[Feature] A command to just download and cache dependencies from lockfile

[rohit-gohri]

I had an idea for something, discovered pnpm already has the feature. Would like to create it as a plugin, any ideas where to start?

Describe the user story

As a developer using Dockerfiles with my monorepo based application, I often have to do lots of hacks to maintain docker cache of yarn install (including creating subsets of package.json with jq, https://stackoverflow.com/a/59606373 ). I would like to be able to separate the download and install/link steps of yarn install so that the download part can be cached in a separate layer (that can then be used as a base image by all the applications in the monorepo).

Describe the solution you'd like

A command similar to pnpm fetch that uses the lockfile to populate the yarn cache with the dependencies required for a full install or a focus install.

This cmd will use just the yarn.lock, .yarnrc.yml, and .yarn folder to populate the yarn cache.

Describe the drawbacks of your solution

Would add some complexity and need to work without a package.json.

Describe alternatives you've considered

• Commit the cache - Too large for monorepos
• Use approach described in https://stackoverflow.com/a/59606373 to create minimal package.json to populate the cache

[edsrzf]

I created #4529 before finding this discussion. (I only searched issues, not discussions!)

I've been able to write a plugin that does this, but ended up having to reimplement parts of the resolution process within the plugin, since there is no API to resolve dependencies without reading package.json files. I haven't published the code because it includes hacks that are specific to my setup. I could avoid these hacks if, for example, there were a way to configure Project.resolveEverything to only read yarn.lock.

[rohit-gohri]

I created a small package that recreates the full workspace structure with dummy package.jsons just from the yarn.lock file - https://github.com/rohit-gohri/yarn-lock-to-package-json

Using it like this

COPY .yarn ./.yarn
COPY yarn.lock .yarnrc.yml ./

RUN yarn dlx yarn-lock-to-package-json

RUN yarn install --immutable

[devthejo]

here is my plugin (based on yarn-lock-to-package-json):
https://github.com/devthejo/yarn-plugin-fetch