All,
There have recently been changes to the Netlify build system, and Dillon’s recommendation for caching Elm packages no longer works.
They now have a generic caching npm package that you can use. For example, this is how the netlify.toml file looks in my projects:
[build]
publish = "dist"
command = "export ELM_HOME=\"elm-stuff\" && npm run build"
[[plugins]]
package = "netlify-plugin-cache"
[plugins.inputs]
paths = ["elm-stuff"]