yarn prune docs lie

[Machiaweliczny]

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

bug

What is the current behavior?

yarn prune v1.13.0
error The prune command isn't necessary. `yarn install` will prune extraneous packages.
info Visit https://yarnpkg.com/en/docs/cli/prune for documentation about this command.

^ This is a lie.

If the current behavior is a bug, please provide the steps to reproduce.

mkdir -p node_modules/foo
cd node_modules/foo
npm init
cd ../..
npx [email protected] install

node_modules/foo will still be there

In contrast yarn install --force does remove node_modules/foo.

What is the expected behavior?
You tell me? Either docs should be updated or behaviour of yarn install changed.
According to docs yarn install should prune unnecessary deps.

Why:
I had in project 2 dependencies having foo as dependency. One was pointing to foo as dependency and the other was pointing as optionalDependency. I got rid of one with dependency and I'm using ----ignore-optional on deployment. The thing is the foo dependency wasn't really optional but I detected it a little too late because I still had stale foo in node_modules.

If docs were honest I would simply run rm -rf node_modules before yarn install on deployments to ensure such things don't happen again.

Please mention your node.js, yarn and operating system version.
node 6.14.3, yarn 1.13.0 and macOS sierra

[arcanis]

Interesting. Yarn has an optimization mechanism that will simply not run the install if it detects that your package.json didn't change. Meaning that when running yarn && yarn, the second one will bailout.

In this case (reproduced by yarn add lodash, removing lodash from the package.json, then running yarn again), it seems there's a bug and Yarn doesn't properly detect that the package disappeared, causing it to bailout instead of running the install. That's weird, I could have sworn it worked before 🤔

[ZendyLim]

Any updates on this?
Confirmed this with

• Node v10.15.3
• Yarn v1.13.0
• Ubuntu 18.04

Removing entries from package.json then running yarn install doesn't remove the packages at all

[JohannesRudolph]

I think there's also some merit to keeping the current behavior as is, i.e. many node packages stuff additional folders into node_modules that can be safely kept (e.g. angular's ngcc) between installations.

If you need to prune, you can always run yarn prune manually, no?

Edit: You're absolutely right about the docs being misleading though

[aalong-tr]

The yarn prune command simply aborts with the error message shared in the original report and didn't seem to have any obvious effect for me. Resorting to yarn install --force instead is not especially obvious. If a standard yarn install run is not going to clean up going forward, a working yarn prune command would be helpful.

[dbackeus]

Please provide a working yarn prune since the implied behaviour of yarn install clearly isn't reliable.

On our CI we cache the node_modules manually and extract the latest cache before running yarn install to install any potentially missing packages.

If manually doing rm -rf node_modules before installing the size is 1.1GB. Meanwhile the cached node_modules directory has bloated to ~2GB.

Running yarn prune currently exits immediately with:

yarn prune v1.22.4
error The prune command isn't necessary. `yarn install` will prune extraneous packages.
info Visit https://yarnpkg.com/en/docs/cli/prune for documentation about this command.