Introduce an option to not use any cache

[victornoel]

Do you want to request a feature or report a bug?
feature

What is the current behavior?
When calling yarn, packages are first downloaded to the global cache before being put in node_modules

What is the expected behavior?
With an option, e.g., --no-cache, calling yarn --no-cache will skip the use of a global cache and directly work at the node_modules level.

Why?
In a CI runner, where only the package used by the project being tested/integrated are of interest, it would make sense to simply populate the node_modules directory instead of the yarn global cache and then copy the dependencies to node_modules.
Coupled with CI caching, one would just need to cache the node_modules directory and call yarn --no-cache --pure-lockfile to get the correct node_modules in a minimum of time.
Currently, the only solution is either to cache the global yarn cache and rebuild node_modules on every build, or to cache both but then we cache twice every dependency!

Please mention your node.js, yarn and operating system version.
yarn v0.15.1, node v6.7.0 and linux

[olingern]

You can actually change your global and cache folders folder, but there seems to be some linking errors at the moment.

yarn --global-folder ./node_modules/ --cache-folder ./node_modules/

[victornoel]

@olingern do you think it will prevent the double actions of downloading and then copying to node_modules? I feel like yarn is not able to realise this specific situation…
The later action is quite slow on CI systems usually, hence the need for not using any cache at all :)

[jdno]

I am also very interested in such a feature, with the same requirements and use case as in #1178. In a Docker image, the cache will never be used again, so it should be possible to just skip it altogether to improve the final disk size.

[deployable]

RUN set -ex; yarn install --prod --cache-folder ./ycache; rm -rf ./ycache

@victornoel it looks like the cache is stored in a different format so I don't think setting the cache to ./node_modules will help. I can't think of a simple way to inject a null or tmpfs into a docker build so I think you are stuck with writing and removing until this is added to yarn.

[victornoel]

@deployable I don't think the solution is via a hack, this should be handled by yarn itself.

[deployable]

@victornoel Agreed, I wasn't suggesting otherwise. Just providing the workaround "until this is added to yarn"

[victornoel]

by the way @deployable, I just realised I was misinterpreting your comment: my need is not to remove after a yarn install (what your workaround does), my need is not to use any cache at all and not download dependencies in the cache before copying them to nodes_modules, that's why I was saying a hack will never do, not even as a workaround.