Yarn support? about fnm

[BrunoRoemers]

I really wanted yarn to play well with fnm, so I came up with the following:

EDIT: Simplest solution
While the original solution is still valid, I ran into some issues while running scripts from package.json files (e.g. Unknown option: '--global-folder').

Turns out there is an astonishingly simple way to change the global folder, binary folder (and many other settings) based on the current shell:

export YARN_GLOBAL_FOLDER="$FNM_MULTISHELL_PATH/yarn-global"
export YARN_PREFIX="$FNM_MULTISHELL_PATH"

These environment variables do not seem to be documented on classic.yarnpkg.com but they work fine on version 1.22.10 nonetheless. (They are documented here for Yarn 2.) They're also mentioned in the changelogs once.

@Schniz maybe this solution is elegant enough to be included in fnm? Users can always override these variables in their dotfiles, after fnm is loaded.

1. Working Solution

# scope global yarn packages to current node version
yarn() {
  # $@ is copied to $args (some positional parameters are filtered)
  local args=()

  # defaults for intercepted paramaters
  local global_folder="$FNM_MULTISHELL_PATH/yarn-global"
  local global_bin_folder="$FNM_MULTISHELL_PATH"

  # intercept certain positional parameters
  while test $# -gt 0; do
    case "$1" in
      --global-folder)
        shift
        global_folder=$1
        shift;;
      --prefix)
        shift
        global_bin_folder=$1
        shift;;
      *)
        args+=$1
        shift;;
    esac
  done

  # run yarn (found in $PATH) and manually pass on intercepted parameters
  command yarn $args --global-folder=$global_folder --prefix=$global_bin_folder
}

If this function is loaded in your terminal (e.g. because it is saved in .bashrc), it will run every time yarn is invoked. It filters out --global-folder <path> and --prefix <path> from the positional parameters. If those options were not provided (which is usually the case), it will provide default values based on $FNM_MULTISHELL_PATH. The actual yarn command (the one that sits in your $PATH) is then called with --global-folder and --prefix, as well as the remaining positional parameters.

--global-folder tells yarn where to store the global node_modules.
--prefix tells yarn where to symlink binaries. Since fnm env puts $FNM_MULTISHELL_PATH/bin on the $PATH, all commands that are installed with yarn global add will be available in your terminal.

Note that I installed yarn using npm, such that the version of yarn that is used, is also scoped to the current node version.

2. Buggy Solution (for reference only, do not use)

FYI for my first attempt I added the following lines to .bashrc or .zshrc:

yarn config set global-folder "$FNM_MULTISHELL_PATH/yarn-global" > /dev/null
yarn config set prefix "$FNM_MULTISHELL_PATH" > /dev/null

This does not play well with --multi however, because yarn config changes $HOME/.yarnrc by default. Each time a terminal window/tab is opened, above lines are run. This means that $HOME/.yarnrc will always contain the paths that belong to the last opened shell. It is possible to pass --use-yarnrc <path> (cf. working solution) and configure yarn via that file, but this is slower than the working solution because of file I/O and more complex overall.

[ljharb]

I’d expect yarn to use whatever npm root -g is; if it isn’t, yarn is broken - if it is, fnm is broken.

nvm and n and nave all “support” yarn afaik with no special handling.

[ljharb]

Yes, but imo if you have to do that, it’s a yarn bug.

[parkerault]

@ljharb this is what I get for the global bin paths:

$ npm -g bin
/home/redacted/.fnm/node-versions/v10.15.3/installation/bin
(not in PATH env variable)
$ yarn global bin
/home/redacted/.yarn/bin

Edit: could something like this work? yarn config set prefix $(npm prefix -g)

[Schniz]

Yes, but imo if you have to do that, it’s a yarn bug.

Indeed. We can also support changing ~/.yarnrc when we switch, but this is very abusive and won't work across shells (with the --multi).

I was thinking about having something like fnm promote-global-bin VERSION BINARY. That could create a script in ~/.fnm/global-binaries that calls the binary using the correct version every time, and fnm env could add it to $PATH too. But I'm not sure it will be used or a good idea 🤷‍♂️

[Schniz]

closing for inactivity