules into /assets/modules. Then in the pipes I just reference that folder (for instance to get Boostrap SCSS into my theme files).
Locally it works because, but when I deploy to Netify (both have Hugo Extended 0.55.6) the routine does not find the postcss-cli binaries, because they are not in node_modules.
My (hack) fix is, to run npm install AND yarn install which obviously is overkill. Is there any way to tell Hugo where to look for the binaries used in the pipes system?
Native dependency management will be addressed in the next release of Hugo.
However what you ask will not be possible out-of-the-box since there will not be native support for either yarn or npm. If anyone can offer a workaround for you then hopefully they will post a reply here.
Instead Hugo will be using Go Modules to manage dependencies and that will require a local Go installation.
You can track the development of this new (and very important) feature in the following issues:
In the case of Hugo Pipes/SASS you can have Bootstrap installed in site/npm_modules, then from site/assets/sass/main.scss you can @import "bootstrap/scss/bootstrap";
You also need to add node_modules to includePaths.