Feature request: Add PNPM support

[jcayzac]

Which problem is this feature request solving?

pnpm is a robust, mature dependency manager for Node.js projects, and is much faster than npm and yarn. It elegantly solves npm doppelgängers problem and has stricter module resolution, solving yarn ghost modules.

Currently, Netlify users need to use workarounds in order to use pnpm, involving altering a proper project configuration and making it less optimal.

Describe the solution you'd like

Build images should have pnpm@latest preinstalled as a global npm module.
If a pnpm-lock.yaml file is detected in the build.base folder, pnpm install --frozen-lockfile should be run instead of npm install (or even better, the install command should just be exposed as a configuration value so that people can run what they want instead of npm install).

Can you submit a pull request?

Yes No Maybe.

[ehmicky]

Hi @jcayzac,

This sounds good!

Would you like to submit a PR?

[erquhart]

Closing - details here: #449 (comment)

Please follow netlify/build#1633 for more.